Method for operating a sheet separator for separating sheets of a printing material stacked in a feeder of a sheet-fed printing press.

Abstract

Method for operating a sheet separator (01) for separating sheets of a substrate (02) stacked in a feeder of a sheet-fed printing press, wherein at least one separating suction cup (08) and at least one front transport suction cup (09) and at least one rear transport suction cup (11) are provided in the transport direction (T) of the sheets, wherein a control unit (18) controls the application of a compressed air source generating a vacuum to the transport suction cups (09; 11), wherein the control unit (18) controls the at least one front transport suction cup (09) by means of a first control element (16) and the at least one rear transport suction cup (11) by means of a second control element (17) separate from the first control element (16), wherein the first control element (16) and the second control element (17) are each designed as control cams (16; 17).wherein the at least one separating suction cup (08) is activated with reference to the first control cam (16) at a first control angle and grasps the sheet lying on top of the stack for the injection of loosening air, wherein the at least one front transport suction cup (09) and the at least one rear transport suction cup (09) are each in their respective starting position with reference to the first control cam (16) at a second control angle that is larger than the first control angle and thus the sheets are each in their rearmost position in the transport direction (T), wherein the at least one rear transport suction cup (11) is activated by means of the second control cam (17) at the second control angle referred to the first control cam (16), while the at least one front transport suction cup (09) is switched with the first control cam (16) and waits for its activation,until the currently gripped sheet has passed the previously fixed position of the at least one front transport suction cup (09) with reference to the sheet separator (01), and wherein the at least one front transport suction cup (09) is activated with the first control cam (16) only at a larger third control angle, which is different from the second control angle and is referenced to the first control cam (16).

Description

[0001] The invention relates to a method for operating a sheet separator for separating sheets of a printing material stacked in a feeder of a sheet-fed printing press according to claim 1.

[0002] US Patent 3,938,800 A discloses a sheet separator with two separating suction cups and with two transport suction cups, wherein the separating suction cups are moved horizontally in the transport direction of the sheets synchronously with the transport suction cups, wherein the separating suction cups and the transport suction cups are each controlled by control cams.

[0003] DE 10 2007 042 376 A1 discloses a device for guiding sheets made of rigid materials in a sheet feeder, comprising separating suction cups that capture and separate the topmost sheet of a sheet stack in the area of ​​the trailing edge, transport suction cups that convey the separated sheets in a sheet transport direction, means for creating an air cushion to support the separation and conveying, and a sheet transport device that captures the sheets in the area of ​​the leading edge and feeds them to the sheet processing machine, wherein at least during the feeding of the separated topmost sheet by the sheet transport device, a holding device is provided that captures and guides the sheet in the area of ​​the trailing edge.

[0004] DE 10 2004 022 233 A1 discloses a device for sheet singulation with at least two pairs of double suction cups, wherein each double suction cup has a suction cup on the underside and on the top side, which serve to remove sheets from a stack of sheets at its leading edge in the conveying direction of the sheets, wherein the double suction cups are each designed as a unit which further has a drive such that the path of movement of each corresponding double suction cup is a closed path leading around the other double suction cup; in that a sheet can be passed from the stack of sheets by intermediate transfer between the double suction cups and then on to a conveying system.

[0005] DE 10 2019 122 496 A1 discloses a device for feeding sheets to a sheet-processing machine comprising at least one processing unit, wherein this device has a sheet separator for intermittently singulating the sheets from a stack and transport suction cups for transporting the sheets to a belt table.

[0006] A sheet-shaped printing material is typically provided on a sheet-fed printing machine by separating a stack of this printing material arranged on a carrier, e.g. on a pallet, in a feeder using a sheet separator and feeding it in a shingle stream preferably via a belt table to the sheet-fed printing machine.

[0007] A sheet separator, also known as a "suction head," includes all the necessary auxiliary and operating components for separating and conveying the sheets, such as multiple blow nozzles, spreading magnets, and brushes, and / or a sensing roller (also called a push foot), as well as usually several separating suction cups and / or transport suction cups, each designed as a rubber suction cup. A control unit for the precise timing and angular control of the aforementioned auxiliary and operating components is also typically part of the sheet separator's equipment.

[0008] Separating and feeding the sheets at precise angles is a critical process, as very little time is available for singulating stacked sheets. Therefore, there is a risk that sheets will not separate completely and that a second sheet will be mistakenly fed into the sheet-fed printing press as a so-called double sheet.

[0009] There is also a risk that the rubber suction cups will not have fully gripped the sheet being fed into the sheet-fed printing press before a mechanically controlled forward movement begins. In this case, the sheet would not be fed to the press at a precise angle, but slightly offset, and would arrive at the press's feed marks at the wrong time. It might also get stuck on a sheet flap.

[0010] Both double arches and offset arches lead to production interruptions and material waste.

[0011] The invention is based on the objective of creating a sheet separator intended for a feeder of a sheet-fed printing press with improved control of its transport suction cups.

[0012] The problem is solved according to the invention by the features of claim 1. The dependent claims relate to advantageous embodiments and / or further developments of the solution found.

[0013] The advantages achievable with the invention consist in particular of the fact that, through the improved control of the transport suction cups, sheets provided in a stack are reliably gripped individually, thereby minimizing the occurrence of double sheets and / or sheets not conveyed at the correct angle, and thus avoiding production interruptions and material waste.

[0014] An embodiment of the invention is shown in the drawings and is described in more detail below.

[0015] They show: Fig. 1 a currently common design of a sheet separator; Fig. 2 a design of the sheet separator according to the invention.

[0016] The Fig. 1 and Fig. Figures 2 and 2 each show, in a schematic and highly simplified manner, a sheet separator 01 on a feeder of a sheet-fed printing press. The same reference numerals are used in both figures for identical machine elements. The sheet separator 01 is typically arranged above a stack of sheet-shaped substrate 02 provided in a feeder of a sheet-fed printing press. The substrate 02 can be in the form of sheets of paper, cardboard, or corrugated board, or of a plastic, or as a sheet of metal. The sheet separator 01 feeds the stacked sheets individually, preferably via a belt table 03, to a sheet-fed printing press (not shown). At the transfer point from the feeder to the belt table 03, a sheet flap 04 and then, for example, a pair of rotating or at least rotatable indexing rollers 06, which work together to convey the individual sheets, are provided in the transport direction T of the sheets.To assist in separating and transporting the sheets, the necessary auxiliary components belonging to the sheet separator 01 are summarized under item 07, e.g., blow nozzles and / or spreading magnets and / or brushes that engage laterally on the stack. The sheet separator 01 also includes at least one separating suction cup 08 and, viewed in the transport direction T of the sheets, at least one front transport suction cup 09 and at least one rear transport suction cup 11. Preferably, several front transport suction cups 09 and / or several rear transport suction cups 11 are arranged side by side transversely to the transport direction T of the sheets. In the preferred embodiment, several front transport suction cups 09 and several rear transport suction cups 11 are arranged one behind the other in two rows in the transport direction T of the sheets.These suction cups 09; 11 grasp the sheet at the top of the stack and transport it forward in the transport direction T until the leading edge of the sheet reaches the indexing rollers 06. The suction cups 09; 11 then release the sheet and return to their starting position to grasp the next sheet. The indexing rollers 06, which preferably rotate in a controlled cycle, then continue transporting the sheets supplied to them by the suction cups 09; 11. The at least one separating suction cup 08 and the suction cups 09; 11 are each connected to a compressed air source that generates a vacuum via compressed air lines 12; 13; 14. The supply of compressed air to the at least one separating suction cup 08 and the suction cups 09; 11 is controlled, for example, by a control unit 18, which is preferably digital.

[0017] Fig. Figure 1 shows a sheet separator 01 with a conventional control system for its transport suction cups 09; 11, wherein in this embodiment the at least one front transport suction cup 09 and the at least one rear transport suction cup 11 are connected to the same compressed air line 13 for the purpose of connecting them to the compressed air source generating a vacuum. Both rows of transport suction cups 09; 11 are jointly controlled by a single control element 16, e.g., a cam. The transport suction cups 09; 11 can therefore only be re-actuated once the indexing rollers 06 have advanced the uppermost sheet sufficiently until the trailing edge of the currently gripped sheet has left the working area of ​​the transport suction cups 09; 11. The bidirectional movement of the transport suction cups 09; 11, directed along the transport direction T of the sheets, is described in the Fig. 1 and Fig. 2 each indicated by a double arrow.

[0018] Fig.Figure 2 shows a sheet separator 01 with a design according to the invention for its transport suction cups 09; 11, wherein, by means of a further control element 17, e.g., a second cam, the row of front transport suction cups 09 and the row of rear transport suction cups 11 are controlled separately from one another. This arrangement with two separate control elements 16; 17 opens up the possibility that the row of rear transport suction cups 11 can be activated by the control unit 18 at an earlier time or at a different angle compared to the row of front transport suction cups 09.In particular, this means that – as soon as the transport suction cups 09 and 11 have returned to their starting position – the rear transport suction cups 11 can be activated immediately to grip the next sheet, while the front transport suction cups 09 are only activated when the end of the currently gripped sheet has passed these front transport suction cups 09. This gives the row of rear transport suction cups 11 more time to securely grip the sheet at the top of the stack. As a result, the sheet is still transported at the correct angle by the rear transport suction cups 11, even if the front transport suction cups 09 are only able to grip the sheet at the top of the stack with a delay, for example, due to a curved sheet surface.

[0019] The invention is illustrated below using the example of a sheet separator 01 having two control cams 16; 17. For example, the separating suction cups 08 are activated with respect to the first control cam 16 at a control angle of, for example, 126° and grasp the sheet at the top of the stack to inject loosening air. The transport suction cups 09; 11 are in their initial position with respect to the first control cam 16 at a control angle of, for example, 210°, i.e., they are back in their rearmost position to separate a subsequent sheet from there.

[0020] By means of the second control cam 17, the row of rear transport suction cups 11 is now activated immediately at the control angle of, for example, 210° relative to the first control cam 16, while the row of front transport suction cups 09 is switched by the first control cam 16 and must wait for its activation until the currently gripped sheet has passed the row of front transport suction cups 09. The row of front transport suction cups 09 is only activated by the first control cam 16 at a control angle of, for example, 258° relative to the first control cam 16. At a control angle of, for example, 275° relative to the first control cam 16, the forward movement of both rows of transport suction cups 09 and 11 begins. This means that the time available to the row of rear transport suction cups 11 to grip a sheet at the top of the stack is almost quadrupled.For while the row of front suction cups 09 only has the time available to sweep over an angle of 17°, i.e. the difference between the control angles of 258° and 275°, so that these suction cups 09, designed as rubber suction cups, correctly capture the arc, the additional control cam extends the duration for the row of rear suction cups 11 from 17° to 65°, i.e. the difference between the control angles of 210° and 275°.

[0021] This results in a sheet separator 01 for separating sheets of a substrate 02 stacked in a feeder of a sheet-fed printing press, wherein at least one front transport suction cup 09 and at least one rear transport suction cup 11 are provided in the transport direction T of the sheet, wherein a control unit 18 is provided, wherein the control unit 18 controls the application of a compressed air source generating a vacuum to the transport suction cups 09 and 11 by means of a control element 16, wherein a first control element 16 is provided for the at least one front transport suction cup 09 and a second control element 17, separate from the first control element 16, is provided for the at least one rear transport suction cup 11. The first control element 16 is preferably designed as a first control cam and the second control element 17 is preferably designed as a second control cam.

[0022] Likewise, a method for operating a sheet separator 01 for separating sheets of a substrate 02 stacked in a feeder of a sheet-fed printing press is provided, wherein at least one front transport suction cup 09 and at least one rear transport suction cup 11 are provided in the transport direction T of the sheet, wherein a control unit 18 controls the application of a compressed air source generating a vacuum to the transport suction cups 09; 11, wherein the control unit 18 controls the at least one front transport suction cup 09 by means of a first control element 16 and the at least one rear transport suction cup 11 by means of a second control element 17 separate from the first control element 16.At the moment when the at least one front suction cup 09 and the at least one rear suction cup 11 are each in their starting position above the stack of stacked sheets, only the at least one rear suction cup 11 is activated by the second control element 17 by supplying it with the compressed air source that generates a vacuum. Preferably, the at least one front suction cup 09 is only activated by the first control element 16 by supplying it with the compressed air source that generates a vacuum when an end of the sheet currently gripped by the at least one rear suction cup 11 and transported in the transport direction T passes the at least one front suction cup 09, i.e.,when the end of the sheet currently gripped by the at least one rear suction cup 11 and transported in the transport direction T reaches the position of the at least one front suction cup 09, which was previously fixed with respect to the sheet separator 01. In the preferred embodiment, the time available to the at least one rear suction cup 11 to grip a sheet lying at the top of the stack is set, e.g., by the control unit 18, to be at least three times longer than the time required for the at least one front suction cup 09 to grip the sheet in question.

[0023] When using sheet metal sheets as the printing material 02, a sheet-fed printing machine designed as a sheet metal printing machine with a feeder is obtained, wherein a sheet separator 01 is arranged above a stack of sheet metal sheets arranged in the feeder for separating the sheet metal sheets stacked in the feeder, wherein at least one front transport suction cup 09 and at least one rear transport suction cup 11 are provided in the transport direction T of the sheet metal sheets to be conveyed from the feeder and printed in the sheet metal printing machine, wherein a control unit 18 is provided, wherein the control unit 18 controls the application of a compressed air source generating a vacuum to the transport suction cups 09; 11 by means of a control element 16, wherein a first control element 16 is provided for the at least one front transport suction cup 09 and a second control element 17, separate from the first control element 16, is provided for the at least one rear transport suction cup 11.As mentioned, the first control element 16 is preferably designed as a first control cam and the second control element 17 is preferably designed as a second control cam.

[0024] The second control cam 17 significantly increases production reliability during sheet separation. This results in fewer production interruptions due to double sheets and / or sheets fed at inaccurate angles, and consequently less material waste. The proposed solution also allows for retrofitting existing production lines. Reference symbol list 01 Sheet separator 02 Printing material 03 Belt table 04 Bow flap 05 - 06 Clock roll 07 Blow nozzles, spreading magnets and brushes 08 Vacuum cleaner 09 front transport suction cup 10 - 11 rear transport suction cup 12 Compressed air line 13 Compressed air line 14 Compressed air line 15 - 16 Control element; cam 17 Control element; cam 18 Control unit T Transport direction

Claims

[1] Method for operating a sheet separator (01) for separating sheets of a substrate (02) stacked in a feeder of a sheet-fed printing press, wherein at least one separating suction cup (08) and at least one front transport suction cup (09) and at least one rear transport suction cup (11) are provided in the transport direction (T) of the sheets, wherein a control unit (18) controls the application of a compressed air source generating a vacuum to the transport suction cups (09; 11), wherein the control unit (18) controls the at least one front transport suction cup (09) by means of a first control element (16) and the at least one rear transport suction cup (11) by means of a second control element (17) separate from the first control element (16), wherein the first control element (16) and the second control element (17) are each designed as control cams (16; 17),wherein the at least one separating suction cup (08) is activated with reference to the first control cam (16) at a first control angle and grasps the sheet lying on top of the stack for the injection of loosening air, wherein the at least one front transport suction cup (09) and the at least one rear transport suction cup (09) are each in their respective starting position with reference to the first control cam (16) at a second control angle larger than the first control angle and are thus in their rearmost position in the transport direction (T) of the sheets, wherein the at least one rear transport suction cup (11) is activated by means of the second control cam (17) at the second control angle referred to the first control cam (16), while the at least one front transport suction cup (09) is switched with the first control cam (16) and waits for its activation,until the currently gripped sheet has passed the previously fixed position of the at least one front transport suction cup (09) with reference to the sheet separator (01), and wherein the at least one front transport suction cup (09) is activated with the first control cam (16) only at a larger third control angle, which is different from the second control angle and is referenced to the first control cam (16). [2] Method according to claim 1, characterized by , that at the time when the at least one front transport suction cup (09) and the at least one rear transport suction cup (11) are each in their starting position above the stack of stacked sheets, only the at least one rear transport suction cup (11) is activated by means of the second control element (17) by being supplied with the compressed air source generating a negative pressure. [3] Method according to claim 2, characterized by, that the at least one front transport suction cup (09) is only activated by means of the first control element (16) by its application to the compressed air source generating a negative pressure when an end of the sheet currently gripped by the at least one rear transport suction cup (11) and transported in the transport direction (T) passes the at least one front transport suction cup (09). [4] Method according to claim 1 or 2 or 3, characterized by , that the time available to the at least one rear transport suction cup (11) to grasp a sheet lying at the top of the stack is set at least three times longer than the time available for the at least one front transport suction cup (09) to grasp the sheet in question.

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