Control of a flexible spherical wrist

In this paper, a new wrist mechanism is introduced. This wrist, although simpler and lighter than conventional wrists, displays nonlinear torsional vibrations. This differs from conventional wrists in that structural flexibility in the mechanism is allowed to occur by design. The dynamic equations of this wrist are derived, and it is shown that the use of conventional rigid body PID controllers on this prototype is inadequate. A tracking controller which compensates for the flexible dynamics of the wrist is implemented with encouraging results. This controller allows the end-effector to be placed at an arbitrary orientation with very little vibration. The effect of the controller is to make the wrist appear to have a much higher structural stiffness