Auto-Injector Rotary Drive Mechanism for Compact Design
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Solution Overview
Problem
Conventional auto-injectors face challenges in compactness due to the longitudinal plunger arrangements, which occupy significant space within the device, making them less portable and efficient.
Innovation Solution
The auto-injector features a plunger unit with a threaded internal surface that engages a threaded rod element, coupled with a tensioned elastic element. When the locking mechanism is disengaged, the elastic element rotates, causing the threaded rod to rotate and push the plunger unit towards the distal end, displacing the medicament without the need for an extending button.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a longitudinal plunger arrangement is used to push the piston, then the medicament can be delivered effectively, but the device becomes longer and less compact
Solution Approach 1:
The patent transitions from a longitudinal plunger arrangement (1D linear motion) to a rotary-driven linear motion system. The rotary motion of the drive shaft, converted to linear motion through the rack and pinion mechanism, allows the plunger to be positioned transversely across the cartridge rather than longitudinally, reducing the device's length while maintaining medicament delivery capability.
Solution Approach 2:
Instead of pushing the piston directly with a longitudinal plunger, the invention uses a rotary drive shaft that engages with a rack to produce linear motion of the plunger. This inverted approach converts rotational motion into linear motion, allowing for a more compact device architecture where the plunger unit can be positioned perpendicular to the main device axis.
2Reliability
If a longitudinal plunger arrangement is used, then the piston can be pushed effectively, but the device occupies more space within the housing
Solution Approach 1:
The plunger unit is repositioned from a longitudinal arrangement to a transverse arrangement, driven by a rotary mechanism. This dimensional change allows the plunger to operate in a different spatial plane, reducing the volume occupied within the housing while maintaining effective piston displacement capability.
Solution Approach 2:
The rack mechanism is integrated within the housing structure, nested alongside other components. The drive shaft and rack assembly are positioned to utilize available space efficiently, with the rack engaging the drive shaft in a compact configuration that minimizes the overall device volume.
3Ease of operation
If manual plunger extension is used, then the button can be reached, but the extension distance is too great causing inconvenience
Solution Approach 1:
The device eliminates the need for manual plunger extension by incorporating an automatic drive mechanism. The rotary drive shaft, powered by a spring or motor, automatically pushes the plunger into the cartridge and maintains contact during medicament delivery, removing the need for the user to extend a button or plunger manually.
Solution Approach 2:
The manual mechanical operation of extending a plunger button is replaced with an automated rotary-to-linear motion conversion system. The spring-driven or motor-driven rotary mechanism automatically performs the plunger extension and medicament delivery functions, eliminating the need for manual intervention and reducing the required extension distance.
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
This configuration reduces the overall length of the auto-injector, making it more compact and portable while ensuring efficient medicament delivery without the issues associated with manual plunger extension.
Implementation Method 1
a tensioned elastic element fixed to the threaded rod element... when the elastic element is rotationally released, the threaded rod element rotates
Implementation Method 2
the threaded rod element rotates in a first direction, causing the plunger unit to translate towards the distal end of the housing
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
An auto-injector for delivering a liquid medicament comprising: a housing arranged to contain a syringe with a piston for sealing the syringe and displacing the medicament, the housing having a distal end and a proximal end intended to be applied against an injection site; a plunger unit arranged between the piston and the distal end of the housing, the plunger unit comprising a threaded internal surface for receiving and engaging a threaded rod element; and a tensioned elastic element fixed to the threaded rod element, the elastic element and the threaded rod element being fixed against rotation in an initial state, wherein when the elastic element is rotationally released, the threaded rod element rotates in a first direction, causing the plunger unit to translate towards the proximal end of the housing and thereby pushing the piston towards the proximal end of the housing to displace the medicament.