Cascade control for compliant joint robots with redundant position sensors

The new generation of robots should coexist with our human beings in every walk of life. As a result, physical Human-Robot Interaction (pHRI) is ubiquitous and robot safety is quintessential. One solution to safety demand is to voluntarily put the series elasticity into joints for shock absorbing. However, side effects in terms of increased oscillations and long settling time occur. To alleviate this predicament, a compliant joint with two rotary position sensors measuring both the link side and motor side positions is devised. Then, a cascade control consisting of the outer position loop with the joint end position measurement and the inner torque loop is posed to improve the robot performance, and its stability is rigorously analyzed by the singular perturbation theory. Finally, experiments are conducted to verify the effectiveness of the suggested control scheme.