US3853315A

US3853315A - Sheet feeder for printing presses

Info

Publication number: US3853315A
Application number: US00250448A
Authority: US
Inventors: H Dahlgren
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-06-17
Filing date: 1972-05-04
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10

Abstract

A sheet transfer conveyor for a sheet-fed printing press comprising spaced gripper bars carried by endless flexible tapes. Movement of the tapes and grippers carried thereby is constantly synchronized with movement of printing surfaces to assure that register between sheets and printing cylinders is never lost from the time a sheet is fed to the press until it has been printed and released at a delivery station. Tape guide wheels are rotatably secured adjacent opposite ends of the printing press and have slotted blocks spaced about the periphery thereof engageable with surfaces on the gripper bars to maintain the gripper bars and tape wheels in synchronized relation.

Description

United States Patent [191 Dahlgren [451 Dec. '10, 1974 SHEET FEEDER FOR PRINTING PRESSES [76] Inventor: Harold P. Dahlgren, 726 Regal Row, Dallas, Tex, 75247 [22] Filed: May 4, 1972 [21] Appl. No.: 250,448

Related US. Application Data [63] Continuation-in-part of Ser. No. 737,521, June 17,

1968, Pat. No. 3,664,261.

[56] References Cited UNITED STATES PATENTS 544,685 8/1895 Porter 74/67 648,865 5/1900 Ganz 74/68 1,046,095 12/1912 McCain 271/79 1,164,802 12/1915 Freeman 271/7 9 1,894,829 1/1933 Otis 198/203 X 2,138,405 11/1938 Huck 101/183 Felts et a1. 271/79 X Dahlgren 101/177 Primary Examiner-Richard A. Schacher Assistant Examiner-Bruce H. Stoner, Jr.

Attorney, Agent, or Firm-Howard E, Moore; Gerald G. Crutsinger [57] ABSTRACT A sheet transfer conveyor for a sheet-fed printing press comprising spaced gripper bars carried by endless flexible tapes. Movement of the tapes and grippers carried thereby is constantly synchronized with movement of printing surfaces to assure that register between sheets and printing cylinders is never lost from the time a sheet is fed to the press until it has been printed and released at a delivery station. Tape guide wheels are rotatably secured adjacent opposite ends of the printing press and have slotted blocks spaced about the periphery thereof engageable with surfaces on the gripper bars to maintain the gripper bars and tape wheels in synchronized relation.

2 Claims, 34 Drawing Figures sumzord A I ll PATENTEU DEC 1 01974 SHEEI 3 0F 4 SHEET FEEDER FOR PRINTING PRESSES CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 737,521, filed June 17, 1968, entitled STRAIGHT FEED PRESS, now Pat. No. 3,664,261.

BACKGROUND OF THE INVENTION No significant advances have been made presenting new concepts in sheet-fed printing systems for decades. Printing systems designed for the sheet-fed printer are basically the same and allow printing on one side of the sheet at a time, requiring sheets to be turned over and rerouted through the press for single or multi-color perfecting. Sheets are progressively and meticulously transferred in serpentine fashion about transfer and impression cylinders and hopefully registered from one cylinder to another and from one printing unit to another until finally they emerge as a printed product. Printing units must be synchronized for color register through numerous drive and idler gears and consequently presses are extremely complex, massive units which are very expensive to manufacture because of numerous transfer and printing cylinders and mechanisms related thereto.

One or two color sheet-fed perfectors have been developed heretofore. However, these machines were specifically designed for specific jobs, such as mass production of paperback books, and are totally unsuitable for high speed production of four-color process printing on both sides of the paper.

Heretofore no commercially successful sheet-fed press had the capability of printing on two sides of a sheet in as many as four colors by passing the paper through the press one time.

[t is the common and accepted practice in the printing industry to run a sheet to be printed through the sheet-fed press a multiplicity of times to attain multicolor printing on two sides of a sheet. After each pass of the sheet through the press, the plates must be changed and the press made ready for the next pass to apply other colors or to print on the back of the sheet. It is readily apparent to those skilled in the printing art that a considerable amount of time is spent making sheet-fed presses ready to print and in attaining proper registry of the numerous components of the press.

In a typical four-color one-side printing press a sheet delivered from the feeder is caught by the gripper bars of a first transfer cylinder. The sheet is folded around the transfer cylinder and carried to the grippers on the first impression cylinder where the grippers of the transfer cylinder release the paper and it is caught by the grippers of the impression cylinder. The grippers on the impression cylinder rotate the paper into contact with the-blanket cylinder where printing is accomplished in one color on one side of the sheet. When the grippers on the impression cylinder release the sheet,

. grippers on a second transfer cylinder grasp the sheet,

causing the printed surface to be in contact with the transfer cylinder while it is rotated to the grippers of a second impression cylinder. The grippers of the second transfer cylinder release the sheet as it is caught by the grippers of the second impression cylinder which rotates the sheet into contact with a second blanket where a second color is applied to the same side of the sheet. Grippers on a third transfer roller catch the sheet as it is released by the grippers of the second impression cylinder and the printed surface is again brought into contact with a transfer cylinder while it is being delivered to the grippers of a third impression cylinder. This process is continued until the sheet passes to delivery. When one side of the sheet is completed, the press is replated, the sheets are turned and re-fed through the press to print the other side of the sheet.

Virtually all sheet-fed printing presses heretofore developed have the characteristic of feeding the sheet serpentine fashion through the press while the grippers associated with each cylinder catch the sheet as it is being released by the grippers of the previous cylinder.

One of the major problems encountered by the printing industry lies in synchronizing the various cylinders whereby the sheet will be grasped and released at the proper moment for maintaining registry between the cylinders of successive towers so that colors do not overlap or separate.

Chains have been used in the past with limited success to transfer sheets from one printing station to another. However, grippers supported by the chain were positively indexed to the printing station cylinders in an attempt to regain register which was periodically lost between printing stations.

A chain has inherent limitations as a smooth transfer media because chordal motion of the links limit smooth flow; linear deformation of the chain results from numerous pivot joints. Lubrication requirements at joints, to help prevent wear, noise, shock and vibration, present maintenance problems.

The gripper and chain transfer media could not, by itself, register the sheet between printing stations, even with the chain travelling precisely at cylinder speeds. As a compromise, grippers had to be loosely supported on the chain, moved from normal position, and indexed to printing station cylinders prior to actual sheet transfer at the cylinder. As soon as sheet transfer was accomplished and the gripper became separated from index with the cylinder, the gripper jumped or jerked back into its normal relation with the chain.

In the transfer system employed and disclosed herein, there is no contact between tape directed gripper bars and the printing cylinders thereby eliminating shock, vibration, wear, noise, mis-register and other apparent problems accompanied by chain supported grippers being indexed to cylinders. The printing cylinders are entirely independent of the sheet transfer mechanism and vice versa except for speed synchronization of cylinder surface speed with that of the tape.

Another problem has been the offsetting of wet ink on transfer cylinders from the freshly printed surface on the paper and consequently back on to the next sheet that is passed through the press. Heretofore, presses with a mulitplicity of towers for applying more than one color of ink to the sheet were driven by a common drive through a complex gear train or through long shafts which have inherent distortion thereby increasing the problem of synchronizing components of the press thereby making precision registry more difficult.

Typical four-color one-side printing presses have an average of about twenty cylinders including the plate cylinders, blanket cylinders, impression cylinders, transfer cylinders and skeleton wheels.

Sheet-fed printing presses heretofore used have relatively low production speeds which never exceed eight thousand impressions per hour.

All sheet-fed presses heretofore used have basically the same complex ink fountain with keys to vary the ink flow and an ink train consisting on an average of about twenty rollers for smoothing and distributing the ink to the plate cylinder.

A universal characteristic of sheet-fed printing presses heretofore used has been the employment of massive bearers on each end of the plate and blanket cylinders to assure rotation of the cylinders without vibration when the cylinder load is reduced because of gaps in the cylinders. The use of bearers has been necessitated by limitations of bearings heretofore incorporated into the design of presses for journaling the cylinders.

Apart from the equipment design being basically the same, one only has to be briefly associated with problems in the industry to see that printing problems, too, are the same for the similarly designed presses; namely, extensive time and effort are required for make-ready; extreme difficulty in obtaining and maintaining register between colors; streaking and slur caused by gear lash and deformation or by vibration and shock of complex mechanism movements; offsetting caused by the printed side of the sheet being in contact with transfer cylinder and skeleton wheel surfaces; sheet or board fatigue; considerable downtime for maintenance caused by breakdown of the complex mechanical systems; problems relating to ghosting on certain printing layouts; problems relating to control of ink-water balance and sometimes the most neglected problem of all, that of requiring personnel having special skills, talents, experience and perseverance to get the job done with the above mentioned type of printing systems.

All the above problems are related basically to problems involving lack of versatility, quality, economy and ease of operation, and are largely caused by the stereotype conventional design of the present day printing system.

Since the problems for the sheet-fed printer are not being readily solved by updating and face-lifting of the old concepts of printing, the only apparent alternative has been to switch to web-offset lithography. Here the printer can print several colors on two sides of the sheet at the same time with increased production. In addition to the mulit-color perfecting capability the web-press is superior to the sheet-fed press in specific situations because higher production rates and lower break-even points are possible.

This at first would seem to be the answer, except for the fact that many of the problems existing in sheetfed printing also exist in web-offset; namely, lack of color register caused by deformation of long drive shafts; basically the same kind of ink fountain with keys used in sheet-fed presses; a complicated train of rollers and conventional water fountain systems; common drive for the entire press; roller or ball-bearings with massive cylinder bearers on the plate and blanket cylinders; and printing cylinders are universally the same circumference as the finished sheet cut-off length, allowing absolutely no time for recovery of the inking form rollers after they finish a printing cylcle.

Apart from problems common to the conventional sheet-fed operation, switching from sheet-fed to weboffset lithography presents other distinct disadvantages.

A web-offset press is limited to one sheet length equal to the circumference of the plate cylinder. When shorter sheet lengths are required excessive waste results from non-use of the unprinted web portion. Another complete press system must be designed, manufactured, purchased and used for printing different sheet sizes to avoid excessive waste of paper. Web presses are generally more expensive because of complex folders, dryers, chill devices, etc., necessary. More time is usually required for make-ready and more waste is encountered since the web must be running through the press and desirably at production speeds while registering and while color correction changes are being made because it is difficult to compensate for wind-up of the drive system when the press is stopped. Crews trained for printing on sheet-fed equipment find that they must learn new skills when using web equipment.

The printing industry is faced with a dilemna of the sheet-fed and web-fed printing operations, each having decided advantages over the other, while sharing common problems which are inherent in this stereotyped press design which has been virtually unchanged for decades.

SUMMARY OF THE lNVENTlON l have developed a novel sheet-fed offset lithographic printing press which incorporates the advantages of sheet-fed equipment heretofore employed and the advantages of the web-press, while eliminating deficiencies of each.

By eliminating elements which did not contribute to the success of the lithographic printing press but which prevented or defeated it, I have developed a sheet-fed printing press which has the capability of perfecting, i.e., printing on both sides of the sheet at the same time, in any desired number of colors while the sheet is passed one time through the printing press.

I have eliminated all transfer cylinders, impression cylinders and skeleton wheels which have been used heretofore for feeding a sheet through the press serpentine fashion.

I have developed a sheet-fed printing press which incorporates a straight through and continuous sheet transfer principle similar to the feeding of style of web presses whereby the sheet is grasped by a gripper bar being delivered to the sheet transfer mechanism by a conventional feeder and the sheet is directed along an uninterrupted pathhaving no abrupt changes in direction to and through one or a plurality of printing towers where printing is accomplished selectively on one side; or, on both sides of the sheet at the same instant, or any combination thereof in any desired number of colors. This eliminates turning the sheet over after printing on one side and re-feeding it through the printing system. This also eliminates the necessity for numerous cylinders, constantly gripping and releasing the sheet as has been required heretofore.

l have eliminated the common drive system and have incorporated a novel system for driving the printing towers by individual drive motors while maintaining register for multi-color printing by the use of synchronizing links for maintaining critical elements of each printing tower and the sheet transfer system in synchronization at all times.

It is a primary object of the invention to provide a sheet-fed printing press which incorporates a sheet transfer system which moves the sheet in virtually a straight horizontal line, eliminating transfer and impression cylinders, in which the sheet length is unrelated to and may be variably less than the circumference of the printing cylinder, thereby incorporating the straight feed characteristic of the web press with the variable cut-off characteristic of the sheet-fed press.

Another object of the invention is to provide a sheetfed press in which the sheet is continuously gripped by a single set of grippers from the time the sheet enters the press until delivery, offering the ultimate in register for rnulti-color printing. I

Another object of the invention is to provide a printing press in which the sheet is grasped at the leading edge by a set of grippers and aerodynamically supported and directed to and through one or more printing towers.

A further object of the invention is to provide a sheet-fed printing press which may be used as a perfector to print any desired number of colors on both sides of the sheet, eliminating the need for a second pass through the press.

A still further object of the invention is to provide a sheet transfer system capable of gripping and registering two sheets simultaneously in a single set of grippers to move the sheets through perfecting printing towers to print on one side of each sheet.

A further object of the invention is to provide a printing press in which the only cylinders which touch the paper are the printing cylinders, thereby eliminating all costly transfer cylinders, impression cylinders, skeleton wheels, and related complex gripper mechanisms commonly used in sheet-fed presses.

A further object of the present invention is to eliminate marking caused by the offsetting of wet inkon sheets exposed to transfer cylinders and subsequent offsetting of the ink to subsequent sheets. a

A still further object of the invention is to provide sheet-fed printing press having a sheet gripping mechanism carried by an endless flexible conveyor having an in-line feeder and delivery, allowing fast but accurate control of the speed of the paper through the press.

A still further object of the invention is to provide a sheet-fed printing press in which the sheet travels through the path of least resistance thereby utilizing natural phenomena such as the cantilever effect on the sheet as it is grasped in the nip between the blanket cylinders. causing the sheet to lie tangent to the blanket cylinders due to its modulus of elasticity and also phenomena involving boundary layers of air and air pressure at the nip between opposing blanket cylinders.

A still further object of the invention is to provide a sheet-fed printing press which may serve as a perfector in which printing is achieved on both sides of the sheet at precisely the same moment as the sheet is drawn between adjacent blanket cylinders and touches the cylinders only at the printing nip.

A still further object of the invention is to provide a sheet-fed printing press in which each blanket cylinder serves the dual purpose of a blanket cylinder for offsetting ink to the sheet and simultaneously as an impression cylinder for the blanket which is offsetting ink to the opposite side of the sheet. I

These and other objects are effected by my invention as will be apparent in the following description taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrating the present invention are provided so that the invention may be better and more fully understood, in which:

FIG. I is a side elevational view of the operator side of the printing press;

FIG. II is a top plan view of the printing press having the inker broken away;

FIG. III is a cross sectional view taken along lines III- III of FIG. II showing a typical tape wheel in the delivery station;

FIG. IV is an enlarged elevational view of a typical gripper bar locking in the direction indicated by the arrows along lines IVIV of FIG. II;

FIG. V is a fragmentary perspective view of a modified form of a tape wheel;

FIG. VI is a cross sectional view taken along line Vl-VI of FIG. V; and

FIG. VII is a diagramatic view illustrating sheet flow.

Numeral references are employed to indicate the various parts as shown in the drawings and like numerals indicate like parts throughout the various figures of the drawing.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIGS. I and VII of the drawings the numeral 1 generally designates a sheet-fed multi-color perfecting lithographic printing press.

A feeder mechanism 2 feeds sheets of unprinted paper from a stack 4 by suitable means to a swing gripper 6. The swing gripper 6 accelerates individual sheets 5 to the velocity of gripper bars 8 carried by the sheet transfer mechanism, generally designated by the numeral 10. Sheet transfer mechanism 10 comprises tape wheels 12a, 12b and 14a, 14b which carry tapes 16a and 1611, having gripper bars 8 mounted therebetween for moving individual sheets 5 through the printing press, as will be hereinafter more fully described.

A plurality of printing towers l8 and 20 is provided, giving the press a multi-color perfecting capability. Conventional leveling devices such as jack screws (not shown) may be utilized for tower leveling.

A delivery mechanism 22 grips the individual sheets 5 as they are released by gripper bars 8 of the sheet transfer mechanism 10 and positions the sheets by suitable means in a stack of printed sheets 24.

Referring to FIG. II of the drawing, each

printing tower

18 and 20 has a side frame 26 on the operator side and side frame 28 on the drive side of the printing press joined by tie bars 30 forming'a strong rigid structure upon which various components of the press are mounted. Feeder'2 and delivery 22 have operator side side frames 2a and 22a and drive side side frames 2b and 22b, respectively. Structural ties 31 join the side frames of individual towers l8 and 20 and side frames of the feeder 2 and delivery 22.

Primary inkers 32 and secondary inkers 34 cooperate with dampeners-36 to provide a proper balance of ink and dampening fluid to the plate cylinders 38, which are duplicated at the upper and lower ends of the tower.

The sheet transfer mechanism, hereinbefore briefly described, includes tape wheels 12 and 12b rigidly connected to tape wheel axles 154 rotatably journaled in the side walls 2a and 2b of feeder station 2 and tape wheels 14a and 14b rigidly connected to tape wheel axle 155 rotatably journaled in tape wheel hangers (not shown) adjustably secured to side walls 22a and 22b of delivery station 2.

Tapes 16a and 16b may be of any length as long as the length of each tape is equal to a multiple of the circumference of plate cylinders 38U and 38L.

It should be noted that the use of the straight line sheet transfer mechanism allows individual printing towers 18 and 20 to be unevenly spaced if it is deemed expedient to do so. Therefore, a multi-color press could have individual printing towers arranged with varying spaces therebetween providing great flexibility, allowing the printing press to be installed in a building without modification where it might be necessary to modify the building for installation of a conventional printing press.

As best seen in FIG. 1 and 11 of the drawing, each tape 16a and 16b is an endless flexible conveyor having sufficient tensile strength so that no appreciable stretch or lineal deformation results within the range of forces applied thereto in its present application. Tapes 16 may be constructed of any suitable material such as a single strand steel tape, a multiple strand cable, or belt. However, a steel tape is utilized in the particular embodiment shown in the drawing. Tape 16a is carried about tape wheels 12a and 14a journaled on one side of the printing press while a second tape 16b is carried about tape wheels 1211 and 14b journaled on the other side of the printing press.

Each tape wheel 12a, 12b, 14a and 14b has V-blocks 158, FIG. I", radially spaced adjacent the circumference thereof. Each V-block 158 has a key 160 extending outwardly from one face thereof which is complementarily received by key way 162 in the tape transfer wheel 14b. V-block 158 is adjustably secured to the tape transfer wheel by bolts [64 extending through elongated holes 168 in V-block 158 to threadedly engage the transfer wheels. A support block 170 is secured to the tape wheels adjacent V-blocks 158 by bolts 172 and has an adjusting screw 174 extending therethrough. V-blocks 158 may be adjusted on the tape transfer wheels by loosening bolts 164, allowing movement of the V-blocks 158 by rotation of adjusting screw 174. When the desired position is attained bolts 164 and jam nut 176 on adjusting screw 174 are tightened; thereby rigidly connecting the V-block to tape transfer wheels. V-blocks 158 are mounted on tape transfer wheels 12a, 12b, 14a and 14b in the same manner.

Each gripper bar assembly 8 includes a support bar 178 rigidly connected to tapes 16a and 16b by any suitable means such as locating pins 180. Heads 182 of locating pins 180 are received by peripheral recesses 184 in each tape wheel 12a, 12b, 14a and 14b. Each support bar 178 has outer guide rollers 186a and 1845b and inner guide rollers 188a and 1881) rotatably mounted on each end thereof. Each guide roller is mounted on axle 190 of support bar 178 which has a bushing 192 rotatably mounted thereon held in proper position by thrust washer 194 and a jam nut 196. A set screw 198 is provided in jam nut 196 to prevent loosening ofjam nut 196.

An actuator shaft 200 is rotatably mounted in backup plate supports 202 which are welded or otherwise rigidly connected to the support bar 178.

A backup plate 204 is rigidly connected by bolts 206 to backup plate supports 202 and extends transversely between tapes 16a and 16b, which are spaced apart, in substantially parallel relationship to support bar 178 and actuator shaft 200.

A plurality of conventional gripper finger support as semblies 208 are rigidly connected to actuator shaft 200 in spaced apart relation throughout the length thereof. A gripper finger 210 is rigidly connected to each gripper finger support assembly 208 by a cap screw 212.

A torsion spring 214 is positioned about and connected between actuator shaft 200 and the backup plate support 202, applying torque to actuator shaft 200 to provide a substantial force, causing pin 200a on shaft 200 to be maintained in engagement with actuator shaft stop 200b extending outwardly from backup plate support 202 to grip a sheet of paper 5 between gripper fingers 210 and backup plate 204.

it is very important that sheet 5 not slip relative to gripper fingers 210 and backup plate 204 after the sheet has been gripped. The spring constant of the torsion spring 214 and the number of gripper fingers 210 necessary to accomplish this result may vary depending upon the size and weight of the sheet 5 for specific printing operations.

Cam followers 216 are rotatably journaled on actuator arms 218 adjacent tape wheels 12a, 12b, 14a and 14b. Arms 218 are rigidly connected to actuator shaft 200. Cams 220 are fixedly secured by bolts 222 to the tape wheel in such a relationship to the cam followers 216 that rotation of the tape wheel will bring the cams 220 into contact with the followers 216, thereby rotating actuator arms 218 and actuator shafts 200 against force exerted by the torsion spring 214, causing gripper fingers 210 to rotate away from backup plate 204. The exact position and configuration of the cams 220 may be varied in a specific operation whereby the gripper fingers 210 will be rotated relative to backup plate 204 to grip a sheet at the precise moment it is swung into proper position by swing gripper 6 from the feeder mechanism 2 and to release the sheet after printing has been accomplished thereon when the sheet has been conveyed to the delivery mechanism 22.

While the specific description has been directed to tape wheel 14a and 14b, it should be noted that tape wheels 12a, 12b and grippers associated therewith have the same general configuration and operate in substantially the same manner. The tape carried gripper assemblies 8, rigidly connected to the endless flexible conveyor tapes 16a and 16b by locating pins 180, grasp a sheet of paper 5 from the swing gripper assembly 6 of the feeding mechanism 2, move the sheet in a straight horizontal line to and through the printing towers l8 and 20, release the sheet when it is gripped by the delivery mechanism 22 and the gripper assemblies 8 return to the feeder mechanism 2 to pick up another sheet.

As best illustrated in FIG. [ll of the drawing V-blocks 158 receive the inner guide rollers 188 as tape wheels 12a, 12b, 14a and 14b rotate, causing the tapes 16a and 16b and the gripper assemblies 8 to rotate therewith.

Inner tracks 224a and 22 th and outer tracks 226a and 22Gb extend longitudinally throughout the printing press at the upper and lower ends thereof and are positioned to receive and guide the inner and

outer guide rollers

188a, 188b and 1860 and 186b respectively, thereby supporting the weight of each gripper bar 8 as it travels between tape wheels 12a, 12b and 14a, 1412. As best seen in FIG. III of the drawing, the path of travel of the gripper bars 8 is defined by the configuration of the opening between the inner track 224 and the outer track 226. One of the outer guide rollers l86b on each support bar 178 has a groove 228 therein which receives and rolls along an upwardly extending portion 230 of the outer track 226 on one side of the press. It should be readily apparent that the gripper bars 8 will be guided by the outer track 226b because lateral alignment is maintained by the groove 228 on the outer guide wheel 1861: while the inner track 2241: above the inner guide roller l88b prevents disengagement of the groove 228 from the upwardly extending portion 230 of the outer track 226b.

The other outer guide roller 186a on each support bar 178 does not have a groove 228 thereabout. This provides means for automatically compensating for thermal expansion of support bar 178 because the guide roller 186a is free to move laterally relative to the outer track 226a.

While guide tracks 224 and 226 are shown to be straight and horizontal in the drawing, it should be readily apparent that the tracks may be inclined or curved to conform with any desired configuration if it is deemed expedient to do so. I anticipate the use of the above described continuous gripping tape controlled gripper bar 8 with tracks curved or inclined in a vertical or horizontal plane for controlling the path of a sheet through a printing press regardless of the geometricconfiguration of individual printing towers and the components thereof.

Sheet 5, accelerated by conventional swing gripper assembly 6, is gripped firmly along its leading edge by the tape carried gripper bar assemblies 8'while the rer mainder of the sheet is aerodynamically supported and floated on air to the first printing tower 18.

Sheet transfer mechanism hereinbefore described causes the sheet 5 to travel along the path of least resistance. thereby causing the sheet to attain a position in a plane parallel with its direction of travel.

A modified form of apparatus employed for indexing tapes 16a' and 16!) relative to tape wheels 14a and 14b and guide tracks 224' and 226' is illustrated in FIGS. V-Vll.

Tape wheels 14a and 14b have projections, such as tooling balls 14!, secured in spaced apart relation about the periphery thereof. Tooling ball 14! has a threaded shank 14s secured in a threaded aperture l4u through disc 14v. Disc Mr is secured in socket 14w, formed in the periphery of wheel 1412. by bolts 14x.

Tapes 16a and 16b have spaced apertures 16! formed to receive tooling balls 14! for positively indexing the gripper assembly 8 relative to wheel 14b.

Guide rollers 186a and 186k rotatably secured to support bar 178 of gripper assembly 8, have flanges 228' formed adjacent the inner edge thereof to engage tracks 224a, 2241), 226a and 22612. Rollers l86b are mounted to permit movement thereof longitudinally of support bar 178' and are urged outwardly by springs 178". It should be apparent that flanges 228 are urged into engagement with the respective guide tracks maintaining lateral register of sheets 5 while permitting thermal expansion of the gripper bar assembly 8.

Printing cylinders 48', illustrated in FIG. VII, of each printing couple l8 and 20 are adapted to form an unobstructed passage permitting movement of gripper assemblies 8' from the feeder station to the delivery station without engagement with structural members other than tracks 224a, 224b', 226a and 226b, said tracks directing the gripper assemblies 8' along a path having no abrupt changes in direction. The tracks are preferably substantially straight or uniformly curved to minimize abrupt changes in speed and direction of the mass of the gripper assemblies 8'. Changes in speed or direction would impart periodic changes in the tension in tapes 16a and 16b and consequently disturb register since exact correspondence of images printed at each

printing tower

18 and 20 must be constantly maintained for quality multicolor printing.

The above description of a sheet transfer mechanism and the mechanism for individually driving printing towers l8 and 20 has been limited to printing towers capable of printing on both sides of a sheet simultaneously. It should be noted, however, that the above description is intended only to illustrate one suitable embodiment of the invention. Obviously, the use of perfecting printing towers is not a prerequisite to success of the sheet transfer mechanism 10 or the drive mechanism which I have developed.

It will be understood that other and further embodiments of the invention may be devised without departing from the spirit and scope of the appended claims.

Having described my invention 1 claim:

1. A device for moving a sheet of paper in a printing press comprising, spaced aligned sheet transfer carrier guide members rotatably journaled adjacent each end of the press; continuous flexible sheet transfer carriers extending about the carrier guide members at each side of the press and being rotatable with the guide members; a plurality of slotted blocks mounted in spaced apart peripheral relationship on the guide members to cause the carriers to rotate with the guide members; means to drive the carriers; a plurality of spaced gripper bars; means to secure opposite ends of said bars to said carriers; surfaces on each of said gripper bars engageable with slots in said blocks; at least one gripper member mounted on each gripper bar for gripping the edge of a sheet; means to actuate the gripper members to engage the edge of the sheet at one end of the press; means to actuate the gripper members to release the sheet at the other end of the press; and gripper bar guide means secured to opposite sides of the press to guidably support the gripper bars, said gripper bar guide means having guide surfaces to direct the gripper bars from one end of the press to the other along a path having no abrupt changes in direction whereby dynamic forces transferred by a gripper bar to the carriers as a gripper bar is moved longitudinally from one end of the press to the other is substantially constant.

2. The combination called for in claim 1 wherein each carrier guide member comprises a tape wheel, with the addition of means for adjusting the peripheral position of each slotted block relative to the tape wheel.