Shaft Torque Measurement via Magnetic Encoding
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Solution Overview
Problem
Conventional torque sensing systems for larger diameter rotating shafts face challenges with accuracy, cost, and practicality due to limitations in magnetostrictive measurement methods, including complex calibration, high current requirements, and difficulties in achieving uniform magnetic encoding across the entire cross-section.
Innovation Solution
A magnetic encoding system that uses conducting members with unipolar current pulses to create sectional encoded regions on the shaft, allowing for non-contact measurement of torque through sensors like Hall Effect or fluxgate sensors, which generates torque-dependent magnetic flux components near the encoded regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetostrictive sensors are used with ferromagnetic shafts to measure torque, then torque measurement capability is achieved, but the magnetostrictive effect is very small requiring complex sensor arrangements and difficult calibration procedures resulting in limited accuracy
Solution Approach 1:
The shaft is divided into multiple magnetically encoded sections along its length, with each section having distinct magnetic polarity. This segmentation allows the use of simpler sensors that detect changes in magnetic field as the shaft rotates, rather than measuring the weak magnetostrictive effect directly across the entire shaft.
Solution Approach 2:
The shaft is pre-encoded with magnetic sections during manufacturing or installation, creating a permanent magnetic pattern. This preliminary magnetic encoding eliminates the need for complex real-time magnetostrictive measurements during operation, as the magnetic pattern provides a stable reference for torque detection.
2Measurement precision
If total shaft encoding is used with current flowing in the axial direction to magnetize the entire cross-section, then magnetic encoding is achieved, but it becomes difficult and costly for larger diameter shafts
Solution Approach 1:
Instead of attempting to magnetize the entire shaft cross-section uniformly, the invention encodes only specific sections or segments of the shaft. This reduces the amount of current required and simplifies the encoding process, making it feasible for larger diameter shafts where full cross-section magnetization would be prohibitively difficult and expensive.
Solution Approach 2:
The magnetic encoding is applied locally to specific regions of the shaft rather than uniformly across the entire cross-section. This localized approach concentrates the magnetization effort where it is most effective for torque detection, reducing overall current requirements and manufacturing complexity while maintaining measurement accuracy.
3Measurement precision
If conventional magnetostrictive measurement methods are used, then torque detection is possible, but complex calibration procedures are required and accuracy is limited
Solution Approach 1:
The shaft is pre-encoded with a known magnetic pattern during manufacturing, creating a stable reference that eliminates the need for complex field calibration procedures. The magnetic sections provide inherent reference points that simplify the calibration process to basic sensor positioning and signal conditioning.
Solution Approach 2:
The magnetic encoding creates a physical copy or representation of the shaft's rotational position and torque state in the magnetic field. Sensors detect this magnetic pattern copy, which is more stable and easier to measure than direct magnetostrictive effects, thereby simplifying calibration and improving accuracy.
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 enhances the accuracy and efficiency of torque measurement by reducing the need for extensive shaft magnetization and minimizing the impact of temperature variations, while allowing for reliable operation in harsh environments.
Implementation Method 1
An encoding source is electrically coupled to the first end of the conducting member and electrically coupled to the other electrode. The encoding source uses unipolar current pulses that are applied to the electrodes and the conducting member, thereby creating sectional encoded regions in the shaft.
Implementation Method 2
In a magnetoelastic system, stress induces an 'easy axis' of magnetization through the strain it produces in the material. This effect is typically used in circularly magnetizing a shaft region, and using a magnetic field sensor to pick up the resulting field.
Implementation Method 3
A magnetic encoding system that uses conducting members with unipolar current pulses to create sectional encoded regions on the shaft, allowing for non-contact measurement of torque through sensors like Hall Effect or fluxgate sensors, which generates torque-dependent magnetic flux components near the encoded regions.
Data Source
AI summary
Direct shaft power measurements of rotating machinery, including a magnetic encoding system for the shaft, having at least one conducting member having a first end and a second end which is disposed proximate the shaft with a gap between the member and the shaft. There is a pair of electrodes proximate each end of said conducting member, wherein the electrodes are electrically coupled to the shaft. One of the electrodes is electrically coupled to the second end of the conductor member. An encoding source is electrically coupled to the first end of the conducting member and electrically coupled to the other electrode, wherein unipolar current pulses from said encoding source are applied to the electrodes and the conducting member, thereby creating sectional encoded polarized magnetic regions in the shaft.