New differential-type SMA actuator for a miniature silicon gripper

This paper presents two new designs for a differential-type SMA actuator for a silicon micro gripper. The basic structure of the micro gripper is fabricated by silicon dry etching. The SMA actuators have been realized by machining a NiTi foil with a thickness of 50 ?m. It has been cut by direct laserwriting using a Q-switched Nd:YAG-laser followed by a wet chemical etch step to remove the heat affected zone (HAT). The first design is an advance of a recently presented actuation system with an optimized configuration of the SMA actuator. A critical aspect is the high force necessary to imply the low temperature shape of the inactive actuator which has to be transmitted by the gripper gear. This problem has been overcome by the second design where these high forces are transmitted directly between the active and the inactive actuator of the differential-type actuator. Tests of this new actuator and a new gipper design modified to meet the requirements of the actuator are described.