Skew sensor calibration

Patent metadata

Field	Value
Publication number	US-10343433-B2
Application number	US-201515748879-A
Country	US
Kind code	B2
Filing date	Oct 30, 2015
Priority date	Oct 30, 2015
Publication date	Jul 9, 2019
Grant date	Jul 9, 2019

Abstract

A skew sensor calibration unit including a scanner providing a scanned image of a sheet as the sheet is conveyed along a transport path, the scanned image including a leading edge of the sheet and a skew detection pattern printed thereon by a printhead. A calibration module measures a top skew of the sheet based on position signals from a plurality of skew sensors indicating a position of a leading edge of a sheet as the sheet is conveyed along the transport path, measure an image skew of the sheet relative to the printhead based on the scanned image, and generates a calibration factor that when applied to the measured top skew provides a calibrated top skew that matches the image skew.

First claim

The invention claimed is:

1. A skew sensor calibration unit comprising:
a scanner providing a scanned image of a sheet as the sheet is conveyed along a transport path, the scanned image including a leading edge of the sheet and a skew detection pattern printed thereon by a printhead; and
a calibration module to:
measure a top skew of the sheet based on position signals from a plurality of skew sensors indicating a position of a leading edge of a sheet as the sheet is conveyed along the transport path;
measure an image skew of the sheet relative to the printhead based on the skew detection pattern in the scanned image; and
generate a calibration factor that when applied to the measured top skew provides a calibrated top skew that matches the image skew.

2. The skew sensor calibration unit of claim 1 , the skew detection pattern comprising a line printed across the sheet crosswise to a transport direction of the sheet along the transport path, and measuring the image skew includes measuring a skew distance from the leading edge to the line at a plurality of locations across the sheet based on pixel values of the scanned image corresponding to the plurality of locations, the plurality of location spaced from one another by predetermined distances and the pixel values representing reflectance values of the sheet.

3. The skew sensor calibration unit of claim 2 , the line of the skew detection pattern having a width in the transport direction so as to form a printed bar, the printed bar being printed on the leading edge of the sheet with a trailing edge of the printed bar spaced from the leading edge of the sheet, the skew distance being a distance from the leading edge of the line to the trailing edge of the printed bar.

4. The skew sensor calibration unit of claim 2 , the skew detection pattern further including a series of parallel lines printed at a predetermined distance from one another, and the calibration unit to measure a scanner skew relative to the printhead by measuring distances between the parallel lines at the plurality of locations across the sheet based on pixel values of the scanned image corresponding to the plurality of locations and adjusting the measured image skew by subtracting the measured scanner skew therefrom.

5. The skew sensor calibration unit of claim 4 , the calibration unit to average the measured distances between the parallel lines at the plurality of locations across the sheet and determine the scanner skew based on comparing the average measured distance to the predetermined distance.

6. The skew sensor calibration unit of claim 1 , the scanner comprising a scanbar comprising a single row of pixels extending across the transport path crosswise to the transport direction.

7. A method of operating a printer comprising:
printing a skew detection pattern on a sheet with a printhead;
measuring a top skew of the sheet by detecting a leading edge of the sheet with a plurality of skew sensors as the sheet moves along a transport path;
generating a scanned image of the sheet including the leading edge and the skew detection pattern;
measuring a print skew of the sheet relative to the printhead based on the skew detection pattern in the scanned image;
generating a calibration factor that when applied to the measured top skew provides a calibrated top skew measurement equal to the print skew,
applying the calibration factor to measured top skews of subsequent media sheets moving along the transport path to provide calibrated top skew measurements.

8. The method of claim 7 , including:
adjusting the position of the sheets based on the corresponding calibrated top skew measurements as the sheets move along the transport so that leading edges of the sheets are aligned with the printhead prior to the sheets reaching the printhead.

9. The method of claim 7 , printing the skew pattern including printing a line across the sheet crosswise to a transport direction of the sheet along the transport path.

10. The method of claim 9 , measuring the print skew including measuring a skew distance from the leading edge to the line at a plurality of locations across the sheet based on pixel values of the scanned image corresponding to the plurality of locations, the plurality of location spaced from one another by predetermined distances and the pixel values representing reflectance values of the sheet.

11. The method of claim 10 , printing the line of the skew detection pattern including print the line with a width in the transport direction so as to form a printed bar, the printed bar being printed on the leading edge of the sheet with a trailing edge of the printed bar spaced from the leading edge of the sheet, the skew distance being a distance from the leading edge of the line to the trailing edge of the printed bar.

12. The method of claim 10 , in addition to printing the line, printing the skew detection pattern including printing a series of parallel lines printed at a predetermined distance from one another, the method including:
measuring a scanner skew relative to the printhead by measuring distances between the parallel lines at the plurality of locations across the sheet based on pixel values of the scanned image corresponding to the plurality of locations; and
adjusting the measured image skew by subtracting the measured scanner skew therefrom.

13. The method of claim 12 , measuring the scanner skew including:
measuring distances between the parallel lines at the plurality of locations across the sheet; and
determining the scanner skew based on comparing the average measured distance to the predetermined distance.

14. A printer comprising:
a printhead; and
a skew correction unit including:
a plurality of skew sensors disposed across a transport path, each providing a position signal indicating a position of a leading edge of a sheet as the sheet is conveyed along the transport path;
a scanner providing a scanned image of the sheet including the leading edge and a skew detection pattern printed on the sheet by the printhead; and
a calibration module to:
measure a top skew of the sheet based on the position signals;
measure a print skew of the sheet relative to the printhead based on the skew detection pattern in the scanned image; and
generate a calibration factor that when applied to the measured top skew provides a calibrated top skew that matches the print skew.

15. The printer of claim 14 , the skew correction unit including:
a deskew mechanism; and
a deskew controller to apply the calibration factor to top skew measurements made by the skew sensors for subsequent sheets to provide calibrated top skew measurements, and to control the deskew mechanism based on the calibrated top skew measurements to adjust the position of the sheets as the sheets move along the transport path so that leading edges of the sheets are aligned with the printhead prior to the sheets reaching the printhead.

Assignees

• Hewlett Packard Development Co

Inventors

• Liu Hsue-Yang
• Sosnowski Luke P
• Mackenzie Mark H

Classifications

• B41J13/03

  driven, e.g. feed rollers separate from platen · CPC title

• B41J2/175

  Ink supply systems {; Circuit parts therefor} · CPC title

• B41J11/0095

  Detecting means for copy material, e.g. for detecting or sensing presence of copy material or its leading or trailing end · CPC title

• B41J13/0009

  control of the transport of the copy material · CPC title

• B41J29/38 Primary

  Drives, motors, controls or automatic cut-off devices for the entire printing mechanism · CPC title