Infusion Pump Dosing Unit Thread Lash Elimination
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Solution Overview
Problem
Infusion pump devices face challenges with precision dosing of small volumes of liquid medicaments due to high friction and thread lash issues, leading to increased energy consumption and reduced shelf life of disposable units.
Innovation Solution
A dosing unit design with a separate bias force element to eliminate thread lash, featuring a plunger shaft with a thread and a cylinder with a threaded sleeve, where the bias force element ensures constant engagement without play, reducing friction and energy consumption while maintaining precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a plunger is displaced to pump small volumes of liquid medicament, then dosing function is achieved, but high friction between plunger and cylinder walls requires high actuating forces
Solution Approach 1:
The dosing unit is separated from the main reservoir, allowing the plunger to operate in a smaller, dedicated dosing cylinder. This segmentation enables precise dosing of small volumes (nanolitre range) while reducing the overall friction forces compared to pumping the entire reservoir volume.
Solution Approach 2:
A threaded spindle acts as an intermediary mechanism between the drive system and the plunger. The threaded engagement converts rotational motion to linear displacement with mechanical advantage, reducing the actuating force required while maintaining precise control over plunger position and dosing volume.
2Length of moving object
If the cross-sectional area of the plunger is reduced to limit device thickness, then compactness is improved, but friction forces increase and precision is compromised
Solution Approach 1:
The threaded spindle mechanism replaces direct mechanical displacement methods. This substitution allows for precise plunger positioning through rotational control while maintaining a compact cross-sectional area. The thread engagement provides fine-grained control over linear displacement, achieving precision dosing without requiring large plunger dimensions.
3Ease of manufacture
If thread lash is present in the threaded engagement, then assembly is simplified, but dosing precision is reduced due to play between threads
Solution Approach 1:
A bias force element is introduced to apply preliminary compressive force to the threaded engagement. This pre-loading eliminates thread lash and play before operation begins, ensuring precise and repeatable plunger displacement. The bias force element maintains constant contact between thread flanks, preventing the play that would otherwise occur during assembly and operation.
4Reliability
If friction between plunger and cylinder is high to ensure sealing, then sealing reliability is improved, but energy consumption increases
Solution Approach 1:
The system dynamically manages friction through the threaded spindle mechanism. During the dosing phase, the thread engagement provides controlled friction for precise positioning. During the return phase, the mechanism allows easier reversal by managing the friction characteristics of the thread engagement, thereby reducing overall energy consumption while maintaining sealing reliability through the plunger-cylinder interface design.
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 enhances precision, reduces energy consumption, and extends the shelf life of disposable units by minimizing thread lash and maintaining consistent frictional forces, thereby improving the overall performance and reliability of infusion pump devices.
Implementation Method 1
A separate bias force element biases the two threads in regard to each other along the longitudinal axis, such that the threaded engagement of inner thread and outer thread is free of play independent of a direction of a rotational movement and linear displacement of the plunger in regard to the cylinder
Implementation Method 2
One of the two threads is an outer thread and the other one is an inner thread, said two threads engaging with each other in such a way that a rotational movement of the plunger around the longitudinal axis results in an additional linear displacement of the plunger along said longitudinal axis
Implementation Method 3
The plunger has a plug sealingly closing the cylinder, thereby defining a metering cavity between the cylinder head and the plug
Data Source
Figure 1(a)~2(b)
Figure 3(a)~6(b)
Figure 4(a)~4(d)
AI summary
A dosing unit (1) for an infusion pump device comprises a piston pump with a pump cylinder (2) and a plunger (3) arranged within said cylinder, coaxially arranged along a longitudinal axis (20). The plunger has a shaft (32) with a thread (33, 33') and the cylinder has a threaded sleeve part (26) with a thread (23, 23'). One of the two threads is an outer thread and the other one is an inner thread, said two threads engaging with each other in such a way that a rotational movement of the plunger around the longitudinal axis results in an additional linear displacement of the plunger along said longitudinal axis. A separate bias force element (5, 6) biases the two threads in regard to each other along the longitudinal axis, such that the threaded engagement of inner thread and outer thread is free of play independent of a direction of a rotational movement and linear displacement of the plunger in regard to the cylinder.