MR-Safe Pneumatic Rotation Stepping Actuator

Magnetic Resonance Imaging (MRI) is widely used not only for diagnosis but also for surgical navigation, etc. Surgeons and surgery-support systems can conduct surgeries less invasively because they derive accurate positional relationships between surgical instruments and anatomical regions of interest from preoperative or intraoperative MRI images. Many surgical robots intended for use within MRI gantries have been developed. Some of them use pneumatic actuators that are difficult to control accurately or that have many components, however, causing high fabrication cost, low durability and low sterilizability. To solve these problems, we have developed a φ30-mm pneumatic rotation stepping actuator. The actuator consists of three Direct Acting gears (D.A. gears) and a Rotation gear (R gear). When all of the D.A. gears are pushed sequentially up by compressed air, the R gear rotates because it engages all of them. In a fundamental performance experiment, the maximum angular error was 2.1° and maximum torque was approximately 150 mNm using 0.6 MPaG. Additionally, in an MR safety evaluation, the actuator was not found to cause any distortion or artifacts in MRI images. The actuator can therefore be applied to MR-safe positioning or puncturing robots.