ON THE USE OF DIFFERENTIAL DRIVES FOR OVERCOMING TRANSMISSION NONLINEARITIES

Nonlinear friction can couple with the internal dynamics of geared red ucers to exhibit the phase characteristics of noncollocation. In the s etting of robot control this is significant, in so far as the addition al phase-lag limits bandwidth. This paper suggests a solution based on the concept of differential actuation, with two actuators driving a s ingle joint arbitrarily in speed and direction. The advantage of the a pproach is that the internal gears are always in constant motion, ther eby avoiding low and zero velocities where friction is strongly nonlin ear. The potential performance of a differential transmission is compa red with that of a conventional gearbox. A scheme for solving the intr insic redundancy of the device is presented and its feasibility demons trated through two controllers: a position collocated controller and a force noncollocated controller. The performance of these controllers is compared with their counterparts implemented on a nondifferential g ear train. (C) 1998 John Wiley & Sons, Inc.