CA1086231A - Document copying apparatus with electronic collating memory - Google Patents

Abstract

Abstract Or the Disclosure Disclosed herein is a document copier which features an electronic collator for automatically producing collated multipage copies of a multipage original. m e copier includes a document reader com-ponent for producing electrical signals representative of the image information contained by the lndlvldual pages Or the multipage original. m e electronic collator includes an addressable multipage memory, responsive to the signals produced by the document reader, for storing an electronic representation of the image information in the multipage original document, and a programmable central processing unit for extracting the stored image information in a predetermined sequence and for repe-titively applying signals representative of such stored information to a printing component. The latter records image information on discrete copy sheets and delivers the copy sheets in a selectable order, such as the page order of the original document. The electronic collator obviates the need of conventional copiers to use either a mechanical sorter to collate the copier output, or a recirculating document feeder to collate the copier input.

Description

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BACKGROUND OF THE INVENTION
Field of the Invention ` The present invention relates to document copying apparatus, and more particularly to an improved apparatus and method for automatically producing a plurality of collated copies of a multipage document.

Description of the Prior Art Conventional document copiers are capable of auto-matically producing a plurality of collated copies of a multi-page original document. Some such copiers effect collation through the use of a sorter mechanism which mechanically sorts the copier output into a plurality of copy sheet receiving bins. More sophisticated copiers effect collation through the ~;~ use of a so-called recirculating document feeder which, in effect, collates the copier input so that the copier output emerges in a collated form. The recirculating document feeder successively presents each page of a multipage original to a document copying position. After each page is copied once, thereby producing a single collated copy of the multipage original, the individual pages of the original are recircu-lated past the document copying position to make additional collated copies, one collated multipage copy for each recir-culation of the multipage original.
While both the sorter mechanism and the recirculating document feeder have proven to be reliable accessories for a document copier, both have certain drawbacks. -For instance, sorter mechanisms are relatively expensive to manufacture and massive in size. Recirculating feeders, on the other hand, subject the original document pages to considerable wear ; inasmuch as each page must be handled once for each collated r i, 2- ;~
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^ "-`` 1~86~31 copy desired. Further, both sorter and recirculating document feeder require that the original document be available to the document copier during the entire copy-making process.

SUMMARY OF THE INVENTION
By the present invention we have provided document copying apparatus wherein a series of electrical signals which are representative of image information on the individual pages of a multipage original document which is to be copied are received by an addressable multiple-page memory for 10 temporary storage. The stored signals are applied to printer means in a page sequence such that a copy of the original multipage document is produced, the pages of the copy being in the same order as the original document pages. After the first collated copy is printed, the stored signals may - again be applied to the printer means in the same sequence until a desired plurality of collated copies is produced.
By such apparatus, we have provided a document copier with the capability of producing a plurality of collated copies of a multipage document without resorting to either the aforementioned recirculation or sorting methods of the prior art.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below.

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BRIEF DESCRIPTION OF THE DRAWINGS
In the detailed description of the preferred embodi-ment of the invention presented below, reference is made to the accompanying drawings in which:
Fig. 1 is a block diagram of various components of the present invention;
Fig. 2 is a schematic view of a document reading device which may be used in conjunction with the present invention;
Fig. 3 is a schematic view of an electrographic printing apparatus which may be used in con~unction with the present invention; and Fig. 4 is a view, similar to Fig. 1, showing a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, the term "document copier" refers t~
to apparatus adapted to read the image information on an original document and to form a second document containing such image information. Further, a "document" refers to any medium bearing visible information; it may include, for .. ~
instance, typewritten information on paper, blueprints, microfiche, etc. An "original" document merely refers to ,. ~
the document being copied; it should not be viewed in the ; limited sense as being in the form of the original manu-script or first-made document.
Referring to Fig. 1 and 2, a document reader 10 is adapted to produce electrical signals representative of the "

image information in an original document. A beam 11 from a ;'~ :
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light source 12, such as a laser source, is incident on cylindrical optics 13 which spreads the beam to form a long, narrow sheet beam and "line" image on the document being scanned at an exposure station 14 so that, after being reflected by a pair of mirrors 15 and 16, the line image scans along an original document from end to end. A relay - -lens 17 transfers the sheet beam to an intermediate pupil plane on the surface of page scan mirror 16. The sheet beam passes through a final imaging lens 18 to provide a good planar image field at exposure station 14. -The original document is shown as a reflective print, and the reflected light beam is once more reflected by page scan mirror 16, driven by a page scan galvanometer 19, through an imaging lens 20 to a charge-coupled device (CCD) array 21 so that successive line scans by array 21 progress down the original document in synchronism with page scan of the illuminating sheet beam. We have constructed a CCD unit 22 of a Fairchild Corp. CCD 121 linear array and a Fairchild demonstration board for the CCD 121. The demonstration board includes a multiphase , . .
clock source 23 to operate the CCD array, a master oscillator 24 to provide line synchronization signals, as explained hereinafter, s and an amplifier 25 for the CCD output. -A document feeder 26 is schematically shown in Figs.
l and 2 for transporting pages of the original document set 27 to exposure station 14. Feeder 26 includes a control unit ; to be discussed in full hereinafter.
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Document reader 10 may take various forms other than as shown in Fig. 2. For instance, U.S. Patent No. 3,783,185, which issued to Richard A. Spaulding on January 1, 1974, ' 30 discloses a document reader in which a scanning light source - directed through a color transparency impinges upon a set of vhree photosensors which are each sensitive to a different one of the selected wavelengths, e.g., red, green or blue.

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~'36231 The photosensors produce electrical signals representative of the red, green and blue information in the transparency.
Another form of document scanning apparatus is disclosed in commonly assigned, copending U.S. Patent :~ B Application ~Qo,~3c, filed May 27, 1975, and such an apparatus would be equally suitable for purpoçes of the present invention.
Those skilled in the art will readily understand that there are many known document readers which are suitable for con-verting visible information on a medium to electrical signals representative of such information.
The output signals of CCD unit 22 of document reader 10 is in analog form and is applied via a communication link 28 to an analog-to-digital converter 29 which changes the signal to a digital set of discrete output levels. This digital data, along with unique sync signals to delineate separate scan lines and page information, transmitted along A communic~ation links ~Ç 31 and 32, respectively, are applied to a read buffer controller 33. The line scan synchronization signals of link 31 may be derived from master oscillator 24 20 which emits a pulse at the start of each line scan by CCD array ;C 21. The page scan sync signals of link 32 may be derived from an incremental shaft angle encoder (S.A.E.) 34 associated with galvanometer motor 19. S.A.E. 34 emits an electrical pulse at the start of each page scan.
Read buffer controller 33 clocks image information ....
signals in an N-bit parallel pattern into one of a pair of read buffers 35 and 36 for temporary storage. Read buffer controller 33 uses conventional up/down counters of a modulus N;
modulus N depending on the size of a pair of read buffers 35 and 30 36. The read buffer controller gates the parallel data to one .
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~36~31 '' of the read buffers depending upon the state of a digital gate therein. Clocking into the read buffer controller is provided .~ ~/f~phq~ e,

2 by conventional means using miltlph~e clock 23 as a clock 1~
source The read buffer controller also provides, by the counting of N parallel bits of encoded data, the necessary addressing for the read buffers- as the read buffers are filled.
Buffers 35 and 36 may take any of a number of forms well known to those skilled in the art, such as for example bi-polar, metal oxide semiconductor (MOS) or charge-coupled device ~; 10 (CCD) memories. For instance, the read buffer memories may be Intel Corporation's Static MOS random access memories No. 2102A
with random logic components as set forth in that company's "Memory Design Handbook" of 1975, pages 7-15. In such event, : read buffer controller 33 may be Digital Equipment Corporation's logic card No. M238 dual synchronous up/down counters together .~,:
with appropriate gating logic.
When one of read buffers 35 and 36 is full as determined by the up/down counters in controller 33, the con-troller so informs a central processor unit (CPU) 37 by means of a vectored interrupt signal. CPU 37 may, for example, be a mini-computer such as the PDP-ll series of mini-computers manufactured by Digital Equipment Corp., and is adapted to perform arithmetic and logic operations and instruction decoding as well as controlling time allocation of peripherals `~- through a bus 38. All computer system components and . peripherals connect to and communicate with each other on bus 38, which may be a UNIBUS manufactured by Digital Equipment Corporation. Communication between controller 33 and bus 38 may be through a general-purpose interface 39 (such as Digital 30 Equipment Corporation's DRll-C) consisting of three functional sections: address selection logic, interrupt control logic and device interface logic.

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~ 1086231 A direct memory access interface 40 (such as Digital Equipment Corporation's DRll-B) operates directly to or from memory and consists of four registers: command and status, word count, bus address and data. Interface 40 provides communication between read buffers 3~, and 36~ and bus 3~. Using conventional software bookkeeping techniques, the bus address for read buffer data is stored in a read/write memory 4l for future retrieval when the encoded data is interfaced to bus 38 by direct memory access interface 40 for storage in one of two main memories 42 and 43 by a memory controller 44. Main memories 42 and 43, and memory controller 44 may take the form af a System Industries, Inc., of Sunnyvale, Calif., disk storage system Model 9500. The bookkeeping task has kept track of all reader buffer transfers to the main memories, and when a page sync signal is sensed by read buffer controller 33, another vector interrupt signal is generated to CPU 37 to allow the CPU
to keep only the starting and ending main memory addresses for i that page in read/write memory 41. Each main, or multi-page, memory 42 and 43 is large enough to store information from a 20 predetermined plurality of original documents. -For purposes of this disclosure, memory devices may be classified as being either "totally accessible", wherein simultaneous requests for access to two different addresses :! can be honored, or "not totally accessible", wherein only those addresses in a particular subset can be accessed at the same time. In the embodiment of Fig. l, we have used "not totally accessible" main memories l4~ and 42, which may be typified by conventional moving-head magnetic disks.
In such a memory, only those addresses lying in a subset 30 called a "cylinder" ean be addressed at the same time. In a :, .
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` copy duplicator as disclosed herein, the file maintenance problem is not solvable if only one such memory is used since the reader and the printer will generally not be working out of the same subset.
: The binary data may be received at read buffer controller .
33 from reader 10 at a rate different than it can be transmitted to main memories 42 and 43. Such a difference is due to the fact that the main memories can be loaded at a rate different than that at which reader 10 runs and the fact that the main memories may not be conditioned to receive data at the same ~:, instant that reader 10 begins transmitting.
For instance, if main memories 42 and 43 are moving-~J'.: ~
head magnetic disk memories, they are typically capable of storing 16-2/3 milliseconds of data transfer time (N bits) per disk revolution following the detection of a header-trailer label on the disk by the magnetic head, and reader operation would have to be delayed until such a label is reached. In the worst case, this might be a full 16-2/3 milliseconds after the reader is ready to transmit. Therefore, read buffer controller 33 operates to load one of read buffers 35 and 36 while the other read buffer is transmltting, or waiting to trans-mit, data to a main memory. That is, direct memory access inter-face 40 provides communication between one read buffer and bus 38 while the other read buffer is connected to converter 29.
In the case of the described magnetic disk memories, each read buffer is preferably capable of storing N bits of data.
Of course, if other forms of main memories are used, the read buffer size and the up/down counters of read buffer controller 33 should match the capabilities of the memories.
As an example of the functions of the elements so far described it will be assumed that the operator desires to make eight collated sets of copies of an original document ... .

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set of, say, twenty original document pages stacked in document feeder 26. The operator sets a job control panel 4~ accordingly.
For purposes of this example, it will further be assumed that each main memory 42 and 43 is capable of storing only that information from fifteen original document pages. The job control panel may be a switch and indicator panel which programs CPU 37 through a general-purpose interface 48 similar to previously described interface 39.
Now, CPU 37 starts in a subroutine pre-programmed according to the switches on control panel 45 to command a reader control unit 49 to begin operation. Reader control unit 49 communicates with the CPU through another general-purpose interface 50 to activate feeder 26, whlch in turn moves a document into exposure station 14. Reader control unit 49 turns on light source 12 and CCD array 21 receives reflected or transmitted light from the document.

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As the scanning progresses, data (including image information and sync signals) are received by, say, read buffer 35 and stored. When read buffer controller 33 has allowed N
bits of data to be transmitted to read buffer 35, the stored data is transmitted to, say, main memory 42 in the manner described, and the encoded data stream is switched over to read buffer 36 CPU 37 monitors the counting operation so that document scanning will be interrupted if both read buffers are full. However, this is not likely to occur since the scanning operation is inherently slow compared to the circuit functions.
;. When read buffer controller 33 has allowed N bits of data to be transmitted to read buffer 36, the data in read buffer 36 can now be transmitted to main memory 42.

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As subsequent original documents are scanned, the processes described above are repeated until either all of the original documents have been scanned and the data therefrom stored in main memory 42 or until that memory is full. It will ; be recalled that in the illustrative example, the operator desi-res to copy a set of twenty original document pages and that each main memory is capable of storing only that data from approximately fifteen original document pages.
CPU 37 is pre-programmed with the capacity of the main memories and a bookkeeping function to keep track of the data loaded into such memories. When main memory 42 becomes full, CPU 37 causes memory controller 44 to begin addressing into main memory 43. Now data can be removed from main memory 42 and transmitted to one of a pair of print buffers 52 and 54 (which may be of a form similar to read buffers 35 and 36) by means of a direct memory access interface 56 (similar to DMA 40) which provides communication between print buffers 52 and 54 and bus 38. Clocking out of a print buffer controller 60, which may be similar to read buffer controller 33 and include up/down counters, to gate data from one of the print buffers, is provided by means using a clock source in a printer ~2 and transmitted via link 63. Communication between controller 60 and bus 38 may be through an interface 64 similar to interface 39.
- In this manner, one print buffer is transmitting data to the printer, the other print buffer can receive data from a main memory, and the printer need not wait for the read head of the ~ main memory to index to the proper disk track and find the -- header-trailer label The printer clock is asynchronous with the reader clock so that the reader and the printer can run at 30 different rates.

10~6~31 Printer 62 may take any of a number of forms selectable from prior art devices. For instance, the printing apparatus B disclosed in U.S. Patent No. 3,783,185, u. s . Patent ~pplic~tion Serial No. 5o,G32 filed May 27, 1975 or U.S. Patent No. 3,689,935 ~-may be used. Again, other suitable devices will occur to those skilled in the art, and one such device is shown in Fig. 3 !. wherein various stations of an electrographic apparatus 71 and an image forming apparatus 72 are schematically illustrated.
A source or radiation, such as a laser source 74, directs a beam through an acoustooptic modulator cell 76. The - modulator cell includes an acoustic transducer and modulates the laser beam by the electrical signals from a digital-to-analog converter 77, also shown in Fig. 1. The modulated beam is deflected at 78 in a manner as described in Spaulding U.S. Patent No.

3,783,185. The beam is focused onto a location 80 on a photo- ~-conductor web member or belt 82.
The photoconductor belt 82 includes a photoconductive layer with a conductive backing. For more specific disclosures, see commonly assigned U.S. Patent Nos. 3,615,406 and 3,615,41~1, both issued October 21, 1971.
The photoconductive belt 82 is trained about drive rollers 84, 85 and 86 and is rotated at a constant velocity by a conventional main drive train mechanism 88 under the control of pre-recorded program through link 89 from bus 38.
The moving photoconductive member 82 sequentially passes through a primary charging station 90 which may, for example, include a conventional corona charger adapted to charge the belt sur~ace to about 500 volts; -the position 80 wherein the light ray is focused onto the moving photoconductive member so that in an electrostatic latent image is formed by the selective .

; -12-lOB6~31 dissipation of charge; and into a development station 92 at which the latent image is contacted with finely divided charged toner particles that adhere to the photoconductive layer in a configuration defined by the latent image. The development station 92 may take various forms known in the art s~ch as a magnetic brush development apparatus. An exemplary development station is more fully disclosed in -commonly assigned U.S. Patent No. 3,5L~3,720 to Drexler et al.
Next, belt 82 enters a transfer station 94 in which the toner particles are transfèrred in the image con-figuration to the receiving surface of a copy sheet 96 on which it can be subsequently fused; before entering the primary charger 90, belt member 82 passes through a conventional cleaning station 98. Copy sheets 96 which may be plain paper or cut sheets of receivlng stock are stored in a hopper 100 -from where they are fed along a path defined by a continuously moving web 102 to transfer station 94. At the transfer station, the copy sheets are respectively brought into contact with the photoconductive belt 82 by way of rollers 85 and a press~lre roller 104, to cause the toner image to be transferred to copy sheet 96. Finally the transferred image is fused to the copy sheet at a station 106 from which the sheet is delivered into a receiver hopper 108.
As will be understood by those skilled in the art, ;~ the information from deflector 78 must be applied in timed relation with the movement of belt 82 so that the relative :.
- position of each discrete image portion on the belt corresponds to the relative position of its respective counterpart area of the original document. Shown schematically is a dotted-line connection 109 from main drive train mechanism 88 to`a conventional ,~ .

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` shaft angle encoder 110. The shaft encoder in turn applies a series of clock signals to print buffer controller 60 (Fig. 1) ; along dotted-line connection 63a (63 in Fig. 1) as mentioned hereinbefore. Line sync. signals derived from master oscillator 24 (Fig. 2) are applied along link 63b (63 in Fig. 1) to a swept ~ -frequency generator 112 (commercially available as a single unit such as Wavetek Corp.'s Model 1002 Sweep/Signal Generator) which includes a ramp generator and a voltage control oscillator.
Swept angle generator 112 converts line sinc. signals into a ~ -~
` 10 variable frequency signal for driving deflector 78.
While printer 62 is working out of one print buffer 52 or 54, the read head of main memory 42 indexes to the proper disk and track for the next N bits of data, as addressed in the read write memory of CPU 37, detects a header-trailer label and ~: begins transmitting data to the other read bùffer. Once all -~
the data stored in main memory 42 has been transmitted to printer 62 (approximately fifteen pages of the twenty-page original document set of the illustrative example), CPU 37, under program control causes removal of stored data from main memory 43 (which has been loaded with data from the last five pages of - the original document set while the printer was working out of main memory 42) for transmittal to the printer. After one copy of all twenty original documents has been printed, main memory 42 is made available to the printer and the process is repeated until the desired eight copy sets are printed. In this manner, all eight copy sets will be automatically collated at the printer output. -The above examples assumed that the original documents were one-sided and that the copies were one-sided. ~y the present invention, it is also possible to print two-sided copies from one-sided originals, one-sided copies from two-sided originals, and two-sided copies from two-sided originals.
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~One way to obtain collated two-sided copies from one-sided ~ originals involves setting control panel ~6 to program ; CPU 37 so that the content of every other original document page is printed on successive copy sheets. Then, the copies are turned over and recirculated through the printer so that the backs are printed with the content of the skipped original : documents.
To print one-sided copies from two-sided originals, one side of each original may be scanned and the information lO therefrom stored in the main memories. Then the originals are turned over and recirculated through exposure station 14 so that the information on the reverse sides may be scanned.
Now, to print, the information from the first original page -~
of the first scan is retrieved, then the information from the first original page of the second scan, then the information , ~ .
from the second original page of the first scan, then the :
; information from the second original page of the second scan, :`
etc. Two-sided coples from two-sided originals may be obtained in a similar manner, it being required only that ` 20 CPU 37 be pro~rammed to withdraw data from memories 42 and 43 in proper page sequence and that the original set ; and copy set be recirculated through the reader and the printer, respectively.
In Fig. 4, we have shown a schematic block diagram of a second embodiment of the invention. Elements of the . . .
- second embodiment which are identical to corresponding elements of the first embodiment have been given the same reference number with a prime mark thereafter. A detailed description of those elements is omitted, and the reader is - 30 referred to the preceding description for a full understanding of the following.

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~086;~1 It will be remembered that in the first embodiment, a pair of main memories 42 and 43 are provided so that the printer may operate out of one main memory while the reader is transmitting data to the other main memory. A pair of read buffers 35 and 36 are provided to reduce waiting time for transmitting data to and from the main memories which would result from the time required for the mechanical elements (the magnetic disks and the read/write head) of the main memories to set.
In ~he second embodiment shown in Fig. 4, data information from reader 10' is transferred to a "totally accessible" electronic memory 120 by way of a direct memory access interface 122 and bus 38' under program control of CPU 37'. It will be recalled that a "totally accessible"
memory is one wherein simultaneous requests for access to two greatly different addresses can be honored. Examples of such memories include core, drum, head-per-track disk and solid state memories using CCD's or magnetic bubbles The data information is transferred to digital to analog con-verter 77' and printer 62' via bus 38 and another direct memory access interface 124 for printing as described with reference to the first embodiment.
The invention has been described in detail with particular reference to preferred embodiments thereof, but ~,~t/~S
~ it will be understood that v~a~ons and modifications can n be effected within the spirit and scope of the in~ention.
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Claims (17)

What is Claimed is:

1. For use in a document copying apparatus of the type including (1) document reading means for producing electrical signals representative of the image information on each of the individual pages of a multipage document being copied; and (2) printer means responsive to applied signals for recording image information on discrete copy sheets;
electronic collating means for producing a plurality of multipage copies of the image information contained by the multipage document, the individual pages of each of such multi-page copies being arranged in a predetermined order, said electronic collating means comprising:
a) multipage memory means responsive to said electrical signals for storing information repre-sentative of said image information, said memory means having a storage capacity sufficient to store infor-mation representative of the image information on all of the individual pages of the multipage document;
and b) control means for repeatedly applying signals representative of said stored image information to said printer means in a selectable sequence, whereby a plurality of copies of the original multipage document may be produced with the individual pages of the multi-page copies being in a selectable order.

2. The invention as defined in claim 1 wherein said selectable sequence is such that the multipage copies are produced with the individual pages of the multipage copies being in the same predetermined order as the multi-page document.

3. The invention as defined in claim 1 wherein said multipage memory means comprises at least two memory units, and wherein said control means is operable in a first state for interconnecting one of said memory units and said reading means, interconnecting another of said memory units and said printer means, disconnecting said one memory unit and said printer means and disconnecting said other memory unit and said reading means, and is operable in a second state for interconnecting said one memory unit and said printer means, interconnecting said other memory unit and said reading means, disconnecting said one memory unit and said reading means, and disconnecting said other memory unit and said printer means, whereby, when said control means is operating in its first state, said one memory unit is available for receiving signals from said reading means and said other memory unit is available for applying signals to said printer means, and, when said control means is operating in its second state, said one memory unit is available for applying signals to said printer means and said other memory unit is available for receiving signals from said reading means.

4. The invention as defined in claim 1 wherein said memory means comprises a totally accessible memory unit, whereby simultaneous requests for access to different addresses can be honored so that said memory unit is simultaneously available to said reading means and said printing means.

5. The improvement as defined in claim 1 further comprising:

a pair of buffer memories adapted to receive, store and transmit electrical signals; and switching means operating in a first state for interconnecting one of said buffer memories and said reading means, interconnecting the other of said buffer memories and said multipage memory means, disconnecting said one buffer memory and said multipage memory means and disconnecting said other buffer memory and said reading means and, operable in a second state for interconnecting said one buffer memory and said multi-page memory means, interconnecting said other buffer memory and said reading means, disconnecting said one buffer memory and said reading means and disconnecting said other buffer memory and said multipage memory means, whereby, when said switching means is operating in its first state, said one buffer memory is available for receiving signals from said reading means and said other buffer memory is available for applying signals to said multipage memory means, and, when said switching means is in its second state, said one buffer memory is available for applying signals to said multipage memory means and said other buffer memory is available for receiving signals from said reading means.

6. In a document copying apparatus of the type including (1) document reading means for producing a series of electrical signals which are representative of image information on successive areas of a document set made up of a plurality of original document pages arranged in a predetermined order, (2) printer means responsive to applied signals for forming image portions on receiver pages, the image portions corresponding to the image information contained in said applied signals and (3) means associated with said reading means and said printer means for controlling the format of said image portions so that the relative position of each such image portion of a receiver page corresponds to the relative position of its respective counterpart area of the respective original document page; the improvement comprising:
multipage memory means, associated with said reading and printer means, for storing information in digital form representative of said electrical signals;
control means for extracting said digital infor-mation from said memory means and for repeatedly applying signals representative of said digital information to said printer means, said control means including a processing unit associated with said memory means, said unit including means for selecting the sequence which said control means repeatedly applies said stored signals to said printer means such that a plurality of multipage copies of the original multi-page document may be produced with the copy pages being in a predetermined order.

7. The invention as defined in claim 6 further comprising:
a first clock source for clocking said electrical signals from said reader means to said memory means, and a second clock source for clocking said electrical signals from said memory means to said printer means, said first and second clock sources being asynchronous, whereby said reader means and said printer means can operate at different speeds.

8. A method for making a plurality of collated sets of an original document set made up of a plurality of original document pages arranged in a predetermined order, said method comprising the steps of:
generating a series of electrical signals which are representative of image information of said original document set;
storing said electrical signals;
repeatedly applying said stored signals to a document printer in a selectable sequence such that a plurality of copy sets of the original document set are produced with the copy set pages in a predetermined order.

9. A document copier comprising:
a) a document reading means for producing electrical signals representative of the image information contained by each of the individual pages of a multipage docu-ment to be copied;
b) multipage memory means responsive to said electrical signals for storing an electronic represen-tation of the image information contained by all of the individual pages of the multipage document;
c) printing means responsive to applied analog signals for forming visible images on discrete copy sheets;
d) means for producing analog signals representa-tive of said stored representation of the image infor-mation; and e) control means for repeatedly applying said analog signals to said printing means in a selectable sequence, whereby a plurality of multisheet copies may be produced with the individual pages of the multisheet copies being arranged in the same selectable order and collectively containing the image information contained by the multipage document.

10. The invention as defined in claim 9 wherein said multipage memory means comprises at least two memory units, and wherein said control means operable in a first state for operatively interconnecting one of said memory units and said reading means, interconnecting another of said memory units and said printer means, disconnecting said one memory unit and said printer means and disconnecting said other memory unit and said reading means, and is operable in a second state for operatively interconnecting said one memory unit and said printer means, interconnecting said other memory unit and said reading means, disconnecting said one memory unit and said reading means, and disconnecting said other memory unit and said printer means, whereby, when said control means is operating in its first state, said one memory unit is available for receiving signals from said reading means and said other memory unit is available for applying signals to said printer means, and when said control means is operating in its second state, said one memory unit is available for applying signals to said printer means and said other memory unit is available for receiving signals from said reading means.

11. The invention as defined in claim 9 wherein said memory means comprises a totally accessible memory unit, whereby simultaneous requests for access to different addresses can be honored so that said memory unit is simul-taneously available to said reading means and said printing means.

12. The invention as defined in claim 9 further comprising:
a first clock source for clocking said electrical signals from said reader means to said memory means; and a second clock source for clocking said electrical signals from said memory means to said printer means, said first and second clock sources being asynchronous, whereby said reader means and said printer means can operate at different speeds.

13. The invention as defined by claim 9 wherein said document reading means comprises an array of charge-coupled devices, and means for imagewise exposing said array to the image information on each of the pages of the multi-page document to be copied.

14. The invention as defined by claim 13 wherein said array is a linear array and said exposing means comprises means for scanning an image of the image information on each document page across said linear array to produce a line-by-line exposure of the image information.

15. The invention as defined by claim 9 wherein said printing means comprises a photoconductive recording element and means for forming developable electrostatic images on said recording element.

16. The invention as defined by claim 15 wherein said image-forming means comprises means for uniformly electrostatically charging said recording element, a laser for producing an intense light beam, means for imparting relative movement between said beam and said recording element, and means for intensity-modulating said beam in accordance with the image information on the multipage docu-ment.

17. The invention as defined in claim 9 wherein said multipage memory means is adapted to receive said digital signals at the same time said control means applies said analog signals to said printing means.