Autoinjector Plunger Position Sensing for High-Speed Delivery
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Solution Overview
Problem
Mechanically powered autoinjectors face challenges in accurately detecting the movement and position of the plunger driver due to high-speed movements, which can lead to unreliable operation and potential failure of bulky mechanical switches, and Hall effect sensors struggle to detect these movements at typical operating speeds.
Innovation Solution
The autoinjector employs contactless proximity sensors, such as Hall effect sensors, with detection features fixed relative to the plunger driver and the main housing, allowing precise detection of the plunger's position and movement using a magnet or ferromagnetic component, and a linear rheostat with a resistance element to provide signals indicative of the plunger's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical switches are used to detect plunger driver position, then detection function is provided, but device size increases and reliability decreases due to bulk and susceptibility to failure at high speeds
Solution Approach 1:
The patent replaces mechanical switches with Hall effect sensors that detect the position of a magnet attached to the plunger driver. This substitution eliminates mechanical contact, reducing device size and improving reliability by avoiding mechanical wear and failure at high speeds.
Solution Approach 2:
The patent introduces a magnet as an intermediary element that couples the plunger driver to the Hall effect sensor. This magnetic intermediary enables contactless detection of plunger driver position, resolving the contradiction between reliable detection and compact design.
2Device complexity
If Hall effect sensors are used to detect plunger driver movement, then device size is reduced, but detection precision deteriorates at high speeds due to limited sampling frequency
Solution Approach 1:
The patent employs multiple Hall effect sensors positioned at different locations along the plunger driver's path. This dynamic arrangement ensures that at least one sensor remains within detection range during high-speed movement, maintaining measurement precision while preserving device compactness.
Solution Approach 2:
The patent divides the detection function across multiple Hall effect sensors rather than relying on a single sensor. This segmentation allows continuous monitoring of plunger driver position throughout its travel, overcoming the limited sampling frequency of individual sensors at high speeds.
3Ease of operation
If micro-switches are used for detection, then detection function is provided, but device reliability decreases due to susceptibility to failure at high speeds
Solution Approach 1:
The patent replaces mechanical micro-switches with Hall effect sensors that provide contactless detection. This eliminates mechanical wear and failure modes, significantly improving operational reliability while maintaining the detection function.
Solution Approach 2:
The patent uses a magnet as an intermediary to transfer position information from the plunger driver to the Hall effect sensor without mechanical contact. This magnetic mediation ensures reliable detection throughout the plunger driver's high-speed travel.
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 solution enables accurate and reliable detection of the plunger's position and movement, ensuring precise drug delivery and user feedback, while maintaining a compact device design and reducing the risk of mechanical failure.
Implementation Method 1
Hall effect sensors struggle to detect these movements at typical operating speeds
Implementation Method 2
a contactless proximity sensor and a detection feature for detection by the contactless proximity sensor
Data Source
AI summary
An autoinjector comprises a main housing for receiving a syringe or cartridge, and a drive mechanism located substantially within the main housing for providing motive force. The drive mechanism comprises a plunger driver movable through the housing, between a stationary start position and a stationary end position, to apply said motive force to a plunger of the syringe or cartridge. The autoinjector further comprises a contactless proximity sensor and detection feature, one of which is fixed with respect to the main housing and the other being fixed with respect to the plunger driver. When the plunger driver is in one of the stationary start position and the stationary end position, the detection feature is located at a position within a sensing region of the contactless proximity sensor and, for substantially all of the travel of the plunger driver between the stationary start position and stationary end position, the detection feature is located outside of the sensing region of the contactless proximity sensor.