Torque Sensor External Field Compensation
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Solution Overview
Problem
Existing electric hand tools with magnetostrictive torque sensors face measurement errors due to external magnetic fields, which can interfere with the accurate determination of torque applied to the shaft.
Innovation Solution
An electric hand tool equipped with a magnetostrictive torque sensor that includes a 3D magnetic field sensor, such as an AMR, TMR, GMR, CMR, or EMR sensor, to measure the total magnetic field, including the field generated by the magnetized torque-transmitting part and external magnetic fields. A processor corrects the total magnetic field for external interference, allowing for accurate torque determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetostrictive torque sensor with coils is used to measure torque, then torque measurement capability is achieved, but measurement precision deteriorates due to interference from external magnetic fields
Solution Approach 1:
The patent converts the harmful external magnetic field interference into a beneficial measurement component. By using a 3D magnetic field sensor to measure the total magnetic field (including external fields) and comparing it with the magnetic field measured during calibration (without external fields), the system extracts only the torque-related magnetic field changes. This approach transforms the previously harmful external fields into a reference baseline that enables more accurate torque measurement through differential measurement.
Solution Approach 2:
The patent introduces a 3D magnetic field sensor as an intermediary measurement device. This sensor acts as a mediator that captures both the torque-generated magnetic field and the external magnetic field interference simultaneously. By using this intermediary sensor to measure the total magnetic field and then processing the data to separate the torque component from external interference, the system achieves accurate torque measurement while accounting for environmental magnetic field conditions.
2Measurement precision
If external magnetic field compensation is implemented, then torque measurement accuracy is improved, but device complexity increases due to additional sensors and processing
Solution Approach 1:
The patent makes the magnetic field sensor multi-functional by using it for both calibration (to capture external field characteristics) and operational measurement (to detect torque-induced field changes). This universal use of the same sensor for multiple purposes reduces the need for separate dedicated sensors for calibration and measurement, thereby reducing overall device complexity while maintaining measurement accuracy through the differential measurement approach.
Solution Approach 2:
The patent performs preliminary calibration to establish a baseline magnetic field profile that includes all external field interferences before actual torque measurement begins. This preliminary action captures the environmental magnetic field characteristics during a torque-free state, creating a reference that is then used during operational measurements to subtract external field effects. This preliminary calibration step simplifies the ongoing measurement process by pre-characterizing the external interference environment.
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 enables more accurate measurement of torque applied to the shaft by compensating for external magnetic fields, thereby improving the precision of torque measurement in electric hand tools.
Implementation Method 1
A magnetostrictive torque sensor for measuring a torque applied to the shaft via the driving unit, wherein the magnetostrictive torque sensor comprises a magnetized torque-transmitting part
Implementation Method 2
a 3D magnetic field sensor, in particular a magnetoresistive sensor, e.g. AMR (anisotropic magnetoresistance), TMR (tunnel magnetoresistance), CMR (colossal magnetoresistance), GMR (giant magnetoresistance) or EMR (extraordinary magnetoresistance) magnetic field sensor
Data Source
Figure 1
AI summary
The invention relates to an electric hand tool comprising a driving unit for driving a shaft of the electric hand tool and configured to drive, via the shaft, a socket of the electric hand tool or a socket connectable to the electric hand tool; a magnetostrictive torque sensor for measuring a torque applied to the shaft via the driving unit; wherein the magnetostrictive torque sensor comprises a magnetized torque-transmitting element and a 3D magnetic field sensor, wherein the 3D magnetic field sensor is configured for measuring a total magnetic field, the total magnetic field including the magnetic field generated by the magnetized portion of the shaft and an interfering external magnetic field; and a processor for at least partially correcting the total magnetic field for the interfering external magnetic field to obtain a corrected magnetic field corresponding to the magnetic field generated by the magnetized torque-transmitting element, and for determining the torque applied to the shaft via the driving unit based on the corrected magnetic field.