Capstan Cable Routing for Miniaturized Surgical Instruments
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Solution Overview
Problem
Current minimally invasive surgical instruments face challenges in reducing size while maintaining effective cable tension and minimizing manufacturing costs, as scaling down components leads to issues like cable stretch, reduced lifespan, and increased complexity in routing and securing cables, particularly in achieving desired degrees of freedom without excessive force and tangling.
Innovation Solution
The design incorporates a medical device with a capstan having a spool and cable guide that allows the cable to wrap around the spool by no more than two revolutions, using a polymeric braided construction and eliminating the need for retention elements, with a mechanical structure that guides slack loops during tensioning, reducing the number of cables required and maintaining tension without additional mechanical features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of wrist mechanism components is reduced to enable miniaturization, then the operating footprint and incision size are reduced, but cable tension maintenance and cable life are compromised due to increased localized forces and smaller bend radii
Solution Approach 1:
The patent employs contoured surfaces and pulleys with optimized curvature radii to reduce cable friction and distribute localized forces. The capstan features a curved wrap surface that guides the cable through a controlled bend radius, preventing stress concentration while maintaining compact dimensions. This allows the wrist mechanism to be miniaturized without compromising cable integrity or tension maintenance.
Solution Approach 2:
The patent optimizes cable routing parameters including wrap angle, bend radius, and contact surface geometry to minimize friction and stress. By carefully selecting the cable path and wrap configuration around the capstan, the design achieves effective cable tension maintenance despite reduced component sizes, balancing miniaturization with reliability.
2Adaptability or versatility
If additional degrees of freedom are implemented through the wrist mechanism, then end effector control capability is improved, but the number of cables and component complexity increase, competing for limited space
Solution Approach 1:
The patent implements a multi-functional capstan structure that can accommodate multiple cables and control multiple degrees of freedom within a single compact component. The capstan is designed with multiple wrap surfaces and routing paths that enable it to control pitch, yaw, and grip motions simultaneously, reducing the need for separate mechanisms for each DOF and minimizing overall device complexity.
Solution Approach 2:
The patent employs nested cable routing where cables are arranged in a compact, space-efficient configuration within the wrist mechanism. The cable paths are routed through overlapping or nested trajectories that minimize the volume required for cable accommodation, allowing multiple cables to coexist in the limited space without excessive complexity.
3Reliability
If cables are routed through the wrist mechanism to maintain tension throughout the range of motion, then operational reliability is improved, but the routing complexity and manufacturing difficulty increase
Solution Approach 1:
The patent incorporates pre-formed cable routing paths and pre-positioned routing features directly into the capstan and wrist mechanism structure during manufacturing. The cable channels, wrap surfaces, and securing points are integrated into the component design, eliminating the need for complex post-assembly routing procedures and simplifying manufacturing while ensuring proper cable tension maintenance.
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 approach enables efficient miniaturization of surgical instruments, reduces manufacturing costs, and maintains cable tension effectively, enhancing the operational reliability and longevity of the devices while simplifying the routing and securing of cables.
Implementation Method 1
pulleys and/or contoured surfaces are generally needed to reduce cable friction
Implementation Method 2
capstan including an upper portion, a lower portion, and a spool between the upper and lower portions
Data Source
AI summary
A medical device includes a chassis component having a bottom and an opening defined in the bottom, and a capstan including an upper portion, a lower portion, and a spool between the upper and lower portions. The upper portion of the capstan is supported within the opening of the chassis component. The spool comprises a cable wrap surface and a side wall opposing the bottom of the upper chassis. The side wall of the spool can optionally slope away from the bottom of the chassis component. The medical device can further include a cable guide and a cable. The cable extends from the cable guide to the cable wrap surface of the spool.