Modeling and desired control of an energy-storing prosthetic knee

A method of assisting a transfemoral amputee with lower limb-involving user tasks, the method comprising the steps of:

• attaching a transfemorally amputated residual limb to an upper leg structure of a prosthetic limb comprising a plurality of components including the upper leg structure, a lower leg structure, a lower leg prosthesis, a fluid actuator, a fluid, a plurality of controllable variable fluid flow resisting devices, an accumulator, and a tunable control system;
• hingedly connecting the lower leg structure to the upper leg structure;
• extending the lower leg structure between the upper leg structure and the lower leg prosthesis;
• moving the lower and upper leg structures pivotally relative to one another during a gait cycle characterized by a plurality of gait periods;
• operatively connecting the fluid actuator to the upper and lower leg structures;
• causing the fluid to flow in a predetermined manner within the fluid actuator responsive to relative pivotal movement of the upper and lower leg structures;
• providing the plurality of controllable variable fluid flow resisting devices, including first and second controllable variable fluid flow resisting devices, arranged in parallel with each other, each controllable variable fluid flow resisting device of the plurality of controllable variable fluid flow resisting devices having a different series resistance;
• providing the accumulator;
• providing the tunable control system which controls the plurality of controllable variable fluid flow resisting devices in different actuation combinations to provide a plurality of response modes, each response mode bearing a direct relationship to a desired force response of the prosthetic limb for a particular user task
• with the control system, controlling the first and second controllable variable fluid flow resisting devices to store, in the accumulator, fluid energy caused by fluid flow within the fluid actuator during gait periods of positive energy and release fluid energy to the fluid flow within the fluid actuator during gait periods of negative energy;
• controlling action of the first and second controllable variable fluid flow resisting devices with the control system in coordination with the gait of the transfemoral amputee;
• and
• actuating the control system to cause storage of the fluid energy for a predetermined length of time and release of the fluid energy at a predetermined time during the gait cycle, both the storage and release of the fluid energy being variable by action of the control system without replacement of components of the prosthetic limb with other, like components for the purpose of causing the variability of the storage and release of the fluid energy.