Velocity Control of a Manipulator Joint Driven Through a Worm Gear Transmission

The design of an individual joint of a robot manipulator typically includes some form of transmission between the prime mover and the joint itself. From a geometric point of view, employing a worm gearset can, in many situations, be a desirable way to realize this function. However, for some robot configurations, the manipulator and the worm gearset give rise to unstable behavior characterized by a growing oscillatory motion. A stabilizing controller for this type of system is necessary. Presented here is a synopsis of such a feedback control design which achieves stabilization. The system differential equations are linearized about a desired trajectory and averaged to obtain a set of linear time invariant equations. These linearized equations are then used as the plant-model for controller synthesis. The design synthesis is accomplished by classical lead-lag compensation. In a physical experiment, velocity feedback from the motor tachometer and digital control are used to implement and verify the control schemes.