Design and Validation of a Cable-Driven Joint Actuator for Pediatric Knee Orthoses

Abstract Robot-assisted gait rehabilitation is an increasingly common therapeutic intervention for enhancing locomotion and improving quality of life for children with lower-limb mobility impairments. However, there are few systems specifically designed for pediatric use, and those that do exist are largely cumbersome, bulky and non-custom devices that ultimately reduce therapy effectiveness. This paper introduces the Cable-Driven Joint System (CDJS), a novel approach for pediatric gait rehabilitation that addresses these shortcomings in a lightweight and compact robotic device using the patient's fitted orthosis. The CDJS consists of a 2.1 kg actuation unit that is held by a clinician which delivers assistive torques through a Bowden cable transmission to a 0.3 kg joint mounted to user-custom bracing. This work details an actuator benchtop evaluation, demonstrating a peak torque of 20 Nm, peak velocity of 7.2 rad/s, bandwidth of 9.7 Hz and a mass moment of inertia of 58.38 kg·cm2. An actuator model was developed and evaluated in simulation, showing a strong correlation with experimental torque data (R-squared = 0.95) and indicating a transmission efficiency of 72%. In-air gait tracking experiments on an emulated subject showed that the CDJS assisted the subject to track a nominal knee trajectory with an average root mean squared error of 2.56° at a continuous torque of 1.37 Nm. These results suggest that the cable-driven actuator meets the design requirements for pediatric gait rehabilitation and is ready for clinical device trials.