Vacuum transfer apparatus for rotary sheet fed printing presses

Abstract: A vacuum assisted sheet transfer assembly 10 has an array of support bars 46 which guide the unprinted side of a freshly printed sheet S along a curved transfer path P. The support bars overlie the airflow inlet 44 of a manifold housing 16, with the support bars providing smooth surfaces for engaging and supporting the unprinted side of the sheet material as it is pulled along the transfer path while simultaneously limiting the flow of inlet air through elongated inlet apertures 52, 54. As air is drawn through the inlet apertures 52, 54, the unprinted side of the sheet is drawn into engagement with the support bars as it moves along the sheet transfer path. The sheet transfer assembly 10 eliminates the need for conventional skeleton wheels and the like. Marking, smearing and smudging are prevented since the printed side of the sheet S is not handled or contacted in any way as the sheet is conveyed along the transfer path P.

Description: This invention relates generally to printing press equipment, and in particular to anti-marking sheet transfer apparatus for conveying printed sheets between successive stations in a sheet-fed rotary printing press. In sheet-fed rotary printing presses, it is customary to transfer the sheets from the impression cylinder of one printing station to the impression cylinder of the next by means of one or more successively coacting transfer cylinders, each of which is provided with grippers for engaging the leading edge of the sheet. Those cylinders usually are formed with substantially continuous peripheral surfaces for supporting and controlling the body of the sheet during its travel between stations. This transfer apparatus has proven to be effective for transferring sheets in precise registration, but has a tendency to cause the sheets to be marked or smeared. Marking and smearing of the freshly printed ink occurs as follows. As each sheet is removed from the impression cylinder, and after having received an inked impression, it is immediately conveyed in a reverse curvilinear path with its printed face in contact with the surface of the transfer cylinder. Movement of the sheet is so rapid that the ink on the sheet does not have time to set before it contacts the transfer cylinder surface; consequently, a portion of the ink accumulates on the transfer cylinder surface. As the next sheet and all subsequent sheets are transferred, they may become marked or smeared by the ink accumulation on the cylinder surface. Marking or smearing of the printed side of the sheet may also be caused by fluttering displacement of the sheet as it transfers through the reverse curvilinear path from the impression cylinder to the next transfer cylinder. Slight lateral fluttering in the nip region between the impression cylinder surface and the transfer cylinder surface occurs because of the sudden reversal in the direction of forces acting on the mass of the sheet as it is pulled through the nip region along the reverse curvilinear path. Moreover, the trailing end portion of the wet, printed side of the sheet may be slapped against the transfer cylinder as it is pulled through the nip region. Both the fluttering movement and the tail slap can cause marking or smearing as the freshly imprinted side of the sheet is contacted against the transfer cylinder. In many printing applications, only one side of the sheet receives ink from the blanket cylinders during each pass through the printing press. It has been determined that in those situations where only one side of the sheet is to be printed, use of a transfer system which engages and supports the printed (wet) side of the sheet may be unnecessary and a transfer system can be used which engages and supports the nonprinted (dry) side of the sheet. For example, in non-perfecter type printing presses, only one side of the sheet is printed during each pass through the press. In such presses, conventional transfer systems which support and engage the printed (wet) side of the sheet can be eliminated, and a transfer system which engages and supports only the nonprinted (dry) side of the sheet can be used. It has been determined that use of a stationary sheet guide, wherein the sheet is drawn onto and pulled against a substantially continuous, solid support surface may result in the sheet being pulled partially or fully from the transfer grippers due to the high frictional force created between the sheet and the substantially continuous supporting surface of the sheet guide, thereby resulting in sheet misalignment and misregistration during subsequent printing. GB-A-2 013 629 discloses a sheet delivery apparatus for transferring sheets printed on either one or both sides of the sheet, in which a sheet guiding assembly is adjustable according to the printing mode. For this purpose, the sheet guiding assembly comprises a first set of sheet guiding elements in the form of rails and a second set of sheet guiding elements in the form of suction boxes, the latter being movable selectively towards and away from the sheet transfer path to suit the printing mode. EP-A-0 491 110 relates to an earlier design of vacuum, transfer apparatus from which the present invention was developed and discloses an arrangement having a vacuum chamber defined by a housing member formed with an airflow inlet port, and a plurality of sheet support bars rotatably mounted across the airflow inlet port. In use, a printed sheet is guided onto the sheet support bars with the aid of suction in the vacuum chamber and the bars rotate as the sheet is drawn across them. The present invention provides an improved transfer apparatus for conveying freshly printed sheets between processing stations within a printing press by supporting the sheets on the nonprinted (dry) side in such a manner as to insure that precise sheet registration is maintained. The apparatus of the invention utilizes vacuum assisted, minimum surface contact support components which are relatively inexpensive to manufacture, highly reliable in use, and can be readily installed in existing presses as a replacement for conventional sheet transfer apparatus, or as an alternative sheet transfer system usable when single-sided sheet printing is being made. In accordance with one aspect of the present invention there is provided a sheet transfer apparatus for use in a printing press of the type including an impression cylinder for applying ink to one side of a sheet, a transfer conveyor having means for gripping and transferring a freshly printed sheet from the impression cylinder and transporting the sheet along a transfer path to a further sheet processing station of the printing press, said apparatus comprising a housing member defining a vacuum chamber having an airflow inlet port disposed adjacent to the transfer path, means coupled to the housing member for drawing ambient air through the airflow inlet port into the chamber, characterised in that sheet support members are rigidly attached to the housing member, said sheet support members overlying the airflow inlet port and providing airflow inlet openings, the sheet support members each having a fixed surface for engaging the unprinted side of a freshly printed sheet as it is transported along the transfer path. The sheet support members are advantageously an array of elongated guide support bars adapted to engage and support the nonprinted side of a freshly printed sheet as it is moved from the impression cylinder along the transfer path. The guide support bars are mounted on a frame in side-by-side spaced relation, and are arrayed to extend laterally across the transfer path. The frame on which the guide support bars are mounted has substantially closed side panels and forms a vacuum chamber with the support bars overlying face of the chamber adjacent the transfer path. The vacuum chamber formed by the frame and support bars is coupled to a vacuum source such as a fan or suction pump for producing a suction pressure within the chamber whereby air is pulled into the chamber between the spaced guide support bars. As air is pulled through the aperture between the guide support bars into the vacuum chamber, the nonprinted side of a freshly printed sheet is drawn into engagement with-the support bars which guide and support the sheet as it is pulled along the transfer path. In this manner, frictional engagement between the sheet and the curved surfaces of the support bars is substantially reduced, thereby reducing the area of frictional engagement and insuring that the sheet is not pulled from the transfer grippers so as to destroy sheet registration. Preferably the manifold airflow inlet opening is concave, and the curved external surfaces of the guide support bars provided a smooth, concave sheet transfer path whereby the dry, unprinted side of the sheet material is pulled against and guided by the curved surfaces of the spaced guide bars as the sheet moves along the sheet transfer path. Consequently, it is unnecessary to handle the wet, freshly printed side in any way, thereby completely avoiding contacting engagement against the freshly printed side which would otherwise cause marking or smearing. In a preferred form of the invention, differential airflow gradients are formed along the sheet transfer path by a first section of guide support bars which have relatively large aperture spacing, thereby producing a series of elongated inlet apertures of relatively large inlet flow areas extending across the manifold airflow inlet opening in that section, and by a second section of guide support bars which have relatively small aperture spacing. According to this construction, a relatively stronger suction force is applied to the gripper edge portion of the sheet material as it is pulled along the sheet transfer path, and a larger airflow volume is produced adjacent the leading edge of the transfer apparatus to facilitate initial sheet redirection or "sheet break" as it leaves the impression cylinder. The suction force stabilizes the sheet against wrinkling and surface distortions which might otherwise be cause by fluttering displacement of the sheet as it is transferred from the nip region between an impression cylinder and a transfer cylinder. Moreover, the unprinted side of the trailing end portion of the sheet is pulled by the suction force against the guide support bar assembly, thereby avoiding tail slap against the transfer cylinder and the marking attendant therewith. The differential airflow gradient is increased by partitioning the inlet air manifold and increasing the airflow rate through the large aperture section. According to another aspect of the invention, there is provided a method of supporting a freshly printed sheet during transfer of the sheet from the impression cylinder of a sheet fed rotary printing press to a further processing station of the press characterised by the following steps: transporting the freshly printed sheet along a transfer path such that the unprinted side of the sheet passes over a housing member defining a vacuum chamber having an airflow inlet port and fixed sheet support members rigidly mounted on the housing member between the airflow inlet port and the transfer path; applying a pressure differential across the sheet as it is pulled over the vacuum chamber by drawing air through airflow inlet openings provided by the sheet support members, whereby the unprinted side of the sheet is drawn into engagement with the fixed support members as the sheet is pulled along the transfer path. The present invention will be understood and appreciated by those skilled in the art upon reading the detailed description which follows with reference to the attached drawings wherein: FIGURE 1 is a perspective view of a vacuum assisted, anti-marking sheet transfer system; FIGURE 2 is a rear perspective view of the air manifold housing shown in FIGURE 1; FIGURE 3 is a side elevational view which illustrates the installation of the sheet transfer assembly installed between the last printing station and the delivery station of the printing press shown in FIGURE 3; FIGURE 4 is a side elevational view which illustrates the sheet transfer assembly as installed in a multi-station printing press; FIGURE 5 is a top plan view, partially broken away and partially in section, of the sheet transfer support assembly shown in FIGURE 1; FIGURE 6 is a sectional view thereof taken along the line 6-6 of FIGURE 5; FIGURE 7 is a top plan view, partially broken away, in which the guide support bars are contoured to provide arcuate slots to provide rotational clearance for grippers; FIGURE 8 is a sectional view thereof taken along the line 8-8 of FIGURE 7; FIGURE 9 is a side elevational view of one of the contoured guide support bars shown in FIGURE 7; FIGURE 10 is a top plan view, partially broken away, in which a perforated back plate is combined with the guide support bars for producing differential airflow; FIGURE 11 is a side elevational view thereof, taken along the line 11-11 of FIGURE 10; FIGURE 12 is a perspective view showing elongated guide support bars which are contoured and intersected by slots which are aligned circumferentially to provide rotational clearance for gripper bars; FIGURE 13 is a sectional view thereof taken along the line 13-13 of FIGURE 12; FIGURE 14 is a perspective view of a sheet transfer assembly in which sheet transfer support is provided by a concave array of curved support bars which are laterally spaced with respect to each other and which extend circumferentially in curved alignment with an arcuate sheet transfer path; FIGURE 15 is a side elevational view thereof taken along the line 15-15 of FIGURE 14; FIGURE 16 is a perspective view thereof in which a curved, perforated back plate is combined with the curved support bars as shown in FIGURE 14 for producing differential airflow along an arcuate sheet transfer path; FIGURE 17 is a sectional view thereof, taken along the line 17-17 of FIGURE 16; FIGURE 18 is a perspective view of a sheet transfer assembly in which sheet guidance and differential airflow are provided by a sheet transfer plate having airflow apertures and small surface nodes which are separated by gripper bar slot indentations; FIGURE 19 is a sectional view thereof, taken along the line 19-19 of FIGURE 18; FIGURE 20 is a perspective view of a semicylindrical sheet transfer plate which is perforated to produce differential airflow gradients along an arcuate transfer path, and which includes surface nodes projecting therefrom for minimizing the area of frictional engagement; FIGURE 21 is a side elevational view thereof, partially broken away, taken along the line 21-21 of FIGURE 20; FIGURE 22 is an enlarged sectional view, partially broken away, of a portion of the semicylindrical back plate shown in FIGURE 20; FIGURE 23 is a perspective view of a sheet transfer assembly in which sheet guidance and differential airflow are provided by a perforated back plate generally in the form of a semicylindrical section, having undulating rib portions and external surface nodes; FIGURE 24 is a sectional view thereof, taken along the line 24-24 in FIGURE 23; FIGURE 25 is a perspective view showing gripper bar slots formed in the longitudinal rib portions of the sheet transfer plate of FIGURE 23; FIGURE 26 is a perspective view of a semicylindrical sheet transfer plate having laterally spaced undulations which provide circumferentially extending rib portions; and, FIGURE 27 is a developed plan view of a portion of the sheet transfer plate assembly shown in FIGURE 26, with the transfer plate having perforations between adjacent ribs for producing differential airflow along a curved sheet transfer path. The vacuum assisted, minimal surface contact anti-marking sheet transfer system 10 of the present invention is designed to completely replace conventional sheet handling rollers of the type sometimes referred to as "skeleton wheels". On a functional basis, the anti-marking sheet transfer system 10 as shown in FIGURE 1 is effective for conveying sheet material from one printing station to another, but without engaging, contacting or otherwise handling the wet (printed) side of sheet material as it is conveyed through a multicolor rotary printing press which may include as many as seven or more printing stations for printing a corresponding number of color impressions upon sheets of material conveyed therethrough. Referring now to FIGURES 1 and FIGURE 2, the anti-marking sheet transfer system 10 of the present invention includes a guide support bar assembly 12 and a vacuum source 14. The guide support bar assembly 12 includes an air suction manifold housing 16 which is coupled in airflow communication with the vacuum source 14 by suction air ducts 18, 20 and 22. The vacuum source 14 includes a suction fan assembly 24 having a squirrel cage suction fan 24F which is mechanically driven by an induction motor 26. The suction air ducts 18, 20 and 22 are connected to a suction air manifold 28 at inlet ports 28A, 28B and 28C, respectively. The suction fan assembly 24 is coupled to the outlet port 28P of the suction air manifold 28, whereby ambient air indicated by the arrow A is drawn through the support bar assembly 12 into the suction air ducts 18, 20 and 22, and thereafter through the suction air manifold 28, for discharge by the suction fan assembly 24. The support bar assembly 12 is supported upright by stanchions 30, 32 which include foundation brackets 34, 36, respectively, for anchoring the assembly 12 onto the printing press frame or onto the floor beneath the printing press. The induction motor 26 is electrically connected to a source of electrical power through a variable speed controller 38 and a power conductor cable 40. The running speed of the induction motor 26 is manually adjustable by the press operator to produce a desired airflow rate through the support bar assembly 12. Operator control of the suction airflow is also manually adjustable by opening and closing a vent plate 42 which is slidably mounted onto a side panel of the suction air manifold 28. The position of the vent plate 42 is adjustable for enlarging and reducing the inlet area of a by-pass inlet port 28D. The airflow through the air ducts 18, 20 and 22 is increased or reduced as the by-pass inlet port 28D is enlarged or reduced by extending or retracting the vent plate 42. Although manual control means are illustrated, the system may be automatically controlled if desired. Referring now to FIGURE 1 and FIGURE 2, the support bar manifold housing 16 is an assembly of side panels 16A, 16B, a front panel 16C, a top panel 16D and a semicylindrical back panel 16E. The side panels 16A, 16B have curved edge portions onto which the semicylindrical back panel 16E is attached. The panel assembly defines a manifold housing having a concave airflow inlet opening 44, which conforms closely with an arcuate sheet transfer path P. Referring now to FIGURES 1, 2, 3, 5 and 6, the support bar assembly 12 includes an array of guide support bars 46 mounted onto the side panels 16A, 16B across the airflow inlet 44, thereby defining a curved sheet transfer path P. The guide support bars 46 are spaced along the curved sheet transfer path P thereby defining a plurality of elongated inlet apertures 48. According to this arrangement, the external surfaces of the guide support bars 46 provide smooth surfaces for supporting and guiding the unprinted side of the sheet material along the curved transport path while simultaneously constraining and limiting the flow of inlet air into the manifold housing 16 through the inlet apertures 48. The arcuate array 12 of guide support bars 46 is disposed along the curved transfer path P to engage and support the nonprinted side of a freshly printed sheet S in such a manner to insure that excessive frictional engagement of the sheet does not occur, and that sheet registration is maintained. The vacuum transfer apparatus 10 of the invention is relatively inexpensive to manufacture, highly reliable in use, and can be readily installed in most conventional presses without modification. For that purpose the guide support bars 46 are rigidly attached to the manifold housing side plates 16A, 16B and arrayed to extend side-by-side in spaced, parallel relation laterally across substantially the full width of the transfer path P. In this instance, the manifold housing 16 forms an internal vacuum chamber 50 enclosed by the front and top panels 16C, 16D, respectively, the laterally spaced side panels 16A, 16B and the semicylindrical rear panel 16E. Each side panel has an arcuate shape corresponding to the arc of curvature of the transfer path P, and the guide support bars 46 are mounted to the side panels opposite the rear panel 16E so that the support bars overlie the vacuum chamber 50 and form an arcuate path corresponding to that of the curved transfer path P. According to one aspect of the invention, a group of guide support bars 46 are relatively widely spaced along the upper chamber section 50B of the concave airflow inlet opening 44, thereby producing a series of elongated inlet apertures 52 which have relatively larger aperture inlet flow areas as compared to the corresponding inlet flow apertures 54 defined between the more closely spaced support bars 46 in the lower chamber section 50A. Accordingly, a greater volume of air can be drawn through the upper suction zone provided by the widely spaced bars 46, thereby compensating for leakage and developing a relatively stronger suction force for application to the leading edge portion of the sheet material as it is pulled along the curved transfer path P. The differential airflow gradient is increased by partitioning the lower support bar manifold chamber 50A with respect to the upper manifold chamber 50B. A partition panel 16P extends longitudinally across the length of the manifold housing 16, thereby separating the two chambers 50A, 50B. Moreover, the lower manifold chamber 50A has a suction port 56 coupled to the suction air duct 22 which is isolated with respect to the upper manifold chamber 50B. The upper manifold chamber 50B has dual suction ports 58, 60 which are coupled to the suction air manifold 28 by the suction air ducts 18, 20, respectively. The larger suction ports 58, 60 are isolated with respect to the lower manifold chamber 50A, and are connected in airflow communication with the upper manifold chamber 50B through the rear semicylindrical panel 16E. According to the foregoing arrangement, airflow through the large apertures 52 is substantially increased relative to the airflow through the smaller apertures 54 in the lower chamber section by the dual suction ports 56, 58 and the dual suction air ducts 18, 20 which more than double the rate of airflow through the support bars in the upper chamber section 50B relative to the lower support bar chamber section 50A. The smooth support provided by the curved support bars 46 stabilizes the sheet against wrinkling and surface distortions which might otherwise be caused by fluttering displacement of the sheet material as it is transferred from the nip region between an impression cylinder and a transfer cylinder. The increased airflow provides sufficient suction to pull the leading edge of the sheet against the guide support bar assembly along the curved transfer path P. Otherwise, the sheet will be pulled straight, and will not transfer properly. Moreover, the unprinted side of the trailing end portion of the sheet is pulled by the suction force against the support bars 46, thereby avoiding tail slap and marking. Initially, only the leading edge of the sheet material is gripped by the rotary grippers, and the leading edge is the only section of the sheet which is exposed to the guide support bars and suction force. Consequently, a stronger suction force is initially required to handle the sheet, as compared to the force required after the sheet has been advanced along the transfer path where there is a much larger sheet area being handled by the suction force developed through the apertures 54 between the more closely spaced support bars 46. In the exemplary embodiment illustrated in FIGURE 1 and FIGURE 3, the two six inch (15.2 cm) diameter suction ducts 18, 20 connect into the upper manifold chamber 50B which defines the relatively strong suction zone and there is one five inch (12.7 cm) diameter duct 22 connected to the lower manifold chamber 50A. There is sufficient air pressure differential above the guide support bar assembly 12 that the unsupported section of the sheet is pulled outwardly and generally assumes the form of a cylindrical surface in the supported region. In the exemplary embodiment of FIGURE 1, the manifold inlet area defined by the concave surface of revolution area is 41 inches (104.14 cm) wide by an arc length of approximately 9-1/2 inches (24.13 cm) which yields approximately 390 square inches (2,516 sq. cm) effective overall inlet area. The total effective aperture area is considerably smaller, with the leading edge of the upper manifold zone 50B having dimensions of approximately 41 inches (104.14 cm) wide by 3 inches (7.62 cm) arc length, with the aperture spacing of approximately 1/8 inch (3.175 mm) between the support bars 46 in the upper zone 50B yielding an effective aperture area of approximately 30 square inches (193.56 sq. cm). The total surface aperture area of the lower support bar section is 41 inches (104 cm) wide by approximately 6-1/2 inches (16.5 cm) arc length by approximately 1/16 inch (1.59 mm) spacing, which yields approximately 20 square inches (129 sq. cm) effective inlet area. Overall, by adding the two zones together, the total effective aperture inlet area is approximately 50 square inches (322.6 sq. cm). With the apertures in the lower and upper zones open, the airflow is approximately 1,900 cubic feet per minute (896.8 liters per sec.) at 3/4 inch of water at 4° C (1.9 X 10³ Kgs. per sq. cm) static pressure. When a sheet is completely in an overlay position across both suction zones, the airflow rate drops to approximately 350 cubic feet per minute (165.2 liters per sec.) at 2 inches of water at 4° C (5 X 10³ Kgs. per sq. cm) static pressure. The flow rate does not drop to zero because there are small openings along the marginal edges through which air is drawn. When the support bar assembly is completely open, the velocity of air through the apertures is approximately 5,500 feet per minute (1676.4 meters per minute). As a result of the creation of a negative or partial vacuum pressure within the chamber 50, air is drawn into the chamber through the apertures 48 between the support bars 46. This airflow creates a suction force along the transfer path P which will cause a sheet S being pulled from an impression cylinder by the transfer conveyor to be drawn into engagement with the curved support surfaces of the support bars 46. Preferably, the support bars 46 are positioned on the side panels 16A, 16B such that the curved supporting surfaces of the bars lie along the transfer path P or very sightly spaced radially outwardly therefrom (that is, toward the vacuum transfer apparatus) so that as a sheet is supported and conveyed along the support bars, the grippers can pass by the support bars and the sheet will not engage any other apparatus in the press, including any conventional transfer system components that may be present. Thus, the printed (wet) side of the sheet will be maintained out of contact with any other apparatus, and cannot be marked, smeared or otherwise marred during the transfer. Referring again to FIGURE 3, the vacuum transfer apparatus 10 is primarily intended for use in a sheet fed, offset rotary printing press of conventional design, to engage and support the nonprinted side of a freshly printed sheet S as it is moved from an impression cylinder 62 of the press to a further processing station within the press. In this instance, sheets S to be printed are pulled by sheet grippers 78 attached to the impression cylinder 62 from the nip between the impression cylinder 62 and a blanket cylinder 66 where ink is applied to one side of the sheet. After ink has been applied to the printed face of the sheet S, a transfer conveyor 68 grips the leading edge of the sheet at the impression cylinder 62, and pulls the sheet from the impression cylinder, around the transfer apparatus 10, and then to a delivery stacking station 70 within the press. The transfer conveyor 68, which is also of conventional design, includes a pair of endless chains 72 (only one of which is shown) entrained about sprocket wheels 74 laterally disposed on each side of the press and centrally supported by a drive shaft 76. Extending laterally across the endless chains 72 at spaced intervals are sheet gripper assemblies 78 carrying a plurality of conventional sheet grippers 78A which operate to grip the leading edge of the sheet S at the impression cylinder 62, and move the sheet along the transfer path P defined by the path of movement of the chain conveyors. It should be noted that in conventional printing presses, the drive shaft 76 supporting the sprocket wheels 74 typically also functions to support many of the conventional sheet transfer components such as skeleton wheels, transfer cylinders, and the like. As will become more apparent hereinafter, the vacuum transfer apparatus 10 of the present invention can be positioned within the press with or without removing the conventional transfer apparatus then existing in the press. In mounting the vacuum transfer apparatus 10 to the press, it is important to attempt to position the upper end of the manifold housing 16 as close to the impression cylinder 62 as practically possible to insure a smooth transfer of sheets S from the impression cylinder to the support bars 46. While different types of mountings may be required for different types of printing presses, the vacuum transfer apparatus 10 of the exemplary embodiment is illustrated mounted in a Heidelberg Model 102 Speedmaster press. As shown, the manifold housing 16 is mounted to the press adjacent its upper end by a pair of mounting brackets 80 coupled to the press frame, and at its lower end by the laterally spaced stanchions 32 supported by the floor on which the press stands. In the various embodiments disclosed herein, each support bar 46 preferably is made of tubular or solid aluminum stock, for example, type 6061TG. The diameter of the support bars is preferably one inch (2.54 cm). Each support bar is rigidly mounted to the side panels 16A, 16B of the manifold housing 16 by screw fasteners removably secured to the side panels 16A, 16B. Referring now to FIGURES 7, 8 and 9, a group of contoured support bars 84 are rigidly mounted along the top section 44B of the concave airflow inlet opening 44. As can be seen in FIGURE 7, the contoured support bars 84 have alternating large diameter segments 84A separated by annular recesses 84S and small diameter segments 84B. The contoured support bars 84 are relatively widely spaced in the upper section thereby defining inlet apertures 86 which have a relatively large cross sectional flow area as compared to the longitudinal flow apertures 88 between the relatively closely spaced support bars 84 in the lower section. Additionally, the annular recesses 84S between the large diameter segments 84A are spaced to permit passage of the grippers 78A. The relatively larger airflow apertures 86 in the upper suction zone 50B establish a differential airflow gradient along the curved transport path P, so that a strong suction force will be applied to the leading edge portion of the sheet material as it is pulled through a reverse curvilinear path P. It should be understood that the printed sheet is otherwise unsupported after it is gripped and pulled from the impression cylinder. Accordingly, a strong suction force is initially required to pull the unsupported sheet material against the support bars 84, and relatively less suction force is required as the sheet material is subsequently conveyed over the relatively closely spaced support bars 84 along the lower chamber section 50A of the curved transfer path P. The slot recesses 84S permits the support bars 84 to be located closer to the transfer path P since the annular recesses provide radial clearance for the grippers 78A of the transfer conveyor 68 to pass below the support surface of the guide support bars. Typically, the grippers 78A of a transfer conveyor project approximately 1/8 inch (3.175 mm) beyond the gripper bar assembly 78 in the direction radially outwardly with respect to the axis of the drive shaft 76 of the sprocket wheels 74. By locating the recesses 84S in the support bars 84 to coincide with the locations of the grippers 78A, the grippers can pass freely through the recesses. Accordingly, the support surfaces 84A of the support bars 84 can be positioned to be substantially tangent to the true transfer path P, thereby providing a smooth and uniform transition for the sheet S as it initially engages the support bars of the vacuum transfer apparatus 10. In the exemplary embodiments, the slot recesses 84S are each approximately 1-9/16 inch (39.7 mm) wide, but are not uniformly spaced along the support bars 84. Rather, the locations of the recesses 84S are selected to coincide with the locations of the grippers 78A found on the transfer conveyor 68 of the particular press on which it is mounted. In the Heidelberg Model 102 Speedmaster press, the grippers 78A are spaced more closely together along the gripper bars from the mid point laterally outwardly toward the ends at the chains 72; consequently, the recesses 84S must be similarly spaced to permit the grippers 78A to travel past the guide support bars 84. While the foregoing specific dimensions have been set forth for the exemplary embodiments shown in the drawings, it should be appreciated that other types of presses may require that the spacing and width of the recesses 84S be altered to suit the particular press. It is important to note that in selecting the particular spacing and width of the recesses 84S, the effective air inlet area into the vacuum chamber upper portion 50B should be approximately twice or more greater than the effective inlet area of the vacuum chamber lower portion 50A. By this arrangement, the airflow volume per unit area through the upper portion is approximately twice or more than that of the airflow volume unit area through the lower portion. This will insure that the sheet S will be smoothly and uniformly drawn rapidly onto the vacuum transfer apparatus 10 as it is initially pulled from the impression cylinder 62 so that the printed side of the sheet can not contact any other apparatus in the press. Moreover, while the exemplary embodiments have been described in combination with a press having a transfer conveyor 68 employing chains 72 and gripper bars, the vacuum transfer apparatus 10 can be used equally well with presses having other types of transfer conveyors since the vacuum transfer apparatus 10 of the invention will prevent the wet inked side of a sheet S from coming into contact with other press apparatus such as transfer wheels and cylinders. Thus, when used for example in a perfecting type press, the vacuum transfer apparatus 10 can be installed to supplement the existing transfer system without requiring removal of the existing transfer system. In such a case, the vacuum transfer apparatus 10 can be used for one sided sheet printing jobs, and then deactivated when the press is used in the perfecter mode for two sided sheet printing jobs. Referring now to FIGURE 4, a dual sheet transfer assembly 90 is installed on a common manifold housing 92 between two stations of a multi-unit rotary printing press 94. The printing press 94 may include as many as seven or more printing stations for printing a corresponding number of color impressions upon sheets fed therethrough. The first station shown in FIGURE 4 receives a sheet S as it is transferred from a dry transfer cylinder 98. The next station as shown in FIGURE 4 is adapted to print a second color impression in superimposed relation on the same printed face of the sheet S, and for this purpose includes an impression cylinder 62 and a blanket cylinder 66. The sheet S is gripped and pulled along the transfer path by grippers 78 mounted on each transfer cylinder. Conventional skeleton wheels or other intermediate transfer cylinders are not required for support purposes since the sheet S is supported entirely on the support bars 46 of the support bar assembly 12. According to this arrangement, the dry, unprinted side of each sheet S is supported by the support bar assembly 12 as it is delivered from a conventional transfer cylinder 96 to the impression cylinder 62. That is, the wet, printed side of each sheet S is not engaged or contacted as it moves along the transfer path P. The sheet S is carried on the impression cylinder 62 to receive an impression from the blanket cylinder 66. After receiving the impression, the sheet S is conveyed on another support bar assembly 12 to a dry transfer cylinder 98 to another printing station, if it is to receive another color impression, or it may be transferred to a delivery sheet conveyor 68 and carried to a delivery stack 70 as shown in FIGURE 3. The transfer assembly shown in Figures 1-9 utilize multiple guide support bars 46 which are closely spaced along the curved sheet transfer path P. Frictional engagement between the sheet material and the external surfaces of the guide support bars is further minimized by providing the guide bar surfaces with a coating of material having a low coefficient of friction, for example, tetrafluoroethylene (TFE) fluorocarbon polymer of the type sold by DuPont under the trademark TEFLON. According to another aspect of the present invention, frictional engagement and drag between the sheet and support components is minimized by reducing the number of guide support bars as shown in Figure 10 and Figure 11. In this embodiment, the guide support bars 46 are relatively widely spaced apart along the curved transfer path P. Differential airflow is provided by a perforated back plate 100. The perforated back plate 100 is a semicylindrical section which is substantially concentric with and radially spaced outwardly with respect to the curved transfer path P. The curved back plate 100 is mounted on the frame and is interposed between the guide support bars 46 and the vacuum chamber 50. The back plate 100 is intersected by plurality of large apertures 102 and by a plurality of relatively smaller apertures 104. Preferably, the airflow apertures 102 which overlie the upper vacuum chamber 50B have a total effective airflow passage area which is relatively greater than the total effective airflow passage area provided by the relatively smaller apertures which intersect the lower section of the back plate which overlies the lower vacuum chamber 50A. The support bars 46 are substantially equally spaced along the transfer path, with the airflow apertures 102, 104 being substantially centered between adjacent support bars. While the airflow apertures 102, 104 which intersect the back plate 100 can have any configuration, they are preferably in the form of elongated slots, with the longitudinal axis of each slot extending generally parallel with the longitudinal axis of the support bars. Referring now to Figure 12 and Figure 13, according to another aspect of the invention, minimum surface contact support bars are provided for guiding and supporting the unprinted surface of a professionally printed sheet. In this embodiment, the sheet material is guided and is supported closely to the vacuum transfer apparatus, thereby reducing suction airflow requirements. This is achieved by an array of guide support bars 106, each of which have a plurality of semicylindrical slots 108, with the semicylindrical slots being separated by support bar segments 110. The support bar segments each have a curved sheet engagable surface 110 which is tangentially aligned with the true sheet transfer path P. Moreover, the semicylindrical slots 108 of adjacent support bars 106 are aligned with each other to permit rotary passage of grippers. The guide support bars 106 which overlie the upper vacuum chamber 50B are relatively widely spaced, thereby defining elongated airflow apertures 112. The guide support bars 106 which overlie the lower vacuum chamber 50A are relatively closely spaced, thereby defining elongated airflow inlet apertures 114. According to this arrangement, a differential airflow gradient is produced along the transfer path P by the relatively greater volume of air which is drawn through the widely spaced airflow inlet apertures 112 relative to the volume of air drawn through the relatively smaller airflow inlet apertures 114. The differential airflow gradient is increased by partitioning the lower support bar manifold chamber 50A with respect to the upper manifold chamber 50B. A partition panel 16P extends longitudinal across the length of the manifold housing 16, thereby separating the two chambers 50A, 50B. As previously described, the lower manifold chamber 50A has a single suction port 56 coupled to the suction air duct 22, which is isolated with respect to the upper manifold chamber 50B. The upper manifold chamber 50B has outlet ports 58, 60 which are coupled to the suction air manifold 28 by the suction air ducts 18, 20, respectively. According to this arrangement, airflow through the large apertures 112 is substantially increased relative to the airflow through the smaller apertures 114 and the lower chamber section. The area of surface engagement between a sheet being conveyed through the sheet transfer apparatus is minimized because the sheet is contacted only by the curved surfaces 110S of the support bar segments 110. Referring now to Figure 14 and Figure 15, minimum surface contact is provided by an array of curved support bars 116 are mounted over the airflow inlet 44. The support bars 116 are curved and have a sheet engaging surface 116 which is substantially concentric with the curved sheet transfer path P. The curved support bars 116 are laterally spaced apart in side-by-side relation, thereby defining a plurality of laterally spaced, circumferentially extending inlet apertures 118. The sheet engaging surface 116S of each support bar provides a smooth surface for supporting and guiding sheet material along the transfer path P while constraining the flow of inlet air through the elongated inlet apertures 118. Differential airflow is provided by the partition panel 16P, together with the air ducts 18, 20 which are coupled to the upper vacuum chamber 50B and by the air duct 22 which is coupled to the lower vacuum chamber 50A. According to this arrangement, a relatively greater airflow per unit area through the upper manifold chamber 50B is produced relative to the airflow per unit area through the lower manifold chamber 50A. Referring now to Figure 16 and Figure 17, the airflow gradient is provided by a perforated back plate 120 which underlies the curved support bars 116. The curved back plate 120 is intersected by large area apertures 122 and small diameter apertures 124. The large area apertures 122 provide flow communication with the upper vacuum chamber 50b while the small area apertures 124 provide airflow communication with the lower vacuum chamber 50A, thereby producing a differential airflow gradient along the transfer path P. Referring now to Figure 18 and Figure 19, according to another aspect of the invention, a curved sheet transfer plate 126 is mounted on the manifold housing 16 and overlies the airflow inlet opening 44. The curved sheet transfer plate 126 has a plurality sheet support sections 126S laterally spaced apart and disposed substantially in concentric relation with the curved transfer path P. The sheet support sections 126S are laterally separated by radially offset transfer plate sections 126P. The transfer plate sections 126P are radially offset into the vacuum chamber 50, thereby defining a plurality of annular slots 128. The transfer plate sections 126P are intersected by a plurality of airflow apertures 130, 132. The apertures 130 which overlie the upper vacuum chamber 50B are relatively large in airflow area as compared to the airflow area of the smaller apertures 132 which overlie the lower vacuum chamber 50A. According to this arrangement, the airflow apertures 130 in the radially offset transfer plate sections overlying the upper chamber region 50B have a total effective airflow passage area which is relatively greater than the total effective airflow passage area provided by the airflow apertures 132 in the transfer plate sections overlying the lower vacuum chamber region 50A. Preferably, the apertures are elongated slots and extend circumferentially along the transfer plate sections 126P. The sheet transfer plate 126 includes radially projecting nodes 134. Each node 134 has a sheet engagable surface 134N which is concentrically positioned substantially in tangential alignment with the true curved transfer path P. According to this arrangement, the sheet materials engaged only by the nodes 134 as it transits along the curved transfer path P. Moreover, the annular slots 128 provide radial clearance for grippers 78A as the sheet is pulled along the curved transfer path P. Referring now to Figures 20, 21 and 22, sheet guidance and support is provided by a curved transfer plate 136 which is mounted onto the manifold housing 16 in substantially concentric alignment with the curved transfer path P. In this embodiment, the curved transfer plate has nodes 134 formed on the sheet engaging side of the plate, and dimples 138 formed on the underside of the transfer plate. Each node surface 134N is concentrically positioned substantially in tangential alignment with the curved transfer path P. Moreover, the curved transfer plate 136 is intersected by large area apertures 140 which overlie the upper vacuum chamber 50B and relatively small area apertures 142 which overlie the lower vacuum chamber 50A. The differential airflow gradient is enhanced by the partition plate 16P. Referring now to Figures 23, 24 and 25, the airflow opening 14 is covered by a semicylindrical, undulating transfer plate 144. In this embodiment, the transfer plate 144 has rib portions 146 which extend transversely with respect to the sheet transfer path P. The ribs 146 are circumferentially spaced with respect to each other and are positioned substantially in circumferential alignment and in concentric relation with the sheet transfer path P. The transfer plate 144 has trough portions 144 which are intersected by large diameter slots 148 and small diameter slots 150. The transfer plate 144 is intersected by a plurality of circumferentially annular slots 152 as shown in Figure 25, thereby permitting rotary passage of gripping means as previously described. The large area airflow apertures 148 in the transfer plate section overlying the upper vacuum chamber region 50B have a total effective airflow passage area which is relatively greater than the total effective airflow passage area provided by the airflow apertures 150 in the transfer plate section overlying the lower vacuum chamber 50A, as shown in Figure 24. According to another aspect of the invention, radially projecting nodes 134 are formed on the surface of the undulating rib portions 146. The radially projecting nodes 134 have sheet engagable surfaces 134N which are positioned substantially in concentric alignment with and in tangential relation to the true sheet transfer path P, as shown in Figure 24. According to this arrangement, the area of surface engagement with the sheet is minimized, thereby reducing frictional engagement and drag as the sheet is pulled along the sheet transfer path P. Referring now to Figures 26 and 27, a sheet transfer plate 154 is mounted on the manifold housing 16 and overlies the airflow inlet opening 44. The sheet transfer plate 154 has undulating rib portions 156 which are laterally spaced apart in side-by-side relation and extend substantially in circumferentially alignment with the sheet transfer path P. The sheet transfer plate 154 has trough portions 158 which are intersected by large area airflow apertures 160 and by relatively smaller airflow apertures 162. Preferably, the circumferentially extending rib portions 156 are laterally spaced apart to permit rotary passage of gripping means as previously discussed. Moreover, the airflow apertures 160 overlying the upper vacuum chamber region 50B have a total effective airflow passage area which is relatively greater than the total effective airflow passage area provided by the airflow apertures 162 which overlie the lower vacuum chamber region 50A. According to this arrangement, the ribs 156 provide smooth surfaces for supporting a sheet S as it is pulled along the transfer path P, with the area of surface engagement being minimized to reduce frictional engagement and drag. It should be understood that the support bars, ribs, nodes and other sheet engaging surfaces as discussed above are preferably covered by a coating of low friction material, such as TEFLON, to further reduce frictional drag. It will be appreciated that in each of the various embodiments described above that surface contact engagement between sheet S and the contacting components, whether it be the straight support bars, the curved (concave) support bars, the nodes, or the undulating ribs, that surface contact with sheet material is minimized, thereby reducing frictional drag. Moreover, in those embodiments which include gripper bar slots, the sheet material can be positioned closely to the vacuum inlet apertures, thereby requiring less suction airflow and minimizing leakage while reducing the suction airflow requirements. A further advantage of the foregoing sheet transfer apparatus is that the conventional transfer components such as skeleton wheels and air cushion cylinders can be completely removed from the press, thereby providing space for auxiliary equipment such as dryers. From the foregoing description, it will be appreciated that the sheet transfer system 10 positively prevents streaking, smudging or smearing of a printed sheet S after the sheet material has been taken from an impression cylinder. This is made possible by the suction force which pulls the dry, unprinted side of each sheet onto the guide support bars, thereby avoiding contact of the printed surface of the sheet material against a transfer cylinder as it is transferred from one printing station to another. Preventative make-ready work which has been required in connection with conventional skeleton wheels is eliminated. The sheet transfer system 10 may be installed directly adjacent to existing transfer cylinders. In new installations, the conventional skeleton wheel and transfer cylinder shells are eliminated. It will be appreciated that since the sheet S is not contacted or engaged by pointed surfaces of a skeleton wheel, that the sheet transfer system 10 does not alter or impose changes in the dimensions of the sheet and its printing registration. Moreover, marking or smearing of the printed side of the sheet material which has previously been caused by fluttering displacement of the sheet as it transfers through a reverse curvilinear path to the next printing station is avoided since the sheet is stabilized and supported against the guide support bars by the suction force applied through the airflow apertures. Marking or smearing of the printed side of the sheet which has previously been caused by tail slap is prevented, since the trailing edge of each printed sheet S is stabilized and pulled against the support bars of the sheet transfer system 10.

Claims: A sheet transfer apparatus for use in a printing press of the type including an impression cylinder for applying ink to one side of a sheet, a transfer conveyor having means for gripping and transferring a freshly printed sheet from the impression cylinder and transporting the sheet along a transfer path to a further sheet processing station of the printing press, said apparatus comprising a housing member defining a vacuum chamber (50) having an airflow inlet port (44) disposed adjacent to the transfer path, means (14) coupled to the housing member for drawing ambient air through the airflow inlet port into the chamber (50), characterised in that sheet support members (46; 106; 116; 126; 136; 154) are rigidly attached to the housing member, said sheet support members overlying the airflow inlet port and providing airflow inlet openings (112; 114; 118, 130, 132), the sheet support members each having a fixed surface for engaging the unprinted side of a freshly printed sheet as it is transported along the transfer path. A sheet transfer apparatus as defined in claim 1, characterised in that the fixed support surfaces are covered by a coating material having a relatively low coefficient of friction. A sheet transfer apparatus as set forth in claim 1, characterised in that the sheet support members comprise elongated bars (46; 106; 116) which are spaced apart in side-by-side relation and extend either transversely with respect to the direction of travel of a sheet along the transfer path, or in a concave curve substantially in alignment with the direction of travel of a sheet along the transfer path. A sheet transfer apparatus as set forth in claim 1, characterised in that the sheet support members comprise elongated bars (106) each having a plurality of slots (108) disposed at longitudinally spaced locations thereon, with adjacent slots being separated by support segments (110) each having a sheet engagable surface (110S), the slots of adjacent sheet support members being aligned with each other to permit passage of gripping means. A sheet transfer apparatus as set forth in claim 3, characterised by a back plate (100; 120) mounted on said frame and interposed between the sheet support members and the vacuum chamber, the back plate being intersected by a plurality of apertures (102, 104; 122, 124) providing airflow communication between the vacuum chamber and the spaces between adjacent sheet support members. A sheet transfer apparatus as set forth in claim 1, characterised in that said sheet support members comprise a sheet transfer plate (126; 136; 144; 154) intersected by the airflow inlet openings (130; 132; 142; 150; 160; 162), said sheet transfer plate having nodes (134) and/or ribs (146; 156) disposed substantially in alignment with the sheet transfer path. A sheet transfer apparatus as set forth in claim 6, characterised in that said sheet transfer plate (126) has offset transfer plate sections (126P) disposed radially offset between adjacent sheet support sections (126S) thereby defining a plurality of slots (128), said slots being spaced apart to permit passage of gripping means, and the offset transfer plate sections being intersected by the airflow inlet openings (130, 132). A sheet transfer apparatus as set forth in claim 6, characterised in that the ribs of the support members (146; 156) are spaced apart in side-by-side relation and extend either transversely with respect to the direction of sheet travel along the sheet transfer path, or substantially in alignment with the direction of sheet travel along the sheet transfer path. A sheet transfer apparatus as set forth in claim 6 or 8, characterised in that said sheet transfer plate (126; 136; 144; 154) has a plurality of slots (128; 152; 158), said slots being aligned and laterally spaced with respect to each other to permit passage of gripping means. A method of supporting a freshly printed sheet during transfer of the sheet from the impression cylinder of a sheet fed rotary printing press to a further processing station of the press characterised by the following steps: transporting the freshly printed sheet along a transfer path such that the unprinted side of the sheet passes over a housing member defining a vacuum chamber (50) having an airflow inlet port and fixed sheet support members rigidly mounted on the housing member between the airflow inlet port and the transfer path; applying a pressure differential across the sheet as it is pulled over the vacuum chamber by drawing air through airflow inlet openings provided by the sheet support members, whereby the unprinted side of the sheet is drawn into engagement with the fixed support members as the sheet is pulled along the transfer path. A method as set forth in claim 10, characterised by the following steps: transporting the freshly printed sheet along a sheet transfer path with the unprinted side of the sheet in contact with an array of support bars (46; 86; 106; 116) which are rigidly mounted on the housing member and spaced apart about the sheet transfer path; and imposing a pressure differential across the sheet material as it is transferred along the sheet transfer path by drawing air through elongated inlet apertures defined between adjacent support bars, whereby the unprinted side of the freshly printed sheet is pulled against the support bars as the sheet material is transferred along the sheet transfer path.

Inventors: DEMOORE HOWARD WARREN, SECOR HOWARD CURTIS, DEMOORE, HOWARD WARREN, SECOR, HOWARD CURTIS
Applicants: PRINTING RESEARCH INC, PRINTING RESEARCH, INC.
Application year: 1991
Main classification: B41F21
IPC codes: B41F21, B65H29, B41J13, B41F22