US3342129A

US3342129A - Method and apparatus for electrostatically driving a sheet in a rotary press

Info

Publication number: US3342129A
Application number: US603058A
Authority: US
Inventors: Weigl William
Original assignee: Harris Intertype Corp
Current assignee: Harris Graphics Corp
Priority date: 1966-12-19
Filing date: 1966-12-19
Publication date: 1967-09-19
Anticipated expiration: 1984-09-19

Description

Sept. 19, 1967 W. wElGL 3,342,129

METHOD AND APPARATUS FOR ELECTROSTATICALLY DRIVING A SHEET IN A ROTARY PRESS Original Filed March 24, 1965 2 Sheets-Sheet 1 INVENTOR.

WILLIAM WEIGL BY W ATTORNEYS Sept. 19, 1967 w. WEIGL 3,342,129

METHOD AND APPARATUS FOR ELECTROSTAT I CALLY DRIVING A SHEET IN A ROTARY PRESS Original Filed March 24, 1965 2 Sheets-Sheet 2 .V 5 4 an mm:

Fl G. 5

INVENTOR.

WILLIAM WEIGL WWW ATTORNEYS United States Patent Ofiice 3,342,129 Patented Sept. 19, 1967 3,342,129 METHOD AND APPARATUS FOR ELECTRO- STATICALLY DRIVING A SHEET IN A RO- TARY PRESS William Weig], Brecksville, Ohio, assignor to Harris-Intitype Corporation, Cleveland, Ohio, a corporation of Continuation of abandoned applications Ser. No. 442,336, Mar. 24, 1965, and Ser. No. 519,554, Jan. 10, 1966. This application Dec. 19, 1966, Ser. No. 603,058

6 Claims. (Cl. 101142) ABSTRACT OF THE DISCLOSURE A printing press includes an impression cylinder and a printing cylinder which define a printing nip through which sheets are advanced by grippers on the impression cylinder. The sheet is then gripped by grippers on a transfer cylinder or delivery cylinder and conveyed thereby away from the impression cylinder. An electrostatic device is located on the output side of the printing nip and operates to apply a force to the sheet to hold it against the surface of the impression cylinder to establish a driving relationship between the sheet and the impression cylinder.

The present application is a continuation of my copending applications Ser. No. 442,336, filed March 24, 1965, and Ser. No. 519,554, filed January 10, 1966 and both of which are now abandoned.

The present invention relates to a printing press and, more particularly, to a printing press having a cylinder or drum with grippers thereon for receiving and carrying a sheet away from the printing unit.

In certain types of printing presses, the sheet being printed is carried through a printing nip by first grippers moving in an arcuate path and is transferred from the first grippers to second grippers on a transfer cylinder or delivey cylinder so that the sheet, after leaving the printing nip, follows a generally S-shaped path. In such a press, the printedside of the sheet will be adjacent the transfer cylinder or the delivery cylinder and smudging or offsetting of the printed surface may occur. Any offsetting of a sheet onto the cylinder may cause subsequent olfsetting from the cylinder ontothe following sheets. While offsetting is not a particular problem in the case of skeleton type cylinders or drums, smudging may occur with such cylinders or drums if the sheet moves relative to the cylinder or drum while in engagement therewith. To help solve the problem of offsetting, cylinders have been undercut. However, the undercutting of the cylinder allows the sheet to straighten and leave the S-shaped path for the sheet. This may result in offsetting and/or smudging if the sheet straightens against the undercut surface of the cylinder. The tendency of the sheet to straighten against the cylinder is accentuated in a lithographic printing press where the tacky ink on the blanket cylinder tends to pull the sheet against the surface of the transfer or delivery cylinder.

Smudging also tends to occur in chain transfers or chain delivery mechanisms where a chain conveyor passes around a drum or cylinder adjacent the impression cylinder to receive a sheet therefrom. In certain types of such mechanisms, the leading edge of the sheet slows as it leaves its arcuate path arount the cylinder or drum and moves onto the straightaway. This slowing provides slack in the sheet and may cause smudging against the drum or cylinder.

An important object of the present invention is to provide a new and improved printing press in which a sheet which follows an S-shaped path as it leaves the printing nip is handled in such a manner that offsetting or smudging against a transfer or delivery cylinder or drum which receives the sheet from the cylinder which carries it through the printing nip is minimized or eliminated.

In accordance with the present invention, a rotating cylinder which moves the sheet through the printing nip has a driving relaitonship with the sheet at a location on the delivery side of the nip and in the first part of the S-shaped path followed by the sheet in leaving the printing nip. As the sheet passes this location, a force is applied to the sheet to hold it against the surface of the cylinder to establish a driving relation therebetween so that the sheet is actually driven by the surface of the cylinder after it leaves the nip and While it is in the first part of its S-shaped path. When the sheet is driven in this manner, the sheet will be moved from the nip through the first part of the S-shaped path and into the second part of the S-shaped path by the driving relationship and any slack which occurs as a result of the undercutting of a transfer cylinder or the slowing of the leading edge of the sheet causes a bowing of the sheet only in the second portion of the S-shaped path and this bowing will be in a direction away from the transfer or delivery mechanism and will prevent smudging and/or offsetting.

Further objects and advantages of the present invention will be apparent from the following description thereof forming a part of the present specification for all subject matter disclosed therein and in which:

FIG. 1 is a diagrammatic view of the printing units of a two-color printing press;

FIG. 2 is a diagrammatic view of the sheet-carrying and printing cylinder of the printing unit and the transfer cylinder which moves the sheet away from the first printin g unit;

FIG. 3 is a view corresponding to FIG. 2 but illustrating an offsetting and/ or smudging condition;

FIG. 4 is a diagrammatic view of the impression cylinder and blanket cylinder of the second printing couple and of the delivery drum showing the bowing of the sheet which occurs in certain situations when the present invention is used; and

FIG. 5 is a cross sectional view taken approximately along line 44 of FIG. 2.

Referring to the drawings, the present invention is shown in a two-color lithographic printing press of the type described in United States Patent No. 2,542,867 issued to Charles W. Harrold. As illustrated in the drawings, the printing press includes a first printing unit 10 and a second printing unit. 11. The sheet is transferred from the first printing unit 10 to the second printing unit 11 by a transfer cylinder 12, which in the illustrated embodiment is a double size transfer cylinder. The sheet is delivered from the second printing unit by a delivery mechanism 14 including a delivery drum 15 which may be of a conventional skeleton type and a chain conveyor 16 for moving the sheets from the second printing unit to a delivery station, not shown.

The first printing unit 10 includes a plate cylinder 20, a blanket cylinder 21 and an impression cylinder 22. The blanket cylinder 21 and the impression cylinder 22 are in pressure relationship to form the printing nip of the first printing unit and the sheet to be printed is fed from a feed board 24 to grippers 25 on the impression cylinder and is carried into and through the printing nip formed by the blanket cylinder 21 and the impression cylinder 22 by the rotation of the impression cylinder. Upon leaving the nip, the sheet follows an S-shaped path. It is moved through the first curved part of the S-shaped path along the periphery of the impression cylinder and then through the reversely curved portion of the path along the surface of the transfer cylinder. The transfer cylinder 12 has two sets of diametrically opposed grippers 27 thereon and one or the other of the grippers will be in position to grip the leading edge of a sheet being printed by the first unit as the leading edge arrives at the point of tangency of the impression cylinder 22 and the transfer cylinder 12. The grippers on the impression cylinder 22 will release the sheet at this point and one set of grippers 27 on the transfer cylinder will take the sheet to carry the sheet through the reversely curved portion of the S-shaped path and to the following printing unit. The transfer cylinder will deliver the sheet being printed to grippers on the impression cylinder 30 of the second printing unit and grippers on the impression cylinder 30 will grip the leading edge of the sheet and carry it to the printing nip formed by the impression cylinder 30 and a blanket cylinder 31 which have a pressure relationship. The second printing unit also has a plate cylinder 32 which cooperates with the blanket cylinder 31. After the printing nip, the sheet being printed in the second unit is transferred to the delivery mechanism 14 at the point of tangency of the delivery drum 15 and the impression cylinder 30. The chain conveyor 16 of the delivery includes grippers 34 which take the sheet from the impression cylinder and carry it to the delivery. It will be seen that the sheet in leaving the printing nip formed by the impression cylinder 30 and the blanket cylinder 31 follows an S-shaped path, the first curved portion of the path being along the periphery of the impression cylinder 31 after the printing nip and the reversely curved portion of the path along the periphery of the delivery drum 15.

It will be noted that the printed sheet in leaving the printing nip of the first printing unit 1% has the freshly printed side facing the surface of the transfer cylinder 12 and the ink on the sheet may offset onto the transfer cylinder 12. Also any relative movement between the surface of the transfer cylinder 12 and the printed side of the sheet while the two are in engagement will cause smudging of the image. Conventionally, the transfer cylinder 12 has been undercut as indicated at 40 on the transfer cylinder to minimize the problem of offsetting. However, when the surface of the transfer cylinder is undercut to minimize the possibility of offsetting, the sheet no longer is constrained to follow an S-shaped path and at times tends to straighten against the transfer cylinder. An undercut transfer cylinder is one where the gripper pads move in a circle having a radius greater than the radius of the sheet engaging surface. The sheet engaging surface may be a continuous surface or one made up of a series of axially spaced discs, as known in the art.

The tendency of the sheet to straighten against the transfer cylinder is a particular problem in lithographic printing. In a lithographic press, the ink on the blanket cylinder is a very tacky ink to which the sheet being printed tends to stick. This may cause the sheet to follow the blanket cylinder after it leaves the nip, as illustrated in FIG. 3, until the slack is removed therefrom by the sheet stretching against the transfer cylinder. Moreover, if any relative movement occurs between the transfer cylinder and the sheet while the latter is in engagement with the surface of the transfer cylinder, smudging may occur.

Smudgin-g also presents somewhat of a problem at the delivery cylinder. In the type of chain delivery illustrated in the drawings, the leading edge of the sheet will slow as it moves from the arcuate path around the delivery drum to the straight line path for delivering the sheet away from the printing unit since the periphery of the drum is undercut with respect to the path followed by the grippers moving around the delivery drum. This slowing of the leading edge will provide slack in the sheet and unless the tail of the sheet has cleared the printing nip, the slack may be straightened or taken out by the pull of the ink on the blanket cylinder. This may cause relative movement between the periphery of the delivery cylinder or drum and the surface of the sheet and tend to produce smudging on that part of the sheet against the periphery of the delivery cylinder or drum.

I have found that the above problems may be eliminated or minimized by tightly holding the sheet against the surface of the impression cylinder at a location between the nip and the transfer or delivery cylinder to establish at the location a driving relationship between the cylinder and sheet which driving relationship is maintained for an appreciable distance as the sheet moves with the impression cylinder. This will cause the sheet to be driven through the first part of the S-shaped path at the same rate as it leaves the printing nip and if any slack occurs in the sheet, the sheet will bow in the reversely curved part of the S- shaped path and in a direction such that the sheet will move away from the transfer cylinder or the delivery cylinder as the case may be. An electrostatic device has been found to be particularly satisfactory in causing the sheet to be forced against the surface of an impression cylinder with sufficient force to establish intimate contact therebetween and the driving relationship necessary to cause the sheet to be fed into the reversely curved part of the S-shaped path at the same rate that it is leaving: the printing nip. Electrostatic devices for this purpose have been shown in FIG. 1 and have been designated by the

reference numerals

42 and 43. The devices are located immediately adjacent the impression cylinders on the delivery sides of the printing nips and extend across the width of the sheet being printed. The manner in which bowing will occur with the

devices

42 and 43 in use is illustrated in FIGS. 2 and 4. FIG. 4 shows the bowing of a sheet at the delivery drum 15 due to the slowing of the leading edge of the sheet, the bowing being designated by the reference number B. The bowing is now in a direction to move the sheet away from the delivery drum.

The

devices

42 and 43 substantially are the same and the device 42 is illustrated in FIG. 5. As shown in FIG. 5, the device 42 comprises an elongated conductive rod-like member 45 which has a plurality of ionizing needles 44, extending radially therefrom toward the surface of the adjacent impression cylinder. The rod-like elongated member 45 is disposed in an insulating covering 46, the internal diameter of the insulating covering being greater than that of the tube and needles. The insulating covering has openings opposite the ends of the needles to expose the needles and includes conductive means (not shown) such as a grounded wire extending along and supported in the covering. The elongated rod-like member is connected by a lead 47 to one side of a high power voltage supply, not shown, while the other side of the supply is connected to the adjacent cylinder, which in normally grounded, so that an electrostatic ionizing field is established between the needles and the surfaces of the impression cylinder. The ionization of the air due to the field and due to the corona discharge at the points of the needles will cause the sheet material to become charged, and to be attracted to the surface of the impression cylinder. An electrostatic force suflicient to hold the sheet in driving engagement with the surface of the impression cylinder is easily produced with such a device so that a driving relationship is maintained between the impression cylinder and a portion of the sheet on the delivery side of the printing nip to cause the surface of the impression cylinder to drive the sheet on the delivery side of the printing nip. The force holding the sheet against the impression is preferably maintained for substantially the full length of the sheet and is particularly advantageous as the tail portion of the sheet is moving from the printing nip,

From the foregoing it can be seen that the present invention minimizes or eliminates smudging or offsetting and assures that any deviation of the sheet from its designed path due to slack in the sheet will occur in the reversely curved portion of the S-shaped path where it causes the sheet to move away from the adjacent transfer or delivery cylinder or drum. In describing the invention the term delivery drum or cylinder has been used. For

the purposes of this invention the structures are equivalent and the terms, unless the context specifically indicates otherwise, are interchangeable.

While the preferred embodiment of the present invention has been described in considerable detail, it is hereby my intention to cover all constructions and modifications which fall 'within the ability of those skilled in the art and within the spirit and scope of the present invention.

Having described my invention, I claim:

1. In a lithographic printing press, a printing unit comprising a blanket cylinder and an impression cylinder defining a printing nip, grippers on said impression cylinder adapted to grip a sheet to be printed and carry it through the printing nip upon the rotation of the impression cylinder, another cylinder adjacent the impression cylinder on the delivery side of the nip and having grippers associated therewith for receiving the leading edge of the printed sheet from the impression cylinder at a transfer location whereby the printed sheet leaving the printing nip moves through a generally S-shaped path, the distance between said printing nip and said transfer location being less than the length of a sheet to be printed so that the leading edge of a sheet is engaged by said grippers associated with said another cylinder while another portion of the sheet is in said nip, electrostatic means disposed at a second location between the printing nip and said transfer location for continuously urging the portion of the sheet moving through the second location against the surface of the impression cylinder to establish a driving relationship therebetween to drive said sheet in the first part of said S-shaped path and operable for at least until the trailing end of the sheet leaves the printing nip to thereby minimize sticking of the sheet to the blanket cylinder, and said another cylinder having a periphery radially inwardly of the path of travel of the sheet grippers.

2. In a lithographic printing press, a first printing unit comprising a blanket cylinder and an impression cylinder defining a printing nip, grippers on said impression cylinder adapted to grip a sheet to be printed and carry it through the printing nip upon the rotation of the impression cylinder, another cylinder adjacent the impression cylinder on the delivery side of the nip and having grippers associated therewith for receiving the leading edge of the printed sheet from the impression cylinder at a transfer location whereby the printed sheet leaving the printing nip moves through a generally S-shaped path, the distance between said printing nip and said transfer location being less than the length of a sheet to be printed so that the leading edge of a sheet is engaged by said grippers associated with said another cylinder while another portion of the sheet is in said nip, first electrostatic means disposed at a second location between the printing nip and said transfer location for continuously urging the portion of the sheet moving through the second location against the surface of the impression cylinder to establish a driving relationship therebetween to drive said sheet in the first part of said S-shaped path and operable for at least until the trailing end of the sheet leaves the printing nip to thereby minimize sticking of the sheet to the blanket cylinder, said printing press including a second printing unit which includes a blanket cylinder and an impression cylinder, transfer means for transferring the sheets between the first and second printing units and including said another cylinder, second electrostatic means disposed on the delivery side of said second unit for establishing a driving relation between the sheet and the impression cylinder thereof, and means for delivering the sheets from the second printing unit including grippers which move along a straightaway after an S-shaped path and slow the leading edge of the sheet relative to the part of the sheet in the S -shaped path and wherein the grippers move in the straightaway while a portion of the sheet remains in the printing nip of said second unit.

'f P c ss of printing where a sheet is printed by PP g e leading edge of the sheet with grippers 6 on a rotating cylinder to carry the sheet through a printing nip for printing the sheet under pressure, the nip being formed by the rotating cylinder and a printing cylinder and after printing moving the sheet away from the rotating cylinder by transferring the leading edge of the sheet to second grippers associated with a second cylinder moving in an arcuate path adjacent the rotating cylinder on the delivery side of the printing nip whereby the path of movement of the sheet as it leaves the nip is generally an S-shaped path through a first curved portion along the surface of the rotating cylinder and then through a reversely curved portion along the path of the second grippers with the freshly printed surface facing the periphery of the second cylinder and wherein the leading edge of the sheet is engaged by the second grippers While another portion of the sheet is in the printing nip, the steps of establishing a driving relationship between the periphery of the rotating cylinder and the part of the sheet between the nip and the transfer point to the second grippers by electrostatically attracting the sheet to the rotating cylinder to establish a driving relationship between the sheet and the rotating cylinder, maintaining the driving relationship at least until the trailing end of the sheet leaves the printing nip whereby the part of the sheet on the delivery side of the nip is continuously driven through the first part of the S-shaped path and the sheet is prevented from following the printing cylinder, printing each sheet in a second printing nip defined by a second printing cylinder and a second rotating cylinder having grippers associated therewith to which said second grippers deliver the sheet, the sheet as it leaves the second nip moving in an S- shaped path defined by the surface of the rotating second cylinder and a reversely curved path of grippers associated with a delivery drum, electrostati-cally attracting the sheet to the second rotating cylinder to establish a driving relationship therebetween during movement of the sheet whereby the sheet is prevented from following the second printing cylinder, and wherein the printing cylinder defining each of the printing nips has a resilient planographic printing surface, and said second cylinder has a periphery radially inwardly of the path of travel of the second sheet grippers.

4. In the process of printing where a sheet is printed by gripping the leading edge of the sheet with grippers on a rotating cylinder to carry the sheet through a printing nip for printing the sheet under pressure, the nip being formed by the rotating cylinder and a printing cylinder and after printing moving the sheet away from the rotating cylinder by transferring the leading edge of the sheet to second grippers associated with a second cylinder moving in an arcuate path adjacent the rotating cylinder on the delivery side of the printing nip whereby the path of movement of the sheet as it leaves the nip is generally an S-shaped path through a first curved portion along the surface of the rotating cylinder and then through a reverse ly curved portion along the path of the second grippers with the freshly printed surface facing the periphery of the second cylinderand wherein the leading edge of the sheet is engaged by the second grippers while another portion of the sheet is in the printing nip, the steps of establishmg a driving relationship between the periphery of the rotating cylinder and the part of the sheet between the nip and the transfer point to the second grippers by electrostatically attracting the sheet to the rotating cylinder to establish a driving relationship between the sheet and rotating cylinder, maintaining the driving relationship at least until the trailing end of the sheet leaves the printing nip whereby the part of the sheet on the delivery side of the mp 18 continuously driven through the first part of the S-shaped path and the sheet is prevented from 01- lowmg the printing cylinder, printing each sheet in a second printing nip defined by a second printing cylinder and a second rotating cylinder having grippers to Which said second grippers deliver the sheet, the sheet as it leaves the second 11 p moving in an S-shaped path defined by the surface of the rotating second cylinder and a reversely curved path of grippers associated with a delivery drum, electrostatically attracting the sheet to the second rotating cylinder to establish a driving relationship therebetween during movement of the sheet whereby the sheet is prevented from following the second printing cylinder, and wherein the printing cylinder defining each of the printing nips has a resilient planographic printing surface, and said grippers comprise delivery grippers which move along a straightaway path after the S-shaped path and wherein the leading edge of the sheet slows relative to the part of the sheet in the S-shaped path, and the delivery grippers move into the straightaway path while a portion of the sheet remains in the printing nip.

5. In a press in which a sheet is printed in a printing nip and transferred therefrom through a generally S- shaped path defined by a first curved path portion and a second reversely curved path portion, a pair of cylinders defining the printing nip, one of said cylinders comprising a printing cylinder and the other of said cylinders comprising an impression cylinder having grippers associated therewith for moving the sheet through the nip and through said first curved path portion at a predetermined speed, transfer means for receiving the sheet from said grippers at a transfer location and engaging the sheet only at the leading edge thereof to move it through said second curved path portion unsupported by said transfer means rearwardly of the leading edge, said transfer means including gripper means movable at said predetermined speed and for engaging the leading edge of the sheet and support means for said gripper means movable through a path spaced inwardly from said second curved path ortion, the distance between said printing nip and said transfer location being less than the length of a sheet to be printed so that the leading edge of a sheet is engaged by said gripper means while another portion of the sheet is in said printing nip, and electrostatic means disposed at an intermediate location between said printing nip and said transfer location for continuously urging the portion of the sheet moving past said intermediate location against the surface of the impression cylinder to establish a driving relationship therebetween to drive said sheet in the first curved path portion and operable for at least until the trailing end of the sheet leaves the printing nip to thereby minimize sticking of the sheet to said printing cylinder.

6. In a method of printing a sheet, the steps of gripping the leading edge of a sheet with grippers on an impression cylinder and rotating the impression cylinder to move the sheet at a predetermined speed through a printing nip formed by the impression cylinder and a blanket cylinder and from the printing nip through a first curved path portion to a transfer location which is located a distance beyond the printing nip less than the length of the sheet, supporting the unprinted side of said sheet in said first curved path portion between said printing nip and said transfer location by said impression cylinder, releasing the leading edge of the sheet from said grippers at said transfer location, moving the sheet through a second curved path portion extending away from said impression cylinder and defining an S-shaped path with said first path portion by gripping and supporting the sheet adjacent the leading edge thereof and moving the leading edge at said predetermined speed through said second curved path portion while so gripped and supported and moving the remainder of the sheet through said second path without supporting the sheet along said second path on the printed side thereof, establishing a driving relationship between the periphery of the impression cylinder and the part of the sheet between the printing nip and the transfer location by electrostatically attracting the sheet to the impression cylinder to establish a driving relationship between the sheet and the impression cylinder, and maintaining the driving relationship at least until the trailing end of the sheet leaves the printing nip whereby the part of the sheet on the delivery side of the printing nip is continuously driven through said first curved path portion and the sheet is prevented from following the curvature of the blanket cylinder.

References Cited UNITED STATES PATENTS 287,957 11/1883 Osborne 271-51 X 2,821,131 1/1958 Spiller et al. 101137 2,940,387 6/1960 Pritchard 101-232 3,039,388 6/1962 Brandt et al. 101232 3,172,657 3/1965 Brandt 101-232 X 3,174,748 3/1965 Roberts et al. 101232 ROBERT E. PULFREY, Primary Examiner.

J. R. FISHER, Assistant Examiner,

Claims

3. IN THE PROCESS OF PRINTING WHERE A SHEET IS PRINTED BY GRIPPING THE LEADING EDGE OF THE SHEET WITH GRIPPERS ON A ROTATING CYLINDER TO CARRY THE SHEET THROUGH A PRINTING NIP FOR PRINTING THE SHEET UNDER PRESSURE, THE NIP BEING FORMED BY THE ROTATING CYLINDER AND A PRINTING CYLINDER AND AFTER PRINTING MOVING THE SHEET AWAY FROM THE ROTATING CYLINDER BY TRANSFERRING THE LEADING EDGE OF THE SHEET TO SECOND GRIPPERS ASSOCIATED WITH A SECOND CYLINDER MOVING IN AN ARCUATE PATH ADJACENT THE ROTATING CYLINDER ON THE DELIVERY SIDE OF THE PRINTING NIP WHEREBY THE PATH OF MOVEMENT OF THE SHEET AS IT LEAVES THE NIP IS GENERALLY AN S-SHAPED PATH THROUGH A FIRST CURVED PORTION ALONG THE SURFACE OF THE ROTATING CYLINDER AND THEN THROUGH A REVERSELY CURVED PORTION ALONG THE PATH OF THE SECOND GRIPPERS WITH THE FRESHLY PRINTED SURFACE FACING THE PERIPHERY OF THE SECOND CYLINDER AND WHEREIN THE LEADING EDGE OF THE SHEET IS ENGAGED BY THE SECOND GRIPPERS WHILE ANOTHER PORTION OF THE SHEET IS IN THE PRINTING NIP, THE STEPS OF ESTABLISHING A DRIVING RELATIONSHIP BETWEEN THE PERIPHERY OF THE ROTATING CYLINDER AND THE PART OF THE SHEET BETWEEN THE NIP AND THE TRANSFER POINT TO THE SECOND GRIPPERS BY ELECTROSTATICALLY ATTRACTING THE SHEET TO THE ROTATING CYLINDER TO ESTABLISH A DRIVING RELATIONSHIP BETWEEN THE SHEET AND THE ROTATING CYLINDER, MAINTAINING THE DRIVING RELATIONSHIP AT LEAST UNTIL THE TRAILING END OF THE SHEET LEAVES THE PRINTING NIP WHEREBY THE PART OF THE SHEET ON THE DELIVERY SIDE OF THE NIP IS CONTINUOUSLY DRIVEN THROUGH THE FIRST PART OF THE S-SHAPED PATH AND THE SHEET IS PREVENTED FROM FOLLOWING THE PRINTING CYLINDER, PRINTING EACH SHEET IN A SECOND PRINTING NIP DEFINED BY A SECOND PRINTING CYLINDER AND A SECOND ROTATING CYLINDER HAVING GRIPPERS ASSOCIATED THEREWITH TO WHICH SAID SECOND GRIPPERS DELIVER THE SHEET, THE SHEET AS IT LEAVES THE SECOND NIP MOVING IN AN SSHAPED PATH DEFINED BY THE SURFACE OF THE ROTATING SECOND CYLINDER AND A REVERSELY CURVED PATH OF GRIPPERS ASSOCIATED WITH A DELIVERY DRUM, ELECTROSTATICALLY ATTRACTING THE SHEET TO THE SECOND ROTATING CYLINDER TO ESTABLISH A DRIVING RELATIONSHIP THEREBETWEEN DURING MOVEMENT OF THE SHEET WHEREBY THE SHEET IS PREVENTED FROM FOLLOWING THE SECOND PRINTING CYLINDER, AND WHEREIN THE PRINTING CYLINDER DEFINING EACH OF THE PRINTING NIPS HAS A RESILIENT PLANOGRAPHIC PRINTING SURFACE, AND SAID SECOND CYLINDER HAS A PERIPHERY RADIALLY INWARDLY OF THE PATH OF TRAVEL OF THE SECOND SHEET GRIPPERS.