GMI Sensor Read Head for Hysteresis-Free Position Detection
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Solution Overview
Problem
Existing measurement systems for length and angle detection face challenges in achieving high accuracy and large sensing distances without hysteresis, while maintaining low manufacturing costs and flexibility, as they are either prone to hysteresis or limited by small scanning areas and high sensitivity to environmental factors.
Innovation Solution
A measurement apparatus utilizing the Giant Magnetoimpedance (GMI) effect with a magnetic scale and a read head featuring a planar sensor unit and evaluation circuitry, where the sensor unit includes ferromagnetic foils arranged with alternating poles, allowing for position-dependent impedance variation detection even when magnetically saturated, and enabling differential signal processing for robust and accurate position determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic measurement systems are used, then robustness against environmental influences and longer scanning distance are achieved, but measurement precision deteriorates due to interpolation errors and hysteresis
Solution Approach 1:
The measurement system divides the magnetic scale into multiple periodic segments with alternating polarity patterns. The read head scans across multiple periods simultaneously, and evaluation circuitry processes signals from different segments to determine position. This segmentation allows the system to maintain robust magnetic field sensing while achieving high resolution through multi-period signal analysis, eliminating the need for single-point interpolation that causes errors in conventional systems.
Solution Approach 2:
The system uses differential signal processing where the read head detects both positive and negative polarity regions of the magnetic scale. By comparing signals from opposite polarities and processing the differential output, the system compensates for hysteresis effects and achieves accurate position measurement without the reversal errors that plague conventional magnetic systems.
2Measurement precision
If inductive measurement systems are used, then measurement precision is improved, but scanning distance deteriorates to very small values
Solution Approach 1:
The system replaces traditional inductive sensing mechanisms with magnetic field-based GMI sensing. The ferromagnetic foil in the read head responds to magnetic field variations from the scale at distances of several millimeters to centimeters, achieving both high precision and large scanning distance by substituting magnetic coupling for near-field inductive coupling.
3Measurement precision
If optoelectronic measurement systems are used, then measurement precision is improved with very short measuring step, but reliability deteriorates due to sensitivity to stress, vibrations and soiling
Solution Approach 1:
The system replaces optical sensing with magnetic field-based GMI sensing. The magnetic scale and ferromagnetic foil sensor operate independently of line-of-sight requirements, making them immune to dust, dirt, and optical contamination. Mechanical vibrations and stresses that affect optical components have minimal impact on the magnetic field coupling between the scale and read head.
4Measurement precision
If conventional GMI sensors are used, then high signal contrast is achieved, but device complexity increases and manufacturing cost rises
Solution Approach 1:
The read head uses a thin ferromagnetic foil as the sensing element, which can be flexed into various shapes and mounted on different substrates. This thin-film approach simplifies the sensor construction compared to bulky conventional GMI sensors, reduces material costs, and enables flexible mounting options while maintaining high signal contrast through the foil's strong magnetoimpedance response.
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 provides high accuracy and resolution with a large scanning area, resistance to hysteresis, and flexibility in sensor carrier choice, achieving higher signal amplitudes and efficiency, suitable for a wide range of applications with a simple and cost-effective design.
Implementation Method 1
The embodiments described here refer to a novel electromagnetic measurement apparatus for position detection which is based on the physical effect 'Giant Magnetoimpedance' (GMI). The physical magnetoimpedance effect is itself well known and is made use of in various kinds of sensors. The magnetoimpedance effect causes a ferromagnetic or soft magnetic foil (wire), through which a high-frequency current flows, to change its impedance depending on an external electromagnetic field.
Implementation Method 2
This behavior can be explained with the well-known Skin effect as follows: where: 'δ'—Skin penetration depth, 'f'—Operating frequency, 'μ'—magnetic permeability, 'σ'—electrical conductivity. The Skin penetration depth δ of the currents flowing through the material may change together with the frequency of the current and/or the magnetic permeability of the material.
Data Source
AI summary
A measuring arrangement for distance or angle measurement and a corresponding measuring method are described. In accordance with one example, the measuring arrangement comprises a scale having magnetization which varies along a measuring direction and which brings about a correspondingly varying magnetic field. The measuring device furthermore comprises at least one scanning head which is permeated by the varying magnetic field depending on the relative position with respect to the scale in the measuring direction. The scanning head comprises the following: at least one ferromagnetic film having, on account of the magneto impedance effect, a local electrical impedance that is dependent on the magnetic field and varies along the measuring direction, and at least one sensor unit configured to generate at least two phase-shifted sensor signals which are dependent on the local electrical impedance of the film.