Tendon-Driven Surgical Instrument Miniaturization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing robotic surgical assemblies face challenges in miniaturization due to high friction and wear in tendon-driven systems, which limit the miniaturization of surgical instruments and compromise their reliability and resistance, especially when sliding friction is involved.
Innovation Solution
The design employs tendons with a polymeric material, such as ultra-high molecular weight polyethylene, that slide over steel alloy surfaces with a total winding angle of 90 degrees or more, reducing friction coefficients from 0.5 to 0.04-0.08, eliminating the need for idle pulleys and guiding channels, and allowing the tendons to lay on the outer surfaces of links, minimizing abrasion and increasing the miniaturization potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If traditional tendon-driven systems with idle pulleys and guiding channels are used, then the surgical instrument can be actuated, but the device size increases and miniaturization is limited
Solution Approach 1:
The patent removes idle pulleys and guiding channels from the surgical instrument design. The tendons are made to slide directly over the outer surfaces of the links, eliminating the need for intermediate guiding components. This extraction of unnecessary elements enables miniaturization while maintaining actuation functionality.
Solution Approach 2:
Instead of routing tendons through internal channels or over idle pulleys as in conventional designs, the patent inverts the approach by having tendons slide over the external outer surfaces of the links. This inversion simplifies the internal structure and enables smaller device dimensions.
2Reliability
If tendons slide over structural member surfaces with high friction coefficients, then the system is simpler, but wear increases and reliability decreases
Solution Approach 1:
The patent changes the material parameters of the tendon, specifying it be made of ultra-high molecular weight polyethylene. This material parameter change reduces the friction coefficient from typical values (0.5) to much lower values (0.04-0.08), thereby reducing wear and improving reliability while maintaining the simplicity of direct surface sliding.
Solution Approach 2:
The patent employs a composite material system where the tendon is made of ultra-high molecular weight polyethylene and the structural members are made of steel alloy. This material combination creates a low-friction interface (friction coefficient 0.04-0.08) that minimizes wear and enhances reliability without requiring complex guiding mechanisms.
3Manufacturing precision
If the surgical instrument is miniaturized, then the surgical precision improves, but the tendon-driven system becomes difficult to drive due to increased angular play
Solution Approach 1:
By changing the friction parameter through material selection (ultra-high molecular weight polyethylene tendons on steel alloy surfaces), the patent achieves low friction (0.04-0.08 coefficient) that maintains tight control in miniaturized systems. This prevents the angular play that typically plagues small tendon-driven systems, enabling both miniaturization and ease of operation.
Solution Approach 2:
The removal of idle pulleys and internal guiding channels eliminates sources of mechanical play and backlash. The direct surface sliding configuration with low-friction materials ensures that actuation forces are transmitted efficiently to the joints, maintaining precision and controllability even in the miniaturized configuration.
4Strength
If steel cables or large diameter cables are used to survive tortuous paths, then the tendon is more resistant, but the device size increases
Solution Approach 1:
The patent eliminates the tortuous paths and trapping mechanisms that require thick, strong cables. By having tendons slide directly over the outer surfaces of links in a simplified configuration, the tendons are not subjected to severe bending and trapping stresses, allowing the use of thinner, more flexible tendons that enable miniaturization while maintaining sufficient strength.
Solution Approach 2:
The change in material to ultra-high molecular weight polyethylene provides high strength-to-weight ratio and abrasion resistance, allowing the use of thinner tendon diameters that can withstand the operational loads without requiring the thick steel cables or large-diameter cables needed in conventional designs with tortuous paths.
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 approach enables the miniaturization of surgical instruments to a transverse diameter below 5 mm without using idle pulleys or guiding channels, reduces friction, and enhances the reliability and strength of the tendons, while maintaining resistance and minimizing wear.
Implementation Method 1
tendons with a polymeric material, such as ultra-high molecular weight polyethylene, that slide over steel alloy surfaces with a total winding angle of 90 degrees or more, reducing friction coefficients from 0.5 to 0.04-0.08
Data Source
AI summary
A robotic surgical assembly includes a slave manipulator connected to a surgical instrument. A jointed subassembly includes at least first, second and third links. The first and second links are associated in a first joint providing a degree of freedom between the first link and the second link. The second and third links are associated in a second joint providing a degree of freedom between the second link and the third link. The surgical instrument includes a tendon for moving a degree of freedom; the tendon including a tendon distal portion secured to the third link. The first link and/or the second link includes a tendon contact surface on which the tendon slides remaining in contact with the tendon contact surface, defining one or more sliding paths on the tendon contact surface. The sum of all sliding paths defines a total winding angle of at least 120°.