JP3898142B2 - Color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus that obtains a color image by superimposing a plurality of colors of visible images.
[0002]
[Prior art]
In an image forming apparatus that obtains a color image, various methods are employed to achieve downsizing of the apparatus, an increase in process speed, or high-precision color superposition. For example, each time a toner image of four colors including three primary colors (yellow, magenta, cyan) and possibly black is sequentially formed on one photosensitive drum, the transfer to the paper is repeated three or four times. A method for obtaining color images. Alternatively, an image forming unit for forming a single color toner image on each photoconductive drum is provided by arranging four colors including three primary colors or black in the paper transport direction, and the color toner images are superimposed on the paper to form a color image. A so-called tandem system is formed. Alternatively, an image exposure unit and a development unit for four colors including three primary colors or black for forming an electrostatic latent image are provided on one photosensitive drum, and toner images of the respective colors are superimposed on the photosensitive drum. There is a multiple development system in which a color image is formed and transferred onto a sheet or the like at once.
[0003]
Regardless of these various image forming methods, a color image forming apparatus that superimposes toner images of a plurality of colors is a sheet that is an assembling accuracy, a processing accuracy, an attachment position error, or a transfer medium for each color exposure device or image forming unit. In some cases, the toner images of a plurality of colors are displaced relative to each other due to uneven conveyance speed, and do not overlap accurately.
[0004]
Conventionally, in order to improve the overlay accuracy by correcting the relative misalignment of the toner images of the plurality of colors, the tandem method uses an image forming unit of each color, and a line parallel to the main scanning direction and the main scanning direction. And a detection pattern consisting of a line that is oblique to both the sub-scanning direction is formed on the transfer belt by shifting it by a predetermined distance, and this detection pattern is then transferred to the optical fiber sensor or line as the transfer belt runs. There is a device that detects using a fixed photodetector such as a sensor or a CCD (Charge Coupling Device) and corrects the positional deviation of the toner image formed by each color image forming unit based on the detected deviation amount ( For example, see Patent Document 1.)
[0005]
[Patent Document 1]
JP-A-8-278680 (8th and 9th pages, FIG. 7)
For example, in Patent Document 1, as shown in FIG. 7, detection patterns 3a and 3b on a transfer belt 1 conveyed in the direction of arrow m are detected by a fixed photodetector 2, and detection patterns 3a and 3b are detected. A relative difference between the distances 4a and 4b crossing each of the toner images is detected, and a deviation of each toner image in the main scanning direction is detected. However, in (Patent Document 1), since the photodetector 2 is fixed, the detection patterns 3a and 3b using diagonal lines are required. However, the diagonal lines have a certain area as shown in FIG. In other words, detection errors occur due to the dots being a collection of toner. That is, irregularities are formed at the straight ends of the detection patterns 3a and 3b, and the irregularities are particularly noticeable on the diagonal lines. The detection patterns 3a and 3b are detected at the positions (A) and (B). Assuming that the reading positions of the oblique lines are (C) and (D), respectively. As a result, if there is no unevenness, the relative difference between the distances 4a and 4b is (e), but the relative difference becomes (f) due to the unevenness due to the dots, so that an accurate shift amount cannot be detected. Accordingly, proper shift correction cannot be performed in spite of detecting the shift amount, resulting in a problem that the overlay accuracy is lowered, the color reproduction of the color image is impaired, and the image quality is deteriorated.
[0006]
[Problems to be solved by the invention]
Accordingly, the present invention solves the above-described problem, and accurately detects a relative position error of a plurality of colors of visible images when color images of a plurality of colors are overlaid, and performs appropriate deviation correction. Accordingly, an object of the present invention is to provide an image forming apparatus that superimposes a plurality of colors of visible images with high accuracy and obtains a clear and high-quality color image having good color reproducibility.
[0007]
[Means for Solving the Problems]
As a means for solving the above-mentioned problems, the present invention scans in the main scanning direction orthogonal to the sub-scanning direction, with one or a plurality of image holders that hold a visible image and can travel in the sub-scanning direction. The , In the image carrier , The visible image or , Having a side parallel to the sub-scanning direction and a side parallel to the main-scanning direction Displays the formation position of the visible image plural One or more image forming means for forming a position information image; Means for running a transfer medium in the sub-scanning direction and transferring a plurality of position information images formed on the image holding body to the transfer medium at a predetermined interval And movably provided at a position facing the transfer medium, and transferred to the transfer medium The position information image is detected by detecting a side parallel to the sub-scanning direction, and the position information image is detected by detecting a side parallel to the main scanning direction transferred to the transfer medium. The sub-scanning direction formation position of the image Detecting a plurality of position information images in the main scanning direction based on a relative difference between the main scanning direction forming positions of the plurality of position information images detected by the detecting means; Correction means for relatively correcting the sub-scanning direction formation positions of the plurality of position information images from a relative difference in the sub-scanning direction formation positions of the position information images of The detecting means rotates to detect a side parallel to the sub-scanning direction and a side parallel to the main scanning direction of the plurality of position information images. Is.
[0008]
As a means for solving the above-mentioned problems, the present invention holds an image and scans it in the main scanning direction orthogonal to the sub-scanning direction, an image holding body capable of traveling in the sub-scanning direction. , In the image carrier , The image or , Having a side parallel to the sub-scanning direction and a side parallel to the main-scanning direction Display the image formation position plural A plurality of image forming means for forming a position information image at a predetermined interval, and a movably provided at a position facing the image holding body, are formed on the image holding body. By detecting a side parallel to the sub-scanning direction, a position in the main scanning direction of the position information image is detected, and by detecting a side parallel to the main scanning direction transferred to the transfer medium. The sub-scanning direction formation position of the information image Detecting a plurality of position information images in the main scanning direction based on a relative difference between the main scanning direction forming positions of the plurality of position information images detected by the detecting means; Correction means for relatively correcting the sub-scanning direction formation positions of the plurality of position information images from a relative difference in the sub-scanning direction formation positions of the position information images of The detecting means rotates to detect a side parallel to the sub-scanning direction and a side parallel to the main scanning direction of the plurality of position information images. Is.
[0009]
With the above configuration, the present invention accurately detects the main scanning direction formation position and the sub-scanning direction formation position of each of the plurality of images, thereby accurately correcting the main scanning direction formation position and the sub-scanning direction formation position. It is possible to obtain an image forming apparatus capable of obtaining a clear, high-quality color image with high overlay accuracy and good color reproducibility.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below with reference to the embodiment shown in FIGS. FIG. 1 is a schematic configuration diagram showing an image forming unit 10 of a four-tandem full-color electrophotographic apparatus which is an image forming apparatus of the present invention. The image forming unit 10 includes four sets of yellow (Y) and magenta (M) that respectively form a single color developed image using yellow (Y), magenta (M), cyan (C), and black (BK) toners. ), Cyan (C), and black (BK) image forming stations 12Y, 12M, 12C, and 12BK are arranged in parallel along a transfer belt 13 that is a transfer medium that transports the paper P.
[0011]
Since the image forming stations 12Y, 12M, 12C, and 12BK for the respective colors have the same configuration, the description will be given with reference to the yellow image forming station 12Y arranged in the preceding stage, and the image forming stations 12M, About 12C and 12BK, the same code | symbol and the suffix which shows each color are attached | subjected to the same part, and the description is abbreviate | omitted.
[0012]
The yellow image forming station 12Y has a photosensitive drum 14Y that is an image holding member and rotates in the direction of arrow s, which is the sub-scanning direction. A charging device 16Y, an exposure device 17Y, a developing device 18Y, a transfer charger 20Y, and a cleaning device 21Y, which are image forming means, are sequentially arranged around the photosensitive drum 14Y. The transfer charger 20Y is disposed opposite to the photosensitive drum 14Y with the transfer belt 13 interposed therebetween. The exposure device 17Y scans and selectively irradiates yellow (Y) light, which opposes the yellow (Y) optical signal, in the main scanning direction perpendicular to the rotational traveling direction of the photosensitive drum 14Y. An electrostatic latent image corresponding to yellow (Y) image information and electrostatic pattern latent images 27Y, 27M, 27C, and 27BK to be described later are formed on 14Y.
[0013]
The transfer belt 13 is stretched between the driving roller 13a and the tension roller 13b, and conveys and travels the paper P in the arrow t direction that is the sub-scanning direction. The conveyance speed of the paper P by the transfer belt 13 is set to be equal to the peripheral speed of the photosensitive drums 14Y, 14M, 14C, and 14BK. A fixing device 24 is disposed on the downstream side of the transfer belt 13. Reference numeral 25 denotes a registration roller, and 26 denotes a transfer belt cleaner.
[0014]
A movable mark detection sensor 28 is disposed opposite to the downstream end of the transfer belt 13. The mark detection sensor 28 detects the main scanning direction formation position and the sub scanning direction formation position of the detection pattern marks 27Y, 27M, 27C, and 27BK, which are position information images formed on the transfer belt 13 at predetermined intervals. The detection result by the mark detection sensor 28 is input to a calculation unit 30 that calculates an appropriate exposure timing. The calculation result by the calculation unit 30 is input to an exposure control device 31 that is a correction unit and controls the exposure devices 17Y to 17BK. The calculation unit 30 may be integrated with the exposure control device 31.
[0015]
The mark detection sensor 28 has a photo sensor 28c at the tip of an arm 28b that can be rotated about a fulcrum 28a, and the detection pattern marks 27Y to 27Y with the arm 28b held substantially parallel to the main scanning direction. The deviation detection of 27BK in the sub-scanning direction is performed, and the deviation of the detection pattern marks 27Y to 27BK in the main scanning direction is detected with the arm 28b substantially orthogonal to the main scanning direction. The rotation angle of the arm 28b is detected by the encoder 28d.
[0016]
As shown in FIG. 2, the mark detection sensor 28 detects the shift in the sub-scanning direction, which is the traveling direction of the paper P, and the detection pattern marks 27 </ b> Y to 27 </ b> BK formed at predetermined intervals have sides 27 </ b> Ya parallel to the main scanning direction. This is done by detecting an interval of 27 BKa. That is, when the interval detected by the mark detection sensor 28 is wider than the predetermined interval, the exposure control device 31 advances the exposure start timing of the subsequent image. When the detected interval is narrower than the predetermined interval, the exposure control device 31 The image exposure start timing is delayed to correct the misregistration of a plurality of color toner images.
[0017]
Further, as shown in FIG. 3, the detection of deviation in the main scanning direction, which is the scanning direction of exposure, by the mark detection sensor 28 is performed when the sides 27Yb to 27BKb of the detection pattern marks 27Y to 27BK perpendicular to the main scanning direction are detected. This is performed by detecting the rotation angle of the arm 28b. From FIG. 3, when the length of the arm 28b is L, and the rotation angle θ of the arm 28b at the time of detection of the detection pattern marks 27Y and 27M is shifted by Δθ between the preceding detection pattern mark 27Y and the subsequent detection pattern mark 27M. The image shift amount in the main scanning direction is (LΔθ). Therefore, the exposure controller 31 corrects misalignment of the toner images of a plurality of colors by changing the installation angle of the folding mirrors (not shown) of the exposure devices 17Y to 17BK or adjusting the timing of irradiation of the polygon mirror. Do.
[0018]
Next, the operation will be described. When the warm-up is started after the power is turned on and the full-color electrophotographic apparatus is in a ready state, the image forming unit 10 first corrects the positional deviation of the toner images formed by the image forming stations 12Y to 12BK. That is, in each of the image forming stations 12Y to 12BK, the photosensitive drums 14Y to 14BK are uniformly charged by the charging devices 16Y to 16BK in accordance with the rotation of the photosensitive drums 14Y to 14BK in the arrow s direction, and then the exposure devices 17Y to 17BK are used. Exposure scanning is performed to form detection pattern marks 27Y to 27BK on the photosensitive drums 14Y to 14BK.
[0019]
Next, the latent images corresponding to the detection pattern marks 27Y to 27BK on the photosensitive drums 14Y to 14BK are developed by the developing devices 18Y to 18BK, and yellow (Y), magenta (M), cyan (on the photosensitive drums 14Y to 14BK). C) Black (BK) detection pattern marks 27Y to 27BK are obtained. Further, the detection pattern marks 27Y to 27BK on the photosensitive drums 14Y to 14BK are transferred to the transfer belt 13 as shown in FIG.
[0020]
When the detection pattern marks 27Y to 27BK reach the mark detection sensor 28 position as the transfer belt 13 travels, the mark detection sensor 28 first detects the side 27Ya of the yellow (Y) detection pattern mark 27Y parallel to the main scanning direction. Then, after obtaining the sub-scanning direction formation position, it rotates in the direction of the arrow u, detects the side 27Yb orthogonal to the main scanning direction of the detection pattern mark 27Y, and performs main scanning from the rotation angle θ of the mark detection sensor 28. The direction forming position is obtained and the result is input to the calculation unit 30. Next, the mark detection sensor 28 rotates in the direction opposite to the direction of the arrow u, and after detecting the side 27Ma parallel to the main scanning direction of the detection pattern mark 27M of magenta (M) to obtain the sub-scanning direction formation position. Rotate again in the direction of the arrow u, detect the side 27Mb orthogonal to the main scanning direction of the detection pattern mark 27M, obtain the main scanning direction formation position from the rotation angle θ of the mark detection sensor 28, and calculate the result Input to unit 30.
[0021]
The calculation unit 30 calculates the shift amount (Δθ) of the formation positions of the yellow (Y) and magenta (M) detection pattern marks 27Y and 27M in the sub-scanning direction from the passage times of the sides 27Ya and 27Ma parallel to the main scanning direction. And input to the exposure control device 31. Further, the calculation unit 30 determines the positions of the yellow (Y) and magenta (M) detection pattern marks 27Y and 27M in the main scanning direction formation position from the rotation angle of the arm 28b when the sides 27Yb and 27Mb orthogonal to the main scanning direction are detected. The deviation angle Δθ is calculated and input to the exposure control device 31. Thereafter, with the yellow (Y) detection pattern mark 27Y as a reference, the mark detection sensor 28 detects the shift amount of cyan (C) and black (BK) in the same manner as magenta (M), and the calculation unit 30 Then, the deviation amount (LΔθ) is calculated.
[0022]
In accordance with the amount of deviation between the reference detection pattern mark 27Y for yellow (Y) and the detection pattern marks 27M to 27BK for magenta (M), cyan (C) and black (BK), the exposure control device 31 is an exposure device. 17Y to 17BK are corrected and controlled.
[0023]
When the detection pattern marks 27M to 27BK are displaced in the sub-scanning direction, the exposure control device 31 adjusts the exposure start timing so that the intervals between the detection pattern marks 27M to 27BK are equal to each other. Correct the deviation. When the detection pattern marks 27M to 27BK are displaced in the main scanning direction, the exposure control device 31 changes the installation angle of the folding mirror (not shown) and shifts the exposure start position to correct each other.
[0024]
Thereafter, the detection pattern marks 27Y to 27BK are formed again on the transfer belt 13, detected by the mark detection sensor 28, the amount of deviation is calculated by the calculation unit 30, and the deviation of the detection pattern marks 27Y to 27BK is corrected mutually. Make sure. If the deviation is not corrected at the time of this confirmation, the exposure control device 31 corrects and controls the exposure devices 17Y to 17BK again. This correction control operation is repeated to confirm the deviation correction of the detection pattern marks 27Y to 27BK, the deviation correction operation is terminated, and then a normal color image forming operation is started.
[0025]
When the image forming operation is started, for example, in the yellow image forming station 12Y, the image forming process is sequentially performed in accordance with the rotation of the photosensitive drum 14Y in the arrow s direction. The photosensitive drum 14Y is uniformly charged by the charging device 16Y, and then an exposure operation is performed by the exposure device 17Y to form an electrostatic latent image corresponding to yellow (Y) image data, and further by the developing device 18Y. Development is performed to form a yellow (Y) toner image. Similarly, toner images of the respective colors are formed on the photosensitive drums 14M, 14C, and 14BK at the magenta (M), cyan (C), and black (BK) image forming stations 12M, 12C, and 12BK. The
[0026]
On the other hand, paper P is supplied from a paper feeding device (not shown) in synchronization with the operation of forming the toner images of the respective colors on the photoconductive drums 14Y to 14BK. Is fed to the transfer belt 13.
[0027]
The sheet P sent to the transfer belt 13 is conveyed in the direction of the arrow t as the transfer belt 13 travels while being electrostatically attracted to the transfer belt 13. Then, while the paper P is conveyed in the direction of the arrow t, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are sequentially transferred at multiple positions on the transfer chargers 20Y to 20BK to form a full color toner image. Then, the image is transported and fixed to the fixing device 24, and then discharged and the image forming operation is completed.
[0028]
On the other hand, after the paper P is peeled off, the transfer belt 13 is rotated as it is, and the adhered toner and paper dust are cleaned by the belt cleaner 26. The photosensitive drums 14Y to 14BK after the transfer of the toner image are rotated and driven as they are, the residual toner and paper dust are cleaned by the cleaning devices 21Y to 21BK, and the next full color image forming process is awaited.
[0029]
Since the toner images may be misaligned due to changes in the surrounding environment while the image forming operation is repeated in this manner, the mark detection sensor 28 detects the detection pattern mark according to an instruction from the operator or at regular intervals. 27Y to 27BK are read, and a toner image misregistration correction operation is performed.
[0030]
With the above configuration, in the present embodiment, by using the mark detection sensor 28 that rotates, the detection includes the sides 27Ya to 27BKa parallel to the main scanning direction and the sides 27Yb to 27BKb orthogonal to the scanning direction. The pattern marks 27Y to 27BK can be read with high accuracy, and the detection pattern marks 27Y to 27BK made of dots can be detected with high accuracy. Therefore, it is possible to perform appropriate deviation correction with high accuracy, to superimpose a plurality of color toner images with high accuracy, and to obtain a high-quality color image with good color reproducibility.
[0031]
Next, the present invention will be described with reference to a second embodiment shown in FIG. This embodiment is different from the first embodiment in the image forming method. In the present embodiment, a multi-development type image forming apparatus corrects color misregistration of a multi-color toner image. The same parts as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. To do.
[0032]
The image forming unit 40 of the multi-development system, which is an image forming apparatus, is an image holding body, for example, a photosensitive drum 41 around a photosensitive drum 41 in which an organic or amorphous silicon photosensitive layer is provided on the surface of a conductive aluminum base tube. Image formation is sequentially performed on the photosensitive drum 41 using yellow (Y), magenta (M), cyan (C), and black (BK) liquid developers along the rotation of the body drum 41 in the direction of the arrow v. First to fourth image forming units 42Y to 42BK, which are image forming means, are arranged.
[0033]
Although the image forming units 42Y to 42BK have basically the same configuration except for the color of the liquid developer to be used, yellow (Y) disposed upstream in the rotation direction of the photosensitive drum 41. The other image forming units 42M to 42BK are denoted by the same reference numerals and subscripts indicating the respective colors, and description thereof is omitted.
[0034]
The yellow (Y) image forming unit 42Y includes a well-known corona charger or scorotron charger, a charging device 49Y for uniformly charging the surface of the photosensitive drum 41, and a yellow (Y) modulated according to image information. The yellow (Y) light 43Y corresponding to the light signal is scanned in the main scanning direction orthogonal to the rotational running direction of the photosensitive drum 41 and selectively irradiated, so that a yellow (Y) image is formed on the photosensitive drum 41Y. It has an exposure device 45Y that forms an electrostatic latent image corresponding to information and electrostatic latent images of detection pattern marks 27Y, 27M, 27C, and 27BK, which will be described later.
[0035]
Further, the yellow (Y) image forming unit 42Y supplies a yellow (Y) liquid developer to the electrostatic latent image formed on the photosensitive drum 41 by the developing roller 46Y, and a developing device 44Y that forms a toner image. Have.
[0036]
At the downstream of each of the image forming units 42Y to 42BK around the photosensitive drum 41, a developing device 44Y to 44BK removes excess carrier liquid on the photosensitive drum 41 after development by the developing devices 44Y to 44BK. Is provided. A transfer device 47 having an intermediate transfer roller 47a and a pressure roller 47b is provided downstream of the removal device 46 around the photosensitive drum 41.
[0037]
While reaching from the removing device 46 around the photosensitive drum 41 to the transfer device 47, the side 27Ya parallel to the main scanning direction of the detection pattern marks 27Y, 27M, 27C, 27BK formed on the photosensitive drum 41 at a predetermined interval. Rotating mark detection sensor 28 that is the same as that of the first embodiment for detecting ˜27BKa and sides 27Yb to 27BKb orthogonal to the main scanning direction is disposed to face. The detection result by the mark detection sensor 28 is input to the calculation unit 30, and the calculation result by the calculation unit 30 is input to an exposure control device 48 that is a correcting unit and controls the exposure devices 45Y to 45BK.
[0038]
Provided downstream of the transfer device 47 around the photoconductor drum 41 is a photoconductor cleaner 50 that removes toner remaining on the photoconductor drum 41 after the primary transfer of the toner image to the intermediate transfer roller 47a is completed.
[0039]
Next, the operation will be described. After the power is turned on, the toner image position deviation is corrected first. The photosensitive drum 41 is uniformly charged by the charging devices 49Y to 49BK in the image forming units 42Y to 42BK according to the rotation of the photosensitive drum 41 in the direction of the arrow v, and then the detection pattern marks 27Y to 27BK are detected by the exposure devices 45Y to 45BK. Electrostatic latent images are formed and developed by developing devices 44Y to 44BK, and detection pattern marks 27Y to 27BK are formed on the photosensitive drum 41 at predetermined intervals.
[0040]
When the detection pattern marks 27Y to 27BK reach the position of the mark detection sensor 28 by the rotation of the photosensitive drum 41, the mark detection sensor 28 is rotated in the same manner as in the first embodiment, and sequentially yellow (Y), magenta. The detection pattern marks 27Y to 27BK of (M), cyan (C), and black (BK) detect the sides 27Ya to 27BKa parallel to the main scanning direction and the sides 27Yb to 27Yb orthogonal to the main scanning direction to detect the sub scanning direction. Detection results of the formation position and the formation position in the main scanning direction are input to the calculation unit 30.
[0041]
The calculation unit 30 calculates the deviation amount of the sub-scanning direction formation position and the deviation amount of the main scanning direction formation position of the detection pattern marks 27 </ b> Y to 27 </ b> BK and inputs them to the exposure control device 31. The exposure control device 31 adjusts the exposure start timing of the exposure devices 45Y to 45BK according to the shift amount to correct the shift in the sub-scanning direction, and changes the installation angle of the folding mirror (not shown) in the main scanning direction. Correct the deviation. Thereafter, the detection pattern marks 27Y to 27BK are formed again on the photosensitive drum 41, detected by the mark detection sensor 28, the amount of deviation is calculated by the calculation unit 30, and the deviation of the detection pattern marks 27Y to 27BK is corrected mutually. Make sure. If the deviation is not corrected, the exposure control device 31 corrects and controls the exposure devices 45Y to 45BK again, and after completing the deviation correction operation, starts a normal color image forming operation.
[0042]
When the image forming operation is started, the photosensitive drum 41 rotates in the direction of the arrow v, and at the same time, toner image forming operations are performed by the image forming units 42Y to 42BK, and first, the yellow (Y) image forming unit 42Y. Then, the photosensitive drum 41 is uniformly charged by the charging device 49Y, and then an electrostatic latent image corresponding to yellow (Y) image data is formed by the exposure device 45Y, and a yellow (Y) toner image is formed by the developing device 46Y. Formed. Similarly, magenta (M), cyan (C), and black (BK) toner images are sequentially superimposed on the photosensitive drum 41 by the subsequent image forming units 42M to 42BK to form a full-color toner image. The
[0043]
After that, the toner image on the photosensitive drum 41 is removed through the removing device 46, the excess carrier liquid is removed, reaches the transfer device 47, is primarily transferred to the intermediate transfer roller 47a, and further between the intermediate transfer roller 47a and the pressure roller 47b. Are secondarily transferred to the paper P conveyed in the direction of the arrow w, a full-color image is completed on the paper P, and the image forming operation is completed.
[0044]
After the primary transfer of the toner image to the intermediate transfer roller 47a is completed, the photosensitive drum 41 is subjected to removal of the residual developer by the photoconductor cleaner 50, and a series of image forming processes is completed and the next color image forming process is awaited.
[0045]
While the image forming operation is repeated in this manner, the detection pattern marks 27Y to 27BK are read by the mark detection sensor 28 according to an operator instruction or at regular time intervals, and a toner image misregistration correction operation is performed.
[0046]
With the above configuration, in this embodiment, as in the first embodiment, the mark detection sensor 28 that rotates is provided, and the sides 27Ya to 27BKa parallel to the main scanning direction and the scanning direction are orthogonal to each other. The detection pattern marks 27Y to 27BK composed of the sides 27Yb to 27BKb can be read with high accuracy, and the detection pattern marks 27Y to 27BK can be detected with high accuracy. Accordingly, it is possible to perform appropriate deviation correction with high accuracy, improve the overlay accuracy of toner images of a plurality of colors, and obtain a high-quality color image with good color reproducibility.
[0047]
It should be noted that the present invention is not limited to the above-described embodiment, and can be changed without changing the gist thereof. For example, the detection means is a photo sensor of the mark detection sensor 52 as in the modification shown in FIG. The detection pattern marks 27Y to 27BK may be detected by reciprocatingly sliding the arm 52b supporting the 52a reciprocally in parallel with the main scanning direction indicated by the arrow w by the feed screw 52c. The mark detection sensor 52 detects a shift of the position information image forming position in the main scanning direction based on the feed amount of the feed screw 52c. The shape of the position information image is also arbitrary, and the detection means is not limited to a photo sensor, but may be a CCD or the like. A correction method for correcting the relative position information images of a plurality of colors is also arbitrary. Further, the position information image may be provided on either the rear side or the front side of the image holding member, and may be arbitrarily provided, for example, on both the rear side and the front side according to necessity.
[0048]
【The invention's effect】
As described above, according to the present invention, since it is possible to obtain an appropriate shift correction by highly accurate detection of a position information image, it is possible to improve the overlay accuracy of visible images of a plurality of colors, and to achieve high color reproducibility. A high-quality color image can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming unit of a color electrophotographic apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic explanatory diagram illustrating a mark detection sensor and a detection pattern mark according to the first embodiment of this invention.
FIG. 3 is a schematic explanatory diagram illustrating detection detection of a detection pattern mark by the mark detection sensor according to the first embodiment of this invention.
FIG. 4 is a schematic explanatory view showing detection pattern marks formed on the transfer belt according to the first embodiment of the present invention.
FIG. 5 is a schematic configuration diagram illustrating an image forming unit of a color electrophotographic apparatus according to a second embodiment of the present invention.
FIG. 6 is a schematic configuration diagram showing a mark detection sensor according to a modification of the present invention.
FIG. 7 is a schematic explanatory diagram showing shift detection by a conventional fixed photodetector.
FIG. 8 is a schematic explanatory view showing a detection error by a conventional photodetector.
[Explanation of symbols]
10. Image forming unit
12Y-12BK ... Image forming station
13. Transfer belt
14Y-14BK ... Photosensitive drum
16Y-16BK ... Charging device
17Y to 17BK ... exposure apparatus
18Y-18BK ... Developing device
20Y ~ 20BK ... Transfer charger
24. Fixing device
27Y-27BK ... Detection pattern mark
28. Mark detection sensor
28b ... Arm
28c ... Photo sensor
28d ... Encoder

Claims (4)

One or more image carriers that retain a visible image and are capable of traveling in the sub-scanning direction;
By scanning in a main scanning direction perpendicular to the sub-scanning direction, on the image holding member, the visible image or a side parallel to the main scanning direction and sides parallel to the sub scanning direction the One or a plurality of image forming means for forming a plurality of position information images for displaying a formation position of a visible image;
Means for running the transfer medium in the sub-scanning direction and transferring a plurality of position information images formed on the image holding body to the transfer medium at a predetermined interval ;
Detecting a main scanning direction formation position of the position information image by detecting a side parallel to the sub-scanning direction that is movably provided at a position facing the transfer medium and transferred to the transfer medium ; Detecting means for detecting a position formed in the sub-scanning direction of the position information image by detecting a side parallel to the main scanning direction transferred to the transfer medium ;
Relative correction of the main scanning direction forming positions of the plurality of position information images from the relative difference of the main scanning direction forming positions of the plurality of position information images detected by the detecting means, Correction means for relatively correcting the sub-scanning direction formation positions of the plurality of position information images from the relative difference in the sub-scanning direction formation positions ;
The color image forming apparatus according to claim 1, wherein the detecting means rotates to detect a side parallel to the sub-scanning direction and a side parallel to the main scanning direction of the plurality of position information images . An image holding body that holds an image and can travel in the sub-scanning direction;
The scanning in the sub-scanning direction and main scanning direction perpendicular to the image carrier, the image or of the image and a side parallel to the main scanning direction and sides parallel to the sub scanning direction a plurality of image forming means for forming at predetermined intervals a plurality of position information image for displaying the forming position,
Movably provided at a position facing the image holding body, and detecting a side in the main scanning direction of the position information image by detecting a side parallel to the sub-scanning direction formed on the image holding body ; Detecting means for detecting a position formed in the sub-scanning direction of the position information image by detecting a side parallel to the main scanning direction transferred to the transfer medium ;
Relative correction of the main scanning direction forming positions of the plurality of position information images from the relative difference of the main scanning direction forming positions of the plurality of position information images detected by the detecting means, Correction means for relatively correcting the sub-scanning direction formation positions of the plurality of position information images from the relative difference in the sub-scanning direction formation positions ;
The color image forming apparatus according to claim 1, wherein the detecting means rotates to detect a side parallel to the sub-scanning direction and a side parallel to the main scanning direction of the plurality of position information images . The color image forming apparatus according to claim 2, wherein the image or the position information image thus formed on the plurality of image forming means, characterized in that a visible image. 4. The color image forming apparatus according to claim 1, wherein the detection unit includes an encoder that measures a rotational movement amount of the detection unit . 5.

Images