Television – Special applications – Manufacturing
Reexamination Certificate
1999-09-02
2002-12-17
Kelley, Chris (Department: 2713)
Television
Special applications
Manufacturing
C348S132000, C356S431000, C382S141000
Reexamination Certificate
active
06496219
ABSTRACT:
This invention relates to a system for automatically detecting in a rotary printing press incipient printing faults on a metallised packaging strip, such as aluminised film, or any other substrate having a high reflecting power.
Frequently used in the packaging industry for printing strips fed from a reel, machines of this kind comprise a plurality of constituent stations, namely, progressing logically from upstream to downstream with reference to the direction of movement of the strip, a feed station comprising a reel holder and an automatic strip connector followed by a strip accumulator as required for each connection, an introduction station comprising a strip straightener and guide, a sequence of one or more printing units provided with dryers, and finally a reel receiving station or, if required, a station which directly introduces the printed strip into a new machine enabling it to be cut either by rotary working or flat working.
The automatic printing fault detection system will be used after this latter unit. Each of the printing units can give rise to different faults which may be in the form of streaks, smudges or blotches, variations in print intensity, print holes, or poor register in the case of a fault due to a shift between the different printing colours.
Numerous display and/or detection systems for these faults do exist in the prior art and generally use a video camera or any other means of picking up the light reflected by the printed strip. However, all these systems are intended primarily for monitoring non-specular colour prints on matt supports which have no particular brightness capable of reflecting the light in a given direction. It is therefore advantageous to differentiate the printing supports and inks designated as matt, in which it is not possible for any image to be reflected, from the metallised printing inks and supports whose reflecting power is associated with the aluminium foils typically used for perishable foods.
When a beam of light illuminates a non-reflecting surface termed matt, the light which is returned by this surface is a diffuse light which is reflected in every direction. On the other hand, if this surface is that of a metallised strip, the incident beam of light will be reflected as in a mirror in a given direction, at an angle of reflection equal to the angle of incidence of the beam. The difficulties that are found when monitoring a metallised strip depend essentially on the actual nature of the strip which has a specular and non-diffusing reflecting property. The subsequent problem in respect of optics or lighting and the sensing, by a camera, of the light reflected by the strip, form the subject of this invention inter alia. To obtain a good image quality, either with good colour rendering or a faithful image of the printed pattern, and avoid any problems in respect of deformation, lack of clarity and non-uniformity of the luminous flux sensed at the surface of its field of view, the camera is advantageously placed along a photographing axis oriented perpendicularly to the plane of the metallised strip. Since the illumination of a metallised strip can be likened to illumination of a mirror, the arrangement of a camera opposite said strip will naturally have the effect of giving rise to reflection of the image of the camera by the metallised strip. Although the camera may for the major part be hidden behind an opaque mask, the camera lens cannot be masked similarly in any case whatsoever. The geometric configuration of the camera lens with respect to the plane of the metallised strip is such that, in view of the specular properties of the strip, the camera can only relentlessly film the image of its own lens. Since the latter is directly connected to the camera photographic chamber, it follows that a black disc having a contour of varying definition depending on the quality of the reflection of the metallised strip will permanently appear at the centre of the image given by the camera. In order that the rays of light reflected by the metallised strip may traverse the lens of the camera in accordance with such a configuration, said rays must originate from a light source disposed on the same axis as the camera lens by virtue of the law of reflection which states equality between the angle of reflection and the angle of incidence of a ray of light. If that is not the case, the rays of light will not traverse the camera lens, and will therefore give rise to a darkened image of the strip on which the metallised surfaces will appear as surfaces of a substantially black tint. This blanking out of the image of the metallised parts of the strip, which is quite specific to such materials or inks having a predominance of specular colours, means that it is no longer possible to exclude any printing fault over the entire monitored surface.
To obviate this problem, various known systems making up the prior art provide a solution, depending on specific needs, to the problems of shade or reflection caused by illumination of strips subject to print or sealing quality control in a specific case.
For this purpose, the patent JP 9 300 596 describes a lighting system enabling a strip of any substrate to be inspected and printing faults to be detected. The system in question comprises a fixed lighting comprising three light tubes disposed opposite the front side of the vertically moving strip, and a light tube which detects the print holes by illuminating the back of the strip. Opposite the strip, two or three lights are disposed symmetrically on either side of its perpendicular and illuminate at an angle of 55° with respect to its surface. These two lights contribute an illumination intended to be reflected by all the diffusing surfaces. The beam of light from the third light is in turn intended to be reflected by specular surfaces. Its inclination with respect to the perpendicular to the strip is 8°. A camera situated opposite the strip standing back from the light fittings films the strip at an angle of the same value so that the reflection of the latter beam traverses the camera lens if it is reflected by a specular surface. Also, the inclined plane defined by the lamp for the front of the strip is such that it includes the axis of the camera lens. The four light tubes operate simultaneously and their lighting power is individually determined and monitored by an electronic monitor.
Another system is given by the patent EP 781 655, in which the inventor proposes apparatus and a method whereby during optical quality monitoring it is possible to reduce the shade effects which typically form on a strip formed by a transparent support moving horizontally above a surface having a diffusing opaque background. Comprising in particular transparent parts and opaque parts, said strip is illuminated on its front surface by an oblique parallel beam of light. The oblique arrangement of the beam is necessary in view of the position of a camera situated opposite the front surface of the strip on an axis perpendicular to the latter. In order to avoid static electricity problems as a result of friction of the strip on the opaque background surface, an indispensable gap separates the moving strip from the background surface. Since the lighting beam incidence to the printed strip is not perpendicular, a shade zone of triangular section proportional to the height of the gap and to the value of the angle of inclination of the incident beam inevitably forms in the gap and around all the opaque surfaces of the strip. To meet this problem, the inventor proposes that the opaque background surface should be replaced by a support consisting of a plurality of layers of a material which diffuses and reflects the light by cascade from one layer to the next. In this way there is created, in depth in each of the layers of said support, a better distribution of the light in every direction contributing to eliminate or attenuate the unwanted shade effect.
The patent JP 4 071 849 describes an optical detector designed for inspection of printed strips, including those having
Porret Olivier
Toma Claude
Bobst S.A.
Kelley Chris
Ostrolenk Faber Gerb & Soffen, LLP
Parsons Charles
LandOfFree
Automatic system for detecting printing faults on metallized... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Automatic system for detecting printing faults on metallized..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Automatic system for detecting printing faults on metallized... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2928946