Remote Torque Transmission for MR-Conditional Haptic Manipulation: A Torsion-Rod Approach

Abstract

Two configurations representing geometric extremes were validated: a square layout incorporating ten 90° bends, and a straight-line layout without corner joints. Most proof-of-concept requirements were satisfied by both configurations, including a control bandwidth exceeding 20 Hz, torque transmission of at least 1.2 N·m, and a range of motion of [−42°, 42°]. The square configuration achieved a resonance frequency of 15.0 Hz and a −3 dB bandwidth of 24.1 Hz; the straight-line configuration achieved a resonance frequency of 27.5 Hz with an extrapolated bandwidth of 46.9 Hz. The square configuration is substantially less stiff than the straight-line configuration (kA = 14.5 N·m/rad versus kB = 48.5 N·m/rad). A series compliance model identified the 3D-printed bearing housings as the dominant compliance source. Pushrod axial stiffness is approximately three orders of magnitude higher than bearing housing compliance and does not contribute to the bottleneck. Including out-of-plane bearing housing deflection at an estimated misalignment fraction of α = 0.3 reduces the model prediction from 38.1 N·m/rad to 19 N·m/rad, approaching the measured value. Replacing the 3D-printed housings with stiffer alternatives is predicted to raise the Square Configuration resonance frequency from 15.0 Hz to approximately 31 Hz, exceeding the 20 Hz target. The current prototype uses steel fasteners and bearings; MR-Conditional material substitution and in-bore validation are identified as the primary next steps toward a clinically deployable system.