System and method for color measurements or other spectral measurements of a material

• US 7,573,575 B2
• Filed: 11/17/2006
• Issued: 08/11/2009
• Est. Priority Date: 12/29/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Shakespeare, John F., Shakespeare, Tarja T.
• Primary Examiner(s): PUNNOOSE, ROY M
• Application Number:
  US11/601,039
• Publication Number:
  US 20070153278A1
• Time in Patent Office: 998 Days
• Field of Search: 356/402
• US Class Current: 356/402
• CPC Class Codes: G01J 2003/1282 Spectrum tailoring
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/50 using electric radiation detectors
• CPC Class Codes: G01J 3/501 Colorimeters using spectrally-selective light sources, e.g. LEDs
• CPC Class Codes: G01J 3/524 Calibration of colorimeters
• CPC Class Codes: G01N 21/86 Investigating moving sheets G01N21/89 takes precedence

Abstract

A system and method for color measurements or other spectral measurements of a material are provided. An illuminating device generates light for illuminating a sample of material. A detector detects light that has interacted with the sample and provides a measurement of the light that has interacted with the sample. A controller adjusts a duty cycle of the illuminating device to control the illumination of the sample. The measurement could be used by an analyzer to determine a spectral characteristic of the sample (such as a color of the sample). The determination of the spectral characteristic could be done without using any measurement of light that has not interacted with the sample. One or multiple light emitting diodes (LEDs) could be used to illuminate the sample, and the duty cycle of individual LEDs or groups of LEDs could be adjusted.

Claims

1. A system, comprising:

an illuminating device operable to generate light for illuminating a sample of material during a plurality of first illumination states, wherein the sample is illuminated differently during different ones of the first illumination states;

a detector operable to detect light that has interacted with the sample during the first illumination states and to provide measurements of the light that has interacted with the sample during the first illumination states;

a controller operable to adjust a duty cycle of the illuminating device to control the illumination of the sample during the first illumination states; and

an analyzer operable to determine a spectral characteristic of the sample based on the measurements, wherein the determined spectral characteristic is associated with a second illumination state that is different than the first illumination states.

2. The system of claim 1, wherein the illuminating device includes at least one light emitting diode (LED).

3. The system of claim 2, wherein the illuminating device includes multiple LEDs, the controller operable to adjust the duty cycle of individual LEDs or groups of LEDs.

4. The system of claim 1, wherein:

the illuminating device includes multiple illuminating devices; and

the detector includes multiple detectors.

5. The system of claim 1, further comprising at least one backing positioned on an opposing side of the sample as the illuminating device.

6. The system of claim 1, wherein the second illumination state is not a linear combination of two or more of the first illumination states.

7. The system of claim 1, wherein the analyzer does not use, when determining the spectral characteristic of the sample, any measurement of light that has not interacted with the sample.

8. The system of claim 1, wherein the analyzer is further operable to control operation of the controller, thereby controlling the illumination of the sample.

9. The system of claim 1, wherein the analyzer is operable to determine the spectral characteristic of the sample by:

determining an illuminator-independent radiance transfer factor of the sample; and

determining a fluorescent emission spectrum of the sample using the radiance transfer factor.

10. The system of claim 1, wherein the spectral characteristic includes a color of the sample.

11. The system of claim 1, wherein the controller is further operable to adjust at least one of a voltage and a current for driving the illuminating device to control the illumination of the sample.

12. The system of claim 11, further comprising a reference detector operable to measure a spectral power distribution of the light generated by the illuminating device;

wherein the analyzer is further operable to cause the controller to adjust at least one of the duty cycle, the voltage, and the current until the measured spectral power distribution is within a specified threshold of a desired spectral power distribution.

13. The system of claim 1, wherein:

the measurement of the light that has interacted with the sample includes a spectral power distribution of the light that has interacted with the sample; and

the duty cycle of the illuminating device represents a percentage of time that the illuminating device is generating light during a measurement interval.

14. A method, comprising:

illuminating a sample of material using at least one light emitting diode (LED) during a plurality of first illumination states, wherein the sample is illuminated differently during different ones of the first illumination states;

detecting light that has interacted with the sample during the first illumination states;

providing measurements of the light that has interacted with the sample during the first illumination states;

determining a spectral characteristic of the sample based on the measurements, wherein the determined spectral characteristic is associated with a second illumination state that is different than the first illumination states; and

adjusting a duty cycle of the at least one LED to control the illumination of the sample.

15. The method of claim 14, wherein:

illuminating the sample includes using multiple LEDs to illuminate the sample; and

adjusting the duty cycle includes adjusting the duty cycle of individual LEDs or groups of LEDs.

16. The method of claim 14, wherein the second illumination state is not a linear combination of two or more of the first illumination states.

17. The method of claim 14, wherein determining the spectral characteristic of the sample includes determining the spectral characteristic of the sample without using any measurement of light that has not interacted with the sample.

18. The method of claim 14, further comprising adjusting at least one of a voltage and a current for driving the at least one LED to control the illumination of the sample.

19. The method of claim 18, further comprising:

measuring a spectral power distribution of light generated by the at least one LED; and

adjusting at least one of the duty cycle, the voltage, and the current until the measured spectral power distribution is within a specified threshold of a desired spectral power distribution.

20. A system, comprising:

at least one light emitting diode (LED) operable to generate light for illuminating a sample of material during a plurality of first illumination states, wherein the sample is illuminated differently during different ones of the first illumination states;

a detector operable to detect light that has interacted with the sample during the first illumination states and to provide measurements of the light that has interacted with the sample during the first illumination states;

an analyzer operable to determine a spectral characteristic of the sample using the measurements, wherein the determined spectral characteristic is associated with a second illumination state that is different than the first illumination states; and

a controller operable to adjust the at least one LED to control the illumination of the sample;

wherein the analyzer, to determine the spectral characteristic of the sample, does not use any measurement of light that has not interacted with the sample.

21. The system of claim 20, wherein the controller is operable to adjust a duty cycle of the at least one LED.