Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrophotometer
Reexamination Certificate
2001-09-10
2003-10-28
Smith, Zandra V. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrophotometer
C356S402000
Reexamination Certificate
active
06639669
ABSTRACT:
Disclosed in the embodiments herein is an improved automatic self-diagnostics system for detecting operational anomalies and the like in the control system of an in situ color sensor. More specifically, particular diagnostics for a color spectrophotometer based system for color detection, calibration and/or correction which is highly suitable for incorporation into the color calibration or control system of various color printing systems or other on-line color control or color processing systems.
The diagnostics systems of the disclosed embodiments have different features or aspects. One is to insure correct interrogation of the operating characteristics of an in situ (on line) color sensor for sensing xerographically printed different color test patterns in a color printer. More specifically, to diagnostically provide assurance that the color sensor is reading the correct (intended) color test target patches and thus is operating to provide reliable color data collection. Especially, for measuring such color test targets on paper sheets moving at variable speeds.
More specifically, in one aspect of the diagnostics systems of the disclosed embodiments, in a diagnostics mode a series of diagnostic test patches are automatically generated, printed on test sheets and read by the spectrophotometer or colorimeter and its output signals are compared to acceptable signal levels, in order to assure that the spectrophotometer or colorimeter measurements represented thereby are correct. In particular, providing a series of test targets of different light absorption density for testing the sensed signal responses to the illumination of the different test targets to their illumination by the respective different LEDs or other light sources. That is, generating a series of solid area test patches of varying optical density, position, and/or colors, which are respectively illuminated and read by the light emitters and photodetectors of the spectrophotometer or calorimeter. Those readings are used to determine whether the device is operating correctly by comparing them to expected readings.
Another aspect of the disclosed diagnostics systems of the disclosed embodiments is to provide automatic confirmation testing for the density and readability of fiducial marks on the test sheets of multiple color test patches, which fiducial marks automatically control the reading of respective said color test patches by an associated spectrophotometer or calorimeter. That is, a periodic automatic diagnostics interrogation for malfunctions in a fiducial mark sensing system comprising xerographically produced fiducial marks and an optical fiducial mark sensor used to trigger the occurrence of a desired event, such as the arrival of a test pattern for measuring a color. This provides assurance that color measuring triggering system is robust enough for reliable color data collection.
In one embodiment thereof the spectrophotometer normally used for color patch color sensing is used in a diagnostics mode for testing the developability (printing) curve for the marking material of the color (usually black) used for the fiducial marks, by printing none, varying amounts, and normal amounts, of the fiducial marking material into what would normally be color test patch areas. That is, assuming the spectrophotometer tests normally, the spectrophotometer may be used, in effect, as a fiducial mark detector for the testing of the (separate) optical fiducial mark detector. As further disclosed in the embodiments, a diagnostic routine of having the fiducial mark detector and the spectrophotometer sensor(s), separately or at the same time, examine a series of automatically printed graded density test patches of the fiducial marking material, starting with the darkest, and counting them until they are no longer detectable, can indicate, inter alia, at which density level of the fiducial marking material on the test sheets the fiducial mark detector will fail to detect fiducial marks (fail to deliver control signals). This diagnostic test can also tell how close the fiducial mark detector is to failure to read normal density fiducial marks.
By way of background, the general concept of fiducial marks adjacent to, and identifying, respective test color patches, and optical fiducial mark detectors separate from (but electronically controlling) the spectrophotometer detector, are known (see the above-cited and other references). However, there are practical restraints, associated with the particular spectrophotometer, etc., on how many distinguishable test patches can be printed on a normal sheet size test sheet, that is, how small they can be and how closely they can be spaced. Also, if the spectrophotometer is fixed relative to a sheet path, and the test sheet is moving normally in one direction in that path, the area of the test sheet in which the test patches can be printed and still be “seen” by the spectrophotometer as the test sheet moves past the fixed position spectrophotometer may be further limited. Also, the movement velocity of the test sheet relative to the spectrophotometer may vary. Yet, more test patches per sheet means that fewer test sheets need be used, and thus is desirable. Furthermore, even the blackest toner may not print sufficiently black fiduciary marks on print media (the test sheets) to be reliably detected if the printer developablity level control is out of adjustment, the black toner supply is depleted, the fiducial mark optical sensor is contaminated with paper lint or toner, the sensor signal amplifiers drift, etc. Yet, accurately knowing which one of the many test patches on a test sheet the spectrophotometer is reading (i.e., which spectrophotometer output signals are for which test color or test gray shade) is vital, and a missed fiducial mark can confuse that. Using mere blank (unprinted white paper) spaces in between color patches read by the spectrophotometer itself as the fiducial indicators for counting reading discrete patches is known, but is not as reliable as separate dark fiducial marks read by a separate detector therefor.
Printing fiducial marks along side of, rather than in between, each color test patch is desirable, although not essential. It can enable closer spacing of the color test patches. Also, it can provide more mounting location lateral freedom or space for a separate fiducial mark optical sensor (detector) without interference with the spectrophotometer illuminator(s) and detector(s).
Further by way of background, there is an additional significant challenge in implementing a multiple (or plural) LED type of spectrophotometer color sensor in a reprographic machine paper path to read accurately in “real time.” That is, utilizing a type of spectrophotometer as shown in the example herein and as further exemplified and described in the above cross-referenced applications, in which each small test patch is sequentially illuminated by different LEDs of different illumination spectra, and the separate reflectances of those separate sequential illuminations of that same test patch are reliably detected, all while the test sheet bearing that and many other such test patches to be read is on normal print media rapidly passing by the spectrophotometer sensing zone in “real time.” As noted above, this “real time” reading accuracy is facilitated by using separate black fiducial or timing marks associated with each test patch, and a separate reflective sensor for those fiducial marks, which may be attached to the side of the multiple LED spectrophotometer. That fiducial mark sensor can be a simple commercially available optical sensor, such as from Vactec 130E01721, which, for example, can change its output signal state from low to high (e.g., ~0.2V to 4.8V) when a black mark imprinted alongside a test patch passes within the illumination/sensing area of that fiducial mark sensor. That control signal can then control the operation of the spectrophotometer LEDs to read the test patches synchronous with the arrival and passage of the desired test patch in the sensing area of the
Diehl Dennis M.
Grace Robert E.
Hubble, III Fred F.
Jackson Eric
Love Tonya L.
Smith Zandra V.
Stock Gordon J
Xerox Corporation
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