Measuring and testing – Liquid level or depth gauge – With illumination
Reexamination Certificate
2000-03-23
2001-09-25
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
With illumination
C073S29000R, C347S007000, C250S227110
Reexamination Certificate
active
06293143
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to ink level sensing apparatus and to methods for detecting low ink levels in ink jet printers.
BACKGROUND
Ink jet printers provide a high degree of versatility with respect to print media and methods for printing multi-color images on print media. These advantages are due in part to the ability to design and provide relatively small printheads having multiple orifices which are in flow communication with an ink supply source or cartridge. In order to improve the quality and speed of ink jet printers, modifications to the printheads, including the use of smaller ink ejection orifices on permanent or semi-permanent printheads continues to evolve. Such printheads are often connected in flow communication with a replaceable ink jet cartridge.
Ink jet cartridges have widely varying design and may contain a capillary member or foam member for retaining ink and maintaining a predetermined back pressure on the ink so that the ink does not flow from the printhead onto the print media except when the ejectors on the printhead are activated. Other ink jet cartridges may contain a bellows or piston-like structure for maintaining ink back pressure in the cartridge. In such ink cartridges, the ink typically occupies a chamber within the cartridge.
Regardless of the means chosen for storing ink in an ink jet cartridge, if the cartridge is devoid of ink, misprinted pages may occur at an inopportune timer. In the worst case scenario, the printhead may be damaged by overheating in the absence of ink or by drying of ink in the passageways to the printheads.
U.S. Pat. No. 5,743,135 to Sayka et al. relates to a liquid level monitor which uses a tube to confine a float to a vertical path. The float is said to be a water filled stainless steel ball or cylinder which is detectable by a optical fiber which is connected to a photodetector. A light source such as a light emitting diode (LED) illuminates the float to provide transmittance or reflectance of light through the optical fiber to the photodetector. It is said that the float may have a fluorescent coating which can induce a frequency shift in reflected light to the source light to enhance detection where stray reflections are a problem.
Other methods for detection of ink levels include the use of prism inserts and an ink supply cartridge having a tank body optical ink level detection section to refract light at an angle with respect to the incident light when ink is present in the light path. Electrodes have also been used to detect the present or absence of ink in an ink container. An estimation of the ink remaining in an ink container may also be made by counting ink drops expelled from the printhead.
Methods for level detection have been proposed for various applications, such as reflecting light off the top surface of a liquid or off a bubble in the liquid. When the liquid is in a turbulent state, the light is said to be reflected from the top surface of the ink erratically. See U.S. Pat. No. 5,596,351 to Stapleton.
Of the foregoing methods, mechanical means for detection of ink level may be less reliable due to interference of a float in a vertical path for containing a float. Electrical means and optical means using prisms or ink tank inserts or special configurations are relatively expensive to implement and require a predetermined location for level detection with respect to an ink tank or cartridge which cannot be changed once the cartridge is manufactured.
There is a need for an ink level sensing device and apparatus which is less constrained with respect to the detection of ink level and which may be adaptable to a wide variety of ink cartridges without significantly changing the cartridge design.
SUMMARY OF THE INVENTION
With regard to the above and other objects and advantages thereof, the invention provides an ink level sensing apparatus including an ink cartridge having an ink chamber containing ink and having at least one substantially transparent side panel adjacent the ink chamber. A fluorescent material is disposed in the ink chamber, the fluorescent material being substantially insoluble in the ink and having a specific gravity which is sufficiently lower than the ink to provide an interface between the ink and the fluorescent material. A relatively narrow band light source for emitting light at a first wavelength along a light path through the substantially transparent side panel of the ink cartridge is provided to emit light sufficient to excite the fluorescent material. A photosensor is provided for receiving light emitted from the excited fluorescent material at a second wavelength when the fluorescent material crosses the light path, wherein the first and second wavelengths are substantially different.
In another aspect the invention provides a method for sensing a liquid ink level in an ink jet cartridge. An ink cartridge including a closed body having an interior chamber and at least one substantially transparent side panel is provided. The ink cartridge contains ink in the interior chamber and a fluorescent material which is substantially insoluble in the ink, the fluorescent material having a specific gravity which is sufficiently lower than the ink to provide an interface between the ink and the fluorescent material. The cartridge is attached to a cartridge body of an ink jet printer. A level sensing device containing light source and a photosensor is attached to the cartridge body adjacent the substantially transparent side panel of the ink jet cartridge. A light path is provided through the substantially transparent panel into the ink chamber of the ink cartridge by activating the light source which is sufficient to excite the fluorescent material. Fluorescent emissions having a wavelength substantially longer than the wavelength of the light source are detected by means of the photosensor when the excited fluorescent material crosses the light path.
Use of a fluorescent material which is substantially insoluble in the ink provides a means for sensing ink level without use of elaborate mechanical means which can get fouled and without the need for redesigning the ink cartridge to provide prismatic light paths. The method and apparatus of the invention is substantially more reliable than ink drop counting and can be adapted for use on a wide variety of ink cartridge designs making it a much more versatile method than methods requiring ink cartridge structures to refract or reflect light. The level sensor is also more readily adaptable to adjustment along the ink level height to provide warning of low levels of ink remaining for various ink jet printing applications.
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Denton Gary Allen
Routt, Jr. Wilson Morgan
Lambert, Esq. D. Brent
LaRose, Esq. David E.
Lexmark International Inc.
Loo Dennis
Williams Hezron
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