Dynamic modeling and control of a conveyance microrobotic system using active friction drive

Presents a new generation of compliant multidegree of freedom piezoelectric microconveyer for microobjects based on the cooperation of arrayed direct-drive micro standing-wave ultrasonic actuators (microSWUMs). Their operating driving principles based on active frictional contact forces offer direct-drive and low-speed characteristics at the microscale. The tradeoff, however, is the complexity of dynamic modeling and control to cope with the optimization of the intermittent friction drive mechanism. A method using an equivalent electromechanical circuit is proposed for estimating and analyzing the optimum driving force, including the dynamic electrical and the mechanical energy conversions. On the basis of the proposed method, the friction drive optimization of the microrobot is performed through the implementation of different controllers: 1) an electromagnetic-field-based preload controller ensuring optimal preload; 2) an open-loop piecewise-modulated controller for self locking and driving force control; and 3) a resonant frequency compensation. Finally, an experimental investigation has been performed on a prototype of ultrasonic microconveyer incorporating 48 arrayed microSWUMs whose overall dimensions are 47 /spl times/ 29 mm/sup 2/ in order to demonstrate the proposed optimized friction drive.