Towards Accessible Mobility Support: User-Centered Design of a Passive, Multi-Functional, Low-Cost Knee Exoskeleton
Yuyu Lin, Yujia Liu, Emma Kim, Alexandra Ion · 2026 · Proceedings of the 2026 CHI Conference on Human Factors in Computing Systems (CHI '26) · doi:10.1145/3772318.3791886
Summary
Lin et al. (Carnegie Mellon) propose a fully passive, unpowered knee exoskeleton that aims to sit in the gap between two unsatisfying options currently available to people with mobility impairments: static knee-ankle-foot orthoses (KAFOs), which are cheap and light but lock the knee in full extension and force unnatural 'hip hike' gaits (reported abandonment rates of 58-79%), and robotic stance-control exoskeletons, which provide adaptive assistance but are heavy, costly, and dependent on sensors, motors, and batteries. The device is built entirely from mechanical elements: a lockable hinge joint with a sliding pin, a Bowden-cable-driven mechanical AND gate, and two pairs of load-triggered bistable switches placed under the heel and toe of a sock. When both switches are compressed (midstance, full foot contact), the AND gate pushes the pin into the locked position; when either heel or toe lifts, the pin disengages and the knee swings freely. The full prototype weighs 0.95 kg and costs roughly USD 38 in materials. Design was grounded in formative semi-structured interviews with four clinicians (physiatrists and physical therapists working with stroke, MS, SCI, and TBI patients) and two orthosis users, yielding three design goals - Functionality, Accessibility, Wearability. The authors then conducted technical evaluations (switch-threshold characterisation across 19 3D-printed samples, locking-strength testing showing 265-510 N holding force, and OptiTrack motion-capture analysis of 24 gait cycles on level ground, slopes, and stairs plus sit-stand transitions) and a second round of evaluation interviews with clinicians and orthosis users reviewing the working prototype as a design probe.
Key findings
Technically, the passive mechanism tracks the gait cycle closely: heel and toe switches activate within 3.2% and 1.7% of the cycle duration, knee lock engages with a 248.6 ms delay (8.2% of cycle) and disengages 318.8 ms later, and the device preserves 6.45-55.81 degrees of knee flexion versus the unbraced 0-70 degree baseline. It supports level walking, uphill/downhill slopes, stair ascent and descent, and sit-to-stand transitions - use cases that rigid KAFOs either prevent or make dangerous. Qualitatively, clinicians and users judged the prototype a potential 'game changer' for patients who need knee-buckling protection but have more strength than a typical solid AFO wearer, such as people in mid-stage stroke recovery or living with MS. Participants praised the automatic lock/unlock (which preserves muscle engagement rather than replacing it), the intuitive load-triggered logic (users quickly understood 'the more weight you put on that leg, the more stable it is'), the low cost, and the sock-based conformal form factor wearable under clothing. Wearability gaps remained: donning and doffing is hard for patients with upper-limb weakness or reduced coordination, the foot unit is bulky inside shoes, the sock is difficult to launder, and clinicians raised concerns about side-to-side ankle instability, audible clicks, and patients needing subtle feedback to know when the lock is engaged.
Relevance
For accessibility practitioners working at the intersection of rehabilitation, assistive technology, and HCI fabrication, this paper is a concrete demonstration that adaptive gait assistance does not require electronics. The 58-79% abandonment rate for static KAFOs is a striking data point for anyone specifying, procuring, or prescribing lower-limb orthoses, and the paper's Functionality/Accessibility/Wearability framing, plus its attention to donning independence, audible signatures, appearance under clothing, and affordability, maps directly onto the design criteria that drive long-term adoption. Limitations are significant: this is a single-wearer research prototype (not a product), there is no longitudinal clinical or biomechanical outcome study, no metabolic-cost measurement, and no safety certification. Practitioners should read it as a design-space contribution and a template for involving clinicians and orthosis users iteratively, rather than as evidence that this specific device is ready for patient use.
Tags: exoskeleton · orthosis · knee brace · mobility · rehabilitation · gait · wearable technology · assistive technology · user-centered design · HCI fabrication · stance-control orthosis · low-cost assistive technology · participatory design