Bent-Beam Electrothermal Actuators--Part II: Linear and Rotary Microengines

This paper reports on the use of bent-beam electrothermal actuators for the purpose of generating rotary and long-throw rectilinear displacements. The rotary displacements are achieved by orthogonally arranged pairs of cascaded actuators that are used to rotate a gear. Devices were fabricated using electroplated Ni, [p.sup.++] Si, and polysilicon as structural materials. Displacements of 20-30 [micro]m with loading forces [is greater than] 150 [micro]N at actuation voltages [is less than] 12 V and power dissipation [is less than] 300 mW could be achieved in the orthogonally arranged actuator pairs. A design that occupies [is less than] 1 [mm.sup.2] area is presented. Long-throw rectilinear displacements were achieved by inchworm mechanisms in which pairs of opposing actuators grip and shift a central shank that is cantilevered on a flexible suspension. A passive lock holds the displaced shank between pushes and when the power is off. This arrangement permits large output forces to be developed at large displacements, and requires zero standby power. Several designs were fabricated using electroplated Ni as the structural material. Forces [is greater than] 200 [micro]N at displacements [is greater than] 100 [micro]m were measured. [624] Index Terms--Inchworm, micromachining, micromotor, positioner, scanner, thermal actuator.