Magnetoelastic Torque Sensor Noise Compensation
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Solution Overview
Problem
Current torque sensor technologies are inadequate in effectively canceling the effects of non-torque dependent magnetic fields, particularly at very low frequencies, and are prone to errors due to external magnetic fields, which can lead to inaccurate torque measurements.
Innovation Solution
A torque sensor system with a hollow longitudinally extending member containing a magnetoelastically active region and multiple magnetic field sensors arranged inside to detect and compensate for ambient magnetic fields, using a configuration of primary and secondary sensors to cancel out near-field noise, including those at DC frequencies, without the need for additional shielding or packaging space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic field sensors are used to measure torque-dependent magnetic fields, then torque measurement capability is achieved, but susceptibility to external magnetic fields (compassing error) occurs
Solution Approach 1:
The sensor system is segmented into multiple magnetic field sensors (at least four sensors) arranged in specific configurations. This segmentation allows the system to differentiate between torque-dependent fields and external ambient fields by measuring field components from multiple perspectives and processing them through differential calculations.
Solution Approach 2:
The patent introduces magnetic field sensors as intermediary measurement devices that detect both torque-dependent and ambient magnetic fields. By using these sensors in conjunction with differential measurement techniques, the system mediates between the desired torque measurement and the unwanted ambient field interference, extracting the torque signal while canceling the ambient component.
2Object-affected harmful factors
If two magnetic field sensors with opposite axial polarity are used to cancel far field effects, then far field noise cancellation is achieved, but near field divergent magnetic fields cause unequal field intensities and measurement errors
Solution Approach 1:
The sensor array is segmented into multiple sensors with different orientations and positions. Instead of relying on a single pair of oppositely polarized sensors, the system uses at least four sensors arranged to capture magnetic field components from multiple angles, enabling differential cancellation of both far field and near field interference through coordinated signal processing.
Solution Approach 2:
The patent extends the measurement approach from a single-dimensional opposite polarity arrangement to a multi-dimensional sensor configuration. Sensors are positioned and oriented in three-dimensional space around the shaft, capturing magnetic field information from multiple spatial dimensions. This allows the system to distinguish between uniform far field effects (affecting all sensors equally) and non-uniform near field effects (affecting sensors differently based on position and orientation).
3Object-affected harmful factors
If shielding structures made from high magnetic permeability materials are used to block external magnetic fields, then external field interference is reduced, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical/physical shielding structures with a magnetic field-based differential measurement system. Instead of using high-permeability materials to physically block external fields, the system uses multiple magnetic field sensors and signal processing algorithms to mathematically cancel out external field interference, substituting a field-based measurement approach for a structure-based shielding approach.
Solution Approach 2:
The sensor system performs self-calibration and self-compensation for external magnetic field interference. By continuously monitoring magnetic field components from multiple sensors and using differential measurement techniques, the system automatically identifies and cancels ambient field effects without requiring external shielding structures or manual calibration procedures.
4Measurement precision
If additional magnetic field sensors are added to cancel near field effects, then measurement accuracy improves, but device complexity and packaging space requirements increase
Solution Approach 1:
The magnetic field sensors serve multiple functions simultaneously: they detect torque-dependent magnetic fields, measure ambient magnetic field interference, and provide spatial information for differential cancellation calculations. This multi-functionality allows the system to achieve high measurement accuracy without requiring separate dedicated sensors for each measurement task, thereby reducing overall device complexity.
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 configuration significantly reduces noise from near-field sources, including very low-frequency magnetic fields, ensuring accurate torque measurements and maintaining stability against mechanical impacts and temperature changes, while eliminating the need for costly shielding materials.
Implementation Method 1
The active region comprises at least one region magnetically polarized such that the magnetized polarity becomes increasingly helically shaped as the applied torque increases
Implementation Method 2
A plurality of primary magnetic field sensor is arranged approximate the at least one region for outputting a first signal corresponding to a torque-dependent magnetic flux emanating from the active region
Implementation Method 3
At least one secondary magnetic field sensor is axially spaced in a first direction by a pre-determined first distance from the plurality of primary magnetic field sensors for outputting a second signal corresponding to an ambient magnetic flux emanating from a near magnetic field source
Implementation Method 4
The effects of the magnetoelastically active region are detectable by magnetic field sensors at the inner surface (inside) the member... There is also a means for adjusting the first signal using the second and the third signals thereby compensating for the effects of the near magnetic field source
Data Source
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AI summary
The invention provides a method for reducing the noise in a signal from a torque sensor caused by near magnetic field sources. The torque sensor comprises: a at least partially hollow longitudinally extending member, a magneto-elastically active region effective at the inner surface of the member in such a manner that torque applied to the member is proportionally transmitted to the active region, the active region comprising at least one region magnetically polarized such that the magnetized polarity becomes increasingly helically shaped as the applied torque increases; a plurality of primary magnetic field sensors arranged approximate the at least one region for outputting a first signal corresponding to a torque-dependent magnetic flux emanating from the active region; at least one secondary magnetic field sensor axially spaced in a first direction by a pre-determined first distance from the plurality of primary magnetic field sensors for outputting a second signal corresponding to an ambient magnetic flux emanating from a near magnetic field source; at least one secondary magnetic field sensor axially spaced in a second direction opposite the first direction by a pre-determined second distance from the plurality of primary magnetic field sensors for outputting a third signal corresponding to the ambient magnetic flux emanating from the near magnetic field source; means for adjusting the first signal using the second and the third signals thereby compensating for the effects of the near magnetic field source, characterized in that the primary and secondary magnetic field sensors are arranged inside the longitudinally extending member.