GB2128139A

GB2128139A - Duplex printing system

Info

Publication number: GB2128139A
Application number: GB08228170A
Authority: GB
Inventors: Thomas Walter Bobick; Frederic Lewis Clark; Barry Curtis Kockler; Henry Wilhelmus Jongerling; Svetislav Mitrovich
Original assignee: Mead Corp
Current assignee: Mead Corp
Priority date: 1982-10-01
Filing date: 1982-10-01
Publication date: 1984-04-26
Also published as: FR2534564A1; DE3236884A1; GB2128139B

Abstract

A printing system for duplex printing a plurality of document page images on a plurality of sheets from a supply station (16) includes memory means (10) for storing print control information which defines the document images. A printer (12) prints the page images on sheets as they are transported past a print station (14) by a vacuum belt transport arrangement (28) defining a closed sheet path. The sheet path is of sufficient length such that a number of sheets are transported simultaneously therethrough. A sheet inverter (40) receives sheets sequentially from the sheet path after the sheets are printed on their first sides and returns them to the sheet path (28) in an inverted orientation prior to printing on the second sides of the sheets. A gate (46) selectively diverts the sheets, after duplex or simplex printing, to an output stack (54). The system makes maximum use of the print capabilities of the printer and maximises the number of sheets which can be printed on both sides in a given period of time. <IMAGE>

Description

SPECIFICATION Duplex printing system and method therefor The present invention relates to a printing system and, more particularly, to a printing system in which multiple-page documents may be duplex printed.

A number of different prior art printing systems have had a duplex printing capability. In most such systems only one sheet is present at any time in the paper path. In one prior art system, after printing on the first side of a sheet it is transported to an output accumulator effectively inverted, returned to the print station, and then transported again to the output accumulator. Only at this point is the next successive sheet of paper supplied to the paper path.

As a consequence, the duplex printing speed of this system is limited by the fact that a substantial amount of time is required between successive printing operations while a sheet is inverted, or removed from the paper path and a new sheet suppled to the paper path. The actual printing operation occupies a relatively small portion of the time required for producing each duplex printed sheet.

In a second type of printing system, each sheet of paper is supplied in sequence to a first printing station, to an inverter station, and finally to a second printing station. Opposite sides of each sheet are printed at the first and second printing stations. This device requires several print stations to accomplish duplex printing. While it is capable of higher speed operation than the above discussed system, nevertheless it requires a substantial amount of space.

Accordingly, it is seen that there is a need for an improved printing system in which high speed duplex printing of a plurality of sheets may be accomplished at a single print station.

According to one aspect of the present invention, a printing system for duplex printing a plurality of document images on a plurality of sheets includes memory means for storing print control information defining the plurality of document images. A printer means selectively prints the document images on sheets as the sheets are transported past a print station. A sheet transport means, which transports the sheets past the print station, defines a closed sheet path of sufficient length that a predetermined number of sheets may travel through the path simultaneously. A sheet supply means supplies sheets to the transport means and an inverter means receives sheets sequentially from the transport means, after printing on a first side thereof, and immediately returns the sheets to the transport means in an inverted orientation.An output means receives sheets from the sheet transport means after duplex printing is completed. A control means selectively directs the sheets in the closed sheet path to the output means or to the inverter means subsequent to printing, whereby a plurality of sheets transported by the transport means past the printer are printed on a first side, inverted, and subsequently printed on a second side prior to being directed to the output means.

The control means comprises means for control ing operation of the sheet supply means such that printed sheets directed to the output means are replaced in the sheet path by sheets from the sheet supply means, whereby the predetermined number of sheets are maintained in the closed sheet path.

The sheet inverter means may include means for returning each inverted sheet to the sheet transport means prior to inversion of the next sheet received by the sheet inverter means.

The printing system may further comprise means for retrieving the print control information from the memory means in a first order for printing on the first sides of the sheets, and for retrieving the print control information from the memory means in a second order for printing on the second sides of the sheets, such that the document images on the first and second sides of the sheets have their upper portions adjacent the same edges of the sheets.

The method by which the printing system operates may include the steps of: (a) sequentially supplying a predetermined plurality of sheets from the sheet supply to the sheet path; (b) sequentially transporting the sheets along the sheet path past the print station for printing selected ones of the document images on the first sides of the sheets; (c) sequentially printing selected ones of the document images on the first sides of the sheets; (d) sequentially removing from the sheet path each of the sheets which is to be duplex printed and inverting each of the sheets; (e) sequentially returning each of the inverted sheets to the sheet path and transporting each of the inverted sheets past the print station for printing selected ones of the document images on the second sides of the sheets to produce duplex printed sheets; and (f) transporting the duplex printed sheets to the output.

The step of sequentially printing selected ones of the document images on the second sides of the inverted sheets may include the step of printing images on the second sides of the inverted sheets in an orientation which is inverted with respect to the orientation in which document images are printed on the first sides of the sheets.

The method may further include the steps of: (a) retrieving the print control informatibn from the memory in a first order to control printing on the first sides of the sheets; and (b) retrieving the print control information from the memory in a second order to control printing on the second sides of the sheets in an orientation which is different with respect to the print station than the orientation in which the first sides of the sheets are printed.

The method may further include the step of periodically sequentially supplying an additional predetermined plurality of sheets from the sheet supply to the sheet path for printing on the first sides thereof after printing on the second sides of at least some of the previously applied predetermined plurality of sheets.

The step of periodically sequentially supplying an additional predetermined plurality of sheets from the sheet supply to the sheet path may include the step of supplying the additional predetermined plurality of sheets to the sheet path such that the additional predetermined plurality of sheets follow the previously supplied predetermined plurality of sheets in the sheet path. The second sides of the previously supplied predetermined plurality of sheets may be printed prior to printing the first sides of the additional predetermined plurality of sheets.

Accordingly, it is an object of the present invention to provide such a printing system and method of printing in which a plurality of sheets are simultaneously transported through a closed sheet path, which path extends past a printing station, and in which each sheet travels past the printing station twice prior to removal from the closed sheet path, whereby each sheet is duplex printed; to provide such a printing system and printing method in which a sheet inverter is provided adjacent the sheet path for receiving therefrom sheets and returning the sheets substantially immediately to the path in an inverted orientation; and to provide such a printing system in which the sheets, having been duplex printed, are delivered to an output in a desired order.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which: Figure 1 is a side view of the printing system of the present invention, illustrating the paper path through the printing system; and Figure 2 is a chart illustrating the print sequence for duplex printing multiple page documents having various numbers of pages; Figure 1 is a schematic representation of a printing system according to the present invention which is capable of either simplex or duplex printing. A computer 10, including an appropriate memory, such as a disc storage unit, provides a means for storing print control information which defines a plurality of document page images which are to be printed.The print control information is supplied from the memory of computer 10 to a printer means 12, such as a thermal matrix printer, laser printer, wire matrix printer, or any other known printer in which the image printed thereby may be controlled by electrical control signals. Printer means 12 selectively prints the desired document images on sheets transported past a print station, indicated generally at 14. A sheet supply means includes a supply station 16 and supply roller 18 which provides blank sheets of paper to associated sheet feed section 20, including rollers 22 and 24 and vacuum belt 26.

Sheets of paper from vacuum belt 26 are applied to vacuum belts 28 which extend around vacuum drums 29,30,31,32 and idler rollers 33,34,35 and 36. Vacuum plenums are provided between drums 29 and 30, drums 30 and 31, and drums 32 and 29 to hold sheets against belts 28, while belt 37 extends around rollers 38 and 39 and provides a means of transporting a sheet from vacuum drum 31 to vacuum drum 32. Sheets supplied to drum 29 are carried on the belts 28 past the print station 14.

When the second side of the sheet is to be printed, the sheet is then delivered to a sheet inverter 40.

Inverter 40 includes a number of wedge shaped sheet diverters 41 which extend upward between belts 37. Diverters 41 deflect a sheet upward between wire guides 42 and into the nip between pinch rollers 43 and 44. Rollers 43 and 44 initially rotate so as to raise a sheet vertically. The rollers 43 and 44 are then rotated in the opposite direction, transporting a sheet downward into contact with diverters 41 and then onto belt 37. The edge of the sheet which was formerly the leading edge is now the trailing edge and inversion is completed. The sheet is then transported to the left, as seen in Figure 1, and raised into contact with vacuum roller 38 by means of wire guides 45.

At a subsequent point in the duplex printing operation, or during simplex printing sheets may be removed from the belts 28 by gate 46 which may be pivoted downward. When so pivoted, gate 46 strips the sheets from belt 28 and delivers them to an output means. The output means includes belts 48 and rollers 50 and 52, which deliver the sheets to an output stack 54.

Thus, it is seen that the printer includes a number of belts, vacuum drums and rollers which act collectively as a sheet transport means for transporting sheets through a closed sheet path past the print station 14. This closed sheet path is sufficiently long with respect to th size of the copy sheets that a plurality of copy sheets may travel the path simultaneously.

A control means, including gate 46, selectively directs copy sheets in the sheet path to the output means or to the inverter means 40 after printing by the printer 12. As described more completely below, this facilitates a duplex printing operation in which a plurality of sheets are transported by the transport means past the printer, printed on a first side, inverted, and subsequently printed on a second side prior to being directed to the output means. Motor 56, responsive to computer 10, provides a means of moving gate 46 into the selected gate position.

Computer 10 receives signals from photo-optical detectors (not shown) positioned along the sheet path so that the timing of the printing operation, gate actuation, and other printing functions may be properly timed in accordance with the movement of sheets through the sheet path.

For simplex printing, sheets are fed from supply, transported past the print station 14, printed on one side only, deflected by gate 46, and accumulated in stack 54. By initially pivoting gate 66 upwards, a sheet of copy paper may be duplex printed. The sheet is supplied from supply 16 and printed on a first side thereof by printer 12 as the sheets moves past the print station 14. The sheet is delivered to the inverter 40 and, subsequently, returned to the closed paper path in an inverted orientation. The sheet is then carried past the print station 14 by belts 28 with its second side facing the printer 12. The sheet has now been printed on both sides. The sheet is stripped from belts 28 by gate 46 and delivered to the stack 54 as may be selected by the system operator.

The closed sheet path is of sufficient length that a plurality of sheets, as controlled by computer 10, may be transported by the transport means through the path simultaneously. In the printer system illustrated, five sheets are simultaneously transported through the closed sheet path. It will be appreciated, however, that when sheets of greater length are printed, it may be necessary to reduce the number of sheets simultaneously circulating through the sheet path.

The sequence in which the page images are printed will vary in dependence upon the number of pages in the document. Figure 2 illustrates a number of such sequences. Each printing sequence is based upon the assumption that five sheets are maintained in the closed sheet path on a continuing basis, i.e., as duplex printed sheets are delivered to the output, they are replaced with unprinted sheets from the sheet supplies. It will be understood, however, that the printing sequence may not be precisely as illustrated in Figure 2 where a very small number of copies of a multipage duplex printed document are to be produced.For instance, if a two-page, one sheet document were to be printed, with only two copies of the document being desired, the printing sequence would be 2-2-1-1, rather than that shown in Figure 2, since it would be unnecessary to supply more than two copy sheets to the closed sheet path.

Additionally, if a lesser or greater number of copy sheets are simultaneously circulated through the closed sheet path, the print sequences will necessarily be altered. The underlining for each of the sequences indicates repeating of the page number sequences. The letter X' has been used to indicate that no page image is printed on a sheet as the sheet passes through the print station.

It will be appreciated that the printing system and method of the present invention provide substantial advantages over prior art systems and methods. The sheets are not stacked in an intermediate inverter tray after a first printing operation and prior to a second printing operation, as is common with prior art duplex printers. As a consequence, the possibility of ink being smudged or transferring to other sheets in a stack is eliminated. By providing a closed sheet path in which a plurality of sheets are continuously and repeatedly circulated past the print station, the present invention makes maximum use of the print capabilities of the printer.Therefore, the number of sheets which may be printed in a given period of time by the printer system of the present invention is substantially greater than that of prior art devices of the type in which both sides of a single sheet are printed prior to supplying any other sheets to the printer sheet transport.

In the above discussion, the orientation of the document images which are duplex printed on the sheets has not been addressed. Typically, each of the sheets is transported through the closed sheet path with one of its shorter edges being the leading edge. If a sheet is transported past the print station 14 with one of its shorter edges being the leading edge and the first side of the sheet printed, and, after inversion, transported past the print station with the other of its shorter edges being the leading edge, it will be appreciated that the image on the second side of the sheet will be inverted with respect to the image on the first side of the sheet if both images are printed top to bottom. For sheets which are to be bound at their left hand edges in a book-like format, it will be further appreciated that such image orientation is unacceptable.

In order for the images to be properly oriented, it is necessary to rotate the data used for controlling printing of the second sides of the sheets through an angle of 180 . This may be accomplished to two successive 90 rotations. Rotation through 902 is accomplished conveniently as shown in Periera U.S.

Patent No. 4,084,195, in Latspeich U.S. Patent No.

4,271,476, or in Evans U.S. Patent No. 4,168,488.

While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention as defined in the appended claims.

Claims

1. In a printing system of the type in which print control information is stored in a memory said print control information defining a plurality of document images which are to be duplex printed on a plurality of sheets, and in which a sheet path extends past a sheet supply a print station an inverter station and to an output the method of printing comprising the steps of:: sequentially supplying a plurality of sheets from said sheet supply to said sheet path sequentially transporting said sheets along said sheet path past said print station for printing selected ones of said document images on the first sides of said sheets, sequentially printing selected ones of said document images on the first sides of said sheets, sequentially inverting each of said sheets which is to be duplex printed and transporting each inverted sheet immediately back toward said print station sequentially printing selected ones of said document images on the second sides of said inverted sheets to produce duplex printed sheets, and transporting said duplex printed sheets to said output.

2. A method according to claim 1 in which said step of sequentially printing selected ones of said document images on the second sides of said inverted sheets includes the step of printing images on the second sides of said inverted sheets in an orientation which is inverted with respect to the orientation in which document images are printed on the first sides of said sheets.

3. A method according to claim 1, further comprising the steps of: retrieving said print control information from said memory in a first order to control printing of said first sides of said sheets, and retrieving said print control information from said memory in a second order to control printing on said second sides of said sheets in an orientation which is different with respect to said print station than the orientation in which said first sides of said sheets are printed.

4. A method according to claim 3 in which the document images on said first and second sides of each of said duplex printed sheets have their top portions adjacent the same sheet edges of said sheets.

5. A method according to claim 1, further comprising the step of: periodically sequentially supplying an additional plurality of sheets from said sheet supply to said sheet path for printing on the first sides thereof after printing on the second sides of at least some of the previously supplied plurality of sheets.

6. A method according to claim 5 in which said step of periodically sequentially supplying an additional plurality of sheets from said sheet supply to said sheet path includes the step of supplying said additional plurality of sheets to said sheet path such that said additional plurality of sheets follow the previously supplied plurality of sheets in said sheet path.

7. A method according to claim 6 in which the second sides of said previously supplied plurality of sheets are printed prior to printing the first sides of said additional plurality of sheets.

8. A printing system for duplex printing a plurality of document images on a plurality of sheets, including memory means for storing print control information defining a plurality of document images, printer means for selectively printing said document images on sheets transported past a print station sheettransport means for transporting sheets past said print station sheet supply means for supplying sheets to said sheet transport means sheet inverter means output means for receiving sheets from said sheet transport means after printing thereon, and control means characterised in that:: said sheet transport means defines a closed sheet path of sufficient length tht a plurality of copy sheets may be transported by said transport means along said path simultaneously, said inverter means includes means for receiving sheets sequentially from said sheet transport means and immediately returning said sheets to said sheet transport means in an inverted orientation, and said control means includes means for selectively directing sheets in said sheet path to said output means or to said inverter means subsequent to printing, whereby a plurality of sheets transported by said transport means past said printer are printed on a first side, inverted, and subsequently printed on a second side prior to being directed to said output means.

9. A printing system according to claim 8further characterized in that said control means comprises means for contolling operation of said sheet supply means such that printed sheets directed to said output means are replaced in said sheet path by sheets from said sheet supply means whereby a predetermined number of sheets are maintained in said closed sheet path.

10. A printing system according to claim 8, further characterized in that said print control information may be retrieved from said memory means in a first order for printing on said first sides of said sheets, and retrieved from said memory means in a second order for printing on said second sides of said sheets, the document images on said first and second sides of said sheets having their upper portions adjacent the same edges of said sheets.

11. A printing system substantially as hereinbefore described with reference to the accompanying drawings.

12. The method of printing both sides of a sheet with document images, substantially as hereinbefore described.