Sand line cutting bending wire servo control method based on visual detection

Abstract

The application discloses a sand line cutting bending wire servo control method based on visual detection and belongs to the technical field of sand line cutting. The method comprises the following steps: setting the angle of the sand line after the calibration of the perpendicularity as a zero angle gamma, setting a desired straightening angle theta and a bending wire limiting angle alpha. The sand line processing area visual detection image is uploaded to the host computer analysis program, and the angle between the sand line and the zero angle line in the image is set as the bending wire angle. When the processing bending wire angle increases and exceeds the set bending wire limiting angle alpha, the lower computer is controlled to disconnect the sampling circuit, stop the machine tool feeding, but keep the wire running system working, and the sand line is continuously straightened. When the bending wire angle is less than the desired straightening angle theta, the lower computer is controlled to turn on the sampling circuit, and the machine tool feeding is continued. The bending wire angle is taken as a feedback signal, the machine tool feeding is started and stopped by controlling the on-off of the sampling circuit, and the bending wire servo control is realized. The method can effectively reduce the processing error caused by the bending wire and the problem of broken wire caused by the bending wire.

Description

Technical Field

[0001] This invention relates to the field of CNC machine tool servo control technology, and in particular to a servo control method for bending wire on a wire cutting machine based on vision detection. Background Technology

[0002] Wire cutting is a high-precision material processing method widely used in the precision machining of hard and brittle materials such as semiconductors, photovoltaics, and sapphire. This technology utilizes tiny diamond particles embedded in a metal wire, which then physically cuts the material using a high-speed moving wire. Because the wire is a flexible cutting tool, wire bending is unavoidable during processing, and the effects of this bending are often negative. When the cutting wire bends, the cutting path deviates from the predetermined design trajectory, leading to increased errors in cutting dimensions and shape. This is unacceptable for manufacturing high-precision products such as semiconductor wafers and photovoltaic silicon wafers. Bending wires can also cause ripples, scratches, or other irregular surface defects on the cut surface, affecting not only the product's appearance but also potentially reducing its performance, especially in optical applications.

[0003] Currently, commonly used detection methods are mostly indirect. For example, there's the optical projection detection method, which proposes a wire bending detection method based on wire position detection by establishing a model of wire deflection and cutting resistance. Another method is wire bending control based on detecting the pressure between the wire and the workpiece during processing, designing a detection and control system operation scheme, including pressure information acquisition, transmission, processing, and feedback control, enabling real-time detection and control of wire bending during processing. However, these methods do not directly reflect the degree of bending and are difficult to apply in practical processing fields. There are also some methods for directly detecting the degree of bending. Existing technology (see patent, inventor: Luo Fuyuan, A Wire Cutting Wire Bending Detection Method Based on Auxiliary Parallel Electrodes, CN110434415B) provides a method where a wire-like or strip-like auxiliary electrode parallel to the cutting line is placed directly behind the cutting direction. The bending of the cutting line can be determined by measuring the change in resistance between the cutting line and the auxiliary electrode. This technology only provides a qualitative analysis of the degree of wire bending and cannot quantitatively and accurately detect it. Furthermore, this technology does not provide further feedback control after detecting bending. Summary of the Invention

[0004] Purpose of the invention:

[0005] This invention provides a vision-based servo control method for bending wire in abrasive wire cutting, addressing the challenges of difficult wire bending detection, unintuitive detection angles, and lack of targeted feedback control. Specifically, this invention introduces a high-precision vision inspection system to monitor the bending state of the abrasive wire in real time and feeds the results back to the servo control system. Based on the vision inspection data, the servo control system dynamically adjusts the machine tool feed start and stop to ensure the wire remains in an ideal state, thereby improving cutting accuracy and stability. Ultimately, this method improves the cutting accuracy and workpiece surface quality of abrasive wire cutting and reduces wire breakage caused by excessive bending angles.

[0006] To achieve this goal, the following technical solution is adopted:

[0007] A servo control method for wire cutting and bending based on vision inspection, the workflow of which is as follows: Figure 1 As shown, the initial setup involves connecting the industrial CMOS camera to the host computer, selecting at least two suitable camera positions in different directions to ensure the camera is focused on the wire. After the industrial CMOS camera acquires an image, it undergoes grayscale processing, binarization, contour detection, noise reduction, and angle analysis before acquiring another image. The zero-position angle γ, desired straightening angle θ, and limit angle α are set according to cutting accuracy and requirements as the basis for the wire cutting machine's feed control. The angle analysis results are compared with the limit angle. When the bending angle is less than the limit angle α, the host computer controls the sampling voltage to be greater than the threshold voltage of the sampling circuit, controlling the machine to continue feeding. When the bending angle is greater than or equal to the limit angle α, the host computer controls the supply voltage to be less than the threshold voltage of the sampling circuit, controlling the machine to stop feeding while maintaining the wire feeding system until the bending angle is less than the desired straightening angle θ. Then, the host computer again controls the supply voltage to be greater than the threshold voltage of the sampling circuit, controlling the machine to continue feeding.

[0008] This invention provides a servo control method for a wire cutting machine tool, comprising:

[0009] Step S1: Initialize the connection configuration between the industrial CMOS camera and the host computer, and select at least two suitable camera positions.

[0010] Step S2: After acquiring an image, perform grayscale conversion, binarization, contour detection, noise reduction, and angle analysis on the image, and then acquire the image again.

[0011] Step S3: Calibrate the perpendicularity of the sand thread and collect the calibrated sand thread bending angle as the zero-position angle γ. Determine the limit angle α and the desired straightening angle θ according to the processing requirements.

[0012] Step S4: After processing, high-speed acquisition and processing of image data, comparison of bending angle and limit angle α, and further control of machine tool feed start and stop in conjunction with lower computer control.

[0013] Step S5: When the bending angle is greater than or equal to the limit angle α, the machine tool stops feeding, and the wire feeding system continues to work for a period of time until the wire returns to its original position and the bending angle is less than the expected straightening angle θ.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. This invention proposes a method for detecting wire bending angle using visual inspection and providing feedback based on the degree of bending, enabling servo control of machine tool feed. This invention provides both a feasible method for directly detecting wire bending angle and a solution for servo feed control of machine tools. The combination of these two approaches creates a robust closed-loop control system for both machine tool feed control and wire bending detection.

[0016] 2. This invention proposes controlling the degree of wire bending for abrasive wire cutting. Maintaining an appropriate degree of wire bending ensures the wire remains straight during cutting, reducing cutting deviations caused by bending and thus improving cutting accuracy. Properly controlling the degree of wire bending can effectively reduce wire wear and extend the wire's service life. Attached Figure Description

[0017] Figure 1 A flowchart of the servo control method for wire cutting based on visual detection of wire bending degree;

[0018] Figure 2 Example diagram of a wire cutting machine tool setup for visually inspecting the degree of wire bending;

[0019] Figure 3 The planar positional relationship between the sand line angle, zero position angle γ, set desired straightening angle θ, and bending wire limit angle α;

[0020] Figure 4 Sampling diagram of the sand line in the Y direction of machine tool feed;

[0021] Figure 5 1. Sanding diagram of the Y-axis feed direction of the machine tool;

[0022] Figure 6 Charts showing machine tool feed angle in the Y direction;

[0023] Figure 7 Sampling circuit diagram for machine tool section.

[0024] In the above diagram: 1. Sanding line; 2. X-feed direction camera; 3. X-camera tripod; 4. Y-feed direction camera; 5. Y-camera tripod; 6. Guide roller on the machine tool. Detailed Implementation

[0025] The present invention is described below based on embodiments, but the invention is not limited to these embodiments. In the detailed description of the invention below, certain specific details are described in detail. Those skilled in the art will fully understand the invention even without these details. To avoid obscuring the essence of the invention, well-known methods, processes, flows, elements, and circuits are not described in detail.

[0026] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0027] At the same time, it should be understood that in the following description of the present invention, the terms "upper", "lower", "vertical", "horizontal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do 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 the present invention.

[0028] Unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as encompassing rather than being exclusive or exhaustive; that is, meaning "including but not limited to."

[0029] In the description of this invention, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0030] The specific details of the present invention will be further illustrated below with reference to embodiments.

[0031] like Figure 2 For a reciprocating wire EDM machine, an industrial CMOS camera for detecting wire bending is positioned in the X-axis feed direction and another in the Y-axis feed direction. The camera connection and acquisition parameters are configured on the host computer to ensure the cameras can begin acquiring and analyzing images. Before machining the workpiece, the wire perpendicularity is calibrated, and an image is acquired and analyzed once, setting the bending angle at this point to zero. During machining, images are continuously acquired and analyzed. The images undergo grayscale conversion, binarization, contour detection, noise reduction, and angle analysis before the data is output to a visualized waveform.

[0032] like Figure 3The figure shows the planar positional relationship between the sand line, sand line angle, zero position angle γ, set desired straightening angle θ, and bending wire limit angle α.

[0033] Set the desired straightening angle to ±0.5° and the limit angle to ±2°, such as... Figure 4 The image shown is the acquired image, processed image, and waveform of the Y-axis detection camera over a certain period of time. Figure 4 To capture the image results, use the selection tool to select the approximate location of the sand line in the resulting image as the analysis area for image processing. Figure 5 The image processing results show the red line in the graph representing the sand line position fitted from the image. The angle values ​​are analyzed based on the fitting results and output to the waveform graph, as shown below. Figure 6 As shown. By Figure 6 It can be seen that the current bending angle is between -1.76° and -1.86°, which is less than the limit angle. Therefore... Figure 7 The lower-level machine's D2 pin remains high, allowing the sampling circuit input to flow through the 24V Zener diode, thus conducting the circuit and enabling the machine tool to continue feeding. As processing progresses, the wire bending angle continuously increases to -2°. At this point, the lower-level machine's D2 pin outputs a low level, preventing flow in the sampling circuit and the frequency converter circuit, causing the machine tool to stop feeding. The wire feeding system continues cutting the workpiece, with the wire continuously returning to the desired straightening angle of -0.5° before continuing to the next feed step.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A servo control method for wire bending in abrasive wire cutting based on vision detection, characterized in that: (a) Initialize and configure the parameters and connection of the industrial CMOS camera to ensure that the camera correctly acquires and analyzes images; (b) Set three angle parameters as the basis for the feed control of the wire cutting machine: zero angle γ, expected straightening angle θ, and limit angle α. The zero angle γ is the angle between the wire and the vertical direction after the wire is calibrated to be perpendicular. The expected straightening angle θ, limit angle α, and bending angle are the deviation angles of the wire from the zero angle γ at a certain degree of bending. The mathematical comparison between the expected straightening angle θ, limit angle α, and bending angle is to compare the absolute values ​​of the angles. (c) When the wire cutting machine continuously feeds and processes, the industrial CMOS camera continuously acquires images and analyzes the angle deviation between the bending angle of the wire and the zero-position angle γ in the images. (d) The bending angle of the sand wire is constantly compared with the limiting angle α. When the bending angle is less than the limiting angle α, the host computer sends a command to the slave computer, requiring the sampling voltage to be greater than the conduction threshold voltage of the sampling circuit in order to keep the sand wire cutting machine tool continuously feeding. (e) The bending angle of the wire is constantly compared with the limiting angle α. When the bending angle is greater than or equal to the limiting angle α, the host computer sends a command to the slave computer, requiring the sampling voltage to be less than the conduction threshold voltage of the sampling circuit to ensure that the wire cutting machine stops feeding and the wire feeding system needs to keep working continuously. (f) The continuous operation of the wire feeding system will gradually reduce the bending angle of the wire. When the bending angle of the wire decreases to less than the expected straightening angle θ, the host computer sends a command to the slave computer, requiring the sampling voltage to be greater than the conduction threshold voltage of the sampling circuit to ensure that the wire cutting machine continues to feed. (g) Continuously collect, analyze, and process the wire bending images, and control the start and stop of the wire cutting machine feed according to the analysis results until the processing is completed.

2. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, Before processing, configure the connection between the industrial CMOS camera and the host computer and determine the position of the industrial CMOS camera to ensure that the sanding wire can continuously collect the bending angle of the sanding wire under good light source.

3. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, It includes an image grayscale processing unit, an image binarization processing unit, a contour detection unit, and a noise processing unit, which continuously acquire, grayscale, extract contours, and denoise the sand wire bending image.

4. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, After acquiring an image of a sand wire bending, immediately analyze, process, and send a signal to the lower-level computer to control the start and stop of the sand wire cutting machine. The sampling rate of the sand wire bending image must be greater than 25 images / second, and the sand wire bending image processing speed must be greater than or equal to the sand wire bending image acquisition speed. The response speed of the lower-level computer should be much greater than the sand wire bending image processing speed to ensure that the changes in the sand wire can be recorded in real time and feedback can be provided.

5. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, When processing images of sand-line bending wires, only the contour and edge analysis of the sand-line's location should be analyzed; other locations should be distinguished or isolated.

6. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, Set the angle parameters for each control sand wire bending wire, including: after the sand wire is calibrated for verticality, acquire the angle between the sand wire and the vertical direction in a sand wire bending wire image, and identify this angle as the zero angle γ of the sand wire; set an angle value as the limit angle α to limit the maximum bending degree; and set an angle value as the expected straightening angle θ to determine the straightening of the sand wire.

7. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, The zero-position angle γ should be small enough to determine the sign of the bending angle. The expected straightening angle θ should be greater than or equal to the zero-position angle γ, and the limiting angle α should be significantly greater than the expected straightening angle θ.

8. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, When the bending angle is less than the limit angle α, the sampling voltage of the wire cutting machine tool can be continuously greater than or equal to the conduction threshold voltage of the sampling circuit, ensuring that the wire cutting machine tool can continuously feed and process; when the bending angle is greater than or equal to the limit angle α, and the sampling voltage of the wire cutting machine tool is less than the conduction threshold voltage of the sampling circuit, the wire cutting machine tool stops feeding but keeps the wire feeding system working continuously.

9. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, At least two directions of the X and Y feed directions of the wire cutting machine tool contain industrial CMOS cameras that acquire images of the bent wire.

10. The servo control method for wire bending in abrasive wire cutting according to claim 1, characterized in that, The sampling circuit should have a voltage regulator as a switch to determine whether the circuit is conducting; in addition, the sampling circuit should be one of the bases for controlling the feed rate or start / stop of the wire cutting machine.

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