WO2012084713A1

WO2012084713A1 - Method for correcting the position of a sheet in transport direction and sheet processing machine

Info

Publication number: WO2012084713A1
Application number: PCT/EP2011/073048
Authority: WO
Inventors: Rolf SPILZ; Dieter Dobberstein; Volker Otto; Karlheinz Peter; Stefan SCHLÜNSS; Hans-Günter Staack
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 2010-12-21
Filing date: 2011-12-16
Publication date: 2012-06-28
Anticipated expiration: 2013-06-21
Also published as: DE102010055422B3

Abstract

In a method for transporting sheets in a printing machine for transfer from a first transport section to a second transport section, a sheet is brought from a first transport speed in an acceleration zone to a second transport speed. With the use of such a method, positioning of a sheet in transport direction can be achieved with unchanged acceleration parameters within a shorter distance in that different acceleration profiles are provided in the acceleration zone. A first acceleration profile can be provided in the acceleration zone in accordance with which the sheet is directly accelerated from the first transport speed to a third transport speed, and the sheet is then directly decelerated from the third transport speed to the second transport speed. The third transport speed is greater than the first and the second transport speeds. It is possible to provide a second acceleration profile in the acceleration zone, in accordance with which the sheet is directly decelerated from the first transport speed to a fourth transport speed, and the sheet is directly accelerated from the fourth transport speed to the second transport speed. The fourth transport speed is lower than the first and second transport speeds. Depending on the time the sheet is input in the acceleration zone, the first or the second acceleration profile is selected in order to transfer the sheet at a pre-specified time to the second transport section.

Description

METHOD FOR CORRECTING THE POSITION OF A SHEET IN TRANSPORT DIRECTION AND SHEET PROCESSING MACHINE

Technical Field

The present invention relates to a method for transporting sheets in a printing machine.

Background Art

In a known method for transporting sheets in a printing machine, the sheets are conveyed, by way of one or more transport devices, from a sheet supply container in a feeder of the printing machine to an alignment unit and, finally, to a printing zone. Depending on the number of sheets to be printed, one or more sheets are fed to the printing machine from the sheet supply container. Those sheets to be printed are normally fed to the printing machine at a fixed feed rate or feed frequency, for example, at 20 to 100 sheets per minute.

After having been fed to the printing machine, the sheets move along a sheet transport path that is defined by a plurality of transport rollers and transport belts. Along the course of the sheet transport path, it is frequently required that the transport speed of successive sheets be increased or decreased. Such a change of the transport speed can be required, for example, during the transfer of the sheet from a first transport section to a second transport section. By reducing the transport speed of a sheet that is in front in transport direction, the distance of this sheet from the subsequent sheet is reduced. Likewise, by accelerating the sheet that is in front, its distance from the subsequent sheet is increased. By changing the transport speed during the transfer between two transport sections, it is possible to establish a preset distance between successive sheets. As a result of this, it is possible to achieve a uniform distribution of the sheets and a uniform utilization of the printing machine.

Figure 4 is a graph of the progression of speed in a known method for transporting sheets in a printing machine. The distance s travelled by the sheet B along the transport path is plotted on the horizontal axis. The speed v of the sheet B in the direction of the transport path is plotted on the vertical axis. An acceleration zone s_a with a starting position s₁ and an end position s₂ is schematically indicated under the horizontal axis. A first pair of rollers is located at the starting position s₁, and a second pair of rollers is located at the end position s₂. In the horizontal zones of the speed progression, the transport speed remains unchanged, for example at v₁ and v₂. In the inclined zones of the speed progression, the sheet B is accelerated and its transport speed v is increased. The acceleration of the sheet B corresponds to the slope of the speed progression. The possible acceleration – and thus the maximum possible slope of the inclined zones of the graph in Figure 4 – is a function of the inertia of the pairs of rollers and their driving motors or transmissions or both.

The known method in accordance with Figure 4 includes a sheet B that is supplied at a first speed v₁ to be brought into engagement with the first pair of rollers, and that then the sheet B is accelerated using the first pair of rollers within an acceleration zone s_a, and that, finally, the sheet B is continued to be transported at a second transport speed v₂. The earliest point at which acceleration can start is when the leading edge of the sheet B has reached the starting position s₁. However, acceleration can also start when the leading edge of the sheet B is located at any point in the middle of the acceleration zone s_a, provided only that the speed of the sheet B has reached the desired second transport speed v₂ at the end of the acceleration zone s_a.

Depending on the length of the sheet B that is to be accelerated, it is not always possible to start acceleration when the leading edge of the sheet B is in the starting position s₁ of the acceleration zone s_a. If the sheet B is long, the rear portion of the sheet B can still be in engagement with the transport members (transport rollers or belts) arranged upstream in the sheet transport path of the printing machine. Before an acceleration of the sheet B is possible, the sheet B have to be continuously moved along the sheet transport path until the trailing edge of the sheet is no longer in engagement with any transport members of the printing machine, said transport members operated at the first transport speed v₁.

If a printing machine processes sheets having different lengths, the acceleration of longer sheets B has to start later than the acceleration of short sheets B, because the trailing edge of the longer sheets B moves later out of the previous transport members. On the other hand, the previous transport members cannot be arranged at an arbitrary distance from the acceleration zone s_a, because the free distance of the transport members is defined by the length of the shortest sheet B that is to be processed. This free distance have to be selected in such a manner that the sheet is always in engagement with the transport member. Thus the sheet B can be safely transferred from one transport member to the next transport member. This means that the leading edge of a longer sheet B in some cases has to move far beyond the starting position s₁ of the acceleration zone s_a until the trailing edge becomes free.

The length of the available acceleration zone s_a is limited in a printing machine. Due to this, there is the problem that the remaining remainder of the acceleration zone s_a will perhaps not suffice to accelerate the sheet B to the desired second transport speed v₂ at a preset maximum acceleration of the sheet B.

Publication DE 10 2005 038 324 A1 has disclosed a method for transporting sheets in a digital printing machine, wherein the remaining remainder of the acceleration zone s_a can be better used. In this method, a sheet to be printed is brought from a first transport speed in a first transport section to a second transport speed in a second transport section. During its transfer from the first transport section to the second transport section, the sheet is given a positive or negative acceleration or both. In a first embodiment, the sheet is decelerated from the first transport speed to a third, lower transport speed, then greatly accelerated to a fourth transport speed beyond a second transport speed and then again decelerated to the second transport speed. Alternatively, the sheet is briefly decelerated from the first transport speed to a third transport speed, then greatly accelerated to a fourth transport speed, and then decelerated to the second transport speed. In both cases, further processing of the sheets is performed at the second transport speed.

The sheets themselves are light-weight and display low inertia; however, they are accelerated or decelerated or both using driving rollers either driving belts that display a rotational inertia. In order to produce strong acceleration or delay of the driving rollers in a short time, great torqueses are required, depending on the size and the weight of the driving rollers as well as on the differences between the transport speeds.

Considering these methods, there is the disadvantage of necessitating great accelerations that have to be provided and tolerated by the driving elements of the printing machine.

However, it is not possible to increase acceleration at will because greater accelerations, in turn, require larger motors or transmissions or both that, in turn, display greater inertia and thus require an even greater torque. For such a solution, the costs for motors and transmissions of the drive will increase further. Likewise, smaller motors cannot be expected to provide any random increase of the driving torque because the wear of the motors and the probability of failure will increase.

Disclosure of Invention

Against the background of the aforementioned prior art, it is the object of the present invention to achieve a positioning of a sheet in transport direction along a shorter distance although the acceleration parameters remain the same.

This object is achieved by a method for transporting sheets in a printing machine for transfer from a first transport section to a second transport section in accordance with Claim 1, wherein a sheet is brought from a first transport speed in an acceleration zone to a second transport speed. The dependent claims relate to preferred embodiments.

In particular, in a first embodiment, this object is achieved with a method for transporting sheets; said method is characterized in that different acceleration profiles can be provided in the acceleration zone. In the acceleration zone, a first acceleration profile can be provided in accordance with which the sheet is directly accelerated from the first transport speed to a third transport speed, and the sheet is then directly decelerated from the third transport speed to the second transport speed. In this embodiment, the third transport speed is greater than the first and the second transport speeds. In the acceleration zone, a second acceleration profile can be provided, in accordance with which the sheet is directly decelerated from the first transport speed to a fourth transport speed, and the sheet is directly accelerated from the fourth transport speed to the second transport speed. In doing so, the fourth transport speed is lower than the first and the second transport speeds. Depending on the input time of the sheet into the acceleration zone, the first or the second acceleration profile is selected to transfer the sheet to the second transport section at a pre-specified time. Constant acceleration parameters are not harmful for the drive, it results in the advantage that positioning of the sheet can be achieved in a shorter available acceleration zone.

Preferably, the second transport speed is equal to a processing speed of the printing machine, thus enabling delay-free continued processing.

In a case, in which the printing machine includes at least one transport member, the sheet is advantageously released in transport direction by the transport member during acceleration or deceleration. In this way, an acceleration or delay or both of the sheets can be achieved without causing tears or a sheet jam.

In accordance with the method, the sheet is released in transport direction by moving the transport member away from the sheet. As a result of this, it is also possible to achieve high acceleration parameters with thin sheets displaying low strength, without tearing the sheets.

Preferably, in this method, the start time of acceleration or deceleration is shifted for adjusting the transfer time. Thus sheets having different length can be processed without performing structural alterations on the printing machine.

In one embodiment of the method, a third acceleration profile is selected as a function of the input time of the sheet in the acceleration zone, wherein a direct acceleration from the first to the second transport speed is performed if neither the first nor the second acceleration profile enables a transfer at the pre-specified time. Thus the sheet can be transferred in numerous cases to the next transport section at the pre-specified time.

The invention, as well as additional details and advantages of said invention will be explained hereinafter with the use of preferred exemplary embodiments and reference to the drawings.

Brief Description of Drawings

Figure 1 a schematic representation of a printing machine wherein the method for transporting sheets of the present invention can be used;
Figure 2 a graph of a first progression of the transport speed of a sheet using a method in accordance with the present invention; and
Figure 3 a graph of a first progression of the transport speed of a sheet using a method in accordance with the present invention; and
Figure 4 a graph of a first progression of the transport speed of a sheet using a method in accordance with prior art.

It should be noted that the concepts above, below, right and left, as well as similar references, refer to the orientations or arrangements shown in the figures and are intended only for the description of the exemplary embodiments. However, these concepts are not to be understood in a restricting sense.

Mode(s) for Carrying Out the Invention

Figure 1 is a schematic diagram of a printing machine 1, wherein the method of the present invention can be used. The only components of the printing machine 1 that are shown are those that are required for understanding the method for transporting sheets. The printing machine 1 includes a feeder 3 that holds a sheet stack 4 that includes a plurality of sheets B. A sheet transport path 7 extends through the printing machine 1, said path is defined by a plurality of transport members and additional, not illustrated, guide elements. Here the transport members are the transport roller pairs 9a – 9f, said transport roller pairs are rotated by a drive 10. Furthermore, the printing machine 1 includes an acceleration unit 11 that is disposed to accelerate or decelerate the sheet or both. A driving motor 12 and the driving rollers 13 are provided in the acceleration unit 11. Furthermore, the printing machine 1 includes an alignment unit 14, as well as a processing unit 15. A sheet B moves along the sheet transport path 7, starting from the feeder 3, in the direction of the processing unit 15.

The sheet B enters the sheet transport path 7 at the feeder 3, where the sheet B is lifted off the sheet stack 4. Then the sheet B moves at a constant first transport speed v₁ through the transport roller pairs 9a – 9f the sheet B are always in engagement with at least one transport roller pair 9a – 9f. This section of the sheet transport path corresponds to a first transport section.

The transport roller pairs 9a – 9f are spring-supported in a frame 17 of the printing machine 1 and exert a constant pressure on a passing sheet B. The sheet first moves through the transport roller pairs 9a – 9d and then continues on through the transport roller pairs 9e and 9f. In the depicted exemplary embodiment, each of the transport roller pairs 9e and 9f includes at least one transport roller that can be moved relative to the frame 17. However, it is also possible for both transport rollers of a

transport roller pair

9e and 9f to be movable. In Figure 1, the movable transport roller is the upper transport roller of the transport roller pairs 9e and 9f. The movable transport roller can assume an engagement position, in which the transport roller pairs are in engagement with sheet B, and a release position, in which the movable transport rollers are lifted off sheet B. By lifting the movable transport rollers of the transport roller pairs 9e and 9f, it is possible to release the sheet B as soon as the sheet B has come into engagement with the acceleration unit 11. The released sheet B can be accelerated or decelerated in the acceleration unit 11.

Alternatively, the transport roller pairs 9e and 9f are provided with an overrunning clutch that is not shown in Figure 1. The overrunning clutch enables the acceleration of the sheet B as soon as it is in engagement with the acceleration unit 11, irrespective of the rotational speed of the transport roller pairs 9e and 9f. With the use of the overrunning clutch, it is possible to release the sheet B in transport direction as soon as the sheet B has come into engagement with the acceleration unit 11. If so, a deceleration of the sheet B is not possible.

In the acceleration unit 11, the sheet B changes its transport speed from the first transport speed v₁ to a second transport speed v₂. The acceleration can occur in the zone (acceleration zone s_a in Figs. 2 through 4) between the acceleration unit 11 and the alignment unit 13. In the alignment unit 13, it is possible to align a fed sheet B regarding its position relative to the sheet transport path 7, for example, regarding its angular positioning and regarding its central positioning with respect to the sheet transport path 7. This section of the sheet transport path corresponds to a second transport section. In the processing unit 15, the sheet B is then processed, in particular, printed, cut, folded, etc. The continuation of the sheet transport path 7 is not shown.

Hereinafter, the method for transporting the sheets B in the printing machine 1 is described with the use of Figures 2 and 3. As soon as a sheet B is in engagement with the acceleration unit 11, said acceleration unit is able to change the transport speed of the sheet B. The change of the transport speed, i.e., an acceleration or deceleration, however, cannot occur until the trailing edge of the sheet B is no longer in engagement with the non-movable transport roller pair 9d. As soon as the trailing edge of the sheet B is out of engagement with the transport roller pair 9d, the movable transport rollers of the transport roller pairs 9e and 9f are moved away from the sheet B and release said sheet. Then, the sheet B continues to be in engagement with the driving rollers 13 of the acceleration unit 11 only.

In accordance with a first embodiment (Figure 2), the method provides that the sheet B be delivered at the first transport speed v₁ through the transport roller pairs 9e and 9f (transport members) to the acceleration unit 11. The driving rollers 13 of the acceleration unit 11 first continue to convey the sheet B at the same transport speed v₁ until the trailing edge of the sheet B is out of engagement with the transport roller pair 9d. At this time, depending on the length of the sheet B, the leading edge of the sheet B is at any point between the alignment unit 14 and the driving rollers 13 of the acceleration unit 11. As mentioned above, the acceleration of longer sheets B has to start later than the acceleration of shorter sheets B because the trailing edge of the longer sheets B moves later out of the previous, not movable, transport roller pair 9d. On the other hand, the non-movable transport roller pair 9d cannot be removed at any distance away from the acceleration unit 11 (the acceleration zone s_a) because the free distance of the transport roller pairs 9a – 9f (transport members) is determined by the length of the shortest sheet B that is to be processed.

As mentioned above, how far the leading edge of the sheet B enters into the acceleration zone s_a before the trailing edge of the sheet B becomes free differs depending on the length of said sheet B. Depending on an input time of the sheet B in the acceleration zone s_a, a first or second acceleration profile is selected in order to transfer the sheet B at a pre-specified time to the second transport section. Exactly as in the above-described Figure 4, Figures 2 and 3 show the possible acceleration zone s_a that is delimited by a starting position s₁ and an end position s₂. A middle position is drawn between the starting position s₁ and the end position s₂. At the starting position s₁ and at the end position s₂ each, a not illustrated sensor can be provided, said sensor detecting the leading and trailing edges of the sheet B. Alternatively or additionally, the starting position s₁ and the end position s₂ are determined by the position of the last driving roller 13 of the acceleration unit 11 as well as the first roller of the alignment unit 14. The selection of the acceleration profiles is accomplished by a not illustrated control device.

Figure 2 shows the speed progression of the first acceleration profile that is selected when the leading edge of the sheet B is located between the starting position s₁ and the middle position when the trailing edge of the sheet B becomes free. Then, the acceleration unit 11 directly accelerates the sheet B at a pre-specified acceleration rate (slope of the speed progression) to a third transport speed v₃. The third transport speed v₃ is greater than the first, as well as the second, transport speeds v₁ and v₂. Thereafter, the sheet B is directly decelerated from the third transport speed v₃ to the second transport speed v₂. Direct acceleration or deceleration is understood here to mean that no disadvantageous overcontrol or undercontrol to above or below the respective transport speed takes place. Such an overcontrol or undercontrol causes harmful positive or negative accelerations that wear out driving rollers, motors and transmissions of the acceleration unit 11. As a result of this, the leading edge of the sheet B reaches a desired position or rated position in a short time over a short acceleration distance. Thus a long sheet B can catch up the distance it has lost because its acceleration process has to start later. As soon as the rated position has been reached, the acceleration unit 11 reduces the transport speed of the sheet B to the second transport speed v₂ that is required in the next transport section, i.e., in the alignment unit 14. Then, the sheet B is continued to be processed at the speed v₂ in the alignment unit 14.

Figure 3 shows the speed progression of the second acceleration profile that is selected when the leading edge of the sheet B is located between the end positions s₂ and the middle position when the trailing edge of the sheet B becomes free. For this second acceleration profile, the method provides that the sheet B be delivered at the first transport speed v₁ through the transport roller pairs 9e and 9f (transport members) to the acceleration unit 11. The driving rollers 13 of the acceleration unit 11 first continue to convey the sheet B at the same transport speed v₁ until the trailing edge of the sheet B is out of engagement with the transport roller pair 9d. Then, the acceleration unit 11 directly decelerates the sheet B at a pre-specified acceleration rate (negative slope of the speed progression) to a fourth transport speed v₄. The fourth transport speed v₄ is lower than the first, as well as the second, transport speeds v₁ and v₂. Then, the acceleration unit 11 directly accelerates the transport speed of the sheet B to the second transport speed v₂ that is required in the next transport section, i.e., in the alignment unit 14. Direct acceleration or deceleration is understood to mean that no disadvantageous overcontrol or undercontrol above or below the respective transport speed occurs. Such overcontrol or undercontrol causes harmful positive or negative accelerations that wear out the driving rollers, motors and transmissions of the acceleration unit 11. As a result of this, the leading edge of the sheet B reaches a desired position or rated position along a short acceleration distance and within a short time. Then, the sheet is continued to be processed in the alignment unit 14 at the speed v₂.

It should be noted that, with the use of the present method, overall an acceleration or deceleration of the sheets B with the transfer from a first transport section to a second transport section can be performed. For an acceleration, the first transport speed v₁ of the first transport section is lower than the second transport speed v₂ of the second transport section. For a deceleration, the first transport speed v₁ of the first transport section is lower than the second transport speed v₂ of the second transport section.

Furthermore, depending on the input time of the sheet B in the acceleration zone s_a, a third acceleration profile can be selected, as is shown in Figure 4. For this third acceleration profile, the sheet B is directly accelerated from the first transport speed v₁ to the second transport speed v₂. The third acceleration profile is used when neither the first nor the second acceleration profile enables a transfer at the pre-specified time. The third acceleration profile can be selected in addition to or as an alternative to the first and second acceleration profiles.

The invention was described with reference to preferred exemplary embodiments, wherein the individual features of the described exemplary embodiments can be freely combined or exchanged or both with each other, provided they are compatible. Likewise, individual features of the described exemplary embodiments can be omitted, unless they are absolutely required. Numerous modifications and embodiments are possible for and obvious to the person skilled in the art, without departing from the inventive idea as a result of this.

Claims

Method for transporting sheets (B) in a printing machine (1) for transfer from a first transport section to a second transport section, whereby a sheet (B) is brought from a first transport speed (v₁) in an acceleration zone (s_a) to a second transport speed (v₂);

characterized in that

a first acceleration profile can be provided in the acceleration zone (s_a) in accordance with which the sheet (B) is directly accelerated from the first transport speed (v₁) to a third transport speed (v₃), and

that the sheet (B) is then directly decelerated from the third transport speed (v₃) to the second transport speed (v₂)

the third transport speed (v₃) is greater than the first (v₁) and the second (v₂) transport speeds,

a second acceleration profile can be provided in the acceleration zone (s_a), in accordance with which the sheet (B) is directly decelerated from the first transport speed (v₁) to a fourth transport speed (v₄), and

the sheet (B) is directly accelerated from the fourth transport speed (v₄) to the second transport speed (v₂) the fourth transport speed (v₄) being lower than the first (v₁) and second (v₂) transport speeds,

whereby, depending on the time the sheet (B) is input in the acceleration zone (s_a), the first or the second acceleration profile is selected in order to transfer the sheet (B) at a pre-specified time to the second transport section.
Method as in Claim 1, whereby the second transport speed (v₂) is equal to one processing speed of the printing machine (1).
Method as in Claim 1 or 2, whereby the printing machine includes at least one transport member (9a – 9f), and whereby the sheet (B) is released by the transport member in transport direction during acceleration or deceleration.
Method as in Claim 3, whereby the release of the sheet (B) in transport direction is accomplished by moving the transport member (9a – 9f) away from the sheet (B).
Method as in one of the previous claims, whereby the start time of acceleration or deceleration is shifted for adjusting the transfer time.
Method as in one of the previous claims, whereby, depending on the input time of the sheet (B) into the acceleration zone (s_a), a third acceleration profile is selected, in accordance with which there is a direct acceleration from the first (v₁) to the second (v₂) transport speed, if neither the first nor the second acceleration profile enables a transfer at the pre-specified time.