Rehabilitation Device for Low-Speed Gait Therapy Using a Passive Stephenson Mechanism on a Commercial Treadmill

This paper introduces a linkage-based rehabilitation device designed for low-speed gait therapy for individuals with neurological gait deficits. Unlike existing devices that operate above 0.5 m/s, our system enables training at speeds between 0.1–0.4 m/s, aligning with optimal rehabilitation thresholds. The device features a passive single DOF, six-link Stephenson-III mechanism mounted on a commercial treadmill. The system is designed to accurately follow an ankle-to-hip meta-trajectory, which has been extracted from 400 gait cycles of healthy individuals and adjusted for a leg length of 800 mm. To ensure adjustability to users with varying physiologies, the design allows for scaling and parameter tuning based on individual anthropometrics. The final optimized mechanism was synthesized using the shadow robot algorithm, exploring 5000 initial configurations. The resulting design supports different gait trajectories through profile blending, enabling motion customization across a wide range of rehabilitation stages. A unique driving accessory transmits treadmill motion directly to the crank links, eliminating the need for separate actuators. A bodyweight support system reduces up to 80% of the patient’s weight and assists in balance control. The setup process has been streamlined for ease of use by inexperienced users by reducing the number of interaction points to two. This minimal constraint allows relative freedom for the remaining joints of the leg, enabling a more natural and patient-friendly walking experience. The device’s performance was validated using OpenSim simulations: hip and knee angle trajectories remained within ±1 standard deviation of experimental data, and root-mean-square errors were below 5 degrees throughout the gait cycle. These results demonstrate the device’s potential to provide safe, accurate, and adjustable gait rehabilitation for individuals with severe mobility impairments.