Bone Cement Dispensing Device with Cam-Driven Thread Switching
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Solution Overview
Problem
Existing bone cement dispensing devices face challenges in precision, cost-effectiveness, and mechanical stability, particularly when dealing with highly viscous cements, as they require constant pressure and have a weak mechanical coupling between threads, leading to increased susceptibility to breakage and operational complexity.
Innovation Solution
A device with a rod-like discharge element featuring an external thread and a switching system with a cuff-like internal thread that allows for reversible switching between coupled and decoupled positions, enabling easy handling and precise control without the need for constant pressure, using a bayonet lock or snap-in hooks for connection, and made from cost-effective materials like glass fiber-reinforced plastic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the internal thread is pressed against the external thread by a spring to enable axial movement, then the dispensing element can move axially, but one hand is tied up operating the switching system and constant pressure is required
Solution Approach 1:
The patent removes the spring component from the switching system entirely. Instead of using elastic force, the system uses a cam mechanism with an inclined surface that converts rotational movement into axial displacement through geometric constraints. This extraction of the spring simplifies the device by eliminating the need for constant pressure application and complex force management.
Solution Approach 2:
Rather than using a spring to push the threads together and rely on operator pressure to maintain engagement, the patent inverts the approach by using a cam mechanism where rotation automatically drives the axial movement. The inclined cam surface passively converts the rotational input into the required axial displacement without needing opposing spring pressure.
2Strength
If the external thread is coupled one-sidedly with the internal thread, then the structure is simple, but uneven material stress increases susceptibility to breakage
Solution Approach 1:
The patent employs asymmetric thread geometry where the cam mechanism creates non-uniform contact between the internal and external threads. The inclined cam surface concentrates contact on one side of the thread engagement, creating an asymmetric stress distribution that is deliberately designed to convert rotational force into axial movement while maintaining strong mechanical coupling throughout the engagement.
3Force
If spring tension alone determines mechanical coupling, then the structure is simple, but the coupling is weak and insufficient for highly viscous bone cements
Solution Approach 1:
The patent inverts the force generation mechanism by replacing spring tension with a cam-driven geometric constraint system. The inclined cam surface passively generates axial force through the conversion of rotational input, eliminating the need for spring tension and providing significantly stronger mechanical coupling capable of handling highly viscous materials.
Solution Approach 2:
The patent transitions from a static spring-based coupling system to a dynamic cam mechanism where the force characteristics change continuously during rotation. The cam profile is designed to provide increasing axial force as rotation progresses, dynamically adapting the coupling strength to match the dispensing requirements and overcome high material viscosity.
4Reliability
If the device includes many moving components like springs, then the switching function is achieved, but the risk of malfunctions increases
Solution Approach 1:
The patent removes the spring component entirely from the device, replacing it with a purely geometric cam mechanism. This extraction eliminates a major source of potential malfunction while maintaining the switching function through the cam's inclined surface that passively converts rotation to axial movement without requiring elastic elements or complex force management.
Data Source
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AI summary
Device (100) for dispensing bone cement (600) from a container (500), comprising a connecting element (240) for reversibly connecting the device to the container, a rod-like dispensing element (300) which has at least a partial external thread (310), a switching system (200) which has at least a partial first internal thread (220), wherein the first internal thread can be coupled to the external thread in such a way that in a first coupled switching system position the dispensing element can be screwed axially into the container and in a second decoupled switching system position the dispensing element can be slid freely axially into the container.