Development and Control of a Macro–Micro Multi-Arm Robotic System for Open Spina Bifida Treatment

Open spina bifida (OSB), a congenital anomaly caused by incomplete spinal column closure, leads to progressive nerve damage. While multi-port minimally invasive procedures are being optimized clinically, single-port access (SPA) surgery presents a promising, less invasive alternative. Beyond reducing scarring, SPA may also decrease the risk of iatrogenic preterm premature rupture of membranes and enhance maternal recovery, as suggested by outcomes in other minimally invasive interventions. However, technical challenges persist in SPA implementations, particularly in instrument miniaturization and control precision. To facilitate this approach, a macro-micro multi-arm robotic system is under development. The system features an 11-mm-diameter insertion port to deploy four instrument arms. The arm design incorporates a hybrid backbone structure. A macro proximal section of concentric tubes provides stable deployment, while a micro distal flexible segment enables the dexterous manipulation. This paper presents dedicated modeling and control strategies to address actuator and transmission nonlinearities arising from stringent miniaturization requirements. A hybrid framework combining joint-level feedback with deep-learning-based feedforward compensation mitigates limitations imposed by pneumatic artificial muscles and tendon transmissions. The system is validated through trajectory-following experiments, each conducted over 10 trials. Preliminary results show an average root-mean-squared error of 0.28 mm, an average maximum absolute error of 0.85 mm, and an average standard deviation of 0.18 mm across both trajectories. These results demonstrate consistent sub-millimeter precision, satisfying the requirement for OSB repair. The feasibility of the system was then verified through a phantom study.