Development and evaluation of a novel actuator using MR magnetic field

Recently, Intra-Operative Magnetic Resonance Imaging (IO-MRI) has attracted attention for the reason of operating quality. In the other hand, surgical assist robot with high accuracy is widely researched. By combining IO-MRI and surgical assist robot to an MR-compatible surgical assist robot, higher quality of operation is expected. In this paper, we introduce a novel actuator for MR-compatible Surgical Assist Robot, which actively uses MR magnetic field and is drive by regulating pulse current. Use of ratchet mechanism enables step wise motion of the rotor similar to stepping motors. The position of the rotor can be controlled without an encoder. Clock-wise rotation, counter clock-wise rotation, constrained and non-constrained conditions were achieved by using this mechanism. Evaluation of the first prototype (84times76times58(mm³), 380 (gram)) shows that it is MR-compatible and has a very high positioning accuracy (step angle CW: 12.04plusmn0.28 (deg), CCW : 12.22plusmn0.36(deg); backlash < 1 (deg)). No-load maximum rotational speed is 35.71(rpm) and maximum torque 15.1times10^-3 (Nm).