Design method of small-size magnetorheological polishing device and polishing device

Abstract

The application relates to a design method of a small-size magnetorheological polishing device and the polishing device, and the method comprises the following steps: S1. determining a magnet structure and magnet parameters of a magnet for a magnetorheological polishing device; wherein the magnet parameters comprise a magnet volume and independent shape parameters; S2. determining a polishing wheel structure and polishing wheel size of a polishing wheel for the magnetorheological polishing device, and determining the magnet volume of the magnet based on the polishing wheel size; S3. establishing a simulation model containing the magnet and the polishing wheel, and performing importance degree sorting on each parameter contained in the independent shape parameters based on the simulation model and by adopting an orthogonal test method and outputting an importance degree sorting result; and S4. optimizing each parameter in the independent shape parameters one by one based on the importance degree sorting result, and completing the design of the magnet.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-precision polishing, in particular to a design method of a small-size magnetorheological polishing device and the polishing device. BACKGROUND

[0002] With the continuous development of various advanced optical systems, there is an increasing demand for small caliber (generally a few millimeters to a few tens of millimeters in diameter), high steepness, and even optical elements with specific relief structures (such as continuous phase elements). These optical elements all need to achieve high surface quality and surface shape accuracy. Magnetorheological finishing is widely used in optical element manufacturing process due to its significant advantages of high determinacy, high material removal stability, high surface quality, and no subsurface damage. In 1995, the University of Rochester in the United States first applied magnetorheological finishing technology to the processing of optical elements. The magnetic field generating device in its processing device provides a flexible polishing tool for polishing, and the polishing platform provides a certain movement for the optical element. The magnetorheological fluid is sprayed onto the surface of the polishing wheel by the centrifugal pump of the circulation system and is recovered into the circulation system with the polishing wheel. By adjusting the magnetic field strength of the magnetic field generating device, a gradient magnetic field can be generated to form a semi-solid Bingham medium polishing ribbon on the surface of the polishing wheel, thereby removing the material on the surface of the optical element and easily obtaining a component with excellent surface quality and high surface shape accuracy. Therefore, the MRF method is particularly widely used in the super-precision machining process of complex optical devices such as aspheric surfaces.

[0003] However, for the existing wheel-type magnetorheological finishing technology, the size of the polishing wheel determines the caliber and removal function of the optical element that can be processed. If an optical element with a smaller size, a higher gradient, or even a surface with a microstructure is processed, using the existing size of the polishing tool will result in non-convergent surface shape or poor surface shape, or even interference between the polishing wheel and the processed element, which cannot be processed. In addition, previous studies have shown that a smaller removal function will have better frequency spectrum correction capability, thereby more effectively suppressing the surface frequency band error of the processed element. Therefore, it is necessary to manufacture a smaller size magnetorheological polishing tool to obtain a smaller removal function, but there is still a lack of related technology. SUMMARY

[0004] The purpose of the present application is to provide a design method of a small-size magnetorheological polishing device and the polishing device.

[0005] To achieve the above-mentioned purpose of the application, the present application provides a design method of a small-size magnetorheological polishing device, comprising the following steps:

[0006] S1. Determine the magnet structure and magnet parameters of the magnet for the magnetorheological polishing device; wherein the magnet parameters include: magnet volume and independent shape parameters;

[0007] S2. determining a polishing wheel structure and a polishing wheel size of a polishing wheel for a magnetorheological polishing device, and determining a magnet volume of the magnet based on the polishing wheel size;

[0008] S3. establishing a simulation model comprising the magnet and the polishing wheel, and performing importance ranking of each parameter contained in the independent shape parameters based on the simulation model and using an orthogonal test method and outputting an importance ranking result;

[0009] S4. optimizing each parameter in the independent shape parameters one by one based on the importance ranking result, and completing the design of the magnet.

[0010] According to an aspect of the present application, in the step of determining a magnet structure of a magnet for a magnetorheological polishing device, the magnet comprises two symmetrical magnetic poles;

[0011] The magnetic pole comprises a magnetic pole upper part and a magnetic pole lower part connected to the magnetic pole upper part;

[0012] The lower end surface of the magnetic pole lower part is arranged parallel to the upper end surface of the magnetic pole upper part, the outer side surface of the magnetic pole lower part comprises a first inclined plane part and a transition part for connecting the first plane part and the lower end surface, and the inner side surface of the magnetic pole lower part comprises a second inclined plane part and a vertical plane part for connecting the second plane part and the lower end surface;

[0013] In the step of determining a magnet parameter of a magnet for a magnetorheological polishing device, the independent shape parameters are obtained based on the magnet structure, which comprises a first inclination angle β of the first plane part, a second inclination angle α of the second plane part, a lower end surface width e2 of the lower end surface, and a half opening width e1 of the magnet lower end opening.

[0014] According to an aspect of the present application, in the step of determining a polishing wheel structure of a polishing wheel for a magnetorheological polishing device, the polishing wheel is in the shape of a circular ring, and the outer ring surface thereof is in the shape of an arc;

[0015] In the step of determining a polishing wheel size of a polishing wheel for a magnetorheological polishing device, the outer diameter of the polishing wheel is 10-15 mm, and the wall thickness is 0.4-1.5 mm.

[0016] According to an aspect of the present application, in the step of determining a magnet volume of the magnet based on the polishing wheel size, the magnet volume of the magnet is determined based on the polishing wheel size of the polishing wheel and the interval between the magnet and the inner ring surface of the polishing wheel.

[0017] According to one aspect of the present application, in the step of sorting the importance of each parameter included in the independent shape parameters based on the simulation model and using the orthogonal test method and outputting the importance sorting result, the importance sorting result includes: a first importance sorting result for indicating the degree of influence on the magnetic field intensity, and a second importance sorting result for indicating the degree of influence on the field intensity decay rate.

[0018] According to one aspect of the present application, in the step of sorting the importance of each parameter included in the independent shape parameters based on the simulation model and using the orthogonal test method and outputting the importance sorting result, the step includes:

[0019] According to the preset optimal design requirement and the size limitation of the polishing wheel, the influence weight of each parameter in the independent shape parameters on the magnetic field intensity and the field intensity decay rate is analyzed based on the simulation model and using the orthogonal test method;

[0020] Each parameter in the independent shape parameters is sorted based on the influence weight; wherein the first importance sorting result is that the influence of e2, e1, β, α on the magnetic field intensity increases in turn; and the second importance sorting result is that the influence of e1, e2, β, α on the field intensity decay rate increases in turn.

[0021] According to one aspect of the present application, in the step of sorting the importance of each parameter included in the independent shape parameters based on the simulation model and using the orthogonal test method and outputting the importance sorting result, the step includes:

[0022] To achieve the above-mentioned purposes, the present application provides a polishing device obtained by using the above-mentioned design method, which includes a magnet and a polishing wheel.

[0023] The magnet is located in the polishing wheel, and the magnet and the inner ring surface of the polishing wheel are arranged with a spacing.

[0024] The magnet includes two symmetrical magnetic poles.

[0025] The magnetic pole includes a magnetic pole upper part and a magnetic pole lower part connected to the magnetic pole upper part.

[0026] The lower end surface of the magnetic pole lower part is arranged in parallel with the upper end surface of the magnetic pole upper part, the outer side surface of the magnetic pole lower part includes an inclined first plane part and a transition part for connecting the first plane part and the lower end surface, and the inner side surface of the magnetic pole lower part includes an inclined second plane part and a vertical plane part for connecting the second plane part and the lower end surface.

[0027] According to one aspect of the present invention, the outer diameter of the polishing wheel is 10-15 mm, and the wall thickness is 0.4 mm-1.5 mm.

[0028] According to one solution of the present invention, the small-size magnetorheological polishing device of the present invention achieves a small size while fully satisfying the stable circulation of the magnetorheological fluid, and has a stable small-size removal function, thereby fully realizing high-precision processing of small-caliber, high-steepness optical parts and obtaining higher frequency band control capabilities.

[0029] According to one scheme of the present invention, the present invention provides a theoretical basis for the manufacture of small-caliber magnetorheological polishing equipment and the selection of removal functions in the magnetorheological processing process through the design of a small-caliber wheel-type magnetorheological polishing device and the study of the frequency band control ability of a small-size removal function, broadens the spectrum correction range and application range of magnetorheological polishing, and has great application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a block diagram schematically showing steps of a design method according to an embodiment of the present invention;

[0031] Figure 2 is a perspective view schematically showing a magnetorheological polishing device according to one embodiment of the present invention;

[0032] Figure 3 1 is a side view schematically showing a magnet according to an embodiment of the present invention, wherein (a) shows a structural diagram of the magnet, and (b) shows a parameter diagram of the magnet;

[0033] Figure 4 Schematic diagram showing the magnetic field intensity distribution of the magnetic pole structure of a 70 mm polishing wheel on the XY plane, where (a) shows the magnetic field distribution along the X direction on the polishing wheel surface, and (b) shows the magnetic field intensity distribution along the Y direction;

[0034] Figure 5 Schematic diagram of the simulation modeling and simulation results of a small-scale (13 mm) magnetorheological polishing device according to one embodiment of the present invention; wherein (a) is a finite element analysis three-dimensional model of the polishing device, (b) shows the finite element analysis mesh division of the polishing device, (c) shows the simulation result of the magnetic induction intensity distribution on the polishing wheel surface, and (d) shows the simulation result of the magnetic flux line distribution around the magnet air gap;

[0035] Figure 6 1 is a diagram schematically showing the relationship between the magnetic field characteristic values ​​and key parameters of a small-scale magnetorheological polishing device according to an embodiment of the present invention;

[0036] Figure 7is a schematic diagram of the magnetic field intensity distribution in the X-Y plane of a small scale magnetorheological finishing device according to an embodiment of the present application, wherein (a) represents the magnetic field intensity distribution of the magnets, and (b) represents an enlarged view of the field intensity distribution of region A in (a);

[0037] Figure 8 is a schematic diagram of the spatial distribution of the magnetic field of a small scale magnetorheological finishing device according to an embodiment of the present application, wherein (a) represents the magnetic field distribution along the X direction of the surface of the polishing wheel, and (b) represents the magnetic field intensity distribution along the Y direction;

[0038] Figure 9 is a schematic diagram of a physical device of a small scale magnetorheological finishing device according to an embodiment of the present application;

[0039] Figure 10 is a three-dimensional removal function of a small scale (13mm) magnetorheological finishing device according to an embodiment of the present application;

[0040] Figure 11 is a short-term stability test result of the removal function of a small scale (13mm) magnetorheological finishing device according to an embodiment of the present application;

[0041] Figure 12 is a long-term stability test result of the removal function of a small scale (13mm) magnetorheological finishing device according to an embodiment of the present application. DETAILED DESCRIPTION

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed in the embodiments will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0043] In the description of the embodiments of the present application, the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" express the orientation or positional relationship shown in the relevant drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the above terms cannot be understood as a limitation of the present application.

[0044] The present application will be described in detail below in conjunction with the accompanying drawings and specific embodiments, which cannot be exhaustively described here, but the embodiments of the present application are not limited to the following embodiments.

[0045] As shown in Figure 1 , according to an embodiment of the present application, a design method of a small-size magnetorheological finishing device of the present application comprises the following steps:

[0046] S1. determining a magnet structure and magnet parameters of a magnet for the magnetorheological finishing device; wherein the magnet parameters comprise: a magnet volume and independent shape parameters;

[0047] S2. determining a polishing wheel structure and polishing wheel size of a polishing wheel for the magnetorheological finishing device, and determining the magnet volume based on the polishing wheel size;

[0048] S3. establishing a simulation model containing the magnet and the polishing wheel, and sorting the importance of each parameter contained in the independent shape parameters based on the simulation model and using the orthogonal test method and outputting the importance sorting result;

[0049] S4. optimizing each parameter in the independent shape parameters one by one based on the importance sorting result, and completing the design of the magnet.

[0050] In combination with Figure 2 and Figure 3 , according to an embodiment of the present application, in step S1, the step of determining the magnet structure of the magnet for the magnetorheological finishing device, the magnet is in a symmetrical structure and is in a U-shaped three-dimensional structure with an open lower end; in this embodiment, the magnet comprises: a left magnetic pole 11, a right magnetic pole 12, a connecting plate 13, and a magnetic conducting plate 14; since the entire magnet is in a symmetrical structure, the left magnetic pole 11 and the right magnetic pole 12 are symmetrically arranged with each other, and the upper ends of the left magnetic pole 11 and the right magnetic pole 12 are connected with the magnetic conducting plate 14, and the connecting plate 13 is arranged between the left magnetic pole 11 and the right magnetic pole 12, and the connecting plate 13 simultaneously realizes the connection with the left magnetic pole 11, the right magnetic pole 12 and the magnetic conducting plate 14. In this embodiment, the left magnetic pole 11 comprises: a magnetic pole upper part a and a magnetic pole lower part b connected with the magnetic pole upper part a; wherein the magnetic pole lower part b is arranged obliquely relative to the magnetic pole upper part a, the magnetic pole upper part a is in a regular rectangular body, and the magnetic pole lower part b is in a special-shaped structure, specifically, the lower end surface b2 of the magnetic pole lower part b is horizontally arranged and arranged parallel to the upper end surface of the magnetic pole upper part a, the outer side surface b3 of the magnetic pole lower part b comprises an inclined first plane part and a transition part for connecting the first plane part and the lower end surface b2, and the inner side surface b4 comprises an inclined second plane part and a vertical plane part for connecting the second plane part and the lower end surface b2, and the front side surface and the rear side surface are arranged flush with the magnetic pole upper part a. In this embodiment, the magnetic pole upper part a and the magnetic pole lower part b are integrated. In this embodiment, since the left magnetic pole 11 and the right magnetic pole 12 are symmetrically arranged, their structures are symmetrical to each other and will not be described here.

[0051] In the embodiment, the left magnetic pole 11 and the right magnetic pole 12 are made of permanent magnetic material, for example, Rb-Fe-B N52; the connecting plate 13 is made of non-magnetic material, for example, aluminum alloy; and the magnetic conducting plate 14 is made of electrical pure iron DT4C.

[0052] In the embodiment, the magnet parameters are determined based on the magnet structure of the magnet, wherein the magnet parameters include the magnet volume and independent shape parameters; in the embodiment, the independent shape parameters include the first inclination angle β of the first planar portion to the vertical direction, the second inclination angle α of the second planar portion to the vertical direction, the lower end face width e2 of the lower end face b2, and the half opening width e1 of the lower end opening of the magnet. In the embodiment, since the lower end of the left magnetic pole 11 and the lower end of the right magnetic pole 12 are inclined to the direction of approaching each other, the gap between the two vertical planar portions is small, and the gap is 2e1, so the half opening width e1 of the gap is small.

[0053] In combination with Figure 2 and Figure 3 As shown in FIG. 2, according to an embodiment of the present application, in step S2, the step of determining the magnet structure of the magnet for the magnetorheological polishing device, the shape of the magnet is circular ring shape, and the outer ring surface of the magnet is arc shape. Further, in the step of determining the magnet size of the magnet for the magnetorheological polishing device, the magnet size includes the outer diameter and the wall thickness of the magnet; wherein the outer diameter of the magnet is 10-15 mm, and the wall thickness of the magnet is 0.4-1.5 mm. Through the above-mentioned setting of the magnet size, by setting the outer diameter of the magnet in the range of 10-15 mm, the small size polishing requirement is achieved, and by setting the wall thickness of the magnet in the range of 0.4-1.5 mm, the structural strength and the magnetic field stability of the magnet are effectively ensured. If the wall thickness of the magnet is less than 0.4 mm, the magnet will be deformed easily, and if the wall thickness of the magnet is greater than 1.5 mm, the magnetic field generated by the magnet cannot play a role around the magnet. It can be seen that by setting the size of the magnet in the above-mentioned range, the structural strength and the working stability of the whole small size are effectively ensured. In the embodiment, the material of the magnet is metal material, for example, 304 stainless steel.

[0054] According to an embodiment of the present application, in step S2, the step of determining the magnet volume of the magnet based on the magnet size, the magnet volume of the magnet is determined based on the magnet size of the magnet and the interval between the magnet and the inner ring surface of the magnet. In the foregoing step, the magnet size of the magnet has been limited, and by further setting the interval between the magnet and the inner ring surface of the magnet, the magnet volume determined based on the foregoing determined magnet structure can be determined.

[0055] According to one embodiment of the present invention, based on the magnet and polishing wheel determined in steps S1 and S2, a mathematical model describing the magnetic field strength of the magnet is further constructed to analyze the influence of independent shape parameters on the magnetic field distribution of the magnet based on the constructed mathematical model, which specifically includes:

[0056] Based on the magnetic structure of the magnet, the magnetic loop of the magnet with an air gap is obtained. For the magnetic loop of a permanent magnet with an air gap in a stable state, it follows the Gaussian theorem of the magnetic field and the Ampere loop theorem. Therefore, the magnetic loop equation of the magnet can be constructed, which is expressed as:

[0057]

[0058] Based on the magnetic circuit equation:

[0059] φ=B m A m =B q A q (2)

[0060] F=-H m L m =H q L q (3)

[0061] Where φ is the total magnetic flux in the magnetic circuit, F is the magnetic potential of the magnet, and B m is the magnetic flux density inside the magnet, B q is the magnetic flux density at the contact surface between the magnet surface and the air gap, H m is the residual magnetic strength in the magnet, H q is the magnetic field strength in the air gap, A m 、A q are the effective areas of the magnet and air gap, L m , L q are the effective lengths of the magnet and the air gap, respectively;

[0062] Multiply formula (2) and formula (3) together, and let B q =μ0H q , μ0 is the vacuum permeability, we can obtain:

[0063]

[0064]

[0065] Where K is the loss coefficient used to represent the leakage loss and magnetic potential loss in the static magnetic circuit, V m is the volume of the magnet, (BH) m is the maximum magnetic energy product of the demagnetization curve of the magnetic material (wherein, when the working point of the magnet is at the maximum magnetic energy product position, the maximum magnetic field intensity can be obtained at the air gap), Vq Volume of the air gap;

[0066] In this embodiment, it is known from formula (4) and formula (5) that the magnetic flux density in the air gap is related to the volume ratio of the air gap to the permanent magnet.

[0067] Based on this, the spatial magnetic field near the air gap of the magnetic field generating device is theoretically analyzed and researched according to the basic theory of static magnetic field. Since the permanent magnet is a passive constant magnetic field, further based on the magnet sub-scheme, the Laplace equation is established for the gap of the magnet, which is represented as:

[0068]

[0069] Wherein, u represents the scalar magnetic potential;

[0070] As shown in Figure 3 , the structure of the magnet is set to be symmetric to the X-Y plane, so when y≥0 and -e2≤x≤e2, formula (6) can be simplified to formula (7):

[0071]

[0072] Applying the separation of variables method to solve formula (7), we obtain:

[0073]

[0074] According to the magnetic field distribution law of the magnet in the X-Y plane symmetric state, the boundary conditions are constructed, wherein the magnetic field distribution law is 1. The magnetic potential of the infinite point is 0, 2. The y-axis is the equipotential line of the infinite distance, 3. When x=e2, the magnetic induction line is parallel to the y-axis, and the boundary condition is represented as:

[0075]

[0076] Based on the above boundary conditions, while the magnetic potential between the magnet and the air gap is continuous, we obtain:

[0077] K 1n =0,K 3n =0 (10)

[0078]

[0079]

[0080] Wherein, e1 represents the lower end face width, and e2 represents the half opening width;

[0081] The formula (10), (11), (12) is brought into the formula (8) to obtain the special solution of the scalar magnetic potential, which is represented as:

[0082]

[0083] Since the magnetic field intensity is the negative gradient of the scalar magnetic potential, the magnetic field intensity can be expressed as:

[0084]

[0085]

[0086] Since the effect of magnetic field strength in space will change with the volume of the magnet, the lateral relative size coefficient R1 and the radial relative size coefficient R2 are added to formula (15) to obtain the magnetic field strength, which is expressed as:

[0087]

[0088]

[0089] Among them, V o represents the reference volume;

[0090] In this embodiment, based on the mathematical model constructed above, it can be seen that the smaller the volume of the magnet, the more significantly the magnetic field strength decreases at the same radial distance from the magnet (i.e., the volume of the magnet is smaller by B). q It is smaller, so the magnetic field strength decreases significantly when y remains unchanged), and the greater the decrease in the magnetic field gradient, the smaller the volume of the magnet must meet the minimum size requirement to ensure the stable formation of the polishing ribbon and its polishing ability. For example, the smaller the volume of the magnet, the smaller the Bq and the smaller the magnetic field strength. For this reason, the magnetic field strength is required to be no less than 150Mt. Under this condition, the volume of the polishing wheel cannot be infinitely small. When it is too small, it reaches its limit, that is, the limit of the polishing wheel size is 8mm.

[0091] Furthermore, simulation calculations are performed based on the constructed mathematical model to verify the rationality of subsequent magnetic field simulations, including:

[0092] A large-scale magnetorheological polishing device is constructed, and simulation calculations are performed based on the large-scale magnetorheological polishing device to obtain a first magnetic field intensity distribution result, and the large-scale magnetorheological polishing device is solved based on a mathematical model to obtain a second magnetic field intensity distribution result; in this embodiment, the large-scale magnetorheological polishing device adopts a magnetorheological polishing device with a 70mm polishing wheel, and the magnetic field intensity distribution of the magnet in the large-scale magnetorheological polishing device on the XY plane is obtained through simulation and mathematical model calculations. Figure 4 (a) shows that the magnetic field intensity in the x direction at the polishing wheel surface is Gaussian, which is conducive to forming a polishing Gaussian polishing ribbon on the polishing wheel. Figure 4 (b) The magnetic field intensity distribution along the y-axis at x = 0. As the radial distance increases, the magnetic field intensity decreases rapidly.

[0093] Compare the first magnetic field strength distribution result and the second magnetic field strength distribution result, and judge whether the mathematical model is effective based on the comparison result, if effective, determine the magnet parameters based on the mathematical model. In the embodiment, see Figure 4 (a) and Figure 4 (b), the scalar magnetic potential and the magnetic field strength theoretical analysis result based on the above mathematical model and the simulation result are basically consistent (there is a certain difference between the theory and the simulation because of the magnetic leakage effect of the actual magnetic field), therefore, the mathematical model obtained based on the foregoing can be used as the theoretical basis for subsequent magnetic field simulation. Wherein, based on Figure 4 (a) and Figure 4 (b), it can be easily found from the magnetic field strength formula of the foregoing mathematical model that the magnet structure based on the magnet sub-scheme basically conforms to the Gaussian distribution along the x-axis direction, and meets the satin belt forming requirement. In order to meet the stable operation of the device and meet the polishing shear force requirement, the minimum point magnetic induction intensity of the polishing satin belt on the polishing wheel needs to be greater than 150mT. However, the magnetic field strength along the y-axis decreases approximately exponentially, therefore, the design of the small size magnetorheological polishing excitation device mainly studies the magnetic field strength change along the y-axis. Therefore, based on the foregoing mathematical model, the magnetic field strength along the y-axis is closely related to e1, e2, α, β, and the magnet volume, and the subsequent simulation result focuses on exploring the influence law of these parameters on the magnetic field strength, and optimizing the magnet parameters e1, e2, α, β.

[0094] According to an embodiment of the application, a simulation model containing a magnet and a polishing wheel is established, and the magnetic field distribution is simulated by COMSOL Multiphysics 6.0 finite element analysis. In the magnet simulation model, the magnet structure of the magnet is constructed by the foregoing structure, the left magnet pole 11 and the right magnet pole 12 are made of Rb-Fe-B N52, the connecting plate 13 is made of aluminum alloy, the magnetic conducting plate 14 is made of pure iron DT4C, and the polishing wheel is made of 304 stainless steel, wherein the key parameters of the materials are shown in Table 1.

[0095] Table 1

[0096]

[0097] Based on the analysis of the aforementioned mathematical model, it can be known that the magnetic field strength along the y-axis decreases exponentially, and in order to obtain a magnetic field strength meeting the polishing requirements at the lowest end of the ribbon, the distance between the magnetic field generating device and the surface of the polishing wheel should be reduced as much as possible. In order to meet the assembly requirements, the gap between the magnetic field generating device and the surface of the polishing wheel is 0.1 mm. In addition, as can be known from formula (16), the volume of the magnetic pole cannot be too small, and a too small wall thickness of the polishing wheel will lead to deformation of the polishing wheel during processing. When the size of the polishing wheel is 10-15 mm, the minimum wall thickness of the polishing wheel should be greater than 0.4 mm. Therefore, the outer diameter of the polishing wheel is selected to be 13 mm and the inner diameter is 12 mm in the simulation. Based on the foregoing steps, the structure and parameters of the magnet have an important influence on the magnetic field distribution around the magnet, and the four independent shape parameters e1, e2, a and b which have an important influence on the magnetic field distribution around the magnetic field generating device have initial values as shown in Table 2. The finite element analysis model and the mesh division thereof are established in COMSOL as shown in Figure 5 (a) and Figure 5 (b).

[0098] Table 2

[0099]

[0100] Based on the foregoing simulation, the simulation result of the magnetic induction intensity distribution of the polishing wheel is shown in Figure 5 (c). As can be known from Figure 5 (c), the magnetic field distribution is symmetrically distributed along the z-axis, the magnetic field strength converges to the center, and there is a maximum value at the center position, which is consistent with the theoretical result. Figure 5 (d) is the simulation result of the magnetic field line distribution around the air gap of the magnetic field generating device, and the magnetic field line leaks below the air gap to form a convex shape similar to a Gauss shape. Such magnetic field strength distribution and shape are conducive to the aggregation of a single stable magnetorheological polishing ribbon at the lowest end of the polishing wheel.

[0101] According to an embodiment of the present application, in the step of sorting the importance of each parameter contained in the independent shape parameters based on the simulation model and using the orthogonal test method and outputting the importance sorting result, the importance sorting result includes: a first importance sorting result for indicating the influence degree on the magnetic field strength, and a second importance sorting result for indicating the influence degree on the field strength decay rate.

[0102] In the embodiment, in the step of sorting the importance of each parameter contained in the independent shape parameters based on the simulation model and using the orthogonal test method and outputting the importance sorting result, the step includes:

[0103] Based on the preset optimal design requirements (i.e., the maximum magnetic field strength and the maximum field strength decay rate) and the size limitation of the polishing wheel, the influence weight of each parameter in the independent shape parameters on the magnetic field strength and the field strength decay rate is analyzed based on the orthogonal test method;

[0104] The independent parameters are ranked based on the influence weight; wherein the first importance ranking result is: the influence of e2, e1, β, and a on the magnetic field strength increases in turn; and the second importance ranking result is: the influence of e1, e2, β, and a on the field strength decay rate increases in turn.

[0105] In the embodiment, according to the theoretical analysis of the aforementioned mathematical model, the magnetic field strength along the y-axis is closely related to e2, e1, the magnetic pole shape parameters a and β. It needs 625 (5 4 ) runs to complete the comprehensive test of four factors and five levels. Due to the huge amount of experiments, it is difficult to study the influence law of each factor on it one by one. The orthogonal test method is an effective method for studying multiple factors and multiple levels. According to the orthogonality, some representative level combinations are selected from the comprehensive test for experiments. The orthogonal test design has been widely used in various research fields due to its high efficiency, speed and economy. For the four-factor five-level test, only 25 experiments are needed to more comprehensively reflect the results.

[0106] Therefore, according to the optimal design requirements and the size limitation of the polishing wheel, the influence weight of each key parameter on the magnetic field strength and the field strength decay rate is analyzed through the orthogonal experiment, so as to obtain the best combination of the key parameters under the comprehensive magnetic field strength and the field strength decay rate. The simulation experiment factors and levels are shown in Table 3.

[0107] Table 3

[0108]

[0109] The magnetic field distribution under different parameters is simulated by COMSOL finite element analysis, and Table 4 lists the magnetic field strength and the field strength decay rate under 25 groups of orthogonal experiments.

[0110] Table 4

[0111]

[0112]

[0113] After the orthogonal experiment is completed and the data is collected, variance analysis is needed. In the test, the maximum range of a certain factor refers to the maximum change of the evaluation index value of the test when the value of the factor changes in the test range. Therefore, the order of the influence of each factor on the evaluation index from large to small is consistent with the order of the range value of each factor from large to small. According to the results of the orthogonal test analysis, the index relationship diagram is drawn as shown in Figure 6 It can be seen that the influence of e2, e1, β, and a on the magnetic field strength increases in turn. For the field strength decay rate, the influence of e1, e2, β, and a on the magnetic field strength increases in turn. This helps to optimize the magnetic pole design.

[0114] According to an embodiment of the present application, in step S4, each parameter in the independent shape parameters is optimized one by one based on the importance ranking result, and in the step of completing the design of the magnet, the first importance ranking result or the second importance ranking result is selected to optimize each parameter in the independent shape parameters one by one, and the selection priority of the first importance ranking result is higher than that of the second importance ranking result.

[0115] In the present embodiment, the combination of the optimal level of each factor is not necessarily the optimal test condition. In theory, if each factor is not affected by the change of the level of other factors, then simply combining the optimal level of each factor is the optimal test condition. However, in fact, the primary and secondary factors are also considered when selecting better test conditions. In the case of meeting the index requirements, the selection level of some relatively secondary factors is appropriately reduced to obtain a better magnetic pole structure that meets the actual requirements. Compared with the magnetic field decay rate, the magnetic field strength is more important in the magnetic pole design. If the magnetic field strength cannot meet the requirements, the material removal efficiency of the magnetorheological finishing device may be unable to be generated, so after comprehensive consideration, the value combination of the independent shape parameters shown in Table 5 is selected as the optimal parameters of the magnetic field generating device structure.

[0116] Table 5

[0117]

[0118] The magnetic field strength distribution of the optimal structure in the X-Y plane is shown in FIG. 5. As can be analyzed in the figure, under the optimal structure, the magnetic field strength on the surface of the polishing wheel reaches 287 mT, and the magnetic field strength at a distance of 0.76 mm from the surface of the polishing wheel can reach 150 mT, which indicates that the formation of the ribbon at a distance of 0.76 mm from the surface under this structure meets the shear force requirements required for polishing. Figure 7

[0119] To further illustrate the effect of the present scheme, a small-size magnetorheological finishing device is tested.

[0120] (a) Magnetic field strength test

[0121] As described above, it is shown that the theoretical analysis results and the simulation results based on the mathematical model are consistent. Based on the above results, a small-size wheel-type magnetorheological finishing device with a polishing wheel diameter of 13 mm is built.

[0122] ​In this embodiment, the small-size MR polishing device can be divided into two independent parts: the polishing part and the spraying and recycling part. The main magnetic field of the magnet is distributed in the polishing area to provide the polishing capacity of the device, and the leakage magnetic field generated in the surrounding space area provides a weak magnetic field for the MR fluid, the strength of which needs to be greater than 15 mT to ensure that the MR fluid is successfully adsorbed on the polishing wheel before being thrown out of the polishing area, so the magnetic field strength distribution of the polishing part and the spraying and recycling part is the key to the normal work of the device. In order to understand the actual magnetic field distribution, we measured the magnetic field distribution on the surface of the polishing wheel using a tesla meter. In the X direction, the magnetic field strength of the polishing area on the surface of the MR fluid was measured, that is, the lowest point of the polishing wheel was tested along the path L, and the test results were basically consistent with the simulation as shown in Figure 8 In (a), the peak value of the magnetic field strength is about 230 mT. The actual result is smaller than the simulation value, and the reason may be that the actual magnet loses magnetic field during magnetization. The magnetic field strength at a distance of 0.75 mm from the surface of the polishing wheel can still reach 150 mT, that is, the equipment still has good polishing capacity when the belt thickness reaches 0.75 mm. By comparing the measurement results with theoretical analysis and finite element simulation, the accuracy of the design method of the small-diameter MR polishing device is verified.

[0123] At the same time, in order to ensure the stable recovery of the MR fluid, the magnetic field in the circumferential direction of the polishing wheel was detected (as shown in Figure 8 (b)) The results of the magnetic field strength in the circumferential direction show that the magnetic field strength of the recycling part is about 18 mT, and the existence of the weak magnetic field is conducive to the stable adhesion of the MR fluid on the polishing wheel, so as to ensure that the liquid does not splash and is successfully recycled with the rotation of the polishing wheel.

[0124] (b) Removal function stability test

[0125] As mentioned earlier, the magnetic field strength of the small-size MR polishing device was detected, and the accuracy of the theoretical analysis and simulation model was verified. In order to further explore the characteristics and stability of the device, experimental tests need to be carried out.

[0126] According to the above model, a small-size MR polishing device was built as shown in Figure 9 It can be seen from Figure 9 that the MR fluid is stably adhered to the polishing wheel and forms a relatively thick polishing belt. In order to more accurately evaluate the processing effect, the removal function of the small device was prepared, and its stability was detected.

[0127] Based on the parameters in Table 6, the removal function of the small MR polishing device was prepared as shown in Figure 10 The profile of the removal function is basically the same as the shape of the removal function of the large polishing device, and the volume removal rate is 4.88 x 10 5 μm3 / min. Its efficiency is about half of the 70 mm polishing wheel, so it can meet the requirements of polishing small size optical elements.

[0128] Table 6

[0129]

[0130] Since the polishing efficiency of the small size MR polishing device is not high, it may take a long time to process larger elements (elements with a diameter of 50 mm to 100 mm), so it is necessary to test the stability of the removal function of the device, including short-term stability test and long-term stability test.

[0131] In the short-term stability test, the time interval for obtaining each removal function is 15 minutes (see Figure 11 ). In terms of volume removal efficiency, the maximum value is 4.94 x 10 5 μm 3 / min, the minimum value is 4.74 x 10 5 μm 3 / min, the fluctuation range is ± 2.1%, which is better than the design target of ± 5%, and can meet the requirements of short-term processing.

[0132] For relatively large diameter elements, in order to ensure the processing effect, the characteristics of the small size MR removal function in long-term processing should be studied, and the time interval for preparing the removal function is 2 hours (see Figure 12 ). According to the experimental results in the figure, the fluctuation range of the volume removal rate is ± 4.5%, which is better than the design target of ± 10%. The results show that according to the short-term and long-term stability test results, it can be seen that the small size MR polishing device proposed in this work can be used for stable processing of small aperture and relatively large aperture (elements with a diameter of 50 mm to 100 mm) optical devices.

[0133] In combination with Figure 2 and Figure 3As shown, according to an embodiment of the present application, the present application provides a small-size magnetorheological polishing device obtained by using the aforementioned design method, which comprises a magnet 1 and a polishing wheel 2. In the embodiment, the magnet 1 is located in the polishing wheel 2, and the magnet 1 is arranged with a spacing from the inner wall of the polishing wheel 2; the magnet 1 has a symmetrical structure, which comprises a left magnetic pole 11, a right magnetic pole 12, a connecting plate 13, and a magnetic conducting plate 14; the left magnetic pole 11 and the right magnetic pole 12 are arranged symmetrically to each other, and the upper ends of the left magnetic pole 11 and the right magnetic pole 12 are connected to the magnetic conducting plate 14 respectively; the connecting plate 13 is arranged between the left magnetic pole 11 and the right magnetic pole 12; the left magnetic pole 11 comprises a magnetic pole upper part a and a magnetic pole lower part b connected to the magnetic pole upper part a; the magnetic pole lower part b is arranged obliquely to the magnetic pole upper part a; wherein the upper end surface and the lower end surface of the magnetic pole lower part b are arranged parallel to each other, the outer side surface of the magnetic pole lower part b comprises an oblique first plane part and a transition part for connecting the first plane part and the lower end surface, the inner side surface of the magnetic pole lower part b comprises an oblique second plane part and a vertical plane part for connecting the second plane part and the lower end surface, and the front side surface and the rear side surface of the magnetic pole lower part b are arranged flush with the magnetic pole upper part a.

[0134] In the embodiment, the structure of the right magnetic pole 12 is the same as that of the left magnetic pole 11, and the specific structure is not described here again.

[0135] According to an embodiment of the present application, the outer diameter of the polishing wheel is 10-15 mm, and the wall thickness is 0.4-1.5 mm.

[0136] Of course, the small-size magnetorheological polishing device of the present application further needs to be provided with a nozzle for spraying the magnetic fluid, a recovery device for recovering the magnetic fluid, a driving device for driving the polishing wheel 2 to run, and a carrier platform and other structures in the application process, and the structure settings belong to common structures and are not described here again.

[0137] The above is only an example of the specific scheme of the present application, and for the devices and structures not described in detail, it should be understood that the general devices and general methods in the art are used to implement them.

[0138] The above is only one scheme of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A design method for a small-sized magnetorheological polishing device, characterized in that: The following steps are involved: S1. Determine the magnet structure and magnet parameters of the magnet for the magnetorheological polishing device; wherein the magnet parameters include: magnet volume and independent shape parameters; wherein, in the step of determining the magnet structure of the magnet for the magnetorheological polishing device, the magnet includes two symmetrical poles; The magnetic pole comprises: a magnetic pole upper portion (a), a magnetic pole lower portion (b) connected to the magnetic pole upper portion (a); The lower end surface of the magnetic pole lower portion (b) is arranged parallel to the upper end surface of the magnetic pole upper portion (a), the outer side surface of the magnetic pole lower portion (b) includes an inclined first plane portion and a transition portion for connecting the first plane portion and the lower end surface, and the inner side surface of the magnetic pole lower portion (b) includes an inclined second plane portion and a vertical plane portion for connecting the second plane portion and the lower end surface; In the step of determining the magnet parameters of the magnet for the magnetorheological polishing device, the independent shape parameters are obtained based on the magnet structure, which include: the first inclination angle of the first planar portion; β , the second inclination angle of the second planar portion α , the lower end surface width of the lower end surface e 2. Half opening width of the lower opening of the magnet e 1; S2. Determine the polishing wheel structure and polishing wheel size of the polishing wheel for the magnetorheological polishing device, and determine the magnet volume of the magnet based on the polishing wheel size; wherein the polishing wheel is annular and its outer annular surface is arc-shaped; the outer diameter of the polishing wheel is 10 to 15 mm and the wall thickness is 0.4 mm to 1.5 mm; S3. Establishing a simulation model comprising the magnet and the polishing wheel, and, based on the simulation model and using an orthogonal test method, ranking the importance of each parameter included in the independent shape parameters and outputting the importance ranking result; S4. Optimize each of the independent shape parameters one by one based on the importance ranking result to complete the design of the magnet.

2. The design method according to claim 1, characterized in that: In the step of determining the magnet volume of the magnet based on the polishing wheel size, the magnet volume of the magnet is determined based on the polishing wheel size of the polishing wheel and the interval between the magnet and the inner annular surface of the polishing wheel.

3. The design method according to claim 2, characterized in that: In the step of ranking the importance of each parameter included in the independent shape parameters based on the simulation model and using the orthogonal test method and outputting the importance ranking results, the importance ranking results include: a first importance ranking result for indicating the degree of influence on the magnetic field intensity, and a second importance ranking result for indicating the degree of influence on the field strength attenuation rate.

4. The design method according to claim 3, characterized in that: The step of ranking the importance of each parameter included in the independent shape parameters based on the simulation model and using an orthogonal test method and outputting the importance ranking result includes: According to the preset optimal design requirements and the limitation of the polishing wheel size, the influence weight of each parameter of the independent shape parameters on the magnetic field intensity and the field intensity attenuation rate is analyzed based on the simulation model and the orthogonal test method; Sort each of the independent shape parameters based on the influence weight; wherein the first importance ranking result is: e 2, e 1, β , α The influence on the magnetic field strength increases in turn; the second importance ranking results are: e 1, e 2, β , α The impact on the field strength attenuation rate increases successively.

5. The design method according to claim 4, characterized in that: Based on the importance ranking result, each parameter in the independent shape parameters is optimized one by one. In the step of completing the design of the magnet, the first importance ranking result or the second importance ranking result is selected to optimize each parameter in the independent shape parameters one by one, and the selection priority of the first importance ranking result is higher than that of the second importance ranking result.

6. A polishing device obtained by the design method according to any one of claims 1 to 5, characterized in that: It includes a magnet (1) and a polishing wheel (2); The magnet (1) is located in the polishing wheel (2), and the magnet (1) and the inner annular surface of the polishing wheel (2) are spaced apart; The magnet includes two symmetrical poles; The magnetic pole comprises: a magnetic pole upper portion (a), a magnetic pole lower portion (b) connected to the magnetic pole upper portion (a); The lower end surface of the lower part of the magnetic pole (b) is arranged parallel to the upper end surface of the upper part of the magnetic pole (a), the outer side surface of the lower part of the magnetic pole (b) includes an inclined first plane portion and a transition portion for connecting the first plane portion and the lower end surface, and the inner side surface of the lower part of the magnetic pole (b) includes an inclined second plane portion and a vertical plane portion for connecting the second plane portion and the lower end surface.

7. The polishing device according to claim 6, characterized in that The outer diameter of the polishing wheel is 10-15 mm, and the wall thickness is 0.4 mm-1.5 mm.

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