MEMS with Microactuators

Presented BySayyan.N.Shaikh

MicrogrippersMicrogrippers 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.

MicromotorsThe 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 motorsIt 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, Germany

MicrovalvesMicrovalves 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 passage 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 micropumpIt 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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