Mems With Microactuators - By Sayyan 5720p

MEMS with Microactuators Presented By Sayyan.N.Shaikh

Microgrippers  Microgrippers are the microactuators which are use to hold the objects.

 The gripping action is initiated by applying the voltage across

the plates attached to the drive arm and closer arm.  The electrostatic force generated by these pair of misaligned plates tend to align them, causing the drive arm to bend, which closes the extension arm for gripping.

 The required gripping forces in a gripper can be provided either by normal forces or by the in plane forces from pairs of misaligned plates.

Micromotors  The driving forces for micromotors are primarily the parallel electrostatic forces between pairs of electrically charged misaligned plates(electrodes).  There are two types of micromoters  Linear stepping motors  Rotary stepping motors

Linear stepping motors  It has number of electrode on the two sets of base plates separated by dielectric material (e.g. quartz film).  One electrode set is fixed and the other may slide over with little friction.  The two sets have slightly different pitch between electrodes

 Energize the set A-A’ will generate a pulling force A’ over A due to initial misalignment.  Once A and A’ are aligned, the pair B and B’ become misaligned.  Energize the misaligned B-B’ will generate electrostatic force pulling B’ over B.  It is now with C’ and C being misaligned.  Energize C’ and C will produce another step movement of the moving set over the stationary set.

 Repeat the same procedure will cause continuous movements of the moving sets.  The step size of the motion = w/3, or the size of pre set mismatch of the pitch between the two electrode sets.

Rotary stepping motors  Involve two sets of electrodes-one set for the rotor and the other for the stator.  Dielectric material between rotor and stator is air.  Electrodes are installed in the outer surface of the rotor pole and the inner surface of the stator poles.  There is pre set mismatch of pitches of the electrodes in the two sets which will generate an electrostatic driving force.

 This motor will rotate at very high speed(10,000 rpm).  With such high speed, the bearing quickly wear off, which results in wobbling of the rotors.

 A micromotor produced by Karlsruhe Nuclear Research Center,

Microvalves  Microvalves are the microactuators which are use to control the flow of the materials.(e.g. gas,liquid)  Microvalves are primarily used in industrial system that require a precision control of gas flow for manufacturing processes, or in biomedical application such as in controlling the blood flow and in pharmaceutical industry.  A microvalve is designed by Jerman in 1990.  The valve is actuated by thermal force generated by heating rings.  Heating rings are made up of aluminium films which is 5 µm thick.  It has circular in geometry, with diaphragm of 2.5 mm in diameter x 10µm thick.

 The heating of the two electrical resistor rings attached to the top diaphragm can cause a downward movement to close the age of flow.  Removal of heat from the diaphragm opens the valve again to allow a fluid to flow.

 The valve has a capacity of 300 cm ³/min at a fluid pressure of 100 psig and Power consumption is 1.5 W.

Micropumps Electrostaticallyactuated micropump  It consist a deformable silicon diaphragm forms one electrode of the capacitor.  It can be actuated and deformed towards the top electrode by applying a voltage across the electrode.  The gap between the diaphragm and the electrode is 4µm.  The upward motion of the diaphragm increases the volume of the pumping chamber and hence reduces the pressure in the chamber.  This reduction of pressure causes the inlet check valve to open to allow in flow of fluid.

 The subsequent cutoff voltage is applied to the electrode prompts the diaphragm to return to its initial position, which cause the reduction of the volume in the pumping chamber.

 This reduction in volume will increase the pressure of the entrapped fluid in the chamber.  The outlet check valve opens when entrapped fluid pressure will reaches a designed value, and fluid is released.  Its pumping rate is 70 µL/min at 25 Hz.

Piezoelectrically actuated pump  Piezoepump is built on the principle of producing wave motion in the flexible wall of minute tubes in which the fluid flows.  It is an effective way to pump fluid through capillary tubes.  Tube wall is flexible.  Outside tube wall is coated with piezoelectric crystal film(e.g. ZnO ) with aluminium interdigital transducers (IDTs).

 When radio-frequency voltage is applied to the IDTs, resulting in mechanical squeezing in section of the tube.  And we get smooth flow with “uniform” velocity profile across the tube cross section.

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