Optics: measuring and testing – By shade or color – With color transmitting filter
Reexamination Certificate
2002-12-04
2003-11-18
Phan, James (Department: 2872)
Optics: measuring and testing
By shade or color
With color transmitting filter
C356S402000, C356S425000, C356S319000, C356S320000, C356S419000, C358S504000, C358S518000, C250S226000
Reexamination Certificate
active
06650416
ABSTRACT:
Disclosed in the embodiments herein is an improved, low cost, color spectrophotometer which may be used for various color calibration or correction systems. It is highly suitable to be used for, or incorporated into, the color calibration or control of various color printing systems or other on-line color control or color processing systems, but is not limited thereto.
The specific embodiment disclosed herein comprises a low cost spectrophotometer for measuring the colors of an illuminated color test target area surface including at least one multi-photo-site photodetector chip and an associated imaging lens system having an optical axis at approximately 45 degrees to said illuminated color test target area surface through which lens system said multi-photo-site photodetector receives at least a portion of said illumination from said illuminated color test target area surface, wherein said multi-photo-site photodetector chip is a low cost commercial photodetector chip which is normally a component part of a document color imaging bar having at least three rows of small closely spaced photo-sites with respective different color filters to provide at least three different spectral responsive electrical output signals, and wherein said photodetector chip is mounted on said optical axis of said imaging lens system oriented substantially in the plane of said image of said reflected illumination of said illuminated color test target area surface through said lens system.
In particular, in this spectrophotometer embodiment, while the optical axis of said imaging lens system is oriented at 45 degrees to said illuminated color test target surface area, said photodetector chip is mounted perpendicular to said illuminated color test target surface area.
Also, the spectrophotometer embodiment disclosed herein provides displacement insensitivity from said illuminated color test target surface area by said imaging lens system having displacement insensitive optics. Said spectrophotometer also preferably provides angular insensitivity of said illuminated color test target surface area relative to said spectrophotometer.
That is, the disclosed spectrophotometer embodiment also provides improved accuracy for color test surfaces which may be tilted, curved, non-planer or otherwise varying in orientation relative to the spectrophotometer. That is particularly desirable for enhancement of the accuracy of a non-contact spectrophotometer which can measure the colors, or color densities of test surfaces spaced from the spectrophotometer, especially moving surfaces, such as printed paper sheets in the output path of a color printer, or toner or liquid ink test patches on a moving photoreceptor or other surface, or other moving color objects, webs or materials, without requiring the test surface material to be constrained against a reference surface or against the spectrophotometer.
Non-contact or spaced color measurement, with freedom of movement of color test material relative to a spectrophotometer, both transversely to and variably spaced from, the spectrophotometer, can be quite desirable in various color measurement applications, such as allowing printed sheets in a color printer to move freely and unobstructedly between relatively widely spaced apart paper path baffles or guides, yet be color analyzed by a spectrophotometer. However, that freedom of movement can allow the color test surface material or media to have variances in spacial and angular alignment relative to the spectrophotometer. The disclosed embodiment can desirably reduce measurement and output signal errors from such positional variances from a spectrophotometer even where the photodetector(s) of the spectrophotometer comprise a multi-photo-site detector.
As will be further described, the improved angular and azimuthal insensitivity of the embodiment herein is fully compatible with, and is shown herein combinable with, various of the spectrophotometer features of the above-cross-referenced copending commonly owned U.S. applications, including the displacement insensitivity system of the above cross-referenced copending commonly owned U.S. application Ser. No. 09/535,007, filed Mar. 23, 2000, by the same Fred F. Hubble, III and Joel A. Kubby; and the contemporaneously filed U.S. application, by said Fred F. Hubble, III, Tonya A. Love and Daniel A. Robins, Attorney Docket No. D/A1024, entitled “Angular, Azimuthal and Displacement Insensitive Spectrophotometer For Color Printer Color Control Systems.” Also the embodiment herein utilizes the multiple different photo-sites chip detectors of the above cross-referenced commonly owned and contemporaneously filed U.S. Application by Jagdish C. Tandon and Lingappa K. Mestha, Attorney Docket No. D/99660, entitled “Color Imager Bar based Spectrophotometer For Color Printer Color Control System.”
In the specific exemplary spectrophotometer embodiment herein further described below, it may be seen that, as in said D/A1024, and herein, plural different color emission LEDs sequentially project their respective illuminations substantially in parallel, perpendicularly to the color test target surface, rather than at an angle thereto, so as to provide a substantially circular, rather than elliptical, commonly illuminated area of the test target. That is, with all the LEDs centrally located together, their illumination pattern on the test target may be formed from rays that hit the target at approximately 90 degrees, i.e., normal to the target. This will produce a circular or nearly circular irradiance pattern on a selected area of the target when the target surface is at 90 degrees thereto. One or more photo-sensors may be optically oriented at 45 degrees to the test target to receive the reflected light from the illuminated test target. As will be further explained herein, when the test target surface deviates from said 90 degrees, by factors such as paper lead or trail edge curl, paper buckle or corrugation, sensor mounting misalignment, or other effects, this circular LED irradiance pattern becomes only slightly elliptical, with little area change, and thus causes little variance in the target irradiance and, therefore, in the signals from the photo-sensors, hence providing improved spectrophotometer angular insensitivity.
An additional feature for improved spectrophotometer accuracy in the disclosed embodiment, as disclosed in said D/A1024, and herein, is to provide averaging of the outputs of plural photodetectors which are angularly viewing the target irradiance area from different positions around it, on opposing sides, so as to average any varying angular and/or azimuthal reflectivity of the target area, and thus further increase the insensitivity to changes in alignment with the target area.
As disclosed in said D/99660, and herein, the exemplary disclosed spectrophotometer desirably utilizes (incorporates in part) a low cost component or part of a low cost commercially available multiple photo-sites, plural spectral responsive, imaging array or bar, such as heretofore commercially used for imaging colored documents in various scanners, digital copiers, and multifunction products. Also disclosed is a relatively simple alternative modification thereof to provide additional differently spectral responsive photo-sites.
Also disclosed in said D/99660 and herein is a low cost spectrophotometer which may employ a small limited number of different spectra LED or other illumination sources, yet providing multiple data outputs from a low cost photosensor having plural different spectral responsive photo-sites detecting light reflected by a colored test target area sequentially illuminated by those illumination sources (or, continuously white light illuminated), to rapidly provide broad spectrum data from a colored test surface.
By way of background, examples of full color document imaging bars include those used in various document scanning systems of various well known Xerox Corporation commercial products (including some being alternatively used for black and white imaging) such as the Documen
Hubble, III Fred F.
Mestha Lingappa K.
Tandon Jagdish C.
Phan James
Xerox Corporation
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