US 3341195 A
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p 1967 c. H. BRANDT ETAL 3,341,195
SHEET HANDLING APPARATUS Filed March 29, 1'965 I. F G. 4 MENTOR G. HERMAN BRANDT CHARLES R MILLER ATTORNEY United States Patent C 3,341,195 SHEET HANDLING APPARATUS Gotlieb Herman Brandt, Shaker Heights, and Charles R. Miller, Bedford, Ohio, assignors to Harris-Intertype Corporation, Cleveland, Ohio, a corporation of Delaware Filed Mar. 29, 1965, Ser. No. 443,406 18 Claims. (Cl. 27151) The present invention relates to sheet hold-down devices and more particularly to sheet hold-down devices for use in printing presses to cause a moving sheet to hug the surface of an impression cylinder.
An important object of the present invention is to provide a new and improved printing press having a sheet hold-down device which is capable of urging sheet material being printed against the surface of the impression cylinder and which is suitable for use with a wide range of stocks from very light and flimsy stocks to heavy stocks such as cardboard.
Another object of the present invention is to provide a new and improved sheet handling apparatus including a sheet hold-down device which is so constructed and arranged that an electrostatic field for electrostatically charging a sheet moving with a surface is established in one plane to hold the sheet against the surface and a second force field for urging the sheets against the surface is established in a plane diverging from the first plane but directed toward the moving'sheet in a direction opposite to sheet movement.
Yet another object of the present invention is to provide a new and improved apparatus for causing a sheet to hug a rotating cylinder in which a stream of air may be directed along a cylinder to effect the holding of a sheet thereagainst, or in which an electrostatic field for electrostatically charging the sheet to cause the latter to hug a moving cylinder may be established, or in which both air and electrostatic fields may be used simultaneously.
Another object of the present invention is to provide a new and improved method and an apparatus for bolding a sheet to a rotating cylinder in a printing press in which an electrostatic field is established in one plane for charging a sheet to cause it to hug the surface of a cylinder moving with the sheet and an air stream which is directed at about 45 to the electrostatic field to apply an air force to the sheet to hold it against the cylinder.
The present invention further contemplates the provision of a new and improved electrostatic sheet holddown device for causing a moving sheet to hug a moving surface adjacent to and moving with the sheet in which the effectiveness of the sheet hold-down device is increased by causing air to move from the device toward and against the sheet in a direction opposite to the direction of sheet movement.
A still further object of the present invention is to provide a new and improved printing press in which an electrostatic field or an air stream, or both may be selectively applied to a sheet to cause it to hug an impression cylinder as it approaches a printing nip with the air field being applied in advance of the electrostatic field.
Still further, the present invention contemplates a new and improved sheet hold-down device which has a housing of insulating material covering a conductive member for establishing electrostatic charges and an electric field and in which air movement is provided from internally of the hold-down device outwardly through openings in the housing for exposing ionizing projections extending outwardly from the conductive member and, preferably, in which air is directed onto the sheet from the device in advance of the hold-down device with the air issuing from said housing and diverging from said field in a direction opposite to the direction of sheet movement.
Further objects and advantages of the present invention will be apparent to those skilled in the art to which it relates from the following detailed description thereof made with reference to the accompanying drawings forming a part of the present invention and in which:
FIG. 1 is a View, partly diagrammatic, showing the present invention embodied in a printing press;
FIG. 2 is a cross-sectional view through an electrostatic device according to the present invention;
FIG. 3 is a view taken approximately along line 33 of FIG. 2; and
FIG. 4 is a simplified schematic control circuit for the hold-down apparatus shown in FIG. 1.
Referring to the drawings, the present invention is shown as embodied in a lithographic printing press for printing sheets and including a printing couple formed by an impression cylinder 10 and a blanket cylinder 11 for printing the sheet under pressure. The sheet to be printed is delivered to the impression cylinder 10 from a feed or transfer cylinder 13 and the leading edge of the sheet is gripped by grippers on the impression cylinder to cause the sheet to move with the impression cylinder and into and through the printing nip formed by the impression cylinder 10 and the blanket cylinder 11. After the leading edge of the sheet passes through the printing nip, the leading edge is transferred to a cylinder 14, which is shown as another transfer cylinder for carrying the sheet to a following printing couple, although it might be a delivery drum.
In accordance with the present invention, the sheet is caused to hug the surface of the impression cylinder 10 by one or more electrostatic sheet hold-down devices. Two such sheet hold-down devices 15, 15' are shown in the drawings. The sheet hold-down device 15 is positioned immediately ahead of the printing nip formed by the blanket cylinder 11 and the impression cylinder, while the sheet hold-down device 15' is positioned in advance of the device 15 adjacent the transfer point between the cylinder 13 and the impression cylinder 10. A hold-down device 15" may also be located adjacent the transfer point between the impression cylinder 10 and the transfer cylinder 14. The hold-down devices are, in the preferred embodiment, identical and therefore only one will be described.
As is shown in FIG. 2, the sheet hold-down device preferably comprises a tubular elongated electrically conductive member 20 disposed within a tubular insulating covering 21. The outside diameter of the conductive member 20 is smaller than the inside diameter of the tubular insulating covering 21 to provide an annular space 22 between the interior wall of the tubular housing 21 and the conductive member 20. The tubular conductive member 20 is supported in end plugs 24, 25 in the tubular housing 21 and communicates through the plug 24 with a hose or conduit 26 for supplying air under pressure to the interior of the tubular conductive member 20. The end plugs are of insulating material. In the preferred embodiment, the housing 21 and the end plugs 24, 25 are of plastic material, for example, polyvinyl chloride, which is void of air spaces and which has fine conductive particles, for example, carbon black, distributed throughout. The carbon black may comprise about 20% by weight of the material.
A plurality of ionizing needles 28 are mounted in the tubular conductive member 20 and are spaced along the length thereof and extend radially outwardly from the member. The needles 28 he in a common plane and terminate short of the interior wall of the tubular housing 21 which has a plurality of openings 30 therein, one adjacent each of the needles 28, for exposing the needles.
The hold-down device is mounted in the printing press so that the ionizing needles point directly toward the impression cylinder and are adapted to provide an electric field between the electrostatic device and the cylinder to electrostatically charge the sheet and cause it to hug the impression cylinder. The electric field is generally perpendicular to a plane tangent to the cylinder 10 directly opposite to the hold-down device.
The elongated conductive member 20 is connected to one side of a unidirectional high voltage power supply by a connection which is led into the bar 20 through the end plug 25 and the cylinder 10 is grounded as is the other side of the high voltage power supply. In operation, the needles 28 cause the air to ionize and the electric field between the needles 28 and the cylinder 10 propels the charges toward the grounded impression cylinder to electrostatically charge the sheet and cause it to be attracted to the surface of the impression cylinder.
The hold-down device of the preferred embodiment is supplied with air under pressure. The air is supplied to the interior of the conductive member 20 through the hose 26 and the conductive member 20 has a plurality of openings 32 in the wall thereof which communicate the interior of the hollow member 20 with the annular space 22. The air issues from the openings 32 into the annular space 22 and from the interior, i.e., annular, space 22, the air moves through openings 34 in the tubular housing. The openings 34 are spaced along the length of the tubular housing and have axes which extend at approximately 45 to the plane of the needles 25. The axes of the openings 34 extend from the hold-down device toward the sheet on the cylinder 10 in a direction opposite to the direction of sheet movement. As is illustrated in FIG. 3, the axes of the openings 32 in the conductive member lie in the same plane as the openings 34 and the openings 32, 34 are aligned.
A holddown device constructed in accordance with the preferred embodiment of the present invention provides a hold-down device which is suitable for use with a wide range of sheet materials. In a printing operation, a printing press might be used to print very light and flimsy sheets or rather stiff or heavy board which is extremely difi'icult to hold against the surface of the impression cylinder. In the case of light paper, an electrostatic holddown tends to crease and fold the paper and the electric field is preferably turned down and some air is supplied to the sheet hold-down device when such papers are being printed. The air then is directed out of the device in a generally tangential direction along the surface of the cylinder, but in a direction opposite to the direction of feed and will function to cause the light sheet to closely hug the impression cylinder without wrinkling or creasing. For normal weight stocks, it is generally necessary to use only the electrostatic sheet hold-down. However, for many of the heavier stocks including cardboard, the combination of the air hold-down and the electrostatic sheet hold-down make it possible to cause very heavy stock to hug the electrically grounded metal impression cylinder. While the air applies a force to the heavy stock which is in addition to that applied by the electrostatic charges, the air also increases the efiectiveness of the holddown device in applying an electrostatic charge to the board.
FIG. 4 illustrates schematically a simple control circuit for operating the hold-down with air, or electrostatic, or both. As is shown therein for each device, the electrostatic effect may be turned off and on by operating a switch 40 connecting the member 20 to a high voltage unidirectional power supply which is grounded as is the metallic impression cylinder 10, while the air may be controlled by a switch 41 for operating an electromagnetic valve 42 for turning the air on and off. The switches may be operated to turn on either the electrostatic hold-down, or the "air hold-down, or both. A manually operated valve 44 isv located ahead of the solenoid valve 42 and is adjustable to control the pressure of the air and in turn the force of the air stream. A gauge 45 is located between the valve 42 and the hold-down device to indicate the air pressure.
As is illustrated in FIG. 1, the electrostatic sheet holddown device 15' which is substantially identical to the device 15 is positioned at the transfer point between the cylinder 13 and the impression cylinder 10. The device 15' is disposed so that the air from the openings 32 of the device is directed tangentially along the cylinders 10 and 13 at their point of tangency. When the cylinder 13 is a transfer cylinder for transferring a sheet from a preceding printing unit to the impression cylinder 10, the sheet will be freshly printed on the side facing the transfer cylinder 13 and the air will aid in preventing offsetting of the printing on the sheet onto the transfer cylinder 11.
Similarly, the device 15" may be oriented so that the air issuing from the openings 32 is directed generally tangentially to the cylinder 10, between the cylinder 10 and the transfer cylinder 14. The electrostatic hold-down device in this location will cause the sheet to hug the surface of the impression cylinder as the sheet leaves the printing nip and moves to the transfer point between the impression cylinder 10 and the transfer cylinder 14 and the air which is directed between the freshly printed surface of the sheet and the transfer cylinder 14 will aid in preventing offsetting onto the transfer cylinder 14 on the delivery side of the nip.
While the preferred embodiment of the present invention and various arrangements thereof have been described in detail, it is intended hereby to cover all constructions, modifications, and arrangements which fall within the scope and spirit of the present invention.
What is claimed is:
1. Sheet hold-down apparatus comprising an electrically conductive elongated member for establishing an electrostatic field, a housing of insulating material for said member providing an air space betwen said member and an interior wall of said housing and having opening means including at least one first opening exposing said :member for establishing an electrostatic field in one plane and at least one second opening for directing air outwardly of said housing in a diverging direction from said plane, a unidirectional high voltage power supply connected to said member, and means for supplying air under pressure to said air space.
2. A hold-down device as defined in claim 1 wherein said first-mentioned opening and second-mentioned opening are in respective planes through said conductive member which diverge at an angle of approximately 45 proceeding from said member to said openings.
3. A hold-down device as defined in claim 1 wherein said elongated member is hollow and air under pressure is supplied to the interior thereof, said elongated member having openings therein communicating the interior thereof with said air space to supply air under pressure to the latter.
4. Sheet hold-down apparatus comprising a tubular housing of insulating material, means for establishing a unidirectional electric field and charged particles in said electric field comprising an elongated conductive member supported within said housing with an annular air space between said member and housing, said conductive member having ionizing projections extending to one side thereof and said housing having first opening means therein on said one side of said conductive member for exposing said conductive member to establish an electrostatic field in a plane from said conductive member through said first opening means, and second opening means in said conductive member on said one side in a plane diverging from said first plane, a high voltage unidirectional voltage supply connected to said member, and means for supplying air under pressure to said annular air space.
5. A hold-down device as defined in claim 4 wherein said planes define an included angle of about 45.
6. A hold-down device as defined in claim 4 wherein said conductive member is hollow and has at least one opening communicating the interior thereof with said annular space and said air supply means is connected to the interior of said conductive member to supply air to said annular space through the opening in said conductive member.
7. A hold-down device as in claim 6 wherein said opening in said conductive member is aligned with an opening in said insulating housing.
8. A hold-down device as in claim 7 wherein said planes define an acute angle of about 45 9. A hold-down device as defined in claim 8 wherein said openings in said conductive member are disposed in a plane defining an angle of about 45 with the plane of said first opening means and an angle of about 0 with the plane of said second opening means.
10. In a rotary sheet handling machine, a rotating cylinder for carrying a sheet to be operated upon, sheet hold-down means for applying a force to said sheet to cause it to closely hug said cylinder comprising means adjacent said cylinder for establishing electric charges and an electric field in a direction from said hold-down means directly toward the surface of said cylinder to electrically attract said sheet to said cylinder including a high voltage unidirectional power supply and means for directing air toward said sheet in a direction diverging from said first direction in a second direction generally opposite to the direction of sheet movement, said sheet hold-down means comprising an elongated electrically conductive member extending along the length of said cylinder for establishing said charges and electric field and a housing of insulating material covering said conductive member and providing an air space between said member and housing, said housing having first opening means in said housing on the side thereof facing said cylinder for exposing said conductive member and second opening means communicating with said space for directing air from said space in said diverging direction, and means for supplying air under pressure to said space.
11. The method of causing a moving sheet to hug an adjacent member moving with the sheet comprising the steps of electrostatically charging the sheet at a first location adjacent the member by providing electrostatic charges and propelling said charges onto said sheet and toward said adjacent member with an electric field established betwen a conductor spaced from said member on the side of said sheet remote from said member, and directing air against said sheet from a location adjacent said conductor to engage the sheet in advance of the field established directly between said conductor and said member to move the sheet portion passing said conductor closer to said member and increase the etfectiveness of the electrostatic charges.
12. In a rotary sheet handling apparatus including at least one rotatably movable member for carrying sheetlike material to be worked on, said material tending to move away from said member as the latter rotates, means for causing said material to closely hug said movable member as said material is being carried thereon comprising hold-down means adjacent said member including electrostatic means for establishing an electric field to charge said material for electrical attraction to said member, said electrostatic means including a conducting member connectable to a high voltage unidirectional power supply and said hold-down means further including air directing means adjacent said conducting member and having opening means in said air directing means, for directing a flow of air against said material ahead of the electric field established directly between said conducting member and said rotatable member to apply a force to said material to move said material passing said hold-down means toward said rotatable member, said air moving said sheet toward said rotatable member and increasing the eflectiveness of said electrostatic means.
13. In a rotary sheet handling apparatus as defined in claim 12 wherein said air directing means includes a hollow member disposed about said conducting member and including a plurality of openings providing said opening means.
14. In a printing press as defined in claim 10 wherein said means for establishing an electric field and said means for directing air are individually controllable and may be used individually and in combination.
15. In a printing press as defined in' claim 10 wherein said hold-down device directs air tangentially along said cylinder.
16. In a printing press as defined in claim 10 wherein said elongated conductive member is hollow and has openings communicating with said space and said air under pressure is supplied to the interior of said conductive member and then through the openings therein to said space.
17. In a printing press as defined in claim 16 wherein said first and second opening means are spaced from each other about the longitudinal centerline of said elongated member at an angle of about 4'5".
18. Hold-down apparatus for use in conjunction with a rotatably movable sheet material carrying member to cause sheet material to closely hug said member compris ing electrostatic hold-down means including an elongate conductor member to be supported adjacent said sheet material carrying member and connectable to a unidirectional electric power supply for establishing an electric field and charging sheet material on said member for electrical attraction to 'said member, a housing member surrounding said conductor member but exposing the latter to establish said field and charge said material, means for introducing pressurized air into said housing, and means defining an opening means in said housing, to direct a flow of air from said housing against said sheet material to urge said material toward said sheet carrying member and increase the eifectiveness of said electrostatic means.
References Cited UNITED STATES PATENTS 287,957 11/1883 Osborne 226-1 1,169,428 1/1916 Rogers. 1,731,030 10/1929 Thompson. 2,973,200 2/1961 Wiener 27l26 X 3,039,388 6/ 1962 Brandt 226--1 X 3,172,657 3/1965 Brandt 27151 3,174,748 3/ 1965 Roberts et al. 271-8 ROBERT B. REEVES, Primary Examiner.