Image printing apparatus and image printing method

Abstract

When images are to be printed on two, front and lower surfaces of a sheet, in order to register the position of the image on the front surface and the position of the image on the back surface highly accurately, an image printing apparatus of this invention includes an image printing section which forms the image for the front surface of the sheet s well as an image of a reference mark on a photosensitive member at one portion in a region outside an image printing region and transfers the images onto the front surface of the sheet, a fixing unit which fixes the transferred images on the sheet, a line sensor which detects the reference mark after fixing printed on the front surface of the sheet, an arithmetic operating section which obtains a shrinkage factor of the sheet on the basis of a size of the reference mark before fixing and a size of the detected reference mark after fixing and calculates a position and magnification of the image to be printed on the back surface on the basis of the shrinkage factor, and a control section which performs control operation to print the image on the back surface of the sheet on the basis of the calculated position and the calculated magnification.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention, and many other attendant features and advantages thereof, will become apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols and numerals indicate the same or similar components, wherein:

FIG. 1 is a sectional view showing the schematic entire arrangement of an image printing apparatus according to the present invention;

FIG. 2 is a view showing an example of a method of determining the position of an image to be printed on the front surface of a sheet;

FIG. 3 is a view showing an image and reference mark printed on the front surface of the sheet;

FIG. 4 is a view showing a reference mark printed on the front surface of the sheet;

FIG. 5 is a view showing an example of a method of detecting a mark when printing an image on the back surface of the sheet;

FIG. 6 is a control block diagram of an image printing apparatus according to the first embodiment;

FIG. 7 is a view for explaining a process of obtaining the position and magnification of an image to be printed on the back surface;

FIG. 8 is a flowchart showing the control operation of the image printing apparatus according to the first embodiment;

FIG. 9 is a control block diagram of an image printing apparatus according to the second embodiment;

FIGS. 10A to 10C are views for explaining a process of obtaining the position and magnification of the image to be printed on the back surface; and

FIG. 11 is a flowchart showing the control operation of the image printing apparatus according to the second embodiment.

Claims

1. An image printing apparatus for printing images on front and lower surfaces of a sheet, comprising: an image printing section which forms the image for the front surface of the sheet as well as an image of a reference mark on a photosensitive member at one portion in a region outside an image region and transfers the images formed on said photosensitive member onto the front surface of the sheet;a fixing unit which fixes the transferred images on the sheet;a line sensor which detects the reference mark after fixing printed on the front surface of the sheet;an arithmetic operating section which obtains a shrinkage factor of the sheet on the basis of a size of the reference mark before fixing and a size of the detected reference mark after fixing and calculates a position and magnification of the image to be printed on the back surface on the basis of the shrinkage factor; anda control section which performs control operation to print the image on the back surface of the sheet on the basis of the calculated position and the calculated magnification.

2. An apparatus according to claim 1, wherein the region outside the image region comprises a region outside the image region in a direction perpendicular to a convey direction of the sheet.

3. An apparatus according to claim 1, wherein said line sensor is set in a direction perpendicular to a convey direction of the sheet.

4. An apparatus according to claim 3, wherein said line sensor scans the reference mark a plurality of number of times in main scanning to read not less than two portions of the reference mark in a sub-scanning direction, thereby detecting the reference mark.

5. An apparatus according to claim 1, wherein the reference mark comprises a first straight line, a second straight line, and a third straight line, the first straight line and the second straight line being parallel to a convey direction of the sheet, and the third straight line intersecting the first straight line and the second straight line.

6. An apparatus according to claim 5, wherein the reference mark comprises a first straight line, a second straight line, and a third straight line, the first straight line and the second straight line being parallel to the convey direction of the sheet, and the third straight line connecting an upstream end of the first straight line in the convey direction and a downstream end of the second straight line in the convey direction.

7. An apparatus according to claim 6, wherein the reference mark has a Z shape.

8. An apparatus according to claim 1, wherein said arithmetic operating section comprises: a first length calculation unit which obtains a first length of the reference mark after fixing in a direction perpendicular to the convey direction on the basis of the read result;a second length calculation unit which obtains a second length of the reference mark after fixing in a convey direction on the basis of a convey speed of the sheet in the convey direction, a time interval of main scanning done by said line sensor, and the first length;a shrinkage factor calculation unit which obtains the shrinkage factor of the sheet after fixing on the basis of the first length and the second length; anda determination unit which determines a position and magnification of the image to be printed on the back surface in accordance with the shrinkage factor.

9. An apparatus according to claim 8, wherein said shrinkage factor calculation unit obtains a shrinkage factor in a direction perpendicular to the convey direction of the sheet from a ratio of the first length of the reference mark before fixing to the first length of the reference mark after fixing which is calculated by said first length calculation unit, and a shrinkage factor in the convey direction of the sheet from a ratio of the second length of the reference mark before fixing to the second length of the reference mark after fixing which is calculated by said second length calculation unit.

10. An apparatus according to claim 1, wherein said arithmetic operating section comprises: a reference point calculation unit which obtains a first reference point where the first straight line and the third straight line intersect and a second reference point where the second straight line and the third straight line intersect on the basis of the read result;a third length calculation unit which obtains a first length between the first reference point and the second straight line and a second length between the second reference point and a point where a line passing through the first reference point and perpendicular to the second straight line intersects the second straight line;a shrinkage factor calculation unit which obtains a shrinkage factor of the sheet after fixing on the basis of the first length and the second length; anda determination unit which determines a position and magnification of an image to be printed on the back surface in accordance with the shrinkage factor.

11. An apparatus according to claim 10, wherein said shrinkage factor calculation unit obtains a shrinkage factor in a direction perpendicular to the convey direction of the sheet from a ratio of the first length of the reference mark before fixing to the first length of the reference mark after fixing which is calculated by said third length calculation unit, and a shrinkage factor in the convey direction of the sheet from a ratio of the second length of the reference mark before fixing to the second length of the reference mark after fixing which is calculated by said third length calculation unit.

12. An apparatus according to claim 1, wherein when the image is to be formed on the front surface of the sheet, said control section prints a cutting mark serving as a mark in cutting the sheet in a region outside the image region, and the reference mark at one portion in the region outside the image region further outside the cutting mark in a main scanning direction and a sub-scanning direction.

13. An apparatus according to claim 1, further comprising a registration roller, upstream of said image printing section in a convey direction of the sheet, which corrects a skew of the sheet, wherein said line sensor is arranged between said image printing section and said registration roller.

14. An apparatus according to claim 1, further comprising a removing member which removes a foreign substance attaching to said line sensor.

15. An image printing method of printing images on front and back surfaces of a sheet, comprising: the first image printing step of forming the image for the front surface of the sheet as well as an image of a reference mark on a photosensitive member at one portion in a region outside an image region and transferring the images formed on the photosensitive member onto the front surface of the sheet;the fixing step of fixing the images on the sheet;the detection step of detecting the reference mark after fixing printed on the front surface of the sheet with a line sensor;the arithmetic operation step of obtaining a shrinkage factor of the sheet on the basis of a size of the reference mark before fixing and a size of the detected reference mark after fixing and determining a position and magnification of the image to be printed on the back surface on the basis of the shrinkage factor; andthe second image printing step of printing the image on the back surface of the sheet on the basis of the position and magnification which are obtained in the arithmetic operation step.

16. A method according to claim 15, wherein the region outside the image region comprises a region outside the image region in a direction perpendicular to a convey direction of the sheet.

17. A method according to claim 15, wherein the line sensor is set in a direction perpendicular to a convey direction of the sheet.

18. A method according to claim 17, comprising scanning the reference mark a plurality of number of times in main scanning by the line sensor to read not less than two portions of the reference mark in a sub-scanning direction, thereby detecting the reference mark.

19. A method according to claim 15, wherein the reference mark comprises a first straight line, a second straight line, and a third straight line, the first straight line and the second straight line being parallel to a convey direction of the sheet, and the third straight line intersecting the first straight line and the second straight line.

20. A method according to claim 19, wherein the reference mark comprises a first straight line, a second straight line, and a third straight line, the first straight line and the second straight line being parallel to the convey direction of the sheet, and the third straight line connecting an upstream end of the first straight line in the convey direction and a downstream end of the second straight line in the convey direction.

21. A method according to claim 20, wherein the reference mark has a Z shape.

22. A method according to claim 18, wherein the arithmetic operation step comprises: the first length calculation step of obtaining a first length of the reference mark after fixing in a direction perpendicular to a convey direction on the basis of the read result;the second length calculation step of obtaining a second length of the reference mark after fixing in the convey direction on the basis of a convey speed of the sheet in the convey direction, a time interval of main scanning done by the line sensor, and the first length;the shrinkage factor calculation step of obtaining the shrinkage factor of the sheet after fixing on the basis of the first length and the second length; andthe determination step of determining a position and magnification of the image to be printed on the back surface in accordance with the shrinkage factor.

23. A method according to claim 22, wherein the shrinkage factor calculation step comprises obtaining a shrinkage factor in a direction perpendicular to the convey direction of the sheet from a ratio of the first length of the reference mark before fixing to the first length of the reference mark after fixing which is calculated in the first length calculation step, and a shrinkage factor in the convey direction of the sheet from a ratio of the second length of the reference mark before fixing to the second length of the reference mark after fixing which is calculated in the second length calculation step.

24. A method according to claim 15, wherein the arithmetic operation step comprises: the reference point calculation step of obtaining a first reference point where the first straight line and the third straight line intersect and a second reference point where the second straight line and the third straight line intersect on the basis of the read result;the third length calculation step of obtaining a first length between the first reference point and the second straight line and a second length between the second reference point and a point where a line passing through the first reference point and perpendicular to the second straight line intersects the second straight line;the shrinkage factor calculation step of obtaining a shrinkage factor of the sheet after fixing on the basis of the first length and the second length; andthe determination step of determining a position and magnification of the image to be printed on the back surface in accordance with the shrinkage factor.

25. A method according to claim 24, wherein the shrinkage factor calculation step comprises obtaining a shrinkage factor in a direction perpendicular to the convey direction of the sheet from a ratio of the first length of the reference mark before fixing to the first length of the reference mark after fixing which is calculated in the third length calculation step, and a shrinkage factor in the convey direction of the sheet from a ratio of the second length of the reference mark before fixing to the second length of the reference mark after fixing which is calculated in the said third length calculation step.

26. A method according to claim 15, wherein the first image printing step comprises, when the image is to be formed on the front surface of the sheet, printing a cutting mark serving as a mark in cutting the sheet in a region outside the image region, and the reference mark at one portion in the region outside the image region further outside the cutting mark in a main scanning direction and a sub-scanning direction.