Miniaturized MIS Wrist Linkage for Low-Friction Cable Routing
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Solution Overview
Problem
Existing minimally invasive surgery (MIS) instruments face challenges in reducing size and cost while maintaining functionality, with issues such as increased friction, complex assembly, and difficulty in routing tension members, which affect cable life and instrument durability.
Innovation Solution
The development of low-friction medical devices with improved wrist mechanisms that include a first and second link system, featuring a curved guide path and tension members with specific routing paths to minimize friction and facilitate easy assembly, using cables with larger cross-sectional areas for increased strength and efficient routing within a miniaturized wrist assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of wrist mechanisms is reduced by scaling down components, then the instrument diameter is reduced for smaller incisions, but cable friction increases and cable life decreases
Solution Approach 1:
Rollers are introduced as intermediary elements between the cables and the wrist mechanism structure. These rollers reduce friction by providing a rolling contact interface instead of sliding contact, thereby extending cable life while maintaining the reduced instrument diameter necessary for minimally invasive surgery
Solution Approach 2:
The patent changes the friction parameter by introducing rollers that transform sliding friction into rolling friction. This parameter change allows the system to maintain small instrument dimensions while improving cable durability through reduced frictional forces
2Reliability
If pulleys and contoured surfaces are added to reduce cable friction, then cable life is extended, but device complexity increases
Solution Approach 1:
The wrist mechanism is segmented into modular components, with rollers that can be independently positioned and configured. This segmentation allows for reduced friction without requiring complex integrated pulley systems, as each roller operates as an independent friction-reducing element
Solution Approach 2:
The rollers are designed to automatically perform their friction-reducing function without requiring external control or adjustment. The system self-regulates cable friction through the inherent rolling contact mechanism, eliminating the need for complex control systems
3Volume of moving object
If smaller structures are used in the wrist mechanism, then instrument size is reduced, but localized forces increase causing cable stretch and creep
Solution Approach 1:
Rollers serve as intermediary elements that distribute localized forces over a larger contact area. By providing a rolling contact interface, the rollers reduce peak stresses on the cables and surrounding structures, preventing cable stretch and creep while maintaining small wrist mechanism dimensions
Solution Approach 2:
The rollers are pre-positioned to optimize force distribution before the instrument is subjected to operational loads. This preliminary configuration ensures that cables are properly supported and force distribution is optimized from the start, preventing progressive deformation during use
4Volume of moving object
If multiple components are integrated into a small diameter instrument, then minimally invasive capability is improved, but assembly difficulty increases
Solution Approach 1:
The wrist mechanism is divided into separable modules that can be assembled independently. Rollers and other components are designed as discrete elements that can be easily positioned and secured, simplifying the assembly process while maintaining the compact integrated structure necessary for minimally invasive surgery
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 solution enables smaller, low-cost, disposable instruments with reduced friction and improved cable durability, allowing for easier assembly and effective operation with multiple degrees of freedom, thereby enhancing the efficiency and cost-effectiveness of MIS procedures.
Implementation Method 1
low-friction medical devices with improved wrist mechanisms that include a first and second link system, featuring a curved guide path and tension members with specific routing paths to minimize friction
Data Source
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AI summary
A low-friction medical device includes a first link, a second link, and a tension member. The first link is coupled to an instrument shaft and a first guide path is defined in the first link. The second link is rotatable relative to the first link through an angular range. A distal end portion of the second link is rotatably coupled to a tool member. A curved guide path is defined within the second link between the tool member and the first guide path. A curved guide surface of the second link defines a portion of the second guide path. A first portion of the tension member is parallel to a centerline of the first guide path, and a second portion is coupled to the tool member. A third portion of the tension member between the first and second portions is in contact with the curved guide surface throughout a portion of the angular range.