JPH08194351A - Image forming device - Google Patents

Abstract

PURPOSE: To prevent a toner image transferred by an image forming unit on the upstream side from being disturbed by the photoreceptor drum of a developing unit on the downstream side which is not submitted for image forming. CONSTITUTION: The image forming units M, C, Y and Bk are disposed in order from the upstream side. The toner image formed on the photoreceptor drum 10M is transferred on a transfer belt 30 by a transfer roller 24. In the case the image forming unit C is not submitted for image forming, the photoreceptor drum 10C is rotated, while the actuation of the developing device is stopped. Thus, toner is prevented from adhering to a transfer material 18 on which the toner image is transferred by the developing unit M in the developing unit C, and the toner image is prevented from being rubbed by the drum 10C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as electrophotographic apparatuses have been miniaturized, highly functionalized, and color-developed, while improving reliability, system deployment, maintenance-free, and human and environment friendly. Demands for being gentle are increasing, and various products have been proposed to meet these demands.

Among these, in order to increase the speed of color image output, an apparatus for stacking a plurality of photoconductors and carrying a transfer material such as paper by a belt-like carrying means while sequentially carrying out multiple transfer of toner images is disclosed. Proposals have been made. As an example, FIG.
Shows an example of a laser beam copying machine for color.

The copying machine shown in FIG. 1 has a plurality of image forming units, and a transfer belt, which is a transfer material conveying means, is arranged vertically through each image forming unit. In each of the image forming units M, C, Y, and Bk, a cylindrical photosensitive member (hereinafter appropriately referred to as “photosensitive drum”) 10M, 10C, 10Y, and 10Bk as an electrostatic latent image carrier is indicated by an arrow a (image. Only the forming unit M is supported so as to be rotatable in the direction shown in the figure and the same in the other directions. 11M, 11C, 11Y,
11Bk is a primary charger, which is a photosensitive drum 10M,
10C, 10Y, and 10Bk are installed at predetermined intervals. Reference numerals 14M, 14C, 14Y, and 14Bk denote laser exposure devices (laser scanners), and the photoconductor 10M is located downstream of the primary chargers 11M, 11C, 11Y, and 11Bk in the rotational direction of the photoconductor drums 10M, 10C, 10Y, and 10Bk. 10C, 10Y, and 10Bk are exposed. Reference numerals 16M, 16C, 16Y, and 16Bk denote developing units that store magenta, cyan, yellow, and black toners, respectively, and are the photosensitive drums 10M, 10C, 10Y, and
The photosensitive drum 1 is provided further downstream than the exposure position of 10 Bk.
It is installed so as to be adjacent to 0M, 10C, 10Y, and 10Bk.

Reference numeral 18 is a transfer material such as paper. Reference numeral 20 denotes a paper feeding unit, which supplies the transfer material 18. Reference numeral 30 is a transfer belt, which is a photoconductor 10M, 10C, 10Y, 10Bk.
And is driven in the direction of arrow b. Reference numeral 32 is a drive roller, and 31 is a separation roller, which drives the stretched transfer belt 30.

The transfer chargers 24M, 24C, 24Y, and 24Bk are arranged in order from the upstream side in the moving direction of the transfer belt 30 to the respective photosensitive drums at the transfer positions so as to sandwich the transfer belt 30. A fixing device 38 is arranged adjacent to the separating roller 31 of the transfer / conveying belt 30.

Denoted at 15M, 15C, 15Y, and 15Bk are cleaners for the respective photosensitive drums, and the respective transfer chargers 24 are provided.
Each photosensitive drum 1 for M, 24C, 24Y, 24Bk
It is installed downstream in the rotational direction of 0M, 10C, 10Y, and 10Bk. 13M, 13C, 13Y, 13Bk are pre-exposure lamps, and each cleaner 15M, 15C, 15Y,
15Bk and each primary charger 11M, 11C, 11Y, 11
It is installed between Bk. A belt cleaner 51 cleans the transfer belt 30.

The operation of the image forming apparatus configured as described above will be described by taking the image forming unit M as an example.
The operation of other image forming units is similar.

First, the photosensitive drum 10M has an optical semiconductor layer on the surface of a conductive substrate such as aluminum, and rotates in the direction of arrow a. Then, the surface is uniformly negatively charged by the primary charger 11M, and then exposure is performed by the laser exposure device 14M to form an electrostatic latent image corresponding to the original. The developing device 16M performs development using negatively charged toner to form a toner image corresponding to the electrostatic latent image on the surface of the photosensitive drum 10M. The toner image formed on the surface of the photosensitive drum 10M is transferred to the transfer material 18 supplied from the paper feeding unit 20 toward the transfer belt 30 in synchronization with the image formation at the rotation speed of the photosensitive drum 10M. .

The above operation is performed in each image forming unit, and the toner image formed on each photosensitive drum is sequentially transferred onto the transfer material 18 held on the transfer belt 30. In the full color mode, M, C,
Transferred in the order of Y and Bk, and in the case of the single color mode or the two or three color mode, the toner of the required color is transferred in the same order as described above.
Multiplexed on top. Copy paper 18 on which the toner image is transferred
Is supplied to the fixing device 38 by the transfer belt 30, and is fixed on the transfer material 18 by being heated and pressed.

On the other hand, in the photosensitive drum 10M from which the toner image has disappeared due to the transfer, the residual toner adhering to the surface is removed by the cleaner 15M, and further the charge is removed by the pre-exposure lamp 13M, so that the next image formation is performed. Be served. The surface of the transfer belt 30 that has finished supplying the transfer material 18 to the fixing device 38 is cleaned by the belt cleaner 51.

A number of such color image forming apparatuses have been proposed, but recently, a simultaneous development cleaning system is adopted for downsizing, ozoneless, and ecological measures by eliminating waste toner. In addition, a copying machine, a print, or the like that employs a cleanerless system that collects and reuses transfer residual toner has been put into practical use. In particular, in the case of adopting such a method, the practicality is further increased by using a spherical toner produced by a polymerization method as the toner.

Here, referring to FIG. 6, the reason why the toner recycling process by the cleanerless and the simultaneous cleaning with the development can be achieved by the spherical toner produced by the polymerization method is described from the viewpoint of the adhesive force between the toner and the photoconductor. explain.

When the toner adheres to the photoconductor by the developing process (bias, latent image potential), the main forces acting on the toner contacting the photoconductor surface are the mirroring force and the Van der Waals force. . The mirroring power largely depends on the amount of electric charge and its distance.

The pulverized toner produced by pulverization, which is a conventional toner, has irregularities in the surface shape, so that electric charges are concentrated on the convex portions during triboelectric charging. On the other hand, the spherical polymerized toner obtained by the polymerization method has a spherical surface or a shape close to a spherical surface, so that the surface is uniformly charged.

In the pulverized toner, the projections come into contact with each other and a large amount of electric charge exists in a very close region, so that the mirroring power is increased. On the other hand, when the toner has a spherical shape like the polymerized toner, the contact state becomes almost point-like, the amount of electric charge in the adjacent region is small, and the mirroring power is smaller than that of the pulverized toner.

The Van der Waals force becomes very large under the condition that the more adjacent regions are in contact with each other and contact with each other in a plane. When the pulverized toner is used, among many toners, a large number of toners come into contact with each other in the state shown in FIG. 6, and in this case, the Van der Waals force becomes very large. On the other hand, since the surface shape of the polymerized toner is spherical, the toner contacts at almost all points. Therefore, the Van der Waals force is also smaller for the polymerized toner.

For the above reasons, in the case of polymerized toner having a nearly spherical shape, the mirroring force, the Van der Waals force, and
That is, the adhesive force becomes small, the transfer residual toner in transfer is small, and the toner collecting effect at the time of simultaneous cleaning at the time of development becomes large, and cleanerless and simultaneous cleaning at the time of development become possible.

In the four-drum (there are four photosensitive drums) full-color printer having the structure shown in FIG.
For example, in the case of the two-color mode (magenta and cyan), the transfer material 18 supported on the transfer belt 30 is sequentially transferred to the magenta, cyan, yellow and black image forming units M, C, Y and Bk. Although the image forming unit passes through, only the desired unit, that is, the magenta and cyan image forming units M and C in the above description, need be operated.

[0020]

However, as described above, the transfer material 18 is the magenta, cyan, yellow, and black image forming units M, C, Y, and Bk sequentially.
And is passed through the gap between the transfer belt 30 and each photosensitive drum. Therefore, when all the image forming processes of the undesired units, that is, the yellow and black image forming units Y and Bk described above are stopped, the transfer material 18
Is a magenta and cyan toner image already formed on the transfer material when passing through the gap between the photosensitive drums 10Y and 10Bk of the yellow and black image forming units Y and Bk and the transfer belt 30 as described above. The black photosensitive drums 10Y and 10Bk rub against each other to disturb the image. In particular, when spherical toner is used as in this example, the toner itself tends to roll, so that the damage caused by printing becomes large.

At this time, the magenta and cyan toners transferred onto the transfer material 18 at this time are electrostatically attracted to the transfer material 18, but the transfer material 18 is yellow.
When passing through the gaps between the black photosensitive drums 10Y, 10Bk and the transfer belt 30, these photosensitive drums 10Y, 10Bk
A part of the magenta and cyan toners may be reversely transferred to Y and 10Bk (transfer offset), and in this case also, there arises a problem that image deterioration is observed.

Further, when the transfer offset as described above occurs, that is, when the magenta and cyan toners are reversely transferred to the yellow and black photosensitive drums, they are collected simultaneously with the development without the drum cleaner, and are thus collected in the developing device. The problem of toner color mixing also occurs.

Furthermore, in such a case, when the transfer material 18 passes through the gap between the photosensitive drum and the transfer belt 30, the transfer material is apt to jam (jam).

Therefore, it is an object of the present invention to provide an image forming apparatus capable of favorably forming a desired toner image on a transfer material.

[0025]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and includes an image carrier movably supported and a latent image formation for forming a latent image on the image carrier. Means, a developing-simultaneous cleaning means for developing a toner image by adhering toner to the latent image, and simultaneously cleaning residual toner after transfer, and a transfer means for transferring the toner image from the image carrier to an image receiving member. In an image forming apparatus in which a plurality of image forming units each including the image receiving member are arranged from the upstream side to the downstream side in the moving direction of the image receiving member, the image forming unit is provided at least on the downstream side of the developing unit currently performing the transfer operation. In the developing unit, at least
The moving operation of the image carrier is continued and the operation of the developing unit is stopped.

An image carrier movably supported,
A latent image forming means for forming a latent image on the image bearing member; a simultaneous development developing means for developing a toner image by adhering toner to the latent image and simultaneously cleaning transfer residual toner after transfer; and the toner. An image forming unit having a transfer means for transferring an image from the image carrier to the image receiving member,
In the image forming apparatus in which a plurality of image forming members are arranged from the upstream side to the downstream side in the moving direction of the image receiving member, in the developing units other than the developing unit which is actually performing the transfer operation,
At least, the moving operation of the image carrier is continued and the operation of the developing unit is stopped.

Further, an movably supported image bearing member, a latent image forming means for forming a latent image on the image bearing member, a toner adhered to the latent image and developed as a toner image, and after transfer. And an image forming unit provided with a transfer means for transferring the toner image from the image carrier to the image receiving member at the same time, from the upstream side in the moving direction of the image receiving member to the downstream side. In a plurality of image forming apparatuses arranged toward the side, image receiving member urging means for selectively urging the image receiving member with respect to each image carrier, and urging of the image receiving member with respect to each image carrier. Image receiving member releasing means for selectively releasing.

In this case, the image receiving member urging means may also serve as the transfer electric field applying means.

In these image forming apparatuses, the image receiving member is a transfer material conveying means that moves while carrying a transfer material on which the toner image on the image carrier is transferred, or a secondary image of the toner image on the transfer material. It may be an intermediate transfer member to which the toner image on the image carrier is primarily transferred prior to transfer.

[0030]

According to the above construction, for example, when the image forming unit on the downstream side of the image forming unit to which the toner image is actually transferred does not form the image, the developing means is not provided in the image forming unit which does not form the image. Since it is stopped, no toner image is formed on the image carrier. Therefore, the toner image is not transferred to the image receiving member (for example, the transfer material or the intermediate transfer member) that passes through the developing unit. Further, since the image carrier moves in this developing unit, the toner image transferred on the upstream side is not disturbed by rubbing or the like.

Further, such an operation can be realized by selectively urging the image receiving member with respect to the image carrier or selectively releasing the urging.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 shows a schematic configuration of an image forming apparatus according to the present invention. It should be noted that members having the same configurations and functions as those of the image forming apparatus shown in FIG. 5 described above are denoted by the same reference numerals, and redundant description thereof will be appropriately omitted.

The image forming apparatus shown in the figure is a 4-drum full color printer. In the present embodiment, a cleanerless device that eliminates a cleaner and performs simultaneous cleaning with development by a developing device is mounted, and as image forming units, image forming units of four colors of magenta, cyan, yellow, and black 10M, 10C, and 10Y. 10 Bk
Have. The image forming unit of each image forming unit will be described by taking the image forming unit M as an example. The photosensitive drum 10M as an image carrier and image forming means arranged around the photosensitive drum 10M, that is, the charging roller 12M and the laser exposure device 14M, A developing device 16M and a pre-exposure lamp 13M are provided. Further, in the present embodiment, a transfer material carrier (image receiving member) located at the transfer portion.
The transfer belt 30 is used as the. The transfer material 18 fed by the paper feed roller 20 is transferred to the transfer belt 30.
Each image forming unit M, C, Y
The transfer rollers 24M, 24 are conveyed to the Bk transfer unit.
The toner image of each color is transferred by C, 24Y, and 24Bk. Further, the transfer material 18 that has completed the transfer process is separated from the transfer belt 30 and the toner image is fixed on the surface by the fixing device 38.

In the following description, the photosensitive drums 10M, 10C, 10Y and 10Bk are simply referred to as "photosensitive drum 10" unless it is necessary to distinguish them.
The same applies to other members.

According to the present invention having the above-mentioned structure, in the monochromatic mode, the two-color or the three-color mode, that is, when all four colors of magenta, cyan, yellow, and black are not used, a color other than the desired color is obtained. Image forming means in the image forming unit, that is, the photosensitive drum 10 and the charging roller 1.
2, laser exposure device 14, developing device 16, transfer roller 2
4. Among the pre-exposure lamps 13, only the operation of the developing device 16 is stopped, and the other process devices are normally operated as in the full color mode.

The term "stopping the operation of the developing device 16" as used herein means that a bias for generating a developing electric field is not applied, or a bias that does not develop is applied, or the photosensitive drum 10 and the developing device 16 are prevented from developing. It is shown that the toner is not developed on the photosensitive drum 10 by separating and, and the means may be a method suitable for the developing device and the developing method to be adopted.

At this time, the transfer roller 24 is an electric field applying means configured to apply an electric field having a polarity opposite to the charging polarity of the toner particles, and in this embodiment, a roller charger as shown in FIG. 1 is used. However, other charging devices may be used as long as the above-mentioned requirements can be satisfied.

Next, the operation of the image forming apparatus having the above configuration will be described by taking the magenta monochrome mode as an example.

Since the magenta single color mode is selected in the image forming apparatus, in the image forming units of the cyan, yellow and black image forming units C, Y and Bk, process devices other than the developing units 16C, 16Y and 16Bk are not used. The operation is performed in the same manner as in the normal full color mode, and in the magenta image forming unit M, all the image forming units are operated as usual.

Transfer material 18 fed from paper feed roller 20
First passes through the magenta image forming unit M, and at this time, a magenta toner image is formed on the surface thereof by a normal image forming process. After that, it passes through the gap between the photosensitive drum 10C of the cyan image forming unit C and the transfer belt 30. At this time, in the cyan unit, the photosensitive drum 10C, the charging roller 12C, the laser exposure device 14
C, the transfer roller 24C, and the pre-exposure lamp 13C are operating, but the developing device 16C is stopped.
Although a latent image may be formed on 0C, the latent image is not developed. Therefore, the cyan toner image is not transferred onto the passing transfer material 18.

Further, even when the transfer material 18 carrying the magenta toner image passes through the gap between the photosensitive drum 10C of the cyan image forming unit C and the transfer belt 30, the surface of the photosensitive drum 10C becomes the transfer belt 30. Since it moves in the same direction, the image is not damaged by the magenta toner image on the transfer material 18 being rubbed against the photosensitive drum 10C, and the electric field having the opposite polarity to the toner is generated by the transfer roller 24C. Since the transfer material 18 is applied to the transfer material 18, the suction force between the transfer material 18 and the toner is strongly maintained.
The magenta toner on No. 8 does not reversely transfer to the photosensitive drum 10C. In addition, in this gap, the transfer material 18 and the transfer belt 30 generate a suction force due to the action of the transfer electric field, and the two are in close contact with each other, so that the transfer material 18 is not jammed.

Hereinafter, even when the transfer material 18 passes through the yellow and black image forming units Y and Bk, the magenta toner image formed on the transfer material 18 is the same as when the transfer material 18 passes through the cyan image forming unit C. Will not hurt. The transfer material 18 that has undergone the transfer process for the above four colors is separated from the transfer belt 30, and the toner image is fixed on the surface of the fixing device 38.

Even in the two-color mode and the three-color mode, it is possible to obtain an image of good quality without disturbing the image on the transfer material as in the case of the single-color mode.

2 and 3 show the operating state of each process device. FIG. 2 shows a normal operating state of each process apparatus at the time of full-color image formation and an operating state of each process apparatus of an image forming unit of a desired color at a single color mode, and FIG. 3 shows a single color mode or a non-full color mode. The operation state of each process device in the image forming unit other than the desired time is shown. <Second Embodiment> In the first embodiment, the transfer belt 3 is used.
The image forming units M, C, Y, and Bk directly transfer the toner image onto the transfer material 18 carried on the image forming apparatus. In this embodiment, an intermediate transfer member (image receiving member) may be used instead of this. As shown in FIG. 4, an intermediate transfer belt (intermediate transfer member) 26 is passed between each image forming unit and the transfer roller 24, and the toner formed on each of the image forming units is sequentially formed on the intermediate transfer belt. Transfer the image. After that, the transfer material 18
The toner image is transferred to at once. <Third Embodiment> Recently, digitalization of copying machines and printers has been progressing along with full colorization and systemization. For example,
Devices such as laser beam printers, which scan a laser beam and form a latent image on a photosensitive drum by turning the laser beam on and off to record a desired image, have become widely known. Its typical application is binary recording of characters and figures. In that respect, since printing of characters, figures, etc. does not require halftones, the printer structure can be simplified.

By the way, there is a printer capable of forming a halftone even with such a binary recording system. As such a printer, one using a dither method, a density pattern, or the like is well known. However, as is well known, a printer adopting the dither method or the density pattern method cannot obtain high resolution.

Therefore, in recent years, a method of forming a halftone pixel in each pixel without lowering the recording density has been proposed. In this method, halftone formation is performed by pulse width modulation (PWM) of a laser beam with an image signal. According to this method, an image with high resolution and high gradation can be formed.

In the present embodiment, for the purpose of downsizing the apparatus and eliminating waste toner, a cleanerless apparatus for eliminating the cleaner and carrying out simultaneous cleaning by the developing apparatus is mounted. Simultaneous development cleaning is a method of collecting transfer residual toner slightly remaining on the photosensitive drum after transfer by a fog removing bias at the time of development after the next step. According to this method, the transfer residual toner is collected and used in the subsequent steps, so that the waste toner can be eliminated. In addition, the advantage in terms of space is great, and the size can be greatly reduced.

The third embodiment will be described with reference to FIGS.

First, as shown in FIG. 7, the original 2 is set on the original table 3 with the side to be copied facing down. Then, copying is started by pressing the copy button. The original 2 is illuminated by the original illumination lamp 4, and the reflected light is input to the CCD sensor 7.

The CCD sensor 7 comprises a light receiving section, a transfer section and an output section. An optical signal is converted into an electric signal in the CCD light receiving part, and is sequentially transferred to the output part in synchronization with the clock pulse in the transfer part, and the charge signal is converted into a voltage signal in the output part, amplified, made into a low impedance and outputted. . The unlogged signal thus obtained is subjected to known image processing, converted into a digital signal, and sent to the printer section.

The printer unit receives the above image signal and forms an electrostatic latent image as follows.

The photosensitive drum 10M is rotationally driven in the direction of the arrow around the central support shaft at a predetermined peripheral speed, and in the course of the rotation, the charging roller 12M receives a uniform negative charging process.
The surface of the photosensitive drum 10 is formed on the surface of the photosensitive drum 10 by scanning the uniformly charged surface with light from the semiconductor laser element 102 (see FIG. 8) which emits ON and OFF in response to an image signal by a rotating polygon mirror 104 rotating at high speed. An electrostatic latent image corresponding to the original image is sequentially formed.

FIG. 2 shows a schematic structure of a laser scanning section 100 for scanning a laser beam in the above apparatus. When the laser beam is scanned by the laser scanning unit 100, the semiconductor laser element 102 is blinked at a predetermined timing by the light emission signal generator 101 based on the input image signal.

The laser light emitted from the semiconductor laser element 102 is converted into a substantially parallel light flux by the collimator lens system 103, and further scanned in the arrow K direction by the rotary polygon mirror 104 rotating in the arrow c direction, and fθ. The lens groups 105a, 105b, 105c form a spot image on the surface to be scanned 106 such as the photosensitive drum.

An exposure distribution for one scan of the image is formed on the surface to be scanned 106 by such scanning with the laser beam, and the surface to be scanned 106 is scrolled by a predetermined amount perpendicular to the scanning direction for each scan. By doing so, an exposure distribution according to the image signal can be obtained on the surface to be scanned 106. The electrostatic latent image formed as described above is developed by the developing device described below.

FIG. 9 is a schematic view of the developing device 16 for two-component magnetic brush development used in this embodiment. Although the developing device 16M containing magenta toner is described in this figure, the other developing devices 16C, 16Y, and 16Bk have the same configuration and operate in the same manner. In the figure, 161 is a developing sleeve,
Reference numeral 162 is a magnet roller fixedly arranged in the developing sleeve, 163 and 164 are stirring screws, 165 is a regulating blade arranged to form a thin layer of developer on the developing sleeve surface, and 166 is a developing container.

Now, a developing process for developing an electrostatic latent image by the two-component magnetic brush method using the developing device 16 and a developer circulation system will be described. First, the developer drawn up by the N2 pole as the developing sleeve 161 rotates is
In the process of transporting from the S2 pole to the N1 pole, the regulation blade 165 arranged perpendicularly to the developing sleeve 161.
And a thin layer is formed on the developing sleeve 161.

Here, when the thin-layered developer is conveyed to the main developing pole S1, the spikes are formed by the magnetic force. The electrostatic latent image is developed by the developer formed in the spike shape, and then the developer on the developing sleeve 161 is returned into the developing container 166 by the repulsive magnetic field of the N3 pole and the N2 pole.

A DC and AC developing bias is applied from a power source to the developing sleeve 161 to apply it to the photosensitive drum 10M.
A toner image is formed on top. The toner image thus formed by the developing device 16M is transferred by the transfer device as described below, while the surface of the photosensitive drum 10 after the toner transfer is repeatedly subjected to image formation with the transfer residual toner remaining. It

The toner remaining after the transfer is charged by the charging roller 1.
By the action of 2M, the polarity is adjusted to the negative regular charging polarity, and is carried to the developing area, and is collected in the developing container 166 by the action of the fog removing bias potential of the developing bias.

The transfer device includes a transfer belt 30 stretched around a drive roller 32, a separation roller 31, transfer rollers 24M, 24C, 24Y, and 24Bk, and a belt cleaner 51 for cleaning the transfer belt 30. Adsorption roller 5 for adsorbing the transfer material 18 on the transfer belt 30
a and an electrode roller 5b which is the counter electrode thereof.

The transfer roller 24M disposed facing each of the photosensitive drums 10M (in this description, the magenta image forming unit M is described as a representative) is provided with a side plate 40 as shown in FIG. Both ends of a locking groove 41 provided in the up and down direction are axially supported, and each of them is biased upward by a magenta biasing means (image receiving member biasing means) 37.

As a result, the transfer belt 30 is in contact with the surface of the photosensitive drum 10M which faces the transfer belt 30. The magenta urging means 37 is mounted between the base portion 370 formed below the locking groove 41 and the end portion of the magenta transfer roller 35M, and the compression spring 37 urges the transfer roller 24M upward.
2 and.

The transfer device 3 has a magenta urging means 3.
It has a magenta releasing means 39 for releasing the contact between the transfer belt 30 and the magenta photosensitive drum 10M by 7. As shown in FIGS. 11 and 13, the magenta releasing means 39 includes a pair of swing levers 393, one ends of which are connected by a connecting lever 391, and a connecting bar 3 via a hook 395.
It is composed of a magenta solenoid 397 which is locked to 91 and swings the swing lever 393. Swing lever 39
3, the substantially central portion of which is axially supported by the side plate 40 by the pin 399, and the lower side of the other end is arranged so as to face the upper side of the magenta transfer roller 24M.

As shown in FIG. 10, the magenta solenoid 397 is turned on / off under the control of the CPU by the operation of a color mode selection key on an operation panel (not shown) or a signal based on the original reading data by the reader. At the same time, the rocking lever 393 is rocked to resist the urging force of the compression spring 372 to push down the magenta transfer roller 24M at the other end of the rocking lever 393 (see FIGS. 12 and 14). ).

Then, the magenta operation stopping means 5 for stopping the operation of the magenta photosensitive drum 10M whose contact is released.
0 is provided in combination with the magenta canceling means 39.

That is, the magenta operation stopping means 50 of the present embodiment, as shown in FIG.
3 has a release lever 500 extending from the other end thereof and integrally provided with the swing lever 393.
The swing lever 393, the magenta solenoid 397, etc. are shared.

The release lever 500 is arranged such that its tip is in contact with a swing bearing 18 that supports a pair of idle gears 17a and 17b meshing with each other. The rocking bearing 18 is swingably provided around the shaft of one idle gear 17b and is attached to the shaft of the other idle gear 17a.
Therefore, the other idle gear 17a is meshed with the drive gear of the magenta photosensitive drum 10M. As a result, when the magenta solenoid 397 is on, the engagement between the drive gear and the idle gear 17a is released (see FIG. 14).

Hereinafter, each of the cyan, yellow, and black image forming units C, Y, and Bk has the same structure.

The color image forming apparatus of this embodiment is configured as described above.

When forming a single color image of only one color with this color image forming apparatus, first, the color mode selection key on the operation panel is operated, or an image is generated by a signal based on the original reading data by the reader. An image forming unit of a desired color used for forming is selected.

Here, for example, when the magenta image forming unit M is selected, the solenoids 397 of the cyan, yellow and black image forming units are turned on and the swing lever 393 swings around the pin 399. To do.
As a result, the other end of the swing lever 393 moves downward against the urging force of the compression spring 372, and the cyan, yellow, and black transfer rollers 24C, 24Y, and 24Bk are pushed downward to transfer the transfer belt 30 and cyan, The contact with the yellow and black photosensitive drums 10C, 10Y, and 10Bk is released.

At the same time, as shown in FIG. 14, the release lever 500 provided integrally with the swing lever 393 moves downward to press the swing bearing 18 downward. As a result, the oscillating bearing 18 has one drive gear and the idle gear 17
Release the mesh with a.

Therefore, the cyan, yellow, and black photosensitive drums 10C, 10Y, and 10Bk are in a state of not contacting the transfer belt 30 without receiving drive transmission from the drive motor. When the cyan, yellow, and black photosensitive drums 10C, 10Y, 10Bk do not operate, the CPU controls so that the cyan, yellow, and black image forming units do not operate.

When the start switch is turned on in this state, first, an electrostatic latent image corresponding to the original image is formed on the surface of the magenta image forming unit M, and this electrostatic latent image is visualized by the developing device 16M. To form a toner image.

On the other hand, the transfer belt 30 orbits at the same speed as the rotational speed of the magenta photosensitive drum 10M. Then, the transfer material 18 is sent out by the registration roller 20 in synchronization with the electrostatic latent image formed on the surface of the magenta photosensitive drum 10M, and is sucked and conveyed onto the transfer belt 30 by the action of the suction roller 5a and the counter electrode roller 5b. To be done.

The transfer material 18 is the magenta photosensitive drum 1.
The toner image on the magenta photosensitive drum 10 is transferred by the transfer electric field applied by the magenta transfer roller 24M at the same time as being sandwiched between 0M and the transfer belt 30 pushed up by the magenta transfer roller 24M.

After that, the transfer material 18 on the transfer belt 30
Is separated from the magenta photosensitive drum 24M and is conveyed without contact with the cyan, yellow, and black photosensitive drums as the transfer belt 30 moves, and is separated from the transfer belt 30 by the separation roller 31 and fixed. 38
The toner on the transfer material 18 is fixed by the heat and pressure action of the fixing device 38, and an image is output.

On the other hand, after the transfer of the toner image, the transfer residual toner remains on the surface of the magenta photosensitive drum 10M and is repeatedly used for image formation. The transfer residual toner is collected in the developing device 166 by the fog removing potential of the developing bias at the time of developing the image formation after the next process.

When the cyan image forming unit Y is selected by the selection key or when a signal based on the image reading by the reader is used, the solenoids of the magenta, yellow, and black image forming units M, Y, and Bk are selected. Is turned on and the solenoid of the cyan image forming unit C is turned off. This gives magenta, yellow,
The black photosensitive drums 10M, 10Y, 10Bk do not receive drive transmission from the drive motor, and the transfer belt 30
Then, the cyan image forming unit C alone forms an image.

Further, when all the image forming units are selected by the selection key or a signal based on the image reading by the reader, the solenoids of all the image forming units are turned off and all the image forming units are formed. The toner images formed by the units are sequentially transferred to the transfer material 18 in a multiplex manner to form a full-color image.

As described above, in the full-color image forming apparatus of the present embodiment, when an image is formed without using all the image forming units as in the case of monochromatic black, the photosensitive drum and the transfer belt 30 which are not used are not used. Since the transfer material is not in contact, the toner already transferred onto the transfer material does not reversely transfer to the unused photosensitive drum, so that the color mixture of the toner due to the simultaneous development collection can be prevented.

Further, since the image forming unit which is not used is controlled so as not to operate, it is possible to omit a wasteful operation, and as a result, the running cost can be reduced. Furthermore, the toner image on the transfer material is not disturbed,
The occurrence of jam can also be prevented.

In this embodiment, a plurality of image forming units are juxtaposed and the transfer belt 30 is arranged so as to vertically penetrate the image forming units. However, for example, instead of the transfer belt 30, An image may be formed by using a transfer drum, an intermediate transfer member, or the like, and a single-component developing method may be used instead of the two-component magnetic brush developing method in the simultaneous development collection.

The latent image forming method and the transfer method are not limited to the description of this embodiment, and the transfer belt 3 is used.
0 and the contact and release mechanism with respect to the photosensitive drum are not limited to the method of moving the transfer electric field applying means up and down as in the present embodiment.
A contact and release means may be separately provided, and the control method for contact and release is not limited to this.

[0086]

As described above, according to the present invention,
The image carrier of the developing unit on the downstream side, which is not used for image formation, prevents the image carrier transferred on the transfer material on the upstream side from being rubbed and disturbed. Also, the jam of the transfer material is reduced.

Further, the toner transferred onto the transfer material at the upstream side is prevented from being retransferred to the image carrier at the downstream side, and therefore, for example, when a developing device by simultaneous development recovery is used, Color mixing of toner in the developing device can be prevented.

[Brief description of drawings]

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

FIG. 2 is a timing chart showing an operating state of the image forming apparatus according to the first embodiment.

FIG. 3 is a timing chart illustrating an operating state of the image forming apparatus according to the first exemplary embodiment.

FIG. 4 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 5 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 6 is a diagram illustrating a relationship between a toner shape and a mirroring force and a Van der Waals force.

FIG. 7 is a schematic configuration diagram of an image forming apparatus according to a third embodiment.

FIG. 8 is a configuration diagram of a laser scanning unit according to a third embodiment.

FIG. 9 is a configuration diagram of a developing device according to a third embodiment.

FIG. 10 is a block diagram of control mainly including a CPU.

FIG. 11 is a side view showing a biasing means and a releasing means.

FIG. 12 is a side view showing a state in which the releasing means is activated.

FIG. 13 is a side view showing the operation stopping means.

FIG. 14 is a side view showing a state in which the operation stopping means is operated.

[Explanation of symbols]

10, 10M, 10C, 10Y, 10Bk image carrier (photosensitive drum) 12, 12M, 12C, 12Y, 12Bk charging device (charging roller) 16, 16M, 16C, 16Y, 16Bk developing device (developing device) 24M, 24C, 24Y, 24Bk transfer means (transfer roller) 26 image receiving member (intermediate transfer member) 30 image receiving member (transfer material carrier, transfer belt) 37 image receiving member urging means (transfer belt urging means) 39 image receiving member releasing means (transfer belt) Release means) M, C, Y, Bk image forming unit

Claims (6)

[Claims] 1. A movably supported image carrier, latent image forming means for forming a latent image on the image carrier, toner attached to the latent image to develop as a toner image, and after transfer. And an image forming unit provided with a transfer means for transferring the toner image from the image bearing member to the image receiving member at the same time, from the upstream side to the downstream side in the moving direction of the image receiving member. In a plurality of image forming apparatuses arranged toward the side, at least in the developing unit arranged at least on the downstream side of the developing unit currently performing the transfer operation, at least the moving operation of the image carrier is continued and the developing operation is performed. An image forming apparatus, characterized in that the operation of the means is stopped. 2. An image bearing member movably supported, a latent image forming means for forming a latent image on the image bearing member, toner attached to the latent image to develop as a toner image, and after transfer. And an image forming unit provided with a transfer means for transferring the toner image from the image carrier to the image receiving member at the same time, from the upstream side in the moving direction of the image receiving member to the downstream side. In a plurality of image forming apparatuses arranged toward the side, in the developing units other than the developing unit that is currently performing the transfer operation, at least the moving operation of the image carrier is continued and the operation of the developing unit is stopped. An image forming apparatus characterized by. 3. An image bearing member movably supported, a latent image forming means for forming a latent image on the image bearing member, toner attached to the latent image and developed as a toner image, and after transfer. And an image forming unit provided with a transfer means for transferring the toner image from the image carrier to the image receiving member at the same time, from the upstream side in the moving direction of the image receiving member to the downstream side. In a plurality of image forming apparatuses arranged toward the side, image receiving member biasing means for selectively biasing the image receiving member with respect to each of the image carriers, and biasing of the image receiving member with respect to each of the image carriers. An image forming apparatus comprising: an image receiving member releasing means for selectively releasing. 4. The image forming apparatus according to claim 3, wherein the image receiving member urging unit also serves as a transfer electric field applying unit. 5. The image receiving member is a transfer material transporting unit that moves while carrying a transfer material onto which a toner image on the image carrier is transferred, according to any one of claims 1 to 4. The image forming apparatus according to any one of the above. 6. The image receiving member is an intermediate transfer member to which the toner image on the image carrier is primarily transferred prior to the secondary transfer of the toner image onto the transfer material. The image forming apparatus according to claim 4.