METHOD AND DEVICE FOR INSPECTION OF THE SURFACE OF A MOVING SHEET

Abstract

A method for inspection of a surface of a sheet moving in a direction, in which the surface is illuminated with first and second light sources, with the first light source emitting light under a first incidence angle range onto a first surface area and the second light source emitting light under a second incidence angle range onto a second surface area of the surface of the sheet. The first and second light sources are operated in pulsed fashion in alternation with a stipulated pulse frequency so that the surface of the sheet is illuminated in alternation with the pulse frequency in the first surface area and the second surface area and the first surface area illuminated by the first light source is observable by an inspector via a mirror in the bright field and the second surface area illuminated by the second light source is observable by the inspector via the mirror in the dark field.

Claims

1. A method for inspection of at least one surface of a sheet moving in a sheet running direction by an inspector, in which the surface of the sheet is illuminated with a first light source and a second light source and in which the first light source emits light under a first incidence angle range onto a first surface area and the second light source emits light under a second incidence angle range onto a second surface area of the at least one surface of the sheet, the method comprising: operating the first light source and the second light source in pulsed fashion in alternation with a stipulated pulse frequency so that the at least one surface of the sheet is illuminated in alternation with the pulse frequency in the first surface area and the second surface area and the first surface area illuminated by the first light source is observable by the inspector via a mirror in the bright field and the second surface area illuminated by the second light source is observable by the inspector via a mirror in the dark field.

2. The method according to claim 1, wherein observation of the first surface area and the second surface area occurs by human eye of the inspector without the aid of a camera.

3. The method according to claim 1, wherein the at least one surface includes both a bottom surface and a top surface of the sheet observed by the inspector, in which the first light source and the second light source are arranged to illuminate the top surface and third and fourth light sources are arranged to illuminate the bottom surface of the sheet.

4. The method according to claim 1, wherein the first surface area at least partially overlaps the second surface area.

5. The method according to claim 1, wherein a third surface area of the at least one surface of the sheet is illuminated by a third light source under a third incidence angle range and is observed by the inspector via the mirror in the dark field.

6. The method according to claim 5, wherein the light emitted by the third light source is pulsed and has a beam direction directed obliquely onto the at least one surface of sheet and the beam direction has a component in or against the sheet running direction.

7. The method according to claim 6, wherein the third surface area at least partially overlaps the first surface area and/or the second surface area.

8. The method according to claim 1, wherein the sheet is moved at a stipulated sheet speed, the pulse frequency being adjustable to the sheet speed.

9. A device for inspection of at least one surface of a sheet moving in a sheet running direction, with a first light source and a second light source, in which the first light source illuminates the at least one surface of the sheet under a first incidence angle range in a first surface area and the second light source illuminates the at least one surface of the sheet under a second incidence angle range in a second surface area and the first light source and the second light source are operated in pulsed fashion in alternation with a stipulated pulse frequency so that the at least one surface of the sheet is illuminated in alternation with the pulse frequency in the first surface area and the second surface area, and a mirror is arranged obliquely and at a distance to the at least surface of the sheet, via which the first surface area illuminated by the first light source and the second surface area illuminated by the second light source is observable by an inspector.

10. The device according to claim 9, wherein a reflection surface of the mirror includes an angle in the range of 30 to 60 to the at least one surface of the sheet.

11. The device according to claim 9, wherein a third light source, which emits light pulsed under a third incidence angle range onto a third surface area of the at least one surface of the sheet, in which the light emitted by the third light source has a beam direction directly obliquely onto the at least one surface of the sheet and the beam direction has a component in or against the sheet running direction.

12. The device according to claim 9, wherein the device is arranged for inspection of both a top surface and a bottom surface of the sheet.

13. The device according to claim 9, wherein the pulse frequency lies in the range of 70 Hz to 400 Hz.

14. The device according to claim 9, wherein the first light source and the second light source are operated in alternation in pulsed fashion in stroboscope manner with a stipulated pulse length in the range of 30 s to 100 s.

15. The device according to claim 9, wherein the first light source and the second light source includes a plurality of LED light strips having several LEDs arranged at a distance relative to each other.

16. The device according to claim 15, wherein the LED light strips of the first and the second light source are each arranged one behind the other in a direction running across the sheet running direction of the sheet, in which the light beam emitted by the first and the second light source includes a direction component running across the sheet running direction of the sheet.

17. The device according to claim 11, wherein each of the first, second, and third light sources includes a plurality of LED light strips having several LEDs arranged at a distance relative to each other with the LED light strip of the third light source arranged one behind the other in the sheet running direction of the sheet, in which the light beam emitted by the third light source includes a direction component running in or against the sheet running direction.

18. The device according to claim 17, wherein the LED light strip of each light source runs parallel at a stipulated spacing from the at least one surface of the sheet.

19. The device according to claim 17, wherein each LED light strip has a shutter that covers a visual field of the inspector to the LEDs of the light strip and in so doing prevents blinding of the inspector.

20. The device according to claim 17, wherein the individual LED light strips of the plurality of LED light strips of each light source can be switched on and switched off independently of the other LED light strips.

21. The device according to claim 9, wherein the first incidence angle range lies between 10 and 50 and/or the second incidence angle range lies between 60 and 90.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and additional advantages and features of the disclosure are apparent from the following practical example described below with reference to the accompanying drawings. The practical example then merely serves to explain the disclosure and is not to be viewed as restrictive for the scope of protection of the disclosure defined in the claims. The drawings show:

[0023] FIG. 1: Schematic view of a device for inspection of the surface of a sheet moving in a sheet running direction in a view in the sheet running direction;

[0024] FIG. 2: Depiction of the bright field generated by a first light source of the device of FIG. 1 on the surface of the bottom of the sheet;

[0025] FIG. 3: Depiction of the dark field generated by a second light source and an additional light source of the device of FIG. 1 on the top and bottom of the sheet;

[0026] FIG. 4: Schematic view of the device of FIG. 1 in a view perpendicular to the sheet running direction;

[0027] FIG. 5: Detailed view of the second light source of the device of FIG. 1;

[0028] FIG. 6: Detailed view of the first light source of the device of FIG. 1;

[0029] FIG. 7: Schematic view of an LED light strip used in the device of FIG. 1 to form the light sources.

DETAILED DESCRIPTION

[0030] The device according to the disclosure and the method according to the disclosure can be used by an inspector to inspect the surface of the sheet moving at a stipulated sheet speed in a sheet running direction. The sheet, for example, can be an uncoated steel sheet (blackplate) or a coated steel sheet, like a zinc- or tin-plated steel sheet (tinplate). The sheet can also have on its surface an organic coating, for example, a paint layer or a polymer coating. The device according to the disclosure enables the inspector to detect surface defects on the surfaces of the sheet in the method according to the disclosure. If the inspector detects a defect, the running sheet can be stopped and the defective area in which the detected surface defect lies can be cut out from the sheet. The device according to the disclosure is then expediently arranged at the end of an installation for production or refining of the sheet and before a winding process for winding of the sheet into a coil.

[0031] The device according to the disclosure and the method according to the disclosure can then also be used in combination with a fully automatic surface inspection device, in which the device according to the disclosure is expediently arranged in the sheet running direction subsequent to the fully automatic surface inspection device. The device according to the disclosure and the method according to the disclosure then serve for additional inspection of the sheet surfaces, in addition to the fully automatic inspection by the surface inspection device. Certain surface defects cannot be detected fully or not precisely enough using the known automatic surface inspection devices in which cameras are used for imaging of the sheet surface. The device according to the disclosure and the method according to the disclosure enable an inspector to subject the defects detected by the fully automatic surface inspection device to further and especially more precise examination in order to decide whether the detected surface defect appears to require cutting out of the sheet area containing the defect.

[0032] The device depicted in FIGS. 1 to 4 for inspection of the surface of a sheet B moving at a stipulated sheet speed in a sheet running direction v, includes a device 10, 10 arranged on the sheet top o and on the sheet bottom u. Typical sheet speeds then lie in the range of 100 to 700 m/min. The sheet speed is then dependent on the speed with which the sheet is moved from a production or refining process, for example, a sheet coating installation.

[0033] The devices 10, 10 depicted in FIG. 1 in a view in the sheet running direction v, which are arranged on the sheet top o and the sheet bottom u of the sheet B, include a first light source 1, 1, a second light source 2, 2 and an additional light source 5, 5 as well as a mirror 4, 4. The first light source 1, 1 of each device 10, 10 is then arranged offset laterally next to as well as above or beneath the sheet B. The second light source 2, 2 is arranged above the sheet or under the sheet B at a distance to the corresponding sheet surface on the sheet top o or the sheet bottom u. The additional light source 5, 5 is again arranged laterally offset and above or beneath the sheet B. The mirror 4 of the device 10 arranged above the sheet B has a mirror surface arranged at a stipulated angle to the surface of the sheet B. The mirror surface of mirror 4 encloses an angle in the range of preferably 30 to 60 and especially 45 with the plane of the sheet B (i.e., with the sheet surface). The mirror 4 arranged beneath the sheet B of the device 10 arranged on the sheet bottom u is correspondingly oriented relative to the surface of the sheet so that the mirror surface of mirror 4 encloses an angle in the range of 40 to 60 and especially 45 with the sheet surface.

[0034] The light sources 1, 1, 2, 2 and 5, 5 each emit light under a stipulated incidence angle range onto a surface of the sheet B, in which light sources 1, 2 and 5 of the device arranged above the sheet B emit light onto the sheet top o and the light sources 1, 2 and 5 of the device 10 arranged beneath the sheet B emit light onto the sheet bottom u. The sheet B illuminated by the light sources 1, 1, 2, 2 and 5, 5 is observed by the inspector I via mirrors 4, 4, in which mirror 4 of the upper device 10 permits observation of the sheet top o and mirror 4 of the lower device 10 permits observation of the sheet bottom u.

[0035] The light emitted from the first light source of the upper or lower device 10, 10 onto the sheet surfaces is observed by the inspector I in the bright field. The light emitted by the first light source 1, 1 and reflected on the corresponding sheet surface is deflected via mirror 4, 4 into the visual field S of inspector I, for which reason the inspector I observes the area of the sheet surface illuminated by the first light source 1, 1 in the bright field.

[0036] Illumination of the sheet surfaces by the first light source 1, 1 in the bright field H is shown in FIG. 2. As is apparent from FIG. 2, the first light source 1, 1 emits a light beam with a light cone stipulated by the employed light source under a stipulated first incidence angle 1 onto the sheet surfaces. The incidence angle 1 in the depicted example is 1=37. A first incidence angle range 1=1 is defined by the incidence angle 1 and the beam angle range of the light cone of the first light source. The beam angle range of the employed light source then expediently lies between 10 and 20 and especially at =15.

[0037] The dark field on the sheet surfaces generated by the second light source 2, 2 and the additional light source 5, 5 is shown in FIG. 3. The light beam directed from the second light source 2, 2 and the additional light source 5, 5 onto the sheet surfaces is back-reflected from the sheet surface and the corresponding mirror 4, 4 from the visual field S of the inspector I, for which reason the inspector I sees the surface areas of the sheet B illuminated by the second light source 2, 2 and the additional light source 5, 5 in the dark field D. Illumination of the sheet surfaces with the second light source 2, 2 and the initial light source 5, 5 therefore enables the inspector I to observe the surfaces of the sheet B on the sheet top o and the sheet bottom u in the dark field.

[0038] As is apparent from FIG. 3, the second light source 2, 2 emits a light beam with a light cone stipulated by the employed light source under a stipulated second incidence angle 2 onto the sheet surfaces. The incidence angle 2 in the depicted example amounts to 2=9011=79. A second incidence angle range a2=a2 is defined by the incidence angle 2 and the beam angle range of the light cone of the second light source 2, 2. Accordingly, the additional light source 5, 5 emits a light beam with a light cone stipulated by the employed light source under a stipulated incidence angle 5 onto the sheet surfaces. The incidence angle 5 in the depicted example amounts to 5=26. An incidence angle range 5=5 is defined by the incidence angle 5 and the beam angle range . As in the first light source, the beam angle range of light sources 2, 2 and 5, 5 then expediently lies between 10 and 20 and especially at =15.

[0039] The incidence angles 1, 2 and 5 of the first light source 1, 1, the second light source 2, 2 and the additional light source 5, 5 preferably lie in the following ranges: [0040] 30145 [0041] 602<90 [0042] 10540

[0043] The first light source 1, 1, the second light source 2, 2 and the additional light source 5, 5 are then operated in alternation in stroboscope manner with a stipulated pulse frequency f so that the surface of the sheet B is illuminated in alternation with the pulse frequency f by the first light source 1, 1 in the bright field (H) and by the second light source 2, 2 in the additional light source 5, 5 in the dark field (D). The inspector I can therefore observe both the bright field H and the dark field D of the sheet surfaces (in succession) with the pulse frequency f of the light sources. The pulse frequency f expediently lies in the range of 70 Hz to 400 Hz and preferably between 100 Hz and 300 Hz. The light pulses emitted from the light sources 1, 1, 2, 2 and 5, 5 expediently have a stipulated pulse length tin the range of 30 s to 100 s and preferably between 50 s and 80 s. Because of the high pulse frequency f and the limited pulse lengths t the inspector I can conduct both bright field and dark field observation almost simultaneously on the running sheet B. This enables the inspector I to detect different surface defects that can be observed either only in the bright field or only in the dark field.

[0044] For this purpose, it is expedient if the surface area (dark field D) illuminated by the first light source 1, 1 and the surface area (dark field D) illuminated by the second light source 2, 2 and (optionally) by the additional light source 5, 5 at least partially overlap on the corresponding sheet surface.

[0045] Each of the light sources 1, 1, 2, 2 and 5, 5 depicted in FIG. 1 emit light under a stipulated incidence angle range and a stipulated beam direction onto the surface of the sheet B, the beam direction of the light sources then having a component across the sheet running direction v (i.e., perpendicular to the sheet running direction v) and a component directed perpendicular to the sheet surface.

[0046] In addition to the light sources 1, 1, 2, 2 and 5, 5 apparent from FIG. 1, additional light sources can also preferably be provided in the device according to the disclosure, in order to uniformly illuminate the sheet surfaces as well as possible. As is apparent from FIG. 4, a third light source 3, 3 and a fourth light source 6, 6 can be arranged above and beneath the sheet B, in which the third light source 3, 3 emits light under a stipulated incidence angle range and a stipulated beam direction against the sheet running direction v onto the sheet surfaces. The incidence angle 3 of the third light source 3, 3 and the optional fourth light source 6, 6 in the depicted example amounts to 3=26 and preferably lies in the range of 10 to 40. At a beam angle range of the light cone of the third light source 3, 3 and the fourth light source 6, 6 a third incidence angle range 3=3 is defined.

[0047] The third light source 3, 3 emits light under the stipulated incidence angle range 3 in a beam direction directed in the sheet running direction v onto the sheet surfaces. The fourth light source 6, 6, on the other hand, emits light under the same incidence angle range 3 and in a beam direction directed against the sheet running direction v onto the sheet surfaces. The beam directions of the third light source 3, 3 and the fourth light source 6, 6 therefore contain a component directed in or against the sheet running direction v (as well as a component of the beam direction directed perpendicular to the sheet surface). The third light source 3, 3 and the fourth light source 6, 6 enable the inspector I to observe the surfaces on the sheet top o and the sheet bottom u in convergent light (i.e., with a beam direction having a component in or against the sheet running direction v). Because of this, additional surface defects can be observed that cannot be observed or only insufficiently observed in the bright field H or the dark field D.

[0048] Like the first, the second and the additional light sources 1, 1; 2, 2; 5, 5, the third light source 3, 3 and the fourth light source 6, 6 are also operated in alternation with the first and second light sources in stroboscope manner with a stipulated pulse frequency and pulse length so that the areas illuminated by the light sources can be observed in alternation by the inspector I in the pulse frequency. The third light source 3, 3 and the fourth light source 6, 6 are then operated in pulsed fashion in step, i.e., the third light source 3, 3 and the fourth light source 6, 6 are simultaneously in step or out of step.

[0049] The light sources used in the device according to the disclosure are preferably formed by several LED light strips 7 arranged at a spacing next to and one after the other. In FIGS. 5 and 6 the second light source 2 arranged above the sheet top o and the first light source 1 arranged beneath the sheet bottom u are shown in detail in a side view. The second light source 2 depicted in FIG. 5 includes five LED light strips 7 running parallel to each other and arranged one behind the other in the depicted practical example. Each of these five LED light strips 7 contains several light-emitting diodes (LEDs) 8 arranged at a spacing in the longitudinal direction of the LED light strip 7. Such an LED light strip having a total of 12 LEDs 8 is shown as an example in FIG. 7.

[0050] In order to avoid blinding of the inspector I, each LED light strip 7 preferably has a shutter 9, which is arranged in the visual field S of the inspector so that the inspector I cannot look either directly or indirectly via the mirror 4, 4 into the light cone emitted by the LEDs 8. This is indicated in FIG. 6, where the edges of the visual field S of the inspector I are shown. As is apparent from FIG. 6, the shutters 9 of the LED light strips 7 cover the visual field S of the inspector I and in so doing prevent blinding of the inspector I. Glare-free and fatigue-free work of the inspector I is therefore permitted.

[0051] It is apparent from FIG. 1 that, by arranging the light sources in the form of several LED light strips 7 arranged one behind the other or next to each other, light sources designed flat are provided. The LED light strips 7 of the light sources then expediently run parallel to the sheet surface. The same also applies to the third light source 3, 3 and the fourth light source 6, 6. Through flat arrangement of the light sources a larger-area illumination of the sheet surfaces is made possible in the visual field S of the inspector I.

[0052] By switching on or switching off the individual LED light strips 7 of the individual light sources, areas of the sheet surface can then be switched to bright or dark. It is also possible to adjust the illuminated area of the sheet surfaces to the width of the sheet B by switching on or switching off the individual LED light strips 7 of the light sources.

[0053] The disclosure is not restricted to the depicted practical example. For example, it is not necessary to maintain the number and arrangement of light sources selected in the depicted practical example. It is sufficient according to the disclosure to merely illuminate the surface of the sheet B with a first and a second light source, in which the first light source illuminates a surface of the sheet in a bright field and the other light source illuminates the same surface of the sheet in a dark field, both light sources being operated in pulsed fashion in alternation with a stipulated pulse frequency so that the surface of the sheet is illuminated in alternation with the pulse frequency in the first surface area in the bright field and in the second surface area in the dark field of the observing inspector I.

[0054] It is also not essential according to the disclosure to arrange a device according to the disclosure both on the sheet top o and also the sheet bottom u. If the inspector I wishes to observe only one surface of the sheet B, for example, the sheet top o, it is sufficient if one device according to the disclosure is arranged only on the sheet top o. However, the disclosure makes possible simultaneous observation of both the surface on the sheet top o and on the sheet bottom u based on observation of the sheet surface by the inspector I via (at least) one mirror 4, 4.