Compact Capstan with Threaded Hub for Cable Angle Reduction
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Solution Overview
Problem
Traditional cable drive systems for robotic surgical arms in minimally invasive surgery face issues with cable wear and damage due to large angles at the take-off point, which can be mitigated by increasing the distance between the capstan and pulley, but this compromises the system's compactness.
Innovation Solution
A compact capstan drive system with a slideable capstan that maintains the take-off points' positions relative to the pulleys, using a spiral groove and threaded hub to allow lateral movement, reducing the cable angle while maintaining compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between the capstan and pulley is increased to reduce the cable angle, then cable wear and damage are reduced, but the system becomes less compact
Solution Approach 1:
The capstan is made movable along the shaft instead of being rigidly fixed, allowing it to dynamically adjust its position. During rotation, the capstan moves axially to compensate for the changing take-off point, maintaining a relatively constant and small cable angle with the pulley throughout the rotation cycle, thus reducing cable wear while keeping the system compact
Solution Approach 2:
The invention changes the positional parameter of the capstan along the shaft during rotation. By making the capstan position variable rather than fixed, the system maintains optimal cable geometry (small angle) throughout the rotation, resolving the contradiction between cable durability and compactness
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 effectively reduces cable wear and damage by maintaining a small angle between the cable and pulley plane, ensuring reliable operation and compactness in minimally invasive surgical procedures.
Implementation Method 1
The capstan includes a drum, a threaded hub, and a shaft rotatably supported in a fixed relationship to a threaded support. The threaded hub is coupled to the first end of the drum and engages the threaded support. The threaded hub and the drum move together laterally along their length relative to the threaded support in response to their being rotated.
Implementation Method 2
The drum has a cylindrical surface, a first end, and an opposite second end. The cylindrical surface of the drum has a spiral or helical groove to receive a cable loop that is wound around the drum.
Data Source
AI summary
A compact capstan includes a drum, a coupled hub, a passage extending through the drum and hub, and a shaft extending through the drum and hub. The shaft engages the passage such that the shaft can transmit a torsional force to the drum and the hub which are free to move along the length of the shaft. The drum includes a spiral groove to receive a cable loop wound around the drum. The hub has a thread with substantially the same pitch as the spiral groove to engage a threaded support such that the hub and the drum move laterally along their length relative to the threaded support as the hub and the drum are rotated. The shaft has a length that is substantially greater than the passage such that the shaft extends beyond both ends of the passage.