Spin-Valve MR Sensor Array for High-Accuracy Position Detection
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Solution Overview
Problem
Conventional magnetic sensor systems face challenges in accurately detecting changes in the relative positional relationship between a scale and a magnetic sensor due to large footprint magneto-sensitive elements, leading to different detection characteristics and noise interference, making it difficult to detect physical quantities with high accuracy, especially when the relative positional relationship changes by two pitches or more.
Innovation Solution
The magnetic sensor system employs spin-valve magnetoresistive elements with a magnetization pinned layer, a free layer, and a nonmagnetic layer, arranged in close proximity to reduce footprint and noise interference, allowing for accurate detection of relative positional changes by generating post-computation signals from detection signals with different phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If anisotropic magnetoresistive elements are used as magneto-sensitive elements, then the magnetic sensor system can detect magnetic field changes, but the footprint of each element becomes relatively large, causing the detection units to be spaced apart and exhibit different detection characteristics
Solution Approach 1:
The patent changes the type of magnetoresistive element from anisotropic to spin-valve type, which fundamentally alters the physical parameters of the detection element. This parameter change enables smaller footprint while maintaining detection sensitivity, allowing detection units to be placed closer together without sacrificing measurement precision.
Solution Approach 2:
The patent uses multiple spin-valve magnetoresistive elements arranged in close proximity to create multiple detection units. These elements are configured to detect magnetic field changes at different positions, and their signals are processed to determine relative movement direction, effectively copying the detection function at multiple locations with minimal spacing.
2Reliability
If the first and second detection units are spaced apart due to large footprint elements, then each element can function independently, but they become susceptible to different noise magnetic fields and have different detection characteristics
Solution Approach 1:
The patent merges multiple spin-valve magnetoresistive elements into a compact array where they are positioned in close proximity. This merging allows the detection units to share a common local environment, reducing the impact of external noise magnetic fields on individual elements while maintaining their independent detection capabilities through signal processing.
Solution Approach 2:
The patent introduces a common reference detection unit that serves as an intermediary for all other detection units. This reference unit provides a baseline for comparing the magnetic field changes detected by other units, helping to cancel out common noise magnetic fields and improve the reliability of relative movement detection.
3Adaptability or versatility
If the relative positional relationship changes by two pitches or more, then the magnetic field direction changes significantly, but accurate detection becomes difficult due to the factors mentioned above
Solution Approach 1:
The patent segments the detection function into multiple discrete spin-valve magnetoresistive elements, each detecting magnetic field changes at its specific position. By processing the signals from these segmented detection units and comparing their phase relationships, the system can accurately detect relative movement over a range of two or more pitches while maintaining precision through the coordinated operation of individual detection elements.
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 enables accurate detection of physical quantities, including the direction of relative movement, with reduced unwanted variation components, even when the relative positional relationship changes by two pitches or more, by minimizing noise and maintaining consistent detection characteristics across the sensor system.
Implementation Method 1
Each of the first to third detection circuits includes a magnetoresistive element. The magnetoresistive element includes: a magnetization pinned layer having a magnetization in a pinned direction; a free layer having a magnetization that varies depending on an applied magnetic field; and a nonmagnetic layer interposed between the magnetization pinned layer and the free layer.
Data Source
AI summary
A magnetic sensor system includes a scale and a magnetic sensor arranged in a relative positional relationship variable in a first direction, and a computing unit. The magnetic sensor includes a first detection circuit, a second detection circuit and a third detection circuit that are disposed at a first position, a second position and a third position, respectively. Each of the first to third detection circuits includes a spin-valve MR element. A difference between two of the first to third positions that are the most distant from each other in a first direction falls within a one-pitch amount of change in the relative positional relationship between the scale and the magnetic sensor. The computing unit generates first and second post-computation signals having mutually different phases by computation using detection signals from the first to third detection circuits.