Cutter lifting type magnetorheological polishing surface shape efficient convergence method based on speed threshold value

Abstract

The invention discloses a cutter lifting type magneto-rheological polishing surface shape efficient convergence method based on a speed threshold value, and belongs to the field of optical polishing. The method comprises the steps that a point removal function is obtained according to a machining tool, and the initial surface shape of a workpiece is measured through an interferometer; and track parameters are set, and the tool feeding speed of each point is calculated based on the convolution principle that the material removal amount is a removal function and residence time. Due to the fact that the removal amount of surface shape low points in the machining process is extremely small, the feeding speed of a machining tool at the low points tends to the limit speed of a machine tool, but material removal is still caused to the surface shape low points, and the convergence efficiency of surface shape errors is affected. A speed threshold value is set, a continuous point area higher than the speed threshold value is separated from a workpiece in a tool lifting mode, over-machining of a surface shape low point is avoided, the tool speed of the surface shape low point area is maintained at the speed threshold value, frequent movement at the limit speed of a machine tool in the machining process is avoided, and machining precision is improved. And the efficiency and the stability of the magnetorheological ultra-precise shape modification are improved.

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 point 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 point 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);

[0051] Step 6: Define the machining area for the low points of the surface. Since the amount of material removed from the low points during machining is small, or even negligible, the theoretical feed rate of the machining tool at these low points needs to be extremely high. Set a 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);

[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 machining area for the low points of the surface. Since the amount of material removed from the low points during machining is small, or even negligible, the theoretical feed rate of the machining tool at these low points needs to be extremely high. Set a 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 high-efficiency convergence method for magnetorheological polishing surface shape based on velocity threshold, characterized in that, Includes the following steps: 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; Step S120: Use an interferometer to measure the initial surface shape of the workpiece and obtain the surface shape error distribution H(x,y); Step S130: Set the point spacing of the trajectory and line spacing ; 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 on the trajectory is solved by inverse solution based on the surface error distribution H(x,y); Step S150: Based on the point spacing And the feed rate distribution V(x,y) of the dwell time T(x,y) calculation tool: ； 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. 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 ; 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.

2. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 1, characterized in that: In step S170, the specific displacement H of the tool lifting and lowering operation is determined based on the deformation d of the tool after contact.

3. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 2, characterized in that: In step S170, generating a new tool feed rate distribution includes: ensuring the tool is no longer in contact with the workpiece after being lifted, and maintaining the tool feed rate between the two points at a threshold value. Generate a new tool feed rate distribution .

4. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 1, characterized in that: The applicable machining tools for the method include: airbag polishing, single-point diamond turning, and wheel polishing; the applicable machining paths include: grating trajectory, spiral trajectory, and random trajectory.

5. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 1, characterized in that: The speed threshold The value range is 80%-95% of the machine tool's maximum feed rate.

6. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 1, characterized in that: The threshold value N for the number of consecutive points is ≥25. .

7. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 1, characterized in that: In step S140, iterative algorithms, including the conjugate gradient method and the Richardson-Lucy algorithm, are used in combination with regularization techniques, including Tikhonov regularization, to inversely solve for the dwell time T(x,y).

8. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 1, characterized in that: Step S160 further includes: using morphological processing methods to optimize the low point regions of the divided surface.

9. The efficient convergence method for the surface shape of lift-up magnetorheological polishing based on velocity threshold as described in claim 1, characterized in that: 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 efficient convergence method for the surface shape of a lift-up magnetorheological polishing tool based on a velocity threshold according to claim 3, characterized in that: The tool lifting height H in step S170 satisfies: H≥1.5d.

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