Pre-Filled Injector Assembly for Air-Gap-Free Piston Positioning
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Solution Overview
Problem
Existing pre-filled injection devices often require a manual priming process to eliminate the air-gap between the piston rod and the plunger, which is inconvenient and can lead to incorrect dose delivery due to manufacturing tolerances.
Innovation Solution
A pre-filled injection device design featuring a piston rod with an outer thread and a rotatable drive element, coupled with a nut element through a one-way ratchet interface, allowing rotation in a single direction to advance the piston rod and eliminate the air-gap during assembly, ensuring contact with the plunger without the need for physical connections like welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If manual priming is required to eliminate air-gap, then device assembly is simpler, but dose delivery accuracy deteriorates and user convenience worsens
Solution Approach 1:
The piston rod is pre-adjusted during assembly to eliminate the air-gap before the device is delivered to the user. The nut element is rotated to advance the piston rod until it contacts the plunger, establishing the correct zero-point position in advance, so that no manual priming is needed during use.
Solution Approach 2:
The position of the piston rod is adjusted by changing the rotational position of the nut element relative to the piston rod. By rotating the nut element, the axial position of the piston rod is modified to eliminate the air-gap, transforming the parameter of piston rod position from a toleranced value to a precise contact position.
2Manufacturing precision
If manual priming is required to eliminate air-gap, then manufacturing tolerances can be larger, but user convenience and time efficiency deteriorate
Solution Approach 1:
The air-gap elimination is performed as a preliminary action during device assembly rather than requiring the user to perform manual priming during operation. The piston rod position is adjusted and fixed before the device reaches the user, eliminating the need for time-consuming priming steps.
Solution Approach 2:
The device performs its own zero-point adjustment automatically during assembly through the rotation of the nut element, without requiring external intervention or user operation. The mechanism self-adjusts the piston rod position to eliminate the air-gap, making the device ready for immediate use.
3Manufacturing precision
If physical connections like welding are used to eliminate air-gap, then position precision improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The nut element serves as an intermediary mechanism between the piston rod and the housing structure. Instead of directly welding or physically connecting the piston rod to achieve precise positioning, the nut element mediates the position adjustment through threaded engagement, allowing precise control without permanent physical connections.
Solution Approach 2:
The mechanical adjustment system using the nut element and threaded piston rod replaces complex physical connection methods like welding. The threaded mechanism provides precise, reversible, and tool-free adjustment capability, substituting permanent mechanical bonds with a controllable mechanical adjustment system.
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 enables easy elimination of the air-gap during assembly, ensuring accurate dose delivery without manual priming and maintaining the integrity of the device, suitable for both multi-use fixed dose and variable dose devices.
Implementation Method 1
a one-way ratchet interface between the nut element and the housing structure, allowing the nut element to be rotated in a first rotational direction, in which the piston rod is advanced
Implementation Method 2
a threaded connection between the piston rod and the nut element, such that rotation of the piston rod in relation to the nut element advances the plunger in the cartridge
Data Source
Figure 1
Figure 2A~2B
Figure 3~4
AI summary
The invention relates to a pre-filled injection device with a non-removable cartridge wherein the drive mechanics comprises a threaded piston rod which is moved helically in a nut secured to a housing structure. During assembly of the injection device it is possible to rotate the nut member to thereby advance the piston rod into a position eliminating any air-gap otherwise occurring between the piston rod and the plunger inside the cartridge