Cycloidal Stepper Motor: A Systematic Approach for Designing a Nonmagnetic Rotary Actuator

Magnetic resonance imaging (MRI) has the ability to provide high-quality images of soft tissues and obtain the positions of surgical tools and target tissues, which is extremely useful in minimally invasive surgery. Hence, there is a significant need for surgical robots capable of working in the MRI environment, but designing MR-conditional actuators is one of the biggest obstacles to developing such robots. This article provides a novel approach to building pneumatic motors. A gear set design inspired by the curtate hypocycloid is applied for the motion of the rotor. The motor's operating principle and mechanical design, including rotor and housing, are presented. The relationship between different transmission ratios and motors is explored, showing that motors with more chambers and higher resolution can be obtained based on this hypocycloid. A physical prototype is made by three-dimensional printing and laser cutting, and the experimental data show that the presented motor can achieve a maximum speed of 2000 r/min and a torque of 11 mN·m.