Quasi-Active Prosthetic Joint with Timed Spring Engagement
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Solution Overview
Problem
Current prosthetic and orthotic devices, particularly ankle prosthetics, face challenges in efficiently mimicking human ankle performance across a wide range of activities, leading to increased metabolic energy expenditure and limited capability in replicating normal gait dynamics, especially during activities like running, navigating uneven terrain, or carrying heavy loads.
Innovation Solution
A quasi-active prosthetic joint system that combines compliant elements, such as springs, with an actuator to engage and disengage the springs at specific times during the gait cycle, mimicking human ankle motion by providing both direct power and timed energy release, thereby reducing energy expenditure and enhancing gait efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If passive spring-based prosthetic devices are used, then energy storage and release is achieved, but energy return efficiency is limited and insufficient power is provided for normal gait
Solution Approach 1:
The patent employs a variable stiffness mechanism that dynamically adjusts the spring stiffness throughout the gait cycle. The stiffness is higher during loading response to store energy efficiently and lower during terminal stance to release energy effectively, thereby improving both energy return efficiency and power delivery to match able-bodied gait characteristics
Solution Approach 2:
The system changes the physical parameter of spring stiffness over time during the gait cycle. By modulating the stiffness parameter dynamically rather than maintaining a constant value, the prosthesis can optimize energy storage during loading and energy release during push-off, resolving the contradiction between energy efficiency and power output
2Loss of energy
If passive compliant members are used, then energy storage is achieved, but energy release is inefficient and limited to single gait speed optimization
Solution Approach 1:
The variable stiffness mechanism allows the prosthesis to adapt to different gait speeds by dynamically adjusting spring stiffness. At faster gait speeds, the stiffness can be modulated to provide appropriate energy storage and release timing, enabling the device to perform efficiently across multiple speeds rather than being optimized for a single speed
Solution Approach 2:
The system implements periodic modulation of spring stiffness that synchronizes with the gait cycle. This periodic action allows the prosthesis to efficiently store and release energy at the appropriate phases of walking or running, improving energy release efficiency while adapting to varying gait speeds through frequency-matched stiffness modulation
3Power
If active devices with microprocessor and actuator are used, then power supply and control is improved, but device complexity increases
Solution Approach 1:
The prosthesis employs sensors that automatically detect gait phase and loading conditions, triggering the variable stiffness mechanism without requiring complex microprocessor control algorithms. This self-service approach provides active power supply capability while minimizing control system complexity by using straightforward sensor-based triggering rather than sophisticated computational control
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 quasi-active joint system effectively reduces metabolic energy consumption and improves gait efficiency by optimizing the timing and release of stored energy, allowing for more natural and efficient movement across various activities, including walking, running, and navigating different terrains.
Implementation Method 1
A spring is able to return only as much energy as is put into the spring, minus efficiency losses
Implementation Method 2
Passive lower limb prosthetics generally rely on compliant members, such as springs, to store and release energy
Data Source
AI summary
A prosthetic joint device includes a foot portion and a main body pivotally coupled to the foot portion at a first joint. A first compliant member is coupled to the main body and foot portion. A first clutch is coupled to the first compliant member. An actuator is coupled to the first clutch to lock and unlock the first clutch and engage and disengage the first compliant member. A control system is coupled to the actuator to control the actuator based on a gait activity. The first clutch is locked to engage the first compliant member. A second compliant member is coupled to the main body and foot portion. A sensor is coupled to the prosthetic joint device to measure a physical state of the prosthetic joint device. The engagement and disengagement of the first compliant member is timed based on the physical state of the prosthetic joint device.