Conical Cable Manipulator Control for Passive Tensioning
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Solution Overview
Problem
Existing cable-driven systems for medical interventional devices require multiple motors to control end-effectors, leading to increased complexity and cost, and lack a passive solution for proportional adjustment of cables to avoid damage and improve accuracy.
Innovation Solution
A cable-driven parallel manipulator control mechanism using a control member with a three-dimensional conical control surface and spring-loaded pistons to actuate multiple cables passively, allowing proportional adjustment and tensioning without motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple motors are used to control cable lengths for end-effector positioning, then positioning accuracy is improved, but system complexity and cost increase
Solution Approach 1:
The patent merges the control of multiple cables into a single master control unit. The master unit contains a control surface with multiple contact points that simultaneously influence multiple cables through a unified mechanical structure, eliminating the need for separate motors for each cable while maintaining positioning accuracy.
Solution Approach 2:
The master control unit serves multiple functions: it controls the length of multiple cables simultaneously, maintains tension on all cables, and provides proportional adjustment for end-effector positioning. This single unit replaces what would traditionally require multiple separate actuators.
2Manufacturing precision
If proportional adjustment of cable lengths is implemented, then end-effector control accuracy is improved, but system complexity increases
Solution Approach 1:
The control surface is designed with a curved or conical geometry that naturally provides proportional adjustment. As the control surface moves, the geometric relationship between the control points and cable attachment points automatically creates proportional changes in cable lengths, eliminating the need for complex control algorithms or additional actuators.
Solution Approach 2:
The control surface acts as an intermediary mechanical element that translates simple user input into proportional cable length adjustments. The geometric relationship between the control surface and cable attachment points mediates the proportional adjustment, providing precise control without complex actuation mechanisms.
3Reliability
If cable tension is maintained to prevent sagging, then system reliability is improved, but the risk of cable damage from excessive tension increases
Solution Approach 1:
The system dynamically adjusts cable tension through the movement of the control surface. As the control surface moves to different positions, the mechanical geometry automatically adjusts the tension in each cable proportionally, maintaining optimal tension for preventing sagging while avoiding excessive tension that could damage cables.
Solution Approach 2:
The control mechanism inherently provides feedback through the mechanical geometry of the control surface and cable arrangement. The proportional relationship between control surface position and cable length changes automatically maintains appropriate tension levels, preventing both insufficient tension (sagging) and excessive tension (damage).
4Ease of operation
If a frame structure is used to leverage cable tension for end-effector steering, then control effectiveness is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the frame structure with the control surface into a single integrated unit. The control surface itself serves as the structural element that leverages cable tension, eliminating the need for separate frame structures. This integration reduces complexity while maintaining steering effectiveness.
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
Enables accurate, passive control and actuation of end-effectors with reduced system complexity, providing haptic feedback and improved maneuverability in confined spaces.
Implementation Method 1
spring-loaded pistons to actuate multiple cables passively
Implementation Method 2
control surface defining a three-dimensional conical control surface... spring-loaded cam followers and a conical control surface acting as the cam
Implementation Method 3
control surface defining a three-dimensional conical control surface... translation of the control member along a two-dimensional plane causes the at least one connector to travel perpendicularly to the two-dimensional plane
Data Source
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AI summary
A mechanism for actuation and control of a device, such as an interventional device, in two dimensions via a cable-driven arrangement. The mechanism can include multiple spring- loaded cam followers and a conical control surface acting as the cam. The translation of the conical cam results in the perpendicular linear motion of the cam followers. With the cables coupled to the cam followers from one end, and to the device of interest at the other end, the motion of the followers results in cable displacements that lead to the manipulation of the interventional device. Adjustment of the cable lengths are made possible with a proportion determined by the cam. This allows maintaining a set tension and while avoiding sagging. The resulting system can be an entirely passive mechanism in some embodiments that allows for accurate device position control, position estimation, and haptic feedback.