Coupled stability characteristics of nearly passive robots

The authors address the problem of designing manipulator control laws such that interaction between manipulator and environment is stable. Taking passive manipulator admittance as a design goal. a metric that bounds the distance between the achieved nonpassive response and a passive target response is introduced. Conditions for coupled stability are developed based on this measure of admittance error, which result in restrictions on allowable environmental characteristics. When environmental conditions for the manipulator are known, the admittance error can be used as a control design specification. Alternatively, the admittance error can be used to measure performance of an existing system, providing a guide to mechanical interface design. A simple example is used to illustrate this approach