Prosthetic Knee Joint Braking via Four-Bar Load Detection
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Solution Overview
Problem
Existing prosthetic leg knee joints face instability during toe strike, particularly when there is no heel contact before toe strike, leading to potential unintentional knee flexion and reduced stability, especially when transitioning from a swing phase to a stance phase.
Innovation Solution
A prosthetic leg knee joint with a four-bar link mechanism that includes a reference position setting unit and a braking unit, where the instant center of the four-bar link mechanism serves as a sensing point to detect the application of load on the foot, allowing the braking unit to be controlled based on this detection, ensuring stable operation regardless of the knee's flexion or extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a load brake is provided with a pin arranged near a load line in a swing transition period, then the brake effectiveness during push-off period is improved, but when transitioning to swing phase with load applied to back side (downhill), the load line moves backward causing the brake to work inappropriately
Solution Approach 1:
The patent applies dynamics by making the pin position adjustable rather than fixed. The pin can be repositioned along the knee plate to change its relative position to the load line depending on walking conditions (uphill, downhill, flat ground). This dynamic adjustment allows the brake to respond appropriately to varying load conditions, preventing the load line from moving backward relative to the pin during downhill walking, thereby resolving the contradiction between brake effectiveness and adaptability.
2Ease of operation
If the compression state of the coil spring is adjusted to prevent trip during swing phase transition, then the braking force during swing phase is reduced, but the braking force during stance phase is also lowered requiring delicate adjustment
Solution Approach 1:
The patent segments the braking control function by separating the spring adjustment (which controls overall brake engagement timing) from the pin position adjustment (which controls brake effectiveness during specific phases). This segmentation allows independent optimization: the spring can be set to prevent trip during swing phase while the pin position can be adjusted to maintain adequate braking force during stance phase, eliminating the need for delicate compromise adjustments.
3Productivity
If there is no heel contact before toe strike, then the switching valve remains open and no hydraulic pressure is generated, but this leads to inability to support weight and potential unintentional knee flexion
Solution Approach 1:
The patent applies preliminary action by positioning the pin forward of the load line during swing phase preparation. This forward positioning creates preliminary braking action that prepares the system for weight bearing before actual heel contact occurs. When toe strike happens without prior heel contact, the pin's forward position ensures the brake is already engaged or ready to engage, generating necessary hydraulic pressure to support weight and prevent unintentional knee flexion, while still allowing smooth swing phase transition.
Data Source
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AI summary
A prosthetic leg knee joint (10) includes a thigh connection part (12) that is provided on the thigh side, a lower leg part (14) that is provided rotatably around a knee shaft (24) connected to the thigh connection part (12), a four-bar link mechanism (18) that sets an instant center (S) whose relative position with respect to the thigh connection part (12) is substantially constant regardless of the relative position between the thigh connection part (12) and the lower leg part (14), and a braking unit (16) that brakes the movement of the lower leg part (14) in accordance with the relative position between the instance center (S) set by the four-bar link mechanism (18) and the lower leg part (14).