Dynamic modeling and adaptable control of the CompAct™ arm

The introduction of physical compliance in robotic actuation systems has attracted increasing attention during recent years, due to the considerable benefits it can provide with respect to interaction safety, mechanical robustness and energy efficiency. However, the incorporation of passive compliant elements also results in systems with more complex dynamics, oscillations and limited bandwidth, requiring the development of sophisticated control strategies. Recently, variable damping mechanisms have been proposed to improve the performance of robots driven by compliant actuators. This study presents the dynamic modeling of the CompAct TM actuator, a series elastic actuator equipped with a semi-active friction damper named Variable Physical Damping Actuator (VPDA) and the extension of this model to the multi-DOF case. Based on the analysed model, a control strategy is designed to modulate the clutch normal force in order to adapt the system dynamics with the task requirements; to make the system "stiff" when a precise motion is needed, and to exploit the passive compliance of the actuator to make it "soft" in the case the flexibility of the system is desirable. Finally, simulation of the arm is performed to verify the effectiveness of the proposed control scheme.