Design of a Square Rotor Driven Pneumatic Stepper Actuator for MR-Guided Therapy

Magnetic resonance (MR) imaging has been widely used in the diagnostics and treatment of soft tissues due to its ability to acquire high-resolution images with outstanding contrast. Therefore, MR-guided therapy and its supporting equipment, including MR-conditional sensors and actuators, have been developed rapidly. In this article, a nonmagnetic pneumatic stepper motor was developed. The working principle was analyzed, and the theoretical static output torque was expressed mathematically. The driven part of the proposed design is a polygon rotor derived from the Wankel engine. Besides, the outline of the inner wall of the housing was investigated. Experiments were conducted with the motor functioning at different speeds under different air pressures; by controlling the air in each chamber sequentially, the rotor can rotate continuously in dual directions with a torque of up to 38 mN.m and a maximum speed of 400 r/min. The MR test showed that no image artifact was found.