Design And Control Of A Robotic Arm 286m6

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, for more enquiries s: Engr. Nathan David Department of Electronic Engineering University of Nigeria Nsukka. E-mail: [email protected].

OR

CHINWEZE, CHIKA DAVE [email protected]

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CHAPTER ONE INTRODUCTION

1.1

PREAMBLE In the modern world, robotics has become popular, useful, and has achieved great successes in several fields of humanity. Robotics has become very useful in medicine, education, military, research and mostly, in the world of manufacturing. It is a term that has since been used to refer to a machine that performs work to assist people or work that humans find difficult or undesirable. Robots, which could be destructive or nondestructive, perform tasks that would have been very tedious for human beings to perform. They are capable of performing repetitive tasks more quickly, cheaply, and accurately than humans. Robotics involves the integration of many different disciplines, among them kinematics, signal analysis, information theory, artificial intelligence, and probability theory. These disciplines when applied suitably, lead to the design of a very successful robot. This project is a continuation of the “Design and Control of a Six Degrees of Freedom Robotic Arm: Pioneer” project done in the Department of Electronic Engineering, University of Nigeria, Nsukka, in the 2005/2006 academic session. We did a thorough 3

analysis of the project, which was not fully completed. Some new features were included, in addition to improvement on existing ones and the completion of the project. Tables 1.1 and 1.2 below give the existing features and the improvements made on them, as well as the new features that were added.

Table 1.1: Improvements on Existing Features of the Project

Features

Original

Robot arm material Interface Software Gears

Steel

Circuit Implementation

The ‘good old’ Vero board technology was used.

Robot Control Circuitry

Decoders were used to select individual motors and discrete transistors were used for driving the motors

Improvements Aluminum was used. It is lighter and yet possesses reasonable strength A richer interface with enhanced functionalities and friendliness A combination of spur gears and spiral gears were used. Spiral gears are used to achieve very high torque amplification within a relatively small space. The printed circuit board (PCB) technology was used. This has the advantage of a neater circuit with practically no wires, hence it is easier to trouble shoot. The microcontroller provides enough pins for selecting motors, hence eliminating the need for decoders. Also, we used transistor driver ICs instead of discrete transistors to simplify the circuit and make it less error-prone.

Limited functions Spur gears were mostly used to amplify the motor torques

Table 1.2: New Features

Features Remote Control (Infrared

Description The robot arm was previously connected directly to the PC via cables. A wireless communication channel between the PC and the robot was established via

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Communication infrared, thereby increasing flexibility Module) Embedded A microcontroller was used to control the robot instead Control of direct control from the PC. The interface and robot control were highly decoupled by placing the robot control functions in the embedded controller, so the PC could easily be replaced with a hand-held remote controller, thereby further increasing the overall flexibility of the system.

1.2

HISTORY OF ROBOTICS The advent of robotics started in the year 350 B.C. when a Greek mathematician Archytas of Tarentum built a mechanical bird, which was called “the pigeon”. This mechanical bird was powered using steam. With further advancements, Leonardo Da Vinci in the year, 1495 designed a mechanical device that looked like an armored knight. The knight was designed to move as if there was a real person inside. In 1898, Nikola Tesla designed the first remote-controlled robot in Madison Square Garden. The robot designed was modeled after a boat. The first industrial robots were Unimates developed by George Devol and Joe Engelberger in the late 50’s and early 60’s. The first patents were by Devol but Engelberger formed Unimation which was the first market robots. Therefore, Engelberger has been called the “father of robotics”. For a while, the economic viability of these robots proved disastrous and thing slowed down for robotics. However, by mid-80’s, the industry recovered and robotics was back on track. George Devol Jr, in 1954 developed the multi-ted artificial arm, which lead to the modern robots. However, mechanical engineer Victor Scheinman, developed the truly flexible arm know as the Programmable Universal Manipulation Arm (PUMA). In 1950, Isaac Asimov came up with laws for robots and these were: •

A robot may not injure a human being, or through inaction allow a human being to come to harm.

•

A robot must obey the orders given it by human beings, except where such orders would conflict with the first law.

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•

A robot must protect its own existence as long as such protection does not conflict with the first or second law (Robotics Introduction. 2001).

Mobile Robotics moved into its own in 1983 when Odetics introduced a six-legged vehicle that was capable of climbing over objects. This robot could lift over 5.6 times its own weight parked and 2.3 times it weight moving. There were very significant changes in robotics until the year 2003 when NASA launched two robots MER-A “Spirit” and MERB “Opportunity” rovers which were destined for Mars. Up till date, Roboticists have kept researching on how to make robots very interactive with man in order to be able to communicate efficiently in the social community.

1.3

CLASSIFICATION OF ROBOTS There are various types of robots, which are used now in the modern world each having one or several tasks that it performs depending on the intelligence applied to it. However, robots can be classified broadly into two types namely: •

Autonomous Mobile Robots

•

Manipulator Robots

1.3.1 AUTONOMOUS MOBILE ROBOTS These are mobile robots provided with the mechanisms to perform certain tasks such as locomotion, sensing, localization, and motion planning. Autonomous mobile robots are capable of adapting to their environment. The intelligence provided to them enables them to be able to sense conditions around their environment and respond correctly to the situations. Examples of Autonomous mobile robots include the autonomous guided vehicle robots which independent of external human actions deliver parts between various assembly stations by following special electrical guide wires using a custom sensor, the HELPMATE service robot which transports food and medication throughout hospitals by tracking the 6

position of ceiling lights, which are manually specified to the robot before hand. Also, in the military, some robots are designed to detect bombs and they are capable of defusing the bombs. These robots are all autonomous in the task they perform because they have been provided with the intelligence to detect and adapt to the environment in which they are supposed to perform their tasks.

1.3.2 MANIPULATOR ROBOTS These are robots that perform particular tasks. They are usually in the form of robot arms and are normally stationary. In most cases, they are bolted at the shoulder to a specific position in the assembly line, and the robot arm can move with great speed and accuracy to perform repetitive tasks such as spot welding and painting. Manipulator robots are very much unlike the autonomous mobile robots whereby the intelligence provided to them does not make them adapt to the environment in which they are. In most cases, most manipulator robots are capable of handling many end-effectors in order to increase the versatility of their use. These various end-effectors can be used for several purposes such as welding, painting, screwing and assembling. Although manipulator robots can be very versatile, they suffer from a fundamental disadvantage, which is lack of mobility. A fixed manipulator robot has a limited range of motion that depends on where it is bolted down, in contrast to a mobile robot that is capable of moving about.

1.4

APPLICATIONS OF ROBOTICS Robotics is becoming almost very popular in today’s world and is now applied in several spheres of the human life. Robotics is applied in the following areas of life.

1.4.1

MEDICINE In the medical field, some robots are used for performing tasks, which are dangerous and unpleasant to humans. Some of these hazardous jobs are handling materials such as blood or urine samples. In addition, some robots are used to transport materials around the 7

hospital. Their main sensor for localization is a camera looking at the ceiling. The camera detects the lamps on the ceiling as landmarks. 1.4.2

MILITARY Robots in the military are used for detecting enemy equipment, detection and defusing of bombs. In rescue operations, robots are also used for searching buildings for fugitives and deep-water search. Also, during military attacks, guided missiles are used to blast specific locations on the earth.

1.4.3

EDUCATION AND RESEARCH Some robots are designed for demonstration purposes, which are used for educating the public. For example, the Howard County Sheriff's department of Kokomo Indiana, in 1999 used a motor robot with a cop in it to attract a lot of attention to promote a seat belt program at a fair and they had the robot with the cop with his seat belt on. In space research and the Mars research, robots are usually sent out with the space shuttle for them to obtain samples and bring them back to earth. These robots are usually controlled from a control room in earth.

1.4.4

ENTERTAINMENT Some robots are used for entertainment purposes. These robots are designed like puppets and could make some funny moves which amuse people. Olden day robots were mainly like this. They were being used to entertain royalties.

1.4.5

INDUSTRY In the industry, robots are used to perform precise and heavy tasks which are very difficult for humans to perform. Autonomous mobile robots could be used for carry heavy components from one place to another using custom sensor that help them get their precise positions. Manipulator robots are used to perform certain tasks such as painting, welding, screwing and other activities that would have been difficult to handle using the human hand. Also, manipulator robots are used in assembly lines where each robot takes care of a particular stage of the assembly process. 8

CHAPTER TWO

LITERATURE REVIEW

2.1

MECHANICS AND MOTION OF ROBOTS Mechanics deals with the analysis of the forces that cause a body to be in physical motion. The motion of the robot arm will be achieved with the use of stepper and dc motors as actuators. Since we will require knowing the exact position of the robot arm, the motors will be operated with . The sensor for the dc motor is connected to the gear box in such a fashion that it triggers when specific positions of the output shaft of the motor are reached, thereby allowing us to know the exact position with relatively high accuracy. Since mechanics involves also the parts of the robot that are acted upon directly by the motors and the gears to achieve motion, the tensile strengths of those areas were designed to withstand the stresses generated due to friction and force of propulsion.

2.1.1

ROBOT ARM Manipulator is a fancy name for a robot or mechanical arm, hence it will be used intermittently with robot arm. A manipulator is an assembly of segments and ts that can be conveniently divided into three sections: the arm, consisting of one or more segments and ts; the wrist, usually consisting of one to three segments and ts; and a gripper or other means of attaching or grasping. Alternatively, the manipulator can be divided into only two sections, arm and gripper, but for clarity the wrist is separated out as its own section because it performs a unique function. Industrial robots are stationary manipulators whose base is permanently attached to the floor, a table, or a stand. In most 9

cases, however, industrial manipulators are too big and use a geometry that is not effective on a mobile robot, or lack enough sensors (indeed many have no environmental sensors at all) to be considered for use on a mobile robot. There is a section covering them as a group because they demonstrate a wide variety of sometimes complex manipulator geometries. We will review the robot arm based on the three general layouts of the arm section of a generic manipulator, and wrist and gripper designs. It should be pointed out that there are few truly autonomous manipulators in use except in research labs. The task of positioning, orienting, and doing something useful based solely on input from frequently inadequate sensors is extremely difficult. In most cases, the manipulator is teleoperated (remotely controlled using radio transmission technology). 2.1.2

POSITIONING, ORIENTING AND DEGREES OF FREEDOM Generally, the arm and wrist of a basic manipulator perform two separate functions, positioning and orienting. There are layouts where the wrist or arm is not distinguishable. In the human arm, the shoulder and elbow do the gross positioning and the wrist does the orienting. Each t allows one degree of freedom of motion. The theoretical minimum number of degrees of freedom to reach to any location in the work envelope and orient the gripper in any orientation is six; three for location, and three for orientation. In other words, there must be at least three bending or extending motions to get position, and three twisting or rotating motions to get orientation. Actually, the six or more ts of the manipulator can be in any order, and the arm and wrist segments can be any length, but there are only a few combinations of t order and segment length that work effectively. They almost always end up being divided into arm and wrist. The three twisting motions that give orientation are commonly labeled pitch, roll, and yaw, for tilting up/down, twisting, and bending left/right respectively. Unfortunately, there is no easy labeling system for the arm itself since there are many ways to achieve gross positioning using extended segments and pivoted or twisted ts. A good example of a manipulator is the human arm, consisting of a shoulder, upper arm, elbow, and wrist. The shoulder allows the upper arm to move up and down which is 10

considered one degree of freedom (DOF). It allows forward and backward motion, which is the second DOF, but it also allows rotation, which is the third DOF. The elbow t gives the forth DOF. The wrist pitches up and down, yaws left and right, and rolls, giving three DOFs in one t. The wrist t is actually not a very well designed t. Theoretically the best wrist t geometry is a ball t, but even in the biological world, there is only one example of a true full motion ball t (one that allows motion in two planes, and twists 360°) because they are so difficult to power and control. The human hip t is a limited motion ball t. On a mobile robot, the chassis can often substitute for one or two of the degrees of freedom, usually fore/aft and sometimes to yaw the arm left/right, reducing the complexity of the manipulator significantly. Some special purpose manipulators do not need the ability to orient the gripper in all three axes, further reducing the DOF. At the other extreme, there are arms in the conceptual stage that have more than fifteen DOF. 2.1.3

ARM GEOMETRIES The three general layouts for three-DOF arms are called Cartesian, cylindrical, and polar (or spherical). They are named for the shape of the volume that the manipulator can reach and orient the gripper into any position within the work envelope. They all have their uses, but as will become apparent, some are better for use on robots than others. Some use all sliding motions, some use only pivoting ts, some use both. Pivoting ts are usually more robust than sliding ts but, with careful design, sliding or extending can be used effectively for some types of tasks. Pivoting ts have the drawback of preventing the manipulator from reaching every cubic centimeter in the work envelope because the elbow cannot fold back completely on itself. This creates dead spaces—places where the arm cannot reach that are inside the gross work volume. On a robot, it is frequently required for the manipulator to fold very compactly. Cartesian or rectangular work envelope On a mobile robot, the manipulator almost always works beyond the edge of the chassis and must be able to reach from ground level to above the height of the robot’s body. This means the manipulator arm works from inside or from one side of the work envelope. 11

Some industrial gantry manipulators work from outside their work envelope, and it would be difficult indeed to use their layouts on a mobile robot. In fact, that is how it is controlled and how the working end moves around in the work envelope. There are two basic layouts based on how the arm segments are ed, gantry and cantilevered. Mounted on the front of a robot, the first two DOF of a cantilevered Cartesian manipulator can move left/right and up/down; the Y-axis is not necessarily needed on a mobile robot because the robot can move back/forward. Cylindrical work envelope This is the second type of robot arm work envelope. Cylindrical types usually incorporate a rotating base with the first segment able to telescope or slide up and down, carrying a horizontally telescoping segment. While they are very simple to picture and the work envelope is intuitive, they are hard to implement effectively because they require two linear motion segments, both of which have moment loads in them caused by the load at the end of the upper arm. In the basic layout, the control code is fairly simple, i.e., the angle of the base, height of the first segment, and extension of the second segment. On a robot, the angle of the base can simply be the angle of the chassis of the robot itself, leaving the height and extension of the second segment. A second geometry that still has a cylindrical work envelope is the SCARA design. SCARA means Selective Compliant Assembly Robot Arm. This design has good stiffness in the vertical direction, but some compliance in the horizontal. This makes it easier to get close to the right location and let the small compliance take up any misalignment. A SCARA manipulator replaces the second telescoping t with two vertical axis-pivoting ts. Polar or spherical work envelope The third, and most versatile, geometry is the spherical type. It is the type used in our project. In this layout, the work envelope can be thought of as being all around. In practice, though, it is difficult to reach everywhere. There are several ways to layout an arm with this work envelope. The most basic has a rotating base that carries an arm segment that can 12

pitch up and down, and extend in and out. Raising the shoulder up changes the envelope somewhat and is worth considering in some cases. The wrist work envelope The arm of the manipulator only gets the end point in the right place. In order to orient the gripper to the correct angle, in all three axes, second set of ts is usually required - the wrist. The ts in a wrist must twist up/down, clockwise/counter-clockwise, and left/right. They must pitch, roll, and yaw respectively. This can be done all-in-one using a ball-in-socket t like a human hip, but controlling and powering this type is difficult. Most wrists consist of three separate ts. The order of the degrees of freedom in a wrist has a large effect on the wrist’s functionality and should be chosen carefully, especially for wrists with only one or two DOF. Grippers work envelope The end of the manipulator is the part the or robot uses to affect something in the environment. For this reason it is commonly called an end-effector, but it is also called a gripper since that is a very common task for it to perform when mounted on a robot. It is often used to pick up dangerous or suspicious items for the robot to carry, some can turn doorknobs, and others are designed to carry only very specific things like beer cans. Closing too tightly on an object and crushing it is a major problem with autonomous grippers. There must be some way to tell how hard is enough to hold the object without dropping it or crushing it. Even for semi-autonomous robots where a human controls the manipulator, using the gripper effectively is often difficult. For these reasons, gripper design requires as much knowledge as possible of the range of items the gripper will be expected to handle. Their mass, size, shape, and strength, etc. all must be taken into . Some objects require grippers that have many jaws, but in most cases, grippers have only two. There are several basic types of gripper geometries. The most basic type has two simple jaws geared together so that turning the base of one turns the other. This pulls the two jaws together. The jaws can be moved through a linear actuator or can be directly mounted on a motor gearbox’s output shaft, or driven through a right angle drive which places the drive motor further out of the way of the gripper. This and similar designs 13

have the drawback that the jaws are always at an angle to each other which tends to push the thing being grabbed out of the jaws.

2.2

MOTORS AND MOTION CONTROL The two types of motors that we employed in the control of the robot arm include stepper and dc motors. The motion control was achieved using both the open loop and closed loop method of motion control. Below is a brief look at the two types of motors.

2.2.1

STEPPER MOTOR A stepper motor is a transducer that converts electrical pulses into mechanical shaft rotation. The number of pulses input to the motor determines the amount of motor shaft movement. Each pulse moves the motor a given amount (step). A stepper motor consists of a rotor (a rotating permanent magnet) and a stator (stationary electromagnet coils). The rotor is made of ferromagnetic material, which has been magnetized into a series of alternating north and south poles. In a typical stepper motor, electric power is applied to the stator in order to alternate its magnetic polarity. Interaction between the rotor and the stator causes the rotor to move one step per stator coil winding polarity change. The stepper motor schematic is shown in fig 2.1 Rotor C Ø4 N

Stator1

+Vdc

S Ø3

D Stator2 Ø2

Ø1 +Vdc

B Schematic A Fig. 2.1: Stepper Motor

2.2.1.1

STEPPER MOTOR DRIVE METHODS

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Three common methods of driving a stepper motor are wave drive, step drive and half step drive. •

Wave drive - Here only one power switch (or phase) is active during each step of the motor. Since only one phase is on, the torque will be reduced. The advantage of wave drive is increased efficiency, while the disadvantage is decreased step accuracy.

•

Step drive - Step drive occurs when two power switches are activated for each step moved. Torque is higher with step drive than with wave drive.

•

Half-step drive - Half-step drive occurs when both wave drive and step drive are employed alternately to activate the coils. When only one coil is activated, a weak step is produced; when two coils are activated, a strong step is produced.

2.2.2

DC MOTOR A dc motor is a transducer that converts electrical energy (d.c.) into mechanical shaft rotation. Its action is based on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Fleming’s Left-hand rule and whose magnitude is given by F = BIL Newton where B =

2.2.3

magnetic flux density

I =

current

L =

length of the conductor in the magnetic field

MOTION CONTROL

2.2.3.1 CONTROL OF STEPPER MOTORS The circuitry is as shown below: Controlling stepper motors using a microcontroller simply involves instructing the microcontroller to send the appropriate bit pattern to the stepper motor in the correct order. From the diagram, the supply voltage to the stepper motor is 12V. Therefore, in order to magnetize any coil, 0V should be sent to the coil for current to flow through it. Since the output of the microcontroller is digital (0V or 5V) and the supply voltage of the stepper motor is 12V, npn transistors are used to amplify the outputs of the microcontroller. To 15

rotate the motor, the pattern sent from the microcontroller determines which coils are energized and the direction in which the rotor rotates.

12V

D C B A

12V

12V

uC D C

A +88.8

B

12V

12V

Fig. 2.2: Interfacing a Stepper Motor to a Microcontroller

For example, suppose the rotor is at position D and is intended to be rotated clockwise a single step using the step mode, the microcontroller is instructed to send the bit pattern, 1001 to its outputs. This would eventually make coil D to be at 0V, coil C 12V, coil B 12V, coil A 0V. As a result, coil D and A are energized and the rotor moves to a point in between them as shown in fig 2.2 above. Similarly, in the wave drive mode, to energize A, the bit pattern 0001 is sent to the outputs of the microcontroller causing the rotor to move to point A. 16

2.2.3.2 CONTROL OF DC MOTORS Controlling the d.c. motor is done using the principle of the H-bridge. The H-bridge is shown in the fig 2.3 below: Assuming switches A and D are closed, current flows through the motor in one direction and the motor rotates in a clockwise direction. If switches B and C are closed, current flows in the opposite direction and the d.c. motor rotates in a counterclockwise direction. If A and B OR C and D are closed, the motor’s terminals are at the same potential and no current flows, hence the motor brakes.

12V

12V

A

B d.c. Motor

+88.8

C

D

THEH-BRIDGE

Fig. 2.3: The H-Bridge 1 2V The H-bridge is represented by12Vthe transistor network shown in fig. 2.4 below: Terminals

A and B are connected to the digital outputs of the microcontroller. The LHS network is a mirror image of the RHS network. This makes bi-directional control possible. Controlling the motor can be analyzed considering fourQ8scenarios: Q4 Q6

Q2

d.c. M otor

A

5V

5V

+88.8

Q5

Q1

Q3

Q7

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TRANSIS TOR H-BRIDGE

B

Fig. 2.4: H-Bridge Transistor Network

The first is when A is ‘LOW’ and B is ‘HIGH’. On the LHS, Q1 is turned on eventually making Q3 to on and conduct. Q2 is turned off, eventually turning off Q4. On the RHS, Q5 is turned off, thereby turning Q7 off also. Q6 is turned on causing Q8 to conduct current. As a result, current flows through Q8, to the d.c. motor and finally to ground through Q3, causing the motor to rotate counter-clockwise. The second is when A is ‘HIGH’ and B is ‘LOW’. On the LHS, Q 1 and Q3 are off while Q2 and Q4 are on. On the RHS, Q5 and Q7 are on while Q6 and Q8 are off. Current flows through the d.c. motor from Q4 to Q7, causing the motor to rotate clockwise. The third is when A is ‘LOW’ and B is ‘LOW’. On the LHS, Q1 and Q3 are on while Q2 and Q4 are off. On the RHS, Q5 and Q7 are on while Q6 and Q8 are off. The motor terminals are then at 0V and the motor brakes.

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The fourtht is when A is ‘HIGH’ and B is ‘HIGH’. On the LHS, Q 1 and Q3 are off while Q2 and Q4 are on. On the RHS, Q5 and Q7 are off while Q6 and Q8 are on. The motor terminals are then at 12V and the motor brakes. 2.3

SENSORS A sensor is a part of a transducer that collects an input from the environment and sends it to the transducer for onward conversion to other forms of energy. From the definition given above of a robot, it follows that it is impossible to design an effective and elegant robot without the use of sensors. There are several types of sensors and these are classified based on the kind of physical quantity being monitored. The list given below gives the most commonly monitored physical quantities: •

Temperature

•

Pressure

•

Flow rate

•

Composition

•

Liquid level

•

Light intensity

In our project work, we used infrared (IR) sensors (in form of optocouplers) and pressure sensors (in form of switches). The pressure sensor is attached to the gripper of the robot arm, its function is to inform the controller when the gripper has exerted the adequate amount of pressure on the object the arm is required to pick. The optocouplers were mounted inside the gear box of each t to give a reference position from which the robots position can be determined at any time.

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CHAPTER THREE

RESEARCH METHODOLOGY

3.1

DESIGN SELECTION OF THE ROBOTIC ARM In choosing the materials and the shape for the fabrication of the robotic arm, the following were taken into consideration: •

The ease of manufacturing the parts

•

The mode of manufacturing

•

Ease of assembly

•

Strength and durability of the parts

•

Weight of robot

•

Cost

The principal requirements for power transmission of robots are: •

Small size

•

Low weight and moment of inertia

•

High effective stiffness

•

Accurate and constant transmission ratio

•

Low energy losses and friction for better responsiveness of the control system.

•

Elimination of backlash

Hence, the combination of these factors has greatly influenced all the choices made in the design selection of the robotic arm.

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3.1.1

MATERIAL SELECTION

In manipulator structures, stiffness-to-weight ratio of a link is very important since inertia forces induce the largest deflections. Therefore, an increase in the Elastic modulus, E would be very desirable if it is not accompanied by an unacceptable increase in specific density, γ. The Elastic modulus is an indication of the material’s resistance to breakage when subjected to force. The best properties are demonstrated by ceramics and beryllium but ceramics have a problem of brittleness and beryllium is very expensive. Structural materials such as magnesium (Mg), aluminum (Al), and titanium (Ti) which are light have about the same E/γ ratios as steel and are used when high strength and low weight are more important than E/γ ratios. Factors like ageing, creep in under constant loads, high thermal expansion coefficient, difficulty in ing with metal parts, high cost and the fact that they are not yet commercially available make the use of fibre-reinforced materials limited though they have good stiffness-to-weight ratios. However, with advances in research, some of the mentioned setbacks have been significantly reduced. Hence, the use of fibrereinforced materials (known as composites) is becoming more attractive. Aluminum lithium alloy have better processing properties and is not very expensive. Alloyed materials such as Nitinol (nickel – titanium – aluminum), aluminum incramute (copper manganese – aluminum) are also commercially available. Therefore the materials recommended for use in this project are •

Al-Li alloys

•

Nitinol (nickel-titanium-aluminum)

•

Incramute (copper-manganese-aluminum)

•

Glass-reinforced Plastic (GRP)

The links have an internal hollow area, which provides conduits for power transmitting components i.e. gears in this case, and the stepper motors. At the same time, their external dimensions are limited in order to reduce waste of the usable workspace. They are as light as possible to reduce inertia forces and allow for the highest external load per given size of motors and actuators. For a given weight, links have to possess the highest possible 21

bending (and torsional) stiffness. The parameter to be modified to comply with these constraints is the shape of the cross-section. The choice is between hollow round and hollow rectangular cross-section. From design standpoint of view, the links of square or rectangular cross-section have advantage of strength and machinability ease over round sections. Despite the recommendations mentioned above as regards choice of materials, our options were narrowed down to a choice between steel, GRP, and aluminium based on feasibility studies carried out. Current trend in robotics (especially industrial robotics) shows a quest to achieve lighter designs with reasonable strength. This design goal has always meant a trade-off in of cost. Composite materials are generally more expensive than most metals used in industrial robots fabrication. For the particular case of our project, we narrowed our options down to composite material – glass reinforced plastic – otherwise known as GRP and aluminum. The original project, upon which we are building, was fabricated with steel sheets. The sheets cost practically nothing because metal scraps were used, but there was a setback of the motors not being able to cope with the weight of the metal. We figured out at least three ways of overcoming the setback mentioned above. One option would have been to redesign the gear trains and increase torque amplification, so that the motors can the load. The torque amplification here would have been limited by the real estate on the arm for the gear train and the maximum speed we would be able to give to the motors, as output speed would reduce with increase in torque. We discarded this idea based on long-term considerations. This would mean that much of the energy expended by the robot would go to lifting its own weight thereby reducing the effective load it can lift.

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Another option would have been to replace the motors with others having higher torque ratings. This, for us, would almost be as expensive as re-fabricating the arm with a lighter material, and the problem of effective load, as mentioned previously, would still be there. A third option was to re-fabricate the arm, or at least part of it, with a lighter material of reasonable strength, and that was the option we went for. It certainly involved increased short-term costs but then we foresaw a pay off in the long term. We would no longer be constrained to jeopardize the speed or maximum effective load of the robot while trying to increase torque; instead, any torque amplification would directly translate to increased effective load the robot can lift. After more research and consultations with our supervisor and some lecturers in the Mechanical Engineering department, who are experts in the field, we settled for aluminium mainly on grounds of cost and workability. 3.1.2

THE GEAR SYSTEM In this work, we have chosen the bevel, spur and spiral types of gears. These were readily available from scrap machines (photocopiers). Spiral gears have the advantage of high torque amplification within a relatively small space. The necessary data for the selection and choice of the gear arrangements at each t are: i.

Power transmitted, P = TW

ii.

Transmitted speed, ω ( rad/s)

iii.

Torque developed , T ( Nm)

iv.

Lewis form factor, Y

v.

Bending stress, σ ,( ultimate tensile strength)

vi.

Ultimate tensile strength, σut

vii.

Factor of safety, n

viii.

Module of gear, m

ix.

Number of teeth, N

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The equations below show the relationship between these parameters. They led to the selection of the gears.

3.1.3

i.

Gear diameter, d = mN

ii.

Pitch line velocity, V =

iii.

Transmitted load, Wt =

iv.

Velocity , KV =

v.

Face width, F =

πdω 60

p V

6 6 +V

Wt K V MY σ P

THE WIRELESS COMMUNICATION SYSTEM Our system design is such that a microcontroller at the base of the robot directly controls the robot movements. However, the interacts with the robot through a graphic interface on a PC, hence the need for some form of communication between the PC and the microcontroller. We chose a wireless communication mode for reasons of flexibility, and we established communication between the PC’s parallel port and the microcontroller via infrared. Infrared has a long successful history in remote control applications so we were faced more with the problem of choice of type of infrared communication system. After some research, we decided to use a one-chip solution in the form of an infrared transmitter/receiver IC (ST12 CODEC). ST12 CODEC is a radio frequency and infrared encoder/decoder IC for remote control applications having unique features and flexibility not available with other remote control encoder decoder ICs. ST12 is truly a single-chip remote control solution. The ST12 combines the functionality of both encoder and decoder in a single package with several unique features for enhanced operation and a reduced component count for transmitter and receiver circuits.

24

However, we could not lay our hands on this IC because it was not readily available. We needed to import it. This led to more research on alternatives that would approximate the desirable qualities of the ST12. We eventually arrived at a microcontroller solution for encoding the intelligence signal at the PC end and decoding it at the base of the robot for appropriate arm control. A schematic diagram of how this is achieved is shown in fig. 3.1 below.

Modulated signal

Carrier frequency generator PC parallel port

IR receiver

IR transmitter

Microcontroller at base of robot (decoder)

Microcontroller (encoder)

Fig. 3.1: The Wireless Communication System

When the selects a particular action from the graphic interface (GUI) on the PC, the command controller generates an 8-bit command code corresponding to the desired action and sends it to the parallel port. The microcontroller at the base of the PC reads this command code and uses it to modulate the carrier signal coming from the carrier generator. A 555 timer IC configured in astable mode was used to generate a carrier signal of 38kHz, since the IR receiver is sensitive to signals at this frequency. The IR receiver is a TSOP infrared receiver IC. It ‘sees’ a 38kHz square wave of an infrared signal as a logic ‘1’, inverts it and places a logic ‘0’ on its output pin. When there is no incident IR signal, it ‘sees’ it as logic ‘0’, inverts it and places logic ‘1’ on its output pin. Hence, any binary sequence can be transmitted serially by activating or deactivating the frequency generator appropriately in sequence. The microcontroller does this by 25

pulsing the reset pin of the 555 timer IC at intervals depending on whether the bit to be sent is a logic ‘1’ or a logic ‘0’. The serial transmitter pin of the microcontroller is most suitable for this task. When the TSOP IR receiver demodulates the IR signal to binary bits, the microcontroller at the base of the robot receives these bits and decodes them as the exact 8-bit word sent from the parallel port, which is the command code. The microcontroller interprets this command code and sends the signals to drive the robot motors appropriately. The baud rate of the microcontroller at the PC base (transmitter) and the microcontroller at the robot base (receiver) are preset, by software, to a common value for correct reception of transmitted bits. The range of the IR transmitter can be increased by increasing the current at the transmitter. Also, using more than one transmitter will increase the range. The transmitter is simply an infrared light emitting diode (LED) and we were able to achieve a range of about 6 metres line of sight.

3.2

ELECTRONIC HARDWARE SELECTION This subsection deals with the materials that we have selected for the control system of the robotic arm. The arm is controlled by a microcontroller driving the actuators (dc and stepper motors) via latches and transistors. The microcontroller receives commands from the parallel port via infrared. Latches were used for demultiplexing, as only two 8-bit microcontroller ports were used to drive six motors. For the transistors, we used a combination of npn/pnp power and switching transistors. The factors considered in choosing these were current (ampere) rating, voltage rating and switching speed. Switching speed of the transistors was a crucial factor as it determined how fast we could drive the stepper motors, hence, the speed of the

26

robot arm movements. Suitable IC packages with multiple transistors were used to achieve a more compact control circuit. 3.2.1

THE PARALLEL PORT In computers, ports are used mainly for two reasons, namely, device control and communication. Parallel ports were originally meant for connecting the printer to the PC. However, one can program this port for many more applications beyond that, such as the control of a robotic arm, as we have done in this project. Parallel ports are easy to program and faster compared to the serial ports. Its disadvantage is that it needs more number of transmission lines but this is only significant for long distance communications. Hence, it proved advantageous for our use. In the parallel port, all the 8 bits of a byte will be sent to the port at a time and a control indication will be sent on another line. This port will allow the input of up to 9 bits or the output of 12 bits at any one given time, thus requiring minimal external circuitry to implement many simpler tasks. The port is composed of 4 control lines, 5 status lines and 8 data lines as shown in fig. 3.2 below. It is commonly located at the back of your PC as a D-Type 25 Pin female connector. IEEE Standard Parallel Ports The IEEE 1284 standard however specifies three different connectors for use with the Parallel Port. •

The IEEE 1284 Type A is the D-Type 25 connector found on the back of most computers.

•

The IEEE 1284 Type B is the 36 pin Centronics connector found on most printers.

•

The IEEE 1284 Type C however, is a 36 conductor connector like the Centronics, but smaller.

For this project, we made use of the IEEE 1284 Type A since it is adequate for the required function. The diagram is shown in the fig 3.2 below

27

Fig. 3.2: D-Type 25 Pin Parallel Port Connector

Table 3.1: Pin Assignments of the D-Type 25 Pin Parallel Port Connector Pin No. (D-Type 25) 1 2 3 4 5 6 7 8 9 10 11

Pin No. SPP Signal (Centronics) 1 2 3 4 5 6 7 8 9 10 11

12

12

13

13

14

14

15 16

32 31

17

36

18 - 25

19 - 30

Direction (In/Out)

nStrobe Data 0 Data 1 Data 2 Data 3 Data 4 Data 5 Data 6 Data 7 nAck Busy Paper-Out/ Paper-End Select nAutoLinefeed nError/Fault nInitialize nSelectPrinter/ nSelect-In Ground

Hardware Inverted

In/Out Out Out Out Out Out Out Out Out In In

Control Data Data Data Data Data Data Data Data Status Status

In

Status

In

Status

In/Out

Control

In In/Out

Status Control

In/Out

Control

Yes

Yes

Yes

Yes

Gnd

Table 3.1 uses "n" in front of the signal name to denote that the signal is active low. For example, the nError signal is used to signify an error. This line is low when an error has 28

occurred. Should the printer be functioning correctly, the line is held High. The "Hardware Inverted" means the signal is inverted by the Parallel card's hardware. Such an example is the “Busy” line. If +5V (Logic 1) was applied to this pin and the status read, it would return back a 0 in Bit 7 of the Status .

The output of the Parallel Port is normally TTL logic levels. The voltage levels are the easy part. The current you can sink and source varies from port to port. Most Parallel Ports implemented in ASIC, can sink and source around 12mA. However these are just some of the figures taken from Data sheets, Sink/Source 6mA, Source 12mA/Sink 20mA, Sink 16mA/Source 4mA, Sink/Source 12mA. As you can see they vary quite a bit. The best bet is to use a buffer, as we are, so the least current is drawn from the Parallel Port.

The Parallel Port has three commonly used base addresses. These are listed in Table 3.2, below. The 3BCh base address was originally introduced used for Parallel Ports on early Video Cards. This address then disappeared for a while, when Parallel Ports were later removed from Video Cards. They have now reappeared as an option for Parallel Ports integrated onto motherboards, upon which their configuration can be changed using BIOS.

LPT1 is normally assigned base address 378h, while LPT2 is assigned 278h as shown in table 3.2 below. However, this may not always be the case as explained later. 378h & 278h have always been commonly used for Parallel Ports. The lower case h denotes that it is in hexadecimal. These addresses may change from machine to machine.

Table 3.2: Port Addresses Usually Assigned to the Parallel Port Address 3BCh - 3BFh

378h - 37Fh 278h - 27Fh

Notes Used for Parallel Ports which were incorporated on to Video Cards - Doesn't E addresses378h - 37Fh Usual Address For LPT 1 Usual Address For LPT 2

29

However, to find the address of LPT1 or any of the Line Printer Devices, you can use a lookup table provided by BIOS. When BIOS assigns addresses to your printer devices, it stores the address at specific locations in memory, so we can find them. Table 3.3: LPT Addresses in the Bios Data Area Start Address

Function

0000:0408 0000:040A 0000:040C 0000:040E

LPT1's Base Address LPT2's Base Address LPT3's Base Address LPT4's Base Address

Table 3.3 above shows the address at which we can find the Printer Port's addresses in the BIOS Data Area. Each address will take up 2 bytes. The parallel port is programmed to control the required circuit or device. 3.2.2

THE MICROCONTROLLER A microcontroller is a type of microprocessor furnished in a single integrated circuit and needing a minimum of chips. Its principal nature is self-sufficiency and low cost. It is not intended to be used as a computing device in the conventional sense; that is, a microcontroller is not designed to be a data processing machine, but rather an intelligent core for a specialized dedicated system. Microcontrollers are embedded in many control, monitoring, and processing systems. Some are general-purpose devices but most microcontrollers are used in specialized systems such as washing machines, telephones, microwave ovens, automobiles, and weapons of many kinds. They are ideal for applications where cost and unit size are important considerations. A microcontroller usually includes a central processor, input and output ports, memory for program and data storage, an internal clock, and one or more peripheral devices such as timers, counters, analog-to-digital converters, serial communication facilities, and watchdog circuits. More than two dozen companies in the world manufacture and market microcontrollers. 30

Certain factors are to be considered when choosing a microcontroller for an application. They include: •

Speed, size of ROM/RAM, number of I/O ports, timers, power consumption and cost per unit.

•

Availability of software development tools like assemblers, debuggers, compilers, simulators and technical .

•

Availability and reliable sources of microcontrollers. Based on the above factors, we chose the AT89S52 microcontroller for our project.

The AT89S52 is a low power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industrystandard 80C51 instruction set and pin out. The on-chip flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit U with in-system programmable flash on a monolithic chip, the Atmel 89S52 is a powerful microcontroller, which provides a highly flexible and costeffective solution to many embedded control applications. The AT89S52 also provides the following standard features: 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector twolevel interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and s two software selectable power saving modes. The Idle Mode stops the U while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. The pin configuration of the AT89S52 is found in Appendix A. 3.2.3

THE CARRIER FREQUENCY GENERATOR

31

The LM555 timer was configured in an astable mode to generate a 38 kHz square wave of infrared signal through the IR transmitter. LM555 is a highly stable device for generating accurate time delays or oscillation. Additional terminals are provided for triggering or resetting if desired. In the time delay mode of operation, one external resistor and capacitor precisely control the time. For astable operation as an oscillator, the free running frequency and duty cycle are accurately controlled with two external resistors and one capacitor. The circuit may be triggered and reset on falling waveforms, and the output circuit can source or sink up to 200mA or drive TTL circuits. LM555 finds application in precision timing, pulse generation, sequential timing, time delay generation, pulse width modulation, pulse position modulation and linear ramp generators. The pin configuration of the 555 timer is shown in appendix A. 3.2.4

THE INFRARED RECEIVER The TSOP2138 series are miniaturized receivers for infrared remote control systems. PIN diode and preamplifier are assembled on lead frame, the epoxy package is designed as IR filter. The demodulated output signal can directly be decoded by a microprocessor. TSOP2138 is the standard IR remote control receiver series, ing all major transmission codes. It includes the following features: photo detector and preamplifier in one package, internal filter for PCM frequency, improved shielding against electrical field disturbance, TTL and CMOS compatibility, active low output, low power consumption, high immunity against ambient light, continuous data transmission possible (up to 2400 bps) and suitable burst length greater than or equal to 10 cycles/burst. The IR receiver is shown in fig. 3.3 below.

Fig. 3.3: TSOP2138 IR Receiver

3.2.5

MOTORS

32

A combination of stepper and dc motors were used in this project. Stepper motors, generally, are easier to drive and more precise than dc motors, while dc motors can generally achieve higher output torques. The electrical compatibility between the motor and the driver are the most critical factors in a stepper motor system design such as ours. Some general guidelines in the selection of these components are: •

Inductance - Stepper motors are rated with varying degrees of inductance. A high inductance motor will provide a greater amount of torque at low speeds and similarly the reverse is true.

•

Driver Voltage - The higher the output voltage from the driver, the higher the level of torque vs. speed. Generally, the driver output voltage should be rated higher than the motor voltage rating.

•

Motor Stiffness - By design, stepping motors tend to run stiff. Reducing the current flow to the motor by a small percentage will smooth the rotation. Likewise, increasing the motor current will increase the stiffness but will also provide more torque. Trade-offs between speed, torque and resolution are a main consideration in deg a step motor system.

•

Motor Heat - Step motors are designed to run hot (50º-90º C). However, too much current may cause excessive heating and damage to the motor insulation and windings. The risk of overheating can be reduced by providing a programmable run/hold current feature.

Since, we were building from an already started project, we made use of the already existing stepper motors, for reasons of cost, but we introduced a dc motor into the base t. 3.2.6

MOTOR DRIVERS The motors operate at higher voltage and current levels than either the microcontroller or the latches that drive them hence the need for intermediate driver circuitry. These drivers

33

are usually power transistors, which can insulate the logic circuit from the effect of the motor current. We selected drivers based on the ratings of the motors, and for circuit space efficiency, we chose transistor IC packages housing several transistors instead of discrete transistors. Separate drivers were used for the stepper and dc motors as they have different control mechanisms and power ratings. 3.2.6.1 STEPPER MOTOR DRIVER The stepper motor driver receives low-level signals from the microcontroller and converts them into electrical (step) pulses to run the motor. One step pulse is required for every step of the motor shaft. Speed and torque performance of the stepper motor is based on the flow of current from the driver to the rotor winding. The factor that inhibits the flow, or limits the time it takes the current to energize the winding, is known as inductance. The lower the inductance, the faster the current gets to the winding and the better the performance of the motor. To reduce inductance, most types of driver circuits are designed to supply a greater amount of voltage than the motors rated voltage. The driver IC used is the ULN2803A Darlington Array. It contains eight darlington transistors with common emitters and integral suppression diodes for inductive loads. Each darlington features a peak load current rating of 600mA (500mA continuous) and can withstand at least 50V in the off state. Outputs may be paralleled for higher current capability. The ULN2803A has a 2.7kΩinput resistor for 5V TTL and CMOS and it is supplied in an 18-lead plastic DIP with copper leads and features the convenient input opposite-output pinout to simplify board layout. The pin configuration of ULN2803A is shown in appendix A. 3.2.6.2 DC Motor Driver The driver IC used for the dc motor is the L298 Dual Full-Bridge Driver. The L298 is an integrated monolithic circuit in a 15-lead multiwatt package. It is a high voltage, high current dual full-bridge driver designed to accept standard TTL logic levels and drive inductive loads such as relays, solenoids, DC and stepper motors. Two enable inputs are provided to enable or disable the device independently of the input signals. The emitters of the lower transistors of each bridge are connected together and the corresponding external terminal can be used for the connection of an external sensing resistor. An additional

34

supply input is provided so that the logic works at a lower voltage. The pin configuration of L298 is shown in appendix A.

3.2.7

LATCHES AND BUFFERS

3.2.7.1 Latches In our research, we found we needed to maximize the utilization of the microcontroller input/output ports. We had only two 8-bit ports available for driving six motors so we decided to use latches to hold the data for each of the motors and enable them when needed. Upon further research on available latches, we found the 74LS573 latch to be suitable for our design. The 74LS573 consists of eight latches with 3-state outputs for bus organized system applications. The flip-flops appear transparent to the data (data changes asynchronously) when Latch Enable (LE) is HIGH. When LE is LOW, the data that meets the setup times is latched. Data appears on the bus when the Output Enable (OE) is LOW. When OE is HIGH the bus output is in the high impedance state. 3.2.7.2 Buffers Buffers were used to isolate the PC parallel port from the transmitter circuitry to avoid damaging the parallel port. The 74HCT541 buffer IC was used. Its pin configuration is shown in appendix A.

3.3

SOFTWARE A robot, by definition, must have intelligence and this actually means some software that directs it on what to do, given zero or more input conditions.

3.3.1

CHOICE OF PROGRAMMING LANGUAGE From analysis on our project, we arrived at the conclusion that two separate pieces of software would be required. One would run on the PC’s processor and would take care of 35

the interface (GUI) or what could be called the robot’s dashboard. For this, we did some extensive research on the programming language that would be most suitable. We chose the Java programming language based on some of its desirable characteristics, including the following: •

Java Is simple – No language is simple, but Java is a bit easier than the popular object-oriented programming language C++, which was the dominant softwaredevelopment language before Java. Java is practically modeled on C++, but greatly simplified and improved. In addition, the number of language constructs is small for such a powerful language. The clean syntax makes Java programs easy to write and read.

•

Java Is Object-Oriented – Object-oriented programming (OOP) models the real world in of objects. OOP provides great flexibility, modularity and reusability.

•

Java Is Interpreted – You need an interpreter to run Java programs. The programs are compiled into Java Virtual Machine code called bytecode. The bytecode is machine-independent and can run on any machine that has a Java interpreter.

•

Java Is Robust – Robust means reliable. No programming language can ensure complete reliability. Java puts a lot of emphasis on early checking of possible errors, because Java compilers can detect many problems that would first show up at execution time in other languages. Java has eliminated certain types of errorprone programming constructs found in other languages. It does not pointers, for example, thereby eliminating the possibility of overwriting memory and corrupting data. Java has a runtime exception-handling feature to provide programming



for robustness. Java forces the programmer to write the code to deal with exceptions. Java can catch and respond to an exceptional situation so that the 36

program can continue its normal execution and terminate gracefully when a runtime error occurs. •

Java Is Architecture-Neutral – The most remarkable feature of Java is that it is

architecture-neutral, also known as platform-independent. With a Java Virtual Machine (JVM), you can write one program that will run on any platform, such as Windows, OS/2, Macintosh, and various UNIX, IBM AS/400, and IBM Mainframes. •

Java Is Portable – Java programs can be run on any platform without being

recompiled, making them very portable. Moreover, there are no platform-specific features in the Java language. The Java environment is portable to new hardware and operating systems. In fact, the Java compiler itself is written in Java. The second piece of software was to exist in the microcontroller code memory, and actually form the intelligence of the robot. The ATMEL series microcontrollers (8051 family) have an instruction set that is more or less a subset of the 8086 assembly language. However, from research, we found out that there were compilers that could permit the use of some high-level languages such as C and BASIC for programming these microcontrollers. The trade-off in using a high-level language instead of the native instruction set to program a microcontroller would be a slightly less efficient utilization of the limited code memory and slightly slower programs. On the other hand, you would have code that is clearer and easier to handle. This outweighed the disadvantages in the case of our project so we chose the C language, which has an almost one-to-one correspondence with the microcontroller assembly language.

37

CHAPTER FOUR

DESIGN AND IMPLEMENTATION OF THE ROBOTIC ARM

In the design of systems, there are generally two methods of approach namely: •

Top-down method

•

Bottom-Up method

The top-down method is usually applied in deg a system from the scratch while the down-top method is used for reverse deg of an already existing system or functional design as in software engineering. The diagram in fig. 4.1 below is a sketch of the robot manipulator.

Figure 4.1: Sketch of the Robot Arm

38

We employed the top-down approach in the design of the robot arm project and fig. 4.2 below shows how the various modules were integrated to arrive at the entire system.

ELECTRONIC HARDWARE

MECHANICAL ARM

SOFTWARE

SYSTEM INTEGRATION

ROBOT ARM/ MANIPULATOR

Figure 4.2: Robot Arm System Design (Top-Down Approach)

A block diagram model of the robot arm control is shown in fig. 4.3. The sensors are optocouplers located on the robot ts which send information to the microcontroller on the robot’s position. The actuators are the stepper and dc motors at each t.

Command + Input R[n]

E[n]

Controlled Controller

U[n]

Actuator

-

System to be Controlled

Sensor

Figure 4.3: Block Diagram Model of the Robot Arm Control

39

Output Y(t) -

4.1

MECHANICAL DESIGN AND FABRICATION It is pertinent to note that this part of the project requires very high expertise in mechanical design and fabrication, hence, and understandably too, it was a major source of concern for us considering our limited exposure in the above mentioned area. We therefore sought the assistance of experts in the mechanical engineering design field, and, with grateful hearts, we want to mention that Engr. Chigbo Mgbemene took it upon himself to assist us in the entire mechanical design and fabrication. Apart from the excitement of seeing abstract drawings transform into real mechanical components, we learnt some important things in the mechanical engineering design field while working with him. We employed the top-down approach (shown in fig 4.4) in the design of the robot arm but the fabrication of the arm was done component by component and eventually, the components were integrated to obtain the whole arm.

ROBOT ARM

BASE

SHOULDER

UPPER ARM

LOWER ARM

WRIST

GRIPPER

Fig. 4.4: Components of the (Mechanical) Robot Arm

Materials for the fabrication were selected based on some constraints that include: •

Weight

•

Work envelope

•

Workability

•

Maintainability 40

4.1.1

THE GEAR SYSTEM Each of the ts are powered by electric motors (stepper and dc motors) whose outputs were mechanically coupled to gear boxes for amplification of the output torque so as to satisfy the weight requirements of the arm and the object being picked. The principal requirements for effective power transmission in the robot arm include: The gear boxes are composed mostly of worm gears and spur gears. Worm gears were coupled directly to the motor’s shaft as it prevents movement in the opposite direction and this characteristic improved the holding torque as well as protects the motor from slipping under heavy loads.: For a typical gear train like the figure shown below: Driven Driver 1

32 3

4 5

6 7

…

Tn

n Driven

Figure 4.5: A typical Gear Train

Tn

=

 ( d × d × .....× ...d ) n− m  n n− 2

( d n− 1 × d n− 3 × .....× d n− m− 1 )  • T1 ............. 

d ....... d n − m • 1  f (d ) = ( d n )  n − 2     d n −1  d n − m +1   d n − m −1  ................ (1)   The following conditions must hold for equation (1) to be correct; i)

n must be even (because Tn =Tn+1)

ii)

n-m = 2

iii)

n>m

Recall :

n = Factor of Safety, 41

m= Module of gear, T = Developed Torque (Nm) T1 is always given as the motor torque and Tn is the torque required to be generated by the gear train to carry the load. This must be greater than the torque due to the load to be lifted and torque due to self weight of the arm (this includes all its appendages). Motor gear must be indicated as 1 in the diagram. Therefore motor gear diameter = d1. Tn = f(d)T1............................................................................................(2) For instance, If T1= 0.24Nm then Tn = 5Nm Then f (d) = 5/ 0.24 = 20.83

 → f (d ) = ( d n )  

d n− 2

....... d n − m • 1     d  .............................................(3) d n −1  d n − m +1   n − m −1  

Each bracket represents gears on the same shaft. Diameter ratios as well as the number of shafts affect the f(d). Angular velocity is also a factor to be considered. For example, given that n = 6, d1 = 14mm, d2 =38mm, d3 = 22mm, d4 =40mm, d5 = 24mm and d6 = 37mm, the torque on the 6th gear can be computed using equation 1 as shown below: Tn

=

37 * 40 * 38 * 0.155 / 24 * 22 * 14

=

1.18Nm

The torque requirements at the various links were obtained using equations 1, 2 and 3, the results are in given in table 4.1. Table 4.1 Result Of Torque Calculation

t Shoulde r Elbow Wrist

Calculated torque (Nm) 5.82 3.61 0.48

42

Gripper

5.82

Table 4.2 Arm Dimensions

Body Part The Waist (base) The Shoulder The Upper Arm The Fore Arm The Wrist

Length(mm)

Height (mm)

Width (mm)

289 271 222

113.3 92.9 100.5

82.4 66.3 54.2

Table 4.3 Gear Dimensions For The Waist

Diameter(D) (Mm)

Bull Spur Pinion Bevel (Spur) Bevel Pinion

252 50.4 225 45

For The Shoulder Bull Spur (7)

Diameter(D) (Mm)

Worm Gear 3

19.5, 28.5, 56.4, 27.9, 43.4, 22.5& 42.8 6.5

For The Elbow

Diameter(D) (Mm)

Bull Spur(7)

16.6, 21.8, 45.5, 26.5, 40.9, 22.9& 42.8 Worm Gear (1) 7.4 For The Wrist

Diameter(D) (Mm)

Bull Spur (7)

19.4, 20.5, 56.4, 37.2, 25.3, 42.5, & 24.6 Worm Gear (1) 7.5 43

4.2

ELECTRONIC HARDWARE DESIGN AND IMPLEMENTATION The electronic hardware design consists of the following modules:

4.2.1

•

The Transmitter Unit

•

The Motor Controller

•

The Interrupt Controller

•

The Power Supply Unit THE TRANSMITTER UNIT

The transmitter circuit consists of a DB-25 connector, a microcontroller (AT89S52), a voltage regulator (7805), a timer IC (555), buffers, infrared LEDs, transistors and resistors. The DB-25 connector links the transmitter circuit to the parallel port of the PC. commands from the robot’s interface are sent to the transmitter microcontroller via the DB-25 connector. The microcontroller is programmed to read the 8-bit command code and use it to modulate the 38 kHz infrared carrier. The modulation (or encoding) is done with the aid of a 555 timer configured in astable mode. The microcontroller pulses the reset pin of the 555 timer in accordance with the logic level of each bit of the command code. For instance if a command code ‘1000 1101’ is read from the parallel port, the bits ‘1’, ‘0’, ‘1’, ‘1’, ‘0’, etc are in turn sent to the reset pin of the 555 timer via the microcontroller serial transmitter pin. Logic ‘0’ at the reset pin will stop oscillation, and logic ‘1’ will resume oscillation. The IR receiver at the robot base senses the presence or absence of incident carrier signal and interprets as logic ‘1’ and logic ‘0’ respectively. Buffers were used to interface the parallel port with the transmitter circuit and transistors were used for switching. The transmitter and receiver serial baud rate have to be equal and the calculation is given below. Also, the calculation for setting the 555 timer to oscillate at 38 kHz is given. 44

4.2.1.1

BAUD RATE CALCULATION We used a baud rate of 1500 bps. To configure the microcontroller for this baud rate, a specific value is loaded in its timer (timer 0 or timer1, but we used timer 1 ) and the calculation is as shown. val

=

256 – ((System frequency / (12 * 32)) / baud)

Where: baud

=

desired baud rate (1500)

System frequency

=

24.00014MHz

Val

=

value to be loaded in to the timer

6  1500 val = 256−   24.00014× 10  ( ) 12 × 32  

= 4.2.1.2

214 approx.

CARRIER FREQUENCY CALCULATION A frequency of 38 kHz implies a signal period of (1/38 kHz), that is 0.0000263s For the 555 timer: t high = 0.693 × ( Ra + Rb ) ×C

tlow = 0.693 × ( Rb ) × C T = t high +tlow

Where: Ra Rb C

= = =

4.7k (fixed resistor value) variable resistor value - to be calculated 0.1uF (fixed capacitance value)

Making Rb subject of formula and substituting fixed values gives Rb 4.2.2

=

16.62kΩ

THE MOTOR CONTROLLER 45

The motor interface is the core control circuitry for the robot. It consists of a microcontroller, latches, Darlington transistor IC packages, diodes, and an L298 dual fullbridge driver. Two out of the four ports of the microcontroller were used to drive the motors. Five stepper motors and one dc motor were used to control each of the six degrees of motion. Each of the stepper motors required four control pins while the dc motor required three. That is twenty-three pins in all. The microcontroller pins therefore, had to be demultiplexed to control the motors in turn, hence latches were used. Control lines were used to select the appropriate latch at any instant. The latch (74HC373) is a TTL IC, and therefore requires a source voltage of 5V. But the motors operate with 12V dc, hence the need for some sort of buffering between the latches and the motors. A Darlington transistor IC package (ULN2803) was used to drive the stepper motors. The dc motor requires a transistor H-bridge in order to drive it in both directions (clockwise and counter clockwise) without changing the source polarity. This was achieved with an L298 dual full-bridge driver. The circuit diagram of the motor controller is shown in Appendix E 4.2.3

THE INTERRUPT CONTROLLER The AT89S52 microcontroller has two external interrupt pins, INT0 and INT1. We used INT0, which was configured such that a ‘high-to-low’ transition at this pin will trigger an interrupt and the corresponding interrupt service routine will be executed. But we have six interrupt sources as from the robot. Five optocouplers for the upper ts and one switch for the gripper. Hence, an interrupt controller circuit was needed to connect these six sources to one interrupt pin. An array of AND gates is used as shown in Appendix E. The circuit is connected in such a way that once any input goes low (the motor s are active low) the output of the AND array goes low. This is connected to the ‘trigger’ pin of a 555 timer configured in monostable mode. The output of the 555 timer is changed from ‘high’ to ‘low’ but it 46

returns to the high state after a while (monostable). The ‘low-to-high’ transition is inverted to a ‘high-to-low’ transition by a schmitt trigger, thereby generating an interrupt on INT0.

47

4.2.4

THE POWER SUPPLY UNIT The power supply unit provides four voltage levels for the robot control. The dc motor requires 15Vdc, the stepper motor requires 12Vdc, the TTL ICs require 5Vdc, and -12Vdc was provided in anticipation of possible need of signal amplification with an operational amplifier. The ac voltage from the mains is stepped down by a centre tapped transformer. The low voltage ac is converted to dc by a bridge rectifier, filtered by capacitors and ed through appropriate voltage regulator ICs to obtain the required dc voltage levels. The 7815, 7812, 7805 and 7912 voltage regulators were used to obtain regulated outputs of 15V, 12V, 5V and -12V dc, respectively. It was observed, during test, that on loading, the output of the voltage regulators (especially the 7815) dropped significantly thereby posing a problem to the correct functioning of the motors. To overcome this problem, a TIP125 power transistor was connected across the voltage regulator as shown in fig. 4.8. Under normal loading, the voltage regulator is able to provide the required current. But when the required current exceeds what can be provided by the regulator, instead of a voltage drop at the output of the regulator, the extra current is drawn directly from the unregulated dc source through the TIP125, thereby preventing a voltage drop. These circuits were all implemented using the printed circuit board (PCB) technology. This process generally involves drawing the circuit diagram with the aid of a PCB design software. The circuit is printed on paper using a laser jet printer. The printed circuit diagram is placed on a copper-coated board known as the printed circuit board. An exact impression of the circuit is made on the board by pressing the printed circuit unto the board with hot iron. The impressed board is then placed in some fluid known as etching fluid, and all the copper, apart from the parts coated by the printed circuit ink (which was transferred by hot iron impression), is ‘etched’ off leaving a copper trace that is an exact reproduction of the printed circuit. Appropriate holes are then drilled and the components soldered. 48

The PCB has the advantage of a neater circuitry (with basically no wires!) hence easier to troubleshoot. Also, since one can have a multi-layered PCB, then larger circuits can be compressed into a smaller space as compared to the conventional vero boards.

4.3

SOFTWARE DESIGN Three separate pieces of software were developed for the robot system. The interface software, which was written in JAVA programming language and two pieces of software for the transmitter microcontroller and the receiver/robot control microcontroller. In all, the top-down design approach was adopted for the software design. JAVA being an object oriented programming language, the universal modeling language specifications were adopted as much as possible.

4.3.1

GUI SOFTWARE DESIGN AND IMPLEMENTATION

4.3.1.1

REQUIREMENTS SPECIFICATION The GUI code is expected to capture the following functions: •

At start up the is offered the option of controlling the robot directly or selecting complete pick and drop actions.

•

If the chooses to use the pick and drop functionality, he is shown a display with options on how fast to pick and drop and how many times. After choosing from the available options and entering his choice using an ‘OK’ button, the GUI code takes note of the choices and encodes it as an 8-bit command code which is sent to the transmitter through the parallel port for onward transmission to the robot controller at the base of the robot.

•

If the chooses the direct control option, he is serviced with a display which, when activated, responds to the appropriate key presses and generates corresponding 8-bit command codes which are sent to the transmitter through the parallel port. 49

4.3.1.2

USE CASE ANALYSIS USE CASE PROPERTIES USE CASE ID: DESCRIPTION:

M001 Generates command code that will control the robot using predefined behaviours already assembled into complete pick and drop tasks

ACTOR: NAME: SCOPE: PRE-CONDITION(S):

Pick and drop Subsystem The must select valid options or combinations of options

POST-CONDITION(S):

The command code that will carry out the pick and drop task has been sent through the parallel port

EVENT/TRIGGER:

The enters his choice using the 'OK' button

CATEGORY: AUTHOR: MANAGEMENT:

Main Robotic arm design group Project Supervisor

DATE:

Apr-07 Table 4.4: Use Case Event Matrix (M001) Event

Action

Response

The enters his choice using the ‘OK’ button

System generates an 8bit command code that corresponds to the ’s choice combination

System sends the 8-bit command code through the parallel port and triggers transmission to the robot controller at the base of the robot

50

Remarks

Table 4.5: Information Needs (M001) WHO NEEDS INFORMATION System

WHAT INFORMATION ’s combination of options for pick and drop

WHERE IS IT NEEDED Pick and drop option page

WHEN IS IT NEEDED During pick and drop mode of robot control

USE CASE PROPERTIES USE CASE ID: DESCRIPTION:

M002 Generates command code that will allow the control the robot directly

ACTOR: NAME: SCOPE: PRE-CONDITION(S):

Direct control Subsystem The must activate this mode of control The command code that will carry out the direct control task has been sent through the parallel port

POST-CONDITION(S):

EVENT/TRIGGER:

The presses one of the robot control buttons on the keyboard

CATEGORY: AUTHOR: MANAGEMENT: DATE:

Main Robotic arm design group Project Supervisor Apr-07

51

HOW IS THE INFORMATION NEEDED 1) By data entry 2) By option selection 3) By slider positioning

Table 4.6: Use Case Event Matrix (M002) Event

Action

Response

The presses one of the robot control buttons on the keyboard

System generates an 8bit command code that corresponds to the ’s choice combination

System sends the 8-bit command code through the parallel port and triggers transmission to the robot controller at the base of the robot

Remarks

Table 4.7: Information Needs (M002) WHO NEEDS INFORMATION

WHAT INFORMATION

WHERE IS IT NEEDED

WHEN IS IT NEEDED

Use Case Diagram of the system is shown in fig 4.6 below

System

Pick and Drop

Direct Control

Fig. 4.6: Use Case Diagram for Robot GUI

52

HOW IS THE INFORMATION NEEDED

Implementation The code for the robot graphic interface (GUI) is given in appendix B. 4.3.2

TRANSMITTER SOFTWARE DESIGN AND IMPLEMENTATION

4.3.2.1

Requirements Specification The transmitter microcontroller code is expected to capture the following functions: •

It should monitor the transmit activation control line from the parallel port

•

If the control line goes low, it should read the 8-bit data from the parallel port and transmit it serially through its serial transmit pin

4.3.2.2 Program Flowchart The flowchart showing how transmitter software is shown below in fig 4.7 START

INITIALIZE SERIAL BAUD RATE

READ TRANSMIT CONTROL LINE

NO IS IT ‘LOW’

?

YES

READ BYTE FROM PARALLEL PORT

TRANSMIT SERIALLY

Fig. 4.7: Program Flowchart for Transmitter Software

53

Implementation The code for the transmitter microcontroller is given in appendix B. 4.3.3

RECEIVER/ROBOT CONTROL SOFTWARE DESIGN AND IMPLEMENTATION

4.3.3.1

Requirements Specification The receiver/robot microcontroller code is expected to capture the following functions: •

It should monitor the command code which is updated in the serial interrupt service routine each time a command is sent by the

•

Each time it reads the command code, it decodes it to determine the ’s request and also extracts some parameters that are present in the command code. A code map which is transparent to both the interface (GUI) code and the robot control code is used to ensure that the two pieces of software understand each other with respect to the meaning of each 8-bit command code

•

Having determined the request, assuming the code is valid, it calls the appropriate function(s) that will execute the ’s request by driving the motors appropriately

4.3.3.2 Program Flowchart Fig 4.8 shows the flowchart for the receiver/robot control software design

54

START

INITIALIZE SERIAL BAUD RATE AND EXTERNAL INTERRUPTS

READ THE RECEIVED COMMAND CODE

DECODE TO GET THE REQUIRED FUNCTION

NO IS CODE VALID ? YES

CALL FUNCTION TO HANDLE THE REQUEST BY DRIVING THE MOTORS APPROPRIATELY

Fig. 4.8: Program Flowchart for Transmitter Software Implementation The code for the receiver/robot control microcontroller is given in appendix B.

4.4

SYSTEM INTEGRATION AND TESTING The robot arm design project was split into smaller tasks to reduce complexity and also to facilitate parallel implementation of independent tasks. The tasks include robot arm fabrication, gear design and assembly, control circuit design and implementation, design 55

and implementation of wireless communication module and software development for both the GUI and microcontrollers. These tasks were allocated among the of the group and we constantly met to establish and update guidelines that will ensure the compatibility of the various modules during system integration. Most of the circuits were first implemented on bread boards before transferring to printed circuit boards apart from the very simple ones. We tested the individual circuit boards for basic errors and also for functionality where applicable. During testing, some components were damaged and replaced. The wireless communication module was implemented and tested with a sample circuit and we were able to achieve a range of about 6 metres line-of-sight. Having tested the various modules, the system integration was done in stages. All the individual circuits were integrated and tested. Some power supply issues were encountered, such as supply voltage dropping significantly when loaded and undue heating of the voltage regulators, and we tried rectifying them but could not do so immediately. We then decided to use an already tested power supply unit obtained from a scrap computer. The gear systems for the ts were coupled with the motors and mounted on the fabricated robot arm. Then control and power lines were drawn from the motors and connected to the control circuitry. A test code for testing the movement of each t was developed in which we tested control of each of the t motors, and the system test was carried out. The results were as follows: •

The gripper motor turned satisfactorily, clockwise and counterclockwise. But the grip force was observed to be quite low.

•

The wrist roll motor worked but we discovered that it was loosely coupled to the gear train. That was rectified.

•

The wrist pitch motor was successfully controlled.

•

The wrist roll motor was successfully controlled. 56

•

The elbow motor was successfully controlled.

•

The waist or base motor was successfully controlled.

We also tested the wireless communication module (now integrated into the entire system). Initially it did not respond but after troubleshooting, it worked.

57

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

This project was basically an analysis of an already existing work with a view to improving on it and possibly adding new features. Some limitations in the original project, apart from the fact that it was not completed, were •

Insufficient motor torque and torque amplification with gears, to the robot and any added weight

•

Heavy weight of robot arm due to material used (steel)

•

Failure to achieve the required six degrees of freedom for the robot arm

•

Lack of flexibility in the entire system since a computer (PC) was directly attached to the robot control circuitry, and a few others.

5.1

ACHIEVEMENTS In spite of some of the limitations and due to the recommendations by the previous group, we were able to achieve the required six-degrees of freedom. The following improvements were made and some new features were added •

A richer interface with enhanced functionalities and friendliness.

•

We used bigger and stronger gears to enable the arm carry its load without slipping. Also a type of gear called the “worm gear” was also used because it has the advantage of being almost impossible to slip. This is due to the fact that it only turns in one direction.

58

•

The weights of all the motors were put into consideration when calculating the torque at each t. This is to make sure the gears are arranged in a way that will produce enough torque to carry the succeeding load.

•

The use of printed circuit boards (PCB) to do the circuits. This reduces the errors due to faulty connections and wiring usually found on other boards.

•

Perhaps one of the most important achievements is that we were able to change the material used for arm fabrication. Due to expert advice from Engr. Mgbemena, we settled for aluminum because of its light weight, strength and resilience.

•

Use of DC motor at the base. The output torque of the DC motor is higher than that of the stepper motors. Using DC motor at this t brought us a step closer to solving the problem of insufficient torque to carry the arm.

•

We used a microcontroller which provides enough pins for selecting motors, hence eliminating the need for decoders. Also, we used transistor driver ICs instead of discrete transistors to simplify the circuit and make it less error-prone.

•

The motors are operated with a mechanism, using optocouplers. This is connected to the gear box in such a fashion that it triggers when specific positions of the output shaft of the motor are reached.

•

For the communication with the robot, we used an infrared circuit. This ensures that the robot is unencumbered by wires running from the system to it. Although the ST12 would have been the ideal choice, since it was not readily available, we settled for a very efficiently designed microcontroller based infrared transmission circuit.

•

The gripper is fitted with pressure sensors that make sure it does not place undue pressure on whatever material it is picking. Since industrial robots are usually made for a particular purpose, the amount of force exerted by the gripper can be preset based on its function.

59

5.2

LIMITATIONS We encountered a number of problems that hampered the fast completion of the project and placed a limitation on the amount of improvements we were able to make. They include: •

Insufficient mechanical knowledge: Engr. Mgbemene, who worked with the last group, was unavailable at the start of our project. This resulted in a lot of mistakes, on our part, based on gear arrangement and material selection. Thankfully, he came back and put us on the right track- but by then, a lot of time and resources had been lost.

•

Unavailability of some integrated circuits One of the improvements in the robot design was in the area of communication. We were supposed to use an integrated encoder-decoder chip called ST12 for infrared communication. Unfortunately, this chip is not available in Nigeria so we had to order it. The time wasted before it arrived was proving to be too much, so we had to search for other options.

•

Irregular power supply The progress of both the mechanical and electronic parts of the project was greatly hampered by the irregularity of the power supply.

•

Inadequate Machines for Fabrication Due to outdated and inadequate machinery in the Mechanical Engineering Laboratory the robotic arm could not be machined using the required lathe machine but had to be built manually. This increased the total amount of time wasted.

•

Lack of well equipped electronics laboratory

60

Most of the work was done in inadequate make-shift laboratories (That is in our room). This retarded the progress of the project because we had to source for materials from other places.

5.3

ROBOTICS IN THE FUTURE Today, robots are doing human labor in all kinds of places. Best of all, they are doing the jobs that are unhealthy or impractical for people. This frees up workers to do the more skilled jobs, including the programming, maintenance and operation of robots.

Robots that work on cars and trucks are used for welding and assembling parts, or lifting heavy parts - the types of jobs that involve risks like injury to your back and arm or wrist, or they work in environments filled with hazards like excessive heat, noise or fumesdangerous places for people. Robots that assemble and pack cookies or other foodstuff do so without the risk of carpal tunnel injury, unlike their human counterparts. Robots that make computer chips are working in such tiny dimensions that a person couldn't even do some of the precision work required.

In the health industry, robots are helping to research and develop drugs, package them and even assist doctors in complicated surgery such as hip replacement and open heart procedures. And the main reason robots are used in any application is because they do the work so much better that there is a vast improvement in quality and/or production, or costs are brought down so that companies can be the best at what they do while keeping workers safe.

The changes in future robots that will revolutionalize our way of living will occur in a subtle fashion. It will happen when we wake up one morning thinking about the past and realize that the things we take for granted are exceptionally different than they were when 61

we were younger. In time, just as innovations like the light bulb and telephone elevated life, as we know it to new standards, so will robotics incorporate itself in our everyday lives. Discussed below are the various ways the field of robotics can affect our lives as proposed by the Robotics Industries Association. Virtual Travel - People will be able to visit each other without traveling. They will do this by taking control of a robot at their desired vacation destination, and use the Internet to transmit all the sensory information back and forth. What will this mean? Doctors will make "house calls" again. Long distance relationships will never be the same. Families spread across the globe can play games together. And perhaps most importantly, people will think nothing of having a satisfying conversation with a mechanical contraption made of aluminum, plastic, and silicon Housekeeping by Choice - The physical environments we live in will take care of themselves. Machines will do the routine chores around the house. We will choose when it is time for the extraordinary. Our houses and apartments will keep themselves swept and scrubbed clean. There will be no piles of laundry, and your basic dinner will be moments away. Machines will not have replaced us. But they will give us the opportunity to build on the routine and create the unusual, brilliant, or just different. Robots will raise the standard upon which we will build. They will give us a chance to dream and the time to live life to the fullest Artificial Intelligence - Perhaps the most dramatic changes in future robots will arise from their increasing ability to reason. The field of artificial intelligence is moving rapidly from university laboratories to practical application in industry, and machines are being developed that can perform cognitive tasks, such as strategic planning and learning from experience. Increasingly, diagnosis of failures in aircraft or satellites, the management of a battlefield, or the control of a large factory will be performed by intelligent computers. Like the term "robot" itself, artificial intelligence is hard to define. Ultimate AI would be a 62

recreation of the human thought process -- a man-made machine with our intellectual abilities. This would include the ability to learn just about anything, the ability to reason, the ability to use language and the ability to formulate original ideas. Roboticists are nowhere near achieving this level of artificial intelligence, but they have had made a lot of progress with more limited AI. Today's AI machines can replicate some specific elements of intellectual ability. Despite the excitement about the development of this industry, questions about the promises and peril concerned with our increased dependence on robots arise. Some of them are discussed below. Roboticists believe that humans will be more comfortable dealing with creatures physically similar to themselves. ASIMO, the amazing Honda robot that can dance and climb stairs, is four feet tall with arms, legs, fingers, and so forth. But ASIMO can be off-putting — all solid wire and plastic and aluminum; no warmth, no DNA. Should robots be designed in man’s image, or as something completely different? If humanoid robots become integral to our daily lives, should they be expected to follow the laws and norms of human society, or should a new set of guidelines be drawn up especially for them? If so, what are the primary elements that need to be addressed to protect robots from humans and humans from robots?

Robots are becoming nurse-bots and roboceptionists, jobs that have most often been performed by women. Many Roboticists, the vast majority of whom are men, dismiss the danger of anthropomorphism yet frequently refer to their creations as “she.” Should robots be gender-specific? Have they already been categorized?

63

As robots become more pervasive in the workplace, what steps should be taken to preserve the livelihood of the human beings they replace? Should a vulnerable labor force be retrained in advance? Should protective legislation be ed?

In the near future there will be robots designed to assist surgeons replace heart valves and knees (and possibly robots to perform surgery independently). Should a patient be able to decline robot-assisted treatment, even if his insurance company considers it cost-effective? What if the surgeon is a human using robotic remote-control technology from a hospital 1,000 miles away?

The Japanese believe that robots will be most useful as personal companions and caretakers for the elderly. Already, robots can take certain vital measurements, such as heart rates. As robots become more skilled and sophisticated, how can we ensure against a future of old people confined to institutions serviced and supervised by machines?

Human environments are fundamentally chaotic, yet robots are sensitive precision instruments that can become unreliable or agitated in unpredictable situations. How should we control environments so that robots can function consistently, and who is responsible if a destabilized robotic system damages personal property or injures a human being? In any case, robots will certainly play a larger role in our daily lives in the future. In the coming decades, robots will gradually move out of the industrial and scientific worlds and into daily life, in the same way that computers spread to the home in the 1980s.

5.4

COST ANALYSIS S/N 1

DESCRIPTION Transformer

QTY 1

64

UNIT COST (N) 370

AMOUNT (N) 370

2 3 4 5 6 7 8 9 10 11 12 13

23 24 25 26 27 28 29 30 31 32

Rectifier Regulator Capacitor Resistor Transistor SIL Connector IR Receiver IR LED 555 Timer Buffer OR Gate IDE Cable and Connector Mica Capacitors DB25-f Microcontroller 24MHz Crystal Switch LED Battery Latch Stepper Motor Driver DC Motor Driver AND Gate Schmitt Trigger Diodes Aluminium Sheet Gears and Motor Transportation Research Printing and Glass Reinforced

33

Miscellaneous

14 15 16 17 18 19 20 21 22

1 5 17 13 6 17 7 7 3 4 1 2

50 50 20 10 70 20 30 20 30 80 80 100

50 250 340 130 420 340 210 140 90 320 80 200

6 1 2 2 2 2 2 3 3

20 200 300 40 20 10 50 100 280

60 200 600 80 40 20 100 300 840

1 2 1 7 1

250 80 80 10 2800

250 160 80 70 2800 8000 3400 2000 4000 10000

Binding Plastic (GRP)

2000

TOTAL

5.5

37940

CONCLUSION The project was time-consuming, work-intensive and economically tasking. However, we are proud as a group to have achieved for the first time, the control of a 6-degree of freedom robotic arm, a pioneer in the department of Electronics Engineering, UNN.

65

From our experience, we recommend that for the future implementation of this project, the following improvements can be made: •

The robot can be fitted with wheels and adequate sensors to make movement possible.

•

Control can be improved by using a remote control or joystick to manipulate the robot instead of devoting a whole computer system to it.

•

The robot can be given added intelligence so that it can sense obstacles respond appropriately.

•

Proper selection of integrated chips should be made and they should be thoroughly tested before purchase to eliminate chances of faulty chips being purchased.

•

It is also advisable to have the arm fabrication done in a workshop with up to date machinery to avoid errors in construction.

The possibilities are endless. Robotics is a relatively untapped field in Nigeria and it has many prospects. Starting with our community, we can, step by step, create robots that will ultimately be used to perform some pertinent tasks that are too bothersome for human beings. The fact that it also combines various disciplines of engineering is also notable.

REFERENCES

Andersen, P. K., Bjedov, G. & Scarbrough, M. G., “Essential C: An Introduction for Scientists and Engineers”. Florida: Saunders College Publishing, 1995. Cormier, J. M.“Robotics Training Systems – Concepts and Applications”. FirstEdition,. Buck Engineering Co. Inc., 1985. John, C. J., “Introduction to Robotics: Mechanics and Control”. Second Edition, India: Pearson Education, Inc., 1989..

66

Kuo, B. C., Golnaraghi Farid, “Automatic Control Systems”. Eight Edition, John Wiley & Sons, Inc., 2003.. Kafrissen, Edward, Stephans, and Mark, Industrial Robots and Robotics. (Virginia: Reston Publishing company, Inc., 1984) Kenjo, Takashi, “Stepping Motors and their Microprocessor Controls” Oxford University Press, c1984. LC number: TK2785 .K4 1984 Vishay Semiconductor GmbH. TCST110. up to TCST230. Lenarcic, j., “Kinematics” in The International Encyclopedia of Robotics. Wiley and Sons, 1988 Liang, Y. D., “Introduction to Java Programming”. 3rd Edition, New Jersey: Prentice-Hall Inc., 2001. Roth, B., Rasteger, J., and Scheinman, V., “On the Design of Computer Controlled Manipulators”, Vol. 1, First CISM-IFToMM Symposium, Sept., 1973 Robotics Training Systems: Concepts and Applications First Edition, By the staff of Buck Engineering. (USA: Buck Engineering Co. Inc., 1988) 5804 BiMOS II Unipolar Stepper Motor Translator/Driver datasheet. By Allegro MicroSystems Inc. 115 Northeast Cuto_, Box 15036, Worcester, Massachussetts, 1998. Scherz, Paul, Practical Electronics for Inventors. Second Edition, New York: Mc-Graw Hill, Inc.,2000.

67

Theraja, B. L. & Theraja, A. K, A Text Book of Electrical Technology. New Delhi: S. Chad & Company Ltd.,1959 Robotics Introduction. (2000). “Definitions” http://www.ee.scu.edu/classes/2000winter/elen337/Lecture1/tsld003.htm; Robot. (2001). “History of Robotic” http://www.ukrobot.co.uk/html/main.htm Robotics Introduction. (2001). “Definitions, Etymology http://www.ee.scu.edu/classes/2000winter/elen337/Lecture1/tsld002.htm; The Robot Factory Inc. (2000). “Education” http://www.robotfactory.com/edu.html, THOMSON Microelectronics The Tech. (2001). “Introduction to Robotics.” http://www.thetech.org/exhibits_events/online/robots/intro/

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GLOSSARY

Accuracy - The accuracy of a robot is a measure of how the robot can reach a position at which it was instructed to reach. Artificial Intelligence - This can be defined as the branch of computer science that deals with writing computer programs that can solve problems creatively. Axis - A pivot point for a type of movement. End-effectors - End-effectors are hand-like devices or special tools placed on the robot’s arm used to perform work. They are designed to mimic the function and structure of the human hand. Industrial Robots - An industrial robot is officially defined by the International Standards Organization as an automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes. The field of industrial robotics may be more practically defined as the study, design and use of robot systems for manufacturing. Number of axes - The number of axes of robot is the number of ts required to reach any point in space. Robot - A robot is simply defined as a device that connects sensing with actuation using a suitable computer logic, which processes the inputs from the sensors and sends out outputs to actuate devices. It can also be defined as a computer-controlled machine that is programmed to move, manipulate objects, and accomplish work while interacting with its environment.

69

Robot Controller - This refers to the computer logic that controls the robot’s actions. The robot controller is a device that has, programmed in it, the instructions which are to be performed by the robot. It is also referred to as the brain of the robot. Robotics - This is the area of artificial intelligence that is concerned with the practical use of robots i.e. robotics is the science and technology relating to use and design of computercontrolled mechanical devices. Work Envelope - This is the region of space a robot can reach.

70

1 40 2 39

APPENDIX A

3 38

PIN4 CONFIGURATIONS 37 5 P1.0 P1.1 P1.2 P1.3 P1.4 P1.5 P1.6 P1.7 RST (RXD) 3.0 (TXD) 3.1 (INT0) 3.2 P3.3 P3.4

36

P3.7 XTAL2 XTAL1 GND

P0.0

35

P0.1

7

P0.2

34

P0.3

8

P0.4

33

P0.5

9

P0.6

32

P0.7

10 31

AT89S52

EA’/VPP ALE/PROG’

11

PSEN’

30

P2.7

12

P2.6 29

P3.5 P3.6

VCC

6

13

P2.5 P2.4

28

P2.3

14

P2.2

27

P2.1

15

P2.0

26 16 25 Fig. A.1: Pin Configuration of AT89S52(MICROCONTROLLER) 17 24 18 23 19 22 20 21

71

GND TRIGGER OUTPUT RESET

1

8

2

7

3

555

4

+VCC DISCHARGE THRESHOLD CONTROL VOLTAGE

6 5

Fig.A.2: Pin Configuration of 555 (TIMER)

OUT 1 IN 1

1

18

IN 2

2

17

IN 3

3

16

IN 4

4

15

IN 5

5

IN 6

6

13

IN 7

7

12

IN 8

8

11

GND

9

10

ULN2803A

14

OUT 2 OUT 3 OUT 4 OUT 5 OUT 6 OUT 7 OUT 8 VSS

Fig. A.3: Pin Configuration of ULN2803A (DARLINGTON ARRAY)

72

Fig. A.4: Pin Configuration of the L298 Dual Full-Bridge Driver

OC’ D0

1

20

VCC

D1

2

19

O0

D2

3

18

O1

D3

4

17

O2

D4

5

16

O3

D5

6

15

O4

D6

7

14

O5

D7

8

13

O6

9

12

O7

10

11

G

GND

74573

Fig. A.5: Pin Configuration 74573 (LATCH)

73

OE1’ A0

1

20

VCC

A1

2

19

OE2’

A2

3

18

Y0

A3

4

17

Y1

A4

5

16

Y2

A5

6

15

Y3

A6

7

14

Y4

A7

8

13

Y5

9

12

Y6

10

11

Y7

GND

74541

Fig. A.6: Pin Configuration 74541 (BUFFER)

1A

1

20

VCC

1Y

2

19

6A

2A

3

18

6Y

2Y

4

17

5A

3A

5

16

5Y

3Y

6

15

4A

GND

7

14

4Y

7414

Fig. A.7: Pin Configuration of 7414 (SCHMITT TRIGGER)

74

APPENDIX B

PROGRAM IMPLEMENTATION (CODES) GUI CODE /* * Pioneer_Ware.java * Created on 25 April 2007, 10:45 */ package com.robot; import javax.swing.Timer; import java.awt.event.*; /** * @author Robotic Arm Design Group */ public class Pioneer_Ware extends javax.swing.JFrame { static Timer welcomeTimer; public final static int WAIT_TIME = 5000; //Time in millisecs static Commands cmd; static Pioneer_Ware pWare; /** Creates new form Pioneer_Ware */ public Pioneer_Ware(){ initComponents(); } /** *Create the GUI and show it. For thread safety, this method should be *invoked from the event-dispatching thread */ private static void createAndShowGUI(){ pWare = new Pioneer_Ware(); cmd = new Commands();

75

cmd.setVisible(true); pWare.setVisible(true); //Instantiate and start the welcome timer, giving it duration 'WAIT_TIME' welcomeTimer = new Timer(WAIT_TIME, new ActionListener() { public void actionPerformed(ActionEvent evt) { pWare.dispose(); //pWare = null; } }); welcomeTimer.setRepeats(false); welcomeTimer.start(); } /** * @param args the command line arguments */ public static void main(String args[]) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); } // Variables declaration - do not modify private javax.swing.JLabel lblRoboPix; // End of variables declaration } /* * Commands.java * Created on 25 April 2007, 12:13 */ package com.robot; import javax.swing.*; import java.awt.Color;

76

import java.awt.event.*; import jnpout32.*; import java.applet.*; import java.net.URL; /** * * @author Robot Arm Design Group */ public class Commands extends javax.swing.JFrame { //Variable declarations static final short DATA_PORT_ADDRESS = 0x378; static final short CONTROL_PORT_ADDRESS = 0x37A; static final int CONTINUOUS = 0; static final int NON_CONTINUOUS = 1; static final int SLOW = 0; static final int MEDIUM = 1; static final int FAST = 2; static final int MAX_NUM_OF_TIMES = 10;

/*Max number one can enter for the 'No of times' option in pick-and-drop*/

int selectedRadioButton = CONTINUOUS; boolean isExecuting = false;

//A flag used to determing the execution status of the arm

AudioClip[] song = new AudioClip[3]; pPort port;

//default selection //some audioclips

//handle to the parallel port data

Action upAction, downAction, leftAction, rightAction; Action gripAction, releaseAction, cwRollAction, acwRollAction;

/** Creates new form Commands */ public Commands() { initComponents(); bindKeys(); initAudio(); initPorts(); }

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/** *Method called when clicks the 'Stop/Reset' button *@ param evt the ActionEvent object */ private void reset(java.awt.event.ActionEvent evt) { // TODO add your handling code here: Timer resetTimer; final int RESET_DURATION = 2000; //to be modified later port.output(DATA_PORT_ADDRESS, (short)0xFF); //send 11111111 to parallel port port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter i.e. the

microcontroller code //reads the LSB of this control byte to decide //whether to move data on port 1 to transmit buffer try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

btnReset.setEnabled(false); btnExecuteCmd.setEnabled(false); //Instantiate and start reset timer with duration 'RESET_DURATION' resetTimer = new Timer(RESET_DURATION, new ActionListener() { public void actionPerformed(ActionEvent evt) { //Things that should happen at the end of the specified duration btnReset.setEnabled(true); btnExecuteCmd.setEnabled(true); txtNoOfTimes.setEnabled(true); rBtnSpecificNo.setEnabled(true); isExecuting = false; /* *Change song *Use a try-catch block for smooth program flow in case the sound file no longer exists

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*/ try{ song[0].stop(); song[1].loop(); }catch(Exception e){ e.printStackTrace(); } } }); resetTimer.setRepeats(false); resetTimer.start(); }

/** * Method called when the 'OK' button on PickAndDrop tab window is clicked * @ param evt the ActionEvent object */ private void executeCmd(java.awt.event.ActionEvent evt) { // TODO add your handling code here: int noOfTimes = 1; //default int speedVal = sldSpeed.getValue(); //Here we get to know the selected speed int execution_duration = 0;

//Default - to be modified later

int unit_exec_duration = 0;

/*Time it takes for one pick-and-drop action in millisecs -

to be modified*/ String requestInfo = ""; String speed = ""; String mode = "";

//Either continuously or a specific number of times

//Determine unit execution duration based on speed switch(speedVal){ case SLOW: speed = "slow"; unit_exec_duration = 2500; break; case MEDIUM: speed = "medium"; unit_exec_duration = 2000; break; case FAST: speed = "fast"; unit_exec_duration = 1500; break; default: speed = "medium"; unit_exec_duration = 2000; //All durations to be determined experimentally

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} if(rBtnContinuous.isSelected()){ selectedRadioButton = CONTINUOUS;

//Here we get to know the selected mode

mode = "continuously."; }else if (rBtnSpecificNo.isSelected()){ if(!TextEntry()){ txtNoOfTimes.requestFocusInWindow(); return; //exit the method }else{ selectedRadioButton = NON_CONTINUOUS;

//Here we get to know the selected mode

noOfTimes = Integer.parseInt(txtNoOfTimes.getText()); /*Here we get to know the selected no. of times*/ mode = noOfTimes + " times."; } } requestInfo = "You want the robot arm to pick and drop at a \n" + speed + " speed " + mode; int option = JOptionPane.showConfirmDialog(this, requestInfo, "Confirm", JOptionPane.OK_CANCEL_OPTION, JOptionPane.INFORMATION_MESSAGE); if(option == JOptionPane.CANCEL_OPTION){ //terminate command return; } //To generate the command code that will be sent to the microcontroller through the parallelport int cmdCode = 0x00; //hexadecimal equivalent of 00000000. it's the default command int tempSpeed = 0; int tempNoOfTimes = 0; switch(selectedRadioButton){ case CONTINUOUS: switch(speedVal){ case SLOW: cmdCode = 0x1B; break; case MEDIUM: cmdCode = 0x0B; break;

80

case FAST: cmdCode = 0x2B; break; } break; case NON_CONTINUOUS: switch(speedVal){ case SLOW: tempSpeed = 0x10; break; case MEDIUM: tempSpeed = 0x00; break; case FAST: tempSpeed = 0x20; break; } switch(noOfTimes){ case 1: tempNoOfTimes = 0x01; break; case 2: tempNoOfTimes = 0x02; break; case 3: tempNoOfTimes = 0x03; break; case 4: tempNoOfTimes = 0x04; break; case 5: tempNoOfTimes = 0x05; break; case 6: tempNoOfTimes = 0x06;

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break; case 7: tempNoOfTimes = 0x07; break; case 8: tempNoOfTimes = 0x08; break; case 9: tempNoOfTimes = 0x09; break; case 10: tempNoOfTimes = 0x0A; break; } cmdCode = tempSpeed | tempNoOfTimes; } //Send the command code to the parallel port port.output(DATA_PORT_ADDRESS, (short)cmdCode); port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter i.e. the

microcontroller code //reads the LSB of this control byte to decide //whether to move data on port 1 to transmit buffer try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

isExecuting = true; /* *Change song *Use a try-catch block for smooth program flow in case the sound file no longer exists */ try{ song[1].stop(); song[0].loop();

82

}catch(Exception e){ e.printStackTrace(); } //JOptionPane.showMessageDialog(this, "Parallel port value is " + Integer.toHexString(port.input(DATA_PORT_ADDRESS))); btnExecuteCmd.setEnabled(false); if(selectedRadioButton == CONTINUOUS){ txtNoOfTimes.setEnabled(false); rBtnSpecificNo.setEnabled(false); } /* *Enable 'OK' and 'Stop/Reset' buttons after expected duration of action and set the isExecuting flag *to false, to indicate that command has finished executing *this should happen only for non-continuous pick-and-drop option */ if(selectedRadioButton == NON_CONTINUOUS){ execution_duration = unit_exec_duration * tempNoOfTimes; Timer executeTimer; executeTimer = new Timer(execution_duration, new ActionListener() { public void actionPerformed(ActionEvent evt) { btnReset.setEnabled(true); btnExecuteCmd.setEnabled(true); isExecuting = false; /* *Change song *Use a try-catch block for smooth program flow in case the sound file no longer exists */ try{ song[0].stop(); song[1].loop(); }catch(Exception e){ e.printStackTrace(); }

83

} }); executeTimer.setRepeats(false); executeTimer.start(); } }

/************************************************************************************* ** *

Code to handle control of the robot arm

***************************************************************************************/ /** * action inner class - for action object that would be bound to the 'up' cursor key */ public class UpAction extends AbstractAction { /** Creates a new instance of UpAction */ public UpAction() { super(); } public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF1); //send 11110001 to parallel port - command for micro c to move robot up port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter

try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

lblMotion.setText("Up"); //May include a timer delay here to give the robot time to complete its task - just in case

84

// holds down the key continuously, as this will keep the serial_isr() at receiver ucontroller //busy, not allowing robot to move. } } /** * action inner class - for action object that would be bound to the 'down' cursor key */ public class DownAction extends AbstractAction { /** Creates a new instance of DownAction */ public DownAction() { super(); } public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF2); //send 11110010 to parallel port - command for micro c to move robot down port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter

try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

lblMotion.setText("Down"); } } /** * action inner class - for action object that would be bound to the 'left' cursor key */ public class LeftAction extends AbstractAction { /** Creates a new instance of LeftAction */

85

public LeftAction() { super(); } public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF3); //send 11110011 to parallel port port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter

try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

lblMotion.setText("Left"); } }

/** * action inner class - for action object that would be bound to the 'right' cursor key */ public class RightAction extends AbstractAction { /** Creates a new instance of RightAction */ public RightAction() { super(); } public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF4); //send 11110100 to parallel port - command for micro c to move robot right port.output(CONTROL_PORT_ADDRESS, (short)0xF0); try{ Thread.sleep(1);

//Delay 1ms

86

//Activate IR transmitter

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

lblMotion.setText("Right"); } } /** * action inner class - for action object that would be bound to the 'G' key */ public class GripAction extends AbstractAction { //pPort port = new pPort(); /** Creates a new instance of GripAction */ public GripAction() { super(); } public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF5); //send 11110101 to parallel port - command for micro c to grip port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter

try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF); lblMotion.setText("Grip"); } }

87

//Deactivate IR transmitter

/** * action inner class - for action object that would be bound to the 'R' key */ public class ReleaseAction extends AbstractAction { //pPort port = new pPort(); /** Creates a new instance of ReleaseAction */ public ReleaseAction() { super(); } public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF6); //send 11110110 to parallel port - command for micro c to release robot gripper port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter

try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

lblMotion.setText("Release"); } } /** * action inner class - for action object that would be bound to the 'C'key */ public class CWRollAction extends AbstractAction { /** Creates a new instance of CWRollAction */ public CWRollAction() { super(); }

88

public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF7); //send 11110111 to parallel port - command for micro c to move robot wrist clockwise port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter

try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

//Deactivate IR transmitter

lblMotion.setText("CWRoll"); } } /** * action inner class - for action object that would be bound to the 'A' key */ public class ACWRollAction extends AbstractAction { //pPort port = new pPort(); /** Creates a new instance of ACWRollAction */ public ACWRollAction() { super(); } public void actionPerformed(java.awt.event.ActionEvent evt) { port.output(DATA_PORT_ADDRESS, (short)0xF8); //send 11111000 to parallel port - command for micro c to move robot wrist anticlockwise port.output(CONTROL_PORT_ADDRESS, (short)0xF0);

//Activate IR transmitter

try{ Thread.sleep(1);

//Delay 1ms

}catch(InterruptedException e){ System.err.println(e.getMessage()); } port.output(CONTROL_PORT_ADDRESS, (short)0xFF);

89

//Deactivate IR transmitter

lblMotion.setText("ACWRoll"); } } /** * @param args the command line arguments public static void main(String args[]) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new Commands().setVisible(true); } }); } */ // Variables declaration - do not modify private javax.swing.JButton btnActivate; private javax.swing.JButton btnDeactivate; private javax.swing.JButton btnExecuteCmd; private javax.swing.JButton btnReset; private javax.swing.JLabel jLabel1; private javax.swing.JLabel jLabel2; private javax.swing.JLabel jLabel3; private javax.swing.J j1; private javax.swing.JTabbedPane jtpCommands; private javax.swing.JLabel lblInstruction; private javax.swing.JLabel lblMotion; private javax.swing.J NoOfTimes; private javax.swing.J PickAndDrop; private javax.swing.J Speed; private javax.swing.J Control; private javax.swing.JRadioButton rBtnContinuous; private javax.swing.ButtonGroup rBtnGrpNoOfTimes; private javax.swing.JRadioButton rBtnSpecificNo; private javax.swing.JSlider sldSpeed;

90

private javax.swing.JTextField txtNoOfTimes; // End of variables declaration }

TRANSMITTER MICROCONTROLLER CODE /*************************************************************************************** *

Project : Design and Control of a Robot Arm *

*

Date : 2007

*

*

Author : Project Group

*

*

Department : Electronic Engineering (UNN)

*

*

Programming Language: C

*

*

Chip type : AT89S52

*

*

Program type : Application

*

*

Clock frequency : 24.00014MHz

*

***************************************************************************************/ #include #define PARALLEL_PORT P1 #define NOT_SENT P3_2 #define TRUE 1 //function declarations void init_serial(); void sendByte(unsigned char); void delay(unsigned int); unsigned char input; /* * Main function */ void main(void){ init_serial();

//call function to initialize serial port

//continuous loop while(TRUE){

91

while(NOT_SENT){

//while send bit is high(deactivated)

//do nothing } //when send bit is low(activated) delay(2);

//wait 50ms for stabilization of activate signal

input = PARALLEL_PORT; sendByte(input);

//takes the input value from the parallel port //call function to send data

//after sending the byte, loop in order to wait for the next send command } }

/* *function that transmits the byte received from the parallel port via the serial port */ void sendByte(unsigned char input){ SBUF = input;

//send data down the serial line

} //serial interrupt service routine using bank 2 void serial_isr(void) interrupt 4 using 2{ ES = 0;

//disable the serial interrupt to avoid data corruption

if(TI){

//if transmission caused the interrupt, TI = 0;

//clear the trnsmit interrupt flag

}else{ //*not so necessary since it is just a transmitter if(RI){

//if reception caused the interrupt, RI = 0;

//clear the receive interrupt flag

ES = 1;

//enable the serial interrupt

} } }

RECEIVER/ROBOT CONTROL MICROCONTROLLER CODE

92

#include //Define constants #define TRUE 1 #define FALSE 0 #define FAST 8

//8ms delay

#define MEDIUM 10

//10ms delay

#define SLOW 12

//12ms delay

#define DC_FAST 15

//A t(HIGH) of 15ms in the 50Hz(20ms) pulse. The larger the t(HIGH) wrt t(LOW), the faster the motor

#define DC_SLOW 5 #define _CONTROL 0

//mode - either control or pick&drop

#define PICK_AND_DROP 1 //declare and initialize global flags volatile unsigned char command = 0x00;

//default command code from interface - "no action"

/************************************************************************************** *

Function Declarations

*

***************************************************************************************/ void gripperOpen(unsigned char mode, unsigned char speed); //Done - but not tested void gripperClose(unsigned char mode, unsigned char speed); //Done - but not tested void wristRollCW(unsigned char mode, unsigned char speed); //Done - but not tested void wristRollCCW(unsigned char mode, unsigned char speed); //Done - but not tested void shoulderUp(unsigned char mode, unsigned char speed); //Done - but not tested void shoulderDown(unsigned char mode, unsigned char speed); //Done - but not tested void wristPitchUp(unsigned char mode, unsigned char speed);//Done - but not tested void wristPitchDown(unsigned char mode, unsigned char speed); //Done - but not tested void elbowUp(unsigned char mode, unsigned char speed); //Done - but not tested void elbowDown(unsigned char mode, unsigned char speed); //Done - but not tested void baseCW(unsigned char mode, unsigned char speed); //Done - but not tested void baseCCW(unsigned char mode, unsigned char speed); //Done - but not tested void pickAndDrop(unsigned char speed, unsigned char times); void Control(unsigned char lowNibble); //low nibble of command code which determines which motor to move

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void stepCW_1_3_5(unsigned char speed); //Rotate appropriate motor 1 clockwise revolution void stepCCW_1_3_5(unsigned char speed); void stepCW_2_4(unsigned char speed); void stepCCW_2_4(unsigned char speed); void delay(unsigned char speed); void stopMotors(void); void initialize(void);

//General initialization function

void reset(void); // open gripper(can check both gripperlimit flag and gripperPos to determine if robot is holding sth //and to act appropriately - esp in control mode,,, raise shoulder ,,, raise elbow ,,, //rotate base to home position,,,lower wrist ,,, make gripper horizontal,,, close gripper ,,, set //'isReset' flag and other limit flags,,, initialize currentXXXPos. /*************************************************************************************** *

NOTES/ASSUMPTIONS

*

*************************************************************************************** *

The stepper motors have 7.5 degrees step angle i.e. 48 steps per rev

*/ void main(){ unsigned char currCommand; unsigned char lowNibble; unsigned char highNibble; initialize(); reset(); while(TRUE){ //This is an endless loop //Update the currCommand currCommand = command; command = 0x00;

//command is updated by the serial interrupt

//Refresh command

lowNibble = currCommand & 0x0F; highNibble = currCommand & 0xF0; if(currCommand == 0x00){ //no action

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}else if(currCommand == 0xFF){ reset(); }else if(highNibble == 0xF0){ // control command Control(lowNibble); }else if(highNibble == 0x00){ //Means that the higher nibble is 0000 => pick&drop medium speed //The lower nibble contains the no. of times and/or mode (i.e. continuous or not) reset(); if(lowNibble == 0x0B){

//i.e xxxx1011 => continuous mode

while(command != 0x00){ //while stop/reset is not clicked on the UI pickAndDrop(MEDIUM, 1);

//pick and drop once

} }else{ pickAndDrop(MEDIUM, lowNibble); } }else if(highNibble == 0x10){ //Means that the higher nibble is 0001 => pick&drop slow speed reset(); if(lowNibble == 0x0B){

//i.e xxxx1011 => continuous mode

while(command != 0x00){ //while stop/reset is not clicked on the UI pickAndDrop(SLOW, 1); //pick and drop once } }else{ pickAndDrop(SLOW, lowNibble); } }else if(highNibble == 0x20){ //Means that the higher nibble is 0010 => pick&drop fast speed reset(); if(lowNibble == 0x0B){

//i.e xxxx1011 => continuous mode

while(command != 0x00){ //while 'stop/reset' is not clicked on the GUI pickAndDrop(FAST, 1); //pick and drop once } }else{

95

pickAndDrop(FAST, lowNibble); } }else{ //do nothing } } } /* * Function called to pick and drop an object */ void pickAndDrop(unsigned char speed, unsigned char times){ unsigned char i; for(i = 0; i < times; i++){ //pick and drop sequence starting at default position wristPitchUp(PICK_AND_DROP, speed); //raise wrist gripperOpen(PICK_AND_DROP, speed);

//open gripper

elbowDown(PICK_AND_DROP, speed);

//lower elbow

gripperClose(PICK_AND_DROP, speed);

//close gripper

elbowUp(PICK_AND_DROP, speed);

//raise elbow

baseCCW(PICK_AND_DROP, speed);

//move base to 'drop' position

elbowDown(PICK_AND_DROP, speed);

//lower elbow

gripperOpen(PICK_AND_DROP, speed);

//open gripper

elbowUp(PICK_AND_DROP, speed);

//raise elbow

baseCW(PICK_AND_DROP, speed);

//return base to default position

if(command == 0x00){ //if reset was requested by reset(); break; } } }

void Control(unsigned char lowNibble){ switch(lowNibble){ //Decode the 4 LSBs of command code for info on what to move and how

96

case 1: //arm up - controls elbow and wrist only if(currentPitchPos < MAX_WRIST_PITCH_REV){ wristPitchUp(_CONTROL, MEDIUM); }else{ elbowUp(_CONTROL, MEDIUM); } break; case 2: //down - controls elbow and wrist only if(isWristPitchLimitTripped == FALSE){ wristPitchDown(_CONTROL, MEDIUM); }else{ elbowDown(_CONTROL, MEDIUM); } break; case 3: //left baseCCW(_CONTROL, MEDIUM); break; case 4: //right baseCW(_CONTROL, MEDIUM); break; case 5: //grip gripperClose(_CONTROL, MEDIUM); break; case 6: //release gripperOpen(_CONTROL, MEDIUM); break; case 7: //CWRoll wristRollCW(_CONTROL, MEDIUM); break; case 8:

97

//raise wrist

//ACWRoll wristRollCCW(_CONTROL, MEDIUM); break; default: //do nothing } }

98

APPENDIX C

STEPPER MOTOR DATASHEETS

99

100

101

APPENDIX D

THE ROBOT’S BODY DIAGRAM

THE ROBOT’S BODY DIAGRAM SPECIFICATIONS TABLE 102

J

1

WRIST T MOTOR

Stepper motor

87mNm

H

1

ELBOW T MOTOR

Stepper motor

155mNm

G

1

SHOULDER T MOTOR

Stepper motor

155mNm

F E D

1 1 1

THE GRIPPER THE WRIST THE FORE ARM

STEEL STEEL STEEL

100×150 250×440 250×500

C

1

THE UPPER ARM

STEEL

400×500

B

1

THE SHOULDER

STEEL

480×550

A

1

THE WAIST

STEEL

310×ø710

ITEM №

NO OF

DESCRIPTION

SYMBOL OF STD

NAME

DATE

DRAWN BY CHECKED BY

MGBEMENE C.A. DR O. ONUBA

6:8:91

APPROVED BY

DR O. ONUBA

DEPARTMENT OF MECHANICAL ENGINEERING UNN

MATERIAL

THE DESIGN OF A ROBOT MANIPULOR ARM

B.ENG PROJECT

*Note: Some of the dimensions above were adjusted during fabrication.

APPENDIX E

103

OVERALL DIMENSION

NOTES SCALES 1:5

REG.№ 86/44740

CIRCUIT DIAGRAMS MOTOR CONTROLLER CIRCUIT 5V

5V

5V

A T89S 52

C1

47uF

IR

R1

1 2 3 4 5 6 7 8 9 10 IN PU T 11 12 R R U P T1 3 14 15 16 17 18 19 20

I N TE

10k

X1 C2 33pF

U2

40 P 1.0 / T 2 VCC 39 P 1.1 / T 2 E X P 0 .0 / A D 0 38 P 1.2 P 0 .1 / A D 1 37 P 1.3 P 0 .2 / A D 2 36 P 1.4 P 0 .3 / A D 3 35 P 1.5 / M OS I P 0 .4 / A D 4 34 P 1 . 6 / M IS O P 0 .5 / A D 5 33 P 1.7 / S C K P 0 .6 / A D 6 32 R ST P 0 .7 / A D 7 31 P 3.0 / R X D ~E A / V PP 30 P 3.1 / T X D A L E / ~ P R O G 29 P 3 . 2 / ~ IN T 0 ~P S E N 28 P 3 . 3 / ~ IN T 1 P 2 .7 / A 1 5 27 P 3.4 / T 0 P 2 .6 / A 1 4 26 P 3.5 / T 1 P 2 .5 / A 1 3 25 P 3.6 / ~ W R P 2 .4 / A 1 2 24 P 3.7/ ~R D P 2 .3 / A 1 1 23 X T A L2 P 2 .2 / A 1 0 22 X T A L1 P 2 .1 / A 9 21 GND P 2 .0 / A 8

F DBK 1 F DBK 2 F DBK 3 F DBK 4 F DBK 5 F DBK 6 B U SY R E AD Y

1 3 4 7 8 13 14 17 18 10

~OE D0 D1 D2 D3 D4 D5 D6 D7 GND

VCC Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 LE

U3

20 2 5 6 9 12 15 16 19 11

1 2 3 4 5 6 7 8 9

74H C373 MO T MO T MO T MO T MO T MO T

OR 1_2 OR 3_4 OR5 OR6 O R _ D IR OR _P W M

1A 2A 3A 4A 5A 6A 7A 8A GND

1Y 2Y 3Y 4Y 5Y 6Y 7Y 8Y Vs

18 17 16 15 14 13 12 11 10

~OE D0 D1 D2 D3 D4 D5 D6 D7 GND

VCC Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 LE

20 2 5 6 9 12 15 16 19 11

Z E N E R (1 2 V )

U5 1 2 3 4 5 6 7 8 9

74H C373

1A 2A 3A 4A 5A 6A 7A 8A GND

1Y 2Y 3Y 4Y 5Y 6Y 7Y 8Y Vs

18 17 16 15 14 13 12 11 10

1 3 4 7 8 13 14 17 18 10

12V - 24V

C4

C5

100nF

100nF

~OE D0 D1 D2 D3 D4 D5 D6 D7 GND

VCC Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 LE

20 2 5 6 9 12 15 16 19 11

U7 1 2 3 4 5 6 7 8 9

74H C373

1 15

9

1A 2A 3A 4A 5A 6A 7A 8A GND

1Y 2Y 3Y 4Y 5Y 6Y 7Y 8Y Vs

18 17 16 15 14 13 12 11 10

ULN2803

4

IN 1 V C C IN 2 IN 3 IN 4 ENA ENB

VS OUT 1 OUT 2 OUT 3

S E N SA S E N SB GN D 8

D2

A4 B4 C4 D4

Z E N E R (1 2 V )

U6

U8

A3 B3 C3 D3

ULN2803

33pF

5 7 10 12 6 11

A2 B2 C2 D2

D1

ULN2803

U4 1 3 4 7 8 13 14 17 18 10

C3

5V

A1 B1 C1 D1

5V

U1

24M Hz

1 2V

OUT 4

2

D4

D6

1N 4004

1N 4004

A6

3

B6

13 14

D5

D7

1N 4004

1N 4004

L298

F ig . 4 . 7 : T h e M o to r C o n t r o lle r C ir c u it

THE TRANSMITTER CIRCUIT

104

A5 B5 C5 D5

D3 Z E N E R (1 2 V )

U22

J4

7805

C8

C O N N -S I L 4

33pF

2C 4R MY S HT Az L

X T A L2

R3 9

C O N N -D 2 5 F

U14 2 3 4 5 6 7 8 9

D D D D D D D D

0 1 2 3 4 5 6 7

Q Q Q Q Q Q Q Q

0 1 2 3 4 5 6 7

1 18 1 27 1 36 1 45 1 54 1 63 1 72 1 81

1 OE1 19 OE2

P P P P P P P P

D10 L E D -R E D

21 P 2 .0 /A 8 22 P 2 .1 /A 9 23 P 2 .2 /A 1 0 24 P 2 .3 /A 1 1 25 P 2 .4 /A 1 2 26 P 2 .5 /A 1 3 27 P 2 .6 /A 1 4 28 P 2 .7 /A 1 5

29 PSEN 30 ALE 31 EA

J3 1 14 2 15 3 16 4 17 5 18 6 19 7 20 8 21 9 22 10 23 11 24 12 25 13

RST

39 D0 38 D1 37 D2 36 D3 35 D4 34 D5 33 D6 32 D7

1 .0 /T 2 1 .1 /T 2 E X 1 .2 1 .3 1 .4 1 .5 1 .6 1 .7

10 P 3 .0 /R X D 11 P 3 .1 /T X D 12 P 3 .2 /IN T 0 13 P 3 .3 /IN T 1 14 P 3 .4 /T0 15 P 3 .5 /T1 16 P 3 .6 /W R 17 P 3 .7 /R D

U15

8

18

0 .0 /A 0 .1 /A 0 .2 /A 0 .3 /A 0 .4 /A 0 .5 /A 0 .6 /A 0 .7 /A

D12 D11 IR L E D IR L E D

4

R

VCC

P P P P P P P P

3

Q DC

5

C11 0 .1 n F

2

7

R V 15 0 K

CV

GND

X T A L1

(1 0 V )

10k

3

U13 19

47uF

VO

TR

T H

6

R4 5k

(1 0 4 ) 1

C9

VI

2

C7 3 3 Xp F2

1

GND

4 3 2 1

100

555

A T 8 9 S 52

V C C = P IN 4 0 , G N D = P IN 2 0

74HCT 541

V C C = P IN 2 0

C10

G N D = P IN 1 0

(1 0 2 )

U21 I n i t i a l i z 2e ( 1 6 ) 3 4 5 6 7 8 9

D D D D D D D D

0 1 2 3 4 5 6 7

Q Q Q Q Q Q Q Q

0 1 2 3 4 5 6 7

1nF

18 17 16 15 14 13 12 11

1 OE1 19 OE2 74HCT 541

F ig . 4 . 6 : T h e T r a n s m itte r C ir c u it

POWER SUPPLY CIRCUIT

105

R5

Q3 B C 547

Q4 T IP 1 25

TR1

BR1 K B P 2 0 86

M A IN S

U17

2 2 0 V /2 4 0 V

R8

5 0 / 60H z

VI

VO

3

GND

10k

C13

2

C12 T R A N -2 P 3 S

(D .C . M o to r L in e )

7815 1

100uF

100uF

(3 5 V )

(2 5 V )

U18

J1

( S t e p p e r M o t o r L i 1n e )

7812 VI

VO

3

2 3 4

GND

1

2

C14

A B C D

C O N N -S IL 4

100uF

(1 6 V )

U19

(IC L in e )

7805 VI

VO

GND C O N N -S IL 4

3

GND

1

J2 1 2 3 4

2

C15 100uF

(1 0 V )

U20

O U T P U T S P E C IF IC A T IO N S

(-v e V o lta g e L in e )

7912 VI

VO

3

A : + 1 5 V , 3 .7 5 A C16

B : + 1 2 V , 1 .3 5 A

100uF

(3 5 V )

1

GND

2

C17 100uF

16V

C : + 5 V , 1 .3 5 A D : -1 2 V , 1 . 3 5 A

F i g . 4 . 9 : T h e P o w e r S u p p l y U n it

THE INTERRUPT CONTROLLER CIRCUIT 106

R2 1k 8

U11

R

VCC

4

Q

2

IN T E R R U P T ( P 3 .2 )

74H C14

GND

CV

T R

1

2

1

7

DC 5

U 1 2 :A

3

6

TH

NE 555

C6 10uF

U 9 :D

U 1 0 :A

U 1 0 :B 4

1 5

9 12

1 5

3

6

8

11

3

6

2 4

10 13

2

U 9 :A

U 9 :B

U 9 :C

74HC 08 74HC 08

74H C08 74H C08

74H C08 74HC 08

F D B K 6 (P 1 . 6 ) F D B K 5 (P 1 . 5 ) F D B K 4 (P 1 . 4 ) F D B K 3 (P 1 . 3 ) F D B K 2 (P 1 .1 ) F D B K 1 (P 1 .0 )

F R O M E N C O D EF R O6 M E N C O D EF RR O5 M E N C O D EF RR O4 M E N C O D EF R O3 M E N C O D EF RR O2 M E N C O D E R 1

F i g . 4 . 8 : T h e I n t e r r u p t C o n t r o l l e r C i r c u it

107