A non-destructive measurement device and method for determining the orientation direction of a permanent magnet

Abstract

The present invention discloses a non-destructive measurement device and method for determining the orientation direction of a permanent magnet. The device comprises a coil device and an electrical unit. The coil device includes an excitation coil group and an induction coil group. The electrical unit includes a microprocessor, a signal source, an AC power source, and an AC measurement module. The output of the microprocessor is connected to the input of the signal source, which is connected to the input of the AC power source. The output of the AC power source is connected to the input of the excitation coil group of the coil device. The input of the microprocessor is connected to the output of the AC measurement module, which is connected to the output of the AC measurement module. The input of the AC measurement module is connected to the output of the induction coil group of the coil device. The present invention determines the orientation of the magnet using an unmagnetized method, which simplifies the process flow, solves the technical difficulties of non-magnetic detection, and prevents substandard finished devices after the magnet is installed.

Description

Technical Field

[0001] The present invention can be applied in the technical field of permanent magnet orientation measurement, and specifically provides a non-destructive measurement device and method for determining the orientation direction of a permanent magnet. Background Art

[0002] The production process for anisotropic permanent magnets encompasses multiple steps, including batching, smelting, powder preparation, magnet orientation and molding, sintering, tempering, machining, surface treatment, testing, and packaging. During the machining stage, the oriented, molded bulk magnets are cut into shapes and sizes that meet user requirements. However, uneven orientation or incorrect cutting methods can cause devices using these magnets to malfunction.

[0003] Anisotropic permanent magnets exhibit optimal magnetic properties in a specific direction, known as the direction of easy magnetization, also known as the orientation direction. When anisotropic permanent magnets are installed in a device for use, it is crucial to ensure that the magnet's easy magnetization direction (orientation direction) aligns with the device's design requirements. Only in this way can the magnet fully realize its optimal performance. For example, if the magnet's orientation is incorrect in a permanent magnet motor, it is very likely to cause insufficient motor torque, reduced efficiency, and even cause the motor to malfunction. Therefore, during the production process, companies urgently hope to be able to detect whether the magnet's orientation direction is correct even when it is not magnetized, and to promptly screen out magnets that have been cut incorrectly or have poor orientation processes, thereby avoiding device failures due to magnet orientation issues.

[0004] In most cases, magnets are packaged in a non-magnetic state. Manufacturers therefore generally desire to be able to measure the orientation and uniformity of magnets in this non-magnetic state. However, current methods struggle to achieve this goal. Current methods require magnetizing the magnets first, then measuring the surface magnetic field with a Gaussmeter or a hysteresis loop to determine the quality of the magnet's orientation. Both of these methods not only require magnetizing the magnets, but also, for magnets packaged in a non-magnetic state, require a subsequent demagnetization process. Alternatively, they can only rely on sampling measurements, which cannot achieve 100% detection and are also relatively inefficient.

[0005] Existing technologies are unable to promptly detect whether a magnet's orientation is correct, nor can they promptly screen out magnets that have been cut incorrectly or have undergone suboptimal orientation. Existing technology solution 1 uses a Gaussmeter to measure the magnetic field on the magnet's surface. The specific operating process is as follows: first, the magnet being measured is saturated magnetized, then the Gaussmeter probe is brought close to the magnet's surface and moved in different directions to measure the magnetic field strength at various locations on the magnet's surface. Because the magnet's surface magnetic field reaches its maximum value in the direction of its orientation, the magnet's orientation can be determined by comparing the magnetic field strength readings in different directions.

[0006] 1) Magnetization and demagnetization issues: This solution requires magnetization before measurement. For magnets that require non-magnetic packaging, demagnetization is required after measurement. Without demagnetization, sampling is the only option, making it impossible to achieve 100% inspection of all magnets.

[0007] 2) Low measurement efficiency: This method requires measuring multiple points in different directions. The measurement process is cumbersome and results in extremely low measurement efficiency.

[0008] In view of this, the present invention innovatively proposes a non-destructive measurement device and method for determining the orientation direction of a permanent magnet, thereby realizing non-destructive measurement of a permanent magnet in an unmagnetized state. Summary of the Invention

[0009] The present invention aims to determine whether the orientation direction of rare earth permanent magnet materials is correct after they are cut into finished products, and provides a non-destructive measurement device and method for determining the orientation direction of permanent magnets.

[0010] The present invention includes a coil device and an electrical unit, wherein the coil device includes an excitation coil group and an induction coil group, and the electrical unit includes a microprocessor, a signal source, an AC power source, and an AC measurement module. The output end of the microprocessor is connected to the input end of the signal source, the output end of the signal source is connected to the input end of the AC power source, the output end of the AC power source is connected to the input end of the excitation coil group of the coil device, the input end of the microprocessor is connected to the output end of the AC measurement module, and the input end of the AC measurement module is connected to the output end of the induction coil group of the coil device.

[0011] Furthermore, the coil device includes a first coil group, a second coil group and a third coil group, the first coil group is a Helmholtz coil group, the second coil group and the third coil group are induction coil groups, the second coil group and the third coil group are respectively arranged on both sides of the first coil group, and the second coil group is arranged at the distal end of the magnetized sample, and the third coil group is arranged at the proximal end of the magnetized sample.

[0012] Furthermore, the first coil group outputs an AC signal of a fixed frequency to generate an AC magnetic field of a corresponding frequency between the coils, the second coil group is used to detect the far-field induced voltage signal generated by the sample in the magnetic field, and the third coil group is used to detect the near-field induced voltage signal generated by the sample in the magnetic field.

[0013] Furthermore, the coil device is provided with a signal processing circuit for accurately extracting a weak signal of a specific frequency from noise by using frequency template matching.

[0014] Furthermore, the background signal of the magnetized sample needs to be adjusted to zero before measurement, and a background signal compensation circuit is provided on the coil to eliminate the background signal by subtraction.

[0015] In a second aspect, a method for non-destructive measurement of a permanent magnet orientation direction is provided, for implementing a non-destructive measurement device for determining the orientation direction of a permanent magnet, comprising the following steps:

[0016] Output a fixed frequency sinusoidal signal to control the AC power source to output an AC signal of a specified frequency, which is input to the excitation to generate a weak alternating magnetic field;

[0017] Magnetize the sample under an alternating magnetic field;

[0018] A voltage change is formed on the induction coil, and the collected voltage is transmitted to the microcontroller to display the AC voltage value;

[0019] When the easy magnetization direction of the magnetized sample is the same as the direction of the magnetic field, a high induced voltage is generated; when the easy magnetization direction of the magnetized sample is perpendicular to the direction of the magnetic field, a low induced voltage is generated, and the weak signal of a specific frequency is accurately extracted from the noise using frequency template matching;

[0020] The orientation direction of the magnet is determined based on the measured effective voltage.

[0021] Furthermore, the method of accurately extracting weak signals of a specific frequency from noise by using frequency template matching specifically includes:

[0022] The signal amplitude is enhanced by a programmable amplifier, and then the noise interference is removed by a filter, retaining the signal components related to the target frequency;

[0023] High-precision digital acquisition of filtered signals;

[0024] Generate sine and cosine waveforms that are exactly the same as the excitation current frequency by multiplying the acquired signal with these two waveforms and integrating them over the entire period;

[0025] A signal component having the same frequency as the excitation current is extracted and synthesized into an effective value of the signal.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention determines the orientation of the magnet by using an unmagnetized method, which reduces the magnetization and demagnetization steps in the production process, simplifies the process flow, solves the technical difficulties of non-magnetic detection, facilitates orientation determination, and effectively prevents unqualified finished devices after the magnet is installed. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the principle diagram of the measuring device of the present invention;

[0029] Figure 2 is a design diagram of the coil device of the present invention;

[0030] Figure 3 This is a schematic diagram of a background signal supplement circuit of the present invention;

[0031] Figure 4 is a schematic diagram of a signal processing circuit of the present invention; DETAILED DESCRIPTION

[0032] In order to more clearly express the technical solution of the present invention, the present invention is further described below with reference to the accompanying drawings.

[0033] In this embodiment

[0034] like Figure 1 As shown, the device consists of a coil device and an electrical unit. The coil device includes an excitation coil group and an induction coil group. The electrical unit includes a microprocessor, a signal source, an AC power source and an AC measurement module. The output end of the microprocessor is connected to the input end of the signal source, the output end of the signal source is connected to the input end of the AC power source, the output end of the AC power source is connected to the input end of the excitation coil group of the coil device, the input end of the microprocessor is connected to the output end of the AC measurement module, and the input end of the AC measurement module is connected to the output end of the induction coil group of the coil device.

[0035] The coil device includes a first coil group, a second coil group and a third coil group. The first coil group is a Helmholtz coil group, and the second coil group and the third coil group are induction coil groups. The second coil group and the third coil group are respectively arranged on both sides of the first coil group, and the second coil group is arranged at the distal end of the magnetized sample, and the third coil group is arranged at the proximal end of the magnetized sample.

[0036] The first coil group outputs an AC signal of a fixed frequency to generate an AC magnetic field of a corresponding frequency between the coils. The second coil group is used to detect the far-field induced voltage signal generated by the sample in the magnetic field. The third coil group is used to detect the near-field induced voltage signal generated by the sample in the magnetic field.

[0037] Figure 2The figure is a schematic diagram of the coil assembly structure of the present invention. The coil assembly consists of six coils. Coil 2 and coil 5 are connected in series and connected in a positive direction, forming excitation coil assembly 1. The input end of coil assembly 1 is connected to an AC excitation power supply. During operation, the AC power supply outputs an AC signal of a fixed frequency, generating an AC magnetic field of a corresponding frequency between the coils. The magnetic field generated by the excitation coils in the present invention is within the Rayleigh region (magnetization reversible region) of the magnet's initial magnetization curve. The magnet must be magnetized when it enters the coil and restored to a non-magnetic state after it leaves the coil. Therefore, the magnetization field is very small, and the magnetic field magnitude is comparable to the Earth's magnetic field.

[0038] The measurement method includes outputting a fixed frequency sinusoidal signal, controlling the AC power source to output an AC signal of a specified frequency, and inputting it into the excitation coil to generate a weak alternating magnetic field.

[0039] The sample is magnetized in an alternating magnetic field.

[0040] A voltage change is formed on the induction coil, and the collected voltage is transmitted to the microcontroller, thereby displaying the AC voltage value.

[0041] When the easy magnetization direction of the magnetized sample is the same as the direction of the magnetic field, a high induced voltage is generated; when the easy magnetization direction of the magnetized sample is perpendicular to the direction of the magnetic field, a low induced voltage is generated;

[0042] The orientation direction of the magnet is determined based on the measured effective voltage.

[0043] Coils 1, 3, 5, and 6 are all detection coils with identical structures. Coils 1 and 6 are connected in series and in a positive direction, forming Coil Group 2. Coils 3 and 4 are connected in a positive direction, forming Coil Group 3. When a sample is present in the center of the coils, it is magnetized by the AC magnetic field, generating inductive voltage signals U2 and U3 in Coil Groups 2 and 3. Coil Group 3 is closest to the sample, resulting in a higher induced voltage U3, while Coil Group 2 is farthest from the sample, resulting in a lower induced voltage U2.

[0044] When measuring, the magnet is in the Rayleigh region, and the background signal is much larger than the effective sensing signal. Therefore, it is necessary to adjust the background signal to zero. The specific implementation method is as follows:

[0045] When there is no sample, as long as the excitation current is input to coil group 1, coil group 2 and coil group 3 will induce U2 and U3. Therefore, when there is a magnet to be measured in the coil, the induced voltage U2 of coil 2 includes the air induced voltage Uair2 and the induced voltage Umag2 of the magnet itself, and the induced voltage U3 of coil 3 includes the air induced voltage Uair3 and the induced voltage Umag3 of the magnet itself. The relationship between the various parameters can be expressed by formula (1) and formula (2).

[0046] U2=Uair2+Umag2 (1)

[0047] U3=Uair3+Umag3 (2)

[0048] Because the magnets are at different distances from coil assemblies 2 and 3, the magnitudes of Uair2 and Uair3 differ, as do the magnitudes of Umag2 and Umag3. Furthermore, the voltages of Uair2 and Uair3 are significantly greater than the induced voltages Umag2 and Umag3 generated by the magnets themselves during flux measurement. Therefore, to achieve the functionality of the present invention, the effects of ambient noise, specifically Uair2 and Uair3, must be eliminated. The design of multiple coils is designed to achieve this goal.

[0049] like Figure 3 As shown in Figure 3, a background signal compensation circuit is designed to eliminate the background signal by subtraction. The induced signals U2 and U3 from coil groups 2 and 3 are input to the input of the signal amplifier, so that the output voltage U of the signal amplifier is equal to the difference between the input voltages, which can be expressed by formula (3).

[0050] U=U3-U2=(Uair3-Uair2)+(Umag3-Umag2) (3)

[0051] Before measuring the magnet, without placing a sample, the signal amplifier's output voltage is U0 = Uair3 - Uair2. By adjusting the signal amplification factor, U0 can be set to 0. The magnet to be measured is then placed in the center of the coil. The signal amplifier's output voltage can be expressed as Equation (4), which contains only the valid signal.

[0052] U=U3-U2=(Uair3-Uair2)+(Umag3-Umag2) = (Umag3-Umag2) (4)

[0053] In this way, the interference of background signals during the magnet measurement process is effectively eliminated, thereby achieving the measurement function of the present invention.

[0054] After the signal amplifier is processed by the background signal elimination method, although the effective measurement signal of the magnet can be obtained, the measurement is performed in the unmagnetized state, and the magnet cannot have residual magnetism after the measurement. Therefore, the induced voltage of coil group 2 and coil group 3 is very small. After the noise elimination circuit, the final output is the signal difference between coil group 2 and coil group 3, so the voltage signal is very weak. In order to accurately process the weak signal, the present invention is designed as follows Figure 4 The circuit shown processes the signal and extracts a voltage signal with the same frequency as the excitation current. The specific algorithm is as follows:

[0055] After the signal is processed by the background signal elimination method, the obtained voltage U enters the subsequent signal processing circuit.

[0056] The signal processing circuit amplifies the voltage U through a programmable amplifier, then filters it and collects it through an analog-to-digital converter (AD). The AD collects the instantaneous voltage value Ui. Ui is multiplied by the sine waveform array Si and cosine waveform array Ci generated by the microprocessor. When the frequency of the sine and cosine waveform arrays is the same as the frequency of the excitation current, these points are multiplied by Ui to obtain P and Q, and finally Urms is calculated. The values ​​of Uref, P, Q, and Urms are calculated using Formulas (5), (6), (7), and (8), respectively.

[0057] (5)

[0058] (6)

[0059] (7)

[0060] (8)

[0061] The present invention determines the orientation of the magnet by using an unmagnetized method, which reduces the magnetization and demagnetization steps in the production process, simplifies the process flow, solves the technical difficulties of non-magnetic detection, facilitates orientation determination, and effectively prevents unqualified finished devices after the magnet is installed.

[0062] The above only describes in detail the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of the present invention, and various changes should be included in the scope of protection of the present invention.

Claims

1. A method for non-destructive measurement of the orientation direction of a permanent magnet, characterized in that: The following steps are involved: Output a fixed frequency sinusoidal signal to control the AC power source to output an AC signal of a specified frequency, which is input to the excitation coil to generate a weak alternating magnetic field; Magnetize the sample under an alternating magnetic field; A voltage change is formed on the induction coil, and the collected voltage is transmitted to the microcontroller to display the AC voltage value; When the easy magnetization direction of the magnetized sample is the same as the direction of the magnetic field, a high induced voltage is generated; When the easy magnetization direction of the magnetized sample is perpendicular to the magnetic field direction, a low induced voltage is generated, and a weak signal of a specific frequency is accurately extracted from the noise using frequency template matching; Determine the orientation direction of the magnet based on the measured effective value voltage; Frequency template matching is used to accurately extract weak signals of specific frequencies from noise, including: The signal amplitude is enhanced by a programmable amplifier, and then the noise interference is removed by a filter, retaining the signal components related to the target frequency; High-precision digital acquisition of filtered signals; The microprocessor generates sine and cosine waveforms that are exactly the same as the excitation current frequency by multiplying the acquired signal with these two waveforms and integrating them over the entire cycle; extracting a signal component having the same frequency as the excitation current, and synthesizing the signal component into an effective value of the signal; The signal processing circuit amplifies the voltage U through a programmable amplifier, and then collects it through an analog-to-digital converter (AD) after filtering. After AD collection, a series of voltage instantaneous values ​​Ui are obtained. Ui is multiplied with the sine waveform array Si and cosine waveform array Ci generated by the microprocessor. When the frequency of the sine and cosine waveform arrays is the same as the frequency of the excitation current, these points are multiplied with Ui to obtain P and Q. Finally, Urms is calculated. The values ​​of Uref, P, Q and Urms are calculated using formulas (5), (6), (7) and (8) respectively. ； The non-destructive measuring device includes a coil device and an electrical unit. The coil device includes an excitation coil group and an induction coil group. The electrical unit includes a microprocessor, a signal source, an AC power source and an AC measurement module. The output end of the microprocessor is connected to the input end of the signal source, the output end of the signal source is connected to the input end of the AC power source, the output end of the AC power source is connected to the input end of the excitation coil group of the coil device, the input end of the microprocessor is connected to the output end of the AC measurement module, and the input end of the AC measurement module is connected to the output end of the induction coil group of the coil device.

2. The method for non-destructive measurement of the orientation direction of a permanent magnet according to claim 1, characterized in that: The coil device includes a first coil group, a second coil group and a third coil group. The first coil group is an excitation coil group, and the second coil group and the third coil group are induction coil groups. The second coil group and the third coil group are respectively arranged on both sides of the first coil group, and the second coil group is arranged at the distal end of the magnetized sample, and the third coil group is arranged at the proximal end of the magnetized sample.

3. The method for non-destructive measurement of the orientation direction of a permanent magnet according to claim 2, characterized in that: The first coil group outputs an AC signal of a fixed frequency to generate an AC magnetic field of the same frequency between the coils. The second coil group is used to detect the remote induced voltage signal generated by the sample in the magnetic field. The third coil group is used to detect the near-induced voltage signal generated by the sample in the magnetic field.

4. The method for non-destructive measurement of the orientation direction of a permanent magnet according to claim 1, characterized in that: The coil device is provided with a signal processing circuit for accurately extracting a weak signal of a specific frequency from noise by using frequency template matching.

5. The method for non-destructive measurement of the orientation direction of a permanent magnet according to claim 1, characterized in that: The background signal of the magnetized sample needs to be adjusted to zero before measurement, and a background signal compensation circuit is provided on the coil to eliminate the background signal by subtraction.

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