Dynamic stability issues in force control of manipulators

Robots in force control mode often become unstable during contact with stiff environments, due mainly to the high gain nature of wrist force-sensor feedback. To achieve stable force control, we propose an essential reliance on fast open-loop joint torque control, and relegate tip force sensor feedback to a slow loop to maintain accuracy. Dynamic stability is analyzed with a simple model of the robot and its environment. The analyses are verified by single-link experiments on the MIT Serial Link Direct Drive Arm.