U.S. patent application number 09/792980 was filed with the patent office on 2001-11-01 for sensing system for detecting presence of an ink container and level of ink therein.
This patent application is currently assigned to Xerox Corporation. Invention is credited to Altfather, Kenneth W., Carlotta, Michael, Dietl, Steven J., Hubble, Fred F. III, Stevens, Donald M..
Application Number | 20010035887 09/792980 |
Document ID | / |
Family ID | 24288538 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035887 |
Kind Code |
A1 |
Altfather, Kenneth W. ; et
al. |
November 1, 2001 |
Sensing system for detecting presence of an ink container and level
of ink therein
Abstract
A low ink sensing system is combined with an ink cartridge
detection system to enable a more efficient ink jet printer. An ink
container which supplies ink to an associated printhead is modified
by the incorporation of two light directing elements, in the
preferred embodiment, a faceted prism and a roof mirror, into a
transparent wall of the container housing. The cartridge,
comprising the ink container and associated printhead, is mounted
on a scan carriage. Periodically, the carriage is conveyed to a
sensing station comprising a pair of light sources and a commonly
used photosensor. A first light source is energized and a beam of
light is directed to a location where the roof mirror, would be
positioned if the cartridge is present. If the cartridge is absent,
lack of a reflected return signal is sensed, indicating a cartridge
has not been inserted. Print operation is halted until a cartridge
is inserted. If a cartridge is properly inserted, the roof mirror
returns most of the incident light to the photosensor which
generates a signal indicating the presence of the cartridge. A
second light source is then energized and directed towards the
faceted prism, which is either immersed in ink or exposed to air
within the interior of the container. If the latter, light is
internally reflected by the prism facets back to the photosensor.
If a print operation has been in progress, and the ink level has
fallen, the common photosensor detects either a strong or weak
redirected light component and initiates a status check and
generates appropriate displays of low ink level or out of ink
warnings.
Inventors: |
Altfather, Kenneth W.;
(Fairport, NY) ; Carlotta, Michael; (Sodus,
NY) ; Dietl, Steven J.; (Ontario, NY) ;
Stevens, Donald M.; (Walworth, NY) ; Hubble, Fred F.
III; (Rochester, NY) |
Correspondence
Address: |
Patent Documentation Center
Xerox Corporation
Xerox Square 20th Floor
100 Clinton Avenue S.
Rochester
NY
14644
US
|
Assignee: |
Xerox Corporation
|
Family ID: |
24288538 |
Appl. No.: |
09/792980 |
Filed: |
February 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09792980 |
Feb 26, 2001 |
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09305990 |
May 6, 1999 |
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6234603 |
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09305990 |
May 6, 1999 |
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08572595 |
Dec 14, 1995 |
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5997121 |
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Current U.S.
Class: |
347/7 ;
347/19 |
Current CPC
Class: |
B41J 2/17566 20130101;
B41J 2/17553 20130101; B41J 2/17546 20130101; G01F 23/2927
20130101; B41J 2002/17573 20130101; B41J 2/17513 20130101; B41J
2002/17569 20130101; G01F 23/2922 20130101 |
Class at
Publication: |
347/7 ;
347/19 |
International
Class: |
B41J 002/195; B41J
029/393 |
Claims
What is claimed is:
1. A sensing system for detecting the presence of an ink container
and the level of ink therein comprising: first light directing
means operatively connected to said container, a first light source
having output beams directed toward said light directing means when
in a container detect mode, photosensor means for detecting the
presence or absence of light directed from said light directing
means and for generating an output signal indicative thereof,
second light directing means operatively connected to said
container, a second light source having output beams directed
toward said second light directing means when in a low ink level
detect mode and photosensor means for detecting light directed from
said second light directing means, the level of detected light and
hence the level of the photosensor output being representative of
the presence or absence of ink adjacent the interior surface of the
second light directing means.
2. The sensing system of claim 1 wherein said first light directing
means is a roof mirror.
3. The sensing system of claim 1 wherein said second light
directing means is a prism with a plurality of facets.
4. The sensing system of claim 3 wherein said prism is constructed
of a plurality of multiple narrow facet sections.
5. The sensing system of claim 1 wherein said photosensor means
commonly and sequentially detects light reflected from both said
first and second light directing means.
6. The sensing system of claim 1 wherein said first and second
light directing means are formed integrally in a container
wall.
7. The system of claim 3 wherein the container is filled with ink
to a depth at least covering said prism causing the light incident
on the prism facets to be almost wholly transmitted into the ink
resulting in a low amount of light being reflected to said
photosensor, said photosensor generating a signal indicative of an
ink level higher than a predetermined low level.
8. The system of claim 3 wherein light is totally internally
reflected along the prism facets when the ink level falls below the
prism resulting in an increased amount of light being reflected
into said photosensor, said photosensor generating a low ink level
signal.
9. The system of claim 1 wherein said first light directing means
is a light pipe.
10. A sensing system for detecting the presence of an ink container
comprising: light directing means operatively connected to said
container, a light source having output beams directed toward said
light directing means when in a container detect mode and
photosensor means for detecting the presence or absence of light
from said light directing means and for generating an output signal
indicative thereof.
11. The sensing system of claim 10 wherein the light directing
means is a reflective member.
12. The sensing system of claim 10 wherein the light directing
means is a light pipe.
13. The sensing system of claim 10 wherein the support for the
light directing means is formed integrally in a wall of said
container.
14. The sensing system of claim 13 wherein the container has a wall
with at least a portion of said wall being transparent and wherein
said reflective member is located in the interior of said container
whereby said light beams from said light source are directed onto
the reflective member through said transmissive portion of said
container wall.
15. The system of claim 11 wherein the reflective member is a roof
mirror.
16. A system for sensing the presence or absence of an ink
cartridge in an ink recording device, said cartridge including a
printhead and an ink container for supplying ink to said printhead,
said system including: at least one printhead for printing each of
a first color onto a recording medium, an associated ink supply
container for providing ink of said first color to said printhead,
said container having at least a partially transparent section of a
wall, said wall having at least a reflective member associated
therewith, means for moving said cartridge along a scan path, an
optical sensing station located along said scan path and comprising
a light source and a photosensor, means for moving said cartridge
into said station so that, if said cartridge is physically present
the reflective member is opposite said light source output and
means for energizing said light source, said photosensor either
sensing a light source output beam reflected from said reflective
member thereby indicating the presence of a cartridge or sensing
lack of an reflected light indicating the absence of a
cartridge.
17. The system of claim 16 further including an optical means
mounted beneath said reflective means, said cartridge detection
station further comprising a second light source aligned so as to
direct a beam of light against said optical means, said light
source energizing means sequentially energizing said light source
with said photosensor generating signals representing the presence
or absence of a cartridge followed sequentially by a ink level
signal, the optical means, when covered with ink, providing a high
ink level signal, and when exposed to air, providing a low ink
level signal.
18. A method for detecting the presence or absence of a cartridge
mounted on a movable carriage and used in an ink jet printer
including the steps of: directing a beam of light into an optical
sensing station, moving said carriage into said optical sensing
station so that a portion of said cartridge, if present, intercepts
said light beam, sensing the presence or absence of light
redirected back from said portion and generating a signal
representative of the presence or absence of a cartridge.
19. The method of claim 18 wherein said directed light is
redirected from a reflective portion of the cartridge.
20. The method of claim 18 wherein said directed light is
transmitted back from a transmissive portion of said cartridge.
21. An ink supply container comprising: a housing defining an
interior space and having an air outlet located at a first position
and an ink outlet located at a second position, at least one wall
of said container at least partially constructed of a light
transmissive material and a reflector integrally formed within said
transparent wall and having at least two reflective facet surfaces
extending away from said wall and into the interior of the housing
and angled toward each other.
22. The ink cartridge of claim 21 further including a second
reflector integrally formed within said wall and having at least
two light transmissive facet surfaces extending away from said wall
and into the interior of the housing, said transmissive surfaces
angled toward each other.
23. A cartridge detecting device for detecting the presence of an
ink cartridge in an ink printer comprising: an ink container having
a reflective element installed in one wall of the container, a
light-emitting source for emitting light along a path intercepted
by said reflective element and a sensor for detecting the presence
of light reflected from said reflective element and for generating
an output signal representative of said detection.
24. A sensing system for detecting the presence of an ink container
and the level of ink therein comprising: first light directing
means operatively connected to said container, a light source
having output beams directed toward said first light directing
means when in a container detect mode, first photosensor means for
detecting the presence or absence of light directed from said light
directing means and for generating an output signal indicative
thereof, second light directing means operatively connected to said
container, said light source having output beams directed toward
said second light directing means when in a low ink level detect
mode and second photosensor means for detecting light directed from
said second light directing means, the level of detected light and
hence the level of the photosensor output being representative of
the presence or absence of ink adjacent the interior surface of the
second light directing means.
25. An ink detecting system for monitoring the level of ink in an
ink container from which ink is gradually withdrawn, comprising: a
multi-faceted prism positioned in the container so as to be
initially covered by the ink contained therein but to be gradually
uncovered as the ink is withdrawn from the container, a light
source having output beams directed toward said prism and incident
on said facets, the light almost wholly transmitted into the ink
when said prism is covered by said ink and totally internally
reflected along the prism facets when the prism is uncovered, a
photosensor positioned so as to detect light reflected from said
prism, said photosensor generating a low ink level output signal
when detecting said totally internally reflected light, means for
monitoring the quantity of ink being withdrawn following generation
of said low ink level detection signal and means for defining an
out of ink status for the container.
26. The system of claim 25 wherein said ink container supplies ink
to a printhead of an ink recording device and wherein said ink
monitoring means include counter means for counting the number of
drops ejected from the printhead and for generating an output
indicative thereof and logic means for monitoring the output of the
counter means and for disabling the recording device when a
pre-established number of drops have been counted by said counter
means.
Description
BACKGROUND AND MATERIAL DISCLOSURE STATEMENT
[0001] The present invention relates to ink jet recording devices
and, more particularly, to a system for detecting the presence of
an ink supply container and also for detecting when the level of
ink in the container is at or below a predetermined level.
[0002] Ink jet recording devices eject ink onto a print medium such
as paper in controlled patterns of closely spaced dots. To form
color images, multiple groupings of ink jets are used, with each
group being supplied with ink of a different color from an
associated ink container.
[0003] Thermal ink jet printing systems use thermal energy
selectively produced by resistors located in capillary filled ink
channels near channel terminating nozzles or orifices to vaporize
momentarily the ink and form bubbles on demand. Each temporary
bubble expels an ink droplet and propels it toward a recording
medium. The printing system may be incorporated in either a
carriage type printer or a pagewidth type printer. A carriage type
printer generally has a relatively small printhead containing the
ink channels and nozzles. The printhead is usually sealingly
attached to an ink supply container and the combined printhead and
container form a cartridge assembly which is reciprocated to print
one swath of information at a time on a stationarily held recording
medium, such as paper. After the swath is printed, the paper is
stepped a distance equal to the height of the printed swath, so
that the next printed swath will be contiguous therewith. The
procedure is repeated until the entire page is printed. In
contrast, the pagewidth printer has a stationary printhead having a
length equal to or greater than the width of the paper. The paper
is continually moved past the pagewidth printhead in a direction
normal to the printhead length at a constant speed during the
printing process. Moving carriage type ink jet printers must either
carry the ink container along with the printhead or provide a
flexible ink supply line between the moving printhead and a
stationary ink container. Pagewidth printers have an ink supply
container located outside the print zone and directly connected to
the printbar ink channels.
[0004] For either a partial width printhead on a moving carriage or
for a pagewidth printbar, it is desirable to have a low ink level
warning to alert a user to replace or refill the ink container so
that the ink does not run out during a print job. Presently, for
some applications (such as plotting), some users choose to install
new print containers prior to starting an extensive printing job
because it is less costly to replace a questionable container
rather than lose one or more colors in the output prints. It is
also important to ensure that the ink supply container is in the
proper location; e.g., fluidly connected to the associated
printhead. In some instances, an out of ink container may be
removed but a replacement container neglected to be inserted.
Printer operation with the container removed could potentially
damage the associated printhead.
[0005] Various prior art methods and devices are known for
detecting reduced levels of ink in an ink supply container. U.S.
Pat. No. 4,342,042 discloses an ink sensing system which includes
output from an LED sensor reflected from a flexible membrane which
serves as the upper surface of an ink supply reservoir. The
membrane contracts as the ink level is depleted, and the LED sensor
detects the contraction and generates a low ink level signal.
[0006] U.S. Pat. No. 5,079,570 provides a method for detecting ink
levels in an ink cartridge where the ink is supplied from a foam
reservoir. A binary fluidic indicator is fluidly coupled with the
foam reservoir and is triggered when the fluid level in the foam
reaches a certain prescribed level.
[0007] U.S. Pat. No. 5,289,211 discloses a low ink detecting system
which includes a pair of electrodes immersed in the ink impregnated
foam reservoir. The electrodes are connected to a bridge circuit
which measures the electrical resistance of the ink between the two
electrodes.
[0008] U.S. Pat. No. 5,414,452 uses a logic circuit which counts
the number of drops expelled and compares the instant number with
the maximum number of drops equivalent to a known value of ink in
the ink reservoir.
[0009] U.S. Pat. No. 5,434,603 discloses a visual indicator system
where sidewalls of the reservoir retreat inwardly during ink
depletion changing the orientation of indicator stripes and
modifying the color visible to an observer through a window.
[0010] U.S. Pat. No. 5,386,224 places a level sensing probe into
the ink supply and senses electrical conductivity changes of the
ink.
[0011] U.S. Pat. No. 5,136,305 discloses a low ink detecting system
wherein a thermistor is placed in the ink supply and periodically
energized. The temperature rise of the ink is measured and compared
with pre-established values to determine the ink depletion state of
the reservoir.
[0012] U.S. Pat. No. 4,639,738 discloses a detection system which
incorporates detection ports in the cartridge for detecting
pressure conditions in the top and bottom of the cartridge. The
ports are coupled to a pressure differential sensor that signals a
refill condition.
[0013] Japanese publication 5-332812 describes a low ink detection
system wherein the cartridge has a transparent optical path member
installed in an opening of a surface of an ink storage tank. An LED
emits a beam of light which is guided into the ink tank and
reflected back to a sensor to provide an indication of low ink
levels.
[0014] Some of the prior art references are relatively expensive
relying on measurement and detection of ink conductivity or drop
detecting circuitry. Further, none of the prior art references
includes means for insuring that the ink tank is in proper position
before beginning the ink level sensing operation.
SUMMARY OF THE INVENTION
[0015] It is, therefore, one object of the present invention to
provide a detection system which confirms the proper installation
of an ink container supplying ink to an associated printhead.
[0016] It is another object to present a detection system for
detecting a low level of ink in the ink container and for providing
a low ink level warning signal.
[0017] Another object of the invention is to provide an ink supply
container which is constructed so as to enable an inexpensive
optical detection system which performs both the ink container
detection as well as the low ink level detection function.
[0018] In the present invention, and in an exemplary embodiment, a
thermal printer is disclosed which includes a printhead for
printing on a recording medium in response to image drive signals.
Ink is supplied to the printhead from an ink container which is
fluidly connected to the printhead. The printhead and container are
mounted on a scanning carriage which moves back and forth across a
print zone, the printhead ejecting ink droplets from nozzles to
form an image on the recording medium. An optical system comprising
two light sources and a light detector is fixedly located along the
path of travel of the carriage and positioned so that light from
the light source is directed into the ink container as it is
positioned opposite the optical system. The ink container has
optical light directing elements formed in a transmissive wall.
Light from the light sources are directed into and onto the
container through the transparent wall and, sequentially, onto the
optical elements. In one embodiment, the light directing elements
are reflective prisms; reflections of light from these elements, or
lack thereof, is sensed by a common photosensor to provide signals
representing the presence or absence of the container and the level
of ink remaining in the container.
[0019] More particularly, the present invention relates to a
sensing system for detecting the presence of an ink container and
the level of ink therein comprising:
[0020] first light directing means operatively connected to said
container,
[0021] a first light source having output beams directed toward
said light directing means when in a container detect mode,
[0022] photosensor means for detecting the presence or absence of
light directed from said light directing means and for generating
an output signal indicative thereof,
[0023] second light directing means operatively connected to said
container,
[0024] a second light source having output beams directed toward
said second light directing means when in a low ink level detect
mode and
[0025] photosensor means for detecting light directed from said
second light directing means, the level of detected light and hence
the level of the photosensor output being representative of the
presence or absence of ink adjacent the interior surface of the
second light directing means.
[0026] Further, the present invention relates to a method for
detecting the presence or absence of a cartridge mounted on a
movable carriage and used in an ink jet printer and the level of
ink in an ink container associated with said cartridge including
the steps of:
[0027] directing a beam of light into an optical sensing
station,
[0028] moving said carriage into said optical sensing station so
that a portion of said cartridge, if present, intercepts said light
beam,
[0029] sensing the presence or absence of light redirected back
from said portion and
[0030] generating a signal representative of the presence or
absence of a cartridge.
[0031] The invention also relates to a system for sensing the
presence or absence of an ink cartridge in an ink recording device,
said cartridge including a printhead and an ink container for
supplying ink to said printhead, said system including:
[0032] at least one printhead for printing each of a first color
onto a recording medium,
[0033] an associated ink supply container for providing ink of said
first color to said printhead, said container having at least a
partially transparent section of a wall, said wall having at least
a reflective member associated therewith,
[0034] means for moving said cartridge along a scan path,
[0035] an optical sensing station located along said scan path and
comprising a light source and a photosensor,
[0036] means for moving said cartridge into said station so that,
if said cartridge is physically present the reflective member is
opposite said light source output and
[0037] means for energizing said light source, said photosensor
either sensing a light source output beam reflected from said
reflective member thereby indicating the presence of a cartridge or
sensing lack of an reflected light indicating the absence of a
cartridge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 illustrates a perspective view of an ink jet printer
which incorporates the ink container and low ink level sensing
system of the present invention.
[0039] FIG. 2 is a cross-sectional view through the ink cartridge
shown in FIG. 1.
[0040] FIG. 3 is an algorithm which is used to sequence the checks
to determine presence or absence of a container as well as level of
ink within the container.
[0041] FIG. 4 is a block diagram of the control circuitry for
controlling operation of the sensing system.
[0042] FIG. 5A is a cross-section of a prism-shaped reflective
element within the cartridge showing the prism container with a
sufficient level of ink.
[0043] FIG. 5B is a cross-section of the prism of FIG. 5A showing
the reflection path in a low ink environment.
[0044] FIG. 6 is a plot of low ink sensing output signals versus
volume of ink depleted from a cartridge.
[0045] FIG. 7 illustrates a perspective view of a full color ink
jet printer which incorporates the ink containers and low ink level
sensing system of the present invention.
[0046] FIG. 8 is an algorithm for the FIG. 7 embodiment which is
used to sequence the presence or absence of a container and the low
ink sensing sequentially.
[0047] FIG. 9 is an alternate embodiment of a cartridge detection
system incorporating a light pipe.
[0048] FIG. 10 is an alternate embodiment of the optical assembly
shown in FIGS. 1 and 2.
DESCRIPTION OF THE INVENTION
[0049] FIG. 1 illustrates a perspective view of a thermal ink jet
printer 8 which incorporates a preferred embodiment of the ink
container and low ink detection system of the present invention.
Printer 8 is exemplary only. The invention can be practiced in
other types of thermal ink jet printers as well as other
reproduction devices such as piezoelectric printers, dot matrix
printers and ink jet printers driven by signals from a document
Raster Input Scanner. Printer 8 includes an ink jet printhead
cartridge 10 mounted on a carriage 12 supported by carriage rails
14. The carriage rails are supported by a frame 15 of the ink jet
printer 8. The printhead cartridge 10 includes a container 16 shown
in detail in FIG. 2, containing ink for supply to a thermal ink jet
printhead 18 which selectively expels droplets of ink under control
of electrical signals received from a controller 50 (FIG. 4) of the
printer 8 through an electrical cable 20. Container 16 comprises a
housing 17 having a wall 17A seating reflective elements 21 and 22,
shown in further detail in FIG. 2. Container 16 is fluidly, but
detachably connected, to printhead 18 and can be replaced when the
ink is depleted therefrom. Alternatively, the entire cartridge can
be replaced upon each depletion depending upon the particular
system requirements. The printhead 18 contains a plurality of ink
channels which carry ink from the container 16 to respective ink
ejecting orifices or nozzles. When printing, the carriage 12
reciprocates back and forth along the carriage rails 14 in the
direction of the arrow 23, the entire width traverse constitutes a
scanning path. The actual printing zone is contained within the
scanning path. As the printhead cartridge 10 reciprocates back and
forth along a print path and past a recording medium 24, such as a
sheet of paper or a transparency, droplets of ink are expelled from
selected ones of the printhead nozzles towards the sheet of paper.
Typically, during each pass of the carriage 12 the recording medium
24 is held stationary. At the end of each pass, the recording
medium 24 is stepped in the direction of the arrow 26. For a more
detailed explanation of the operation of printer 8, reference is
hereby made to U.S. Pat. No. 4,571,599 and U.S. Pat. No. Reissue
32,572, which are incorporated herein by reference.
[0050] Also shown in FIG. 1 is an optical sensing assembly 30.
Referring to FIGS. 1 and 2, assembly 30 includes a housing 31
within which are mounted a first light source 34, a second light
source 36 and a photosensor 38 located between the two light
sources and commonly used therewith as will be seen. The light
sources are electrically connected to a power source while the
photosensor 38 output is electrically connected into the system
controller circuits as will be seen. Container 16, in a preferred
embodiment, is designed as a two compartment unit. Assembly 30 is
mounted in the carriage path so that, as container housing wall 17A
moves into a position opposite the assembly 30, the light from
light source 34 is directed toward light directing element 21, and
light from light source 36 is directed toward light directing
element 22 Photosensor 38 is positioned to detect light directed
from either element 21 or element 22 in the manner described in
further detail below.
[0051] FIG. 2 includes a cross-sectional view of the printhead
cartridge 10 along the line 2-2 of FIG. 1 and shows the housing 17
and the printhead 18 attached to the container. The printhead 18 is
fluidly but detachably connected to the container 16. The housing
17 is made of a lightweight but durable plastic, which in a
preferred embodiment, is polypropylene. Housing 17 has an air inlet
32 and an ink outlet 34 formed within wall 17B. The air inlet 32
provides for the transfer of air between the interior of housing 17
and the ambient. Ink outlet 34 provides for fluid transfer of ink
contained in the ink container 16 from the interior of the housing
17 to the ink jet printhead 18. Manifold 37 directs filtered ink
from the ink outlet 34 into printhead 18 and to the ink ejecting
orifices for ejecting ink onto the recording medium 24.
[0052] Housing 17 defines an interior space partitioned into a
first chamber 40 and a second chamber 42 by a dividing member 44.
The dividing member 44 extends from one side wall of the housing 17
to an opposite side wall of the housing and essentially divides the
housing into the first chamber 40 and the second chamber 42 such
that the second chamber 42 is larger than the first chamber 40.
[0053] The first chamber 40 contains an ink retaining member 46
typically made of a foam material to hold liquid ink. Liquid ink
48, stored in the second chamber 42, is transferred from the second
chamber 42, which is substantially free of ink retaining material,
to the ink retaining material 46 through an ink inlet 41 defined by
the dividing member 44. A fill port 49 allows for filling the
cartridge with ink.
[0054] The ink 48 passes into the ink retaining material 46 through
the ink inlet 41 and ink is released through ink outlet 34 as
necessary to supply the printhead 18 with ink for printing. To
maintain a proper amount of ink in the ink retaining material 46
for supply to the printhead 18, the housing 17 includes a mechanism
for transferring ink from the second chamber 42 to the first
chamber 40 by maintaining a proper amount of air pressure above the
liquid ink 48 for filling the material 46 with ink when necessary.
This mechanism includes a directing member 60, which defines, with
the dividing member 44, an air transfer passageway 62 having a vent
inlet 64 coupled to a vent outlet 66 for pressurizing the second
chamber 42 to a static (no flow) condition. The directing member 60
does not extend from one sidewall to an opposite sidewall as does
the dividing member 44, but instead forms a vent tube.
[0055] The construction of the container 16 compartments as
described to this point is exemplary. There are other known ways of
constructing an ink supply container with dividing sections while
maintaining an appropriate back pressure to the printhead nozzle.
See for example, the container described in U.S. Pat. No. 5,138,332
and in co-pending application Ser. No. ______ (D/94372), both of
which are incorporated by reference. For purposes of the present
invention, it is understood that the container is constructed so
that, during operation, ink moves from chamber 42 to chamber 40
through the passageway between the two compartments under pressure
conditions established by techniques well known to those skilled in
the art. Of interest to the present invention is the modification
made to the ink container 16 by introducing the prism member 21 and
roof mirror 22 to the wall 17A defining the rear of chamber 42.
[0056] Referring particularly to FIG. 2, in a preferred embodiment,
light directing element 21 is a reflector integrally formed in the
bottom half of wall 17A and made of the same light transmissive
material as the wall; e.g. polypropylene, in a preferred
embodiment. Polypropylene, or other hydrophilic materials are
preferred. The prism is constructed with facet surfaces 21A, 21B
extending into the interior of compartment 48 and angled toward
each other at an approximately 82.degree. angle. The prism has a
truncated pyramidal shape with surfaces 21A, 21B connected by facet
surface 21C. The prism may be constructed of multiple narrow facet
sections to avoid sink commonly encountered when injection molding
large sections and also to provide enhanced light pipings.
[0057] Light directing element 22 is also formed as part of wall
17A. In the preferred embodiment, element 22 is a prism having two
facet surfaces 22A, 22B extending into the interior of compartment
48 and angled towards each other and connected by surface 22C.
Element 22 is formed into a roof mirror by placing reflective
films, foils or tapes 22D, 22E on surfaces 22A, 22B,
respectively.
[0058] It will be appreciated from the above that only a portion of
wall 17A need be transmissive; e.g., the portion accommodating
reflective element 21. Further, while the preferred embodiment has
the reflective elements constructed integrally with the housing
wall, the elements could be separately positioned adjacent the
interior surface of wall 17A.
Operation of Sensing System
[0059] The sensing system of the present invention, which is
considered to comprise the combination of reflective elements 21,
22 and the optical assembly 30, is designed to be enabled to
perform an ink container presence and a low ink level check
following a specific events such as the start of a print job or
after the printing of a certain amount of prints. To perform the
checks, the printer follows an algorithm that requires the ink
container to be positioned adjacent assembly 30 and then sequenced
through a series of detection steps. FIG. 3 is one embodiment of an
algorithm that can be used. FIG. 4 shows control circuitry for
implementing the ink container and ink level sensing system. A main
controller 50 conventionally includes a CPU, a ROM for storing
complete programs and a RAM. Controller 50 controls the movement of
carriage 12 as well as other printer functions described below.
[0060] When a line recording operation is performed, each resistor
associated with a jet in printhead 18 is driven selectively in
accordance with image data from a personal computer P/C 52 or other
data source sent into controller 50. Controller 50 sends drive
signals to the printhead heater resistors causing ink droplets to
be ejected from the jets associated with the heated resistor thus
forming a line of recording on the surface of the recording medium
24. With continued operation of the printhead, ink contained in
chamber 42 of container 16 gradually becomes depleted until a level
is reached which has been predetermined to constitute a low ink
level.
[0061] For purposes of description, the sensing system will be
considered as being activated, first at the beginning of a print
job, and at a later time following a preset period of printer
operation.
Operation at Start of Print Job
[0062] Referring to FIGS. 1-4, image signals from the P/C 52 to
controller 50 initiate a start print sequence. Carriage 12 is moved
to sensing station 41 so as to position housing wall 17A of
container 16 adjacent and facing the optical assembly 30. Under
control of controller 50, a power source 56 first energizes light
source 36. Source 36, in a preferred embodiment, is an LED with a
peak wavelength in the range of 880 to 940 nm. A beam of light is
directed towards housing wall 17A and, if a container is present,
light is reflected from reflective surfaces 22D, 22E of roof mirror
22 and redirected so as to impinge on photosensor 38. The two
reflections allow the beam to be stepped vertically downward to
avoid a higher than acceptable angle of incidence at the detector.
The output signal from photosensor 38 is sent to logic circuitry
within controller 50 which determines that the signal is within a
preset range. The controller then sequences to power the second
light source 34.
[0063] If a container 16 is not present, the light output of source
36 will not be reflected back to photosensor 38. The lack of output
from the photosensor will be recognized in the computer as a
"container missing" status. The printer will be disabled, and a
warning display will be activated at P/C Display 55 informing the
user that a) printing of the color associated with the missing tank
will be prevented and b) the correct container should be installed
to prevent potential damage to the printhead.
[0064] In a preferred embodiment, light source 34 is also an LED
with characteristics similar to source 36. Source 34 emits a beam
of light which is transmitted through wall 17A and is incident on
facet 21A of prism 21. FIG. 5A is a cross section of prism 21 and a
schematic reproduction of the assembly 30 showing the path of the
light beam when the prism is still immersed in ink and, hence, the
level of ink exceeds a preset low level.
[0065] The low ink detection is enabled by application of the
principle of total internal reflection. Total internal reflection
occurs when a ray, passing from a higher to a lower index of
refraction (from N to N'), has an angle of incidence whose sine
equals or exceeds N'/N. The critical angle I.sub.c is expressed by
the equation:
I.sub.c=arc sin N'/N (1)
[0066] As shown in FIG. 5A, the output beam of LED 34 passes
through wall 17A which, being polypropylene and with an index of
refraction of approximately 1.492, is almost completely transparent
to the light, allowing approximately 96% of the light incident
thereon to pass through and be incident on facet surface 21A at an
angle of incidence of about 45.degree.. Since the back side of
surface 21A is immersed in ink with an index of refraction of about
1.33, and the critical angle is not reached, approximately 99% of
the incident light will be transmitted into the ink and at an angle
of refraction of about 51.4.degree. and only approximately <1%
will be reflected to facet 21B. Since the interior facing side of
facet 21B is also immersed in ink, >99% of the 1% will also be
transmitted into the ink. Only a very small amount (approximately
0.01%) of the original incident energy will be reflected towards
the photosensor 38. The output signal from the photosensor at
controller 50 will register a low light level falling outside a low
ink level preset range set in controller memory. The controller
will compare this signal to a previous status signal to determine
whether a container, previously identified as being in a low ink
situation, has been replaced or refilled. A status log is then set,
or reset, to a "not empty" level, and the printhead drive circuit
61 in controller 50 is enabled to send drive signals to the
printhead to initiate a print sequence. The low ink level threshold
for this embodiment has been set at 20% of the container 16 fill
level.
[0067] To summarize the operation of the sensing system thus far,
the presence of an ink container is confirmed. Further, it has been
confirmed that the ink within the container is above preset levels,
and therefore, a print job can be started. The ink level sensing
system operation will now be described at a second time set to
occur following some predetermined operational time.
Operation During Printing Job
[0068] As printer 8 begins to print a print job corresponding to
image input signals from P/C 52, ink is drawn from the foam in
compartment 40 (FIG. 2) thereby reducing the saturation of the
foam. A flow path is created that allows ink from compartment 42 to
replenish the foam. Thus, the level of ink in compartment 42
gradually falls during usage of the printer. A low ink check can be
initiated at the end of each print job or after some predetermined
number of pixels, e.g., 7.times.10.sup.6 pixels printed for any one
color since the last check For purposes of illustration, it will be
assumed that a print job has been concluded drawing down the ink
level in compartment 42 to a point below a predetermined trip point
level represented by dotted line 80. A low ink level sensing
procedure is initiated at this point.
[0069] Continued printing is interrupted and, as previously
described, carriage 12 is moved to a position so that the housing
wall 17A and prism 21 is opposite the sensing assembly 30. The
controller again sequences through energization of light sources
34, 36 (the container detection may be omitted). FIG. 5B shows the
effect of the low ink level on the light beam. Light from source 34
passes through wall 17A and is incident on facet 21A at about
45.degree.. Since the ink level has dropped below the 20% fill
level, ink is no longer in contact with the back surface of facet
21A which is now exposed to air with an index of refraction of 1.0.
The critical angle of 42.9.degree. is exceeded by the incident
light on the facet; therefore, none of the incident light is
transmitted through the surface. The rays are totally reflected
back into the denser media resulting in total internal reflection
(TIR) of the beam. All of the incident energy is reflected towards
facet 21B. Since the back of that facet is also exposed in air, all
of the energy is now directed back towards photosensor 38. About
92% of the incident energy (minus any absorption) is returned to
impinge on photosensor 38. The output signal from the photosensor
is recognized by controller logic as being within a preset low ink
level range. The controller performs a status check to see if the
change from a previous station status is from "not empty" to
"empty". Since this is the case for the instant example, the status
log memory in controller 50 is set to "empty" status and a low ink
level signal is generated and displayed at P/C display 55. The low
ink signal can be used, depending on the system requirements, to
merely display a low ink level to an operator, to halt print
operation until a cartridge refill or replacement is performed or,
in the preferred embodiment, to allow operation to continue but
with a modified "low ink" status. As shown in FIGS. 3 and 4, the
controller sends a signal to P/C 52 which displays an appropriate
warning defining the ink container that has just been checked is
low on ink. Each ink container contains a remaining quantity of ink
which can be correlated into a number of pixels (or drops)
remaining. This number may be different for each ink color. The low
ink signal generated in the controller logic enables counter 60 to
begin counting the number of pixels (drops) ejected from the
printhead jets and the drawing down of ink within the ink tank.
When the pre-established number of pixels have been counted, the
ink tank is defined as out of ink, and printing is automatically
disabled. The termination occurs before the tank is completely
exhausted (level of about 2-5%) in order to insure that the
printhead and its ink channel lines are not emptied, a condition
which would jeopardize the reliability of the printhead. During the
time between the first detection of low ink and declaration of out
of ink, increasingly urgent messages may be displayed at the P/C
display. It is understood that the pixel value of the remaining ink
is dependent upon the frequency of the low ink checks.
[0070] The above scenario posited a condition wherein prism 21 was
either completely immersed in ink or completely free of ink. In
between these two cases is a transition represented by a
monotonically increasing light level to the signal from LED 34 as
the ink level gradually exposes more and more of facet 21A to air.
FIG. 6 shows a plot of ink, in milliliters (ml), delivered to the
printhead against sensor output in volts. For the first 70% of ink
delivered, the sensor current is low, and the voltage output across
a comparison circuit in controller 50 is high. Between 70 and 75%
depletion, a rapid transition occurs as the LED 34 output beam
begins to be totally internally reflected from facets 21A and 21B
of prism 21 thus increasing the output current from sensor 38 and
causing a rapid voltage drop in the circuit.
[0071] The invention may be used in other types of ink jet printing
systems including full color printers. FIG. 7 shows a full color
scanning type of printer. Referring to FIG. 7, a thermal ink jet
printer 70 is shown. Several ink supply cartridges 72, 73, 74, 75,
each with an integrally attached thermal printhead 76 to 79, are
mounted on a translatable carriage 77. During the printing mode,
the carriage 77 reciprocates back and forth on guide rails 78 in
the direction of arrow 81. A recording medium 80, such as, for
example, paper, is held stationary while the carriage is moving in
one direction and, prior to the carriage moving in a reverse
direction, the recording medium is stepped a distance equal to the
height of the stripe of data printed on the recording medium by the
thermal printheads. Each printhead has a linear array of nozzles
which are aligned in a direction perpendicular to the reciprocating
direction of the carriage. The thermal printheads propel the ink
droplets 82 toward the recording medium whenever droplets are
required, during the traverse of the carriage, to print
information. The signal-carrying ribbon cables attached to
terminals of the printheads have been omitted for clarity. The
printer 70 can print in multiple colors, wherein each cartridge 72
to 75 contains a different color ink supply. For a representative
color printer and additional control details, see for example, U.S.
Pat. No. 4,833,491, the disclosure of which is incorporated herein
by reference.
[0072] According to the invention, each of the ink containers
forming part of cartridges 72-75 are of the same construction as
the cartridge shown in FIG. 2, and for the purposes of the
invention, each cartridge has an ink container having two prism
reflectors formed in the wall facing outward. One reflector is
associated with cartridge presence detection and the other with low
ink detection. Cartridge 72 is shown having an ink container 80
with reflective members 82, 84. Cartridges 73-75 have similar
containers and reflective members not specifically called out for
ease of description. As in the single cartridge embodiment, a
sensing assembly 90 includes a housing 92 within which are mounted
a first light source 94 and a second light source 96 and a
photosensor 98 located between the two light sources.
[0073] In operation and referring to FIGS. 4, 7 and 8, image
signals from P/C 52 to controller 50 initiate a start print
sequence. Carriage 77 is moved so as to position the cartridge 72
with first ink container 80 opposite the sensing assembly 90. Under
control of controller 50, power source 54 is caused to sequentially
energize light sources 94, 96 while measuring the output of
photosensor 98. The sequencing and detection operation for
cartridge 72 is the same as that previously described for cartridge
10. Source 96 is first energized to check that the cartridge is
present (reflections from roof mirror 84 to the photosensor is
within range), source 94 is turned on, and the ink level in the
container system is determined after making comparisons with the
previous status. (Reflections from prism 82 front surface are
sensed by photosensor 98). Once cartridge 72 is serviced, carriage
77 is moved to position the next cartridge 73 in position to be
sensed. The preceding process is enabled for each cartridge until
all cartridges have been confirmed as being in place and all ink
levels in the assembly ink containers are either within the
acceptable levels or appropriate low ink level warnings have been
displayed at the P/C.
[0074] While the embodiment disclosed herein is preferred, it will
be appreciated from this teaching that various alternative
modifications, variations or improvements therein may be made by
those skilled in the art. For example, the detection of the
presence or absence of the ink container can be accomplished by
using other light directing elements. One example is a light pipe
shown in FIG. 9. FIG. 9 shows a portion of a container 16' with an
optical element 22' positioned on the outside of the housing wall
17A'. Element 22' is a light pipe curved so as to redirect light
entering end 22'A and exiting end 22'B onto photosensor 38'.
Optical element 22' may alternately be an optical fiber. With
either embodiment, the same function is performed as reflective
element 22 in FIG. 2. If the container is present, a high current
is generated in photosensor 38'.
[0075] The light transmission embodiments may be preferred for some
systems since the reflective foil or tape used to form the roof
mirror 22 for the FIG. 2 embodiment may not adhere well to the
prism facet surfaces.
[0076] And while the optical assembly 30 of the FIG. 1 embodiment
is believed optimum, other arrangements of the light sources and
photosensors of the assembly are possible consistent with the
invention. One example is shown in FIG. 10 which uses one light
source and two photosensors. As shown, an optical assembly 100
which includes a first and second photosensor 102, 104 and whose
output is read by the controller. An LED light source 106 is
connected to a power source. The operation for detecting the
container is the same as the preceding description. The light level
will be sensed at photosensor 104 with an appropriate signal sent
to the controller. Correspondingly, the low ink reading is made at
sensor 102. In this embodiment, the LED may be either operated
continuously or intermittently (pulsed).
[0077] Another less efficient arrangement is possible (not shown)
where a light source and sensor are associated with each reflective
element 21, 22 in FIGS. 1 and 2.
[0078] As another example, while the FIG. 1 and FIG. 7 embodiments
show the ink container mounted on a scanning carriage which is
periodically moved to a detection station, the ink containers may
be positioned in a fixed location and connected to the scanning
printhead via a flexible ink supply line. For the FIG. 1
embodiment, container 16 would be fixed in position opposite
optical assembly 30 and connected to printhead 18 via a flexible
tube. For the FIG. 7 embodiment, four optical assemblies would be
located outside the print zone opposite from an associated ink
container, each of the ink containers connected to the respective
printhead cartridge via flexible ink couplings. For the case of a
full width array printhead of the type disclosed, for example, in
U.S. Pat. No. 5,221,397, a remote ink container is connected to an
ink manifold which connects ink with the plurality of input modules
which are butted together to form the full width array. One or more
optical assemblies would be located opposite the modified ink
container.
* * * * *