Miniaturization of MR Safe Pneumatic Rotational Stepper Motors

Pneumatic rotational stepper motors can be used to actuate MR (magnetic resonance) safe robotic systems. This paper describes novel techniques to minimize the volumetric size and/or step size of such motors in order to cope with the limited space requirements while still delivering high precision. Three designs are presented: the R-10 measures 1.0 cm ³, has step size 12.9° and torque 1.2 N mm. The R-40 measures 25.6 cm ³, has step size 1.01° and torque 470 N mm. The R-54 measures 46.7 cm ³, has step size 1.01 m° and torque 240 N mm. The particularly small step size in the R-54 motor is achieved by using a high-reduction planetary gear.These three motors demonstrate that small-scale rotational stepper motors with a wide range of step sizes and good torque characteristics can be constructed that surpass state-of-art designs by a considerable margin. This allows the advancement of MR safe robotics towards more compact and versatile designs, and also overcome certain existing limitations by combining multiple motors with different specifications.