Gear-Driven Pin Cutter for Controlled Bone Shaft Shearing
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Solution Overview
Problem
Existing pin cutter devices for bone surgery often require long levers to generate high shearing forces, which can lead to uncontrolled forces that loosen the implant in the bone, and using two large handles can destroy the connection between the screw and the bone or fixator, posing user safety risks.
Innovation Solution
A pin cutter tool with a stationary handle and a rotating handle connected via a gear system, allowing for a twisting motion between two tubular elements to shear the shaft without relative twist, maintaining the connection between the screw and the bone or fixator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If long levers are used to generate high shearing forces, then the cutting capability is improved, but uncontrolled forces are transferred to the pin which may result in loosening of the implant in the bone
Solution Approach 1:
A controlled rotational mechanism serves as an intermediary between the user's manual input and the shearing action. The controlled rotation of the cutting element through a limited angular range (e.g., 90-180 degrees) mediates the force application, allowing high shearing forces to be generated through mechanical advantage while preventing uncontrolled force transfer to the implant-bone interface.
Solution Approach 2:
The cutting mechanism changes from linear lever motion to rotational motion with a controlled angular parameter. By defining a specific rotation angle range and using a gear or cam mechanism to limit the rotation, the system achieves high shearing forces through rotational mechanical advantage while controlling the magnitude and direction of forces applied to the pin, thereby protecting the implant stability.
2Force
If two large handles are used for rotation, then the shearing capability is improved, but the connection between the screw and the bone or fixator may be destroyed
Solution Approach 1:
A single handle with a gear or cam mechanism acts as an intermediary that translates simple rotational motion into controlled twisting motion of the cutting elements. This intermediary mechanism provides mechanical advantage for generating high shearing forces while precisely controlling the rotation angle and force application, preventing harmful effects on the screw-bone or screw-fixator connection.
Solution Approach 2:
The traditional two-handle direct twisting mechanism is replaced with a single-handle gear-driven or cam-driven system. This substitution changes the mechanical system from direct manual twisting to a controlled rotational actuation mechanism, achieving the same shearing function with better control over force magnitude and rotation angle, thereby eliminating the risk of connection destruction.
3Force
If two handles are used for twisting motion, then the cutting capability is improved, but user control and precision are reduced leading to mistakes
Solution Approach 1:
A gear train or cam mechanism serves as an intermediary between the user's single-handle rotation and the cutting elements' twisting motion. This intermediary automatically provides the required mechanical advantage and motion transformation, eliminating the need for the user to coordinate two handles while maintaining precise control over the twisting force and rotation angle.
Solution Approach 2:
The mechanism is designed to be self-regulating through the gear or cam geometry, which automatically limits the rotation angle and controls the force application. The user simply rotates the single handle through a comfortable range of motion, and the mechanism itself ensures proper force distribution and cutting action without requiring user skill or attention to coordinate multiple handles, thereby improving ease of operation and reducing mistakes.
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 tool effectively breaks the shaft while maintaining a strong connection between the screw and the bone or fixator, reducing the risk of loosening and improving user safety by eliminating the need for uncontrolled manual forces.
Implementation Method 1
The second handle is a turning handle mounted on the first tubular element for a rotation around an axis and comprising a gear engaging the second tubular element for transmittal of a rotation of the turning handle into a rotation of the second tubular element for said twisting movement.
Data Source
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AI summary
A tool (1) for breaking a shaft comprises a first (3) and a second (4) tubular element, both provided with inner through bores (41, 42) adapted to receive a first and second portion of said shaft in a parking position of the tool (1). A first handle (5) is fixedly connected with the first tubular element (3), wherein the second tubular element (4) is connected to a second handle (6). A bottom surface (33) of the second tubular element (4) is in contact with a neck surface of the first tubular element (3) forming a shearing plane (I) perpendicular to the main axis (T) of the tool. Starting from said parking position, a rotation between the two tubular elements (3 and 4) around this axis (T) creates a twisting movement of the two shaft portions received in the two tubular elements (3, 4), respectively, and shears the shaft portions at the interface (33) between them. The second handle is a turning handle (6) mounted on the first tubular element (3) for a rotation around an axis (R.) and comprising a gear (10, 44) engaging the second tubular element (4) for transmittal of a rotation of the turning handle (7) into a rotation of the second tubular element (4, 10) for said twisting movement.