Injection Device Contact Detection via Motor Current Monitoring
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Solution Overview
Problem
Existing injection devices face challenges in accurately positioning the dispensing member relative to the reservoir, leading to potential liquid drug dispensing issues due to delayed motor control and reaction times.
Innovation Solution
An injection device with a controller that compares a reference motor value to a captured instantaneous motor value, detecting contact between the dispensing member and reservoir element by monitoring changes in their relationship, ensuring the motor force is below the breakaway force required to move the reservoir, thereby preventing unintended drug dispensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the motor is stopped immediately when the dispensing member contacts the piston, then the piston position can be detected accurately, but the control circuit shows reaction time or lag time making immediate stopping challenging
Solution Approach 1:
The system performs preliminary monitoring of motor current values during the approach phase before actual contact occurs. By continuously capturing and comparing instantaneous motor current values against reference values, the system detects the impending contact condition and triggers motor stopping in advance, compensating for the control circuit's reaction time and ensuring accurate piston position detection.
2Manufacturing precision
If the motor force is increased to move the reservoir element, then the dispensing member can be positioned accurately, but liquid drug may be dispensed unintentionally
Solution Approach 1:
The system continuously monitors the motor current value during the approach phase and uses this feedback to detect when the dispensing member contacts the piston. By comparing the instantaneous motor current against reference values, the system identifies the contact condition and stops the motor immediately, preventing any further force application that would cause unintended drug dispensing while ensuring accurate positioning.
3Reliability
If the motor current is monitored continuously, then contact detection is improved, but the device complexity increases
Solution Approach 1:
The system uses the motor's own current consumption as the detection signal, eliminating the need for separate sensors. The control circuit monitors the motor current value that is already being drawn by the motor during operation, and by comparing this self-generated signal against reference values, the system detects contact conditions without adding external sensing components, thus maintaining simplicity while improving reliability.
Data Source
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AI summary
The invention relates to an injection device (1) for dispensing a liquid drug from a reservoir (5). The injection device (1) comprises a controller (50) that is provided with a reference motor value for operating a motor (53) of the injection device (1) and a captured instantaneous motor value. The controller (50) is further adapted to determine a relationship between the reference motor value and the instantaneous motor value. When the moving dispensing member (21, 20) abuts the reservoir element (6) the relationship changes and the controller (50) is adapted to detect the contact based on the change, wherein a force exerted by the dispensing member, when driven by the motor according to the reference motor value, onto the reservoir element is below a breakaway force required to overcome a static friction force of the reservoir element (6).