OF PACKAGING BLANKS

TECHNICAL FIELD

The present invention relates to an apparatus for controlling the quality of material blanks used for creating packaging containers, in particular rectangular blanks. The present invention also relates to a method for performing such quality control. BACKGROUND

In the production of packaging containers of a paper-based material two main tracks are utilized. The first track involves using a continuous web of material, forming said web into a tube, and, for the tube, perform filling, sealing and cutting into individual packaging container in a simultaneous process. This technique is well-known to the skilled person. The second track involves cutting the web of packaging material into individual sheets. Each sheet is then wrapped into a tubular sleeve, sealed and combined, in one end thereof, with a top section comprising the opening device for forming a complete packaging container. After filling the packaging container through the other end, said other end is sealed and folded to form an individual packaging container. One container of this type is commercialized as Tetra Top® and the underlying technique is well known for the skilled person too.

The packaging material may in a typical case be a laminate formed by laminating barrier materials to the sides of a paper core. The barrier materials may be thermoplastic materials, such as polyethylene, which are used to prevent moist from the content or from the outside to contact the paper core. Other examples include a metallic foil, such as an aluminium foil, arranged on the inside of the packaging container.

The present invention emanates from the fact, that the step of wrapping the packaging blank is a high-precision process which is performed at high-speed. If the packaging blank is not perfectly rectangular or tilted in some way, the two edges being sealed or fused for forming the sleeve may be misaligned. This misalignment may in turn result in cosmetic errors, since a design printed on the packaging material would be distorted, yet more importantly it may lead to problems related to the integrity of the packaging container. One reason for the integrity problems is that it will be more difficult to attach the top section to the sleeve if the end of the sleeve has a saw-tooth shape in it.

In order to remove one reason for the misalignment the present invention provides an apparatus and a method for ensuring that the packaging blank truly is a rectangle, such that features of the web or of the cutting process does not result in e.g. a blank formed as a skewed rectangle.

Prior art involves extracting in the order of 50 blanks in series and to perform manual measurements using a regular scale and measuring from a reference mark of the packaging blank. This method is functional yet cumbersome, and it also contains room for systematic errors and random errors caused by the human factor.

SUMMARY OF THE INVENTION

With the aim of providing an improved device and method the present invention provides an apparatus for determining the perpendicularity of a rectangular blank of packaging material. The apparatus comprises a base, defining a surface onto which the blank may be arranged; a first ruler, which is fixedly attached to the base, and adapted to be abutted by a first edge of said blank; a second ruler, which is attached to the base at an approximate right angle to the first ruler, and arranged to pivot in a plane defined by the base. The second ruler is adapted to be abutted by a second edge of said blank, wherein the first edge is adjacent to the second edge. The apparatus further comprises a measurement device for measuring the position of one end of the second ruler.

In one or more embodiments a third ruler is arranged on the base in an opposed relationship to the first ruler, and the third ruler is arranged to be abutted by a third edge of the blank opposing said first edge of the blank.

In further embodiment the third ruler may be biased towards the first ruler in order to push a blank towards abutment with the first ruler.

In one or several embodiments the third ruler has a floating attachment, i.e. it is movably connected, to the base, such that it may accommodate blanks of varying widths, and in related embodiments the floating attachment or connection is accomplished by guide pins of the base arranged in oblong openings in the third ruler.

Further, the apparatus may in one or more embodiments be provided with a lid portion arranged at a small distance from the base surface, such that a slot is defined between the lid portion and the surface of the base, which lid portion may be fully or partially transparent.

In one or several embodiments the measurement device is an electronic device being coupled to a database for storage of measurement results.

According to another aspect the present invention also relates to a method for determining the perpendicularity of a rectangular blank of packaging material, in an apparatus according to any previous or following embodiment of the present invention. The method comprises the steps of:

arranging the rectangular blank of packaging material in abutment with the first ruler,

- forcing the packaging blank into abutment with the second ruler, and retrieving the result from the measurement device.

In one or more embodiments the method may further comprise the step of, following the step of retrieving the result from the measurement device, transferring the result to a database.

In one or several embodiments the method further comprises the steps of, prior to the step of arranging the rectangular blank:

arranging a rectangular template in abutment with the first ruler, and forcing the template into abutment with the second ruler, wherein the measurement device may be calibrated in relation to the result shown when the template is arranged.

Advantages relating to the characteristic features of the present invention and the various embodiments thereof will be elucidated in the following detailed description of embodiments. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig. 1 is a schematic top view of an apparatus according to a first

embodiment of the present invention. Fig. 2 is a schematic top view of an apparatus according to a second embodiment of the present invention.

Figs. 3A and 3B illustrate a method according to one embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 illustrates an apparatus according to a first embodiment of the present invention. The apparatus 1 comprises a base 2 with a surface onto which a first ruler 4 is arranged. The first ruler 4 is fixed relative to the base, and is bolted onto the base in this case. Several other attachment methods may be used, and the ruler 4 may instead be welded or glued into place, just to give two examples. A second ruler 6 is pivotably arranged onto the base 2, and arranged to pivot in the plane of the surface of the base 2. In the disclosed example the pivot point 8 is arranged in the approximate middle of the ruler 6.

In this context, and to better understand the construction of the apparatus 1, it may be noted that the blanks are cut from the web by a pair of rectilinear knives (not shown). The width of the blank is determined by the width of the web, and the length of the blank is determined by a forward indexing of the web between cuts. Typical errors therefore involve that the web is misaligned relative to the knives, for one reason or the other. The result of such errors is that the cut edge is slanted relative to the cross direction of the web, and this error is what an inventive device is arranged to determine.

A measurement device 10 is arranged for measuring the position of a first end 3 of the second ruler 6. In this embodiment the measurement device 10 is simply a digital indicator 10' having its spring plunger 10" in contact with the end 3 of the second ruler 6, which is shown in Fig. 1.

As a blank 18 (shown in figures 3 A and 3B) is arranged in the apparatus 1 and arranged in abutment with the first ruler 4 it may be slid into contact with the second ruler 6. This is generally performed in such a manner that what was the longitudinal edge of the web, a first edge 5, is arranged in abutment with the first ruler 4, and the cut edge, a second edge 7, is arranged in contact with the second ruler 6. Due to the pivotable arrangement the second ruler 6 will accommodate to the extension of the cut or second edge 7. Since the longitudinal or first edge 5 is in contact with the first ruler 4, the digital indicator 10' will display a measure which reveals any inclination of the cut edge 7 relative to the longitudinal edge 5. Given that the longitudinal edge 5 is used as a reference, the apparatus 1 will provide a quantitative measure of the inclination of the cut edge 7. In the illustrated example the readout from the digital indicator 10' will reveal the inclination in terms of e.g. mm per half the blank width (since the pivot point 8 is arranged in the approximate middle of the ruler 6 and also the middle of the blank 18). The digital indicator may obviously be replaced by a manual indicator, or by another device able to measure the position of a point on the second ruler 6 or the inclination thereof.

Fig. 2 illustrates a second embodiment of the present invention. Due to the similarities the same reference numerals are applied for similar components. The additional component in this second embodiment is a third ruler 12. This third ruler 12 is used to abut the other longitudinal edge, a third edge 9, of the blank 18. It is beneficial if the third ruler 12 is biased towards the first ruler 4, since this makes it possible to accommodate blanks having a slight variation in width. In cases where the two longitudinal edges 5, 9 of a blank 18 are not perfectly parallel it is further beneficial if the third ruler 12 has a floating attachment to the base 2. The term "floating attachment" relates to the third ruler 12 being able to pivot in the plane of the base 2 and at the same time being able to move its centre of gravity towards and away from the first ruler 4. One way of achieving such a connection is illustrated in Fig. 2, where two oblong openings or slots 14, 16 of the third ruler 12 are arranged to receive respective guide pins 11, 13 projecting from the surface of the base 2.

Thereby, the ruler 12 is allowed to pivot and move back and forth (towards the first ruler 4) at the same time. The biasing function may be achieved in numerous ways obvious to the skilled person, and in the present embodiment it is provided by a single leaf spring 15, or a resilient bar. In this way the third ruler 12 may push a blank into continuous abutment with the first ruler 4 even if the width or parallelity of the blank varies in relation to other blanks. The biasing force of the third ruler should be quantified such that it prevents an arranged blank from being pushed out of position by the second ruler 6 (the biasing action provided by the measurement device 10). According to yet one or several embodiments a lid portion 17 (schematically illustrated in figure 1) is arranged at a small distance from the base surface, such that a slot is defined between the lid portion 17 and the surface of the base 2. The slot preferably has a width corresponding to the thickness of the blank, such that it may serve the purpose of preventing the blank from bulging during measurement. The lid portion 17 may also serve the purpose of protecting the apparatus. It is beneficial if the lid portion is transparent, either fully transparent or at least transparent in critical locations, i.e. location where a user benefits from being able to confirm visually that an abutment is proper, etc. The lid portion may be fixedly attached to the apparatus, or easily openable.

In one or more further embodiments the rulers, at least the first 4 and third ruler 12, may have an undercut cross section, such that the edges of the blank are firmly held in place. This feature may be applied to any embodiment described.

The measurement device 10 may preferably be connected to a computer, either in a wireless manner or not. This facilitates the transfer of data from the measurement device 10 to the computer or other data collection means.

Figs. 3A and 3B illustrates how a measurement according to one embodiment of the present invention may be performed. The blank 18 is slid into place in the apparatus 1 (Fig. 3A) and the measurement result is transferred to a processing unit (CPU) (Fig. 3B). A convenient way of obtaining good-quality measurement is to use a blank template (not shown). The blank template has the dimensions of a "correct" blank, in particular relating to the corner angles (being 90°) and other dimensions. After inserting such a template in the apparatus the measurement device may be calibrated (in the case of the digital indicator its zero is set with the template in the correct position). By using this technique the readout from the measurement device is easily interpreted.