Nondestructive measurement device and method for judging orientation direction of permanent magnet

Abstract

The invention discloses a lossless measuring device and method for judging the orientation direction of a permanent magnet, the lossless measuring device comprises a coil device and an electrical unit, the coil device comprises a magnet exciting coil group and an induction coil group, and the electrical unit comprises a microprocessor, a signal source, an alternating current power source and an alternating current measuring module. The output end of the microprocessor is connected with the input end of the signal source, the output end of the signal source is connected with the input end of the alternating-current power source, the output end of the alternating-current power source is connected with the input end of a magnet exciting coil group of the coil device, the input end of the microprocessor is connected with the output end of the alternating-current measuring module, and the output end of the alternating-current measuring module is connected with the output end of the signal source. And the input end of the alternating current measurement module is connected with the output end of the induction coil group of the coil device. The orientation condition of the magnet is judged in a non-magnetizing mode, the technological process is simplified, the technical problem of non-magnetic detection is solved, and the situation that a finished product device is unqualified after the magnet is installed is prevented.

Description

Technical Field

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

[0002] The production process of anisotropic permanent magnets covers multiple links, including batching, smelting, powder making, magnet orientation and molding, sintering, tempering, machining, surface treatment, testing and packaging. In the machining stage, the large magnets that have been oriented and molded will be cut into shapes and sizes that meet user requirements. However, if the orientation is uneven or the cutting method is incorrect, the device using the magnet will not work properly.

[0003] Anisotropic permanent magnets exhibit optimal magnetic properties in a specific direction, which is the direction of easy magnetization, also known as the orientation direction. When anisotropic permanent magnets are installed in devices for use, it is crucial to ensure that the easy magnetization direction (orientation direction) of the permanent magnets is consistent with the design requirements of the device. Only in this way can the magnets give full play to their optimal performance. Taking permanent magnet motors as an example, if the direction of the magnets is wrong, it is very likely to cause insufficient motor torque, reduced efficiency, and even cause the motor to fail to operate normally. Therefore, during the production process, companies are eager to detect whether the orientation direction of the magnets is correct when the magnets are not magnetized, and to promptly screen out magnets that are cut incorrectly or have poor orientation processes, thereby avoiding the occurrence of device failures due to magnet orientation problems.

[0004] In most cases, magnets are packaged in a non-magnetic state. Based on this, manufacturers generally expect to be able to complete the measurement of the orientation direction and orientation uniformity of magnets in a non-magnetic state. However, it is difficult to achieve this goal with current methods. The current method must first magnetize the magnet, and then measure the surface magnetic field with a Gaussmeter, or measure the hysteresis loop to determine the orientation quality of the magnet. These two methods not only require magnetizing the magnet first, but also require a demagnetization process for magnets that require non-magnetic packaging; or only sampling measurement can be used, which cannot achieve 100% detection and the measurement efficiency is also relatively low.

[0005] The existing technology cannot detect whether the orientation direction of the magnet is correct in time, nor can it screen out magnets due to cutting errors or poor orientation processes in time. The first existing technical solution uses a Gaussmeter to measure the magnetic field on the surface of the magnet. The specific operation process is: first saturate magnetize the magnet to be measured, then bring the Gaussmeter probe close to the surface of the magnet, and move the probe in different directions to measure the magnetic field strength at various locations on the surface of the magnet. Since the surface magnetic field of the magnet reaches its maximum value in the orientation direction of the magnet, the orientation direction of the magnet can be determined by comparing the magnetic field strength readings in different directions.

[0006] 1) Magnetization and demagnetization problems: The magnet must be magnetized before measurement can be carried out in this solution. For magnets that require non-magnetic packaging, an additional demagnetization process is needed after measurement; if demagnetization is not carried out, only sampling measurement can be used, which makes it impossible to achieve 100% detection of all magnets. 2) Low measurement efficiency: This method requires measuring multiple different points in different directions, and the measurement process is cumbersome, resulting in extremely low measurement efficiency. In view of this, the present invention innovatively proposes a non-destructive measurement device and method for determining the orientation direction of permanent magnets, realizing non-destructive measurement of permanent magnets in the unmagnetized state. Summary of the Invention

[0007] The present invention aims to determine whether the orientation direction of rare earth permanent magnet materials is correct after being cut into finished products, and provides a non-destructive measurement device and method for determining the orientation direction of permanent magnets.

[0008] The present invention includes a coil device and an electrical unit. The coil device includes an exciting 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 exciting coil group of the coil device. The input end of the microprocessor is connected to the output end of the AC measurement module. The input end of the AC measurement module is connected to the output end of the induction coil group of the coil device.

[0009] Further, 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. The second coil group is arranged at the far end of the magnetized sample, and the third coil group is arranged at the near end of the magnetized sample.

[0010] Further, the first coil group outputs an AC signal with a fixed frequency, generating an AC magnetic field with the corresponding frequency between the coils. The second coil group is used to detect the far-end induced voltage signal generated by the sample in the magnetic field. The third coil group is used to detect the near-end induced voltage signal generated by the sample in the magnetic field.

[0011] Further, a signal processing circuit is provided on the coil device to accurately extract weak signals with specific frequencies from noise by using frequency template matching.

[0012] Furthermore, before measurement, the background signal of the magnetized sample needs to be adjusted to zero, and a background signal compensation circuit is set on the coil to eliminate the background signal by subtraction.

[0013] In a second aspect, a non-destructive measurement method for determining the orientation direction of a permanent magnet, which is used to implement a non-destructive measurement device for determining the orientation direction of a permanent magnet, includes the following steps: Output a sine signal with a fixed frequency, control the AC power source to output an AC signal with a specified frequency, and input it to the excitation to generate a weak alternating magnetic field; Magnetize the sample under the alternating magnetic field; A voltage change is formed on the induction coil, and the voltage is collected and transmitted to the microcontroller to display the AC voltage value; When the easy magnetization direction of the magnetized sample is the same as the magnetic field direction, 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 with a specific frequency is accurately extracted from the noise by using frequency template matching; Determine the magnet orientation direction according to the measured effective value voltage.

[0014] Furthermore, the accurate extraction of a weak signal with a specific frequency from the noise by using frequency template matching specifically includes: Enhance the signal amplitude through a programmable amplifier, then remove the noise interference through a filter, and retain the signal components related to the target frequency; Perform high-precision digital acquisition of the filtered signal; Generate sine and cosine waveforms that are exactly the same as the excitation current frequency, and perform full-cycle integration by multiplying the collected signal with these two waveforms respectively; Extract the signal components with the same frequency as the excitation current, and synthesize the signal components into the effective value of the signal.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The present invention uses an unmagnetized method to determine the orientation of the magnet, reduces the magnetization and demagnetization links in the production process, simplifies the process flow, solves the technical problem of non-magnetic detection, facilitates the determination of the orientation degree, and effectively prevents the unqualified situation of the finished device after the magnet is installed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the schematic diagram of the measurement device of the present invention; Figure 2 It is the design drawing of the coil device of the present invention; Figure 3 It is the schematic diagram of the background signal compensation circuit of the present invention; Figure 4 It is the schematic diagram of the signal processing circuit of the present invention; Detailed implementation mode In order to more clearly express the technical solution of the present invention, the present invention will be further described below with reference to the accompanying drawings. In this embodiment

[0017] Such as Figure 1 As shown, the device consists of a coil device and an electrical unit. The coil device includes an exciting 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 exciting 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.

[0018] 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. The second coil group is arranged at the far end of the magnetized sample, and the third coil group is arranged at the near end of the magnetized sample.

[0019] The first coil group outputs an AC signal with a fixed frequency, generating an AC magnetic field with a corresponding frequency between the coils. The second coil group is used to detect the far-end induced voltage signal generated by the sample in the magnetic field, and the third coil group is used to detect the near-end induced voltage signal generated by the sample in the magnetic field.

[0020] Figure 2 It is a schematic structural diagram of the coil device of the present invention. The coil group is composed of 6 coils. Among them, coil 2 and coil 5 are connected in series and connected in the positive direction to form exciting coil group 1. The input end of coil group 1 is connected to the AC exciting power supply. During operation, the AC power supply outputs an AC signal with a fixed frequency, generating an AC magnetic field with a corresponding frequency between the coils. In the present invention, the magnetic field generated by the exciting coil is in the Rayleigh region (magnetization reversible region) of the initial magnetization curve of the magnet. It is necessary to magnetize the magnet when the magnet enters the coil and restore it to the non-magnetic state after the magnet leaves the coil. Therefore, the magnetization field is very small, and the magnetic field size is equivalent to the geomagnetic field.

[0021] The measurement method includes outputting a sine signal with a fixed frequency, controlling the AC power source to output an AC signal with a specified frequency, inputting it into the exciting coil to generate a weak alternating magnetic field, Magnetizing the sample under the alternating magnetic field, Forming a voltage change on the induction coil, collecting the voltage and transmitting it to the microcontroller, thereby displaying the AC voltage value.

[0022] When the easy magnetization direction of the magnetized sample is the same as the magnetic field direction, 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. Determine the magnet orientation direction according to the measured effective voltage.

[0023] Coils 1, 3, 5, and 6 are all detection coils and have exactly the same structure. Among them, Coil 1 and Coil 6 are connected in series and forward-connected to form Coil Group 2. Coil 3 and Coil 4 are connected in series and forward-connected to form Coil Group 3. When there is a sample in the central area of the coil, it will be magnetized by the alternating magnetic field. At this time, inductive voltage signals U2 and U3 will be obtained in Coil Group 2 and Coil Group 3. Among them, Coil Group 3 is closest to the sample, so the induced voltage U3 is larger, and Coil Group 2 is farthest from the sample, so the induced voltage U2 is smaller.

[0024] The magnet is in the Rayleigh region during measurement, and the value of the background signal is much larger than the effective induction signal. Therefore, it is necessary to adjust the background signal to zero. The specific implementation method is as follows: When there is no sample, as long as an excitation current is input to Coil Group 1, U2 and U3 will be induced in Coil Group 2 and Coil Group 3. Therefore, when there is a magnet under test in the coil, the induced voltage U2 of Coil 2 includes the air induced voltage Uair2 and the magnet's own induced voltage Umag2, and the induced voltage U3 of Coil 3 includes the air induced voltage Uair3 and the magnet's own induced voltage Umag3. The relationship between the parameters can be expressed by Formula (1) and Formula (2).

[0025] U2 = Uair2 + Umag2 (1) U3 = Uair3 + Umag3 (2) Because the magnet is at different distances from Coil Group 2 and Coil Group 3, the magnitudes of Uair2 and Uair3 are different, and the magnitudes of Umag2 and Umag3 are also different. Moreover, the voltage values of Uair2 and Uair3 are much larger than the induced voltage Umag2 or Umag3 generated by the magnet itself when measuring the magnetic flux. Therefore, in order to achieve the function of the present invention, it is necessary to eliminate the influence of environmental noise, that is, Uair2 and Uair3. The design of multiple coils is also for this purpose.

[0026] As Figure 3 shown, a background signal compensation circuit is designed for this purpose, and the background signal is eliminated by subtraction. The induced signals U2 and U3 of Coil Group 2 and Coil Group 3 are input to the input end 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).

[0027] U = U3 - U2 = (Uair3 - Uair2) + (Umag3 - Umag2) (3) Before measuring the magnet, in the state without placing a sample, the output voltage of the signal amplifier is U0 = Uair3 - Uair2. By adjusting the amplification factor of the signal amplification, U0 can be made equal to 0. Then, place the magnet to be measured at the center of the coil. At this time, the output voltage of the signal amplifier can be expressed by formula (4), that is, it only contains the effective signal.

[0028] U = U3 - U2 = (Uair3 - Uair2) + (Umag3 - Umag2) = (Umag3 - Umag2) (4) In this way, the interference of the background signal during the magnet measurement process is effectively eliminated, and the measurement function of the present invention is realized.

[0029] The signal processed by the signal amplifier after eliminating the background signal can obtain the effective measurement signal of the magnet. However, because it is measured in the unmagnetized state and there should be no residual magnetism after measurement, the induced voltages of coil group 2 and coil group 3 are very small. After passing through the noise cancellation 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 designs a circuit as shown in Figure 4 the following figure to process the signal and extract the voltage signal with the same frequency as the exciting current. The specific algorithm is as follows: After the signal is processed by the method of eliminating the background signal, the obtained voltage U enters the subsequent signal processing circuit.

[0030] The signal processing circuit amplifies the voltage U through a programmable amplifier, then filters it and collects it by an analog-to-digital converter (AD). After AD collection, a series of voltage instantaneous values Ui are obtained. Ui is multiplied by the sine waveform array Si and cosine waveform array Ci generated in the microprocessor. When the frequencies of the sine and cosine waveform arrays are the same as the frequency of the exciting 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.

[0031] (5) (6) (7) (8) The present invention uses the unmagnetized method to determine the orientation of the magnet, reduces the magnetization and demagnetization links in the production process, simplifies the process flow, solves the technical problem of non-magnetic detection, facilitates the determination of the orientation degree, and effectively prevents the finished device from being unqualified after the magnet is installed.

[0032] The above only elaborates in detail on the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A non-destructive measuring device for determining the orientation direction of a permanent magnet, comprising a coil device and an electrical unit, characterized in that: 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.

2. A non-destructive measurement device for determining 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, 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, the second coil group is arranged at the far end of the magnetized sample, and the third coil group is arranged at the near end of the magnetized sample.

3. A non-destructive measurement device for determining 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 a remote induced voltage signal generated by the sample in the magnetic field. The third coil group is used to detect a near-induced voltage signal generated by the sample in the magnetic field.

4. A non-destructive measurement device for determining 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 non-destructive measurement device for determining the orientation direction of a permanent magnet according to claim 1, characterized in that: Before measuring the magnetized sample, the background signal needs to be adjusted to zero, and a background signal compensation circuit is set on the coil to eliminate the background signal by subtraction.

6. A method for non-destructive measurement of the orientation direction of a permanent magnet, used to realize the function of the non-destructive measurement device for determining the orientation direction of a permanent magnet as claimed in any one of claims 1 to 5, 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 into the excitation coil to generate a weak alternating magnetic field; Magnetizing 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 by using frequency template matching; The orientation direction of the magnet is determined based on the measured effective value voltage.

7. A non-destructive measurement method for determining the orientation direction of a permanent magnet according to claim 6, characterized in that: Use frequency template matching 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 period; A signal component having the same frequency as the excitation current is extracted, and the signal component is synthesized into an effective value of the signal.

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