WO2008010763A1

WO2008010763A1 - Method and means by which a pressure different from ambient pressure is generated and fed to a sheet feed printing machine in order to effectuate or control the feed of sheets in the printing machine

Info

Publication number: WO2008010763A1
Application number: PCT/SE2007/000685
Authority: WO
Inventors: Peter Tell
Original assignee: Xerex AB
Current assignee: Xerex AB
Priority date: 2006-07-19
Filing date: 2007-07-13
Publication date: 2008-01-24
Anticipated expiration: 2009-01-19
Also published as: DE112007001617T5; SE0601582L; JP2009543748A; SE530098C2

Abstract

A method is disclosed by which an air pressure different from the atmospheric pressure is generated and distributed to a sheet of paper in a sheet feed printing machine, comprising the step of generating a work-pressure in means arranged to discharge the work-pressure to the sheet and thereby to effectuate or control the transport of the sheet in the printing machine. The method is characterized through a continuous adjustment of the work-pressure that is discharged from each singular discharge means or from each singular set of discharge means to a work- pressure which is adapted to the subject sheet and/ or the subject process in the printing machine, and which is operative for control or transport, in response to detecting at all times the work-pressure discharged from each singular discharge means or from each singular set of discharge means. In analogy herewith an assembly in a sheet feed printing machine is disclosed, the assembly comprising means that are movably arranged in the printing machine and arranged for discharging to a sheet of paper a pressure that is different from the atmospheric pressure, and by means of the discharged work-pressure effectuates or controls the transport of the sheet in the printing machine. The assembly is characterized in that the discharge means comprises means for continuous adjustment of the discharged work-pressure to a work-pressure which is adapted to the subject sheet and/or the subject process in the printing machine, and which is operative for control or transport, in response to detecting at all times the work-pressure being discharged from each singular discharge means, or from each singular set of discharge means.

Description

International Application No. PCT/SE2007/000685 (Agent's ref. No.: P07565PCO0)

TITLE

Method and means by which a pressure different from ambient pressure is generated and fed to a sheet feed printing press in order to effectuate or control the feed of sheets through the printing press.

TECHNICAL FIELD OF THE INVENTION

The invention is referred to the feed of singular sheets of paper in sheet feed printing machines. More precisely, the invention relates to a method by which a pressure different from ambient atmospheric pressure, such as an over-pressure or a sub-pressure, is generated and discharged to the sheet, and by which the feed of sheets in the printing machine is effectuated or controlled, as stated in the preamble of claim 1. Analogously therewith, an assembly as stated in the preamble of attached independent apparatus claim is likewise provided by the invention.

BACKGROUND AND PRIOR ART

In print production techniques, pressure and sub-pressure are commonly used in different positions of a printing machine in order to effectuate and/or control the transport of sheets in the printing machine. Heavier sheet feed printing machines may be designed to operate by pressure/ sub-pressure at more than 10 discrete positions of a feed path for sheets. Thus, pressure may for example be used for separating sheets that are stacked onto each other in a stack of sheets located at an in-feed end of the printing machine, by means of a stream of air that is directed through a slot towards a front end of the sheet stack, as viewed in the feeding direction, in order to avoid adhesion between sheets upon separation and insertion into the print cylinder assembly. Another example on the use of pressure to mention here is a stream of air that is directed towards the trailing end of a sheet as the same is fed in or fed out from a fast rotating printing cylinder or a feed cylinder, in order to avoid accelerations causing a whiplash in the trailing end, as viewed in the feed direction. A typical example on the use of sub-pressure to mention here is the discharge of a sub-pressure to the surface of a sheet by means of movable gripping means which are operable for lifting and transport of the sheet, the way this usually is effectuated at the in- feed end of the printing machine in order to separate and feed an uppermost sheet from the stack of sheets. It is likewise known to discharge, towards the surface of a sheet which is supported on a band conveyor, a sub-pressure through perforations formed in the band conveyor in order to fixate the sheet in transport on the band conveyor. Another specific example on the use of sub-pressure to mention here is the retardation of a sheet ejection velocity that is effectuated by means of retardation cylinders having perforations through which sub-pressure is discharged to the surface of the sheet in order to generate an adhesion force, by which the velocity of the sheet is reduced to be equal to or near to a controlled peripheral velocity of the retardation cylinder.

The subject sub-pressures in printing machine applications seldom or never reach a condition of absolute vacuum, but may at different locations in a printing machine vary from about 10 % to about 80 % of the ambient atmospheric pressure. Operative sub-pressures are thus also related to local variations in the atmospheric pressure, such as those associated with the subject height above sea level, but associated also with variations in climate.

Sheet feed printing machines, in which the invention is primarily to be implemented, may be designed for one- or multicolour printing on paper of different grades, of different weight by area and different paper sizes, usually in the standardized formats of A4 (210x297 mm) to AO (840x1188 mm), or even special formats. As for the smaller formats, the printing capacity in modern sheet feed offset printers may amount to about 20,000 sheets/h, and a capacity of about 10- 12,000 sheets/h for the larger formats. Transport speeds in the order of 3 m/sec or more is thus possible, while at the same time the accuracy of printing and indexing in multicolour printing can require a mismatch to be 2/ 100 mm at the most. It shall further be noticed that paper is a material containing organic fibres which are prone to react on environmental changes, such as changes in humidity/ temperature, that may affect the properties of the paper during production, transport and storage, and not least during printing when printing ink is applied while the paper is fed over printing cylinders and feed cylinders. The high capacity of printing machines and changing properties of paper sets high demands on mechanics and gripping accuracy in pressure discharge means which are arranged for gripping and moving the sheets in the printing machines.

Gripping means used in printing machines are mainly suction cups that are connected to a source of sub-pressure. The grippers are usually arranged in sets to effect distribution of the sub-pressure over the surface of sheets such that sheets adhere by suction to the suction cups. The grippers are movable in the printing machine and driven for lifting and moving the sheets, from a gripping position to a delivery position where the sub-pressure is cut off. It will be noticed that, in addition to an accurate and reliable mechanical structure driving the motions of the grippers, short cycle times are required in the sub-pressure system in order to meet and achieve the maximum printing capacity in the printing machine.

Sub-pressure systems in printing machines typically comprise centralized sub- pressure sources/vacuum pumps that supply one or several sets of grippers via valves which control the total supply of sub-pressure to multiple suction cups. In systems of this type, the distance between sub-pressure source and suction cup limits the possibility to achieve short operation cycles. This is due to a delay in switching between sub-pressure and atmospheric pressure in the suction cup, resulting from long supply lines. Centralized supply systems are also usually driven at excessive power output and thus at excessive sub-pressure, this way compensating for leakage at the suction cups and ensuring sufficient gripping capacity in spite of varying sheet properties with respect to surface texture, porosity, weight, or other parameters affecting the paper, which is sensitive to temperature and humidity.

SUMMARY OF THE INVENTION

The present invention aims to avoid the problems that are discussed above. The object is met in a method by which short operation cycles and operative work- pressures can be ensured in every means that is operable in a sheet feed printing machine for effectuating or controlling the feed of sheets trough the printing machine.

The object is met in a method as defined in accompanying claims.

Briefly, the present invention provides a method by which a pressure different from the atmosphere is generated and distributed to a sheet in a sheet feed printing machine, comprising the step of generating a work-pressure in discharge means arranged to apply the work-pressure to the sheet and thereby to effectuate or control the feeding of the sheet in the printing machine. The method is characterized by the steps of continuously adjusting the applied pressure, in each singular discharge means or in each singular set of discharge means, to a work- pressure operative for control or feeding which is adapted to the subject sheet and/ or the subject process in the printing machine, in response to detecting at all times the work-pressure applied from each singular discharge means or from each singular set of discharge means, respectively. In a preferred embodiment, the method further comprises the following steps: -supplying a drive-pressure to a high-pressure operated ejector; -detecting a work-pressure that is discharged from the ejector, and -adjusting the drive-pressure to the ejector in response to a comparison between detected work-pressure and a predetermined work-pressure.

Detection of work- pressure is performed on a sub-pressure or on an over-pressure discharged from the ejector.

Advantageously, in each singular discharge means or in each singular set of discharge means, a difference between the at all times detected work-pressures and the atmospheric pressure is used to proportionally adjust the drive-pressures to ejectors that are individually arranged in each singular discharge means or in each singular set of discharge means, respectively.

Preferably, in each singular discharge means, the drive-pressure to the ejector is adjusted to effect discharge of a work-pressure that corresponds to a SET-value that is stored in a micro processor which is comprised in the subject discharge means. In the micro processor, a detected IS-value is compared to the SET-value, and the drive-pressure to the ejector is adjusted from the micro processor via an electric magnetic valve, likewise comprised in the subject discharge means, said valve controlling the drive-pressure to the ejector.

SET-values for drive-pressures to discharge means in the air system are stored in a control unit from which all discharge means are simultaneously set to individual SET-vales. Predetermined SET-values that are determined with respect to type of sheets and/ or type of operation in the printing machine are stored in the control unit. Preferably, SET-values are determined with respect to sheet format, sheet weight per area, and surface smoothness of sheets.

Analogously herewith, an assembly for a sheet feed printing machine is provided. The assembly comprises discharge means that are movably supported in the printing machine and effective for applying to a sheet a work-pressure that is different from the atmospheric pressure in order to effectuate or to control, by the work-pressure, the feed of sheets through the printing machine. The assembly is characterized in that each discharge means comprises means for continuously adjusting the discharged pressure to a work-pressure operative for controlling or feeding which is adapted to the subject sheet and/or the subject process in the printing machine, in response to detecting at all times the work-pressure discharged from each singular discharge means or each singular set of discharge means, respectively.

In a preferred embodiment the assembly comprises, within said discharge means, a high-pressure operated ejector, an electromagnetic valve controlling the pressure which operates the ejector, a micro processor controlling the electro magnetic valve, and a pressure sensor arranged for feeding to the micro processor an electric signal in response to a detected work-pressure that is discharged from the ejector.

The discharge means are structured as suction means effective for discharge of a sub-pressure, or as blowing means effective for discharge of an over-pressure. For example, the discharge means can be realized as suction cups, as perforated conveyor bands, as elongate slot sections in retardation cylinders, as nozzles or similar discharge means, installed in printing machines for effecting or for controlling the transport of sheets.

SHORT DESCRIPTION OF THE DRAWINGS

The invention is further explained below with reference being made to the accompanying, diagrammatic drawings, wherein

Fig. 1 is a longitudinal section through a sheet feed printing machine in which a pressure different from the atmosphere is used to effectuate or to control the feed of sheets in the printing machine;

Fig. 2 is a sectional view through a discharge means comprising a suction cup and arranged to carry out the method according to the invention;

Fig. 3 is a sectional view through a retardation cylinder which is operated by sub- pressure to reduce the velocity of a sheet being discharged.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the expression "discharged sub-pressure" shall be read to define an evacuation of air aiming to establish a pressure that is lower than the atmospheric pressure. The expression "work-pressure" shall be read to define a pressure different from the atmospheric pressure, such as either a sub-pressure or an over- pressure. The expression "drive-pressure" shall in this description be read to define a high-pressure that is effective for driving an ejector.

With reference to fig. 1, a sheet feed printing machine is schematically shown, and wherein sheets of paper to be printed are fed individually in a general feed direction D from an in-feed end towards a discharge end. A stack of sheets 1 is located at the in-feed end, the sheet stack including sheets that are stacked one above the other. The sheet stack 1 may be movable in a vertical sense to allow for successively lifting the sheet stack towards a gripper 2 which is movably arranged in the printing machine. The gripper 2 is operative for lifting, one at a time, the uppermost sheet in the stack and to transfer the sheet to a printing unit 3 which is arranged downstream in the feed direction. In order to prevent adhesion between sheets in the sheet stack, a nozzle 4 may be arranged to direct over-pressure air towards a front end of the uppermost sheets in the stack, as viewed in the feed direction, this way separating the sheets before lifting and transfer to the printing unit. Though not disclosed in further detail, the printing unit 3 conventionally includes ink transfer cylinders and printing cylinders by which coloured ink is applied to the sheets. Also included in the printing unit may be cylinders and nozzles effective for controlling the transport of sheets in and out from the printing unit, by means of sub-pressure and over-pressure, respectively. Multi colour printing machines usually comprise at least one printing unit for each colour of red, yellow, blue, and black.

To provide linear transport of sheets in the printing machine, or between the printing machine and any auxiliary equipment, an endless conveyor band 5 may be formed with perforations there through, and through which a sub-pressure is discharged to the sheet surface in order for fixation of the sheet onto the conveyor band during transport. Further, in the discharge end of the printing machine, retardation cylinders 6 may be formed with a perforated cylinder wall through which a sub-pressure is discharged towards the sheet surface in order to adhere the sheet to the cylinder by suction, this way forcing the sheet to adjust its own moving speed to a controlled peripheral velocity of the retardation cylinder.

It should be noted, that the general description given above is only a schematic illustration of the field of application of this invention, and is not aiming to give a comprehensive and detailed description of a modern, sheet feed offset printing machine. Referring to fig. 2, a gripper 2 shown in a sectional view is arranged for applying a sub-pressure to the surface of a sheet of paper, and by means of the sub-pressure holding the sheet in order to effect or control the transport of the sheet in the printing machine. The gripper comprises a funnel- like suction cup 7 which is shaped at its peripheral edge 8 to be brought into sealing contact with the surface of the sheet, defining a cavity 9 to which sub- pressure is discharged as will be more closely explained below.

Sub-pressure is supplied to the gripper via a channel 10 that is in flow communication with the cavity 9 internally of the suction cup. A pressure sensor 11 is arranged in the channel 10, the pressure sensor at all times detecting a work- pressure existing in the channel 10 and thus in the cavity 9. Preferably, the pressure sensor 11 is a pressure difference sensor sensing a difference between the current pressure in the channel 10 and the atmospheric pressure. A piezoelectric sensor, for example, or other pressure transducer which is sensitive to pressure differences of at least +/- 1 bar, may be used. The work- pressure that is detected in the channel 10 is an IS-value that is sent from the pressure sensor 11 to a micro processor 12 in the form of an electric signal. In the micro processor, the IS-value is compared with a SET-value which is set in advance for the subject gripper and the subject application. The SET-value is a preset, operative work-pressure which is determined at least with respect to format and weight of the subject singular sheet of paper, and when appropriate also with respect to other parameters which are relevant for the operation of the gripper, such as surface smoothness, coating, humidity factor, planarity, porosity, etc., of the subject sheet of paper.

In connection herewith it will be mentioned that predetermined SET-values for different types of paper sheets, and/ or different types of printing procedures, can be stored in a control unit from which SET-values are called upon and signalled to the micro processor 12 when the printing machine is switched over, such as in connection with an exchange of paper sheet format, or in switching between coated and uncoated paper, etc. SET-values for different types of production in the printing machine can this way be stored in matrices for a simultaneous setting of all work- pressure discharging means in the sub-pressure system upon shifting between processes.

When a difference between SET-value and IS-value is detected, en electrical signal that is proportional to the magnitude of difference is put out from the micro processor 12 to an electric magnetic valve 13. The valve 13 controls the supply of sub-pressure to the gripper 2. In a centralized sub-pressure system, the valve may be arranged to proportionally throttle a flow communication between the gripper and a channel dedicated for supplying sub-pressure within the system.

In accordance with what is preferably teached through the present invention, the sub-pressure that is applied via the grippers will be generated by means of ejectors that are operated by high-pressure air, and which are known per se. The valve 13 is thus arranged for adjustment of the supply of high-pressure P to an ejector 14, the efficiency of which is this way adjustable for maintaining a predetermined SET- value in the discharged work-pressure. By continuously monitoring the current work-pressure in the gripper, and by continuously and proportionally adjusting the efficiency of the ejector, not only a constant work-pressure can be established, but also an operative work-pressure that is at all times adapted to the subject paper sheet.

Advantageously, the ejector 14 is a multi-stage ejector of smaller size suitable for integration with the gripper. Each singular gripper is in this way individually supplied with a work-pressure which is adapted to the subject application. Also, the distance between the gripper and the high-pressure source driving the ejector is no longer of significance. Furthermore, the necessity associated with centralized sub- pressure systems for an over-dimensioning of the sub-pressure in grippers in order to secure sufficient work-pressures in spite of any leaks in one or several grippers, can thus be avoided. Several examples of mini-pumps that are suitable for integration or mounting in grippers are available. The rotation-symmetric ejector 14 illustrated herein is one example only, however preferred, and which is particularly suitable for integration in correspondence with an ejector which is manufactured by the applicant under the trade name COAX®. A more detailed explanation of that ejector, which is known by the skilled person, is available from EP 1 064 464 Bl and a detailed description will thus not be required here.

Whereas each singular gripper can be individually operated through a dedicated pump/ejector as already explained, the air volume that needs to be evacuated in order to establish a work-pressure in the gripper can be substantially reduced, as compared to the dead volume that results from flow communications to a centrally located sub-pressure source in a centralized sub-pressure system. This way, extremely short operation cycles are available that correspond well with the maximum capacity of a modern sheet feed offset printing machine. The high degree of individual adjustment of work- pressure in the grippers further provides the advantage that the work-pressure applied can be adapted to local variations in a sheet of paper. Such local variations may otherwise jeopardize the gripper's ability to hold the sheet correctly. Also, the need for operating the grippers at oversized work-pressures in order to ensure sufficient gripping capacity can this way be avoided, avoiding hereby also the risk for damages on the sheet caused by exaggerated work-pressures.

A partial gain from this advantage is possible to achieve also when singular or several grippers are driven in sets by a common ejector, if said ejector is located in close vicinity to the set of grippers, or being integrated into one gripper in the set of grippers. In order to lift and to transfer individual sheets of paper from a stack of sheets 1 to a printing unit 3, a number of grippers 2 are usually organized in a matrix distributing the work-pressure to the surface of sheets, having different sizes. To this purpose, all grippers included in the matrix can be operated individually through separate pumps for each one of the grippers. Alternatively, several grippers can be jointly operated by a pump which is common for a set of grippers included in the matrix. In both cases, the work-pressure will be adjusted in result of a choice made from corresponding matrices of SET-values that are stored in the external control unit and which correspond to the subject sheet size. Sets of grippers, or individual grippers, can then be controlled into a non-operative or non-pressurized condition when formats are printed that do not require the operation of all grippers in the matrix.

In accordance with what has been previously explained in connection with the gripper 2, the retardation cylinder 6 may be arranged to provide a constant work- pressure which is adapted to the subject process in the printing machine. The retardation cylinder 6 is basically a cylinder driven in rotation, and is divided axially into sections 15. The sections 15 comprise a perforated cylinder wall 16 through which a work-pressure is distributed to the surface of a sheet of paper in order to effectuate or to control the transport of the sheet over the cylinder. More specifically, the retardation cylinder is effective for reducing the feed velocity of a printed sheet that is ejected from that printing unit which is the last one, as viewed in the feed direction. As explained above the feed velocity may amount to the order of 3 m/sec for sheet formats of AO, which may risk to cause damage to the sheet in case of a sudden stop. In order to avoid a hard ramming into an end- stop, the retardation cylinder is operated for suction of the sheet of paper towards the cylinder surface, this way urging the sheet to be slowed down to, or close to, the controlled peripheral velocity of the retardation cylinder. The sections of the retardation cylinder may be delimited and separated from each other, and each section may be operated individually through separate pumps /ejectors for each one of the sections. In analogy with the previous description of the gripper 2, the sections of the retardation cylinder may be operated in sets through pumps /ejectors which are common for a set of sections. Work-pressure is transferred to the sections via the centre of the retardation cylinder, or at the periphery thereof via channels 17 arranged for supplying the work-pressure. In said channels, or in direct communication with the same, pressure sensors 11 are correspondingly arranged as stated above to adjust, via a micro processor 12 and electric magnetic valve 13, the drive-pressure for a high-pressure operated ejector 14 that supplies work-pressure to the subject section.

The sections of the retardation cylinder are thus controlled individually or in sets in order to maintain or re-establish, in case of a detected deviation, a work-pressure corresponding to a SET-value which is determined with respect to each type of paper sheet or each type of process operated in the printing machine. The necessity, as well as the advantage of this ability to adjust and to distribute different work- pressures over the length of the retardation cylinder, is explained and appreciated by the fact that locally the weight by area of the paper sheet changes substantially in result of the applied printing ink, as compared to non-inked portions of the sheet. Added weight results in increased kinetic energy which may cause a displacement of sheets when these are unequally inked. By providing in the retardation cylinder a location of higher work-pressure, and thereby an increased retardation capacity, such displacement can be counteracted and a correct stacking of ejected sheets is achievable.

Further in analogy with the above said, the basic teachings of the invention may also be applied in order to establish and to maintain a predetermined work- pressure in blowing means, such as the nozzle 4 or any other blowing means included in a sheet feed printing machine. In such case, the pressure sensor 11 will obviously be positioned in the outlet V from the ejector, the pressure sensor detecting a difference between the atmospheric pressure and the over-pressure that is discharged from the ejector. The adjustment of the ejector's drive-pressure P is accomplished as described above in order to maintain a SET-value that is preset in the micro processor, in accordance with the above description of the gripper and the retardation cylinder.

Claims

1. A method by which a pressure different from the atmospheric pressure is generated and distributed to a sheet of paper in a sheet feed printing machine, comprising the step of generating a work-pressure in means arranged to discharge the work-pressure to the sheet and thereby to effectuate or control the transport of the sheet in the printing machine, characterized by the following steps: -supplying a drive-pressure to a high-pressure operated ejector (14);

-detecting a work-pressure discharged from the ejector, and

-adjusting the drive-pressure supplied to the ejector in response to a comparison between the detected work-pressure and a pre-set work-pressure, whereby a continuous adjustment of the work- pressure that is discharged from each singular discharge means or from each singular set of discharge means to a work-pressure which is adapted to the subject sheet and/ or the subject process in the printing machine, and which is operative for control or transport, is accomplished in response to detecting at all times the work-pressure discharged from each singular discharge means or from each singular set of discharge means.

2. The method of claim 1, characterized in that detection of work- pressure is performed on a sub-pressure discharged from the ejector.

3. The method of claim 1, characterized in that detection of work-pressure is performed on an over-pressure discharged from the ejector.

4. The method of claims 1 or 2, characterized in that in each singular discharge means or in each singular set of discharge means a difference between the at all times detected work-pressure and the atmospheric pressure is used for the proportional adjustment of driving pressure supplied to an ejector arranged in the singular discharge means or in the singular set of discharge means.

5. The method of claim 4, characterized in that, in each singular discharge means, the drive-pressure to the ejector is controlled to discharge a work-pressure corresponding to a SET- value that is set in a micro processor arranged in the subject discharge means, and in that the micro processor compares a detected IS- value with the preset SET-value, and in that the micro processor adjusts the drive- pressure to the ejector via an electric magnetic valve that is supported in the subject discharge means and controls the supply of drive-pressure to the ejector.

6. The method of claim 5, characterized in that SET-values of work-pressures for discharge means included in the air system are stored in a control unit, by which all discharge means are simultaneously set to individual SET-values for each discharge means.

7. The method of claim 6, characterized in that preset SET-values which are adapted to the type of paper sheet and/or type of process operated in the printing machine are stored in the control unit.

8. An assembly in a sheet feed printing machine, the assembly comprising means that are movably arranged in the printing machine and arranged for discharging to a sheet of paper a pressure that is different from the atmospheric pressure, and by means of the discharged work-pressure effectuates or controls the transport of the sheet in the printing machine, characterized in that a high-pressure operated ejector is supported in the discharge means, an electric magnetic valve by which the supply of drive-pressure to the ejector is adjustable, a micro processor which controls the electric magnetic valve, and a pressure sensor arranged for output, to the micro processor, of an electric signal corresponding to the work-pressure being discharged from the ejector, whereby said discharge means is arranged for a continuous adjustment of the discharged work-pressure to a work-pressure which is adapted to the subject sheet and/or the subject process in the printing machine, and which is operative for control or transport, in response to detecting at all times the work-pressure being discharged from each singular discharge means or from each singular set of discharge means.

9. The assembly of claim 8, characterized in that the discharge means is a suction means operative for discharging a sub-pressure.

10. The assembly of claim 8, characterized in that the discharge means is a blowing means operative for discharging an over- pressure.

11. The assembly of claim 9, characterized in that the discharge means is a suction cup.

12. The assembly of claim 9, characterized in that the discharge means is a perforated conveyor band.

13. The assembly of claim 9, characterized in that the discharge means is a section of a retardation cylinder.

14. The assembly of claim 10, characterized in that the discharge means is a blow nozzle.