Method for improving and controlling stability of magnetic field intensity of magnet and high-uniformity magnet

Abstract

The invention relates to a method for improving and controlling the stability of the magnetic field intensity of a magnet and the high-uniformity magnet, belongs to the technical field of high-uniformity magnet preparation, and solves the problems that in the prior art, a magnet magnetic field control technology is insufficient in stability, low in control precision and prone to causing magnet performance loss. The method comprises the following steps: detecting surface magnetic field distribution of magnetic poles, and respectively taking an average value and a minimum value as an upper limit and a lower limit of adjustment; carrying out thermal demagnetization treatment on the magnet with the non-uniformity greater than 5% until the non-uniformity is less than or equal to 5%; and performing magnetization correction on the region higher than the upper limit by using the pulsed magnetic field until the magnetic field intensities of all detection points are between the upper limit and the lower limit. The high-uniformity magnet is prepared through the method, the magnetic field intensity uniformity of the magnet is smaller than or equal to 1.5%, and the overall magnetic performance loss is smaller than or equal to 1%. Unification of high uniformity and low performance loss is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-uniformity magnet preparation, and particularly relates to a method for improving the stability of the magnetic field strength of a magnet and a high-uniformity magnet prepared by the method. BACKGROUND

[0002] Rare earth permanent magnet materials, especially sintered rare earth permanent magnet materials, are widely used in high-end technical fields such as electric vehicles, aerospace equipment, high-end numerical control machine tools and precision sensors due to their excellent magnetic properties. The continuous development of these applications puts forward very high requirements for the uniformity (i.e. consistency) of the magnetic field strength distribution of the permanent magnet. Poor uniformity of the magnetic field of the magnet will directly lead to torque fluctuation and noise increase of the precision motor, or reduce the measurement accuracy of the magnetic sensor, which seriously restricts the further improvement of the performance of high-end equipment.

[0003] At present, the improvement of the uniformity of the magnetic field of the magnet mainly starts from two ways: one is to optimize the whole preparation process of the magnet from powder making, orientation forming to sintering, so as to obtain a magnet with better intrinsic uniformity; the other is to adjust the magnetization state of the magnet after magnetization by external means to compensate for the deviation caused in the manufacturing process. However, the preparation process of the magnet is complex and has many links, and it is difficult and costly to completely rely on process optimization to achieve very high uniformity. Therefore, the magnet field regulation technology after magnetization is particularly important.

[0004] The existing regulation technology, such as overall demagnetization or simple local magnetization correction, generally has low regulation accuracy, poor stability and uncontrollable process. In the regulation process, the magnetic field is prone to fluctuate sharply due to over-regulation or inaccurate regulation area, which not only makes it difficult to achieve the expected uniformity target, but also may cause irreversible performance loss of the magnet. Therefore, developing a method that can stably, accurately and controllably adjust the uniformity of the magnetic field of the magnet and maximize the retention of the performance of the magnet has become a technical problem to be solved in the field. SUMMARY

[0005] In view of the above analysis, the embodiments of the present application aim to provide a method for improving the stability of the magnetic field strength of a magnet and a high-uniformity magnet, to at least solve one of the technical problems of the existing magnet field regulation technology, such as insufficient stability, low control accuracy and easy performance loss of the magnet.

[0006] In one aspect, the embodiments of the present application provide a method for improving the stability of the magnetic field strength of a magnet, comprising the following steps:

[0007] S1, fixing the magnet with saturated magnetization, and detecting the magnetic field strength distribution on the surface of the magnetic pole of the magnet;

[0008] S2, according to the magnetic field intensity distribution, taking the average value of the magnetic field intensity distribution as the upper limit value of adjustment, and taking the minimum value of the magnetic field intensity distribution as the lower limit value of adjustment;

[0009] S3, for the magnet with initial magnetic field intensity non-uniformity > 5%, first heat the area with magnetic field intensity higher than the upper limit value of adjustment by using the thermal demagnetization effect until the magnetic field intensity non-uniformity of the magnet is reduced to below 5%;

[0010] S4, for the magnet treated by step S3 or with initial magnetic field intensity non-uniformity ≤ 5%, the detected area with magnetic field intensity higher than the upper limit value of adjustment is corrected in magnetization state by using pulse magnetic field until the magnetic field intensity of all detection points is between the lower limit value of adjustment and the upper limit value of adjustment.

[0011] Further, in step S4, the pulse magnetic field is generated by a pulse magnetic field coil, the pole head size of the pulse magnetic field coil is 2-6mm, the distance between the pole head and the surface of the magnet is 0.2-1mm; and the detection position of the magnetic field intensity corresponds to the center position of the pulse magnetic field.

[0012] Further, in step S3, the heating temperature of the thermal demagnetization effect is 100-400℃, and a stepwise heating mode is adopted, and the temperature rising gradient of single adjustment is ≤ 50℃.

[0013] Further, in step S4, the control voltage range of the pulse magnetic field is 200-700V, and the initial voltage is ≤ 200V.

[0014] Further, in step S4, according to the magnetic field intensity change rate caused by single pulse magnetic field, the control voltage value of the next pulse magnetic field is adjusted, and the adjustment method is as follows:

[0015] If the magnetic field intensity change rate is ≤ 0.5%, the control voltage is increased by 30-50V;

[0016] If the magnetic field intensity change rate is > 0.5% and ≤ 1%, the control voltage is increased by 10-30V;

[0017] If the magnetic field intensity change rate is > 1% and ≤ 1.5%, the control voltage is increased by 2-10V.

[0018] Further, step S4 is: identifying the maximum value point position exceeding the upper limit value of adjustment in the current magnetic field intensity distribution; using pulse magnetic field to adjust the maximum value point position single or multiple times; re-detecting the magnetic field intensity distribution; if there is still a point exceeding the upper limit value of adjustment, identifying the new maximum value point position and adjusting, and so on until there is no maximum value point position exceeding the upper limit value of adjustment.

[0019] Further, after a complete step S4 is performed, the average value and the minimum value of the magnetic field intensity distribution are recalculated according to the new magnetic field intensity distribution result, and are set as a new upper limit value and a lower limit value of adjustment, and then step S4 is repeated until the magnetic field intensity uniformity of the magnet reaches a preset final target value.

[0020] Further, in step S4, when the maximum value point position is adjusted, the adjustment angle of the pulse magnetic field pole head is ≤15°, and the positioning correction angle of the detection position and the magnetic field adjustment corresponding position is ≤2°.

[0021] Further, the magnet is a sintered permanent magnet material, the room temperature coercive force of the sintered permanent magnet material is not less than 5kOe, and the surface processing size precision after the magnetic field regulation is better than 0.05mm.

[0022] On the other hand, the application provides a high-uniformity magnet prepared by the above method, the magnetic field intensity uniformity of the magnet is ≤1.5%, and the overall magnetic performance loss of the magnet after regulation is ≤1%.

[0023] Compared with the prior art, the application can achieve at least one of the following beneficial effects:

[0024] 1) The application is aimed at a magnet with a large magnetic field intensity non-uniformity (>5%), and first uses thermal demagnetization for coarse adjustment, quickly and gently reduces the overall non-uniformity to a lower level (≤5%), avoids over-regulation or local performance changes caused by direct use of a pulse magnetic field. Then, for the remaining small deviation, the pulse magnetic field is used for fine adjustment. This step-by-step gradient adjustment method effectively reduces the regulation risk and ensures the stability of the process.

[0025] 2) The application establishes a quantitative relationship between the magnetic field intensity change rate and the voltage increment, so that the system can automatically decide the regulation strength of the next time according to the regulation effect of the last time. This closed-loop control method enables the regulation process to have self-learning and self-adaptive capabilities, and can push the magnetic field intensity into the target range, solving the problem of inaccurate control and poor stability caused by fixed parameters in traditional open-loop adjustment.

[0026] 3) The method of the application does not process all high value points at the same time, but only targets the current highest extreme point for point removal each time, and through repeated detection, positioning and adjustment cycles, the magnetic field distribution quickly tends to be uniform. By dynamically updating and narrowing the upper and lower limits of the regulation target after each cycle, the magnet uniformity can be optimized step by step until it reaches a high standard of within 1.5%, while the overall performance loss of the magnet is controlled to be below 1%, which preserves the core performance of the magnet while improving the uniformity.

[0027] The technical solutions in the present application can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the following description, and some advantages will become apparent from the description or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and obtained by the content particularly indicated in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this application. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0029] Figure 1 Figure 1 is a comparison chart of the magnetic field intensity distribution of the magnet in Example 1 of the present application before and after the magnet is regulated by the method of the present application. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present application will be described in detail below with reference to the drawings, in which the drawings constitute a part of this application. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application, but are not intended to limit the scope of the present application.

[0031] In the prior art, the adjustment of the uniformity of the magnetic field of a magnet is often single in means or rough in control, and it is difficult to improve the uniformity while ensuring the stability of the regulation process and the retention of the performance of the magnet. Based on the understanding of the demagnetization and magnetization mechanism of a magnet, the present application innovatively proposes a step-by-step and controllable compound regulation strategy.

[0032] In one specific embodiment of the present application, a method for improving the stability of the regulation of the magnetic field intensity of a magnet is disclosed, which comprises the following steps:

[0033] S1, fixing a magnet saturated by magnetization, and detecting the magnetic field intensity distribution on the surface of the magnetic pole of the magnet;

[0034] S2, according to the magnetic field intensity distribution, taking the average value of the magnetic field intensity distribution as the upper limit value of adjustment, and taking the minimum value of the magnetic field intensity distribution as the lower limit value of adjustment;

[0035] S3, for the magnet with an initial magnetic field intensity non-uniformity > 5%, first heating the area with a magnetic field intensity higher than the upper limit value of adjustment by using the thermal demagnetization effect until the magnetic field intensity non-uniformity of the magnet is reduced to ≤ 5%;

[0036] S4, for the magnet treated by step S3 or with an initial magnetic field intensity non-uniformity ≤ 5%, correcting the magnetization state of the detected area with a magnetic field intensity higher than the upper limit value of adjustment by using a pulse magnetic field until the magnetic field intensity of all detection points is between the lower limit value of adjustment and the upper limit value of adjustment.

[0037] Specifically, the "magnetic field strength non-uniformity" is a quantitative index for characterizing the fluctuation degree of the magnetic field strength on the surface of the magnet. The smaller the value is, the higher the uniformity of the magnetic field of the magnet is. It can be calculated in a manner known to those skilled in the art, for example, based on the ratio of the standard deviation to the average value of the magnetic field strength distribution, or based on the relative deviation of the maximum value and the minimum value, etc. In the present application, the maximum absolute deviation between the maximum value (B max ), the minimum value (B min ) and the average value (B avg ) of the magnetic field strength distribution on the surface of the magnet is used to calculate the percentage of the average value, and the magnetic field strength non-uniformity δ is calculated according to the following formula:

[0038] The "magnetic saturation" refers to applying an external magnetic field to the magnet that exceeds its intrinsic coercivity, so that the magnetization reaches a technical saturation state.

[0039] In implementation, first, the sintered neodymium-iron-boron magnet that has completed the magnetization is fixed on a worktable that can be precisely moved by a non-magnetic clamp. A magnetic field measuring device such as a Hall probe or a magnetoresistive sensor is used to obtain a magnetic field strength distribution map on the surface of the magnetic pole (as shown in FIG. 1) in a dot matrix scanning manner. Based on the distribution data, the average value and the minimum value are calculated, and the average value is used as the initial adjustment upper limit value, and the minimum value is used as the initial adjustment lower limit value. This setting method can adaptively determine the target interval according to the actual state of the magnet, avoiding the blindness of artificially setting fixed target values. Figure 1

[0040] Compared with the prior art which uses a single control method or fixed parameters for overall processing, the scheme provided in the present embodiment lays a reliable foundation for subsequent fine control by first setting a dynamic target range and then processing in steps.

[0041] The present application realizes hierarchical processing of problems of different scales by explicitly dividing the control process into two stages of thermal demagnetization coarse adjustment for large deviations and pulse magnetic field fine adjustment for small deviations. This hierarchical processing method enables the use of the thermal demagnetization effect to gently and extensively reduce the magnetic field strength when dealing with severe non-uniformity, avoiding local overshoot and performance mutation that may be caused by the pulse magnetic field; and when fine correction is performed, the advantages of fast response and accurate positioning of the pulse magnetic field can be utilized, thereby achieving the unity of control stability and accuracy as a whole.

[0042] Further, in order to realize precise local control of the magnetic field, in step S4, the pulse magnetic field is generated by a pulse magnetic field coil, the pole head size of the pulse magnetic field coil is 2-6 mm, the distance between the pole head and the surface of the magnet is 0.2-1 mm, and the detection position of the magnetic field strength corresponds to the center position of the pulse magnetic field. ​

[0043] Specifically, the choice of magnetic pole head size is crucial. Too small a size (e.g., <2mm) may result in an insufficiently small effective area and low adjustment efficiency; too large a size (e.g., >6mm) will affect positioning accuracy and easily affect adjacent areas that should not be adjusted. Similarly, controlling the distance within the range of 0.2–1mm ensures sufficient magnetic field strength and concentration. Too far a distance will cause the magnetic field to diverge and weaken, while too close a distance poses a risk of mechanical collision. Simultaneously, reducing the relative fluctuation gradient of the magnetic field strength is beneficial for obtaining sufficient adjustment amplitude control accuracy. The detection position corresponds to the center of action, ensuring spatial consistency between the control area and the measurement feedback area, which is a prerequisite for achieving high-precision closed-loop control. This series of parameter settings allows the control energy to be focused on a small target area, laying the foundation for high stability in single-step adjustment.

[0044] Furthermore, considering the stability and controllability of heat treatment, in step S3, the heating temperature for the thermal demagnetization effect is 100-400℃, and a stepped heating method is adopted, with a temperature increase gradient of ≤50℃ for each adjustment.

[0045] Thermal demagnetization utilizes the principle that the magnetization of magnetic materials reversibly decreases with increasing temperature below the Curie temperature. The choice of a temperature range of 100–400℃ is based on the significant thermal demagnetization effect of common rare-earth permanent magnet materials (such as neodymium iron boron) within this range, while remaining well below their Curie temperature to avoid irreversible magnetic property damage. Employing a stepped heating method with a single temperature gradient ≤50℃ allows the operator to monitor magnetic field changes after each heating and determine the next step based on the feedback. This effectively avoids excessive demagnetization and performance loss caused by excessively high temperatures in a single operation, ensuring a smooth and controllable adjustment process.

[0046] This invention uses a 5% magnetic field strength non-uniformity as the dividing point between steps S3 and S4, based on a comprehensive consideration of method characteristics and process efficiency. The thermal demagnetization method in step S3 has a wide range of application and a large adjustment range, suitable for global coarse adjustment; the pulsed magnetic field method in step S4, on the other hand, has a precise application point and controllable adjustment force, suitable for local fine adjustment. When the non-uniformity is >5%, it indicates a macroscopic deviation, requiring rapid reduction of the non-uniformity to below 5% via thermal demagnetization to lay the foundation for subsequent fine adjustment; if the initial non-uniformity is ≤5%, it indicates a local micro-area deviation, allowing direct pulsed magnetic field fine adjustment, thus avoiding the performance damage risk that thermal demagnetization may cause.

[0047] Furthermore, in order to precisely control the intensity of the pulsed magnetic field, in step S4, the control voltage range for applying the pulsed magnetic field is 200 to 700V, and the initial voltage is ≤200V.

[0048] The pulsed magnetic field energy is generated by capacitor discharge, and its voltage value is positively correlated with the peak value of the final generated magnetic field strength. Limiting the voltage range to 200–700V provides a gradient of control from gentle to strong. Setting the initial voltage to ≤200V is based on the principle of robust startup; a small amount of energy is used for trial adjustments to observe the magnet's response. This effectively prevents a sudden drop in magnetic field strength due to excessive energy in the first adjustment step, thus avoiding the risk of over-adjustment and is a key setting to ensure stability throughout the fine-tuning phase.

[0049] Furthermore, this invention introduces an intelligent feedback mechanism. In step S4, the control voltage value for the next pulsed magnetic field is adjusted based on the rate of change of magnetic field strength caused by a single application of the pulsed magnetic field. The adjustment method is as follows: if the rate of change of magnetic field strength is ≤0.5%, the control voltage is increased by 30-50V; if the rate of change of magnetic field strength is greater than 0.5% and ≤1%, the control voltage is increased by 10-30V; if the rate of change of magnetic field strength is greater than 1% and ≤1.5%, the control voltage is increased by 2-10V.

[0050] Using the above control method, when the previous adjustment effect is not significant (change rate ≤ 0.5%), the control intensity will be increased, resulting in a larger voltage increase (30–50V). When the adjustment effect is moderate (0.5%–1%), it indicates that the current control intensity is appropriate, and only a slight increase (10–30V) is needed to continue approaching the target. When the adjustment effect is already very significant (1%–1.5%), only a very small increase (2–10V) is needed for fine-tuning, thus greatly avoiding the possibility of over-adjustment. Based on real-time feedback adaptive voltage regulation, the entire control process dynamically matches the most suitable control parameters, thereby significantly improving the accuracy of the adjusted magnetic field changes and the repeatability of the entire process.

[0051] Further, step S4 specifically involves: identifying the location of the maximum value point in the current magnetic field strength distribution that exceeds the adjustment upper limit; using a pulsed magnetic field to adjust the location of the maximum value point only once or multiple times; re-detecting the magnetic field strength distribution; if there are still points exceeding the adjustment upper limit, identifying new maximum value point locations and adjusting them, iterating in this way until there are no maximum value point locations exceeding the adjustment upper limit.

[0052] The advantage of this strategy is that it addresses only the most prominent problem (the highest point) at a time, rather than attempting to suppress all high-value points simultaneously. This single control objective simplifies the control logic and increases stability. By eliminating peak after peak, the overall magnetic field distribution converges quickly and smoothly to the target range. This method is particularly advantageous for controlling the adjustment amplitude, avoiding unnecessary interference or weakening of low-value regions, thus effectively preserving the overall performance of the magnet while improving uniformity.

[0053] Furthermore, in order to achieve a higher uniformity standard, after a complete execution of step S4, the average value and minimum value of the magnetic field strength distribution are recalculated based on the new magnetic field strength distribution results and set as the new upper and lower adjustment limits. Then, step S4 is repeated until the uniformity of the magnet's magnetic field strength reaches the preset final target value.

[0054] Once a round of peak removal is completed, the overall uniformity of the magnet has improved, and the original upper and lower limits may become more lenient. By recalculating and narrowing the target window, the system can begin a new round of optimization at a higher precision level. This multi-round cyclic mechanism allows the magnetic field uniformity of the magnet to be optimized layer by layer, gradually approaching the final target (such as 1.5%), achieving a step-by-step leap in control precision.

[0055] Furthermore, in step S4, when adjusting the position of the maximum value point, the adjustment angle of the pulse magnetic field pole head is ≤15°, and the positioning correction angle between the detection position and the corresponding position of the magnetic field adjustment is ≤2°.

[0056] This requirement ensures the positioning accuracy of the control. Excessive adjustment and correction angles of the electrode tip can cause the control center to deviate from the predetermined high point, not only failing to effectively correct the target point but also potentially damaging surrounding areas and introducing new inhomogeneities. Strictly limiting the angles to within 15° and 2° ensures that each pulse of energy accurately targets the core position of the predetermined control area, forming the physical basis for achieving high-precision control.

[0057] Furthermore, the method of the present invention has requirements for the magnet substrate, wherein the magnet is preferably a sintered permanent magnet material, such as rare earth permanent magnets such as neodymium iron boron (NdFeB) and samarium cobalt (SmCo). The room temperature coercivity of the sintered permanent magnet material is not less than 5 kOe, and the dimensional accuracy of the surface processing for magnetic field control needs to be better than 0.05 mm.

[0058] The high coercivity of at room temperature, not less than 5 kOe, ensures that the magnet has sufficient magnetic stability when subjected to local thermal demagnetization and pulsed magnetic field disturbances. It can effectively resist uncontrollable excessive demagnetization and is the material basis for achieving an overall performance loss of ≤1% in the magnet.

[0059] The high dimensional accuracy of the surface processing is better than 0.05mm, which ensures that the magnetic field detection probe and the pulse magnetic pole head maintain a constant optimal distance from the magnet surface during operation, thereby avoiding measurement errors and inaccuracies in magnetic field strength caused by distance fluctuations.

[0060] High coercivity and high dimensional accuracy together provide a stable and regular foundation for subsequent fine control, which is a necessary condition for achieving the goal of high uniformity and low performance loss.

[0061] On the other hand, in a specific embodiment of the present invention, a highly uniform magnet is disclosed, which is prepared by the method described above, and has a magnetic field strength uniformity of ≤1.5%, and after adjustment, its overall magnetic performance loss is ≤1%.

[0062] The overall magnetic performance loss is a key indicator for measuring the change in magnetic field strength during the uniformity adjustment of a magnet. It refers to the minimum magnetic field strength (B) within a specified measurement area on the magnet surface after adjustment. min (after) relative to the minimum magnetic field strength (B) in the same measurement area before adjustment min The reduction rate of (before). The calculation formula is as follows:

[0063]

[0064] The highly uniform magnets prepared by the method of this invention employ a gentle process of heating before magnetization, supplemented by precise control strategies such as adaptive feedback and iterative peak clipping. This ensures that the magnetic moments of the magnet undergo only minor and controllable reorientation in the localized areas requiring adjustment, while the main phase structure and most of the magnetization properties are well preserved. Therefore, it is possible to significantly reduce magnetic field strength fluctuations to within 1.5% while suppressing the loss of core magnetic properties to an extremely low level of 1%.

[0065] Compared with existing technologies, the high-uniformity magnet provided in this embodiment successfully resolves the technical contradiction of the difficulty in achieving both high uniformity and high performance. It does not sacrifice magnetic properties for uniformity, but rather, while preserving the inherent properties of the magnet to the maximum extent, it stimulates its inherent uniformity potential through advanced post-processing control techniques.

[0066] The magnetic field uniformity (≤1.5%) of the magnet provided by this invention can directly improve the performance and stability of application end products (such as high-end servo motors and precision magnetic encoders); while its extremely low performance loss (≤1%) ensures the high magnetic energy output of the magnet body, meeting the stringent requirements of high-end equipment for power density and efficiency. This makes the magnet particularly suitable for advanced manufacturing fields with extremely high requirements for both magnetic field stability and magnetic performance.

[0067] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0068] Example 1

[0069] In this embodiment, the magnet pole tuning surface of the magnet has an arc structure to adjust the uniformity of the circumferential magnetic field distribution. The magnet's dimensional machining accuracy is 0.01 mm, and its coercivity is 18.5 kOe. The method for improving the stability of the magnet's magnetic field strength is as follows:

[0070] S1. After saturating the magnet with magnetization, use a magnet magnetic field strength test probe to closely adhere to the magnet surface, perpendicular to the magnetic pole orientation plane, and detect the magnetic field strength distribution on the magnet pole surface (e.g., Figure 1 (As shown). The measured maximum magnetic field strength was 261.9 mT, the minimum was 244.1 mT, and the average was 251.5 mT. The initial magnetic field strength inhomogeneity was Max(|261.9-251.5|,|244.1-251.5|) / 251.5×100%=Max(10.4,7.4) / 251.5×100%=4.13%.

[0071] S2. Set the average strength value of 251.5mT as the upper limit of adjustment and the minimum strength value of 244.1mT as the lower limit of adjustment.

[0072] S3. Since the initial magnetic field strength non-uniformity (4.13%) is ≤5%, this step is skipped.

[0073] S4. A magnetic pole head with a 4mm pulsed magnetic field coil is positioned 0.7mm from the magnetic pole surface, corresponding to the center area of ​​the test location. The angle range of the highest value area is controlled within 12°, and the angle between the test location and the magnetic field positioning correction is 0°. The pulsed magnetic field control voltage is initially set to 200V. Subsequently, the voltage is adjusted sequentially at the identified highest value positions, with adjustments made to 250V, 300V, 330V, 350V, 370V, 380V, and 396V. The magnetic deviation position is repeatedly detected and its uniformity adjusted accordingly.

[0074] After adjustment, the maximum magnetic field strength of the magnet was 246.7 mT, the minimum was 242.4 mT, and the average was 244.8 mT. The final magnetic field strength non-uniformity was Max(|246.7-244.8|,|242.4-244.8|) / 244.8×100%=Max(1.9,2.4) / 244.8×100%=0.98%. The overall magnetic performance loss (the decrease in the minimum magnetic field strength in the specified measurement area on the magnet surface after adjustment compared to the minimum magnetic field strength in the same measurement area before adjustment)=(244.1-242.4) / 244.1×100%=0.7%.

[0075] Example 2

[0076] In this embodiment, the magnet's pole tuning surface has a circular arc structure to adjust the uniformity of the circumferential magnetic field distribution. The magnet's dimensional machining accuracy is 0.05 mm, and its coercivity is 22.1 kOe. The method for improving the stability of the magnet's magnetic field strength is as follows:

[0077] S1. After saturating the magnet with magnetization, a magnetic field strength test probe was placed tightly against the magnet surface, perpendicular to the magnetic pole orientation plane, for testing. The measured maximum magnetic field strength was 363.3 mT, the minimum was 311.5 mT, and the average was 328.3 mT. The initial magnetic field strength non-uniformity was Max(|363.3-328.3|,|311.5-328.3|) / 328.3×100%=Max(35.0,16.8) / 328.3×100%=10.7%.

[0078] S2. Set the upper limit to 328.3mT and the lower limit to 311.5mT.

[0079] S3. Due to the initial magnetic field strength non-uniformity (10.7%) > 5%, thermal demagnetization is performed first. Starting from the position of the maximum value, a stepped heating temperature is applied within an angle range of 10°, starting from 100°C, and successively 150°C, 170°C, 180°C, and 190°C, processing is carried out step by step starting from the high value region.

[0080] S4. After thermal demagnetization, the magnetic field strength non-uniformity decreased to 3.9% (maximum value 329.7mT, minimum value 309.1mT, average value 321.6mT). Subsequently, fine-tuning of the pulse magnetic field was performed. A 4mm pulse magnetic field coil was used, with a distance of 0.2mm and a positioning correction angle of 2°. The initial pulse magnetic field control voltage was 200V, and the voltage was adjusted sequentially at the highest value position, with adjustments made to 250V, 320V, 330V, 335V, and 337V respectively.

[0081] After adjustment, the maximum magnetic field strength of the magnet was 315.2 mT, the minimum was 308.9 mT, and the average was 311.1 mT. The final magnetic field strength non-uniformity was Max(|315.2-311.1|,|308.9-311.1|) / 311.1×100%=Max(3.1,3.2) / 312.1×100%=1.3%. The overall magnetic performance loss (the decrease in the minimum magnetic field strength in the specified measurement area on the magnet surface after adjustment compared to the minimum magnetic field strength in the same measurement area before adjustment)=(311.5-308.9) / 311.5×100%=0.8%.

[0082] Example 3

[0083] In this embodiment, the magnet pole tuning surface has a planar structure, adjusting the uniformity of the magnetic field distribution in the planar area. The magnet's dimensional machining accuracy is 0.035 mm, and its coercivity is 9.6 kOe. The method for improving the stability of the magnet's magnetic field strength is as follows:

[0084] S1. After the magnet is saturated with magnets, a magnetic field strength test probe is placed close to the magnet surface and perpendicular to the magnetic pole orientation plane for testing. The maximum magnetic field strength was measured to be 412.7 mT, the minimum to be 393.1 mT, and the average to be 406.5 mT. The initial magnetic field strength non-uniformity was calculated to be 3.3%.

[0085] S2. Set the upper limit of adjustment to 406.5mT and the lower limit of adjustment to 393.1mT.

[0086] S3. Since the initial magnetic field strength non-uniformity (3.3%) is ≤5%, this step is skipped.

[0087] S4. Using a 6mm pulsed magnetic field coil, align the magnetic pole head with the center area of ​​the test position, 0.5mm from the magnetic pole surface, to detect and locate the highest value position. Adjust the magnetic field using the position area obtained by the pulsed coil magnetic pole head, controlling the angle range of the highest value area within 15°. The correction angle between the test position and the magnetic field positioning is 0°. The initial pulsed magnetic field control voltage is 200V. Test and adjust the highest value area sequentially, adjusting the voltage to 250V, 280V, 300V, 315V, and 320V. Repeat the detection and uniformity adjustment of the magnet deviation position sequentially.

[0088] After adjustment, the maximum magnetic field strength of the magnet was 397.9 mT, the minimum was 390.2 mT, and the average was 394.2 mT. The final magnetic field strength non-uniformity was Max(|397.9-394.2|,|390.2-394.2|) / 394.2×100%=Max(3.7,4.0) / 394.2×100%=1.0%, and the overall magnetic performance loss was (393.1-390.2) / 393.1×100%=0.7%.

[0089] Example 4

[0090] In this embodiment, the magnet pole tuning surface has a planar structure, adjusting the uniformity of the magnetic field distribution in the planar area. The magnet's dimensional machining accuracy is 0.03 mm, and its coercivity is 26 kOe. The method for improving the stability of the magnet's magnetic field strength is as follows:

[0091] S1. After saturating the magnet with magnetization, a magnetic field strength test probe was placed tightly against the magnet surface, perpendicular to the magnetic pole orientation plane, for testing. The measured maximum magnetic field strength was 329.7 mT, the minimum was 301.5 mT, and the average was 310.5 mT. The initial magnetic field strength non-uniformity was calculated to be 6.2%.

[0092] S2. Set the upper limit of adjustment to 310.5mT and the lower limit of adjustment to 301.5mT.

[0093] S3. Due to the initial magnetic field strength non-uniformity (6.2%) > 5%, thermal demagnetization is performed first. Starting from the position of the maximum value, with a position angle range of 10°, the thermal demagnetization is performed at heating temperatures of 100℃, 150℃, 200℃, 230℃, 250℃, and 265℃, starting from the high value region and proceeding in steps.

[0094] S4. After thermal demagnetization, the magnetic field strength non-uniformity decreased to 2.8% (maximum value 312.5mT, minimum value 299mT, average value 307.8mT). Subsequently, fine-tuning of the pulsed magnetic field was performed. The magnetic pole head of a 2mm pulsed magnetic field coil was aligned with the center area of ​​the test position, 0.5mm from the magnetic pole surface, to detect and locate the highest value position. The magnetic field was adjusted using the position area obtained by the pulsed coil magnetic pole head, with a correction angle of 1° between the test position and the magnetic field positioning. The initial pulsed magnetic field control voltage was 200V. The highest value position was tested and adjusted sequentially, with voltages of 250V, 300V, 350V, 400V, 450V, 500V, 550V, 580V, 600V, and 605V. The magnet deviation position was repeatedly detected and its uniformity adjusted sequentially.

[0095] After adjustment, the maximum magnetic field strength of the magnet was 303.5 mT, the minimum was 298.5 mT, and the average was 301.1 mT. The final magnetic field strength non-uniformity was Max(|303.5-301.1|,|298.5-301.1|) / 301.1×100%=Max(2.4,2.6) / 301.1×100%=0.86%, and the overall magnetic performance loss was (301.5-298.5) / 301.5×100%=1.0%.

[0096] Comparative Example 1

[0097] The magnet is the same as in Example 1. The method for improving the stability of the magnetic field strength of the magnet is basically the same as in Example 1, except that in step S4, the angle range of the highest value region is expanded to 20°, and the pulse magnetic field control voltage is initially set to 700V.

[0098] After adjustment, the magnetic field value in the high-value region exhibited significant uncontrollable changes. After the adjustment was completed, the range of changes in the magnetic field strength distribution of the magnet deteriorated to 42%, and the overall magnetic performance loss was as high as 48%.

[0099] Comparative Example 2

[0100] The magnet is the same as in Example 2. The method for improving the stability of the magnetic field strength of the magnet is basically the same as in Example 2, except that the S3 (thermal demagnetization) step is omitted, and the S4 (pulse magnetic field) control is performed directly. The angle range of the highest value region is 10°. To obtain a sufficient adjustment range, the pulse voltage needs to be continuously increased (up to 410V), which leads to an expansion of the adjustment area and large fluctuations in the magnetic field value of some magnetic pole regions.

[0101] The final magnetic field strength non-uniformity of the magnet was 1.7%, the overall magnetic performance loss was 2.8%, and the adjustment cycle was extended.

[0102] Comparative Example 3

[0103] The magnet is the same as in Example 3. The method for improving the stability of the magnetic field strength of the magnet is basically the same as in Example 3, except that in step S3, a thermal demagnetization operation is initially used, and the magnet demagnetizes by more than 5% at a temperature of 100°C. Subsequently, in step S4, after adjusting the voltage to 300V, the adjustment voltage is further increased by 50V.

[0104] After adjustment, the magnetic field strength non-uniformity of the magnet was 5.3%, and the overall magnetic performance loss was 7.8%.

[0105] Characterization results and analysis

[0106] The characterization results of the above-described embodiments and comparative examples are shown in Table 1 below.

[0107] Table 1. Performance Comparison of Examples and Comparative Examples

[0108]

[0109]

[0110] like Figure 1 As shown, this is a comparison of the distribution curves of the surface magnetic field strength (B) of the magnet before and after the application of the method of the present invention in Example 1, showing the change with the polar angle (Grad). Curve AT represents the magnetic field distribution after adjustment, and curve NT represents the initial magnetic field distribution before adjustment. It can be clearly seen that after adjustment by the method of the present invention, the fluctuation of the magnetic field strength distribution is significantly reduced, and curve AT becomes extremely flat compared to curve NT. This proves that the method of the present invention is effective in improving the uniformity of the magnetic field.

[0111] As shown in Table 1, the method of the present invention (Examples 1-4) can significantly reduce the magnetic field strength inhomogeneity under different initial conditions and magnet structures, and successfully control it below 1.5%, while strictly limiting the overall magnetic performance loss of the magnet to within 1%. This proves that the method of the present invention has excellent universality and stability, and effectively solves the technical problem of the difficulty in balancing high uniformity and low performance loss.

[0112] In contrast, the comparative examples that did not fully follow the key steps of this invention all experienced different forms of failure: Comparative Example 1 suffered severe performance degradation due to improper parameter control; Comparative Example 2 experienced a significant increase in overall magnetic performance loss due to skipping the thermal demagnetization step; and Comparative Example 3 suffered from unsatisfactory uniformity and overall magnetic performance loss due to incorrect application of thermal demagnetization. These comparative examples, from the opposite perspective, verify the necessity of each key step and parameter range in the technical solution of this invention.

[0113] In summary, this invention, through a stepwise gradient adjustment of the temperature field and a specific pulsed magnetic field, can achieve high-precision control of magnetic field strength uniformity without significantly impairing magnet performance, providing a reliable solution for the fabrication of high-performance magnetic components.

[0114] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the stability of the magnetic field strength of a modulated magnet, characterized in that, Includes the following steps: S1. Fix the magnet that has been magnetized to saturation and detect the magnetic field strength distribution on the surface of the magnet's magnetic poles; S2. Based on the magnetic field strength distribution, adjust the upper limit value using the average value of the magnetic field strength distribution and adjust the lower limit value using the minimum value of the magnetic field strength distribution; S3. For magnets with an initial magnetic field strength non-uniformity > 5%, the area with a magnetic field strength higher than the upper limit of adjustment is first heated using the thermal demagnetization effect until the magnetic field strength non-uniformity of the magnet is reduced to below 5%. S4. For magnets that have been processed in step S3 or whose initial magnetic field strength non-uniformity is ≤5%, use pulsed magnetic field to correct the magnetization state of the areas where the detected magnetic field strength is higher than the upper limit of adjustment, until the magnetic field strength of all detection points is between the lower limit of adjustment and the upper limit of adjustment.

2. The method according to claim 1, characterized in that, In step S4, the pulsed magnetic field is generated by a pulsed magnetic field coil. The size of the magnetic pole head of the pulsed magnetic field coil is 2-6 mm, and the distance between the magnetic pole head and the surface of the magnet is 0.2-1 mm. The detection position of the magnetic field strength corresponds to the position of the center of action of the pulsed magnetic field.

3. The method according to claim 1, characterized in that, In step S3, the heating temperature for the thermal demagnetization effect is 100-400℃, and a stepped heating method is adopted, with a temperature increase gradient of ≤50℃ for each adjustment.

4. The method according to claim 1, characterized in that, In step S4, the control voltage range for applying the pulsed magnetic field is 200 to 700V, and the initial voltage is ≤200V.

5. The method according to claim 4, characterized in that, In step S4, the control voltage value for the next pulsed magnetic field is adjusted based on the rate of change of magnetic field strength caused by a single pulsed magnetic field application. The adjustment method is as follows: If the rate of change of the magnetic field strength is ≤0.5%, the control voltage is increased by 30-50V; If the rate of change of the magnetic field strength is greater than 0.5% and less than or equal to 1%, the control voltage is increased by 10 to 30V. If the rate of change of the magnetic field strength is greater than 1% and less than or equal to 1.5%, the control voltage is increased by 2 to 10V.

6. The method according to claim 1, characterized in that, Step S4 specifically involves: identifying the location of the maximum value point in the current magnetic field strength distribution that exceeds the adjustment upper limit; using a pulsed magnetic field to adjust the location of the maximum value point only once or multiple times; re-detecting the magnetic field strength distribution; if there are still points exceeding the adjustment upper limit, identifying new maximum value point locations and adjusting them, iterating in this way until there are no maximum value point locations exceeding the adjustment upper limit.

7. The method according to claim 1, characterized in that, After a complete execution of step S4, based on the new magnetic field strength distribution results, the average and minimum magnetic field strength distribution values ​​are recalculated and set as the new upper and lower adjustment limits. Then, step S4 is repeated until the uniformity of the magnet's magnetic field strength reaches the preset final target value.

8. The method according to claim 6, characterized in that, In step S4, when adjusting the position of the maximum value point, the adjustment angle of the pulse magnetic field pole head is ≤15°, and the positioning correction angle between the detection position and the corresponding position of the magnetic field adjustment is ≤2°.

9. The method according to claim 1, characterized in that, The magnet is a sintered permanent magnet material with a room temperature coercivity of not less than 5 kOe and a surface processing dimensional accuracy better than 0.05 mm for magnetic field control.

10. A highly uniform magnet, characterized in that, The magnet is prepared by any one of claims 1 to 9, the magnetic field strength uniformity of the magnet is ≤1.5%, and after adjustment, the overall magnetic performance loss of the magnet is ≤1%.

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