Drug Delivery Motor Blockage Detection Using Differential Back-EMF
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Solution Overview
Problem
Existing drug delivery devices with elastic plunger moving assemblies face challenges in accurately detecting blockages and occlusions, as traditional methods relying on motor current or Back EMF voltage signals become unreliable due to the elasticity, leading to increased complexity and cost when additional sensors are required.
Innovation Solution
A system and method using a brushless electric motor with a novel evaluation of Back EMF voltage signals, involving commutation cycles, measuring windows, and convergence values to detect blockages by analyzing the divergence of voltage signals across driving contacts, without the need for extra sensors in the fluid path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional blockage detection methods using motor current or Back EMF voltage signals are used in devices with elastic plunger moving assemblies, then the device complexity and cost are reduced, but the detection reliability deteriorates due to signal unreliability caused by elasticity
Solution Approach 1:
The patent changes the detection parameter from traditional motor current or single-point Back EMF voltage to a differential voltage signal obtained by subtracting two Back EMF voltage signals from opposite commutation positions. This parameter transformation eliminates the effect of elastic deformation on the detection signal, thereby maintaining detection reliability without adding device complexity
Solution Approach 2:
The patent introduces a differential measurement approach as an intermediary method. Instead of directly measuring the absolute Back EMF voltage which is affected by elasticity, the system measures the difference between two symmetric voltage signals, using the differential approach as a mediator to cancel out the elastic deformation effects
2Reliability
If additional sensors such as optical sensors or pressure sensors are added to detect blockages, then the detection reliability is improved, but the device complexity and cost increase
Solution Approach 1:
The patent makes the existing motor coils serve dual functions: both as driving elements and as sensing elements for blockage detection. By measuring Back EMF voltages during commutation, the same motor windings provide both propulsion and detection capabilities, eliminating the need for separate sensors and reducing device complexity
Solution Approach 2:
The motor system performs self-diagnosis by using its own operational parameters (Back EMF voltages during commutation) to detect blockages. The system monitors its own performance characteristics without requiring external sensing components, achieving self-service detection functionality
3Measurement precision
If the plunger moving assembly is made rigid to improve blockage detection accuracy, then the detection precision is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent transforms the detection parameter to a differential voltage measurement that is inherently insensitive to elastic deformation. This parameter change allows the use of compliant, easier-to-manufacture plunger assemblies while maintaining high detection precision, as the differential measurement cancels out the effects of material elasticity
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
Enables reliable blockage detection in drug delivery devices with non-rigid actuating assemblies, reducing complexity and cost by directly monitoring the motor's Back EMF voltage signals, ensuring accurate and efficient drug delivery.
Implementation Method 1
An alternative concept for motor control is known as 'back electro-motive force' (Back EMF or BEMF). Sensors are placed at the contacts of an electric motor to sense the voltage induced by motor coils passing the sensor if the motor is rotating.
Data Source
AI summary
A system and a method detects blockage of an actuating assembly in a drug delivery device with a brushless DC or stepper motor. The Back EMF voltage is periodically measured at the driving contacts of the motor. A blockage indication value is periodically calculated based on the divergence of voltages measured at different driving contacts, and an alarming and/or mitigation action is initiated if the blockage indication value meets a predefined criterion such as exceeding a minimum or maximum value.