Methods and apparatus for correcting rotational skew in duplex images

• US 6,490,421 B2
• Filed: 02/12/2001
• Issued: 12/03/2002
• Est. Priority Date: 02/12/2001
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: McIntyre, C. Kevin
• Primary Examiner(s): PENDEGRASS, JOAN H
• Application Number:
  US09/781,826
• Publication Number:
  US 20020110380A1
• Time in Patent Office: 659 Days
• Field of Search: 399/15, 399/16, 399/395, 399/401, 358/1.18, 358/296, 358/401, 382/112, 382/294
• US Class Current: 399/15
• CPC Class Codes: B41J 11/008 Controlling printhead for accurately positioning print image on printing material, e.g. with the intention to control the width of margins
• CPC Class Codes: B41J 29/393 Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns
• CPC Class Codes: B41J 3/60 for printing on both faces of the printing material
• CPC Class Codes: G03G 15/234 by inverting and refeeding the image receiving material with an image on one face to the recording member to transfer a second image on its second face, e.g. by using a duplex tray; Details of duplex trays or inverters
• CPC Class Codes: G03G 2215/00569 Calibration, test runs, test prints
• CPC Class Codes: H04N 1/00002 Diagnosis, testing or measuring; Detecting, analysing or monitoring not otherwise provided for error detection, error correction or monitoring in digital computers or digital computer components G06F11/00
• CPC Class Codes: H04N 1/00015 Reproducing apparatus
• CPC Class Codes: H04N 1/00031 Testing, i.e. determining the result of a trial H04N1/00029 takes precedence; using test signals for transmission mode changing H04N2201/33371
• CPC Class Codes: H04N 1/00063 using at least a part of the apparatus itself, e.g. self-testing
• CPC Class Codes: H04N 1/00068 Calculating or estimating
• CPC Class Codes: H04N 1/00087 Setting or calibrating picture signal circuits H04N1/40
• CPC Class Codes: H04N 1/00578 using at least part of a loop, e.g. using a return loop
• CPC Class Codes: H04N 1/0058 using at least one dead-end path, e.g. using a sheet ejection path
• CPC Class Codes: H04N 1/00602 Feed rollers
• CPC Class Codes: H04N 2201/0098 User intervention not otherwise provided for, e.g. placing documents, responding to an alarm

Abstract

Methods and apparatus for reducing or eliminating rotational skew between images formed on opposing sides of a media sheet during duplex printing. An image forming device is configured to print out a test page having a skewing scale formed thereon. A rotational skew correction factor can be determined from the skewing scale and provided to the image forming device, which is configured to alter placement of images on a media sheet in response to the rotational skew correction factor to compensate for rotational skew.

Claims

1. A method of at least partially compensating for rotational skew while printing duplex images with an image forming device, comprising:

imaging a first portion of a skewing scale on one side of a media sheet, said first portion including mutually orthogonal coordinate axes intersecting at an origin, a skew axis intersecting one of said mutually orthogonal coordinate axes, and oriented substantially perpendicular thereto; and

a plurality of tick marks spaced along said skew axis;

imaging a second portion of said skewing scale on an opposing side of said media sheet;

comparing said second portion of said skewing scale against said first portion of said skewing scale to observe rotational skew between said first and second portions;

selecting a rotational skew correction factor based upon said observed rotational skew; and

providing said rotational skew correction factor to a controller of said image forming device.

2. The method of claim 1, further comprising:

providing another media sheet to said image forming device, said another media sheet to have first images formed on a first side thereof and second images formed on an opposing second side thereof; and

altering a rotational orientation of at least one of said first and second images in response to said rotational skew correction factor.

3. The method of claim 2, wherein said act of altering a rotational orientation of at least one of said first and second images comprises modifying a coordinate transformation matrix associated with one of said first and second sides of said media sheet in response to said rotational skew correction factor.

4. A method of at least partially compensating for rotational skew while printing duplex images with an image forming device, comprising:

imaging mutually orthogonal coordinate axes on one side of a media sheet, said mutually orthogonal coordinate axes intersecting at an origin;

imaging a skew axis on said one side of said media sheet, said skew axis intersecting one axis of said mutually orthogonal coordinate axes and oriented perpendicular thereto, said skew axis including a plurality of tick marks spaced therealong;

imaging a substantially straight skew line on an opposing side of said media sheet, said skew line intersecting said origin of said mutually orthogonal coordinate axes;

comparing said skew line against said mutually orthogonal axes and said skew axis to observe a point of intersection of said skew line with said skew axis;

determining which tick mark of said plurality of tick marks is most closely located to said point of intersection and selecting a rotational skew correction factor corresponding to said most closely located tick mark; and

providing said rotational skew correction factor to a controller of said image forming device.

5. The method of claim 4, further comprising:

providing another media sheet to said image forming device, said another media sheet to have first images formed on a first side thereof and second images formed on an opposing second side thereof; and

altering a rotational orientation of at least one of said first and second images in response to said rotational skew correction factor.

6. The method of claim 5, wherein said act of altering a rotational orientation of at least one of said first and second images comprises modifying a coordinate transformation matrix associated with one of said first and second sides of said media sheet in response to said rotational skew correction factor.

7. A test page for use in correcting rotational skew while printing duplex images with an image forming device, comprising:

a first portion of a skewing scale formed on one side of a media sheet, said first portion comprising mutually orthogonal coordinate axes intersecting at an origin;

a skew axis intersecting one of said mutually orthogonal coordinate axes and oriented substantially perpendicular thereto; and

a plurality of tick marks spaced along said skew axis; and

a second portion of said skewing scale formed on an opposing side of said media sheet, said second portion configured for comparison against said first portion to observe rotational skew.

8. The test page of claim 7, said first portion further comprising a plurality of rotational skew correction factors, one rotational skew correction factor of said plurality of rotational skew correction factors corresponding to each tick mark of said plurality of tick marks.

9. The test page of claim 7, wherein said plurality of tick marks are equidistantly spaced along said skew axis.

10. The test page of claim 7, wherein distances between any two adjacent tick marks of said plurality of tick marks correspond to a standard unit of measurement.

11. The test page of claim 10, wherein said standard unit of measurement comprises a standard unit angle as measured about said origin of said mutually orthogonal axes.

12. The test page of claim 7, said second portion comprising a substantially straight skew line intersecting said origin of said mutually orthogonal axes, said skew line configured for comparison against said mutually orthogonal axes and said skew axis to observe said rotational skew.

13. The test page of claim 12, said first portion further comprising a rotational skew correction factor corresponding to a tick mark of said plurality of tick marks most closely spaced from a point of intersection of said skew line with said skew axis.

14. An image forming device, comprising:

a source device configured for receiving a plurality of media sheets;

a print engine configured to form images on one side of a media sheet received from said source tray;

an output device configured for receiving media sheets having images formed thereon from said print engine;

a duplexer configured for receiving a media sheet having images on one side thereof from said print engine and for presenting an opposing side of said media sheet to said print engine for printing;

a path selection gate configured to direct a media sheet to said output device or to direct said media sheet to said duplexer; and

a controller configured to print a test page, said test page comprising a first portion of a skewing scale formed on one side of said test page, said first portion comprising mutually orthogonal coordinate axes intersecting at an origin, a skew axis intersecting one of said mutually orthogonal coordinate axes and oriented substantially perpendicular thereto, and a plurality of tick marks spaced along said skew axis and a second portion of said skewing scale formed on an opposing side of said test page, said second portion configured for comparison against said first portion to determine a rotational skew correction factor indicative of a rotational skew between said first and second portions, said controller further configured to receive said rotational skew correction factor and to at least partially correct said rotational skew in response to said rotational skew correction factor.

15. The image forming device of claim 14, wherein said source device comprises one or more source trays configured for receiving a plurality of media sheets, and said controller is configured to receive and store at least one rotational skew correction factor indicative of a rotational skew associated with each of said one or more source trays.

16. An image forming device, comprising:

a print engine configured to form first images on a side of a media sheet presented to said print engine and to form second images on an opposing side of said media sheet presented to said print engine;

a controller configured to receive a rotational skew correction factor indicative of a rotational skew between said first and second images, said rotational skew correction factor formed from a skewing scale used for said first and second images, said skewing scale including mutually orthogonal coordinate axes intersecting at an origin and a skew axis intersecting one of the coordinate axes and oriented perpendicular thereto, said controller further configured to direct said print engine to alter positioning of one of said first and second images in response to said rotational skew correction factor to at least partially remove said rotational skew.

17. The image forming device of claim 16, said controller further configured for printing a test page, said test page comprising:

a first portion of a skewing scale formed on one side of said test page; and

a second portion of said skewing scale formed on an opposing side of said test page, said second portion configured for comparison against said first portion to determine said rotational skew correction factor.

18. The image forming device of claim 17, said first portion comprising:

mutually orthogonal coordinate axes intersecting at an origin formed on one side of said test page;

a skew axis formed on said one side of said test page and intersecting one of said mutually orthogonal coordinate axes and oriented substantially perpendicular thereto;

a plurality of tick marks spaced along said skew axis formed on said one side of said test page; and

plurality of rotational skew correction factors formed on said one side of said test page, one rotational skew correction factor of said plurality of rotational skew correction factors corresponding to each tick mark of said plurality of tick marks.

19. The image forming device of claim 18, said second portion comprising a substantially straight skew line formed on an opposing side of said test page, said skew line intersecting said origin of said mutually orthogonal axes and configured for comparison against said mutually orthogonal axes and said skew axis to observe said rotational skew.

20. An image forming device, comprising:

a print engine configured to form first images on a first side of a media sheet presented to said print engine and to form second images on an opposing second side of said media sheet presented to said print engine;

a set of executable instructions stored in memory of a controller, said set of executable instructions enabling said controller to receive a rotational skew correction factor indicative of a rotational skew between said first and second images, said set of executable instructions further enabling said controller to direct said print engine to alter positioning of one of said first and second images in response to said rotational skew correction factor to at least partially remove said rotational skew, said rotational skew correction factor formed from a skewing scale used for said first and second images, said skewing scale including mutually orthogonal coordinate axes intersecting at an origin and a skew axis intersecting one of the coordinate axes and oriented perpendicular thereto.

21. The image forming device of claim 20, said set of executable instruction further enabling said controller to print a test page, said test page comprising:

a first portion of a skewing scale formed on one side of said test page; and

a second portion of said skewing scale formed on an opposing side of said test page, said second portion configured for comparison against said first portion to determine said rotational skew correction factor.

22. The image forming device of claim 20, said set of executable instructions including at least one coordinate transformation matrix associated with one of said first and second sides of said media sheet, said executable instructions further configured to modify said at least one coordinate transformation matrix in response to said rotational skew correction factor.