Design and Control of a Single-Leg Exoskeleton with Gravity Compensation for Children with Unilateral Cerebral Palsy

Area of Science:

• Biomedical Engineering
• Rehabilitation Robotics
• Pediatric Assistive Technology

Background:

• Children with cerebral palsy (CP) face challenges in mobility and independence, impacting their quality of life.
• Lower-limb exoskeletons (LLEs) show potential for improving walking in children with CP, but few prototypes exist.
• No single-leg exoskeleton (SLE) has been specifically developed for children with CP.

Purpose of the Study:

• To design and develop the first size-adjustable single-leg exoskeleton (SLE) for children with CP.
• To target children aged 8-12 across Gross Motor Function Classification System (GMFCS) levels I-IV.
• To address increased metabolic cost in individuals with CP by implementing a gravity-compensating controller.

Main Methods:

• Designed a size-adjustable SLE with active hip, knee, and ankle joints actuated by brushless DC motors and harmonic drive gears.
• Developed a model-based gravity-compensator impedance controller to reduce metabolic burden.
• Derived and validated a dynamic model of user-exoskeleton interaction using Euler-Lagrange formulation and Denavit-Hartenberg rules in Simscape™ and Simulink®.

Main Results:

• A novel systematic simplification method was developed for dynamic modeling.
• The dynamic model was validated with high precision.
• Simulations demonstrated the controlled SLE's ability to improve walking functionality and accuracy in following target trajectories.

Conclusions:

• The designed adjustable SLE is a novel assistive device for children with CP.
• The gravity-compensating controller effectively addresses metabolic cost concerns.
• The SLE shows significant potential to enhance walking ability and independence in children with CP.