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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.
QUESTIONS…?
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