Magnetic Position Sensor with Flux Density Detection
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Solution Overview
Problem
Existing noncontact position sensors using soft-magnetic cores are sensitive to external magnetic fields, leading to measurement errors due to nonlinear magnetization and impedance changes, particularly in active magnetic bearing systems where sensors are close to electromagnetic actuators.
Innovation Solution
The position sensor determines target displacement based on the distribution of the AC magnetic field in the air gap between the sensor head and target, using a soft-magnetic core with a high impedance excitation coil and a magnetic flux density sensor, minimizing the impact of soft-magnetic core properties and orthogonal displacements on the measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a soft-magnetic core is used in the position sensor, then the sensor can generate magnetic flux in the magnetic circuit, but the sensor becomes sensitive to external magnetic fields causing measurement errors
Solution Approach 1:
The patent introduces a magnetic shielding structure as an intermediary element between the soft-magnetic core and external magnetic fields. This shielding layer mediates the interaction by blocking external magnetic field lines from penetrating into the sensor core, thereby protecting the measurement system while preserving the core's magnetic flux generation capability for normal sensor operation
Solution Approach 2:
The patent modifies the magnetic properties of the core material by changing its operating parameters, specifically operating the core in a linear magnetization region by controlling the excitation coil current. This parameter change ensures that the core responds linearly to applied fields, reducing measurement errors caused by nonlinear magnetization effects
2Measurement precision
If the excitation coil operates at high voltage to improve signal strength, then the measurement sensitivity increases, but the coil overheats due to excessive current
Solution Approach 1:
The patent changes the operating parameters of the excitation coil by increasing the excitation frequency while maintaining moderate voltage levels. This frequency change allows the system to achieve sufficient signal strength through improved magnetic coupling and faster flux changes, without requiring high voltages that would cause excessive current and overheating
Solution Approach 2:
The patent employs periodic AC excitation at optimized frequencies to generate magnetic flux in the magnetic circuit. This periodic action at the right frequency maximizes the induced signal in the pickup coil while allowing the coil to dissipate heat between cycles, preventing continuous overheating that would occur with DC or low-frequency high-voltage operation
3Length of moving object
If the sensor target is displaced in orthogonal directions to improve measurement range, then the sensor can detect larger displacements, but measurement accuracy decreases due to nonlinear effects
Solution Approach 1:
The patent divides the measurement function into two independent components: a primary sensor for measuring displacement in the main direction (X-axis) with high accuracy, and a secondary sensor for measuring orthogonal displacement (Y-axis). This segmentation allows each sensor to operate within its optimal linear range, maintaining measurement precision while extending the overall measurement capability through coordinate transformation
Solution Approach 2:
The patent addresses orthogonal displacement effects by introducing measurement in a second dimension. Instead of allowing orthogonal displacement to degrade single-axis measurement accuracy, the system measures both X and Y displacements independently and uses coordinate transformation to calculate the true position, effectively converting a source of error into additional useful measurement information
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 approach reduces measurement errors caused by external magnetic fields and allows for high voltage operation without overheating, providing accurate and robust position sensing with reduced sensitivity to soft-magnetic core properties and orthogonal displacements.
Implementation Method 1
a conductive excitation coil coiled around the soft-magnetic core and adapted to produce an AC magnetic flux in the magnetic circuit
Implementation Method 2
a magnetic flux density sensor fixed in relation to the sensor head and residing in the air gap between the soft-magnetic core and the sensor target, the magnetic flux density sensor configured to detect magnetic flux density in a portion of the air gap
Data Source
AI summary
Noncontact measuring of positions of objects is achieved through measurements of parameters characterized by the distribution of an AC magnetic flux in the air gap between stationary and moveable portions defining a sensor magnetic circuit. A sensor head fixed relative to a stationary element includes a soft-magnetic core. A sensor target is fixed relative to a movable element, the soft-magnetic core and the sensor target separated by an air gap and defining a magnetic circuit. A coil around the soft-magnetic core is adapted to produce a magnetic flux in the magnetic circuit. A magnetic flux density sensor fixed relative to the sensor head resides in the gap between the soft-magnetic core and the sensor target and is configured to detect magnetic flux density in a portion of the gap. A controller in communication with the magnetic flux density sensor is configured to receive an output signal of the magnetic flux.