Hydraulic accumulator-based energy-regenerative prosthetic knee: System design and energy recovery performance

A large and growing number of lower limb amputees exist worldwide, making high-performance, low-energy-consumption prosthetic knee joints of significant engineering and clinical value for improving motor function and quality of life of patients. To address the industry pain points of insufficient energy during the sit-to-stand (STS) transition in passive prostheses and limited battery life without energy regeneration mechanisms in active prostheses, a semiactive hydraulic accumulator-based energy-regenerative prosthetic knee joint without active actuation units was proposed in this study, which realizes gait energy recovery and assisted drive through the direct conversion between mechanical energy and hydraulic energy. Based on the biomechanical principles of human lower limbs, a hydraulic circuit consisting of a micro hydraulic cylinder, a bladder-type accumulator, and a micro proportional valve was developed to achieve efficient bidirectional conversion between mechanical energy and hydraulic energy during knee flexion and extension. A programmable logic controller (PLC)-based gait simulation experimental platform was constructed for two core motion modes: STS transition and level-ground walking, and systematic performance verification experiments were carried out. Experimental results showed that the system exhibited stable pressure fluctuation characteristics during the STS transition. Under accumulator precharge pressures of 0.5 MPa and 0.7 MPa, the maximum energy recovery efficiencies reached 25.96% and 32.89%, respectively. The proposed system achieved a good balance between bionic motion performance and energy recovery efficiency, and its energy recovery and release characteristics were fully consistent with design expectations. During level-ground walking, the system also demonstrated continuous dynamic changes in accumulator oil pressure and distinct energy recovery behavior throughout the gait cycle. The experimental results preliminarily verified the feasibility of the system's energy conversion and assisted drive functions. Under laboratory conditions, the proposed system validated the feasibility of applying the semiactive hydraulic accumulator scheme to prosthetic energy regeneration, providing theoretical and experimental reference for the design of novel high-efficiency, low-energy-consumption prosthetic knee joints.