Stepper Motor Control 174l14

Practical Stepper Motor Control

Control System Engineering Practical Report

Kr. Rajeev Ranjan Sumeet Sharma Manish Thakur Ajay Kumar

07438 07434 07425 07439

Practical STEPPER MOTOR CONTROL

Aim: To Interface Stepper Motor to 8086 using 8255 and write Assembly Language Program to rotate Stepper Motor in Clockwise & Anticlockwise direction and control it’s Speed.

Apparatus: Sl. No. 1 2 3 4 6 6

Apparatus 8085 Microprocessor Trainer KIT 20 Pin FRC Cable SMC Card 8225 uP Interface Stepper Motor Power Supply

Specification 8 bit-uP 230V, 1 ø, 50Hz

Quantity 01 01 01 01 01 01

Theory: Introduction: A stepper motor (or step motor) is a brushless, synchronous electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any mechanism (see Open-loop controller), as long as the motor is carefully sized to the application Fundamentals of Operation Stepper motors operate differently from DC brush motors, which rotate when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple "toothed" electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external control circuit, such as a microcontroller. To make the motor shaft turn, first one electromagnet is given power, which makes the gear's teeth magnetically attracted to the electromagnet's teeth. When the gear's teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one, and from there the process is repeated. Each of those slight rotations is called a "step," with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle.

Practical STEPPER MOTOR CONTROL

Stepper motor characteristics 1. Stepper motors are constant power devices. 2. As motor speed increases, torque decreases. (most motors exhibit maximum torque when stationary, however the torque of a motor when stationary is of little use, torque is more important when the motor is actually spinning) 3. The torque curve may be extended by using current limiting drivers and increasing the driving voltage (sometimes referred to as a 'chopper' circuit, there are several off the shelf driver chips capable of doing this in a simple manner). 4. Steppers exhibit more vibration than other motor types, as the discrete step tends to snap the rotor from one position to another, (this is important as at certain speeds the motor can actually change direction). 5. This vibration can become very bad at some speeds and can cause the motor to lose torque (or lose direction). You must pay attention to the torque of the motor) 6. The effect can be mitigated by accelerating quickly through the problem speeds range, physically damping (frictional damping) the system, or using a micro-stepping driver.

Practical STEPPER MOTOR CONTROL 7. Motors with a greater number of phases also exhibit smoother operation than those with fewer phases (this can also be achieved through the use of a micro stepping drive)

Types There are three main types of stepper motors: 1. Permanent Magnet Stepper (can be subdivided in to 'tin-can' and 'hybrid', tin-can being a cheaper product, and hybrid with higher quality bearings, smaller step angle, higher power density) 2. Hybrid Synchronous Stepper 3. Variable Reluctance Stepper Permanent magnet motors use a permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor PM and the stator electromagnets. Variable reluctance (VR) motors have a plain iron rotor and operate based on the principle of that minimum reluctance occurs with minimum gap, hence the rotor points are attracted toward the stator magnet poles. Hybrid stepper motors are named because they use a combination of PM and VR techniques to achieve maximum power in a small package size.

Procedure: 1. 2. 3. 4. 5. 6.

Switch on the 8085 microprocessor trainer KIT. Connect 20 PIN FRC cable from 8225 I connector to SMC card. Connect the stepper motor cables to given stepper motor card Connect the motor to the power supply. Enter the given program from 2000 address and execute the program. Change the code for changing the direction and controlling its speed and execute the program again.

WORKING: The stepper motors have been designed to work with digital circuits. Binary level pulses of 0-5V are required at its winding inputs to obtain the rotation of the shafts. The sequence of the pulses can be decided, depending upon the required motion of the shaft. By suitable sequence of the pulses the motor can be used in three modes of operation.

  

One phase ON (medium torque) Two phase ON (high torque) Half stepping (low torque)

8255 is interfaced with 8086 in I/O mapped I/O. port C (PC0, PC1, PC2, PC3) is used to give pulse sequence to stepper motor. The 8255 provides very less current which will not be able to drive stepper motor coils so each of the winding of a stepper motor needs to be interfaced using high speed switching Darlington transistors with max 1A, 80V rating with heat sink, with the output port of 8255. Output the sequence in correct order to have the desired direction to rotate the motor.

Practical STEPPER MOTOR CONTROL

Program: Address 2000 2002 2004 2006 2008 200B 200D 200F 2012 2014 2016 2019 201B 201D 2020

Mnemonics MVI A, 80 OUT 00 START: MVI A, FA OUT 00 CALL DELAY MVI A, F6 OUT 00 CALL DELAY MVI A, F5 OUT 00 CALL DELAY MVI A, F9 OUT 00 CALL DELAY JMP START

Hex-Code 3E 80 D3,00 3E,FA 03,00 CD,30,20 3E,F6 D3,00 CD,30,20 3E,F5 D3,00 CD,30,20 3E,F9 D3,00 CD,30,20 C3,04,20

Delay Routine: Address

Pnemonics DELAY LXI D, 2030 0000 2033 CALL DELAY 2038 RET

Hex-Code 11,00,00 CD,BC,03 C9