JPH10274871A - Image forming device - Google Patents

Abstract

(57) Abstract: A toner image formed by first and second developing means is sequentially transferred onto an intermediate transfer member, and the toner image is transferred to a transfer material to form a superimposed toner image. Depending on the state of the original or the state of the obtained image, it is important to prioritize the prevention of the occurrence of an image with a noticeable black color or the prevention of the occurrence of an image with an unstable black. Provided is a selectable image forming apparatus. SOLUTION: Preceding operation of black developing device 7 and multicolor developing device 6
A changeover switch for switching between the preceding operation and the preceding operation is provided. The formed image is prevented from becoming an unstable black image by the preceding operation of the black developing device 7, or the formed image becomes an image in which the black is conspicuous by the preceding operation of the multicolor developing device 6. To prevent this.

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 such as a copying machine, a facsimile, and a printer.

[0002]

2. Description of the Related Art As a conventional image forming apparatus of this type, there is known a color image forming apparatus which forms a color image by superposing toner images of a plurality of colors. As such an image forming apparatus, a first developing unit that performs development using a black developer, and a developer of one or more colors other than black, for example, yellow,
There has been proposed an image forming apparatus including a second developing unit including one or more developing units for performing development using magenta and cyan developers, respectively. In the image forming apparatus having such a configuration, for example, a toner image formed on a photoconductor as a latent image carrier is superimposed on, for example, an intermediate transfer body as a recording body to form an image. Specifically, first, in a state where the second developing unit is separated from the photoconductor,
A black toner image is formed on the photoreceptor by the first developing means and is transferred onto an intermediate transfer member. Thereafter, the second developing means is brought into contact with a photoreceptor, and the yellow, magenta,
A cyan toner image is sequentially formed, and each toner image is superimposed and transferred on the intermediate transfer member. Then, the toner image is collectively transferred from the intermediate transfer body to a transfer material such as transfer paper to form a superimposed toner image.

[0003]

There is provided first developing means for developing using the above-mentioned black developer, and one or more developing devices for developing using one or more developers other than black, respectively. And an image forming apparatus having a second developing means.
When the uppermost layer of the superimposed toner image formed on a transfer material such as transfer paper is a black toner layer, an image in which black is conspicuous is obtained. Then, when the formed image is a color image using a lot of black characters, the black characters are excessively emphasized,
If the color image uses many colors other than black, black may be too conspicuous. In order to prevent an image formed in this way from becoming an image in which black is emphasized, it is preferable to form a superimposed toner image such that a layer other than black covers the black layer. Therefore, for example, in the case of an image forming apparatus configured to form an image using the intermediate transfer member, it is preferable to operate the second developing unit first, and to directly transfer the transfer paper from the photosensitive member. In the case of an image forming apparatus having a configuration in which a toner image is sequentially transferred onto a transfer material to form a superimposed toner image, it is desirable to operate the first developing unit first.

In the above image forming apparatus, when a black toner image is transferred to a transfer material or an intermediate transfer member after other toner images, the black image may become unstable. is there. On transfer material and intermediate transfer body,
The black toner image and the other toner images are not always stacked. For this reason, when one or more layers of another toner image have already been transferred to the area where the black toner image is to be transferred, a voltage drop occurs according to the resistance of that layer, and the transfer electric field decreases. Therefore, the black toner image is less likely to be transferred than when no other toner image is transferred. Therefore, when the black toner image is configured to be transferred to a transfer material or an intermediate transfer member after the other toner images, the amount of the black toner adhered to the image due to the transfer is not stable, and a sparse layer is formed. As a result, an image in which black is not stable is formed. In order to prevent the image formed in this way from becoming an image in which black is not stable, it is desirable to first transfer the black toner image to a transfer material or an intermediate transfer member.

[0005] Whether the generation of such an image in which black is conspicuous or the generation of an image in which black is not stable depends on environmental conditions, an image to be formed, and the like. However, after the toner image formed by the first developing unit and the toner image formed by the second developing unit are sequentially transferred onto an intermediate transfer member, the toner image is transferred onto a transfer material to form a superimposed toner image. In an image forming apparatus capable of performing the above-described operations, an apparatus configured to precede the developing operation by the first developing unit cannot cope with a case where it is desired to prevent formation of an image in which black is conspicuous. Second
The apparatus configured to precede the developing operation by the developing means cannot cope with a case where it is desired to prevent formation of an image in which black is not stable.

In the above image forming apparatus, the first developing means and the second developing means apply a high voltage such as a developing bias on the main body of the apparatus except at the time of each development in order to reduce costs. In many cases, the terminal is disconnected from the power supply terminal. In such a case, for example, in a case where the developing operation by the first developing unit precedes, after forming a black toner image, the second developing unit is connected to a power supply terminal for applying a developing bias on the apparatus main body side, The first developing means is electrically disconnected from the power supply terminal. However, the disconnection may cause a voltage fluctuation in which the voltage becomes unstable, and the potential of the Gnd terminal or the like which is set to the ground potential may become unstable. Generally, the color toner is less likely to adhere to the photosensitive member than the black toner, and generally uses different voltages for the color developing bias and the black developing bias in order to obtain a desired amount of toner adhesion. . However, it has been found by the present inventors that the above-mentioned voltage fluctuation is particularly likely to occur when the developing means is electrically disconnected from the power supply terminal after switching the developing bias applied to the developing means. For this reason, it is necessary to switch the developing bias before cutting off the first developing means for layout reasons, etc., and switch the developing bias before cutting off the second developing means. If it is not necessary, the former is more likely to cause voltage fluctuation. Then, in order to increase the speed, a reference mark formed on the surface of the intermediate transfer member, for example, which is a reference for superimposing colors, is detected without causing a voltage blur to occur and the GND terminal to be in a stable state. When a mark detection signal (hereinafter, referred to as a reference mark signal) is electrically transmitted, noise may be added to the reference mark signal. As a result, the toner images to be superimposed may be displaced, so that a so-called color shift may occur.

Whether the occurrence of such a color shift or the occurrence of an image in which black is not stable is more likely to occur depends on the environmental conditions, the image to be formed, and the like. However, in an image forming apparatus capable of forming a superimposed toner image by superimposing the toner image by the first developing unit and the toner image by the second developing unit, the developing operation by the first developing unit is performed. The apparatus configured to take the lead cannot cope with the case where it is desired to prevent the occurrence of color misregistration, and the apparatus configured to take the lead in the developing operation by the second developing means leads to an image in which black is not stable. Could not cope with the case where it was desired to prevent the formation of

The present invention has been made in view of the above background, and a first object of the present invention is to form a toner image by the first developing means and a toner image by the second developing means. In an image forming apparatus capable of forming a superimposed toner image by transferring the toner image to a transfer material after sequentially transferring the toner image onto the intermediate transfer body, a black image is formed according to the state of the original or the state of the obtained image. It is an object of the present invention to provide an image forming apparatus which can select which of the following is preferentially performed: prevention of generation of an image with conspicuousness and prevention of generation of an image in which black is not stable.

Another object of the present invention is to provide an image forming apparatus capable of forming a superimposed toner image by superimposing a toner image formed by a first developing means and a toner image formed by the second developing means. In the image forming apparatus, it is possible to select, according to the state of the original document or the state of the obtained image, whether to preferentially prevent the occurrence of color shift or the occurrence of an image in which black is not stable. To provide.

[0010]

In order to achieve the first object, the invention according to claim 1 comprises a first developing means for developing using a black toner and a toner for one or more colors other than black. A second developing means for performing development by using a first developing means, and an intermediate transfer means for transferring the toner image by the first developing means and the toner image by the second developing means so as to be sequentially superimposed on the intermediate transfer body. An image forming apparatus capable of forming a superimposed toner image by transferring a toner image superimposed on the intermediate transfer member to a transfer material, wherein the first developing means And a switching unit for switching between forming the toner image by the first developing unit and forming the toner image by the second developing unit first.

In order to achieve the second object,
According to a second aspect of the present invention, the first power supply terminal of the apparatus main body is configured to be electrically connectable and disconnectable, and a first developing unit for performing development using black toner; The second power supply terminal is configured so as to be electrically connectable and disconnectable, performs development using toner of one or more colors other than black, and performs first power supply of the first developing unit. A second developing unit that is less likely to generate noise when disconnecting from the second power supply terminal than when disconnecting from the terminal; Each of the means is electrically disconnected from the power supply terminal except when the development is performed, and the toner image by the first developing means and the toner image by the second developing means are overlapped. In an image forming apparatus capable of forming an image together, When forming the image by superimposing the toner image by the image unit and the toner image by the second developing unit, the formation of the toner image by the first developing unit may be performed first, or the second developing unit may be used. A switching means for switching whether to form a toner image first.

Further, the invention of claim 3 has a recording body position detecting means for detecting a moving position of a recording body on which the toner image is superimposed on the surface so as to be a reference for superimposing the toner image. Item 2. The image forming apparatus according to Item 2, further comprising noise detection means for detecting noise in the detection signal by the recording medium position detection means, and switching control means for controlling the switching means based on the detection result by the noise detection means. It is characterized by having been provided.

According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the switching control means is configured to be capable of selecting whether or not to perform switching control by the switching control means. It is assumed that.

In the image forming apparatus according to the first aspect, when forming the superimposed toner image, the switching means may perform the formation of the toner image by the first developing means first or the second developing means. It is possible to switch whether the toner image is formed first by the means. In this manner, the order of development by the two developing units is switched according to the state of the original or the state of the obtained image, thereby preventing the occurrence of an image in which black is conspicuous and the occurrence of an image in which black is not stable. It is possible to select which of the above is performed preferentially. For example, when an image in which black is not stable is likely to be formed,
It is possible to switch the development order in which the black toner image is first transferred to the transfer material or the intermediate transfer member, specifically, to activate the first developing means first. This can prevent the formation of an image in which black is not stable. In the case where an image in which black is conspicuous is easily formed, the second developing means is operated first in the order of development such that the uppermost part of the formed image does not become the black toner layer. It is possible to switch as follows.
Thereby, it is possible to prevent the formation of the image in which the black color is conspicuous.

In the image forming apparatus according to the present invention, when the toner image formed by the first developing means and the toner image formed by the second developing means are superimposed to form an image, the switching means makes use of the switching means. It is possible to switch between forming the toner image by the first developing unit first and forming the toner image by the second developing unit first.
In this manner, the order of development by the two developing units is switched according to the state of the original or the state of the obtained image, and either of preventing the occurrence of an image in which black is not stabilized and preventing the occurrence of color misregistration is achieved. It is possible to select whether to perform the processing with priority.
For example, when an image in which black is not stable is likely to be formed, the first developing unit is first arranged in the order of development in which the black toner image is first transferred to a transfer material or an intermediate transfer member. It can be switched to operate. This can prevent the formation of an image in which black is not stable. Further, in the case where noise is likely to be generated when the first developing means for performing development is disconnected from the first power supply terminal, the noise is hardly generated when the first developing means is disconnected from the power supply terminal. Can be switched so that the developing means is operated first. Thereby, the noise can be reduced.

Further, when an image in which black is conspicuous is easily formed, the order of development can be switched so that the top of the formed image does not become the black toner layer. Specifically, in the case of an image forming apparatus having a configuration in which a toner image is sequentially transferred onto an intermediate transfer member and then collectively transferred onto a transfer material to form a superimposed toner image, the second developing unit is operated first. What is necessary is just to switch so that it may be performed. Alternatively, in the case of an image forming apparatus configured to form a superimposed toner image by sequentially transferring the toner images by the developing unit directly onto a transfer material, the first developing unit may be switched to operate first. . Thereby, it is possible to prevent the formation of the image in which the black color is conspicuous.

Further, in the image forming apparatus of the present invention, the noise detecting means detects noise in the detection signal by the recording medium position detecting means, and the switching control means detects the noise based on the detection result. Control the switching means. For example, when the noise is larger than a preset reference value, the toner image is formed first by the second developing unit so that noise is hardly generated, otherwise, the first image is formed. The formation of the toner image by the developing means is performed first so that the formed image can be prevented from becoming an unstable black image.

Further, in the image forming apparatus according to the fourth aspect, it is possible to select whether or not to perform switching control by the switching control means. Thus, even if some color misregistration occurs, it is possible to forcibly perform the development by the first developing unit first when it is desired to form a stable black image.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to a color printer as a color image forming apparatus (hereinafter referred to as a printer).
An embodiment applied to (1) will be described. First, a schematic configuration and operation of the entire printer according to the present embodiment will be described. FIG. 1 is a diagram illustrating a schematic configuration of a printer according to the present embodiment. The printer in the illustrated example employs a reversal development system, a so-called negative-positive development system, in which development is performed using a toner having negative charging characteristics and a carrier of magnetic particles having positive charging characteristics. In FIG. 1, a flexible belt-shaped photoconductor (hereinafter, referred to as a “photoconductor belt”) 1 as a latent image carrier is provided between support rollers 2 and 3, and driven by the support rollers 2 and 3. It is rotated in the direction of arrow A (clockwise) in the figure. Around the photoreceptor belt 1, a discharge lamp L for removing residual charges on the surface of the photoreceptor belt, a charging charger 4 for uniformly charging the surface of the photoreceptor belt, and an exposure device for forming an electrostatic latent image Laser writing unit 5, and a plurality of developing units, specifically, three developing units 6Y, 6M, 6 containing yellow, magenta, and cyan color developers, respectively.
A multi-color developing device 6 as a second developing device in which C is switchably supported, a black developing device 7 as a first developing device containing a black developer separate from the multi-color developing device 6, and the like. Are arranged.

The multicolor developing device 6 and the black developing device 7 each include a developing roller as a developer carrying member which comes close to or in contact with the photosensitive belt 1 at a predetermined position, and an electrostatic latent image on the photosensitive belt 1 is provided. Has a function of visualizing by a non-contact development or a contact development method. In the illustrated printer, the developing position of the multi-color developing device 6 is
Is located on the upstream side in the rotation direction of the photosensitive belt from the developing position. The multicolor developing device 6 includes a plurality of developing devices 6Y, 6M, 6
Rotation about a rotation axis perpendicular to the paper surface of FIG. 1 is controlled so that any one of Y moves to a developable position in synchronization with the development timing of the corresponding color. By the rotation of the multicolor developing device 6 by 120 degrees, the developing device facing the developing position is switched. When the multicolor developing device 6 operates, the rotation of the cam 45 is controlled so that the black developing device 7 moves to a position separated from the photosensitive belt 1.

Further, an intermediate transfer belt 10 which is a belt-shaped intermediate transfer body as a recording body on which a toner image is superimposed on a surface thereof comes into contact with a portion of the photosensitive belt 1 wrapped around the support roller 3 on the upper side. It is provided as follows.
The intermediate transfer belt is stretched between rotating rollers 11 and 12, and is conveyed in a counterclockwise direction indicated by an arrow B by driving the rotating rollers 11 and 12. At the position of the support roller 3 where the intermediate transfer belt 10 is in contact with the photosensitive belt 1, the toner image on the photosensitive belt 1 is transferred to the intermediate transfer belt 10.
Is transferred to At the time of transfer of the toner image, a bias voltage is applied by a bias unit 13 disposed on the back side of the intermediate transfer belt 10. In the illustrated device, 1800 V is applied as the bias voltage.

On the intermediate transfer belt 10, a predetermined number, for example, ten, belt marks (not shown) for detecting the position of the intermediate transfer belt are provided along the circumferential direction. The mark is formed so as to have a reflectance different from that of the intermediate transfer belt, and this is detected by a mark sensor (not shown) as a recording medium position detecting unit. The timing of exposure, development bias, and transfer bias is determined using one of the marks as a reference timing. This is used as a reference for superimposing toner images.

Cleaning device 15 for photoreceptor belt
Is a cleaning blade 15A that constantly contacts the photoconductor belt 1 and cleans the toner on the photoconductor belt 1;
A waste toner collecting container 15B and the like are provided. Further, the cleaning device 16 for the intermediate transfer belt includes a cleaning blade 16A for cleaning the surface of the intermediate transfer belt at a portion where the intermediate transfer belt 10 is wound around the rotation roller 11, an auger 16B for toner conveyance, and the like. . Cleaning blade 16 for intermediate transfer belt
A is maintained at a position separated from the surface of the intermediate transfer belt 10 when a toner image is transferred from the photoreceptor belt 1 during image formation by a blade contacting / separating arm (not shown). Only the surface of the intermediate transfer belt 10 is brought into contact with the surface of the intermediate transfer belt 10 as shown in FIG.

Next, the outline of the image forming operation of this printer will be described.
However, an explanation will be given using examples of Bk, C, M, and Y. FIG. 2 is a timing chart at the time of this image formation. When the image forming operation is started, the photosensitive belt 1 is uniformly charged by the charger 4. At this time, the belt mark is detected by a belt mark sensor (not shown). The laser writing unit 5 scans a laser beam (laser beam) 5F modulated on the basis of the black image information to perform exposure, thereby performing optical writing. As a result, a Bk electrostatic latent image is formed on the surface of the photoreceptor belt 1.
The black image information is obtained by decomposing a desired full-color image into yellow, magenta, cyan, and black color information and obtaining single-color image information. A laser beam 5F generated by a semiconductor laser (not shown) based on the image information is rotationally scanned by a polygon mirror 5B driven at a high speed by a drive motor 5A, passes through an f-θ lens 5C, and passes through an optical path by a reflection mirror 5D. Adjusted.

During the optical writing of the Bk electrostatic latent image, the black developing device separated from the photosensitive belt 1 comes into contact with the photosensitive belt 1 by the rotation of the cam 45, and It is moved to a position where development is possible. The black developing device has a developing bias for black development,
For example, −300 V is applied, and the Bk electrostatic latent image formed on the photoreceptor belt 1 is developed by the black developing device 7 with black toner. Thereafter, the developing operation of the Bk latent image area is continued. However, when the rear end of the latent image passes through the opposing portion between the multicolor developing device 6 and the photoreceptor belt 1, the next developing operation by the cyan developing device is performed. The multicolor developing device 6 is rotated to position the cyan developing device 6C at a position where development can be performed so that the cyan electrostatic latent image can be formed immediately after the formation of the cyan electrostatic latent image on the belt 1. At this time, the multicolor developing device is connected to the power supply terminal of the main body, and the developing bias is also applied to the multicolor developing device 6. When the trailing edge of the Bk latent image passes through the Bk developing position, the developing bias voltage is immediately switched to a developing bias for color, for example, -400 V, and a voltage of -400 V is applied to the black developing device and the multicolor developing device. With the voltage applied, the black developing device is moved to a position separated from the photoreceptor belt 1 by the rotation of the cam 45, and the black developing device is electrically disconnected from the power supply terminal. Then, cleaning of the photosensitive belt 1 and formation of a cyan electrostatic latent image are performed, and development is performed by the cyan developing device of the multicolor developing device 6. In this manner, the cleaning, the formation of the electrostatic latent image, and the development are repeated, and the respective color images (toner images) are sequentially formed on the photosensitive belt 1.

The single-color images (toner images) sequentially formed on the photoreceptor belt 1 rotating in the direction of arrow A include a bias brush 13 for each of black, yellow, magenta, and cyan.
The intermediate transfer belt 10 rotates in the direction of arrow B in synchronization with the photosensitive belt 1 by a predetermined transfer bias applied to the intermediate transfer belt 10.
The images are superimposed and transferred sequentially at the same position above.

The color image superimposed on the intermediate transfer belt 10 is transferred to a transfer material such as paper or plastic by a transfer roller 14 as a transfer material transfer unit.
For example, at the time of transfer to paper, the paper 17A stored in the paper feed table (paper feed cassette) 17
8, through the transport roller pair 19 and the registration roller pair 20,
The intermediate transfer belt 10 and the transfer roller 1 are timed so that the position of the image on the sheet 17A becomes a regular position.
4 (hereinafter referred to as a secondary transfer section). The image superimposed on the intermediate transfer belt 10 is collectively transferred by the transfer roller 14 onto the sheet 17A conveyed to the secondary transfer section. After the transfer, the sheet 17A is sent to the fixing device 50 where the toner image is fixed, and a full-color image is completed. The sheet 17 </ b> A on which the full-color image is formed is discharged to a discharge stack 52 via a pair of discharge rollers 51.

The waste toner scraped off from the intermediate transfer belt 10 by the cleaning blade 16A is
The toner is conveyed toward the front of the drawing by an auger 16B provided in the cleaning device 16, and further conveyed to a waste toner collecting container 15B by a conveyance unit (not shown). When a predetermined amount or more of the waste toner is stored in the waste toner collecting container 15B, the container is appropriately replaced.

The photoreceptor belt 1, the charging charger 4, the intermediate transfer belt 10, the cleaning device 16, the registration roller 20B, the conveyance guide, and the like are integrally formed as a process cartridge 31 so that they can be replaced when their life is over. Is configured. The waste toner collecting container 15B is removably incorporated into the process cartridge.

In addition to replacing the process cartridge,
The multi-color developing device 6, the black developing device 7 and the like are also replaced at the end of their service life. It is structured so that it can be rotated and opened.

On the left side of the apparatus main body in FIG. 1, an electric equipment / control device 100 is housed. Above the fan 70, a fan 70 is provided to exhaust air to prevent an excessive rise in temperature in the apparatus. Also, on the right side of the apparatus main body in FIG.
A relatively small-sized paper feeding device 80 is provided.

FIG. 3 is a block diagram showing a schematic configuration of a control system of the printer. The control unit of the printer, which controls a series of operations for image formation described above, includes a CPU (central processing unit) 101, a ROM 102,
AM 103, I / O control unit 107, etc.
These are connected by a bus line 120. The bus line 120 further includes a controller I / F circuit 109 serving as an interface between the printer controller 108 and the CPU 101 for translating image output information and the like from an external device such as a personal computer, a writing unit 110, and various settings by an operator. A panel I / F circuit 111 which is an interface between the operation panel 112 for performing operations and the like and the CPU 101 is connected.

The CPU 101 controls the system of the printer. The CPU 101 controls the printer according to the program stored in the ROM 102 while using the RAM 103 as a work area. The above I
The / O control unit 107, based on the instruction of the CPU 101,
Signal inputs from various sensors 105 that perform mark detection and the like, which will be described later, which serve as references for paper size detection, jam detection, and color superposition, and drive various actuators for performing mechanical operations such as paper feeding and discharging. Driver circuit 106
The control of the output of the control signal to is performed.

In this printer, when a toner image of the next color, for example, a cyan toner image is formed by the multicolor developing device 6 after a black toner image is formed by the black developing device 7, the developing bias is set as described above. -300V for black
Then, the black developing device 7 is disconnected from the power supply terminal on the main body side immediately before the formation of the cyan toner image after switching to -400 V for color. According to the study of the present inventor, when the black biasing device 7 is opened from the power supply terminal after the switching of the developing bias, noise is more generated when the contacts are opened than when the switching of the developing bias is not performed. It was found that it was easy to occur. If the noise is superimposed on the mark detection signal by the mark sensor via Gnd, the output timing of the write signal may be shifted and color shift may occur. In the case where the illustrated printer is configured to precede the developing operation by the black developing device 7, the black developing device 7 is electrically connected to the power supply terminal after switching the developing bias for convenience in layout. Need to cut. Specifically, in the illustrated printer, the multi-color developing device 6 used for developing the next color is a black developing device 7.
Than the photoreceptor belt one rotation direction,
The traveling distance of the photoreceptor belt 1 from the position where the electrostatic latent image is formed to the developing position by the multicolor developing device is short. For this reason,
The black developing device 7 must be separated from the photoreceptor belt 1 in order to enable development by the multicolor developing device 6 before the electrostatic latent image of the next color reaches the portion facing the multicolor developing device 6. And before the electrical cutting, the multicolor developing device 6
It is necessary to move the multicolor developing device 6 to a developable position and to apply a color developing bias to the multicolor developing device 6 in a state where the developing can be performed. Accordingly, the developing bias is switched from the black developing bias to the color developing bias while the black developing device 7 and the multicolor developing device 6 are connected to the power supply terminal.
Need to be electrically disconnected, the above-described color shift is likely to occur.

When the printer is configured to perform a preceding operation by the black developing device 7, a toner layer is formed on the intermediate transfer belt in the order of black, cyan, magenta, and yellow from the bottom. Then, when this toner layer is collectively transferred onto a sheet 17A as a transfer material,
On A, a toner layer adheres in order from black, cyan, magenta, and yellow, and the uppermost layer becomes a black toner layer. For this reason, the formed image tends to be an image in which black is conspicuous.

On the other hand, when the printer is configured to perform the preceding operation by the multi-color developing device 6, before the multi-color developing device 6 is electrically disconnected from the power supply terminal, the developing process for the color is performed. It is not necessary to switch the bias to the developing bias for black. This is because the traveling distance of the photosensitive belt 1 from the position where the electrostatic latent image is formed to the developing position by the black developing device 7 is long, so that the black electrostatic latent image reaches the portion facing the black developing device 7. In order to make the developing operation by the black developing device 7 possible by the time, each developing device of the multicolor developing device is separated from the photoreceptor belt 1 and before the black is electrically cut, This is because the developing device does not need to be in a state capable of developing. FIG. 4 shows that the order of the developing operation is C, M,
6 is a timing chart at the time of image formation in an example of Y and Bk. When the developing operation by the yellow developing device 6Y is completed,
Disconnect the multicolor developing device from the power supply terminal. At this time, the black developing device 7 is not yet connected to the power supply terminal, and the developing bias supplied from the power supply unit is changed to black for use with both the multicolor developing device 6 and the black developing device 7 disconnected from the power supply terminal. Switch to developing bias (not shown). Thereafter, the black developing device is electrically connected to a power supply terminal to which the black developing bias is supplied, and the black developing device 7 is moved to a position where development is possible. As described above, when the developing operation by the multi-color developing device is performed in advance, it is not necessary to switch the bias before the developing device is electrically disconnected from the power supply terminal.
The above-described noise is less likely to occur, and color shift can be prevented.

However, when the printer is configured to perform the preceding operation by the multi-color developing device 6, when the black toner image is transferred to the intermediate transfer belt 10, the toner of another color is already used. The image has been transferred to the intermediate transfer belt. When one or more toner layers already formed are transferred to the area where the black toner image is to be transferred, a voltage drop occurs according to the resistance of the layer, and the transfer electric field decreases. Would. Therefore, the black toner image is less likely to be transferred in an area where the number of toner layers already formed is large, the amount of black toner adhering to the image is not stable, and an image in which black is not stable may be formed.

Therefore, in the printer according to the present embodiment, the black developing device 7 performs the preceding operation of forming the toner image by the black developing device 7 first, or the multicolor developing device 6
Of the multicolor developing device 6 for forming a toner image in advance by using a configuration in which the order of development can be switched. Thus, the order of development by the two developing devices is switched in accordance with the state of the original or the state of the obtained image to prevent the occurrence of color misregistration and the occurrence of an image in which black is noticeable, and It is possible to select which of the two methods of preventing generation of an unstable image from being performed with priority. For example, if noise is likely to occur at the time of mark detection and color misalignment is likely to occur, the order of development in which noise is less likely to occur when disconnecting from the power supply terminal, specifically, the multicolor developing device 6 Can be switched to perform the preceding operation. Thereby, the noise can be reduced and color shift can be prevented. Further, when the multi-color developing device 6 is switched to perform the preceding operation, the uppermost part of the image formed on the sheet 17A does not become the black toner layer, and the black toner layer is formed of another color toner layer. Since the image is covered, it is possible to prevent an image in which black is conspicuous.
When an image in which black is not stable is easily formed,
It is possible to switch the order of development so that the black toner image is first transferred onto the intermediate transfer belt, specifically, to perform the preceding operation of the black developing device. Thereby, when the black toner image is transferred, a transfer electric field is uniformly applied to the toner, so that the amount of the black toner adhering to the image is stabilized,
The formation of an image in which black is not stable can be prevented.

In order to allow the user to change the order of development, a changeover switch may be provided on a control panel (not shown).

Further, in this printer, there is provided noise detecting means for detecting noise in a detection signal by the mark sensor as the intermediate transfer member position detecting means, and based on the detection result by the noise detecting means, the black developing means is provided. A configuration is adopted in which the CPU 101 having a function as a switching control means controls whether the toner image is formed first by the device 7 or the toner image is formed first by the multicolor developing device 6. . Hereinafter, the switching control of the printer will be described in detail with reference to FIGS.

FIG. 5 is an explanatory diagram for explaining noise detection. The mark detection signal from the mark sensor 105a is input to the above-described I / O control unit 107 and also to a noise detection unit 108 as noise detection means. FIG. 6 shows an example of the noise detection unit 108.
This noise detection unit 108 includes resistors R1, R2, R3, R
4 and an operational amplifier 108a. The input terminal IN of the noise detection unit 108 to which the mark detection signal is input is connected to the inverting input terminal of the operational amplifier 108a via the resistor R1. The operational amplifier 1
The output voltage 08a is fed back to the inverting input terminal via the resistor R2. A power supply terminal E to which a predetermined voltage VE is applied is connected to a non-inverting input terminal of the operational amplifier 108a via a resistor R3. Further, the non-inverting input terminal is grounded via a resistor R4. As a result, the reference voltage Vx determined by the predetermined voltage VE and the resistors R3 and R4 is applied to the non-inverting input terminal. The reference voltage Vx is Vx = VE ·
It is represented by R4 / (R3 + R4), and is set to, for example, the peak value of the mark detection signal. The mark detection signal ideally has a pulse waveform with a peak value of, for example, 0 (V) and Vx (V), as shown in FIG. However, when noise is present on the signal, as shown in FIG. 7B, the noise signal α is superimposed on the pulse waveform, and the higher peak value becomes Vx + α (V). When such a mark detection signal is input to the noise detection unit 108 shown in FIG. 6, only noise corresponding to the mark detection signal is R2 / R
It is amplified and output one-fold. FIG. 7C shows the output waveform. In the figure, the signal VN, which is a signal obtained by amplifying the noise, is represented by VN = R2 · (Vx + α−Vx) /
It is represented by R1. The signal VN is transmitted to the CPU 101
To determine whether or not the noise level is higher than a predetermined standard, for example, a level that may cause an erroneous detection such as a failure to superimpose the colors of the output image.

Further, the printer according to the present embodiment is configured so that it is possible to select whether or not to activate the function of switching the order of development. For example, a changeover switch for turning on and off the switching function is provided on a control panel (not shown) so that a user can select whether to activate the function. Thus, even if a slight color shift occurs, when it is desired to form an image with stable black, the black developing device 7 can forcibly perform the development first. (Hereinafter, margin)

FIG. 8 is a flowchart showing a control example of the switching control. When an image output command or data relating to image output information is received from a personal computer or the like (step s1), it is determined whether or not it is set to operate the black developing device 7 first to perform development (step s).
2). If the black developing device 7 is set to operate first (Y in step s2), the black developing device 7 is operated first to form a black toner image, and then the multi-color developing device 6 is operated to form a color toner image and a superimposed toner image (step s3). Then, noise on the mark detection signal is detected by the noise detection unit 108, and when switching to the multicolor developing device 6, a predetermined signal is added to the mark detection signal by electrical disconnection from the power supply terminal of the black developing device 7. It is determined whether or not noise larger than the level is detected (step s4). Then, when noise larger than the predetermined magnitude is detected (Y in step s4), it is determined whether or not the development order switching function is ON (step s5).
When the switching function is ON, that is, when the function is operated (Y in step s5), for the subsequent image formation, the multicolor developing device 6 is operated first to form the color toner image. After the formation, the black developing device 7 is operated to form a black toner image, thereby forming a superimposed toner image (step s6). Since the developing bias voltage applied to the multicolor developing device 6 is smaller than the developing bias voltage applied to the black developing device 7, when the developing device that performs development is switched to the black developing device 7, Even when electrical disconnection from the power supply terminal is performed, noise hardly occurs. Thus, noise generated at the time of mark detection can be reduced, and color shift due to the noise can be prevented.

If the multi-color developing device 6 is set to operate first in step s2 (step s2
In step N), the multicolor developing device 6 is operated first to form a color toner image, and then the black developing device 7 is operated to form a black toner image, thereby forming a superimposed toner image (step s7). ). If no noise larger than the predetermined magnitude is detected in step s4 (step s4).
4 and N) or when the function of switching the order of development is OFF in step s5 (step s5).
5) N), for the subsequent image formation, the black developing device 7 is operated first to form a black toner image, and then the multicolor developing device 6 is operated to form a color toner image. A toner image is formed (Step s8).

If a desired copy image cannot be obtained even if the order of the development is changed, a serviceman may deteriorate the charging characteristics of the developer (deterioration of the developer) or the photosensitive member. To request repairs.

As described above, according to the embodiment, it is possible to switch between forming the black toner image by the black developing device 7 first and forming the toner image by the multicolor developing device 6 first. Thus, the order of development by the two developing units is switched in accordance with the state of the original or the state of the obtained image to prevent the occurrence of color misregistration, the prevention of an image in which black is conspicuous, and the image in which black is not stable. It is possible to select which of the above and the prevention of occurrence is to be preferentially performed.

According to the above-described embodiment, the switching is automatically performed by the CPU 101 as the switching control means based on the detection result of the noise detection unit 108 which detects noise in the mark detection signal. Can be. Therefore, when the noise is likely to occur due to environmental conditions or the like, the preceding operation of the multicolor developing device 6 in which the noise is unlikely to occur is automatically performed, so that the operability is good.

Further, according to the above-described embodiment, since the function of switching the order of development can be turned ON / OFF, it is possible to form an image in which black is stable even if a slight color shift occurs. Since the development by the first developing means can be forcibly performed first, the usability is good.

In the above-described embodiment, only an example in which a toner image of a plurality of colors is sequentially superimposed and transferred onto an intermediate transfer belt as an intermediate transfer body to form a superimposed toner image has been described. An image forming device that forms a superimposed toner image by superimposing a toner image directly on a photoconductor as an image carrier and then transferring it onto a transfer paper as a transfer body, or as a transfer body without using an intermediate transfer body For example, the present invention can be applied to an image forming apparatus that forms a superimposed toner image by sequentially superimposing and transferring a toner image onto a transfer paper.

[0050]

According to the first aspect of the present invention, it is possible to prevent the occurrence of an image in which black is conspicuous and the occurrence of an image in which black is not stable in accordance with the state of a document or the state of an obtained image. There is an excellent effect that it is possible to select which one is preferentially performed.

According to the second to fourth aspects of the present invention, priority is given to either the prevention of color misregistration or the prevention of occurrence of an image in which black is not stable, depending on the state of the document or the state of the obtained image. There is an excellent effect that it is possible to select whether to perform the process. By switching the order of development so that the uppermost layer of the image to be formed is not a black toner layer, there is also an effect that an image in which black is conspicuous can be prevented from being formed.

According to the third and fourth aspects of the present invention, the switching control means can automatically switch the developing means to be operated first based on the detection result by the noise detecting means. Therefore, when the noise is likely to be generated due to environmental conditions or the like, the preceding operation of the second developing unit, which is less likely to generate the noise, is automatically performed, so that there is an excellent effect that operability is good.

In particular, according to the fourth aspect of the present invention, it is possible to select whether or not to perform the switching control by the switching control means, so that even if a slight color shift occurs, it is possible to form an image in which black is stable. If you want to
There is an excellent effect that the development by the developing means can be performed first and the usability is good.

[Brief description of the drawings]

FIG. 1 is a front view illustrating a schematic configuration of a color printer according to an embodiment.

FIG. 2 is a timing chart at the time of image formation in an example in which the order of the developing operation is Bk, C, M, and Y.

FIG. 3 is a block diagram showing a schematic configuration of a control system of the printer.

FIG. 4 is a timing chart at the time of image formation in an example in which the order of the developing operation is C, M, Y, and Bk.

FIG. 5 is an explanatory diagram for describing noise detection.

FIG. 6 is a circuit diagram showing an example of a noise detection unit 108.

FIG. 7 is an explanatory diagram for describing a mark detection signal.

FIG. 8 is a flowchart illustrating a control example of switching control of the printer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor belt 4 Charging charger 5 Laser writing unit 6 Multicolor developing device 7 Black developing device 10 Intermediate transfer belt 101 CPU 105a Mark sensor 108 Noise detector

Claims (4)

[Claims] A first developing means for developing using black toner; a second developing means for developing using toner of one or more colors other than black; and a toner image formed by the first developing means. An intermediate transfer means for sequentially transferring the toner image formed by the second developing means and the toner image formed by the second developing means on an intermediate transfer body, and transferring the toner image superimposed on the intermediate transfer body onto a transfer material to form a superposed toner image. In the image forming apparatus capable of forming the toner image, when forming the superimposed toner image, the formation of the toner image by the first developing unit may be performed first, or the formation of the toner image by the second developing unit may be performed. An image forming apparatus provided with a switching unit for switching whether to perform printing first. A first developing means configured to be electrically connectable and disconnectable to a first power supply terminal of the apparatus main body and performing development using black toner; and a second developing means of the apparatus main body. It is configured to be electrically connectable and disconnectable to the power supply terminal, performs development using toner of one or more colors other than black,
And a second developing unit that is less likely to generate noise when disconnecting from the second power supply terminal than when disconnecting from the first power supply terminal of the first developing unit. Have
Each of the first developing means and the second developing means is
Except when developing, the power supply terminal is electrically disconnected from the power supply terminal, and the toner image formed by the first developing unit and the toner image formed by the second developing unit are overlapped to form an image. An image forming apparatus capable of superposing a toner image formed by the first developing unit and a toner image formed by the second developing unit to form an image. An image forming apparatus comprising: a switching unit that switches between forming first and forming the toner image by the second developing unit first. 3. A recording medium position detecting means for detecting a moving position of a recording medium on which a toner image is superimposed on a surface, as a reference for superimposing the toner images.
In the above image forming apparatus, noise detecting means for detecting noise in the detection signal by the recording body position detecting means is provided, and switching control means for controlling the switching means based on a detection result by the noise detecting means is provided. An image forming apparatus comprising: 4. An image forming apparatus according to claim 3, wherein said switching control means is configured to enable selection of whether or not to perform switching control by said switching control means.