Printhead having non-uniformity correction based on spatial energy profile data, a method for non-uniformity correction of a printhead, and an apparatus for measuring spatial energy profile data in a printhead

• US 20030007062A1
• Filed: 06/26/2001
• Published: 01/09/2003
• Est. Priority Date: 06/26/2001
• Status: Active Grant

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Wong, Victor C., Narayan, Badhri
• Granted Patent: US 6,603,499 B2
• Time in Patent Office: Days
• US Class Current: 347/236
• CPC Class Codes: B41J 2/45 using light-emitting diode [LED] or laser arrays
• CPC Class Codes: H04N 1/4015 of the reproducing head

Abstract

A printhead having a plurality of exposure elements (18) with improved non-uniformity correction. Spatial variance of the energy emitted by the exposure elements (18) is measured and used to establish spot size characteristics for each exposure element. A sensor (26) scans multiple points along the pixel area written by each exposure element (18)and measures a corresponding output power value at each point. The output power values are evaluated to determine a maximum output power value for the exposure element (18) and to obtain a spot size for the exposure element (18) based on full-width at half-power values. Both spot size data, which can thus be obtained and stored only once, and output power values are then used to correct for non-uniformity'"'"'s between the exposure elements (18).

Claims

1. A printhead assembly for imaging onto a medium, the printhead assembly comprising:

a printhead having a plurality of exposure elements, each exposure element capable of emitting exposure energy into an area; and

a memory coupled to the printhead and containing a compensation value for each of at least some of said exposure elements, said compensation values being determined by obtaining a plurality of positional output power measurements corresponding to a set of predefined spaced-apart positions within the area to determine a spatial characteristic of exposure energy emitted by the corresponding exposure element.

2. A printhead assembly of claim 1, wherein the spatial characteristic is a beam spot diameter of the energy calculated by determining a maximum of the positional output power measurement for a corresponding exposure element and calculating a distance between two of the predefined spaced-apart positions at which positional output power measurements have approximately a predefined relationship to the maximum of the positional output power measurement for the exposure element.

3. A printhead assembly of claim 2, wherein said predefined relationship is where positional output power measurements are approximately one half of the maximum of the positional output power measurement for the exposure element.

4. The printhead assembly of claim 1 wherein said exposure elements apply light energy to the medium.

5. The printhead assembly of claim 1 wherein said exposure elements comprise light valves.

6. The printhead assembly of claim 1 wherein said exposure elements comprise a laser.

7. The printhead assembly of claim 1 wherein said exposure elements comprise an LED.

8. The printhead assembly of claim 1 wherein said memory is a read-only memory.

9. An apparatus for obtaining a spatial profile of exposure output power from an exposure element in a printhead comprising a plurality of exposure elements, the apparatus comprising:

a sensor configured to obtain positional output power measurement for said exposure elements corresponding to a portion of the exposure output power of the corresponding exposure element emitted at each one of a plurality of predefined positions;

a translation apparatus for configuring said sensor for measurement at each one of said plurality of predefined positions for said exposure element to thereby permit said sensor to obtain a sequence of said positional output power measurements for a corresponding one of said exposure elements;

control logic programmed to accept the positional output power measurements from said sensor and to generate, for said exposure element, spatial profile characteristic information using the sequence of the positional output power measurements; and

a memory operatively coupled to said control logic and storing the spatial profile characteristic information for said exposure elements.

10. The apparatus of claim 9 wherein said is a read-only memory device.

11. The apparatus of claim 9 wherein said translation apparatus comprises means for moving said sensor.

12. The apparatus of claim 11 wherein said means for moving comprises a piezoelectric actuator.

13. The apparatus of claim 11 wherein said means for moving comprises a leadscrew.

15. The method of claim 14, wherein said deriving step comprises determining a spot size value for said exposure element.

16. The method of claim 15, wherein said determining step comprises determining a maximum of the positional output power measurement for a corresponding exposure element and calculating a distance between two of the predefined spaced-apart positions at which positional output power measurements have approximately a predefined relationship to the maximum of the positional output power measurement for the exposure element.

17. The method of claim 16 wherein said predefined relationship is where positional output power measurements are approximately one half of the maximum of the positional output power measurement for the exposure element.

18. The method of claim 14 further comprising:

measuring overall output power emitted by said exposure element; and

deriving the correction value for said exposure element from said overall output power and said beam spot characteristic value.

19. The method of claim 18 wherein the step of measuring overall output power comprises the step of providing a sensor capable of obtaining a power measurement.

20. The method of claim 14 wherein the step of calculating a beam spot characteristic value comprises:

identifying a maximum output power measurement in said sequence of output power measurements;

dividing said maximum output power measurement by two to obtain a half maximum output power measurement value;

identifying, from said sequence of output power measurements, a rising-edge full-width reference value as the output power measurement, in that portion of said sequence of output power measurements that precedes said maximum output power measurement, nearest to said half maximum output power measurement value, and identifying a first full-width position as said predetermined position within said predefined pixel area that corresponds with said rising-edge full-width reference value;

identifying, from said sequence of output power measurements, a falling-edge full-width reference value as the output power measurement, in that portion of said sequence of output power measurements that follows said maximum output power measurement, nearest to said half maximum output power measurement value, and identifying a second full-width position as said predetermined position within said predefined pixel area that corresponds with said falling-edge full-width reference value; and

computing a linear distance between said second full-width position and said first full-width position.

21. The method of claim 14 wherein said step of obtaining a sequence of output power measurements comprises adapting a sensor to receive output power emitted over a predefined fraction of said predefined area, establishing a reference position for said sensor, and performing an ordered repetition of the following steps:

moving said sensor to a sensing position, said sensing position being a fixed incremental distance from said reference position, said fixed incremental distance being a fraction of the distance across said predefined pixel area;

obtaining one of said output power measurements from said sensor at said sensing position;

storing said output power measurement within said sequence of output power measurements; and

establishing said sensing position as said reference position.

14. A method for compensating for non-uniformity of exposure elements in a printhead comprising a plurality of exposure elements, wherein said exposure elements each emit exposure energy an area, the method comprising:

obtaining a sequence of output power measurements for said each of exposure elements, each said output power measurement in said sequence corresponding to a predetermined position within the area;

deriving a correction value based on the sequence of output power measurements;

storing the correction value for each of said exposure elements; and

applying the correction values to control of said exposure elements.

22. A method for printing using a printhead that employs a plurality of exposure elements, wherein each exposure element emits exposure energy within a predefined area, the method comprising:

obtaining a spatial profile characteristic value for each exposure element from a sequence of measurements made at successive positions within said predefined area;

deriving exposure element compensation values based said spatial profile characteristic value; and

controlling said exposure elements based on said exposure element compensation values.