Abstract
Magnetic resonance imaging (MRI) can provide high-contrast soft tissue visualization without ionizing radiation, which makes it an attractive imaging modality for interventional procedures. However, the strong magnetic and radiofrequency fields impose significant challenges to the development of robotic systems within the MR environment. Designing MRI-compatible actuators is essential for the development of MRI-guided robotic systems. This paper reports the design, control, and characterization of a gear-based pneumatic stepper motor. The motor is designed with three actuating piston units and a geared rotor. The three actuating pistons are driven sequentially by the compressed air to push the geared rotor and to generate bi-directional step-wise motion. Experiments were performed to characterize the motor in terms of torque, speed, control, and MRI compatibility. The experiment demonstrates the motor can provide 475 mNm maximum continuous torque at 80 PSI (0.55 MPa) with 9 m air hoses. The closed-loop control evaluation demonstrates the steady-state error of position tracking was 0.81 ± 0.52°. The MRI compatibility study indicates negligible image quality degradation. Therefore, the proposed pneumatic stepper motor can be used for MRI-guided robotic applications.
