Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
178
BAC~CGROU~D OF THE I~VE~TIO~
Laser sca~ning techniques for writing or printing
on a medium sen-~itlve ~o the laser beam h~ve been disclosed
in the prior art as shown, for example, ln U. S. Patent
~o~ 3,922,485. In general, ~he laser beam is intensity
modulated in accordance wit.h information to be printed
on a receiving medium, the mwdulated laser beam beLng
directed to a ro~atl~g scanner, or reflector, such aq a
multi-aceted pol~gon. The rotating scanner in turn
causes the modulated laser beam to scan, iQ se~uence,
across a sensitive medium located a distance away from
the scanner. The information contained in the i~tensity
modulated laser beam can be directly written on the medium
if the medium is se~sitive to the laser beam, or in an
alternative em~odiment, ~he laser ~eam can selectively
S~h C~5 C` p~ ,o~
discharge a charged insulating or semiconducting s~r~ace~
in accordance with the intensity of ~he beam~ In the
alterna~ive embodiment, the degree o~ charge dissipation
corresponds to the mormation contaLned in the intensity
of ~he laser beam~ The areas of the medium which are not
discharged by the laser beam are subsequently developed,
~or example, ~y standard xerographic techniques.
Present day ~opiers which are commercially
available which utilize the xerographic proc~ss include
a platen upon which the document to be reproduced is
placed, the platen being flat or cuxved. The document
is generally 100d illuminated or scanned wi~h light
and the reflections there~rom are imaged via a copy lens
to a charged photoconductive medium to discharge the
medium in accordancQ with the image formed on the
document.
The Telecopier~ 200, a facsimile transceiver
~ 2-
,~
178
manufactured by the Xerox Corporation, Stamford,
Connecticut, directs reflections from a laser scanned
document onto a photosensitive transducer, the electrical
signal output thereof being transmitted to another
location and used to modulate a :Laser beam to rep~oduce
the scanned document. However, the Telecopier 200 is gene-
rally not considered a copier type device since, inter
alia, a scanning platen and other copier features are
not available.
Although copiers now commercially available are
not adapted to utilize scanning techniques to scan a
document placed on the copier platen line by line to
produce a serial bit stream corresponding to the scanned
information (i.e. a raster type scanning system), it
would be advantageous if such copiers could be modified
to incorporate the laser printing technique disclosed,
for example, in the aforementioned patent, the modified
copier thus requiring a system which provides for two-
dimensional raster input scanning. A system for two-
dimensional raster input scanning which utilizes ala er, is described, for example, in U. S. Patent No.
3,~70,359. U. S. Patent No. 4,012,585, issued March 15,
1977, assigned to the assignee of the present invention,
provides a flying spot scanning system which is
capable of scanning an unmodulated beam to a reading
station for reading a stationary document and a
modulated beam to an lmaging station for, inter alia,
reproducing the scanned document thereat.
The availability of a copier which utilizes
two-dimensiona:L input scanning, such as the raster-
type input scanning of a document placed on a
X
~ ~17 ~7~
platen and laser scanniny techniques for wri~ing on~a
laser sensiti~e medium would provids many advantages
inherent with the use o~ lasers and raster type input
scanning, such as Lncreased copying speeds and reso-
lution. In particular, it would be advantageous i~ an
i~termediate storage medium was provided be~ween the
~nput and output scanning stations to allow ~or ~ani-
pulation and stora~e o~ the scanned information, and,
in particular, to yrovide for electronic precollation
which electronically arra~ge~ representations o~ images
to all~w collated set~ of documents to be reproduced.
Other desirable eature~ o~ such a copier would include
input scan rev~rsal for alternate bound page~ during
bound volume scannLng, qynchronization o~ the system by
a clock associated with the storage member, a synchronous
~/11 system reducing the size and cost of a' ~ bu~er
: aqsociated therewith, input/output interleaving with a
print interrupt eature, image cent~r~ng and edge adeout
for image xeduction, and independent magniication/demagni-
fication by s~parat~ly variable ras~er ~pacins.
~ .
S~RY OF TEE PRES~ I~ TION
rhe present int7eIltiorl provides a reproduction
sca~ning system having ~term~diate s~orage between
input and outptlt scanning sta~ions wherein an input
: document is scanned in first and second directions, the
~irst direction being orthogonal to said second direction,
and the electrical signals representation o~ information
on said scanned document ~eing stored on an intermediate
storage member,::preferabl~ a magnetic disc, for manipulation,
storage, or other signal proc~ssing via a sync~ronizing
buffer. The i~ormation stored in the storage member
~ ;7~
may be read out via the synchronizing buf~er and reproduced
on a reproducing medium which may, for example, be incor-
porated in a xerographic processor. Other s~stem 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 t
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
., ,~q ~
inven-tion to providQ 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 alte~nate page in a bound volume
is being input scanned.
It is an object of an aspect of the present
invention to provide a svstem of the type described here-
inabove wherein the system is synchronized by a clock
associated with the magnetic d:isc 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
i.n 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:
A scanning system for scanning information
formed on an information containing original supported
on a platen at a first location and reproducing the inform-
:
-6-
~L7~71~
~tion on a me~ium at a second location comprisiny
means for scanning said original and pro~
ducing electrical signals corresponding to the information
contained on said original, sàicl original being scanned
as a plurality of scan lines,
means for loading said electrical signals
into a buffer memory in a first mode of operation,
means for unloading said electxical siynals
from said buffer memory into memory means in said first
mode of operation,
means for loading said electrical signals
from said memory means into said buffer memory in a second
mode of operation, and
means for unloading said electrical signals
in said buffer memory in said second mode of operation
and coupling said electrical signals to a modulator, said
modulator being adapted to modulate a light heam incident
thereon in response to the electrical signals coupled
thereto, said modulated light beam being scanned across
said medium on a line to line basis in spatial corres-
pondence with the scanning of said input original whereby
said information is reproduced thereon.
A method for scanning information formed
on an information containing original supported at a first
location and reproducing the information on a medium at
a second location comprising the steps of:
scanning said original and producing elec-
trical signals corresponding to the information contained
on said original, said original being scanned as a plurality
of scan lines,
-6a-
~"'` '' . .
73L~
loading said electrical signals into a buffer
memory in a first mode of operation,
unloading said electr.ical signals from said
buffer memory into a memory in said first mode of operation,
loading said elect:rical signals from said
memory into said buffer memory in a second mode of operation,
and
unloading said electrical signals in said
buffer memory in said second mode of operation and coupling
said electrical signals to a modulator, said modulator
being adapted to modulate a light beam incident thereon
in accordance with the electrical signals coupled thereto,
said modulated light beam being scanned-across said medium
on a line to line basis in spatial correspondence with
the scanning of said input original whereby said information
is reproduced thereon.
BRIEF DESCI;~IPTION 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:
.
-6b-
u~: J
~7~
Figure 1 shows in simplified 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 i.llustrate a disc surface and
a typical recording pattern formed on the disc which may be
utilized in the present invention;
Figures 4A and 4B are more detailed block
diagrams of the system of the present invention;
Figure 5 illustrates in more detail the opera-
tion of the synchronizing bufer which comprises a portion
of the system o the present invention;
Figure 6 is a more detailed block dlagram of an
output shift register which may be utillzed in the present
invention; and
Figures 7A and 7B illustrate how a reduced image
may be centered on an output medium.
DESCRIPTION OF THE.PREFERRED EMBODIMENT
Referring now to Figure 1, a simplified
representa~ion of an optical system which may be utilized
in the present invention 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 preferably lasers which provide collimated beams of
monochromatic light, laser 10 comprising a helium-cadmium
laser which generates blue.laser light at a wavelength of
4416A and laser 12 comprises a helium-neon laser which
generates red laser light at a wavelength of 6328A. The
use of the two laser. beams ensures that the document
scanner i5 not insensitive at the wavelengths of lasers
10 or 12 and hence, the system is suitable for detecting
~ILi7i~
light fluxes reflected from multi-colored documents in
addition to the fact that a choice of laser beams is
available 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. l`he 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 double.t 30, the
split doublet 30 allowing the separate beams incident
thereon to be focused on the platen 62 or drum 76.
Rotating scanner 28, shown as comprising a polygon having
a plurality of reflecting facets 38, is driven by motor
40 via drive shaft 42.
Scanner 28 rotates in the direction of an
arrow 44 causing the laser spot (combined laser beam)
incident thereon to deflect in the x-direction at mirror
2S 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,
--8-
~':
-,~,
~1~7~
element 46 beiny afflxed to cable 55, element 46 being
driven at 1/2 the speed of elements 48 and 50 to maintain
a constant focal length between the platen 62 and mlrror
43. This technique is ~enerally referred to as 1/2 rate
S mirror scan, such a techniqlle being disclosed in U. S.
Patent No. 3,970,359. A scan spot 58 is produced which
moves along scan line 60, formed in the x-direction at
platen 62, as scanner 28 continues to rotate. Although
not shown in the figure, a document, or a page in a
bound volume, to be scanned is placed face down on the
top surface of transparent platen 62. Since motor 52
is bidirectional, the direction of y scan is selectable
by an operator by appropriate activation of buttons
formed.on an operator's.panel 92 (shown schematically
in Figure 2) which in turn.causes a system controlling
microprocessor 90 ~Figure 2) to generate the appro-
priate control signals. As will be set forth herein-
after, the particular scan direction selected is deter-
mined by the type of input being scanned, alternate
pages of a bound volume generally requiring reversal
of the normal scan direction.
When a document is placed 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 scanned.
A fraction of the reflected flux is detected by one or
more photomultiplier tubes (or other photosensitive
device) represented by a single photomultiplier tube 66
~ ,r~
.
'
~;11 7~7~
located under the platen 62 via mirror 64. The photo-
multipliers convert the variation in intensity o~ 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
L5 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 4B 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 o~ 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
0--
~,
7178
hereinabove are ~ixed platen scanners (document stationary
on platen) it is to be noted that the system can be arranyed
such that the input document moves along the Y direction
of the platen 62, the input scanning mechanism thereby
S being stationary.
As shown in Fig. 1, 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 scanniny 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 repxoduction 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-
> .
.
71~
a signal when the scan on drum 76 (a portion of -the
xerographic processor 77 shown in Figure 2) is initiated
and end of scan cletector 84 is provided adjacent mirror
72 to provide a signal when each scan line is cornpleted.
It should be noted that although a single polygon scan-
ner is shown for both input and output scanning, separate
polygon scanners which are synchronously driven may be
utilized. Re~erence may be ~lade to the teachings of the
aforementioned U. S. Patant No. 4,012,585 which
provides, inter alia, for scanning an unmodulated laser
beam at a reading station for reading a stationary
document thereat and directing a modulated laser beam to
an imaging station for reproducing the document image
thereat and which utilizes single scanner element.
Figure 2 is an optically simplified version
of Figure 1 and further shows, in a simplified form,
the electronic input scanning signal processingt
storage and output scanning functions of the present
invention.
The speed of drum 76 of xerographic processor
77 is assumed to be 12"~second for purposes of the calcu-
lations to follow 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 paperJ is provided, for example, by
the Xerox 4000 copier manufactured by the Xerox Corporation,
is initiated on demand under control of the system micro-
processor controller 90. It shouId be noted that the
function of microprocessor 90 is that o~ system manage-
ment and when properly programmed, controls the operating
sequence of the entire system of the present invention.
It also sets up the appropriate operating parameters
derived from user controls on panel 92, such as magnifi-
cation ratlo, mode of operation, normal or reverse scan-
ning mode, etc. In general, the system controller
issues appropriate commands to xerographic processor 77,
receives status signals therefrom, issues scan and
storage control parameters and the start of scan signals,
receives status signals from the rest of the system and,
of course, interacts with the user panel 92. Any
properly programmed microprocessor, such as the Intel
8080 or the Motorola 6800 or minicomputers such as the
Nova series manufactured by the Data General Corporation,
Southboro, Massachusetts, can perform these functions.
Since the present invention is directed to the general
interrelationship of the system elements, a specific
description of the microprocessor system controller 90
and the operating software therefor is 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 intend-
ed to limit the scope of the present invention.
In one embodiment, input scanning is providedon a ~lat platen 62 (14"x17" for example), the scan
mirrors moving across the short (14 lnch) dimension of
the platen as shown in Figure 1 to provide for y scan-
ning.
The X direction scanning in the long (17 inch)
-12-
r
l78
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.~3 inches over scan at each end of the 17" platen which
S allows the scan c~ock generato;r 94 to be resynchronlzed
prior to the start of the next scan line.
Resolution in the X and Y directions oE scan
is assumed to be equal. That is, the bits/inch (pixels/
inch) in the X direction e~uals the lines/inch in the Y
direction for both input and output scanniny.
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 ~hould 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
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7~
lasers are utilizecl to read the information formed on the
disc) have been disclvsed in the prior art and may be
utilized in the present inven-tion. A read-write optical
disc memory i9 disclosed, for example, in an article by
D. Chen, Applied ~ptics, October, 1972, Vol. 11, No. 10,
Pages 2133-2139, the teachings oE which may be adapted
to the present invention. In general, the output rom
the input scanning device can be utilized directly to
modulate a laser, via synchroniz:Lng bufer 98, the laser
in turn writing the appropriate :Lnformation 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-
L78
track-q preferably beLng Eormed in a helical pattern.
. The total capacity of the disc 96 pre~erably is selected
to be approx-
--13,a--
~i~71'7~
imately 8 x 108 bits which allows storag~ ~8,
8-1/2 x 11" Lmpres~ions tpageq) scanned at approximatel~
423 lines/inc~. The average data bit rate to the disc
system 96 (the system including a magnetic disc 97,
positioning arm~ alSc drive etc~ ) is assumed to be
23.59 megabits/second.
Synch~onization in the scann~lg s~tem o~ the
present invention is derived from the disc system itsel~.
pximary clock rate o~ approximately 28.62 megabits/
second i9 ~ormed by the timer block 100 in conjunction
with the disc and is used to con~rol the recording o
in~ormation thereon from buffer 98. This clo~k rate,
which will also be synchronous with data read from ~he
disc ~7 (sinca the second disc is identical to disc 97,
only disc ~7 will be re~er~ed to hereinafter~. is cou~ted
do~n in timer tor clock) 100, to produce appropriate
2-phasa AC signals to drive a s~nchronous scanner motor
40, the Y ~can mirror drive motor 52 and appropriate
clock signal ~rom
clock signals to synchronizing bu~er 98. The/scan clock
generator 94 (used to control the timing o~ data that
modulates tha laser beam on output scanning and to sample
the photodetec~or signals on input scanning) is generated
in bursts, unde~ the ~ontrol o~ the start-of-scan and end-
of-scan photode~ectoxs 82 and 84, xespectively. The scan
clock generator 94 is therefor slaved to thc speed o~
polygon 28 which in turn is derived from the disc system
96. the scanning system timing there~or being synchron-
. i~put scan
ized with the disc speed. The/speed relationships are
chosen to cause data ~o be generated at an average rate
equal to the ability Qf ~:the disc 97 to store it. If the
rotational speed of disc:97 was to change slightly, the
scanner 28 a~d scan clock 94 will follow the change.
-14-
~7~78
This synchronous sy~tem tlming met~od allows the size
of the synchronizin~ buffer 98 to be signi~icantl~
reduced in size (and cost) and substantially les~ than
the capacity of one helical tur~ on the diqc 97 (as
will be set forth hereLnafter, one tu~n o the disc 97
is capable o~ storing 4 (surfaces) x 48 (sector3 per
turn) x 4096 (bits per sector), w~ich is 48 times les3
than the size of the synchronizing bufEer which prererably
will be utilized). Synchronizing bu~fer 98 is required
since the peak data rate during input scan is approx-
imately 38 megabits/second, which is hig~er than the
rate that disc 97 can accept the input data (approximately
28 megabits/second). ~he average bit rates over a number
of scan lines, however, will be approximately equalv
Further, synchronizing ~uffer 98 smooths out any gaps
b~tween sectors on disc 97, the sectors includin~ 4096
data bit , when the reproduction system is in the print
mode, ~he system controller 90 preventing gaps (and
sector headings, labels, etc.) from being stored in the
synchronizing buf~er during the prlnt mode o~ operation.
The time to scan an original on the input platen
62 (see Figure 1) is selected to be the same as the time
re~uired to expose the xerographic drum 76 ln xerographic
processor 77 to reduce the time required for output and
the size of synchronizing buffer 98.
The following relationships are given to
provide an indication o system performance. The follow-
ing deinitions are useul.
ABR = Average bit ra~e ~or magnetic disc 97 (bits/sec)
BPS = Bits per scan line
BPP = Bits ~pixels3 per page
CPPS = Clock pulses per sector for the magnetic disc ~7
--15--
178
DBC = Disc data capacity in bits
DPC = Di9c data capacity in page~
DR = Divide ratio for generatlng polygon drive frequency
Lp a Output paper lenyth (in.) (Parallel to axis o~
xexographic drum 76.
Ls = Input platen scan length includlng oversca~ (in.)
(Ass~med to be 17 .~85 in.)
M = M~gnification ratio (1.0 to 0.61)
; ~ = Number o ~acets on the polygon scanner 20 (assumed
to be 26)
SDi = Input scan den~ity (lines~inch ar bits/inch)
SDo = Output scan density (lines/inch or bits/inch)
SLS = 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 angular velocity (rpm)
Vy = scan veloci~y (in/se~)
Wp = Output paper width (in.)
.There~ore, from the geometries ana character-
istics o~ the system, the following is obtained:
(a) Output scan aenSity
71 SDo = ~ABR~d\)(~p))] 1/2
~ (b) Polygon rpm required ~or output sczn
: Vp = 60(SDo) (Vd)/N~
(c) Bits (pixel~ per output page)
BPP = (SDo) Wp) (SDo) (Lp)
:. (d) Input scan density
SDi = (SDo) (M) or M ~ SD;
(e) Input Y scan velocity
Vy ~ Vd/M or M ~ V SDi ~eing inversely
proportional to Vy
L7~
( f ) Scanner rpm required ~or input sca~ ~
~/11 vp =60 (SLS)/N=60 (SDi~ (V~-60 (SDo) (Vd)/
(g) Scan line per second
SLS = ~(Vp)/60 -- (SDc~) (Vd) .
(h) PeaX input scan bit ra;te
SPBRi - (SLS) (Ls) (sDi) - (M~ (1,5) (Vd~ (SDo) 2
(i) ~he total number of pages that may be stored on
the dis c
DPC = DBC/BPP ~ DBC/ (SDo) 2 (Wp) (Lp)
Tho followlng suImnarizes some of the system
characteristics ~o:r 8-1/2 x 11" output paper.
TABLE I
Average bit rate (~bps) 23.sg
Output scan density (lpi) as dete~mined
by the speed of drum 76 and the disc clock
rate . 422~77
Output scanner velocity ( rpm) 11, 707
Bits/ll" llne 4, 650.47
Megabits/output page 16 o71
Storage Capacity of Disc in pages 48.19
Peak input rate (mbs) 38.30
a maximum reduction factor of 0.61 is
assumed, the input scarl density in lines/inch and bits/ .
inch is reduced from 422~77 to 257.89. The output copy
rom xeroqraphic processor 77 is still produced at the
maximum scan density of 422~77 scan lines per inch,
The total nu~iber of pixels per output page is constant
and independent of magniication and therefore allows
ror a sim~le and ef~ective way of controlling magni' i-
cation by controlling input scan density.
--17--
~117~
The input Y di.rection san mirror velocity is
increased from 12 inches/second to lg.67 inches/second
for the 0.61 magni~ication ratio. The peak input bit
scan rate accordingly drops from 38.30 megabits/sec~nd
to 23.36 megabits/second~
When larger output paper is used, the scan li~e
density and disc page storage capacity are reduced.
Table II lists system characteristics wherein 10.12" x
14.33" output paper is~u~ed. Note that sin~e the bit
rate is ~ixed and the paper area is larger than in the
Table I example, the output scan density will be les~.
TABLE II
Average bit rate (mbps) 23~59
Output scan density (lpi)370.41
Output scanner velocity (rpm~10,257
Bits/14.33" lLne .5,307~91
Magabits/output page 19.89
Storase capacity in pages40.4~
Peak input rate (mbs) 2~.40
At a reduction ratio o~ 0~1, the input scan
density becomes 225.95 lines/Lnch with output scanning
remaining at 370.41 scan lines per inch.
Although the Lnvention described herein is
pre~erably utilized to provide for electronic pre-
colla~ion (precollation being pro~ided in simplex oper-
ation by copying the number of input origlnals in
seguence onto the disc 97 and printLng a predetermLned
number of copies o~ each sequence via the xeroyraphic
processor 77), it should be obvious that by changing
control- p~rameters and the sof~ware used ~y the micro-
processor 90 that many additional features may be
18-
provided i~e. providing a small alphanumeric_dLsplay for:interactive guidance for the sys~e~ user; a small portion
on the large disc capacity can be used to store statistics
on system use; the disc could be used to store software
diagnostic routines to be used by the microprocessor
90 ~or trouble diagnosis; a scan density compatible
with easy conversion to facsimile could be selected, etc.
The disc 97 to be utilized with ~he present
invention is assumed to comprise two platters (four
sur~aces) recorded and read in parallel, one surface 99
of which is illustrated in simplified form in Figure 3.
~he data is recorded, or examplet in 1024 discontinuou~
sectors lOl within angular area 102, 48 such angular aréas,
being ormed in band area 103 around'the disc circumference
(approximately 50,000 sectors thereby being pro~ided).
Each sector lOl is subdivided into 3 main sections. The
first section contains a space 104 for a fixed header
identifying the sector number~ The second section 105
is a rewritable control area of 128 useful bits identi-
fied a~ "lakel". The third section 107, separated from
section 104 by gap lll, is the normal data area of 4096
data bit~. There are 48 such sectors per turn, each
sector being separated ~y gaps 113. Information is
preferably recorded in a spiral (helical) pattern
(similar to a phonograph record) with a total o~ 1024
active data turns. The spiral type pattern (track) allows
data to be read-continuously with the disc read/wri.e heads
following the track as in a phonograph record. The
header area loa of each sector may be arranged to contain
a pattern that is used to ser~o con~rol the radial
position of the recording-playbac~ head to allow it to
follow the spiral data path.
The number of circumferential clock periods
-19-
7~715~
(not shown in the figure) r~uired in eac~sector ~or
gaps, header and label (error detection and correction
bits may be provided if desired) is a~umed to be 872.
Therefore, the tot~l sector length is 4968 clock periods.
Table III summarizes typical performance characteristics
~or the disc systam 96:
TABLE III
Data bit~/qector (each surface) 4,096
Clock periods/sector . 4,968
Data bits/sactor (4 suraces)16,3~34
Sectors/tl~n 48
Turns/surace 1,024
Data bits/turn (on each surface) 196,608
Data ~its/turn (4 sur~aces~786,432
Average data bit ra~e/sur~ace (mb~) . 5.89
(30 x 48 x 4096) whe~ein the aisc
rotation ra~e is 30 revolutions per
second
Average bit rate for 4 tracks (mbs) 23.59
Peak bit rate/sur~ace (mbs)7~15
(30 x 4~) (4096 ~ 872~
Total peak bit rate (mbs)28.61
Total data capacity (bits) 805,306,365
Although not considered part o~ the present
invention, it should be noted th~t the large size of
the data blocks in this system maXe the use o~ isolated
and burst error detecting and correcting codes e~fi~ient
and attractive.
The seeX operation wherein the radial disc
arms seek the starting sector on the disc 97 is defined
by specifying a uniaue sector number out o the total of
-20-
~L17~78
4g,152 sectors along the spiral txack by .the~system,
controller 30 and having a controller speci~ied acceler-
ation motion to enable the disc arms ko locate the correct
sector. ~ew information (representing :Lmages in this syqtem)
is written directly ovex ol~ data without a separate erase
pa~s to save system tlme.
Figure 4 i~ a more detailed block diagram o~
the preqent invention~ It should be not:ed that signal3
to and from the microcode programmed microprocesqor syskem
control}er 90 are indicated in th~ figures by circles
adjacent to a label o~ a ~unction enterins or comlng ~rom
a particular elec~ronic subsystem block.
Direction control de~ice 121 receives an input
~Y ~can drive frequency) on lead 122 ~rom reduc~ion counter
130, the system control~.er 90 introducing the si~nal "start
scan" on lead 124~ The velocity and direction of the Y
sca~ motor 52 are set up by the system controller 90~ The
sca~ velocity (Y scan drive re~uency) is determined by.
the "magniication ratio" control parameter on lead 128
specified by an opera~or via panel 92 (Figure 23 which is
used to determine the clocX frequency division ratio in
the svstem timing counter 129 (logically a se~ of counters,
~he count ratio being changed by ~he selected ma~nifi-
cation ratio)and the reduction counter 130. The magni~i-
cation ratio signal is applied to reducti~n counter 130
via lead 127 a reduced clock signal being applied thereto
from system timing counter 129 vla lead 119~ The direction
control device 121 causes a Y ~can pass to be ~
a~ter the "start scan" signal and direction informa.ion are
provided by the system controller 90 the direction information
being initially set up hy an operator via panel 92 . Logic
-21-
. .
3l ll;~l~7171~
circuits within direction control d~vice r21~~eterminë
the proper polarity of the Y scan drive ~~applied
to motor 52 for the correct direction o~ scal~. In the
-21a-
~7~7~
normal (non-inverted mode) it is assumed that the Y
direction of scan i9 in the +Y direction from an initial
position 61 (Figure 1) wh~reas in the inverted mode of
operation the Y direction of scan i5 in the -Y direction
from initial position 63.
The start of Y scan time is derived by the
system controller 9Q from informat:ion it has about the
starting sector number for the next page of information
to be entered into the disc 96 during input scanning.
The 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 13~. The controller 90
checks the Y scan status from the direction control block
on lead 126 prior to initiating 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 observed that since the input
scan line density must be changed ~reduced) to vary the
magnification ratio it is preferable to change the size
o the scan spot for input scanning, in 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
apertuxe control 133 is utilized during input æcanning,
the aperture control incrasing the size of the scanning
spot in the direction associated therewith via a signal
from sys*em controller 90 on lead 135. On input scan-
ning, the effective X dimension of the spot (in the
direction of high speed scan) may be controlled by
22-
3 715~
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 effecti~e 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 ~rom 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 tbat
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.
-23-
7~7~
The voltage controlled oscillator 138, oscillating
a-t 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 stzlrt 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 magniflcation ratio and output
paper size utilized. The preferred range is rom approxi-
mately 423 bits/inch to approximately 226 bit/inch tinput
scan onto 14.33 paper at magnification of 0.61). When the
preset number oE bits (voltage cycles) (bits/inch 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 average signal fre~uency 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-
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 ganerate 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
-24-
X
~1~7~L7~3
processor 76 is transEerred by standard tec~niques in
the preset mode~ The range tco~nt) i~ 4656 to 5312
bits/line which is less than the range ~or counter 142
since ths latter count is preset on the basis of the
input platen scan line length and including overscan
These numbers are slightl~ larger than those listed
-24a-
L78
in rrables 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. Even 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 cloc~ gate 148 releases precisely timed
bursts of clock pulses on lead 200 at the start of its
countdown cycle ranging in fre~uency from 38.30 to 17.93
megabits/second as determined by the system controller 90
(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 c oc;; gate 148 is used
to control the timing of loading the synchronizing 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-
~ !
178
user control to help remove background and otherwise clean
up inferlor originals. Existance of the image inEormation
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 ll" paper)
the active scan time is only 11/17.855 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 ard paper size. In that
case, "white border bits" are generated to fill 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 (RAM) chips. Each input and each output
operation of the RAM handles 16 bits inparallel. It is
-26-
~.,
178
assumed that chlps operating a-t 200 nanoseconds ull
cycle tlme will be utilized. This will provide a peak
rate o~ 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, ~irst-out oper-
ation mode of operation, a load address counter 180 sel-
ected by address selection gates 181, sequences through
t~le 1024 addresses in R~M 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 parallel~
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
25 shift register 176 via lead 206 and unload address
counter 182 timing via lead 204. The threshold detec-
tor 150 (Figure 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 from RAM 170
going tc disc 97. Similarly, for output scanning (print-
ing) the disc clock on lead 201 controls the input to RAM 170
via shift register 172 and load timing via load address
-27-
'
~17~78
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
S 62, successive pages of the vol~ne 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 (scan inversion is accomplished by
operator selection o~ 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 t~e scanner 28. The X-scan
direction is therefor reversed electronically as follows:
For an 8-1/2 x-11" lnput 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 mode) load address counter 180 via address
selection gates 181 causes the input scan information
from photodetector 66 (291) sixteen bit words) to be
stored in se~uence, 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
-28-
X
~17~7~il
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 dlscs 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 g7 via write ampli-
fiers 223 ~ g. 4). When the information read out from
RAM 170 lS to be applied to modulator 32 and therea~ter
reproduced by xerographic processor 76, the signal on
lead 250 enables the information to be read out serially
on lead 125. In a similar manner although not shown in
the figure lnput shlft register 172 is adapted Ivia 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.
-29-
~17~71~
The next scan line is recorded ln 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 rom 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
wordsr 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 is in the print mode, as deter-
mined by operator energization of a "PRINT" button on
panel 92 (not shown), the~output from discs 97 is read
out via read pre-ampliflers 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 regis*er 183 to output shift register 174. It
.
178
should be noted, as set forth hereinabove, that since the
scan lines have already been reve~sed prior to being stored
on disc 97, unload address counter 182 i5 not caused to
count down by a signal from buffer control 202 on lead 177.
The data which is beiny read out therefor is electronically
reversed in the x-scan direction.
The scan clock on lead 200 is utillzed 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 dlsc 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
a,.d control information from the data stored in the shift
registers. The system controller 90 will supply header
and check logic 131 with the following parameters: Lines/
page, bits/line, and page start sector number which in
turn modifies the data stored in the RAM 170 with this
information prior 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
-31-
~17~71~
scan line of each page may start at a sector boundary
identified ~y -the page s-tart 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 o~ as completely deEining the ormat and other rele-
vant information about the data to follow.
The header and cneck 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-
ni~ues 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
20 counter 129 are also applied to buffer control 202 (approxi-
mately 28.2 megabitsjsec) and header and disc logic 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 wiIl 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.
The header and check logic 131 will issue sector
-32-
. . .
111 7178
number co~nands to the seek control block 206 via lead 224
that controls the positioner (not shown) or disc arms 115.
Seek complete status is lndica-ted to the system controller
90 via lead 207 when the commanded sector has been acqùired
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 khe
helical track) from the playback voltage on lead 211 whlch
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
counter 129 via lead 228.
The gear clock PL~ 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 turn) a magnetic detector
pickup mounted on the disc support structure generating
a pulse as each tooth rotates therepast, a pulse stream
thereby being generated having a frequency proportional
to the rotational speed of disc 96. A typical input to
gear clock phase locked loop 212 is 192 pulses~second.
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
-33-
detector is qeparated from the recording discs 97 and
is always available w~ether the disc system 96 i5
reading or writing~ It is to b~ noted that system
tLming counter 124 supplies a plurality of pulse signal,
including pulse rates reduced in frequency ~rom the
28.62 mb~ input on its output counter leads to pro~ide
appropriate timins 5isnals to the variou3 syste~ elemen~s .
For example, a frequency.o~ 100 cycles is generally
required to drive motors 40 and 152. The count ratio of
counter 129 is varied by the ma~nification rat~o on
lead 128.
Three ~asic modes of operation are involved
in the operation of the pre~ent systemO The ~irqt 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 scannins where copies are
produced xerographically.
`
.
: ~ , ' -
-33a-
~L~17~7~
~ _ Y
During the job set up, the system controller
90 furnishes a starting sector n~mber or the ~irst page.
The disc seek control 206 will ~ind that sector issued
by headex and check logic 131, and then sek up the idle
mode holding pattern and indicate a seek complete
condition to the system controller 90 on lead 207.
Similarly, the proper timing ratlos will have been
i3~ued to cause the scanner 28 rpm ta ~ qelected and
stabilizedO The scan cloc~ phase locked loop will be
generating the co~rect number o~ bits/inch and bits/scan
lin~ for the selec~ed magn~ication. ratio and output .
page size, the proper scanclock thereby being applied ~o
lead 200. The header control losic,l31 will h~ve been
set up with the bits/sca~ line and scan lines/page para-
meters. The controller 90 will generate the sector
number to start each page, and these will ~e pro~ided
sequentially to the seek control 206 as the job progres-
ses in order to allow or electro2lic precollation.
The controller 90 has been given the number of pages/
book and the number of books (cop.ies)/job by the user
thxough the control panel 92.
The controller 90 may derive or be told by the
operator of the sLmplex/duplex status of each output
page and computes appropriate Fage start sector numbers
to provide the optimum sequence for duplex output
production (if the ~:erograE~ic processor 77 is capable
. .
of duplex operation).
Ater the job is set up, the Lnput scanning
operation can proceed. The operator places his first
original on ~he platen and pushes eLther the "Normal"
or "In~er~" scan bu~ton on panel 92. This causes the
system controller 90 to initiate a scan on eit~er the
+Y or-Y direction (Figure 1) at an initial starting
~1~717 !3
.
posi.tlon. ~he Y scan rnotor 52 will start~w~th a lea'd
tLme (with re~pect to the axrival of the page start
sector number of th~ disc) to allow the Y scan mirror
to accelerate an~ stabilize at the selected ~elocity
(as detarmined by the selected reduction ratio) and
depending on normal or reverse scan direction, both
parameters being operator initiated. As was men~ioned
here~nabove for reverse ,scanning, one or more complete
scan llnes must be loaded into the synchro~izlng bu~er
98 prior to the arrival of the page start sector at.
read heads of the disc, At this t~me, the dlsc system ~6
will demand output from the buffer 98 in lnverted ~or 1IFO)
mode. The data ~low into the bu~fer 98 from the photo-
detector 6~` is timed according to the scan clock synchron-
ization circuits,and is not detexm~ned by the position of
the Y scan drive motor 52. Variations Ln the position
o the Y scan mirror at the s~axt of electrical scan
are equivalent to a shift in t~e position of the original
on the platen (in the Y direction) and do not a~fect
the synchronizin~ bu~erO A position detector can be
provided to check ~he timin~ of this operation to allow
the system controllex 90 to adjust the lead time
parameter.
. The system runs to the end,of t~e page and the
disc system 96 see~s the next page start sector number.
If the input scanning is being done for s~mplex output
pri~ting, the next page will start at the next sector
following the last sector used in the previo~s page~
For duplex output, appropriate page start position
interlace will::have been ~enerated by the system
. -35-
~i~7~78
controll~x 90. T~at i3, thq sequence o~ pages alo~g the
spiral track on di~c 96 will be arranged during input
scann~Lg for the benefi-t o~ high thruput output~
Operation during the third mods, output
scanning, is sLmilar. In the idle conditian, the disc
system 96 acquires the page start sector. The paper
feed from either the duplex recirculation ~aper pat~
or the normal paper supply path from xe~ographic processor
77 can be triggered on demana ~rom the system controller
90. Collation is t~Len done electronically as each page
is read from the disc in sequence to form a book, the
number of books that will be generated being depende~Lt
on operator selection of the appropriate button3 on
panel 92.
Interleaved input and output may be required
for example, when a job requirlng 25 copies of a 13-page
original has been loaded and the system is Ln the output
(print) mode, The operator then wishes to load a new
job~ Thi9 ~act, plus the ot~er normal job set up
quantities are entered via the control keyboard 92 and
the irst original of the new job is placed on the platen
62. W~Len the start button is pushed, the system co~troller
90 finishes printIng the output page in process and then
momentLLrily interrupts the output printing operation.
l~Le sys~em controller 90 resets the scan clock rate
and an input sc~n takes place. The system then Lmmedi-
ately resumes output printing while t~e operator changes
to the next original on the input platen, ths process
being repeated until the first job is completed and all
the originals of the new job have been scanned.
The following sets for~h an anaLysis of some o~ -
the factors that may be utilized to determine the size
of synchronizing buffer 170 and the syste~ timing
-36-
~L17178
relationships and con~id~rs t~e case of ~np~ scan~i~y,
using 8-1/2 x 11" output pape~ size and the normal
(no reduction) mode. Thi~ appears to place the most
stringent demands on the size o~ bufer 170. Table ~V
hereinbelow lists some data, (time~ being in micro-
seconds and bit rates in rnegabits/second)~or the systemdescri~ed hereinabove.
TABLE IV
~otal sector time 106/30 x 48 694.44
Active sector time 16, 384/28 .61 572~55
Inter sector ~ime (assumed gap time) 121.89
Total scan lino tim~ 60 x 106/(~)(Vp 197.11
Active scan line time 4656/38.~ 121~58
Inactive scan line ~ime 75.53
Total bits/sc~n lin~ 4656
Total bits/sector 16,384
Number o scan lin~s/sector '3~51
Peak bit rate to disc 28.62
Peak bit rate ~rom scanner38.~0
The most stringent demand~ made on synchronizing buffer
- . . . .
is in the Lnverted page mode where at le~st one complete
scan line must be lo~ded into tha bu~er memcry 170
prior to removal of information for ~he disc 96. The
minimum lead time for information supplied to the bu~fer
memory from the input scanner that is required to preven~
the disc unload re~uirem0nts from overtaking the data
available in the buffer should be det~nmined.
Time will be measured, in the following calcu-
lation, with respect to the instant, time to,that data
bits mu~t be supplied to the 96 disc f~om the buf~er
170. The time to load the 4656 bits o the first scan
line into the disc 96 is
4656/28.62 = 162.71 microseconds.
The disc tkere~or accepts a line o~ data in less than
the 197.11 microseconds total scan line time. Thereeore,
.
717~3
when disc 76 is r~ady to receive the begrn~ng o~-the
fourth scan line n~ar the end o~ the ~irst disc sector
which will occur at
t~ = 3 x 162.71 ~ 488.12 micro~econds
after to~ the input scanner at t4 mus~ have loaded
four complete s~an line~ :into the buffer 170. The
time required to load n scan lines into the buf~er is
given by ..
n (197.11) -75.53
I TL denotes the lead tLme in microseconds with respect
to the s~art o~ the data block (to~t
4 (197.11? - 75~53 -TL = 488.12,
TL ~ 224.79,
. .. . .~ , . .
t - ---694. 1_ ", __ 69~
; 573 ~ . .
.D~sc tim~ng -- 1 2 3 4 ¦_ x ~, 1 5 , 6. ~ 7 ~, x
~ - 225 _ 4~8 . ~ : :
. . ,: ' ' ' : '
. ~ tir~nq TI 1 x ~ 2 x, 3 x, 4 x, 5 - ~ x 6 , ~ ~ 7 , x 8 , x
' ~ ' ' ' . : ' . '._' . ' .
1, 2, 3 ... represent scan lLne numbers (both disc and
scan)
x represen~s inactive time
Thus, TL represents th latest start time at which
input scan signals may start to enter the synchroniælng
buffer 170 measured with respect to time to, the lniti-
ation of the unload to the disc, the unload i~itiationprocess bei.ng controlled by bu~fér control 202,
The earliest start time is determined by the
-38-
~il'7~L78
upper limit on the size o~ buf~er 170, A~r ~eedlng
three scan lines into the buf~er without removing any
information or the disc 96 there will be
(16,384 - 3 x 4656) = 2416
bit position~ left in the buffer 170. The start o~
transfer to the diqc 96 from ~he bu~er (to) will
occur at some time during the loadi~g o~ the fourth scan
line into the bu~er 170. Prior to to~ the net input
rate to the buffer 170 will be ~8,30 megabits/~econd
input. The differential input rate after to will be
38~306 -28~62 a 9.68 megabits/second~
. _ , . - _ . .... ...
.. . . . .
-.;
Disc ~ 163
ti~ng 1 . . . . . ..
-- .. __. . 2 ~ 3 _ j 4
~ ~a ~ ~121.6 ~
3 I x ~; ~ 4 1 x I S _1 x ~ 6 ~ x ~
~1 to t2 :, ' ''. .' ' - . :
, input scan tim~.ng
:. - , . ,. . :.
~, ' , .
.... _.. _ .;.. ..... _ _
The active tim~ ~or scanning the fourth scan line (121~58
microseconds) can be devided into two intervals ~ tl + ~2
tl~+ t2 = 121.58.
The total net increase in bits contained in the buffer
}70 during the input of the fourth SCaIl line cannot -
exceed-the remaining capacity o~ the buffer 170 t2~16
bits).~ Therefore,
tl x 38.30 ~ t2 ~ 9.68 = 2416.
tl = 43.30 microsecondsO
- 3 9-
~1717~
,
The ~arliest lead tLme that the~scanning input
can start i~, th~refore,
TE ~ 3 x 197vll + 43.30 - 634,63 microseconds.
Tho optimum load time with respect to to
normally would be conQider.ed to be the average of the
earlieQt and latest lead times, i.e~ 430 microsecond~.
Eowever, the scan line start times precess with re~pect
to ~he disc sector start× The op~imum enab~e
time fo~ allowing the input scanner to start loading
will leave t~e bufæer 170 e~ual margins beore the
earliest allowed time and after the late~t pos3ible
occurring ~ime (after enable), Thes~ possible data
load start timeQ are 3eparated by one total scan time ~
- -or 197~11 microsecond-Q. Thus, if m - margin time,
2m + 1~7,11 9 6~3.63 - 224079.
m = 110.87
Thereore, for the case o 8-1/2 ~ 11"
output paper size inverted scanning, no reduction,
~he optimum time ~o initiate input scan loadins of
th~ syn~hronizing buffer 170 is
- . TE ~m 9 532.77 microseconds
befoxe to~ .
,' - , `"' . . .'. '' . " ' " ' - :'-''''
. , ~ , .
t -- 644
. ~ . . ..
533 ~
111 ~ 197 _ llL ~ 225 ~-
margin scan s$2rt ¦~argin ~ -
t
~E sc~n start enabl e
~ ' ' .
-40-
fll~717~
An e~cample o~ how the normal f~ in fiFs~-
out oper3.tion might function duxing non-synchronous
interlaced load and unload cycleq is set forth hereln-
a~ter. As~ume agairl the 8-1/2 x 11" output paper, no
reduction, ~nput scan case. 16-bit words will be
available in the lnput data holding register 173
(Figure 5) at intervals o~
16/38 ~ 3 - O . 4178 microseconds,
This in~ormation must ~e loaded into the RAM 170 at
som~ -time before the ne~t 16-bit data word i9 aggembled
in the input shi~t register, i.e. before 417~8 nano-
seconds have elapsed.
Similarly, the output shift register 17
-~Oa-
1~7178
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. E'or
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 tLmes of occurrence o 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 cycle or after any new non-
synchronous memory cycle request is generated. The
times listed for completion of memory cycles, and also
for the availability of 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 intervals 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.
-41-
717~3
TA:3~E III
IFC)) Tim~ng Example
Inter:~al
Cloc~
Puïs~ T~me E~ld~ng Regi~3ter S
~wr~er nsec ~tion In~ut Out~ut
O O resync. 101 ready 1 ready
17 . 5 ~tar~ load 101
~S 217 . 5 e~d load 101 em~y
13 227.1 re~c.
14 244 . 6 ~ta:~t u~load
~S 417.8 102re~dy
~S 444 ~ 6 end u~load 1 . e~
26 454 a 2 req~~
27 471.7 ~ta~ load 102
:2 559 0 ? ready
;~S 671.7 end load 102 emq?ty
39 68103 r~ c.
4û 69~.8 s~a~t unloaa 2
~S 835.6 103ready
~S ~398.8 end ur~load 2 emp~
52 908.4 resync.
53 925.9 start load 103
64 1118 . l 3 ready
~; ~5 11 5 . 9 e:nd load 103 empty
1135 ~ 6 resync.
66 1153 ~. O s~ar~ unload 3
~S 1253.4 104ready
~353 . O end unload 3 empt~
78 1362.7 resync.
7g 1380.1 start load 104
NS 1580.1 end load 104 empty emp~y
***~o acti~rity - waitins for re~uest*~*
~S 1671. 2 105 ready
~i -4 2 -
~ ..
~ 8
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
MS 2089.0 106 ready
The point to notice is that the FIF0
sequence catches up with the com~ined input and output
tasks at 1580.1 nsec after the start of the e~ample.
It waits ~or the generation oE a new reque~t which
comes at 1671.2 nqec when a nonsynchronous load
r~queqt is g2nerated, and the pa~tern starts to repeat.
An input scan timing problem occurs when.
the reduction ratio causas the reduced image o~ the
input to be smaller than the output paper size. The
siz~ of the original (s) on the platen 62 is o~ no
~ ~ concern if the cover is closed. Th~ video signal
:~ variation due~to ~he difference in re~lectivity o~ ~
the platen cover and the unmarked areas of the paper
: can be set below the slicing level o-E the threshold
detector 150 and~should not be noticableO
.
: Figure 7(a) is a repxesentation of a
reduced imase 270~orm~d on output paper 272 (this
~an also correspond, for examplej to the electrost tic
dot pattern formed on drum 7~ within the xerographic
processor 7~ As can be seen, in order to center the
imase 270 o~ output paper 272, the left hand and right
hand borders (as viewed from the paper) 274 and 276,
respectively,~ ana the upper and lower borders 278 and
280, respectively, must be appropriately generate-d ~o
center ~he Lmage.270.
Figure 7 (b) shows apparatus which may
-~3-
171il
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, with 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~ 0.84 for 14.33 paper). In these
cases, there would be fewer input bits available than is
required for one output scan line tSDo) (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 regardlng the X position of scan from bits per line
counter 146~ Register 286 is similarly loaded 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
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
-44-
`'.7~'1 '
_ ~,
1~17~'~8
to the modulator 32 to cause the laser 10 to generate the
necessary white margins (the beam from laser lO discharges
the appropriate margin areas o~ drum 96l. 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 lO to reproduce collated 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 ll" paper (or M~ 0.72 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 pase. The SUl -
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
-45-
1117~7~3
3~ 7 (BPS) (N) (~ /60 = ABR _ _~
~herein BPS is the bits per scan line rounded upwards
~he peak bit rate of the disc 96 is related to the
average bit rate by t~e ratio of the number o~ clock
pulses/sector, CPPS, to ~he data bit times per sectsr
or CPPS/4096. The polygon drive requency divide ratio,
DR, is selected such that
/11 ~(CPPS) ~BR)/4096)]/DR = 4 (V~/60 = 4 ~ABR)/(BgL)(~)
DR - (CPPS) (BSh) (~)/16,384
with CPPS = 4968, ~S~ - 465~ 6,
DR = 36,707
W~ he invention has been descxibed with
xeference to it~ preferred embodiments, it will be
understood by those skill~d in ~ha'art ~hat ~arious
changes may be made and equivalents may be substituted
for elements thereof without departing ~rom ~he true
spirit and scope of the invention In addition, many
di~icatisns may be made to adapt a particular situ-
ation or material to the teaching of the invention
withou~ departing from its ~ential teachi gs
'
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: - .
-46-
