U.S. patent application number 14/231374 was filed with the patent office on 2015-10-01 for system for detecting inoperative inkjets in printheads ejecting clear ink using thermal substrates.
This patent application is currently assigned to Xerox Corporation. The applicant listed for this patent is Xerox Corporation. Invention is credited to Patricia J. Donaldson, William H. Wayman.
Application Number | 20150273917 14/231374 |
Document ID | / |
Family ID | 52807565 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150273917 |
Kind Code |
A1 |
Donaldson; Patricia J. ; et
al. |
October 1, 2015 |
System For Detecting Inoperative Inkjets In Printheads Ejecting
Clear Ink Using Thermal Substrates
Abstract
An apparatus detects inoperative inkjets during printing. The
apparatus operates the printhead or printheads in the printer to
form test pattern on a thermal substrate. The heat of the materials
used to form the test pattern change the optical density of the
areas where the materials land. The area where the test pattern is
formed is imaged and the image data are analyzed to identify
inoperative inkjets.
Inventors: |
Donaldson; Patricia J.;
(Pittsford, NY) ; Wayman; William H.; (Ontario,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xerox Corporation |
Norwalk |
CT |
US |
|
|
Assignee: |
Xerox Corporation
Norwalk
CT
|
Family ID: |
52807565 |
Appl. No.: |
14/231374 |
Filed: |
March 31, 2014 |
Current U.S.
Class: |
347/19 |
Current CPC
Class: |
B33Y 30/00 20141201;
B33Y 70/00 20141201; B29C 64/393 20170801; B33Y 50/02 20141201;
B41J 2/04535 20130101; B41J 2/16579 20130101; B41J 2/2114 20130101;
B41J 2/04585 20130101; B41J 2/14153 20130101; B29C 64/112 20170801;
B41J 2/21 20130101; B41J 2029/3935 20130101; B41J 2/2107 20130101;
B41J 29/393 20130101; B41J 2/2142 20130101; B41J 2/125
20130101 |
International
Class: |
B41J 29/393 20060101
B41J029/393 |
Claims
1. A printer comprising: a printhead configured with a plurality of
inkjets to eject material; a supply of thermal substrate configured
to move thermal substrate to a position opposite the printhead to
receive material ejected from the printhead, the supply of thermal
substrate having a plurality of thermal substrates; a support
member having a pivot that enables the support member to rotate; an
actuator operatively connected to the support member; an optical
sensor configured to generate electrical signals corresponding to
an optical density of a location on the thermal substrate; an
actuator operatively connected to the optical sensor to move the
optical sensor to a position opposite the thermal substrate onto
which material has been ejected; and a controller operatively
connected to the actuator connected to the optical sensor, the
optical sensor, the actuator connected to the support member, and
the printhead, the controller being configured to operate another
actuator to move a single thermal substrate from the plurality of
thermal substrates onto a support member at the position opposite
the printhead, to operate the printhead to eject a predetermined
number of material drops from each inkjet onto the thermal
substrate to enable the predetermined number of material drops to
form a test dot for each inkjet on the thermal substrate, to
operate the actuator connected to the optical sensor to move the
optical sensor to a position opposite the thermal substrate, to
identify inoperative inkjets in the printhead with reference to the
data received from the optical sensor that corresponds to optical
densities of the thermal substrate at a plurality of locations on
the thermal substrate, and to operate the actuator connected to the
support member to rotate the support member about the pivot to
enable a thermal substrate to drop from the support member.
2-3. (canceled)
4. The printer of claim 1 further comprising: a collection tray
positioned to receive thermal substrates dropping from the support
member.
5. The printer of claim 4 wherein the collection tray is configured
for removal from and reinstallation in the printer to enable
removal of the thermal substrates from the collection tray.
6-7. (canceled)
8. The printer of claim 1, the controller being further configured
to operate the actuator to move the optical sensor away from the
position opposite the thermal substrate.
9. The printer of claim 1, the controller being further configured
to identify inkjets that do not eject material drops of a
predetermined size with reference to the data corresponding to the
optical densities of the thermal substrate.
10. The printer of claim 1 wherein the printhead is configured to
drop build material to form three-dimensional objects.
11. An apparatus comprising: a supply of thermal substrate having a
plurality of thermal substrates; a support member having a pivot
configured to enable the support member to rotate; an actuator
operatively connected to the support member; an optical sensor
configured to generate electrical signals data corresponding to an
area of material drops on the substrate; an actuator operatively
connected to the optical sensor to move the optical sensor to a
position opposite the thermal substrate onto which material has
been ejected; and a controller operatively connected to the
actuator connected to the optical sensor, the optical sensor, the
actuator connected to the support member, and the printhead, the
controller being configured to operate another actuator to move a
single thermal substrate from the plurality of thermal substrates
onto a support member at the position opposite the printhead, to
operate the printhead to eject a predetermined number of material
drops from each inkjet onto the thermal substrate to enable the
predetermined number of material drops to form a test dot for each
inkjet on the thermal substrate, to operate the actuator connected
to the optical sensor to move the optical sensor to a position
opposite the thermal substrate, to identify inoperative inkjets in
the printhead with reference to the data received from the optical
sensor that corresponds to optical densities of the thermal
substrate at a plurality of locations on the thermal substrate, and
to operate the actuator connected to the support member to rotate
the support member about the pivot to enable a thermal substrate to
drop from the support member.
12-13. (canceled)
14. The apparatus of claim 11 further comprising: a collection tray
positioned to receive thermal substrates dropping from the support
member.
15. The apparatus of claim 14 wherein the collection tray is
configured for removal from and reinstallation in the printer to
enable removal of the thermal substrates from the collection
tray.
16-17. (canceled)
18. The apparatus of claim 11, the controller being further
configured to operate the actuator to move the optical sensor away
from the position opposite the thermal substrate.
19. The apparatus of claim 11, the controller being further
configured to identify inkjets that do not eject material drops of
a predetermined size with reference to the data corresponding to
the optical densities of the thermal substrate.
Description
TECHNICAL FIELD
[0001] The device disclosed in this document relates to printers
that detect inoperative inkjets in printheads and, more
particularly, to accurate detection of inoperative inkjets in
printers that use clear inks.
BACKGROUND
[0002] Printing of documents on substrates, such as paper, are
well-known. Newer forms of printing now include digital
three-dimensional manufacturing, also known as digital additive
manufacturing. This type of printing is a process of making a
three-dimensional solid object of virtually any shape from a
digital model. Three-dimensional printing is an additive process in
which one or more printheads eject successive layers of material on
a substrate in different shapes. Three-dimensional printing is
distinguishable from traditional object-forming techniques, which
mostly rely on the removal of material from a work piece by a
subtractive process, such as cutting or drilling.
[0003] The production of a three-dimensional object with these
printers can require hours or, with some objects, even days. One
issue that arises in the production of three-dimensional objects
with a three-dimensional printer is consistent functionality of the
inkjets in the printheads that eject the drops of material that
form the objects. During printing of an object, one or more inkjets
can deteriorate by ejecting the material at an angle, rather than
normal, to the printhead, ejecting drops that are smaller than an
inkjet should eject, or by failing to eject any drop at all. An
inkjet suffering from any of these operational deficiencies is
known as an inoperative inkjet. Similar maladies in printheads are
known in document printing with printheads. If the operational
status of one or more inkjets deteriorates during three-dimensional
object printing, the quality of the printed object cannot be
assessed until the printing operation is completed. Consequently,
print jobs requiring many hours or multiple days can produce
objects that do not conform to specifications due to inoperative
inkjets in the printheads. Once such objects are detected, the
printed objects are scrapped, restorative procedures are applied to
the printheads to restore inkjet functionality, and the print job
is repeated. Even in document printing at high speeds on a moving
web, unacceptable images may be produced over a long length of the
web and this portion of the web may have to be scrapped.
[0004] Although systems have been developed in document printing
systems to detect inoperative inkjets, the detection of inoperative
inkjets in object printing systems is more problematic.
Particularly problematic in both object printing and document
printing systems are the use of the clear materials and inks. These
materials and inks are difficult to detect by imaging systems
because the contrast between the clear inks/materials on the
substrates on which they are ejected is low. Consequently, the
noise in the image data of the patterns on the substrate makes
analysis of the test pattern difficult. An apparatus that enables
detection of inoperative inkjets while printing with clear ink or
clear materials would enable restorative procedures to be applied
during object printing so printing that can produce a properly
formed object or document could continue. In this manner, product
yield for the printer is improved and its printing is more
efficient.
SUMMARY
[0005] An apparatus that enables inoperative inkjet detection in
three-dimensional printers includes a supply of thermal substrate,
an optical sensor configured to generate electrical signals data
corresponding to an area of material drops on the substrate, an
actuator operatively connected to the optical sensor to move the
optical sensor to a position opposite the thermal substrate onto
which material has been ejected, and a controller operatively
connected to the actuator, the optical sensor, and the printhead,
the controller being configured to operate the printhead to eject a
predetermined number of material drops from each inkjet onto the
thermal substrate to enable the predetermined number of material
drops to form a test dot for each inkjet on the thermal substrate,
to operate the actuator to the optical sensor to a position
opposite the thermal substrate, and to identify inoperative inkjets
in the printhead with reference to the data received from the
optical sensor that corresponds to optical densities of the thermal
substrate at a plurality of locations on the thermal substrate.
[0006] A printer that incorporates the apparatus for detecting
inoperative inkjets includes a printhead configured with a
plurality of inkjets to eject material, a supply of thermal
substrate configured to move thermal substrate to a position
opposite the printhead to receive material ejected from the
printhead, an optical sensor configured to generate electrical
signals corresponding to an optical density of a location on the
thermal substrate, an actuator operatively connected to the optical
sensor to move the optical sensor to a position opposite the
thermal substrate onto which material has been ejected, and a
controller operatively connected to the actuator, the optical
sensor, and the printhead, the controller being configured to
operate the printhead to eject a predetermined number of material
drops from each inkjet onto the thermal substrate to enable the
predetermined number of material drops to form a test dot for each
inkjet on the thermal substrate, to operate the actuator to the
optical sensor to a position opposite the thermal substrate, and to
identify inoperative inkjets in the printhead with reference to the
data received from the optical sensor that corresponds to optical
densities of the thermal substrate at a plurality of locations on
the thermal substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The foregoing aspects and other features of an apparatus or
printer that detects inoperative inkjets during three-dimensional
printing are explained in the following description, taken in
connection with the accompanying drawings.
[0008] FIG. 1 is a perspective view of a three-dimensional object
printer.
[0009] FIG. 2 is front view of a three-dimensional object printer
having a housing that depicts a space within the housing for a
module that enables inoperative inkjets in the printhead to be
detected during a printing operation.
[0010] FIG. 3 is a perspective view of a module for detecting
inoperative inkjets that fits in the space shown in FIG. 2.
[0011] FIG. 4 is a flow diagram of a method for operating the
module of FIG. 3.
[0012] FIG. 5 is an alternative embodiment of a printer having a
module for detecting inoperative inkjets during printing of a
three-dimensional object.
[0013] FIG. 6 is a flow diagram of a method for operating the
module of FIG. 5.
[0014] FIG. 7 is a static sensitivity graph for an exemplary
thermal substrate used in the systems of FIG. 3 and FIG. 5.
[0015] FIG. 8 is a dynamic sensitivity graph for the exemplary
thermal substrate described in the graph of FIG. 6.
DETAILED DESCRIPTION
[0016] For a general understanding of the environment for the
device disclosed herein as well as the details for the device,
reference is made to the drawings. In the drawings, like reference
numerals designate like elements.
[0017] FIG. 1 shows a configuration of components in a printer 100,
which produces a three-dimensional object or part 10. As used in
this document, the term "three-dimensional printer" refers to any
device that ejects material with reference to image data of an
object to form a three-dimensional object. The printer 100 includes
a support material reservoir 14, a build material reservoir 18, a
pair of inkjet printheads 22, 26, a build substrate 30, a planar
support member 34, a columnar support member 38, an actuator 42,
and a controller 46. Conduit 50 connects printhead 22 to support
material reservoir 14 and conduit 54 connects printhead 26 to build
material reservoir 18. Both inkjet printheads are operated by the
controller 46 with reference to three-dimensional image data in a
memory operatively connected to the controller to eject the support
and build materials supplied to each respective printhead. The
build material forms the structure of the part 10 being produced,
while the support structure 58 formed by the support material
enables the build material to maintain its shape while the material
solidifies as the part is being constructed. The support material
also allows the build material to bridge gaps in the underlying
object. After the part is finished, the support structure 58 is
removed by washing, blowing, or melting.
[0018] The controller 46 is also operatively connected to at least
one and possibly more actuators 42 to control movement of the
planar support member 34, the columnar support member 38, and the
printheads 22, 26 relative to one another. That is, one or more
actuators can be operatively connected to structure supporting the
printheads to move the printheads in a process direction and a
cross-process direction with reference to the surface of the planar
support member. Alternatively, one or more actuators can be
operatively connected to the planar support member 34 to move the
surface on which the part is being produced in the process and
cross-process directions in the plane of the planar support member
34. As used herein, the term "process direction" refers to movement
along one axis in the surface of the planar support member 34 and
"cross-process direction" refers to movement along an axis in the
planar support member surface that is orthogonal to the process
direction axis in that surface. These directions are denoted with
the letters "P" and "C-P" in FIG. 1. The printheads 22, 26 and the
columnar support member 38 also move in a direction that is
orthogonal to the planar support member 34. This direction is
called the vertical direction in this document, is parallel to the
columnar support member 38, and is denoted with the letter "V" in
FIG. 1. Movement in the vertical direction is achieved with one or
more actuators operatively connected to the columnar member 38, by
one or more actuators operatively connected to the printheads 22,
26, or by one or more actuators operatively connected to both the
columnar support member 38 and the printheads 22, 26. These
actuators in these various configurations are operatively connected
to the controller 46, which operates the actuators to move the
columnar member 38, the printheads 22, 26, or both in the vertical
direction.
[0019] A three-dimensional object printer having a housing is shown
in FIG. 2. Printer 60 has a housing 64 that is mounted to a frame
68. Within the housing 64 are six compartments that are generally
cubic in shape. The housing 64 is shown in FIG. 2 without the doors
that close to conceal the compartments. Compartment 72 includes a
planar support 78 on a movable platform 82. Movable platform 82 is
configured with one or more actuators and guide members (not shown)
to enable the movable platform 82 to move up and down in a vertical
direction. The planar support 78 is the surface on which a
three-dimensional object is formed. In some embodiments, the
printhead 86 has a length that is approximately equal to the length
of the planar support 78 in the direction from the back wall of
compartment 72 to the opening at the front of the compartment. In
these embodiments, printhead 86 is mounted on support member 92 in
the space between sidewalls 96 and 100 of housing 64 for linear
reciprocating movement only. In other embodiments, the printhead 86
has a length that is less than the length of the planar support 78
in the direction from the back wall of compartment 72 to the
opening at the front of the compartment. In these embodiments,
printhead 86 is mounted on support member 92 in the space between
sidewalls 96 and 100 of housing 64 for reciprocating movement in
two orthogonal directions in a plane above compartment 72. In these
various embodiments, one or more actuators 104 are operatively
connected to the printhead 86. Controller 108 operates the
actuators 104 to move the printhead 86 either linearly back and
forth on support member 92 or to move the printhead in two
orthogonal directions within a plane. By selectively operating the
inkjets in the printhead 86 and vertically moving the support
platform 82 and horizontally moving the printhead 86 on the member
92, a three-dimensional object can be formed on the planar support
78.
[0020] The area 112 outlined in dashes in FIG. 2 identifies the
placement of a module that prints a test pattern on thermal
substrates to detect inoperative inkjets in the printer 60. As
noted above, if an inkjet fails during printing of an object by
either completely or partially failing to eject material or by
errantly ejecting material in a skewed direction, the object being
produced is malformed. Currently, this malformation cannot be
detected until production of the object is finished. By using area
112 for optically sensing material ejected onto a thermal
substrate, printer 60 can be configured to detect inoperative
inkjets during object production as described more fully below.
Some components within the module 300 can move in the horizontal
direction H, depth direction D, and vertical direction V as shown
in the figure.
[0021] One embodiment of a module that detects inoperative inkjets
during object printing is shown in the block diagram of FIG. 3.
While the module 300 is described as being installed in a printer
that produces three-dimensional objects, it can also be used in
printers that eject inks to produce printed documents, particularly
those that use one or more types of clear ink. The module 300 is
configured to fit within area 112 of printer 60. The module 300
includes an optical sensor 304, a thermal substrate supply 308, a
support member 312, one or more actuators 316, a collection tray
320, and a controller 324. The optical sensor 304 is mounted for
movement along guide rail 328 and the guide rail 328 is operatively
connected to an actuator 316 to move the optical sensor 304 from a
position over the substrate supply 308 to a position over the
support member 312 and back again. The controller 324 is
operatively connected to the actuators 316 to move the optical
sensor 304 and guide rail as described, to displace a thermal
substrate 332 from the supply 308 to the support member 312, and to
pivot the support member 312 to drop a thermal substrate from the
support member 312 into the collection tray 320. Alternatively, the
guide rail 328 and the optical sensor 304 can be fixedly mounted to
the printhead 86 so controller 108 can operate actuators 104 to
move the printhead and the sensor 304. Alternatively, the optical
sensor can be fixedly mounted over the collection tray 320, in a
manner that enables the sensor to scan the paper as it is fed into
the tray. As shown in the figure, printhead 86 can include an
ejector head 2a, a curing device 2b, and a planarizer 2c, although
the curing device 2b and planarizer 2c are not needed for materials
that do not require curing or trimming.
[0022] The thermal substrates 332 in the substrate supply 308 are
planar members made of a substance that supports the build material
and the support material ejected from the printhead 86, such as
paper, which is coated with a heat sensitive dye that changes color
in response to exposure to heat contained within the build material
or support material. These dyes increase in optical density with
reference to a known function of optical density per unit of heat
energy input to the substance of the thermal substrate. FIG. 7
shows a static sensitivity curve for KL475RX paper made by Kanzaki
Specialty Papers, Inc. of Springfield, Mass. This curve graphs
optical density of the paper versus temperature and it indicates
that the paper changes optical density in a temperature range
centered about 90 degrees C. This paper would therefore be a good
choice for detecting clear ink jetted at 90 C, which is a typical
material temperature for three-dimensional printing. FIG. 8 shows a
dynamic sensitivity range graph, which gives the optical density
response as a function of input energy, for the KL475RX paper. This
graph is important for applications in which the material drops
cool quickly after ejection from the printhead. These drops may be
at high temperature for a relatively short time before cooling
below the sensitivity threshold of the paper. Kanzaki KL475RX has a
nearly linear response to input energy, which is useful for
quantifying the amount of heat that needs to be delivered to the
paper to produce the optical density change.
[0023] The substrate supply 308 includes a lifting mechanism 336
that lifts the thermal substrates 332 as a pushing mechanism 340
removes a single substrate from the supply and positions it onto
the support member 312. The lifting mechanism 336 can be a
spring-loaded mechanism, an air spring, a mechanically actuated
jack, or the like. The pushing mechanism 340 can be a solenoid or
the like. The guide rail that supports the optical sensor 304 is
operatively connected to one of the actuators 316 to move the guide
rail 328 and the optical sensor 304 between the position over the
substrate supply 308 and the position over the support member 312
in a reciprocating manner between the two positions. When the guide
rail 328 and the sensor 304 are over the substrate supply 308, the
printhead 86 can be moved above a thermal substrate 332 on the
support member 312 to enable printing of a test pattern on the
substrate. The heat energy of the build material and support
material on the substrate increases the optical density of the
thermal substrate at the point of impact and the immediately
surrounding area. The extent of the optical density spread
corresponds to the amount of heat energy carried by the material
mass ejected by the inkjets. When the guide rail 328 and the sensor
304 are over the support member 312, the sensor 304 is moved along
the guide rail 328 to enable generation of image data of the test
pattern on the thermal substrate 332.
[0024] A method of operating a printer that produces
three-dimensional objects is shown in FIG. 4. In the description of
this method, statements that a process is performing some task or
function refers to a controller or general purpose processor
executing programmed instructions stored in a memory operatively
connected to the controller or processor to manipulate data or to
operate one or more components in the printer to perform the task
or function. The controller 324 noted above can be such a
controller or processor. Alternatively, the controller 324 can be
implemented with more than one processor and associated circuitry
and components, each of which is configured to form one or more
tasks or functions described herein.
[0025] At predetermined times in the printing operation, the
controller 108 (FIG. 2) operates an actuator 104 to move the
printhead 86 into the module 300 located in the area 112 (block
404). In response to the controller 324 detecting the printhead in
the module 300, controller 324 operates the pushing mechanism 340
to move a thermal substrate 332 onto the support member 312 (block
408). Controller 324 then generates a signal to the controller 108
to operate the inkjets in the printhead to print a test pattern on
the thermal substrate (block 412). In one embodiment, each inkjet
in the printhead is repetitively operated to form a pile of
material, also called a test dot, on a portion of the thermal
substrate 332 opposite the inkjet. After the test pattern is
printed, controller 108 moves the printhead 86 out of the module
300 and generates a signal for controller 324. In response to the
signal from controller 108, controller 324 operates an actuator 316
to move the guide rail 328 and the optical sensor 304 to a position
opposite the test pattern on the thermal substrate 332 (block 416).
The optical sensor 304 is then moved along the guide rail 328 to
emit a light towards the test pattern on the substrate 332, receive
the reflections from the test pattern and thermal substrate, and
generate measurements of the test pattern on the thermal substrate
332 (block 420). The reflected light from the areas where the
thermal energy has increased the optical density of the thermal
substrate are substantially different from those where the optical
density is unaffected. These measurements are analyzed with
reference to the function relating optical density to the heat
energy of each drop ejected onto the thermal substrate to identify
inoperative inkjets (block 424) and, if inoperative inkjets are
identified, a signal indicative of the defective printhead is
generated for the operator of the printer (block 428). The operator
can then take appropriate action. The process continues by the
controller 324 operating an actuator 316 to rotate the support
member 312 about one end of the member to enable the substrate on
which the test pattern was printed to drop into the collection tray
320 (block 432). The actuator operation is then reversed to return
the support member 312 to the position for receiving the next
thermal substrate 332 (block 436). By operating another actuator
316, the controller 324 returns the guide rail 328 and the optical
sensor 304 to the position over the substrate supply 308 (block
440).
[0026] In another embodiment shown in FIG. 5, the module 300' is
formed with a roller supporting a supply of thermal substrate for
the printing of test patterns that are moved to a take-up roller.
The module 300' is also configured to fit within area 112 of
printer 60. Using like numbers for like components, the module 300'
includes an optical sensor 304, a supply roll 310 of thermal
substrate on a roller, a take-up roller 314, one or more actuators
316, a pair of support members 318, and a controller 324. The
optical sensor 304 is positioned to image the test pattern on the
substrate pulled from supply 310 after printhead 86 has printed the
test pattern on the substrate. The controller 324 is operatively
connected to the actuator 316 to drive the take-up roller 314 and
pull substrate from the supply roll 310. Alternatively, the optical
sensor can be fixedly mounted within the module, so the sensor does
not physically interfere with the printhead. The thermal substrate
on the roll 310 can be made of a material that supports the build
material and the support material ejected from the printhead 86 and
that changes optical density in response to heat energy. For
example, the thermal substrate roll could be a roll of the thermal
paper available from Kanzaki Specialty Papers, Inc. noted
above.
[0027] A method of operating a printer that produces
three-dimensional objects is shown in FIG. 6. In the description of
this method, statements that a process is performing some task or
function refers to a controller or general purpose processor
executing programmed instructions stored in a memory operatively
connected to the controller or processor to manipulate data or to
operate one or more components in the printer to perform the task
or function. The controller 324 noted above can be such a
controller or processor. Alternatively, the controller 324 can be
implemented with more than one processor and associated circuitry
and components, each of which is configured to form one or more
tasks or functions described herein.
[0028] At predetermined times in the printing operation, the
controller 108 (FIG. 2) operates an actuator 104 to move the
printhead 86 into the module 300 located in the area 112 (block
604). In response to the controller 324 detecting the printhead in
the module 300, controller 324 operates an actuator 316 to rotate
take-up roller 314 and pull a clean portion of the thermal
substrate from the supply on the roll 310 to a position beneath the
printhead 86 (block 608). Controller 324 then generates a signal to
the controller 108 to operate the inkjets in the printhead to print
a test pattern on the substrate (block 612). In one embodiment,
each inkjet in the printhead is repetitively operated to form a
pile of material, also called a test dot, on a portion of the
substrate roll 310 opposite the inkjet. As noted above, the optical
density in the areas of the substrate that absorb the heat of the
ejected material changes. After the test pattern is printed,
controller 108 moves the printhead 86 out of the module 300' and
generates a signal for controller 324. In response to the signal
from controller 108, controller 324 operates the actuator 316 to
move the printed portion of the thermal substrate to a position
opposite the optical sensor 304 (block 616). The optical sensor 304
is operated to emit a light towards the test pattern on the portion
of the printed thermal substrate, receive the reflections from the
test pattern and thermal substrate, and generate electrical signals
corresponding to the optical densities of the test pattern on the
thermal substrate (block 620). These electrical signals are image
data that are analyzed with reference to the function relating
optical density to the heat energy of each drop ejected onto the
substrate to identify inoperative inkjets (block 624) and, if
inoperative inkjets are identified, a signal indicative of the
defective printhead is generated for the operator of the printer
(block 628). The operator can then take appropriate action. The
controller 324 determines if the supply roll 310 is empty (block
630), and if it is, generates a signal that indicates another
supply roll is needed (block 634). An operator can then remove the
take-up roll and provide another supply roll 310 of thermal
substrate. If an adequate supply of thermal substrate remains, the
controller 324 waits for the printhead to return to the position
for printing another test pattern (block 604).
[0029] While the embodiments discussed above are within a printer
that forms three-dimensional objects, thermal substrates and the
system that detects inoperative inkjets from the changes in optical
density on such substrates can be used in two dimensional document
printing systems, particularly those that use clear inks. Thus, as
used in this document, the word "material" refers to substances
that can be used to form three dimensional objects as well as inks
used in document printing. In such systems, a second supply of
thermal substrates can be maintained and, from time to time,
printed with a test pattern that is analyzed to identify
inoperative inkjets. Likewise, printheads ejecting clear ink onto a
moving web or an imaging member, such as a drum, can be moved
opposite a thermal substrate, either in sheet form or from a roll
supply, for printing and detection of inoperative inkjets.
[0030] It will be appreciated that variants of the above-disclosed
and other features and functions, or alternatives thereof, may be
desirably combined into many other different systems, applications
or methods. Various presently unforeseen or unanticipated
alternatives, modifications, variations or improvements may be
subsequently made by those skilled in the art that are also
intended to be encompassed by the following claims.
* * * * *