Robust Torque Control in Flexion/ Extension Wrist Movement

This study explores the feasibility of implementing robust torque control in a wrist flexion and extension rehabilitation device using a proportional-integral-controller (PID) controller. A simulation model was developed, consisting of an ideal DC motor, a biomechanical hand model, a torque estimator, and a PID feedback controller. The wrist was modeled as a rotational mass-spring-damper system, capturing essential mechanical behavior while enabling rapid prototyping. The control system used a sigmoid torque input to mimic gradual clinical force application and avoid abrupt joint loading. Robustness was evaluated by varying biomechanical parameters across 1,000 simulations. Results showed consistent performance, with maximum overshoot below 3% and settling times under 0.22 seconds. The controller also maintained accurate torque tracking under external disturbances. These findings indicate that a well-tuned PID controller can provide reliable torque control despite variability in human biomechanics.