Impedance control with autonomous mode switching

Impedance control is a general robust approach to controlling robot arms since, in principle, stability can be guaranteed for both free motion and constrained trajectories and even for transitions between the two regimes. Three modes of operation (free, transition and constrained) and their desired dynamic characteristics are defined for an impedance-controlled arm. Interfaces between the impedance control layer and other layers in a NASREM-type controller have been outlined. An algorithm for autonomous switching between the three modes is described that ensures stability throughout all phases of a task. A simple method is presented for computing the optimum impedance control parameters for the constrained modes. The control system described is the core element in an intelligent manipulation system under development.<>