Method and apparatus for detecting ink level

The present disclosure relates to an inkjet printing system for depositing ink on media. The inkjet printing system includes an ink containment vessel formed from a material having optical characteristics selected to block light in the visible light spectrum. Also included is an energy source for providing energy having characteristics that are selected to allow energy passage through the ink containment vessel. Finally, an energy detector is included for detecting energy provided by the energy source that passes through the ink containment vessel. Energy from the energy source impinging upon ink is altered so that an energy detector output signal is indicative of ink within of the ink containment vessel.

BACKGROUND OF THE INVENTION
 The present invention is related to inkjet printing devices. More
 particularly, the present invention is related to inkjet printing devices
 that make use of an optical technique for determining ink level in an ink
 container.
 Inkjet printers frequently make use of an inkjet printhead mounted within a
 carriage that is moved back and forth across print media, such as paper.
 As the printhead is moved across the print media, a control system
 activates the printhead to deposit or eject ink droplets onto the print
 media to form images and text. Ink is provided to the printhead by a
 supply of ink that is either carried by the carriage or mounted to the
 printing system not to move with the carriage. For the case where the ink
 supply is not carried with the carriage, the ink supply can be in fluid
 communication with the printhead to replenish the printhead or the
 printhead can be intermittently connected with the ink supply by
 positioning the printhead proximate to the filling station whereupon the
 printhead is replenished with ink from the refilling station.
 For the case where the ink supply is carried with the carriage, the ink
 supply may be integral with the printhead where upon the entire printhead
 and ink supply is replaced when ink is exhausted. Alternatively, the ink
 supply can be carried with the carriage and be separately replaceable from
 the printhead or drop ejection portion.
 Regardless of where the supply of ink is located within the printing system
 it is critical that the printhead be prevented from operating when the
 supply of ink is exhausted. Operation of the printhead once the supply of
 ink is exhausted results in poor print quality, printhead reliability
 problems, and if operated for sufficiently long time without a supply of
 ink can cause catastrophic failure of the printhead. This catastrophic
 failure results in permanent damage to the printhead. Therefore, it is
 important that the printing system be capable of reliably identifying a
 condition where the ink supply is nearly exhausted or exhausted. This
 technique should be accurate, reliable, and relatively low cost thereby
 tending to reduce the cost of the printing system.
 SUMMARY OF THE INVENTION
 The present invention is an inkjet printing system for depositing ink on
 media. The inkjet printing system includes an ink containment vessel
 formed of a material having optical characteristics selected to block
 light in the visible light spectrum. Also included is an energy source for
 providing, energy having characteristics that are selected to allow energy
 passage through the ink containment vessel. Finally, an energy detector is
 included for detecting energy provided by the energy source that passes
 through the ink containment vessel. Energy from the energy source
 impinging upon ink is altered so that an energy detector output signal is
 indicative of ink within the ink containment vessel.
 Another aspect of the present invention is an inkjet printing system that
 includes an ink containment vessel for containing ink. The ink containment
 vessel has characteristic properties that vary with ink level within the
 ink containment vessel. An energy source is included for providing energy
 having an energy characteristic related to the energy source. Energy
 provided by the energy source impinges on the ink containment vessel. Also
 provided is an energy detector for detecting energy provided by the energy
 source. The energy detector is configured to discriminate against ambient
 energy not having the energy characteristic. The energy detector provides
 an energy detector output signal indicative of ink level within the ink
 containment vessel.
 In one preferred embodiment, the energy source is an optical light source
 and a modulator for providing temporal modulation of light energy provided
 by the optical light source. In this preferred embodiment the energy
 detector is a bandpass filter that is tuned to a frequency associated with
 the energy characteristic. Also included in the energy detector is an
 optical detector for detecting light energy passed by the bandpass filter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 FIG. 1 depicts an inkjet printing system 12 that includes a printhead
 portion 14 for selectively depositing ink on print media (not shown) under
 the control of controller 16. Ink is provided to the printhead 14 by ink
 container 18. The ink container 18 includes a fluid outlet 20 for
 providing ink to the printhead 14 thereby replenishing the printhead 14
 with ink. An ink level sense apparatus determines ink level in the ink
 container 18 and provides ink level information to the controller 16.
 The controller 16 is capable of preventing further operation of the
 printhead 14 once the ink container is depleted of ink. In addition, the
 controller 16 provides ink level information to the customer so that a
 replacement ink container 18 is on hand to avoid interruption in printing.
 In the case where the printhead 14 is a thermal inkjet printhead, it is
 critical that the printhead 14 be prevented from operation without an
 adequate supply of ink. Operation of the thermal inkjet printhead 14
 without an adequate supply of ink can result in reliability problems as
 well as a reduction in print quality. If operated for a sufficient period
 of time without an adequate supply of ink the printhead 14 can result in
 catastrophic failure and permanent printhead damage. It is critical that a
 low ink or out-of-ink condition for the ink container 18 is detected and
 that this information be provided to the controller 16 to prevent
 operation of the printhead 14 to ensure that permanent damage to the
 printhead 14 does not occur.
 The ink level sense apparatus 22 of the present invention provides a
 reliable and cost efficient method for determining ink level information
 in the ink container 18 for preventing damage to the printhead 14 as well
 as providing notification that the ink container 18 is soon in need of
 replacement.
 Although the ink container 18 is shown as a replaceable ink container that
 mounts directly to the printhead 14, other configurations can also be used
 in conjunction with the ink level sense apparatus 22 of the present
 invention. For example, the ink container 18 can be integrally formed with
 the printhead 14 in which case the entire assembly is replaced when the
 ink is depleted. For this example, the ink level sense apparatus 22 is
 used to determine ink level information in the entire assembly. Another
 example, just to name a few, is where the ink container 18 is mounted off
 of the scanning carriage. Fluid conduits are provided for fluidically
 connecting the printhead 14 mounted in the scanning carriage with the ink
 container 18. In this configuration, the ink level sense apparatus 22
 monitors ink level information in the ink container 18 in this off
 carriage location. An additional ink level sense apparatus can be used to
 monitor ink level in the printhead portion 14, for additional accuracy.
 FIGS. 2 and 3 depict one preferred embodiment of the ink level sense
 apparatus 22 of the present invention for determining ink level
 information in the ink container 18. An ink level 24 represents ink level
 in the ink container 18. The ink container 18 in FIG. 2 is shown partially
 filled with ink and the ink container 18 in FIG. 3 is shown substantially
 depleted of ink.
 The ink level sense apparatus 22 of the present invention includes an
 energy source 26 and an energy detector 28. The energy source 26 provides
 energy having characteristics that are selected so that emitted energy
 passes through the ink containment vessel 18 as represented as energy beam
 30. The ink container 18 is conversely formed from a material that allows
 energy provided by the energy source 26 to pass through the ink container
 18. Energy passing through the ink container 18, represented by beam 30,
 is attenuated by ink within the ink container 18. As a result of this
 attenuation energy received by the detector 28 is either absent or greatly
 attenuated. The detector 28 provides an output signal to the controller 16
 that is indicative of ink level within the ink container 18.
 As shown in FIG. 3, once the ink level 24 falls below a threshold level the
 energy beam 30 is allowed to pass from the energy source 26 to the
 detector 28 without impinging ink. In this case the detector 28 receives
 an energy signal of higher intensity that the energy signal received when
 ink is present to attenuate the signal. The detector output signal is
 indicative of energy intensity and therefore indicative of whether ink is
 present at a given ink level in the ink container 18. A plurality of
 energy beams 30 can be provided at a plurality of different levels on the
 ink container 18 tor providing ink level information at a plurality of ink
 levels, if desired.
 In the preferred embodiment, the ink container 18 is formed from a material
 having optical characteristics that are selected to block light or greatly
 attenuate light in the visible light spectrum. However, the ink container
 material is substantially transmissive to light from the energy source 26.
 Therefore, the ink container 18 allows the ink level sense apparatus 22 to
 sense ink level in the ink container 18 while preventing visible light to
 pass through the ink container. Preventing visible light to pass through
 the ink container 18 allows the ink container 18 to more esthetically
 pleasing. The ink container 18 frequently contains various apparatus such
 as foam or some form of regulator for ensuring proper back pressure within
 the printhead 14. As ink is consumed, these pressure regulation devices
 become visible which is not only unsightly but also can be confusing to
 the customer. The use of an ink container that does not pass visible light
 obscures various devices such as back pressure regulating devices from the
 customer. In addition, the use of ink container materials that greatly
 attenuate visible light allows the ink container to be color coded for
 various purposes. One example of the use of color-coding is to identify
 various parts according to maintenance requirements such as designating
 customer replaceable parts with a certain color. It is then readily
 apparent to the customer which things they should replace and which things
 they should not replace when maintenance is required.
 Another example of a use of colored ink containers that substantially block
 visible light is for color coding the ink containers to aid in
 installation of the proper ink container in the proper location in the
 printing system 12. In the case of ink containers that are transparent to
 visible light it is difficult to determine ink color from visual
 inspection because the inks tend to be opaque to visible light. The use of
 ink containers 18 that arc colored using some color coding scheme can aid
 in the installation of the ink container 18 in the proper location to
 ensure ink compatibility.
 In a preferred embodiment the energy source 26 is an infrared light source.
 In this preferred embodiment the ink container 18 is formed from a plastic
 material that is transparent to infrared light. A colorant is added to the
 plastic that blocks or greatly attenuates visible light, but at the same
 time is substantially transparent to infrared light. The ink containment
 vessel 18 allows infrared light to pass through for sensing ink level
 while at the same time allowing the ink container 18 to be colored to
 prevent the passage of visible light.
 Infrared light provided by the energy source 26 is greatly attenuated or
 blocked by ink within the ink container 18. As the ink level 24 falls
 below the energy beam 30 as shown in FIG. 3, infrared light is allowed to
 pass completely through the ink container 18 from the energy source 26 to
 the detector 28. In a preferred embodiment, one or more lenses 32 and 34
 may be used to collimate or gather light. The lens 32 gathers light energy
 emitted from the energy source 26 and focuses this energy at a location on
 the ink container 18. The lens 34 gathers light energy that tends to
 disperse while passing through the ink container 18 and ink. The lens 34
 focuses this gathered light and directs this light to the detector 28. In
 one preferred embodiment, the energy source 26 and lens 32 are integrated
 together as a light emitting diode (LED). Alternatively, lens 32 and 34
 can be formed integrally with the ink container 18.
 In yet another preferred embodiment, the ink level sense apparatus 22
 includes a modulator 36 and a filter 38. In this preferred embodiment, the
 modulator 36 modulates energy provided by the energy source 26. In this
 preferred embodiment the modulator 36 provides a characteristic to the
 energy that is emitted by the energy source 26. In one preferred
 embodiment, the modulator 36 modulates the energy source 26 in a temporal
 fashion. The use of temporal modulation or pulse modulation of the energy
 source 26 is to add a characteristic to the energy that does not effect
 the transmission of energy through the ink container 18. The energy
 entering the ink container 18 is at a wavelength or frequency that is
 passed by the ink container. However, the energy is provided in periodic
 pulses that have a characteristic pulsing frequency. It is this
 characteristic pulsing frequency that is selectively passed by the filter
 that allows the ink level sense apparatus 22 of the present invention to
 discriminate against ambient energy.
 The filter 38 is preferably a bandpass filter that is tuned to the
 modulation or pulse frequency of the modulator 36. The filter 38 tends to
 discriminate or exclude energy such as ambient energy having
 characteristic frequencies different from the characteristic frequency of
 the energy provided by the modulator 36. Therefore, the energy that is
 passed to the detector 28 is substantially that energy that is produced by
 the energy source 26. In this manner, the ambient energy such as that from
 fluorescent lights, as one example, can be discriminated against to
 provide a greater signal to noise ratio at the detector 28. This improved
 signal to noise ratio tends to produce a more accurate and reliable ink
 level sense apparatus 22.
 FIGS. 4 and 5 show an alternative embodiment to the embodiment shown in
 FIGS. 2 and 3. Similar numbering is used in this alternative embodiment to
 represent similarly functioning elements. The embodiment shown in FIG. 4
 represents the ink level sense apparatus 22 of the present invention for
 sensing fluid level in an ink container 18 that is partially filled with
 ink that is represented by ink level 24. FIG. 5 depicts the ink level
 sense apparatus 22 of FIG. 4 with the ink level 24 shown below a threshold
 level in ink container 18.
 The ink level sense apparatus 22 is similar to the ink level sense
 apparatus 22 shown in FIGS. 2 and 3. However, instead of providing energy
 from the energy source 26 which passes entirely through the ink container
 18 to an energy detector 28 disposed adjacent the ink container 18
 opposite the energy source 26, both the energy source 26 and the energy
 detector 28 are disposed on the same side of the ink container 18. The ink
 level sense apparatus 22 shown in FIGS. 4 and 5 makes use of changes in
 reflected light resulting from a change in index of refraction within the
 ink container 18 as ink level 24 falls below a threshold level.
 The energy source 26 produces a beam of energy represented by energy beam
 30 that is incident on the ink container 18. The ink container 18 is
 selected from a material that is transmissive to the energy produced by
 the energy source 26. The ink container 18 is formed from a material that
 has a characteristic index of refraction. In addition, ink within the ink
 container 18 also has a characteristic index of refraction. The index of
 refraction for the ink container 18 is selected to be similar to the index
 of refraction associated with the ink within ink container 18. At an
 interface between the ink container 18 and the ink within the ink
 container 18 the energy beam 30 tends to continue on into the ink
 container instead of reflecting energy back towards the energy detector
 28.
 However, in the case where the ink level has fallen below a threshold level
 as shown in FIG. 5, the incident energy represented by beam 30 at the
 interface encounters air instead of ink. Air within the ink container 18
 has a characteristic index of refraction that is very different from
 either ink or the ink container material. Because the incident energy
 represented by energy beam 30 encounters a very different index of
 refraction at the interface energy tends to be reflected from this
 interface as represented by beam 40 toward the energy detector 28.
 Therefore, ink level can be determined by the energy detector 28 by
 sensing changes in energy intensity for reflected light from a condition
 where ink is encountered at the interface, as represented by FIG. 4, and
 for a condition where ink is not encountered at the interface, as
 represented by FIG. 5. The energy detector 28 provides an output signal to
 the controller 16 shown in FIG. 1 that is indicative of ink level within
 the ink container 18.
 In one preferred embodiment the ink container 18 is selected from a
 material that blocks or substantially attenuates transmission of visible
 light while substantially transmitting energy provided by the energy
 source 26. In this preferred embodiment the energy source 26 provides
 energy in the infrared spectrum that is selected to pass through the ink
 container 18 material with little or no attenuation.
 In another preferred embodiment the ink level sense apparatus 22 includes a
 modulator 36 and a filter 38 for improving the signal to noise ratio in a
 manner similar to the embodiment discussed previously with respect to
 FIGS. 2 and 3.
 In addition, in this preferred embodiment, the ink level sense apparatus
 includes a light collimator or collector 32 and 34. The light collector 32
 tends to collect light from the energy source 26 and focus this light
 toward the ink container 18. The light collector 34 tends to collect light
 reflected from the ink container 18 and focus this light to the energy
 detector 28.
 The embodiment shown in FIGS. 4 and 5 allows the ink level sense apparatus
 22 to be positioned on one side of the ink container 18. Positioning the
 ink level sense apparatus 22 on one side of the ink container 18 allows
 the technique of the present invention to be used in applications where a
 through beam is undesirable. One example is where the ink container 18 is
 a plurality of ink containers with each ink container associated with a
 particular color. In this case, certain orientations of the through beam
 would require the beam to go through each of the plurality of ink
 containers. The technique for sensing ink level of the present invention
 shown in FIGS. 4 and 5 allows positioning of the ink level sense apparatus
 22 on one side of the ink containers so that the energy beam need only
 enter the interface portion of the ink container instead of passing
 entirely through the ink container 18. This technique is well suited for
 groupings of ink containers. In addition, because the energy beam does not
 pass through the ink container 18 this technique is well suited to
 applications where back pressure devices such as foam or pressure
 regulators are contained within the ink container 18.
 Although, the present invention has been described with respect to
 determining ink level in an ink container, the present invention is also
 suitable for determining fluid level in a wide variety of fluid
 containers. The present invention provides a relative low cost and highly
 reliable method of determining fluid level. In addition, the present
 invention allows the fluid container to be opaque or nearly opaque to
 visible light for applications where this is desirable.