Abstract This paper presents the design, analysis, and experimental validation of an MRI-conditional robotic system for abdominal intervention featuring a mechanically stationary remote center of motion (RCM). The proposed architecture employs a decoupled dual-parallelogram mechanism with flexure-based compliant joints, achieving compactness and wear-free operation. The actuation layout of the flexures was optimized using Freedom and Constraint Topology (FACT) to minimize parasitic deflection and improve transmission efficiency. An inchworm-type pneumatic insertion module with flexure-integrated gripping enables long-stroke needle advancement within the constrained MRI bore. The fabricated prototype, measuring 296 × 230 × 190 mm3, provides three active degrees of freedom (2R1T) driven entirely by nonmagnetic pneumatic actuators. Experimental characterization demonstrates an azimuthal motion range of ±20°, pitch range of −40° to +25°, and translational range of 50.8 mm. The compliant virtual pivot achieves a ±24° rotation range with stresses maintained within 80% of yield strength, confirming structural safety. RCM accuracy tests using an OptiTrack motion capture system revealed RMS errors of 0.65 mm (pitch) and 1.04 mm (yaw) without stabilizing flexures, validating precise geometric constraint through the flexure-based joints. The pneumatic collet gripper generated a maximum gripping force of 13 N at 100 psi, exceeding clinical puncture-force requirements. These results confirm that the decoupled parallelogram–flexure architecture achieves the desired balance of MRI compatibility, geometric precision, and mechanical robustness, establishing a foundation for compact, safe, and fully pneumatic robotic assistance in MRI-guided abdominal interventions.
Wu et al. (2026) studied this question.