ADAPTIVE EXPLICIT FORCE CONTROL OF POSITION-CONTROLLED MANIPULATORS

This article presents a new adaptive outer-loop approach for explicit force regulation of position-controlled robot manipulators. The strate gy is computationally simple and does not require knowledge of the man ipulator dynamic model, the inner-loop position controller parameters, or the environment. It is shown that the control strategy guarantees global uniform boundedness of all signals and convergence of the posit ion/force regulation errors to zero when applied to the full nonlinear robot dynamic model. If bounded external disturbances are present, a slight modification to the control scheme ensures that global uniform boundedness of all signals is retained and that arbitrarily accurate s tabilization of the regulation errors can be achieved. Additionally, i t is shown that the adaptive controller is also applicable to robotic systems with PID inner-loop position controllers. Computer simulation results are given for a Robotics Research Corporation (RRC) Model K-12 07 redundant arm and demonstrate that accurate and robust force contro l is achievable with the proposed controller. Experimental results are presented for the RRC Model K-1207 robot and confirm that the control scheme provides a simple and effective means of obtaining high-perfor mance force control. (C) 1996 John Wiley & Sons, Inc.