Knee Joint Four-Bar Linkage Hinge Transition
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Solution Overview
Problem
Existing mechanical joints, such as endoprostheses for human knee joints, fail to replicate the natural joint's functionality across the entire angular range, particularly deviating from natural kinematics at large flexion angles, which limits their functionality in activities like cycling and squatting.
Innovation Solution
A mechanical joint design that transitions between a four-bar linkage mechanism for small flexion angles and a hinge joint for larger angles, maintaining stability and natural kinematics through specific curvature and contact point management, allowing for improved range of motion and reduced material stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a mechanical joint is designed to replicate natural joint functions across the entire angular range, then the joint's ability to mimic natural movement is improved, but the device complexity increases due to the need for multiple joint sections with specific curvature relationships
Solution Approach 1:
The joint is divided into a first joint section and a second joint section, each with specific curvature characteristics. The first joint section has a first curvature radius and the second joint section has a second curvature radius, allowing different parts of the joint to handle different angular ranges independently, thus achieving natural movement replication without excessive overall complexity
Solution Approach 2:
The patent implements a dynamic transition between four-bar linkage and hinge mechanisms based on the flexion angle. At small flexion angles, the four-bar linkage mechanism is active, while at large flexion angles, the hinge mechanism takes over. This dynamic switching allows the joint to adapt its behavior to match natural knee kinematics across the entire range of motion
2Measurement precision
If the joint uses a four-bar linkage mechanism for small flexion angles, then the kinematics accuracy is improved, but the range of motion is limited for large flexion angles
Solution Approach 1:
The joint dynamically switches between two mechanical mechanisms based on the flexion angle. For small flexion angles (0°-30°), the four-bar linkage mechanism provides accurate kinematics matching natural knee movement. For large flexion angles (>30°), the hinge mechanism takes over to enable full range of motion activities like squatting and cycling, thus resolving the contradiction between accuracy and range
3Adaptability or versatility
If the joint is designed for large flexion angles, then the range of motion is improved, but the material stress and wear increase
Solution Approach 1:
The dynamic mechanism switching reduces material stress and wear by utilizing the hinge mechanism for large flexion angles where the four-bar linkage would generate excessive stress. The hinge mechanism's simpler rotational motion is better suited for large angle movements, thereby protecting the joint materials from excessive wear while maintaining full range of motion capability
Solution Approach 2:
The patent changes the mechanical parameter (mechanism type) based on the operating condition (flexion angle). By transitioning from a four-bar linkage to a hinge mechanism at appropriate angles, the system optimizes the stress distribution and material loading conditions, reducing harmful wear and stress effects during large range of motion activities
Data Source
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AI summary
A mechanical joint is described, in particular an endoprosthesis for a human joint. The mechanical joint comprises a first and a second joint part. The two joint parts form a four-link coupling for pivot angles in a first angle range and a hinge joint for pivot angles in a second angle range.