Injection Device Dose Setting Mechanism
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Solution Overview
Problem
Existing injection devices for medicaments lack a simple and reliable mechanism for setting and correcting doses, particularly in devices with compression springs, which can be complex and less efficient compared to torsional springs.
Innovation Solution
The injection device incorporates a compression spring mechanism with a dose setting sleeve, toothed gear, ratchet arms, and a piston rod with ratchet teeth, allowing for precise dose selection and adjustment through a rotatable dose knob and axially translatable button, enabling the user to increase or reduce dose volume and reset the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a compression spring mechanism is used in the injection device, then the construction is simpler and the device is smaller, but the mechanism for setting and correcting doses becomes more complex
Solution Approach 1:
The patent combines multiple functions into integrated components. The dose setting sleeve integrates both dose selection (through rotational engagement with the dose knob) and dose correction (through ratchet arm engagement with the toothed gear) functions. The driving element combines threaded connection for axial movement with ratchet teeth for unidirectional locking, merging positioning and locking functions into a single component.
Solution Approach 2:
The toothed gear serves multiple purposes: it engages with ratchet arms for dose correction, interacts with the driving element for axial translation, and works with the button sleeve for reset functionality. The ratchet arms both prevent backward movement during dose setting and enable correction when engaged with the toothed gear, demonstrating multi-functionality that reduces overall system complexity.
2Volume of moving object
If a compression spring is used instead of a tensed spring, then the spring can be mounted directly between movable elements and is smaller, but the mechanism for storing and releasing energy becomes more complex
Solution Approach 1:
The energy storage and release mechanism is segmented into distinct functional phases. The compression spring is pre-loaded during the dose setting phase through rotational movement of the dose knob, which translates to axial compression of the spring. During the injection phase, the spring automatically releases its stored energy to drive the piston rod. This segmentation of loading and release phases simplifies the overall mechanism compared to systems requiring active control of energy release.
Solution Approach 2:
The compression spring is pre-loaded with potential energy during the dose setting phase before injection is required. This preliminary action of storing energy in advance eliminates the need for complex active control mechanisms during injection. The pre-compressed spring automatically releases its stored energy when the trigger is activated, providing a simple and reliable energy delivery system.
3Measurement precision
If the dose setting sleeve is rotationally engaged with the dose knob and axially moved by threaded connection, then precise dose selection is achieved, but the mechanism becomes more complex
Solution Approach 1:
The patent employs rotational movement of the dose knob to drive the dose setting sleeve through a threaded connection. This converts rotational motion into precise axial displacement, where each rotation increment corresponds to a specific dose volume. The circular threading geometry provides mechanical advantage and precise positioning, while the ratchet arms with teeth engage the toothed gear to prevent backward movement and enable discrete dose corrections.
Solution Approach 2:
The dose setting sleeve acts as an intermediary component that translates rotational input from the dose knob into axial positioning for dose selection. It mediates between the user's rotational input and the piston rod's axial position, using the threaded connection to convert motion types and the ratchet mechanism to maintain precise positioning and enable correction.
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 mechanism provides a simple, reliable, and compact solution for delivering precise medicament doses, allowing users to select, increase, or reduce dose volumes, and reset the device efficiently, suitable for therapies requiring multiple injections.
Implementation Method 1
Automatic injectors comprise an element for storing energy which is subsequently used for driving the piston rod during injection of a dose. This element is usually a spring which is preloaded by a user by means of a knob, the displacement of which is transferred to the spring by the mechanism of the injector. The deformation of the spring results in that energy is stored within.
Implementation Method 2
a non-rotatable tubular driving element slidingly mounted in the housing, the driving element being engaged with the dose setting sleeve by a threaded connection
Implementation Method 3
the dose setting sleeve is equipped with at least one ratchet arm cooperating with the toothed gear; the piston rod has at least one row of ratchet teeth on its external surface
Data Source
AI summary
An injection device comprising a housing (1) and a cartridge holder (2, 20), the housing (1) being provided on the proximal side with a rotatable dose knob (4, 40) and an axially translatable button (5, 50). The housing (1) comprises: a dose setting sleeve (6, 60), a non-rotatable tubular driving element (7, 70) slidingly mounted in the housing (1) and engaged with the dose setting sleeve (6, 60) by a threaded connection, a non-rotatable axially sliding piston rod (15,150), a toothed gear (8, 80) comprising teeth (8.1, 80.1), a driving spring (13, 130). The dose setting sleeve (6, 60) is equipped with at least one ratchet arm (6.4, 60.4) cooperating with the toothed gear (8, 80); the piston rod (15, 150) has at least one row of ratchet teeth (15.1, 150.1) on its external surface; the driving element (7, 70) is on its distal side fixedly connected with at least one driving arm (14, 140) cooperating with the ratchet teeth (15.1, 150.1) of the piston rod (15, 150). The injection device further comprises: a non-rotatable and axially slidable button sleeve (9, 90) engaged on its proximal side with the button (5, 50), an immovable auxiliary sleeve (10, 100) located within the driving element (7, 70), wherein the button sleeve (9, 90) is detachably and slidingly engaged with the toothed gear (8, 80) and the button sleeve (9, 90) is slidingly engaged with the auxiliary sleeve (10, 100) by means of a coupling spring (12, 120).