Method of printing test pattern and printing apparatus for the same

• US 6,310,637 B1
• Filed: 07/22/1998
• Issued: 10/30/2001
• Est. Priority Date: 07/31/1997
• Status: Expired due to Fees

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Shimada, Kazumichi, Liu, Sa
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Stewart, Jr., Charles W.
• Application Number:
  US09/120,340
• Time in Patent Office: 1,196 Days
• Field of Search: 347/19, 347/37, 347/116, 347/133, 347/41, 347/40, 347/15, 400/120.02, 400/70, 400/61, 400/120, 400/76, 400/119
• US Class Current: 347/19
• CPC Class Codes: B41J 19/142 with a reciprocating print head printing in both directions across the paper width
• CPC Class Codes: B41J 19/145 Dot misalignment correction
• CPC Class Codes: B41J 29/393 Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns

Abstract

In a printer that allows dual-way printing, a test pattern is formed to adjust the print timing with a high accuracy, or more concretely to eliminate a deviation of dots created in the course of a main scan in a backward direction from dots created in the course of the main scan in a forward direction. The test pattern is based on a normal dither matrix. The test pattern includes a plurality of dots that are regularly arranged both in a main scanning direction and in a sub-scanning direction. When the test pattern is printed at an appropriate timing, it is observed as a substantially homogeneous state without unevenness of the density. In case that the dot print timing is deviated, on the other hand, a deviation in dot interval causes unevenness of the density. The deviation of the dot print timing is accurately detected, based on the presence or the non-presence of such unevenness of the density. When the interval of the dots is set equal to the interval that realizes a spatial frequency giving a high visual sensitivity, unevenness of the density is observable more prominently. The deviation of the dot print timing may alternatively be detected by taking advantage of a moire pattern, which is caused by an overlap of an inspection pattern with oblique reference lines.

Claims

1. A method of printing a test pattern on a printing medium by driving a print head to create dots while carrying out a main scan, which moves said print head forward and backward relative to said printing medium in a main scanning direction, said method comprising the steps of:

(a) creating dots at a first timing that forms a first pattern in the course of the main scan in the forward direction, wherein said first pattern comprises a dark portion having a certain area and a light portion having an area greater than the area of said dark portion that alternately appear at a first cycle in the main scanning direction in a predetermined first section of said printing medium; and

(b) creating dots at a second timing that are supposed to form a second pattern in the course of the main scan in the backward direction, wherein said second pattern comprises a dark portion having a certain area and a light portion having an area greater than the area of said dark portion that alternately appear at a second cycle in the main scanning direction in a predetermined second section of said printing medium, said predetermined second section at least partly overlapping said predetermined first section, and wherein said dark portion of said first pattern and said dark portion of said second pattern appear at a fixed interval in the main scanning direction in said overlapped area.

2. A method in accordance with claim 1, wherein said step (a) creates a plurality of dots that are apart from each other by a predetermined first interval in the main scanning direction and apart from each other by a predetermined second interval in a sub-scanning direction, and

wherein said step (b) creates a plurality of dots at positions that are to satisfy at least either one of a position that is apart from each of said plurality of dots created in said step (a) by approximately half the predetermined first interval in the main scanning direction and a position that is apart from each of said plurality of dots created in said step (a) by approximately half the predetermined second interval in the sub-scanning direction.

3. A method in accordance with claim 1, wherein either one of said step (a) and said step (b) forms a third pattern superposed upon said first pattern and said second pattern, said third pattern enabling a relative deviation of a printing position of said second pattern from a printing position of said first pattern to be observed as appearance of light-dark stripes.

4. A printing medium used in a method of printing a test pattern in accordance with claim 1, wherein a test pattern to be formed in said step (a) and in said step (b) is printed in advance in a specified area at an optimum dot formation timing during the main scan in the backward direction, wherein said specified area at least partly does not overlap said predetermined first section in which said first pattern is formed in said step (a) or said predetermined second section in which said second pattern is formed in said step (b).

5. An inspection printing medium used in a method of printing a test pattern in accordance with claim 1, said inspection printing medium having a third pattern that is printed in advance in a specified area of said inspection printing medium, wherein said specified area at least partly overlaps said predetermined first section in which said first pattern is formed in said step (a) and said predetermined second section in which said second pattern is formed in said step (b), and wherein said third pattern enables a relative deviation of a printing position of said second pattern from a printing position of said first pattern to be observed as appearance of light-dark stripes.

6. A printing apparatus that drives a print head to create dots while carrying out a main scan, which moves said print head forward and backward relative to said printing medium in a main scanning direction, said printing apparatus carrying out a sub-scan that moves said printing medium relative to said print head in a sub-scanning direction, which is perpendicular to the main scanning direction, thereby printing an image on said printing medium, said printing apparatus comprising:

a forward-course pattern formation unit that drives said print head at a first timing that forms a first pattern in the course of the main scan in the forward direction, wherein said first pattern comprises a dark portion having a certain area and a light portion having an area greater than the area of said dark portion that alternately appear at a first cycle in the main scanning direction in a predetermined first section of said printing medium; and

a backward-course pattern formation unit that drives said print head at a second timing that are supposed to form a second pattern in the course of the main scan in the backward direction, wherein said second pattern comprises a dark portion having a certain area and a light portion having an area greater than the area of said dark portion that alternately appear at a second cycle in the main scanning direction in a predetermined second section of said printing medium, said predetermined second section at least partly overlapping said predetermined first section, and wherein said dark portion of said first pattern and said dark portion of said second pattern appear at a fixed interval in the main scanning direction in said overlapped area.

7. A printing apparatus in accordance with claim 6, wherein said forward-course pattern formation unit drives said print head to create a plurality of dots that are apart from each other by a predetermined first interval in the main scanning direction and apart from each other by a predetermined second interval in a sub-scanning direction, and

wherein said backward-course pattern formation unit drives said print head to create a plurality of dots at positions that are to satisfy at least either one of a position that is apart from each of said plurality of dots created by said forward-course pattern formation unit by approximately half the predetermined first interval in the main scanning direction and a position that is apart from each of said plurality of dots created by said forward-course pattern formation unit by approximately half the predetermined second interval in the sub-scanning direction.

8. A printing apparatus in accordance with claim 7, wherein said print head comprises a plurality of nozzles that are disposed at a predetermined nozzle interval, which is greater than a printing pitch of dots in the sub-scanning direction,

one of the predetermined second interval and the predetermined nozzle interval being an integral multiple of the other.

9. A printing apparatus in accordance with claim 6, wherein said first pattern and said section pattern comprise a plurality of parallel lines arranged at an equal interval in the main scanning direction.

10. A printing apparatus in accordance with claim 6, wherein said dark portion of said first pattern and said dark portion of said second pattern alternately appear in the main scanning direction at a spatial frequency of 0.4 to 2.0 cycles/mm in said overlapped area.

11. A printing apparatus in accordance with claim 6, wherein either one of said forward-course pattern formation unit and said backward-course pattern formation unit drives said print head to form a third pattern superposed upon said first pattern and said second pattern, said third pattern enabling a relative deviation of a printing position of said second pattern from a printing position of said first pattern to be observed as appearance of light-dark stripes.

12. A printing apparatus in accordance with claim 11, wherein said third pattern comprises a plurality of parallel lines arranged at a fixed interval.

13. A printing apparatus in accordance with claim 11, wherein each pf said first pattern and said second pattern comprises a plurality of parallel lines arranged at a predetermined interval.

14. A printing apparatus in accordance with claim 11, wherein said third pattern comprises a plurality of parallel lines that obliquely intersect a plurality of parallel lines constituting said first pattern and said second pattern at a predetermined angle.

15. A printing apparatus in accordance with claim 14, wherein said predetermined angle is in a range of not less than 2 degrees and not greater than 10 degrees.

16. A printing apparatus in accordance with claim 11, said printing apparatus further comprising:

a camera with which a pattern printed on said printing medium is shot; and

a detection unit that detects the relative deviation of the printing position of said second pattern from the printing position of said first pattern based on light-dark stripes appearing in said pattern shot with said camera.

17. A printing apparatus in accordance with claim 6, said printing apparatus further comprising:

a single-way pattern formation unit that drives said print head during the main scan only either in the forward direction or in the backward direction to print a pattern that is to be formed by both said forward-course pattern formation unit and said backward-course pattern formation unit in a specific area on said printing medium, said specific area being different from said predetermined first section in which said first pattern is formed by said forward-course pattern formation unit and said predetermined second section in which said second pattern is formed by said backward-course pattern formation unit.

18. In a printer that creates dots while carrying out a main scan, which moves a print head forward and backward relative to a printing medium, a method of designing a test pattern formed by the main scan both in the forward direction and in the backward direction,

wherein said test pattern comprises a plurality of dots created at a predetermined interval in a predetermined area,

said method comprising the steps of:

specifying a spatial frequency that gives a maximum visual sensitivity of a human'"'"'s eye with respect to lightness; and

determining said predetermined interval of said dots, in order to cause a spatial frequency of said test pattern to be substantially equal to said specified spatial frequency.

19. A recording medium on which a program for driving a print head and forming a test pattern, which comprises a plurality of dots, on a printing medium is stored in a computer readable manner,

said program comprising:

a first program code unit that causes a computer to realize a function that drives said print head at a first timing that forms a first pattern in the course of a main scan in a forward direction, wherein said first pattern comprises a dark portion having a certain area and a light portion having an area greater than the area of said dark portion that alternately appear at a first cycle in the main scanning direction in a predetermined first section of said printing medium; and

a second program code unit that causes the computer to realize a function that drives said print head at a second timing that forms a second pattern in the course of the main scan in a backward direction, wherein said second pattern comprises a dark portion having a certain area and a light portion having an area greater than the area of said dark portion that alternately appear at a second cycle in the main scanning direction in a predetermined second section of said printing medium, said predetermined second section at least partly overlapping said predetermined first section, and wherein said dark portion of said first pattern and said dark portion of said second pattern appear at a fixed interval in the main scanning direction in said overlapped area.