Slack-Eliminating Capstan for Surgical Drive Cable Tension
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Solution Overview
Problem
Existing robotic surgical systems face challenges in maintaining consistent and predictable performance of end effectors due to slack in drive cables within the cable driven motion system.
Innovation Solution
A capstan drive assembly is designed to maintain minimum cable tension by using upper and lower capstans with one-way bearings, ensuring that rotating the input shaft in one direction disengages one capstan while driving the other to pull the respective drive cable in a linear direction, thereby eliminating slack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a cable driven motion system is used to articulate the end effector, then the degrees of freedom and natural hand-like articulation are improved, but slack in the drive cables causes inconsistent and unpredictable performance
Solution Approach 1:
The patent extracts the slack-elimination function from the cable system by introducing a separate capstan mechanism with one-way bearing. This dedicated component continuously removes excess cable length and maintains tension, preventing slack from compromising the reliability of the cable-driven articulation system while preserving its full range of motion capabilities.
Solution Approach 2:
The capstan mechanism performs preliminary action by continuously maintaining cable tension before the cable-driven articulation occurs. The one-way bearing ensures that the capstan continuously removes slack and maintains minimum tension, preparing the cable system to respond predictably to articulation commands without delay or inconsistency.
2Ease of operation
If drive cables are used to control the end effector articulation, then the surgical tool can be remotely operated with natural hand movements, but maintaining adequate cable tension is difficult
Solution Approach 1:
The capstan mechanism with one-way bearing provides self-service tension control. As the cable is pulled during articulation, the one-way bearing automatically engages to maintain tension and prevent slack. When the cable releases, the capstan automatically resets, creating a self-regulating system that maintains adequate tension without requiring complex external control mechanisms.
3Reliability
If a capstan drive assembly is introduced to eliminate cable slack, then the reliability and precision of robotic surgical tools are improved, but the device complexity increases
Solution Approach 1:
The tension control function is segmented into a separate, dedicated capstan assembly with one-way bearing, rather than integrating it into the main cable-driven articulation mechanism. This modular segmentation allows the capstan to independently handle slack elimination while the articulation system maintains its full range of motion capabilities, making the added complexity manageable and localized.
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 ensures consistent and predictable articulation of the end effector by maintaining adequate tension in the drive cables, enhancing the reliability and precision of robotic surgical tools.
Implementation Method 1
an upper capstan rotatably mounted to the input shaft with a first one-way bearing, and a lower capstan rotatably mounted to the input shaft with a second one-way bearing
Implementation Method 2
drives the upper capstan in the first angular direction to pull the first drive cable in a first linear direction
Data Source
AI summary
A surgical tool includes a drive housing having an elongate shaft extending therefrom, an end effector operatively coupled to a distal end of the shaft, a drive input rotatably mounted to the drive housing and having an input shaft extending therefrom, an upper capstan assembly rotatably mounted to the input shaft and having a first drive cable coupled thereto and extending to the end effector, a lower capstan assembly rotatably mounted to the input shaft and having a second drive cable coupled thereto and extending to the end effector, and a compliant member mounted to the input shaft and arranged in-line and extending between the upper and lower capstan assemblies, the compliant member providing a constant opposing torsional load on the upper and lower capstan assemblies and thereby removing slack in the first and second drive cables as the input shaft rotates.