On the stiffness design of intrinsic compliant manipulators

The incorporation of intrinsic compliance in robotic actuation systems has attracted the attention during recent years due to the considerable benefits which is not possible to achieve with conventional “stiff” actuation systems. However, despite the numerous compliant robots developed, a systematic method for tuning the passive elasticity of the individual joints is still missing. This tuning is typically performed using experimental trial and error processes and very little information on the criteria and methodologies used is available. This work studies the effects of passive compliance on the key parameters of the robotic systems including natural frequency, damping ratio, Cartesian stiffness and energy storage capacity. Criteria are then defined based on the desired performance of the system; and a method for the selection of the passive stiffness of compliant actuated arms is introduced. The proposed method is evaluated on a four degrees of freedom (DOF) compliant arm and the compliance of its joints is tuned. The sensitiveness of the main dynamic and static parameters of the robot with respect to the stiffness of joints is illustrated to show the effect of the compliance of each individual joint.