Towards high-torque electrostatic tubular motor

A new generation of electrostatic micro-motors is investigated using cooperation of arrayed direct-drive actuators. Electrostatic scratch-drive actuators (SDA), which combine active frictional contact mechanisms with electrostatic actuation, are particularly analyzed. Active polysilicon sheets of 2*3 mm(2) that integrate up to several thousands of electrostatic scratch drive actuators are fabricated by silicon surface micro-machining process. Each elementary actuator provides its contribution according to the driving force superposition principle, with internal forces as high as 10(5)uN are available from this sheet. According to their natural flexibility, active polysilicon sheets can be coated onto large surfaces. A new generation of self-assembled tubular electrostatic micromotors is developed using this concept. A prototype of a cylindrical micromotor, whose external diameter and length are 1 mm and 2 mm, respectively, has been realized through the insertion of a flexible active polysilicon sheet at the rotor/motor-frame interface. After final assembling, the sheet has to be jammed onto the chassis, in order to allow the rotor to be moved with respect to the motor frame. Thus, the sheet must be in closed contact with both the rotor and the motor frame, whatever the gap, which separates the two macroscopic parts. The problem related to the micro/macro world interfacing is solved during the design of sheet in allowing an out-of-plane motion of SDA in order to provide a self gap compensation, whatever both the thermal expansion effects and the macroscopic machining tolerances. The expected driving characteristics show the interest of both cooperative arrayed microactuators and direct drive frictional mechanisms.