Biopsy Device Asymmetric Cam Arming Mechanism
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Solution Overview
Problem
Existing biopsy devices face issues with jamming and deformation of the needle due to manufacturing tolerances, particularly in single-hand operation, leading to reduced usability and increased force requirements.
Innovation Solution
A biopsy device with a cylindrical body and a sliding arming button that performs two distinct functions for arming the cannula and stylet, minimizing friction through symmetrical guidance and propulsion elements, and using smaller springs to reduce frictional forces, allowing for easier one-handed operation and reduced jamming risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tight manufacturing tolerances are used to ensure optimal sliding of the stylet in the cannula, then the sliding motion is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent introduces asymmetric elements including an off-center stylet positioned within the cannula, and a cam mechanism with asymmetric engagement surfaces. The stylet is deliberately offset from the cannula's central axis, creating asymmetric contact points that reduce binding and improve sliding motion without requiring extremely tight tolerances throughout the entire assembly.
Solution Approach 2:
The patent employs a cam mechanism that converts rotational motion into linear displacement of the stylet and cannula. This dynamic approach allows controlled movement through varying contact surfaces, enabling smooth arming and firing sequences while accommodating normal manufacturing variations through the cam's geometric progression rather than relying on uniform tight tolerances.
2Speed
If a powerful spring is used to propel the cannula effectively, then the displacement speed is improved, but the force required to arm the device increases
Solution Approach 1:
The patent divides the propulsion function into two separate springs: a first spring for propelling the cannula and a second spring for propelling the stylet. This segmentation allows each spring to be optimized for its specific mass and travel distance, reducing the overall force required compared to a single powerful spring moving both components simultaneously.
Solution Approach 2:
The arming mechanism uses a cam-operated system that releases the stylet and cannula in sequential periodic action. The cam rotates to first release the stylet, then subsequently releases the cannula, creating a staged propulsion sequence that reduces peak arming force requirements while maintaining effective displacement speeds through the cumulative effect of both springs.
3Manufacturing precision
If the stylet and cannula are tightly fitted to minimize clearance, then the sample trapping is improved, but the jamming risk increases
Solution Approach 1:
The patent implements a nested configuration where the stylet is positioned within the cannula with controlled clearance. The asymmetric positioning and cam-operated movement create dynamic clearance patterns that maintain tight fitting for effective sample trapping in the notch, while allowing sufficient play to prevent binding and jamming during the arming and firing cycles.
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 device ensures optimal sliding of the stylet within the cannula, reducing jamming and deformation risks, making it easier to use and allowing for more samples to be taken without the need for excessive force, while maintaining high displacement speed.
Implementation Method 1
a spring (35, 29) for propelling, respectively, the stylet and the cannula
Implementation Method 2
minimising the friction between the stylet and the cannula
Data Source
Figure 1~2
AI summary
This invention relates to a device (10) for taking at least one sample of soft tissue from an organ, said device comprising a body (11) and a needle (12) formed by a stylet and a cannula coaxial with said stylet. The device comprises a mechanism for arming the needle, designed for sequentially moving the cannula and then the stylet from a rest position wherein the stylet and the cannula are extended towards the outside of the body, to a shooting position wherein the stylet and the cannula are retracted towards the rear of the body, and a triggering mechanism designed to release the stylet then the cannula and to allow their displacement from the shooting position to the rest position. The cannula is coupled kinematically to a cannula slider (24) comprising at least one retaining element(26) for maintaining the cannula slider in a shooting position. The stylet is coupled kinematically to a stylet slider (30) comprising at least one retaining element(32) for maintaining the stylet slider in a shooting position and means for unlocking the cannula slider. This device is characterized in that the stylet (13) comprises a sampling tip (51) able to slide into the cannula (14) and a displacement rod (42) connecting said sampling tip with the stylet slider (30), the sampling tip (51) being separate from the displacement rod (42).