Medicament Delivery Device Spring Plunger Rod Design
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Solution Overview
Problem
Conventional medicament delivery devices are cumbersome due to the length required for plunger rods, which becomes more pronounced with added functionality, making them less discreet and less user-friendly, especially for self-administration in public.
Innovation Solution
A medicament delivery device design featuring a compression spring that acts as both a drive mechanism and plunger rod, guided on both the outside and inside, with a dual function activation member and guide means to eliminate buckling and control delivery speed, allowing for a shorter and more compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional plunger rod is used to push the stopper, then the medicament can be delivered, but the device becomes longer and less discreet
Solution Approach 1:
The patent combines the plunger rod and compression spring into a single integrated component. The plunger rod serves dual functions: as a structural element to push the stopper and as a guide for the compression spring. This merging eliminates the need for a separate spring housing and guide structure, significantly reducing device length while maintaining the ability to deliver medicament discreetly
Solution Approach 2:
The compression spring is nested within the plunger rod structure. The spring is guided by the plunger rod itself, with the spring positioned inside the hollow portion of the plunger rod. This nesting arrangement allows the spring mechanism to be contained within the existing structural elements, minimizing additional length and maintaining a compact, discreet device form factor
2Quantity of substance
If the plunger rod moves forward a long distance to deliver large doses or multiple doses, then the required medicament volume is delivered, but the device becomes even longer
Solution Approach 1:
The patent introduces a dynamic compression spring mechanism that allows the plunger rod to move forward in a controlled manner. The spring provides progressive force as it expands, enabling the plunger rod to travel longer distances smoothly while delivering large volumes of medicament. The dynamic nature of the spring allows for adjustable delivery rates and maintains device compactness even when long plunger travel is required
Solution Approach 2:
The compression spring mechanism enables periodic or controlled delivery of medicament through the plunger rod's forward movement. The spring can be pre-compressed to a specific degree, allowing for controlled, stepwise delivery of medicament volumes. This periodic action mechanism allows the device to deliver large total volumes through multiple controlled movements rather than requiring an excessively long single-stroke plunger rod
3Length of moving object
If a compression spring is used instead of a conventional plunger rod, then the device becomes shorter, but the spring may buckle during operation
Solution Approach 1:
The plunger rod acts as an intermediary structural element between the compression spring and the stopper. The hollow plunger rod provides a rigid guide structure that confines the compression spring, preventing lateral buckling while allowing axial expansion. The plunger rod's wall structure serves as both the pushing mechanism and the spring guide, eliminating the need for additional buckling prevention structures
Solution Approach 2:
The plunger rod is designed with specific local structural qualities to prevent spring buckling. The hollow cylindrical structure of the plunger rod provides localized rigid support around the compression spring, creating a confined space that restricts lateral movement of the spring. This local structural quality of the plunger rod wall acts as a natural guide and support, preventing buckling without adding overall device length
4Adaptability or versatility
If additional functionality is added to the injector, then the device becomes more versatile, but the device length increases due to components like dose setting buttons and needle shields
Solution Approach 1:
The plunger rod is designed as a multi-functional component that serves multiple purposes: it acts as the pushing mechanism for the stopper, provides a guide structure for the compression spring, and can be integrated with additional functional elements such as dose setting mechanisms and needle shield attachments. This universal design allows various functionalities to be added without proportionally increasing device length, as they are integrated into the existing plunger rod structure
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 solution results in a more discreet and user-friendly device with reduced material and component usage, eliminating the need for a conventional plunger rod and preventing buckling, while enabling controlled medicament delivery.
Implementation Method 1
a compression spring having a predetermined compressed length and a predetermined outer diameter, wherein the compressed length is the length of the spring when it is in a pre-tensioned state
Data Source
AI summary
The present invention relates to a medicament delivery device (10) comprising a front housing (12) and a rear housing (14) connected to each other; a medicament container (18) disposed within the front housing (12), wherein the container (18) has a front opening with or for a delivery member for delivering the medicament therethrough and at least one movable stopper (25); and a compression spring (26) having a predetermined compressed length and a predetermined outer diameter, wherein the compressed length is the length of the spring when it is in a pre-tensioned state; wherein the device further comprises a first guide means comprising a front part (28) having a predetermined first length (61), a middle part (42) having a predetermined second length (62), and a rear part (34) having a predetermined third length (63), wherein said predetermined third length corresponds to the predetermined compressed length of the compression spring, wherein the front part (28) is arranged to be in contact with the movable stopper (25), wherein the middle part comprises an annular ledge (41) and first lock-release means (43), and wherein the rear part (34) is fully surrounded by the compression spring when it is in its pre-tensioned state; and a second guide means which constitutes a generally tubular inner wall (32) of the rear housing (14) having a predetermined fourth length (64), a rear end surface (31), a predetermined inner diameter, and second lock-release means, wherein the predetermined fourth length corresponds to the predetermined first (61) and the predetermined second (62) lengths together, and wherein the predetermined inner diameter of the second guide means is somewhat larger than the predetermined outer diameter of the compression spring, such that the compression spring is fully arranged inside said second guide means between the rear end surface (31) and the annular ledge (41) when it is in its pre-tensioned state.