Antagonistic Impedance Control for Pneumatically Actuated Robot Joints

This letter presents a novel joint torque-based impedance controller for antagonistically driven flexible joints actuated by pneumatic cylinders and compares it with the current state of the art. The work targets on transferring soft-robotics control concepts from classical motor-gear-torque sensor setups to pneumatic systems, with the goal of achieving similar performance levels in comparison to this well established technology. A detailed flexible joint model is derived that incorporates the pneumatic and mechanical dynamics of the proposed antagonistic design. This model is used for analyzing model-based control approaches, which in turn are based on reduced order dynamics. The tendon-based joint level impedance controller enables the simultaneous adjustment of closed-loop stiffness and damping. The proposed scheme shows good simulation results for both, position tracking and compliance performance, respectively. Experimentally, an angular position tracking of 7 Hz could be achieved. Also, stable rigid contacts could be established at considerable impact speed.