EP2110355A1 - Device for optical recording of the lateral location of features on moving material sheets and method for operating this device - Google Patents

Abstract

The second lighting unit is a point source (10) with focusing optics (12). The unit is located and oriented such that its beams converge into the objective (15) of the imaging system following specular reflection at the detection region. The lighting units are switched on as a function of the types of features to be detected. To detect regions of the same color, which are only differentiated by their reflection behavior, only the second lighting unit (10) is switched-on. An independent claim IS INCLUDED FOR the method of operation.

Description

The invention relates to a device for the optical detection of features on moving webs of material and a method in the operation of this device.

Devices of this type are used in industry to control the lateral position of moving webs of material so that the detected feature of the web is maintained at a desired lateral position, even when interfering influences on the web. Control circuits that perform this task are known and often described. An early form is in the patent US 3 431 425 (1969 ).

In order to meet the increasing demands of the processing industry, these control circuits have been developed over time. In particular, the optical sensor for detecting the control feature was the goal of continuous development in order to use difficult to detect features for lateral material web control. Features in the sense considered here can be given in the case of printed material webs through parts of a printed image, but also color differences in the material web itself or partial coatings of the web surface should often be used as a feature to regulate the position of the web.

This type of optical sensor usually includes one or more light sources, one or more photosensitive receiving elements, light beam forming elements such as lenses, apertures and mirrors and electronic elements for processing the output signals of the photosensitive receiving elements. If necessary, keys and display elements for the operation of the sensor can still be present. As photosensitive receiving elements integrated CMOS or CCD circuits are nowadays used, in which a plurality of these receiving elements are combined on a semiconductor crystal and which are preferably arranged in rows for the object under consideration here. Together with the imaging optical elements of such a sensor, this results in a line-shaped scanning region on the surface of the material web which is preferably arranged orthogonal to the direction of movement of the material web.

On the one hand, the features to be recorded can, as already in U.S. 3,431,425 specified, linear features or recurring patterns such as bar codes, which are often printed on packaging material. Other, clearly recognizable patterns can also be used as a control feature with the methods of image processing available today. Likewise, the edge of the web itself can give a corresponding contrast to the surface of a supporting roll and then be used as a feature for position control.

Furthermore, devices are demanded that respond to features that arise in that surface sections differ in their luster from your neighborhood. For example, on drug packages, their glossy coating is a pencil writing, pen or felt pen does not allow properly, a small field excluded from the coating to the handwritten entry of z. B. allow dosage rules. These matte fields are not different in color or brightness from the environment, but only by their reflection behavior.

Gloss differences of the kind considered can also arise, for example, at the border between glossy coating and uncoated, non-glossy material surface. The same can also be caused by partial mechanical surface treatment or other forms of surface treatment. It is also possible that the edge of a glossy, transparent material surface should be used for position regulation, in contrast to a not less shiny back-up roller or against another background. A recurring task is to use color characteristics of the material web for position control at one and the same point in a system for a production process and gloss features for another production process.

Already in DE 36 37 874 A1 (1988 ) has described a device that allows the edge of a glossy, transparent material surface to be scanned against a less shiny background. In DE 100 22 597 (2001 ) describes a complete sensor for both tasks, namely first the scanning of bright features and secondly the scanning of color features, here for the two tasks dedicated lighting sources are provided for the scanning area, which are turned on alternatively and cumulatively.

Also in US 6,566,670 (2003 ) such a combination device is described. In all three devices mentioned, a flat diffuse light source is used to illuminate the glossy surface, which consists essentially of a ground-glass, which is illuminated from behind.

It has now been found that devices of the above type, in particular, do not give a good contrast between glossy and non-glossy surface when the non-glossy surface is light in color. This effect is caused by the diffuse light source. In a diffuse light source, light rays emanate from every part of their surface in all spatial directions. Only a small part of these rays of light has the correct angle when hitting the shiny surface in order to reach the receiving elements under the mirror condition of angle of incidence = angle of reflection. The much larger part of the radiation of the diffuse light source does not reach the receiving elements after the reflection on the shiny surface. But if there is no glossy but the non-shiny area of the surface in the field of view of the sensor, then ensure all the light rays of the diffuse light source that meet this field of view for a lightening of the web. This explains the low contrast difference in the case in question.

Similar problems exist with printed material webs which are additionally partially coated with a transparent layer. The printed image underlying the transparent layer reflects all the light rays of the diffuse light source according to the printing ink used, while the transparent layer again reflects only the light rays which satisfy the mirror condition to the receiving elements reflected. A secure detection of the boundary between coated and uncoated surface parts is now disturbed by the fact that parts of the printed image shine through the transparent coating and these are not sufficiently covered by the reflection of the light on the transparent coating.

The invention is based on the object of providing an optical combination sensor which can be switched over in order to scan color features, even if they lie under a transparent glossy coating, and on the other hand can be used to reliably detect features which are in the form of gloss differences the surface of a material web are present, even if they are applied to light substrates or printed material webs.

The solution of the problem is specified in the claims.

The second illumination device to be used for detecting gloss features is formed by a point source as light as possible and an optical condenser. As point light source is a single-color LED in question, since on the one hand, the light-emitting surface of such a light-emitting diode is very small and thus the punctiform light source is approximated in a very good manner and on the other hand, because in the light reflection on shiny surfaces, the light color (wavelength) plays a subordinate role. Another possibility is the use of a diaphragm with a correspondingly small light exit opening.

The maximum diameter of the light emitting diode or a diaphragm depends on the minimum required resolution on the receiver side and the parameters of the light guide. In a specific embodiment with regard to the number and arrangement of the lenses, diaphragm size and other relevant parameters, a specific requirement for the resolution results from a size of the photosensitive receiving elements of 12.5 μm and for a length of the detection range (extension perpendicular to the running direction of the material). of 30 mm and a required resolution of about 125 lines a maximum diameter of the light source of 1 mm.

Now if the optical geometry, namely the distance between the punctiform light source and the condenser (to be considered as a preferred example of the focusing optics), the focal length of the condenser lens (s) and the sum of the distances between the condenser and the detection area and between the detection area and the lens Imaging system is selected according to claim 1, then it is ensured that all reflected in the detection range of the material web rays also reach the receiving elements.

• Fig. 1 schematisch in der Draufsicht, einer Seitenansicht und einer Querschnittsansicht einen Abschnitt einer partiell mit farblichen Merkmalen bedruckten und partiell glänzend beschichteten laufenden Materialbahn;
• Fig. 2 schematisch die Anordnung der Baugruppen einer erfindungsgemäßen Vorrichtung;
• Fig. 3a den Strahlengang eines auf eine vollständig spiegelnde Oberfläche auftreffenden Lichtstrahls;
• Fig. 3b den Fall von Fig. 3a bei glänzender Oberfläche;
• Fig. 3c den Fall von Fig. 3a bei matter, d. h. diffus reflektierender Oberfläche;
• Fig. 4a schematisch die zur Erfassung glänzender Elemente bestimmten Teile der Vorrichtung, wobei die optisch äquivalente entfaltete Darstellung des Strahlengangs gestrichelt gezeichnet ist;
• Fig. 4b die um 90° gedrehte Darstellung von Fig. 4a, in der die Materialbahn in die Zeichenebene hineinläuft;
• Fig. 5 die Situation gemäß Stand der Technik;
• Fig. 6 die Strahlengänge bei einer Unterbringung der Lichtquellen in einem gemeinsamen Gehäuse und Verwendung eines konkaven Spiegelstreifens als fokussierende Optik;
• Fig. 7 schematisch eine Vorrichtung mit allen wesentlichen Baugruppen;
• Fig. 8 schematisch den signaltechnischen Aufbau der Vorrichtung.

The invention will be further explained by the description of embodiments with reference to the accompanying drawings. It shows:

• Fig. 1 schematically in plan view, a side view and a cross-sectional view of a portion of a partially printed with color features and partially glossy coated running material web;
• Fig. 2 schematically the arrangement of the modules of a device according to the invention;
• Fig. 3a the beam path of a light beam impinging on a completely reflecting surface;
• Fig. 3b the case of Fig. 3a with a glossy surface;
• Fig. 3c the case of Fig. 3a in the case of a matt, ie diffusely reflecting surface;
• Fig. 4a schematically the parts intended for the detection of shiny elements of the device, wherein the optically equivalent unfolded representation of the beam path is shown in dashed lines;
• Fig. 4b the rotated by 90 ° representation of Fig. 4a in which the material web runs into the plane of the drawing;
• Fig. 5 the situation according to the prior art;
• Fig. 6 the beam paths in a housing of the light sources in a common housing and use of a concave mirror strip as focussing optics;
• Fig. 7 schematically a device with all the essential components;
• Fig. 8 schematically the signal structure of the device.

The in Fig. 1 only by way of example and not to scale shown in three views section of a material web to be scanned consists of running in the direction of the arrow material web 1, on which are shown as obliquely hatched squares pattern 3 printed. Other areas are provided with a transparent glossy coating 5, said shaded areas in the running direction partially overlap with the patterns 3. Furthermore, marked with 7 of the detection area on the web, which is evaluated cyclically repeated by the optical sensor. Depending on the web speed, the various combinations of print image and gloss coating run through the detection area.

Fig. 2 shows schematically the components of a device according to the invention. Above the material web 1 running in one of the directions of the arrows, an optical imaging system is arranged, which consists of an objective 14 and receiving elements 16, wherein the objective 14 images the image of the material web in the detection region 7 onto the receiving elements 16. The imaging system is inclined to the normal to the web 1; his ray of sight closes with this one angle α.

In order to illuminate the material web 1 running in the direction of the arrow in the detection area, there is a first illumination device 20 which lies on the same side as the imaging system and whose light beams impinge at a smaller angle β. Insofar as specular reflection takes place in the detection area, the rays reflected at the same angle β go far past the objective 10 of the optical imaging system.

This first illumination device 20 is used primarily for scanning color features. Only rays of diffuse reflection accordingly 3 c can reach the lens 14. For the detection of color features, the illumination device 20 is composed of a plurality of light elements, which have different light colors and can be switched on and off individually. Preferably, light emitting diodes which emit light of different wavelengths are used for this purpose. For sensors designed to distinguish color characteristics similar to human color perception, light-emitting diodes with the colors red, green and blue are used. For sensors, which are to evaluate technical color features in other wave ranges, different colored LEDs are added as needed, for example, light emitting diodes in the infrared range or in the UV range light.

A second illumination device consists of a point light source 10 and a focusing optics 12 and is relative to the normal to the web 1 on the other side at the angle α, so that their rays are directed at the lens 14 in specular reflection.

• Fig.3a zeigt das Verhalten eines Lichtstrahls, wenn dieser von einer Lichtquelle 10 auf eine vollständig spiegelnde Materialbahn 1 fällt. Er wird reflektiert und kann nur in einer Richtung α von einem Empfangselement registriert werden. An der Position 10' ist das Spiegelbild der Lichtquelle zu beobachten. Fig.3b zeigt das Verhalten des Lichtstrahls auf glänzenden Materialbahnen und Fig.3c das Verhalten des Lichtstrahls auf ausschließlich diffus reflektierenden Oberflächen.
• Fig.4a ergänzt die Darstellung Fig.3a um die Elemente des optischen Abbildungssystems und der zweiten Beleuchtungseinrichtung. Die Spiegelbilder der näherungsweise punktförmigen Lichtquelle 10 und der Kondensorlinse 12 sind mit 10' und 12' bezeichnet. Der Strahlengang der Lichtquelle und der abbildenden Optik ist jeweils so zur Materialbahn angeordnet, dass die Spiegelbedingungen eingehalten sind, das heißt, daß sie gleiche Winkel (α) zur Materialbahn aufweisen.
• Fig.4b zeigt die Elemente der Darstellung in Fig.4a in einer um 90° gedrehten Ansicht, wobei die realen Elemente 10 und 12 zur Vermeidung von Überdeckungen weggelassen sind und nur deren Spiegelbilder 10' und 12' gezeichnet sind. Zusätzlich sind strichpunktiert die Ebenen der optischen Wirkung eingezeichnet, die die Kondensorlinse 12' und das Objektiv 14 als ideal dünne Linsen hätten. Ebenso sind die Gegenstandsweite g und die Bildweite b der Kondensorlinse 12' eingezeichnet. Diese erfüllen die Bedingung, daß das ausgangsseitige Strahlenbündel der Kondensorlinse 12' und somit ein vom Erfassungsbereich 7 spiegelnd reflektiertes Strahlenbündel der realen Kondensorlinse 12 im Objektiv 14 konvergiert.
• Bei Verwendung eines Normalobjektivs muß der Abstand zwischen Abbildungssystem 14/16 und Materialbahn konstant gehalten werden oder es müssen Toleranzen bezüglich der Erkennungsgenauigkeit zugelassen werden. Diese Einschränkungen können entfallen, wenn ein allerdings teureres Spezialobjektiv, insbesondere ein telezentrisches Objektiv Verwendung findet und die fokussierende Optik in gleicher Weise wie oben beschrieben an dessen Strahlengang angepaßt wird, wobei die Vorteile einer solchen Ausbildung insbesondere dann zum Tragen kommen, wenn im Betrieb der Vorrichtung die Charakteristika der zyklisch abgetasteten Bilder des Erfassungsbereichs verglichen werden mit einem abgespeicherten Muster oder einer erlernten Vorlage und es dabei um Abstände von einem Farbübergang zu einem anderen geht.
• Fig. 5 zeigt ergänzend in der Spiegeldarstellung, wie bei den bekannten Erfassungsvorrichtungen gemäß Stand der Technik an der Stelle der fokussierenden Optik 12' eine Mattscheibe 18' angeordnet ist, von der Lichtstrahlen in alle Raumrichtungen ausgehen, sodaß jeder Punkt der Materialbahn 1 im Auswertebereich des Sensors aus einem ganzen Winkelbereich beleuchtet wird.
• Wenn also nach dem vorliegenden Vorschlag nur solche Lichtstrahlen auf den ausgewerteten Bereich der Materialbahn fallen, die nach den Spiegelgesetzen die Empfangselemente erreichen und keine weiteren Lichtstahlen, die diese Forderung nicht erfüllen, dann stellt sich ein deutlicher Amplitudenunterschied zwischen nicht glänzenden und glänzenden Oberflächenteilen ein. Wenn dagegen, wie beim Stand der Technik, noch weitere Lichtstrahlen unter anderen Winkeln hinzukämen, dann würden im wesentlichen die nicht glänzenden Bereiche der Materialbahn aufgehellt und der Amplitudenunterschied zwischen nicht glänzenden und glänzenden Oberflächenteilen verringerte sich oder verschwände völlig.
• Die Anordnung nach Fig.6 erfüllt denselben Zweck wie die Anordnung nach Fig.2. In dieser ist der aus einer Linse bestehende Kondensor ersetzt worden durch einen konkaven Spiegelstreifen 13, der die Lichtstrahlen der punktförmigen Lichtquelle 10 ebenso fokussiert und gleichzeitig so ablenkt, daß sie unter Einhaltung der Spiegelbedingung unter dem Winkel des Sehstrahls der abbildenden Optik 14 auftreffen. Bei dieser Anordnung kann die punktförmige Lichtquelle 10 der zweiten Beleuchtungseinrichtung und die erste Beleuchtungseinrichtung 20 zu einer Einheit zusammengefaßt werden, sodaß die elektrische Energiezufuhr und die Wärmeableitung einfacher und wirksamer zentral erfolgen kann.
• Fig.7 zeigt schließlich schematisch eine Gesamtanordnung mit einem Gehäuse 24 und einer in der Gehäusewand vorgesehenen transparenten Scheibe 22. Diese schützt den Sensor vor Staub und anderen schädlichen Umgebungseinflüssen.
• Diese Scheibe ist nun so anzuordnen, daß keine Lichtreflexion von ihrer inneren Oberfläche in das Objektiv 14 gelangen kann. Vorzugsweise ist diese Scheibe rechtwinklig zu dem Strahlengang des Objektivs angeordnet. Die Materialbahn wird vorzugsweise in der Nähe oder auf einer Stützwalze 40 abgetastet um eine stabile Geometrie der Anordnung zu gewährleisten. Ein Anschluß für den elektrischen Signalaustausch zu den weiteren Komponenten einer Bahnlaufregelung ist mit 28 bezeichnet. Dieser Signalaustausch soll vorzugsweise als digitale Schnittstelle ausgeführt sein um auch komplexe Informationen übertragen zu können. Bei geringeren Anforderungen kann aber auch ein analoger Signalaustausch verwendet werden. Auf diese Weise steht die sensor-interne Signalverarbeitungseinheit 30 mit den weiteren Komponenten der Bahnlaufregelung in Verbindung. Weiterhin ist noch ein Bedienfeld 26 vorgesehen.
• Fig.8 zeigt den signaltechnischen Zusammenhang der einzelnen Komponenten des Sensors. Das Bedienfeld 26 steht mit der Signalverarbeitungseinheit 30 in Verbindung. Dieses Bedienfeld kann mit mechanischen Tasten oder einer Folientastatur gestaltet sein und Leuchtdioden und/oder ein LCD-Display für die Benutzerführung enthalten. Insbesondere ist vorgesehen, dass der Benutzer über dieses Bedienfeld auswählt, ob Farbmerkmale oder ob Glanzmerkmale vom Sensor ausgewertet werden sollen. Eine zusätzliche Betriebsart soll es aber auch erlauben, diese Auswahl über den elektrischen Signalaustausch 28 von außen vorzunehmen. So wird die Signalverarbeitungseinheit 30 in die Lage versetzt die richtige Lichtquelle 10 oder 20 auszuwählen. Weiterhin stehen die lichtempfindlichen Empfangselemente 16 mit der Signalverarbeitungseinheit 30 in Verbindung, damit es dieser möglich ist, die Merkmalsposition zu ermitteln und im Falle von Farbmerkmalen diejenige Lichtfarbe der ersten Beleuchtungseinrichtung 20 automatisch zu wählen, welche für das erfaßte Merkmal die höchsten Signalamplituden an den Empfangselementen 16 erzeugt.

The optical properties of this second illumination device should meet certain conditions, for the explanation of which the following considerations serve:

• 3a shows the behavior of a light beam when it falls from a light source 10 onto a completely reflecting material web 1. It is reflected and can only be registered in one direction α by a receiving element. At position 10 ', the mirror image of the light source is observed. 3b shows the behavior of the light beam on shiny material webs and 3 c the behavior of the light beam on exclusively diffusely reflecting surfaces.
• 4a completes the presentation 3a around the elements of the optical imaging system and the second illumination device. The mirror images of the approximately point-shaped light source 10 and the condenser lens 12 are designated by 10 'and 12'. The beam path of the light source and the imaging optics is respectively arranged to the material web that the mirror conditions are met, that is, that they have the same angle (α) to the material web.
• 4b shows the elements of the illustration in 4a in a rotated by 90 ° view, the real elements 10 and 12 are omitted to avoid overlaps and only their mirror images 10 'and 12' are drawn. In addition, the planes of the optical effect, which would have the condenser lens 12 'and the objective 14 as ideally thin lenses, are shown by dot-dash lines. Likewise, the object width g and the image width b of the condenser lens 12 'are shown. These satisfy the condition that the output-side beam of the condenser lens 12 ', and thus a reflected by the detection area 7 beam of the real condenser lens 12 in the lens 14 converges.
• When using a normal lens, the distance between the imaging system 14/16 and web must be kept constant or it must be tolerated in terms of recognition accuracy. These restrictions can be omitted if a more expensive special lens, in particular a telecentric lens is used and the focusing optics in the same manner as described above is adapted to the beam path, the benefits of such training in particular come into play when in operation of the device the characteristics of the cyclically scanned images of the detection area are compared with a stored one Pattern or a learned template that deals with distances from one color transition to another.
• Fig. 5 shows in addition in the mirror representation, as in the known detection devices according to the prior art at the location of the focusing optics 12 'a ground glass 18' is arranged, go out of the light rays in all directions, so that each point of the web 1 in the evaluation of the sensor from a entire angle range is illuminated.
• Thus, according to the present proposal, if only those light rays fall on the evaluated area of the material web which reach the receiving elements according to the laws of the mirror and no further light beams which do not meet this requirement, then a clear amplitude difference arises between non-shiny and shiny surface parts. On the other hand, if, as in the prior art, other light rays were added at different angles, then substantially the non-glossy areas of the web would be lightened and the amplitude difference between non-glossy and glossy surface parts would be reduced or disappeared altogether.
• The arrangement after Figure 6 fulfills the same purpose as the arrangement Fig.2 , In this, the existing of a lens condenser has been replaced by a concave mirror strip 13, which focuses the light rays of the punctiform light source 10 as well and at the same time deflects so that they impinge upon observing the mirror condition at the angle of the visual ray of the imaging optics 14. With this arrangement, the point light source 10 of the second illumination device and the first illumination device 20 are combined into one unit, so that the electrical power supply and the heat dissipation can be made easier and more effective centrally.
• Figure 7 Finally, schematically shows an overall arrangement with a housing 24 and provided in the housing wall transparent disc 22. This protects the sensor from dust and other harmful environmental influences.
• This disc is now to be arranged so that no light reflection from its inner surface can get into the lens 14. Preferably, this disc is arranged at right angles to the beam path of the lens. The web is preferably scanned in the vicinity or on a support roller 40 to ensure a stable geometry of the arrangement. A connection for the electrical signal exchange to the other components of a web guiding is designated by 28. This signal exchange should preferably be designed as a digital interface in order to be able to transmit complex information. For lower requirements, however, an analog signal exchange can also be used. In this way, the sensor-internal signal processing unit 30 is in communication with the other components of the web guiding system. Furthermore, a control panel 26 is still provided.
• Figure 8 shows the signaling connection of the individual components of the sensor. The control panel 26 is in communication with the signal processing unit 30. This control panel can be designed with mechanical keys or a membrane keyboard and LEDs and / or a LCD display for user guidance included. In particular, it is provided that the user selects via this control panel, whether color characteristics or whether gloss features from the sensor to be evaluated. However, an additional mode should also allow to make this selection via the electrical signal exchange 28 from the outside. Thus, the signal processing unit 30 is enabled to select the proper light source 10 or 20. Furthermore, the light-sensitive receiving elements 16 are in communication with the signal processing unit 30, so that it is possible to determine the feature position and automatically select in the case of color features that light color of the first illumination device 20, which for the detected feature, the highest signal amplitudes at the receiving elements 16th generated.

Claims (9)

Device for optically detecting the lateral position of features on moving material webs - With an optical imaging system of a lens (14) and line-shaped light-sensitive receiving elements (16), wherein the lens (14) oriented transversely to the direction of strip-shaped detection area (7) on the material web (1) on the photosensitive receiving elements (16) - and with two illumination devices for illuminating the detection area (7), - The first (20) is arranged so that the rays emanating from her do not come under mirror reflection to the imaging system, characterized in that the second illumination device consists of a punctiform light source (10) and a focusing optic (12; 13), which are arranged and arranged such that the rays (11) emanating from it
converging after mirror reflection at the detection area (7) in the objective (14) of the imaging system, - Wherein the involvement of the lighting devices is done depending on what kind of features to capture - And to capture the same color, only by their reflection behavior different areas only the second illumination device (10/12) is turned on. Device according to Claim 1, characterized in that the image width (b) of the focusing optics (12, 13) is equal to the distance between the latter and the detection area (7) plus the distance between the detection area (7) and the objective (14). Apparatus according to claim 1 or 2, characterized in that the
focusing optics is a condenser lens (12). Apparatus according to claim 1 or 2, characterized in that the focusing optics is a concave mirror strip (13). Device according to one or more of the preceding claims, characterized by the use of a monochrome light-emitting diode as a punctiform light source (10). Device according to one or more of claims 1 to 4, characterized in that the punctiform light source is formed by the light exit opening of a diaphragm. Device according to one or more of the preceding claims, characterized in that the first illumination device (20) consists of a plurality of differently colored, individually switchable light-emitting elements. Device according to one or more of the preceding claims, characterized in that the lighting elements of the first lighting device (20) and the light source (10) of the second lighting device are combined to form a structural unit and the arrangement of focusing mirror strip (13) of the mirror condition is sufficient. A method of operating a device according to claim 5, characterized in that for detecting colored features and the first illumination means (20) is turned on and their lighting elements are turned on after a program in succession and the lighting is selected, in which there is the largest signal swing at the receiving elements (16).

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