EP1862309B1 - Sensor device - Google Patents

Description

1. 1. Zeilenkameras können durch ihre hohe Zahl von ca. 10000 Pixel pro Sensor die notwendige geometrische Auflösung von 0.1 mm pro Pixel in axialer Richtung erreichen, jedoch ist die Auflösung in Transportrichtung wegen der Zeilenfrequenz des Sensors von maximal 10 kHz bei hohen Transportgeschwindigkeiten von 5 m/s auf 0,5 mm eingeschränkt.
2. 2. Industrie-Flächenkameras besitzen gegenwärtig eine Auflösung von ca. 2000 x 1500 Pixel, die sich bei RGB- Kameras auf 3 Farbkanäle verteilen. Für die Erfassung der gesamten Bedruckstoffbreite mit der notwendigen geometrischen Auflösung von 0.1 mm/Pixel müsste die Kamera quer zur Transportrichtung verfahrbar auf eine Traverse montiert und mit seitlichen Verstellbewegungen nacheinander auf kleine Abschnitte von beispielsweise 200 mm Breite gerichtet werden, wobei ein seitlicher Vorschub nach jeder Druckbildabtastung erfolgt. Dies erfordert beträchtlichen mechanischen Aufwand und die Notwendigkeit, zur Erfassung eines kompletten Messwertsatzes für eine Bedruckstoffbreite von beispielsweise 2 m mindestens 10 aufeinander folgende Druckbilder abzutasten, zwischen denen bereits signifikante Unterschiede im Druckbild auftreten können und eine Vergleichbarkeit einschränken.

The invention relates to a sensor device for the optical detection of strip-shaped printing surfaces on along a printing substrate moving substrates according to the preamble of the first claim.
In rotary printing machines, line or area cameras have been used for a long time as sensors for image control on moving substrates. The geometric resolution of the cameras should be at 0.1 mm / pixel.
If the task is to detect only relatively short, in the transport direction, but relatively long, in the axial direction (substrate width) but quite long areas, such as pressure control strips, the following problems arise:

1. 1. Line scan cameras can achieve the necessary geometrical resolution of 0.1 mm per pixel in the axial direction due to their high number of approx. 10000 pixels per sensor, however the resolution in transport direction is maximum 10 kHz at high transport speeds of 5 m due to the line frequency of the sensor / s restricted to 0.5 mm.
2. 2. Industrial area cameras currently have a resolution of approximately 2000 x 1500 pixels, which are distributed over RGB channels in 3 color channels. For capturing the entire width of the substrate with the necessary geometric resolution of 0.1 mm / pixel, the camera would have to be mounted transversely to the transport direction movable on a crossbar and directed with lateral adjustment movements successively to small sections, for example, 200 mm width, with a lateral feed after each print image scanning he follows. This requires considerable mechanical effort and the need to scan at least 10 consecutive printed images to capture a complete set of measured values for a substrate width of, for example, 2 m, between which already significant differences in the printed image can occur and limit comparability.

A parallelization of the measurements with several cameras distributed across the substrate width would also be possible to increase the resolution.
From the DE 10 2004 033 495 A1 a method for the synchronized operation of a plurality of electronic cameras is known in which the individual cameras simultaneously record one image in response to a trigger signal and the image data of the individual cameras are combined to form an overall image. After completing the image acquisition, a first number of image lines are first read from each camera and discarded. Subsequently, a second predetermined number of image lines are read in succession in a predetermined order of the cameras from each camera, and processed into an overall image. Finally, after reading the second number of picture lines independently of the other cameras, the remaining image lines are read out and the read-out image data discarded. A disadvantage of this solution is the cost of the large number of cameras, the cost of synchronizing the cameras and the low image data processing speed due to the complex data handling.

From the DE 41 36 461 A1 For example, a method and apparatus for large-scale image inspection is known. Also in this document it is proposed to use several parallel operable surface sensors to increase the resolution.

The invention is therefore based on the object, the effort for a sensor device with strip-shaped detection range, which is suitable for a spectral density measurement or color control based on print control strips to reduce.

This object is achieved by a sensor device with the features of the first claim.

It is proposed to provide a sensor device by the combination of a low-cost RGB or SW area camera having a matrix sensor, with an arrangement of mirrors or prisms, wherein successive by the optical means in the direction of the main extent of the strip-shaped printing surface to be controlled Area sections (in the case of print control strips, this is generally the width of the substrate) are adjacent to each other and can be projected line by line onto the matrix sensor.

The invention has the advantages that the native resolution of the sensor matrix is fully utilized by the optical splitting of the printing surface strip into strip sections and at the same time the disadvantage of CCD matrix sensors, which consists in that the matrix sensor can not be addressed line by line, but the entire sensor matrix is read out serially must be overcome.

Figur 1

eine vereinfachte Darstellung der Sensoreinrichtung mit einem Spiegelsystem in einer Ansicht von oben

Figur 2

die Sensoreinrichtung in einer Ansicht von vorn

The invention will be explained in more detail on an embodiment in which the strip-shaped printing surface is designed as a print control strip. The accompanying drawings show in

FIG. 1

a simplified representation of the sensor device with a mirror system in a view from above

FIG. 2

the sensor device in a view from the front

Like from the FIG. 1 it can be seen, a surface camera 3 is arranged laterally on a printing material web in a rotary printing press, wherein the printing material 2 roll or curved can be. The printed material 2 transported in the direction of the arrow has conventional print control strips 1.K, which extend as a strip-shaped printing surface 1 in printed image edge regions transversely to the transport direction and are applied for color control or print quality control.
At an approximately constant distance from the substrate surface optical means, designed as a mirror 5.S, distributed in regular, dependent on the resolution of the matrix sensor 4 distances over the substrate width, the mirror 5.S partially avoid the mutual shading perpendicular to the optical Axis 8 of the area camera 3 are offset by their width to each other and approximately parallel rays directed to the matrix sensor 4. Instead of the mirrors 5.S, prisms for beam deflection can also be used on the matrix sensor 4.
Each mirror 5.S is assigned a section 6.1... 6.5 of the print control strip 1.K whose image is reflected by the mirror 5.S in the direction of the area camera 3. The mirrors 5.S are aligned in such a way that the images of the juxtaposed sections 6.1... 6.5 of the print control strip 1.K can be projected among one another on line groups 7.1... 7.5 of the matrix sensor 4 (FIG. Fig. 2 ).
To avoid motion blur in fast-moving substrates 2, a lighting device 9 is arranged on the printing substrate, which is synchronized with the surface camera 3 and the adjacent sections 6.1 ... 6.5 of the pressure control strip 1.K pulsed linearly illuminated. A linear lighting can be realized, for example, with cylindrical lenses.
The illumination device 9 has a short flash time and can be formed from light sources with different monochromatic light spectra, for example red, blue and green LED groups. By flashing with different illumination spectra, it is possible to use the area camera 3 as a spectral, Tristimulusfarb- or density sensor.
The light sources are expediently controllable in sections in their flash intensity to different emission characteristics of the light sources and the different projection distances (object widths) between the sections 6.1 ... 6.5 of the print control strips 1.K and the area camera 3 and the associated different light intensities of the matrix sensor. 4 to compensate for projected images.

The illumination device 9 is advantageously arranged at a vertical angle of 0 or 45 ° to the mirrors 5.S to minimize reflections.
The area camera 3 is advantageously slightly oblique to the surface of the printing material 2, in order to achieve a flat as possible arrangement and the projection of a rectangular strip on the matrix sensor 4.

The mirrors 5.S are preferably equipped with different radii of curvature to compensate for different magnifications depending on the object's width. Advantageously, special lenses can be used for the area camera 3, in which the beam path does not open, but runs parallel. Thus, regardless of the object's distance, the same magnification always applies and the mirrors 5.S can be made simpler.

For the operation of the device according to the invention:

When the print control strip 1.K enters the detection area of the sensor device, the sensor device is activated, the lighting device 9 is triggered and an image of the print control strip 1.K is detected by the area camera 3 and stored in a known manner or further processed for a printing machine control.
A print control strip 1.K has, for example, the dimensions of B x H = 1000 mm x 20 mm. Of the arranged above the substrate 2 and distributed transversely to the transport direction across the substrate width, for example, five mirrors 5.S is the print control strip 1.K in five sections 6.1 ... 6.5 of 200 mm x 20 mm each extension on the matrix sensor 4 with eg 2000 x 1500 pixels, wherein the originally adjacent sections 6.1 ... 6.5 - arranged one below the other - form an area of 200 mm x 100 mm and are projected onto the matrix sensor 4 so that each of sections 6.1 ... 6.5 on a stanza 7.1 ... 7.5 is shown. This results in optimal geometrical ratios, a theoretical resolution of 0.1 mm per pixel in the horizontal and 0.07 mm per pixel in the vertical direction. With this resolution, measuring strips can be digitized, visualized or measured with sufficient accuracy.
By determining the reflectance, density or spectral measured values in array form, search methods in the data array can subsequently be applied to the image acquisition in order to separate the desired image data from the non-relevant image data. This is particularly advantageous in the case of narrow print control strips 1.K if print image areas surrounding the print control strip 1.K are also detected by matrix sensor 4, which do not belong to print control strip 1.K and therefore from the image data array before further processing for a substrate quality control, color control or printing machine control must be discarded.
The proposed sensor device is not limited to the image analysis of print control strips 1.K, but also for all other image acquisition functions of strip-shaped printing surfaces 1 with a dominant direction of extension can be used transversely or longitudinally to the transport direction.

List of used reference numbers

1

Print area

1.K

Print control strip

2

substrate

3

Areascan

4

array sensor

5.S

mirror

6.1 ... 6.5

Section of the printing surface

7.1 ... 7.5

stanza

8th

optical axis of the area camera

9

lighting device

Claims (8)

1. Sensor device for optical detection of strip-shaped printed surfaces (1) on printing materials (2) moved along a printing material path, consisting of an area camera (3), which is associated with the printing material path, with a matrix sensor (4), wherein the strip-shaped printed surfaces (1) have a dominating length direction transversely to or longitudinally of the transport direction, characterised in that originally adjacently disposed sections (6.1 ... 6.5) of the printed surface (1) can be projected adjacently to one another arranged in line groups with respect to one another on the matrix sensor (4) by optical means arranged upstream of the area camera (3).
2. Sensor device according to claim 1, characterised in that the optical means

   - are distributed at regular spacings over the printing material width along the optical axis (8) of the area camera (3) and are each associated with a respective section (6.1 ... 6.5) of the printed surface (1),

   - are offset with respect to one another relative to the optical axis (8) of the area camera (3) and

   - project images of the respectively associated sections (6.1 ... 6.5) of the printed surface (1) onto adjacent line groups (7.1 ... 7.5) of the matrix sensor (4), wherein the sequence of the sections (6.1 ... 6.5) corresponds with the sequence of the line groups (7.1 ... 7.5).
3. Sensor device according to claim 1 or 2, characterised in that the strip-shaped printed surface (1) is a printing check strip (1.K) extending transversely to the transport direction.
4. Sensor device according to claim 1 or 2, characterised in that the optical means comprise mirrors (5.S) or prisms.
5. Sensor device according to claim 4, characterised in that the mirrors (5.S) are so shaped that they provide compensation for magnification, which is dependent on the article width, of the sections (6.1 ... 6.5).
6. Sensor device according to any one of the preceding claims, characterised in that a lighting means (9) provides pulsed lineal illumination of the strip-shaped printed surface (1).
7. Sensor device according to claim 6, characterised in that the lighting device (9) is constructed for emission of different lighting spectra.
8. Sensor device according to claim 6 or 7, characterised in that the lighting intensity of the lighting device (9) provides compensation for different subject widths of the sections (6.1 ... 6.5).

Images