Flux Gate Magnetometer with Demagnetization Coil for Torque Sensing
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Solution Overview
Problem
Magnetic hysteresis in magnetoelastic torque transducers leads to inaccuracy in torque measurements due to non-zero magnetic field amplitude after stimulus removal, affecting the reliability of force sensors.
Innovation Solution
A magnetometer design featuring inner and outer coils with magnetically saturatable elements, generating alternating magnetic fields that oppose and cancel external fields, reducing hysteresis by maintaining zero net flux and minimizing residual magnetism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flux gate sensor is used to detect magnetic field asymmetry, then measurement capability is provided, but magnetic hysteresis causes the zero-torque magnetic field to not return to zero amplitude, reducing measurement precision
Solution Approach 1:
The patent applies preliminary anti-action by generating a demagnetization field that opposes and cancels the residual magnetic flux in the magnetoelastic material. The flux gate sensor detects the asymmetry in the magnetic field, and a demagnetization coil generates an opposing field to actively counteract the hysteresis effect, ensuring the magnetic field returns to zero after torque removal.
Solution Approach 2:
The patent implements feedback by using the flux gate sensor to continuously monitor the magnetic field asymmetry and using this information to control the demagnetization coil. The sensor output feeds back to the demagnetization system, which adjusts the demagnetization field strength to actively compensate for and eliminate the residual magnetic flux caused by hysteresis.
2Ease of operation
If alternating current is used to provide periodic magnetic saturation, then sensing capability is enabled, but magnetic hysteresis varies with the square of the magnetic flux, creating measurement errors
Solution Approach 1:
The patent uses an intermediary approach by introducing a demagnetization coil as a mediator between the flux gate sensor and the magnetoelastic material. This coil generates a controlled demagnetization field that actively manages the magnetic flux in the magnetoelastic material, reducing hysteresis effects while preserving the sensing operation enabled by alternating current excitation.
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
The solution enhances measurement accuracy by reducing magnetic hysteresis, providing precise and reliable torque sensing by minimizing residual magnetic flux and improving the overall performance of the torque sensor assembly.
Implementation Method 1
A flux gate sensor, which is fabricated as a coil of magnet wire that generates a magnetic field to magnetically saturate a core of magnetically saturatable material
Implementation Method 2
The magnetic field produced by the force transducer is superimposed on the periodic magnetic field generated by the coils. The superimposing the magnetic field produced by the torque transducer shaft creates an asymmetry in the magnetic saturation of the coils. Changes in the inductance of the coils due to the magnetic saturation results in a voltage that is induced to the coils
Implementation Method 3
The force transducer element typically includes a magnetoelastic material that responds to the application of force by generating a magnetic field. The application of force to the magnetoelastic material creates shear stresses within the magnetized regions causing the direction of the magnet field generated by the force transducer element to shift from a substantially circumferential direction to a helical direction
Implementation Method 4
The inner coils generate a magnetic field in a first direction and the outer coils generate a magnetic field in a second direction that is opposite the first direction. The opposing magnetic fields created by the inner and outer coils concentrate the emitted field into the magnetically saturable elements, and largely cancel any externally magnetic field
Data Source
AI summary
A magnetometer for a force sensor assembly includes first inner and outer coils that are spaced axially apart from second inner and outer coils. Between the inner and outer coils is a plurality of magnetic strips. These magnetic strips are disposed at axially distinct portions within the inner and outer coils to detect magnetic field asymmetry. A drive circuit is connected to the inner coils and the outer coils generate an alternating magnetic field. The magnetometer of this invention creates an artificially enhanced demagnetization field reducing hysteresis within the sensor assembly.