The invention concerns a method for cutting narrow strips transversely to a wide supply web, as well as an apparatus for cutting narrow strips from a wide web and comprising a cylinder divided into angular sections and a cutter with a cutting edge in the longitudinal direction of the cylin- der, said cutter being adapted to cut a strip from the wide web by penetration between the sections of the cylin¬ der.

Devices adapted to cut narrow strips from wide supply webs are used in many industrial fields. For example for apply¬ ing handles to cans and other forms of packages, where there is a need e.g. for cutting narrow sheet strips from a wide sheet web of a soft material, said web having been made partly self-adhesive for subsequent glue application of the finished handles.

A technique comprising a cylinder is usually preferred for cutting material from a supply web, since both the web and the strip just cut can be retained by simple means, e.g. by means of vacuum, so that the web is tightened during the cutting process, and so that the strip can be retained after cutting.

Using such a cylinder in the cutting of strips, the simplest technique will be to press a cutting edge against the cylinder, so that a cutting line transversely to the web cuts a strip. Though this involves a principle where knife and cylinder may be constructed in a simple manner, the wish for a great web width makes huge requirements with respect to the stiffness and accuracy of the con¬ struction, in particular in case of thin and tough web

materials. The edge of the cut strip will often have a dissatisfactory quality for many purposes.

Usually, cutting of strips from sheet webs is preferably performed with a cutting system which operates according to the shears principle where the cylinder is divided into longitudinal sections, each of which has a cutting edge which together with a knife blade forms a pair of shears. Each section comprises a plurality of web retaining suc- tion holes connected with a channel in the cylinder sec¬ tions and from there with a vacuum system through con¬ trolled valves.

The cutting edge of the knife may be rectilinear. To ob- tain correct cutting of the strip, it must be ensured that the sheet web is not subjected to impacts which may cause displacement of the sheet along the roller. The angle be¬ tween the cutting edge and the roller must therefore be kept within quite narrow tolerances, where 3° - 5° will typically be acceptable.

A sheet width of 500 mm will cause great knife travel even with a cutting angle of 3°. During the rotation of the roller a clearance of 5 mm is typically required, and a cutting depth of minimum 3 mm is required for ensuring correct cutting, which gives a knife travel of 34 mm. For each cutting operation, the knife is to be moved 34 mm forwardly and then 34 mm rearwardly, which results in great knife velocities as well as considerable accelera- ions in case of high production rates.

Another well-known system for cutting sheet strips is the disc knife system, where a circular knife together with a roller forms the pair of shears. If the generally used disc knives with a diameter of about 100 mm or less are to be moved into the knife roller, a cut of 500 mm is per-

formed and is moved out of the knife roller again in e.g. 0.2 sec., this will require very great accelerations and velocities.

The object of the invention is to provide a method of cut¬ ting strips from a wide web, using a knife which forms a substantially constant angle with the wide web during cut¬ ting of strips, the knife travels and knife acceleration being reduced considerably with respect to the prior art.

This object is achieved as stated in claim 1, the cutting edge of the knife being constructed so as to ensure that the return movement of the knife can begin before cutting has been terminated, and that cutting still takes place at an acceptable angle, even though one end of the knife is returned. This ensures that the knife is not futher inside the cylinder than the required insertion depth, e.g. 3 mm, at the termination of cutting, which gives a return move¬ ment which is considerably smaller than in the prior art, so that there is no need for the great accelerations and velocities which were previously necessary for returning the knife and which subjected the tool to inexpedient stresses.

The invention moreover concerns an apparatus of the type mentioned in the opening paragraph with means for moving the cutter so that the strip is cut in that a first end of the cutter is moved toward the cylinder, so that the cut¬ ting edge forms a cutting point, which is moved trans- versely to the web during cutting, with a substantially constant angle between the cutting edge of the cutter and the longitudinal axis of the cutting cylinder, and that the means for moving the cutter are adapted to return the first end of the cutter before the termination of cutting. The cutter or the knife will thus be caused to perform a rocking movement so that the parts of the knife having

contributed to the cutting process are returned to a position outside the contour of the cylinder already before the termination of cutting.

As stated in claim 3, the sectionally divided cylinder may advantageously comprise a plurality of cutting edges arranged in the longitudinal direction, which then coope¬ rate with the knife during the cutting process. Claim 4 states how the cutter may be moved by means of angularly displaced cranks which, as stated in claim 5, may be connected with respective attachment points at the ends of the cutter through piston rods. One of these attachment points may be a pivot, as stated in claim 6, while the other may be a linear guide in the longitudinal direction of the cutter. Claim 7-10 state how the sectionally di¬ vided cylinder may comprise means for retaining the web as well as the cut strips, and that these means may be formed by suction holes connected with an external vacuum pump through a valve system. The effect of the suction holes may be increased considerably by providing part of the surface of the cylinder in connection with the suction holes with roughnesses, which may e.g. be established by sand blasting part of the surface of the individual cy¬ linder sections. Thus, the web cannot be hermetically sealed against the sand blasted surface which will thus be actively sucking, but still supports the web so that the web does not curl.

The invention will be explained more fully below in connection with preferred embodiments and with reference to the drawing, in which

fig. 1 is a perspective view of a known cylinder divided into angular sections,

fig. 2 is a schematic view of the cylinder shown in fig. 1 in connection with a known linear knife,

fig. 3 schematically shows the parameters on which the calculation of the cutting edge curvature is based,

fig. 4 is a perspective view of a preferred embodiment of an apparatus according to the invention for cutting strips,

fig. 5 shows the movement of the knife shown in fig. 4, and

fig. 6 is a perspective view of a section of the cylinder shown in fig. 4.

Fig. 1 shows a sectionally divided cylinder known per se for use in the cutting of strips from a sheet web which is advanced at a high velocity. The cylinder 10 is divided into a plurality of sections 11 provided on the face di¬ rected toward the sheet web with a plurality of suction holes 12, which are connected with an external, valve- controlled vacuum source (not shown) via internal channels in the cylinder, so that the suction holes 12 in a section 11 can be caused to suck and thereby retain the sheet web during cutting, while a knife is moved into the gaps formed between the sections.

Fig. 2 illustrates the. shortcomings of the prior art and shows the cylinder 10 whose center line is marked with a dot-and-dash line. A knife 22 with a linear cutting edge 23 is caused to perform a translatory movement by e.g. two hydraulic cylinders, which, through two shafts 21, impart a reciprocating movement to the knife 21 which is con- trolled with two guides 20. The cylinder 10 can either advance the web continuously, so that the apparatus more-

over comprises means for guiding the cutting mechanism in a movement such that the knife blade follows the knife cylinder during cutting and is moved to a new position upon termination of the cutting, or advance the web in jumps so that the cylinder 10 stands still during the ac¬ tual cutting procedure. When the knife 22 and the cylinder 10 are moved with respect to each other, a clearance f is required, which will typically be of the order of 5 mm. With an angle of 3' between the cutting edge 23 and the cylinder 10 and with a cutting length of 500 mm, one side of the cutting edge will be 26 mm closer to the cylinder than the other, which is shown by h in the figure. A mini¬ mum insertion i of the cutting edge 22 is required to en¬ sure correct cutting, where i will typically be of the order of 3 mm. The knife travel v will here be the sum of these three parameters and corresponds to the distance be¬ tween the two extreme positions of the knife, and in this example v will be 33 mm.

Fig. 4 shows an apparatus according to the invention for cutting narrow strips from a wide web 50, where the strips in this example are to be used for applying handles to cans; the web 50 is therefore shown as a transparent sheet web with applied adhesive, the adhesive power at the ac- tual grip having been neutralized by applying a paper web 51 on the center of the self-adhesive sheet web.

A knife 40 with a cutting edge 49 is caused to cut a strip from the sheet web 50 by moving the knife 40 inwardly be- tween the sections of the cylinder, which may advantag¬ eously also be provided with a cutting edge forming to¬ gether with the cutting edge 49 a pair of shears. The knife 40 is moved by a shaft 41 with two cranks 43 which are mutually angularly displaced by an angle w. Each of the cranks 43 are connected through a connecting rod with pivot joints 45 with a cross-head transferring the rotary

movement of the crank to a linear movement of piston rods 42. The liniear reciprocation of the piston rods are en¬ sured by guides 46, but may also be obtained by replacing the pivot joints 45 with a cross-head which is moved in guide planes such that the rotary movement is converted to a linear movement of the piston rod 42.

The knife 40 is rotatably connected at one side with a pivot 48 on one piston rod. At the other side, the knife 40 has a linear guide or a recess for accommodating a pivot 47 on the other piston rod. The knife 40 can hereby follow the linear reciprocation of the two piston rods 42. By shaping the cutting edge 49 of the knife 40 in a suit¬ able manner, it can be achieved that cutting of the web 50 begins in that the right side of the knife 40 is moved forwardly to form a cutting point which is moved trans¬ versely to the web 50 and is terminated at the left side of the knife 40, the right side of the knife 40 having already been disengaged from the cylinder at this time.

It will be appreciated that other mechanisms than a common crank shaft can perform this translatory movement of the knife, but with this principle it will be possible to pro¬ vide a simple and reliable construction. Alternatively, the movement can take place by using two hydraulic cy¬ linders which are suitably caused to move the ends of the knife.

Like the prior art, the cylinder 10 can either advance the web continuously or in jumps, and depending upon this, the apparatus will either comprise means for advancing the cutting mechanism with a cylinder or means for advancing the web from the supply roller, so that violent tensions in the web 50 will not occur because of the discrete ad- vance.

Fig. 3 shows how a point on the cutting edge 49 of the knife 40 shown in fig. 4 is calculated, and also shows the most essential parameters of the cutting edge shape. A point on the cutting edge is designated P, and the line K is parallel with the cylinder axis and extends through the point P. The dot-and-dash lines L and mark the direction of the movement of the piston rods, and the distance be¬ tween the piston rods is marked c. The point 0 is the attachment point to one piston rod about which the knife can rotate. A point G is the attachment point of the knife to the other piston rod, and this attachment point is held by a linear guide. A line B extends through the attachment points 0 and G. The attachment points of the knife can ro¬ tate about a line A. The crank shaft rotates with an angle of rotation v, and the cranks are mutually angularly dis¬ placed w. The distance between the point P on the cutting edge and the line A about which the attachment points can move is indicated by a. R, u are a radius vector to P in a polar system of co-ordinates with O as origin and B as base line, while X and Y are the corresponding rectangular co-ordinates to P. rl and r2 are the maximum distance of the two attachment points 0 and G from the line A. By suitably forming equations for the point P, a computer can calculate a possible shape of the cutting edge. This can be done when a plurality of the machine-conditioned para¬ meters has been determined. Then, it is possible to obtain e.g. the knife shape shown in fig. 5a, where the line P marks the cutting edge of the knife and the line B marks the line extending through the attachment points of the knife. Fig. 5b shows how the knife will move in the se¬ lected example, where four different knife positions are shown simultaneously. The lines P and B are marked with conntected index numbers, such that the knife in the first position (PI, Bl) is contacted with the cutting edge of the cylinder, which is marked by I. The knife is then advanced further so that the cutting point is moved to the

left and is marked by II corresponding to the knife position (P2, B2). The attachment point at the left side of the knife will continue to be advanced, while the re¬ turn of the attachment point at the right side has already commenced, the cutting point having been moved to the left side marked with III, while the right side of the cutting edge in this position (P3, B3) is about to leave the cy¬ linder. In the last position (P4, B4) an essential part of the knife has been moved out of the cylinder, and the ac- tual cutting is about to be terminated, following which also the left attachment point is returned. By providing the cutting edge with a suitable shape and providing a drive mechanism capable of imparting a rocking movement to the knife, it can thus be obtained that a considerable part of the knife has been moved out of the cylinder prior to the termination of cutting, so that the violent move¬ ments and strong accelerations of the prior art are avoided.

Fig. 6 shows a preferred embodiment of the cylinder shown in figs. 1 and 4, where part of the surface of the section 11 in contact with the web sheet 50 is provided with a form of roughness 14, which may e.g. be established by sand blasting. Alternatively, the roughnesses may be in the form of lines or the like.