Nonlinear Contact Control for Space Station Dexterous Arms

ITL October 1996, a research and development task um initiated at JPL to develop and demonstrate nonlinear contact control schemes for the dexterous robotic arms planned for the Space Station. This paper reports on the progress made to-date in this task. Specifically, the paper introduces a new class of contact controllers comprised of a nonlinear gain in cascade with a linear jixedgain PIforce controller and PD compliance controller. The nonlinear gains used are simple hyperbolic functions of force emor and contact force, respectively. The stability of the closed-loop systems incorporating nonlinear PIand PD controllers are investigated using the Popov Stability Criterion. Experirnenta lresults arc pmsentedto demonstrate the eflicacy of the nonlinearforce and compliance control schemes jora dexterous 7-DOF Robotics Research arm. These results highlight the advantages of the proposed nonlinear contact controllers compared to li71ear controllers.