Design and Preliminary Evaluation of a Powered Pediatric Lower Limb Orthosis Available to Purchase

This paper describes the first stages of hardware development and preliminary assessment for a powered lower limb orthosis designed to provide gait assistance and rehabilitation to children with walking impairments, such as those associated with cerebral palsy and spina bifida. The design requirements, including range of motion, speeds, torques, and powers, are investigated and presented based on a target user age range of 6–11 years old. A three stage joint actuator is designed, built, and tested against the design requirements. The 0.6 kg actuator produced 4.2 Nm continuous torque and 17.2 Nm peak torque, and was able to run up to a speed of 480 deg/s. Backdrivability was characterized in terms of rotational friction, which was measured at 1.1 Nm. Finally, a 5.1 kg prototype orthosis was developed consisting of a hip segment, left and right thigh segments, and left and right shank segments, with four identical actuator prototypes installed in the thigh segments to actuate the hips and knees. Control electronics and a basic control structure were implemented to test the joint tracking capability of the orthosis against a predefined set of trajectories which were representative of pediatric gait patterns. Fitted to a dummy, the controlled limb successfully tracked the desired trajectories with a root-mean-square error of 9% and 4% of full scale for the hips and knees, respectively. With the dummy loaded with additional weight to representing a 32 kg child, the limbs also successfully tracked the trajectories with a root-mean-square error of 15% and 6% of full scale for the hips and knees, respectively.