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Claims  |
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What is claimed is:
1. In an electrostatic printing press, for printing a succession of images
on a web of print receiving material, including
supply means and delivery means supported in spaced relation and means for
driving and guiding a web of print receiving material therebetween along a
predetermined printing path;
an electrostatic printing engine including
a) a cylinder having a photoreceptor surface and means supporting said
cylinder along the printing path in a position to contact said material,
b) means for rotating said cylinder such that said surface has a peripheral
velocity and direction corresponding to movement of the material,
c) charging means for creating a uniform electrostatic charge on said
surface at a first high potential,
d) a digital exposure means extending transversely of said surface for
directing radiant energy onto predetermined non-image pixel areas on the
charged cylinder surface to cause selective dissipation of the charge on
such discrete areas to a second low potential, thereby to form an
electrostatic latent image on said surface,
e) developing means for applying a developer including toner particles to
the latent image and a development electrode means for contacting the
developer, and
f) means for applying to said development electrode means a third potential
intermediate the first and second potentials whereby the toner particles
are attracted to the image areas on said cylinder surface and repelled
from the non-image areas of said cylinder surface;
the improvement comprising
a programmable speed controller included in said means for driving the web.
2. A printing press as defined in claim 1, further including
means for circulating the liquid developer through said developing means to
refresh developer depleted of toner particles and to flush concentration
of toner particles away from said development electrode means.
3. A printing press as defined in claim 2, wherein said exposure means
directs discrete beams of radiant energy at a resolution in the order of
at least 300 per inch selectively onto said non-image pixel areas,
said developing means including a shoe member contoured to said surface of
said cylinder for containing the liquid developer in contact across a
substantial area of said surface carrying the electrostatic latent image,
means guiding the web into contact with said photoreceptor surface at a
region past said developing means in the direction of rotation of said
cylinder, and
means for transferring the toner particles from the latent image and at
least part of the carrier liquid onto the web.
4. A press as defined in claim 1, further comprising
said driving means including a line shaft coupled to said supply means,
said delivery means, and said cylinder for rotating said cylinder such
that said photoreceptor surface has a peripheral velocity and direction
corresponding to movement of the material,
means for generating latch pulses at a rate equal to the peripheral
velocity of said cylinder in inches/second times 300 whereby resolution
around said cylinder at least equals resolution of said exposure means
across said cylinder,
means for supplying imaging data to said exposure means under the control
of said means for generating latch pulses.
5. A press as defined in claim 4, further including
said charging means creating a uniform electrostatic charge on said
cylinder surface at a potential of at least 1000 Volts,
said developing means applying to said photoreceptor surface a liquid
developer including toner particles having a size in the range of 1 to 10
microns and a negative charge in the range of 60 to 75 picamhos/cm
dispersed in a volatile carrier liquid,
said development electrode means having a potential in the order of 200 to
600 Volts applied thereto whereby the toner particles in the liquid
developer are attracted to the image areas on said cylinder surface and
repelled from the non-image areas of said cylinder surface.
6. A press as defined in claim 1, said digital exposure means including
an array of closely spaced LEDs extending transversely of said surface and
directing separate beams of light onto the predetermined non-image pixel
areas on the charged cylinder surface;
driving circuits switching each LED on and off at a rate greater than the
velocity of the photoreceptor surface past said exposure means and control
circuits for selectively operating said driving circuits according to
digital imaging data,
said speed controller including voltage level adjustment means for
increasing said first, second and third potentials, and for adjusting said
driving circuits to increase the driving current to the LEDs with increase
in press operating speed.
7. A press as defined in claim 6, wherein said voltage level adjustment
means also adjusting the potential applied to said charging means in
direct relation to press operating speed.
8. A printing press as defined in claim 6, said driving circuits including
register circuits for selectively operating said driving circuits
according to digital imaging data for a line of pixel areas,
an encoder driven in synchronism with said cylinder and generating a string
of latch pulses per each cylinder revolution identifying lines of pixel
areas across said image area,
said driving means rotating said cylinder such that said surface has a
peripheral velocity and direction corresponding to movement of the web,
a data interface unit including memory means for holding digital image
information,
means for transferring image information from said data interface unit to
said register circuits on a line-by-line basis, and
means for driving said exposure means at a rate dependent upon the output
of the corresponding encoder.
9. An electrostatic web printing press as defined in claim 8, further
comprising
there being a plurality of said electrostatic printing engines arranged
along the path to print images successively on the web,
said speed controller operating said driving means to rotate said cylinders
in synchronism and such that each of said surfaces has a velocity and
direction corresponding to movement of the web,
said speed controller including voltage level adjustment means for
increasing said first, second and third potentials, and for adjusting said
driving circuits to increase the driving current to the LEDs, with
increase in press operating speed.
10. A press as defined in claim 9, further including a single fusing means
along said web path downstream from all said printing engines and
operating to fuse all transferred toner particles from the different
printing engines to the web at the same time.
11. A printing press for printing a succession of images on print receiving
material as defined in claim 9, further including
encoders driven in synchronism with each said cylinder and generating
strings of latch pulses per each cylinder revolution identifying lines of
pixel areas across said image area,
a plurality of data interface units, one for each printing engine,
including memory means for holding digital image information,
means for transferring image information from said data interface units to
said register circuits of the corresponding printing engines on a
line-by-line basis, and
means for driving said LED arrays of each printing engine at a rate
dependent upon the output of the corresponding encoder.
12. A printing press as defined in claim 11, including
said memory means being divided into a fixed image memory section and a
variable memory section, and
said means for transferring image information combining the digital image
information from each memory section into composite image data which is
transferred into said register circuits.
13. A printing press as defined in claim 12, further including
said means for transferring image information combining digital information
from the fixed and variable memory sections on a line-by-line basis.
14. A press as defined in claim 1, wherein
said exposure means includes an array of closely spaced individual light
beam generators and driving circuits for said light beam generators to
switch each generator on and off,
said driving circuits including individual control circuits for selectively
operating said driving circuits according to digital imaging data, and
means for supplying imaging data to said driving circuits at a rate
sufficient to refresh the data for each driving circuit at a rate greater
than the number of pixel areas circumferentially of said surface.
15. A press as defined in claim 14, including
means for generating latch pulses corresponding to the peripheral velocity
of said cylinder and at a rate to divide said surface into pixel areas at
least equal to the spacing of light beam generators whereby resolution
around said cylinder at least equals resolution of said exposure means
across said cylinder, and
means for supplying imaging data to all said driving circuits at a rate
greater than the latch pulse rate.
16. A press as defined in claim 15, including
means for directing the latch pulses to said control circuits of said
driving circuits, to coordinate the driving of the LEDs to the latch pulse
rate,
means for generating a fixed number of timebase pulses between latch
pulses, and
means for actuating said driving circuits during certain of said timebase
pulses centered about the midpoint between latch pulses, whereby the
on-time of the LEDs is centered within the pixel areas.
17. A press as defined in claim 1, including
an encoder driven by said driving means in synchronism with said cylinder
and generating a string of latch pulses per each cylinder revolution to
identify pixel areas around said surface.
18. A press as defined in claim 17, further including a processing section
having at least a cross perforation unit for forming transverse
perforations in the web at regularly spaced intervals.
19. A press as defined in claim 18, including a sensor cooperating with
said cross perforator to generate registration pulses each time the
perforator forms a cross perforation, and
means for applying the registration pulses to said exposure means to
control the registration of images with respect to the space on the web
between successive cross perforations. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to printing presses, particularly to web presses,
and has special applicability to a special form of web press which is
known as a forms press, used to manufacture printed business forms which
combine unique printed material with various physical attributes. These
include cross-perforations which delineate successive forms that are
connected and zig-zag folded, line feeding perforations which are usually
marginal, other perforations to define separable segments of the forms,
and successive numbering of the individual forms. A typical forms press of
this type is described in U.S. Pat. No. 4,177,730; current models of such
a press include provisions for changing the size of the printing and
processing cylinders of such a press.
Business forms are rapidly increasing in use, particularly single-part
forms, and the demand is extending into so-called short run forms, where a
customer may only order a relatively small quantity, for example 5,000 to
10,000 forms. The makeready of the press, particularly of the offset
printing units or towers, occupies a greater percentage of the total run
time in shorter runs. In order to control costs, keep prices reasonable,
and still meet the demand for these relatively smaller orders of business
forms, the forms manufacturing industry needs a forms press which requires
a minimum of makeready, can operate at different speeds (which may vary
considerably) up to a reasonably fast printing speed (e.g. 500 ft./min),
preferably can make changes in the printed material of the form without
time consuming shut-down and makeready, and which has the capability of
providing a wide variety of forms.
Various attempts have been made to adapt laser printing systems to the
printing of variable information on pre-printed webs. Those systems
utilize powder developers, which are quite expensive when their particle
size is reduced to increase resolution to that comparable to other types
of printing such as lithography. Furthermore, such particle size reduction
makes powder toners even more difficult to handle, and increases the
already present serious problems of pollution control as part of handling
such powder developers. Equipment maintenance is also a potential problem
with powder toner systems, because the attendant "powder cloud" permeates
the equipment and its ambience, and tends to deposit on surfaces such as
corona wires, lenses, belts, etc. where such deposit adversely affect
operation, beyond being a clean-up nuisance.
Relatively sophisticated copy machines have been developed, using powder
toner, and while a few of these have capability of printing on web
material those units are essentially a variation of similar sheet fed
copiers. They all have operating speeds in the eighty-five to one hundred
copy/minute range, and this speed is fixed. Their exposure and development
systems will not tolerate variation in speed. Such prior art copiers, by
their very nature, are also sensitive to characteristics of the copy
material, e.g. the sheet on which the copy is made. In general, those
copiers have difficulty making good reproductions on certain coated
papers, or on pressure sensitive paper with encapsulated dyes, or on
sheets of variable thickness as where a blank label is already adhered to
the sheet.
SUMMARY OF THE INVENTION
The present invention provides a novel electrostatic printing engine, a
unique web press using one or more of these printing engines, and a forms
press combining one or more such printing engines with a processing
section to achieve manufacturing of successive runs of different business
forms with significantly reduced makeready time between the runs. Under
some circumstances the press of the invention can proceed from one run to
another without stopping the press, and in fact without any reduction in
speed of the press, provided the basic operations of the press remain
constant.
While the principal novelty of this press resides in unique features of its
printing engine (or engines), the combination of these with the processing
section results in a synergistic effect that has resulted in a vastly
improved and more efficient press for business forms and other
applications which require printing information from a data base which
changes periodically, and/or printing of job runs where information
changes from job to job, and/or printing of forms or copies wherein
information changes from one form to the next, or one page to the next.
This unique press also has capability to combine digital image information
from two different sources (e.g. memories) into composite digital image
data which is then used to drive a single imaging system.
Such a press, according to the invention, employs
(a) digital electronic image creation, generation, and merging;
(b) electrophotographic printing, e.g. electrostatic printing of images
using liquid toner for image development;
(c) the type and versatility of web handling associated with forms presses
or the like;
(d) web feeding under controlled tension, which in turn contributes to
accurate length control, an important factor in continuous forms
manufacturing or other repetitive printing wherein the various pages must
be of uniform length for further handling;
(e) ability to print on a substantial variety of materials, of different
thickness or other characteristics; and
(f) ability to maintain quality electronically printed product at
substantial speeds, in a range of at least 100 to 300 feet/minute (or even
greater), and during speed changes within that range.
Because of these features, the press and the unique methods of printing
have application in a large variety of businesses, to wit, business forms
printing, direct mail (promotional) printing, printing of tags and/or
labels, government or financial printing, documentation printing (where
documents need periodical updating), and check printing.
In a comprehensive embodiment, the invention is a unique combination of
digital electronic image creation and generation, combining fixed and
variable digital image information, producing the resulting images by
electrophotographic methods, developing those images using liquid toner,
transferring and fixing those images onto web material using forms press
web handling techniques. Thus, as necessary, the invention may include
performing processing steps on the web material to produce the features of
continuous business forms which adapt them to automatic feeding, bursting,
combination into multi-part forms and later separation during use of the
forms. The inclusion of successive numbering, by arabic numerals and/or
bar code, is preferably accomplished as a part of the variable information
recorded and developed as mentioned above. If desired, the press can be
assembled to include other types of printing units, such as one or more
lithographic printing towers, flexographic printing units, etc. so as to
achieve a wide variety of printing capabilities.
The printing engine uses a unique form of high speed electrophotographic
printing which is capable of continuous printing, preferably on web
material, at speeds and sizes, and with resolution and accuracy,
essentially equal to offset printing. Images are created in the printing
engine by a digital dot-image exposure system which is electronically
driven from imaging data which can be refreshed, a page at a time, to
produce successive identical copies of desired forms, and which can also
be modified without slowing of the printing engine so as to print variable
data (e.g. forms numbering or bar coding) or to switch "on the run" to an
entirely new form as part of the next job. The direct digital input of the
printing engine also allows immediate running of the different related
parts of a multi-part form, merging of form information, rapid customizing
of standard forms, creation of new forms using high speed electronic
digitizing and editing equipment, and the establishment of a digitized
library of customer's forms which can be quickly recalled and re-run upon
short demand.
The unique printing engine utilizes a drum having a surface photoreceptor,
e.g. a photoconductive surface as the active surface on which developed
electrostatic images are created, and an offsetting arrangement by which
these images are transferred to the forms material, most commonly a paper
web. The drum is rotatably driven at a peripheral velocity equal to web
speed through the press. Special high intensity charging,
exposing-discharging, developing and cleaning systems assure the drum
surface is discharged, cleared of residual toner, and has a uniform
electrostatic charge applied to its photoconductive surface each
revolution. That charge is in the order of at least 1000 Volts DC.
A digital imaging device, preferably in the form of a relatively high
intensity LED array mounted to extend transversely of the rotating drum
surface, operates to discharge the background or non-image areas of the
passing drum surface to within a range of substantially lower potential,
e.g. 100 to 300 Volts DC, by exposing individual dot areas to focused
radiation at a predetermined frequency and intensity, and in area size in
the order of 0.0033 inch diameter, whereby the remaining or image areas(s)
comprise a latent electrostatic image of the printed portions of the form.
The size of these dots or pixels provides an acceptably high resolution
image for forms printing, and in fact the resolution is comparable to good
quality lithographic offset printing. Solid coverage of desired areas is
attainable.
The four basic components of the imaging system are a Scheduler Control
Unit (SCU), a Raster Image Processor (RIP) which includes character
generator capability, a Data Interface Unit (DIU), and the novel LED
array. The controlling intelligence behind the imaging system is
accomplished through the SCU. The SCU synchronizes all print data to the
web, prepares all imaging resources that are required, channels text data
from a host computer, and controls all data transfer through the system.
The raster image processor (RIP) is basically a form of a commercially
available character generator. It accepts information, such as ASCII
character codes, and outputs bit-mapped information for generating such
characters in a dot pattern, based on the font(s) selected.
The DIU contains all the storage and location circuitry required for
storing text and baseforms in rasterized bit-map format. Pairs of DIU
memory sections cooperate with each other to provide bit-mapped fixed
(e.g. base form) and bit-mapped variable image data. In use, one pair of
memory sections is scanned to output data to registers at the LED array,
while the other pair is loaded with data. Thus enough memory is available
in each DIU for both base form and variable information for two images.
The SCU controls the input and output of data to and from the DIUs, and
transfers pixel initiating data to the LED array, line-by-line.
The LED array is divided into twenty four modules of 256 LEDs each,
together with latching shift register circuits, comparator circuits, and
driver circuits for each LED, as is generally known in the prior art. A
set of EPROMs receives data clocked into them from the DIU. This data may
be termed "pixel initiating" or writing data, since it determines whether
a pixel is or is not printed at a given location, e.g. this data
determines whether or not any specific LED is to be driven in exposing a
line of pixel areas by driving the array.
A bank of EPROMS provide a memory storing compensation information (in a
typical embodiment four-bit codes) which determines modification of LED
on-time to compensate for non-uniform light emissions from different ones
of the LEDs. Data is clocked simultaneously into the EPROMS from the DIU
via data lines which extend to the respective EPROMS. Thus pixel writing
data is transferred in parallel to the EPROMS. A system clock controls
loading data from a DIU into the memory which passes on compensated pixel
driving data distributed serially into individual latch/registers. Thus,
data is loaded simultaneously through the EPROMs and to the latch register
set for each module, but sequentially into the latch/registers, and the
loading time is that for only one module.
A driver circuit for each LED applies power to the LED for generating a
small light beam onto the drum surface at a given pixel location. Each
driver circuit is in turn controlled by a comparator circuit which
distributes the compensated driving data from the latch/registers to the
correct LED driver circuit.
Each EPROM uses an on-off writing signal from the DIU as an address line
into the EPROM. An "off" signal will result in a four-bit zero code, while
an "on" signal will result in a four-bit compensation value to the
register/latch circuit in the appropriate module.
The writing data from the DIU memory is clocked into the EPROM circuits and
thence to the latch/registers under control of the SCU at a rate which is
greater than the fastest usage of the data to refresh the state of the LED
drivers for each line. Utilization of the LED driving data will, however,
be at a variable rate depending upon web and drum speed. Thus, data is fed
to the LED array from the DIU at a high rate, compensation data is added,
and the resultant driving data is fed to the latch/registers at the module
inputs at this high rate. This driving data is distributed to the
individual driver circuits, at a lower rate which varies dependent upon
web and drum speed. The driver circuits are also compensated to increase
the driving current of all of them as higher printing speeds are called
for.
An encoder pulse generator is driven with the photoreceptor drum and
provides outputs equal to one-eighth of a pixel height, i.e. eight pulses
per pixel. That output divided by eight is the source of a latch pulse
train, each latch pulse coinciding with the top border of a line of square
pixel areas across the photoreceptor surface. Due to the variable speed
capability of the apparatus, the duration between successive latch pulses
will vary considerably, in a range of at least three to one, as web/drum
speed is changed.
The SCU receives the divided PG outputs, divides the time between leading
edges of successive latch pulses by sixty-four, and generates a time base
count which equals 1/64th of the latch/reset interval. This represents the
maximum time, at a chosen drum and web speed, during which an LED can be
driven. This timebase information is sent to the time base drivers and
also to the latch-reset drivers which cause the module shift registers to
output data to each comparator. This time between latch pulses in effect
represents a time interval or window during which the LEDs may be driven,
depending upon the state of the pixel initiating data bits (on or off).
The comparative data stored in the EPROMs is also latched into the
comparator circuits as part of the LED driving instructions, and this
determines at which one of the timebase counts the drivers will be
effective to apply power to their corresponding LEDs.
The latent image then is carried, as the drum rotates, past a developing
station wherein it is subjected to the action of a special high speed
liquid toner developer, thus forming a developed or visible image with
merged liquid toner particles, which image is thence transferred and fixed
to the paper web or other material. The developer is a special proprietary
combination of small particle size toner dispersed in a carrier liquid.
The liquid developer supply system constantly recirculates developer
through a specially constructed shoe, which is closely fitted to the
moving drum surface, for example at a spacing of about 500 microns (0.020
inch).
The developer is monitored and refreshed as needed to maintain a
predetermined concentration of toner particles in volatile carrier liquid,
at a negative charge of 60 to 75 picamhos/cm. The developer shoe is
electrically isolated from the drum, and functions as an electrode which
is maintained at a potential in the order of +500 to 600 V DC. Thus the
negatively charged toner particles are introduced into the shoe and
dispersed among electrical fields between the image areas and the
developer electrode, on the one hand, and between the background or
non-image areas and the developer electrode on the other hand. Typically,
the electrical fields are the result of difference in potential a) between
the image areas (+1000 to 1450 V) and the developer electrode (+200 to 600
V), which cause the toner particles to deposit on the images areas, and b)
between the background areas (+100 to 300 V) and the developer electrode
(+200 to 600 V), which causes toner particles to migrate to the developer
shoe in those areas. Expressed another way, the electrical fields in the
image and non-image areas are reversed, and are in the order of at least 2
V/micron. The result is a high quality distinction between image and
background, and good coverage of solid image areas. The tendency of toner
particles to build up on the developer shoe or electrode is overcome by
the circulation of liquid toner through the shoe at rates in the order of
7.57 to 37.85 liters/min. (2 to 10 gal./min.) back to the toner refreshing
system.
As the drum surface passes from the developer shoe, a reverse rotating
metering roll, spaced parallel to the drum surface by about 50 to 75
microns (0.002 to 0.003 inches), acts to shear away any loosely attracted
toner in the image areas, and also to reduce the amount of volatile
carrier liquid carried by the web with the toner deposited thereon, and to
scavenge away any loose toner particles which might have migrated into the
background areas. This metering roll has applied to it a bias potential in
the order of +200 to 600 V DC, varied according to web velocity.
The web path then leads to an image transfer station where idler rollers
guide the web material into contact with a band-like area across the drum
surface. Behind the web path at this location is a transfer corotron to
which is applied a voltage of +6600 to 8000 V DC. The web is driven at a
speed equal to the velocity of the drum surface to minimize smudging or
disturbance of the developed image on the drum surface, and to assure that
the printed image is of the proper length. Both toner particles and liquid
carrier transfer to the web, including carrier liquid on the drum surface
in the background areas.
A second printing engine, identical to the first, is arranged to receive
the web material from the first printing engine, and produce another image
using other toner, as of a different color if more than one color is
desired in a single printing operation, or if a perfecting (printed both
sides) operation is desired, in which case the web can be turned by
conventional turn bar mechanisms before passing the second such printing
engine. Due to the digital electronic driving of the printing engines,
registration of the successively printed images can be adjusted, if need
be, on an almost instantaneous basis. Also, the developed image
transferred to the web from the first printing engine will be maintained
during the second transfer, thus only after both images have been
superimposed on the web material is the composite image fused to the web.
It should be noted that, due to the continuous nature of the photoreceptor
surfaces, and the "line at a time" exposure by | | |
