PneuScape

Abstract

A future version of the DEMCON Needle Placement System (NPS) for use in the Magnetic Resonance Imaging (MRI) scanner requires accurate and small actuators that are MR (Magnetic Resonance) safe; actuators that can safely operate without interfering with the MR environment. The pneumatic stepper motor was chosen for actuation of the aiming segments of the future NPS. The pneumatic stepper motor can be made out of MR safe materials and its actuation principle is MR safe. MR safe, small size pneumatic stepper motors that produce high resolution motion however, do not exist. The goal of this thesis is to design and prototype such a pneumatic stepper motor and test its performance. An MR safe, high resolution pneumatic stepper motor was designed. This motor, called the PneuScape, was designed to fit in the orientation module of the NPS. The design of the PneuScape is based on an escapement mechanism. A torque is applied to move the output and the escapement anchor indexes this movement, creating a step. The PneuScape currently has the smallest designed step size st = 0.83º of any MR safe pneumatic stepper motor. A prototype of the Pneuscape was developed using rapid prototyping techniques and its performance was evaluated. The total prototype did not meet all design requirements, in particular the requirement of maximum positioning error. Torque application does not work reliably and results in the motor skipping steps, diminishing the motor's accuracy. The escapement mechanism however, shows promising results in its performance. Recommendations were given to improve the prototype. If the prototype is improved with aid of the recommendations, a future version of the PneuScape is expected to meet the design requirements. Finally, the work in this thesis has made science take a step towards high resolution MR safe actuation.