Robotic Ankle System with Constant Force Spring
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Solution Overview
Problem
Gait disorders, particularly affecting the elderly and those with neurological or trauma-related injuries, compromise the strength of plantar flexor muscles, making it difficult to walk and propel oneself forward, as they require significant torque during the ankle push-off phase, which existing assistive devices like ankle-foot orthoses do not adequately address.
Innovation Solution
A robotic ankle system that uses a constant force spring to store energy from the user's body weight and releases it during the heel-up phase, assisted by a solenoid-activated locking mechanism, providing an assistive force to reduce muscle activation and improve gait efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a robotic ankle system with solenoid and locking mechanism is used, then assistive force is provided to reduce muscle effort, but device complexity increases
Solution Approach 1:
The constant force spring is pre-loaded and stored in a locked position during the stance phase, preparing the energy in advance for release during the swing phase. This preliminary action allows the system to provide assistive force on demand without requiring continuous power input, reducing overall system complexity.
Solution Approach 2:
The constant force spring automatically stores energy from the user's body weight during descent and releases it during ascent without requiring external control. The locking mechanism and solenoid work passively to hold and release the spring, allowing the system to serve itself and reduce muscle effort without complex control systems.
2Use of energy by moving object
If energy is stored in a constant force spring during stance phase, then assistive force is available for swing phase, but energy loss occurs during transitions
Solution Approach 1:
The constant force spring maintains continuous tension throughout the gait cycle, storing energy during the stance phase and releasing it during the swing phase without interruption. The locking mechanism ensures seamless transition between energy storage and release phases, minimizing energy loss and maintaining continuous useful action.
3Loss of energy
If locking mechanism is used to hold constant force spring, then energy is retained, but reliability decreases due to potential failure of locking components
Solution Approach 1:
The solenoid receives electrical signals to activate the locking mechanism at appropriate times during the gait cycle, creating a feedback-controlled system that ensures the constant force spring is locked during energy storage and released during energy discharge. This feedback mechanism enhances reliability by preventing premature or failed locking/unlocking events.
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 robotic ankle system reduces muscle effort by up to 38% in plantar flexor muscles, enhancing mobility and locomotion, as demonstrated by reduced electromyography values during assisted walking compared to non-assisted walking trials.
Implementation Method 1
storing, in the robotic ankle system and responsive to a downward force arising by a first step of the user, energy in a constant force spring
Implementation Method 2
a solenoid to disengage the locking mechanism
Data Source
AI summary
A robotic ankle system provides an assistive force for the heel-up portion of a user gait. Energy is stored in a spring responsive to a heel-on portion of the gait, and then released as the heel-up portion begins. In this manner, the gait of a user is assisted. The systems and methods are of particular use for those affected by stroke or in connection with rehabilitation activities.