Device for optically scanning a moving web of material and...

Optics: measuring and testing – By monitoring of webs or thread

Reexamination Certificate

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C356S430000, C356S431000

Reexamination Certificate

active

06757064

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Applicant claims priority under 35 U.S.C. §119 of German Application No. 101 18 886.2 filed Apr. 18, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for optically scanning a moving web of material. The device is formed by at least one CCD camera directed against the material web. The camera includes a lens and a CCD receiving element scanning an area of the material web. The invention also relates to a method for adjusting the moving web of material.
2. The Prior Art
A device for scanning and analyzing the surface of a moving web of material is known from German Patent No. 37 09 500 C2. This device is formed by a CCD camera, which is directed against the web of material. The CCD camera includes a lens and a CCD receiving element. To completely analyze the surface of a very wide web of material, a plurality of such devices must be mounted next to one another. It is important in this connection that the scanned areas of the CCD receiving elements are coordinated so that they are exactly aligned with each other.
A device for measuring the speed of a jet of fluid and the detected length in a combined manner is known from German Patent No. 32 00 508 C2. From these two measured quantities, it is possible to determine the volume flow over the cross section of the jet. For this purpose, the devices include a receiving element that is formed by a plurality of diodes. Light reflected by the jet of fluid acts upon the diodes via a lens and a beam divider. By displacing the receiving element axially relative to the lens, it is possible to vary the area of the jet of fluid detected by the receiving element and to measure the illuminated area of the fluid.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a device for optically scanning a moving web of material that permits a simple and highly sensitive adjustment of the area scanned by the CCD camera. Furthermore, the aim of the invention is to specify a simple method for adjusting the scanned area.
In accordance with the invention, these and other objects are accomplished by providing a device for optically scanning a moving material web formed by at least one CCD camera directed against the material web. The camera includes a lens and a CCD receiving element scanning an area of the material web. For adjusting the scanning range of the device, a template can be fixed in the area of the plane of the material web. The template has at least one structure extending transversely in relation to the direction of movement of the material web, which is detectable by the CCD camera. The CCD receiving element can be adjusted in relation to the lens transversely to its optical axis by at least one drive. The drive is actively connected with a controlling device responsive to signals from the CCD camera.
The template may include a digital coding detectable by the CCD camera. This coding is formed by a sequence of bits, in which any desired partial sequence of an “n” number of directly successive bits of the sequence supplies a clear n-bit code for the absolute position of the CCD camera along the template.
The device as defined by the invention serves for optically scanning a moving web of material. In particular, the device serves to control the surface of the moving web of material optically so as to detect any weaving, printing and dying defects. The device may also be used to detect the marginal edge or a printed marking of the web of material in order to detect the course along which the material web is moving. The device is formed by at least one CCD camera that is directed against the web of material and includes a lens and a CCD receiving element. Because the web of material is moving past the camera, the CCD receiving element may take the form of a line receiving element, with all light-sensitive photodiodes in the element arranged next to each other. By generating a plurality of images of the line that are offset in terms of time, it is possible to obtain a complete image of the surface of the web of material due to the movement of the material web. In particular in connection with wide webs of material, the range scanned by one single CCD camera is not adequate for detecting the surface of the web of material over the entire width of the material. Several CCD cameras generally are employed for that reason that are distributed over the width of the web of material. These CCD cameras have to be coordinated with each other. Specifically, their scanning ranges will be aligned with one another, so that the individual CCD cameras combined will supply a through-extending scanning line extending transversely in relation to the direction in which the web is running. In this way it is assured that the images generated by the individual CCD cameras can be correctly assembled to obtain an overall image, so that defects located in the area of transition between two CCD cameras can be correctly detected as well; so that the CCD cameras may scan the web of material without any gaps, it is important that the scanning ranges are correctly adjusted to one another, with a minor overlap, and to a narrow marking illuminated along the web of material. But even if only one single CCD camera is used, it is important that the CCD camera be positioned so that the area of the material web illuminated along a line is located within the range scanned by this CCD camera. To permit very fine adjustment of the areas of the web scanned by the CCD cameras, in accordance with the invention, the CCD receiving element of the CCD camera is adjusted transversely to the optical axis of the lens of the camera. In this way, adjusting the relatively lightweight CCD receiving element alone is sufficient without also having to drive the lens along with the help of an automatically focusing (“autofocus”) control device that may be installed. Because the lens of the CCD camera is not driven with the CCD receiving element, the CCD receiving element will be shifted away from (or to the outside of) the optical axis of the lens; however, this shifting is acceptable, particularly for finely adjusting the scanning range. So that the CCD cameras can be correctly aligned, a template can be fixed at the level of the plane of the material web with at least one structure aligned transversely to the direction of movement of the material web. In particular, the template is provided with a line extending transversely in relation to the direction in which the web of material is moving. This line supplies an adequately high optical contrast vis-à-vis the rest of the template, so that this line can be easily detected by the CCD camera. So that the adjustment process can be carried out in the simplest manner possible, the CCD receiving element is set by drives that are actively connected with a controlling device. This controlling device is influenced or regulated by the signals emitted by the CCD receiving elements. In this way, the CCD receiving elements are automatically adjusted to the structure on the template, so that adjustments are executed quickly and always with a constantly high quality.
So as to achieve an exact alignment of the scanning ranges of the CCD camera, it is sufficient to displace the CCD receiving element in the direction in which the material web is running, as well as transversely to the optical axis of the lens. Any additional transverse displacement of the CCD receiving element relative to the moving direction of the material web is unnecessary because these alignment errors can be taken into account by selecting a suitable amount of overlap between the CCD cameras.
So that the individual image lines generated by the CCD receiving elements can be easily assembled to form an image, it is important that the receiving elements be aligned in parallel with one another. However, the overall structure of the holding devices for mounting the CCD cameras contain manufacturing tolerances with respect to the alignment of the receiving line of the CCD receiving element. Such tole

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