CA1119239A - Reproduction scanning system having intermediate storage between input and output scanning stations - Google Patents

Abstract

D/76669/76674/76675/76677 Combination REPRODUCTION SCANNING SYSTEM HAVING INTERMEDIATE
STORAGE BETWEEN INPUT AND OUTPUT SCANNING STATIONS

ABSTRACT OF THE DISCLOSURE
A reproduction scanning system having inter-mediate storage between input and output scanning stations wherein an input document is scanned in first and second directions, the first direction being orthogonal to said second direction, and the electrical signals representative of information on said scanned document being stored on an intermediate storage member for storage, signal processing or data manipulation. The information stored in the storage member may be read out and reproduced on a' reproducing medium. Other system features include input scan reversal for alternate bound pages during bound volume scanning, synchronization of the system by a clock associated with the storage member, input/output interleaving with a print interrupt feature, image centering and edge fadeout for image reduction, and independent magni-fication demagnification by separately variable raster spacing.

Description

~g;239 BACKGROU~D OF T~ TION
Laser scanning techniques for writing or print~ng on~a medium sensitive to the laser beam ha~e been disclosed in the prior art as shown, for example, in U. S. Patent ~o. 3,922,485. In general, the laser beam is intensity modulated in accord~nce with information to be printed o~ a receiv~ng medium, the modulated laser beam be~ng directed to a ro~ating scanner, or reflector, such as a multi-faceted polygon. The rotat~ng scanner in tusn causes the ~odulated laser beam to scan, in sequence, across a sensitive medium located a distance away from the scanner. The ~formation conta~ned ~n the intensity dulated laser beam can be directly written on the medium if the medium is sensiti~e to the lases beam, or in an alternative embodiment, the laser beam can selectively , such as a photoconductor discharge a chasged insulating or semiconducting surface/
in accordance with ~he intensity of the beam. In the alt-rnative embodiment, the degree of charge dissipation corresponds to the information contained in the intensity of the laser beam. The areas of the medium which are not dischar~ed by the laser beam are subsequontly developed, for examp~e, by standard xerographic te~iques.
Present day copiers which are commercially available which utilize the xerographic process incl~de a platen upon which the document to be re~roduced is placad, the platen being flat or curved. The document is generally flood illuminated or scanned with light and the raflections therefrom are imaged via a copy lens to a charged photocon-duc.ive medium to discharse the medium in accordance with the image fcrmed on the document.
~he Telecopier~ 200, a facsimile transceiver

-2-manufactured by the Xerox Corporation, Stamord, Connecticut, directs re~lections from a laser scanned document onto a photosensitive transducer, ~he electrical signal output thereof being transmitted to another location and used to modulate a laser beam to reproduce the scanned document. ~owever, the Telecopier 200 is generally not considered a copier type device since, intOE alia, a sc G ing platen and other copier ~eatures are not a~ailable.
Although copiers now commercially available are not adapted to utilize scanning techniq~e to ~can a document placed on the copier platen line by line to produce a serial bit stream correspondlng to the scanned information (i.e. a ra~ter type scann~ng system), it would be advantageou~ if ~u~h copier~ could ~e modi~ied to incorporate the laser printing technique disclosed, for example, in the a~orementioned p~tent, the modified copier ~hus re~uiring a system which provide~ ~or two-d~men~ional raster input scanning. A system for two-dimensional raater input scanning which utilizes a laser, i9 d~scribed, for example, in U.S. Patent ~o.

3,970,359. U. S. Patent No. 4,012,585, issued March 15, 1977 assigned to the a~signee of the present invention, provides a flying spot scanning sys~em which is capa~le o~ scanning an unmod~lated beam to a reading station for reading a stationary document and a modulated beam to an imaging station for, inter alia, reproducing the scanned document thereat~
The availability of a copier which utilizes two-dimensional input scanning, such as the raster-type input scanning of a document placed on a platen and laser scanning techni~ues for wri~lng on-a~
laser sensitive medium would pro~ide many advantages inherent with the use of lasers and raster type input scanning, such as increase~ copying speeds and reso-lution. In particular, it would be advantageous if an intermediate storage medium was provided between the ~nput and output scanning stations to allow ~or mani-pulation and storage of the ~canned information, and, in partic~lar, to provide for electronic precollation which electronically arranges representations of images to allGw collated set~ of documents to be reproduced.
Other desirable feature~ of such a copier would ~nclude input scan reversal for alternate bound pzge3 during bound volume scanning, synchronization of the system by a clocX associated with the storage member, a synchronous 3~ system reducing the size and cost of a ~ buffer a~sociated therewith, input/output interleaving with a print interrupt feature, image centering and edge fadeout for image reduction, and independent magnification~demagni-fication by separately variable raster spacing.

SUMMA~Y OF ~ PRESENT I~VENTIO~
The present invention provides a reproduction scanning system hav~ng intermediate storage between lnput and output scann~ng stations wherein an input document is scanned ln irst and second directions, the first direction being orthogonal to said second direction, and the electrical signals representation of information on said scanned document being stored on an intermediate storage member, preferably a magnetic disc, for manipulation, storage, or other signal processing via a synchronizing buffer. The information stored in the storaga member lil~`239 may be read out via the synchronizing buffer and reproduced on a reproducing medium which may, for example, be incor-porated in a xerographic processor. Other system features include input scan reversal for alternate bound pages during bound volume scanning, synchronization of the entire system by a clock associated with the storage member, input/output interleaving with a print interrupt feature, image centering and edge fadeout for image reduction and independent magnification/demagnification by separately variable raster spacing.

OBJECTS OF THE PRESENT INVENTION

It is an object of an aspect of the present invention to provide a reproduction scanning system having intermediate storage between input and output scanning stations.
It is an object of an aspect of the present invention to provide a reproduction scanning system having a storage member for writing information thereon, said input information being derived from an input scanning station and directed to an output scanning station wherein the information is reproduced.
It is an object of an aspect of the present invention to provide a reproduction scanning system wherein an input document is scanned in mutually orthogonal direc-tions, the scanned information being stored in a storagemember, such as a magnetic disc memory via a synchronizing buffer, the stored information being read out from the storage member through the synchronizing buffer and directed to an output scanning station wherein the information is reproduced.
It is an object of an aspect of the present _5_ invention to provide a system of the type described herein-above wherein the input scan may be reversed, electro-mechanically in one direction and electronically in the other direction when an alternate page in a bound volume is being input scanned.
It is an object of an aspect of the present invention to provide a system of the type described here-inabove wherein the system is synchronized by a clock associated with the magnetic disc storage member.
It is an object of an aspect of the present invention to provide a system of the type described here-inabove wherein the reproduced image is centered by using edge fadeout techniques when an input image is to be reduced in size on an output medium, the reduced image being smaller in size than the output medium.
It is an object of an aspect of the present invention to provide for magnification or demagnification in one scan direction which is independent of the magnific-ation or demagnification in the other scan direction in the system described hereinabove by separately varying the spacing of the input scan i.e. variable raster spacing.
It is an object of an aspect of the present invention to provide a system of the type described here-inabove wherein input scanning of a first original (document) and output printing (scanning) thereof is interleaved and includes a print interrupt feature to allow a second original to be input scanned.
Various aspects of the invention are as follows:

~119Z39 A scanning system having the capability of scan-ning originals having images formed thereon in either a normal or inverted mode of operation such that electrical signals r.epresenting the scanned images can be stored in storage means such that when the scanning system reads the stored representations of the images to reproduce the images on a recording medium the reproduced images each having the same image sense comprising: first means for scanning said originals in a first direction in the normal mode and in a second direction, opposite to said first direction, in the inverted mode, second means for scanning said originals in a third direction, which is orthogonal to said first and second directions whereby said originals are completely scanned with light, means for converting the light reflected from said originals into corresponding electrical signals as the originals are scanned on a line to line basis, buffer memory means for storing said electrical signals in the order in which the electrical signals are generated, and means for unloading said electrical signals stored in said buffer memory means into said storage means in a se~uence determined by whether the scanning system is in the inverted or normal mode of operation.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the following figures wherein:

-6a~

Figure 1 shows in simplfied form-~ an~optical:
arrangement which may be utilized in the present invention Figure 2 is a simplified block diagram of the overall system of the present invention;

Figures 3A and 3B illustrate a dlsc surface and a typical record~ng patte~n formed on the disc which may be utilized in the present invention, Figures 4A and 4B are m~re detailed block diagrams of the system of ~he present invention:
Figure 5 illustrateq in more detail the operatio~ of the synchronizing buffer which comprises a portion of the system of the present invention, ' Figure 6 is a more detailed block diagram of an output shi~t register which may be utilized in the present invention, and Figures 7A and 7B illustrate how a reduced image may be centered on an output n~Ylium.

DESC~rPTIO~ OF I~IE P~LEElERURED EIIBODI~rE~rr Referring now to Figure 1, a simpli~ied representation of an optical system which may be utilized in the present Ln~ention is shown. Light sources 10 and 12 provide original beams 14 and 16, respectively, for utilization by,the scanning system.
Light sources 10 and 12 are preerably lasers which provide collimated beams of monochromatic light, laser la comprisins a helium-cadmium laser which generates blue laser light at a wavelength of 4416A and laser 12 com?rises a heli~m-neon laser wnich generates red laser light at a wavelensth of 6328A. The use of the t~o las~r beams ensures that the document scanner is not insensitive at the wavelensths ~l~S?39 of lasers lO or 12 and hence, the system is suitable for detecting light fluxes reflected from multi-colored documents in addition to the fact that a choice of laser beams is avail-able for forming information on a laser sensitive medium.
Light beam 14 is incident upon beam splitter 18 which directs a portion of light beam 14 to dichroic mirror 20.
Light beam 16 is also incident on dichroic mirror 20, which is positioned to reflect the flux in beam 14 as a combined beam 22 (combined with transmitted beam 16). Beam 22 is incident upon pre-image cylinder lens 24 which transmits the beam to mirror 26 which directs the beam to a rotating scanner 28 via a split doublet 30. The portion of beam 14 transmitted by beam splitter 18 is incident on modulator 32 which may either be an acousto-optic or electro-optic type device, the output thereof being incident on scanner 28 via pre-image lens 34, mirror 36 and split doublet 30, the split doublet 30 allowing the separate beams incident thereon on the platen 62 or drum 76. Rotating scanner 28, shown as comprising a polygon having a plurality of reflect-ing facets 38, is driven by motor 40 via drive shaft 42.
Scanner 28 rotates in the direction of an arrow 44causing the lase. spot (combined laser beam) incident there-on to deflect in the x- direction at mirror 43, the output beam being directed to a movable scanning assembly 45, shown in a simplified representational form, which comprises mirror 46, cylinder lens 48, mirror 50, bidirectional motor 52 having a stepped pulley 53 on its output shaft, cables 54 and 55 and pulleys 56 and 57.
Elements 48 and 50 are rigidly affixed to cable 54, X

111~3~39 element 46 being a~fixed to cable 55~element 46 bei~g driven at 1/2 the speed of elements 48 and 50 to maintaLn a constant focal length between the platen 62 and mirror 43. This techni~ue is generally referred to as 1/2 rate mirror scan, such a technique being disclosed in ~.S.
Patent ~o. 3,970,359~

~ scan spot 58 i9 produced which moves along scan line 60, formed in the x-direction at platen 62, as scanner 28 continue-~to rotate. Although not shown in the figure, a document, or a page in a bound volume, to be scanned is placed face dcwn on the top sur~ace o~ transparent platen 62. Since ..
motor S2 is bidirectional, the direction of y scan is ~electable by an ~perator by appropriate activation of bu.ttons formed on an operator's panel 92 (shown schem-atically in Figure 2~ which in turn cause~ a system controlli~g microprocessor 90 (Figure 2) to generate the appropriate control signals. As will be set forth herein-after, the partic~lar scan direction s~lected is determined by the type of input being s~anned, alternate pages of a bound volume generally re~uiring r~versal of the normal scan direction~
When a document is placod face down on platen 62, it is scanned by the two color laser beam spots 22, the document reflecting the incident radiation flux in accordance with the document information being scannedO
A fraction o~ the reflected flux is detect-d by one or more photom~lltiplier tubes (or other photosensiti~e device) represented by a single photomultiplier tube 66 _9_ located under the platen 62 via mirror 64. The photo-multipliers convert the variation in intensity of the reflected laser beam into electrical information signals which may be transmitted to an intermediate storage device 96 via a synchronizing buffer 98 (shown in Figures 2 and 4) and thence to a recording device via the intermediate storage device, synchronizing buffer and mod-ulator 32 for producing a copy of the document scanned as will be explained hereinafter. The scanner 28 and scan system 45 are arranged to scan the material on platen 62 in a manner whereby a plurality of scan lines 60 are gener-ated across the width of platen 62 such that the material on the transparent platen is completely scanned. In essence, the scanning path is as follows. The beam reflected from mirror 43 passes under elements 48 and 50, is reflected by mirror 46 (approximately one-half the light is reflected, the other half being lost) and passes through lens 46 and is reflected by mirror 50 to platen 62, light reflected from the document on platen 62 is incident on mirror 50, passes through lens 48 and is incident on mirror 46, approximately half the light passing therethrough and being incident on mirror 64. This light beam is then reflected down to photomultiplier tube 64.
It should be noted that the present invention can be adapted to utilize other input scanning techniques, such as arrays of phototransistors, charge coupled devices (CCD~ or MOS photodiodes. The use of either type array (the reflections from the document on platen 62 being imaged thereon) in image sensors has been disclosed in the prior art as for example, in an article by R. Melen, in Electronics, May 24, 1973, pages 106-111 Although the input scanning techniques described ' 111~;Z39 hereinabove are fixed platen scanners (document stationary on platen) it is to be noted that the system can be arranged such that the input document moves along the Y direction of the platen 62, the input scanning mechanism thereby being stationary.
As shown in Fig. l, the single beam reflected from mirror 36 is also incident on the facets 38 of scanner 28 and caused to scan mirror 70 which directs the beam to mirror 72, mirror 72 in turn scanning the incident beam on cylinder lens 74. Cylinder lens 74 focuses the beam on a recording member 76, such as a xerographic drum, rotating in the direction of arrow 78. A plurality of scan lines 80 are formed on the surface of drum 76 in a similar spatial relationship (the reproduction not being accomplished in time synchronism since the output from the photomultiplier tubes are initially directed to the intermediate storage device 96 via a synchronizing buffer 98 in the preferred embodiment) with the information being scanned on platen 62 to thereby reproduce a copy of the image on drum 76 in a manner as described in the aforementioned Patent No. 3,922,485. A start of scan detector 82 is provided adjacent to mirror 72 to provide -lOa-lllSZ3~

a signal when the scan on dru~ 76 ta portian o~ the~
xerographic processo~ 77 shown in Figure 2) is initiated and end of scan detector 84 is provided adjacent mirror 72 to pro~ide a signal when each scan lLne is completed.
It should be noted that although a single polygon scanner is shown for ~oth input and output scanning, separate polygon scanners which are synchronously driven may be utilized, Reference may be made to the teachings of the afor2mentioned U. S. Patent No. 4,Ql~2,~85 .
which pro~ides, inter alia, for scanning an unmodulated laser beam at a reading station for reading a stationary document the~eat and directing a ~odulated laQer beam to an imaging s~ation for reproducing the document image thereat and which utilizes single sc nner element.

, ., , . ~ .
Figuré 2 is an optically simplified version o~
Figure 1 and further shows, in a simplified form, the electronic input scanning signal procsssing, storage and output s~anning functions of the present invention.
The speod of drum 76 of xerographic processor 77 is assumed to be 12"/second or purpases o~ the calcu-latio~s ~o foll~w but is not intended to limit the scope of the present invention. The paper feed for both simplex (printing on one side of the output paper) and duplex operation (duplex operation, printing on both sides of the output paper) is provided, for example, by the Xerox 4000 copier manufactured by the Xerox Corporation, is initiated on demand under control o~ the system micro-processor controller 90. It should be noted tnat the -11- j function of microprocessor 90 is that of syste~ manage-ment and when properly programmed, controls the operat~ng se~uenc~ ~ of the entire system of the present invention. It also sets up the appropriate operating parameters derived from uqer controls on panel 92, such as magnification ratio, de of operation, normal or reverse scanning mode, etc. In general, the sy~tem /11 controller issues appropriate ~ xerographic - proce~sor 77, receives status signals ~herefrom, issueq scan and storage control parameters and the start of scan sisnals, receives status signals from the rest of the system and, of course, interacts with the user panel 92.
Any properly ~rogrammed microprocessor, such as the Intel 80~0 or the Motorola 6800 or minicomputers such as the -Xova series manufactured by the Data General Corporation, Sou~boro, Massachusetts, can perform these functions.
Since the present invention is directed to the general interrelationship of t~e system elements, a specific description of the microprocessor system controller 90 and the operating software therefor i~ not set forth herein.
It should be noted that the dimensions and the calculations that follow are approximate and are set forth for illustration purposes only and are not intended to limit the scope of the present invention.
In one embodLment, input scanning is provided on a flat platen 62 (14"x17" for exam~le), the ~can mirrors moving across the short tl4 inch) dimension of the platen a~ shown in Figure 1 to provide for y sc~nins.
The X direction scanning in the long (17 inch) ~19Z39 dimension in the preferred embodiment, is produced by a multifaceted rotating polygon 28 having 26 facets. The actual total length of scan is 17.85 inches, which provides 0.43 inches over scan at each end of the 17" platen which allows the scan clock generator 94 to be resynchronized prior to the start of the next scan line.
Resolution in the X and Y directions of scan is assumed to be equal. That is, the bits/inch (pixels/
inch) in the X direction equals the lines/inch in the Y
direction for both input and output scanning.
For a given output paper size, the output scan density (this refers to resolution and not with optical density) is constant, with reduction in image size being accomplished by reducing the input scan density (resolution), the number of pixels per output page being independent of the reduction ratio selected. Reducing the input scan density in the Y direction is accomplished by increasing the Y scan mirror velocity by operator selection of a desired magnification value (the range, for example, being from 1.0 to 0.61) the input scan density in the X direction being reduced by decreasing the number of bits/inch in the X-scan direction by varying the scan clock generator 94 by the magnification ratio selected. This allows inde-pendent control over the reduction/magnification in the X and Y directions if desired and makes good use of the capacity and bandwidth of the storage system 96, the storage system preferably utilizing a magnetic disc 97. In this regard, it should be noted that alternate image storage media (and associated readout systems) can be utilized in the present invention. For example, a video or optical disc system for recording and reading out information (wherein lasers may be utilized to record information on the disc and wherein l~lS239 lasers are utilized to read the information formed on the disc) have been disclosed in the prior art and may be utilized in the present invention. A read-write optical disc memory is disclosed, for example, in an article by D. Chen, Applied Optics, October, 1972, Vol. 11, No. 10, Pages 2133-2139, the teachings of which may be adapted to the present invention. In general, the output from the input scanning device can be utilized directly to modulate a laser, via synchronizing buffer 98, the laser in turn writing the appropriate information on the optical disc. The information read from the optical disc can be stored in synchronizing buffer 98, manipulated or otherwise processed and then coupled to the printing portion of the disclosed system. Other alternate image storage media may utilize magnetic bubbles or CCD technologies, for example.
Images scanned and readout by photodetector 66 are stored in uncompressed, binary, digital format prefer-ably on a dual platter, 4 track parallel, moving arm magnetic disc system 96 via synchronizing buffer 98, the -13a-111~239 imately 8 x 108 bits which allows storage ~8, 8-1/2 x 11" impressions ~pages) scanned at approximately 423 lines/inch. The average data bit rate to the disc system 96 (the system includ~ng a magnetic disc 97, positioning arms disc drive etc.)is assumed to be 23.59 megabits/second.
Synchronization in the scanning system of the pr~sent invention is deriv~d from the disc system itself.
A primary clock rate of approx~mately 28.62 megabits/
sec~nd is ~ormed ~y the timer block 100 in conjunction with the disc and ~s used to control the recording of information thereon f~om buf~er 98. This clock rate, which will also be synchronous with data read from the disc 97 (since the 3econd disc is identical to disc 97, only disc 97 will be referred to hereinafter~ is counted d~wn Ln timer (or clock) 100, to produce appropriate 2-phase AC signals to drive a synchronous scanner tor 0, the Y scan mirror dri~e motor 52 and appropriate cloc~ signal from clocX signals to synchronizing buf~er 98. ~he/scan clocX
~enerator 94 (used to control the timing of data that modulates the laser ~eam on output scanning and to sample tho photod~tector signals on input scanning) is generated in burst~, under the control of the start-of-scan and end-o~-scan photodetectors 82 and 84, respectively. The scan clock generator 94 is therefor slaved to the speed o~
polygon 28 which in turn is derived 'rom the disc system 6 the scanning systam timing therefor being synchron-nput scan ized with the disc speed. The/speed relationships are chosen to cause da'a to be generated at an average rate e~ual to the ability o~ tne disc 97 to store it. Ir the rotational speed of disc 97 was to change slightly, the scanner 28 and scan clock 94 will follow the change.

lllgZ39 This synchronous system .imLng method al}ows the size of the synchronizing buffes 98 to be significantly reduced in size ~and cost) and substantially less than the capacity of one helical turn on the disc 97 (as will be set forth herelnafter, one turn of the disc g7 is capable of stosing 4 (surface~) x 48 ~sectors per turn) x 4096 (bits per sector), which is 48 times less than the size of the synchronizing buffer which preferably will be utilized~. Synchronizing buffer 98 is required ~ince the peak data rate during input scan i~ approx-imately 38 meg2bits/second, which is higher than the rate that disc 97 can accept the input data (approximately 28 megabits/second). The average bit rates over a number of scan lines, however, will be approximately e~ual.
Further, synchronizing buffer 98 smooths out any gaps between sectors on disc 97, the sectors including 4096 data bits, when the reproduction system is in the print de, the system controller 90 preventing gaps (and sector headings, labels, etc.~ from being stored in the synchronizing buffer auring the print de of operation.
The tLme to scan an original on the input platen 62 (see Figure l) i8 selected to be the same as the time ~e~uired to e-~pose the xerographic drum 76 in xerographic procsssor 77 to reduce the time required for output and the ~ize of synchronizing buffer 98.
The following relationships are given to provide an indication of ~ystem performance. The follow-ing definitions are useful.
ABR = Avera~e bit rate for magnetic disc 97 (bits/sec) BPS = Bits per scan line 3PP = Bits (p~xels) per page CPPs = ClocX pulses per sector for the masnet~c disc ~7 DBC. = Disc data capacity in bits DPC = Disc data capacity in pages DR = Divide ratio for generating ~olygon drive fre~uency Lp = Output paper length (in.) (Parallel to æ is of xerographic drum 76.
Ls 2 Input platen scan length including overscan tin.) (As~umed to be 17.885 in.~
M = Magnification ra~io (1.0 to 0.61) = ~umber of facets on the polygon scanner 20 (a=sumed to be 26) SDi = ~nput scan de~sity (lines~in~h or ~its/incn) SDo = Output scan density (lines/inch or bits/inch) S~S - Scan lines per second SPBRi = Peak input scan bit rate (bits/sec) Vd = Xerographic drum surface velocity (in/sec) (assumed to be 12 ips) Vp = Polygon a~gular velocity (rpm) Vy = scan ~elocity (in/sec) Wp = Output paper width (in.) .~herefore, from the ge~metries and character-istics of the system, the following is obtained:
(a) Output scan density SDo - rABR~ d~ ~))] 1/2 (b) Polygon rpm re~uired for output scan ~p , 60(SDo) (Vd)/N' (c) Bits (pixels per output page) BPP = (SDo) Wp) (SDo) (Lp) (d) Input scan density SDi - tSDo) (M) or ~'I ~ SD;

(e) Input Y scan velocity Vy = Vd/M or M ~ V SDi being ~nvers~ly prooo~tional to Vv .

(f) Scanner rpm re~uired for input scan ~/11 vp =6o(sLs)/~=6o(sDi) (V~ N=60 (SDo) (Vd)/~
(g) Scan lines per second SLS = ~(Vp)/60 = 5SDo~ (Vd). ..
(h) Peak input scan bit rate SPBRi - (SLS) (Lg) (SDi) = (~) (L5~ (Vd) (SDo) 2-(i) The total number of pages that may be stored on the disc DPC = DBC/BPP = DBC/~SDo)2(Wp) (Lp) ~he following summzrizes some of the system characteristics for 8-1/2 x 11" o~tput paper.
TABLE I
Average bit rate (m~ps) 23.59 Output scan density (lpi) as determined by the speed of drum 76 and the disc clock rate 422.77 Output scanner velocity (rpm) 11,707 Bits/ll" line 4,650.47 Megabits/output page 16.71 Storage Capacity of Disc in pages 48.19 Peak input rate ~mbs) 38.30 If a maximum reduction factor o~ 0.61 is assumed, the Lnput scan denqity in lines/inch znd bits/ .
inch is reduced from 422.77 to 257.89. The output copy from xerographic processor 77 is still produced at the max~mum scan density of 422.77 scan lines per inch.
The~total number of pixels per output page is constant and independent of magni~ication and therefore allows ror a simple and eff_ctive way o~ controll~ng masnifl-cation ~y controlling input scan density.

-~7-The inpu~ Y direction scan mirror veioci.y is increased from 12 inches/second to 19.67 inches/second for the 0.61 magni~ication ratio. The peak input bit scan rate accordingly dxops ~rom 38.30 megabits/sec~nd to 23.36 megabits/second.
When larger output paper is used, the scan line density and disc page storage caDacity are reduced.
Table II lists system characteristics wherein 10.12" x 14.33" output paper is~used, Note that s~nce the bit rate is fixed and the paper area is larger than Ln the Table I example, the output scan density will be-less.
TABLE II
Average bit rate (mbps) 23.59 Output scan density (lpi)370.41 Output scznner velocity ~rpm)10,257 Bits/14.33" line 5,307.91 Magabits/output page 19.89 ; Storage capacity in pages40.47 PeaX input rate (mbs) 2g~40 At a reduction ratio of 0.61, the input scan density becomes 225.95 lines/inch with output s~anning rema~ning at 370.41 scan lLnes per inch.
Although the in~ention deccsibed here~n is preferably utilized to provide for electronic pre-collation (precollation being provided in simplex oper-ation ~y copying the number of lnput originals in se~uence onto the disc 97 and printing a pre~etermined number of copies of each seouence via the xerographic processor 77), it should be obvious tkat by c~anging control parameters and the sor~ware used by the micro-processor 90 that many additionzl features may be lll~Z39 provided i.e. providing a small alphanumeric_dLsplay for:
interactive guidance for the system user; a small portion on the large disc capacity can be used to store statistics on sys.em use; the disc could be used to store software diagnostic routines to be used by the microprocessor 90 for trouble diagnosis; a scan density compatible with easy conversion to facsimile could be selected,-etc.
The disc 97 to be utilized with the present invention is assumed to comprisa two platters (four surfaceq) recorded and read ~n parallel, one sur~ace 99 of which is illustrated in simplifie~ form in Fisure 3.
The data is recorded, for e~ample, in 1024 discontinuous sectors 101 withLn angular area 102, 48 such angular areas, being formed in band area 103 around~the disc circumfe~ence ~approximately 50,000 sector~ thereby being provided).
Each sec~or 101 is subdivided into 3 main sections. The first section contains a space 104 for a fixed header identifying the sector number. ~he second section 105 is a rewritable control area of 12~ useful bits identi-fied a3 "label". The third section 107, separated from section 104 by gap 111, is the normal data area of 4096 aata bits. There are 48 such sectors per tur~, each sector being separated by gaps 113. Information is preferably recorded in a spiral (helical) pattern (similar to a phonogxaph record) with a total of 1024 active data turns. The spiral type pattern (trac~) allows data to be read continuously with the disc read/wri.e heads //G
11J following ~he trac~ as in a phonograph reco~d. The header area 104 of each sector may be arran5ed to contain a patter~ that is usad to servo con~rol the radial position of the recording-playbac~ head to allow it to follow the spiral data path, ~he number of circ~mferential cloc~ periods -19-' ' I

(not shown in ~he figure) re~uired Ln eac~-sector fo~
gaps, header and label (error detection and correction bits may be provided if desired) i9 assumed to be 872.
There~ore, the total sector length is 4968 clocX periods.
Table III summarizes typical performa~ce characteristics for the disc syst~m 96:
~ABLE III
Data bits/sector (each surface) 4,096 Clock periods/sector 4,968 Data bits/sector (4 surfaces) . 16,384 Sectors/turn 48 - ~urns/surface 1,024 Data bits/turn (on each surace) 196,608 Data bits/turn t4 surfaces~ 786,432 Average data ~it rate/surface (mbs~ . 5.89 ~30 x 48 x 4096) wherein the disc rotation rate is 30 revolutions per second Average bit rate for 4 tracks (mbs) 23.59 ` Peak bit rate/susface ~mbs) 7.15 (30 x 4~) (4096 + 872) Total peak bit rate (mbs) .28.61 ~otal data capacity ~bits) 80~,306,365 - Althcugh not considered part of the present invention, it should be noted that the large size of the data bloc~s in this system make the use of isolated and burst error detecting and correcting codes e'ficient and attxactive.
The seek operation wherein the radial disc arns seek the starting sector on the disc 9~ is def~ned by specifying a uni~ue sector number out of the total o~

-~0- ~

lll9Z39 49,152 sectors along the spiral track by the-~system_ :
controller 90 and hav~ng a controller speciCied accoler-ation motion to enable the disc arms to locate the correct sector. ~ew information (represent~ng ~ages in this system) is written directly over old data without a separate erase pas3 to save system time.
Figure 4 is a more detailed bloc~ diagræm of the present invention. It should be noted that si$nals to and from the m crocode programmed microprooe~sor system controller ~0 are indicated in the figures by circles adjacent to a label of a function entering or coming from a partic~lar electronic subsystem block.
Direction control device 121 receives an input (Y scan drive fre~uency) on lead 122 from reduction counter 130, the system controlle~ 90 ~ntroduc~ng the signal l'start scan" on lead 124. The velocity and direction of the Y
scan motor 52 are set up by the sys~em controller 90. The scan velocity ~Y scan drive fre~uency) is determi~ed by the "magnification ratio" control parameter on lead 128 3~0cified by an operator via panel 92 (Figure 2) which is used to determine the clock fre~uency division ratio in the system timLng counter 129 (logically a set of counters, the coun~ ratio being changed by the selected magnifi-cation ratio)and the reduction counter 130~ The magnifi-cation ratio signal i~ applied to reduction counter 130 via lead 127 a reduced clocX sisnal being applied there~o from syste~ timLng counter 129 via lead 119. The directio~
control device 121 causes a Y scan pass to be after the "start scan" signal and direction ~nfor~ation a-~provided by the syst~m controller 90 the direction ln~ormation being initially set up by an operator via panel 9~ . Logic ~g~39 circuits within direction control device I2I~~determ~ne the proper polarity of the Y scan dri~e ~ pplied to mctor 52 for the correct direction of scan. In the , ' ;: ' -21a-lllgZ39 normal (non-inverted mode) it is assumed that the Y
direction of scan is in the +Y direction from an initial position 61 (Figure 1) whereas in the inverted mode of operation the Y direction of scan is in the -Y direction from initial position 63.
The start of Y scan time is derived by the system controller 90 from information it has about the starting sector number for the next page of information to be entered into the disc 96 during input scanning.
~he system controller 90 receives information about where the disc 96 is as it rotates from the header and check logic block 131 on output lead 132. The controller 90 checks the Y scan status from the diraction control block on lead 126 prior toinitiating a start scan command to be sure the scanner is in the correct home, or initial position. The correct home position obviously is depen-dent upon whether scanning is to proceed in the normal or reversed modes of operation.
It should be obser~ed that since the input ~ 20 scan line density must be changed Ireduced) to vary the magnificat or. ratio it is preferable to change the size of the scan spot for lnput scanning, ~n order that the scanning spot cover the entire area of the document thereby maintaining the optimum ratio of scanning aperture size to scan line density. To incrase the Y dimension of the scan spot optically (anamorphically), optical aperture control 133 is utilized during input scanning, the aperture control incrasing the size of the scanning spot in the direction associated therewith via a signal from system controller 90 on lead 135. On input scan-ning, the effecti~e X dimension of the spot (in the direction of high speed scan) may be controlled by lllSZ39 changing the electronic bandwidth of the aperture control 134 following the photodetector 64 via a signal from system controller 90 on lead 135. During output scanning, the effective size of the spot in the X direction (which is maintained essentially constant since the output scan line density is maintained constant) is controlled by the timing of signals supplied to the acousto-optic modulator 32 via lead 125 under control of the scan clock generator 94.
As set forth hereinabove with reference to Figure 1, a blue and red laser 10 and 12 are assumed for input scanning to avoid color blindness which would occur if monochromatic illumination were used. In the system shown, both lasers are used for input scanning, and the blue laser is used for output scanning.
Although it would be cost effective to use a single polygon X scanner 20 for both input and output scanning, it may be preferable to use a second polygon which uitilize a separate 2-phase synchronous drive motor.
In the single scanner design, one pair of scan synchronizing detectors will normally suffice i. e. end-of-scan detector 84 and start-of-scan detector 82.
Signals from these two devices allow the generation of precisely controlled streams of "bit clocks" for sampling the signal from photodetector 66 on input scanning or controlling the timing of image data fed to the laser modulator 32 on output scanning. It should be noted that the system mode of operation (whether input scanning or output printing) is determined by the operator via panel 92. The scan clock frequency is controlled by phase detector 136, start-stop control device 137, voltage con-trolled oscillator 138, linearizer 140, and bits~inch counter 142.

-~rl -23-The voltage controlled oscillator 138, oscillating at a present frequency, does not operate continuously, but is released to start oscillating on each scan by the start of scan pulse and is stopped at the end of scan via start/
stop control 137. The phase comparison in phase detector 136 is also initiated when the start of scan pulse is received via lead 141. The count down ratio of the bits~
inch counter 142 is set by the system controller 90 accord-ing to the operator selected magnification ratio and output paper size utilized. The preferred range is from approxi-mately 423 bits/inch to approximately 226 bit/inch (input scan onto 14.33 paper at magnification of 0.61). When the -preset number of bits (voltage cycles) (bitslinch times the input scan length including overscan) from oscillator 138 have been counted in the bits/inch counter 142, a pulse is coupled to the phase detector 134 via lead 144.
If the avexage signal frequency from oscillator 138 is correct, a pulse will be received from the end of scan detector 84 at the same time. If, for example, the poly-;~ 20 gon 28 had speeded up slightly, the end of scan pulse will arrive at the phase detector before the bitslinch counter pulse on lead 144. This will cause the phase detector 136 to generate a voltage error signal to increase the frequency of oscillator 138. Note that there are 26 such samples of scanner rotation rate for each rotation of the scanner 28 since it has been assumed that scanner comprises 26 facets.
The bits/line counter 146, synchronized by os-cillator 138 via lead 145, counts down from a preset count which corresponds to the various sizes of output paper to which the developed image formed in the xerographic , .
,,, . I

lil9239 processor 76 is transferred by standard techniqu~s in the preset ~ode. ~he range (count) is 4656 to 5312 bits/line which is less than the range for counter 142 since the latter count is preset on the basis of the input platen scan line length and including overscan.
These numbers are slightly larger than those listed -24a-in Tables I and II in order to be compatible with the operation of the synchronizing buffer 98, the number of bits/
line being rounded upward to the nearest multiple of 16.
The linearizer 140 generates a second input to oscillator 138 via lead 147 to correct for non-uniform velocity of the scan spot, the bits/line counter 146 providing a signal to linearizer 140 via lead 149 to provide an indi-cation where in the scan line the spot is located at any instant. It has been observed that the instantaneous scan velocity normally is higher at the edges of a scan that at the center of the scan. ~ven though the input and output scan nonlinearities might compensate each other, electronic linearity correction of the image data stored in the disc by scan clock variation may be preferable to allow later coupling between machines with different scan geometries.
The scan clock gate 148 releases precisely timed bursts of clock pulses on lead 200 at the start of its countdown cycle ranging in frequency from 38.30 to 17.93 megabits/second as determined by the system controller 90 ;~ 20 (output paper size and magnification ratio). The number of pulses in the clock burst is determined by the countdown ratio set in counter 146. The scan clock gate 148 is used to control the timing of loading the synchronlzing buffer assembly 98 with signals from the photodetector 66 in the input scanning mode, the unloading-of the synchronizing buffer 98 to the disc system 96 for input scanning being under the control of the disc clock, to be described here-inafter.
The threshold detector 150, with its input control parameter on lead 151 is used in simple signal processing operations to produce, in effect, extremely high gamma. A threshold slicing level may be modified under -25/25a-~T

lll~Z3g user control to help remove bac~ground and otherwise clean up inferior originals. Existance of the image information in electronic form makes possible a wide range of image enhancement techniques.
The timing of the entire scanning system is slaved to the disc clock. On input scanning, signals from the photodetector 66 will come in bursts since (for 11" paper) the active scan time is only llJ17.855 of the total scan line period for the case of no reduction. This produces a peak input scan bit rate (SPBRi) of 38.30 megabits/second.Similarly, the disc input and output data flows in bursts to compensate for the overhead necessary for sector gaps, headers and labels. The peak disc data rate is 28.62 mega-bits/second. Therefore, total peak instantaneous bit rate for the synchronizing buffer is 38.30 plus 28.62 megabits second. The average input rate is equal to the average output rate for most modes of operation and is equal to 23.59 megabits~second. An exception occurs when the reduced image of the 14" x 17" input platen is smaller than the output paper size, as determined by the operator selected magnification ratio and paper size. In that case, "white border bits" are generated to ~ill the out-put page as is described hereinafter.
Figure 5 shows some of the functional blocks enclosed in the dotted outline corresponding to the synchronizing buffer 98 of the block diagram of Figure 4.
The buffer storage 170 required to accommodate the bursts of data is assumed to be made up of 16, lK random ' access memory (RA~) chips. Each input and each output 0 operation of the RAM handles 16 bits inparallel. It is -~6-l~lg239 assumed that chips operating at 200 nanoseconds fullcycle time will be utilized. This will provide a peak rate of 80 megabits. Serial to parallel shift register 172 and parallel to serial shift register 174 make the necessary conversions at input and output, respectively for the random access memory 170.
For the non-inverted first-in, first-out oper-ation mode of operation, a load address counter 180 sel-ected by address selection gates 181, sequences through the 1024 addresses in RAM 170, sequentially and circular-ly to load data therein from the threshold detector 150 in the input scanning mode of operation. Similarly, an unload address counter 182 provides sequential unload addresses for the RAM 170 under control of address selection gates 181 when data is to be unloaded to the disc 97.
The data selection gates 186 contain parallell digital gates that switch the input and output bit streams to and from the synchronizing buffer 98. For input scan-ning, the peak input scan bit rate clock on lead 20 controls the input shift register 172 via the shift register clocks on lead 206 and load address counter 180 timing via the load/unload clocks on lead 204. The peak bit rate disc clock on lead 201 controls output shift register 176 via lead 206 and unload address counter 182 timing via lead 204. The threshold detec-tor 150 IFigure 3) is the input data source to the data selection gates 186 via input shift register 172 and holding register 173, the output image data ~rom RAM 170 going to disc 97. Similarly, for output scanning (print-ing) the disc clock on lead 201 controls the input to RAM 170 via shi~t register 172 and load timing via load address ~1~9239 counter 180 while the scan clock on lead 200 controls the output of RAM 170 via output shift register 174 and the unloading address counter timing via counter 182.
When a bound volume is placed on the input platen 62, successive pages of the volume may be placed upside down on the platen to make use of the book edge feature incor-porated in copiers commercially available. In order to reverse the image so that all pages will be right side up when the output is generated, the X and Y scan directions both must be reversed Iscan inversion is accomplished by operator selection of a "Scan Invert" button (not shown) on panel 92. Note that if only the Y scan direction were reversed a mirror image of the document scanned would be reproduced). Although the Y scan direction can be changed by appropriate control of the Y scan direction control device 121 thereby resetting the initial start position and direction of scan mechanically changing the X scan-ning direction is not feasible due to the inertia and high operating speeds of the scanner 28. The X-scan direction is therefor reversed electronically as ~ollows:
For an 8-1/2 x 11" input document, it is assumed that approximately 291 sixteen bit words comprise one scan line in the 11 inch X-scan direction. During the input scan (the system is assumed to be in the inverted input scanning made) load address counter 180 via address selection gates 181 causes the input scan info~mation from photodetector 66 (291) sixteen bit words) to be stored in sequence, for example in storage locations O to 290 in RAM 170, at least one complete scan line being stored therein. Lead 230 is appropriately energized to allow storage to be accomplished when the store mode of operation is selected. Preset address ~:1 ~ ., 111~239 counter 179 is caused to be set to a first preset address 290 in the inverted mode of operation, a signal on lead 177 causing the unload address counter 182 via address selection gates 181 to count down sequentially from storage location 290 (i.e. 289, 288, ... ) such that the scan line information is read out word by word in the reverse order in which it was stored, an appropriate control signal being applied to lead 230 to enable RAM
170 to be read out. The information read out is coupled to output shift register 174 via lead 175, data selection gates 186, and output holding register 183 and thereafter to disc 97. As shown in Figure 6, output shift register 174 is coupled to the 16-bit output holding register 183 and comprises four shift registers 240, 242, and 246.
When information is to be recorded on discs 97 and appro-priate control signal from system controller 90 is applied to register 174 on lead 250 to enable the infor-mation to be read out in four-bit blocks to be applied to the disc write block 222 and thereafter to be applied to the 4 recording surfaces of the discs 97 via write ampli-fiers 223 ~Fig. 4). When the information read out from RAM 170 is to be applied to modulator 32 and thereafter reproduced by xerographic processor 76, the signal on lead 250 enables the inormation to be read out serially on lead 125. In a similar manner although not shown in the figure input shift register 172 is adapted (via a signal from system controller 90 on lead 251) in the input scan mode, to convert the input serial data stream into 16-bit parallel format and to convert the four bit word from the discs 97 via amplifiers 225 and data recovery circuits 220 into 16-bit parallel words in the print (write) mode.

~, ., The next scan line is recorded in locations 291 through 580 in RAM 170 and the preset address counter 179 is set to address 580, the data in these addresses being read out in a manner as described hereinabove with refer-ence to locations 0 through 290.
In the inverted mode of operation, the bits inoutput shift register 174 are shifted from left to right and read out on lines 239, 241, 243 and 245 whereby each bit in the scan line is transposed for reverse scanning.
In the normal (non-inverted) mode of operation, the bits in each scan line are shifted right to left and read out on lines 237, 247, 249 and 253 with no transposition of the bits comprising the scan line occurring. In other words, shift register 174 is bidirectional, data bits being shifted out right-to-left in the inverted mode of operation whereas the data bits are shifted left to right in the normal FIFO (first in, first out) mode of buffer operation. It should be noted that input shift register 172 need not be bidirectional since, in the print mode of operation, the transposed bits stored on the discs 97 will be in the correct sequence when read out.
When the system ls in the print mode, as deter-mined by operator energLzation of a "PRINT" button on panel 92 (not shown), the output from discs 97 is read out via read pre-amplifiers 225 and initially stored in memory 170 in the address specified by load address counter 180, counter 180 being selected by address selection gates 181 to store information in RAM 170. To unload data to the modulator 32, unload address counter 182 is selected by gates 181 and caused to transfer the informa-tion in RAM 170 via data selection gates 186 and output holding register 183 to output shift register 174. It X

: .

1~19239 should be noted, as set forth hereinabove, that since the scan lines have already been reversed prior to being stored on disc 97, unload address counter 182 is not caused to count down by a signal from buffer control 202 on lead 177.
The data which is being read out therefor is electronically reversed in the x-scan direction.
The scan clock on lead 200 is utilized to control the timing of loading the RAM 170 with signals from the photodetector 66 on input scanning, the unloading of the RAM 170 being controlled by the clock signal derived from the disc system 96 on lead 201. For output scanning, the loading of the RAM 170 is controlled by the clock signal from disc system 96 whereas the unloading of the RAM 170 is controlled by the scan clock signal on lead 200. The load and unload address clocks are applied to lead 204 and shift register clocks are applied to lead 206 via synchronizing buffer control 202.
The header and check logic 131 (Figure 4) is connected to the shift registers 172, 174 via leads 227 and 228 to enable the acquisition and loading of header and control information from the data stored ln the shi~t registers. The system controller 90 will supply header and check logic 131 with the following parameters: Lines~
page, bitslline, and page start sector number which in turn modifies the data stored in the RAM 170 with this information priox to loading the discs 97. Since four surfaces of the disc are used in parallel, the basic disc data block is 4 x 4096 = 16,384 data bits which cor-responds to the timing of one disc sector. Since the largest number of bits in a scan line may be greater than 4096 data bits, the start of successive scan lines may not occur at sector boundaries. It is assumed that the first lil9239 scan line of each page may start at a sector boundary identified by the page start sector number.
The label information associated with each sector may identify the number of lines remaining in the current page and the location of the boundaries between successive scan lines for each sector. This information can be thought of as completely defining the format and other rele-vant information about the data to follow.
The header and check logic block 131 will check sector identification and will preferably also verify data integrity by generating and comparing error detection and correction redundancy patterns by standard computer tech-niques although this does not form part of the present invention. Sector number checking is aided by the avail-ability of the current sector position of the disc derived from the system timing counter 129 of Figure 4 which supplies sector pulses ~approximately 48,000 pulses per disc revolution) to sector counter 240 via lead 241 (approximately 50,000 total for 1024 turns). As shown, pulses from timing counter 129 are also applied to buffer control 202 (approxi-mately 28.2 megabits/sec) and header ~nd disc loglc 131 (one index pulse per disc revolution) via leads 201 and 242, respectively. The clock for disc data recovery circuit 220 is derived from the recorded data during a read operation, the clock for the disc write logic circuits 222 being derived from the system timing counter 129 during record-ing. Each of the four independent data recovery circuits 220 will generate its independent read timing clock although the disc system timing clock controls the combined output data stream as it is passed to the main synchronizing buffer 98.

~1 ~ . ...

111~239 number commands to the seek control block 206 via lead 224 that controls the positioner Inot shown) for disc arms 115.
Seek complete status is indicated to the system controller 90 via lead 207 when the commanded sector has been acquixed by the seek control 206. The system controller 90 can then issue the start scan signal to the seek controller 206 to allow the disc heads to follow the spiral track either for recording or playback of the disc data.
The position detector 210 generates radial head position error signals (i.e. radial deviation from the helical track) from the playback voltage on lead 211 which may be generated by the position control pattern permanent-ly recorded in the fixed header segment of each sector.
Timing for this operation is derived from the system timing 15 counter 129 via lead 228.
The gear clock PLL 212 is a phase locked loop frequency multiplier used to generate the 28.62 megabit/
second basic system timing signal. The input for this block is derived from a multi-toothed gear mounted to the disc drive hub, (a plurality of teeth corresponding to each of the 48 sectors per t~lrn~ a magnetic detector pickup mounted on the disc suppc t structure generating a pulse as each tooth rotates therepast, a pulse stream thereby being generated having a frequency proportionai to the rotational speed of disc 96. A typical input to gear clock phase locked loop 212 is 192 pulses~sacond.
In order to provide the required maximum system pulse rate of 28.62 mbs, gear clock 212 multiplies the input pulse rate by a factor of approximately 5500. The . , l~lg239 detector is separated from the recording discs 97 and is always available whether the disc system 96 is reading or writing. It is to be noted that system timing counter 124 supplies a plurality of pulse signals, includLng pulse rates reduced in frequency from the 28.62 mbs input on its output counter leads to provide appropriate timlng signals to ~he ~arious system elemen~s.
For exzmple, a frequency of 100 cycles is generally re~uired to drive motors 40 and 152. The count ratio o~
counter 129 is varied by the magnification ratio on lead 128.
Three basic modes of opera~ion are involved in the operation o~ the present system. The ~ixst is a preparatory one noted as job set up, the second is input scanning where originals are scanned and written on the disc, the third is output scanning where copies are produced xerographically.

-33a-lllg239 During the job set up, the system controller 90 fu~ni~hes a starting sector number for the first page.
The disc seek control 206 will find that sector issued by header and chec~ logic 131, and then set up ~he idle mode holding pattern and ~ndicate a seeX complete condition to the system controller 90 on lead 207.
S~milarly, the proper timing ratio~ will have been issued to cause the sca~ner 28 rpm to be selected and stabilized. The scan clocX phase loc~ed loop will be generating the correct number o~ bits/inch and bits/scan line for the selected magni~ication ratio and output page size, the proper scan clock there~y being applied to lead 200. The header control logic 131 wi}l have been set up with the bits/scan line and scan lines/page para-meters. The controller 90 will generate the sector number to start each page, and these will be pro~ided se~uentially to the seek control 206 as the job progres-ses in order to allow for electronic precollation.
The controller 90 has been gi~en the number of pages/
~ook and the number of booXs ~copies)/job by the user through the control panel 92.
The controller 90 ma~ derive or be told by the opexator of the sLmplex/duplex status of each output page and computes appropriate page start sector numbers to provide the optimum sequence for duplex output production (if the ~erographic ~rocessor 77 is capa~le of duplex operation)~
After the job is sat up, the input scanning operation can p~oceed. The operato- places his ~irst original on the platen and pushes either the `'~or~al"
or "Invert" scan button on panel 92. ~his causes the syste~ controller 90 to initiate a scan on either the Y or-Y direction (Figure 1) at an initial start~ng lii9239 pcsition. The Y scan motor 52 will starL wi~h a lead time (with respect to the arrîval of the page st?rt sector number of the disc) to allow the Y scan mirror to accelerate and stabilize at the selected velocity ~as determined by the selected reduction rati~) and depending on normal or reverse scan direction, both parameters be~ng operator initiated. As was mentioned hereinabove for reverse scanning, one or more complete scan lines must be loaded into the synchronizing bu~fer 98 prior to the arrival of the page start sector at read heads of the disc. At this time, the disc ~ystem 96 will demand output from the buf~er 98 in inverted (or ~IFO) mode. The data ~low into the buffer 98 from the photo-~etector 6~' is timed according to the scan clock synchron-ization circuits and is not determined by the position of the Y scan drive motor 52. Variations Ln the position of the Y scan mirror at the start of electrical scan are e~uivalent to a shift ~ t~e position of the original on the platen t~n the Y direction) and do not affect the synchroniz~ng buffer. A position detector can be provided to chec~ the timing o this operation to allow the system controller 90 to adju~t the lead time paræmeter.
The system runs to the end of the page and the disc system 96 see~s the next page start sector number.
If the input scanning is being done for simplex output printing, the next page will start at the next sector following ~he last sector used in the previous page.
For duplex output, appropriate page start position interlace will have ~een generated by the system I

~1~9~39 controller 90. That is, the sequence of pases alo~g the ~piral track on disc 96 will be arranged during input ~canning ~or the benefit of high thruput output.
Operation during the third mode, output scanning, is similar. In the idle condition, the disc system 96 ac~uires the page start sector. The paper feed from either the duplex recirculation paper path or the normal paper supply path from xerographic processor 77 can be triggered on demand from the system controller 90. Collation is then done electronically as each page is read from the disc in se~uence to fon~ a bo~k, the number of bco~s ~hat will be generated being dependent on operator selection of the appropriate buttons on panel 92.
Interlea~ed input and output may be requ~red for example, when a job requiring 2S copies o~ a 13-page original has been loaded and the system is Ln the output (print) de. The operator then wishes to load a new ~0~. Thi8 fact, plus th~ other normal jo~ set up ~uantit~es are entered via the control Xeyboard 92 and the first original of the new job is placod on the platen 62. When the start button is pushed, the system controller 90 f~nishes printing the output page in proces~ and then mcment rily interrupts the output printing operation.
The system controller 90 res~ts the scan clock rate and an input scan takes place. The system then immedi-ately resumes output printing while the operator changes to the next original on the input plat~n, the process being repeated until the first job is com?leted and 211 the originals of the new job have been scanned.

The following sets forth an analysis of some of the factors that may be utilized to determine the size of synchronizing buffer 170 and the system timinq ~ . . .

111~239 relationships and considers the case of-~np~ scan~ing, using 8-1/2 x 11" output paper size and the normal (no reduction) mode. This appears to place the most stringent demands on the size of buffer 170. Table rv hereinbelow lists some data, (times being in micro seconds and bit rates in megabits/second)for the system described hereinabove.
TABLE rv Total sector time 106/30 x 48 694.44 Active sector time 16,384/28.61 572.55 Inter sector time (assumed gap time) 121.89 Total sc~n line tim~ 60 x 106/~)(Vp 197.11 Active scan line time 4656/38.3O 121.5a Inactive scan line time 75.53 Total bits/scan line 46~6 Total bits/sector 16,3~4S
~umber of scan lin~s/sector '3.51 PeaX bit rate to disc 28.62 Peak bit rate from scanner 38.30 The most stringent demands made on sy~chronizing buffer . .
is in the inverted page mode wh~re at least one complete scan l~ne muct be loaded into the buffer memory 170 prior to removal o~ inform~tion for the disc 96. The minimu~ lead time for informatian supplied to the ~uf~er memory ~rom the input s~anner that is re~uired to prevent the disc unload requirements from overtaking the data available ~n the buffer should be dete~mined.
Time will be measured, ~n the follow~ng calcu-lation, with respect to the instant,time to,tnat data ~its must be su~plied to the 96 disc from the bu~rer 170. The time to load the 4656 ~its of the first scan line Lnto the aisc 96 is 4656/~8.62 - 162~71 microseconds.
The disc therefor accepts a line of data Ln less than the 197.11 microseconds total scan line time. Therefore, -37- ~

when disc 76 is ready to receive the beg~nn~hg of the fourth scan line near the and of the first disc sector which will occur at t4 = 3 x 162.71 = 488.12 microseconds after to~ the lnput scanner at t4 ~ust have loaded four complete scan lLnes into the buffer 170. The time re~uired to load n scan lines Lnto the buffer is given by ..
n (197.11) -75.53 If T~ denotes the lead time in microseconds with respect to the start of the data blocX ~to)~

4 (197.11) - 75.53 -T = 488.12, Tl, = 224~79.
~ . . . , ... .~ ?
.
t '694 ~ --- 694 , 573 .

.. Disc ti~ng -- 1 Z , 3 4 ¦ x ! 4 ~5 , 6 ~ 7 ~, x ~ 225 .J 488 . .: .
~ 2 X 1 3 , X L 4 _ X, 5 ~ X, 6 , X ~ 7 ~ X, 8 ~ X

1, ~, 3 ... represent scan line numbers (both disc and scan~ , x represents inactive time Thus, TL re~rssents the latest start time at which input scan ~ig~als may start to enter the sync~ronizing buffer 170 measured with respect to time to, the initi-ation of the unload to fhe disc, the unload initiation process being controlled by bu~fér control 202.
The earliest start time is determined by the -38- , upper limit on the size of buffer 170. Aft~r feedLng three scan lines into the buffer without removing any informatlon for the disc 96 there will be (16,384 - 3 x ~656) = 2416 bit positions left in the buffer ~70. The start of transfer to the disc 96 from the buffer (to) will oc~ur at some time during the loading of the fourth scan lLne into th~ buffer 170. Prior to to~ the net Lnput rate to ~he buffer 170 will be 38.30 megabits/second input. The diferential input rate after to will be 38.306 -28.62 = 9.68 megabits/second~
. . ., ~ ... _ . ...

.
. ~ . , - , Disc ~ 163 , ti~ir.g 1 2 3 ~ 4 . . . ~ ~ .' . ' '.

--I 43 ~ 78 1 ~ 121,6 ~ .

3 ~ X ~ 1 4 I x ~ 6 J x -I
tl to, t2- ' ' ' '',, " '. '-' . ....... . ' ~, input scan ~:isnir.g ,: .' , :.

The active time for scanning the fourth scan line (121.58 microseconds) can be devided into two intervals, tl ~ t2 tl + t2 = 121.58.

The total net inorease in bits contained in the buffer 170 during the input of the fourt~ scan line cannot exceed the rema~nins capacity of tke buffer 170 (2~15 bits). Thererore, tl x 38.30 ~ t2 x 9.68 = 2416.

tl = 43.30 microseconds.

lllg;~39 The earliest lead time that the~scannlng input can start is, there~ore, TE = 3 x 197.11 ~ 43.30 = 634.63 microseconds.
The optimum lead time with respect to to normally would be considered to be the average of the e2rliest and latest lead times, i.e. 430 microseconds.
Rowever, the ~can lLne start times precess with respect to the disc sector start times. The opti~um ena~le ~ime for a}lowing the input scanner to start loading will leave the buffer 170 equal margins before the earliest allowed time and after the late~t pos~ible occurri~g time (after enable). These possible data load start times are separated by one total scan time or 197.11 microseconds. Thus, if m - margin time, 2m 1 197.11 - 643.63 - 224.79. -m = 110.87 Therefore, ~or the case of 8-1/2 x 11"
output paper size inverted scanning, no reduction, the optimum time to initiate input scan loadLng o~
the synchroniz~ng buffer 170 is TE -m - 532.77 micro~econds bofore to~

:', - ` ` ' ' : ' 644, - _ 111 ~ 7 ~ . 225 maYgin scan start ¦ ~argln t ~t~val ~

~F , sc,~n star. enable T~ ~

-40- j .

An example o~ how the normal ~rst-in fi~9~-out operation might function during non-synchronous interlaced load and unload cycles is set forth herein-after. Assume again the 8-1/2 x 11" output paper, no reduction, input scan case. l~-~it words will be available Ln the input data holding register }73 (Figure S) a~ intervals of 16/3a.3 = 0.4178 microseconds.
Thi~ information must be loaded into the ~M 170 at somo time before the next 16-bit data word is assembled in the input shift register, i.e. before 417.8 nano-seconds have elapsed.
5imilarly, the output shift register 174 , -40~- 1 ~Z39 will require a new 16-bit word from its output holding register 183 at intervals of 16/28.62 = 0.55905 microseconds.
If there is a coincidence in the time at which an input word is ready and an output word can be accepted, input is given priority, since inputs come faster, when simultaneous requests for RAM operation occur. Table III
illustrates (in simplified terms neglecting logic delays of a few nanoseconds~ a possible sequence of events. For this example, it is assumed that an internal sync buffer logic clock on lead 201 running at 57.24 mega pulses/sec instead of the 28.62 megabits per second set forth herein-after is made available by the gear clock phase locked loop 212.
Therefore, internal events can be initiated only at the times of occurrence of these clock pulses or about every 17.47 nanoseconds. Each RAM memory cycle (either store (load) or read (unload) is assumed to take 200 ns. Assume that the memory cannot be recycled until at least the second clock pulse occurs following the completion of any memory ~ycle or after any new non-synchronous memory cycle request is generated. The times listed for completion of memory cycles, and also for the availability o~ input words, are not synchronous with the internal buffer clock and are designated as "NS" in the table. In this arrangement, RAM output requests will occur synchronously at inter~als of 32 internal clock periods.
For purposes of identification, the input words being loaded are designated as 101, 102, etc., while the words being unloaded are 1, 2, 3 etc.

TABLE III
RAM (FIF0) Ti~ng Example I~t~al Cloc~c Puls~ Time ~oldlng Register S
~u~er_ nsec ~ OPeration ~n~ut Out~u~
O O reqyssc. 101 ready 1 ready 17.5 start load 101 IJS 217.5 end load 101 emDty 13 227.1 re~ync.
14 244.6 ~tart unload 1 ~S 417.8 102ready WS 4~4 . 6 end u~load 1 . empty 454.2 re~y~c.
27 471.7 sta~t load 102 32 559.0 2 Eesdy ~S 671.7 end lc~ad 102 empty 39 681.3 re~ync.
69~3.8 start unloaa 2 ~S 835 .6 103ready E~S 8g8.8 end us~load 2 . ~npty 52 908.4 resync.
53 925.9 ~tart lcad 103 64 111~.1 3 r-ady ~5 1125 . 9 end load 103 empty 1135 . 6 resync.
66 1153 . O start u~load 3 l!~S 1253.4 104ready ~S -L3S3 . O OEld ~load 3 empty 78 1362.7 ~esync~
79 1380.1 start load 104 ~S 15aO.l end load loa empty e.~np~y ***~o acti~rity - waitlng ~or r~uest***
~S 1671. 2 105 ready ~:39 96 1677.1 resync. ~~ ~ ~ 4 ready 97 1694.6 start load 105 NS 1894.6 end load 105 empty 109 1094.2 resync.
110 1921.7 start unload 4 NS - 2089.0 106 re~dy The poin~ to notice is that the FIF0 se~uence catches up with the combined input and output tasks at 1580.1 nsec after the start of the example.
It waits for the generation of a n~w request which comes at 1671.2 n~ec when a nonsynchxonous load re~uest is generated, and the pattern starts to repeat.
An input scan tIming prob}em occurs when the reduction ratio causes the reduced Lmage of the input to be smaller than the output paper size. The size of the original (s) on the platen 62 is of no concern if the cover is closed. The viaeo signal variation due to the difference Ln re~lectivity of ; the platen cover and the unmarked areas of the paper can be set below the slicing level of the threshold detector 150 and should not ~e noticable.
Figure 7(a) i9 a representation of a reduced image 270 formed on output paper 272 (this can also c~rrespond, for example, to the electrostatic dot pattern formed on drum 76 within the xerographic processor 7~ A-~ can be seen, in order to center the image 270 on output paper 272, the left hand and right hand borders tas viewed from the paper) 274 and 276, respecti~ely, ~nd ~he upper and lower borders 278 and 280, respectively, must be appropriately generated to center tne Lmage 270.
Figure 7 (b) s'no~s apparatus ~hich may .

'~

be utilized to center the image 270 shown in Figure 7 (a).
The system controller 90 via leads 280 and 282, loads regis-ters 284 and 286, respectively, wit~ appropriate data (dependent on magnification ratio and output paper size~
relating to the borders 274, 276, 278 and 280. For the X
input scan direction, a problem arises if 17M<Lp. For 11"
paper, this is M~ 0.65 (M~ o.84 for 14.33 paper). In these cases, there would be fewer input bits available than is required for one output scan line (SDo) (Lp), the input scan bit rate being less than the average disc bit rate.
Register 284 is therefor loaded with appropriate data corresponding to borders 278 and 280, the output of register 284 being compared in comparator 290 with infor-mation regarding the X position of scan from bits per line counter 146. Register 286 is similarly }oaded by microprosessor 90 via lead 282 and is compared with the Y
position of scan from Y scan position counter 294 (i.e.
compares the scan position with the known border conditions).
~ When 17 (M) C Lp (determined by system controller 90), the ;~ 20 necessary "white margin zeros" are split equally between the beginning and end of each scan line, the output on line 126 being correspondingly controlled. Referring to Figure 4A, the output on lead 126 is coupled to a logic device 300 which comprises AND gates 301 and 303. The output on lead 126 is coupled to one input of AND gate 301 and to an inverting input of AND gate 303. The output from data selection gates 186 is applied to the other input of AND gate 301 whereas a voltage Vc is applied to the other input of AND gate 303. When lead 126 is low AND gate is enabled and passes the voltage Vc ~,'1 ~9Z39 to the modulator 32 to cause the laser 10 to generate the necessary white margins Ithe beam from laser 10 discharges the appropriate margin areas of drum 96). If lead 126 is high, gate 303 is disabled, gate 301 is enabled and the data signals on lead 125 passes to modulator 32 to modulate the laser light from laser 10 to reproduce colla~ed pages in xerographic processor 77.
Although not shown in the figures, the Y scan position counter 294 is adapted to cooperate with the shaft of motor 52 in a known manner to provide signals representing the Y position of the scan line.
Similarly, for 14(M)~ Wp, the width of the platen, as reduced, is less than the output paper width, when M ~0.61 for 11" paper (or M~ Q.72 for 14.33 paper).
For this situation register 286 is appropriately loaded with data corresponding to borders 274 and 276, a string of completely blank scan lines being generated both before and after the Y scan starts and finishes producing valid data within the width of the image on drum 76.
These procedures will center the reduced image of the platen area on the output page. The sur-rounding white borders will be electronically generated by causing the laser to perform the function of an adjustable fade out lamp.
It should be noted that the drive frequency for the 2 pole polygon motor 40 is Vp¦60 Hz. In order to generate a 2-phase quadrature motor drive signal, a quadruple frequency clock rate is required.

The correct value will cause scan bits to be generated at the average data rate of the disc. Then 'J'~
_ . .

`
~ 3~ 7 (BPS) (~) (V~/60 = ABR.
Wherein BPS is the bits per soan line rounded upwards.
The peak bit rate of the disc g6 is related to the average bit rate by the ratio of the number of clock pulses/sector, CPPS, to the data bit times per sector or CPPS/4096. The polygon drive frequency divide ratio, DR, is selected such that ~(CPPS) tABR)/4096)]/DR = 4 (V~/60 - 4 ~ABR)/(BSL)(~
DR = (CPPS) (~SL~ (~)/16,384.
with CPPS = 4968, BS~ = 4656, ~ = 26, DR - 36,707.
While the i~vention has been ~escribed with refarence to its preferred embodiments, it will be understood by those skilled in the;art that various changes may be made and e~uivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situ-ation or material to the teaching of the invention without departing from its essential teachings.

Claims (7)

WHAT I S CLAIMED I S:

1. A scanning system having the capability of scan-ning originals having images formed thereon in either a normal or inverted mode of operation such that electrical signals representing the scanned images can be stored in storage means such that when the scanning system reads the stored representations of the images to reproduce the images on a recording medium the reproduced images each having the same image sense comprising: first means for scanning said originals in a first direction in the normal mode and in a second direction, opposite to said first direction, in the inverted mode, second means for scanning said originals in a third direction, which is orthogonal to said first and second directions whereby said originals are completely scanned with light, means for converting the light reflected from said originals into corresponding electrical signals as the originals are scanned on a line to line basis, buffer memory means for storing said electrical signals in the order in which the electrical signals are generated, and means for unloading said electrical signals stored in said buffer memory means into said storage means in a sequence determined by whether the scanning system is in the inverted or normal mode of operation.

2. The system as defined in claim 1 wherein the system is in the inverted mode and further including means for unloading the electrical signals stored in said buffer memory into said storage means in the reverse order, on a scan line to scan line basis, from which the electrical signals were stored in said buffer memory.

3. The system as defined in claim 2 wherein the electrical signals representing each scan line comprises binary digits grouped into a plurality of words, each word in the scan line being read into said storage means in the reverse order in which it was stored in said buffer memory.

4. The system as defined in claim 3 further including means for reversing each bit in said wood before being stored in said storage means.

5. The system as defined in claim 4 wherein a plurality of words are stored in said storage means cor-responding to a completely scanned image and further including means to read out said stored image from said storage means in a manner to reproduce said image on said recording medium, the image formed on said recording medium having the same image sense as an image which would be reproduced on said recording medium if the system was in the normal mode of operation.

6. The scanning system as defined in claim 1 wherein said scanning light is produced by laser means.

7. The scanning system as defined in claim 1 wherein said originals are supported on an input platen.