Capstan Clutch Mechanism for Surgical Drive Cable Tensioning
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Solution Overview
Problem
Current robotic surgical systems require complex and costly procedures for pre-tensioning drive cables, which involve welding and multiple manufacturing steps, and lack a method to maintain tension over the device's lifespan without welding.
Innovation Solution
A surgical tool with a drive housing and capstans that utilize a clutch feature and ratchet teeth mechanism to pre-tension and maintain tension in drive cables, allowing for independent rotation of capstans during tensioning and simultaneous rotation for operation, eliminating the need for welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If welding is used to pre-tension drive cables, then tension can be initially set and retained, but the manufacturing process becomes complex and costly with multiple steps requiring plastic overmold and metal inserts
Solution Approach 1:
The patent extracts the welding process and associated metal inserts from the system by using a purely plastic capstan design. The drive cable is retained through friction engagement between the cable and the plastic capstan surface, eliminating the need for welding operations and metal inserts while maintaining tension retention capability.
Solution Approach 2:
The patent employs a disposable plastic capstan that is molded as a single piece without expensive metal inserts. The plastic capstan is designed to be replaced with each instrument, and its friction-based retention mechanism provides sufficient tension maintenance without requiring durable, expensive materials or complex assembly processes.
2Manufacturing precision
If welding is used to pre-tension drive cables, then tension can be initially set, but the cost increases due to plastic overmold and metal inserts
Solution Approach 1:
The patent removes the welding process and metal inserts from the manufacturing process. The drive cable is attached and tensioned using only the plastic capstan structure, which is molded as a single piece. This extraction of complex subsystems dramatically reduces manufacturing cost while maintaining the ability to set and retain cable tension through friction engagement.
Solution Approach 2:
The patent changes the retention mechanism from mechanical welding to friction-based engagement. By modifying the surface properties and geometry of the plastic capstan, the system achieves adequate frictional retention of the drive cable without requiring expensive welding operations or metal inserts, thereby reducing manufacturing cost while maintaining tension setting capability.
3Ease of operation
If capstans are designed for independent rotation during tensioning, then pre-tensioning becomes possible, but the structure becomes more complex
Solution Approach 1:
The patent segments the capstan function into two operational modes: during pre-tensioning, the capstan rotates independently on its mounting axis to wind the drive cable; during operation, the entire capstan assembly rotates with the input shaft to drive the surgical instrument. This segmentation of rotational functions allows pre-tensioning capability while maintaining a relatively simple integrated structure.
Solution Approach 2:
The patent designs the capstan with dynamic characteristics that allow it to function differently in different operational phases. The capstan can rotate independently during tensioning and then lock or engage with the input shaft for simultaneous rotation during surgical operation. This dynamic behavior enables pre-tensioning capability without requiring a permanently complex mechanical structure.
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 and cost-effective pre-tensioning and maintenance of drive cable tension, simplifying the manufacturing process and ensuring consistent performance throughout the device's life without the need for welding.
Implementation Method 1
A surgical tool with a drive housing and capstans that utilize a clutch feature and ratchet teeth mechanism to pre-tension and maintain tension in drive cables
Data Source
AI summary
A surgical tool includes a drive housing having an elongate shaft extending therefrom and an end effector arranged at a distal end of the shaft. At least one linkage is pivotally coupled to a distal end of the shaft about a pivot axis, and a camming feature is defined on the at least one linkage. The camming feature includes a rounded edge between a lateral side and a proximal face of the at least one linkage such that engagement of the camming feature with the distal end of a trocar will pivot the at least one linkage into alignment with a longitudinal axis of the shaft. The camming feature edge may be arranged to provide a large moment when the linkage is articulated to a high articulation angle and a smaller moment when the linkage is articulated to lower articulation angles.