Artificial Knee Mechanism with Cam-Actuated Stance Lock
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Solution Overview
Problem
Traditional knee-ankle-foot orthosis (KAFO) systems lock the knee in full extension, leading to gait deviations and overuse injuries, while existing stance control orthosis (SCO) mechanisms require sensors and actuators, making them complex and costly.
Innovation Solution
A passive artificial knee mechanism using a four-bar linkage and compression spring to resist knee flexion during stance and facilitate flexion during swing, mimicking human knee behavior without the need for sensors or actuators, allowing for a natural gait with adjustable torque profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a traditional KAFO locks the knee in full extension, then patient stability during weight-bearing is improved, but gait deviations and overuse injuries occur
Solution Approach 1:
The patent applies a dynamic locking mechanism that transitions between locked and unlocked states based on gait phase. The knee is locked during stance phase for stability, then unlocks during swing phase to allow natural flexion, eliminating the harmful effects of continuous locking while maintaining stability when needed.
Solution Approach 2:
The mechanism employs periodic locking and unlocking actions synchronized with the gait cycle. The knee joint is locked during the stance phase and unlocked during the swing phase, creating a rhythmic pattern that matches natural walking mechanics and prevents gait deviations.
2Ease of operation
If an SCO allows knee flexion during swing phase, then gait naturalness is improved, but sensors and actuators are required increasing complexity and cost
Solution Approach 1:
The mechanism is self-regulating through passive mechanical elements. The cam-follower system automatically locks and unlocks the knee based on its own motion and gravitational forces, without requiring external sensors or actuators to detect gait phase or control the locking action.
Solution Approach 2:
The patent replaces electronic sensor-actuator systems with a purely mechanical cam-follower linkage system. The cam profile geometry encodes the locking/unlocking timing, substituting complex electronic control with simple mechanical geometry that achieves the same functional result.
3Stability of the object's composition
If a cam-follower mechanism is used for stance control, then knee locking during stance is achieved, but the mechanism complexity increases
Solution Approach 1:
The locking mechanism is segmented into independent modular components: the cam element, the follower, and the locking linkage. This segmentation allows each component to be optimized independently and simplifies manufacturing and assembly while maintaining the overall locking function.
Solution Approach 2:
The follower acts as an intermediary element between the cam and the locking mechanism. It translates the cam's rotational motion into linear motion that actuates the lock, providing a simple mechanical interface that reduces overall system complexity.
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 mechanism provides effective weight support during stance and toe clearance during swing, reducing the risk of overuse injuries and simplifying the orthosis design by eliminating the need for sensors and actuators, promoting a more natural and efficient gait.
Implementation Method 1
a compression spring to resist knee flexion during stance
Implementation Method 2
a compression spring to resist knee flexion during stance
Implementation Method 3
a four-bar linkage and compression spring to resist knee flexion during stance and facilitate flexion during swing
Data Source
AI summary
Systems, methods, and apparatus provide artificial knees. Artificial knees include a thigh link configured to move in unison with a thigh of the person, a shank link configured to be rotatably coupled to the thigh link, and a compression spring rotatably coupled to the thigh link and coupled to a second end of shank link with a second end of the compression spring. During a first range of motion, the compression spring is configured to provide an extension torque between the thigh link and the shank link causing the artificial knee to resist flexion. After the first range of motion, the compression spring is configured to provide a flexion torque between the thigh link and the shank link encouraging the artificial knee to flex resulting in toe clearance during the swing phase. During the swing phase, the compression spring provides no torque between the thigh link and the shank link.