Magnetoelastic Torque Sensor Near Field Rejection
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Solution Overview
Problem
Current torque sensors are prone to measurement errors due to divergent near magnetic fields, which cannot be effectively canceled using existing shielding or flux director methods, especially when near fields propagate through shafts or are influenced by ferromagnetic structures, leading to inaccurate torque readings.
Innovation Solution
A configuration of three sets of magnetic field sensors placed above different sections of a shaft, with the central sensor having opposite polarity to the side sensors, effectively cancels out near field measurements by averaging and opposing the signals, while preserving torque-induced magnetic field measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If shielding materials with high magnetic permeability are used to block external magnetic fields, then field rejection is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The invention extracts and separately measures the interfering near field component using additional magnetic field sensors, then subtracts it from the total measurement. This approach removes the harmful near field effect through measurement and calculation rather than through physical shielding structures.
Solution Approach 2:
The invention replaces the mechanical/physical shielding approach (using high permeability materials) with a computational approach. Instead of blocking fields with physical barriers, the system uses mathematical processing of sensor signals to eliminate near field interference.
2Productivity
If flux directors are used to guide torque dependent magnetic fields to sensors, then measurement efficiency is improved, but susceptibility to external fields perpendicular to shaft axis increases
Solution Approach 1:
The invention applies different functional qualities to different parts of the sensing system. The three sensors are positioned at different locations with different orientations, allowing each to capture specific components of the magnetic field. This local differentiation enables selective measurement of torque-dependent fields while rejecting external interference.
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 significantly reduces measurement errors caused by near fields, providing more accurate torque readings without the need for shielding materials or flux directors, and is applicable to various magnetized region configurations on the shaft.
Implementation Method 1
a magnetoelastically active region with one or more regions circumferentially magnetized on a shaft to detect a torque-dependent magnetic flux emanating from the active region
Implementation Method 2
three sets of magnetic field sensors placed above different sections of a shaft
Implementation Method 3
the central sensor having opposite polarity to the side sensors, effectively cancels out near field measurements by averaging and opposing the signals
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The present invention involves a method and apparatus for canceling the effects of magnetic field noise in a torque sensor by placing three sets of magnetic field sensors around a shaft, the first set of field sensors being placed in the central region of the shaft and the second and third sets of field sensors being placed on the right side and left side of the field sensors placed at the central region, respectively. A torque-induced magnetic field is not cancelled with this arrangement of field sensors but a magnetic near field from a near field source is cancelled.