Joint Stiffness Tuning for Compliant Robots: Protecting the Robot under Accidental Impacts

This paper presents a systematic study on setting the joint stiffness for a 4-DOF compliant humanoid robot arm in order to protect the actuators form impact torques generated during accidental collisions. Based on the dynamic equations of the manipulator system integrated with an impact model, the worst configurations in which the torque of each joint is maximized can be searched in the whole workspace. These results are then applied to the impact simulation and appropriate stiffness values are selected for each joint to ensure that the joint torque does not exceed the maximum torque of the actuator. The method is applied to analyze a 2-DOF planar manipulator, which results in a selection of stiffness for the two compliant joints. Subsequently the method is extended to a 4-DOF compliant humanoid robot arm and the stiffness upper limits are given based on the worst under impact configurations for each joint. . 1

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