Capstan Cable Routing for Medical Instrument Miniaturization
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Solution Overview
Problem
Current medical instruments for minimally invasive surgery face challenges in miniaturization, cost reduction, and efficient cable management, as they require multiple cables and retention elements, which increase complexity and expense, and struggle with maintaining cable tension and reducing friction.
Innovation Solution
The design incorporates a medical device with a shaft, tool member, and capstans that utilize a polymer cable routed through a drive pulley and coupling spool, secured by a cross-over wrap configuration without retention features, reducing the number of cables needed and utilizing capstan grooves for frictional securing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple cables and retention elements are used to maintain cable tension and reduce friction, then cable reliability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes retention elements (crimps, clips, adhesives) from the cable assembly. The cable is secured to the capstan solely through friction generated by the wrap configuration, eliminating the need for additional retention components and reducing system complexity while maintaining reliability.
Solution Approach 2:
The cable wrap configuration generates its own securing mechanism through friction. The cross-over wrap pattern creates sufficient frictional force to maintain cable tension and prevent slippage without requiring external retention elements, allowing the cable system to secure itself.
2Reliability
If traditional cable routing with retention elements is used, then cable security is improved, but manufacturing cost and assembly time increase
Solution Approach 1:
The patent eliminates retention elements (crimps, clips, adhesives) from the cable assembly. The cable is secured to the capstan solely through friction generated by the wrap configuration, eliminating the need for additional retention components and reducing system complexity.
Solution Approach 2:
The cable wrap configuration generates its own securing mechanism through friction. The cross-over wrap pattern creates sufficient frictional force to maintain cable tension and prevent slippage without requiring external retention elements.
3Duration of action of stationary object
If cable friction is reduced through pulleys and contoured surfaces, then cable life is improved, but device complexity and size increase
Solution Approach 1:
The patent removes traditional pulleys and complex contoured surfaces from the design. Instead, it uses a simplified capstan with a groove that guides the cable wrap, reducing the number of moving parts and structural complexities while still minimizing cable friction through the wrap configuration.
Solution Approach 2:
The patent uses a flexible polymer cable with a smooth surface that naturally conforms to the capstan groove. This flexible cable design reduces friction through its interaction with the groove geometry without requiring rigid pulleys or complex contoured surfaces.
4Volume of moving object
If smaller instrument size is achieved by scaling down components, then minimally invasive capability is improved, but cable tension maintenance and friction reduction become more difficult
Solution Approach 1:
The cable wrap configuration generates its own securing mechanism through friction. The cross-over wrap pattern creates sufficient frictional force to maintain cable tension and prevent slippage without requiring external retention elements.
Solution Approach 2:
The patent changes the material properties by using a flexible polymer cable instead of traditional rigid cables. This material change allows the cable to conform to the capstan groove and generate sufficient friction in miniaturized configurations, maintaining reliability at smaller scales.
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
This solution enables efficient movement in three degrees of freedom with fewer cables, reduces manufacturing costs, and enhances control precision while minimizing cable stretch and wear, facilitating miniaturization and reducing operational complexity.
Implementation Method 1
routed about a drive surface of the drive pulley and is wrapped at least one revolution about the coupling spool to secure the distal portion of the cable to the tool member
Implementation Method 2
utilizing capstan grooves for frictional securing
Data Source
AI summary
A tool member is rotatably coupled to a distal end portion of a shaft and includes a drive pulley and a coupling spool. A mechanical structure is coupled to a proximal end portion of the shaft and includes first and second capstans. The first and second capstans each include a first portion and a second portion. A distal portion of the cable is wrapped at least one revolution about the coupling spool. A first proximal end of the cable is wrapped about the second portion of the first capstan such that a second portion crosses over a first portion of the first proximal end of the cable. The second proximal end of the cable is wrapped about the second portion of the second capstan such that a second portion of the second proximal end of the cable crosses over a first portion of the second proximal end of the cable.