Full width array mechanically tunable spectrophotometer

• US 20060132787A1
• Filed: 12/20/2004
• Published: 06/22/2006
• Est. Priority Date: 12/20/2004
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wang, Yao Rong, Kubby, Joel A., Mestha, Lalit Keshav
• Granted Patent: US 7,333,208 B2
• Time in Patent Office: Days
• US Class Current: 356/454
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0218 using optical fibers
• CPC Class Codes: G01J 3/0256 Compact construction
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems

Abstract

Apparatus and methods are provided for implementing a full width array material scanning spectrophotometer by integrating a Fabry-Perot cavity filter with a silicon photodetector and a light focusing device (an optical guide or a SELFOC® lens). The material to be scanned is illuminated by a broad band illumination source (white LEDs or a fluorescence light source). The Fabry-Perot cavity gap can be tuned electromechanically to get multiple measurements to resolve the spectral distribution of the transmitted light signal. The array spectrophotometric architecture facilitates an elongated, substantially linear band detection and the associated spectral reconstruction technique resolves spectral distribution in the presence of multiple resonant peaks.

Claims

1. A full width array spectrophotometer (FWAS) for scanning analysis of a material, comprising an illumination source for illuminating the material, and an array of microelectronically tunable spectrophotometers comprising an array of more than one closely spaced tunable spectrophotometer adjacent to the illumination source, said spectrophotometers being positioned to receive light reflected from the material.

2. The FWAS as claimed in claim 1 wherein the illumination source comprises a broad band light source.

3. The FWAS as claimed in claim 2 wherein the broad band light source comprises at least one of a white LED, a fluorescent light source, an infrared source or a UV source.

4. The FWAS as claimed in claim 1 wherein the spectrophotometers comprise an electromechanically tunable Fabry-Perot optical filter and a switching circuit for selectively tuning the filter for transmitting selected multiple frequencies of the reflected light to a one of the photodetectors.

5. The FWAS as claimed in claim 4 further including a sampling circuit associated with the one photodetector, wherein as the switching circuit selectively adjusts a voltage source to the optical filter, the sampling circuit correspondingly samples an output signal from the one photodetector for generating a spectra representative of the material.

6. The FWAS as claimed in claim 4 further including a light focusing device assembly for communicating the reflected light from the material to the spectrophotometer.

7. The FWAS as claimed in claim 6 wherein the material comprises at least one of print media, paints, textiles, electronic cameras, materials for analysis, environmentally monitorable media, medically identifiable media or bio-samples.

8. The FWAS as claimed in claim 1 wherein the material comprises a print media and the full width array of tunable spectrophotometers are disposed to transversely substantially span a printer paper path in a xerographic assembly.

9. The FWAS as claimed in claim 1 wherein a one of the spectrophotometers comprises a plurality of photodetectors.

10. The FWAS as claimed in claim 9 wherein the plurality of photodetectors are associated with a single light focusing device.

11. A method of full width scanning analysis of a transversely extensive test target in a test target path with a full width array spectrophotometer, comprising:

illuminating at least one substantially linear elongated array of illumination sources, said sources transversely spanning said test target path to illuminate a transverse illuminated band of said test target in said test target path, and

detecting and analyzing light reflected from said sources with a microelectronically tunable spectrophotometers for selectively filtering the reflective light.

12. The method as defined in claim 11 wherein the spectrophotometer includes a Fabry-Perot optical filter and the method includes selectively tuning the filter for correspondingly communicating selective frequencies of the reflected light to a photodetector.

13. The method as defined in claim 12 wherein the analyzing comprises measuring the selected frequencies distinguished by the selectively tuning for generating a spectra representative of the test target.

14. A method of full transverse scanning color analysis of color printed sheets moving in a color printer path with a full width array spectrophotometer, comprising:

illuminating at least one substantially linear elongated array of illumination sources extending sufficiently in a substantially linear dimension to transversely substantially span said color printer path to illuminate with a transverse illumination source extending transversely across said color printed sheets moving in said color printer path,

detecting reflected light from said illumination source with a full width array of tunable spectrophotometers being positioned to receive light reflected from said transverse illumination source fully across said print media sheet moving in said paper path; and

,

selectively filtering the reflected light with a full width array of tunable optical filters associated with photodetectors for generating a detected spectra from the printed sheets representative of a color thereof.

15. A method for generating a reflectance spectra from a selected set of sampled signals reflected from a material and transmitted through an optical filter comprising:

sampling the selected set of signals relative to a corresponding input signal;

using a characteristic processing matrix representative of filter operations; and

,

processing the processing matrix with sampled signals to determine processed output spectral frequencies comprising the reflectance spectra of the material.

16. The method as defined in claim 15 wherein the optical filter comprises a Fabry-Perot device having a limited spectral resolution, and the computing includes deriving output spectral frequencies corresponding to input spectral frequencies beyond the limited spectral resolution.

17. The method as defined in claim 15 wherein the optical filter comprises either a single or multiple peak Fabry-Perot cavity filter and the computing comprises forming a full resolution spectra from the selected set of output spectral frequencies.

18. The method as defined in claim 15 wherein the processed output spectral frequencies are beyond the spectral resolution of the optical filter.