Rapid compensation of material removal rate instability due to polishing pad wear

Abstract

The application discloses a kind of quick compensation methods of unstable material removal rate caused by polishing pad wear, comprising: based on Preston equation, the velocity distribution and contact stress distribution of polishing contact area are analyzed, and polishing material removal function is obtained;Using observation device, image data matching with polishing area contact area is collected regularly and quantitatively;Using Unet convolutional neural network segmentation algorithm, the above-mentioned image data is labeled, training and test data set is made, training, test data set is calculated, and contact area is calculated;Based on the mathematical relationship between the amount of pressing, polishing time and contact area, the compensation function of polishing pad wear is obtained;The compensation function is substituted into the polishing material removal function.The application provides a kind of quick compensation method of unstable material removal rate caused by polishing pad wear, which can shorten the service life and replacement frequency of airbag polishing pad to a certain extent, can shorten product processing time to a certain extent, improve efficiency, provide reference for airbag polishing technology development and application promotion.

Description

Technical Field

[0001] This invention relates to the field of material polishing. More specifically, this invention relates to a rapid compensation method for unstable material removal rates caused by polishing pad wear in small-to-medium aperture optical elements. Background Technology

[0002] Airbag polishing technology was proposed around 2000 by Zeeko Ltd. in the UK and DD Walker et al. of the Optical Laboratory at University College London. The controllable range of material removal in airbag polishing is a volumetric removal rate of 0.025–120 mm. 3 / min. The airbag polishing head is a flexible spherical tool that not only ensures a high degree of fit between the polishing head and the surface of the workpiece, but also allows for control of polishing efficiency and processing quality by adjusting the internal pressure of the airbag and the downward pressure of the polishing head on the workpiece. It is a highly promising method for polishing spherical and aspherical surfaces.

[0003] Airbag polishing technology uses a spherical rubber airbag with a certain inflation pressure as the polishing tool, with a polishing pad attached to its surface. As polishing progresses, the surface of the polishing pad gradually wears down, reducing surface roughness and deteriorating the spherical shape. This affects the polishing efficiency and stability of airbag polishing, ultimately impacting the quality and processing efficiency of the workpiece. The wear of the polishing pad directly reduces the downward pressure of the airbag during polishing, thus decreasing the contact area of ​​the polishing zone and the polishing force, consequently affecting the material removal rate.

[0004] To date, there is no available device for observing the contact area of ​​the airbag polishing contact zone. This hinders the statistical analysis of polishing pad wear patterns and the study of their impact on the stability of material removal rates. Consequently, there is no feasible method to provide real-time parameters during the polishing process to control the pressure of the polishing head on the workpiece, thereby improving polishing efficiency and processing quality. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] To achieve these objectives and other advantages of the present invention, a rapid compensation method is provided for unstable material removal rates caused by polishing pad wear, comprising:

[0007] Step 1: Establish the maximum stress calculation expression for the polished contact area using Hertzian contact theory and elasticity theory. Based on this, establish the stress distribution calculation expression for the contact area according to the stress distribution rules of the elliptical contact area.

[0008] Step 2: Establish a velocity distribution model of the polishing contact area based on the polishing contact geometry model;

[0009] Step 3: Based on the contact area stress distribution model from Step 1, the contact area velocity distribution model from Step 2, and the Preston equation, obtain the polishing material removal function.

[0010] Step four: Use an observation device to collect image data that matches the contact area of ​​the polishing zone at regular intervals and in quantitative quantities;

[0011] Step 5: The Unet convolutional neural network segmentation algorithm is used to sequentially label, create training and test datasets for the image data in Step 4, calculate the contact area of ​​the polishing contact area, and obtain the variation law of the contact area S of the polishing contact area with the polishing process time t.

[0012] Step 6: Based on the mathematical relationship between the pressure and the contact area, and the polishing process time and the contact area, obtain the mathematical expression for the wear of the polishing pad, i.e., the polishing pad wear compensation function;

[0013] Step 7: Substitute the compensation function from Step 6 into the polishing material removal function from Step 3 to compensate for the downward pressure in real time during the polishing process.

[0014] Preferably, in step one, the formula for the contact stress distribution in the polishing contact area is obtained based on classical Hertzian contact theory and elasticity theory, and its conversion process is as follows:

[0015] S10,

[0016]

[0017] in,

[0018]

[0019] S11, according to the theory of elastic contact, the stress distribution in the elliptical contact area should satisfy:

[0020]

[0021] S12, therefore, the formula for the contact stress distribution in the polishing contact area can be obtained:

[0022]

[0023] Where P0 is the contact stress at the center of the polishing contact area, E is the Young's modulus of the airbag polishing head, v is the Poisson's ratio of the airbag polishing head, d is the downward pressure of the polishing head, a is the radius of the major axis of the polishing elliptical contact area, b is the radius of the minor axis of the polishing elliptical contact area, x is the abscissa of any point A in the contact area, y is the ordinate of any point A in the contact area, and F... n For the center load of the contact area, R b Let be the radius of the airbag polishing head, and P be the contact stress distribution in the polishing contact area.

[0024] Preferably, in steps two and three, the method for obtaining the velocity distribution in the polishing contact area is as follows:

[0025] S20, Based on the contact geometry model of airbag polishing, in the airbag polishing contact area, let A(x,y) be any point within the contact area, then the velocity V of point A... A for:

[0026]

[0027] S21, based on geometric relationships, we know that:

[0028]

[0029] |BP|=|BD|cosθ=(|BO1|+|O1D|)cosθ;

[0030] Where, |O1D|=tanθ|OO1|=tanθ(Rd);

[0031] but:

[0032] |BP|=|BD|cosθ=(|BO1|+|O1D|)cosθ=(|y|+tanθ(Rd))cosθ;

[0033]

[0034] Therefore, the formula for the velocity at point A can be expressed as:

[0035]

[0036] Where n is the polishing spindle speed;

[0037] S22, based on the Preston equation, the formula for the amount of polishing material removed (MRR) is: MRR=K*P*V*Δt

[0038] Where K is the Preston coefficient, P is the contact stress distribution in the polishing contact area, V is the velocity distribution in the polishing contact area, and Δt is the dwell time of the polishing head on the workpiece surface.

[0039] S23, Substitute the velocity formula obtained in S21, the stress distribution formula in the polishing contact area obtained in S11, and Δt into the polishing material removal function in S22:

[0040]

[0041] Where ω is the polishing spindle speed, B is the intersection of the perpendicular line drawn from any point A in the contact area with the x-axis, O1 is the airbag center, D is the intersection of the airbag spindle and the x-axis, P is the intersection of the perpendicular line drawn from point A with the airbag spindle, O2 is the contact area center, and θ is the angle between the polishing spindle and the workpiece normal.

[0042] In step six, the compensation function for the wear of the polishing pad is obtained as follows:

[0043] S60, contact area S:

[0044] S=πab=πf(d)g(d)

[0045] Wherein, f(d) and g(d) can be obtained from the relationship between the long and short semi-axis of the contact area and the downward pressure, respectively;

[0046] a = f(d) = 1.63095 + 5.23757d

[0047] b = g(d) = 1.63095 + 5.23757d

[0048] S61, the wear amount of the polishing pad is:

[0049]

[0050] Combining the relationship between the contact area and the polishing pad wear time described in step five with the above expression, the compensation function for the polishing pad wear amount can be expressed as:

[0051] d=d(t)=d0+(0.981+0.0026t)t×10 -3 ;

[0052] In step six, substituting the compensation function d into the polishing material removal function from step three, we get:

[0053]

[0054] Where d0 is the initial pressure of the airbag polishing head, and t is the polishing process duration.

[0055] Preferably, the observation device is configured to include:

[0056] The mounting platform used to support the workpiece to be measured is slidably connected to the base through a matching X-axis and Y-axis displacement mechanism.

[0057] The polishing mechanism, which is mounted on the upper part of the mounting platform, is slidably connected to the gantry frame through a matching Z-axis displacement mechanism.

[0058] A camera assembly mounted on a base and configured in the opposite direction to the polished area;

[0059] A polishing fluid recovery mechanism is installed along the outer edge of the workpiece or mounting platform;

[0060] The gantry frame is mounted on the base, and the polishing mechanism is connected to the Z-axis displacement mechanism through a matching clamping assembly.

[0061] The mounting platform has a corresponding through groove at the camera component insertion position, and the mounting platform has a light-transmitting hole and / or light-transmitting component at the position that mates with the polishing area.

[0062] Preferably, the X-axis and Y-axis displacement mechanisms are configured to include:

[0063] A Y-axis connecting plate that mates with a Y-axis slide rail on the base, wherein an X-axis slide rail is provided on the Y-axis connecting plate;

[0064] X-axis connecting plate that mates with the X-axis slide rail;

[0065] Telescopic power mechanism I and telescopic power mechanism II are mounted on the base and respectively cooperate with the Y-axis connecting plate and the X-axis connecting plate;

[0066] The Y-axis connecting plate and the X-axis connecting plate are respectively provided with a matching Y-direction slide groove and an X-direction slide groove I.

[0067] Preferably, the Z-axis displacement mechanism is configured to include:

[0068] Z-guide plate that mates with the clamping assembly;

[0069] Z-guide rails are installed on the gantry frame;

[0070] The X-axis connecting plate is provided with a Z-axis sliding groove that cooperates with the Z-axis guide rail, and the gantry is provided with a telescopic power mechanism Ⅲ that cooperates with the Z-axis guide plate.

[0071] Preferably, the clamping assembly is configured to include:

[0072] The fixture is positioned opposite to the polishing head spindle and has a clamping part that cooperates with the polishing head spindle.

[0073] A rotary power mechanism IV is mounted on the Z-guide plate and cooperates with the fixture mounting end;

[0074] A sensing mechanism is provided between the output end of the power mechanism IV and the fixture mounting end.

[0075] Preferably, the camera assembly is configured to include:

[0076] Camera structure;

[0077] A mounting component used to fix a camera mechanism, which has an observation window on the side of the camera mechanism that mates with the camera.

[0078] A camera bracket used to support the spatial position of a camera mechanism;

[0079] The mounting component is connected to the camera bracket via a positioning mechanism;

[0080] The camera bracket is provided with an X-axis slide groove II for the positioning mechanism to adjust its position in the X direction. The positioning mechanism is provided with a slider that cooperates with the X-axis slide groove II. A telescopic power mechanism V that cooperates with the positioning mechanism is provided on one side of the camera bracket.

[0081] The present invention has at least the following beneficial effects: First, the present invention provides a rapid compensation method for the unstable material removal rate caused by the wear of the polishing pad during the airbag polishing process. The method substitutes the compensation function into the polishing material removal function to obtain the pressure compensation amount at different times during the polishing process. Therefore, it can shorten the product processing time and improve efficiency to a certain extent. At the same time, it can shorten the service life and replacement frequency of the airbag polishing pad to a certain extent.

[0082] Secondly, the image processing in the compensation method of the present invention uses a deep convolutional neural network to achieve image segmentation, and the contact area statistics have high reliability.

[0083] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0084] Figure 1 This is a schematic diagram of the polishing contact geometry model of the present invention;

[0085] Figure 2 This is a schematic diagram illustrating the mathematical relationship between the semi-major axis a of the elliptical contact area and the downward pressure d, obtained by measuring and fitting the polishing spot size under different pressures according to the present invention.

[0086] Figure 3 This is a schematic diagram illustrating the mathematical relationship between the minor semi-axis b of the elliptical contact area and the downward pressure d, obtained by measuring and fitting the polishing spot size under different pressures according to the present invention.

[0087] Figure 4 This is a schematic diagram showing the change of the contact area S of the polishing contact zone with the wear time t of the polishing pad in this invention.

[0088] Figure 5 A schematic diagram showing the effect of polishing pad wear compensation on contact area in a comparative experiment of pressure compensation and no compensation in this invention.

[0089] Figure 6 This invention provides a comparative experiment on the impact of polishing pad wear compensation on material removal volume, comparing the effects of pressure compensation and non-compensation on the pressure applied in this invention.

[0090] Figure 7 This is a schematic diagram of the spatial layout structure of the observation device for the contact area of ​​the airbag polishing contact zone of the present invention.

[0091] Figure 8 for Figure 7 A schematic diagram of a cross-section on one side;

[0092] Figure 9 This is a schematic diagram of the structure of the airbag polishing head of the present invention;

[0093] Figure 10 This is a structural schematic diagram of the camera mechanism mounting component of the present invention. Detailed Implementation

[0094] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0095] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not imply the presence or addition of one or more other elements or combinations thereof.

[0096] It should be noted that in the description of this invention, the orientation or positional relationship indicated by the terms is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0097] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0098] This invention provides a device for observing the contact area of ​​the airbag polishing contact zone. This device can be used for real-time observation of the contact area of ​​small tool polishing (such as wheel polishing, jet polishing, stress disk polishing, magnetorheological polishing, and asphalt disk polishing) similar to airbag polishing. It helps to study the impact of polishing pad wear on material removal stability in small tool polishing techniques, or to conduct research on the movement trajectory of abrasive particles in polishing fluid. Through this device, the change law of polishing pad wear over time can be quickly obtained, thereby obtaining the real-time compensation amount of the airbag polishing pressure. This not only ensures the stability of material removal, but also further shortens the replacement cycle of polishing pads and extends their service life.

[0099] The observation device of this invention is structurally based on a gantry-type four-axis polishing machine. 1-Base; 2-Y-axis guide rail; 3-X-axis guide rail; 4-Z-axis guide rail; 5-Gantry; 6-Pressure sensor mounting plate; 7-Clamp; 8-Pressure sensor; 9-Light-transmitting hole on the mounting platform; 10-Rotating spindle; 11-Mounting platform; 12-Airbag polishing head; 13-Camera bracket; 14-Y-axis connecting plate; 15-X-axis connecting plate; 16-Camera mechanism; 17-Y-axis slide rail; 18-Z-axis guide column; 19-Camera support plate; 20-X-axis guide column; 21-Connecting seat; 22-Polishing fluid recovery mechanism; 23-Z-axis guide plate; 24-Spindle clamp positioning hole; 25-DD motor positioning hole; X-axis slide rail I-26; X-axis slide rail II-27; Observation window-28; X-axis slider-29; The connection relationships of each component are as follows:

[0100] The mounting platform 11, used to support the workpiece to be tested, is slidably connected to the base through a matching X-axis and Y-axis displacement mechanism. In this structure, the mounting platform can be composed of an L-shaped bracket and a matching mounting platform, or it can be an integrated П-shaped structure. This structural mode allows the mounting platform to have a through slot into which the camera component can be inserted, and the quality of the equipment is controllable. In actual operation, the X-axis and Y-axis displacement mechanism is mounted on the base, the L-shaped bracket is mounted on the workpiece X-axis and Y-axis moving platform formed by the X-axis and Y-axis displacement mechanism, and the workpiece mounting platform is mounted on the L-shaped bracket. The polishing fluid recovery tank is mounted on the mounting platform, and the workpiece is mounted on the workpiece mounting platform. In this solution, the mounting platform and the workpiece to be polished can be distinguished by different materials and different connection methods, such as any one of bonding, screw connection, or snap-fit.

[0101] The mounting platform is equipped with light-transmitting holes and / or light-transmitting components at positions that align with the polishing area, so that the camera mechanism can observe the working status of the polishing head. Of course, the light-transmitting components and / or light-transmitting holes 9 can be installed on the side wall of the mounting platform so that the operator can observe in real time from the side. At the same time, a corresponding supplementary lighting mechanism can be installed on the top of the mounting platform or on the gantry as needed via connecting parts.

[0102] The X-axis and Y-axis displacement mechanisms are configured to include:

[0103] A Y-axis connecting plate 14 that cooperates with the Y-axis slide rail 2 on the base 1, wherein an X-axis slide rail 3 is provided on the Y-axis connecting plate;

[0104] X-axis connecting plate 15 that mates with the X-axis slide rail;

[0105] Telescopic power mechanism I and telescopic power mechanism II (not shown) are mounted on the base and respectively cooperate with the Y-axis connecting plate and the X-axis connecting plate. The telescopic power mechanism can select the cooperation method between the motor, lead screw and sleeve as needed.

[0106] The Y-axis connecting plate and the X-axis connecting plate are respectively provided with matching Y-direction sliding groove 17 and X-direction sliding groove Ⅰ26. In this structure, the telescopic power mechanism provides reciprocating force, so that the workpiece on the mounting platform can be adjusted in real time in the X and Y directions as needed to complete the polishing operation of the workpiece surface. The mounting platform and the X-axis connecting plate can be connected by matching adapters or directly connected to the X-axis connecting plate.

[0107] The polishing mechanism is mounted on the mounting platform and is slidably connected to the gantry through a matching Z-axis displacement mechanism. The polishing mechanism includes a polishing head 12 and a rotating spindle 10 that matches it. Of course, the rotating spindle needs to be connected to a corresponding motor for transmission. Since its structure is existing technology, its connection relationship will not be described.

[0108] A camera assembly mounted on a base and configured to work in reverse with the polishing area, wherein the camera is positioned upwards and directly opposite the polishing area of ​​the polishing head, the camera assembly being configured to include:

[0109] Camera device (not shown), an industrial camera is used in this solution;

[0110] The mounting component 16, used to fix the camera mechanism, has an observation window 28 on the side of the camera mechanism that mates with the camera, which is used to ensure that the working field of view of the camera mechanism is not restricted.

[0111] Camera bracket 13 for supporting the spatial position of the camera mechanism;

[0112] The mounting component and the camera bracket are connected by a positioning mechanism. The camera bracket is provided with an X-axis slide groove II 27 for the positioning mechanism to adjust its position in the X-axis direction. The positioning mechanism is configured to include a Z-axis guide post 18, an X-axis slider 29 that mates with the X-axis slide groove II, an L-shaped camera support plate 19 that mates with the mounting component, and an X-axis guide post 20. The Z-axis guide post and the X-axis guide post are connected by a matching connecting seat 21. In application, both the Z-axis guide post and the X-axis guide post are provided with matching threads. The height in the Z-axis direction and the extension length in the Y-axis direction are adjusted by the threads. The engagement of the X-axis slider with the X-axis slide groove II allows the position of the camera bracket in the X-axis direction to be adjusted as needed.

[0113] A telescopic power mechanism V (not shown) is provided on one side of the camera bracket to cooperate with the positioning mechanism. It is used to provide reciprocating force so that the camera mechanism can be adjusted in the X direction, thereby cooperating with image acquisition of polished areas at different positions.

[0114] The polishing fluid recovery mechanism 22 (also called the recovery tank) is set on the outer edge of the workpiece or the mounting platform. It is used to contain the polishing fluid during the polishing process. At the same time, it can also be provided with a matching recovery hole so that when the polishing fluid reaches the position of the recovery hole, it will be recycled back to ensure that the height of the polishing fluid is controllable. Meanwhile, the bottom surface of the polishing fluid recovery mechanism should be spatially lower than the polishing surface of the workpiece by a predetermined distance.

[0115] The gantry frame 5 is mounted on the base, and the polishing mechanism is connected to the Z-axis displacement mechanism via a matching clamping assembly. The Z-axis displacement mechanism is configured to include:

[0116] Z-guide plate 23 that mates with the clamping assembly;

[0117] Z-guide rail 4 is installed on the gantry frame;

[0118] The X-axis connecting plate is provided with a Z-axis sliding groove (not shown) that cooperates with the Z-axis guide rail, and the gantry is provided with a telescopic power mechanism Ⅲ (not shown) that cooperates with the Z-axis guide plate.

[0119] The clamping assembly is configured to include:

[0120] The fixture 7 is arranged opposite to the polishing head spindle and is provided with a clamping part (not shown) that cooperates with the polishing head spindle, which is used to clamp and fix the rotating spindle of the polishing head in space.

[0121] A rotary power mechanism IV (not shown) is mounted on the Z-guide plate and mates with the fixture mounting end. It is configured to use a DD motor, i.e. a torque motor.

[0122] The power mechanism IV has a corresponding sensing mechanism 8 between its output end and the fixture mounting end. The fixture and DD motor are configured to be connected or fixed using corresponding spindle fixture positioning holes 24 and DD motor positioning holes 25. The Z-axis DD motor is mounted on the Z-guide plate, and the Z-axis pressure sensor is mounted between the Z-axis DD motor and the fixture via a pressure sensor fixing plate 6. The rotating spindle of the polishing head is mounted in the clamping part of the fixture and locked by a locking screw. The airbag polishing head is mounted on the rotating spindle of the polishing head.

[0123] In practical applications, the X-axis and Y-axis displacement mechanisms serve to adjust the polishing position of the workpiece in the X-axis and Y-axis directions in real time during polishing operations.

[0124] The function of the Z-axis displacement mechanism is to adjust the distance between the polishing head and the workpiece surface so that the polishing head contacts the workpiece surface, and at the same time adjust the downward pressure of the polishing head as needed.

[0125] The motor that works with the fixture is used to adjust the rotation angle of the polishing head.

[0126] The function of the power mechanism that works in conjunction with the camera mechanism is to adjust the position of the camera mechanism on the Y-axis to match the image acquisition needs of the polishing area at different positions. These five adjustments constitute the gantry-based four-axis polishing machine tool as described in this invention.

[0127] In use, the camera bracket is installed on the polishing machine base, and the high-definition industrial camera is installed on the camera bracket and located directly below the polishing head (the relative positions of the polishing head and the high-definition industrial camera are fixed). The high-definition industrial camera is connected to a PC, and the supplementary light source is installed above the high-definition industrial camera. The polishing operation is realized by moving the polishing head down to contact the workpiece. The camera acquisition software on the PC can realize real-time observation and image saving of the polishing contact area / polishing pad wear. The saved image can be used to obtain a statistical model of the polishing contact area through an image segmentation algorithm. Based on this model, a mathematical model of the polishing pad wear can be obtained. Based on this model, the pressure parameter of the polishing program can be compensated in real time to realize the compensation of material removal stability.

[0128] The procedure for a rapid compensation method to address unstable material removal rates caused by polishing pad wear is as follows:

[0129] 1. Install the workpiece mounting platform “L” bracket, workpiece mounting platform, polishing fluid recovery tank, high-definition industrial camera bracket, high-definition industrial camera, and light source in sequence. Connect the light source power cord to an external power supply and the high-definition industrial camera power supply to the PC.

[0130] 2. Open the airbag polishing contact area image acquisition software on the PC, set the exposure and gain parameters of the camera mechanism, create an image storage folder, and enter the contact area / polishing pad wear recording preparation state.

[0131] 3. Turn on the power of the polishing machine, reset the polishing machine to zero, manually install the workpiece on the mounting platform, move it to the high-definition industrial camera so that it corresponds to the polishing area, adjust the Z-axis displacement of the polishing head and make it contact the workpiece to be polished.

[0132] 4. Calculation formula based on the amount of polishing material removed from the airbag:

[0133] MRR=K×P×V×Δt

[0134] Wherein, K is a parameter related to the polishing environment, which can be obtained from reference materials; P is the contact stress distribution in the polishing contact area; P0 is the contact stress at the center of the polishing contact area; V is the velocity distribution in the polishing contact area; and Δt refers to the dwell time of the polishing head on the workpiece surface.

[0135] A review of the literature reveals that:

[0136]

[0137] therefore,

[0138]

[0139] Where E is the Young's modulus of the polishing head, v is the Poisson's ratio of the polishing head, d is the downward pressure of the airbag polishing head, a is the major axis radius of the elliptical contact area of ​​the airbag polishing head, b is the minor axis radius of the elliptical contact area of ​​the airbag polishing head, a and b can be obtained according to the polishing spot size under different downward pressure, x is the abscissa of any point A in the contact area, y is the ordinate of any point A in the contact area, and F... n Where R is the center load of the contact area, and R is the radius of the airbag polishing head; in this invention, by measuring and fitting the polishing spot size under pressure of 0.03 / 0.06 / 0.09 / 0.12 / 0.15 / 0.18 / 0.21mm, the mathematical relationship between the major and minor semi-axes of the elliptical contact area and the pressure d can be obtained as follows: Figures 2-3 As shown;

[0140] Airbag polishing contact geometry model as follows Figure 1 As shown. In the airbag polishing contact area, let A(x,y) be any point within the contact area:

[0141] The velocity of point A is:

[0142]

[0143] From geometric relationships, we know that:

[0144]

[0145] |BP|=|BD|cosθ=(|BO1|+|O1D|)cosθ

[0146] in,

[0147] |BO1|=|y|

[0148] |O1D|=tanθ|OO1|=tanθ(Rd)

[0149] so:

[0150] |BP|=|BD|cosθ=(|BO1|+|O1D|)cosθ=(|y|+tanθ(Rd))cosθ

[0151] Therefore:

[0152]

[0153] so:

[0154]

[0155] Therefore, the airbag polishing material removal function is:

[0156]

[0157] Where R is the radius of the airbag polishing head, n is the rotational speed of the airbag polishing head, ω is the rotational speed of the polishing spindle, B is the intersection of the perpendicular line drawn from any point A in the contact area with the x-axis, O1 is the center of the airbag, D is the intersection of the airbag spindle with the x-axis, P is the intersection of the perpendicular line drawn from point A with the airbag spindle, O2 is the center of the contact area, and θ is the angle between the polishing spindle and the workpiece normal (also known as the airbag polishing precession angle).

[0158] 5. The airbag polishing process typically takes tens of hours. In this invention, the airbag polishing process is set to 60 hours. Polishing operations begin, and every 12 hours (0 / 12 / 24 / 36 / 48 / 60 hours), the contact area of ​​the polishing zone (the downward pressure of the airbag polishing head is constant, i.e., d = 0.2 mm) is recorded using a camera mechanism. A total of 6 sets of image data are generated, with 1000 images in each set.

[0159] In a training dataset of 1200 images (200 images randomly selected from each of the six image datasets), the remaining 4800 images were used as the test dataset. The Unet convolutional neural network segmentation algorithm was used for training. After training, the test dataset was tested, and the area of ​​the target region in the binary image was calculated as the contact area. Data at each time point was statistically analyzed, and a polynomial fitting algorithm was used to obtain the curve showing the change in the contact area S of the airbag polishing contact area with the wear time t of the polishing pad.Figure 4 As shown;

[0160] 6. The mathematical relationship between the downward pressure and the contact area, such as... Figure 5 As shown;

[0161] 7. Based on the mathematical models S=f(t) and S=f(d), obtain the mathematical model of polishing pad wear as a function of polishing pad usage time—the polishing pad wear compensation function:

[0162] The contact area S = πab = πf(d)g(d);

[0163] Wherein, f(d0) and g(d) can be obtained from the relationship between the long and short semi-axis of the contact area and the downward pressure, respectively;

[0164] f(d) = 1.63095 + 5.23757d

[0165] g(d) = 1.63095 + 5.23757d

[0166] The wear amount of the polishing pad is:

[0167]

[0168] Combining the relationship between the contact area and the polishing pad wear time described in step five with the above expression, the compensation function for the polishing pad wear amount can be expressed as: d = d(t) = d0 + (0.981 + 0.0026t)t × 10 -3 t is the polishing process duration, t = 1h, 2h, 3h...;

[0169] 8. Substituting the above compensation function into the airbag polishing material removal function, we get:

[0170]

[0171] Where d0 represents the initial pressure of the airbag polishing head. During the polishing process, the pressure d0 can be compensated in real time according to the above expression.

[0172] 9. Based on the above expression, improve the airbag polishing program code and complete the polishing comparison experiment. That is, verify the above expression through a comparison experiment with and without pressure compensation. The experimental results are as follows: Figures 6-7 As shown:

[0173] As can be seen from the contact area statistics and the three-dimensional morphology of material removal per unit time, compared with no pressure compensation, the contact area of ​​the polishing contact area and the amount of material removed per unit time are significantly more stable after pressure compensation.

[0174] This demonstrates that the material removal stability compensation method provided by this invention significantly improves the material removal instability caused by polishing pad wear in airbag polishing. Furthermore, the instability in airbag polishing material removal is mainly due to the deterioration of the airbag polishing pad's surface shape and the decrease in surface roughness. Historically, this has primarily relied on polishing pad reshaping for improvement. Compared to the thickness loss (tens to hundreds of micrometers, depending on the process) caused by a single reshaping operation (the thickness of a conventional polishing pad is 1.5mm-2mm), the method provided by this invention can reduce the number of polishing pad reshaping operations to a certain extent, and also significantly improves the service life of the polishing pad.

[0175] This invention provides a real-time observation and recording device for the contact area / polishing pad wear of the airbag polishing contact zone in small and medium-diameter optical components. The device records the contact area and polishing pad wear images as the polishing pad changes over time using a high-definition industrial camera in the reverse observation device. The image segmentation algorithm of the image convolutional neural network can obtain a model of the change law of the contact area and polishing pad wear over time. Then, the wear of the polishing pad is compensated by the processing program, thereby ensuring the stability of material removal and the service life of the polishing pad to a certain extent.

[0176] The above solution is merely an illustration of a preferred example and is not limited thereto. When implementing this invention, appropriate substitutions and / or modifications can be made according to the user's needs.

[0177] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0178] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method for quickly compensating for unstable material removal rates caused by polishing pad wear, comprising: Comprise: Step one, the maximum stress calculation expression of polishing contact area is established by Hertz contact theory, and the stress distribution calculation expression of contact area is established based on elastic contact theory and the stress distribution rule of elliptical contact area; Step two, the velocity distribution model of polishing contact area is established based on the polishing contact geometry model; Step three, the polishing material removal function is obtained based on the stress distribution model of contact area in step one, the velocity distribution model of contact area in step two and Preston equation; Step four, the image data matched with the contact area of polishing area is collected by observation device at regular time and quantity; Step five, the image data in step four is sequentially labeled, training and testing dataset is made by using Unet convolutional neural network segmentation algorithm, training and testing dataset, contact area calculation, so as to obtain the change rule of contact area S of polishing contact area with polishing process time t; Step six, the mathematical expression of polishing pad wear amount, that is, polishing pad wear compensation function, is obtained based on the mathematical relationship between down pressure, contact area and polishing process time and contact area; Step seven, the compensation function in step six is substituted into the polishing material removal function in step three, so as to establish the polishing material removal compensation model, so as to compensate the down pressure in real time during polishing process, and ensure the stability of polishing material removal of air bag; In steps two and three, the velocity distribution of polishing contact area is obtained in the following way: S20, based on the air bag polishing contact geometry model, in the air bag polishing contact area, let A(x, y) be any point in the contact area, then the velocity V of the A point is: A V = V0+ V1+ V2 S21, based on geometric relationship, it can be known that: |BP|=|BD|cosθ=(|BO1|+|O1D|)cosθ; Wherein, |O1D|=tanθ|OO1|=tanθ(R-d); Then: |BP|=|BD|cosθ=(|BO1|+|O1D|)cosθ=(|y|+tanθ(R-d))cosθ; Therefore, the velocity formula of point A is: Wherein, n is the rotation speed of polishing spindle; S22, based on Preston equation, the polishing material removal amount MRR formula is: MRR=K*P*V*Δt Wherein, K is Preston coefficient, P is contact stress distribution of polishing contact area, V is velocity distribution of polishing contact area, and Δt is the residence time of polishing head on the workpiece surface; S23, the velocity formula obtained in S21, the polishing contact area stress distribution formula obtained in S11 and Δt are substituted into the polishing material removal function in S22: Wherein, ω is the rotation speed of polishing spindle, B is the intersection of the vertical line of any point A of contact area and x axis, O1 is the center of air bag, D is the intersection of air bag spindle and x axis, P is the intersection of the vertical line of point A and air bag spindle, O2 is the center of contact area, θ is the angle between polishing spindle and normal of workpiece, and B is the intersection of the vertical line of any point A of contact area and x axis; In step six, the compensation function of polishing pad wear amount is obtained in the following way: S60, the contact area S of contact area is: S=πab=πf(d)g(d) Wherein, f(d) and g(d) can be obtained from the relationship between the long and short semi-axes of contact area and down pressure; a=f(d)=1.63095+5.23757d b=g(d)=1.63095+5.23757d S61, the polishing pad wear amount is: In combination with the relationship between the contact area and the polishing pad wear time described in step five and the above expression, the compensation function of the polishing pad wear amount can be expressed as: d = d(t) = d0 + (0.981 + 0.0026t) t x 10 -3 ; In step six, the compensation function d is substituted into the polishing material removal function of step three, and then there is: Where d0 is the air bag polishing head down pressure at the initial time, and t is the polishing process time.

2. The method of claim 1, wherein the polishing pad wear-induced material removal rate instability compensation is performed by: determining a current material removal rate instability value; determining a current pad wear value; and determining a current compensation value based on the current material removal rate instability value and the current pad wear value. In step one, the polishing contact area contact stress distribution formula is obtained based on the classical Hertz contact theory and the elastic theory, and the conversion process is as follows: S10， Where S11, according to the elastic contact theory, the stress distribution of the elliptical contact area should satisfy: S12, so the polishing contact area contact stress distribution formula can be obtained: wherein P0 is the contact stress at the center of the polishing contact area, E is the Young's modulus of the airbag polishing head, v is the Poisson's ratio of the airbag polishing head, d is the down force of the polishing head, a is the long axis radius of the polishing elliptical contact area, b is the short axis radius of the polishing elliptical contact area, x is the horizontal coordinate of an arbitrary point A in the contact area, y is the vertical coordinate of the arbitrary point A in the contact area, F n is the load at the center of the contact area, R b is the radius of the airbag polishing head, and P is the contact stress distribution of the polishing contact area.

3. The method of claim 1, wherein the polishing pad wear-induced material removal rate instability compensation is performed by: determining a current material removal rate instability value; determining a current pad wear value; and determining a current compensation value based on the current material removal rate instability value and the current pad wear value. The observation device is configured to include: An installation platform for supporting the workpiece to be tested is slidably connected to the base through a matched X-axis and Y-axis displacement mechanism; A polishing mechanism provided on the installation platform is slidably connected to the gantry through a matched Z-axis displacement mechanism; A camera assembly provided on the base and reversely matched with the polishing area; A polishing liquid recovery mechanism provided on the outer edge of the workpiece or the installation platform; Wherein, the gantry is provided on the base, and the polishing mechanism is connected with the Z-axis displacement mechanism through a matched clamping assembly; The installation platform is provided with a matched through slot at the position where the camera assembly extends in, and is provided with a light transmission hole and / or a light transmission part at the position matched with the polishing area.

4. The method of claim 3, wherein the polishing pad wear-induced material removal rate instability compensation is performed by: determining a current material removal rate instability value; determining a current pad wear value; and determining a current compensation value based on the current material removal rate instability value and the current pad wear value. The X-axis and Y-axis displacement mechanism is configured to include: A Y-axis adapter plate matched with the Y-direction sliding rail on the base, the Y-axis adapter plate is provided with an X-direction sliding rail; An X-axis adapter plate matched with the X-direction sliding rail; A telescopic power mechanism I and a telescopic power mechanism II provided on the base and matched with the Y-axis adapter plate and the X-axis adapter plate respectively; Wherein, the Y-axis adapter plate and the X-axis adapter plate are respectively provided with a matched Y-direction sliding groove and an X-direction sliding groove I.

5. The method of claim 4, wherein the polishing pad wear-induced material removal rate instability compensation is performed by: determining a current material removal rate instability value; determining a current pad wear value; and determining a current compensation value based on the current material removal rate instability value and the current pad wear value. The Z-axis displacement mechanism is configured to include: A Z-direction guide plate matched with the clamping assembly; A Z-direction guide rail provided on the gantry; Wherein, the X-axis adapter plate is provided with a Z-direction sliding groove matched with the Z-direction guide rail, and the gantry is provided with a telescopic power mechanism III matched with the Z-direction guide plate.

6. The method of claim 5, wherein the polishing pad wear-induced material removal rate instability compensation is performed by: determining a current material removal rate instability value; determining a current pad wear value; and determining a current compensation value based on the current material removal rate instability value and the current pad wear value. The clamping assembly is configured to include: Oppositely arranged clamps provided with clamping parts matched with the polishing head main shaft; A rotary power mechanism IV provided on the Z-direction guide plate and matched with the clamp mounting end; Wherein, the output end of the power mechanism IV and the clamp mounting end are provided with a matched sensing mechanism.

7. The method of claim 6, wherein the polishing pad wear-induced material removal rate instability compensation is performed by: determining a current material removal rate instability value; determining a current pad wear value; and determining a current compensation value based on the current material removal rate instability value and the current pad wear value. The camera assembly is configured to include: A camera mechanism; An installation part for fixing the camera mechanism, which is provided with an observation window on the side matched with the camera head of the camera mechanism; A camera bracket for supporting the spatial position of the camera mechanism; Wherein, the installation part and the camera bracket are connected through a positioning mechanism; The camera bracket is provided with an X-direction sliding groove II for the positioning mechanism to adjust the position in the X-direction, the positioning mechanism is provided with a sliding block matched with the X-direction sliding groove II, and one side of the camera bracket is provided with a telescopic power mechanism V matched with the positioning mechanism.

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