Reversible Actuation Micro Gripper with Thick SMA Film for Bio-sheet Handing

Abstract

A micro-gripper of reversible operation mechanism was designed and fabricated from a flash-evaporated SMA film of 30 µm in thickness. Thin film Pt heaters, strain gauges, and Pt-Au thermo-couple circuits were integrated on the SMA gripper. The gripper is closed at low temperature because both outer and inner arms of the gripper were similarly deflected due to intrinsic film stress. The gripper has a mechanism to be opened by the outer arm heating for flat shape recovery. The deflection propertied of the SMA gripper was evaluated. The outer arm of the gripper was reversibly deformed to 15 µm or larger when it was heated in water. The gripper was not opened enough for gripping thick bio-films because the temperature of the SMA outer arm was not reached to the peak deformation temperature of the SMA film (～60^oC). The inner arm was also deformed to several microns due to the thermal conduction from the heated outer arm. In air operation, the heated outer arm and non-heated inner arm were deformed to 45 µm and 15 µm, respectively. The outer arm was heated to 300^oC which was too high to use for bio-film handling. Spring constants of the inner arm were measured as 29.4 N/m which corresponds to a gripping force of 1.6 mN when a 50 µm thick sheet is held by the gripper.