Illumination system having an intensity calibration system

• US 6,188,427 B1
• Filed: 04/20/1998
• Issued: 02/13/2001
• Est. Priority Date: 04/23/1997
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Anderson, Charles H., Allen, John B.
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): PHAM, HAI CHI
• Application Number:
  US09/063,027
• Time in Patent Office: 1,030 Days
• Field of Search: 347/237, 347/238, 347/239, 347/240, 347/246, 347/236, 347/247, 347/255, 347/256, 364/528.21, 355/85, 355/400, 359/15, 359/224, 348/755, 348/764, 348/770, 348/771, 250/551, 362/242, 362/246
• US Class Current: 347/255
• CPC Class Codes: B41J 2/465 using masks, e.g. light-switching masks

Abstract

An illumination system (10) having an automated calibration system (62) for adjusting the light intensity of individual elements (14) of an array of light emitting elements (12). An optical sensor (30) can be positioned in several locations (A,B,C) to sense incident light from a spatial light modulator (20) as the modulator is sequentially actuated one zone (50) at a time. The light output from each zone (50) of the spatial light modulator is characterized and compared to a golden standard, and the light emitting elements of the array associated with illuminating the zones that are deficient in light are ascertained. Adjustment circuitry (62) responsively adjusts and increases the drive current to the associated light emitting elements (14) that are deficient in light output. A look-up table is utilized to determine which LEDs (14) need adjustment to their drive currents to insure uniform illumination in the process and cross-process direction at an image plane. The present invention is ideally suitable for xerographic printers.

Claims

1. An illumination system, comprising

a) an array of individual light emitting elements for emitting light, said light emitted by each of said light emitting elements having an intensity;

b) a light mixing device mixing said light emitted by said light emitting elements to provide a mixed light output;

c) a spatial light modulator having an array of pixels illuminated by said mixed light output, said array of pixels arranged as a plurality of pixel zones, each pixel zone containing a subarray of said array of pixels, each of said light emitting elements having a greater potential illuminating effect on certain ones of said subarrays of pixels relative to other ones of said subarrays of pixels;

d) a light sensor providing a light sensor output indicative of the amount of light sensed by said light sensor, said light sensor being illuminated by said mixed light output transmitted from said array of pixels; and

e) adjustment circuitry selectively controlling individual ones of said subarrays of said array of pixels for light transmission to said light sensor and, in response to said light sensor output, said adjustment circuitry individually adjusting the intensity of the individual light emitting elements of said light emitting device more closely associated with illumination of the selected subarray as a function of said light sensor output in accordance with a predetermined standard.

2. The illumination system as specified in claim 1 wherein said adjustment circuitry selectively controls the entire pixel array to characterize the intensity of the emitted light of each said light emitting element.

3. The illumination system as specified in claim 1 further comprising a projector lens focusing light from said spatial light modulator, along an optical path to an image plane, wherein said sensor is positioned adjacent said projector lens.

4. The illumination system as specified in claim 3 further comprising a reflector selectively positionable in said optical path to direct said light from said projector lens to said sensor.

5. The illumination system as specified in claim 4 further comprising a lens positioned between said reflector and said sensor.

6. The illumination system as specified in claim 1 wherein said spatial light modulator comprises a digital micromirror device (DMD) having an array of reflectable elements, each deflectable between an on-state and an off-state, said sensor being positioned to sense reflected light from said reflectable elements in the off-state.

7. The illumination system a s specified in claim 1 wherein said array of light emitting elements is elongated.

8. The illumination system as specified in claim 7 wherein said elongated array of light emitting elements are arcuately arranged.

9. The illumination system as specified in claim 1 wherein said light mixing device comprises a holographic diffuser.

10. The illumination system as specified in claim 1 further comprising a cylindrical lens compressing said emitted light from said light emitting elements.

11. The illumination system as specified in claim 1 wherein said light sensor is adjacent said spatial light modulator.

12. The illumination system as specified in claim 11 wherein said light sensor is integral to said spatial light modulator.

13. An illumination system, comprising:

a) an array of individual light emitting elements emitting light, said light emitted by each of said light emitting elements having an intensity;

b) a light mixing device mixing said light in a lateral direction;

c) a spatial light modulator having an array of pixel elements illuminated by said mixed light;

d) a plurality of light sensors positioned about a periphery of said spatial light modulator adjacent said spatial light modulator and integral to said spatial light modulator providing a light sensor output, said light sensors also illuminated by said mixed light; and

e) adjustment circuitry individually adjusting said intensity of said individual light emitting elements as a function of said light sensor output.

14. A method of calibrating individual light emitting elements of an array of light emitting elements which comprises the steps of:

providing an array of light emitting elements, each of said light emitting elements emitting light of a measurable intensity;

mixing the light emitted from said light emitting elements to provide a mixed light output;

providing a spatial light modulator having an array of pixels illuminated by said mixed light, said pixels arranged as a plurality of pixel zones, each pixel zone containing a subarray of said array of pixels, each of said light emitting elements having a greater potential illuminating effect on certain ones of said subarray of pixels relative to other ones of said subarrays of pixels;

modulating the mixed light output received from said light emitting elements with said spatial light modulator;

providing a light sensor for sensing said modulated mixed light and providing a light sensor output indicative of the amount of light sensed by said light sensor;

providing an indicator for an acceptable range for the amount of light sensed by said light sensor; and

selectively controlling individual ones of said subarrays of said array of pixels for light transmission to said light sensor and, in response to said light sensor output and individually adjusting the intensity of said individual light emitting elements of said light emitting device more closely associated with illumination of the selected subarray as a function of said light sensor output in accordance with said indicator.

15. The method of claim 14 wherein said steps of modulating include the steps of modulating said mixed light to one of off-state, on-state or a portion of the light projected in the on-state.