This paper presents a study on setting the joint stiffness for compliant robots in order to protect the actuators when the arm comes up against impact. System dynamic equations of compliant manipulators integrated with impact model are linearized to identify the maximum joint torques in the impact. Based on this, different directions of end-effector velocity and impact normal in different configurations in the robot workspace are calculated based on a given magnitude of end-effector velocity. By tuning the stiffness for each compliant joint to ensure the joint torque does not exceed the maximum value of the actuator, candidate stiffness values are obtained to make the compliant actuators safe in all cases when the robot end-effector moves with a velocity within the fixed magnitude value used in the calculation. The theory and procedure are firstly laid and demonstrated in a 1-DOF planar manipulator, then the work is applied to a 2-DOF compliant manipulator and the candidate stiffness is obtained based on the method.

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