ES2363284B1 - BINARY ACTIVE LIGHTING SYSTEM - Google Patents

Abstract

Binary active lighting device for transparent parts with flat or curved surfaces comprising a source of lighting and means capable of generating a binary pattern of alternating light and dark stripes, characterized in that the means capable of generating the binary pattern are a panel mesh LCD and lighting source is of great luminance. Thanks to the fact that the system incorporates an LCD mesh, data processing is facilitated and the system is given more dynamism in terms of strip size, etc.

Description

Binary active lighting system.

Field of the Invention

The present invention applies to the field of inspection of parts using computer vision systems. In particular, it applies to the inspection of transparent parts.

Background of the invention

For a satisfactory surface quality control on transparent objects, it is necessary to characterize what types of defects are interested in detecting and of course the geometry and material of the surface under inspection.

An example of transparent surfaces to be inspected would be the lenses of the vehicle projectors, which are transparent and have a convex shape with some flat regions or very little curvature. These areas are located, essentially, in their parts seen, so the level of quality of the finish, that is, the absence of defects, is extremely important.

The inspection of transparent parts is a complicated task, since the environment must be perfectly controlled so as not to have unwanted reflections. Using the appropriate lighting system it is possible to obtain an image without reflections in which the characterization of defects is possible.

The selection of a suitable lighting system for an application based on computer vision requires an experimental phase in which the type of lighting to be tested will depend on the characteristics of the application we are interested in solving. Most industrial vision systems relate to one of the following types of inspection:

one.

Dimensional quality inspection.

2.

Surface quality inspection.

3.

Component assembly inspection.

Four.

Operational quality inspection (correct operation).

Considering these types of parts to be inspected, it is important that the lighting system is diffuse to avoid as far as possible shadows and reflections that may hinder the process of extracting the defect in the image captured by the vision sensor.

As in the case of transparent surfaces, the reflectants also have problems of unwanted reflections but their automatic inspection has been studied in greater depth. A widely used lighting technique is structured lighting (Aluze, D., 2002; Puente León, F. & Kammel, S., 2006; Leopold, J. et al., 2003; Seulin, R., 2001; Seulin, R., 2002). Imperfections on a surface cause significant deviations in the reflection of light and this property is used to detect them. Structured lighting is of a binary type and is composed of a succession of strips without light intensity and with maximum intensity. Under these conditions, a defect appears in the captured image as a set of white pixels on a dark background. In these systems, mechanical devices are used to move the strips, which makes them less flexible.

Among the existing lighting systems in the market, those that in principle could be able to highlight defects on transparent surfaces would be:

to. Diffuse backlight system (based on fluorescent or LED)

In this form of illumination, the sensor is directed directly to the light source, observing a completely uniform white surface. Any object interposed between the sensor and the light source produces a shadow that is detected by the sensor as a black shape on the white background. This type of lighting is usually used for the detection of impurities in transparent or translucent objects. However, the disadvantage of this system is that it is only possible to characterize the types of non-transparent defects such as blackheads and grease spots.

b. Low angle diffused lighting systems (also called dark field)

It consists of a high intensity direct light that is struck at a very high angle to the normal of the surface under inspection. In this way, it is achieved that on surfaces that have crevices or elevations, they interfere with the light path, producing bright areas. A typical application in which it is used is to highlight imperfections and contours on flat surfaces. In this case, the disadvantage of this system is that if it is applied to transparent objects, with areas of less curvature, it only manages to highlight surface dirt such as dust spots.

Another referenced lighting technique (Dallas et al., 2003 and Rosati et al., 2008), which is used when characterizing defects on curved reflective surfaces, does not use structured lighting and a mirror system that allows the image to be concentrated. re fl ected in the vision sensor. To detect transparent defects on surfaces that are too, using structured lighting techniques, it is essential that the CCD camera is saturated, and for this to occur, high exposure times are required. This would not allow its applicability at the industrial level, since the image acquisition time, and therefore the cycle time, would prevent the inspection process from being carried out within the defined times to obtain the established rates.

Object of the invention

The invention aims to alleviate the technical problems mentioned in the previous section. To do this, it proposes a binary active lighting device for transparent parts that comprises a source of lighting and means capable of generating a binary pattern of alternating light and dark stripes, where the means capable of generating the binary pattern are a mesh of an LCD panel and the source of illumination is of a luminance between 100 and 50,000 lux. The device may further comprise a light diffuser and / or a thermal insulator (composed for example of a double glass separated by air) between the light source and the LCD mesh. The lighting source may be for example a plurality of LEDs or a plurality of fluorescent tubes.

The mesh of an LCD panel (liquid crystal) consists essentially of:

-

Switching power supply

-

Liquid crystal panel (LCD), which can also incorporate thin film transistor (TFT) technology.

-

Electronic card / s for processing and conditioning the control signals of the liquid panel.

-

Digital data interface (for example: DVI, HDMI ...) or analog (e.g. VGA).

The device the invention incorporates a backlight system based on this LCD system that is subsequently illuminated. Subsequently, the images captured by the computer vision system in charge of performing the inspection are processed in order to achieve an aspect image in which the defects are characterized. .

The fundamental advantage of this binary active lighting system compared to other systems is the high flexibility offered by an LCD as a light source, facilitating its application to automated defect characterization systems. The orientation, size of stripes, lag between stripes in consecutive images and even the possibility of setting up a uniform background make the same lighting system suitable for detecting transparent defects of various sizes, orientations and even non-transparent defects, if the Stripless system, acting as a conventional backlight system.

In addition, with the proposed system, it is possible to easily configure, at the software level, the optimal strip pattern to be able to show defects of different size, orientation and typology. This is another advantage of the proposed system with respect to other previous systems, since to make this type of adjustment it was necessary to structurally modify the lighting device with the consequent economic cost.

The second advantage of this system is its light output, which allows it to reduce the detection and characterization times of defects.

Another of the advantages offered by this system is that it eliminates the need to use previous simulation systems that allow optimizing the number and size of strips that the definitive lighting system should have, since the system itself serves as a platform for experimentation for the adjustment of said parameters.

Finally, one last advantage of this lighting system is that it significantly reduces the computational cost necessary to process the images captured by the vision system.

Brief description of the fi gures

In order to help a better understanding of the features of the invention in accordance with a preferred example of practical realization thereof, the following description of a set of drawings is attached, where the following has been represented by way of illustration:

Figure 1 is a diagram of the device of the invention and its placement with respect to the surface to be studied.

Figure 2 is a flow chart of the defect characterization process.

Figure 3 describes the physical principle of defect detection with structured light.

Detailed description of the invention

The present invention raises as a solution to the technical problems raised above using an LCD mesh (liquid crystal panel with a switched power supply, electronic card for signal processing and conditioning and a digital data interface), to which You have placed a light source on its back. This can be formed, for example, by high-frequency fluorescent, or LEDs, to which a diffuser could subsequently be interposed between the LCD and the light source. The different elements of the device (9) can be seen in Figure 1. The light source (1) and the LCD screen (3) can be accompanied by a diffuser and / or thermal insulator (2). The emitted light (4) becomes diffused light (5) thanks to the fi lter performance. This becomes structured light (6) as it passes through the mesh (3). After passing through the object to be inspected (7) the light is collected by the computer vision camera (8).

The lighting source should be of high luminance, in a lighting range between 100 and 50,000 lux and as homogeneous as possible to avoid specific concentrations. It is also interesting that it does not reach high temperatures so as not to damage the LDC mesh that is positioned next to it. One option would be the use of lighting based on high intensity LEDs, in which case, and because it is a point lighting, it would be advantageous to use a diffuser. Another option would be the use of conventional fluorescent high luminance which could also include a diffuser and a thermal insulator, since they reach high temperatures but are cheaper than other systems. In this, the possibility of including a transparent or diffuse thermal fi lter between both the mesh and the fluorescent should be considered. The fi lter can be composed for example of a double crystal separated by air. The diffuser is made of a non-opaque material that allows the received light to be homogenized.

The operation principle of the invention is described in more detail below:

Figure 3 shows the physical principle of defect detection by structured light, that is, with light (5) and dark stripes (6), and the type of image that the vision sensor (1) would obtain. In the event that there was no defect

(4) On the surface, the refraction of the light does not reach the unlit strip. On the contrary, if there is a defect (2, 3), the refraction of the light will reach the unlit strip and the defect would appear as a set of illuminated pixels in the black strip. In addition, for the defect to appear contrasted and the processing algorithms necessary to characterize it are simplified, it is convenient to saturate the vision sensor.

The invention proposes to use an illuminated LCD mesh. This represents a great advantage over previous systems, since the LCD system in cooperation with a high luminance light source, in the range of 100 to 50,000 lux, offers greater flexibility than mechanical systems, with no limitations on the time to set and move the stripe pattern or even remove it and place a white background.

To ensure the detection of any defect in the sensor's field of vision, the strip pattern must scan all of this surface. For the types of non-transparent defects that might be interesting to detect as well (black dots and other spots), it would be interesting to have a backlight system without stripes. In our case, the invention provides a more efficient lighting system as it also offers the following advantages:

•

Have a dynamic strip pattern configurable in orientation and size (especially width).

•

Having the possibility of eliminating the strips to, illuminating with white light, detect opaque defects.

•

Greatly reduce overexposure times by overlighting the object.

The proportion between the width of strips of different luminance allows to detect defects of different sizes. This ratio will be adjusted to highlight the smaller transparent defect that we are interested in inspecting.

The method used to achieve the characterization of transparent aesthetic defects using the proposed lighting system is shown in Figure 2.

First, the binary lighting must sweep the field of vision of the camera, therefore alternating the capture of images with the movement of stripes. All captured images are made up of what is called aspect image. In this image the background appears in an intermediate gray level and the defects in a very high gray level. Being so contrasted, segmentation (division of the image into regions that have similar attributes or properties) does not require complex processing techniques and will only be applied to areas of the image that have no borders, defined as regions of interest. (ROIs). Once the defects in the image are segmented, the transparent object should be accepted or rejected based on the dimensions of the defect and the area of the glass in which it was detected.

Obtaining the aspect image

Define binary dynamic illumination as a periodic square waveform that must be displaced N times so that the width of the white strip Tb covers the entire period.

Being

•

Δ: Offset between stripes in two consecutive images

•

α: Duty cycle,

the homogeneous background of the aspect image will be obtained by averaging (M) the N outdated square waveforms Δ.

Since dynamic lighting is achieved with a monitor, the minimum displacement between strips will be that corresponding to a pixel. The lower the offset between strips, the lower the intensity level will be in the aspect image, resulting in a lower contrast between the defects and the background; however, the homogeneity of the fund will increase. The vision system of the invention is also not subject to the inaccuracies of movement of the mechanical system. The appearance images obtained with the monitor and movements between unit strips are of a background homogeneity that allows to avoid the preprocessing of the image before performing the segmentation of defects, greatly reducing the computational load of the image processing.

In addition we define:

If we consider a single period we will have: Expressing p (x) of the sign function we will have:

The homogeneity of the intermediate gray level is critical when it comes to segmenting defects in the aspect image, so to obtain an aspect image with a homogeneous background, in which the defects appear contrasted, it is essential to consider the following parameters:

•

White stripe size.

•

Period of the fringes.

•

Offset between stripes in consecutive images.

At most the offset can reach the size of the white strip. In this way the number of images necessary to compose the aspect image will be smaller but the background of it will not be uniform.

The homogeneity of the image (h) can be obtained from the equation (Seulin, R., 2002):

Where MyN are the dimensions of the image, μ the level of average intensity in the image and f (x, y) the level of intensity of the pixel x, y. The closer it gets, the greater the homogeneity of the image.

Therefore, with the proposed system, it is possible to easily configure, and at the software level, the optimal strip pattern to be able to show defects of different size, orientation and typology. This is another advantage of the proposed system with respect to other previous systems, since to make this type of adjustment it was necessary to structurally modify the lighting device.

In addition, the proposed system eliminates the need to use previous simulation systems that allow optimizing the number and size of strips to be counted by the definitive lighting system, since the device of the invention serves as a calibration platform for the adjustment of these parameters. Calibration is performed depending

20 of the type of defect to be found, since the size of the strips is directly proportional to that size.

Claims (5)

1. Binary active lighting device for transparent parts comprising a lighting source (1) and means capable of generating a binary pattern of alternating light and dark stripes (3), characterized in that 5 the means capable of generating the binary pattern are a mesh of an LCD panel and the illumination source is of a luminance between 100 and 50,000 lux. 2. Device according to claim 1 characterized in that it further comprises a light diffuser (2) between the light source (1) and the LCD mesh (3). 3. Device according to any of the preceding claims characterized in that it comprises a thermal insulator between the light source (1) and the LCD mesh.

Device according to claim 3 characterized in that the thermal insulator is composed of a double glass separated by air.

5. Device according to any of the preceding claims characterized in that the lighting source is a plurality of LEDs.

Device according to any of claims 1-4 characterized in that the source of illumination is a plurality of fluorescent tubes.

SPANISH OFFICE OF PATENTS AND BRANDS SPAIN REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl. See Additional Sheet twenty-one Application No.: 200930628 22 Date of submission of the application: 27.08.2009 32 Date of priority: RELEVANT DOCUMENTS

 Category

 Documents cited  Claims Affected

x

US 2008111989 A1 (DUFOUR CHRISTIAN ET AL.) 05/15/2008, 1.2

Figure 1, paragraph [11].

Y

   3-6

Y

US 2007 081344 A1 (CAPPAERT BART ET AL.) 04/12/2007, 3-6

Figure 14, paragraphs [107-109]; paragraph [4].

TO

US 2005035311 A1 (ASAKAWA JIN ET AL.) 02/17/2005, 2

paragraphs [14-15]; paragraph [78].

  Category of the documents cited x: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

  This report has been produced � for all claims � for claims No:

 Date of realization of the report 13.07.2011

 Examiner R. Molinera de Diego  Page 1/5

TECHNICAL STATUS REPORT CLASSIFICATION OBJECT OF THE APPLICATION G01N211958 (2006.01) G01N21188 (2006.01) G01811125 (2006.01) G01811130 (2006.01) G02F1113 (2006.01) Minimum documentation sought (classification system followed by classification symbols) G01N, G01B, G02F Electronic databases consulted during the search (name of the database and, if possible, search terms used) INVENTIONS, EPODOC  WRITTEN OPINION Date of Written Opinion: 13.07.2011 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims 1-6 YES

Claims

NO

Inventive activity (Art. 8.1 LP11 / 1986)

Claims YES

Claims 1-6

NO

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Basis of Opinion.- This opinion has been made on the basis of the patent application as published.  WRITTEN OPINION 1. Documents considered.- Below are the documents pertaining to the state of the art taken into consideration for the realization of this opinion.

Document

Publication or Identification Number Publication Date

D01

US 2008111989 A1 (DUFOUR CHRISTIAN et al.) 05.15.2008

D02

US 2007 081344 A1 (CAPPAERT BART et al.) 04/12/2007

D03

US 2005035311 A1 (ASAKAWA JIN et al.) 02.17.2005

2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement Of all the documents found, document US 2008111989 A1 is considered to be the closest to the state of the technique, from now on it will be named as D1. US 2007081344 will be named as D2. The claims of the application are then compared with this document.  First claim Document D1 shows a binary active lighting device for transparent parts (see paragraph 11) comprising a lighting source (100) and means capable of generating a binary pattern of alternating light and dark stripes (100), in which the means capable of generating the binary pattern are a mesh of an LCD panel. Therefore, the first claim of the application analyzed presents the following differences with respect to document D1:

-

First difference: document D1 does not separately contemplate a source of illumination and a liquid crystal display. Regarding this first difference, it is necessary to indicate that the document D1 has the illumination source integrated into the liquid crystal display device or LCD itself. Therefore, the aforementioned difference would not have a technical effect on document D1. The objective technical problem in this case would be how to find an alternative to the structural solution contemplated in the first claim. Said constructive variant is considered within the scope of the usual practice followed by the person skilled in the art on the date on which the application was filed, since it is known that modern LCD screens are constructed with an internal light source that is usually the first layer of the bottom of the panel.

-

Second difference: the first claim of the application indicates that the source of illumination is of an illuminance between 100 and 50,000 lux. It is considered that this difference with respect to document D1 consists in the selection of a range that has no unexpected effects or properties. In addition, the reading of the request does not reveal details that justify the choice of such range of values and the choice of such value would be arbitrary. Therefore, the first claim would lack inventive activity and as set forth in Article 8 of the Spanish Patent Law, Law 11/1986 of March 20.

 Second claim Document D1 does not show a light diffuser between the lighting source (100) and the LCD mesh (100). It is considered that the fact of integrating a diffuser between the illumination source and the LCD mesh is something belonging to the common technical knowledge and its implementation in document D1 would be evident to a person skilled in the art on the date of the request. To support this statement, it is sufficient to address, for example, the document cited with category A in report US2005035311, which discloses a diffuser located on LEDs to obtain diffused light, transmitting a light with a uniform brightness distribution, avoiding shadows and reflections. Therefore, the second claim would lack inventive activity.  Third claim Document D1 does not show a thermal insulator between the light source and the LCD mesh. The technical effect of this difference is that the passage of heat generated by the light source towards the LCD mesh is avoided. The problem of heat generated by the light sources of these applications is well known. Therefore, the identification of this problem or would involve preventive activity. The opposite solution would also be timeless to preventive activity. Document D2 (Figure 14, paragraphs 0107 and 0108) collects a thermal insulator between the light source and the LCD screen. The combination of D1 with D2 would not involve inventive activity: both documents belong to the same field of state of the art, liquid crystal displays or LCDs. Therefore, the inclusion of the thermal insulator between the light source and the LCD mesh of document D1 would be apparent to one skilled in the art, and the third claim would lack inventive activity. WRITTEN OPINION  Fourth Claim Document D2, although it does not specifically show a thermal insulator composed of a double glass separated by air, if it shows a thermally insulated cavity or air chamber that is mounted around the LCD panel. Enter the source of light and and the LCD panel is located a thermal barrier (75) that includes walls that have transparent parts with the aim of allow the passage of light, also indicates that they can be made of glass to increase resistance. Therefore this feature provides the same advantages as in the present application. For all the above, the fourth claim would lack inventive activity.  Claims � fifth and sixth Document D2 shows that the source of illumination is a plurality of LEDs or fluorescent lamps. For this reason, the fifth and sixth claims would lack inventive activity. As indicated in article 5.2.c of Regulation 2245/1986 for the execution of the Patent Law, and in order to obtain a better understanding of the invention, it is suggested that in the later stages of the procedure an indication of the documents D1 and D2, commenting on the most important contribution they make to the state of the art. Such indication cannot extend the object of the invention, as originally presented.