Roller-Assisted Tension Members for Low-Friction Medical Tools
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Solution Overview
Problem
Existing minimally invasive surgery (MIS) instruments face challenges in reducing size and cost while maintaining functionality, as scaling down components leads to increased friction, cable stretch, and difficulty in routing conductors and cables, which affects instrument life and reusability.
Innovation Solution
Incorporating a roller-assisted tension member system with a curved guide path and low fleet angles to reduce friction and improve cable routing within a miniaturized wrist mechanism, allowing for increased strength and reduced component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of wrist mechanism components is reduced to enable smaller instrument diameter, then the instrument can be inserted through smaller incisions, but friction increases and cable stretch occurs reducing instrument life
Solution Approach 1:
A Teflon-coated cable is introduced as an intermediary between the cable and the wrist mechanism components. This coating acts as a low-friction interface that reduces wear and prevents cable stretch during actuation, thereby extending instrument life while maintaining the reduced instrument diameter
Solution Approach 2:
The friction characteristics of the cable interface are changed by applying a Teflon coating. This material parameter change reduces the coefficient of friction between cable and pulley/surface contact points, preventing cable degradation and extending operational life in the miniaturized mechanism
2Reliability
If pulleys and contoured surfaces are added to reduce cable friction, then cable life is extended, but device complexity increases
Solution Approach 1:
Instead of adding complex pulley mechanisms throughout the wrist assembly, the low-friction Teflon coating is applied locally to the cable at specific contact points within the wrist mechanism. This provides the necessary friction reduction and cable life extension without the complexity of additional mechanical components
3Volume of moving object
If the instrument shaft is reduced in size, then smaller incisions are possible, but routing conductors and cables becomes difficult
Solution Approach 1:
The cable routing strategy transitions from linear routing along the instrument shaft to a three-dimensional arrangement within the wrist mechanism. By utilizing the spatial volume of the wrist assembly and implementing cables at specific angles and positions, adequate routing space is created despite the reduced overall instrument shaft diameter
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 enables low-friction, cost-effective, and disposable MIS instruments with enhanced cable management, reducing friction and wear, and enabling a wider range of motion with fewer components.
Implementation Method 1
A curved guide path is defined within the second link and the tension member extends through the curved guide path from the first link to tool member. The roller is coupled to the second link and has a roller surface aligned with a portion of the curved guide path. When the second link is in a first orientation with respect to the first link, the roller surface contacts a portion of the tension member in the curved guide path and rotates when tension is applied to the tension member.
Data Source
AI summary
A low-friction medical device is provided having roller-assisted tension members and a friction-reducing curved guide path. The device includes a first link, a second link, and a tension member. A proximal end portion of the first link is coupled to an instrument shaft. A proximal end portion of the second link is rotatably coupled to a distal end portion of first link about a first axis. The second link defines a curved guide path and a cable extends from the first link through the curved guide path to a distal end of the second link and couples with a tool member. A roller having a roller surface is coupled to the second link such that the roller surface is aligned with a portion of the curved path and contacts the cable therein. The curved guide surface has a small fleet angle.