Electrostatic Impact-Drive Microactuator M. Mita*, M. Arai*, S. Tensaka**, D. Kobayashi*$, P. Bassett, A. Kaisert, P. Masqueliert, L. Buchaillott, D. Collardt and H. Fujita*j zyx *University of -Tokyo 7-22-1 Roppongi, Minato-ku, Tokyo 106-8558, Japan. zyxw ** Tokyo Denki University, 2-2 Kanda-nishiki-cho, Chiyoda-ku, Tokyo 101-8457 Japan. tIEMN / Dpt ISEN Cite scientifique Avenue Poincare, BP 69 59652 Villeneuve d Ascq Cedex, FRANCE $Also with CREST, Japan Science and Technology Corporation (JS'I') ABSTRACT A fully packagable micromachined actuator was devel- oped for generating precise but unlimited displacement. A suspended silicon mass is encapsulated between glass plates and driven by electrostatic force. By hitting a stop- per, it generates impact force to drive the whole actuator in a small step (WlOnm). It is a micromachined and elec- trostatic version of the impact-drive actuator. INTRODUCTIONS Micro or nanoscopic positioning control is more and more important for micro or nano metric operation and manipulations. A micromachine is a very suitable device for such application due to its small size. Therefore a lot of micro-actuators and micro-systems for nano displacement are intensively studied. The posi- tioning control needs long driving distance and large force to move a object. However, most microactuators have too small force to move object or too small moving range limited by the flex- ibility of suspensions. Impact actuation is one solution to such problems zyxwvutsr [l]. This actuation can realize nano scale displacement control by using inertia and friction zyxwvuts [a]. We propose a new impact drive microacutuator which is driven by electrostatic force. We named Electrostatic Impact-drive Microactuator (EIM). The impact of the movable mass against the stopper is the source of the ac- tion. The movable mass is accelerated by the electrostatic force. It collides with the stopper that is fixed to the base of the actuator. When the impact force, that is given to the stopper by the movable mass, exceeds the maximum static friction, the actuator begins to move. The actuator stops (eventually because of the dynamic friction. The actuator can generate high power, maintain a po- sition precisely, and move a long distance. STRUCTURE AND DRIVING MECHANISM Our impact actuator is composed of movable mass, which supported by suspension, driving electrodes, stop- pers and frames as show in Figure 1. / . z suspension (a) Top view stopper Cover /I Base plate' (b) Cross sectional view Figure 1: Structure of impact actuator Figure 2 shows driving mechanism. (a) First step: We apply voltage between the driving electrode and the mov- able mass. The mass is accelerated to the stopper by electrostatic force. In this step, we adjust the voltage low enough to keep the inertia force, which is opposite to the motion, smaller than static friction between the actuator and a base surface. zyxwv Fs~f > zyxw Fe where Fsf is static friction force, Fe is electrostatic force. (b) Second step: The mass is accelerated until it col- lides with the stopper and its momentum is transmitted to the stopper. The impact force is high enough to over- come the static friction and the actuator moves until the kinetic energy is consumed by dynamic friction. 0-7803~~5998-4/01/$10.00 (92001 IEEE 590