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.
Lower-limb exoskeletons have undergone significant developments for aiding in the ambulation of adults with gait impairment. However, advancements in exoskeletons for the pediatric population have comparatively been lacking. This paper presents a newly developed joint actuator designed to drive the hip and knee joints of a pediatric lower-limb exoskeleton. The performance requirements associated with the actuators were determined based on a target audience of children ages 6–11 years old. The developed actuators incorporate a hybrid belt-chain transmission driven by a frameless brushless DC motor. One actuator underwent benchtop testing to evaluate its performance with respect to their torque production, bandwidth properties, backdrivability in terms of inertia and friction characteristics, speed capabilities, and operational noise levels. As a preliminary validation, a set of actuators were placed in a prototype orthosis to move a pediatric test dummy in gait tracking via state-feedback control. The results showed that the newly developed actuators meet the design specifications and are suitable for use in the pediatric exoskeleton being developed.
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