Note: Descriptions are shown in the official language in which they were submitted.
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_ck~round of the Invention
My invention relates to a photographic printer
and more particularly to a photographic printer which
responds to electrical signals encoding information to
be printed.
Various types of photographic duplicating machines
are known in the prior art. For example, the.e is Xnown an ~ -
electrophotographic copier incorporating a photoconductor
on the surface of which a latent electrostatic is formed for
subsequent development and possible transfer to a sheet of
paper. These machine~ have the advantage of being fast in
operation, of producing copies of good ~uality and of being ~-~
relatively inexpensive for the result produced. It is
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desirable that the advantageous characteristics of these
machine~ be employed in printing data which is encoded in
the form of electrical signals. It would be particularly
de~irable if an apparatus could be designed which could
function both as a traditional photocopier and also a~ a
prlnter of electronic information.
- 20 EffortJ have been made in the prior art to useprinters wlth photosensitive surfaces to print electronically
encoded information. ~ system embodying one such effort 1
diaclo~ed in I~M ~echnical Disclosure Bulletin, Vol, 19,
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No. 7, December 1976. Light from a common light souree
ts directed through a thin slit to a plurality of liquid
crystal light beam modulators which are activated by
electrical signals selcctively to allow light to fall upon
a plurality of respective small areas on the surface of a
photoc~nductive drum to form a latent electrostatic image
of the information represented by the electrical ~ignals.
One difficulty with this apparatus is its large size,
which renders it unsuitable for use in a machine whieh is
designed to operate both as a printer of electronic
~- information and a conventional photocopier. More signifi-
cantly the system requircs a large light source, much of
the light produced by which is not used. In addition the
source generates excessive heat which results in a further
waste of energy.
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SummarY of thc Invention
Onc objcct of my invention is to provide a
photographic ~rinter which responds to electrically encoded
~nformation.
~0 Another object of my invention i8 to provide a
photographic printer which responds both to information in
electronic form and to information in optical formO
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A further o~ject of my inventio* is to prov~de a
photographic printer which responds to electronically encoded - -
'' information while minimi~ing the amount of waste light
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generated in the process of convcrting the electronically ~ '-
' 5 encoded information into lightO - -- ' ' ~'
A still further object of my invention is to pro- ~ :
vide a photographic printer which responds to electronically
encoded information and which is relatively small for the
result produced thcreby.
Yet another object of my invention is'to provide-
a photographic printer which responds to electronic'ally~' ~ '
~, encoded information which requires very few moving partiO~-~
Other and further o~jects of my invention will
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appear from the following description.
In general my invention.contemplates a printer
incorporating a plurality of light sources, each of which
is responslve to a rcspective electrical signal to direct
light onto a small portion of a photosensitive surface, to
direct a pattern of light on the photosensltive surface ~n
accordance wlth the information-represented by the electrlcal
oignalr. For.example, a plurality of light~emittlng diodes
tLEDe) may be arranged in a row across the photoconductlve
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drum of a plain paper copier, perpendicular to the direction
of motion of thc drum's surface, and in response to ~ignals
applied to the LEDsO a latent image of the information
represented by the signals would be produced on the drum
surface. The latent images thus produced would be developed
and transferred to a sheet of suitable copy material.
Brief Description of~the Drawin~s
In the accompanying drawings which form part of
the instant specification and which are to be read in
conjunction therewith and in which like reference numberals
are used to indicate like parts in the various views.
PIGURE 1 is a schematic view of the image forming
and developing apparatus of an electrophotographic copying
machine embodying my multiple variable light source printer.
FIGURE 2 is an elevation of one array of ~ED chips
and light pipes which may be used in my multiple variable
light source printer.
FIGURE 3 is an elevation of an LED component which
may be u~ed in my variable light source printer.
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FIGURE 4 is a schematic diagram of one form o~
electrical control circuit which can be used in my variable
light source printer.
Description of the Preferred Embodiment
S Referring now to FIGURE 1, a photoconductive drum,
indicated generally by numeral 2, is coated with a thin layer
4 of photoconductivc material which is applied to a conductive
substrate 6. A motor 8 drives a sprocket wheel 10 to drive
a chain 12, ~hich drives a sprocket wheel 14, which drives
drum 2 in a counterclockwise direction as viewed in FIGURE 1.
The copying apparatus is provided with a charging
coro"a 16 which is connected alternatively to one of two
voltage ~ources, a positive dcvelopment voltage source 18 or
a negative development voltage source 20. Positive develop-
ment voltage source 18 has a ~700 volt output which may be
connected to corona 16, while negative development voltage
~ource 20 has a -700 volt output which may be connected to
corona 16. Both of the voltage sources 18 and 20 are
refe~enced to ground. A brush 21 engaging substrate 6 ia
grounded. A swLtch 22 is actuated alternatively to connect
an alternating currcnt power supply 24 to source 18 or source
20 to cause the corona 16 to apply with a positive charqe
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or a negative charge to the surface of photoconduc~
layer 4.
After the surface of photoconductor 4 has recelved
a charge from the corona lG it moves past an exposure system
26 of any suitable type known to the art which may expoQe
- the surface to a light i~nage of a document 28, for example,
at an exposure station, indicated generally by the reference
character 29. After leaving the station 29, the surface of
photoconductor 4 passes a second exposure station, indicated
f 10 generally by the reference character 30, at which it may be
exposed to a light pattern produced in response to incoming
data in the form of electrical signals.
At station 30 I mount respective first and second
rows, indicated generally by the reference characters32 and
34, of light emitting diodes 35. It will readily be
appreciated by those skilled in the art that the number Gf
LEDs required to porform the task at hand is quite large,
probably over 2000, based on 250 elernents per inch and at
least 8 1j2 inches of paper width. Presently a single in-
expen~ive array of LED3 8 1/2 inche~ long cannot be obtained.
I have overcome this problem by the u3e of a multiplicity of
component arrays. For example, as indicated in FIGURE 2,
row 32 may include a plurality of component arrays each of
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which includes sight active LED chip areas 35 carried by a
support 60 for the active areas~ Each of the chips 60,
may for example, have a length of 1/4 inch. In order to
provide the effect of a continuouq line of LEDs acros-~ the
surface of drum 2, I space the chips 60 of cach row 32 and
34 axially of the drum 2 and stagger the rows with respect
to each other. The amount of staggering is such that the
chips of one row "overlap" the chips of the other row by
an axial distance which accounts for the inactive chip areas
at the ends of the chips.
Owing to the circumferential spacing of the LEDs
of one row with reference to LEDs of the other row, it would
be necessary to delay the signals associated with the leading
row with reference to the direction of movement of the drum
2 relative to the LEDs. I avoid this necessity by providing
a plurality of light pipes 36 associated with the LEDs 35.
orient the light pipe3 36 with first ends 64 thereof
ad~acent to the respectivé LED~ 35 of rows 32 and 34 and
with the other ends 66 thereof adjacent to the drum 3ur~ace
in axially aligned axially relationship and are in close
proximity to the drum surface.
In addition to the foregoing problem, it may not
be pos~ible to posi~ion the LED active area~ 3$ of a component
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array a~ close to each other on the supporting chip~ 60 a~
is indicated in FIGURE 2. In ~hiY event I form the active
area~ of a componen~ on a chip 60 as a pair of staggered rows
of area~ 35a and 35b as indicated in FIGURE 3. In YUCh case
it may be necessary to delay the signals to one of the
eomponent rows. The problem could be obviated by the u~e
of optical filter light pipes.
I provide my apparatus with an electronie eontroller
38 which reeeives information from a data source 40 and con-
verts the information into electrical impulses whieh are fedto the respective LE~s in properly timed sequenee to produce
a latent eleetrostatie image of the information on the surfaee
of drum 2. Data source 40 might, for example, supply digital
information ~ueh as is used by eomputers and word procesJing
maehines, or other forms of eleetronie in~ormation sueh as
faesimile information.
Following the station 30 in the direetion of
rotation of drum 2 i9 developing apparatus, indieated gen
erally by numeral 42. Apparatus 42 ineludes a developer
tank 44 eontalning a liquid toner 46 having negative or
positive toner particles~ and a developer electrode 48 whiCh
iB connected to the ~lO0 volt output of voltage souree 18
and the -650 volt output of voltage ~ource 20, one or the
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other of ~hich i8 active depending upon whether positive or
negati~e development i~ usedO
Alternative to thc use of light pipe8 36~ lt i~
possible to place LEDs directly adjacent to surface 4 of
photoconductive drum 2. For example, as is shown in FIGURE
4, a chip 70 containing a plurality of LEDs 72 could be
placed in row 32 and a similar chip 71 could be placed ~ n
row 34. Rows 32 and 34 could each be pliaced sufficiently
close to the surface of ~kum 2 so that the light from any
given LED 72 would fall only upon a small portion o ~urface
4, and thus no optical fiber would be required to guide such
light. It should be noted, however, that if, as is ~hown in
FlGUREi 4, light from the various light emitting sourceq does
not fall upon photoconductive surface 4 in a straight line
perpendicular to its path of motion, controller 38 will have
to delay the illumina~ioh of tho~e light sources which ar~
leading with respect to the path of motion relative to the
lllumination of those light sources which trailing to produce
the effect of aligned light sources.
. The number of connections required to control the
large number of LEDs necessary ~or creating high resolution
printing may be roduccd appreciably by the use of coincident
addre3slng. I connect the lines 74A to 74D and 76A to 76D
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of two groups of lines 74 and 76D to the respective ~EDs to
form a matrix by virtue of which concomitant energization
of only one line of eacll group will result in activation of
one and only one LED 35. For example, if line 74A and line
76A are bo~h energized, LED 72A will be activated. Similarly,
if line 74D and line 76C are both energized, LED 72B will be
activated.
In operation of the apparatus shown in FIGURE 1,
it is capable of opcrating as a traditional photocopier
merely by using optical image forming apparatus 26 to make
a lat~nt image of document 28 upon surface 4 of drum 2 at
optical exposure station 29. In conventional electrophoto-
graphy, it is most common to use positive development.
Positive development means that toner is applied to those
portions of photoconductive s~lrface 4 which, after having
been charged with a voltage by corona 16, are not discharged
by light. For example, during positive development switch
22 18 POgitiOned 50 as to supply power to positive develop-
ment voltage sourcc 18. AB a result, corona 16 will apply
approximately a ~700 volt charge to the surface of photo
conductive drum 2. As thi~ surface rotates, it will pass
optical exposure station 29. ~t this point, an optical
image of a portion of document 28 is focused upon surface
4 of drum 2. Where this image contains light~ photocon-
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ductive surface 4 will conduct electricity. This will causccharge deposited on surface 4 by corona 16 to be conducted
to conductive substrate 6, reducing the charge on the
illuminated portion of surface 4 to around +50 volts. ~hos~
portions of surface 4 upon which no light impinges, however,
will not discharge to any appreciable extent. The resulting
varied pattern of charge upon photoconductive surface 4 after
it has passed optical exposure station 29 is a latent image
of the light pattern to which the drum has been subjected.
As drum 2 rotates, thc latent image will pass through developer
station 42. Here, negatively charged toner particles will be
attracted to those portions of photoconductive surface 2
which have not been discharged, and thus which maintain a
charge of approximately +700 volts. A developer electrode 48
will have a voltage of +100 volts applied to it by voltage
source 18, preventing negative toner particles from being
attracted to those portions of surface 4 which have been dis-
charged by light to approximately +50 volts. As a re~ult of
the attraction of negatively charged toner partlcles to those
portions of surface 4 upon which light is not ~hown, a pattern
of toner will be deposited upon surface 4. This pattern of
toner can be transferred to a plece of paper by means well~
known ln thc art to producc an electrophotographic copy o
document 28,
When the apparatus is operatcd as an elcctronic
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printer, the only change is that light emitting diodes in
electronic exposure station 30 emit light so as to discharge
photoconductive surface 4 rathcr than ~he optical image
forming apparatus 26 being used to form a ~atent image. It
is, however, possible to operate both optical image forming
apparatus 26 and elcctronic exposure station 30 at the same
time so as to print elcctronically derived information on
top of optically derived information.
Light from LEDs 35 which shines on small portions
of photoconductive surface 4 causes those portion3 to
discharge in the same manner as light from optical image
forming apparatus 26. Similarly, those portions o surface
4 upon which no light is directed by the light emitting diodes
retain their charge and, when doveloped, attract toner,
creating corresponding dar~ spots on any copy which was made
from the developed latent image formed by such LEDs. By
controlling the timing with which various LEDs are turned on
and off as drum 2 rotates past ~hem, it is possible to create
upon surface 4 a latent image containing textural or graphic
information. The timing at which various LEDs are turned
on and off must be accurately coordinated with the rotation
of drum 2, just as thc timing with which an electron beam
ln a raster scanned telcvision picture has to be accurately
coordinatcd with the timing of that picture's scan rateO In
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a m~nner an~logous to the manncr in which controller3 for
video monitor~ convert digital information into a ~erie~
of dots which rcpresent alphanumeric characters upon a
televiYion screen, controller 38 conver~s digital informa-
tion from source 40 into a series of properly timed dot~created by electronic exposure station 30 upon the surface
o~ photoconductive drum 2. Alternatively, data source 40
could supply controller 38 with facsimile information which
conveys graphic information in terms of dots along scan
lines. Such facsimile information could easily be converted
by controller 38 into a corresponding pattern of timed LED
illuminations along thc line of dots which can be created
by elec~ronic exposure station 30.
Most documents contain a much greater light area
than darX area. Therefore, in order to save electricity and
prevent unnecessary light and heat near the site of the
electrophotographic process, it may be desirable to use
nega~ive development in conjunction with electro~ic exposure
station 30. In negative development, toner particles are
attracted to those portions of thc photoconductive surface
4 which have been illuminated by lightO rather than to those
portions which remain unilluminated. When operating in the
negative dcvelopment mode, switch 22 is positioned ~o a~ to
connect power supply 24 to negative development voltage
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~ource 20. As a result, a charge of -700 volts is ~uppli~d
to corona 16. A chargc o approximately -700 volts i~
placed on the surface of photoconductive drum 2~ A~ that
charged surface passes electronic exposure station 30, those
- 5 portions of it which are illuminated by LEDs will conduct
electrons toward conductive sub3trate 6, thus losing much
of their negative charge. As a result, those portions of
surface 4 which are illuminated by LEDs will have their
- voltage reduced to approximately -50 volts, whereas those
portions which have not been illuminated will remain at
approximately -700 volts. As a result, a latent electro-
photographic image will be produced on the surface of drum
2. As this latent image pa~se~ through developing station
42, neqative toner particles will be attracted to those
portion3 of the drum which have been discharged to approxi-
mately -50 volts. This is because development electrode 48
is supplied by voltage source 20 with a voltage of -650
volts, creating a field which causes negative toner particles
to migraté toward those portions of photoconductive surface 4
which are charged with -50 volts and which cause~ those toner
particles to be repelled from the portions of photoconductivc
surface 4 which still have a charge of appro~imately -700
volts. A~ a result, a distribution of toner will be placed
upon photoconductive surface 4 which can be transferred to
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a piece of paper so aq to make a copy by mean~ well-known in
the electrophotographic art,
It will be seen that I have accomplished the
objects of my inventionO I have provided a printer of
electronic information which taXes advantage of the high
speed of many printing processes which use photosensitive
surfaces. I have provided means of producing photocopier~
which are able to print eleceronic information, as well as
creating conventional photocopies. Furthermore, I have
provided a means for converting electronic information into
light information for the use of printing processe-q which
use photosensitive surfaces, which means do not waste ligbt
energy and spa~e and which do not have many moving parts.
ItlwlIl be understood that certain eatures and
subcombinations are of utility and may be employed without
reference to other features and subcombinations. This is
contemplated by and is within the scope of my claims. It
is further obvious that various changcs may be madc in
details within the scope of my claims without departing from
the spirit of my invention. It is, therefore, to be under-
~tood that my invcntion is not to be limited to the specific
details shown and de~cribed.
~aving thus described my invention, what I clalm
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