Magnetic encoding system based on self-biased anisotropic magnetoresistive sensors and calibration method

Abstract

A magnetic encoding system based on self-biased anisotropic magnetoresistance sensor belongs to the technical field of angle measurement. The magnetic encoding system comprises a magnetic field generating device for generating a periodic spatial magnetic field, a sensor probe for detecting the magnetic field and outputting two-way orthogonal voltage signals, and a signal processing unit for receiving and processing the two-way orthogonal voltage signals to solve the angle information; wherein the probe comprises two self-biased anisotropic magnetoresistance linear magnetic field sensors arranged orthogonally in space. The self-biased AMR linear sensor is used to construct the orthogonal measurement system, and the external bias magnet necessary in the traditional scheme is omitted, so that the structure is significantly simplified, and the cost and volume are reduced. At the same time, by introducing the system level calibration algorithm based on ellipse fitting, the inherent amplitude error, zero offset and orthogonality deviation of the discrete sensor system are effectively eliminated, and high-precision angle measurement is realized.

Description

Technical Field

[0001] This invention belongs to the field of angle measurement technology, and specifically relates to a magnetic coding system based on anisotropic magnetoresistive effect and its calibration method for improving measurement accuracy. Background Technology

[0002] Magnetic encoders, as non-contact position and angle sensors, are widely used in industrial automation, robotics, automotive motors, and aerospace due to their high reliability, long lifespan, and resistance to harsh environments. Their basic principle is to detect changes in the periodic magnetic field generated by a magnetic scale or magnetic ring using a magnetic sensing element, and then calculate the angle or linear displacement.

[0003] In existing technologies, magnetic sensors based on the anisotropic magnetoresistive effect are among the commonly used magnetic sensing elements. Traditional AMR angle sensors typically employ an orthogonal Wheatstone bridge structure photolithographically etched on a silicon wafer. To achieve angle measurement, such sensors must operate in a saturated magnetic field region, meaning their internal magnetization vector needs to be aligned with the direction of the external magnetic field. This usually requires the introduction of an additional strong bias magnet to provide a saturated magnetic field. This design results in a complex system structure, increased size, and higher cost. Furthermore, the magnet's performance is prone to degradation at high temperatures, affecting system stability.

[0004] On the other hand, AMR linear sensors are mainly used to measure the magnitude of magnetic field strength. By introducing structures such as Barber electrodes, their operating point can be set in the linear range of the resistance-magnetic field response curve, thereby achieving "self-biased" measurement without the need for an external bias magnetic field. However, there are fundamental technical obstacles to directly using these sensors optimized for linear field measurement for high-precision angle measurement: a single linear sensor cannot sense the direction of the magnetic field; and when multiple discrete linear sensors are combined to construct an orthogonal measurement system, serious systematic errors are introduced, such as amplitude mismatch between the two channels, zero-point drift, and orthogonality deviation caused by inaccurate installation.

[0005] Therefore, there is an urgent need in this field for a magnetic coding scheme and calibration method that can retain the advantages of low cost and high sensitivity of AMR sensors, avoid complex bias magnetic circuits, and effectively solve the errors of multi-sensor systems. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the background technology by proposing a magnetic coding system and calibration method based on a self-biased anisotropic magnetoresistive sensor, which achieves high-precision, low-cost, and convenient angle measurement.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A magnetic coding system based on a self-biased anisotropic magnetoresistive sensor includes:

[0009] A magnetic field generator used to produce a periodic spatial magnetic field;

[0010] A sensor probe comprising two spatially orthogonal self-biased anisotropic magnetoresistive linear magnetic field sensors for detecting the magnetic field and outputting two orthogonal voltage signals.

[0011] A signal processing unit, electrically connected to the sensor probe, is used to receive and process two orthogonal voltage signals to calculate angle information;

[0012] The self-biased anisotropic magnetoresistive linear magnetic field sensor includes a Wheatstone bridge and a Barber electrode structure disposed thereon. The Barber electrode is configured such that the linear range of the resistance-magnetic field response curve of the sensor includes the zero-point magnetic field.

[0013] Furthermore, the angle between the extension direction of the Barber electrode and the long side of the Wheatstone bridge arm is 35° to 45°, preferably 40°.

[0014] Furthermore, in the self-biased anisotropic magnetoresistive linear magnetic field sensor, the Wheatstone bridge is formed by a sensitive thin film with a multilayer film structure containing a transition metal magnetic layer, and a nano-intercalation of a strong spin-orbit coupling material is inserted in or between the transition metal magnetic layers.

[0015] Furthermore, the strong spin-orbit coupling material is Pt, and the thickness of the nano-intercalation layer is 1~3 nanometers, preferably 2 nanometers.

[0016] Furthermore, the magnetic field generating device is a radially magnetized multipole magnetic ring coaxial with the rotation axis, with a pole pair number of N.

[0017] Furthermore, the signal processing unit includes:

[0018] Analog conditioning circuitry is used to amplify and filter two orthogonal voltage signals;

[0019] An analog-to-digital converter is used to convert conditioned analog voltage signals into digital signals;

[0020] A processor is used to execute instructions stored in memory to calibrate and calculate the angle of the digital signal.

[0021] A calibration method for a magnetic coding system based on a self-biased anisotropic magnetoresistive sensor includes the following steps:

[0022] Multiple pairs of orthogonal voltage signals collected within one complete cycle of the magnetic field generator are acquired, and after passing through an analog conditioning circuit and an analog-to-digital converter, multiple pairs of original signal pairs are output.

[0023] Based on the obtained multiple pairs of original signals, a coordinate system is established, and the least squares method is used for elliptic fitting to solve for the set of correction parameters used to compensate for the amplitude error, zero-point offset and orthogonality error between the two signals.

[0024] The set of calibration parameters is stored in non-volatile memory.

[0025] An angle measurement method based on a magnetic coding system with a self-biased anisotropic magnetoresistive sensor includes the following steps:

[0026] (1) System power-on initialization;

[0027] (2) The initial electrical cycle count m0 ​​is determined by the micro-motion detection method and the non-volatile memory method;

[0028] (3) Load the stored correction parameter set from the non-volatile memory. The correction parameter set includes zero offset Os, Oct, gain Gs, Gc, and orthogonal compensation factor β.

[0029] (4) After entering normal operation, the processor acquires the original signal pair (S1, C1) in real time, performs correction using the loaded correction parameter set, and obtains the corrected quadrature signals S and C:

[0030] S = Gs · (S1 - Os)

[0031] C = Gc · (C1 - Oc) + β · S where Os corresponds to the zero-point offset of the digital signal output by the magnetic field sensor in the x-axis direction, Oc corresponds to the zero-point offset of the digital signal output by the magnetic field sensor in the y-axis direction, Gs corresponds to the gain of the digital signal output by the magnetic field sensor in the x-axis direction, Gc corresponds to the gain of the digital signal output by the magnetic field sensor in the y-axis direction, and β is the orthogonality compensation factor.

[0032] (5) Calculate the electrical angle θe = atan2(S, C) of the real-time acquired raw signal pair;

[0033] Calculate the absolute mechanical angle θ based on the number of pole pairs N of the magnetic field generator and the current electric period m:

[0034] θ = (360° / N) * (m + θe / 360°).

[0035] Furthermore, in step (5), within a complete mechanical cycle (360° rotation) of the magnetic field generating device, the states of multiple pairs of orthogonal signals S and C are determined, and the electrical cycle m is updated according to the state changes.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention constructs an orthogonal measurement system using a self-biased AMR linear sensor, eliminating the need for an external bias magnet required in traditional solutions, significantly simplifying the structure and reducing cost and size. Simultaneously, by introducing a system-level calibration algorithm based on elliptic fitting, it effectively eliminates the inherent amplitude errors, zero-point offsets, and orthogonality deviations of discrete sensor systems, achieving high-precision angle measurements. This solution organically combines sensor structure optimization, system architecture design, and calibration algorithms to form a complete high-precision magnetic coding solution. Attached Figure Description

[0038] Figure 1 This is a structural block diagram of the magnetic encoding system based on a self-biased anisotropic magnetoresistive sensor of the present invention.

[0039] Figure 2 This is a schematic diagram of the magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to the present invention.

[0040] Figure 3 This is a schematic diagram of the structure of two spatially orthogonally arranged self-biased anisotropic magnetoresistive linear magnetic field sensors of the present invention.

[0041] Figure 4 This is a schematic diagram of the Barber electrode structure in a magnetic field sensor. Detailed Implementation

[0042] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0043] The terms "first" and "second" in this invention are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0044] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to welding, bolting, or riveting; they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0045] Example

[0046] like Figure 2The diagram shown is a schematic of the magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to an embodiment, including a magnetic field generating device, a sensor probe, and a signal processing unit.

[0047] The magnetic field generating device is a radially magnetized multipole magnetic ring (with N pole pairs) coaxial with the rotation axis. The sensor probe is mounted parallel to the rotation axis.

[0048] like Figure 3 As shown, the sensor probe includes two identical self-biased anisotropic magnetoresistive linear magnetic field sensors, which are precisely orthogonal in space (sensitivity axis angle 90°). Each linear magnetic field sensor employs a Wheatstone bridge structure, containing four magnetoresistive bars. The power supply terminals of the bridge are connected to excitation voltages Vin+ and Vin-, and the differential output terminals output two voltage signals Vx+ (or Vy+) and Vx- (or Vy-).

[0049] like Figure 4 As shown, each self-biased anisotropic magnetoresistive linear magnetic field sensor includes a Wheatstone bridge and Barber electrodes covering it. The preferred parameters for the Barber electrodes are: a width of 5 μm, a spacing of 5 μm, and an angle α of 40° between their extension direction and the long side of the bridge arm (i.e., the initial magnetization direction M0). This "self-biased" characteristic enables the sensor to exhibit good linear response near zero external magnetic field (e.g., ±20 Oe).

[0050] In a self-biased anisotropic magnetoresistive linear magnetic field sensor, the Wheatstone bridge is formed by a sensitive thin film with a multilayer film structure containing a transition metal magnetic layer. The sensitive thin film is preferably a Ta (5nm) / NiCo (40nm) / Pt (2nm) / NiCo (40nm) / Ta (5nm) multilayer structure, wherein the 2nm thick Pt intercalation can effectively improve the AMR value to more than 3%.

[0051] The signal processing unit includes analog conditioning circuitry (such as amplification and filtering circuitry based on an instrumentation amplifier), analog-to-digital converters (ADCs) (such as 16-bit Σ-Δ ADCs), and processors (such as FPGAs or MCUs).

[0052] The calibration and measurement method of the magnetic coding system based on the embodiment can be divided into a calibration stage and an operation stage.

[0053] Calibration phase:

[0054] (1) Control the magnetic field generating device to go through a complete mechanical cycle (rotate 360°) and acquire multiple pairs of uncalibrated orthogonal voltage signals Vx and Vy collected in a complete cycle of the magnetic field generating device. After passing through the analog conditioning circuit and analog-to-digital converter, multiple pairs of original signal pairs (S0, C0) are output. S0 corresponds to the digital signal output by the magnetic field sensor in the x-axis direction, and C0 corresponds to the digital signal output by the magnetic field sensor in the y-axis direction.

[0055] (2) Based on the obtained multiple pairs of original signals, establish a coordinate system, use the least squares method for ellipse fitting, and solve for the set of correction parameters required to transform this ellipse into a standard circle. The set of correction parameters includes zero offsets Os and Oc, gains Gs and Gc, and orthogonal compensation factor β. Among them, Os corresponds to the zero offset of the digital signal output by the magnetic field sensor in the x-axis direction, Oc corresponds to the zero offset of the digital signal output by the magnetic field sensor in the y-axis direction, Gs corresponds to the gain of the digital signal output by the magnetic field sensor in the x-axis direction, and Gc corresponds to the gain of the digital signal output by the magnetic field sensor in the y-axis direction.

[0056] (3) Store the set of calibration parameters obtained in step (2) into a non-volatile memory (such as Flash) for subsequent real-time measurement.

[0057] Operation phase:

[0058] (1) System power-on initialization;

[0059] (2) The initial electrical cycle count m0 ​​is determined by the micro-motion detection method and the non-volatile memory method;

[0060] (3) Load the stored correction parameter set from the non-volatile memory. The correction parameter set includes zero offset Os, Oct, gain Gs, Gc, and orthogonal compensation factor β.

[0061] (4) After entering normal operation, the processor acquires the original signal pair (S1, C1) in real time, performs correction using the loaded correction parameter set, and obtains the corrected quadrature signals S and C:

[0062] S = Gs · (S1 - Os)

[0063] C = Gc · (C1 - Oc) + β · S where Os corresponds to the zero-point offset of the digital signal output by the magnetic field sensor in the x-axis direction, Oc corresponds to the zero-point offset of the digital signal output by the magnetic field sensor in the y-axis direction, Gs corresponds to the gain of the digital signal output by the magnetic field sensor in the x-axis direction, Gc corresponds to the gain of the digital signal output by the magnetic field sensor in the y-axis direction, and β is the orthogonality compensation factor.

[0064] (5) Calculate the electrical angle θe = atan2(S, C) of the real-time acquired raw signal pair;

[0065] Calculate the absolute mechanical angle θ based on the number of pole pairs N of the magnetic field generator and the current electric period m:

[0066] θ = (360° / N) * (m + θe / 360°).

[0067] Furthermore, in step (5), within a complete mechanical cycle (360° rotation) of the magnetic field generating device, the states of multiple pairs of orthogonal signals S and C are determined, and the electrical cycle m is updated according to the state changes (if the state remains unchanged, then m remains unchanged).

[0068] Specifically, within one complete mechanical cycle (360° rotation) of the magnetic field generator, multiple pairs of original signals acquired in real time are corrected to obtain multiple pairs of corrected orthogonal signals S and C; based on the states of the multiple pairs of corrected orthogonal signals S and C, the electrical cycle m is updated.

[0069] First, define four states:

[0070] State I: S > 0, C ≥ 0

[0071] State II: S ≤ 0, C > 0

[0072] State III: S < 0, C ≤ 0

[0073] State IV: S ≥ 0, C < 0

[0074] When the state completes one full cycle in the sequence I → II → III → IV → I, it is determined that the magnetic ring has rotated one revolution in the positive direction. At this time, the electric cycle count m = m0 + 1.

[0075] When the state completes one full cycle in the order of I → IV → III → II → I, it is determined that the magnetic ring has rotated in the opposite direction for one full cycle, and at this time the electric cycle count m = m0﹣1.

[0076] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope described in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A magnetic encoding system based on a self-biased anisotropic magnetoresistive sensor, characterized in that, include: A magnetic field generator used to produce a periodic spatial magnetic field; A sensor probe comprising two spatially orthogonal self-biased anisotropic magnetoresistive linear magnetic field sensors for detecting the magnetic field and outputting two orthogonal voltage signals. A signal processing unit, electrically connected to the sensor probe, is used to receive and process two orthogonal voltage signals to calculate angle information.

2. The magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to claim 1, characterized in that, The self-biased anisotropic magnetoresistive linear magnetic field sensor includes a Wheatstone bridge and a Barber electrode structure disposed thereon, wherein the Barber electrode is configured such that the linear range of the sensor's resistance-magnetic field response curve includes the zero-point magnetic field.

3. The magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to claim 2, characterized in that, The angle between the extension direction of the Barber electrode and the long side of the Wheatstone bridge arm is 35° to 45°.

4. The magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to claim 2, characterized in that, In the self-biased anisotropic magnetoresistive linear magnetic field sensor, the Wheatstone bridge is formed by a sensitive thin film with a multilayer film structure containing a transition metal magnetic layer, and a nano-intercalation of a strong spin-orbit coupling material is inserted in or between the transition metal magnetic layers.

5. The magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to claim 4, characterized in that, The strong spin-orbit coupling material is Pt, and the thickness of the nano-intercalation layer is 1~3 nanometers.

6. The magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to claim 1, characterized in that, The magnetic field generating device is a radially magnetized multipole magnetic ring coaxial with the rotation axis.

7. The magnetic coding system based on a self-biased anisotropic magnetoresistive sensor according to claim 1, characterized in that, The signal processing unit includes: Analog conditioning circuitry is used to amplify and filter two orthogonal voltage signals; An analog-to-digital converter is used to convert conditioned analog voltage signals into digital signals; The processor is used to calibrate and calculate the angle of the digital signal.

8. A calibration method based on the magnetic coding system of claim 1, comprising the following steps: Multiple pairs of orthogonal voltage signals collected within one complete cycle of the magnetic field generator are acquired, and after passing through an analog conditioning circuit and an analog-to-digital converter, multiple pairs of original signal pairs are output. Based on the obtained multiple pairs of original signals, a coordinate system is established, and the least squares method is used for elliptic fitting to solve for the set of correction parameters used to compensate for the amplitude error, zero-point offset and orthogonality error between the two signals. The set of calibration parameters is stored in non-volatile memory.

9. A method for measuring the angle of the calibrated system according to claim 8, characterized in that, Includes the following steps: (1) System power-on initialization; (2) Determine the initial electrical cycle count m0; (3) Load the stored correction parameter set from the non-volatile memory. The correction parameter set includes zero offset Os, Oct, gain Gs, Gc, and orthogonal compensation factor β. (4) The processor acquires the original signal pair (S1, C1) in real time, performs correction using the loaded correction parameter set, and obtains the corrected orthogonal signals S and C: S = Gs · (S1 - Os) C = Gc · (C1 - Oc) + β · S Where Os corresponds to the zero-point offset of the digital signal output by the magnetic field sensor in the x-axis direction, Oc corresponds to the zero-point offset of the digital signal output by the magnetic field sensor in the y-axis direction, Gs corresponds to the gain of the digital signal output by the magnetic field sensor in the x-axis direction, Gc corresponds to the gain of the digital signal output by the magnetic field sensor in the y-axis direction, and β is the orthogonality compensation factor. (5) Calculate the electrical angle θe = atan2(S, C) of the real-time acquired raw signal pair; Calculate the absolute mechanical angle θ based on the number of pole pairs N of the magnetic field generator and the current electric period m: θ = (360° / N) * (m + θe / 360°).

10. The angle measurement method according to claim 9, characterized in that, In step (5), within a complete mechanical cycle of the magnetic field generator, the states of multiple pairs of orthogonal signals S and C are determined, and the electrical cycle m is updated according to the state changes.

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