Variable Pitch Threads for Injection Pen Force Reduction
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Solution Overview
Problem
Existing drug delivery pens have limited mechanical advantage, making it difficult to perform intradermal medication injections due to high backpressure, requiring excessive force and being costly to manufacture, while existing solutions either fail to provide sufficient force amplification or reduce the maximum dose range.
Innovation Solution
A pen injector system with variable pitch dose setting threads that provide a mechanical advantage by increasing the pitch at the beginning of the injection to reduce the required force, gradually transitioning to a smaller pitch to maintain the maximum dose deliverable without increasing the device length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If standard pitch threads are used in the pen injector system, then the device structure is simple and manufacturing is easy, but the required injection force is excessive for intradermal medication injection
Solution Approach 1:
The patent applies the dynamics principle by implementing a variable pitch thread design where the pitch changes along the length of the thread. The proximal portion has a larger pitch to provide higher mechanical advantage and reduce injection force, while the distal portion has a smaller pitch to maintain dose range. This dynamic variation in thread geometry allows the system to adapt its mechanical properties along the direction of force application, resolving the contradiction between reducing force and maintaining structural simplicity.
Solution Approach 2:
The patent applies parameter changes by varying the pitch parameter of the thread along its length. The pitch transitions from a larger value at the proximal end to a smaller value at the distal end. This continuous or stepped change in the geometric parameter allows optimization of force requirements at different stages of injection while maintaining the overall functionality of the dosing mechanism.
2Force
If the pitch of dose setting threads is increased to reduce required force, then injection force is reduced, but the maximum dose deliverable is compromised
Solution Approach 1:
The patent applies local quality by assigning different pitch characteristics to different portions of the thread. The proximal portion (closer to the user's thumb) has a larger pitch optimized for reducing injection force, while the distal portion (closer to the cartridge) has a smaller pitch optimized for maintaining maximum dose delivery. This spatial differentiation of thread properties allows each portion to fulfill its specific function without compromising the other.
3Ease of operation
If variable pitch threads are implemented to reduce injection force, then force amplification is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the thread into distinct portions with different pitch characteristics. Rather than attempting to manufacture a continuously variable pitch thread, the design segments the thread into a proximal portion with larger pitch and a distal portion with smaller pitch. This segmentation simplifies manufacturing while still achieving the desired force reduction effect during the critical initial phase of injection.
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 variable pitch design reduces the force needed for intradermal medication injection, allowing for a comfortable thumb force and higher dose range without compromising the maximum dose deliverable, while maintaining efficient manufacturing costs.
Implementation Method 1
variable pitch threads provide a mechanical advantage to reduce the required injection force for an intradermal medication injection
Data Source
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AI summary
A pen body assembly (100) for a drug delivery pen includes a pen body (101) and a dose setting body (111) movably connected to the pen body (101). A knob (109) is connected to the dose setting body (111) for moving the dose setting body (111) relative to the pen body (111). One of the pen body (101) and the dose setting body (111) has a thread groove (107) having a varied pitch disposed thereon and the other one has a protrusion (105) engaging the thread groove (107).