Modeling and Control of a Manipulator Joint Driven Through a Worm Gear Transmission

Abstract

The worrnscrew gearset provides a potential advantage for some robot manipulator designs because of its simplicity, compactness, and capacity for large speed-reduction ratios. However, an oscillatory behavior has been observed in such implementations that, depending on the extension and loading of the manipulator, tends to grow as the manipulator is lowered under the influence of gravity and disappears as the manipulator is raised. The oscillations can become quite large, crippling the utility of the manipulator The growing oscillations are indicative of an instability. However, it is not immediately apparent why such a system should be unstable. The objectives of this work were to find the source of the oscillatory behavior and to determine whether feedback control can be employed to stabilize such a system.