Capstan Drive Device for Surgical Tool Backlash Elimination
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Solution Overview
Problem
Existing surgical manipulators face challenges in converting rotational force from a motor into linear motion for driving end effectors, leading to complex device structures and reduced backdrivability due to backlash issues.
Innovation Solution
A drive device utilizing a capstan assembly with a pair of cables wound in opposite directions, connected to a rod that moves linearly with capstan rotation, and a reaction force applying unit to ensure pre-tension and high backdrivability without backlash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a ball screw mechanism is used to convert rotational motion to linear motion, then the surgical device structure is simplified, but the device becomes elongated in the axial direction and backlash occurs reducing reliability
Solution Approach 1:
The patent replaces the traditional ball screw mechanical conversion mechanism with a direct-drive motor configuration. The motor's rotational output is directly coupled to the surgical instrument through a flexible cable or belt transmission system, eliminating the ball screw component entirely. This substitution resolves the backlash and backdrivability issues inherent in ball screw mechanisms while maintaining the essential function of converting rotational motion to linear motion at the instrument level.
Solution Approach 2:
The patent extracts and removes the ball screw mechanism from the surgical device architecture. By taking out the problematic ball screw component, the design eliminates the sources of backlash and poor backdrivability. The rotational-to-linear motion conversion function is instead achieved through the cable tension system or belt transmission, which does not suffer from the same mechanical defects as ball screws.
2Ease of operation
If a rotational-to-linear motion converting device is added to drive the end effector, then the linear motion function is achieved, but the device structure becomes complicated and larger in size
Solution Approach 1:
The patent replaces complex mechanical motion conversion mechanisms with a direct-drive approach using flexible transmission elements. Instead of incorporating gears, cam mechanisms, or ball screws within the device, the system uses a motor coupled to a cable or belt that transmits motion externally. This substitution dramatically simplifies the internal device structure while preserving the linear motion capability at the end effector.
Solution Approach 2:
The patent segments the motion conversion function from the main device body. The motor and transmission elements (cables or belts) are separated as distinct components, allowing the device itself to remain compact and simple while the motion conversion occurs through the flexible transmission system. This segmentation avoids the need for complex internal mechanisms within the device housing.
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 efficient conversion of rotational force to linear motion, providing high backdrivability and eliminating backlash, thus enhancing the precision and reliability of surgical tool operation.
Implementation Method 1
a capstan assembly including a capstan that performs a linear motion by rotation of the capstan, a cable that is wound around the capstan, and a rod that is connected to the cable and performs a linear motion
Implementation Method 2
a reaction force applying unit that applies a reaction force to rotate the first capstan and the second capstan in directions opposite to each other between the first capstan and the second capstan, and applies a pre-tension force to the pair of cables
Data Source
AI summary
A drive device that drives an end effector is provided.The drive device includes: a capstan; a cable wound around the capstan; and a rod that has one degree of freedom in linear motion, and performs a linear motion by rotation of the capstan, the cable being connected to the rod. In the drive device, an end effector is driven by the linear motion of the rod. The capstan assembly includes a reaction force applying unit that applies a reaction force to rotate the first capstan and the second capstan in directions opposite to each other between the first capstan and the second capstan, and applies a pre-tension force to cables by winding the cables around the first capstan and the second capstan by rotation caused by the reaction force.