Self-Reversing Biopsy Cutter Drive to Minimize Cable Whip
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Solution Overview
Problem
MRI-guided biopsy procedures face challenges due to the phenomenon of 'cable whip' in rotary drive cables, which causes procedural delays and instability due to torque imbalances leading to cable deformation and unpredictable movement.
Innovation Solution
The implementation of a cutter drive mechanism that allows the cutter to rotate and translate simultaneously with a rotary input from the cable in a single direction, eliminating the need to reverse the cable's rotation direction, thereby reducing torque changes and minimizing cable whip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the cutter is driven by a rotary drive cable that reverses rotation direction to translate the cutter bidirectionally, then the cutter can perform cutting and retraction movements, but cable whip occurs due to torque imbalances causing cable deformation and unpredictable movement
Solution Approach 1:
The patent applies dynamics by making the drive system movable and adjustable. The cutter driver includes a rotation assembly and translation assembly that can dynamically adapt their configuration. The translation assembly uses a toggle mechanism with links and joints that can change their mechanical configuration during operation, allowing the system to optimize its mechanical advantage and eliminate the need for cable reversal while maintaining bidirectional cutter movement capability.
Solution Approach 2:
The patent introduces an intermediary mechanical system between the cable and cutter. The cutter driver acts as a mediator that converts unidirectional cable rotation into bidirectional cutter movement through its translation assembly. This intermediary mechanism absorbs and manages torque variations, preventing them from causing cable whip while still achieving the required bidirectional cutter motion for cutting and retraction.
2Measurement precision
If the rotary drive cable reverses rotation direction frequently, then the cutter can be positioned accurately at different locations, but torque changes increase causing cable whip and procedural delays
Solution Approach 1:
The patent implements continuity of useful action by enabling the cable to rotate in a single continuous direction without reversal. The translation assembly converts this continuous unidirectional rotation into bidirectional cutter movement, eliminating interruptions and torque reversals that would cause cable whip. This continuous operation maintains precise cutter positioning while avoiding procedural delays associated with cable whip events.
Solution Approach 2:
The dynamic translation assembly continuously adapts its mechanical configuration to maintain precise cutter positioning throughout the full range of motion. As the cutter moves through different positions, the toggle mechanism dynamically adjusts the mechanical advantage ratio, ensuring accurate positioning is maintained throughout the entire stroke without requiring cable direction changes that would interrupt the continuous action.
3Adaptability or versatility
If a rotary drive cable system is used to power the cutter, then the device can be operated remotely with MRI compatibility, but cable whip occurs due to torque imbalances leading to device wear and operator vibrations
Solution Approach 1:
The cutter driver serves as an intermediary mechanical system between the MRI-compatible rotary cable and the cutter. This intermediate mechanism absorbs and manages torque imbalances locally at the cutter assembly, preventing them from propagating back to the cable and causing whip. The translation assembly with its toggle mechanism acts as a shock absorber and torque manager, protecting both the cable from excessive wear and the operator from vibrations while maintaining remote MRI-compatible operation.
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
This configuration stabilizes the biopsy process by maintaining consistent cutter movement, reducing wear on the device and operator vibrations, and preventing sudden cable deformations, thus enhancing procedural efficiency and accuracy.
Implementation Method 1
the translation assembly includes a self-reversing screw configured to translate the cutter in a first direction in response to rotation of the driver assembly in a single rotation direction
Data Source
AI summary
A biopsy device includes a body, a needle, a cutter, and a cutter drive mechanism. The needle extends distally from the body. The cutter is movable relative to the needle to sever a tissue sample. The cutter drive mechanism is driven by a rotary drive cable and is configured to both rotate and translate the cutter. The cutter drive mechanism is further configured to reverse the transition direction of the cutter wile the drive provided by the rotary drive cable is in a continuous rotary direction.