Collar Cam Lock Mechanism for Low-Force Auto-Injectors
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Solution Overview
Problem
Existing auto-injectors require high activation and hold forces, leading to user discomfort, incorrect device operation, and incomplete drug delivery due to difficulties in applying these forces, which can result in wet injection sites and partial drug delivery.
Innovation Solution
An injection device with a rotary collar and cam track mechanism that converts axial motion of the needle shroud into rotational motion, featuring a non-return surface to prevent retraction, reducing the required activation and hold forces by using a self-locking mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a needle cover spring is used to automatically extend the needle cover for shielding, then needle shielding is provided automatically, but high hold force is required during injection to counteract the spring force
Solution Approach 1:
A cam mechanism acts as an intermediary between the needle cover spring and the injection plunger. The cam converts the axial spring force into a rotational moment, allowing the force to be applied more efficiently to drive the plunger without requiring the user to directly counteract the full spring force during injection.
Solution Approach 2:
The cam mechanism changes the directional parameter of the spring force, converting axial force into rotational motion. This parameter transformation allows the spring force to be utilized more effectively for plunger activation while reducing the opposing force the user must apply.
2Ease of operation
If high activation force is required to compress the needle cover spring, then the needle cover can be pushed in for activation, but users have difficulty applying this force leading to incorrect operation
Solution Approach 1:
The cam mechanism serves as a mediator that transforms the activation action. Instead of directly compressing a high-force spring, the user rotates the collar which engages the cam track, converting a rotational motion with lower resistance into the linear motion needed to activate the injection mechanism.
Solution Approach 2:
The direct linear compression mechanism is replaced with a rotational cam engagement system. This substitution changes the mechanical interaction from axial force application to rotational moment application, which is easier for users to apply and control.
3Productivity
If the needle cover is held in place during injection, then complete drug delivery is achieved, but users experience discomfort and may remove the device early
Solution Approach 1:
The cam mechanism mediates between the needle cover position and plunger drive, allowing the needle cover to be held in place while the plunger is driven forward through the cam's rotational motion. This separates the holding function from the driving function, improving user comfort while ensuring complete delivery.
4Force
If a rotary collar with cam track is used to convert axial motion to rotational motion, then activation and hold forces are reduced, but the device complexity increases
Solution Approach 1:
The rotary collar with cam track performs multiple functions: it converts axial to rotational motion, provides mechanical advantage to reduce activation force, and includes a non-return surface to prevent accidental retraction. By combining multiple functions into a single component, the added complexity is minimized while achieving multiple benefits.
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 device reduces the activation and hold forces, ensuring smoother operation, complete drug delivery, and secure needle retraction, enhancing user comfort and usability.
Implementation Method 1
a cam track engageable with the shroud pin. The cam track includes: a first portion configured to, during retraction of the needle shroud into the injection device body, guide the shroud pin from an initial position to a hold position and cause the collar to rotate relative to the injection device body
Implementation Method 2
a non-return surface configured to, subsequent to the extension, prevent further retraction of the needle shroud into the injection device body
Data Source
AI summary
According to a first aspect of this disclosure, there is described an injection device includes: a body; a needle shroud retractable into the body including a shroud pin; a collar rotatable with respect to the body and including a cam track engageable with the shroud pin. The cam track includes: a first portion configured to, during retraction of the needle shroud into the body, guide the shroud pin from an initial position to a hold position and cause the collar to rotate relative to the body; a second portion configured to, during extension of the needle shroud from the body subsequent to the retraction, guide the shroud pin from the hold position to a final position and cause the collar to further rotate relative to the body; and a non-return surface configured to, subsequent to the extension, prevent further retraction of the needle shroud into the body.