Design and Validation of a Compact Concentric-Tube Robot for Percutaneous Nephrolithotomy

Concentric-tube robots (CTRs) have garnered significant attention in various minimally invasive procedures due to their small size and dexterity. Despite extensive technical advancements in the development of CTRs, there is a lack of design approaches specific to their function as surgical instruments. This study proposes a compact CTR specifically designed for percutaneous nephrolithotomy (PCNL), adaptable for both hand-held operation and mounting on a passive arm. We employ a parallel carriage-based design to reduce the device's cross-sectional footprint (46 mm diameter, 322 mm length) and localize the center of mass (570 g mass) beneath the grip area, enhancing ergonomic comfort and control. An ergonomic evaluation of the robot during the handling of the robot by expert urologists, as well as non-clinicians, showed better ergonomics than standard hand-held PCNL devices. Additionally, closed-loop position control of the distal end of the CTR was implemented based on resolved-motion rate inverse kinematics. The performance of the robot was empirically validated through experiments on a life-size abdominal phantom. The results showed mean closed-loop position errors of 1.2±0.8 mm for autonomous navigation to 100 target points on the stone, indicating a performance level in line with the specific requirements of PCNL.