Towards Accessible Mobility Support: User-Centered Design of a Passive, Multi-Functional, Low-Cost Knee Exoskeleton

Paper Title

Towards Accessible Mobility Support: User-Centered Design of a Passive, Multi-Functional, Low-Cost Knee Exoskeleton

Publication Info

• Topic area: Design and evaluation of a passive knee exoskeleton for mobility assistance.
• Keywords: Passive exoskeleton, knee brace, gait rehabilitation, user-centered design, assistive technology, load-triggered mechanism, wearability, accessibility, human-computer interaction, rehabilitation devices.

Background and Problem

• Problem / challenge: Existing knee braces are either static, causing unnatural gait patterns and high abandonment rates, or robotic, which are heavy, complex, and expensive. There is a lack of accessible, adaptive knee support solutions.
• Significance: Addressing this gap could improve mobility, safety, and rehabilitation outcomes for individuals with knee impairments, especially those experiencing knee buckling or instability.
• Motivation and related work: Prior research has focused on static braces and robotic exoskeletons, but these fail to balance adaptability, cost, and usability. This paper aims to bridge this gap by designing a passive, adaptive knee exoskeleton informed by user-centered methods.

Solution

• Proposed approach: A fully passive knee exoskeleton that uses mechanical triggers under the foot to lock and release the knee joint in sync with the gait cycle, enabling natural walking without electronics or motors.
• Novelty:
  1. Development of a load-triggered locking mechanism that adapts to the gait cycle.
  2. Fully passive design combining the accessibility of static braces with the adaptability of robotic systems.
  3. User-centered design process involving clinicians and orthosis users to identify needs and constraints.
  4. Technical and qualitative evaluation of the prototype, highlighting its feasibility and potential for rehabilitation.
• Procedure and key techniques:
  1. Design of a lockable knee joint, mechanical AND logic gate, and load-triggered switches.
  2. Integration of these components into a lightweight, sock-like wearable form factor.
  3. Evaluation of the prototype through technical tests (e.g., locking strength, response timing) and stakeholder interviews.

Results

• Concrete findings:
  • The exoskeleton weighs 0.95 kg and costs $38 in materials.
  • Locking mechanism supports up to 510 N of force, sufficient for typical knee loads during walking.
  • Response delays: 248.6 ms for locking and 318.8 ms for unlocking, aligning well with the gait cycle.
  • Knee motion range during walking with the device: 6.45°–55.81°, slightly reduced compared to natural walking (0°–70°).
• Advantage over baselines:
  • Combines the lightweight, low-cost nature of static braces with the adaptive functionality of robotic systems.
  • Supports natural gait mechanics, including walking on uneven surfaces, stairs, and sit-stand transitions.
• Experiments / evaluation:
  • Technical tests: Load-triggered switch thresholds, locking mechanism strength, and functional response during gait cycles.
  • Qualitative evaluation: Interviews with 6 participants (4 clinicians, 2 patients) highlighting functionality, accessibility, and wearability.
• Limitations and future work:
  • Current prototype tailored to a single user; broader testing and personalization are needed.
  • Materials (PLA, nylon) unsuitable for long-term use; exploration of durable alternatives required.
  • Challenges in donning, shoe compatibility, and sock hygiene need refinement.
  • Future directions include gait studies, clinical evaluations, and integration of advanced materials and customization tools.

Summary

This paper introduces a fully passive, low-cost knee exoskeleton that uses mechanical triggers to adaptively lock and release the knee joint in sync with the gait cycle. The design combines the accessibility of static braces with the adaptability of robotic systems, addressing key challenges in knee assistance. Technical evaluations demonstrate its feasibility, while qualitative feedback from clinicians and patients highlights its potential for rehabilitation and everyday use. Future work will focus on broader user testing, material durability, and further refinements to enhance wearability and personalization.