Bypassable Overrunning Clutch for Prosthetic Knee Stance Control
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Solution Overview
Problem
Current prosthetic knees, especially mechanical ones, face challenges in providing reliable and cost-effective rotational constraints during the stance phase while allowing free rotation during the swing phase, often requiring complex designs, high costs, and significant user training, making them inaccessible and unreliable for many individuals, especially in developing countries.
Innovation Solution
A two-way, by-passable, overrunning clutch mechanism using a dual-wrap-spring clutch element that prevents counter-clockwise rotation during the stance phase and allows free rotation in both directions during the swing phase, enabling a mechanical prosthetic knee to mimic natural gait patterns without the need for microprocessors or complex electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If complex electromechanical prosthetics with microprocessors are used to control motion, then simulated natural motion and biological-limb-like operational characteristics are achieved, but cost increases to tens of thousands or hundreds of thousands of dollars
Solution Approach 1:
The patent replaces complex electromechanical systems with a purely mechanical overrunning clutch mechanism. The clutch uses spring-loaded cam followers and friction surfaces to provide stance-phase stability and swing-phase freedom, eliminating microprocessors, sensors, and power sources while achieving natural gait simulation through passive mechanical means
Solution Approach 2:
The mechanical clutch system is self-regulating, using the user's own body weight and motion dynamics to automatically engage and disengage the clutch mechanism. The spring-loaded cam followers respond passively to loading conditions, requiring no external control systems or user training, thereby reducing cost and complexity while maintaining operational effectiveness
2Device complexity
If mechanical prosthetic knees are used to reduce cost, then affordability improves, but reliable rotational constraints during stance phase and free rotation during swing phase are difficult to achieve
Solution Approach 1:
The clutch mechanism dynamically adapts its constraint characteristics based on loading conditions. During stance phase, body weight compresses the springs to engage the clutch and prevent backward rotation. During swing phase, reduced loading allows the springs to expand and disengage the clutch, permitting free forward rotation. This dynamic behavior provides reliable rotational control without complex electronics
Solution Approach 2:
The clutch mechanism is divided into independent friction surfaces and spring-loaded cam followers that can engage and disengage separately. This segmentation allows the system to provide bidirectional control: constraining rotation in one direction during stance while allowing free rotation in the opposite direction during swing, achieving reliable bidirectional rotational control through simple mechanical components
3Reliability
If overrunning clutch mechanisms are used to provide rotational constraints, then stance phase stability is achieved, but the mechanism must be by-passable to allow free rotation during swing phase
Solution Approach 1:
The clutch mechanism dynamically transitions between engaged and disengaged states based on loading conditions. During stance phase, compressive loading engages the friction surfaces to provide rotational constraint and stability. During swing phase, reduced loading allows the spring-loaded cam followers to disengage, permitting free rotation. This dynamic state transition achieves both stance stability and swing freedom within a single passive mechanical system
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 stable and efficient rotational constraints during weight-bearing phases while allowing unencumbered movement during unweighted phases, enhancing the usability and affordability of prosthetic knees, reducing maintenance needs, and offering a durable, fault-tolerant solution.
Implementation Method 1
the wrap spring is configured to frictionally engage the arbor shaft
Implementation Method 2
The cam-like force adjustor and dimensional constraint (218) adjusts a position of the dual-wrap-spring clutch element (202) in response to an applied mechanical force
Data Source
AI summary
The current document is directed to a two-way, by-passable, overrunning clutch incorporated within a mechanical prosthetic knee that provides functionality similar to a biological knee or incorporated in another articulated device, such as a robotic or orthotic articulated device or member. The currently disclosed two-way, by-passable, overrunning clutch allows for two-way free rotation when disabled, but, when enabled, prevents rotation in one direction while allowing free rotation in the other direction. In the mechanical prosthetic knee, the two-way, by-passable, overrunning clutch is enabled by application of a mechanical force and disabled by removal of the mechanical force.