JPH10148779A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect displacements of each image in high accuracy in an image forming device multiplex-transferring images formed by two or more image forming units. SOLUTION: This laser printer multiplex-transfers toner images formed by two or more image formation units on a transfer body 10. Resist patterns KS0 , YS0 , MS0 , CS0 , etc., are transferred on the transfer body 10 for each color multiplex-transferred. The transcript body 10 moves in the direction of an arrow b, and along with this movement, each resist pattern is detected by detectors 111, 112, 113. Each detector detects the resist pattern in a main scanning direction (a) by photoelectric transducers 251, 252 at two places.

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 Application Laid-Open No. 1-141746 proposes a method of detecting a registration mark extending in the main scanning direction and the sub-scanning direction by a CCD having a tilted arrangement. In Japanese Patent Application Laid-Open No. 4-131750, a registration mark is formed by a straight line extending in the main scanning direction and an oblique line extending obliquely, and this is detected by a single photosensor to determine the amount of displacement. A method of measuring and correcting has been proposed.

[0004]

However, in the former method, since the registration mark is read by a charge accumulation type CCD, the sampling period becomes large and the resolution as detection accuracy cannot be made fine. And the cost of the processing unit is greatly increased. On the other hand, the latter uses a non-integral sensor,
Although it is possible to avoid the problem caused by the sampling period, since the mark is detected at one point in the main scanning direction,
If the movement (sub-scanning direction) of the transfer body becomes uneven,
A problem occurs that the reading position is detected as an error in the main scanning direction.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of detecting a resist pattern with high accuracy by using non-integrating type detection means which is inexpensive and easy to control and process.

[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. Control means for sequentially transferring the resist pattern onto the transfer member, and detecting each of the resist patterns transferred onto the transfer member at two points in a direction (main scanning direction) orthogonal to the moving direction of the transfer member, and performing non-integral detection. Detecting means for outputting a value.

In the present invention, since a non-integrating type detecting means is used as a resist pattern detecting means, it is possible to obtain a temporally continuous detection output, a high pattern detection resolution, and control and detection data detection. Easy to process and inexpensive. Then, the resist pattern is moved by 2 in the main scanning direction.
By reading two detection intervals in the sub-scanning direction to detect at the location, the position of the resist pattern in the main scanning direction can be accurately detected even if the moving speed of the transfer body is uneven.

[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. Therefore, in the present embodiment, means for detecting the amount of displacement of each image,
Means is provided for correcting the position of the image formed by each unit in accordance with the detected positional shift amount. That is, a resist pattern having a predetermined shape is formed at a predetermined position for each unit, multiple transfer is performed on the transfer belt 10, the transferred resist pattern is optically detected, and the shift amount is calculated. The shape of the resist pattern is, as shown in FIGS. 1 and 2, a straight portion 55 extending in the main scanning direction, and two inclined portions extending obliquely in the left-right direction from the center of the straight portion 55. 56, 56.

The resist pattern is as shown in FIG.
Black patterns K _S0 , K _C0 , K _E0 , and yellow patterns Y _S0 , Y _C0 , Y at three locations at predetermined intervals in the main scanning direction a.
_E0 , magenta patterns M _S0 , M _C0 , M _E0 , and cyan patterns C _S0 , C _C0 , C _E0 are also formed at predetermined intervals in the sub-scanning direction b. Further, the patterns (K _S1 , Y _S1 , Y _S1) are located at the same position as K _S0 in the main scanning direction and at predetermined intervals in the sub scanning direction.
M _S1 , C _S1 ), (K _S2 , Y _S2 , M _S2 , C _S2 ),... (K
_Si , Y _Si , _MSi , _CSi ).

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 as shown in FIG. 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 of the curvature in the sub-scanning direction,
A shift in tilt in the main scanning direction, a shift in magnification in the sub-scanning direction, a shift in partial magnification in the sub-scanning direction, and the like occur 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. Each detector includes a light emitting element 211 and a photoelectric conversion element 25 as shown in FIG.
1, 252 and lenses 221, 241. The light radiated from the light emitting element 211 passes through the spot forming lenses 221 and 221 and, on the transfer belt 10, two small spots 231 and 231 separated by a predetermined distance in the main scanning direction.
32 are formed. The reflected light from the spots 231 and 232 passes through the condenser lenses 241 and 241 and passes through the photoelectric conversion element 2.
Light is condensed on 51 and 252. Photoelectric conversion elements 251, 25
Reference numeral 2 converts the amount of received light into an electric signal and outputs the electric signal to a signal processing unit. The outputs of the photoelectric conversion elements 251 and 252 change with time due to the difference in light reflectance between the background portion of the transfer belt 10 and each resist pattern. The signal processing unit compares the output voltage with a reference voltage for each color and performs binarization. The reference voltage is the signal level corresponding to the pattern of each color and the transfer belt 1
The signal level is set to an intermediate value between 0 and the signal level corresponding to the background portion. 4A and 4B show the binarized photoelectric conversion element 2
5 shows output signals 51 and 252.

The positional deviation is detected by measuring the amount of deviation of the image of another color from the image of the reference color. 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.

Next, a method of detecting a position shift will be described. The black pattern K _S0 in the detector 111 shown in FIG.
The relative amount of displacement ΔXy _S0 of the yellow pattern Y _{S0 in} the main scanning direction with respect to is represented by the following equation (1). ΔXy _S0 = α ₁ {(Tk ₁ −Tk ₂ ) − (Tk ₁ −Ty ₂ )} (1) α ₁ : constant Tk ₁ : time when the black pattern crosses the spot 231 Tk ₂ : time when the spot 232 crosses the black pattern Ty ₁ : Time when the yellow pattern crosses the spot 231 Ty ₂ : Time when the yellow pattern crosses the spot 232

The pattern K_S0And pattern Y_S0Side run of
Relative displacement ΔYy in the scanning direction _S0Is given by the following equation (2)
Is represented. ΔYy_S0= Α_Two(Tky₁+ Tky_Two) …… (2) α_Two: Constant Tky₁: Black pattern crosses spot 231
From the beginning until the tip of the yellow pattern reaches Tky_Two: Black pattern crosses spot 232
From when the tip of the yellow pattern reaches

Similarly, the relative displacement amounts ΔXm _S0 , ΔYm of the magenta pattern M _S0 and the cyan pattern C _S0.
S0 , ΔXc _S0 and ΔYc _S0 can be detected. Further, the positional shift amounts ΔXy _C0 , ΔYy _C0 , ΔXm _C0 , ΔYm _C0 , ΔXy _C0 , ΔYy _C0 , of each pattern in the other detectors 112, 113.
Xc _C0 , ΔYc _C0 , ΔXy _E0 , ΔYy _E0 , ΔXm _E0 , Δ
Ym _E0 , ΔXc _E0 , and ΔYc _E0 can be similarly detected.

The detection of the displacement will be described in more detail with reference to FIG. When Tk ₁ −Tk ₂ = 0, the center of the black pattern K _S0 coincides with the middle position between the spots 231 and 232. When Tk ₁ −Tk ₂ ≠ 0, the pattern K
_{S0 is} off. That is, when Tk ₁ −Tk ₂ <0, the pattern K _S0 is shifted to the left as shown in FIG. When Tk ₁ −Tk ₂ > 0, it is shifted to the right. Therefore, the deviation of the direction from the intermediate position of the pattern K _S0 by Tk ₁ -Tk ₂ value, the amount can be determined. This is the same for the yellow pattern Y _S0 and other patterns. That is, (Tk ₁ −T
_{k 2), (Ty 1 -Ty} 2) by that absolute position of the pattern can be _{determined, (Tk 1 -Tk 2) -} (Ty 1 -T
y ₂ ), the amount of positional deviation between the patterns in the main scanning direction can be determined.

In this embodiment, one pattern is detected at two places in the main scanning direction by two light receiving elements. However, when one pattern is detected at only one place by one element 252 (spot 232), the speed of the transfer belt 10 is increased. When unevenness occurs, a detection error increases. That is, the speed of the transfer belt 10 is changed from V to k
V, Ty ₂ becomes kTy ₂ and α ₁ (Tk ₂ −
kTy ₂ ) is detected as the amount of deviation of the pattern Y _{S0 in} the main scanning direction. However, in the present embodiment, k (Ty ₁ −Ty ₂ ) is obtained for the pattern Y _S0 , and the shift amount in the main scanning direction is α
₁ {(Tk ₁ −Tk ₂ ) −k (Ty ₁ −Ty ₂ )}. Comparing the two, | Ty ₁ −Ty ₂ | <Ty
_In this embodiment, the detection error due to the uneven speed of the transfer belt 10 is reduced to the timer value error level.

As described above, the relative positional deviation of the image includes the main scanning write position deviation, the sub-scan write position deviation, the main scanning magnification deviation, the main scanning partial magnification deviation, the main scanning direction curvature deviation, and the sub-scanning 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
The resist pattern is detected at two points in the main scanning direction at each location, and the amount of displacement in the main scanning direction and the sub-scanning direction is calculated, and optimal correction is performed.

The main scanning write start position shift is one scan line.
Error in the timing of writing image data for each
You. This is caused by adjustment errors and mounting accuracy errors of the optical device.
Cause. Is light reception signal of optical sensors SOS1 and SOS2 generated
By changing the time until the image is
Correct (see FIG. 6). In the present embodiment, the polygon scan
The deflection surface of the scanner 5 deflects the black and yellow scanning beams.
Deflects the magenta and cyan scanning beams
And the optical sensor S0S1 is black and yellow.
And the optical sensor SOS2 is provided for magenta and shear
It is provided for Therefore, ΔXy_S0Is set in advance
Ε ₁Below
Thus, the yellow image is generated from the light reception signal of the optical sensor SOS1.
Correction by changing the delay time until image writing
I do. Similarly, ΔXm_S0, ΔXc _S0Is ε₁Below
Make corrections as follows.

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 performed by changing the time from when the sub-scanning synchronization signal is generated until when the image is written (see FIG. 6). 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 ΔYy _S0 is equal to or less than the preset allowable amount ε _{2 of} the sub-scanning writing position shift amount.
Similarly, ΔYm _S0, ΔYc _S0 performs correction so that the epsilon ₂ or less.

The deviation in the main scanning magnification 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 shift 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. 7 shows that the main scanning partial magnification changes depending on the inclination of the photosensitive member in the depth direction with respect to the optical device.
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 between the inclination of the photoconductor in the depth direction with respect to the optical device is estimated from the amount of displacement of the image in the main scanning direction, and optimal correction is performed.

More specifically, when correcting a yellow image, ｛(ΔXy _S0 −ΔXy _C0 ), (ΔXy _E0 −ΔX
y _E0 ) The number and position of the image data to be thinned out or interpolated are determined by the combination of｝. 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. 6).

Similarly, when correcting magenta and cyan images, {(ΔXm _S0 −ΔXm _C0 ), (ΔXm _E0 −ΔXm _E0 )} {(ΔXc _S0 −ΔXc _C0 ), (ΔXc _E0 −ΔXc _E0) )｝
Determines the number of image data to be thinned out or interpolated and their positions. 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, {(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 caused by a temporal change in the position of the transfer belt with respect to the writing position in the main scanning direction. This is mainly due to the meandering of the transfer belt. The deviation in the sub-scanning direction is caused by the optical sensors SOS1, S
The correction is performed by changing the time from when the detection signal of the OS 2 is generated to when the writing of the image is started for each scanning line. Specifically, the amounts of displacement of the yellow pattern with respect to the black pattern in the main scanning direction are ΔXy _C0 , ΔXy _S1 ... ΔXy _Sn . Assuming that the line to be corrected is between the patterns Y _Sj and Y _{Sj + 1} , the correction amount ΔXy _ji of the i-th line from the leading end position of the pattern Y _Sj
Is calculated by the following equation (3), and the image writing start time is changed from the generation of the detection signals of the optical sensors SOS1 and SOS2 to make correction. _{ΔXy ji = ΔXy Sj = ΔXy S0} + (ΔXy Sj + 1 -ΔXy Sj) × (i / m) ...... (3) Magenta, also similarly corrected cyan image.

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 (4). Ey ₁ = ΔYy _S1 −ΔYy _S0 (4)

[0038] by Ey ₁ value, determines the number and the location of the image data to be thinned or interpolated. Uncorrected amount εy
₁ is given by the following equation (5), and the uncorrected amount εy ₁ is added to the next section to obtain a corrected target amount. εy ₁ = Ey ₁ −P · k (5) P: pitch in the sub-scanning direction k: integer that minimizes | εy ₁ |

The advance prepared in advance a table for determining the number and the location of the image data to be thinning or interpolating the correction target amount Ey ₁ value, it 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 changed 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 resist pattern formed on a transfer belt in the printer.

FIG. 3 shows a detector of the resist pattern, (A)
Is a plan view, (B) is a side view, (C) is a front view, and (D) is a perspective view.

FIG. 4 is a chart showing an output waveform of the detector.

FIG. 5 is an explanatory diagram of a detection state of a resist pattern.

FIG. 6 is a conceptual diagram showing a method for electrically correcting image data.

FIG. 7 is an explanatory diagram showing a change in the main scanning partial magnification.

[Explanation of symbols]

10 ... transfer belt 11 to 14 ... laser diode 91 to 94 ... the photosensitive drum 111 to 113 ... detector 251 and 252 ... pair of photoelectric conversion elements _{K S0 ~K Si, Y S0 ~Y} Si, M S0 ~M Si, C _S0 -C _Si ... resist pattern

Claims (3)

[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 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, An image forming apparatus, comprising: detecting means for detecting at two points in a direction orthogonal to the moving direction of the transfer body and outputting a non-integrated detection value. 2. The method according to claim 1, wherein the detecting unit detects the resist pattern at two locations in a direction orthogonal to the moving direction of the transfer body, and at two locations in the moving direction of the transfer body, and at four convenient locations. The image forming apparatus according to claim 1. 3. The resist pattern includes a linear portion extending in a direction orthogonal to a moving direction of the transfer body, and two inclined portions extending obliquely in the left-right direction from the center of the linear portion. The image forming apparatus according to claim 1, wherein: