WO1997046393A2 - Desk-top printer and related method for two-sided printing - Google Patents

Abstract

A printing system includes a first printer (12) and a second printer (14) for printing documents encoded in computer generated signals. The documents generally include alphanumeric characters, charts and graphics. A computer (38) for generating a signal encoding a multiple page document is coupled to the printers for transmitting odd pages in encoded form to one of the printers and even pages to the other printer. The paper used by the printing system may be a series of individual or separate sheets or a series of paper sheet portions connected to one another in a continuous web of paper. The printer assemblies are disposed one above the other, the paper web or single paper sheets being simply inverted along a U or C path between the output port (22) of the first printer assembly and the paper feed port (24) of the second printer.

Description

DESK-TOP PRINTER AND RELATED METHOD FOR TWO-SIDED PRINTING

Background of the Invention

This invention relates to an apparatus for two-sided printing. More particularly, this invention relates to a desk-top laser printer responsive to computer generated signals for printing a document on two sides.

At the present time, thousands of banks, brokerage houses and other financial institutions are printing millions of weekly, bi-weekly and monthly statements on one side of pre-printed statement forms For the most part, these statements are printed off of mainframe

or large-scale mini-computers. Affordable printers capable of handling mainframe and mini-

computer output are either chain or dot-matrix printers. Consequently, printing both sides of paper having the conventional quality would masticate the paper.

Conventional two-sided photocopying and book printing present problems which have

perhaps inhibited efforts to develop two-sided printing of financial type statements. Such

problems include a warping of the paper which results from the high levels of heat employed. More moisture flees from the side of the paper in contact with the heated elements than from the more remote side of the paper. In addition, the deposition of electrostatic charges causes

the paper sheets to cling to one another and to other surfaces. Both the warping of the paper

sheets and the deposited electrostatic charge cause paper jams in the machinery. Avoiding or

clearing the paper jams requires personnel to be present to monitor and correct problems as

they occur. Sometimes, papers printed on one side are placed aside for flattening prior to

printing on the opposite side. Such efforts increase costs and delay the production of the

desired documents. Summary of the Invention

An object of the present invention is provide a printing system or apparatus for printing two-sided documents in response to computer-generated signals encoding the documents

Another object of the present invention is to provide such a system or apparatus which can handle mainframe and other large-scale computer output

A further object of the present invention is to provide such a system or apparatus which prints on each side of a sheet of paper in real time

Yet another object of the present invention is to provide such a system or apparatus which can utilize laser printer technology and basic or conventional printer driver

programming

An additional object of the present invention is to provide such a system or apparatus which is simple to manufacture, assemble and implement

These and other objects of the present invention will be apparent from the descriptions

and drawings hereof

A printing system comprises, in accordance with a general embodiment of the present

invention, a first printer assembly for printing documents encoded in computer generated signals and a second printer assembly foi printing documents encoded in computer generated

signals The documents generally include alphanumeric characters, charts and graphics A computer for generating a signal encoding a multiple page document is coupled via connection componentry to the pπnters for transmitting odd pages in encoded form to one of the printers

and even pages to the other printer The paper used by the printing assembly may be a series of paper sheet portions

connected to one another in a continuous web of paper In that event, the printer assemblies

are connected in tandem to one another via the multiple-page continuous paper web The web

extends from a paper output port of the first printer assembly to a paper feed port of the

second printer assembly Alternatively, a printing system in accordance with the invention can print on a series of

individual or single sheets.

Preferably, the printer assemblies are disposed one above the other, the paper web or single paper sheets being simply inverted along a U or C path between the output port of the

first printer assembly and the paper feed port of the second printer assembly. In the case that

the printing substrate is a continuous web, a tensioning device may be placed in contact with

the web between the paper output port of the first printer assembly and the paper feed port of the second printer assembly for guiding the web and providing it with a predetermined amount of tension The tensioning device exemplarily includes a spring loaded, electrically conductive

element such as a roller which is electrically grounded to siphon away electrostatic charge deposited on the paper by the first printer assembly

Preferably, the connection componentry includes a page splitting module for detecting

odd pages and even pages in the document and separating odd pages from even pages. The

connection componentry further includes a synchronizer for timing the operation of the first printer assembly and the second printer assembly so that opposite sides of essentially every

sheet portion bear consecutive pages The connection componentry may additionally include

an electronic buffer. The synchronizer or timing module is operatively connected to the page

spitting component and includes a delay for transmitting pages of a given document to one printer assembly only after lapse of a predetermined interval after an initial transmission of

pages of the document to the other printer assembly

In a more specific embodiment of the present invention, the two printer assemblies are

off-the-shelf components, preferably desk-top type laser printers

In a printing method in accordance with the present invention, a first printer assembly

for printing documents encoded in computer generated digital signals is disposed in tandem to a second printer assembly for printing documents encoded in computer generated digital signals A computer for generating a digital signal encoding a multiple page document is operatively connected to data inputs of the two printer assemblies. Odd pages of the multiple

page document are then transmitted in encoded form from the computer to one of the printer assemblies and even pages of the multiple page document are transmitted from the computer to

the other printer assembly. The printer assemblies then print the respective even and odd

pages on opposing sides of paper sheets which are guided from a paper output port of a first

printer assembly to a paper feed port of the other printer assembly.

In accordance with another feature of the present invention, the printer assemblies are disposed one above the other Whether a continuous web of paper or a series of separate sheets are used as the printing substrate, the substrate is simply inverted in a U or C shape

between the output port of the first printer assembly and the paper feed port of the second printer assembly Where the paper or printing substrate is a continuous web, a guide such as a tensioning roller is placed in contact with the web between the output port of the first printer

assembly and the feed port of the second printer assembly Where the paper sheets are

separate, a guide such as an arcuate or curved surface is provided to direct the paper sheets from the first printer assembly to the second printer assembly

A printing apparatus comprises, in accordance with another embodiment of the present

invention, a desk-top printer housing having a paper input port, a paper output port and a data

input port A digital processor is disposed in the housing and is operatively connected to the

data input port. The processor is programmed to detect odd pages and even pages in an

electronically encoded document arriving via the data input port and to separate odd pages of

the document from even pages thereof A paper moving engine including rollers is disposed in the housing for moving a paper sheet through the printer housing from the paper input port to the paper output port along a predetermined path A first laser printing assembly is disposed in

the housing along one side of the path for printing an odd-numbered page of the document

along one side of the paper sheet A second laser printing assembly is disposed in the housing along an opposite side of the path for printing an even-numbered page of the document along an opposite side of the paper sheet The processor is operatively connected to the laser

printing assemblies for controlling the first laser printing assembly to print the odd-numbered page of the document along the one side of the paper sheet and for controlling the second laser printing assembly to print the even-numbered page of the document along the opposite side of

the paper sheet

Preferably, in this embodiment of the invention, the paper path is essentially linear One of the laser printing assemblies is located above the path while the other laser printing assembly

is located below the path Because the paper travels along a linear or straight path from one

laser printing assembly to the other, the paper is easily aligned There is less paper jamming

and less paper warping than there would be in a printer with a curved paper path between the two laser print stations Because the laser print stations can be located essentially right next to one another, there is no need to provide the processor with multiple buffers for temporarily storing several pages At most, a single output buffer is necessary to store one side of a page

while the other side is being printed Conventional RAM is sufficient to implement the output buffer

It is to be noted that the laser printing assemblies in this embodiment of the invention

are essentially identical to laser printing assemblies in conventional desk-top laser printers

Each laser printing assembly includes, for example, a drum having a photosensitive surface, a toner reservoir, a laser, a toner waste reservoir, an erase lamp, and a corona wire

It is preferable in this embodiment of the invention that one laser printing assembly is located below the paper path while the other laser printing assembly is located in a more conventional position above the paper path. The laser printing assembly located above the

paper path is essentially identical to existing laser printing assemblies. Moreover, only minor

modifications are necessary to adapt a conventional laser printing assembly for disposition

below the paper path. Generally, this second laser printing assembly is in an upside down configuration, with alterations in structure necessary to accommodate that inverted arrangement being made.

In accordance with a feature of this embodiment of the present invention, the two laser printing assemblies are mounted to a carriage which is movably disposed in the housing. Thus, the laser printing assemblies may be easily removed from the housing for servicing. One of the

laser printing assemblies may be mounted to an upper side of the carriage, while the other laser

printing assembly is mounted to an underside of the carriage. Accordingly, a toner cartridge of the one laser printing assembly is removed from above the carriage whereas a toner cartridge

of the other laser printing assembly is removed from below the carriage.

Generally, it is contemplated that the laser printer apparatus has only one engine for

moving the paper. The one engine is coupled to a sufficient number of rollers placed in appropriate locations to move the paper along the linear path past the first print station and

subsequently the second print station and out the paper output port.

The processor is programmed to synchronize operation of the first laser printing

assembly and the second laser printing assembly so that opposite sides of essentially every

sheet bear consecutive pages. The processor is further programmed to generate the document

from (1) encoded information peculiar to the document and (2) standard textual and graphic

information incorporated into a plurality of documents.

A printing system or assembly in accordance with the present invention is a high- volume printing system which can print customer data, e g., on financial statements, in real time, using black and white laser printing technology and basic or conventional printer driver

programming

A printing system or assembly in accordance with the present invention reduces the

number of sheets of paper necessary to print financial statements by 50% or more,

concomitantly reducing printing and mailing costs In addition, the system eliminates the need

to use expensive pre-printed paper stock for financial statements Logos may be printed on the

front of each sheet in real time, while legal compliance information is printed only on the last face of a statement The quality of the printed characters may be significantly improved over

conventional methods of statement printing, up to the highest laser standards. Moreover, development costs can be substantially decreased through the utilization of existing (off-the- shelf) laser printer engines (preferably using powerful RISC processors)

A printing system or assembly for printing two-sided documents in accordance with the

present invention can handle mainframe and other large-scale computer output. The printing

occurs without essential delay (in real time) in response to computer generated signals. In contrast, in photocopying and other printing methods, there is a substantial delay between

printing of one side and printing of the opposing side

A system or assembly in accordance with the present invention utilizes laser printer technology and basic or conventional printer driver programming

A laser printer or printing assembly for two-sided laser printing in accordance with the present invention does not require any memory space over and above that normally present in

desk-top printers. The conventional RAM space is sufficient for the storage requirements of the present laser printer

A laser printer system for two-sided laser printing in accordance with the present invention is not size or speed sensitive and can be used in a wide range of printer powers and sizes The two-sided laser printer system is easy to maintain and repair Paper handling is minimized Accordingly, paper jamming and alignment problems are reduced

A laser printer system for two-sided laser printing in accordance with the present invention is useful for myriad applications, not just high-speed high-volume financial

statements Brief Description of the Drawing

Fig 1 is a schematic side elevational view, partly in block diagram form, of a printing

system, showing two laser printers disposed in cascade with respect to one another, in accordance with the present invention

Fig 2 is a block diagram of a programmable buffer/interface shown in Fig 1

Fig 3 is a block diagram of a control unit shown in Fig 2

Fig 4 is a schematic side elevational view, partly in block diagram form, of a modified printing system in accordance with the present invention

Fig 5 is a block diagram of a computer unit utilizable to perform the functions of the

programmable buffer/interface of Figs 1 and 4

Fig 6 is a schematic side elevational view of a modified second printer of a pair of

ganged or cascaded printers shown in Fig 4

Fig 7 is a schematic top plan view of a paper guide at a paper input port of the printer

of Fig 6

Fig 8 is a schematic partial cross-sectional view taken along line VIII- VIII in Fig 7, on

an enlarged scale, showing the paper guide and paper infeed port of the printer of Fig 6

Fig 9 a schematic partial cross-sectional view, on an enlarged scale, of a modified paper supply or stacker, a paper guide, and a paper infeed port of a first printer of the pair of ganged or cascaded printers of Fig 4

Fig 10A-10H are interconnected portions of a block diagram illustrating operations of

the computer unit of Fig 5, and more particularly a processor component of the computer unit

Fig 1 1 is a schematic cross-sectional view of a laser printer for two-sided printing in

accordance with the present invention

Fig 12 is a schematic cross-sectional view of an upper laser printing assembly in the

laser printer of Fig 1 1

Fig 13 is a schematic cross-sectional view of a lower laser printing assembly in the

laser printer of Fig. 1 1

Fig 14 is a block diagram of a programmable processor in the laser printer of Fig 1 1

Fig 15 is a schematic isometric view of the laser printer of Fig 1 1 , showing a carriage

to which the laser printing assemblies of Figs 12 and 13 are attached

Description of the Preferred Embodiments

As illustrated in Fig 1 , a printing assembly or system comprises a pair of printers 12 and 14 disposed one above the other, for example, on shelves of a cart or rack (not illustrated)

Printers 12 and 14 are preferably laser printers for printing documents (alphanumeric characters, charts and graphics) encoded in computer generated signals More specifically,

printers 12 and 14 are off-the-shelf desk-top-type laser printers

Printers 12 and 14 are connected in tandem to one another via a multiple-page

continuous paper web 18 extending along a U- or C-shaped path 20 from a paper output port 22 of a first printer 12 to a paper feed port 24 of the second printer 14 Paper web 18 is stored

in a Z-fold configuration (not shown) in a paper supply container 26 and is fed from that

container to a paper feed port 28 of the first printer 12 A micro-switch sensor 29 is provided in printer 12 near paper feed port 28 for detecting whether paper web 18 is properly positioned.

Generally, web 18 comprises a series of sheet portions (not shown) connected end to

end. Preferably, the sheet portions of web 18 each bear an end-of-page tab (not shown) at the

trailing edge of the respective sheet portion. The end-of-page tabs are magnetically encoded, by means of the ink used to encode banking checks, and are detectible by an end-of-page

sensor 31 disposed in printer 12 near paper output port 22 thereof.

At paper output port 22, a rear door 30 of the first printer 12 is unlatched and left in an opened configuration, to facilitate a guiding of paper web 18 along path 20 so that the paper turns from an upside-up to an upside-down orientation Similarly, at a paper output port 32 of

second printer 14, a rear door 34 of the second printer is kept opened to facilitate a feeding of

the paper web 18 to a Z-fold stack 36. Printer 14 is provided with a micro-switch sensor 37 near paper feed port 24 for detecting whether paper web 18 is properly positioned, while an

end-of-page sensor 39 is disposed in printer 14 near paper output port 32 thereof for detecting

magnetically encoded end-of-page tabs at the trailing edges of the successive sheet portions of web 18. End-of-page sensors 31 and 39 replace the page break sensor (not illustrated) which

is standard on laser jet printers. Of course, switches or other sensors (not shown) provided in printers 12 and 14 for disabling the printing process when doors 30 and 34 are opened are

themselves disabled, bypassed or otherwise neutralized to enable the execution of printing

operations. As further illustrated in Fig. 1 , the printing assembly or system also comprises a

mainframe, desk-top, mini, or LAN server computer 38 which, in addition to other normal

functions, generates a digital signal encoding a multiple page document such one or more ganged bank or financial statements. Computer 38 is coupled to printers 12 and 14 via a

programmable buffer/interface 40. Buffer/interface 40 is connected at an input to computer 38 via a cable 42 for receiving, from the computer, the digital signal encoding the multiple page document Buffer/interface 40 detects page breaks in the document and determines which pages are odd and which are even Pursuant to that determination, buffer/interface 40

transmits odd pages to a data input of printer 12 over a cable 44 and even pages to a data input

of printer 14 over a cable 46

As additionally illustrated in Fig 1 , a tensioning device 48 is placed in contact with

paper web 18 between paper output port 22 of printer 12 and paper feed port 24 of printer 14, for providing web 18 along path 20 with a predetermined amount of tension Tensioning

device 48 includes a spring loaded, electrically conductive roller 50 which is electrically grounded at 51 to remove electrostatic charge deposited on paper web 18 by printer 12

Tensioning device 48 may be designed to collapse upon experiencing pressure in excess of a

predetermined safety limit In that event, both printers 12 and 14 will be idled and an

appropriate error condition will be displayed (see display 106, Fig 5)

As shown in Fig 2, buffer/interface 40 includes a memory 52 which stores decoding

instructions for different types of computers and different database programs In response to

instructions from RAM resident control software 54, a control unit 56 accesses memory 52 to

enable the control unit to detect different pages of the multiple page document received by buffer/interface 40 from computer 38 over cable 42 The incoming multiple page document is temporarily stored in a buffer 58 which, together with cable 42, couples computer 38 to

control unit 56

As depicted in Fig 3, control unit 56 includes a page splitting module 60 which detects

and splits the odd pages from the even pages in the multiple page document generated by

computer 38 Page splitter module 60 feeds the odd pages in sequence to printer 12 via an

output buffer 62 (Fig 2) and feeds the even pages in sequence to printer 14 via a delay 64 (Fig 3) and an output buffer 66 Buffers 62 and 66, together with cables 44 and 46, couple page splitter module 60 to printers 12 and 14

Under the control of a timing signal from a time base 68, delay 64 postpones the transmission of the even page sequence to printer 14 by an interval substantially equal to the transit time of paper web 18 from paper output port 22 of printer 12 to paper feed port 24 of

printer 14, thereby synchronizing the operation of the two printers so that opposite sides of

essentially every sheet of web 18 bear consecutive pages

As further depicted in Fig 3, control unit 56 includes a programming selector 70 which

selects prestored document decoding instructions from memory 52 in response to a selection

made by RAM-resident software 54 Software 54 senses and communicates to programming selector 70 the type of machine that computer 38 is or the type of operating system used by computer 38, as well as the identity of the database or word processing program which computer 38 uses to generate the multiple page document This information permits control

unit 56 and, more specifically, programming selector 70 and page splitter 60 to analyze the

multiple page document for page breaks

RAM-resident software 54 may also be used to inform control unit 56 of the type of

printers connected to buffer/interface 40 and possibly an approximate distance along path 20

from output port 22 to paper feed port 24 The input of the approximate distance along path

20 enables control unit 56 to modify the timing of the second printer's operation relative to the first printer's operation To that end, programming selector 70 is connected to delay 64, as

depicted in Fig 3

Fig 4 illustrates another printing assembly or system for two-sided printing on separate paper sheets 71 comprises a pair of printers 72 and 74 disposed one above the other on shelves

of a cart or rack (not illustrated) Printers 72 and 74 are essentially identical to printers 12 and 14 except that printers 72 and 74 are provided at their paper input ports 76 and 78 with

respective paper stackers 80 and 82 and at their paper output ports 86 with standard page- break sensors (not shown), rather than end-of-page sensors 31 and 39 (Fig 1). In addition, the second printer 74 is provided with an arcuate paper guide or surface 84 removably attached to

paper stacker 82 for guiding paper sheets 71 from a paper output port 86 of printer 72 to stacker 82 so that the paper sheets are turned over in transit from output port 86 to input or feed port 78. A door 88 at output port 86 is angled downwardly and also serves a paper

guiding function Otherwise, the assembly of Fig. 4 is structurally essentially identical to the

assembly or system of Fig 1 Like reference numerals in Figs 1 and 4 denote identical

structural components

Fig. 5 depicts a computer unit 102 with a keyboard 104 and a visual display 106

Computer unit 102 is an alternative embodiment of the programmable buffer/interface 40 of

Figs. 1 and 4. Computer unit 102 includes an input interface 108 connected to mainframe, desk-top, mini, or LAN server computer 38 (Figs 1 and 4) for receiving therefrom a multiple page document such one or more ganged bank or financial statements The incoming

document is loaded into one of two mass storage components or input queues 1 10 and 112, under the control of a processor component 1 14 of computer unit 102. Processor 1 14

communicates with keyboard 104 and display 106 via respective interface modules 1 16 and 1 18 and with input queues 1 10 and 1 12 via a mass storage interface 1 19 Processor 1 14

includes an internal RAM (not illustrated) with resident control software.

Computer unit 102, more particularly, processor 114, performs several operations on a

multiple page document which has been loaded into input queue 1 10 or 1 12 Processor 1 14

detects odd pages and even pages in the document, separates odd pages from even pages, and

transmits odd pages of the document to laser printer 12 or 72 and even pages of the document to laser printer 14 or 74 Processor is additionally programmed to synchronize operation of the odd-page laser printer 12 or 72 and the even-page laser printer 14 or 74 so that opposite

sides of essentially every sheet bear consecutive pages It is also contemplated that computer

unit 102 or processor 1 14 actively generates the ultimate printed pages by combining encoded information from computer 38 peculiar to a particular document with predetermined standard

textual and graphic information incorporated into a plurality of different documents For

example, processor 1 14 will combine individual financial statement data such as banking transactions with standard text and graphics including logos, headings, dates and legally

required information Processor 1 14 is programmed to delay page transmission to the even-page laser printer

14 or 74 by a predetermined number of pages The length of the delay depends chiefly on the distance between the paper output port of the first printer and the paper infeed port of the

second printer

As further illustrated in Fig 5, computer unit 102 also includes a first print buffer,

LPT1 print buffer 120 (with interface), for temporarily storing a document page to be

transmitted to the first laser printer 12 or 72 Five second print buffers 122 (with interface), individually labeled LPT2 print buffers A-E, are provided for temporarily storing a plurality of

document pages to be transmitted to the second laser printer 14 or 74 Processor 114 has a

signaling module 123 which interfaces with print modules 120 and 122 Print buffers 120 and 122 are preferably areas of processor memory dedicated to

output page storage Print buffers 122 are one greater in number than the number of pages by

which printing in the second printer 14 or 74 is delayed relative to the start of printing in the

first printer 12 or 72

Figs 6-8 illustrate a modified paper infeed assembly 124 for printer 74 Sheets of paper 126 which drop from paper output port 86 of printer 72 (Fig 4) are caught by a paper

stacker or guide 128 attached to printer 74 Paper guide 128 includes an arcuate back and lower wall 130 and a pair of vertical side walls 132 and 1 4 (Fig 7) Side wall 134 is laterally

shiftable to accommodate paper sheets 126 of different widths An upstream end portion 136

of side wall 134 is angled laterally outwardly to provide a "funnel" effect Along an inner

surface (not labeled) wall 130 is provided with a large step 138 defining the rear end of a stacking zone 140 Wall 130 is further provided along its inner surface with a small step 142

which abuts a rear edge of a pre-existing paper tray 144

As shown in Fig 8, paper sheets 126 are fed one sheet at a time through paper infeed port 78 (see also Fig 4) Port 78 is just wide enough to accept one sheet only of twenty to twenty-eight pound laser printing paper On an inner side of a printer rear wall 146 are disposed a gπpper roller 148 and a sensor 150 Gπpper roller 148 rises to pull a single paper

sheet 126 through port 78 The infeed of that sheet is detected by sensor 150 via a pivoting of

a trigger or microswitch lever 152 Upon the passage of a paper sheet 126 past roller 148 and

sensor 150, trigger 152 falls and sensor 150 transmits a signal to the main electronic module

(not illustrated) of printer 74 The main electronic module in turn signals gπpper roller 148 to

shift to a lowered position to enable gravity feed of the next paper sheet

Fig 9 illustrates a portion of a modified paper supply or stacker 156 provided at an input to printer 72 (see also Fig 4) Stacker 156 is electrically connected to printer 72 via a

power cable 155 and a signaling cable 157 A stack 158 of paper sheets 126 is disposed on a

feed ramp or guide plate 160 of a stacker frame 162 The papei sheets 126 are delivered one

at a time through an opening or slot 164 between a front face 166 of stacker frame 162 and

feed ramp 160 In response to a signal from the main electronics (not shown) of printer 72, a

motor-driven gπpper roller 168 feeds a single paper sheet 126 through opening or slot 164 Under the control of the main electronics of printer 72, gripper roller 168 is lowered to position the next sheet for feeding and subsequently raised to prevent the next sheet from

slipping down into the feed path

At a lower end, feed ramp 160 abuts an upper end of a printer paper tray 170 Paper tray extends to a paper input port 76 (see also Fig 4) where, on an inner side of a printer panel

172, are disposed a gripper roller 174 and a sensor 176 with a trigger 178 loaded by a coil

spring 180. Gripper roller 174 and sensor 176 function similarly to roller 148 and sensor 150.

Figs. 10A-10H generally illustrate respective subroutines in the operation of processor

1 14 Fig 10 A relates to general initialization procedures Fig 1 OB concerns core page

processing operations. Fig 10C is directed to steps undertaken at the end of each record in a

print file. Fig 10D depicts printing operations using just one printer (for example, during the first several pages of a pint job) Fig 10E involves printing operations utilizing both printers Fig 1 OF relates to procedures for correcting printing errors Fig 10G deals with steps performed at the last record of a print file Fig 10H shows processing operations at the end of

a print job

Upon initialization, processor 1 14 oversees the loading of print files into queues 1 10

and 112 (Fig 5), as indicated at steps 200 and 202 in Fig 10A Each print file includes a

multiplicity of documents or records In the printing of bank financial statements, the records

constitute lists of bank financial transactions which have occurred during a month period (the statement period) Each record includes at least one page of the print file and more frequently

includes more than one page Processor 1 14 must track the succession of records as they are

being printed. To that end, processor 1 14 has a record counter 204 (see Fig 10A) in a defined area of internal memory For each page to be printed, processor 1 14 must also track the file

page number and the record number. Accordingly, processor 1 14 has a file page counter 206 and a record page counter 208 as reserved areas of internal memory.

Among the operations executed by processor 114 are ( 1 ) merging standard text and

graphics, stored in internal memory areas 210 (Fig 10B) and 212 (Fig IOC), with the

individual record data, (2) determining the first and last page of each record in a print file, (3) synchronizing or timing the printing in the two printers 12, 14 or 72, 74, and (4) transmitting print data to the printers to enable printing As mentioned above, the main subroutine for

controlling the printing operations is illustrated in Fig 10E, while print initialization operations

are shown in Fig 10D The synchronization or timing of printing in the two printers 12, 14 or 72, 74 is accomplished by using LPT2 buffer registers 122 (Fig 5) to delay the feeding of even

pages to the second printer 14 or 74 essentially by the time required for a paper sheet to travel

from paper infeed port 28 or 76 of the first printer 12 or 72 to the paper infeed port 24 or 78

of the second printer 14 or 74 The delay thus depends in part on the speed of printing in the

first printer 12 or 72 but also depends on the distance between the paper output port 22 or 86 of the first printer 12 or 72 and the paper infeed port 24 or 78 of the second printer 14 or 74

The steps taken to synchronize or time printing operations in the two printers 12, 14 or 72, 74

are included in the core page processing subroutine of Fig 10B

Upon beginning print operations for a job loaded into queue 110 or 112, processor 1 14

checks on the contents of file page counter 206 at an inquiry 214, as illustrated in Fig 10A If

the contents are non-zero, processor 1 14 zeroes the contents in a step 216 Once the contents

of file page counter 206 are determined to be zero, the contents are then incremented by one in

a step 218 Processor 1 14 then engages in an inquiry 220 into the contents of record counter

204. If the contents are not zero, the processor resets counter 204 in a step 222 The contents

of record counter 204 are then augmented by one in a step 224 Subsequently, processor 114 investigates at 226 the contents of record page counter 208 Non-zero contents are cleared away in a step 228 and the contents of record page counter 208 are then increased by one in a

step 230. Processor 114 then makes a check 232 into the contents of an active record page

register 234. If the contents of that register are zero, processor 1 14 increments the contents by

one in a step 236. If, however, the contents are determined in check 232 to be non-zero,

processor clears register 234 in a step 238 and then proceeds to incrementation step 236. In a

final inquiry 240 of the initialization subroutine of Fig. 10A, processor 114 determines whether the contents of a print buffer register 242 are zero. If so, the contents of register 242 are stepped up by one at 244. If not, register 242 is first reset in a step 246.

The contents of register 242 indicate which print buffer A-E of LPT2 buffer registers

122 is currently active, i.e., ready to receive a built-up even-numbered page for temporary storage to implement the delay between printing operations in the first printer 12 or 72, on the

one hand, and printing operations in the second printer 14 or 74, on the other hand. During

active printing operations, the contents of active LPT2 print buffer register 242 vary from one

to four (A through D), where there is a four page delay between printing operations in the two

printers. Like counters 204, 206, and 208, registers 234 and 242 are implemented as

respective memory cells or locations internal to processor 1 14

Upon the proper initialization of counters 204, 206 and 208 and registers 234 and 242, processor 1 14 proceeds from the initialization subroutine of Fig. 10A to the core page processing subroutine of Fig 10B, as indicated by an encircled letter B in those drawing

figures. Processor 114 first determines at a decision junction 248 whether the numeral stored

in encoded form in file page counter 206 is odd or even, indicating whether the current page in

the print job is an odd page, to be reproduced by first printer 12 or 72, or an even page, to be

reproduced by second printer 14 or 74. If the current page in the print job is odd, as

determined by processor 114 at decision junction 248, processor 1 14 executes a step 250 in which it accesses active record page register 234 to identify the active record page and transfers that page from the active input queue 110 or 112 (Fig. 5) to a page build buffer 252

realized in internal processor memory. Processor 1 14 builds the page at 254 and then queries

at 256 whether the contents of the record page counter are unity. If so, processor 1 14

performs a step 258 in which it accesses internal memory area 210 to obtain standard first page

text and graphics and then merges the active record page data with the standard first page text

and graphics in the build page buffer 252. Subsequently, processor 1 14 moves the contents of

page build buffer 252 to LPT1 print buffer 120 (Fig. 5) in a step 260 and clear the page build buffer in a step 262. Processor 1 14 then checks at 264 whether the contents of file page counter 206 are greater than 8. If the file page counter contents are 8 or less, then the second printer has not yet started its printing operations on the current print job. Processor 1 14 then

increments file page counter 206 in a step 266 and investigates at 268 whether the end of the

current record has been reached. If not, the processor increments record page counter 208 in a

step 270 and proceeds to initial print operations depicted in Fig 10D, as indicated by an

encircled letter D in Figs. 10B and 10D.

If processor 1 14 determines at check 264 that the number encoded in file page counter

206 is greater than 8, the processor enters into the printing subroutine of Fig. 10E, as indicated

by an encircled letter E in Figs. 10B and 10E. If processor 1 14 determines at investigation 268 that the end of the current record has been reached, the processor executes the subroutine

of Fig. 10C, as indicated by an encircled letter C in Figs 10B and 10C

If the contents of file page counter 206 are even, as determined by processor 1 14 at

decision junction 248, processor 1 14 executes a step 272 in which it accesses active record

page register 234 to identify the active record page and transfers that page from the active

input queue 1 10 or 112 (Fig. 5) to page build buffer 252. Processor 1 14 builds the page in a step 274 and then, in a step 276, checks the contents of internal memory register 242 and

moves the contents of the active buffer A-D of LPT2 print buffer registers 122 (Fig. 5) to the fifth print buffer (E) of LPT2 print buffer registers 122 In subsequent steps 278 and 280, processor 1 14 moves the contents of the page build buffer 252 to the active buffer A-D of

LPT2 print buffer registers 122 and clears page build buffer 252 Processor 1 14 then

increments the contents of internal memory register 242 in a step 282 However, if the active LPT2 print buffer register of registers 122 is buffer D (#4), as determined by processor 114 at

a decision junction 284, the processor first zeroes the contents of internal memory register 242

in a step 286 Processor 1 14 then checks at 288 whether the contents of file page counter 206

are greater than 8 If the file page counter contents are 8 or less, then the second printer has not yet started its printing operations on the current print job Processor 1 14 then increments file page counter 206 in a step 290 and investigates at 292 whether the end of the current record has been reached If not, the processor increments record page counter 208 in a step

294 and returns to decision junctions 248 If processor 1 14 determines at check 288 that the number encoded in file page counter

206 is greater than 8, the processor enters into the printing subroutine of Fig 10E, as indicated

by an encircled letter E at an affirmative outcome of check 288 If processor 1 14 determines

at investigation 292 that the end of the current record has been reached, the processor executes

the subroutine of Fig 10C, as indicated by an encircled letter C in Figs 10B and 10C

At the beginning of the end-of-record processing subroutine of Fig 10C, processor 114

decides at a junction 296 whether the current page of the print job, as indicated by the contents of file page counter 206, is an odd page or an even page It is to be understood that current page is a blank page, the last data page of the current record having been processed already If

the contents of file page counter 206 indicate an even page number (a back side of a sheet), processor 114 moves text and graphics of a standard final page from internal memory area 212 to page build buffer 252 in a step 298, builds the page in a step 300 and then, in a step 302, accesses register 242 to determine which buffer A-D is active and moves the contents of that

buffer to print buffer E (#5) of LPT2 print buffer registers 122 (Fig. 5). Subsequently, in a

step 304, processor 1 14 moves the contents of page build buffer 252 to the active buffer of LPT2 print buffer registers 122 (Fig. 5) and, in a step 306, clears page build buffer 252. Processor 1 14 again accesses internal memory register 242 in an inquiry 308 to ascertain

whether the active buffer A-D of LPT2 print buffer registers 12 is the last one (D). If not, the

contents of register 242 are incremented in a step 310. If so, the contents of register 242 are

first cleared in a step 312 prior to incrementation in step 310. Processor 1 14 then increments

file page counter 206 in a step 314, increments record counter 204 in a step 316, clears record

page counter 208 in a step 318, and increases the zeroed contents of record page counter 208

to unity in a step 320. Processor 1 14 then checks at 322 whether the contents of file page

counter 206 are greater than 8. If the file page counter contents are 8 or less, then the second

printer has not yet started its printing operations on the current print job. Processor 1 14 then proceeds to initial print operations depicted in Fig. 10D, as indicated by an encircled letter D in Figs. 10C and 10D. If processor 114 determines at check 322 that the number encoded in file page counter 206 is greater than 8, the processor enters into the printing subroutine of Fig.

10E, as indicated by an encircled letter E in Figs. 10C and 10E.

If processor 114 finds at decision junction 296 that the contents of file page counter

206 are an odd number (a front side of a sheet), the processor moves text and graphics of the

standard final page from internal memory area 212 to page build buffer 252 in a step 324,

builds the page in a step 326, moves the contents of the page build buffer to LPT1 print buffer 120 (Fig. 5) in a step 328, clears the page build buffer in a step 330, and increment file page counter 206 in a step 332 Processor 1 14 then accesses another internal memory area 334 and

moves a blank page from that memory area to page build buffer 252 in a step 336 and builds

the page in a step 338 At that juncture, processor 1 14 the end-of-record processing subroutine sequence starting with step 302

In a first inquiry 340 in the printing subroutine of Fig 10D, processor 1 14 checks

whether the first printer 12 or 72 is ready and makes the printer ready in a step 344, if necessary Processor 114 then monitors the position of the paper at a query 346 and positions

the paper, if required, in a step 348 Subsequently, processor 1 14 transmits the contents of LPT1 print buffer 120 (Fig 5) to the first printer 12 (Fig 1 ) or 72 (Fig 4) in a step 350 and

transmits a print command to that printer in a step 352 After the transmission of a print command to the first printer 12 or 72 in step 352, processor 1 14 institutes a check 354 as to whether printing was successful If so, LPT1 print buffer 120 is cleared in a step 356 and the

processor returns to the core page processing subroutine of Fig 10B If not, the first printer

12 or 72 is idled in a step 358, while processor 1 14 searches for the fault in an investigation

360 and displays an error message regarding the fault in a step 362 After the operator

rectifies the printing error, as confirmed by processor 1 14 in a step 364, the processor returns to the start of printing operations in Fig 10 A, as indicated by an encircled letter A in Figs 10D

and 10A

When utilizing both printers 12 (or 72) and 14 (or 74), processor 1 14 executes the

subroutine of Fig 10E Processor 1 14 first confirms at 366 whether the first printer 12 or 72

is ready and rectifies the situation in a step 368, if necessary Processor 1 14 then verifies the

position of the first printer's paper at 370 and locates the paper, if required, in a step 372 In a

step 374, processor 1 14 sends the contents of LPT1 print buffer 120 (Fig 5) to the first printer

12 or 72 Processor 1 14 then detects at 376 whether the second printer 14 (Fig 1) or 74 (Fig 4) is ready and, in the event that the second printer is not ready, corrects the printer's readiness in a step 378 Once the printer is ready, processor 1 14 scans the positioning of the paper at a junction 380 and arranges the paper in a step 382, if called for When the second printer 14 or

74 and its paper are prepared, processor 114 transfers the contents of fifth buffer E of LPT2

print buffers 122 to the second printer in a step 384 Processor 1 14 then transmits print

commands to the two printers in respective steps 386 and 388 and retards the execution of that

print command by an interval of a predetermined number of milliseconds (step 390)

In an inquiry 392, processor 1 14 determines whether printing has been successful If

there is a problem with the printing, the processor executes an error handling subroutine shown in Fig 1 OF If the printing proceeds as intended, processor 1 14 makes a check 394 as to whether the last record in the queue 1 10 or 112 has just been printed and that there are further

records in the other print queue 1 12 or 1 10 If the check yields an affirmative determination,

processor 1 14 proceeds to the last-record subroutine of Fig 10G, to switch printing to the

other queue A negative determination at check 394 leads processor 1 14 to inquire at 396 as

to whether the job has been finished, i e , whether both queues 1 10 and 1 12 are empty If so,

processor 1 14 executes end-of-job processing (Fig 10H) If not, processor clears LPT1 print buffer 120 in a step 398 and buffer E of LPT2 print buffers 122 in a step 400

As illustrated in Fig 10F, processor 1 14 first idles both printers in a step 402 when a

printing error or malfunction has been detected Processor 1 14 then determines the nature of

the fault in a step 404, displays an error message in a step 406, and awaits operator intervention in a step 408 Upon rectification of the error by human intervention, processor

1 14 queries at 410 whether the printing is being done on continuous form sheets If

continuous sheets are being used, processor 1 14 first waits in a step 412 for the operator to

form feed to the first printer 12 or 72 the equivalent of four blank print forms (where there is a four page delay between the first printer 12 or 72 and the second printer 14 or 74). A message

may be displayed at this point to remind the operator of the procedure. If printing is being

undertaken on separate sheets, processor 1 14 waits in a step 414 for the operator to form feed a single print form to the first printer 12 or 72. Again, a message may be displayed at this point to remind the operator of the proper procedure. In subsequent steps 416 and 418, the

processor waits while the operator removes and disposes of pages representing records which

will be reprocessed and clears and resets both printers. Again, prompts may be provided to the operator to ensure that proper rectification steps are performed.

At a decision junction 420, processor 1 14 investigates the contents of file page counter

206. If the file page counter contains an odd numeral, processor 1 14 decrements record counter 204 in a step 422. If the file page counter contains an even numeral, processor 114 first increments file page counter 206 in a step 424. Subsequently, processor 114 sets the

contents of record page counter 208 at unity in steps 426 and 428, sets the contents of active

record page register 234 at unity in steps 430 and 432, and sets the contents of register 242 at unity in steps 434 and 436. Processor 1 14 then clears LPTl print buffer 120 and buffers A-E

of LPT2 print buffers 12 in steps 438 and 440 and returns to decision junction 248 at the

beginning of the core page processing subroutine in Fig. 10B.

Fig. 10G depicts a subroutine for switching from one input queue 1 10 or 112 to the other during the processing of a single print job. Thus, the last-record subroutine of Fig. 10G

serves to begin a portion of a print job stored in the other input queue 1 12 or 110 and for

loading further print data from a mainframe, etc., 38 into the queue 110 or 112 holding the job

portion which has just been printed. Processor 114 makes a check 442 into the state of a

memory or software switch 444 to determine whether the second input queue 112 is active, i.e., has been accessed by the processor during a printing operation. If so, processor 114 switches to the first input queue 1 10 in a step 446, rebuilds or reloads the second input queue

1 12 in a step 448 and sets a memory or software switch 444 for the second queue 112 to an

inactive state in a step 450. If the second input queue 1 12 is not active, as established at check 442, processor 1 14 switches to that second queue in a step 452, rebuilds the first input queue 110 in a step 454, and sets memory or software switch 444 to an active state in a step 456.

As illustrated in Fig. 10H, a subroutine executed at the end of a print job begins with processor 1 14 accesses record page counter 208 to determine in an inquiry 458 whether the file page number is greater than 8. If so, processor ] 14 terminates processing operations in a

step 460 and displays a message in a step 462 indicating that the job has been finished. If the

page number in file page counter 208 is eight or less, processor 1 14 moves a blank page from

internal memory area 334 to page build buffer 252 in a step 464, builds a page at 466, moves the contents of the page build buffer to LPTl print buffer 120 (Fig. 5) in a step 468, and clears

page build buffer 252 in a step 470. Processor 1 14 then moves the contents of the active print

buffer B, C, or D of LPT2 print buffers 122 to buffer E of print buffers 122 in a step 472 and subsequently accesses internal memory register 242 in an investigation 474 to determine whether the active LPT2 print buffer is the fourth buffer D. If so, processor 114 zeroes the active LPT2 print buffer register 242 in a step 476. Processor 1 14 then increments register

242 in a step 478, and increments record page counter 208 in a step 480. After incrementing the record page counter, processor 1 14 executes the printing routine of Fig. 10E.

It is recommended that woven or smooth paper be used, rather than "laid" or textured

paper. Paper weight should be at least 20 lb. and the printers will accept 24 to 28 lb. Good

results have been obtained with Hammeril Laser 24 lb. bond single sheets and Hewlett-Packard "Z-fold" continuous form stripped of perforated side strips.

Cost savings can be realized by eliminating the letter paper tray, rollers for raising paper from the paper tray, and rollers used to push printed documents out the tops of the printers. Antistatic material, laminates or coatings effective at different humidities can be

provided for the various guide surfaces. Japanese patent document No. 116807 discloses such

materials with respect to lids and bags.

In the embodiment of Fig. 1 (continuous form sheet feed), one or more photoelectric sensors (not shown) may be provided for monitoring the paper path. Upon a detecting of light, indicating that the paper form has been interrupted, a signal from the photosensor(s) triggers

an error condition.

As illustrated in Figs. 1 1-13, a desk-top laser printer has a housing 500 provided with a paper input port 502, a paper output port 504 and a data input port 506. Data input port 506 is connected to a digital processor 508 which is disposed in housing 500 and which is

programmed to detect odd pages and even pages in an electronically encoded document

arriving via data input port 506 and to separate odd pages of the document from even pages thereof. A single print engine assembly 510 is provided in housing 500 and includes a motor or

drive (not separately illustrated) operatively coupled to a plurality of rollers 514, 516, and 518

for moving a paper sheet 520 through printer housing 500 from paper input port 502 to paper

output port 504 along a predetermined path 522.

Path 522 includes a linear segment 524 along which two laser printing assemblies 526 and 528 are disposed at respective print stations. The first laser printing assembly 526 is

disposed in housing 500 along an upper side of path segment 524 for printing an odd- numbered page of the document on a first side of paper sheet 520. The second laser printing

assembly 528 is disposed in housing 500 along a lower side of path segment 524 for printing an

even-numbered page of the document along an opposite side of paper sheet 520. Processor

508 is operatively connected to the laser printing assemblies 526 and 528 for controlling the printing assemblies to print consecutive odd and even pages of the document on opposite sides of a train of paper sheets The paper sheets may be separate single sheets or sheets connected

to one another in a Z-fold, as described above.

Because paper sheet 520 travels along a linear or straight path segment 524 from one laser printing assembly 526 to the other 528, the paper is easily aligned There is less paper

jamming and less paper warping than there would be in a printer with a curved paper path

between the two laser print stations

As illustrated in Figs 1 1 and 12, laser printing assembly 526 includes a drum 530 having a surface made of an organic photoconductive material, a toner reservoir 532 containing a toner powder 534, a laser source 536 including directional optics (not separately

illustrated), a toner waste reservoir 538, an erase lamp 540, and a corona wire 542. A magnetic developer roller 544 is provided at an outlet of the toner reservoir 532 for drawing toner from the reservoir through a gap defined by a so-called doctor blade 546 and for

enhancing the magnetic properties of the toner

The toner which is delivered to photoconductive drum 530 by developer roller 544 is

magnetically attached to the drum at points which were exposed to radiation 548 from source 536 The toner particles on drum 530 are transferred to an upper surface of paper sheet 520

from the drum, while maintaining the relative distribution pattern of the toner This transfer is

also effectuated via magnetic attraction between the toner particles and the paper which is magnetized by a corona wire 550 Subsequently, the toner is melted and fused to the paper by heat and pressure applied via a fuser roller 552 and a pressure roller 554 The surface

temperature of the fuser roller 550 is raised by a heater lamp 556 provided in a fuser casing 558

Toner particles remaining on drum 530 after toner transfer to paper 520 are removed from drum 530 by a wiper blade 560 and fall into waste reservoir 538 having a separator baffle 564. Erase lamp 540 irradiates drum 530 for purposes of clearing residual charge on the drum. Corona wire 542 then deposits a uniform charge distribution on drum 530 prior to irradiation of drum with laser energy from source 536 in a pattern determined by the content of a

document encoded in a signal transmitted from a mainframe or other computer over data input port 506 to processor 508.

Laser printing assembly 528 is substantially similar to laser printing assembly 526. As

depicted in Figs. 11 and 13, laser printing assembly 528 includes a photoconductive drum 566,

a toner reservoir 568 holding a toner powder 570, a scanning laser source 572, a toner waste

reservoir 574, an erase lamp 576, and a corona wire 578. A magnetic developer roller 580 disposed at an outlet of toner reservoir 568 extracts toner from the reservoir through a gap

between the developer roller and a doctor blade 582 and for enhancing magnetic fields of the

toner particles.

The toner particles deposited on drum 566 in a predetermined pattern are transferred

via magnetic attraction to a lower surface of paper sheet 520, while maintaining the same

pattern. The transferred toner is melted and fused to paper sheet 520 by heat and pressure

applied via a fuser roller 584 and a pressure roller 586. Fuser roller 584 is mounted to a fuser

casing 588 and is heated by a lamp 590 provided in casing 588.

Toner particles remaining on drum 566 after toner transfer to the lower surface of

paper sheet 520 are removed from drum 566 by a wiper blade 592 and fall into waste reservoir 574. Waste reservoir 574 does not have a baffle (see baffle 564 of laser printing assembly

526). Erase lamp 576 clears residual charge from drum 566, while corona wire 578 deposits a

uniform charge distribution on drum 566 prior to irradiation of the drum with laser energy

from source 572. As shown in Fig 14, processor 508 includes a memory 594 which stores decoding instructions for different types of computers and different database programs. In response to

instructions from RAM resident control software 596, a control unit 598 accesses memory 594

to enable the control unit to detect different pages of the multiple page document received by a buffer/interface 600 from a mainframe or other document-generating computer via data input

port 506. The incoming multiple page document is temporarily stored in buffer 600.

Control unit 598 has an internal structure and operation similar to that described

hereinabove with reference to control unit 56 and Fig 3 Thus, control unit 598 also includes page splitter module 60 (Fig 3) for detecting and splitting the odd pages from the even pages

in a multiple page document arriving via data input port 506 Page splitter module 60 (Fig. 3)

feeds the odd pages in sequence to laser source 536 (Figs 1 1 and 12) via an interface module 602 and feeds the even pages in sequence to laser source 572 (Figs 1 1 and 13) via delay or buffer 64 (Fig 3) and an interface module 603 (Fig. 14) In the printer of Figs 11-14, a

timing signal from a time base 605 in processor 508 controls delay 64 to postpone the

transmission of the even page sequence to laser printing assembly 528 by an interval substantially equal to the transit time of paper sheet 520 from one laser printing assembly 526 to the next 528, thereby synchronizing the operation of the two laser printing assemblies so

that opposite sides of essentially every sheet of sheet 520 bear consecutive pages The

operation of programming selector 70 is as discussed above As illustrated in Fig 15, laser printing assemblies 526 and 528 are mounted to a

carriage 604 in housing 500 Housing 500 is provided with a front panel 606 hinged for

swinging sideways, as shown, to enable a moving of carriage 604 at least partially out of the

housing To that end, carriage 604 is translatably mounted to housing 500, e.g., via roller

bearings, (not shown) Accordingly, laser printing assemblies 526 and 528 may be easily removed from housing 500 for servicing. Laser printing assembly 526 is mounted to an upper

side of carriage 604, while laser printing assembly 528 is mounted to an underside of carriage

604. Toner cartridge or reservoir 532 of laser printing assembly 526 is replaced from above

carriage 604 whereas toner cartridge or reservoir 568 of laser printing assembly 528 is

removed from below the carriage.

Processor 508 is programmed, as described above, to generate a printed document from (1) encoded information peculiar to the document and (2) standard textual and graphic

information incorporated into a plurality of documents

As illustrated in Figs. 12 and 13, pressure rollers 554 and 586 may be implemented as fuser rollers which are disposed in respective fuser casings 608 and 610. The provision of fuser rollers on opposite sides of paper sheet 520 at toner fusing stations serves to eliminate paper warping which occurs when one side of a paper sheet is heated. The elimination of heat-

induced paper warping reduces incidents of paper misalignment and jamming.

Although the invention has been described in terms of particular embodiments and

applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of

the claimed invention. For example, it may be possible to print even pages of a document with the first printer 12 or 72 and odd pages with the second printer 14 or 74. Accordingly, it is to

be understood that the drawings and descriptions herein are proffered by way of example to

facilitate comprehension of the invention and should not be construed to limit the scope

thereof.

Claims

CLAIMS:

1. A printing system comprising:

a desktop-type first laser printer assembly;

a desktop-type second laser printer assembly; a digital processor operatively connected to said first laser printer assembly and said

second laser printer assembly, said processor being programmed to detect odd pages and even

pages in an electronically encoded document, to separate odd pages from even pages, and to

transmit odd pages of said document to said first laser printer assembly and even pages of said document to said second laser printer assembly; and a paper guide disposed between said first laser printer assembly and said second laser

printer assembly for guiding paper from a paper output port of said first laser printer assembly to a paper feed port of said second laser printer assembly

2. The printing system set forth in claim 1 wherein said first laser printer assembly and

said second laser printer assembly are disposed one above the other, said paper being simply

inverted by said paper guide in a U or C shape between said output port and said paper feed port.

3. The printing system set forth in claim 2 wherein a multiple-page continuous web of paper extends from said paper output port to said paper feed port, said paper guide including a tensioning device for providing a strip of said web between said paper output port and said paper feed port with a predetermined amount of tension

4. The printing system set forth in claim 3 wherein said tensioning device is spring loaded.

5 The printing system set forth in claim 3 wherein said tensioning device places an electrically grounded element in contact with said web

6 The printing system set forth in claim 1 wherein said paper includes a series of paper sheet portions, said processor including page splitting means for detecting odd pages and even

pages in said document and separating odd pages from even pages, said processor further

including synchronizing means for timing the operation of said first laser printer assembly and

said second laser printer assembly so that opposite sides of essentially every sheet portion bear

consecutive pages

7 The printing system set forth in claim 1 wherein said first laser printer assembly and said second laser printer assembly are off-the-shelf laser printers

8 The printing system set forth in claim 1 wherein said paper includes a series of

separate paper sheets, said guide including an arcuate surface extending up from said paper

feed port at least partially to said paper output port

9 The printing system set forth in claim 8 wherein said paper guide further include an

opened door at said paper output port

10 The printing system set forth in claim 1 wherein said first laser printer assembly and

said second laser printer assembly are disposed in a common housing and on opposite sides of a paper feed path extending through said housing from a main paper input port to a main paper output port, further comprising paper moving means disposed in said housing for moving said

paper through said printer housing from said main paper input port to said main paper output port along said path

1 1 The printing system set forth in claim 10 wherein said path is essentially linear, one

of the laser printing assemblies being located above said path and the other of said laser printing assemblies being located below said path

12 The printing system set forth in claim 11, further comprising a carriage movably

mounted to said housing, said printing assemblies being mounted to said carriage for enabling an extraction of said laser printing assemblies from said housing for servicing

13 The printing system set forth in claim 12 wherein one of said laser printing assemblies is mounted to an upper side of said carriage, the other of said laser printing assemblies being mounted to an underside of said carriage, whereby a toner cartridge of said one of said laser printing assemblies is removed from above said carriage whereas a toner

cartridge of said other of said laser printing assemblies is removed from below said carriage

14 The printing system set forth in claim 13 wherein said paper moving means includes

only one print engine

15 The printing system set forth in claim 10 wherein said first laser printing assembly

and said second laser printing assembly each include a drum having a photosensitive surface, a toner reservoir, a laser, a toner waste reservoir, an erase lamp, and a corona wire.

16. The printing system set forth in claim 10 wherein said paper moving means includes only one print engine.

17. The printing system set forth in claim 1 wherein said processor is programmed to generate said document from (1) encoded information peculiar to said document and (2)

standard textual and graphic information incorporated into a plurality of documents.

18. A printing method comprising:

providing:

a first printer assembly for printing documents encoded in

computer generated digital signals;

a second printer assembly for printing documents encoded in

computer generated digital signals; and

a digital processor for generating a digital signal encoding a multiple page document; transmitting odd pages of said multiple page document in encoded form from said processor to one of said first printer assembly and said second printer assembly and even pages

of said multiple page document from said processor to the other of said first printer assembly and said second printer assembly,

feeding paper sheet portions from a paper output port of said first printer assembly to a

paper feed port of said second printer assembly; and

operating said first printer assembly and said second printer assembly to print on opposite sides of a plurality of said paper sheet portions so that opposite sides of essentially every printed sheet portion bear consecutive pages

19. The printing method set forth in claim 18, further comprising operating said

processor to detect odd pages and even pages in said document and to separate odd pages

from even pages, also comprising operating said processor to time the operation of said first printer assembly and said second printer assembly so thai opposite sides of essentially every

sheet portion bear consecutive pages

20. The printing method set forth in claim 18, further comprising disposing said first printer assembly and said second printer assembly one above the other, the feeding of said

paper sheets portions including simply inverting said paper sheet portions along a U- or C-

shaped path between said output port and said paper feed port

21. The method set forth in claim 18, wherein the laser printer assemblies are disposed

in a single desk-top housing, said processor also being disposed in said housing, said paper sheet portions being moved through said housing from a main paper input port to a main paper

output port along a predetermined path, said laser printing assemblies being disposed along opposite sides of said path, said laser printing assemblies being mounted to a carriage in turn

movably mounted to said housing, further comprising moving said carriage and said laser

printing assemblies at least partially out of said housing for equipment servicing purposes

22 The printing method set forth in claim 21 wherein one of said laser printing

assemblies is mounted to an upper side of said carriage, the other of said laser printing assemblies being mounted to an underside of said carriage, further comprising removing a toner cartridge of said one of said laser printing assemblies from above said carriage and a

toner cartridge of said other of said laser printing assemblies from below said carriage.

23 The printing method set forth in claim 18, further comprising operating said

processor to generate said document from (1) encoded information peculiar to said document

and (2) standard textual and graphic information incorporated into a plurality of documents