JPH10268610A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately correct image deviation by surely and accurately detecting the positional deviation of each image in an image forming device where the images formed by plural image forming units are multiply transferred. SOLUTION: In a laser printer where the toner images formed by plural image forming units are multiply transferred to a transfer body 10; registration patterns KSO, YSO, MSO and CSO are transferred to the transfer body 10 by every color multiply transferred. Each registration pattern is extended obliquely to the moving direction (b) of the transfer body 10 and constituted of two lines having one intersection. The center positions of the respective registration patterns are detected by detectors 111, 112 and 113 with the movement in the direction (b) of the transfer body 10, so that the deviation is arithmetically calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, in particular, an electrophotographic copying machine, a laser printer, an ink jet printer, etc., which forms an image by synthesizing a plurality of images on a single transfer member. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art In recent years, it has become an important issue in an image forming apparatus such as a copying machine to reproduce full color without image shift (color shift). In particular, a tandem system in which a plurality of image forming units integrating photoreceptor, charging device, and developing device elements are installed according to each color, and the image formed by each unit is multiple-transferred onto a single transfer member In this case, it is necessary to detect and correct an image forming position error for each image forming unit in order to obtain highly accurate image reproducibility.
Therefore, a predetermined registration mark or pattern is formed on a transfer body by each image forming unit, and these are read by a detector and aligned.

For example, Japanese Patent Laid-Open No. 4-131750 discloses that a resist pattern is formed by a horizontal line extending in the main scanning direction and a vertical line orthogonal to the horizontal line or an oblique line extending obliquely. A method has been proposed in which the shift amount is detected, calculated, and corrected.

[0004]

However, in the above-mentioned detection / correction method, since a combination of horizontal lines, vertical lines or inclined lines is used as a resist pattern, if the pattern is blurred or partially missing, it is detected. It may be impossible.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of reliably and accurately detecting the occurrence of a slight defect in a resist pattern and appropriately correcting the displacement of a superimposed image. .

[0006]

SUMMARY OF THE INVENTION To achieve the above object, an image forming apparatus according to the present invention includes a plurality of recording units for visualizing an image based on respective image data;
A transfer unit that multiple-transfers an image visualized by the plurality of recording units onto a single transfer body that moves in one direction; and the plurality of recording units visualizes a resist pattern having a predetermined shape by the plurality of recording units. A resist pattern control unit for sequentially transferring the resist pattern onto the transfer body, a detection unit for detecting each of the resist patterns transferred on the transfer body, and a shift amount of the resist pattern detected by the detection unit is calculated. Correction control means for correcting the position of an image formed by the recording unit based on the image data, wherein the resist pattern extends diagonally with respect to the moving direction of the transfer body, and has two intersections. It is composed of lines.

According to the present invention, the resist pattern is formed by two lines oblique to the moving direction.
A plurality of position information can be detected by the detection means, and by averaging the detected data, even if a line is partially blurred or there is a white spot, the center position is reliably and accurately detected and the position of those positions is detected. The shift amount can be calculated, and as a result, the position shift of the image can be accurately corrected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In the embodiment described below, the present invention is applied to a tandem-type full-color printer.

In FIG. 1, a full-color printer generally has images of C (cyan), M (magenta), Y (yellow) and Bk (black) on photosensitive drums 91, 92, 93 and 94 arranged side by side. Is formed as an electrostatic latent image, and the developed toner image is multiply transferred on a sheet conveyed in the direction of arrow b on the transfer belt 10 to obtain a full-color image. Image forming elements such as a charger and a developing device are arranged around each of the photosensitive drums 91 to 94, however, an image forming process of this type by electrophotography is well known, and details thereof are omitted.

An electrostatic latent image is formed on each of the photosensitive drums 91 to 94 by a multi-beam scanning optical device. This optical device comprises four sets of laser diodes 11, 12, 1
3, 14 and collimator lenses 21, 22, 23, 24
, A polygon scanner 5 rotating at a constant speed, and a number of mirrors and lenses. The modulation of the laser diodes 11 to 14 is controlled based on image data input to a drive circuit (not shown). Laser diode 11 is C (cyan) image data, laser diode 1
2 is M (magenta) image data, laser diode 13
Are driven based on Y (yellow) image data, and the laser diode 14 is driven based on Bk (black) image data.

The light beam emitted from the laser diode 11 is converted into substantially parallel light by the lens 21, passes below the mirror 41, and enters the lower half of the cylindrical lens 31. The light beam is condensed linearly near the deflection surface of the polygon scanner 5 by the lens 31 and is deflected at a constant angular velocity based on the rotation of the scanner 5. The deflected light beam passes through the upper halves of the scanning lenses 611 and 612, and
, And is reflected downward by the mirror 81. Further, the light beam passes through the scanning lens 613, forms an image on the photosensitive drum 91, and scans in the direction of arrow a.

The light beam emitted from the laser diode 12 is converted into substantially parallel light by the lens 22, reflected by the mirror 41, and enters the upper half of the cylindrical lens 31. The light beam is condensed linearly near the deflection surface of the polygon scanner 5 by the lens 31 and is deflected at a constant angular velocity based on the rotation of the scanner 5. The deflected light beam passes through the lower halves of the scanning lenses 611 and 612 and is reflected downward by the mirror 71. Further, the light beam is transmitted to the mirror 8
The light is reflected at 2, 83, passes through the scanning lens 614, forms an image on the photosensitive drum 92, and scans in the direction of arrow a.

The light beam emitted from the laser diode 13 is converted into substantially parallel light by a lens 23, reflected by a mirror 42, and enters the lower half of the cylindrical lens 32. The light beam is condensed linearly near the deflection surface of the polygon scanner 5 by the lens 32 and deflected at a constant angular velocity based on the rotation of the scanner 5. The deflected light beam passes through the upper halves of the scanning lenses 621 and 622 and is reflected downward by the mirror 72. Further, the light beam is transmitted to the mirror 8
The light is reflected at 5, 86, passes through the scanning lens 624, forms an image on the photosensitive drum 93, and scans in the direction of arrow a '.

The light beam emitted from the laser diode 14 is converted into substantially parallel light by the lens 24, passes over the mirror 42, and enters the upper half of the cylindrical lens 32. The light beam is condensed linearly near the deflection surface of the polygon scanner 5 by the lens 32 and deflected at a constant angular velocity based on the rotation of the scanner 5. The deflected light beam passes through the lower half of the scanning lenses 621 and 622,
Is reflected downwards. Further, the light beam passes through the scanning lens 623, forms an image on the photosensitive drum 94, and scans in the direction of arrow a '. A two-dimensional electrostatic latent image is formed on each of the photosensitive drums 91 to 94 by the main scanning in the direction of arrow a or a 'and the sub-scanning by rotating the drums 91 to 94 in the direction of arrow b'.

Scan lenses 611-614, 621-62
Reference numeral 4 has an imaging characteristic for forming an image of the light beam on the photosensitive drums 91 to 94 and an fθ characteristic for correcting the light beam deflected at a constant angular velocity by the polygon scanner 5 to a constant velocity in the main scanning direction. However, when the correction processing of the fθ characteristic is performed on the image data itself, it is not necessary to give the scanning lens the fθ characteristic.

The optical sensors SOS1 and SOS2 are mirrors 4
The light beams reflected by the light sources 3 and 44 are received on the upstream side in the scanning direction a or a ′ and output an image writing start signal, and are used to synchronize the image in the vertical direction (sub-scanning direction). Used for The optical sensor SOS1 receives the light beam from the laser diode 11, and is also used for scanning with the light beam from the laser diode 12. The optical sensor SOS2 receives the light beam from the laser diode 14 and is also used for scanning with the light beam from the laser beam 13.

As described above, in an apparatus that reproduces a full-color image by multiple-transferring a toner image formed by a plurality of image forming units onto a sheet, the position of the image formed by each image forming unit is adjusted. is important. If the position of each image is shifted, the color will change or the color will be shifted, and the image quality will be significantly reduced.

For this reason, the present embodiment has means for detecting the amount of displacement of each image and means for correcting the position of the image formed by each unit in accordance with the detected amount of displacement. I have. That is, a resist pattern having a predetermined shape is formed at a predetermined position for each unit, multiplex-transferred onto the transfer belt 10, the transferred resist pattern is optically detected, and the shift amount is calculated. As shown in FIG. 1 and FIG. 2, the shape of the resist pattern extends obliquely with respect to the moving direction (arrow b) of the transfer belt 10 and has two lines 55 and one having an intersection. 56.

The resist pattern, as shown in FIG.
The black pattern K _S0 , K _C0 , K _E0 , and the yellow pattern Y _S0 , Y are respectively located at a predetermined distance from the predetermined reference position X of the transfer belt 10 in the sub-scanning direction b at predetermined intervals in the main scanning direction a. _C0 , Y _E0 , magenta patterns M _S0 , M _C0 ,
M _E0 and cyan patterns C _S0 , C _C0 , and C _E0 are also formed at predetermined intervals in the sub-scanning direction b. Further, in order to improve the detection accuracy by performing a plurality of samplings, a plurality of these groups of resist patterns may be formed.

When there is no deviation in the image position of each color, each resist pattern is regularly formed on the transfer belt 10 at predetermined intervals. However, in practice, with respect to the optical device, the deviation of the writing position in the main scanning direction, the deviation of the writing position in the sub-scanning direction, the deviation of the magnification in the main scanning direction, the partial deviation of the magnification in the main scanning direction, the deviation in the main scanning direction, Of the transfer belt 10, the meandering, wrinkling, waving, and skew of the transfer belt 10 cause the deviation in the curvature in the sub-scanning direction, the deviation in the inclination in the main scanning direction, the deviation in the magnification in the sub-scanning direction, and the deviation in the sub-scanning direction. , Etc., occurs in a complex manner. As a result, misregistration occurs in each color image, and the resist pattern is not formed at a predetermined position. In other words, the displacement of the image appears as a displacement of the resist pattern from a predetermined position.

In order to detect the position of the resist pattern, detectors 111, 112 and 113 are provided corresponding to the pattern forming position in the main scanning direction. As shown in FIG. 2, each detector uses a line sensor long enough to cover the resist pattern in the main scanning direction. The position of the resist pattern and its detection output waveform are as shown in FIG. The center position of each resist pattern can be detected by averaging these output waveforms.
Even if the output waveform A is unclear, it can be detected by calculating the middle between the output waveforms B and B 'and C and C' and the middle between the output waveforms B and B 'or C and C'. And
The position shift amount is calculated by comparing the detected center positions of the respective resist patterns.

The displacement detection is performed by calculating the amount by which the other color image is displaced from the reference color image. In the present embodiment, the misregistration of an image of another color is detected based on a black image, and correction is performed. As will be described in detail later, since the correction is performed by thinning out and interpolating the image data, the correction slightly deteriorates the image quality. Therefore, the image positions of other colors are corrected based on the most conspicuous black, and the total image deterioration due to the correction is minimized. It is needless to say that the image deterioration here is minute compared to the case where the positional deviation is not corrected.

Black pattern K_SOYellow based on
-Pattern Y_SOΔ is the relative positional shift amount in the main scanning direction.
Xy_SOAnd Also, the pattern K_SO, Y_SOSub-scanning direction
ΔYy_SOAnd Similarly, bra
Pattern K_SOMagenta pattern M based on_SO,
Cyan pattern C_SOΔXm_SO,
ΔYm_SO, ΔXc_SO, ΔYc_SOAnd In addition, other inspections
Position of each resist pattern in the output units 112 and 113
ΔXy_C0, ΔYy_C0, ΔXm_C0, ΔYm_C0, Δ
Xc_C0, ΔYc_C0, ΔXy_E0, ΔYy_E0, ΔXm_E0, Δ
Ym_E0, ΔXc _E0, ΔYc_E0And

As described above, the relative positional deviation of the image includes the main scanning writing position deviation, the sub-scanning writing position deviation, the main scanning magnification deviation, the main scanning partial magnification deviation, the main scanning direction curvature deviation, and the sub-scanning direction deviation. The main deviations are directional curve deviation, main scanning direction inclination deviation, sub-scan magnification deviation, and sub-scan partial magnification deviation. In the present embodiment, the 3
A resist pattern is detected at a position, a shift amount in the main scanning direction and a shift amount in the sub-scanning direction are calculated, and optimal correction is performed.

The main scanning writing position shift means an error in the timing of writing image data for each scanning line. This is caused by an adjustment error and an installation accuracy error of the optical device. The correction is performed by changing the time from when the light receiving signals of the optical sensors SOS1 and SOS2 are generated to when the image is written (see FIG. 4). In the present embodiment, since the deflecting surface of the polygon scanner 5 is different between the surface for deflecting the black and yellow scanning beams and the surface for deflecting the magenta and cyan scanning beams, the optical sensor SOS1 is provided for black and yellow. The optical sensor SOS2 is provided for magenta and cyan. Therefore, as will become less than the allowable amount epsilon ₁ of the main scan write start position shift amount shift amount [Delta] xy _S0 is set in advance, it is corrected by changing the delay time until the yellow image writing from the light receiving signal generated in the optical sensor SOS1. Similarly, the deviation amount DerutaXm _S0, perform correction so DerutaXc _S0 becomes equal to or less than the allowable amount epsilon _1.

The sub-scanning writing position shift means an error in the timing of writing an image. This is caused by an adjustment error and an installation accuracy error of the optical device. The correction is made by changing the time from when the sub-scanning synchronization signal is generated until when the image is written (see FIG. 4). That is, the correction is performed by changing the delay time from the generation of the sub-scanning synchronization signal to the writing of the yellow image so that the shift amount ΔYy _S0 is equal to or less than the allowable sub-scanning writing position shift amount ε ₂ or less. . Similarly, the deviation amounts ΔYm _S0 and ΔYc _S0 are equal to the allowable amount ε ₂
Correction is performed as follows.

The main scanning magnification shift means an error in the length of the scanning line. This is caused by an error in the optical path length due to an adjustment error or mounting accuracy error of the optical device, a focal length error of the scanning lens, or the like. The main scanning partial magnification shift means a tilt in the depth direction of the photoconductor with respect to the optical device and a variation in fθ property of the scanning lens. This is due to processing errors, adjustment errors, mounting accuracy errors, and the like of the scanning lens. The main scanning magnification deviation is corrected by adjusting the main scanning partial magnification deviation. That is, if the partial magnifications match in the whole area, the total magnification also matches.

The variation in the fθ characteristic of the scanning lens does not appear as a deviation if the characteristics of the scanning lenses 611, 612, 621, and 622 are the same. In the case of a scanning lens molded from a resin material, deviation from fθ characteristics may occur due to molding distortion. However, if the gate side of the mold is matched in terms of molding technology, it can be kept within an allowable range. Therefore, the main scanning partial magnification error to be corrected, that is, the shift of the other color image with respect to the black image is mainly caused by the tilt of the photoconductor with respect to the optical device in the depth direction.

FIG. 5 shows that the main scanning partial magnification changes depending on the inclination of the photosensitive member with respect to the optical device in the depth direction.
This change is due to the fact that the rate of change of the main scanning partial magnification differs depending on the angle of incidence of the scanning beam on the photosensitive member surface. In the present embodiment, the difference in the inclination of the photoconductor in the depth direction with respect to the optical device (the difference between the black image and the other color image) is estimated from the shift amount of the image in the main scanning direction, and the optimal correction is performed.

More specifically, when correcting a yellow image, the number of image data to be thinned out or interpolated and their positions are determined by the combination of {(ΔXy _S0 −ΔXy _C0 ), (ΔXy _E0 −ΔXy _E0 )}. . A table in which the combination and the number and position of the image data to be thinned out or interpolated are prepared in advance, and the table is determined with reference to this table. The main scanning partial magnification is corrected by thinning out or interpolating the image data at the determined location (see FIG. 4).

Similarly, when correcting magenta and cyan images, {(ΔXm _S0 −ΔXm _C0 ), (ΔXm _E0 −ΔXm _E0 )} {(ΔXc _S0 −ΔXc _C0 ), (ΔXc _E0 −ΔXc _E0) ) The number and position of the image data to be thinned out or interpolated are determined by the combination of｝. The main scanning partial magnification of the magenta and cyan images is corrected by thinning out or interpolating the image data in the same manner as described above. When the shift amount is large and the correction range needs to be set wide, it is practical to divide the image data in the main scanning direction and uniformly change the magnification of the divided range.

The main scanning direction curvature is the curvature of the scanning line,
This bending deviation is caused by a processing error, an installation error, and an adjustment error of the optical element. Main scanning method inclination means that the scanning line is inclined with respect to the rotation axis of the photoconductor. This inclination shift is mainly caused by an installation error of the optical device and an installation error of the photosensitive drum. The curvature deviation in the main scanning direction and the inclination deviation in the main scanning direction are corrected by dividing the image data of one scanning line into a plurality of regions and shifting the writing timing for each region (writing one line of image with a plurality of scanning lines). I do. That is, the combination of {(ΔYy _C0 −ΔYy _S0 ), (ΔYy _E0 −ΔYy _S0 )} determines the amount of shift between the divided area of the image data of one scan line and the write timing. A table that specifies the combination, the divided area of the image data of one scan line, and the amount of timing shift is prepared in advance, and the table is determined with reference to this table. By changing the address of the image data in accordance with the determined divided area and the write timing, the curvature deviation and the inclination deviation are corrected (see FIG. 6). Magenta and cyan images are similarly corrected.

The curvature deviation in the sub-scanning direction is determined by writing in the main scanning direction.
Position of the transfer belt 10 with respect to the
It is caused by This is mainly due to the transfer belt 10
Due to meandering. The deviation in the sub-scanning direction is caused by the optical sensor SO.
Start writing the image based on the detection signals of S1 and SOS2.
To change the time before starting for each scan line
Therefore, correction is made. For more information,
The amount of misalignment of the yellow pattern with respect to the main scanning direction
Respectively, ΔXy_S0, ΔXy_S1..... DELTA.Xy_SnAnd Supplement
The line to be corrected is pattern Y_SjAnd Y_{Sj + 1}Be between
And the pattern Y _SjCorrection amount Δ of the i-th line from the tip position of
Xy_jiIs obtained by the following equation (1), and the optical sensors SOS1, SOS
Change the image writing start time from the generation of the detection signal 2
to correct. ΔXy_ji= ΔXy_Sj-ΔXy_S0+ (ΔXy_{Sj + 1}-ΔXy_Sj) × (i / m) (1) Magenta and cyan images are similarly corrected.

The sub-scanning magnification deviation and the sub-scanning partial magnification deviation are as follows:
This is caused by uneven speed of the transfer belt, a relative rotational speed difference of the photosensitive drum, and the like. These are caused by rotational speed errors and uneven rotation of the drive motor, eccentricity of the rotating shaft of the photosensitive drum, diameter difference of the photosensitive drum, eccentricity of the transfer belt supporting roller, and the like. These magnification shifts are thinned out for each image data of one scan line, and corrected by interpolation. The positional deviation amount in the sub-scanning direction of the yellow pattern for black pattern, respectively, and _{ΔXy S0, ΔXy S1 ...... ΔXy Sn} . Correction target amount Ey ₁ is represented by the following formula (2). Ey ₁ = ΔYy _S1 −ΔYy _S0 (2)

[0035] by the correction target amount Ey ₁ value, determines the number and the location of the image data to be thinned or interpolated. Uncorrected amount .epsilon.y ₁ is given by the following equation (3), and the uncorrected amount .epsilon.y ₁ was added to the next section as a correction target amount. εy ₁ = Ey ₁ −P · k (3) P: pitch in the sub-scanning direction k: integer that minimizes | εy ₁ |

A table for determining the number of image data to be thinned out or interpolated and the position thereof based on the value of the correction target amount Ey ₁ is prepared in advance, and the table is determined by referring to this table. Magenta and cyan images are similarly corrected.

The image forming apparatus according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In particular, the present invention can be applied to a wide variety of image forming processes, such as an ink jet printer, in addition to a tandem type full-color process, as long as the device forms an image by superimposing images based on a plurality of image data.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a full-color laser printer according to an embodiment of the present invention.

FIG. 2 is a plan view showing a positional relationship between a resist pattern formed on a transfer belt and a line sensor in the printer.

FIG. 3 is a chart showing a position of a resist pattern with respect to a line sensor and a sensor output waveform.

FIG. 4 is a conceptual diagram showing a method for electrically correcting image data.

FIG. 5 is an explanatory diagram showing a change in a main scanning partial magnification.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Transfer belt 11-14 ... Laser diode 55, 56 ... Resist pattern line 91-94 ... Photoconductor drum 111-113 ... Detector _KS0 , _YS0 , _MS0 , _CS0 ... Resist pattern

Claims (1)

[Claims] 1. A plurality of recording units for visualizing an image based on respective image data, and a single transfer body for moving each image visualized by the plurality of recording units in one direction A transfer unit that performs multiple transfer onto the transfer unit; a resist pattern control unit that visualizes a resist pattern of a predetermined shape with the plurality of recording units and sequentially transfers the resist pattern onto the transfer body; and each resist transferred onto the transfer body. A detection unit for detecting a pattern, a correction control unit for calculating a shift amount of the resist pattern detected by the detection unit, and correcting a position of an image formed by the recording unit based on the shift amount, An image forming apparatus, wherein the resist pattern extends obliquely with respect to the moving direction of the transfer body and includes two lines having one intersection. .