CHEVRON,len,wid,thc,ht,pwr,den,α,cond,sph,sel
Design of a thermal bent beam actuator

len        length of one arm of the beam in m
wid       width of the beam in m
thc        thickness of the beam in m
ht          bent beam height in m
pwr       total heating power in mW
den       density in kg/m3
α           thermal expansion coefficient in 1/K
cond     thermal conductivity in W/mK
sph       specific heat capacity in J/kgK
sel        number denoting the selected result.
             Use 1 for maximum deflection, 2 for response time and 3 for maximum temperature change

Thermal bent beam chevron actuator

Notes

Thermal actuators generate large force, but displacements from linear thermal expansion alone is small. So some type of geometrical amplification can be used to obtain larger displacements. The bent beam actuator shown above is used to geometrically amplify the small thermal expansion of the beams. This structure is also called chevron actuator.

This design interface can be used to calculate the maximum deflection produced by this actuator for the supplied power. The maximum deflection is the amplified output obtained at the tip of the bent beam. The beams can be heated using resistors implanted on the beams. The thermal power supplied to both the beams is required for this calculation. The maximum change in temperature with respect to the anchor temperature is estimated. The anchor is maintained at the normal temperature and the maximum temperature change is observed at the tip of the bent beam.

Compared to capacitive and piezoelectric actuators, thermal actuators have slower response time. There is a lag between the application of voltage on the heater elements and the temperature change. This slow response is dictated by the time constants for heating and cooling of the actuator. This design form estimates the time it takes for the actuator to generate the maximum deflection and attain the change in temperature.

The plot shows the transient response of the actuator to a heating and cooling cycle. The actuator heats up and reaches the maximum deflection where the curve flattens out. The time it takes to reach that state is the actuator response time. Then the power is switched off immediately and the actuator cools off returning to its original position. The response time can be read off the plot.

Assumptions

-Only conductive heat transfer is considered, convection and radiation are ignored.
-The anchors remain at constant temperature.
-The beams are heated uniformly throughout its length.
-The change in material properties with temperature is ignored.
Menu Path

Actuation > Thermal > Bent beam


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