The present invention relates to a cross-cutting apparatus for a web of paper sheets, especially for trimming the edge of bundles of paper sheets formed by printed matter, said apparatus comprising a cutting roll and a counter roll between which the web of paper sheets runs and which are driven at a peripheral speed slightly higher than the run¬ ning speed of the web of paper sheets, a crosswise cutting blade associated with the cutting roll and fastened to a blade carrier which is mounted on the cutting roll to rotate therewith and which is movable relative to the cutting roll during the course of cutting action, as well as a counter blade associated with the counter roll and the cutting blade placing itself alongside it during said cutting action, a pivotable mounting axle whereby the blade carrier is mounted on the cutting blade, and a follower wheel eccentrically connected to the end of the mounting axle and forced to follow a fixed guide surface, having a curvature which forces the mounting axle and, respectively, the blade carri¬ er together with its blade to pivot in the direction oppo¬ site to the rotating direction of the cutting roll.

Typically, the case is not about severing a continuous web but, instead, about trimming the pages (side edge) of at least partially folded newspapers or magazines.

An apparatus of the invention can be used as a part of the folding mechanism in a printing machine or also separated therefrom. For example, the cross-cutter located in the vicinity of a folding apparatus can be supplied with papers from a temporary storage. The cross-cutter can also be included in individual binding lines which are supplied from a bundle of papers by means of a suitable feeding mechanism.

In conventional cross-cutting, effected by the folding mechanism of a printing machine, the cutting blade is fixed-

ly mounted on a cutting cylinder and emerges a certain distance from the cutting cylinder so as to extend inside the padding of a counter cylinder. Paper is cut between the cylinders as the latter make a turn. In particular, when dealing with a thick (5 mm) web of paper sheets, the cutting blade must be emerged to such an extent that said blade makes a contact with the web of paper long before the point of cutting and, thus, is inclined backwards at the start of cutting and inclined forward at the end of cutting. This faulty movement produces a poor cutting result.

Patent publication EP-0 423,529 discloses a similar type of cutting-trimming device, wherein the cutting blades are adapted to be movable in such a manner that the same cutting cylinders can be used for cutting to various format lengths. This is based on the fact that the cutting blades can be set for peripheral speeds that are different from those of the cutting cylinders. This prior known device suffers from exactly the same blade attitude defects as the above-de- scribed devices, in which the blades are fixedly mounted on cylinders. In other words, the impairment of cutting result caused by the change of attitude between blade and web has not been eliminated.

Patent application FI-932623 discloses a device of the above-described type, whereby cross-cutting is effected to the length of a certain format, yet in such a manner that the change of attitude between blade and web is avoided during cutting. This prior known device is provided with a leverage for retaining the blade at all times perpendicular relative to the web of paper sheets while pressing the blade away from the cutting roll during cutting. However, the leverage in this prior known device is structurally diffi¬ cult to design.

An object of the invention is to provide a structurally simple cross-cutting apparatus, which is capable of retain-

ing the blade perpendicular relative to the plane of a sheet or a bundle of sheets to be cut.

This object of the invention is achieved on the basis of the characterizing features set forth in the annexed claim 1.

The non-independent claims disclose preferred embodiments of the invention.

The invention will now be described in more detail with reference made to the accompanying drawing, in which

fig. 1 is a schematic side view of the essential compo¬ nents included in a cross-cutting apparatus of the invention at the initial stage of a cutting sequence;

fig. 2 shows one example of the curved shape of a guide surface included in the follower wheel, when the eccentricity and other such dimensions of a follow- er wheel 7 comply with the case of fig. 1; and

fig. 3 shows another example of the curved shape of a guide surface included in the follower wheel, when the eccentricity of a follower wheel 7 has been substantially increased as compared to fig. 1.

The web of paper sheets to be cut can be produced in the folding mechanism of a newspaper or magazine printing ma¬ chine. Thus, the web consists of separate, at least partial- ly folded papers which are subjected to trimming effected by way of cross-cutting. The web of paper sheets travels through between a cutting roll 1 and a counter roll 2. The rolls 1 , 2 have a peripheral speed which is slightly higher than the speed of the web of paper sheets and, thus, the rolls 1 , 2 are not in contact with the web which is carried e.g. by means of belt conveyors on either side of the rolls 1, 2. A cutting roll 3 is mounted on a blade carrier 4 which

is secured to the cutting roll 1 by way of a mounting axle 5. The mounting axle 5 is journalled to be rotatable rela¬ tive to the roll 1. The other end of the mounting axle 5 is provided with an eccentric pin 6 which is surrounded by a follower wheel 7 that is pressed e.g. by a spring force against a fixed guide surface 8. As the roll 1 is rotating, the follower wheel 7 rolls along the guide surface 8 and determines the angular position for the mounting axle 5. Thus, the shape of said guide surface 8 can have an effect on the angular position of the blade 3. Naturally, this is also affected by the distance of the mounting axle 5 from a line c connecting the centre axes of rolls 1, 2, the dis¬ tance of the point of blade 3 from the centre line of mount¬ ing axle 5, and the eccentricity of the follower wheel 7 relative to the mounting axle 5. The drawing illustrates one preferred case for selecting the mutual relationships be¬ tween these dimensions. It is natural that variations of these dimensions have an effect on the shape of a guide surface. For example, increasing the eccentricity of a follower wheel requires increased asymmetry for a guide surface as compared to the case of fig. 2. Thus, one possi¬ bility is to employ a curved shape as shown e.g. in fig. 3.

The guide surface 8 is preferably provided with four differ- ent curved sections successively (Figs. 2 and 3; curved sections I-IV). The first curved section I, having an arc length of e.g. about 30°, produces the movement of blade 3 and blade carrier 4 in a rotating direction A of the cutting roll 1 and away from the cutting roll 1 prior to the arrival of said blade 3 in the cutting position shown in the figure. During the cutting action (about 12° forward from the illus¬ trated position) the wheel 7 follows the curved section II of the surface 8, producing the movement of blade 3 against the rotating direction A of cutting roll 1 and towards said cutting roll 1. This movement of blade 3 in relation to roll 1 achieves the desired perpendicularity between the blade 3 and a sheet. Alongside the blade 3 are contact blocks 13 of

resilient polyurethane for pressing a sheet to be cut against the surfaces of a counter blade 9. Although the rolls 1 , 2 have a speed difference relative to the web of paper, the curved section II is such that the contact blocks 13 and the blade 3 have a speed which is equal to that of the web of paper. The movement of blade 3 towards roll 1 is slight that, as the rolls 1 and 2 are rotating, the blade 3 extends into a slot in the counter blade 9 and performs the cutting. The cutting edge of blade 3 may be inclined, such that one end of the blade commences and finishes the cutting before the other end. The third curved section III of guide surface 8, followed by the wheel 7 after the cutting, accel¬ erates the movement of blade 3 and blade carrier 4 towards the cutting roll 1 and, thus, the web of paper sheets is as briefly as possible grabbed between contact blocks 13 and counter blade 9. The fourth curved section IV of guide surface 8 returns the blade 3 and blade carrier 4 to the commencing position of curved section I with minimum decel¬ eration and acceleration forces.

The movements of the counter blade 9 are arranged consis¬ tently with those of the blade 3. Therefor, the counter blade 9 is secured to the roll 2 through the intermediary of a pivotable mounting axle 10. The axle 10 is pivoted by means of an eccentric follower wheel 11 and a guide surface 12.