Impact modeling and control for industrial manipulators

The impact-force behavior is experimentally studied on a 6-DOF commercial manipulator interacting with a very hard granite surface. It is shown that the elastic-joint robot model proposed by Spong (1987) completely explains frequency and damping of impact-force oscillations, so that oscillations can be totally ascribed to joint compliance, while links behave as rigid bodies. This article shows, through analysis and experiments, how to effectively employ integral control even in the transition phase, maintaining contact with the environment without bounce despite the potential problems of integrator wind-up. We begin by describing the experimental setup and how the manipulator model is derived. We then report the experimental results and model validation and discuss the open-loop permanent contact and impact. We also give an analysis of the wind-up problem of integral control, propose methods to avoid or counteract it, and report bounceless experimental controlled impacts.