Design and control of a novel multi-state compliant safe joint for robotic surgery

In this paper, we propose a novel design of compliant safe joint, which has flexibility when the work load exceeds a predefined threshold. The compliance is generated by a spring. We design a special transmission mechanism to convert axial motion into circumferential motion such that the linear compliance can be converted into circular one. When the end-effector of a surgical robot actuated by the compliant safe joints collides with patient´s body, the compliance of the joints will protect the patient by absorbing part of the collision energy. Because of the system´s special mechanical structure, the control methods should be different when it works under different states. We propose a simple algorithm to choose control methods so that the system can work both under rigid and flexible states with different controllers. We have built a prototype to validate the design and the controller.