Device and method for the alignment of sheets

For a device for the alignment of sheets, which comprises at least one first and one second driving roller (20) and at least one pressure roller (21), as well as at least one first and one second rotary drive (26) for rotating said first and second driving rollers (20), respectively, about an axis of rotation (28), a simple and cost-effective setup is achieved by at least one displacement drive for shifting at least the driving rollers (20) along the axis of rotation in such a manner that there is a change of distance between the driving rollers.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and a method for the alignment of sheets for a printing machine.

BACKGROUND OF THE INVENTION

Printing machines for printing individual sheets can print sheets of different materials and of different sizes. Such printing machines for printing individual sheets comprise, as a rule upstream of at least one printing unit, a sheet-alignment unit. This sheet-alignment unit serves to exactly align supplied sheets with respect to the sheet transport path through the printing unit, before the sheets are passed on for printing or further processing. To accomplish this, the position of the supplied sheets is detected by sensors and forwarded to a control device. Usually, the control device controls various alignment rollers that align a misaligned sheet relative to the sheet transport path.

Known sheet-positioning arrangements comprise, for example, adjacent axially shiftable pairs of rollers that are capable of shifting a supplied sheet in a direction transverse to the sheet transport path (crosstrack alignment). Furthermore, sheet-alignment arrangements are known that comprise pairs of rollers transverse to the sheet transport path at a distance from each other, which pairs of rollers can be driven in different ways in order to align the lead edge of a supplied sheet in a direction perpendicular to the sheet transport path, before said sheets pass through the printing machine (angle or skew alignment).

The accuracy in determining and correcting a misalignment of a sheet depends on the distance of the alignment rollers from each other and on the sensors that are being used (skew sensors that measure the incoming lead edge of a sheet). For a rigid installation, the distance of the alignment rollers is determined by the smallest sheet width that is to be processed by the printing machine. The resolution of a potential angle adjustment of the sheet is highly dependent on the distance between the alignment rollers. At a small distance of the alignment rollers and with large sheet formats, an accurate angle adjustment of the sheet is not possible. A small distance of the alignment rollers primarily restricts the accuracy of the angle adjustment process. Therefore, it is desirable to adapt the distance between the alignment rollers to the width of the supplied sheet.

In most instances, known sheet-positioning and sheet-alignment arrangements are complicated because they, on the one hand, comprise pairs of rollers for positioning the sheet in a direction transverse to the sheet transport path through the machine and, on the other hand, comprise pairs of sheet alignment rollers for aligning the lead edge of a sheet in a direction perpendicular to the sheet transport path. EP 0 469 866 A also discloses an arrangement that performs a skew alignment and a crosstrack alignment by way of the same pairs of rollers. However, the moved masses are very large in crosstrack alignment. This is disadvantageous for a rapid adjustment of the pairs of rollers.

Other known arrangements have been disclosed in U.S. Pat. No. 5,322,273 and in publication DE 101 60 382. U.S. Pat. No. 5,322,273 discloses a complex device that, among other things, is suitable for a sheet alignment perpendicular to the sheet transport path (de-skewing). The rollers or segmented cylinders provided therefor comprise appropriate drives. DE 101 60 382 discloses driven support rollers that can be shifted in transverse direction by a spindle mechanism that is located on the inside.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a simple and cost-effective device for the alignment of sheets for a printing machine. The object of the invention is achieved by a device for the alignment of sheets, which comprises at least one first and one second driving roller and at least one pressure roller, as well as at least one first and one second rotary drive for rotating said first and second driving rollers, respectively, about an axis of rotation. Furthermore, at least one displacement drive is provided for shifting at least the driving rollers along the axis of rotation in such a manner that the distance between the driving rollers changes. As a result of this, a good resolution of the angle alignment of a sheet is achieved.

It is advantageous if the device for the alignment of sheets has a shared pressure roller for the first and second driving rollers because, as a result of this, a second pressure roller becomes unnecessary, and costs can be lowered. Alternatively, one pressure roller each may be provided for the first and the second driving rollers in order to achieve good adjustability of the rollers relative to each other and in order to avoid an axial relative movement between the rollers.

In the device for the alignment of sheets, preferably at least one pressure roller is fixed in position in the direction of the axis of rotation and has a width dimension that corresponds at least to the width of the driving roller plus a displacement path of the driving roller in the direction of the axis of rotation. With such a width dimension, no shifting of the pressure roller in the direction of the axis of rotation need be provided, and costs can be lowered.

Advantageously, in the device for the alignment of sheets, the driving rollers have a section displaying a reduced diameter in order to permit an unencumbered insertion of the sheet between the driving roller and the pressure roller.

In the device for the alignment of sheets, the driving rollers and the at least one pressure roller can preferably assume a first operative position, in which they are positioned radially adjacent to each other, and a second operative position, in which they are radially at a distance from each other. Consequently, a sheet guided between the rollers can be held firmly or released by said rollers.

The displacement drive of the device for the alignment of sheets is preferably connected with the driving rollers in order to directly control their displacement. Alternatively, the displacement drive is preferably connected to the driving rollers and their associate pressure rollers for their joint movement in the direction of the axis of rotation so as to achieve synchronous shifting.

The displacement drive preferably comprises a threaded spindle drive with counter-rotating threaded sections that are associated with each driving roller. As a result of this, it becomes possible to perform a precise high-resolution displacement in the direction of the axis of rotation. It is also possible for each driving roller to be associated with its own displacement drive with a threaded spindle drive in order to provide as many adjustment options as possible. Alternatively, the displacement drive may also comprise a cable pull mechanism in order to save weight and costs.

Advantageously, the driving roller is supported on its drive shaft so as to be shiftable in the direction of the axis of rotation because, as a result of this, the support of the drive shaft can be done in a stable manner and can be implemented with cost-effective components. Alternatively, the driving roller can also be fixed on its drive shaft in the direction of the axis of rotation, and it may be possible for the drive shaft to be shifted in the direction of the axis of rotation. As a result of this, any tilting and/or blocking of the driving roller during the displacement on its drive shaft can be avoided.

In one embodiment of the invention, the driving roller and/or the pressure roller are arranged in a roller support carriage that can be shifted in axial direction. In this way, a stable support of the rollers and the ability to shift them in the direction of their axis of rotation is achieved at the same time.

Furthermore, the object of the invention is achieved by a method for the alignment of a sheet for printing said sheet in a printing machine, wherein a sheet is transported along a sheet transport path to a sheet alignment device, which comprises one first and one second driving roller and at least one pressure roller, wherein a skewed position of the sheet is detected and wherein a distance between the first and second pressure rollers is adjusted in response to a width of the sheet. Subsequently, the sheet is grasped by the driving rollers and the at least one pressure roller, and the first and second driving rollers are individually rotated in order to compensate for a skewed position of the sheet. As a result of this, high accuracy is achieved regarding the correction of the skewed position of the sheet.

It may be advantageous to have sensors detect the width of the sheet in order to determine the optimal position of the rollers for the supplied sheet. Alternatively, the width of the sheet may also be prespecified by a control device of the printing machine, as a result of which additional sensors may be omitted.

Preferably, the method for the alignment of a sheet also comprises the adjustment of the distance of two pressure rollers corresponding to the distance of the driving rollers in order to achieve good abutment pressure and an alignment of the rollers relative to each other.

Advantageously, a lateral deviation of the current position (actual position) of the sheet from a desired position (setpoint) is also detected with this method, and the sheet, if it is grasped between the driving rollers and the at least one pressure roller, is shifted in parallel direction by the driving rollers in the direction of said driving rollers' axis of rotation as a function of the lateral deviation. As a result of this, a transverse alignment of the sheet relative to the intended sheet transport path is achieved.

Furthermore, the method preferably comprises the parallel shifting of the pressure rollers in the direction of the axis of rotation corresponding to the shifting of the driving rollers in order to achieve good abutment pressure and alignment of the rollers relative to each other.

DETAILED DESCRIPTION OF THE INVENTION

In the description hereinafter, the terms right, left, top and bottom, and similar terms, refer to the shown figures and should not be understood to have any restrictive meaning. It will be obvious to the person skilled in the art that the depicted components may also be arranged in a different alignment. The devices for the alignment of sheets for a printing machine as shown inFIGS. 1 and 2are depicted in such a manner that a passing sheet would be moved into the plane as shown in the drawings.

FIG. 1shows a first embodiment of a device10for the alignment of sheets to be printed by a not illustrated printing machine, said device10comprising a left roller pair11and a right roller pair12having axes of rotation parallel to each other. The device10comprises a left rotary drive13and a right rotary drive14for driving the roller pairs11,12about their axes of rotation. In addition, the device10comprises a left displacement drive15and a right displacement drive16for shifting the roller pairs11,12in the direction of the axis of rotation. Furthermore, a not illustrated control device is provided for the control of the rotary drives13,14and the displacement drives15,16. The control device may also be an integral part of a general control device for the control of other functions of the printing machine.

Each roller pair11,12comprises one driving roller and one pressure roller21, said rollers being positioned opposite each other and being in peripheral contact over a prespecified rotation section of the driving roller20(FIG. 3a). On its circumference, the driving roller20has a section or a segment displaying a reduced diameter, so that the pressure roller21and the driving roller20are not in contact with each other when the reduced-diameter section of the driving roller20faces toward the pressure roller21(FIG. 3b). In their basic position, the roller pairs11,12are arranged symmetrically with respect to a central axis22of a sheet transport path through the printing machine, although an asymmetrical alignment is also possible.

A sheet23consisting of paper, for example, that should preferably be aligned symmetrically and at a right angle relative to the central axis22is held between the roller pairs11,12. However, if the section of the driving roller20displaying the reduced diameter is arranged opposite of its associate pressure roller21, the sheet23can be freely moved between the driving roller20and the pressure roller21.

Each of the left and the right rotary drives13,14for the left and the right roller pairs11,12comprises a rotary drive motor26, an (optional) gearing27as well as a drive shaft28on which the driving rollers20are arranged. The rotary drive motor26is preferably a stepper motor, and the gearing27is, for example, a spur gearing.

The driving rollers20are arranged on their drive shaft28in a torque-proof but axially shiftable manner. This torque-proof connection of a driving roller20and its drive shaft28may comprise, for example, a fitting key, a spline shaft or similar shaft/hub connections, with a fitting key29being shown inFIG. 1. The pressure rollers21are arranged on a carrier axle31that is supported in a roller support carriage32that can be shifted toward the right and toward the left. The pressure roller21is resiliently supported relative to the driving roller20in order to be able to accommodate sheets23having different thicknesses.

The left and the right displacement drives15,16comprise a follower36that is connected with the driving roller20. The follower36has a U-shaped recess having an inside width corresponding to the width of the driving roller20plus a minimal play. The lateral surfaces of the driving roller and/or the inside lateral surfaces of the U-shaped recess comprise a material that has a low coefficient of friction, for example, Teflon. Consequently, the driving roller20can rotate freely in the U-shaped recess of the follower36. The follower36is supported so that it can be shifted, perpendicularly to the central axis22, toward the right and toward the left in the direction of the axis of rotation.

Furthermore, the displacement drive15,16comprises several additional deflecting rollers38, an adjustment roller39and a traction cable40. The adjustment roller39is connected to a not illustrated adjustment roller motor. The axes of rotation of the deflecting rollers38and the adjustment roller39extend parallel to the central axis22.

The traction cable40extends from the follower36around the adjustment roller39, is deflected by the deflecting rollers38, and is finally connected to the roller support carriage32. The traction cable40is completely passed around the adjustment roller39in order to improve a power transmission by friction. Furthermore, the traction cable40is maintained tensioned by a first tension spring41between the follower36and a fixed anchor on the housing of the printing machine, and by a second tension spring42that is tensioned between the roller support carriage32and the housing of the printing machine.

During operation of the roller adjustment arrangement10of the first embodiment, a sheet32is first supplied in the direction of the central axis22of the printing machine. Lateral sensors (crosstrack sensors) not illustrated measure the width and the arrangement of the sheet23relative to the central axis22. Likewise, alignment sensors (skew sensors) not illustrated measure the alignment or angular inclination of the lead edge of the sheet23relative to the central axis22.

The distance of the roller pairs11,12is adapted to different sheet widths in that the roller pairs11,12are moved by their respective displacement drives15,16in opposing directions. They may be moved away from each other in outward direction in order to be able to accommodate large sheets23. Likewise, small sheets23can be grasped by the roller pairs11,12when the roller pairs11,12are moved by their respective displacement drives15,16toward each other in inward direction.

The displacement operation explained hereinafter describes the displacement of the right roller pair12in the direction of the axis of rotation toward the right. The displacement operation works in reverse direction with an adjustment of the right roller pair12toward the left, in which case the displacement roller39is then driven in clockwise direction. Analogously, a displacement operation of the left roller pair11toward the right and left occurs in the direction of the axis of rotation.

In order to displace the driving roller20of the right roller pair12in the direction of the axis of rotation to the right, the adjustment roller39of the right rotary drive16is rotated in counterclockwise direction. As a result of this, the traction cable40is moved to the right and pulls the follower36against the pull of the tension spring41to the right. At the same time, the part of the traction cable40between the adjustment roller39and the roller support carriage32is relaxed, the tension spring42pulling the roller support carriage32also to the right. The length by which the traction cable40is wound onto the adjustment roller39—and thus the distance by which the follower36is moved to the right—is unwound, at the same time, from the other side of the adjustment roller39. Consequently, the follower36and the roller support carriage32are moving in parallel (i.e., by the same distance) to the right.

Hereinafter, the expression “parallel displacement” is used to mean that a displacement of the left and right rollers or roller pairs by respectively the same distance in the direction of the axis of rotation occurs toward the left or toward the right. When the distance of the rollers or roller pairs changes, said rollers or roller pairs move together toward each other or away from each other in the direction of the axis of rotation.

If the lead edge of the sheet23is not perpendicular to the central axis22, the size of the angular deviation is measured by the alignment sensors and transmitted to the control device. Said control device individually controls the appropriate rotary drives13or14of the driving rollers20in a manner known per se, until the lead edge of the sheet23is aligned perpendicular to the central axis22.

This may be achieved, for example, in that the roller pairs11,12grasp the sheet23respectively at the same distance from the lead edge of the sheet23and are then driven by their respective rotary drive13or14either faster or more slowly in order to compensate for an inclined position of the sheet23and, at the same time, release said sheet.

Unless the sheet23is aligned symmetrically with respect to the central axis22, the degree of the deviation from the central position is measured by the lateral sensors and transmitted to the control device. While the sheet23is being grasped by the roller pairs11,12(for example, position as inFIG. 3b), said sheet is moved in parallel direction by said roller pairs by means of the right and left displacement drives15,16out of the central position toward the left or toward the right. As a result of this, the deviation of the sheet23from the central position is minimized or eliminated.

FIG. 2shows another embodiment of a device110for the alignment of sheets in accordance with a second embodiment of the present invention. The device110comprises a left roller pair111, a right roller pair112, a left rotary drive113, a right rotary drive114, as well as a left displacement drive115and a right displacement drive116.

Each of the left and the right roller pairs111,112comprises a driving roller120and a pressure roller121, said rollers being located opposite each other. As in the first embodiment, the driving rollers120have a section or a segment displaying a reduced diameter. In a position, in which the section displaying the reduced diameter is located opposite the pressure roller121, a sheet23can be freely moved between the driving roller120and the pressure roller121(see alsoFIG. 3a). The pressure rollers121are arranged opposite the corresponding driving roller120and have a width that corresponds at least to the width of the driving roller plus a prespecified displacement path of the driving roller120in the direction of the axis of rotation.

The left rotary drive113and the right rotary drive114are set up symmetrically so that only one side will be described here. The description may be applied, laterally reversed, to the other side. Each of the left and the right rotary drives113,114comprises a rotary drive motor126, a gearing127and a hollow drive shaft128that support the driving roller120in a fixed, torque-free and axially rigid manner.

The left and the right displacement drives115,116are also arranged symmetrically and the description of one side may be applied, laterally reversed, to the description of the other side, Hereinafter, the right displacement drive116will be explained.

The right displacement drive116comprises a spindle nut135that is arranged inside the hollow drive shaft128and can be rotated relative to said drive shaft, and comprises a threaded spindle136. The threaded spindle136extends through the spindle nut135and is connected to a displacement motor138via an optional gearing137. The spindle nut135is connected in a torque-free but axially shiftable manner with the housing of the printing machine. The hollow drive shaft128can be freely rotated relative to the spindle nut135but cannot be shifted axially in the direction of the axis of rotation in a manner relative to said axis of rotation.

A rotation of the displacement motor138drives the threaded spindle136via the optional gearing137. The spindle nut135moves, depending on the direction of rotation of the threaded spindle136, toward the right or toward the left. This means that the drive shaft128follows an axial movement of the spindle nut135toward the right or toward the left in the direction of the axis of rotation.

Alternatively, it is also possible to provide only one displacement motor138that is connected, via at least one gearing, with the two displacement drives115,116. The gearing may be reversible in order to achieve a corotational or counter-rotational rotation of the respective threaded spindles. As a result of this, only one displacement motor138is necessary to provide a parallel shifting of the rollers in a direction transverse to the sheet transport path, on the one hand, and to provide a distance change of the rollers, on the other hand. Alternatively, the gearing may not be reversible and permit either a parallel shifting of the rollers in a direction transverse to the sheet transport path or permit a distance change of the rollers. This embodiment offers the advantage that the lateral displacement of the rollers by the gearing is always synchronous, and that the right and left displacement motors138need not be driven synchronously with respect to each other.

An angular deviation of a supplied sheet23may be compensated for as in the first embodiment. Said deviation works analogously to the description above and will thus not be explained again at this point.

In the embodiment in accordance withFIG. 2, too, an adaptation of the roller distance to the width of the sheet23is possible, and the driving rollers120can be shifted relative to the central axis22in the direction of the axis of rotation in an inward or outward direction.

Different from the embodiment in accordance withFIG. 1, the distance change of the driving rollers120is accomplished in that the threaded spindles136of the right and left displacement drives115,116are rotated by the displacement motors138. The spindle nuts135and the driving rollers120of the right and left roller pairs111,112connected therewith are shifted toward each other or away from each other in order to grasp large or small sheets23.

The pressure roller121is not shifted in the direction of the axis of rotation because it has a width such that the driving roller120will move on said pressure roller in any position. This means that in the second embodiment only the driving rollers120are shifted corresponding to the width of the sheet23. Like in the first embodiment, the driving roller120and the pressure roller121are supported so as to be resilient relative to each other in order to be able to accept sheets23having different thicknesses.

In the case of the embodiment in accordance withFIG. 2, a parallel, lateral displacement of the sheet23is also possible if a misalignment of a supplied sheet23relative to the central axis22is being detected. Then, the driving rollers120grasp the sheet23and can be shifted, parallel together with said sheet, relative to the central axis22in the direction of the axis of rotation toward the right or toward the left.

The parallel lateral displacement of the driving rollers120is accomplished in that the threaded spindles136of the right and left displacement drives115,116are rotated correspondingly by the displacement motors138. The spindle nuts135and the driving rollers120of the right and left roller pairs111,112connected therewith are shifted parallel toward the right or toward the left in order to minimize or eliminate the misalignment of a supplied sheet23relative to the central axis22.

Additional combinations of the depicted components are conceivable. For example, it is possible to use the wide pressure roller121of the second embodiment (FIG. 2) in the first embodiment (FIG. 1), whereby the lateral displacement of the pressure roller21may then be omitted. In this case, the displacement drive for the driving roller20comprises only the tension spring41, the follower36, the traction cable40and the adjustment roller39. Alternatively, in the second embodiment, it is possible to provide shiftable pressure rollers with drives that correspond, for example, to the displacement drives115,116.

Another modification of the pressure roller121that can be used in both embodiments is a pressure roller121that essentially extends across the entire width of the sheet transport path and supports the sheet23across the entire width. Consequently, only one wide pressure roller or pressure cylinder121would be required for the two sides.

In the second embodiment ofFIG. 2, it would be possible to provide only one displacement drive115or116. In this instance, the threaded spindles136of the left and right displacement drives115,116inFIG. 2would be connected in the center. Such a continuous shared threaded spindle136′ then has a region with a left-hand thread and a region with a right-hand thread. During a rotation of the threaded spindle136′, the left and right roller pairs111,112are either shifted toward each other or away from each other. With a displacement of the shared threaded spindle136′ by a corresponding displacement unit, it would then be possible to perform a lateral shift or crosstrack shift, if necessary.

Furthermore, it is possible to fix the driving roller20in position on its drive shaft28so as to be torque-proof and axially rigid, in which case the respective drive shaft28is shifted in its support in the housing of the printing machine when a lateral displacement of the roller pairs11,12occurs.

The invention has been described with reference to preferred embodiments, wherein the individual features of the described embodiments may be freely combined and/or interchanged with each other, provided that they are compatible. Numerous modifications and forms are possible for and obvious to the person skilled in the art, without departing from the inventive idea as a result of this.