JPH11160922A - Image forming device and its image adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device and an image adjusting method by which plural developer images are superposed on a sheet base material without deviation in a position. SOLUTION: Latent image patterns are respectively formed on photoreceptors 2c and 3m by using a mark on an endless belt 32. The latent image pattern is detected by a potential sensor 18. a time (time difference) from the time when the potential sensor detects the latent image pattern on the photoreceptor 2c until the potential sensor detects the latent image pattern on the photoreceptor 2m is found. Next, when an error exists between this time difference and previously decided reference time difference, a timing for starting toner image formation with respect to the photoreceptors 2c and 2m is adjusted so as to eliminate the error based on the time difference, for example.

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 which forms developer images on the outer peripheral surfaces of a plurality of photoreceptors, and superimposes these developer images on, for example, a sheet substrate to form an image. The present invention relates to an image adjusting method, and more particularly to an image forming apparatus and an image adjusting method in which a plurality of developer images are superimposed on the sheet substrate without displacement.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, a copying machine which creates a full-color image by superposing toner images of different colors on a sheet base material such as paper,
Printers are known.

However, in a full-color image forming apparatus, if a toner image of each color is not formed at a predetermined timing determined for each apparatus, a color shift (position shift) appears in a superimposed final image, and a full-color image is formed. Image quality is significantly impaired.

In order to solve the problem of color misregistration, in the image forming apparatuses described in JP-A-2-40667 and JP-A-3-1171, a pattern for measuring misregistration is formed on a transfer belt. Each color toner image is formed, and then this pattern is detected by a reflection type sensor to detect the positional deviation of each color toner image, and the image formation start timing of each color toner image is adjusted based on the detection result.

[0005]

However, in the case where a semiconductive belt manufactured by dispersing carbon in a resin or the like is used as the transfer belt, the surface of the transfer belt is black, and therefore, a yellow belt is used. Depending on the toner, it may be difficult to distinguish the pattern formed on the transfer belt from the belt, or it may be difficult to achieve high detection accuracy. In addition, there is a problem that the relative positional relationship between the toner images cannot be adjusted with high accuracy.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above problems, and an image forming apparatus according to the present invention comprises a first image forming unit and a second image forming unit. The first and second image forming sections form a rotatable photoreceptor and a developer image on the photoreceptor in cooperation with the photoreceptor according to an electrophotographic image forming method. Image forming means each having an image forming element; and first and second image forming units respectively opposed to the photoconductors of the first and second image forming units and corresponding to the first and second image forming units. And a transfer means for forming a transfer area, and an endless support member passing through the first and second transfer areas. The transfer means are formed on the photoreceptors of the first and second image forming sections, respectively. The developer image is transferred to the endless carrier member in the first and second transfer areas by the transfer means. It is to be transferred to a sheet substrate held on the endless carrier member.

The image forming apparatus may further include a mark formed on a part of the endless supporting member and having a different electric resistance value from other parts of the endless supporting member excluding the part. Patterns for forming first and second patterns corresponding to the marks on the photoreceptors of the first and second image forming units in the first and second transfer areas using the marks of the shape carrier member Creating means, pattern detecting means for detecting the first and second patterns, time difference calculating means for obtaining a difference between times when the pattern detecting means respectively detects the first and second patterns, and time difference calculating means From the time difference obtained by the means, the developer image creation start timings in the first and second image forming units are adjusted to the developer image created in the first and second image forming units by the endless carrier member or Nothing And control means for adjusting as are overlapped without displacement on the sheet substrate held on Jo bearing member, and a.

According to a first aspect of the present invention, there is provided an image adjusting method comprising: an endless support member; and a plurality of photosensitive members arranged opposite to the endless support member. Used in an image forming apparatus that creates an image by superimposing a plurality of developer images respectively created on the endless carrier member or on a sheet substrate held by the endless carrier member. Using the mark formed on the member,
A step of forming a corresponding pattern on the plurality of photoconductors, a step of detecting each pattern formed on the plurality of photoconductors, and a step of calculating a difference between times when the respective patterns are detected, Based on the obtained time difference, development on the respective photoconductors is performed such that the plurality of developers are overlapped without displacement on the endless support member or the sheet substrate held on the endless support member. Adjusting the timing of forming the agent image.

In the image forming apparatus and the image forming method, a latent image pattern formed on each of the plurality of photoconductors corresponding to the mark is used as the pattern, and the latent image pattern is detected by a potential detector. It may be.

Alternatively, a developer image formed on each of the plurality of photoconductors corresponding to the mark may be used as the pattern, and the developer image may be detected by an optical detector. .

In the image forming apparatus and the image forming method, the mark is either an insulating film formed on the endless supporting member or a hole formed by cutting a part of the endless supporting member. Is also good.

According to a second aspect of the present invention, there is provided an image adjusting method for an image forming apparatus for forming an image on an endless support member or a sheet substrate held by the endless support member. Forming a reference developer image on the photoreceptor of the first image forming unit, transferring the reference developer image to an endless carrier in a first transfer area, A step of transferring the transferred reference developer image onto the photoconductor of the second image forming unit in a second transfer area, and a step of detecting the reference developer image transferred to the second image forming unit And determining a time difference between a predetermined time related to the creation of the reference developer image in the first image forming unit and a time from the detection of the reference developer image in the second image forming unit. Based on the determined time difference, the first or The developer image creation start timing of at least one of the image forming units of the second and the second image forming units is set to the endless carrier member or the endless carrier member. Adjusting the sheet so as to be superimposed on the held sheet substrate without displacement.

[0013]

According to the image forming apparatus of the present invention described above, the pattern forming means uses the mark on the endless support member (for example, endless belt) to form the first image.
The first and second patterns (latent image or developer image) are formed on the photoconductors of the second and second image forming units, respectively. These first and second patterns are then detected by pattern detection means (potential detector or optical detector), respectively. The time (time difference) from when the pattern detecting means detects the first pattern to when the pattern detecting means detects the second pattern is obtained by the time difference calculating means. Then, based on the time difference, the control means, for example, if there is an error between the time difference and a predetermined reference time difference, the first and second image forming units so as to eliminate the error. To adjust the timing of starting the development of the developer image in step (1).

As described above, according to the image forming apparatus and the image adjusting method of the present invention, while the conventional image forming apparatus detects the toner image formed on the transfer belt, the image formed on each photosensitive member is detected. Since the pattern (latent image or developer image) is detected by the corresponding pattern detection means (potential detector or optical detector), each pattern can be detected with high accuracy, and therefore, color shift adjustment can be performed with high accuracy. Also,
In a mode in which the latent image pattern is detected by the potential detector, the developer is not wastefully consumed.

[0015]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a main part of a full-color image forming apparatus (for example, a copying machine or a printer). The image forming apparatus 1 includes four image forming units 2 (2c,
2m, 2y, and 2k), and each image forming unit 2 includes a photoconductor 4 (4c, 4m, 4y, and 4k). Other known photoconductors (for example, a belt-type photoconductor) can be used as the photoconductor 4, but in the present embodiment, a metal cylindrical drum-shaped organic photoconductor that is negatively charged is used. Further, in the present embodiment, each photoconductor 4 has the same configuration and size, is arranged in parallel on a single horizontal plane at a predetermined interval, and is individually driven by a motor (not shown) in the direction of the arrow (clockwise in the drawing). (Rotational direction) at a constant speed.

Around each photoconductor 4, a plurality of image forming elements—a charging device 8, an exposure device 10, a developing device 12, a cleaning device 14, and a neutralization device 16 —are arranged along the rotation direction of the photoconductor 4. They are arranged in this order. Exposure device 1
0 and a developing device 12, a potential sensor 18 for detecting an outer peripheral surface potential of the photoconductor 4 is disposed, and a photoconductor 18 is provided downstream of the developing device 12 in the photoconductor rotation direction and upstream of the cleaning device 14 in the photoconductor rotation direction, respectively. A first optical sensor 20 for detecting a developer image formed on the outer peripheral surface of the body 4;
Of optical sensors 22 are arranged. In this embodiment,
The positional relationship between the image forming element and the sensor with respect to the photoconductor 4 is the same in each image forming unit 2.

More specifically, each of the image forming elements and the like will be described. The charging device 8 charges the outer peripheral surface of the photosensitive member 4 to a predetermined potential, and uses a scorotron or a non-contact discharger of a corotron. However, the charging device 8 is not limited to this, and other known charging devices, for example, a contact-type charger such as a brush roller or a blade may be used.

A known laser optical system that emits a laser based on digital image information is preferably used as the exposure device 10. The exposure device 10 exposes the charged area of the photoconductor 4 charged by the charging device 8 to the laser to expose the image information. To form a latent image corresponding to.

The developing device 12 is a known developing device using a so-called one-component developer or a two-component developer. The developing devices 12 for the image forming units 2c, 2m, 2y, and 2k are respectively cyan, magenta, and yellow. Contains black toner. Each developing device 12 also includes a developing roller 24. The developing roller 24 is connected to a developing bias power supply 26 so that a predetermined developing bias can be applied to the developing roller 24. Based on a potential difference between the developing bias and the surface potential of the photoconductor 4, the developing roller 24 Toner (in the present embodiment, toner charged to a negative polarity) is supplied to the body 4 to form a developer image, that is, a toner image. In order to avoid complicating the drawing, only the developing bias power supply 26 of the image forming unit 2c at the right end in the drawing is shown, and the other image forming units 2m, 2y and 2k are shown.
Are omitted from the drawing.

The cleaning device 14 has a blade 28. The blade 28 is arranged in parallel with the photoconductor 4,
One end side is fixed, and the other free end side corner is in pressure contact with the outer peripheral surface of the photoconductor 4 so that untransferred toner is removed from the photoconductor 4. The cleaning device 14 is not limited to a blade-type cleaning device, but may use another type (for example, a rotating brush type or a fixed brush type) of cleaning device. In the case of an image forming section in which the untransferred toner is collected in the developing device, this cleaning device is unnecessary.

A lamp is used as the static eliminator 16,
The surface of the photoreceptor before charging is illuminated to remove the residual charge and prepare for the next charging. The static eliminator 16 may use another type of static eliminator (for example, a corotron or scorotron type static eliminator or a blade or brush type static eliminator).

The potential sensor 12 detects the potential of the outer peripheral surface of the photoreceptor, and is used for detecting a latent image pattern (described in detail below) formed on the outer peripheral surface of the photoreceptor 4.

The optical sensors 20 and 22 generally include a light-emitting element and a light-receiving element, irradiate the light emitted from the light-emitting element to the outer peripheral surface of the photoconductor 4, and detect the reflected light by the light-receiving element. The intensity of the light detected by the light receiving element is obtained, and is used for detecting a developer pattern obtained by developing the latent image pattern.

A transfer device 30 is provided below the photoreceptor 4 (4c, 4m, 4y, 4k). The transfer device 30 has an endless carrying member, that is, an endless belt 32. The belt 32 is made of an insulating film such as polyvinylidene fluoride or polyethylene terephthalate, or a film (thickness) of about 108-1012 Ω · cm obtained by dispersing carbon in a resin base material containing fluorine or polycarbonate to impart conductivity. About 75-150 μm) is preferably used. The belt 32 is also driven by a pair of rollers (a driving roller 36 and a driven roller 38) disposed inside the belt 32.
0). Drive roller 36
Is connected to a motor (not shown) so as to rotate in the direction of the arrow (counterclockwise in the drawing) based on the driving of the motor.

As shown in FIG. 2, a coating made of an insulating material is applied to the inner peripheral surface of the belt 32 or an insulating film is adhered to the inner surface of the belt 32 so as to have a predetermined size (for example, a width). 1
mm, the length of which is 20 mm), that is, the mark 42 is formed so that its longitudinal direction coincides with the width direction of the belt 32, so that the impedance in the thickness direction of the belt portion 321 on which the mark 42 is formed is other than that. Of the belt portion 322 in the thickness direction. The size, shape and arrangement direction of the mark 42 are as follows.
It is not limited to this embodiment.

Returning to FIG. 1, inside the belt 32, the belt 32 is connected to each of the photosensitive members 4 (4c,
4m, 4y, and 4k) are provided. Each transfer roller 44 (44c, 44m, 44
(y, 44k) are connected to a transfer bias power supply 46 so that the transfer bias applied to the transfer roller 44 can be switched to a different value.

In the vicinity of the driven roller 38, the driven roller 3
A paper feed guide 50 for feeding the sheet base material 48 is provided on the outer periphery of the upper belt portion moving from 8 to the drive roller 36. A charging roller 5 for charging the sheet base material 48 supplied to the upper belt portion to a predetermined polarity as described above is provided above the driven roller 38.
2 are provided. A belt cleaning device 54 is provided near the belt portion supported by the driven roller 38. The belt cleaning device 54 includes a blade 56, and one end of the blade 56 can be brought into contact with and separated from the outer peripheral surface of the belt 32.

On the other hand, in the vicinity of the drive roller 36, the electric attraction between the belt 32 and the sheet base 48 supported by the belt 32 is removed to remove the belt 32 and the sheet base 4 from the belt 32.
There are provided a charge removing roller 58 for separating the sheet 8 and a roller pair 60 for conveying the sheet base material separated from the belt 32 to the next step.

The image forming operation of the image forming apparatus 1 having the above configuration will be described. At the time of image formation, each photoconductor 4 (4c,
4m, 4y, 4k) rotate in the direction of the arrow, and the outer peripheral surface of each of the charging devices 8 has a predetermined potential (for example, −600).
V). Next, each photoconductor 4 (4c, 4m, 4
On the outer peripheral surfaces of (y, 4k), image light corresponding to the colors of cyan, magenta, yellow, and black is exposed by the exposure device 10, respectively, and latent images corresponding to these image lights are formed. Next, the photoconductor 4 (4c, 4m, 4
In the latent images on (y, 4k), negative toners of cyan, magenta, yellow, and black colors are supplied from the developing device 12 to their exposed portions (potential attenuating portions), respectively, and visible images are formed as toner images. Be transformed into

Here, the development is performed on the photosensitive member 4 (4c, 4m,
4y, 4k) and the respective developing rollers 38
(For example, -300 V)
The toner is charged to the negative polarity from the developing device 12 on the basis of the potential difference between the toner and the toner.

Sheet base material 48 to which the toner image is transferred
Is guided by the paper feed guide 50 and supplied onto the upper belt portion. Above the sheet substrate 48 that has reached the belt 32, the charging roller 52 is activated, whereby the sheet substrate 48
A positive charge is injected into the. Next, the sheet substrate 48 is conveyed with the rotation of the belt 32, and the respective photoconductors 4 (4c,
4m, 4y, and 4k) pass through the transfer position 40 (40c, 40m, 40y, and 40k) in contact with the belt 32.

The sheet base 48 is transferred to the transfer position 40 (40c,
40m, 40y, and 40k), a positive voltage (+2000 V) is applied to each of the transfer rollers 44 (44c, 44m, 44y, and 44k).
The negative toner images (cyan, magenta, yellow, and black toner images) formed on (4c, 4m, 4y, and 4k) are sequentially electrically attracted to the sheet base 48 and are then transferred onto the sheet base 48. Can be stacked. As described above, the sheet base material 48 on which all the toner images have been transferred has its charge removed by the discharge of the charge removing roller 58 on the drive roller 36,
After being released from the electric attraction to the belt 32, the belt 32 is separated from the belt 32 by its own stiffness and is conveyed by a roller pair 60 to a fixing step (not shown), where the toner image is transferred to the sheet substrate. 48 is permanently fixed. On the other hand, the portion of the belt 32 separated from the sheet base material 48 is a driven roller 38
At the contact area with the cleaning blade 56, deposits such as paper dust are removed by the cleaning blade 56.

The toner image formed on the outer periphery of the photosensitive member 4 is not completely transferred to the belt 32, and untransferred toner exists on the outer peripheral portion of the photosensitive member 4 after passing the transfer position 40. The untransferred toner is scraped off from the photoconductor 4 by the blade 28 of the cleaning device 14 as the photoconductor 4 rotates. The outer peripheral portion of the photoreceptor 4 from which the untransferred toner has been removed is then subjected to residual charge removal by the charge removing device 16 to prepare for the next image formation.

FIG. 3 shows a control (position shift adjustment) for eliminating a position shift (color shift) of a plurality of toner images superimposed on the belt 32 and a configuration for executing this control.
This will be described with reference to FIGS. FIG. 3 shows a control circuit for adjusting the displacement, and the control device 70 includes the potential sensor 1 described above.
8, optical sensors 20 and 22 are connected, and output signals of these sensors 18, 20 and 22 are input to the controller 70. The controller 70 also includes
A read-only memory (ROM) 72, a random access memory (RAM) 74, and a timer 76 are connected, and these functions will be described below together with the processing contents of the displacement adjustment.

This displacement adjustment is performed during non-image formation (immediately before starting the image forming operation or after the image forming operation is completed).
Or during a continuous image forming operation).
More specifically, with reference to FIG. 4, in the positional deviation adjustment, first, a latent image pattern 78 is formed on the outer peripheral surface of each photoconductor 4 using the mark 42 provided on the inner peripheral surface of the belt 32. Specifically, first, the charging device 8 and the static eliminator 18 are set to the operating state while each photoconductor 4 is rotating, and the outer peripheral surfaces of these photoconductors 4 are set to a predetermined negative potential (for example, −60).
0V). Next, a bias (+500 V in the present embodiment) of a voltage different from that at the time of the above-described image formation is applied to each transfer roller 44 from a transfer bias power supply 46 to rotate the belt 32, and each charged photoconductor is charged. The belt portion 321 holding the mark 42 is brought into contact with the outer peripheral surface of the belt 4. Here, since the belt portion 321 holding the mark 42 has a higher impedance than the other belt portions 322, the current flowing from the transfer roller 44 to the corresponding portion of the photoconductor 4 through the belt portion 321 holding the mark 42 is Belt portion 322 not holding mark 42
Is smaller than the current flowing from the transfer roller 44 to the corresponding portion of the photoconductor 4 through the transfer roller 44. As a result, the photosensitive member portion 401 in contact with the belt portion 321 holding the mark 42 is charged to a higher voltage on the negative polarity side than the photosensitive member portion 402 in contact with the belt portion 322, whereby the latent image corresponding to the mark 42 is formed. A pattern 78 (see FIG. 5) is formed. next,
When the formation of each latent image pattern 78 is completed, the control device 70
Denotes a charging device 8 and a static elimination device 16 of each image forming unit 2.
Turn off. Thus, the formed latent image pattern 78
Is not erased.

The latent image pattern 78 is detected by the potential sensor 18, and the detection result is transmitted to the control device 70.
Photoconductor 4 detected by potential sensor 18 of each image forming unit 2
Are shown in FIG. 6 and voltage peaks (voltage drop portions) Mc1, Mm1, and My1 in each potential graph.
Image pattern 7 on which each of Mk1 and Mk1 has been formed
8 is shown.

Next, the control device 70 detects the voltage peak Mc1 from the potential sensor 18 of the image forming section 2c, and starts the timer 76 when the voltage peak Mc1 is detected. Subsequently, the potential sensors 1 of the other image forming units 2m, 2y, and 2k
When detecting the voltage peaks Mm1, My1 and Mk1 from FIG. 8, the control device 70 measures the actual measurement times Tm1 ′, Ty1 ′ and Tk1 ′ from the detection of the voltage peak Mc1 to the detection of the other voltage peaks Mm1, My1 and Mk1. Respectively.

As described above, the actual measurement times Tm1 ', Ty1' and Tk1 'depend on the positional relationship between the belt 32 and the photoconductor 4 and the potential sensor 18 in each image forming section 2, and the rotation of each photoconductor 4 Assuming that the speeds are completely the same, the speeds should coincide with certain values (reference times) Tm1, Ty1, and Tk1 obtained in advance by calculation. However, in reality, each photoconductor 4 has its own dimensional error, mounting error, and rotational speed error. for that reason,
The actually measured times Tm1 ', Ty1', and Tk1 'include time errors tm1, ty1, and tk1. That is,
Between the measured time, the reference time and the time error, Tm1 '=
Tm1 + tm1, Ty1 '= Ty1 + ty1 and Tk
1 ′ = Tk1 + tk1 holds.

Therefore, in the present control circuit, the reference time T
m1, Ty1, and Tk1 are stored in the ROM 72, and the control device 70 reads the reference time Tm from the ROM 72.
1, Ty1 and Tk1 are read, and
Time errors tm1 and t1 with respect to m1 ', Ty1' and Tk1 '
y1, tk1 are obtained, and the time errors tm1, ty1, t
k1 is stored in the RAM 74. And the control device 70
Are the time errors tm1, ty1, t
Using k1, the exposure start timing of the exposure device 10 is adjusted so that the toner images superimposed on the belt 32 completely match.

The above adjustment operation may be repeatedly performed until the measured time errors tm1, ty1, and tk1 fall within predetermined ranges, respectively. In this case, the positional deviation is adjusted with higher accuracy. (Correction).

FIG. 7-9 shows a second embodiment of the displacement adjustment.
This will be described with reference to FIG. In this embodiment, in order to form a latent image pattern on the photoconductor 4, a hole 82 obtained by cutting a part of the belt 32 is used as a mark instead of the mark of the first embodiment. The hole 82 has a size of, for example, about 1 mm in width and about 20 mm in length, and is preferably formed so that the longitudinal direction thereof is oriented in the width direction of the belt 32. It is not limited to.

When adjusting the displacement, first, the charging device 8 and the static eliminator 18 are turned on while rotating each photoconductor 4, and the outer peripheral surface of the photoconductor 4 is exposed to a predetermined negative potential (for example, −600).
V), and a transfer bias power supply 46
+ 100V is applied. Here, the impedance at the position of the hole 82 is lower than the impedance of the belt portion other than the hole 82. As a result, the holes 82 of the belt 32
A larger amount of current flows into each photoreceptor portion 411 in contact with the belt portion except the holes 82 than the photoreceptor portion 412 facing the belt portion, and the photoreceptor portion 411 has a potential different from that of the photoreceptor portion 412. 84 is formed (FIG. 8).
reference). When the formation of each latent image pattern 84 is completed, the control device 70 turns off the charging device 8 and the charge removing device 16 of each image forming unit 2. As a result, the formed latent image pattern 84 is not erased.

Next, the latent image pattern 84 on each photoconductor 4 is detected by each potential sensor 18. FIG. 9 shows the potential of the outer peripheral surface of the photoconductor 4 detected by the potential sensor 18 of each image forming unit 2, and the voltage peaks (voltage rising portions) Mc2, Mm2, My2, and Mk2 in each potential graph are represented by the respective photosensitive elements. The potential of the latent image pattern 84 formed on the body 4 is shown.

Subsequently, the controller 70 detects the voltage peak Mc2 from the potential sensor 18 of the image forming section 2c, and starts the timer 76 when the voltage peak Mc2 is detected, as in the above embodiment. Next, the other image forming units 2m, 2m
y, 2k, voltage peaks Mm2, M from the potential sensor 18
When detecting y2 and Mk2, the control device 70 sets the other voltage peaks Mm2 and My2 from the detection of the voltage peak Mc2.
And the actual measurement times Tm2 ′ and Ty2 ′ until the detection of Mk2.
And Tk2 ′, respectively. Further, the control device 70 reads the reference times Tm2, Ty2, and Tk2 from the ROM 72, and reads the reference times Tm2 ', Ty2', and Tk2.
The time errors tm2, ty2, and tk2 from 2 ′ are obtained, and the time errors tm2, ty2, and tk2 are stored in the RAM 74. Finally, the control device 70 uses the time errors tm2, ty2, and tk2 to form the belt 3 during the subsequent image formation.
The exposure start timing of the exposure device 10 is adjusted so that the toner images superimposed on 2 completely match. If necessary, the control device 70 sets the time errors tm2, ty2, tk2
Is repeated until the value falls within a predetermined range.

In the above two embodiments, a latent image pattern was formed on each photoreceptor 4 and the position was corrected by detecting the latent image pattern with a potential sensor. The positional deviation may be corrected by visualizing the image as an image and detecting the image with an optical sensor 20 disposed downstream of the developing device 12.

For example, in the present embodiment, the above-described hole 82
The image forming conditions of each image forming unit 2 are set the same as in the second embodiment using the belt 32 having Specifically, the charging device 8 and the static eliminator 18 are turned on while rotating each of the photoconductors 4 while rotating the belt 32 to bring the outer peripheral surfaces of these photoconductors 4 to a predetermined negative potential (for example, −600 V). The transfer roller 44 is charged by +10
0 V is applied. Here, since the impedance at the position of the hole 82 is lower than the impedance of the belt portion other than the hole 82, the latent image pattern in which the photosensitive member portion 411 has a different potential from the photosensitive member portion 412 is provided on each photosensitive member 4. 8
4 (see FIG. 10) is formed.

Next, in each image forming section 2, a toner charged negatively on the latent image pattern 84 is electrically attached to the photosensitive member portion 411 by the corresponding developing device 12 to form a toner image. Each of the developed toner images is stored in each of the image forming units 2.
Is detected by the optical sensor 20. The potential on the outer peripheral surface of the photoconductor 4 detected by the optical sensor 20 of each image forming unit 2 is shown in FIG.
1, voltage peaks (voltage rising portions) Mc3, Mm3, My3 and Mk3 in each potential graph represent the potential of the toner image formed on each photoconductor 4.

As in the case of the above embodiment, the control device 70 sets the actual measurement time Tm from the time when the voltage peak Mc3 is detected to the time when the other voltage peaks Mm3, My3 and Mk3 are detected.
3 ′, Ty3 ′ and Tk3 ′ are obtained, respectively,
2, the reference times Tm3, Ty3 and Tk3 are read,
The time errors tm3, ty3, and tk3 from the actually measured times Tm3 ', Ty3', and Tk3 'are obtained, and the time errors tm3,
ty3 and tk3 are stored in the RAM 74, and the time error tm3, ty3 and tk3 are used to form the belt 3 during the subsequent image formation.
The exposure start timing of the exposure device 10 is adjusted so that the toner images superimposed on 2 completely match. If necessary, the control device 70 sets the time errors tm3, ty3, t
The above processing steps are repeated until k3 falls within a predetermined range.

In the above embodiment, a latent image pattern or a toner image is formed on the photoreceptor 4 of each image forming unit 2 and detected by the corresponding potential sensor or optical sensor of the image forming unit 2 to determine the position. Although the misalignment was adjusted, the toner image created on the photoconductor of one image forming unit was transferred to the photoconductor of another image forming unit, and the transferred toner image was detected by the other image forming unit. By doing so, it is also possible to perform the displacement adjustment.

In this embodiment, the outer peripheral surface of the photosensitive member 4 is charged to a predetermined potential (for example, -600 V) by driving the charge removing device 16 and the charging device 8 in each image forming section 2. Next, the first to third image forming units 2 (2c, 2m, 2y)
In other words, except for the fourth image forming unit 2 (2k),
The reference image is exposed from the exposure device 10 to form a reference latent image on the photoconductor 2, and is developed by the corresponding developing device 12 to obtain a toner image (reference developer image). The toner image is
For example, a photoreceptor having a length of about 20 mm in the axial direction and a length of about 4 dots in the rotation direction of the photoreceptor is preferably formed, but its size, shape, arrangement, etc. are limited to those described above. It is not done. Further, each image forming unit 2 (2
c, 2m, and 2y), the image formation is different. First, image formation is started in the first image forming unit 2 (2c), and after a predetermined time, the image is formed in the second image forming unit 2 (2m). Start forming. Similarly, the second image forming unit 2 (2
The image formation in the third image forming unit 2 (2y) is started after the predetermined time has elapsed since the image formation was started in m).

Next, the first to third image forming units 2 (2
c, 2m, and 2y) are transferred to the belt 32 at the corresponding transfer positions 40. At this time, the voltage applied to each transfer roller 44 is + 500V.
The toner image transferred to the belt 32 is conveyed together with the rotation of the belt 32, and these photoconductors 4 (at the transfer position 40 of the adjacent image forming unit 2 (2 m, 2 y, 2 k) on the downstream side in the rotation direction of the belt 32 are transferred. 4m, 4y, 4k). During this transfer, the transfer roller 42 has a voltage of -1000 V
Is applied to the photosensitive member 2 (2m, 2y, 2k) charged to -600V, so that the negative toner image is electrically attracted and adhered. Photoconductor 2 (2m, 2y, 2
The toner image attached to k) is conveyed with the rotation of the photoconductor, and is detected by the optical sensor 22.

The potential of the outer peripheral surface of the photosensitive member 4 detected by the optical sensor 22 of the image forming section 2 (2m, 2y, 2k) is shown in FIG.
2, voltage peaks (voltage rising portions) Mm4, My4, and Mk4 in each potential graph represent the potential of the toner image formed on each photoconductor 4. Also, in the drawing, each of the image forming units 2 (2c, 2m, 2y) has an image formation start time Sc4, Sm4, Sy4, and a downstream image adjacent to the image formation start time Sc4, Sm4, Sy4. Measurement time Tm4 ', Ty until the optical sensor 22 of the forming unit 2 (2m, 2y, 2k) detects the corresponding toner image.
4 ′ and Tk4 ′ are indicated.

Then, the control device 70 sets the actual measurement time T
m4 ', Ty4', and Tk4 ', respectively,
72, the reference times Tm4, Ty4 and Tk4 are read, and the time error tm between these reference times Tm4, Ty4 and Tk4 and the actually measured times Tm3 ', Ty3' and Tk3 '.
3, ty3, tk3 are obtained, and the time errors tm3, ty
3, tk3 are stored in the RAM 74, and the exposure start timing of the exposure device 10 is adjusted using the time errors tm3, ty3, and tk3 during the subsequent image formation so that the toner images superimposed on the belt 32 completely match. If necessary, the control device 70 sets the time errors tm3, ty3, tk3
Is repeated until the value falls within a predetermined range.

In this embodiment, the latent image pattern is created by exposure from the optical system 10 in the same manner as in the normal image forming operation. However, as in the first to third embodiments, the latent image pattern is formed on the belt. The latent image pattern may be formed on the required photoreceptor 2 using the above method.

In the above, four image forming units 2 (2c, 2c, 2c)
Although an example in which the present invention is applied to an image forming apparatus having (m, 2y, 2k) is shown, the present invention can be applied to any image forming apparatus having two or more image forming units.

For the sake of simplicity, the positional relationship of the image forming elements in each image forming unit is the same as that in the other image forming units, but the positional relationship of the image forming elements in each image forming apparatus is different. May be different from that of the image forming unit.

Further, the endless carrying member is not limited to the endless belt, but may be a rigid cylindrical body.

Further, in the above description, the sheet base material is held around the endless belt, that is, the endless support member,
The final image was created by superimposing a plurality of toner images on this sheet substrate.First, a plurality of toner images were superimposed directly on the endless carrier, and then the superimposed composite toner image was transferred to the sheet substrate. The present invention is also applicable to an image forming apparatus that performs the above.

In the above description, only one mark is provided on the outer periphery of the endless belt, that is, the endless carrying member. However, marks corresponding to each image forming portion are provided.
A latent image pattern or a developer image may be formed on the photoconductor of the corresponding image forming unit using these marks. Even in this case, since the positional relationship between the plurality of marks formed on the belt is determined in advance, the positional deviation can be eliminated by adjusting the image forming start time in each image forming unit using the data. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an image forming apparatus according to the present invention.

FIG. 2 is a partial perspective view of the belt, showing marks formed on the belt.

FIG. 3 is a diagram of a control circuit for implementing the image adjustment method according to the present invention.

FIG. 4 is a perspective view of a photoconductor and a belt for explaining the first embodiment.

FIG. 5 is a potential diagram of a latent image pattern formed on a photoreceptor in the first embodiment.

FIG. 6 is a voltage waveform output from each potential sensor in the first embodiment.

FIG. 7 is a perspective view of a photoconductor and a belt for describing a second embodiment.

FIG. 8 is a potential diagram of a latent image pattern formed on a photoconductor in a second embodiment.

FIG. 9 is a voltage waveform output from each potential sensor in the second embodiment.

FIG. 10 is a potential diagram of a latent image pattern formed on a photoreceptor in a third embodiment.

FIG. 11 is a voltage waveform output from each potential sensor in the third embodiment.

FIG. 12 is a voltage waveform output from each potential sensor in the fourth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2c, 2m, 2y, 2k ... Image forming part, 4c, 4m, 4y, 4k ... Photoconductor, 18 ... Potential sensor, 30 ... Transfer device, 42 ... Mark.

Claims (11)

[Claims] 1. An image forming apparatus comprising: a first image forming unit and a second image forming unit, wherein the first and second image forming units are rotatable by a photosensitive member and an electrophotographic image forming method. Image forming means each including an image forming element for forming a developer image on the photoconductor in cooperation with the photoconductor, and opposing the photoconductors of the first and second image forming units, respectively. A transfer unit that forms first and second transfer areas corresponding to the first and second image forming units; and an endless carrier that passes through the first and second transfer areas. The developer images formed on the photoconductors of the first and second image forming units are held by the endless carrier or the endless carrier in the first and second transfer areas by the transfer means. An image forming apparatus configured to transfer the image on a sheet substrate, wherein a part of the endless supporting member is A mark formed and having a different electric resistance value from the other portion of the endless carrier except for a part thereof; and a mark of the endless carrier using the mark of the endless carrier in the first and second transfer areas. Pattern creating means for creating first and second patterns respectively corresponding to the marks on the photoreceptors of the first and second image forming units; and pattern detecting means for detecting the first and second patterns. A time difference calculating means for calculating a difference between times when the pattern detecting means detects the first and second patterns, respectively, and a developer image in the first and second image forming units based on the time difference calculated by the time difference calculating means. The developer start timings of the developer images formed in the first and second image forming units are overlapped without displacement on the endless carrier member or the sheet substrate held on the endless carrier member. An image forming apparatus comprising control means for adjusting, in that it comprises a so. 2. The first and second patterns correspond to the first and second marks in the first and second transfer areas.
A first and a second latent image pattern formed on the photosensitive member, respectively, wherein the pattern detecting means is a first and a second potential detector provided in the first and the second image forming units, respectively. 2. The image forming apparatus according to claim 1, wherein the first and second potential detectors detect the first and second latent image patterns, respectively. 3. The first and second patterns correspond to the first and second marks in the first and second transfer areas.
First and second developer images obtained by visualizing the first and second latent image patterns respectively formed on the photoreceptor by the image forming elements of the first and second image forming units, respectively. The pattern detecting means has first and second optical detectors provided in the first and second image forming units, and the first and second optical detectors are provided.
2. The image forming apparatus according to claim 1, wherein the optical detector detects the first and second developer images, respectively. 4. The image forming apparatus according to claim 1, wherein the mark is an insulating film formed on the endless supporting member. 5. The mark according to claim 1, wherein the mark is a hole formed by cutting off a part of the endless carrier.
4. The image forming apparatus according to any one of claims 1 to 3, 6. An endless supporting member, and a plurality of photoconductors arranged opposite to the endless supporting member, and a plurality of developer images respectively formed on the plurality of photoconductors are transferred to the plurality of developer images. In an image adjusting method of an image forming apparatus for creating an image by overlapping an endless supporting member or a sheet base material held on the endless supporting member, the mark is formed on the endless supporting member. Forming a corresponding pattern on the photoreceptor, detecting each pattern formed on the plurality of photoreceptors, and obtaining a difference between times when the respective patterns are detected. The developer applied to each photoconductor so that the plurality of developer images are superimposed on the endless support member or the sheet substrate held on the endless support member without displacement based on the difference in time. Image creation And the step of adjusting the timing,
An image adjustment method comprising: 7. The method according to claim 1, wherein the pattern is a latent image pattern formed on each of the plurality of photoconductors, and the step of detecting the pattern includes detecting the latent image pattern using a potential detector. The image forming apparatus according to claim 6. 8. The method according to claim 1, wherein the pattern is a developer image formed on each of the plurality of photoconductors, and the step of detecting the pattern includes detecting the developer image using an optical detector. The image forming apparatus according to claim 6. 9. The image forming apparatus according to claim 6, wherein the mark is an insulating film formed on the endless supporting member. 10. The image forming apparatus according to claim 6, wherein the mark is a hole formed by cutting off a part of the endless supporting member. 11. An image forming apparatus for forming an image by superimposing a plurality of developer images respectively created by a plurality of image forming units on an endless carrying member or a sheet base material held by the endless carrying member. In the image adjusting method, a step of forming a reference developer image on a photoreceptor of a first image forming unit; a step of transferring the reference developer image to an endless carrier in a first transfer area; Transferring the reference developer image transferred to the shape support member onto a photoconductor of a second image forming unit in a second transfer area; and transferring the reference developer image to the second image forming unit. And a time difference between a predetermined time related to the creation of the reference developer image in the first image forming unit and a time from the detection of the reference developer image in the second image forming unit. The process of finding and the time difference The developer image creation start timing of at least one of the first and second image forming units is changed to the timing in which the developer images created in the first and second image forming units are respectively supported by the endless carrier. Adjusting the sheet or the sheet substrate held on the endless support member so that the sheet is superimposed on the sheet substrate without displacement.