Design and Analysis of an End-Effector with Dual RCM Mechanism for Robotic Extracorporeal Shock Wave Therapy in Orthopedics

Robotic assistance in extracorporeal shock wave therapy (ESWT) has drawn attention in orthopedics for its automated operation instead of the time-lasting manual operation of physician, which dramatically alleviates the operation intensity of medical staff. It should be noticed that the dexterous operation in the small working space around the treatment site is an essential step for robotic ESWT. Considering the inverted cone shape of the working space around the treatment site in ESWT, this paper proposes and simulates a 3-DOFs robotic end-effector scheme with dual RCMs. A mechanism with PRR-type is determined which working space of $200 * 200 * 100 \mathrm{~mm}^{3}$ is verified through forward and inverse kinematic analysis. A $\Pi$-shaped structure is designed for rigidly connecting two RCM units which realizes compact assembly of end-effector. The Lagrange equation-based dynamic model of the mechanism is established, and the dynamic simulation demonstrated that the mechanism needs no torque in probe’s vertical position and larger torques are required when the probe moves towards the two ends. The proposed end-effector can be installed at the end of the robotic arm and provides a reference scheme for dexterously local operation with robot navigation in orthopedic ESWT.