Series J-Spring Actuation for Ankle-Foot Prosthesis
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Solution Overview
Problem
Commercially available ankle-foot prostheses struggle to adapt to changes in walking speed, ground slope, or stair ascent/descent, and lack net positive work during the late stance period, leading to increased musculoskeletal stress and metabolic consumption, while being too heavy or bulky for lightweight users.
Innovation Solution
A microprocessor-controlled ankle-foot prosthesis with a series-elastic actuator and a novel architecture that includes a shank member connected to a foot keel spring via an ankle rotational joint, featuring a heel leaf spring for shock absorption and a J-spring for energy storage, enabling impedance and spring equilibrium modulation across gait phases and terrains with reduced mass and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If active prostheses with powerful motors are used to provide net positive work during late stance, then walking comfort and economy are improved, but device mass and build height increase significantly
Solution Approach 1:
The patent combines passive elastic energy storage (through the J-spring and carbon fiber foot structure) with active motor assistance in a series-elastic actuator configuration. This merging allows the system to leverage both passive mechanics and active control, providing net positive work during late stance while reducing the motor size and overall device mass compared to purely active solutions
Solution Approach 2:
The prosthesis employs dynamic modulation of ankle impedance and spring equilibrium position through computer-controlled adjustment of the series-elastic actuator. This allows the device to adapt its mechanical properties in real-time during the gait cycle, optimizing performance across different walking conditions while maintaining a compact design
2Weight of moving object
If passive composite spring structures are used to approximate ankle function, then device mass is reduced, but adaptability to changes in walking speed, ground slope, or stair ascent/descent is lost
Solution Approach 1:
The patent implements computer-controlled modulation of the series-elastic actuator to dynamically adjust ankle impedance and spring equilibrium position. This enables the prosthesis to adapt to varying walking speeds, ground slopes, and stair conditions while maintaining a lightweight design, overcoming the limitations of static passive spring structures
3Adaptability or versatility
If quasi-passive prostheses with computer-controlled damping modulation are used, then adaptability to various tasks is improved, but net positive work during late stance and controlled plantar flexion are still not provided
Solution Approach 1:
The patent merges passive elastic energy storage with active motor assistance in a series-elastic configuration. The active element provides controlled plantar flexion and net positive work during late stance, while the passive J-spring stores and releases energy, achieving both adaptability and energy positivity that quasi-passive designs cannot accomplish
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The prosthesis provides powered plantar flexion with net mechanical work during late stance, reducing musculoskeletal stress and metabolic consumption, while maintaining a comfortable gait and adapting to various walking conditions with a lighter and more compact design.
Implementation Method 1
The posterior end of the heel spring touches the ground first at heel strike in a walking gait cycle, compressing towards the posterior aspect of the keel leaf spring to enable an increased level of shock absorption at foot strike
Implementation Method 2
Powering the ankle-foot device may be a series-elastic actuator optimized for the user to ensure a comfortable walking gait with low noise and reduced mass. The actuator comprises an upper leaf spring, specifically a J-spring (a passive-elastic, curved leaf-spring), spanning from the anterior aspect of the prosthetic keel spring to the posterior-proximal region of the device above the ankle rotational joint
Data Source
AI summary
An ankle-foot prosthesis comprises a foot structure having a foot keel leaf spring, a heel leaf spring, and an upper J leaf spring above the keel leaf spring. An ankle bearing block is mounted to the keel leaf spring and a shank shell is mounted to the ankle bearing block. A shank interface mounts to the shank shell. A processor controlled active element extends along an axis between the shank shell and the upper leaf-spring.