Optics: measuring and testing – By monitoring of webs or thread
Patent
1996-09-23
1998-06-16
Font, Frank G.
Optics: measuring and testing
By monitoring of webs or thread
356430, 356375, 356394, 25055939, 2505594, 25055944, 25035945, G01N 2184, G01N 2100, G01N 2186
Patent
active
057679754
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for sensing the position of a crease line or similar embossment in a moving packaging web or the like. The invention also relates to a device for carrying out this method.
BACKGROUND OF THE INVENTION
A crease line in a packaging web can be regarded as a fold notch, along which a package, which is manufactured from the packaging web, is folded. Each package blank is thus provided with a number of crease lines, which can go in different directions on the packaging web.
In different cases there can be reasons to control a subsequent process based on a crease line, which can be transverse or longitudinal. One example is when a pull strip is to be placed in an accurately defined position in close proximity to a transverse crease line in order later to obtain the intended function of the finished package. Another example is when it is desired to decrease the width (for example from four to two packaging widths) of a packaging material with crease lines but without print. Presently, a longitudinal line is printed on the paper for controlling the cutting process. If it is possible to control a longitudinal crease line, the printing costs and the material waste for the black control line could be reduced.
Due to the difficulties to assess the position of a crease line, earlier attempts have been made to start from a characteristic part of the printed material on the packaging web; this printed material is regarded as being correctly positioned in relation to the crease lines. For different reasons the printing does not, however, obtain the right position in relation to the crease lines with satisfactory precision. This means, for example, that a pull strip, which is positioned in relation to the printing, is not necessarily at a correct position in relation to the intended crease line.
It is accordingly desirable to start from the primary element "the crease line" rather than the secondary element "the print" as the position of for example a pull strip.
A crease line is visible as a generally very weak embossment on the backside of a packaging web. A typical crease line can have a width of 1.8 mm and a height of only 0.03 mm. The crease line is further not especially well defined in its shape. The height of the crease line is further so small that irregularities of the packaging web can cause difficulties with the sensing of a crease line.
The difficulties to assess the position of a crease line in a packaging web are great at a web which is covered with aluminum, which rather often is the case, and even greater when not.
At the outset of the work leading up to the present invention a number of optical methods to sense crease lines were tested. Light was directed in different ways against a moving packaging web, and this light was received by means of photo detectors for creating a measuring signal. It appeared that several of these methods were completely impossible to continue with; a certain method could function for a web covered with aluminum but not for a web without aluminum.
It has already been said that a crease line has a very low height, that sometimes is hidden among normal surface irregularities, which means that it not only is a difficulty to obtain a signal from the crease line but also thereafter to treat this signal in such a way that a reliable and exact indication of the position of the crease line can be obtained.
The Invention
The solution to the problems mentioned above to sense the position of a crease line in a moving packaging web is according to the invention based on the principles: emanating from a light beam directed against the web at an angle in relation to the reflected light, is received by means of at least one photo detector, which creates an electrical signal or picture of the packaging web and the crease line, are brought together to a measuring signal, which is compared in an electronic signal processor with a reference signal, which is stored in the processor and is representative for a reference crease line, and wh
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Font Frank G.
Tetra Laval Holdings and Finance
Vieera-Eisenberg Jason D.
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