Auto-Injector Needle Retraction Mechanism
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Manual injection devices pose challenges such as requiring continuous user effort, potential for underdosing, high injection forces, and dexterity issues, while current auto-injectors may prematurely halt injection if lifted during use.
Innovation Solution
An auto-injector design featuring a compression spring mechanism with a thrust tube and plunger system that allows for automatic needle insertion and retraction, triggered by a skin trigger sleeve, ensuring complete dose delivery even if the device is lifted during use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a spring mechanism is used to automatically insert and retract the needle, then ease of operation is improved, but reliability deteriorates because the injection may prematurely halt if the device is lifted during use
Solution Approach 1:
The system transitions from a static locked state to a dynamic injection state through the trigger mechanism. The spring mechanism is held static during transport, then dynamically activates during injection. The plunger's threaded engagement with the thrust tube creates a dynamic coupling that maintains injection continuity even when the device is lifted, resolving the reliability issue while preserving ease of operation.
Solution Approach 2:
The threaded connection between the plunger and thrust tube acts as an intermediary mechanism that couples the spring's retraction force to continuous medicament delivery. This intermediary ensures that even when the device is lifted and the spring begins to retract, the threaded engagement maintains plunger pressure on the stopper, preventing premature injection halt and ensuring complete dose delivery.
2Force
If manual pressure is applied continuously during injection, then injection force can be controlled, but ease of operation deteriorates due to user dexterity requirements and hand shaking
Solution Approach 1:
The system performs the injection function automatically once activated. The spring mechanism self-generates the injection force without requiring continuous manual pressure application. The user simply triggers the device and holds it steady, eliminating the need for continuous dexterous manipulation during injection and reducing hand shaking issues.
Solution Approach 2:
The injection process is transformed from continuous manual pressing to a periodic automatic action driven by the spring. The spring stores energy during the loading phase and releases it periodically during injection, providing controlled injection forces without requiring sustained user effort or dexterity.
3Reliability
If the button/plunger extension is made long to ensure complete dose delivery, then reliability is improved, but ease of operation deteriorates due to difficulty in reaching and controlling the button
Solution Approach 1:
The solution moves the activation mechanism from a linear extension along the injection axis to a rotational trigger mechanism at the proximal end. This dimensional change allows the user to activate the long plunger mechanism through a compact rotational motion at the trigger, maintaining complete dose delivery capability while dramatically improving accessibility and ease of operation.
Solution Approach 2:
The plunger is pre-positioned and pre-loaded within the thrust tube during device assembly. The threaded connection is pre-configured to engage at a specific position. When the trigger is activated, the pre-positioned plunger automatically engages the thrust tube and begins injection without requiring the user to manually extend or position any components, ensuring complete dose delivery while simplifying user interaction.
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 auto-injector ensures complete and comfortable medicament delivery with reduced user dexterity requirements and prevents premature needle retraction if the device is lifted during injection.
Implementation Method 1
spring means capable of, upon activation: pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end for insertion into an injection site
Implementation Method 2
The thrust tube and the plunger exhibit corresponding first and second threads having a first direction, e.g. right-handed or left-handed arranged to be engaged at least in an initial state
Data Source
Figure 1~2
Figure 3~5
Figure 6~8
AI summary
The invention refers to an auto-injector (1) comprising an elongate housing (2), a syringe (5) with a hollow injection needle (6) and a stopper (13), wherein the syringe (5) is arranged in a syringe carrier (4) slidably with respect to the housing (2), -a single compression spring (7) capable of, upon activation: -pushing the needle (6) from a covered position inside the housing (2) into an advanced position through the orifice and past the proximal end (P) for insertion into an injection site, -operating the syringe (5) to inject the dose of medicament (M), and -retracting the syringe (5) with the needle (6) into the covered position after at least partially delivering the medicament (M), -activating means (3) arranged to lock the spring means (7) in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the compression spring (7) for injection. A thrust tube (8) is arranged to transmit load from the compression spring (7) via a plunger (9) to the syringe (5) and/or the stopper (13), wherein the thrust tube (8) is arranged to be rotationally constrained relative to the housing (2), wherein the thrust tube (8) and the plunger (9) exhibit corresponding first and second threads (9.3, 8.2) having a first direction arranged to be engaged at least in an initial state. The plunger (9) is arranged to be rotationally released upon removal of the auto-injector (1) from the injection site resulting in rotation of the plunger (9) and consequently disengagement of the corresponding first and second threads (9.3, 8.2). The thrust tube (8) translates further and engages a corresponding third thread (12.1) of a retract collar (12) which is engaged to the syringe carrier (4) by corresponding fourth and fifth threads (12.2, 4.1) having the opposite direction of the first direction so that continued translation of the thrust tube (8) in proximal direction (P) results in rotation of the retract collar (12) and translation of the syringe carrier (4) in distal direction (D) for needle retraction.