Autoinjector Cap Plug Mechanism for Needle Shield Engagement
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Solution Overview
Problem
Existing autoinjector designs face issues with the 'creep effect' of clamping means for needle shields, leading to unreliable engagement during assembly, and require a time-consuming push-back step that exposes the needle shield to the user.
Innovation Solution
A cap with a tubular body and inner sleeve that includes a plug with movable portions to push the needle shield back in the proximal direction, ensuring the clamping means return to their rest position, preventing creep and enabling reliable engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the clamping means are deflected by the syringe barrel during insertion, then the needle shield is engaged, but the clamping means may creep over time and fail to properly engage the needle shield during cap removal
Solution Approach 1:
The patent implements a push-back mechanism that performs preliminary action by pushing the needle shield back in the proximal direction after insertion. This preliminary action causes the clamping means to return to their rest position before the cap is removed, preventing creep deformation and ensuring reliable engagement. The push-back step is integrated into the assembly process, occurring before the product is ready for storage and use.
2Reliability
If a machine push-back step is used to push the needle shield back, then the clamping means return to rest position, but this operation is time-consuming
Solution Approach 1:
The patent implements a self-service mechanism where the plug automatically pushes the needle shield back in the proximal direction as part of the normal assembly process. The plug is moved from a first position to a second position, and this movement inherently performs the push-back function without requiring separate machine intervention. The system uses its own structural components (the plug and its movement mechanism) to accomplish the push-back task, eliminating the need for additional time-consuming machine operations.
3Productivity
If the central hole of the cap is used for push-back operation, then the needle shield can be pushed back, but the needle shield becomes visible to the end user which may be confusing
Solution Approach 1:
The patent extracts the push-back function from the cap structure itself. Instead of using the central hole of the cap for push-back operations, the invention uses a separate plug component that performs the push-back action. This extraction allows the cap to be designed without a central hole, thereby maintaining a clean, simple appearance that does not confuse the end user, while still achieving the necessary push-back function through the plug mechanism.
Data Source
Figure 1A
Figure 1B~1C
Figure 1D~2A
AI summary
The cap (1) includes a tubular body (2) extending along a longitudinal axis A. The tubular body (2) has a distal end (21) and an opposite proximal end (20) for attachment to a bottom housing (104) of an autoinjector (100). An inner sleeve (3) proximally extends inside the tubular body (2) from said distal end (21), the inner sleeve (3) defining an inner cavity (34) for receiving the needle shield (110). The cap (1) has clamping means for clamping the needle shield (110) when the needle shield (110) is inserted inside the inner cavity (34), the clamping means including an axial abutment surface (42) for abutting against a proximal end (111) of the needle shield (110), and a plug (5) at least partially extending inside the inner cavity (34), the plug (5) having a distal end portion (6), a proximal end portion (7) and an intermediate portion (8) extending between the distal end portion (6) and the proximal end portion (7). At least the proximal end portion (7) of the plug (5) is movable between a first position, in which the proximal end portion (7) allows the proximal end (111) of the needle shield (110) to distally pass the axial abutment surface (42) of the clamping means, and a second position, in which the proximal end portion (7) of the plug (5) moves in the proximal direction to push the needle shield (110) back towards the axial abutment surface (42).