Electrophotography – Control of electrophotography process – Forming test image
Reexamination Certificate
2000-11-27
2004-03-30
Beatty, Robert (Department: 2852)
Electrophotography
Control of electrophotography process
Forming test image
C399S301000, C399S395000, C347S116000
Reexamination Certificate
active
06714748
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, which is to be used in electrophotographic machines, such as printers, copiers and facsimiles, for forming a full-color image as the individual color images formed by plural electrostatic recording unite are overlapped. Also, the invention relates to a recording medium in which a test-pattern image forming program is recorded, a test-pattern image forming method, and a skew angle calculating method.
2. Description of the Related Art
As electrophotographic color printers, a tandem type is hitherto known in which a plurality of electrostatic recording units (image forming units) are arranged in sequence in the direction of conveyance of recording paper.
The typical tandem color printer is equipped with four electrostatic recording units for four colors, i.e. black (K), cyan (C), magenta (M) and yellow (Y). Each of the four electrostatic recording units forms a latent image by optically scanning a photosensitive drum based on image data, and then develops the latent image with color toner of the individual color in a developing device. After having been developed with color toner of the individual colors on these four electrostatic recording units, the four-color toner images are transferred onto the recording paper, which is being conveyed at a constant speed, as overlapped one over another in the order of yellow (Y), magenta (M), cyan (C) and black (K). Subsequently this composite image is fixed on the recording paper by a fixing device to complete a full-color print.
For improving the quality of color print in such tandem-type color printer, it is necessary to minimize positional errors (print errors) of the toner images, which are to be transferred onto the recording paper by the individual electrostatic recording units, to increase the precision of color registration.
For example, if the solution in either of the primary scanning direction (perpendicular to the direction of conveyance of the recording paper) and the secondary scanning direction (the direction of conveyance of the recording paper) on the recording paper is 600 dpi (dots per inch), the inter-dot pitch is approximately 42 &mgr;m; the positional errors of the toner images must be limited to the pixel pitch within this range.
Consequently it has been customary to previously detect amounts of errors in a primary scanning direction, a secondary scanning direction and an oblique direction (inclined with respect to the direction of conveyance of the recording paper) and then to correct these positional errors.
As one example, image data corrected in accordance with the individual amounts of positional errors is expanded on a bitmap memory (image memory). And as another example, the timing to read out the expanded image data from the bitmap memory. As still another example, the error of position in the secondary scanning direction in particular is corrected by varying the timing of exposure by an exposure device.
For realizing effective utilization of positional error correction to restrict the positional error extents within the range of less than approximately 42 &mgr;m in pixel pitch, it is necessary to exchange parts and adjust mechanical positions with precision prior to shipping from a factory or when maintenance, inspection or repairing by a custom engineer (CE) after installation of a product printer at user's site.
For example, in the presence of a problem in accuracy of manufacture, such as when an exposure device equipped with the individual electrostatic recording unit curves in the scanning direction, when the inter-dot pitch of the exposure device is poor, or when the axis of a photosensitive drum is off the center line, it is hard to correct the positional errors. As that is the case, it would then be more important to exchange parts and adjust mechanical positions so that the positional errors can be within a predetermined allowance by the above-mentioned correction of position error amounts.
Consequently, when shipping from a factory, for example, it is necessary to grasp a cause for positional error by printing a test-pattern image to check what kind of the positional error has occurred in a printer to be shipped. Then, the position is corrected mechanically or the involved part is exchanged with a new one to provide an allowance of positional errors will cope with by the above-mentioned correction.
However, since possible positional errors with color printers include those which would occur with lapse of time, irrespective of the accuracy of manufacture of various parts, it is necessary to grasp causes of positional errors by printing a test-pattern image also at the time of maintenance, inspection and repairing by a custom engineer (CE) likewise at the time of the above-mentioned shipping at a factory and observing the positional errors. And then it is necessary to mechanically correct the positions and/or to exchange of the parts. Thus it has long been cherished to perform the necessary procedure efficiently without expert's labor.
Even if such test-pattern image is printed, it yet would take time to discriminate what kinds of causes for the positional errors. Thus, after printing a test-pattern image, the operator ensures whether a positional error or errors have occurred from the printed test-pattern image. The operator then makes positional adjustments and exchange with respect to the parts that are presumably causes for the positional errors, whereupon the operator makes a print of a test-pattern image again and ensures whether the positional adjustments have been made with precision. If the positional errors have not been corrected as this result, it has been a common practice to repeat positional adjustment and/or exchange of other parts, which would be time-consuming and need expert's labor.
One solution technology has been proposed which is accomplished by grasping the positional errors using a variety of test-pattern images and discriminating causes for the errors.
Specifically, as the test-pattern images, {circle around (1)} a single line is printed in black (K) and three other lines are printed in parallel to the black line in yellow (Y), magenta (M) and cyan (C), or {circle around (2)} the yellow (Y), magenta (M) and cyan (C) lines are printed so as to extend beyond the black (K) line, or {circle around (3)} the yellow (Y), magenta (M) and cyan (C) are printed so as to cross the black (K) line to form a two-color cross mark.
In this conventional technology, since the test-pattern image printed for grasping the positional errors has to identified using a microscope or a magnifying glass, it is very meticulous so that efficient jobs would hardly been achieved.
As an alternative solution, Japanese Patent Laid-Open Publication No. HEI 9-304992 discloses a technology in which a test-pattern image composed of longitudinal or transverse lines are printed in fragments on recording paper, and printing errors in the primary, secondary and oblique scanning directions are detected for information enabling the operator to make adjustments without difficulty.
According to this conventional technology, although the extent of a positional error can be recognized by eyes, it is impossible to grasp a continuous change of the positional error as the test-pattern image is arranged only in fragments on recording-paper. Further, when non-uniform printing occurs due to the difference in extent of positional error between local positions of the recording paper, it is impossible to grasp the cycle and amplitude of the non-uniformity of printing. As a result, it is difficult to judge the cause for the positional error exactly.
As still another alternative solution, Japanese Patent Laid-Open Publication No. HEI 10-115955 discloses a technology which comprises previously providing a memory with a test-pattern image composed of plural groups of lines extending parallel to the primary scanning direction, printing an overlapped test-pattern image of a reference color (magenta, for exampl
Imado Susumu
Nakayasu Hirofumi
LandOfFree
Image forming apparatus, recording medium in which... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus, recording medium in which..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus, recording medium in which... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3191640