WO2012007782A1

WO2012007782A1 - Device for the micro-inspection of flat surfaces and method of use

Info

Publication number: WO2012007782A1
Application number: PCT/IB2010/001740
Authority: WO
Inventors: Antonio Jose Sanchez Salmeron; Carlos Ricolfe Viala
Original assignee: Ppg Iberica, S.A.
Priority date: 2010-07-15
Filing date: 2010-07-15
Publication date: 2012-01-19

Abstract

Device for the micro-inspection of flat surfaces and method of use, specially conceived to automatically perform micro-inspection of micro characteristics in flat surfaces coated with paint or other coatings, the device has a transport system (3) equipped with stabilization and mobilization means for the plate (6) to be analyzed, on which a lighting system is established (2) and a vision system (1), with means to capture images with a resolution that allows the detection of the smallest defects intended to be analyzed. A control system (4) coordinates the acquisition of the image with the transport system, providing a complete image of the plate (6), while an analysis system (5), equipped with image processing means detects the defective areas of the plate surface (6). In order to do so, the method used is based on the analysis of variations of luminosity in the columns of pixels that form the image.

Description

DEVICE FOR THE MICRO-INSPECTION OF FLAT

SURFACES AND METHOD OF USE

BACKGROUND OF THE INVENTION

[0001] It is common knowledge that, in the painting industry, superficial defects occur in the finishing and application phases. Craters are one of the most common defects, and probably one of the most difficult ones to solve. A crater is a depression in the coating that occurs in the presence of a contaminant of low superficial tension on or under the paint. The paint draws back from the low superficial tension area, leaving a circular defect. The size of the same may vary from 1 mm to 0.001 mm.

[0002] The increasing demand for greater quality in the industry requires exploring the mechanization processes to achieve stability in the procedures repeated.

[0003] However, up until now, the process for detecting defects in paint has been performed by means of a visual inspection, carried out by several qualified workers, of a plate on which the mix to be analyzed is extended, so that they proceed to detect the number of micro defects and the size thereof within the surface of the plate.

[0004] Obviously, this process is tedious, repetitive but delicate, so the result is conditioned both by the worker performing the inspection and the time of the shift in which it is made, and the analysis conditions existing at the time of the inspection. As a consequence of this inspection, the finished product batch can be rejected, or accepted with the significant risk of rejecting a well finished product or accepting a defective product.

[0005] Currently there is no mechanism in the market allowing performance of these operations in a totally automatic manner, thereby avoiding the above described human factor.

SUMMARY OF THE INVENTION

[0006] This invention refers to a device specifically conceived to perform, fully automatically, the micro-inspection of micro-characteristics in flat surfaces, understanding as micro-characteristic a feature in the flat surface of a size in the order of micrometers.

[0007] The device which is the object of the invention is applied in the sector of industrial chemical processes, where it is necessary to control the properties of the mix based on the aspect of the same when applied to flat surfaces. The aspect may change with the formation of micro-pores or micro-cracks in the surface, produced by an unbalanced mix. The visual micro inspection device includes means that analyze the mix that has been previously extended on a flat surface. [0008] An aspect of the present invention is to provide a device for the micro- inspection of flat surfaces comprising a plate to which a coating has been applied, the device comprising a transport system including stabilization and mobilization means for the plate to be analyzed, a lighting system for illuminating the plate, a vision system for capturing images of the plate including means for capturing images with a resolution that allows the detection of small defects, a control system which coordinates the acquisition of the images with the transport system to provide a complete image of the plate, and an analysis system including image processing means to detect defective areas of the plate surface.

[0009] The invention also concerns the method to use such device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] To illustrate the description being made and for the purposes of better understanding the characteristics of the invention, in accordance with a preferred example of the practical embodiment thereof, attached as an integral part of this description is a set of drawings where the following has been represented, for illustrative purposes and without limitation.

[0011] Figure 1 shows an outline drawing of the different elements that take part in a device for the micro inspection of flat areas performed in accordance with the object of the present invention.

[0012] Figure 2 shows a view in perspective of a plate to be analyzed set on the transport system, being able to observe how the vision and lighting systems are placed in the same.

[0013] Figure 3 shows a plan view with an enlarged detail of one of the images captured by the vision system.

[0014] Figure 4 shows the drawing obtained for the reflection-shadow measured by levels of luminosity within the image of a certain defect.

DESCRIPTION OF THE INVENTION

[0015] . The device for the micro-inspection of flat surfaces proposed in the invention satisfactorily solves all of the above described problems, allowing the performance of a specific and exact analysis of the finished mix and, additionally, allowing to correct imperfections that appear during the manufacturing process. [0016] For such purpose, there is a vision system in the advocated device that captures the images of the surface to be inspected, with a resolution that allows the detection of the smallest defects intended to be inspected.

[0017] The vision system is supplemented with a lighting system that allows highlighting the characteristics of the defects intended to be detected in the surface of the plate. This lighting system works with a frequency higher than the operating frequency of the image capturing system.

[0018] The elements to be inspected will be placed on a transport system in charge of moving the plates to be inspected, so that the entire surface thereof may be inspected through the same. For such purpose, it is planned that the system will incorporate stabilization means for the mentioned plates.

[0019] The vision system and the transport system are linked to a control system in charge of coordinating the acquisition of images with the transport system, in order to obtain a complete image of the plate.

[0020] The device of the invention has an image analysis system that uses image processing methods to detect the defective surface areas according to the previously established characteristics. This system incorporates an interface to interact with the user, which allows reading the results obtained in the invented device.

[0021] More specifically, the transport, vision and lighting systems are coordinated in such a way that the lighting system directs a light to the surface to be illuminated so that a reflection and shadow effect is generated in each defect that appears in the surface, which is captured by the vision system. The transport system is located in such a way that it is possible to obtain focused images of the surface and the generation of reflection-shadow in each defect is as uniform as possible. This way, the control system coordinates the transport and vision systems by moving the surface so that the captured images are ordered in such a way that an image of the entire surface is obtained. Finally, the analysis system contains methods that allow examining the image, looking for the reflection-shadow pairs generated by each defect. The intensity of the reflection-shadow combination is gauged to determine some of the characteristics used to classify the defects.

[0022] Once the invented device is gauged, it is possible to measure the defects of a surface in a standard manner, allowing an exact determination of the parameters that define the defects and achieving a classification thereof in accordance with previously established rules, which shall always be the same, regardless of the worker using the machine. [0023] Therefore, a device is achieved that allows finding craters and mountains in the examined surface, understanding as crater a depression in the surface and mountain as the opposite defect. These are generated by the interactions that take place between the chemical elements of the mix, which is extended on a plate and is submitted to a drying process. The plate painted with the mix to be analyzed is placed in the transport system and the invention device detects the number of craters present therein, as well as their size.

[0024] In accordance with all of the above, the method for using the device is the following:

[0025] - The plate to be analyzed is placed on the illuminated transport system.

[0026] - The plate begins to move and the images are captured, which are ordered successively until the movement stops and the final image is obtained.

[0027] - Through the image obtained, it looks for the reflection/shadow generated in the image from the luminosity of the pixels representing the defect.

[0028] - The lighting of the plate is normalized for this purpose, so that the color of the background is the same in all plates, regardless of the color of the mix being analyzed.

[0029] - From there, variations in luminosity are sought in the pixel columns that form the image, to find the reflection-shadow variation that generates the defect.

[0030] - The size of the defect is measured by the distance existing between the position of the pixel with the greatest luminosity and the position of the pixel with the least luminosity.

[0031 ] - The depth of the same is also measured as the difference between the maximum luminosity and the minimum luminosity in the area of the image that represents the defect.

[0032] - The results obtained are shown in the user interface for the analysis thereof.

[0033] The analysis system is gauged so that the interpretation of the image matches the one that experts in detecting craters would make. The defects detected in the image are classified in accordance with this pre-established criterion.

[0034] In view of the mentioned figures, and particularly Figures 1 and 2, it can be observed that the advocated device comprises a vision system (1), a lighting system (2), a transport system (3), a control system (4) and an analysis system (5), which make it possible to detect and quantify the superficial irregularities presented by a plate (6) coated with a coating such as paint. [0035] More specifically, in one embodiment the vision system (1) is made up of a monochrome lineal camera that provides an 8192 pixel line. The image is formed by the successive alignment of the different lines of pixels. In this specific case, 12000 lines are aligned, obtaining an image of 12000x8192, and 98 Mega pixels. Taking into account an area of 24000 mm² for a plate (6) at the inspection, there is a resolution of 4096 pixels per mm² which allows the detection of faults of an approximate size of a 0.001 mm diameter.

[0036] Regarding the lighting system (2), it incorporates a led based directional source of light. The directionality of the light allows for the better adjustment of the collision angle which permits the generation of the reflection/shadow pair in each of the defects.

[0037] On the other hand, the transport system (3) incorporates a linear axis (7) through which the plate moves (6) in the vertical direction of the same. This transport system has grips that allow holding the plate with the mix extended and dried on the same. In this case, they are a pair of combs (8) with stops (9), combs that open and close so that they adjust perfectly to the width of the plate (6).

[0038] This grip system ensures that the plate will be in a horizontal position at all times, so that the distance between the camera and the source of light to the surface of the plate is always the same. This fixed distance ensures that the reflection/shadow pair generated by each reflection will have the same characteristics for identical defects, and will allow the determination of the size and depth of the defects in the event of variation in the size of the reflection and the shadow.

[0039] Regarding the control system (4), it will be materialized in a PLC that allows control of the lineal axis with the formation of the image. It also manages the interface with the user so that the movement of the plate and the capture of the image begin when the worker places the plate in the gripping combs and presses a button. As a result, the lines of pixels captured in the vision system are ordered successively until movement stops and the final image is obtained.

[0040] The analysis system (5) analyses the image looking for any defects that may appear. The defects appear through the reflection-shadow pair, as it is observed in the enlargement of Figure 3. The analysis method looks for the reflection/shadow generated in the image by the luminosity of the pixels that represent the defect. In first place, there is a process whereby the lighting of the plate is normalized so that the background color is the same in all plates, regardless of the color of the mix that is being analyzed. From there, variations in luminosity are sought in the pixel columns that make up the image, so that they match the reflection-shadow variation that generates the defect. [0041] From this information, graphs are obtained as the one shown in Figure 4, so that line (10) represents the luminosity value at which the color of the mix is normalized and the curve (1 1) represents the nonnalized luminosity values taken by the pixels when a defect exists. The size of the defect can be measured by the distance existing between the position of the pixel with the greater luminosity (12) and the position of the pixel with the least luminosity (13). The depth of the same is also measured as the difference between the maximum luminosity and the minimum luminosity of the area of the image that represents the defect. The results obtained by the analysis system are shown in the interface with the user.

10042] Lastly, as it has been pointed out above, it can be indicated that the analysis system is gauged so that the interpretation of the image matches the one that the experts in crater detection would make, while the defects detected in the image are classified in accordance with this pre-established criterion.

[0043] While various embodiments of the invention have been described herein, it should be apparent, however, that various modifications, alterations and adaptations to those embodiments may occur to persons skilled in the art with the attainment of some or all of the advantages of the present invention. The disclosed embodiments are therefore intended to include all such modifications, alterations and adaptations without departing from the scope and spirit of the present invention as set forth in the appended claims.

Claims

CLAIMS:

1. A device for the micro-inspection of flat surfaces comprising a plate (6) to which a coating has been applied, the device comprising a transport system (3) including stabilization and mobilization means for the plate (6) to be analyzed, a lighting system (2) for illuminating the plate (6), a vision system (1) for capturing images of the plate (6) including means for capturing images with a resolution that allows the detection of small defects, a control system (4) which coordinates the acquisition of the images with the transport system (3) to provide a complete image of the plate (6), and an analysis system (5) including image processing means to detect defective areas of the plate surface (6).

2. The device for the micro-inspection of flat surfaces according to Claim 1, wherein the vision system (1) comprises a monochrome lineal camera.

3. The device for the micro-inspection of flat surfaces according to Claim 1, wherein the lighting system (2) comprises an LED directional source of light.

4. The device for the micro-inspection of flat surfaces according to Claim 1 , wherein the transport system (3) comprises a linear axis (7) along which the plate (6) moves and gripping means for the plate (6) comprising a pair of combs (8) with stops (9) adaptable to a width of the plate (6).

5. The device for the micro-inspection of flat surfaces according to Claim 1 , wherein the control system (4) comprises a PLC that allows control of the movement of a lineal axis of the plate (6) with the formation of the image, and comprises means for the management of a user interface.

6. A method for the use of the device described in any of Claims 1-6, the method comprising:

placing the plate to be analyzed on the illuminated transport system; capturing the images during movement of the plate that are ordered successively until the movement ends and a final image is obtained;

identifying reflection and shadow pairs generated in the images according to luminosity of pixels that represent a defect, wherein lighting of the plate is normalized so that background color is the same in all plates;

identifying luminosity variations in pixel columns that form the image so that they match a reflection and shadow that corresponds to the defect;

measuring a size or depth of the defect according to a distance existing between a position of a pixel with greater luminosity and a position of the pixel with less luminosity; and displaying the results obtained on a user interface for the analysis thereof.