Controlling an MR Safe Robot Arm with Six Pneumatic Stepper Motors using Eight Tubes

Magnetic resonance imaging (MRI)-guided interventions are difficult to perform by hand and may benefit from robotic assistance. The MRI safety requirement excludes the use of electromagnetic motors; a suitable alternative is utilizing pneumatic stepper motors as these can be fabricated from plastic materials and do not use electricity. One such motor is typically actuated by three to six pneumatic tubes; a design with two double-acting cylinders generally uses four tubes. Conventionally, the total number of tubes is 4n with $n$ the number of joints. The total bundle of tubes takes up significant volume and mass, possibly interfering with the medical procedure, restricting range of motion and/or adding parasitic stiffness to joints.

The aim of this research is to control a six degrees of freedom (DOF) MR safe robot arm using only eight tubes. In the results, we show that 2k tubes can actuate n=(k choose 2) joints in such a way that each joint can still be operated to its setpoint position with a deviation of at most one step.