Development, control, and MRI-compatibility of the MR-SoftWrist

This paper presents the MR-SoftWrist: a parallel 3DOF MR-compatible wrist robot with compliant actuation. Through a design that aligns the wrist joint axes to the device DOFs and uses custom MR-compatible force-feedback actuation, the MR-SoftWrist can measure and support wrist movements during fMRI. The device has a circular workspace for wrist flexion/extension and radial/ulnar deviation with 18 deg radius, and is capable of generating 1.75 Nm joint torque. Control experiments validate the device's workspace, along with position and zero torque control capabilities. In zero torque mode the maximum force felt by the user is 0.15 Nm, less than 10% of the device's torque output. The device is shown to have no significant affect on imaging quality during fMRI.