A speed threshold-based efficient convergence method for fly-cutting magnetorheological finishing surface shape

Abstract

The application discloses a kind of based on speed threshold's lifting tool magnetic fluid polishing surface efficient convergence method, belong to optical polishing field, including: according to the point removal function obtained by processing tool, and the initial surface shape of workpiece is measured using interferometer;Setting track parameters, based on material removal amount is the convolution principle of removal function and residence time, the tool feed speed of each point is solved out.Due to the removal amount of surface low point in processing process is very little, so that the feed speed of processing tool in low point tends to the limit speed of machine tool, but still can cause material removal to surface low point, influence the convergence efficiency of surface error.Through setting speed threshold, and the continuous point area higher than speed threshold is taken tool lifting mode to contact with workpiece, avoid over-processing of surface low point, and the tool speed of surface low point area is maintained at speed threshold, avoid frequent movement with the limit speed of machine tool in processing process, improve the efficiency and stability of magnetic fluid super-precision shaping.

Description

Technical Field

[0001] This invention belongs to the field of optical polishing, specifically a high-efficiency convergence method for surface shape in lift-up magnetorheological polishing based on a velocity threshold. Background Technology

[0002] Ultra-precision optical components are one of the core foundational parts of modern technology, and their surface accuracy and quality directly determine the performance limits of the optical system. Because surface errors cause light to deviate from its ideal path, resulting in problems such as image blurring, distortion, reduced resolution, and decreased contrast, high-precision reshaping is essential for achieving high-resolution, low-distortion imaging. The core idea of ​​the entire reshaping process is to move the high points of the surface closer to the low points. By controlling the dwell time distribution of the tool on the workpiece surface, precise control of the amount of material removed can be achieved. However, since the amount of material removed from the low points during processing is small, or even negligible, the feed speed of the machining tool at these low points is forced to approach the machine tool's limit speed. This still results in material removal at the low points, affecting the convergence efficiency of surface errors.

[0003] The main method to solve this problem is to optimize the path generation area and generate random trajectories only in the high point area of ​​the surface. However, this method increases the difficulty of calculating the dwell time drastically, and the alignment accuracy between the theoretical trajectory and the workpiece surface is required to achieve high-precision shaping, which leads to a surge in processing costs. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems and provide a high-efficiency convergence method for magnetorheological polishing surface shape based on a speed threshold. This method can define the low point region of the surface shape in the trajectory by setting a tool feed speed threshold, and adopt a tool lifting and constant speed control in the low point region. While preserving the advantages of the global trajectory, it solves the problem of reduced stability and lifespan of CNC machine tools caused by large changes in tool feed speed at the low point of the surface shape. It also solves the problem of over-machining at the low point of the surface shape without increasing additional costs.

[0005] To achieve the above objectives, this invention provides an efficient convergence method for the surface shape of a lift-up magnetorheological polishing device based on a velocity threshold. The specific steps are as follows:

[0006] Step S110: Obtain the removal function F(x,y): Perform point processing according to the process parameters of the tool in the actual processing process to realize the extraction of the removal function, or use the determined removal function;

[0007] Step S120: Use an interferometer to measure the initial surface shape of the workpiece and obtain the surface shape error distribution H(x,y);

[0008] Step S130: Set the point spacing of the trajectory and line spacing ;

[0009] Step S140: Based on the principle that the material removal amount is obtained by the convolution of the removal function F(x,y) and the dwell time T(x,y), the dwell time T(x,y) of each point of the trajectory is solved by inverse solution based on the surface error distribution H(x,y);

[0010] Step S150: Based on the dot spacing And the feed rate distribution V(x,y) of the dwell time T(x,y) calculation tool:

[0011] ;

[0012] Step S160: Divide the surface low point machining area: Set the tool feed rate threshold Set the feed rate to continuously exceed The threshold for the number of points is N, and it is only applied when the feed rate exceeds... Only when the number of consecutive points exceeds N is the region designated as a low-point region of the surface.

[0013] Step S170: Set tool lifting and lowering operations at the starting and ending points of the machining area at the low point of the surface, and maintain the tool feed rate between the two points at the threshold value. Generate a new tool feed rate distribution .

[0014] Step S180: Based on the feed rate distribution The CNC code is generated, imported into the CNC machine tool, and the workpiece surface shape error is converged by controlling the tool's feed speed and position, thus completing the workpiece surface shaping.

[0015] Compared with existing processing methods, the advantages of this invention are as follows:

[0016] This invention maintains the advantage of low complexity in solving the global trajectory dwell time. Based on surface data, it can flexibly define the low point region of the surface by setting the tool feed speed threshold. In the low point region of the surface, the tool is lifted and the speed is kept constant to make the machining tool detach from the workpiece, thus solving the problem of overmachining at the low point of the surface and avoiding frequent movement at the machine tool's limit speed during the machining process. This is of great significance for improving the surface convergence efficiency and accuracy of large-area and complex surfaces. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the efficient convergence method for a lift-up magnetorheological polishing surface shape based on a velocity threshold according to the present invention.

[0018] Figure 2 A schematic diagram of the removal function F(x,y) for magnetorheological processing;

[0019] Figure 3 The first image shown is an initial surface shape of the workpiece to be shaped in the embodiment, wherein (a) shows the initial surface shape used to generate the grating trajectory, and (b) shows the initial surface shape used to generate the spiral trajectory.

[0020] Figure 4 A schematic diagram of the parameter settings for the trajectory, where (a) shows the point spacing and line spacing of the grating trajectory, and (b) shows the point spacing and line spacing of the spiral trajectory;

[0021] Figure 5 The diagram shows the dwell time distribution T(x,y), initial velocity distribution V(x,y), and velocity distribution after dividing the low point region of the machining trajectory. (a) shows the dwell time distribution calculated based on the grating trajectory, (b) shows the initial velocity distribution based on the grating trajectory, and (c) shows the velocity distribution after setting a velocity threshold based on the grating trajectory. (d) shows the dwell time distribution calculated based on the helical trajectory; (e) shows the initial velocity distribution based on the helical trajectory; and (f) shows the velocity distribution after setting a velocity threshold based on the helical trajectory. ;

[0022] Figure 6 The image shows the surface shape of the workpiece after reshaping, where (a) shows the surface shape using a raster trajectory-based method. The processed surface shape, (b) shows the application of a spiral trajectory-based method. The surface shape after processing. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] Figure 1 This is a schematic flowchart of an efficient convergence method for magnetorheological polishing surface shape based on a velocity threshold according to the present invention. See below for reference. Figure 1 The process of this method is described. The description uses a magnetorheological tool, a deterministic machining tool, as an example; however, the process is equally applicable to single-point diamond turning, wheel polishing, and other machining methods.

[0025] like Figure 1 As shown, the method includes:

[0026] Step S110: Obtain the removal function F(x,y): Perform point processing according to the process parameters of the tool in the actual processing process to realize the extraction of the removal function, or use the determined removal function;

[0027] Step S120: Use an interferometer to measure the initial surface shape of the workpiece and obtain the surface shape error distribution H(x,y);

[0028] Step S130: Set the point spacing of the trajectory and line spacing ;

[0029] Step S140: Based on the principle that the material removal amount is obtained by convolving the removal function F(x,y) with the residence time T(x,y), the residence time T(x,y) of each point on the trajectory is solved by inverse solution based on the surface error distribution H(x,y).

[0030] In one implementation, iterative algorithms (such as the conjugate gradient method or the Richardson-Lucy algorithm) combined with regularization techniques (such as Tikhonov regularization) can be used to inversely solve for the dwell time T(x,y).

[0031] Step S150: Based on the dot spacing And the feed rate distribution V(x,y) of the dwell time T(x,y) calculation tool:

[0032] ;

[0033] As can be seen from the above, in step S150, the tool feed rate distribution is essentially composed of the surface error distribution H(x,y) and the point spacing of the trajectory. A joint decision.

[0034] Step S160: Divide the surface low point machining area. Since the amount of surface low point removal during the machining process is small, or even unnecessary, the theoretical feed rate of the machining tool at the low point needs to be extremely fast, i.e., set the tool feed rate threshold. Set the feed rate to continuously exceed The threshold for the number of points is N, and it is only applied when the feed rate exceeds... Only when the number of consecutive points exceeds N is the region designated as a low point region of the surface.

[0035] Speed ​​threshold The value range is 80%-95% of the machine tool's maximum feed rate. The threshold value N for the number of consecutive points ranges from ≥25. .

[0036] In one embodiment, the step may further include: using morphological processing methods to optimize the divided surface low point regions.

[0037] Step S170: Set tool lifting and lowering operations at the starting and ending points of the machining area at the low point of the surface, and maintain the tool feed rate between the two points at the threshold value. Generate a new tool feed rate distribution .

[0038] The tool lifting and lowering operations are configured, with the specific displacement determined based on the tool's deformation after contact. This ensures the tool is no longer in contact with the workpiece after lifting, and maintains the tool feed rate between the two points at a threshold value. Generate a new tool feed rate distribution .

[0039] Among them, the tool feed rate between the two points is maintained at a threshold. This is to avoid the machine tool frequently moving at its maximum speed, which would reduce the stability of the mechanical structure and affect the lifespan of the CNC machine tool. The tool lifting height H in step S170 must satisfy: H ≥ 1.5d.

[0040] Step S180: Based on the feed rate distribution The CNC code is generated, imported into the CNC machine tool, and the workpiece surface shape error is converged by controlling the tool's feed speed and position, thus completing the workpiece surface shaping.

[0041] The method may further include: after step S180, measuring and verifying the surface shape of the modified workpiece, and adjusting the speed threshold based on the verification results. And / or the threshold N for the number of consecutive points.

[0042] This invention is applicable to a variety of processing tools (such as airbag polishing, single-point diamond turning, wheel polishing, etc.) and processing paths (such as grating trajectory, spiral trajectory, random trajectory, etc.), and is of great significance for improving the shaping efficiency and accuracy of optical components.

[0043] The following two examples illustrate the specific application of the above methods.

[0044] Example 1:

[0045] Application environment: The magnetorheological rotation speed is 190 rpm, and the workpiece to be shaped is... A 1000mm fused silica plane.

[0046] Step 1: According to the process parameters of the tool in the actual processing, point processing is performed per unit time, and the surface shape data before and after processing is subtracted using an interferometer to achieve the extraction of the removal function, such as... Figure 2 As shown, let F(x,y) be the removal function;

[0047] Step 2: Use an interferometer to measure the initial surface shape of the workpiece and obtain the surface shape error distribution H(x,y), such as... Figure 3 As shown in (a); where RMS refers to the root mean square error of surface accuracy, which is the core indicator for evaluating the deviation between the optical surface and the ideal surface. The smaller the value, the smoother the surface and the higher the accuracy.

[0048] Step 3: Set the track to a raster track, such as... Figure 4 As shown in (a), the point spacing is set. The line spacing is 4mm. It is 2mm;

[0049] Step 4: Based on the principle that the material removal amount is obtained by convolving the removal function F(x,y) with the residence time T(x,y), the residence time T(x,y) at each point of the trajectory is solved by inversely based on the surface error distribution H(x,y), such as... Figure 5 As shown in (a) in the figure.

[0050] Step 5: Calculate the tool's feed rate distribution V(x,y) based on the point spacing D1 and dwell time T(x,y), such as... Figure 5 As shown in (b) in the image;

[0051] Step 6: Define the low-point machining area of ​​the surface. Since the amount of low-point removal during the machining process is small, or even unnecessary, the theoretical feed rate of the machining tool at the low points needs to be extremely high. Set the tool feed rate threshold. If the speed is 3000 mm / min and the threshold N for the number of consecutive points is 30, then the area formed by connecting more than 30 consecutive points with a speed exceeding 3000 mm / min is defined as the surface low point processing area.

[0052] Step 7: Set tool lifting and lowering operations at the starting and ending points of the machining area at the lowest point of the surface, and maintain the tool feed rate between the two points at 3000 mm / min to generate a new tool feed rate distribution. ,like Figure 5 As shown in (c) in the figure.

[0053] Step 8: Based on the feed rate distribution CNC code is generated, imported into the CNC machine tool, and by controlling the tool's feed rate and pose, the workpiece surface shape error is converged, resulting in a machined surface like... Figure 6 As shown in (a), the surface accuracy was reduced from RMS 153.67 nm to 12.63 nm, achieving efficient surface reshaping of the workpiece.

[0054] Example 2:

[0055] Application environment: The magnetorheological rotation speed is 190 rpm, and the workpiece to be shaped is a 300 mm fused silica plane.

[0056] Step 1: According to the process parameters of the tool in the actual processing, point processing is performed per unit time, and the surface shape data before and after processing is subtracted using an interferometer to achieve the extraction of the removal function, such as... Figure 2 As shown, let F(x,y) be the removal function;

[0057] Step 2: Use an interferometer to measure the initial surface shape of the workpiece and obtain the surface shape error distribution H(x,y), such as... Figure 3 As shown in (b) in the image;

[0058] Step 3: Set the trajectory to a spiral trajectory, such as... Figure 4 As shown in (b) above, the point spacing is set. The line spacing is 1mm. It is 1mm;

[0059] Step 4: Based on the principle that the material removal amount is obtained by convolving the removal function F(x,y) with the residence time T(x,y), the residence time T(x,y) at each point of the trajectory is solved by inversely based on the surface error distribution H(x,y), such as... Figure 5 As shown in (d) in the figure.

[0060] Step 5: Based on the point spacing And the feed rate distribution V(x,y) of the dwell time T(x,y) calculation tool, such as Figure 5 As shown in (e);

[0061] Step 6: Define the low-point machining area of ​​the surface. Since the amount of low-point removal during the machining process is small, or even unnecessary, the theoretical feed rate of the machining tool at the low points needs to be extremely high. Set the tool feed rate threshold. If the speed is 1400 mm / min and the threshold N for the number of consecutive points is 15, then the area formed by connecting more than 15 consecutive points with a speed exceeding 1400 mm / min is defined as the surface low point processing area.

[0062] Step 7: Set tool lifting and lowering operations at the starting and ending points of the machining area at the lowest point of the surface, and maintain the tool feed rate between the two points at 1400 mm / min to generate a new tool feed rate distribution. ,like Figure 5 As shown in (f) in the figure.

[0063] Step 8: Based on the feed rate distribution CNC code is generated, imported into the CNC machine tool, and by controlling the tool's feed rate and pose, the workpiece surface shape error is converged, resulting in a machined surface like... Figure 6As shown in (b), the surface accuracy was reduced from RMS 239.97nm to 6.24nm, achieving efficient surface reshaping of the workpiece.

[0064] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0065] Although the invention has been described with respect to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of explaining or limiting the subject matter of the invention.

Claims

1. A speed threshold based fly-cutting magnetorheological finishing (MRF) surface profile efficient convergence method, characterized in that, The method comprises the following steps: Step S110: obtaining a removal function F(x, y): point processing is performed according to the process parameters of the tool in the actual processing process to realize removal function extraction, or a determined removal function is used; Step S120: measuring the initial surface shape of the workpiece surface using an interferometer to obtain a surface error distribution H(x, y); Step S130: Setting point interval of trajectory and line interval ; Step S140: according to the principle that the convolution of the removal function F(x, y) and the residence time T(x, y) is the material removal amount, the residence time T(x, y) of each point of the trajectory is inversely solved based on the surface error distribution H(x, y); Step S150: calculating the feed speed distribution V(x,y) of the tool from the point distances and the residence time T(x,y) ； Step S160: dividing the low point of surface machining area: setting the tool feed speed threshold , setting the number threshold of the points that the feed speed continuously exceeds , only when the number of the points that the feed speed continuously exceeds exceeds N, the area is divided into the low point of surface area. Step S170: Set tool lift and drop operations at the start and end points of the face low point machining area, and keep the tool feed speed between the two points at a threshold value , generate a new tool feed speed distribution ; Step S180: generating the feed speed distribution according to the feed speed distribution The numerical control code is generated, imported into the numerical control machine tool, and the convergence of the workpiece surface shape error is realized by controlling the feed speed and the pose of the tool, and the workpiece surface modification is completed.

2. The method of claim 1, wherein the method is based on a speed threshold. In step S170, the tool lifting and lowering operation is set, and the specific displacement H is determined according to the deformation amount d after the tool contacts.

3. The method of claim 2, wherein the method is a high-efficiency convergence method for polishing a surface profile based on a speed threshold. In step S170, generating the new feed rate profile for the tool comprises: lifting the tool out of contact with the workpiece and maintaining the tool feed rate between the two points at a threshold value , generating the new feed rate profile for the tool .

4. The method of claim 1, wherein the method is based on a speed threshold. The machining tool to which the method is applicable includes a gas bag polishing tool, a single-point diamond turning tool and a wheel polishing tool, and the machining path to which the method is applicable includes a grating trajectory, a spiral trajectory and a random trajectory.

5. The method of claim 1, wherein the method further comprises: said speed threshold ranges from 80% to 95% of the maximum feed speed of the machine tool.

6. The method of claim 1, wherein the method is a high-efficiency convergence method for polishing a surface profile based on a speed threshold. The continuous point number threshold N is in the range of ≥25 .

7. The method of claim 1, wherein the method further comprises: The iterative algorithm used in step S140 includes a conjugate gradient method, a Richardson-Lucy algorithm and a regularization technique including Tikhonov regularization.

8. The method of claim 1, wherein the method further comprises: Step S160 further comprises: using a morphological processing method to perform regional optimization on the divided surface low point region.

9. The method of claim 1, wherein the method further comprises: The method further includes: after step S180, measuring and verifying the surface shape of the modified workpiece, and adjusting the speed threshold according to the verification result. And / or the threshold N for the number of consecutive points.

10. The method of claim 3, wherein the method is a high-efficiency convergence method for polishing a surface profile based on a speed threshold. The tool lifting height H in step S170 satisfies: H≥1.5d.

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