Traveling Capstan Cable Drive for Constant Take-Up Angles
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Solution Overview
Problem
Cable drive systems in manipulator systems experience issues such as excessive wear, increased friction, and cable deviation due to changing take-up angles, leading to potential failure and inefficiency.
Innovation Solution
Implementing a traveling capstan mechanism with a guide element that engages with a helically spiraling groove on the capstan to maintain a constant take-up angle by translating the capstan relative to the take-up pulley, reducing friction and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cable winds onto a stationary capstan, then the cable is driven along its path, but the take-up angle changes causing excessive wear, increased friction, and cable deviation
Solution Approach 1:
The capstan is made movable along the cable path instead of being stationary. The capstan translates in the direction of cable motion while rotating, dynamically adjusting its position to maintain a constant take-up angle between the cable and capstan surface. This dynamic adjustment eliminates cable deviation and reduces wear and friction on both the cable and capstan groove.
2Productivity
If the capstan rotates to wind cable, then cable motion is achieved, but the changing take-up angle causes cable to run off pulley or out of groove
Solution Approach 1:
The capstan simultaneously rotates and translates along the cable path. The translation distance is proportional to the rotation angle, creating a synchronized motion that maintains the cable's contact point stable within the groove or on the pulley. This dynamic coordination prevents cable run-off and maintains stable cable path engagement throughout the winding operation.
3Ease of operation
If a traditional cable drive system is used, then motion is transmitted, but the system requires larger space and has higher complexity
Solution Approach 1:
The capstan combines two functions into a single component: rotation to wind the cable and translation along the cable path. This merged design eliminates the need for separate mechanisms to control capstan position and rotation, reducing overall system complexity and space requirements while maintaining efficient cable drive operation.
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 mitigates take-up angle deviation, reduces wear and friction, and allows for a more compact design while maintaining efficient cable operation.
Implementation Method 1
a groove spiraling helically around the outer lateral surface of the capstan. The groove is configured to receive and guide one or more cables to spool onto the capstan as the capstan rotates
Implementation Method 2
The guide roller is engaged with the groove, the guide roller causing the capstan to move in translation along the spline drive shaft in response to rotation of the capstan
Data Source
AI summary
A cable-driven device, such as a joint or instrument of a computer-assisted manipulator system, may comprise a capstan mechanism to wind/unwind cables. The capstan mechanism comprises a capstan that has a groove in an outer surface of the capstan to guide the cables, which are routed from a take-up pulley, to spool onto the capstan as the capstan rotates. A guide element is engaged with the groove. The guide element is held translationally stationary relative to the take-up pulley, while there is relative translation between the capstan and both the guide element and the take-up pulley. Thus, as the capstan rotates, the guide element engages with the groove and forces the capstan and the take-up pulley to translate relative to one another. This relative translation of the capstan and the take-up pulley may prevent deviation of a take-up angle of the cable as the cable spools onto the capstan.