Injection Device Housing Latch Design for Cartridge Stress Reduction
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Solution Overview
Problem
Existing injection devices for medicaments, particularly those with glass cartridges, face mechanical stress issues during assembly due to snap feature connections, which can lead to cartridge deformation and potential fracture.
Innovation Solution
A housing design for injection devices featuring a tubular cartridge holder and body with radially inwardly protruding latch elements that engage in a nested configuration, reducing radial deformation and stress on the cartridge by minimizing the radial dimensions of the latch elements and strategically positioning them near the proximal end of the cartridge holder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If snap features are used to connect cartridge holder and body, then assembly is simplified and manufacturing efficiency is improved, but radial deformation occurs causing mechanical stress on the glass cartridge
Solution Approach 1:
The connection mechanism is divided into two independent parts: latch elements for securing the cartridge holder to the body, and support elements for protecting the glass cartridge. This segmentation allows each element to perform its specific function without interfering with the other, eliminating the need for snap features that cause radial deformation.
Solution Approach 2:
Support elements are introduced as intermediary components between the cartridge holder and the glass cartridge. These elements act as mediators that prevent direct mechanical stress transmission from the housing structure to the fragile cartridge, while still allowing the latch elements to secure the assembly.
2Strength
If latch elements with sufficient radial dimension are used to ensure secure connection, then connection strength is improved, but radial deformation of the cartridge holder increases
Solution Approach 1:
The connection function is separated from the support function. Latch elements provide secure connection through angular engagement surfaces that create strong mechanical interlocking, while support elements independently protect the cartridge from deformation. This segmentation allows optimization of each element for its specific purpose.
Solution Approach 2:
Instead of relying on radial dimensions of latch elements, the connection strength is achieved through angular geometry and mechanical interlocking in the axial direction. The latch elements engage with complementary surfaces that prevent disengagement through lever action, providing strong connection without radial deformation.
3Ease of manufacture
If through holes are provided in the cartridge holder for latch elements, then assembly of latch elements is simplified, but structural integrity of the cartridge holder is reduced
Solution Approach 1:
Latch elements are designed to be engaged with the cartridge holder and body in a predetermined sequence during assembly. The engagement process follows a specific path that allows the latch elements to snap into place without requiring pre-drilled holes, maintaining structural integrity while simplifying assembly through predetermined engagement geometry.
Data Source
AI summary
A housing includes a body and a cartridge holder. The body can accommodate a drive mechanism including a piston rod to operably engage with a piston of a cartridge filled with a liquid injectable medicament. The cartridge holder has a cartridge receiving space. The cartridge holder has an insert section at a proximal end. The body has a receptacle to receive the insert section. The cartridge holder includes a first latch element located on the insert section. The body includes a second latch element located in the receptacle and protruding inwardly from a side wall section of the receptacle. A radial extension of the first latch element is less than a thickness of the side wall of the insert section or of the receptacle. A radial protrusion of the second latch element is less than a thickness of the side wall sections of the insert section or of the receptacle.