Design of a Low-Cost Solenoid Actuated Stance Control Knee Orthosis

A new microprocessor-controlled knee joint has been developed for incorporation into custom-fabricated knee-ankle-foot orthoses. The system is intended to provide reliable knee locking at any angle for support during the stance phase of gait while also providing reliable knee unlocking even under load for a consistent swing phase. The knee joint contains a novel solenoid mechanism which draws together serrated rings to lock against rotation. The geometry of the interfacing mechanical features on the serrated rings was optimized to produce holding torque which neither slipped nor self-locked under increasing loads. Knee angle and inertial sensors within the joint provide real-time measurements of the gait cycle, which then control solenoid activation. Bench testing characterized the performance of the solenoid lock and demonstrated holding torque production of ~19 Nm/A. Minimizing cost, weight, size, and complexity was prioritized in the design to reduce barriers to adoption for this technology.Clinical Relevance- This novel stance control orthosis offers enhanced functionality relative to locked knee-ankle-foot orthoses, enhanced reliability relative to stance control orthoses, and increased accessibility due to a low-cost design.