On the use of differential drives for overcoming transmission nonlinearities

Abstract

Nonlinear friction can couple with the internal dynamics of geared reducers to exhibit the phase characteristics of noncollocation. In the setting of robot control this is significant, in so far as the additional phase-lag limits bandwidth. This paper suggests a solution based on the concept of differential actuation, with two actuators driving a single joint arbitrarily in speed and direction. The advantage of the approach is that the internal gears are always in constant motion, thereby avoiding low and zero velocities where friction is strongly nonlinear. The potential performance of a differential transmission is compared with that of a conventional gearbox. A scheme for solving the intrinsic redundancy of the device is presented and its feasibility demonstrated 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 gear train. © 1998 John Wiley & Sons, Inc.