Four-Cable Wrist Mechanism for Surgical Instruments
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Solution Overview
Problem
Conventional robotically controlled surgical instruments with wrist mechanisms require six cables for three degrees of freedom, complicating miniaturization and increasing costs, while also needing pulleys to manage cable tension and friction, and cauterizing tools face challenges with electrical power delivery and isolation.
Innovation Solution
A four-cable wrist mechanism that uses integrated cable-guiding surfaces and a backend mechanism with motor-driven capstans and levers to control pitch, yaw, and grip, eliminating the need for pulleys and enabling efficient electrical isolation for cauterizing tools using brush-type contacts and insulating materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If six cables are used for three degrees of freedom in the wrist mechanism, then the wrist mechanism can provide full rotational control (pitch, yaw, and grip), but the instrument size and complexity increase
Solution Approach 1:
The patent combines the control of multiple degrees of freedom into a single capstan mechanism. By routing cables in a specific configuration where one cable controls both yaw and grip while another controls pitch, the system merges what would traditionally require separate control mechanisms into a unified structure, reducing the total cable count from six to four
Solution Approach 2:
The patent makes the cables serve multiple functions simultaneously. Each cable is routed through multiple pulleys and attachment points to control multiple rotational axes. For example, a single cable is attached to both the yaw axis and grip mechanism, allowing one cable to influence multiple degrees of freedom, thereby reducing the total number of cables needed
2Reliability
If pulleys are added to reduce cable friction, then cable operation becomes smoother and instrument life increases, but device complexity and cost increase
Solution Approach 1:
The patent removes the pulleys from the wrist mechanism entirely, extracting this component from the traditional cable-driven wrist design. Instead of using pulleys to guide cables, the invention uses direct cable attachment points and routing channels integrated into the wrist structure, eliminating the need for separate pulley components while maintaining cable control functionality
Solution Approach 2:
The patent replaces the mechanical pulley system with a direct cable routing and attachment system. Instead of using pulleys to transmit force and guide cables, the invention uses integrated routing channels and direct attachment points that eliminate the need for rotating pulley components, thereby reducing complexity while maintaining cable operation
3Manufacturing precision
If more cables are used to control wrist mechanism, then precise control of pitch, yaw, and grip is achieved, but manufacturing cost increases
Solution Approach 1:
The patent merges the control functions into fewer cable lines by strategically routing cables through multiple attachment points. This consolidation reduces the number of separate cable assemblies, attachment hardware, and routing components that need to be manufactured and assembled, thereby reducing manufacturing cost while maintaining control precision through the multi-functional cable routing
4Device complexity
If four cables are used instead of six, then instrument size is reduced and cost decreases, but cable routing complexity increases
Solution Approach 1:
The patent incorporates cable routing channels and attachment points into the wrist mechanism structure during the initial manufacturing process. By pre-integrating the cable pathways and mounting features into the wrist components, the cable routing is simplified during assembly, as the channels and attachment points are already in place to guide and secure the cables without requiring additional routing operations or complex assembly steps
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 four-cable wrist mechanism reduces instrument size, cost, and friction, allowing for more precise and efficient robotic control with fewer parts, and provides effective electrical isolation for cauterizing instruments, facilitating miniaturization and cost-effective production of smaller surgical instruments.
Implementation Method 1
Each capstan can be controlled using two cables that are attached to the capstan so that one side pays out cable while the other side pulls in an equal length of cable
Implementation Method 2
The first mechanism is operable to pull in one of the first and second cables while simultaneously feeding out the other of the first and second cables
Implementation Method 3
the effector is a bipolar cauterizing tool that employs a brush type contact for electrical connection to movable parts of the effector
Implementation Method 4
effective isolation of electrical voltages
Data Source
AI summary
A transmission or backend mechanism for a medical instrument connects four cables to three motorized degrees of freedom. The transmission employs a first drive mechanism attached to first and second cables and a second drive mechanism attached to third and fourth cables, where each mechanism can include a capstan or a lever system that pulls in one cable while simultaneously feeding out another cables. A third drive mechanism has a first pivot about which a portion of the first drive mechanism rotates, a second pivot about which a portion of the second drive mechanism rotates, and a third pivot about which the third drive mechanism rotates. Rotation of the third drive mechanism about the third pivot pulls in at least one of the first and second cables and feeds out at least one of the third and fourth cables.