Surgical Roll Joint Tendon Guide Surface Design
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Solution Overview
Problem
Existing roll joints in surgical robotic systems face limitations due to the use of small pulleys, which restrict load-carrying capability and increase volume, leading to a loss of one degree of freedom motion at 90° pitch and overlap with other rotational movements, making it difficult to achieve a compact and rigid structure.
Innovation Solution
A roll joint design utilizing tendon guide surfaces to redirect actuator tendons, eliminating the need for pulleys by changing the direction of tendon motion from axial to rotational within a compact space, allowing for a more robust and compact roll joint with fewer parts and larger features, enabling distal roll motion without the constraints of pulley-based systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If small pulleys are used to transition roll drive tendons from axial to perpendicular orientation, then the roll joint can achieve rotational motion, but the load carrying capability is limited and the volume consumed conflicts with structural stiffening requirements
Solution Approach 1:
The patent removes the pulley component entirely from the system. Instead of using small pulleys to redirect tendons, the invention uses a different mechanical arrangement where the tendon attaches directly to the rolling joint mechanism, eliminating the intermediate pulley that limited load capacity and consumed volume.
Solution Approach 2:
Rather than using a pulley to change the direction of the tendon force (axial to perpendicular), the invention inverts the approach by having the tendon attach in a configuration that directly produces the rolling motion without requiring directional conversion through a pulley. This reverses the conventional approach and eliminates the problematic component.
2Ease of operation
If small pulleys are used to redirect actuator tendons, then roll motion can be achieved, but the volume consumed conflicts with making use of the same volume to stiffen the structure
Solution Approach 1:
The pulley component is completely extracted from the wrist mechanism. By eliminating this intermediate element, the volume it occupied is freed up and can be used for structural stiffening purposes, directly resolving the volume conflict described in the contradiction.
3Volume of moving object
If very small axles are used in pulley-based roll joints, then the mechanism can be compact, but the axles are difficult to assemble and have limited load carrying capability
Solution Approach 1:
The small axle component is removed from the design by eliminating the pulley-based mechanism. The tendon attachment is redesigned to work directly with the rolling joint without requiring a separate axle, thereby eliminating the assembly difficulty and manufacturing challenges associated with very small axles.
Data Source
AI summary
A roll joint utilizes at least one tendon guide surface to guide actuator tendons for distal roll off and on their respective drums on a central shaft of the roll joint. The tendon guide surface turns the actuator tendon in an axial direction in a more compact space than might be required for a pair of pulleys, while using fewer parts with larger features more easily formed on a small scale.