Centering method of four-axis sphere grinding and polishing device

Abstract

The centering method of the four-axis sphere grinding and polishing device comprises the following steps that firstly, any grinding shaft is selected as a reference shaft and marked as a shaft IV, and the other three grinding shafts are calibrated shafts and marked as a shaft I, a shaft II and a shaft III; 2, selecting any point on the axis of the reference shaft as a centering position; step 3, calibrating the axis I: S3.1, determining the positions of the two cameras; s3.2, calibrating the x-direction position of the axis I by taking the axis IV as a reference, and extracting an error value x1; then, calibrating the angle of a shaft I, aligning the axis of the shaft I to a space intersection point O, and extracting an error value y1; the centering error between the shaft I and the shaft IV is calculated, and if the centering error is smaller than or equal to a threshold value, calibration of the shaft I is completed; step 4, calibrating the shaft II according to the same way of calibrating the shaft I in the step 3; and step 5, calibrating the shaft III according to the same way of calibrating the shaft I in the step 3. The comparison method has the advantages of being easy to implement and high in centering precision.

Description

Technical Field

[0001] The present invention relates to the technical field of precision machining of spheres, and specifically relates to a centering method for a four-axis sphere lapping and polishing device. Background Art

[0002] Precision spheres are key components of high-end mechanical basic components such as high-performance bearings, high-precision ball screws, and high-precision linear guides. Their shape accuracy, surface quality, and dimensional consistency directly affect the performance and service life of mechanical basic functional components, and further affect the performance of high-end equipment. Their precision machining technology occupies an important position in multiple fields. After the ball blank of the precision sphere is formed, lapping and polishing are the key processes for final ball formation.

[0003] In the current sphere machining technology field, four-axis sphere lapping and polishing devices have the characteristics of high machining accuracy and high material removal rate. The core component of this lapping and polishing device is a four-axis lapping tool, which consists of four grinding shafts symmetrically arranged in three-dimensional space. The grinding shafts can rotate forward and backward under the drive of a servo motor. According to the positional relationship between the grinding shaft in the vertical direction and the other three grinding shafts, the device can be divided into two configurations: a right-side-up regular tetrahedron and an inverted regular tetrahedron. Among the four grinding shafts, one grinding shaft is arranged in a plumb state, and the other three grinding shafts are arranged at an inclination angle of β = 19.47° with the horizontal plane, and the included angle of their projections on the horizontal plane is ψ = 120°. From the perspective of the spatial structure, these four grinding shafts form a regular tetrahedron, and the included angle between any two shafts is φ = 109.47°. The centroid of this regular tetrahedron, that is, the intersection position of all shafts, is exactly the center of the ball of the ball blank to be machined.

[0004] In order to ensure the uniformity of four-axis machining, centering operations must be carried out before machining the sphere. The essence of centering is to calibrate the four grinding shafts to the ideal position as much as possible when installing the grinding shafts. However, the centering process of the existing four-axis grinding machines is relatively difficult, and there is no publicly available centering method for four-axis sphere lapping and polishing devices. Technicians usually use visual observation, with poor centering accuracy and inability to quantify the error value, and inaccurate centering will directly lead to poor sphere grinding accuracy. Therefore, how to provide a method that can effectively improve the centering accuracy of four-axis grinding machines is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a centering method for a four-axis sphere lapping and polishing device. This centering method has the advantages of being easy to implement and having high centering accuracy; at the same time, the centering method of the present invention can quantify the error value and provide a reference basis for process research.

[0006] The technical solution of this application is as follows:

[0007] Centering method for a four-axis spherical grinding and polishing device, comprising the following steps:

[0008] Step 1: Arbitrarily select one grinding axis as the reference axis, denoted as axis Ⅳ, and the other three grinding axes as the axes to be calibrated, denoted as axis Ⅰ, axis Ⅱ, and axis Ⅲ; set the plane formed by the reference axis and the axes to be calibrated as a coplanar plane, and axis Ⅰ, axis Ⅱ, and axis Ⅲ respectively correspond to coplanar plane I, coplanar plane Ⅱ, and coplanar plane Ⅲ; set the plane containing the reference axis and perpendicular to the coplanar plane as the vertical plane, and coplanar plane I, coplanar plane Ⅱ, and coplanar plane Ⅲ respectively correspond to vertical plane I, vertical plane Ⅱ, and vertical plane Ⅲ;

[0009] Step 2: Select any point on the axis of the reference axis as the centering position, denoted as the spatial intersection point O;

[0010] Step 3: Calibrate axis Ⅰ:

[0011] S3.1: Determine the positions of two cameras: Adjust the position of the first camera until the axes of axis Ⅰ and axis Ⅳ are parallel in the image. At this time, the plane where the first camera is located is coplanar plane I; the second camera is set at an angle of 90° to the first camera, and the plane where the second camera is located is vertical plane I; set up a coordinate system, where the x-axis is perpendicular to coplanar plane I and the y-axis is on the axis of the reference axis;

[0012] S3.2: Taking axis Ⅳ as the reference, align the axis of axis Ⅰ with the axis of axis Ⅳ to calibrate the x-direction position of axis Ⅰ, and extract the deviation between the two axes as the error value x1; then, align the axis of axis Ⅰ with the axis of axis Ⅳ to calibrate the angle of axis Ⅰ so that the angle error is within the allowable range. Then, calibrate the y-direction position of axis Ⅰ, align the axis of axis Ⅰ with the spatial intersection point O, and extract the deviation between the axis of axis Ⅰ and point O as the error value y1; calculate the centering error between axis Ⅰ and axis Ⅳ. If the centering error is less than or equal to the threshold value, the calibration of axis Ⅰ is completed. If the centering error is greater than the threshold value, re-perform the calibration in the x-direction and y-direction until the centering error is less than or equal to the threshold value;

[0013] Step 4: Calibrate axis Ⅱ in the same way as calibrating axis Ⅰ in Step 3;

[0014] Step 5: Calibrate axis Ⅲ in the same way as calibrating axis Ⅰ in Step 3.

[0015] Compared with the prior art, the centering method of the present invention can improve the centering accuracy of the four-axis spherical grinding and polishing device by adopting specific method steps, thereby improving the processing accuracy of the four-axis grinding and polishing device. When centering, first select the reference axis, set up the coordinate system, and set the cameras according to specific rules, and then calibrate the axes to be calibrated, so that the centering error and angle error can be controlled within the set range, and the whole process is easy to operate and can be applied industrially; at the same time, the centering method of the present invention can quantify the error value and provide a reference basis for process research.

[0016] Further, as a preferred solution, in step one of the centering method of the aforementioned four-axis spherical grinding and polishing device, select the grinding axis in the plumb direction as the reference axis, denoted as axis Ⅳ, and adjust it to be perpendicular to the workbench and aligned with the center of the feeding device. When implementing the method of the present invention, selecting the grinding axis in the plumb direction as the reference axis can make subsequent operations more convenient.

[0017] Further, as a preferred solution, in step two of the centering method of the aforementioned four-axis spherical grinding and polishing device, preferably select the intersection point of the axis of the reference axis and the end face of the grinding tool as the spatial intersection point O.

[0018] Further, as a preferred solution, in the centering method of the aforementioned four-axis spherical grinding and polishing device, the threshold value of the centering error is 10 micrometers. From the perspective of processing accuracy, the smaller the threshold value of the centering error, the better. However, the smaller the threshold value of the centering error, the greater the difficulty of centering, and it may even lead to the requirement not being met after repeated calibration. Setting the threshold value of the centering error to 10 micrometers can not only ensure the processing accuracy of four-axis grinding, but also facilitate centering.

[0019] Further, as a preferred solution, in the centering method of the aforementioned four-axis spherical grinding and polishing device, the allowable range of the angular error is ±10 arcseconds. Similarly to the centering error, from the perspective of processing accuracy, the smaller the angular error, the better. However, if the allowable range of the angular error is too narrow, it will increase the difficulty of centering, and it may even lead to the requirement not being met after repeated calibration. Controlling the angular error within 10 arcseconds can not only ensure the processing accuracy of four-axis grinding, but also facilitate centering.

[0020] Further, as a preferred solution, in the centering method of the aforementioned four-axis spherical grinding and polishing device, the hardware for implementing this centering method includes a first camera, a second camera, and a computer that is signal-connected to the first camera and the second camera; during operation, the first camera and the second camera transmit the captured images to the computer, and the operator adjusts the axis to be calibrated according to the images displayed and output on the computer to achieve the calibration purpose. With the computer processing the images, it is beneficial to improve efficiency and reliability.

[0021] Further, as a preferred solution, in the centering method of the aforementioned four-axis spherical grinding and polishing device, during centering, the computer analyzes the images and calculates the centering error and the angular error. Using the computer to analyze the images and calculate the centering error and the angular error not only has good accuracy but also high efficiency.

[0022] Further, as a preferred solution, in the centering method of the aforementioned four-axis spherical grinding and polishing device, the hardware for implementing this centering method further includes a light source; a set of light sources is respectively configured for the first camera and the second camera. The setting of the light source can reduce image noise or distortion caused by environmental light fluctuations or object surface reflections.

[0023] Further, as a preferred solution, in the centering method of the aforementioned four-axis spherical grinding and polishing device, magnifying lenses are installed on both the first camera and the second camera.

[0024] Further, as a preferred solution, in the centering method of the aforementioned four-axis spherical grinding and polishing device, during centering, start the grinding shaft driving device to make the grinding shaft rotate; the computer performs image fusion on the video recorded by the camera to obtain the contour of the grinding shaft during rotation. Thus, it is possible to avoid the influence of the radial runout of the grinding shaft on the centering accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the principle of the centering method of the present invention;

[0026] Figure 2 is a schematic diagram for calibration (calibrating the I axis) according to the image captured by the first camera in the coplanar position in the centering method of the present invention;

[0027] Figure 3 is a schematic diagram for calibration (calibrating the I axis) according to the image captured by the second camera in the vertical plane position in the centering method of the present invention;

[0028] Figure 4 is a schematic diagram of the state (top view) when calibrating the I axis in the method of the present invention;

[0029] Figure 5 is a schematic diagram of the state (top view) when calibrating the I axis in the method of the present invention;

[0030] Figure 6 is a schematic diagram of the state (top view) when calibrating the III axis in the method of the present invention;

[0031] Figure 7 is the actual magnified image of the first camera in the coplanar position;

[0032] Figure 8 is the actual magnified image of the second camera in the vertical plane position.

[0033] Reference Signs:

[0034] 1 - Axis IV; 2 - Axis I; 3 - Axis II; 4 - Axis III; 5 - First Camera; 6 - Second Camera. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The following further illustrates the present application with reference to the drawings and embodiments, but it shall not be used as a basis for limiting the present application.

[0036] Embodiment (see Figure 1-8 )

[0037] See Figure 1, in this embodiment, the hardware for centering includes a first camera 5, a second camera 6, and a computer that is signal - connected to the first camera 5 and the second camera 6. During operation, the first camera 5 and the second camera 6 transmit the captured images to the computer, and the operator adjusts the shaft to be calibrated according to the images displayed and output on the computer to achieve the calibration purpose.

[0038] In this embodiment, during centering, the computer analyzes the images and calculates the centering error and the angular error.

[0039] In this embodiment, the hardware for implementing this centering method further includes a light source; a set of light sources are respectively configured for the first camera and the second camera.

[0040] In this embodiment, magnifying lenses are installed on both the first camera and the second camera.

[0041] In this embodiment, during centering, the grinding shaft driving device is started to make the grinding shaft rotate; the computer performs image fusion on the video recorded by the camera to obtain the contour of the grinding shaft during rotation.

[0042] In this embodiment, the centering method of the four - axis spherical grinding and polishing device is as follows:

[0043] Step 1: Select the grinding shaft in the plumb direction as the reference shaft, denoted as shaft Ⅳ1, and the other three grinding shafts as the shafts to be calibrated, denoted as shaft Ⅰ2, shaft Ⅱ3, and shaft Ⅲ4; set the plane formed by the reference shaft and the shafts to be calibrated as a coplanar plane. Shaft Ⅰ2, shaft Ⅱ3, and shaft Ⅲ4 respectively correspond to coplanar plane I, coplanar plane Ⅱ, and coplanar plane Ⅲ; set the plane containing the reference shaft and perpendicular to the coplanar plane as the vertical plane. Coplanar plane I, coplanar plane Ⅱ, and coplanar plane Ⅲ respectively correspond to vertical plane I, vertical plane Ⅱ, and vertical plane Ⅲ;

[0044] Step 2: Select the intersection point of the axis of the reference shaft and the end face of the grinding tool as the centering position, denoted as the spatial intersection point O.

[0045] Step 3: Calibrate shaft Ⅰ:

[0046] S3.1: Determine the positions of the two cameras: Adjust the position of the first camera until the axes of shaft Ⅰ and shaft Ⅳ are parallel in the image. At this time, the plane where the first camera is located is coplanar plane I; the second camera is set at an angle of 90° with respect to the first camera, and the plane where the second camera is located is vertical plane I; set up a coordinate system, where the x - axis is perpendicular to coplanar plane I and the y - axis is on the axis of the reference shaft;

[0047] S3.2: Taking shaft Ⅳ as the reference, align the axis of shaft Ⅰ with the axis of shaft Ⅳ to calibrate the x - direction position of shaft Ⅰ, and extract the deviation between the two axes as the error value ; Then, align the axis of shaft I with the axis of shaft IV, calibrate the angle of shaft I, and the computer outputs an angular error of 6 arcseconds, which is within the allowable range (10 arcseconds). The angle calibration of shaft I is completed. Then, calibrate the y-direction position of shaft I. Align the axis of shaft I with the spatial intersection point O, and extract the deviation between the axis of shaft I and point O as the error value. ; The computer calculates the centering error between shaft I and shaft IV. , the centering error exceeds the set threshold (10 microns). After re-calibrating the x-direction and y-direction, the x-direction error value , the y-direction error value , the centering error , is less than 10 microns, and the calibration of shaft I is completed;

[0048] Step Four: Calibrate shaft II:

[0049] S4.1. Determine the positions of the two cameras: Adjust the position of the first camera until the axes of shaft II and shaft IV in the image are parallel. At this time, the plane where the first camera is located is coplanar I; the second camera is set at an angle of 90° from the first camera, and the plane where the second camera is located is perpendicular plane I; Set up a coordinate system, where the x-axis is perpendicular to coplanar I, and the y-axis is on the axis of the reference axis;

[0050] S4.2. Using shaft IV as the reference, align the axis of shaft II with the axis of shaft IV, calibrate the x-direction position of shaft II, and extract the deviation between the two axes as the error value ; Then, align the axis of shaft II with the axis of shaft IV, calibrate the angle of shaft II, and the computer outputs an angular error of 8 arcseconds, which is within the allowable range (10 arcseconds). The angle calibration is completed. Then, calibrate the y-direction position of shaft II. Align the axis of shaft II with the spatial intersection point O, and extract the deviation between the axis of shaft II and point O as the error value ; Calculate the centering error between shaft II and shaft IV , the centering error exceeds the set threshold (10 microns). After re-calibrating the x-direction and y-direction, the x-direction error value , the y-direction error value , the centering error , is less than 10 microns, and the calibration of shaft II is completed;

[0051] Step Five: Calibrate shaft III:

[0052] S4.1. Determine the positions of the two cameras: Adjust the position of the first camera until the axes of shaft III and shaft IV in the image are parallel. At this time, the plane where the first camera is located is coplanar I; the second camera is set at an angle of 90° from the first camera, and the plane where the second camera is located is perpendicular plane I; Set up a coordinate system, where the x-axis is perpendicular to coplanar I, and the y-axis is on the axis of the reference axis;

[0053] S4.2. Align the axis of the third axis with the axis of the fourth axis with the fourth axis as the reference, calibrate the x-direction position of the third axis, and extract the deviation between the two axes as the error value. ; Then, align the axis of the third axis with the axis of the fourth axis, calibrate the angle of the third axis, and the computer outputs an angular error of 8 arcseconds. Within the allowable range (10 arcseconds), the angle calibration is completed. Next, calibrate the y-direction position of the third axis, align the axis of the third axis with the spatial intersection point O, and extract the deviation between the axis of the third axis and point O as the error value. ; Calculate the centering error between the third axis and the fourth axis. , and the centering error is less than the set threshold (10 microns), and the calibration of the third axis is completed;

[0054] Step Six: Calculate the final centering error. , in this embodiment, take , , the maximum value among them .

[0055] In this embodiment, 50 single-crystal silicon balls with a diameter of 2.5 mm are prepared. Before processing, the initial roundness error distribution is measured to be 0.9 - 1.5 μm, and the initial surface roughness Ra = 130 - 190 nm. They are divided into two groups and centered according to the ordinary naked-eye method and the method of the present invention respectively. A group is randomly selected from the processed balls. Table 1 shows some processing results of centering by the ordinary naked-eye method, and Table 2 shows some processing results of centering by the method of the present invention.

[0056] Comprehensively analyzing the experimental results, the following conclusions can be drawn. The surface roughness of both groups of balls has been greatly improved, but the roundness of the balls centered by the ordinary naked-eye method has not changed much, and the roundness error distribution is 0.9 - 2.0 μm. Even for some balls, the roundness has deteriorated. However, when centering by the method of the present invention, the roundness after processing has a relatively large improvement, and the roundness error distribution is 0.4 - 1.1 μm, which can achieve a higher circular accuracy.

[0057] Table 1:

[0058]

[0059] Table 2:

[0060]

[0061] The centering process of the existing four-axis grinding machine is relatively difficult. There is no publicly available centering method for a four-axis spherical grinding and polishing device. Technicians usually use visual observation, resulting in poor centering accuracy and the inability to quantify the error value. Inaccurate centering will directly lead to poor grinding accuracy of the sphere, especially the roundness error. The method of the present invention provides a new method and means for centering a four-axis spherical grinding and polishing device, which has the advantages of being easy to implement and having high centering accuracy, and has good practical benefits.

[0062] The above general description of the invention involved in the present application and the description of its specific implementation should not be understood as a limitation on the technical solution of the invention. Those skilled in the art can, based on the disclosure of the present application, without departing from the constituent elements of the invention involved, add, subtract or combine the disclosed technical features in the above general description or / and specific implementation (including embodiments) to form other technical solutions within the scope of protection of the present application.

Claims

1. A centring method for a four-axis ball polishing device, characterized in that: The steps include: Step 1, select any one grinding axis as the reference axis, denoted as axis IV, and the other three grinding axes as the calibrated axes, denoted as axis I, axis II and axis III; set the plane formed by the reference axis and the calibrated axis as coplanar, axis I, axis II and axis III correspond to coplanar I, coplanar II and coplanar III respectively; set the plane containing the reference axis and perpendicular to the coplanar as the vertical plane, coplanar I, coplanar II and coplanar III correspond to vertical plane I, vertical plane II and vertical plane III respectively; Step 2: Select any point on the reference axis as the centering position and record it as the spatial intersection point O; Step 3: Calibrate axis I: S3.

1. Determine the positions of the two cameras: adjust the position of the first camera until the axes of axis I and axis IV in the image are parallel, and the plane where the first camera is located is coplanar I; the second camera is set at an angle of 90° to the first camera, and the plane where the second camera is located is vertical plane I; set the coordinate system, in which the x-axis is perpendicular to the coplanar I, and the y-axis is located on the axis of the reference axis; S3.

2. Take the IV axis as the reference, align the axis of the I axis with the axis of the IV axis, calibrate the x-direction position of the I axis, and extract the deviation of the two axis lines as the error value x1; then, align the axis of the I axis with the axis of the IV axis, calibrate the angle of the I axis so that the angle error is within the allowable range, then calibrate the y-direction position of the I axis, align the axis of the I axis with the spatial intersection point O, and extract the deviation between the axis of the I axis and the O point as the error value y1; calculate the centering error between the I axis and the IV axis If the centering error is less than or equal to the threshold, the I-axis calibration is completed. If the centering error is greater than the threshold, re-calibrate the x-direction and y-direction until the centering error is less than or equal to the threshold. Step 4: Calibrate axis II in the same way as calibrating axis I in step 3; Step 5. Calibrate axis III in the same way as calibrating axis I in step 3.

2. The centering method of the four-axis ball polishing device according to claim 1, characterized in that: In step 1, the grinding axis in the plumb direction is selected as the reference axis.

3. The centering method of the four-axis ball polishing device according to claim 1, characterized in that: In step 2, the intersection point of the reference axis and the end surface of the grinding tool is selected as the spatial intersection point O.

4. The centering method of the four-axis ball polishing device according to any one of claims 1 to 3, characterized in that: The threshold of the centering error is 10 microns.

5. The centering method of the four-axis ball polishing device according to any one of claims 1 to 3, characterized in that: The permissible range of the angle error is ±10 arc seconds.

6. The centering method of the four-axis ball polishing device according to any one of claims 1 to 3, characterized in that: The hardware for implementing the centering method includes a first camera, a second camera, and a computer connected to the first camera and the second camera signals; when working, the first camera and the second camera transmit the captured images to the computer, and the operator adjusts the calibrated axis according to the images output on the computer to achieve the calibration purpose.

7. The centering method of the four-axis ball polishing device according to claim 6, characterized in that: During centering, the computer analyzes the image and calculates the centering error and angle error.

8. The centering method of the four-axis ball polishing device according to claim 6, characterized in that: The hardware for implementing the centering method also includes a light source; the first camera and the second camera are respectively equipped with a set of light sources.

9. The centering method of the four-axis ball polishing device according to claim 6, characterized in that: A magnifying lens is installed on both the first camera and the second camera.

10. The centering method of the four-axis ball polishing device according to claim 6, characterized in that: When centering, start the grinding shaft drive device to make the grinding shaft rotate; the computer performs image fusion on the video recorded by the camera to obtain the contour of the grinding shaft during the rotation process.

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