CN102328493A

CN102328493A - Positioning method in novel silk screen printing CCD (charge coupled device) image identification

Info

Publication number: CN102328493A
Application number: CN201110254692A
Authority: CN
Inventors: 邹垂国; 潘红斌; 路小军; 杨定香; 何杏兴
Original assignee: Nanjing Panda Electronics Co Ltd; Panda Electronics Group Co Ltd
Current assignee: Nanjing Panda Electronics Co Ltd; Panda Electronics Group Co Ltd
Priority date: 2011-08-31
Filing date: 2011-08-31
Publication date: 2012-01-25

Abstract

The invention discloses a positioning method in novel silk screen printing CCD (charge coupled device) image identification, comprising the following steps of: (a) conveying PCBs (printed circuit boards) to an operating platform part to be initially positioned and clamped by virtue of an introducing part and an operating platform conveying part; (b) obtaining a CCD positioning identification template by adopting a manually programming method; (c) calculating angular deviation and distance deviation by virtue of the PCBs and MARK points on a silk screen, controlling the operating platform to correspondingly adjust position and angle; and (d) moving an image acquisition device to the position above the PCBs and the MARK points, respectively shooting the PCBs and the MARK points of the silk screen by virtue of a CCD camera, matching the obtained image with the CCD positioning identification template, and carrying out automatic printing after a matching requirement is achieved. The invention provides a whole set of system, the system can automatically detect offset between the center of an object window required to be retrieved by a user and the center of any pattern, the offset is namely correction, the correction is added during counterpoint calculation, and counterpoint actuating quantity is calculated and a counterpoint action is executed. For various patterns used for counterpoint of a base plate, the various patterns can be simply counterpointed without high correction proficiency requirement, and printing counterpoint accuracy can be improved.

Description

Novel positioning method for screen printing CCD image recognition

Technical Field

The invention relates to the technical field of CCD image recognition, in particular to a novel positioning method for CCD image recognition of silk screen printing.

Background

In the SMT industry, screen printing devices are an important component. A general screen printing apparatus is classified into: the device comprises a transmission part for transmitting a substrate, a workbench part with a lifting mechanism and a substrate clamping and positioning function, a transmission part for transmitting the substrate, a mesh plate part corresponding to the substrate, a scraper, a tool hanging head with a scraper lifting mechanism and a horizontal moving mechanism, a control device for controlling each mechanism and a CCD recognition device. When the substrate reaches the workbench part through the transmission part, the workbench part temporarily clamps and fixes the substrate once, secondly, the CCD is utilized to identify the substrate and the marks of the two parts with the screen plate corresponding to the substrate pattern, the offset of the two parts is calculated, and then the workbench adjusts and corrects the position according to the offset, so that the screen plate corresponds to the substrate position. Finally, the table part is lifted to make the screen plate contact the substrate, paste such as soldering paste is filled in the opening of the screen plate while the screen plate contacts the substrate by the scraper, the scraper finishes the whole substrate, the table is lowered to separate the screen plate and the substrate with the paste such as soldering paste, and the printed substrate is delivered by the delivery conveying part. The entire printing process is completed. The most important link in the whole printing process is that the CCD identifies the marks of the two parts of the substrate pattern and the corresponding screen plate, and calculates the deviation of the two parts. The general CCD image recognition and positioning method can not realize the accurate recognition and the accurate positioning of the substrate pattern and the corresponding screen plate, and the printing precision is influenced.

Disclosure of Invention

The invention overcomes the defects in the prior art, and provides the method for accurately identifying the two side marks of the substrate pattern and the corresponding screen plate by the CCD to realize accurate positioning, so that a user can obtain high-precision alignment precision by simple operation, and a high-quality PCB is printed.

The technical scheme of the invention is as follows:

a novel positioning method for identifying a silk-screen printing CCD image comprises the following steps: (a) the PCB is transmitted to the workbench part through the transmission part and the workbench transmission part to be initially positioned and clamped; (b) obtaining a CCD positioning identification template by a manual programming method; (c) calculating angle deviation and distance deviation through MARK points on the PCB and the silk screen, and controlling the workbench to make corresponding position and angle adjustment; (d) moving the image acquisition device above the MARK points of the PCB, respectively shooting the MARK points of the PCB and the silk screen by a CCD camera, matching the obtained image with a CCD positioning identification template, and automatically printing after the matching requirement is met;

furthermore, the step (b) of obtaining the CCD positioning and identifying template by a manual programming method comprises the steps of: moving the image acquisition device above a MARK point of the PCB, turning on a lower light source, and moving the CCD to enable the center of the view to coincide with the center of the MARK point; moving the silk screen to enable the MARK point of the silk screen to be at the center of the CCD view as much as possible; storing the prepared MARK point image as a template for CCD positioning identification;

and, the angle deviation and the distance deviation described in the step (c) are calculated by MARK points on the PCB board and the screen.

And (d) the image matching in the step (d) is realized by adopting a template matching identification method.

The invention has the beneficial effects that:

the invention provides a whole set of system, which can automatically detect the offset of the center of a window to be searched by a user and the center of any pattern, wherein the offset is a correction amount, and the correction amount is added during the alignment calculation to calculate the alignment action amount and carry out the alignment action. In contrast, various patterns used for alignment of a substrate can be easily handled without requiring a degree of skill in position correction, and printing alignment accuracy can be improved.

Drawings

Fig. 1 is a schematic structural diagram of a novel screen printing CCD image recognition device of the present invention.

FIG. 2 is a printing flow chart of the positioning method of the novel silk-screen printing CCD image recognition of the invention.

FIG. 3 is a schematic diagram of the template recognition of the positioning method for the novel silk-screen CCD image recognition of the present invention.

Fig. 4 is an alignment diagram of the screen and the substrate of the novel screen printing CCD image recognition device of the present invention.

Detailed Description

The invention is further described below with reference to the figures and examples.

Fig. 1 is a schematic view showing the structure of the entire screen printing apparatus. In fig. 1, 1 is a mechanical structure, 20 is a control part, and the control is divided into upper computer (PC) control and lower computer (PLC) control. The upper computer provides a human-computer interaction interface, image processing and MARK point position deviation calculation; the lower computer receives the instruction of the upper computer to drive the mechanical part to move relatively. The structure that adopts is that the transmission part has three parts: a transfer unit 6, a stage transfer unit 12, and a transfer unit 7. The table unit 10 mainly functions to position the PCB 9 and a table lifting unit 13. The image acquisition device 8 mainly comprises a CCD camera 15, an upper light source 14 and a lower light source 14, and adopts a single-camera double-light-source alignment system. When MARK points of the PCB are collected, the lower light source is turned on, and the CCD collects MARK point images of the PCB; when the MARK point on the screen 5 is collected, the upper light source is turned on, and the CCD collects the MARK point image of the screen. The upper part of the steel mesh is provided with a scraper head 2, the scraper head 2 is provided with a scraper 3, and the scraper head 2 is respectively provided with a moving mechanism for controlling the horizontal movement and a lifting mechanism for controlling the vertical movement.

The operation flow of the printing unit of the present invention will be specifically described below.

The specific operation flow is shown in fig. 2. The PCB 9 is transferred to the table part 10 through the incoming part 6 and the table transferring part 12 for initial positioning and clamping, and its purpose is mainly to fix the PCB so that it does not move. If the PCB is manufactured for the first time, a MARK point image template is obtained by manually manufacturing a program; if the program is ready, then automatic printing of the PCB board can begin. When the program is made, the image acquisition device 8 is moved to the position above the MARK point of the PCB, the lower light source is turned on 14, the CCD15 is moved to make the center of the view coincide with the center of the MARK point, and the silk screen is moved to make the MARK point of the silk screen be at the center of the CCD view as much as possible. The purpose of this is to improve the recognition accuracy in automatic printing and to improve the production efficiency. And storing the well-made MARK point image as a template for CCD positioning identification. Automatically printing after the program is finished, automatically moving a CCD camera to be above MARK points of a PCB (printed Circuit Board) plate, respectively shooting the MARK points of the silk screen and the PCB, matching the obtained image with a target template during the program making, and automatically printing until all actions are finished if the matching value meets the requirement; otherwise, giving a corresponding prompt and then transmitting the PCB version.

The principles and methods for image target recognition are many, and in practical application, a template matching method and a neural network method are generally adopted. Because the neural network method is difficult to meet the real-time requirement due to large calculation amount, the identification method adopted in the invention is based on a template matching identification method. The main principle is as follows:

as shown in FIG. 3, let T be the image template of the known target object, n × m in size, and W × H (W) be the image S to be examined>n，H>m). The matching process is to try to superimpose the template T on S and compare T with the sub-image S of S it covers^i,jThe difference in (a). If the difference is less than some preset threshold, the sub-image S of T and S is considered to be at the position^i,jThere is a better match, i.e. the target object is found. Scanning the whole image to be matched pixel by pixel and implementing the operation, whether or not the target object determined by the template T exists in the image I can be determined. The mathematical description of the matching process is:

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or

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(1)

Wherein the first and third terms represent the autocorrelation of the corresponding subset of images S and the template T, respectively. The second term gives the cross-correlation of the two. The larger this term isThe smaller the value of (A), the sub-image S representing the image field^i,jThe better the match with the template T.

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A zero indicates a perfect match. The method is simple and practical, but the calculated amount is large, and the requirement on light is high. However, in the invention, the MARK point is smaller, so that the calculation speed can completely meet the requirement. And in a relatively dim environment, the influence of light on the environment is relatively small.

As shown in FIG. 4, the center coordinates of MARK1 and MARK2 on the screen are (x)_M1，y_M1），（x_M2，y_M2) (ii) a The center coordinates of MARK3 and MARK4 on the substrate are respectively (x)_b1，y_b1），（x_b2，y_b2). Firstly, calculating the deviation angle between the screen and the platform, and then calculating the deviation angle between the substrate and the platform, wherein the two angle differences are the deviation angles between the screen and the substrate. Since the screen is stationary, the stage can make the angle between the substrate and the screen zero by adjusting this offset angle. And finally, calculating the distance deviation in the horizontal direction and the vertical direction. The specific calculation formula is as follows:

of screens and platformsDeviation angle: (2)

deviation angle of substrate and stage: (3)

deviation angle of screen from substrate:

Figure DEST_PATH_913052DEST_PATH_IMAGE006

(4)

the deviation of the screen MARK from the substrate MARK in the horizontal and vertical directions is calculated as follows:

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(5)

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(6)

wherein,

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,is a constant of the origin coordinates.

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(7)

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(8)

(9)

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(10)

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(11)

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(12)

The deviation distance from the screen plate is as follows:

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(13)

the angle and distance of the movement of the working table are as follows:

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(14)

the whole identification and positioning process is completed, the workbench is adjusted in angle and position correspondingly, and then the PCB with good effect can be printed.

The foregoing shows and describes the general principles and features of the present invention, together with the advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof. The invention has wide application range and is suitable for any form of MARK point shape. The method can be used for not only a screen printing device, but also the alignment among devices in an SMT line, and even can be used in any occasion needing CCD positioning.

The parts not involved in the present invention are the same as or can be implemented using the prior art.

Claims

1. A novel positioning method for identifying a silk-screen printing CCD image is characterized by comprising the following steps:

the PCB (9) is conveyed to a workbench part (10) through a conveying-in part (6) and a workbench conveying part (12) to be initially positioned and clamped;

obtaining a CCD positioning identification template by a manual programming method;

calculating angle deviation and distance deviation through MARK points on the PCB (9) and the silk screen (5), and controlling the workbench (10) to make corresponding position and angle adjustment;

and moving the image acquisition device (8) above the MARK points of the PCB, respectively shooting the MARK points of the PCB (9) and the silk screen (5) by a CCD camera (15), matching the obtained image with the CCD positioning identification template, and automatically printing after the matching requirement is met.

2. The novel positioning method for silk-screen printing CCD image recognition according to claim 1, characterized in that: the step (b) of obtaining the CCD positioning identification template through a manual programming method comprises the following steps:

moving the image acquisition device (8) above a MARK point of the PCB (9), turning on a light source under the light source (14), and moving the CCD (15) to enable the center of the view to coincide with the center of the MARK point;

moving the silk screen (5) to enable the MARK point of the silk screen (5) to be at the center position of the CCD view as much as possible;

and storing the well-made MARK point image as a template for CCD positioning identification.

3. The novel positioning method for CCD image recognition by screen printing according to claim 1, wherein the angular deviation and the distance deviation in step (c) are calculated from MARK points on the PCB (9) and the screen (5).

4. The novel positioning method for silk-screen printing CCD image recognition according to claim 1, wherein the image matching in step (d) is realized by template matching recognition.