FABRICATION OF ROTARY COMB DRIVES WITH FLOATING CENTER

Rotary comb drives have been recently adopted to operate MEMS-Technology based micro systems. In several cases it is convenient to adopt a kinematic structure based on the four-bar linkage, where the coupler link has the guiding function for a generic tool as, for example, one jaw of a gripper. In this case the grasping function is granted by two symmetric jaws that are guided by two symmetric four-bar linkage structures. Since the ordinary kinematic pairs are not suitable for most planar fabrication methods of micro machining, compliant flexures must be used, with the consequence that some flexures must be embedded in the mechanical structure. For example, a microgripper based on two symmetric four-bar linkages needs 8 flexures. With the aim of coping with the problem of providing higher power to inflect all these flexures, this paper presents a new concept design which allows the coupler to be directly actuated by a second cooperating rotary comb drives, in addition to the fixed axis rotary comb drive (RCD) that actuates the crank link. The secondly added comb drive has also the advantage that its rotation center can be adjusted during the design stage with considerable freedom of choice in the plane, including positions that are not physically placed within the wafer. A microgripper prototype has been obtained by applying Deep Reaction Ion Etching (DRIE) on a Silicon on Insulator (SOI) wafer and then herein presented.