Auto-Injector Gearbox Adapts Spring Force for Consistent Dosing
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Solution Overview
Problem
Auto-injectors driven by springs face challenges in delivering a consistent dose due to varying spring force throughout the injection cycle, leading to potential underdosing, discomfort, and increased risk of needle breakage, particularly in elderly or dexterity-impaired users.
Innovation Solution
A gearbox is introduced to convert the translational force of a compression spring into a modified output force and distance, allowing for the adaptation of spring force to reduce initial impact, ensure steady dose delivery, and provide consistent needle insertion, using screw threads with varying pitch angles and cam tracks to distribute load effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a spring is used to drive the injection, then the injection can be automated, but the spring force varies throughout the injection cycle causing inconsistent dose delivery
Solution Approach 1:
A gearbox mechanism is introduced as an intermediary between the spring and the plunger. The gearbox includes a drive collar connected to the spring, a drive sleeve with a first screw thread engaged to the drive collar, and a plunger with a second screw thread engaged to the drive sleeve. This mechanical intermediary transforms the varying spring force into a more consistent output force applied to the plunger, resolving the contradiction between automation and dose consistency.
Solution Approach 2:
The patent employs screw threads with varying pitch angles to change the mechanical parameters of force transmission. By using a first screw thread with a first pitch angle and a second screw thread with a second pitch angle, the system transforms the spring's varying force into a modified output force that maintains more consistent pressure on the plunger throughout the injection cycle, ensuring reliable dose delivery.
2Speed
If high spring force is applied at the beginning of injection, then needle insertion is achieved, but the risk of needle breakage and user discomfort increases
Solution Approach 1:
The gearbox mechanism dynamically adapts the force transmission ratio during the injection cycle. The varying pitch angles of the screw threads create a dynamic mechanical advantage that automatically adjusts the output force based on the injection stage. During needle insertion, the gear ratio limits the peak force transmitted to the needle, reducing breakage risk while still achieving sufficient insertion speed. This dynamic parameter adjustment resolves the contradiction between insertion speed and safety.
3Device complexity
If manual button pressing is used, then the device structure is simple, but the user must continuously apply force causing hand shaking and discomfort
Solution Approach 1:
The spring-driven gearbox mechanism performs the injection task autonomously without requiring continuous user force application. The spring automatically converts its stored energy through the gearbox to drive the plunger, eliminating the need for the user to continuously press a button. This self-service mechanism resolves the contradiction by accepting increased device complexity in exchange for dramatically improved ease of operation and user comfort.
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 gearbox reduces user discomfort, minimizes the risk of needle breakage, ensures consistent dose delivery, and improves the repeatability of the injection cycle by adapting the spring force, allowing for tailored force application during different operational steps.
Implementation Method 1
A drive sleeve is rotatably arranged at least partially inside the drive collar, engaged to the drive collar by a first screw thread... A plunger is arranged at least partially inside the drive sleeve, engaged to the drive sleeve by a second screw thread
Data Source
Figure 1A~1B
Figure 1C~3
Figure 4A~4B
AI summary
The invention relates to a gearbox for converting a first translation into a second translation, the gearbox comprising a drive collar (13) connectable to a translative drive means (11) and prevented from rotating with respect to a ground (12) of the drive means (11), a drive sleeve (14) rotatably arranged at least partially inside the drive collar (13), engaged to the drive collar (13) by a first screw thread (15) and prevented from translating, wherein a plunger (8) is arranged at least partially inside the drive sleeve (14), engaged to the drive sleeve (14) by a second screw thread (16) and prevented from rotating.