Resilient Coupling Shoulder for Auto-Injection Spring Engagement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing auto-injection devices are costly due to tight manufacturing tolerances required for couplings that secure injection springs to plunger rods, making them prohibitively expensive for widespread use, especially for medically untrained users and in situations requiring automatic needle retraction.
Innovation Solution
A coupling design with a spring rest and a resiliently moveable shoulder that can be radially or diametrically offset, allowing for secure engagement and disengagement of the injection spring with the plunger rod, enabling cost-effective assembly and reducing manufacturing tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tight manufacturing tolerances are used for couplings, then reliability of spring-plunger connection is improved, but device cost increases
Solution Approach 1:
The coupling design changes the geometric parameters of the shoulder and spring rest to create a more tolerant engagement interface. The shoulder is positioned radially offset from the spring rest, allowing for larger dimensional variations while maintaining reliable spring-to-plunger connection. This parameter modification enables standard manufacturing tolerances to achieve the same functional reliability that previously required tight tolerances.
Solution Approach 2:
The coupling incorporates a resiliently moveable shoulder that can dynamically adjust its position during assembly and operation. This dynamic element compensates for manufacturing variations by self-adjusting to maintain proper engagement between the spring and plunger rod, thereby achieving reliable connection without requiring tight manufacturing tolerances.
2Reliability
If tight manufacturing tolerances are used for couplings, then secure engagement of spring to plunger is improved, but manufacturing complexity increases
Solution Approach 1:
The coupling design modifies the spatial parameters by radially offsetting the shoulder from the spring rest and positioning them at specific angular intervals (e.g., 90 degrees apart). These parameter changes create a more forgiving engagement geometry that maintains secure spring-to-plunger connection while allowing standard manufacturing tolerances, thereby reducing manufacturing complexity.
Solution Approach 2:
The coupling is designed with discrete engagement features (shoulders and spring rests) positioned at specific angular intervals around the plunger rod. This segmentation approach distributes the engagement requirements across multiple points, allowing each feature to be manufactured with standard tolerances while collectively providing secure engagement.
3Reliability
If complex coupling mechanisms are used, then reliability of injection mechanism is improved, but ease of assembly by users is worsened
Solution Approach 1:
The coupling mechanism is designed to be self-actuating during the injection process. The resilient shoulder automatically engages and disengages from the plunger rod ribs based on the injection spring's compression and expansion, without requiring user intervention. This self-service mechanism maintains reliability while simplifying user operation to merely triggering the device.
Solution Approach 2:
The coupling uses a dynamically moveable shoulder that automatically adjusts its engagement state based on the injection cycle. During injection, the shoulder is compressed into engagement with the plunger rod; after injection, it resiliently returns to disengage. This dynamic behavior provides reliable automated operation while keeping the user interface simple.
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 coupling design allows for a cost-effective auto-injection device that can be assembled by users, separates medicine cartridge expiration from the device, and provides a hermetic seal, enabling efficient and safe automatic injection and retraction without requiring precise assembly, thus reducing costs and improving accessibility.
Implementation Method 1
The shoulder is normally in the second position and is resiliently moveable to the first position
Data Source
AI summary
A coupling for selectively securing a spring to a plunger is provided. The coupling has a first end defining a spring rest for receiving the spring and a second end defining a shoulder. The shoulder is moveable to a first position into contact with the plunger and to a second position out of contact with the plunger. The shoulder is normally in the second position and is resiliently moveable to the first position.