Sand wire cutting and bending servo control method based on visual inspection

Abstract

The invention discloses a sand line cutting and wire bending servo control method based on visual inspection, which belongs to the technical field of sand line cutting and comprises the following steps: calibrating a sand line angle after perpendicularity calibration as a zero angle gamma, and setting an expected squareness returning angle theta and a wire bending limiting angle alpha. And the sand line processing area visual detection image is uploaded to an upper computer analysis program, and the included angle between the sand line and the zero angle line in the image is set as the wire bending angle. And when the machining wire bending angle is increased and exceeds the set wire bending limiting angle alpha, the lower computer is controlled to disconnect the sampling circuit and stop feeding of the machine tool, but the wire conveying system is kept working, and the sand wire is continuously straightened. And when the wire bending angle is smaller than the expected straightening angle theta, the lower computer is controlled to enable the sampling circuit to be switched on, and the machine tool continues to feed. The wire bending angle serves as a feedback signal, feeding start and stop of the machine tool are achieved by controlling on-off of the sampling circuit, and wire bending servo control is achieved. According to the method, the problems of machining errors caused by wire bending and wire breakage caused by wire bending can be effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of servo control of numerically controlled machine tools, and in particular to a wire bending servo control method of an abrasive wire cutting machine tool based on visual detection. Background Art

[0002] Wire cutting technology is a high-precision material processing method that is widely used in the precision processing of hard and brittle materials such as semiconductors, photovoltaics, and sapphire. This technology uses fine diamond particles embedded in metal wires to physically cut the material through high-speed moving wires. Since the wire is a flexible cutting tool, wire bending is inevitable during processing, and the impact of wire bending is often negative. When the cutting wire is bent, the cutting path will deviate from the predetermined design trajectory, resulting in increased cutting size and shape errors. This is unacceptable for the manufacture of products such as semiconductor wafers and photovoltaic silicon wafers that require high precision. Bent cutting wires may cause ripples, scratches or other irregular surface defects on the cut surface, which not only affects the appearance of the product, but may also reduce its performance, especially in optical applications.

[0003] At present, the commonly used detection methods are all indirect detection, such as establishing a model of the deflection amount and cutting resistance of the sand wire, and proposing a light projection detection method based on the detection of the sand wire position. There is also a wire bending control method based on the detection of the pressure between the sand wire and the workpiece during the processing process. The detection control system operation plan is designed, including pressure information collection, transmission, processing, feedback control, etc., so that the amount of sand wire bending can be detected and controlled in real time during the processing. These methods do not intuitively reflect the degree of wire bending and are difficult to be applied in the actual processing field. There are also some methods for directly detecting the degree of wire bending. The prior art (see patent, inventor: Luo Fuyuan, a wire cutting wire bending detection method based on auxiliary parallel electrodes, CN110434415B) provides a wire or strip auxiliary electrode parallel to the cutting line placed just behind the cutting direction of the cutting line. By measuring the change in resistance between the cutting line and the auxiliary electrode, it can be determined whether the cutting line is bent. This technology only has a qualitative analysis of the degree of bending of the sand wire, and cannot be quantitatively and accurately detected, and this technology does not make further feedback control after detecting the bending wire. Summary of the invention

[0004] Purpose of the invention:

[0005] The present invention provides a servo control method for sand wire cutting wire bending based on visual detection, which is used to solve the problems of difficulty in detecting the bending state of the sand wire, non-intuitive detection angle, and non-targeted feedback control. Specifically, the present invention introduces a high-precision visual detection system to monitor the bending state of the sand wire in real time, and feeds back the detection results to the servo control system. The servo control system dynamically adjusts the start and stop of the machine tool feed according to the visual detection data to ensure that the wire material is always kept in an ideal state, thereby improving the cutting accuracy and stability. This method can ultimately improve the cutting accuracy and workpiece surface quality of sand wire cutting, and reduce the problem of wire breakage caused by excessive bending angles of the sand wire.

[0006] In order to achieve this goal, the following technical solutions are adopted:

[0007] A wire bending servo control method for sand wire cutting based on visual detection is to initialize and configure the industrial CMOS camera to connect with the host computer, select at least two suitable camera positions in different directions, and ensure that the camera focuses on the sand wire. After the industrial CMOS camera captures a picture, the picture is grayed, binarized, contour detected, noise reduced, and angle analyzed before capturing the image again. According to the cutting accuracy and requirements, the zero angle γ, the expected straightening angle θ, and the limit angle α are set as the basis for controlling the feed control of the sand wire cutting machine tool. The angle analysis result is compared with the limit angle. When the wire bending angle is less than the limit angle α, the lower computer controls the sampling voltage to be greater than the threshold voltage flowing through the sampling circuit, and controls the machine tool to feed continuously; when the wire bending angle is greater than or equal to the limit angle α, the lower computer controls the supply voltage to be less than the threshold voltage flowing through the sampling circuit, controls the machine tool to stop feeding, and maintains the wire feeding system to continue working, until the wire bending angle is less than the expected straightening angle θ, then the lower computer controls the supply voltage to be greater than the threshold voltage flowing through the sampling circuit again, and controls the machine tool to feed continuously.

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

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

[0010] Step S2: After collecting a picture, grayscale processing, binarization processing, contour detection, noise reduction processing, and angle analysis are performed on the picture before collecting the image again.

[0011] Step S3, calibrate the verticality of the sand wire, collect the calibrated sand wire bending angle as the zero angle γ. According to the processing requirements, determine the limit angle α and the expected straightening angle θ.

[0012] Step S4: After processing, the image data is collected and processed at high speed, and the start and stop of the machine tool feed are further controlled according to the comparison between the wire bending angle and the limit angle α and the control of the lower computer.

[0013] Step S5, when the wire bending angle is greater than or equal to the limit angle α, the machine tool stops feeding, and the wire transport system continues to work for a period of time until the sand wire returns until the wire 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. The present invention proposes a method for detecting the wire bending angle by visual detection and providing certain feedback according to the degree of wire bending, which can servo control the feeding of machine tools. The present invention not only provides a feasible method for directly detecting the wire bending angle, but also provides a solution for the servo feeding control of machine tools. The combination of the two forms a good closed-loop control in the feeding control and wire bending detection of machine tools.

[0016] 2. The present invention proposes to perform sand wire cutting by controlling the degree of wire bending. Controlling the sand wire to an appropriate degree of wire bending can ensure that the sand wire maintains straightness during the cutting process, reduce cutting deviation caused by bending, and thus improve cutting accuracy. Reasonable control of the degree of wire bending can effectively reduce the wear of the sand wire and extend the service life of the sand wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 , Workflow chart of the servo control method for abrasive wire cutting based on visual detection of wire bending degree;

[0018] Figure 2 , a sample diagram of the construction of an abrasive wire cutting machine tool for visual inspection of wire bending degree;

[0019] Figure 3 , the plane position relationship of the sand line angle, the zero angle γ, the desired straightening angle θ, and the wire bending limit angle α;

[0020] Figure 4 , Sand line sampling diagram of machine tool feeding Y direction;

[0021] Figure 5 , Sand line processing diagram of machine tool feeding Y direction;

[0022] Figure 6 , Machine tool feed Y direction angle data chart;

[0023] Figure 7 , sampling circuit diagram of some machine tools.

[0024] In the above figure: 1. Sand line; 2. X feed direction camera; 3. X camera tripod; 4. Y feed direction camera; 5. Y camera tripod; 6. Guide wheel on the machine tool. DETAILED DESCRIPTION

[0025] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. It is possible for a person skilled in the art to fully understand the present invention without the description of these details. In order to avoid confusing the essence of the present invention, known methods, processes, flows, components and circuits are not described in detail.

[0026] In addition, persons of ordinary skill in the art will appreciate that the drawings provided herein are for illustration purposes 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, it should be understood that the terms "upper", "lower", "vertical", "horizontal", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0028] Unless the context clearly requires otherwise, throughout the specification and claims, the words "include", "comprising" and similar words should be interpreted in an inclusive sense rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to".

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

[0030] The specific contents of the present invention are further illustrated below in conjunction with embodiments.

[0031] like Figure 2 For a reciprocating wire-cutting sand wire cutting machine, an industrial CMOS camera for detecting wire bending in the X-direction is arranged in the X-feed direction of the machine, and an industrial CMOS camera for detecting wire bending in the Y-feed direction is arranged. Configure the connection and acquisition parameters of the camera on the host computer to ensure that the camera can start to acquire and analyze images. Before starting to process the workpiece, calibrate the verticality of the sand wire, collect and analyze the image once, and set the wire bending angle at this time to the zero angle. When starting processing, continuously collect and analyze images, grayscale the image, binarize it, perform contour detection, noise reduction, and angle analysis, and then output the data to a visual waveform chart.

[0032] like Figure 3 As shown, the planar position relationship among the sand line, sand line angle, zero angle γ, desired straightening angle θ, and wire bending limit angle α.

[0033] Set the desired straightening angle to ±0.5° and the limit angle to ±2°. Figure 4 The figure shows the captured image, processed image and waveform of the Y-direction detection camera over a period of time. Figure 4 To collect the image results, use the selection tool to select the approximate position of the sand line in the result image as the analysis area for image processing. Figure 5 is the image processing result. The red line in the figure is the sand line position result obtained by image fitting. The angle value is analyzed based on the fitting result and output to the waveform graph, such as Figure 6 As shown. Figure 6 It can be seen that the current processing wire bending angle is -1.76° to -1.86°, which is smaller than the limit angle. Figure 7 The D2 pin of the lower computer in the process maintains a high level, and the sampling circuit input can flow through the 24V voltage regulator diode to make the circuit conductive, and the machine tool continues to feed. As the processing progresses, the wire bending angle continues to increase to -2°, and the D2 pin of the lower computer outputs a low level, the sampling circuit cannot flow and the frequency conversion circuit cannot be conductive, and the machine tool stops feeding. The wire feeding system still keeps cutting the workpiece, and the sand wire continues to return until the desired straightening angle is -0.5° before continuing the next feeding work.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A servo control method for abrasive wire cutting and bending based on visual detection, characterized in that: (a) Initialize the parameters and connections of the industrial CMOS camera to ensure that the camera can correctly capture and analyze images. (b) Set the zero angle γ, the expected straightening angle θ, and the limit angle α as the basis for controlling the feed control of the sand wire cutting machine. The zero angle γ is the angle between the sand wire and the vertical direction after the verticality of the sand wire is calibrated as the reference. The expected straightening angle θ, the limit angle α, and the wire bending angle are all the deviation angles of the sand wire from the zero angle γ at a certain wire bending degree. The mathematical comparison between the expected straightening angle θ, the limit angle α, and the wire bending angle is the absolute value of the angle for comparison. (c) When the wire cutting machine tool (hereinafter referred to as the "machine tool") continuously feeds and processes, the industrial CMOS camera continuously collects images and analyzes the angle deviation between the bending angle of the wire in the image and the zero angle γ. (d) The bending angle of the abrasive wire is constantly compared with the limit angle α. When the bending angle is smaller than the limit angle α, the machine tool is kept feeding continuously. (e) When the wire bending angle is greater than or equal to the limit angle α, the upper computer sends a command to the lower computer, requiring the sampling voltage to be less than the feed voltage of the sampling circuit to ensure that the machine tool stops feeding, and the wire feeding system needs to continue to work. (f) The continuous operation of the wire feeding system will gradually reduce the wire bending angle. When the wire bending angle is reduced to the expected straightening angle θ, the upper computer sends a command to the lower computer, requiring the sampling voltage to be greater than or equal to the threshold voltage of the sampling circuit to ensure that the machine tool continues to feed. (g) Continuously collect, analyze and process the sand wire bending images, and control the start and stop of the machine tool feed according to the analysis results until the processing is completed.

2. The sand wire cutting servo control method according to claim 1, characterized in that: Before processing, configure the connection between the industrial COMS camera and the host computer and determine the position of the camera to ensure that the bending degree of the sand wire can be continuously collected under a good light source.

3. The servo control method for abrasive wire cutting according to claim 1, characterized in that: Sand line image processing includes image grayscale processing unit, image binarization processing unit, contour detection unit and noise processing unit, which continuously collect, grayscale, extract contours and reduce noise on sand line images.

4. The sand wire cutting servo control method according to claim 1, characterized in that: After collecting a sand wire bending image, it is immediately analyzed, processed, and a signal to control the start and stop of the machine tool is sent to the lower computer. The sampling rate of the sand wire image must be greater than 25 images / second, and the image processing speed must be greater than or equal to the image acquisition speed. The response speed of the lower computer should be much greater than the image processing speed. Ensure that the changes in the sand wire can be recorded in real time and feedback can be given.

5. The sand wire cutting servo control method according to claim 1, characterized in that: During image processing, only the contour analysis and edge analysis of the sand line position should be performed, and other positions should be distinguished or isolated.

6. The sand wire cutting servo control method according to claim 1, characterized in that: The angle parameters of each control sand wire bending wire are set, including: after the sand wire is calibrated for verticality, the angle between the sand wire and the vertical direction is collected once, and this angle is identified as the zero angle Y of the sand wire, an angle value is set as the limit angle α to limit the maximum value of the wire bending degree, and an angle value is set as the expected straightening angle θ to determine the judgment basis for the straightening of the sand wire.

7. The servo control method for abrasive wire cutting according to claim 1, characterized in that: The zero angle γ should be small enough to determine the positive or negative nature of the wire bending angle. The expected straightening angle θ should be greater than or equal to the zero angle Y, and the limit angle α should be significantly greater than the expected straightening angle θ.

8. The sand wire cutting servo control method according to claim 1, characterized in that: When the wire bending angle is less than the limit angle α, the sampling voltage of the machine tool can continue to be greater than or equal to the threshold voltage of the sampling circuit, ensuring that the machine tool can continue to feed processing; when the wire bending angle is greater than or equal to the limit angle α, the sampling voltage of the machine tool is less than the threshold voltage of the sampling circuit, the machine tool stops feeding but the wire transport system can continue to work.

9. The sand wire cutting servo control method according to claim 1, characterized in that: In the plane where the X-feed direction and the Y-feed direction of the machine tool are located, there are industrial CMOS cameras in at least two directions to collect the bending degree of the sand wire.

10. The servo control method for abrasive wire cutting according to claim 1, characterized in that: The sampling circuit should have a voltage stabilizing element as a switch to determine whether the circuit is on. In addition, the sampling circuit should be one of the control bases for the feeding speed or start and stop of the machine tool.

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