JPH10142880A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct color smear with high accuracy, regardless of the present of a transfer material. SOLUTION: The image forming device provided with plural photoreceptor drums 1 and a transfer belt 7, to successively transfer single color toner images formed on each photoreceptor drum 1 to the transfer material (P) on the transfer belt 7 is premised. In such a case, the image forming device is provided with a color smear correcting means for forming a color smear correcting pattern on a specified paper sheet (P), so as to adjust the operations of the photoreceptor drums 1 and the transfer belt 7, based on the pattern, when the paper (P) is set in the image forming device and on the transfer belt 7, so as to adjust the operations of the photoreceptor drums 1 and the transfer belt 7, based on the pattern, when the paper (P) is not present.

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 used for a color copying machine, a color printer, and the like. More specifically, the present invention relates to a method for superposing a plurality of single color toner images on a transfer material and transferring the multicolor toner image. The present invention relates to an image forming apparatus that forms a color image on a transfer material by fixing the color image on a transfer material.

[0002]

2. Description of the Related Art Conventionally, the above-mentioned image forming apparatus has, for example, four monochromatic toner images each having a photosensitive drum and forming thereon a black toner image, a yellow toner image, a magenta toner image or a cyan toner image. Forming section, and a transfer material transport section for transporting a transfer material such as paper by a transfer belt, by arranging the four photosensitive drums in a line and arranging the transfer belt along the array, The single-color toner images formed on the respective photosensitive drums are sequentially transferred onto the transfer material held on the transfer belt in a superimposed manner, and then the multi-color toner images are heated and pressed by a fixing unit to form a color image on the transfer material. Some form images.

[0003]

However, the monochromatic toner images of the respective colors are superimposed on each other by sequentially transferring the monochromatic toner images from the respective photosensitive drums onto the transfer belt held on the transfer belt as described above. When a color image is formed in accordance with this, if the photosensitive drums and the transfer belt are not properly aligned, the transfer portions of the single-color toner images on the transfer material are relatively shifted. As a result, a hue change or a color shift occurs.

Specifically, for example, if the alignment or the rotation speed is deviated, the timing at which each photosensitive drum and the transfer belt move to the transfer position facing each other is determined by the timing at which the single-color toner image on the photosensitive member and the transfer belt move. Therefore, the transfer portion of the monochrome toner image on the transfer material is shifted. Further, even if the transfer material conveyance direction of the transfer belt at the transfer position and the rotation direction of the photosensitive drum are shifted for the same reason, the transfer portion of the monochrome toner image on the transfer material is shifted. Next, when the rotation of the photoconductor drum or the transfer belt is uneven or the roundness of the photoconductor drum is poor, the linear velocity of the peripheral surface of the photoconductor at the transfer position or the linear velocity of the peripheral surface of the transfer belt at the transfer position is determined. Fluctuates, and density unevenness occurs in the monochromatic toner image on the transfer material. Further, since the rotation unevenness of the photosensitive member and the transfer belt changes depending on the temperature and humidity in the apparatus, the manner of occurrence of the above-described various image quality changes also changes depending on the use time. .

Therefore, prior to the development of the present invention, the inventors formed a single color misregistration detection pattern on each photosensitive drum and superimposed them on a transfer material held on a transfer belt. An image forming apparatus is proposed in which a pattern for detecting multi-color misregistration on a transfer material is detected by a sensor, and the rotation speed of the photosensitive drum and the rotation speed of the transfer belt are adjusted based on the detection result. (Japanese Patent Application No. 8-175170). When the color rubbing detection pattern is formed on the transfer material in this way, the degree of deflection of the transfer belt and the like are reproduced in the same state as when the actual output image was formed. A color misregistration detection pattern having a color misregistration amount similar to the color misregistration amount sometimes occurring can be formed, and the color misregistration can be corrected with high accuracy.

However, in the image forming apparatus, since the color misregistration detection pattern formed on the transfer material is detected by the sensor, it can pass through the detection position of the sensor (of size). Unless a predetermined transfer material is set in the image forming apparatus, the operation of the color rub correction cannot be performed.

Accordingly, an object of the present invention is to correct color shift regardless of the presence or absence of a predetermined transfer material.
An object of the present invention is to develop an image forming apparatus capable of correcting color misregistration with high accuracy.

[0008]

That is, the present invention provides a plurality of monochromatic toner image carriers on which a monochromatic toner image is formed;
A transfer material carrier for holding and transporting the transfer material, which is arranged to face each single color toner image carrier, and a single color misregistration detection pattern is formed on each single color toner image carrier to detect the single color misregistration. And a color misregistration detecting means for detecting a color misregistration based on the superimposed patterns, and sequentially transferring the single color toner images formed on each single color toner image carrier onto the same transfer material, and performing the transfer. In the image forming apparatus in which the plurality of single-color toner images are superimposed on a material, the color misregistration detection unit transfers the transfer material when there is a transfer material capable of transferring the color misregistration detection pattern. While the color misregistration detection pattern is superimposed on the transfer material by being held by the material carrier, if there is no transfer material capable of transferring the color misregistration detection pattern, the transfer is performed on the transfer material carrier. For color shift detection An image forming apparatus for superimposing a turn.

In the present invention, the single-color toner image carrier may be any one capable of forming a single-color toner image. Examples thereof include a photosensitive drum and an intermediate transfer belt using an organic photosensitive material. In order to form a single-color toner image on the photosensitive drum, for example, the photosensitive drum is rotatably disposed, and the photosensitive drum is set at a uniform potential around the photosensitive drum. Uniform charging means for charging, exposure means for exposing the photosensitive drum in accordance with image information of each color to form an electrostatic latent image, and developing the electrostatic latent image with a developer to form a monochromatic toner image What is necessary is just to provide a developing means. Further, in order to form a monochromatic toner image on the intermediate transfer belt, for example, the monochromatic toner image formed on the photosensitive drum may be transferred.

The transfer material carrier may hold and convey the transfer material, and may be one in which the plurality of single-color toner images are superimposed on the transfer material. For example, the transfer material carrier may be arranged along the arrangement of the photosensitive drums. There is a transfer belt that is rotatably disposed to transfer a transfer material by electrostatically adsorbing the transfer material, and forms the plurality of single-color toner images in a superimposed manner on the transfer material transferred by the transfer belt. .

The color misregistration detecting means forms a single color misregistration detection pattern on each single color toner image carrier when there is a transfer material capable of transferring the color misregistration detection pattern. The material is carried on a transfer material carrier,
A plurality of color misregistration detection patterns are superimposed on the transfer material, and color misregistration detection is performed based thereon. If the predetermined transfer material is not present, a single color misregistration detection pattern is carried on each single color toner image. What is necessary is just to form it on the body, superimpose a plurality of color misregistration detection patterns on the transfer material carrier, and perform color misregistration detection based on it. For example, while a predetermined pattern is formed on each of the photosensitive drums, if there is a predetermined transfer material, the transfer material is supplied to a transfer belt, and the color on each of the photosensitive drums is changed. The pattern is transferred to the transfer belt or the transfer material at the transfer position, the multicolor pattern is read by an optical detection member arranged opposite to the transfer belt, and the amount of color misregistration is calculated based on the read image. In some cases, settings of the apparatus such as the rotation speed of the photosensitive drum are corrected based on the color shift correction amount.

The optical detecting member may be a so-called transmission type optical detecting member in which a light emitting element and a light receiving element are arranged opposite to each other via a transfer material carrier, or a light emitting element and a light receiving element. There is a so-called reflection type optical detection member provided side by side on the transfer material transport surface side of the transfer material carrier. When a color misregistration detection pattern on a transfer material is detected using these optical detection members, the majority of the transfer material used in the image forming apparatus is white opaque paper. A reflective type is effective. On the other hand, when a color misregistration detection pattern on a transfer material carrier is detected by using these optical detection members, yellow, magenta, cyan, and black toners are used as toners of the image forming apparatus. On the other hand, in the current technology, a transparent or black transfer material carrier is used. Therefore, when the detection is to be performed by a reflection type, a black transfer material carrier and a black toner are used. The output of the light emitting element must be increased in order to compensate for the low contrast between the two, and the settings such as the threshold for pattern discrimination must be switched according to the intensity of the scattered and reflected light that differs for each color of toner. It is preferable to use a transparent transfer material carrier and use a transmission type optical detection member (in the case where the same light receiving element is used, In order to obtain the amount of detected light, the output of a reflective light emitting element generally needs to be 10 times or more the output of a transmissive light emitting element. When detecting toner, several tens of times of output is required.) Therefore, the optical detection member is
It has a configuration having both a reflection type optical detection member and a transmission type optical detection member, and when detecting a pattern on a transfer material, the reflection type is used while a pattern on the transfer material carrier is used. In the case of detection, it may be switched to use a transmission type.

When the optical detecting member is composed of both a reflection type optical detecting member and a transmission type optical detecting member, the light emitting element or the light receiving element is used for simplifying the configuration. It is good to use one of the elements in common. In particular, when the light receiving element is shared, a member that generates a threshold value to be compared with the received light amount can be shared, so that the effect of simplifying the configuration is great. On the other hand, when the light emitting element is shared, control for selecting the light receiving element and control for switching the input current to the light emitting diode may be performed. When a common light emitting element is used, 1
A single light emitting diode may be used to control the current, or a plurality of light emitting diodes may be provided in parallel and only appropriate diodes may be lit.

Further, in the above-mentioned optical detection member in which the light emitting element or the light receiving element is shared, it is preferable that the respective members are arranged so that the optical path for transmission detection is substantially perpendicular to the transfer material carrier. Accordingly, it is possible to suppress a detection error of an edge portion of a pattern due to a shadow of a thickness of a toner, which is a problem when an optical path for transmission detection is set obliquely with respect to a transfer material carrier. Accuracy can be improved.

In the image forming apparatus of the present invention, the operation of the color misregistration detecting means is switched between when there is a transfer material capable of transferring the color misregistration detection pattern and when there is no transfer material. When there is a transfer material, the transfer material can be carried on a transfer material carrier, a plurality of color misregistration detection patterns can be superimposed on the transfer material, and the color misregistration can be corrected based on the pattern. When there is no predetermined transfer material, a plurality of color misregistration detection patterns can be superimposed on the transfer material carrier, and the color misregistration can be corrected based on it.

In the present invention, the term "holding the transfer material on the transfer material carrier" basically means that only the transfer material on which the color misregistration detection pattern is formed is held.
It is not limited to that. For example, when the transfer material carrier can hold a plurality of transfer materials at the same time, preferably, the color misregistration correction is performed in a state where the transfer materials are held at all of the plurality of transfer material holding positions. It is good to do so. This makes it possible to form the color misregistration detection pattern under the same conditions as in the output image formation with the rigidity and the degree of bending of the transfer material carrier. It is also preferable that the transfer material is conveyed in the same state as in the case of continuously forming an output image, and the color misregistration detecting means is operated in that state. Accordingly, it is possible to obtain the color misregistration correction amount in a state including the color misregistration caused by the belt walk generated when the transfer material is bridged between the transfer material carrier and the members before and after the same, for example, the fixing roll and the registration roll. Can be.

When a color misregistration detection pattern is transferred onto a transfer material carrier in the present invention, the color misregistration detection means corrects the setting of the apparatus based on the color misregistration amount itself detected by the pattern. Alternatively, a similar color misregistration correction pattern is formed on the transfer material and the transfer material carrier, and the difference between the color misregistration amounts detected in the respective patterns is held in advance as a detection error amount, and the detection is performed. It is better to correct the setting of the apparatus with the color shift amount corrected by the error amount. Thus, even when there is no transfer material, it is possible to correct color misregistration in the same manner as when a color misregistration detection pattern is formed on a transfer material.

The detection error amount may be set before shipping the image forming apparatus, or may be set (changed) as appropriate after shipping the image forming apparatus. When the detection error amount is set after shipping, the operation for detecting the color misregistration detection pattern on the transfer material in a state where the transfer material carrier and all the single-color toner image carriers are continuously rotated. The operation of detecting the color misregistration detection pattern on the transfer material carrier may be continuously performed. This makes it possible to minimize variations in image forming conditions and environmental conditions between the two detections, and to obtain a highly reliable detection error amount.

Further, according to the present invention, the color misregistration can be corrected regardless of which transfer material is set in the image forming apparatus. Therefore, the color misregistration detection pattern is always formed together with the output image during image formation. Good to do.
As a result, if a color shift occurs, it can be corrected immediately, and the variation range of the color shift occurring in the output image can be suppressed to a very narrow range.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image forming apparatus of the present invention will be described below in detail with reference to the accompanying drawings.

Embodiment 1 FIG. 1 shows a full-color copying machine according to this embodiment. The image forming apparatus includes an image processing apparatus (IPS) 30 that extracts black, yellow, magenta, and cyan color image information from predetermined full-color image information, forms a single-color toner image of each color, and forms the plurality of single-color toner images. And an image output device 31 for forming a multicolor toner image and thus a predetermined full-color image by superimposing on a transfer material, a user interface device 33 having many input keys and inputting image forming conditions such as the number of copies. And a main control unit 32 that outputs an operation signal and the like to the image processing device 30 and the image output device 31 according to the image forming conditions.

The image output device 31 includes four single-color toner image forming units K, Y, M, and K for forming single-color toner images of respective colors.
C, and a transfer material transport unit that transports a transfer material P such as paper or an OHP sheet.
Y, M, and C are arranged in a line, and a transfer material transport section is provided so that the transfer material P can be transported along the arrangement.

Each of the above-described monochromatic toner image forming sections is provided with a rotatable photosensitive drum 1 and a uniform charging corotron which is disposed opposite to the photosensitive drum 1 and charges it to a predetermined charging potential. 2, a laser exposure unit 3 for exposing the photosensitive drum 1 to form an electrostatic latent image on the photosensitive drum 1 according to image information of a predetermined color, and containing a toner of the same color as the color of the image information A developing device 4 for developing the electrostatic latent image with the toner, a transfer corotron 5 for transferring the toner image to a transfer material P, a photoconductor cleaning unit (not shown), and a photoconductor drum 1 A photosensitive drum driving stepping motor 6 which is driven to rotate in a cycle. The position of the photosensitive drum 1 to be exposed by the laser exposure device 3 is called an exposure position, and the space between the photosensitive drum 1 and the transfer corotron 5 is called a transfer position.

The laser exposure unit 3 receives one rotatable polygon mirror 3a, one laser diode 3b that emits light in response to a predetermined light emission control signal, and image information of each color. A light emission control unit 3c that outputs a light emission control signal in accordance with the image information at the timing described above, and an SOS sensor (scanning start sensor) 3 that detects the rotation phase of the polygon mirror 3a from the reflected light.
d, a polygon mirror driving stepping motor 3 for rotating the polygon mirror 3a at a predetermined cycle and phase.
The laser diode 3b emits light in accordance with image information, and the light is reflected by the polygon mirror 3a to expose the photosensitive drum 1. In FIG. 1, reference numerals are given only to the black toner image forming unit K, but the same applies to other single-color toner image forming units.

Then, each of the single-color toner image forming sections K,
Y, M and C are uniformly charged corotron 2 and photosensitive drum 1
And a laser exposure unit 3 exposes the photosensitive drum 1 according to image information of each color to form an electrostatic latent image on the photosensitive drum 1, and a developing unit 4 develops the electrostatic latent image to form a photosensitive drum. 1
A single color toner image of each color is formed thereon.

The above-described monochrome toner image forming sections K, Y,
M and C are the photosensitive drums 1 as shown in FIGS.
When the image writing start signal is input to the light emission control unit 3c while the polygon mirror 3a is being rotated, and the detection signal of the SOS sensor 3d is further input, the light emission control unit 3c outputs the image information. The light emission of the laser diode 3b is controlled accordingly. As a result, an electrostatic latent image of one pixel width is formed on the photosensitive drum 1 along the rotation axis direction (FIGS. 2A to 2C and FIG. 3).
(A)). Further, the photosensitive drum 1 rotates by one scanning width until the next reflection surface (the reflection surface of No. 2) of the polygon mirror 3a rotates to the irradiation position of the laser diode 3b (FIG. b)), then,
When the detection signal of the SOS sensor 3d is input to the light emission control unit 3c, the light emission control unit 3c controls the light emission of the laser diode 3a in accordance with the image information, and places the next one pixel width on the photosensitive drum 1. (See FIG. 3C). The single-color toner image forming units K, Y, M, and C form a predetermined electrostatic latent image on the photosensitive drum 1 by repeating this process a predetermined number of times.
As a result, a monochromatic toner image can be formed.

The transfer material transport section includes a plurality of transfer material storage trays 24 capable of storing a large number of transfer materials P having a size up to A3, and the single-color toner image forming sections K, Y, and K.
A transparent transfer belt 7 that is rotatably disposed so as to pass through all the transfer positions of M and C, and that can simultaneously carry four A4 sheets, and a transfer belt drive that rotationally drives the transfer belt 7 A stepping motor 22, a registration roll 9 for supplying a transfer material P to the transfer belt 7 at a predetermined timing,
And a transfer material adsorber 10 for electrostatically adsorbing the transfer material P to the transfer belt 7, and a transfer material adsorber 10 for disposing the transfer material P to remove electricity from the transfer belt 7. A transfer material peeling device 11 for peeling, a pair of fixing rollers 26 for heating and pressing the transfer material P, a transfer material discharge tray (not shown) for storing a transfer material on which an image is fixed, and a pair of forward and reverse rotatable rollers; A reversing roller 25, and a sheet P other than the sheet P, which is disposed inside the apparatus main body and is used when a sheet jam occurs.
And a purge tray 23 that discharges as much as possible.
The size of the paper stored in each transfer material storage tray 24 and the size of the paper stored in the manual feed tray (not shown) and the presence or absence of the paper are always detected, and the paper information is transmitted to the main controller. It has become.

When an image is formed on only one side of the transfer material P, the transfer material transport unit transfers the transfer material P stored in the transfer material storage tray 24 to the registration roll 9 and the transfer belt 7. The sheet is sequentially conveyed by the fixing roller 26 and discharged to a transfer material discharge tray. When images are formed on both sides of the transfer material P, the transfer material P discharged from the fixing roller 26 is reversed by the reversing roller 25 in the transport direction of the transfer material P, and then the registration roller 9 is re-formed. The sheet is sequentially conveyed by the transfer belt 7 and the fixing roller 26 and is discharged to a transfer material discharge tray. When a paper jam occurs, the fixing roller 26 and the reversing roller 25 are used.
The transfer material P is discharged to the purge tray 23 via the.

In the image forming apparatus configured as described above,
For example, when predetermined image forming conditions are set in the user interface device 33 and the image processing device 30 is activated in that state, the image processing device 30 converts the image information into black, yellow, and magenta based on a control signal from the main control device 32. , C, Y, C, Y, and C.
The laser beam is supplied to the M and C laser exposure devices 3, and the respective monochrome toner image forming sections K, Y, M, and C form a monochrome toner image based on the color information. An image can be formed on the transfer material P by sequentially transferring the transfer material P onto the material P in an overlapping manner, and then separating the transfer material P from the transfer belt 7 and supplying it to the fixing roll 26. Also,
For example, in the case of image forming conditions for forming a plurality of images based on the same image information, the image forming unit operates by repeating the image forming operation for the set number of times.

By the way, in the image output device 31, in order to form the desired multi-color toner image by superimposing the single-color toner images on the transfer material P, a predetermined full-color image is eventually formed on the transfer material P. In order to form the toner, it is necessary to synchronize the operations of the four single-color toner image forming units K, Y, M, and C with the operation of the transfer material conveying unit.

Therefore, in the present embodiment, an image writing start signal to each of the monochromatic toner image forming sections K, Y, M, and C,
Coarse synchronization control unit 1 for generating an operation signal to a registration roll 8 of a transfer material conveying unit with a fixed timing relationship
2, and a fine synchronization control unit for finely adjusting the image writing start timing of each of the single-color toner image forming units K, Y, M, and C as appropriate.

The coarse synchronization control unit 12 includes, for example, the linear velocity of the photosensitive drum 1, the linear velocity of the transfer belt 7, the arrangement angle between the exposure position and the transfer position, the registration roll 9 and each transfer position in the design specification. Based on the distance to
Based on the design, the image writing start signal and the registration roll operation signal are generated so that synchronization can be achieved. The timing relationship is as shown in FIG. 4, for example.

The above-mentioned fine synchronization control section controls the image writing start timing in the single color toner image forming section Y for yellow toner image, the single color toner image forming section M for magenta toner image and the single color toner image forming section C for cyan toner image, and The rotation cycle and phase of all the photosensitive drums 1 and the transfer belt 7 are controlled, and fine timing adjustment is performed so that the monochromatic toner images of the respective colors overlap each other and are transferred onto the transfer material P. In the present embodiment, specifically, for all the toner images, the magnification change in the toner images,
In addition to controlling the density of the pixels, the control is performed so that the yellow toner image, the magenta toner image, and the cyan toner image overlap with the black toner image, respectively. It should be noted that even if the start timing of image writing and the rotation cycle of the photosensitive drum 1 in all the monochromatic toner image forming units K, Y, M, and C are controlled, it is possible to superimpose the monochromatic toner images. Needless to say.

The control of the light emission control start timing of the light emission control unit 3c by the fine synchronization control unit is performed, for example, as shown in FIG. 5, after the start of image writing is input to each of the light emission control units 3c. The delay time setting means 15 for setting the delay time until the start of the operation may be provided, and the delay time set value of the delay time setting means 15 may be changed according to the positional deviation correction amount.

The control of the rotation phase of the polygon mirror 3a by the fine synchronization control unit is performed by, for example, an oscillator 16 that outputs a clock signal of a predetermined cycle as shown in FIG.
A frequency divider 17 for converting the clock signal into four frequency-divided clock signals having different phases, and three selectors 18 for outputting one frequency-divided clock signal according to the setting from the four frequency-divided clock signals. And outputs of the three selectors 18 to the respective monochrome toner image forming units Y, M,
C is input to the polygon mirror driving motor 3e.
The configuration may be such that the selection of the two selectors 18 is changed in accordance with the positional deviation correction amount. FIG. 7 shows the relationship between the frequency-divided clock signal and the resulting rotation phase in an example in which the polygon mirror 3a is formed on six surfaces.

Further, the rotation period and phase of the photosensitive drum 1 are controlled by the fine synchronization control unit, and the transfer belt 7 is controlled.
The control of the rotation period and the phase of the photosensitive drum 1
As shown in FIG. 8A, the reference voltage generator 19 which outputs a reference voltage corresponding to the above-described position shift correction amount.
A voltage-controlled oscillating circuit 20 for outputting a signal having a predetermined cycle according to the reference voltage; a stepping motor 6 for driving the photosensitive drum or a stepping motor for driving the transfer belt based on the signal having the predetermined cycle. And the drive control circuit 21 for driving the drive. Then, for example, as shown in FIG. 8B, when the signal of the predetermined cycle is adjusted, the time required for the photosensitive drum 1 to move from the exposure position to the transfer position, or the transfer belt 7 is adjacent to the adjusted position. Since the time required to move between the two transfer positions changes, the timing at which the toner image reaches the transfer position or the timing at which the transfer material P on the transfer belt reaches the next transfer position can be adjusted. Note that, as shown in FIG. 8C, the voltage-controlled oscillation circuit 20 is configured to change only during non-image formation because the cycle of the output signal is disturbed if the reference voltage is changed. .

The fine synchronization control section detects a color misregistration correction pattern formed by the image output device at both ends of the A3 paper, or at a portion on the transfer belt corresponding to the both ends, and based on the detection result. The amount of fine timing adjustment described above is determined accordingly. Specifically, for example, as shown in FIG. 9, both ends of the A3-sized paper P held on the transfer belt 6 are arranged so as to be detectable.
The two optical detection members 13 and the operation of the two optical detection members 13 are controlled in accordance with a start signal from the main control device 32, and the color misregistration correction pattern detection information from the two optical detection members 13 is output. And a position shift correction amount calculating means 14 for setting a predetermined position shift correction amount on the basis of the single-color toner image forming units Y and Y in accordance with the position shift correction amount.
The light emission control start timing of the light emission control unit 3c for M and C, the rotation phase of the polygon mirror 3a for each of the single color toner image forming units Y, M, and C, the single color toner image forming units K and
The rotation period and the phase of the Y, M, and C photosensitive drums 1 and the rotation period and the phase of the transfer belt 7 are controlled.

Each of the optical detection members 13 is described in detail below.
A CCD arranged opposite to the transfer belt 7 so as to correspond to one end of the A3-sized paper P held on the transfer belt 6
A transmission light emitting diode 13 disposed opposite to the CCD sensor 13a via the transfer belt 7 and setting an optical path perpendicular to the transfer material conveying surface of the transfer belt 7;
b, and a reflective light emitting diode 13c disposed adjacent to the CCD sensor 13a.
b is turned on, and the light is transmitted to the CCD sensor 13.
a, and outputs a read image of a color misregistration detection pattern from the CCD sensor 13a.

The position shift correction amount calculating means 14 includes a selector 14a for selectively lighting one of the transmission light emitting diode 13b and the reflection light emitting diode 13c.
An arithmetic unit 14b that detects the amount of color shift in the images read from the two CCD sensors 13a and calculates / outputs a position shift correction amount based on the detection result;
The color misregistration amount when the color misregistration detection pattern formed on the nobby paper P is detected using the reflection light emitting diode 13c and the color misregistration detection pattern formed on the transfer belt 7 are transmitted through the light emitting diode 13b. A non-volatile storage element 14c for holding a difference from the color misregistration amount at the time of detection as a detection error amount, and detecting a color misregistration correction pattern formed on the A3 nobby paper P. In addition to turning on the light emitting diode 13c for reflection,
While calculating / outputting the positional deviation correction amount based only on the color deviation occurring in the read image, when detecting the color deviation correction pattern formed on the transfer belt 7, the transmission light emitting diode 13b Is turned on, the color shift occurring in the read image is corrected by the detection error amount, and the position shift correction amount is calculated / output based on the correction amount.

The detection error amount stored in the non-volatile storage element 14c can be updated by a maintenance person in the maintenance mode. Specifically, after the maintenance and inspection person sets the A3-size paper P in the image forming apparatus, the user operates the user interface device 33 to switch from the user mode for image formation to the maintenance mode, and detects a detection error in the maintenance mode. It is executed by giving a quantity update instruction. As shown in FIG. 10, this detection error amount updating sequence is a state in which the A3-sized paper P is set in the image forming apparatus and the photosensitive drum 1, the polygon mirror 3a, and the transfer belt 7 are continuously rotated. (See S1 and S8), two sequences (an on-paper correction sequence and an on-belt correction sequence) that are selectively executed in a color misregistration correction cycle when the apparatus is started, which will be described later, are sequentially executed (S2). ＳS5), a difference between correction amounts in each sequence is calculated and stored as a detection error amount (S6〜S7). Accordingly, the manner of rotation of the photosensitive drum 1, the polygon mirror 3a, and the transfer belt 7 does not change, and fluctuations in image forming conditions and environmental conditions between the two detections can be suppressed as much as possible. A high detection error amount can be obtained.

In the present embodiment, a color misregistration correction sequence is executed at the start-up of the apparatus and at the time of image formation. In each of these sequences, the image output apparatus 31 forms a predetermined color rub detection pattern, and Fine adjustment by the fine synchronization control unit is performed. In addition,
FIG. 11 shows a color misregistration detection pattern formed in the present embodiment. This figure shows a state in which a color misregistration detection pattern is formed on an A3-sized paper P, where A is an image forming area on the sheet, B is a color misregistration detection pattern, and C is the sheet. The reference position mark (generally referred to as a register mark) when an image area is cut out from the mark. FIG. 12 shows an example of the state of occurrence of color shift occurring in the color shift detection pattern. In the shift amount of the measurement register pattern of the figure with respect to the ideal register pattern of the figure (in the case of matching the black pattern in the figure),
ΔX _Y , ΔX _M , and ΔX _C are detected as color shift amounts occurring in each color.

The color misregistration correction sequence at the start-up of the apparatus is started when the apparatus is turned on, and as shown in FIG. Is determined, and a different correction sequence is executed between the case where the sheet P is set and the case where the sheet P is not set (S9).

When a sheet P of A3 size is set, the light emitting diode 1 for reflection is used as a light emitting element.
3c is selected (S10), and conveyance of the sheet is started (S11). Then, first, a calibration cycle is performed to adjust the sensitivity of the sensor itself (S12), and then a DC coarse tuning cycle for correcting a color shift of about several mm is performed (S13), and several μm to several hundred μm are performed. An AC correction cycle for correcting the degree of color shift is performed (S14),
Then, a DC fine adjustment cycle for correcting a color misregistration of about several μm is performed (S15), and then the conveyance of the sheet is terminated (S15).
16) Complete. The above series of operations (S10 to S
16) is a correction sequence on paper.

Each of these correction cycles (S13 to S13)
In S15), as shown in FIG. 11, first, a color misregistration detection pattern is formed on each photosensitive drum 1 while continuously transporting the A3-size paper P at the same speed as that during image formation. The pattern of each color is transferred to both end portions of the transfer material P to form a predetermined color shift detection pattern on the paper P (S22). Next, while the paper P is continuously conveyed, the color misregistration detection pattern formed on the paper P is sampled by the image reading sensor 13 (S23), and the color misregistration amount of each color is determined from the read image. Then, a correction value is calculated based on the respective color shift amounts (S24). Finally, the correction value is set for each of the members (S25), and the cycle ends. Therefore, in each correction cycle (S13 to S15), the color misregistration correction pattern can be formed after reproducing the degree of deflection of the transfer belt 7 during image formation, and the transfer belt 7 and the fixing rolls before and after the transfer belt 7 can be formed. Since the color misregistration correction pattern can be formed in a state where the paper P is bridged between the registration roll 26 and the registration roll 9, the color misregistration correction amount can be obtained in each situation. Hereinafter, a series of cycles (S22 to S24) from the formation of the color misregistration pattern to the calculation of the correction value will be referred to as a correction amount detection cycle at the time of paper detection.

In the present embodiment, the paper P used in the color misregistration correction cycle is discharged to the purge tray 23 so as not to be mixed with the paper P on which the output image is formed. Further, the calibration cycle (S12) is replaced with the series of color misregistration correction cycles (S13 to S13).
This is performed only at the beginning of S15), and the paper transport speed of the transfer belt 7 during the execution of the cycle (S12) is set lower than the paper transport speed at the time of forming a normal image. The number of sheets consumed in the calibration cycle (S12) is set to one. Furthermore, the reversing roll 25 is appropriately operated so that the color misregistration detection pattern is formed on both sides of each sheet P, so that the number of sheets consumed in each cycle (S13 to S15) is reduced to approximately half. I did it.

On the other hand, when the paper P of the A3 size is not set, the transmission light emitting diode 13b is selected as the light emitting element (S17), and the calibration cycle is performed without any transfer material P being conveyed. After adjusting the sensitivity and the like of the sensor itself (S18), a DC coarse tuning cycle for correcting a color shift of about several mm is performed (S19), and an AC for correcting a color shift of about several μm to several hundred μm is performed. A correction cycle is performed (S20), and a DC fine adjustment cycle for correcting a color shift of about several μm is performed (S20).
21) Complete. The above series of cycles (S17)
To S21) are the on-belt correction sequence.

Each correction cycle (S19 to S2) for detecting a color misregistration detection pattern formed on the transfer belt 7 is performed.
In 1), specifically, as shown in FIG.
First, a pattern for detecting color misregistration is formed on each photoconductor drum 1 and the pattern of each color is transferred to the transfer belt 7.
A predetermined color shift detection pattern is formed on the transfer belt 7 (S26). Next, the color misregistration detection pattern formed on the transfer belt 7 is sampled by the image reading sensor 13 (S27), the color misregistration amount of each color is calculated from the read image, and the nonvolatile storage element The correction value of the color shift amount is calculated in consideration of the detection error amount stored in 14c (S28). Finally, the correction values are set for the respective members (S29), and the cycle ends. Hereinafter, a series of cycles (S26 to S28) from the formation of the color misregistration pattern to the calculation of the correction value is referred to as a correction amount detection cycle at the time of belt detection.

The color misregistration correction cycle at the time of image formation is started when an image formation signal is output to the image output device 31, as shown in FIG. 16 (S30). Next, in the color misregistration correction cycle, it is determined whether or not the sheet P on which an image is to be formed is A3-size (S3).
1). If the paper P is A3 sized, the light emitting diode 13c for reflection is selected as the light emitting element (S32), and a correction amount detection cycle for paper detection is executed (S33) to calculate a correction value. On the other hand, when the paper P is other than the A3-sized one, the transmission light emitting diode 13c is selected as the light emitting element (S35) and the correction amount detection cycle for belt detection is executed (S36) to calculate the correction value. I do. Finally, the correction amount is set after the image formation on the paper P is completed (S34). Therefore, if a color shift occurs, the color shift can be corrected immediately, so that the variation range of the color shift that occurs in the output image can be suppressed to a very narrow range.

After the detection error amount update sequence and the color misregistration correction cycle at the time of startup are executed, a predetermined full-color image is formed on the paper P by the image forming apparatus. As a result, regardless of whether or not the A3-sized paper P is set in the image forming apparatus, no color misregistration occurs in the full-color image, and a high-quality image can be obtained. In particular, even when the A3 noble paper P is not set, the color misregistration correction cycle is executed,
The image quality of the output image could also be made as high as that of the case where A3-size paper was set.

In the present embodiment, the optical detection member 1
As No. 3, the CCD sensor 13a as the light receiving element is made common and the transmission optical path is set perpendicular to the transfer belt 7. However, as shown in FIG. Regardless of the configuration in which the optical path is set perpendicular to the transfer belt 7 or the configuration in which the light receiving element is simply made common as shown in FIG. Alternatively, the configuration may be such that the light emitting elements are simply made common, or further, as shown in FIG. 3D, the configuration may not be made such that the members are shared. When the transmission light path is set perpendicular to the transfer belt 7, no shadow is generated due to the thickness of the toner layer (each pattern is formed of toner) on the transfer belt 7, and therefore, the influence is given. The detection position of each pattern does not shift, and the pattern can be detected with high accuracy. Further, when the light receiving element is shared, a member that generates a threshold value to be compared with the amount of received light can be shared, so that the effect of simplifying the configuration is great. On the other hand, when the light emitting elements are shared, control for selecting the light receiving elements and control for switching the output of the light emitting elements may be performed.

[0051]

As described above, in the image forming apparatus of the present invention, the operation of the color misregistration detecting means is switched between when there is a transfer material capable of transferring the color misregistration detection pattern and when there is no transfer material. Since the misregistration correction is performed in the operation, the misregistration can be corrected regardless of the presence or absence of the predetermined transfer material.

Further, in the image forming apparatus of the present invention, when the predetermined transfer material is present, the transfer material is carried on a transfer material carrier, and a plurality of color misregistration detection patterns are superimposed on the transfer material. In addition, since the color misregistration is corrected based on this, that is, the multicolor color misregistration detection pattern is formed in a state where the state at the time of actual output image formation is reproduced, so that the color misregistration is corrected with high accuracy. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram (part 1) of a process of forming a monochromatic toner image in the image forming apparatus of FIG. 1;

FIG. 3 is an explanatory view (part 2) of a process of forming a single color toner image in the image forming apparatus of FIG. 1;

FIG. 4 is a timing chart of an output signal of a coarse synchronization control unit in the image forming apparatus of FIG. 1;

5 is a configuration diagram (part 1) of a main part of a fine synchronization control unit in FIG. 5;

FIG. 6 is a configuration diagram (part 2) of a main part of the fine synchronization control unit in FIG. 5;

FIG. 7 is an explanatory diagram of a relationship between a frequency-divided signal and a phase of a polygon mirror.

8 is a configuration diagram (part 3) of a main part of the fine synchronization control unit in FIG. 5;

9 is a conceptual diagram of the overall configuration of a fine synchronization control unit in the image forming apparatus of FIG.

FIG. 10 is a measurement flowchart of a detection error amount.

FIG. 11 shows an example in which a color misregistration correction pattern is formed together with an output image on a transfer material.

12 is an explanatory diagram of a color shift amount generated in the color shift correction pattern in FIG.

FIG. 13 is a flowchart of a color misregistration correction cycle when the apparatus is powered on.

14 is a detailed flowchart of each correction cycle for forming a color misregistration correction pattern on the sheet of FIG.

FIG. 15 is a detailed flowchart of each correction cycle for forming a color misregistration correction pattern on the transfer belt of FIG. 13;

FIG. 16 is a flowchart of a color misregistration correction cycle during image formation.

FIG. 17 is a modified example of the optical detection member.

[Explanation of symbols]

1: photosensitive drum (monochromatic toner image carrier), 7: transfer belt (transfer material carrier), 13: optical detection member (color misregistration detecting means), 14: misregistration correction amount calculating means (color misregistration detecting means) ), P: transfer material.

Claims (6)

[Claims] A plurality of single-color toner image carriers on which a single-color toner image is formed; a transfer material carrier disposed to face each single-color toner image carrier for holding and transporting a transfer material; Forming a detection pattern on each single-color toner image carrier, superimposing the single-color color shift detection pattern, and detecting a color shift based on the color shift detection means,
In the image forming apparatus in which the single-color toner images formed on each single-color toner image carrier are sequentially transferred onto the same transfer material and the plurality of single-color toner images are superimposed on the transfer material, the color shift detection is performed. The means, when there is a transfer material capable of transferring the pattern for color shift detection, holding the transfer material on a transfer material carrier and superimposing the pattern for color shift detection on the transfer material, When there is no transfer material capable of transferring the color misregistration detection pattern, the color misregistration detection pattern is superimposed on the transfer material carrier. 2. The color misregistration detecting means according to claim 1, wherein said color misregistration detecting means detects a difference between a color misregistration amount detected from the color misregistration detection pattern on the transfer material and a color misregistration amount detected from the color misregistration detection pattern on the transfer material carrier. An amount is held in advance, and when a color misregistration detection pattern on the transfer material carrier is detected, the color misregistration is corrected after correcting the detection amount with the detection error amount. 2. The image forming apparatus according to 1. 3. An operation for detecting a color misregistration detection pattern on a transfer material in a state where the transfer material carrier and all the single-color toner image carriers are continuously rotated. 3. The image forming apparatus according to claim 2, wherein the operation of detecting the color misregistration detection pattern on the carrier is continuously performed, and thereby the detection error amount is held. 4. The image forming apparatus according to claim 1, wherein a color misregistration detection pattern is formed together with the output image at any time during image formation. 5. The color misregistration detecting means includes a light emitting element and a light receiving element which are arranged to face each other with a transfer material carrier interposed therebetween.
A transmission type optical detection member for detecting a color misregistration detection pattern on the transfer material carrier, and a light emitting element and a light receiving element arranged side by side on the transfer material transport surface side of the transfer material carrier; The image forming apparatus according to claim 1, further comprising: a reflection-type optical detection member that detects a color misregistration detection pattern. 6. A light-emitting element of a reflection-type optical detection member and a light-emitting element of a transmission-type optical detection member, or a light-receiving element of a reflection-type optical detection member and a light-emitting element of a transmission-type optical detection member. 6. The image forming apparatus according to claim 5, wherein a common light receiving element is used, and an optical path for transmission detection is set substantially perpendicular to the transfer material carrier.