Ultra-precision plane machining process

Abstract

The invention relates to the technical field of plane machining, and provides an ultra-precision plane machining process which comprises the following steps: S1, measuring the thickness distribution condition of a workpiece, and determining the removal amount of each point on the workpiece; s2, according to a measurement result, selecting a corresponding matching algorithm, calculating residence time distribution or walking speed distribution of each point on the workpiece on the grinding disc, and generating a motion instruction for controlling a motion mechanism to act; s3, the workpiece is installed on a movement mechanism, and the to-be-machined face of the workpiece is tightly attached to the disc face of a grinding disc on the grinding machine; s4, the grinding machine is started, meanwhile, a movement instruction is input into the movement mechanism, and the movement mechanism controls the workpiece to move on the grinding disc according to the movement instruction in the step S2; s5, the movement mechanism stops acting, the grinding machine is closed, the workpiece is taken down, and the thickness distribution condition of the workpiece is measured; and S6, according to a measurement result, selecting to finish machining or repeating the steps S2 to S5 until the thickness distribution condition of the workpiece meets an error requirement.

Description

Technical Field

[0001] The present invention relates to the technical field of planar processing, and particularly relates to an ultra-precision planar processing technology. Background Art

[0002] Ultra-precision machining of workpieces refers to a machining method that uses processes and corresponding equipment such as grinding, polishing, airbag precession, ion beam, plasma, and magnetorheological to perform global or local machining on workpieces, so that the surface shape of the workpieces reaches micron or nanometer-level accuracy.

[0003] Global machining is to fit the surface to be machined of the workpiece with a grinding disk or polishing disk, and use the high-speed rotation of the disk surface, combined with the action of pressure and abrasive, to remove materials from the entire workpiece, which has high machining efficiency.

[0004] Local machining, also called computer-controlled optical surface forming, is a process that uses machining technologies such as small grinding heads, magnetorheological, airbag precession, ion beam, and plasma to remove local materials from the surface of the workpiece. Compared with global machining, the machining area of this type of process is much smaller than that of the workpiece, and only a local area of the workpiece is machined at each moment. The longer the machining time (i.e., the dwell time) or the smaller the traveling speed, the more materials are removed. The machining tool moves on the workpiece at a specific path and speed under the control of a computer. By controlling the dwell time of the machining tool at different positions, the material removal amount of different areas on the surface of the workpiece during polishing is controlled, so as to correct the surface shape error and improve the surface shape accuracy. The surface shape error of local machining can often reach the nanometer level.

[0005] Global machining mainly relies on the surface shape accuracy of machining tools such as grinding disks and the uniformity of the relative movement trajectory between the workpiece and the grinding disk to control the surface shape of the workpiece. However, due to the influence of the surface shape accuracy of the grinding disk itself and the angle fluctuation during the machining process, the surface shape error of the workpiece after machining is often at the micron level and cannot achieve nanometer-level accuracy machining. And local machining has the problem of low efficiency due to the small size of the machining tool. The time required to remove the same volume of materials is often dozens or even hundreds of times that of global machining. Therefore, designing a planar processing technology with high machining accuracy and high machining efficiency is an urgent problem to be solved in this field. Summary of the Invention

[0006] Aiming at the defects in the prior art, the purpose of the present invention is to provide an ultra-precision planar processing technology, which has the advantages of high machining accuracy and high machining efficiency.

[0007] To achieve the above purpose, the present invention is realized through the following technical solutions. An ultra-precision planar processing technology includes the following steps:

[0008] S1. Measure the thickness distribution of the workpiece and determine the removal amount of each point on the workpiece.

[0009] S2. According to the measurement results, select the corresponding matching algorithm, calculate the dwell time distribution of each point on the workpiece on the grinding disc, and generate a motion command to control the action of the motion mechanism.

[0010] S3. Install the workpiece on the motion mechanism and make the surface to be machined of the workpiece closely fit with the surface of the grinding disc on the grinding machine.

[0011] S4. Start the grinding machine, and at the same time input the motion command into the motion mechanism. The motion mechanism controls the workpiece to move on the grinding disc according to the motion command in step S2.

[0012] S5. The motion mechanism stops acting, turn off the grinding machine, remove the workpiece and measure its thickness distribution.

[0013] S6. According to the measurement results, select to end the machining or repeat steps S2 to S5 until the thickness distribution of the workpiece meets the error requirements.

[0014] Further, transform the dwell time distribution algorithm into an optimization problem to minimize the error between the final removal amount and the target removal amount, that is:

[0015] min∫ W [∫ A t(x,y)r(ξ,η;x,y)dxdy - R obj (ξ,η)] 2 dξdη

[0016] s.t.t(x,y)≥0

[0017] Wherein, the integral region A is the residence range of the center of the workpiece on the grinding disc, the integral region W is the geometric shape of the workpiece itself, x and y are the global coordinates of each point of the center of the workpiece on the grinding disc, ξ and η are the local coordinates of each point on the workpiece, t(x,y) is the dwell time of the center of the workpiece at each point on the grinding disc, r(ξ,η;x,y) is the removal rate of each point (ξ,η) on the workpiece when the center of the workpiece is located at (x,y) on the grinding disc, and R obj (ξ,η) is the target removal amount of each point on the workpiece.

[0018] Further, r(ξ,η;x,y) is given by the following formula:

[0019]

[0020] Among them, k is the Preston coefficient, p is the pressure of the interaction between the workpiece and the polishing pad, ω is the rotation speed of the polishing pad, and R P is the radius of the polishing pad.

[0021] Furthermore, the algorithm in S2 is the deconvolution method or the convolution iteration method, and the calculated dwell time is converted into the moving speed of the workpiece on the polishing pad.

[0022] Furthermore, the motion mechanism applies a downward pressure to the workpiece.

[0023] Beneficial effects: An ultra-precision planar machining process provided by the present invention combines the characteristics of large machining area in global machining and the ability to adjust the dwell time or walking speed of the workpiece according to the thickness distribution of the workpiece in local machining to solve the contradiction between insufficient global machining accuracy and low local machining efficiency. Based on a global machining grinder, it realizes machining by combining the control method of dwell time in local machining, and has the advantages of high machining accuracy and high machining efficiency. Description of the Drawings

[0024] Figure 1 is a schematic block diagram of the process structure of the present invention;

[0025] Figure 2 is the rate distribution diagram of the polishing pad;

[0026] Figure 3 is the real-time position parameter diagram of the workpiece;

[0027] Figure 4 is the thickness distribution diagram of the workpiece before machining;

[0028] Figure 5 is the thickness distribution diagram of the workpiece after machining. Detailed Embodiments

[0029] To make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0030] As Figures 1-5 shown, the present invention provides an ultra-precision planar machining process, including the following steps:

[0031] S1. Use a measuring tool to measure the thickness distribution of the workpiece, so as to determine the removal amount of each point on the workpiece.

[0032] S2. According to the measurement results, select the corresponding matching algorithm, calculate the dwell time distribution of each point on the workpiece on the polishing pad, and generate a motion command for controlling the action of the motion mechanism. After the workpiece is installed on the motion mechanism, the motion mechanism can drive the workpiece to any position on the polishing pad.

[0033] S3. Mount the workpiece on the motion mechanism through a specific fixture, and make the surface to be machined of the workpiece closely fit the surface of the grinding disc on the grinding machine.

[0034] S4. Start the grinding machine. The grinding disc on the grinding machine starts to rotate to polish the workpiece. At the same time, input the motion command into the motion mechanism, and the motion mechanism controls the movement of the workpiece on the grinding disc according to the motion command in step S2.

[0035] S5. The motion mechanism stops operating, turn off the grinding machine, disassemble the fixture, remove the workpiece and use a measuring tool to measure its thickness distribution.

[0036] S6. According to the measurement results, select to end the processing or repeat steps S2 to S5 until the thickness distribution of the workpiece meets the error requirements.

[0037] It should be noted that during the processing, the workpiece stays at each point or moves slowly on the grinding disc (the moving speed is much slower than the linear speed of the grinding disc surface). The workpiece area with a larger target removal amount will obtain a longer residence time or a slower walking speed (the slower the walking speed, the equivalent to the longer the residence time) near the edge of the grinding disc (the removal rate is larger); while the workpiece area with a smaller target removal amount will obtain a longer residence time or a faster walking speed (the faster the walking speed, the equivalent to the shorter the residence time) near the center of the grinding disc (the removal rate is smaller) or outside the disc surface (the removal rate is 0).

[0038] The control of the residence time or walking speed of the workpiece in different areas on the grinding disc is realized by any programmable control motion mechanism. For example, a robotic arm composed of a servo motor and a connecting rod. The motion mechanism can drive the workpiece to move to any position on the grinding disc. The motion mechanism is a prior art, and its specific structure will not be described in detail. The control instructions of this motion mechanism include: the global coordinates of the center of the workpiece at each point on the grinding disc, the residence time or moving speed of the center of the workpiece at each point on the grinding disc, and the rotation angle θ of the workpiece relative to the initial state when it is located at each residence point.

[0039] In one embodiment, the residence time of the workpiece in each area of the grinding disc surface depends on the distribution of the target removal amounts at different points on the workpiece. The calculation from the removal amount distribution to the residence time requires a corresponding supporting algorithm. In this embodiment, the residence time distribution algorithm is transformed into an optimization problem to minimize the error between the final removal amount and the target removal amount, that is:

[0040] min∫ W [∫ A t(x,y)r(ξ,η;x,y)dxdy - R obj (ξ,η)] 2dξdη

[0041] s.t. t(x, y) ≥ 0

[0042] Wherein, the integration region A is the residence range of the center of the workpiece on the polishing pad, the integration region W is the geometric shape of the workpiece itself, x and y are the global coordinates of the center of the workpiece at each point on the polishing pad, ξ and η are the local coordinates of each point on the workpiece, t(x, y) is the residence time of the center of the workpiece at each point on the polishing pad, r(ξ, η; x, y) is the removal rate of each point (ξ, η) on the workpiece when the center of the workpiece is located at (x, y) on the polishing pad, and R obj (ξ, η) is the target removal amount of each point on the workpiece.

[0043] In one embodiment, r(ξ, η; x, y) is given by the following formula:

[0044]

[0045] Wherein, k is the Preston coefficient, p is the pressure of the interaction between the workpiece and the polishing pad, ω is the rotational speed of the polishing pad, and R P is the radius of the polishing pad.

[0046] In one embodiment, the algorithm in S2 is the deconvolution method or the convolution iteration method or other optimization algorithms, and the calculated residence time is converted into the moving speed of the workpiece on the polishing pad.

[0047] In one embodiment, a spring structure or a counterweight can be designed on the motion mechanism to apply a downward pressure to the workpiece so as to obtain a better processing effect.

[0048] The above shows and describes the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed by the present invention.

[0049] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An ultra-precision plane machining process, characterized in that: The following steps are involved: S1. Measure the thickness distribution of the workpiece and determine the removal amount at each point on the workpiece; S2. According to the measurement results, a corresponding matching algorithm is selected to calculate the residence time distribution or travel speed distribution of each point on the workpiece on the grinding disk, and generate a motion instruction for controlling the motion mechanism; S3, installing the workpiece on the motion mechanism, and making the surface to be processed of the workpiece closely fit with the surface of the grinding disc on the grinding machine; S4, starting the grinding machine, and inputting the motion instruction into the motion mechanism, wherein the motion mechanism controls the workpiece to move on the grinding disc according to the motion instruction in step S2; S5, the motion mechanism stops moving, the grinder is turned off, the workpiece is removed and its thickness distribution is measured; S6. According to the measurement result, choose to end the processing or repeat steps S2 to S5 until the thickness distribution of the workpiece meets the error requirement.

2. The ultra-precision plane machining process according to claim 1, characterized in that: The residence time distribution algorithm is transformed into an optimization problem to minimize the error between the final removal amount and the target removal amount, that is: min∫ W [∫ A t(x,y)r(ξ,η;x,y)dxdy-R obj (ξ,η)]dξdη stt(x,y)≥0 Wherein, the integral area A is the residence range of the center of the workpiece on the grinding disk, the integral area W is the geometric shape of the workpiece itself, x, y are the global coordinates of the center of the workpiece at each point on the grinding disk, ξ, η are the local coordinates of each point on the workpiece, t(x, y) is the residence time of the center of the workpiece at each point on the grinding disk, r(ξ, η; x, y) is the removal rate of each point (ξ, η) on the workpiece when the center of the workpiece is located at (x, y) on the grinding disk, R obj (ξ,η) is the target removal amount for each point on the workpiece.

3. The ultra-precision plane machining process according to claim 2, characterized in that: r(ξ,η; x,y) is given by: Wherein, k is the Preston coefficient, p is the interaction pressure between the workpiece and the grinding disc, ω is the rotation speed of the grinding disc, and R P is the radius of the grinding disc.

4. The ultra-precision plane machining process according to claim 1, characterized in that: The algorithm in step S2 is a deconvolution method or a convolution iteration method, and the calculated dwell time is converted into the moving speed of the workpiece on the grinding disc.

5. The ultra-precision plane machining process according to claim 1, characterized in that: The motion mechanism applies downward pressure to the workpiece.

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