A high-precision encoder magnetic grating material and a method for fabricating the encoder magnetic grating.

Abstract

This invention relates to the field of magnetic encoder technology, and discloses a high-precision encoder magnetic grating material and a method for preparing the encoder magnetic grating. By weight, the encoder magnetic grating material raw materials include: 20-95 parts of anisotropic samarium iron nitrogen or its composite magnetic powder, 0.1-1 parts of coupling agent, 5-80 parts of polymer resin, and 0.1-1.5 parts of additives. The preparation method includes mixing the raw materials and injection molding for orientation, demagnetizing to obtain a semi-finished product, and then magnetizing to obtain a high-precision encoder magnetic grating. This invention coats the samarium iron nitrogen magnetic powder with a coupling agent and adjusts the reasonable formula components. The encoder magnetic grating obtained after magnetic field orientation, demagnetization, and magnetization has good corrosion resistance, impact resistance, and good thermal stability, and possesses highly uniform surface magnetic intensity and zero-crossing accuracy of the magnetic pole waveform.

Description

Technical Field

[0001] This invention relates to the field of magnetic encoder technology, specifically to a high-precision encoder magnetic grating material and a method for preparing the encoder magnetic grating. Background Technology

[0002] Magnetic encoders have many advantages, such as simple structure, resistance to dust, fast response speed, small size, and low cost, and are widely used in industrial automation fields such as precision machinery, CNC machine tools, and robots.

[0003] A magnetic encoder mainly consists of a magnetic grating, a sensing element, and a signal processing circuit. The magnetic grating is the core component of the encoder, manufactured from permanent magnet materials. Magnetic gratings come in various structural shapes, such as magnetic drums, magnetic disks, magnetic rings, and linear magnetic scales, to meet the structural and installation requirements of different magnetic encoders. Different manufacturing processes can create alternating N and S poles on the magnetic grating. The magnetic field information possessed by these poles, such as surface magnetic strength and accuracy, zero-crossing accuracy of the pole waveform, coercivity, and temperature characteristics, has a crucial impact on the accuracy and resolution of the magnetic encoder. The magnetic field information of the grating poles is entirely determined by the material and manufacturing method of the grating.

[0004] Encoder magnetic grating materials are required to possess magnetic properties such as high remanence, high coercivity, high energy product, and wide temperature range. Most existing encoder magnetic grating permanent magnet materials use ferrite, neodymium iron boron, etc. For example, CN10968860A and CN102873325A both use ferrite or neodymium iron boron magnet materials.

[0005] CN10968860 A discloses an absolute magnetic rotary encoder, including a rotating shaft, a plurality of rotatable wheels, a plurality of encoding units corresponding one-to-one with the plurality of wheels, and one or more permanent magnet assemblies providing magnetic field bias for the plurality of encoding units. Each encoding unit includes a magnetically conductive encoder disk with a structure configured to make its permeability different with different positions relative to the rotating shaft, and a sensor unit including a plurality of magnetic sensors, wherein the permanent magnet assembly is made of one of barium ferrite, cobalt ferrite, neodymium iron boron, or ferrite.

[0006] CN102873325A discloses a layered feeding method for pressing neodymium iron boron magnetic powder into a mold. Common manufacturing methods for these materials and magnetic gratings include pressing ferrite with rubber or coating ferrite magnetic powder with a mixed oil adhesive. However, for applications requiring precision magnetic gratings with complex structures, compact dimensions, and multiple magnetic poles, the aforementioned materials and manufacturing methods suffer from problems such as low surface magnetic strength and accuracy, poor zero-crossing accuracy of magnetic pole waveforms, low coercivity, weak anti-electromagnetic interference ability, and poor corrosion resistance. Summary of the Invention

[0007] This invention addresses the problems of poor accuracy, low coercivity, and weak electromagnetic interference resistance of magnetic gratings made of ferrite and neodymium iron boron. It provides a material for encoder magnetic gratings with anisotropic samarium iron nitrogen as the main material. The encoder made from this material has good corrosion resistance, impact resistance, and good thermal stability, as well as highly uniform surface magnetic intensity and zero crossover accuracy of magnetic pole waveform.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A high-precision encoder magnetic grating material, by weight, comprises: 20-95 parts of anisotropic samarium iron nitrogen or its composite magnetic powder, 0.1-1 parts of coupling agent, 5-80 parts of polymer resin, and 0.1-1.5 parts of additives.

[0010] The anisotropic samarium iron nitrogen or its composite magnetic powder includes anisotropic samarium iron nitrogen magnetic powder and / or anisotropic samarium iron nitrogen and anisotropic ferrite composite magnetic powder.

[0011] Anisotropic samarium iron nitrogen (SMR) magnetic powder possesses excellent magnetic properties, comparable to anisotropic neodymium iron boron (NdFeB) and far superior to isotropic NdFeB and anisotropic ferrite magnetic powders. Furthermore, its corrosion resistance is significantly higher than that of neodymium-based magnetic powders. When used to fabricate encoder gratings, it can achieve higher surface magnetic intensity, enhancing the magnetic signal resolution space and signal-to-noise ratio. Simultaneously, anisotropic SMR magnetic powder exhibits high coercivity, more than twice that of anisotropic ferrite magnetic powders, which can improve the reliability of encoder gratings in electromagnetic environments.

[0012] However, there is very little research on the use of samarium iron nitrogen magnetic powder to prepare encoder gratings in the existing technology. Due to the unstable magnetic properties of samarium iron nitrogen magnetic powder, the encoder gratings manufactured using it have large fluctuations, poor surface magnetic accuracy and zero crossover accuracy of magnetic pole waveforms. Moreover, the encoder gratings made of samarium iron nitrogen magnetic powder have high requirements for magnetic field orientation magnitude and orientation consistency.

[0013] In this invention, anisotropic samarium iron nitrogen (SMR) or its composite magnetic powder, polymer resin, additives, and auxiliaries are uniformly mixed in a high-speed mixer, melt-blended, and extruded to obtain granules. These granules are then injection molded to obtain encoder magnetic gratings. The SMR magnetic powder is pre-coated with a coupling agent to overcome its magnetic instability and improve its compatibility with the polymer resin. By adjusting the formula components, the resulting permanent magnet material produces encoder magnetic gratings with good corrosion resistance, impact resistance, and thermal stability, exhibiting highly uniform surface magnetic intensity and zero-crossing accuracy of the magnetic pole waveform.

[0014] Preferably, the composite magnetic powder contains at least 20% by mass of anisotropic samarium iron nitrogen magnetic powder. Adding ferrite magnetic powder can effectively adjust the magnetic properties of the encoder grating, while ferrite magnetic powder also possesses good oxidation resistance.

[0015] Preferably, the anisotropic samarium iron nitrogen (SFI) or its composite magnetic powder is coated and modified with a coupling agent before use. To overcome the problems of unstable magnetic properties and easy surface oxidation of SFI, this invention uses a coupling agent to first coat and modify the SFI or its composite magnetic powder, making its magnetic powder properties more stable. Long-term contact with air will not cause adverse effects on magnetic powder properties such as oxidation. Simultaneously, the coated and modified magnetic powder is easily oriented under a magnetic field, ensuring the surface precision and quality of the encoder magnetic grating manufacturing.

[0016] More preferably, the anisotropic samarium iron nitrogen or its composite magnetic powder coating modification process specifically includes the following steps: immersing the anisotropic samarium iron nitrogen or its composite magnetic powder in a solvent containing a coupling agent, stirring at 30-60°C for 0.1-3 hours to ensure thorough and uniform mixing, and then drying to obtain surface-treated magnetic powder. Excessive temperature will cause the organic solvent to evaporate during the mixing process, resulting in uneven mixing.

[0017] The drying temperature is 80-120℃, and the drying time is 1-6 hours. The purpose is to remove the solvent and to make the coupling agent uniformly coated and bonded to the surface of the magnetic powder. If the temperature is below 80℃, it is difficult to dry completely and the bonding strength between the coupling agent and the magnetic powder is low. If the temperature is above 120℃, it is easy to cause the performance of the magnetic powder to degrade.

[0018] The solvent includes any one of ethanol, isopropanol, and acetone;

[0019] The coupling agent includes one or more of aluminate coupling agents, silane coupling agents, and titanate coupling agents;

[0020] The adjuvants include one or more of palmitamide, N,N'-ethylene bis-stearamide, and bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate;

[0021] The polymer resin includes one or more of nylon, polyphenylene sulfide, polyethylene, and polypropylene;

[0022] Preferably, the coupling agent is an aluminate coupling agent or a silane coupling agent, which provides better coating effect; the additives include at least two of palmitamide, N,N'-ethylene bis-stearamide, and bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; and the polymer resin is nylon or polyphenylene sulfide.

[0023] The anisotropic samarium iron nitrogen magnetic powder has an average particle size of 1-5 μm. The anisotropic samarium iron nitrogen magnetic powder has a fine and concentrated particle size, generally 1-5 μm, which is much finer than neodymium-based magnetic powders such as neodymium iron boron (generally 50-200 μm). It can be more evenly distributed in the encoder magnetic grating, thereby achieving higher zero-crossing accuracy of the magnetic pole waveform and enabling the fabrication of thinner encoder magnetic gratings.

[0024] This invention also provides a method for fabricating a high-precision encoder magnetic grating, comprising the following steps:

[0025] Step 1: Immerse 20-95 parts of anisotropic samarium iron nitrogen or its composite magnetic powder in a solvent containing 0.1-1 parts of coupling agent, stir and mix at 30-60°C for 0.1-3 hours, and dry to obtain surface-treated magnetic powder;

[0026] Step 2: Mix the magnetic powder treated in Step 1, 5-80 parts of polymer resin, and 0.1-1.5 parts of additives, then melt-extrude and granulate to obtain composite granules; the maximum magnetic energy product of the composite granules is 3.0-16.0 MGOe; the density is 3.60-16.0 g / cm³. 3 The larger the maximum magnetic energy product, the higher the magnetic strength of the encoder grating after magnetization. In practical applications, composite granules with different properties can be flexibly selected according to the requirements of the encoder grating.

[0027] Step 3: Inject the composite granules into shape and then demagnetize the oriented encoder grating to obtain a semi-finished encoder grating.

[0028] Step 4: Magnetize the encoder magnetic grating semi-finished product according to the requirements of the encoder magnetic grating poles to obtain a high-precision encoder magnetic grating that meets the requirements.

[0029] In this invention, anisotropic samarium iron nitrogen or its composite magnetic powder is first coated and modified with a coupling agent to improve its magnetic stability and compatibility with polymers. Then, it is mixed with polymer resin and additives and melt-extruded into a powder. The maximum magnetic energy product of the composite granules needs to reach 3.0 to 16.0 MGOe. The anisotropic samarium iron nitrogen and its composite material obtained by granulation are injection molded into the encoder molding cavity. During the injection molding process, an electromagnetic field, magnetic field or permanent magnetic field is used for orientation. Under the magnetic field orientation, the magnetic powder can be arranged in an orderly manner according to the orientation direction.

[0030] In step 3, an electromagnetic field or a permanent magnetic field is used for orientation; during the orientation process, the forming mold of the encoder magnetic grating should have a magnetic circuit channel set on the magnetic grating sensing surface.

[0031] During injection molding, the magnetic field strength of the orientation magnetic field is at a 90-degree angle to the magnetic grating sensing surface, and the magnetic field strength is not less than 0.6T. If the orientation strength is less than 0.6T, there is an incomplete or insufficient orientation state, and the magnetic powder cannot be completely aligned with the orientation direction, so the encoder magnetic grating cannot perform well in the subsequent magnetization process, resulting in low magnetic strength on the surface of the magnetic grating.

[0032] After injection molding, the magnetic domain orientation degree of the magnetic grating sensing surface is 60-99%, and the difference in magnetic domain orientation degree at each point is no more than 5%. If the magnetic domain orientation degree is too low, that is, the magnetic domain arrangement is not consistent, it will also lead to the encoder magnetic grating not being able to perform well in the subsequent magnetization process, resulting in low surface magnetic intensity. If the difference in magnetic domain orientation degree at each point exceeds 5%, it will lead to a deterioration in the non-uniformity of the magnetic grating surface, and a decrease in the accuracy of zero crossover of magnetic pole waveform during the magnetization process.

[0033] The surface magnetic field of the encoder grating semi-finished product after demagnetization is below 1mT; if the residual surface magnetic field after demagnetization exceeds 1mT, the surface magnetic field accuracy will deteriorate during the magnetization process of the encoder grating, which will also affect the zero-crossing accuracy of the magnetic pole waveform of the encoder grating.

[0034] In step 4, the encoder magnetic grating semi-finished product is magnetized by pulse unipolar magnetization or by overall magnetization using a fixture;

[0035] For encoder gratings with a pole pitch of less than 1 mm, pulse unipolar magnetization is used, and the width of the magnetizing pole head should be less than 87% of the encoder grating pitch. If the width of the magnetizing pole head exceeds 87% of the encoder grating pitch, it will interfere with adjacent poles during the magnetization process, causing the magnetized poles to be covered and the unmagnetized poles to be magnetized, directly affecting the accuracy of the encoder grating.

[0036] Preferably, the encoder magnetic grating includes various structural shapes such as magnetic drums, magnetic disks, magnetic rings, and linear magnetic scales. Encoder magnetic gratings manufactured using precision injection molding offer advantages such as high dimensional accuracy, no deformation, no need for secondary processing, and high freedom in shape and structural forming. Furthermore, adjusting the proportion of anisotropic samarium iron nitrogen magnetic powder allows for the manufacture of encoder magnetic gratings with different performance requirements. Simultaneously, the thermal fluidity of the material can be altered to customize encoder magnetic gratings of various shapes and structures according to application needs. This provides a structural guarantee for the development of high-resolution, high-precision magnetic encoders.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) Anisotropic samarium iron nitrogen powder has a finer particle size and higher accuracy of the zero cross point of the magnetic poles after magnetization. Compared with neodymium iron boron materials, it is not easy to rust in salt spray and other environments. Compared with ferrite materials, it has higher surface magnetic strength and has higher coercivity, making it less prone to demagnetization and other effects.

[0039] (2) The injection molding method can manufacture encoder magnetic grids with complex structures and thinner thicknesses, and can also include inserts or integrate inserts into injection molding to meet the requirements of large-scale production.

[0040] (3) The maximum magnetic energy product of anisotropic samarium iron nitrogen and its composite materials is 3.0 to 16.0 MGOe, which can be used to manufacture encoder magnetic gratings with different performance requirements and improve the output magnetic signal and signal-to-noise ratio of encoder magnetic gratings. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the encoder magnetic grating fabrication process in Example 1.

[0042] Figure 2 The orientation requirements for the encoder magnetic grating semi-finished product in Example 1. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0044] The raw materials used in the following specific embodiments are all purchased from the market. The ferrite magnetic powder has a particle size of 1-3 μm, and the anisotropic samarium iron nitrogen magnetic powder has a particle size of 1-5 μm.

[0045] The following specific implementation method is to manufacture an encoder magnetic grid with an outer diameter of 30mm, an inner diameter of 24mm, a height of 2mm, and 64 axial poles.

[0046] Example 1

[0047] A schematic diagram of the fabrication process of a high-precision encoder magnetic grating is shown below. Figure 1 As shown:

[0048] (1) Dissolve 0.5 parts of aluminate in ethanol and immerse 88.5 parts of anisotropic samarium iron nitrogen magnetic powder in it, with the amount of ethanol just enough to immerse and coat the magnetic powder. After stirring and homogenizing at 40°C, dry it under vacuum at 95°C.

[0049] (2) The coated magnetic powder obtained in step (1) is mixed with 10.5 parts of nylon 12, 0.1 parts of palmitamide, 0.3 parts of N,N'-ethylene bis-stearamide, and 0.1 parts of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate. The proportioned raw materials are then uniformly mixed in a high-speed mixer at a speed of 800 r / min to obtain a mixed raw material.

[0050] (3) The mixed raw materials obtained in step (2) are melt-blended at 200°C, and then extruded and granulated to obtain composite granules. The maximum magnetic energy product of the composite granules is 9.42 MGOe, and the density is 4.33 g / cm³. 3 ;

[0051] (4) The composite material obtained in step (3) is melted and injected into the mold cavity by injection molding. During the orientation process, the encoder magnetic grating molding die should have a magnetic circuit channel set on the magnetic grating sensing surface. During the injection molding process, the encoder magnetic grating is oriented using an electromagnetic field under a magnetic field strength of 0.7T. Figure 2 As shown, the magnetic field strength of the orientation magnetic field during injection molding is at a 90-degree angle to the magnetic grating sensing surface. The encoder magnetic grating is then demagnetized; the surface magnetic field of the demagnetized encoder magnetic grating is 0.5 mT, thus manufacturing a semi-finished encoder magnetic grating.

[0052] Orientation tests were conducted on the encoder magnetic grating semi-finished product. The magnetic domain orientation of the magnetic grating sensing surface was 85%, and the difference in magnetic domain orientation at each point was 3%.

[0053] (5) According to the requirements of the encoder magnetic grating poles, the entire fixture is magnetized with 64 poles to obtain the finished encoder magnetic grating.

[0054] Comparative Example 1: No coating treatment was performed.

[0055] (1) 88.5 parts of anisotropic samarium iron nitrogen magnetic powder, 10.5 parts of nylon 12 resin, 0.5 parts of aluminate coupling agent, 0.1 parts of palmitamide, 0.3 parts of N,N'-ethylene bis-stearamide, and 0.1 parts of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate were mixed in a high-speed mixer at a speed of 800 r / min to obtain a mixed raw material;

[0056] (2) The mixed raw materials obtained in step (1) are melt-blended at 200°C, and then extruded and granulated to obtain composite granules with a maximum magnetic energy product of 9.36 MGOe and a density of 4.33 g / cm³. 3 ;

[0057] (3) The composite granules obtained in step (2) are melted and injected into the mold cavity by injection molding. The mold for the encoder magnetic grating should have a magnetic circuit channel on the magnetic grating sensing surface. During the injection molding process, the encoder magnetic grating is oriented under a magnetic field strength of 0.7T. The magnetic field strength of the orientation magnetic field is at a 90-degree angle to the magnetic grating sensing surface during injection molding. The encoder magnetic grating is then demagnetized. The surface magnetic field of the demagnetized encoder magnetic grating is 0.5mT. The encoder magnetic grating semi-finished product is then manufactured.

[0058] Orientation tests were conducted on the encoder magnetic grating semi-finished product. The magnetic domain orientation of the magnetic grating sensing surface was 82%, and the difference in magnetic domain orientation at each point was 5%.

[0059] (4) According to the requirements of the encoder magnetic grating poles, magnetize it with 64 poles to obtain the finished encoder magnetic grating.

[0060] Comparative Example 2: Low Orientation Magnetic Field Strength

[0061] (1) Dissolve 0.5 parts of aluminate coupling agent in ethanol and immerse 88.5 parts of anisotropic samarium iron nitrogen magnetic powder in it, with the amount of ethanol just enough to immerse and coat the magnetic powder. After stirring and homogenizing at 40°C, dry it under vacuum at 95°C.

[0062] (2) The coated magnetic powder obtained in step (1) is mixed with 10.5 parts of nylon 12, 0.1 parts of palmitamide, 0.3 parts of N,N'-ethylene bis-stearamide, and 0.1 parts of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate. The mixed raw materials are uniformly mixed in a high-speed mixer at a speed of 800 r / min to obtain a mixed raw material.

[0063] (3) The mixed raw materials obtained in step (2) are melt-blended at 200°C, and then extruded and granulated to obtain composite granules with a maximum magnetic energy product of 9.42 MGOe and a density of 4.33 g / cm³. 3 ;

[0064] (4) The composite granules obtained in step (3) are melted and injected into the mold cavity by injection molding. The molding mold for the encoder magnetic grating should have a magnetic circuit channel on the magnetic grating sensing surface. During the injection molding process, the encoder magnetic grating is oriented under a magnetic field strength of 0.4T. The magnetic field strength of the orientation magnetic field during injection molding is at a 90-degree angle to the magnetic grating sensing surface. The encoder magnetic grating is then demagnetized. The surface magnetic field of the demagnetized encoder magnetic grating is 0.5mT. The encoder magnetic grating semi-finished product is then manufactured.

[0065] Orientation tests were conducted on the encoder magnetic grating semi-finished product. The magnetic domain orientation of the magnetic grating sensing surface was 55%, and the difference in magnetic domain orientation at each point was 7%.

[0066] (5) According to the requirements of the encoder magnetic grating poles, magnetize it with 64 poles to obtain the finished encoder magnetic grating.

[0067] Comparative Example 3: Higher surface magnetism after demagnetization

[0068] (1) Dissolve 0.5 parts of aluminate in ethanol and immerse 88.5 parts of anisotropic samarium iron nitrogen magnetic powder in it, with the amount of ethanol just enough to immerse and coat the magnetic powder. After stirring and homogenizing at 40°C, dry it under vacuum at 95°C.

[0069] (2) The coated magnetic powder obtained in step (1) is mixed with 10.5 parts of nylon 12 resin, 0.1 parts of palmitamide, 0.3 parts of N,N'-ethylene bis-stearamide, and 0.1 parts of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate. The mixed raw materials are uniformly mixed in a high-speed mixer at a speed of 800 r / min to obtain a mixed raw material.

[0070] (3) The mixed raw materials obtained in step (2) are melt-blended at 200°C, and then extruded and granulated to obtain composite granules with a maximum magnetic energy product of 9.42 MGOe and a density of 4.33 g / cm³. 3 ;

[0071] (4) The composite granules obtained in step (3) are melted and injected into the mold cavity by injection molding. The mold for the encoder magnetic grating should have a magnetic circuit channel on the magnetic grating sensing surface. During the injection molding process, the encoder magnetic grating is oriented under a magnetic field strength of 0.7T. The magnetic field strength of the orientation magnetic field is at a 90-degree angle to the magnetic grating sensing surface during injection molding. The encoder magnetic grating is then demagnetized. The surface magnetic field of the demagnetized encoder magnetic grating is 1.5mT. The encoder magnetic grating semi-finished product is then manufactured.

[0072] (5) According to the requirements of the encoder magnetic grating poles, magnetize it with 64 poles to obtain the finished encoder magnetic grating.

[0073] Example 2

[0074] (1) Dissolve 0.5 parts of aluminate in ethanol, and immerse 45 parts of anisotropic samarium iron nitrogen magnetic powder and 41 parts of anisotropic ferrite magnetic powder in it. The amount of ethanol is just enough to immerse and coat the magnetic powder. After stirring and homogenizing at 40°C, dry it under vacuum at 95°C.

[0075] (2) The coated magnetic powder obtained in step (1) is mixed with 13 parts of nylon 12 resin, 0.1 parts of palmitamide, 0.3 parts of N,N'-ethylene bis-stearamide, and 0.1 parts of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate. The mixed raw materials are uniformly mixed in a high-speed mixer at a speed of 800 r / min to obtain a mixed raw material.

[0076] (3) The mixed raw materials obtained in step (2) are melt-blended at 200°C, and then extruded and granulated to obtain composite granules with a maximum magnetic energy product of 3.62 MGOe and a density of 3.55 g / cm³. 3 ;

[0077] (4) The composite granules obtained in step (3) are melted and injected into the mold cavity by injection molding. During the orientation process, the forming mold of the encoder magnetic grating should be provided with a magnetic circuit channel on the magnetic grating sensing surface. During the injection molding process, the encoder magnetic grating is oriented under a magnetic field strength of 0.7T. The magnetic field strength of the orientation magnetic field is at a 90-degree angle to the magnetic grating sensing surface during injection molding. The encoder magnetic grating is then demagnetized. The surface magnetic field of the demagnetized encoder magnetic grating is 0.5mT. The encoder magnetic grating semi-finished product is then manufactured.

[0078] (5) According to the requirements of the encoder magnetic grating poles, magnetize it with 64 poles to obtain the finished encoder magnetic grating.

[0079] Comparative Example 4: Neodymium Iron Boron Magnetic Powder

[0080] (1) Dissolve 0.5 parts of aluminate in ethanol and immerse 91 parts of isotropic neodymium iron boron magnetic powder in it, with the amount of ethanol just enough to immerse and coat the magnetic powder. After stirring and homogenizing at 40°C, dry it under vacuum at 95°C.

[0081] (2) The coated magnetic powder obtained in step (1) is mixed with 8 parts of nylon 12 resin, 0.1 parts of palmitamide, 0.3 parts of N,N'-ethylene bis-stearamide, and 0.1 parts of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate. The mixed raw materials are uniformly mixed in a high-speed mixer at a speed of 800 r / min to obtain the mixed raw materials.

[0082] (3) The mixed raw materials obtained in step (2) are melt-blended at 200°C, and then extruded and granulated to obtain composite granules with a maximum magnetic energy product of 5.61 MGOe and a density of 4.82 g / cm³. 3 ;

[0083] (4) The composite granules obtained in step (3) are melted and injected into the mold cavity by injection molding to manufacture encoder magnetic grid semi-finished products;

[0084] (5) According to the requirements of the encoder magnetic grating poles, magnetize it with 64 poles to obtain the finished encoder magnetic grating.

[0085] Comparative Example 5: Manufacturing encoder magnetic grids using injection-molded anisotropic ferrite

[0086] (1) Dissolve 0.5 parts of aluminate in ethanol and immerse 89.5 parts of anisotropic ferrite magnetic powder in it, with the amount of ethanol just enough to immerse and coat the magnetic powder. Stir and homogenize at 40°C and then vacuum dry at 95°C.

[0087] (2) The coated magnetic powder obtained in step (1) is mixed with 9.5 parts of nylon 12 resin, 0.1 parts of palmitamide, 0.3 parts of N,N'-ethylene bis-stearamide, and 0.1 parts of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate. The mixed raw materials are uniformly mixed in a high-speed mixer at a speed of 800 r / min to obtain a mixed raw material.

[0088] (3) The mixed raw materials obtained in step (2) are melt-blended at 200°C, and then extruded and granulated to obtain composite granules with a maximum magnetic energy product of 1.96 MGOe and a density of 3.58 g / cm³. 3 ;

[0089] (4) The composite granules obtained in step (3) are melted and injected into the mold cavity by injection molding. During the orientation process, the forming mold of the encoder magnetic grating should be provided with a magnetic circuit channel on the magnetic grating sensing surface. During the injection molding process, the encoder magnetic grating is oriented under a magnetic field strength of 0.7T. The magnetic field strength of the orientation magnetic field is at a 90-degree angle to the magnetic grating sensing surface during injection molding. The encoder magnetic grating is then demagnetized. The surface magnetic field of the demagnetized encoder magnetic grating is 0.5mT. The encoder magnetic grating semi-finished product is then manufactured.

[0090] (5) According to the requirements of the encoder magnetic grating poles, magnetize it with 64 poles to obtain the finished encoder magnetic grating;

[0091] The encoder magnetic gratings prepared in Examples 1-2 and Comparative Examples 1-5 were subjected to performance tests including surface magnetic strength and accuracy, zero-crossing accuracy of magnetic pole waveforms, corrosion resistance, and electromagnetic interference resistance. The test results are shown in Table 1. Surface magnetic strength and accuracy, and zero-crossing accuracy of magnetic pole waveforms were tested using a waveform measuring instrument: Standard T / MBJX 0008—2021; corrosion resistance was tested using a salt spray test: Standard GB / T2423.17 (the degree of rust is used as the standard for judging good and poor performance; after 12 hours of salt spray testing, no rust is considered good corrosion resistance, and rust is considered poor corrosion resistance); electromagnetic interference resistance: Standard GB / T17626.8 (after testing the encoder magnetic grating in an electromagnetic interference environment, if the change rate of surface magnetic strength, accuracy, and zero-crossing accuracy is within 3%, it is considered strong; within 3%-5%, it is considered relatively strong; and exceeding 5%, it is considered weak).

[0092] Table 1. Performance test results of the examples and comparative examples.

[0093]

[0094] As shown in Table 1, the encoder magnetic grating made of anisotropic samarium iron nitrogen has higher surface magnetic strength and accuracy, higher zero-crossing accuracy of magnetic pole waveform, and better corrosion resistance than the encoder magnetic grating made of isotropic neodymium iron boron. The encoder magnetic grating made of anisotropic samarium iron nitrogen and anisotropic ferrite composite has higher surface magnetic strength and accuracy, higher zero-crossing accuracy of magnetic pole waveform, and stronger anti-electromagnetic interference capability than the encoder magnetic grating made of anisotropic ferrite.

[0095] Comparing Example 1 and Comparative Example 1, the samarium iron nitrogen magnetic powder in Comparative Example 1 was not coated with a coupling agent, which made its surface easy to oxidize, resulting in poor corrosion resistance; while Comparative Example 2 had low surface magnetic strength due to low magnetic field strength and incomplete orientation during the orientation process.

[0096] In Example 2, a composite magnetic powder of samarium iron nitrogen and ferrite was selected. The magnetic powder contains ferrite, which has a low maximum magnetic energy product, resulting in low surface magnetic strength. However, since the coercivity of ferrite magnetic powder is low, its coercivity can be improved after being combined with samarium iron nitrogen magnetic powder. This makes its anti-electromagnetic interference ability better than that of ferrite magnetic powder. Its surface magnetic accuracy and anti-electromagnetic interference ability are both good, and it can have excellent encoder magnetic grating manufacturing characteristics.

[0097] In Comparative Example 3, the residual surface magnetism after demagnetization caused uneven distribution of the encoder's magnetic grating surface magnetic intensity and waveform during subsequent magnetization, resulting in reduced surface magnetic accuracy and zero-crossing point accuracy.

[0098] Comparative Examples 4 and 5 respectively used neodymium iron boron magnetic powder and ferrite magnetic powder, which are commonly used in the prior art. Because neodymium iron boron magnetic powder has a large particle size and its surface is easily oxidized by oxygen, its surface magnetic accuracy is poor after magnetization, and it is prone to rusting after a period of use, making it unsuitable for long-term use. Ferrite magnetic powder, due to its low coercivity, is prone to demagnetization in electromagnetic interference environments, affecting the working performance of the encoder's magnetic grating.

[0099] Therefore, the encoder magnetic grating made of anisotropic samarium iron nitrogen and its composite material of the present invention has excellent performance and has many advantages in encoder magnetic grating manufacturing and application.

Claims

1. A method for fabricating a high-precision encoder magnetic grating, characterized in that, Includes the following steps: Step 1: Immerse 20-95 parts of anisotropic samarium iron nitrogen or its composite magnetic powder in a solvent containing 0.1-1 parts of coupling agent, stir and mix at 30-60°C for 0.1-3 hours, and dry to obtain surface-treated magnetic powder; Step 2: Mix the magnetic powder treated in Step 1, 5-80 parts of polymer resin and 0.1-1.5 parts of additives, and then melt-extrude and granulate to obtain composite granules; the maximum magnetic energy product of the composite granules is 3.0-16.0 MGOe; Step 3: Inject and oriented the composite granules, then demagnetize to obtain a semi-finished encoder magnetic grating; during injection molding, the magnetic field direction of the orientation magnetic field is at 90 degrees to the magnetic grating sensing surface, and the magnetic field strength is not less than 0.6T; after injection molding, the magnetic domain orientation degree of the magnetic grating sensing surface is 60-99%, and the difference in magnetic domain orientation degree at each point is not greater than 5%; after demagnetization, the surface magnetism of the semi-finished encoder magnetic grating is below 1mT; Step 4: According to the requirements of the encoder magnetic grating poles, magnetize the encoder magnetic grating semi-finished product to obtain a high-precision encoder magnetic grating that meets the requirements. In step 4, the encoder magnetic grating semi-finished product is magnetized by pulse unipolar magnetization or by the whole fixture; for encoder magnetic gratings with a pole pitch of less than 1mm, pulse unipolar magnetization is used, and the width of the magnetizing pole head is less than 87% of the encoder magnetic grating pitch.

2. The method for fabricating a high-precision encoder magnetic grating according to claim 1, characterized in that, In step 3, an electromagnetic field or a permanent magnetic field is used for orientation. During the orientation process, the forming mold of the encoder magnetic grating sets up a magnetic circuit channel on the magnetic grating sensing surface.

3. The method for fabricating a high-precision encoder magnetic grating according to claim 1, characterized in that, The composite magnetic powder contains at least 20% by mass of anisotropic samarium iron nitrogen magnetic powder.

4. The method for fabricating a high-precision encoder magnetic grating according to claim 1, characterized in that, The coupling agent includes one or more of aluminate coupling agents, silane coupling agents, and titanate coupling agents.

5. The method for fabricating a high-precision encoder magnetic grating according to claim 1, characterized in that, The adjuvants include one or more of palmitamide, N,N'-ethylene bis-stearamide, and bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate; And / or, the polymeric resin includes one or more of nylon, polyphenylene sulfide, polyethylene, and polypropylene; And / or, the average particle size of the anisotropic samarium iron nitrogen magnetic powder is 1-5 μm.

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