Dual-Strain Spring Mechanism for Injection Device Needle Protection
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Solution Overview
Problem
Existing injection devices with pre-tensioned springs for moving needle protecting sleeves face issues such as deformation of plastic components during storage and an imbalance of forces required for shifting the sleeve between positions, making it difficult to handle and ensuring reliable needle protection.
Innovation Solution
An injection device design where the needle protecting sleeve spring is pre-tensioned during activation and delivery, allowing it to move from an initial to an activating position and then to an end position, with a larger strain in the second direction to ensure reliable needle coverage, using a dual-strain mechanism to balance forces and prevent accidental needle exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pre-tensioned spring is used to force the needle protecting sleeve to move to cover the injection needle, then the needle protecting sleeve can reliably assume an end position in which it fully covers the injection needle, but the plastic components may deform during long-term storage
Solution Approach 1:
The spring pre-tension is dynamically adjusted based on the operational state. During storage, the spring maintains a first, lower pre-tension level that preserves plastic component stability. During activation and delivery, the spring transitions to a second, higher pre-tension level that ensures reliable needle coverage. This dynamic adjustment resolves the contradiction between reliability and stability.
2Reliability
If the spring force is increased to ensure reliable needle coverage, then the needle protecting sleeve can be reliably moved to the end position, but the force needed to shift the needle protecting sleeve in the distal direction increases, making it harder to handle
Solution Approach 1:
The spring force is dynamically adjusted based on operational phase. During normal handling and activation (distal movement), the spring maintains a lower pre-tension level, reducing the force required by the user and improving ease of operation. During the delivery phase (proximal movement), the spring transitions to a higher pre-tension level that ensures reliable needle coverage. This resolves the contradiction between reliability and ease of operation.
3Reliability
If the spring is pre-tensioned with a large amount to ensure reliable needle protection, then the needle protecting sleeve can be forced to cover the needle, but the spring force becomes excessive during activation and delivery processes
Solution Approach 1:
The spring pre-tension is dynamically adjusted to match operational requirements. During storage, a first pre-tension level provides sufficient force for reliable needle protection without being excessive. During activation and delivery, the spring transitions to a second pre-tension level that balances the forces involved in moving the needle protecting sleeve. This dynamic adjustment resolves the contradiction between reliability and force balance.
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 dual-strain mechanism ensures reliable needle protection and easier handling by maintaining a low force requirement for distal movement while increasing spring force for proximal movement, reducing the risk of plastic deformation and accidental needle exposure.
Implementation Method 1
the spring force decreases according to the rules of Hooke's Law
Implementation Method 2
the spring force decreases according to the rules of Hooke's Law
Data Source
Figure 1
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Figure 3
AI summary
An injection device having a distal and a proximal end comprising; a housing (1); a needle protecting sleeve (2) longitudinally movable relative to the housing (1); a container holder (20) longitudinally movable relative to the housing (1) towards the proximal end of the device from a non-delivery position into a delivery position; a needle protecting sleeve spring (5) operably coupled between the needle protecting sleeve (2) and the container holder (20) such that the needle protecting sleeve (2) can be longitudinally moved towards the distal end of the device from an initial position into an activating position and towards the proximal end of the device from the activating position into an end position. The invention is characterized in that the needle protecting sleeve spring(5) is strained by a first amount when the a needle protecting sleeve (2) moves from its initial position to the activating position, and by a second amount when the container holder (20) moves from its non-delivery position to the delivery position.