U.S. patent application number 13/356213 was filed with the patent office on 2013-07-25 for image feedforward laser power control for a multi-mirror based high power imager.
This patent application is currently assigned to XEROX CORPORATION. The applicant listed for this patent is Jorge A. Alvarez, Martin Edward Hoover, Peter PAUL. Invention is credited to Jorge A. Alvarez, Martin Edward Hoover, Peter PAUL.
Application Number | 20130188229 13/356213 |
Document ID | / |
Family ID | 48796990 |
Filed Date | 2013-07-25 |
United States Patent
Application |
20130188229 |
Kind Code |
A1 |
PAUL; Peter ; et
al. |
July 25, 2013 |
IMAGE FEEDFORWARD LASER POWER CONTROL FOR A MULTI-MIRROR BASED HIGH
POWER IMAGER
Abstract
A power saving apparatus and method for imaging modules in a
variable data lithography system is provided. The imaging modules
are arranged adjacent to each other to project a scan line of
imaging data on a rotating imaging member in a variable data
lithography system. The imaging module includes a look ahead buffer
which stores imaging data and from which the stored data is read
out for projection on the imaging member. The power saving
apparatus uses an image look ahead concept to save part of the
power consumed in the imaging modules in the projection mode of
operation by selectively powering each laser source based on the
imaging data in the look ahead buffer.
Inventors: |
PAUL; Peter; (Webster,
NY) ; Alvarez; Jorge A.; (Webster, NY) ;
Hoover; Martin Edward; (Rochester, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PAUL; Peter
Alvarez; Jorge A.
Hoover; Martin Edward |
Webster
Webster
Rochester |
NY
NY
NY |
US
US
US |
|
|
Assignee: |
XEROX CORPORATION
Norwalk
CT
|
Family ID: |
48796990 |
Appl. No.: |
13/356213 |
Filed: |
January 23, 2012 |
Current U.S.
Class: |
358/475 ;
315/362; 713/320 |
Current CPC
Class: |
B41P 2227/70 20130101;
B41F 7/26 20130101; H04N 1/12 20130101; H04N 2201/0082 20130101;
B41J 2/465 20130101; B41J 2/471 20130101; H04N 1/1135 20130101;
B41F 7/02 20130101 |
Class at
Publication: |
358/475 ;
713/320; 315/362 |
International
Class: |
H04N 1/04 20060101
H04N001/04; H05B 37/02 20060101 H05B037/02; G06F 1/32 20060101
G06F001/32 |
Claims
1. A printing system to project an image on a reimageable surface
layer on a rotating imaging member, the system having at least one
imaging module each placed at individual zones adjacent to each
other across from the imaging member to form a scanline of the
image, each imaging module comprising: an energizable laser source
for generating a laser beam when energized; a look ahead buffer for
storing scanline data of the image to be projected on the imaging
member, wherein the look ahead buffer has top scanline data and
bottom scanline data; an optical assembly positioned to direct the
laser beam at the individual zones to project the top scanline data
in the look ahead buffer on the imaging member; and a logic circuit
to selectively power the energizable laser source based on the
scanline data in the look ahead buffer by: determining if the
scanline data in the look ahead buffer has at least one pixel to be
illuminated by the laser beam; if the scanline data in the look
ahead buffer has at least one pixel to be illuminated then
energizing the laser source so that the optical assembly can
project the top scanline data on the imaging member; else
deenergizing the laser source by interrupting electrical power to
the laser source.
2. The printing system according to claim 1, the logic circuit
further performing: removing the top scanline data in the look
ahead buffer.
3. The printing system according to claim 2, the logic circuit
further performing: moving remaining scan line data up one scanline
in the look ahead buffer.
4. The printing system according to claim 3, the logic circuit
further performing: appending additional scanline data of the image
to the look ahead buffer; repeating the steps of determining,
deciding, removing, moving, and appending until the look ahead
buffer is empty.
5. The printing system according to claim 4, wherein the optical
assembly includes a digital light projector multi-mirror array.
6. The printing system according to claim 5, wherein the
reimageable surface layer on the rotating imaging member comprises
silicone.
7. The printing system according to claim 4, wherein the size of
the look ahead buffer is based on the rotational speed of the
imaging member, laser source settling time, and a quality safety
factor.
8. A power conservation method for at least one imaging module in a
digital printing system with a reimageable surface layer on a
rotating imaging member, each imaging module placed at individual
zones adjacent to each other across from the imaging member to form
a scanline of an image, the method comprising: generating a laser
beam from an energizable laser source when energized; storing in a
look ahead buffer scanline data of the image to be projected on the
imaging member, wherein the look ahead buffer has top scanline data
and bottom scanline data; directing with an optical assembly the
laser beam at the individual zones to project the top scanline data
in the look ahead buffer on the imaging member; and selectively
powering the energizable laser source based on the scanline of
image data in the look-ahead buffer by a logic unit performing the
steps of: determining if the scanline data in the look ahead buffer
has at least one pixel to be illuminated by the laser beam; if the
scanline data in the look ahead buffer has at least one pixel to be
illuminated then energizing the laser source so that the optical
assembly can project the top scanline data on the imaging member;
else deenergizing the laser source by interrupting electrical power
to the laser source.
9. The method according to claim 8, the logic circuit further
performing the steps of: removing the top scanline of the scanline
of image data in the at least one look ahead buffer;
10. The method according to claim 9, the logic circuit further
performing the steps of: moving remaining scanline of image data up
one scanline in the at least one look ahead buffer.
11. The method according to claim 10, the logic circuit further
performing the steps of: appending scanline of image data of an
image to the at least one look ahead buffer; repeating the steps of
determining, deciding, removing, moving, and appending until the
optical assembly has projected the image on the substrate.
12. The method according to claim 11, wherein the optical assembly
includes a digital light projector multi-mirror array.
13. The method according to claim 12, wherein the reimageable
surface layer on the rotating imaging member comprises
silicone.
14. The method according to claim 12, wherein the size of a look
ahead buffer is based on the rotational speed of the imaging
member, laser source settling time, and a quality safety
factor.
15. A printing apparatus with at least one imaging module each
placed at individual zones adjacent to each other to form a
scanline of an image on a moving surface, the printing apparatus
comprising: at least one energizable laser source for generating a
laser line beam when energized; at least one look ahead buffer for
storing scanline image data of an image to be ablated on the moving
surface; at least one optical projection system positioned to
direct the laser line beam for projecting a scanline of image data
onto a target area of the moving surface; a control system for
controlling the at least one energizable laser source whenever the
target area on the moving surface has moved a distance in a process
direction by performing the steps of: determining if a scanline of
the scanline image data in the at least one look ahead buffer to be
projected on the moving surface has at least one pixel to be
ablated by the at least one energizable laser source; if the
scanline of the scanline image data has at least one pixel to be
ablated on the target area of the moving surface then energizing
the at least one energizable laser source; else deenergizing the at
least one energizable laser source by interrupting the electrical
power.
16. The printing apparatus according to claim 15, wherein the
determining is based on the scanline image data in the at least one
look ahead buffer.
17. The printing apparatus according to claim 16, the control
system further performing the steps of: removing the top scanline
of the scanline image data in the at least one look ahead buffer;
moving remaining scanline image data up one scanline in the at
least one look ahead buffer.
18. The printing apparatus according to claim 16, the logic circuit
further performing the steps of: appending scanline image data of
an image to the at least one look ahead buffer; repeating the steps
of determining, deciding, removing, moving, and appending until the
optical assembly has projected the image on the moving surface.
19. The printing apparatus according to claim 18, wherein the
optical assembly includes a digital light projector multi-mirror
array.
20. The printing apparatus according to claim 19, wherein the
moving surface can be of different configurations, comprising a
plate, a cylindrical drum, a scroll, or an endless flexible
belt.
21. The printing apparatus according to claim 19, wherein the
moving surface is treated with a dampening solution.
22. The printing apparatus according to claim 21, wherein the
optical projection system deflects individual mirrors to form
pixels on a silicone surface on the moving surface, and wherein the
size of a look ahead buffer is based on the speed of the moving
surface, laser source settling time, and a quality safety
factor.
23. A control system for a laser comprising: a laser processor, the
laser processor configured to: determine from a data buffer if a
laser controlled by the laser processor is to be utilized, wherein
the data buffer holds a partial column of data corresponding to
divided regions of an area to be radiated by the laser; change
laser power state based on the determined laser utilization from
the partial column of data in the data buffer; wherein selectively
powering the laser based on the column of data in the data buffer
conserves power consumption during laser utilization.
24. The control system according to claim 23, wherein the laser
power state is selected from a group consisting of "ON" state, and
"OFF" state.
25. The control system according to claim 24, the laser processor
further configured to: remove top entry of the column of data in
the data buffer.
26. The control system according to claim 25, the laser processor
further configured to: move remaining entries of the column of data
up in the data buffer.
27. The control system according to claim 26, the laser processor
further configured to: append additional data to the data buffer;
repeating the steps of determining, changing, removing, moving, and
appending until the data buffer is empty.
28. The control system according to claim 27, the laser processor
further configured to: receive instructions from a remote source to
configure the laser processor to control the laser.
Description
CROSS REFERENCE TO RELATED PATENTS AND APPLICATIONS
[0001] This application is related to the following co-pending
applications, which is hereby incorporated by reference in its
entirety: "JOINT FEEDFORWARD AND FEEDBACK CONTROL OF A KEYED INK
TRAIN FOR UNIFORM INKING IN DIGITAL OFFSET PRINTING SYSTEMS",
Attorney Docket No.: 056-0423, U.S. patent No. [Unknown], filed
herewith, by Peter Paul et al.
[0002] This application is related to the following co-pending
applications, which is hereby incorporated by reference in its
entirety: "IMAGE DATA BASED TEMPERATURE CONTROL OF A KEYLESS INKER
FOR DIGITAL OFFSET PRINTING SYSTEMS", Attorney Docket No.:
056-0424, U.S. patent No. [Unknown], filed herewith, by Peter Paul
et al.
[0003] This application is related to the following co-pending
applications, which is hereby incorporated by reference in its
entirety: "VARIABLE DATA LITHOGRAPHY SYSTEM", Attorney Docket
No.:20091609-US-NP, application Ser. No. 13/095,714, U.S. patent
No. [Unknown], filed on 27 Apr. 2011, by Timothy D. Stowe et
al.
BACKGROUND
[0004] The present disclosure is related to marking and printing
methods and systems, and more specifically to a method and
apparatus for variably marking or printing data at reduced power
consumption.
[0005] Offset lithography is a common method of printing today.
(For the purpose hereof, the terms "printing" and "marking" are
interchangeable.) In a typical lithographic process a printing
plate, which may be a flat plate, the surface of a cylinder, belt,
etcetera, is formed to have "image regions" formed of hydrophobic
and oleophilic material, and "non-image regions" formed of a
hydrophilic material. The image regions are regions corresponding
to the areas on the final print (i.e., the target substrate) that
are occupied by a printing or a marking material such as ink,
whereas the non-image regions are the regions corresponding to the
areas on the final print that are not occupied by the marking
material.
[0006] The Variable Data Lithography (also referred to as Digital
Lithography or Digital Offset) printing process begins with a
fountain solution used to dampen a silicone imaging plate on an
imaging drum. The fountain solution forms a film on the silicone
plate that is on the order of about one (1) micron thick. The drum
rotates to an `exposure` station where a high power laser imager is
used to remove the fountain solution at the locations where the
image pixels are to be formed. This forms a fountain solution based
`latent image`. The drum then further rotates to a `development`
station where lithographic-like ink is brought into contact with
the fountain solution based `latent image` and ink `develops` onto
the places where the laser has removed the fountain solution. The
ink is hydrophobic. An ultra violet (UV) light may be applied so
that photo-initiators in the ink may partially cure the ink to
prepare it for high efficiency transfer to a print media such as
paper. The drum then rotates to a transfer station where the ink is
transferred to a printing media such as paper. The silicone plate
is compliant, so an offset blanket is not used to aid transfer. UV
light may be applied to the paper with ink to fully cure the ink on
the paper. The ink is on the order of one (1) micron pile height on
the paper.
[0007] The formation of the image on the printing plate is done
with imaging modules each using a linear output high power infrared
(IR) laser to illuminate a digital light projector (DLP)
multi-mirror array, also referred to as the "DMD" (Digital
Micromirror Device). The mirror array is similar to what is
commonly used in computer projectors and some televisions. The
laser provides constant illumination to the mirror array. The
mirror array deflects individual mirrors to form the pixels on the
image plane to pixel-wise evaporate the fountain solution on the
silicone plate. If a pixel is not to be turned on, the mirrors for
that pixel deflect such that the laser illumination for that pixel
does not hit the silicone surface, but goes into a chilled light
dump heat sink. A single laser and mirror array form an imaging
module that provides imaging capability for approximately one (1)
inch in the cross-process direction. Thus a single imaging module
simultaneously images a one (1) inch by one (1) pixel line of the
image for a given scan line. At the next scan line, the imaging
module images the next one (1) inch by one (1) pixel line segment.
By using several imaging modules, comprising several lasers and
several mirror-arrays, butted together, imaging function for a very
wide cross-process width is achieved.
[0008] Due to the need to evaporate the fountain solution, in the
imaging module, power consumption of the laser accounts for the
majority of total power consumption of the whole system. It is
therefore vital to scheme how much electric power of the laser and
the electronics is saved in terms of realizing power saving of the
whole system. Such being the case, a variety of power saving
technologies for the imaging modules have been proposed. For
example, the schemes to reduce the size of the image formed on the
printing plate, changing the depth of the pixel, and substituting
less powerful image creating source such as a conventional Raster
Output Scanner (ROS). To evaporate a one (1) micron thick film of
water, at process speed requirements of up to five meters per
second (5 m/s), requires on the order of 100,000 times more power
than a conventional xerographic ROS imager. In addition,
cross-process width requirements are on the order of 36 inches,
which makes the use of a scanning beam imager problematic. Thus a
special imager design is required.
[0009] An over looked area of power conservation is the operation
of the lasers in the digital lithographic printing process. The
lasers are not modulated to create each pixel as in a ROS, but
continuously illuminate the mirror arrays. The laser is always "ON"
whether or not a pixel is being created on the plate. The mirrors
deflect the light energy for each pixel either to the imaging plate
or to the dump. The mirror arrays are able to simultaneously image
on the order of 1024 pixels in the cross-process direction. Typical
document area coverage levels are 5% for black and 3% each for
cyan, magenta, and yellow. Thus most of the laser power in this
imager is deflected into the dump, rather than onto the imaging
plate to form the image. For example, the power consumption to
create a six color image of thirty six inch (36) width with an
imaging module per linear inch (36 imagers) requires on the order
of 7.5 kW of power. Further, when the above coverage areas are
factored in there is on the order of 6.5 kW of that power is ending
in the beam dump of the DLP mirror.
SUMMARY
[0010] A power saving apparatus and method for imaging modules in a
variable data lithography system is provided. The imaging modules
are arranged adjacent to each other to project a scan line of
imaging data on a rotating imaging member in a variable data
lithography system. The imaging module includes a look ahead buffer
which stores imaging data and from which the stored data is read
out for projection on the imaging member. The power saving
apparatus uses an image look ahead concept to save part of the
power consumed in the imaging modules in the projection mode of
operation by selectively powering each laser source based on the
imaging data in the look ahead buffer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is an illustration of one out of M imager modules
arranged to project a scan line of imaging data on a rotating
imaging member in a variable data lithography system in accordance
to an embodiment;
[0012] FIG. 2 is a block diagram of an overview of an optical
patterning subsystem to form an image on a rotating imaging member
in a variable data lithography system in accordance to an
embodiment;
[0013] FIG. 3 is an illustration of the image look ahead concept on
a text and graphic document in accordance to an embodiment;
[0014] FIG. 4 is an illustration of the image path architecture
that may be implemented to use an image look ahead concept to save
consumable power in accordance to an embodiment;
[0015] FIG. 5 illustrates a block diagram of a controller to
selectively power the energizable laser source based on the
scanline of image data in the look ahead buffer in accordance to an
embodiment;
[0016] FIG. 6 is a flowchart of a method that may be implemented in
an imager module for laser power control in accordance to an
embodiment;
[0017] FIG. 7 is a side view of a system for variable lithography
in accordance to an embodiment;
[0018] FIG. 8 is a cut-away side view of a reimaging portion of an
imaging drum, plate or belt, without and with an intermediate
layer, respectively in accordance to an embodiment;
[0019] FIG. 9 is a cut-away side view of a reimaging portion of an
imaging drum, plate or belt in accordance to an embodiment; and
[0020] FIG. 10 is a magnified cut-away side view of the reimaging
portion shown in FIG. 8, having a dampening solution applied
thereover and patterned by a beam B in accordance to an
embodiment.
DETAILED DESCRIPTION
[0021] The disclosed embodiment pertains to a "green" energy saving
method for Variable Data Lithography that operates by intelligently
turning off lasers. The method operates by using an image buffer
for a look-ahead determination of potential laser usage for a given
laser. Specifically, the disclosed embodiment proposes that each
imaging module have a look-ahead buffer to determine if in the one
inch by N pixel (1.times.N) sub-image any pixels are ON. If any
pixels are ON, the laser must remain ON, if all the pixels are OFF,
the laser is turned OFF. For the next scan line, the buffer is
indexed forward and new scan line data is entered into the last
line in the buffer. The new scan line is examined to determine if
any pixels are ON, if any are ON, the laser is turned ON, if not,
the laser remains OFF. The buffer is large enough so that by the
time new scan line data with ON pixels reaches the top of the
buffer, the laser is fully ON and any settling time requirements
have been met. The buffer could be contone or binary.
[0022] Aspects of the disclosed embodiments relate to a variable
data lithography system to project an image on a reimageable
surface layer on a rotating imaging member, the system having at
least one imaging module each placed at individual zones adjacent
to each other across from the imaging member to form a scanline of
the image, each imaging module comprising an energizable laser
source for generating a laser beam when energized; a look ahead
buffer for storing scanline data of the image to be projected on
the imaging member, wherein the look ahead buffer has top scanline
data and bottom scanline data; an optical assembly positioned to
sweep the laser beam at the individual zones to project the top
scanline data in the look ahead buffer on the imaging member; and a
logic circuit to selectively power the energizable laser source
based on the sub-image in the look ahead buffer by: determining if
the scanline data in the look ahead buffer has pixels to be
illuminated by the laser beam; if the scanline data in the look
ahead buffer has pixels to be illuminated then energizing the laser
source so that the optical assembly can project the top scanline
data on the imaging member; else deenergizing the laser source by
interrupting electrical power to the laser source.
[0023] In yet further aspects of the disclosed embodiments relate
to a variable data lithography system where the logic circuit
further performing removing the top scanline data in the look ahead
buffer.
[0024] In yet further aspects of the disclosed embodiments relate
to a variable data lithography system where the logic circuit
further performs moving remaining scan line data up one scanline in
the look ahead buffer.
[0025] In yet further aspects of the disclosed embodiments relate
to a variable data lithography system where the logic circuit
further performs appending additional scanline data of the image to
the look ahead buffer; repeating the steps of determining,
deciding, removing, moving, and appending until the look ahead
buffer is empty.
[0026] In yet further aspects of the disclosed embodiments relate
to a variable data lithography system wherein the optical assembly
is a digital light projector multi-mirror array.
[0027] In yet further aspects of the disclosed embodiments relate
to a variable data lithography system where wherein the reimageable
surface layer on the rotating imaging member comprises
silicone.
[0028] In yet further aspects of the disclosed embodiments relate
to a variable data lithography system where wherein the size of the
look-ahead buffer is based on the rotational speed of the imaging
member, laser source settling time, and a quality safety
factor.
[0029] Further aspects of the disclosed embodiments include a power
conservation method for at least one imaging module in a variable
data lithography system with a reimageable surface layer on a
rotating imaging member, each imaging module placed at individual
zones adjacent to each other across from the imaging member to form
a scanline of an image, the method comprising generating a laser
beam from an energizable laser source when energized; storing in a
look ahead buffer scanline data of the image to be projected on the
imaging member, wherein the look ahead buffer has top scanline data
and bottom scanline data; sweeping with an optical assembly the
laser beam at the individual zones to project the top scanline data
in the look ahead buffer on the imaging member; and selectively
powering the energizable laser source based on the scanline of
image data in the look ahead buffer by a logic unit performing the
steps of: determining if the scanline data in the look ahead buffer
has pixels to be illuminated by the laser beam; if the scanline
data in the look ahead buffer has pixels to be illuminated then
energizing the laser source so that the optical assembly can
project the top scanline data on the imaging member; else
deenergizing the laser source by interrupting electrical power to
the laser source.
[0030] In yet further aspects of the disclosed embodiments relate
to an apparatus to operate at least one imaging module in a power
conservation mode, the at least one imaging module ablating the
surface of a rotating and substantially cylindrical drum in a
variable data lithography system, each imaging module placed at
individual zones adjacent to each other across from the
substantially cylindrical drum to form a scanline of an image, the
apparatus comprising at least one energizable laser source for
generating a laser beam when energized; at least one look ahead
buffer for storing scanlines of image data of an image to be
ablated on the surface of the drum; an optical projection system
positioned to sweep the laser beam for projecting a scanline of
image data onto a target area of the drum surface; a control system
for controlling the laser beam in relation to the angular position
of the drum such that laser beam occur whenever the target area on
the drum surface has moved a distance in the direction of rotation
by performing the steps of: determining if a scanline of the
scanline of image data in the at least one look ahead buffer to be
projected on the drum surface has pixels to be ablated by the laser
beam; if the scanline of the scanline of image data has pixels to
be ablated on the target area of the drum surface then energizing
the laser source by supplying electrical power to the at least one
laser source to generate the laser beam; else deenergizing the
laser source by interrupting the electrical power to the at least
one laser source.
[0031] Embodiments as disclosed herein may also include
computer-readable media for carrying or having computer-executable
instructions or data structures stored thereon for operating such
devices as controllers, sensors, and electromechanical devices.
Such computer-readable media can be any available media that can be
accessed by a general purpose or special purpose computer. By way
of example, and not limitation, such computer-readable media can
comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,
magnetic disk storage or other magnetic storage devices, or any
other medium which can be used to carry or store desired program
code means in the form of computer-executable instructions or data
structures. When information is transferred or provided over a
network or another communications connection (either hardwired,
wireless, or combination thereof) to a computer, the computer
properly views the connection as a computer-readable medium. Thus,
any such connection is properly termed a computer-readable medium.
Combinations of the above should also be included within the scope
of the computer-readable media.
[0032] The term "print media" generally refers to a usually
flexible, sometimes curled, physical sheet of paper, cloth,
cardboard, plastic or composite sheet film, ceramic, glass, wood,
sheet metal or other suitable physical print media substrate for
images.
[0033] The term "variable data printing" or "digital printing"
generally refers to a system that can print or mark variable data
documents, that is, documents that vary in image content from
page-to-page.
[0034] As used herein relational terms such as "first," "second,"
and the like may be used solely to distinguish one entity or action
from another entity or action without necessarily requiring or
implying any actual such relationship or order between such
entities or actions. Also, relational terms, such as "offset",
"upstream", "downstream", "top," "bottom," "front," "back,"
"horizontal," "vertical," and the like may be used solely to
distinguish a spatial orientation of elements relative to each
other and without necessarily implying a spatial orientation
relative to any other physical coordinate system. The terms
"comprises," "comprising," or any other variation thereof, are
intended to cover a non-exclusive inclusion, such that a process,
method, article, or apparatus that comprises a list of elements
does not include only those elements but may include other elements
not expressly listed or inherent to such process, method, article,
or apparatus. An element proceeded by "a," "an," or the like does
not, without more constraints, preclude the existence of additional
identical elements in the process, method, article, or apparatus
that comprises the element. Also, the term "another" is defined as
at least a second or more. The terms "including," "having," and the
like, as used herein, are defined as "comprising."
[0035] FIGS. 7-10 shows the hardware and operating environment of
variable data lithography in which different embodiments can be
practiced.
[0036] FIG. 7 illustrates therein a system 10 for variable
lithography according to one embodiment of the present disclosure.
System 10 comprises an imaging member 12, in this embodiment a
drum, but may equivalently be a plate, belt, and the like,
surrounded by a number of subsystems described in detail below.
Imaging member 12 applies an ink image to substrate 14 at nip 16
where substrate 14 is pinched between imaging member 12 and an
impression roller 18. A wide variety of types of substrates, such
as paper, plastic or composite sheet film, ceramic, glass, and the
like may be employed. For clarity and brevity of this explanation
we assume the substrate is paper, with the understanding that the
present disclosure is not limited to that form of substrate. For
example, other substrates may include cardboard, corrugated
packaging materials, wood, ceramic tiles, fabrics (e.g., clothing,
drapery, garments and the like), transparency or plastic film,
metal foils, and the like. A wide latitude of marking materials may
be used including those with pigment densities greater than ten
percent (10%) by weight including but not limited to metallic inks
or white inks useful for packaging. For clarity and brevity of this
portion of the disclosure we generally use the term ink, which will
be understood to include the range of marking materials such as
inks, pigments, and other materials which may be applied by systems
and methods disclosed herein.
[0037] The inked image from imaging member 12 may be applied to a
wide variety of substrate formats, from small to large, without
departing from the present disclosure. In one embodiment, imaging
member 12 is at least 38 inches (38'') wide so that standard 4
sheet signature page or larger media format may be accommodated.
The diameter of imaging member 12 must be large enough to
accommodate various subsystems around its peripheral surface. In
one embodiment, imaging member 12 has a diameter of 10 inches,
although larger or smaller diameters may be appropriate depending
upon the application of the present disclosure.
[0038] As shown in FIG. 7 at a first location around imaging member
12 is a dampening solution subsystem 30. Dampening solution
subsystem 30 generally comprises a series of rollers (referred to
as a dampening unit) for uniformly wetting the surface of
reimageable surface layer 20. It is well known that many different
types and configurations of dampening units exist. The purpose of
the dampening unit is to deliver a layer of dampening solution 32
having a uniform and controllable thickness. In one embodiment this
layer is in the range of 0.2 .mu.m to 1.0 .mu.m, and very uniform
without pinholes. The dampening solution 32 may be composed mainly
of water, optionally with small amounts of isopropyl alcohol or
ethanol added to reduce its natural surface tension as well as
lower the evaporation energy necessary for subsequent laser
patterning. In addition, a suitable surfactant is ideally added in
a small percentage by weight, which promotes a high amount of
wetting to the reimageable surface layer 20. In one embodiment,
this surfactant consists of silicone glycol copolymer families such
as trisiloxane copolyol or dimethiconecopolyol compounds which
readily promote even spreading and surface tensions below 22
dynes/cm at a small percentage addition by weight. Other
fluorosurfactants are also possible surface tension reducers.
Optionally dampening solution 32 may contain a radiation sensitive
dye to partially absorb laser energy in the process of patterning,
described further below. In addition to or in substitution for
chemical methods, physical/electrical methods may be used to
facilitate the wetting of dampening solution 32 over the
reimageable surface layer 20. In one example, electrostatic assist
operates by way of the application of a high electric field between
the dampening roller and reimageable surface layer 20 to attract a
uniform film of dampening solution 32 onto reimageable surface
layer 20. The field can be created by applying a voltage between
the dampening roller and the reimageable surface layer 20 or by
depositing a transient but sufficiently persisting charge on the
reimageable surface layer 20 itself. The dampening solution 32 may
be electronically conductive. Therefore, in this embodiment an
insulating layer (not shown) may be added to the dampening roller
and/or under reimageable surface layer 20. Using electrostatic
assist, it may be possible to reduce or eliminate the surfactant
from the dampening solution.
[0039] After applying a precise and uniform amount of dampening
solution, in one embodiment an optical patterning subsystem 36, see
FIG. 2, is used to selectively form a latent image in the dampening
solution by image-wise evaporating the dampening solution layer
using laser energy, for example. It should be noted here that the
reimageable surface layer 20 should ideally absorb most of the
energy as close to an upper surface 28 (FIG. 8) as possible, to
minimize any energy wasted in heating the dampening solution and to
minimize lateral spreading of the heat so as to maintain high
spatial resolution capability. Alternatively, it may also be
preferable to absorb most of the incident radiant (e.g., laser)
energy within the dampening solution layer itself, for example, by
including an appropriate radiation sensitive component within the
dampening solution that is at least partially absorptive in the
wavelengths of incident radiation, or alternatively by choosing a
radiation source of the appropriate wavelength that is readily
absorbed by the dampening solution (e.g., water has a peak
absorption band near 2.94 micrometer wavelength). It will be
understood that a variety of different systems and methods for
delivering energy to pattern the dampening solution over the
reimageable surface may be employed with the various system
components disclosed and claimed herein. However, the particular
patterning system and method do not limit the present
disclosure.
[0040] Returning to FIG. 7, following patterning of the dampening
solution layer 32, an inker subsystem 46 is used to apply a uniform
layer 48 of ink over the layer of dampening solution 32 and
reimageable surface layer 20. In addition, an air knife 44 may be
optionally directed towards reimageable surface layer 20 to control
airflow over the surface layer before the inking subsystem 46 for
the purpose of maintaining clean dry air supply, a controlled air
temperature and reducing dust contamination. Inker subsystem 46 may
consist of a "keyless" system using an anilox roller to meter an
offset ink onto one or more forming rollers 46a, 46b.
Alternatively, inker subsystem 46 may consist of more traditional
elements with a series of metering rollers that use
electromechanical keys to determine the precise feed rate of the
ink. The general aspects of inker subsystem 46 will depend on the
application of the present disclosure, and will be well understood
by one skilled in the art.
[0041] In order for ink from inker subsystem 46 to initially wet
over the reimageable surface layer 20, the ink must have low enough
cohesive energy to split onto the exposed portions of the
reimageable surface layer 20 (ink receiving dampening solution
voids 40) and also be hydrophobic enough to be rejected at
dampening solution regions 38. Since the dampening solution is low
viscosity and oleophobic, areas covered by dampening solution
naturally reject all ink because splitting naturally occurs in the
dampening solution layer which has very low dynamic cohesive
energy. In areas without dampening solution, if the cohesive forces
between the ink are sufficiently lower than the adhesive forces
between the ink and the reimageable surface layer 20, the ink will
split between these regions at the exit of the forming roller nip.
The ink employed should therefore have a relatively low viscosity
in order to promote better filling of voids 40 and better adhesion
to reimageable surface layer 20. For example, if an otherwise known
UV ink is employed, and the reimageable surface layer 20 is
comprised of silicone, the viscosity and viscoelasticity of the ink
will likely need to be modified slightly to lower its cohesion and
thereby be able to wet the silicone. Adding a small percentage of
low molecular weight monomer or using a lower viscosity oligomer in
the ink formulation can accomplish this rheology modification. In
addition, wetting and leveling agents may be added to the ink in
order to further lower its surface tension in order to better wet
the silicone surface.
[0042] In addition to this rheological consideration, it is also
important that the ink composition maintain a hydrophobic character
so that it is rejected by dampening solution regions 38. This can
be maintained by choosing offset ink resins and solvents that are
hydrophobic and have non-polar chemical groups (molecules). When
dampening solution covers layer 20, the ink will then not be able
to diffuse or emulsify into the dampening solution quickly and
because the dampening solution is much lower viscosity than the
ink, film splitting occurs entirely within the dampening solution
layer, thereby rejecting ink any ink from adhering to areas on
layer 20 covered with an adequate amount of dampening solution. In
general, the dampening solution thickness covering layer 20 may be
between 0.1 .mu.m-4.0 .mu.m, and in one embodiment 0.2 .mu.m-2.0
.mu.m depending upon the exact nature of the surface texture. The
thickness of the ink coated on roller 46a and optional roller 46b
can be controlled by adjusting the feed rate of the ink through the
roller system using distribution rollers, adjusting the pressure
between feed rollers and the final form rollers 46a, 46b
(optional), and by using ink keys to adjust the flow off of an ink
tray (show as part of 46). Ideally, the thickness of the ink
presented to the form rollers 46a, 46b should be at least twice the
final thickness desired to transfer to the reimageable layer 20 as
film splitting occurs. It is also possible to use a keyless system
which can control the overall ink film thickness by using an anilox
roller with uniformly formed ink carrying pits and maintaining the
temperature to achieve the desired ink viscosity. Typically, the
final film thickness may be approximately 1-2 mm. Ideally, an
optimized ink system 46 splits onto the reimageable surface at a
ratio of approximately 50:50 (i.e., 50% remains on the ink forming
rollers and 50% is transferred to the reimageable surface at each
pass). However, other splitting ratios may be acceptable as long as
the splitting ratio is well controlled. For example, for 70:30
splitting, the ink layer over reimageable surface layer 20 is 30%
of its nominal thickness when it is present on the outer surface of
the forming rollers. It is well known that reducing an ink layer
thickness reduces its ability to further split. This reduction in
thickness helps the ink to come off from the reimageable surface
very cleanly with residual background ink left behind. However, the
cohesive strength or internal tack of the ink also plays an
important role.
[0043] There are two competing results desired at this point.
First, the ink must flow easily into voids 40 so as to be placed
properly for subsequent image formation. Furthermore, the ink
should flow easily over and off of dampening solution regions 38.
However, it is desirable that the ink stick together in the process
of separating from dampening solution regions 38, and ultimately it
is also desirable that the ink adhere to the substrate and to
itself as it is transferred out of voids 40 (FIG. 10) onto the
substrate both to fully transfer the ink (fully empting voids 40)
and to limit bleeding of ink at the substrate. The ink is next
transferred to substrate 14 at transfer subsystem 70. In the
embodiment illustrated in FIG. 1, this is accomplished by passing
substrate 14 through nip 16 between imaging member 12 and
impression roller 18. Adequate pressure is applied between imaging
member 12 and impression roller 18 such that the ink within voids
40 (FIG. 10) is brought into physical contact with substrate 14.
Adhesion of the ink to substrate 14 and strong internal cohesion
cause the ink to separate from reimageable surface layer 20 and
adhere to substrate 14. Impression roller or other elements of nip
16 may be cooled to further enhance the transfer of the inked
latent image to substrate 14. Indeed, substrate 14 itself may be
maintained at a relatively colder temperature than the ink on
imaging member 12, or locally cooled, to assist in the ink transfer
process. The ink can be transferred off of reimageable surface
layer 20 with greater than 95% efficiency as measured by mass, and
can exceed 99% efficiency with system optimization.
[0044] With reference to FIG. 8, a portion of imaging member 12 is
shown in cross-section. In one embodiment, imaging member 12
comprises a thin reimageable surface layer 20 formed over a
structural mounting layer 22 (for example metal, ceramic, plastic,
etc.), which together forms a reimaging portion 24 that forms a
rewriteable printing blanket. Reimaging portion 24 may further
comprise additional structural layers, such as intermediate layer
(Not Shown) below reimageable surface layer 20 and either above or
below structural mounting layer 22. Intermediate layer may be
electrically insulating (or conducting), thermally insulating (or
conducting), have variable compressibility and durometer, and so
forth. In one embodiment, intermediate layer is composed of closed
cell polymer foamed sheets and woven mesh layers (for example,
cotton) laminated together with very thin layers of adhesive.
Typically, blankets are optimized in terms of compressibility and
durometer using a 3-4 plylayer system that is between 1-3 mm thick
with a thin top surface layer 20 designed to have optimized
roughness and surface energy properties. Reimaging portion 24 may
take the form of a stand-alone drum or web, or a flat blanket
wrapped around a cylinder core 26. In another embodiment the
reimageable portion 24 is a continuous elastic sleeve placed over
cylinder core 26. Flat plate, belt, and web arrangements (which may
or may not be supported by an underlying drum configuration) are
also within the scope of the present disclosure. For the purposes
of the following discussion, it will be assumed that reimageable
portion 24 is carried by cylinder core 26, although it will be
understood that many different arrangements, as discussed above,
are contemplated by the present disclosure.
[0045] Reimageable surface layer 20 consists of a polymer such as
polydimethylsiloxane (PDMS, or more commonly called silicone) for
example with a wear resistant filler material such as silica to
help strengthen the silicone and optimize its durometer, and may
contain catalyst particles that help to cure and cross link the
silicone material. Alternatively, silicone moisture cure (aka tin
cure) silicone as opposed to catalyst cure (aka platinum cure)
silicone may be used. Reimageable surface layer 20 may optionally
contain a small percentage of radiation sensitive particulate
material 27 dispersed therein that can absorb laser energy highly
efficiently. In one embodiment, radiation sensitivity may be
obtained by mixing a small percentage of carbon black, for example
in the form of microscopic (e.g., of average particle size less
than 10 .mu.m or nanoscopic particles (e.g., of average particle
size less than 1000 nm) or nanotubes, into the polymer. Other
radiation sensitive materials that can be disposed in the silicone
include graphene, iron oxide nano particles, nickel plated nano
particles, and the like.
[0046] Alternatively, reimageable surface layer 20 may be tinted or
otherwise treated to be uniformly radiation sensitive, as shown in
FIG. 9. Still further, reimageable surface layer 20 may be
essentially transparent to optical energy from a source, described
further below, and the structural mounting layer or layers 22 may
be absorptive of that optical energy (e.g., layer 22 comprises a
component that is at least partially absorptive), as illustrated in
FIG. 10.
With reference to FIG. 10, which is a magnified view of a region of
reimageable portion 24 having a layer of dampening solution 32
applied over reimageable surface layer 20, the application of
optical patterning energy (e.g., beam B) from optical patterning
subsystem 36 results in selective evaporation of portions the layer
of dampening solution 32. Evaporated dampening solution becomes
part of the ambient atmosphere surrounding system 10. This produces
a pattern of dampening solution regions 38 and ink receiving voids
40 over reimageable surface layer 20. Relative motion between
imaging member 12 or moving surface and optical patterning
subsystem 36, for example in the direction of arrow A, permits a
process-direction patterning of the layer of dampening solution
32.
[0047] FIG. 1 is an illustration of one out of M imager modules 100
arranged to project a segment of a scan line of imaging data on a
rotating imaging member in a variable data lithography system in
accordance to an embodiment.
[0048] The imager module uses digital light projector (DLP) 137
that has an array of mirrors that deflect in response to a command
from an internal controller (not shown). A projection lens 145
projects the scan line of imaging data on the surface of rotating
imaging member 12 Before projecting an image on the imaging member
12, the surface of the member is prepared with a reimageable
surface 20 layer created from a fountain solution which forms into
a film on the silicone plate of the imaging member 12 that is on
the order of one micron (1 .mu.m) thick.
[0049] A single laser 132 and optical assembly 130 form an imaging
module that provides imaging capability for approximately one inch
(1'') in the cross-process direction 127. It uses a linear output
high power infrared (IR) laser 132 to illuminate a DLP multi-mirror
array, also referred to as the "DMD" (Digital Micromirror Device).
The mirror array is similar to what is commonly used in computer
projectors and some televisions. The laser 132 provides constant
illumination to the mirror array. The mirror array deflects
individual mirrors to form the pixels on the reimageable surface
20. The directing of the DLP modulated laser beam 125 evaporates
the fountain solution on the silicone plate in a pixel-wise
fashion. Thus a single imaging module simultaneously images a one
inch (1'') by one (1) pixel line of the image for a given scan
line. At the next scan line caused by the rotation 115 of the
imaging member 12, the imaging module images the next one inch
(1'') by one (1) pixel line segment. If a pixel is not to be turned
on, the mirrors for that pixel deflect such that the laser
illumination for that pixel does not hit the silicone surface, but
goes into a chilled light dump heat sink 135. By using several
imaging modules, comprising several lasers and several
mirror-arrays, each placed at individual zones adjacent to each
other across from the imaging member to form a complete scanline of
the image a very wide cross-process width is achieved. Of course,
the imaging modules need to be calibrated to each other to remove
image alignment and uniformity defects between modules, very
similar to modular printheads in ink jet printing. To improve the
power consumption response of the imaging modules a controller 140
is provided for selectively powering the laser 132 based on the
content in a look-ahead buffer (not shown).
[0050] The DLP or digital micromirror device (DMD) includes a
semiconductor chip, in which several to hundreds of thousands to
millions of driving micromirrors (cells) are integrated in a flat
plate form. That is, the size of one cell is very small, which is
determined by a micro unit. Typically, the digital micromirror
device xxx is operated in such a manner that it enlarges and
projects light using an image signal inputted from a computer or
other appliance. In addition, because such a micromirror device
includes hundreds of thousands or millions of micromirrors for
switching the paths of reflected beams no more than several times
per sec to hundreds of thousands of times per sec, each of the
micromirrors can control collected beams in a digital method.
Typically, each of the micromirrors in the digital micromirror
device is turned from one mechanical state or to another mechanical
state by electric voltage, thereby being positioned in a desired
orientation.
[0051] FIG. 2 is a block diagram of an overview of an optical
patterning subsystem 200 to form an image on a rotating imaging
member 12 in a variable data lithography system in accordance to an
embodiment. A signal 220 is received at the print bar control
module 230 such as a dynamic FPGA which allows a designer to make
changes on the fly such as increasing the size of the look ahead
buffer. The received signal 220 eventually results in a laser beam
that is reflected by mirrors in the respective head module 270, the
reflected beam is directed to imaging member 12 where a linear
image is formed. The movement of the imaging member is measured by
an encoder 210 which serves as basis for indexing the buffer
forward (next line) and new scan line can be projected on the
imaging member 12. A reflex clock generator 260 uses the encoder
signal 210 to fire up the lasers to produce the desired dots per
inch (dpi) The dump chiller manage cooling 240 performs active
thermal management components to control the temperature increases
produced from the dumping of the "OFF" pixels. The cooling is done
by a circulating cooling fluid/radiator system to radiate heat from
the heat spreading assembly to the outside. A laser power regulator
250 adjusts laser power so that individual lasers within the head
modules 270 can be altered and controlled by the print bar control
module 230. The control module may increase or decrease laser power
resulting in normalizing head modules 270 to each other.
[0052] FIG. 3 is an illustration of the image look ahead concept on
a text and graphic document in accordance to an embodiment. A
possible print job 300 consisting of one or more images is received
at the variable data lithography system. An original image 310
consisting of graphics and text is shown. The four process
components 320 (Cyan, Magenta, Yellow and Black (CMYK)) of the
image is shown with a signal representation 330 of laser usage. As
can be seen from signal 337 there are occasions where lasering can
be selectively turned "ON" or "OFF". For example, signal 337 shows
that in the middle portion of the cycle there are opportunities for
power conservation. These power conservation opportunities can be
realized based on the look ahead concept discussed with reference
to method 600 shown in FIG. 6.
[0053] FIG. 4 is an illustration of the image path architecture 400
that may be implemented to use an image look ahead concept to save
consumable power in accordance to an embodiment. The imager video
data module 410 receives the print job consisting of a plurality of
images. The print job is separated into component images each
representing a page of a document to be reproduced. The component
images are then individually fed to the videodatabuffer N-Lines for
head delay Yreg and laser power null data control (videodatabuffer)
420 where the image gets processed for each imaging module to
look-ahead to determine potential laser usage for a given laser.
Each imaging module has an assigned look ahead buffer 490 for
storing a one pixel by N pixel sub-image. Where "N" is based on the
width of the imager model. The look-ahead buffer 490 has a top
scanline data 494 and a bottom scanline data 496. The difference
between the top and bottom of the buffer is indicative of the size
of the buffer or the depth of the buffer 492. As general rule the
size of the look-ahead buffer is a function of the settling time of
the laser ('.OMEGA.), process speed (.omega.) which is proportional
to the rotational speed of the imaging member, and safety factor
(.mu.). For a one meter per second (1 m/s) process speed, and a 2.5
msec settling time, and 100% safety buffer, a 5 mm buffer size is
required. This is approximately equivalent to 120 pixels at a 600
dpi resolution. In an embodiment, the look-ahead buffer size is
determined by the following equation:
B=.mu..times.'.OMEGA..times..omega..times.dpi.times.1000/25.4. The
look-ahead buffer could be at the contone part of the image path or
at the halftone part of the image path. It is noted that a separate
look-ahead buffer is required for each image module.
[0054] The controller 140 looks at the content in the look-ahead
buffer 490 to determine if there are pixels to be illuminated by
the laser 132. Every controller 140 has a null video data block
detection module 430. The function of the module is to determine if
there are any "ON" pixels for the horizontal scanline data for that
imaging module. If at the start of the printing cycle the laser is
"ON" and the look-ahead buffer has only "OFF" pixels the laser
would be deenergized. However, if there are any "ON" pixels the
laser is energized, i.e., kept on. The laser power on/off module
440 receives a determination from the null video data block
detection module 430 to supply electrical power to the laser 132.
The laser illumination module 450 powers the laser based on the
received signal from the laser power on/off module 440 and
introduces it into the laser 132 so as to project the image laser
light 480 on the imaging member 12. The DLP also receives a signal
from the image video active line data module 460 which indicates
which mirrors are to be in a state for the laser light impinging on
the mirrors to be projected onto the imaging member 12 and which
mirrors are to be in a state for the laser light impinging on the
mirrors will be scrapped using the chilled light dump heat sink
135.
[0055] FIG. 5 illustrates a block diagram of a controller 500 to
selectively power the energizable laser source based on the
scanline of image data in the look-ahead buffer in accordance to an
embodiment.
[0056] The controller 500 may be embodied within devices such as a
desktop computer, a laptop computer, a handheld computer, an
embedded processor, a handheld communication device, or another
type of computing device, or the like. The controller 500 may
include a memory 520, a processor 530, input/output devices 540, a
display 550 and a bus 560. The bus 560 may permit communication and
transfer of signals among the components of the computing device
500.
[0057] Processor 530 may include at least one conventional
processor or microprocessor that interprets and executes
instructions. The processor 530 may be a general purpose processor
or a special purpose integrated circuit, such as an ASIC, and may
include more than one processor section. Additionally, the
controller 500 may include a plurality of processors 530.
[0058] Memory 520 may be a random access memory (RAM) or another
type of dynamic storage device that stores information and
instructions for execution by processor 530. Memory 520 may also
include a read-only memory (ROM) which may include a conventional
ROM device or another type of static storage device that stores
static information and instructions for processor 530. The memory
520 may be any memory device that stores data for use by controller
500.
[0059] Input/output devices 540 (I/O devices) may include one or
more conventional input mechanisms that permit a user to input
information to the controller 500, such as a microphone, touchpad,
keypad, keyboard, mouse, pen, stylus, voice recognition device,
buttons, and the like, and output mechanisms such as one or more
conventional mechanisms that output information to the user,
including a display, one or more speakers, a storage medium, such
as a memory, magnetic or optical disk, disk drive, a printer
device, and the like, and/or interfaces for the above. The display
550 may typically be an LCD or CRT display as used on many
conventional computing devices, or any other type of display
device.
[0060] The controller 500 may perform functions in response to
processor 530 by executing sequences of instructions or instruction
sets contained in a computer-readable medium, such as, for example,
memory 520. Such instructions may be read into memory 520 from
another computer-readable medium, such as a storage device, or from
a separate device via a communication interface, or may be
downloaded from an external source such as the Internet. The
controller 500 may be a stand-alone controller, such as a personal
computer, or may be connected to a network such as an intranet, the
Internet, and the like. Other elements may be included with the
controller 500 as needed.
[0061] The memory 520 may store instructions that may be executed
by the processor to perform various functions. For example, the
memory may store instructions to selectively power the energizable
laser source based on the sub-image in the look ahead buffer,
instructions for controlling a laser beam in relation to the
angular position of the drum such that laser beam occur whenever
the target area on the drum surface has moved a distance in the
direction of rotation, instruction to regulate laser power,
instructions in determining the size of the look-ahead buffer, and
other instructions that are well known to those in the art.
[0062] FIG. 6 is a flowchart of a method 600 that may be
implemented in an imager module for laser power control in
accordance to an embodiment.
[0063] Method 600 is a process implemented on each imaging module
so that the module can achieve power conservation by selectively
turning the laser "ON and OFF". It is, however, within the skill of
those in the art to implement this process in a single processor
for all the imaging modules through such well know techniques as
buffer allocation and synchronized instruction routing in
multiprocessor environments.
[0064] Action 605, Start Job, begins method 600. The print job
starts in a normal fashion. The machine cycles up and each imaging
module is prepared to receive imaging data. Control is then passed
to action 610 where the laser 132 is put in the "ON" state. It
should be noted that the laser could initially be in the "OFF"
state provided there is a delay before imaging that is at least
equal to the cycle time of the laser. It is assumed that when the
method is started there will be imaging data available to be
processed immediately. It is foreseeable, however, that delays such
as calibration of the electronics could influence that decision. In
action 610, the laser 132 is placed in the ON state in preparation
for imaging.
[0065] In action 615, the look-ahead buffer is filled with image
data. The initial image data is tiled into a sub-image of vertical
scan data that is assigned to a corresponding imaging module. For
example, in a lithography system having thirty six (36) imaging
module the original image is chopped into thirty six distinct
strips that are assigned to the imaging modules equally. The
look-ahead buffer is then filled with image data for this module.
The imaging module will store the strip in a suitable storage
device such as a RAM for quick access. The received strip is then
streamed or continuously fed into the look-ahead buffer until the
strip is completely projected on the imaging member. Since all the
imaging modules are acting in concert the image is projected on the
member where the scan line is across the member (horizontal) and
the rotation of the member provides the other scan line axis
(vertical).
[0066] In action 620, the look-ahead buffer is analyzed to
determine if the buffer has any pixels "ON". If is determined that
the buffer does not have any "ON" pixels, the Laser is turned "OFF"
in action 625. Regardless of whether the look-ahead buffer has any
pixels "ON" or "OFF" control is passed to action 630. In action
630, the DLP uses the scanline data at the top of the buffer. As
noted above if the top entry in the buffer indicates any "OFF"
pixels, but the column data indicates an "ON" laser condition, the
laser energy is reflected by the DLP into the dump 135 since the
laser has to be kept "ON" to illuminate that pixel when it reaches
the top of the Queue. In action 630, a signal is used to drive DLP
mirrors with one scan line at the top of the buffer. The scanline
data at the top of the buffer is used to drive the DLP mirrors to
image one scanline. Light is directed onto the imaging plate for
one scanline to evaporate fountain solution and create the `latent
image` for one scanline.
[0067] In action 635, the method moves the data up one scan line in
the buffer. In action 635, the buffer is "POP"-ed which is the
removal of the "oldest" element in the queue (top scanline). The
"POP" function causes the entries to move up one row leaving, at a
minimum, an open row that can be filled with data. In action 640,
the look-ahead buffer is inspected to determine if a "NULL"
condition exists, i.e. the method determines if the buffer is
empty. If the buffer is found to be empty the method is terminated
in action 645. If the buffer is not empty control is passed to
action 650 for further processing.
[0068] In action 650, the method loads new scan line data into the
bottom of the buffer. In action 650, the top entry of the remaining
image data is "PUSH"-ed into the look-ahead buffer. The "PUSH"
function adds a new element at the end of the queue, after its
current last element, i.e., the uppermost element of the remaining
image data is appended to the scan line data in the buffer. Control
is then passed to action 655 for further processing. In action 655,
If the new scan line data contains any "ON" pixels, then move to
action 660 to turn Laser "ON" and return to action 620 for further
processing. However, if the scan line data does not contain any
"ON" pixels control is passed to action 620 for further
processing.
[0069] In the preceding paragraphs, example embodiments of the
invention were described. These embodiments are presented for
purposes of illustration rather than of limitation, and minor
changes may be made to the example embodiments without departing
from the inventive principle or principles found therein. It will
be appreciated that various of the above-disclosed and other
features and functions, or alternatives thereof, may be desirably
combined into many other different systems or applications. Also,
various presently unforeseen or unanticipated alternatives,
modifications, variations or improvements therein may be
subsequently made by those skilled in the art, and are also
intended to be encompassed by the followings claims.
* * * * *