Sensorless Armature Position Detection in Electromagnetic Actuators
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Solution Overview
Problem
Existing electromagnetic actuators face challenges in determining the position of an actuating member without additional sensors, particularly when used in temperature-dependent environments, as the position determination is influenced by temperature and viscosity of fluids.
Innovation Solution
An electromagnetic actuator comprising two coils and a power electronics element connected to a logic unit, where the armature is slidably mounted between the coils, and the position is measured by controlling current and measuring voltage gradients, with a subtractor computing a third voltage gradient based on the armature's position, independent of temperature and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the position of the armature is detected by determining the differential induction of the coil, then the position can be measured without additional sensors, but the measurement is highly dependent on temperature due to resistance changes
Solution Approach 1:
The patent changes the measurement parameter from resistance-based differential induction to inductance-based voltage gradient measurement. By measuring the voltage gradient dU/dt during current reversal and relating it to the inductance L (where L depends on armature position), the system achieves temperature-independent position measurement since inductance changes are dominated by geometric factors rather than resistive temperature effects
Solution Approach 2:
The patent replaces the electrical resistance measurement method with an electromagnetic inductance measurement method. Instead of measuring voltage based on resistance changes (which are temperature-dependent), the system measures the voltage gradient resulting from inductance changes, thereby substituting one measurement principle with another that is less sensitive to temperature
2Measurement precision
If the position is determined by counter-induction during armature movement, then position can be measured, but the measurement is highly dependent on fluid viscosity and temperature
Solution Approach 1:
The patent performs the measurement action before the harmful effect (fluid viscosity) can influence the result. By applying a voltage step and measuring the initial voltage gradient dU/dt at the moment of current reversal, the system captures the inductance state before fluid drag and viscosity effects significantly alter the armature velocity, thereby eliminating fluid-dependent measurement errors
3Measurement precision
If additional sensors are used for position detection, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent makes the existing coils serve multiple functions: they act as both actuating elements (generating electromagnetic force to move the armature) and as measurement sensors (detecting armature position through inductance changes). This multi-functionality eliminates the need for separate position sensors, reducing device complexity while maintaining measurement capability
Solution Approach 2:
The patent merges the actuation function and measurement function into a single integrated system. The same coils that generate electromagnetic force for armature actuation are also used to detect position through their inductance characteristics, combining what would traditionally require separate components into one unified system
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 precise position determination of the actuating member without additional sensors, reducing costs and installation space, while being independent of temperature and interference effects.
Implementation Method 1
the inductance of a coil increases when an armature is inserted. Since the resistance of a coil depends on the inductance thereof, the armature position influences the voltage gradient
Data Source
AI summary
An electromagnetic actuator and a method for controlling the actuator comprising at least one armature (3) and two coils (1, 2). The voltage gradient at the two coils (1, 2) is measured during a sudden increase in voltage. From this measured data, a subtractor (16) computes a third voltage gradient (25) from which a logic unit (17) determines the position of the armature (3) without the use of an additional sensor.