WO2006128317A1

WO2006128317A1 - Method for illumination, and illumination arrangement

Info

Publication number: WO2006128317A1
Application number: PCT/CH2006/000297
Authority: WO
Inventors: Joachim Schwarz; Johann HÄRTL
Original assignee: Elpatronic Ag
Priority date: 2005-06-03
Filing date: 2006-06-01
Publication date: 2006-12-07

Abstract

The invention relates to a method and an illumination arrangement (10) for illuminating picture areas (8) for recordings of frame sequences by a sensor head (9) with a frame repetition time of 60 ms or shorter and with an illumination period of no more than 20 s per pulse, said method providing a total light intensity of at least 5 W on a picture area of 1 cm2. It comprises a multiplicity of individually activatable light sources (12) of suitable light intensity with surface-emitting laser diodes, of which those light sources (12) which provide optimum illumination for the picture area (8) can be selectively activated for each pulse of a frame sequence.

Description

Method of lighting and lighting arrangement

Reference to related applications

This application claims priority to Swiss Patent Application No. 00936/05, filed Jun. 3, 2005, the entire disclosure of which is hereby incorporated by reference.

background

The invention relates to a lighting method and a pulsable illumination arrangement for illuminating image areas for taking pictures of image sequences by a sensor head according to claim 1 or claim 8.

State of the art

In the industry lighting systems are used in many places, for example for the optical

Quality check of technical processes. Laser welding seams have been optically checked for defects in the weld seams for years. Just behind a laser, which connects the sheets to be welded together, a sensor head is mounted for this purpose, which takes pictures sequentially with an image area of about 10 x 10 mm. These image sequences are then optically-evaluated. First, the welds and then on the welds, the defects that appear through black dots must be recognized. At a relative running speed between the laser with the sensor head and The sheets to be welded from 20 to 50 cm / s thus result in very short image repetition times. These are usually 40 to 60 ms, but can also be shortened to 10 ms in special cases. The recording time of the sensor head is about 2 ms. The remaining time until the next pulse is used for the transmission and evaluation of the data and for the feed until the next image section is within the field of view of the sensor head. During the recording time of 2 ms, the respective image section must be illuminated. This is done with a very short pulsed illumination system of at most 20 μs, preferably between 5 and 10 μs. This ensures that the images are sharp and not blurred by the continuous relative motion between the sensor head and the image surface.

According to the prior art, the light of a sufficiently bright xenon flash lamp is used for the illumination and projected onto the image plane by means of light guides. The design of the light guide allows it to be mounted on both sides with respect to the direction of movement of the sensor head next to this and directed vertically downwards. They are located approximately halfway between the image surface and the sensor head. These lamps allow a pulsed illumination in the required intensity of at least 5 W / cm ^, preferably about 10 W / cm2 in the required pulse times and repetition rates. Lighting arrangements are known from DE-C-101 17 048, US-A-5,365,084, US-A-5,264,678, DE-U-20004 014797, US-A-5,978,090, DE-A-195 05 832, EP-A-0 431 751, EP-AI 455 179 and US-A-205/0041852.

However, fault detection becomes problematic when the weld seam connects two unevenly thick sheets. In this case, the weld seam itself is no longer horizontal, but is located in an angled to the horizontal connecting surface of the sheets. The light is at this angled weld from the sensor head scattered so that it appears dark for the sensor head. Although this facilitates the seam finding, since the seam appears much darker than the horizontally lying sheets, but makes it difficult to find the flaws, since these differ in color hardly from the seam.

Presentation of the invention

The object of the invention is to describe a method and a lighting arrangement which, independently of the individual sheet thicknesses used, always illuminates each image surface optimally for each image of an image sequence in such a way that both the seam and the defects can be found well.

This object is achieved by a method or a lighting arrangement according to the features of claim 1 or 8. The method or the illumination arrangement serves to illuminate image areas for taking pictures of image sequences of a step forming welds. The recording is carried out in particular by a sensor head with a picture repetition time of 60 ms or shorter and with an illumination duration of at most 20 μs per pulse and delivers a total light intensity of at least 5 W on a screen of 1 cm 2. A multiplicity of individually activatable light sources are used which have surface-emitting laser diodes, wherein for each pulse of an image sequence those light sources can be optionally activated which optimally illuminate the image area or so that the contrast between the weld seam and possibly existing defects is maximum is. Brief description of the drawings

The invention will be described in more detail with the aid of the drawings. Showing:

Fig. 1-4: In each case a profile through two connected to a weld sheets of different thickness with incident and reflecting light beams with different angles of incidence of the light sources; Fig. 5-8: In each case an image taken at a sensor head of a corresponding configuration;

Fig. 9: A profile through two with a

Weld bonded panels with an inventive lighting system and a sensor head; and Fig. 10: a module with it mounted

Light sources.

Ways to carry out the invention

Fig. 1 shows a profile through two connected to a weld seam 2 sheets 1, 2, wherein the one sheet 1 is thicker than the other sheet 2. The arrows 5 in the sheet direction denote incident, which deflected away from the sheets arrows 6 light rays.

It can be seen from FIG. 1 that the light beams 5 impinging on the weld seam 3 are not reflected perpendicularly like the other light beams striking the sheets 1, 2, but are deflected at a certain angle according to the arrow 7. FIG. 2 represents the same facts as Fig. 1 with the only difference that the thickness difference of the sheets 1, 2 is greater. As a result, the light beams 7 reflected at the welding seam 3 are deflected considerably more strongly from the normal. Figures 5 and 6 illustrate the corresponding images taken by a sensor head on the respective image surfaces.

The sheets 1, 2 are very bright in both pictures, since the reflected light beams 6 directly to the

Get sensor head. The weld seam 3 is to some extent easily recognizable in FIG. 5 as a gray stripe, and in FIG. 6 as a black stripe even very well. A defect 4 will appear on a picture as a black dot. Such a point is still fairly well recognizable in FIG. 5, but hardly any longer in FIG.

An alternative illumination system, shown in Fig. 3 and 4, illuminates the sheets 1, 2 at a 45 ° angle, wherein the difference of the sheet thicknesses 1, 2 in Fig. 3 and small in Fig. 4 is larger, according to Fig. 1 and 2. It can be seen from the figures that the light rays 7 reflected at the weld seam 3 hardly reach the sensor head in the arrangement according to FIG. 3, which is arranged (not shown) perpendicularly above the weld seam 3. The in Fig. 4 at the

Weld seam 3 reflected light rays 7, however, can be very well recognized.

FIGS. 7 and 8 again show the corresponding images which can be picked up by a sensor head on the corresponding image surfaces.

The sheets 1, 2 are very dark in both images, since the reflected light beams 6 hardly reach the sensor head. The weld seam 3 is barely discernible in FIG. 7 as a dark gray stripe, but is very good in FIG. 8 as a light stripe. A defect 4 in turn appears as a black dot in appearance. Such a point 4 is only weakly recognizable in FIG. 7, but again very good in FIG. 8, since the contrast from the weld seam 3 to the fault point 4 is optimal.

It is therefore desirable to illuminate the sheets 1, 2 at a certain angle, so that they are in the Picture to be displayed in black. However, the weld seam 3 should be able to be displayed as light as possible, so that a defect 4, which always appears black, can be recognized simply and reliably by maximum contrast to the weld seam 3. The optimum angle of incidence accordingly changes with the difference in thickness of the sheets 1, 2: the greater the difference in thickness, the more the optimum irradiation direction 5 of the illumination system must deviate from the normal. It should be noted that different thicknesses are connected to one another in a weld seam 3, so that the optimum irradiation direction 5 changes during a weld seam.

The inventive method or arrangement solves the problem with immovable components, apart of course from the movement in the direction of the weld 3. A movable lighting system would have to meet very high mechanical requirements in view of the high image repetition rate in order to always be in the correct position ,

FIG. 9 shows an example of a lighting arrangement 10 according to the invention, which can illuminate an image area 8 in the area of a weld seam 3 between two sheets 1, 2. In the middle above the weld seam3, a sensor head is received at a distance of about 10 mm along the entire weld seam.

The arrangement 10 is arranged approximately in the middle between the sensor head 9 and the image surface 8 and consists of a plurality of light sources 12, which are arranged on both sides of the sensor head 9 in the direction of the weld seam 3. A typical distance to the sheets 1, 2 is 30 to 50 mm. These light sources 12 are all directed onto the image surface 8 and are preferably arranged on a circular arc at different angles of incidence with respect to the image surface 8. Depending on the angle of the surface 3 of the

Welding seams are preferably made of other of these light sources. len 12 used to 'optimal lighting to achieve. The image area is approx. 10 x 10 mm.

In this embodiment, 6 such light sources 12 are shown on both sides. You can also choose any other number between 2 and 10. In this advantageous embodiment, two light sources 12 were combined to form a module 11, as shown in FIG. Alternatively, for example, all the light sources 12 can be combined in one, two or four modules, or each light source 12 can be mounted individually in the illumination system 10.

These light sources 12 must meet very high requirements. They must be pulsatile with a pulse repetition time of 60 ms or shorter, with the

Duration of illumination may not exceed 20 μs, preferably between 5 and 10 μs. In addition, the light intensity must be so strong that each image is illuminated with about 10 W. For example, these 10 watts can be distributed over four light sources 12. In this case, every light source 12 must provide 2.5W.

Such a light source 12 is achieved by diode lasers, also called semiconductor lasers, wherein surface-emitting laser diodes are used. Preferably, diodes in which multimodes are used, so that no interference occurs because they could disturb the image analysis as bright points. Surface emitting laser diodes are known by the name VCSEL (Vertical Surface Emitting Laser). These are semiconductor lasers that emit their light in a cylindrical beam vertically from the semiconductor wafer. These lasers are used for optical communication and can operate, for example, in wavelengths of 780 nm and 850 nm. The light sources 12 are very powerful and consist of a plurality of laser diodes 13, which are arranged for example in a row or in a circle. For example, a light source 12 includes about 30 to 70, preferably 50 laser diodes 13 in a row to about 10 mm in length.

The diode lasers can be flexibly arranged at any angle of incidence and switched from image to image. As a result, for each image, those of the light sources 12 can be activated, which overall result in optimum illumination of the weld seam 3 for the sensor head, so that, on the one hand, these are easily recognizable in the weld seam compared to the sheets 1, 2 and, on the other hand, a fault location 4 is.

This switching from image to image can come about in several ways. For example, the illumination arrangement 10 can have stored, predetermined data for each pulse of an image sequence which contain the information of the light sources 12 to be activated in order to optimally illuminate the image area 8. These data can be determined in a series production in advance in test runs. For this purpose, in addition to the weld seams 3, a certain number of triangulation points on the sheets 1, 2 are measured in the pictures, on the basis of which the relevant geometries, in particular the differences in thickness of the sheets 1, 2 and / or the inclination of the weld seam 3, are determined can. From these data, the optimal illumination directions are determined and those light sources 12 are determined which are to be activated for the respective pulse. These data are then stored and made available at each repetition of the same welding process, for the control of the inventive lighting system.

Another possibility is the interactive determination of the optimal lighting. For this purpose, the arrangement contains a controller which, for each pulse of an image sequence on the basis of evaluations of at least one previous image, can interactively determine the information about those light sources which optimally illuminates the respective image area. For the first Picture is a default setting. For this purpose, triangulation points on the metal sheets 1, 2 are measured in the same way as in the first example and evaluated to determine the light sources 12 to be activated for each pulse. In contrast to the first example, this determination and evaluation is performed interactively. The necessary data for a pulse are obtained from the evaluations of one of several data previously determined in the same image sequence. This allows individual adaptation and is desirable above all for large fluctuations in the sheet metal parameters.

While preferred embodiments of the invention have been described in the present application, it is to be understood that the invention is not limited thereto and may be practiced otherwise within the scope of the following claims.

Claims

claims

1. Method for illuminating a picture surface

(8) comprising a weld seam (3) which connects two sheets (1, 2) of different thicknesses by means of a lighting arrangement (10) with a plurality of pulsably operable light sources (12) for taking up image sequences of the weld seam by means of a sensor ( 9), wherein each light source (12) comprises a plurality of surface emitting laser diodes (13), the light sources (12) are individually activated and for each pulse of an image sequence at least one light source is activated, the at least one light source or more light sources activated is or become that the image surface (8) is illuminated so that the contrast between the weld seam (3) and defects (4) of the weld is maximum.

2. The method of claim 1, wherein the recording of the image sequences with a repetition time of 60 msec or shorter and with an illumination duration of at most 20 microseconds per pulse and a light intensity of at least 5 watts on an image area (8) of 1 cm ^ follows ,

3. The method of claim 1 or 2, wherein the illumination arrangement comprises stored predetermined data indicating which light sources (12) are to be activated for each pulse of an image sequence.

4. The method of claim 1 or 2, wherein for a pulse of an image sequence based on the evaluation of at least one previous image of the image sequence to be activated light sources are determined.

5. The method of claim 1, wherein the laser diodes (13) are multimode laser diodes.

6. The method according to any one of claims 1 to 5, wherein the light sources (12) on two sides of the sensor head (9) are arranged.

7. The method according to any one of claims 1 to 6, wherein each of the light sources (12) is designed in a line having a certain angle of incidence to the image surface (8).

8. Pulsable illumination arrangement (10) for illuminating image areas (8) for taking picture sequences by a sensor head (9) with a picture repetition time of 60 ms or shorter, with a lighting duration of at most 20 μs per pulse and a total light intensity of at least 5 W on a picture surface (8) of 1 cm ^, wherein the arrangement consists of a plurality of individually activatable light sources (12), of which for each pulse of an image sequence those light sources (12) can be activated, which the image surface (8) optimally illuminate, each light source (12) comprises a plurality of surface emitting laser diodes (13).

9. Illumination arrangement according to claim 8, wherein the laser diodes (13) are multimode laser diodes.

10. Lighting arrangement according to one of claims 8 or 9, wherein the light sources (12) on two sides of the sensor head (9) are arranged.

11. Lighting arrangement according to one of claims 8 to 10, wherein each of the light sources (12) is designed in a line having a certain angle of incidence to the image surface (8).

12. Lighting arrangement according to claim 11, wherein in each line between 30 and 70 laser diodes are arranged.

13. Lighting arrangement according to one of claims 8 to 10, wherein each of the light sources (12) is designed circular, having a certain angle of incidence to the image surface.

14. Lighting arrangement according to one of claims 8 to 13, wherein the distance from the image surface (8) to the light sources (12) between 20 and 70 mm, preferably 30 to 50 mm.

15. Lighting arrangement according to claim 11 or 12, wherein in each case between 2 and 10 lines of light sources (12) are arranged on two sides of the sensor head (9).

16. Illumination arrangement according to one of claims 8 to 15, wherein the arrangement has stored, predetermined data for each pulse of an image sequence containing the information of the light sources (12) to be activated in order to optimally illuminate the image surface (9).

17. ^• lighting arrangement, which second for each and another pulse, at least one previous image to determine an image sequence on the basis of evaluations, the details of those light sources (12) interactively according to any one of claims 8 to 16, wherein the assembly includes a controller, which the respective image surface (8) optimally illuminates.

18. Lighting arrangement according to one of claims 8 to 17, wherein the illuminated image area is about 10 mm x 10 mm.