An efficient energy storage & return prosthesis

• Main Author: Bari, Abu Zeeshan
• Published: University of Salford 2013
• Subjects: 610; Health and Wellbeing
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.588695

Amputee gait is characterised by a higher metabolic cost of walking compared with anatomically intact subjects. Anatomically intact gait kinetics reveals that tendons crossing the ankle joint store and return strain energy during the stance phase of walking to provide forward propulsion. One of the main reasons for the high-energy cost of amputee gait is that passive prosthetic feet store little energy compared with the equivalent human structure and hence cannot provide the required energy at push-off. In addition, passive prosthetic feet are uncontrolled in the storage and release of strain energy, and do not provide natural levels of resistance and propulsion. Therefore, designing a passive prosthesis to efficiently store and transfer energy between joints, with continuous control over ankle torque, remains a research challenge. With the aim of developing an energy efficient passive prosthesis capable of mimicking the controlled energy recycling behaviour seen in an anatomically intact limb, a hydraulics-based design was investigated in this work. A first design concept, based on a hydraulic accumulator, a variable displacement hydraulic actuator (VDA), a gearbox, and a low-pressure oil tank, was developed. The accumulator served as energy storage medium, where VDA served as the only actuator to provide ankle torque. Simulation showed that the design outperformed commercial passive prostheses as well as a recent novel design based on a spring-clutch mechanism. For level walking, it provided 86% and 69% of the peak power required by the anatomical ankle whilst providing near normal ankle torques. The system was able to store all of the available energy during gait and provide correctly timed release of energy. However, a feasibility study showed problems with size and weight of a potential prototype. To address this problem a second design was developed with the aim of reducing the size and weight of VDA in design I. The second design comprised of a spring to provide ankle torque and to reduce the torque load on the VDA. The spring is connected to the ankle via a lever arrangement, and the VDA is used to vary the lever arm to continuously control ankle torque. Simulation results showed that design II outperformed design I; it delivered higher values of peak power, and a feasibility study showed that, using bespoke component designs, it might be possible to incorporate it into a lower limb prosthesis.