A Cyber-Physical System for Dynamic Exoskeleton Impedance Control Using a Fractional-Exponent Saturation Model

A fundamental challenge in the design of powered exoskeletons and rehabilitative robotics is balancing kinematic transparency with user safety. Traditional linear impedance controllers or hard mechanical stops often restrict natural movement or fail to react smoothly to sudden kinematic anomalies, such as tripping or spasticity. This paper introduces a novel dynamic impedance control architecture that models user movement intent as a linear driving process bounded by a cubic structural constraint. By dynamically calculating a fractional-exponent saturation threshold, the system creates a responsive "kinematic safety envelope." The control loop provides near-zero resistance during normal motion but geometrically scales impedance during rapid anomalies, offering a highly effective, computationally lightweight method for active fall prevention and joint protection.