JP4619259B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus employing an electrophotographic system and the like, and more particularly to an image forming apparatus capable of forming a full-color image and a monochrome image.

  In recent years, electrophotographic systems have been widely adopted for image forming apparatuses such as copying machines, printers, and facsimiles. Moreover, an electrostatic system, a magnetic system, etc. may be employ | adopted. Such an image forming apparatus forms an image by forming a latent image on a photoreceptor or various recording media, and then visualizing the latent image with toner or the like, and further transferring and fixing the image on a predetermined sheet. .

  In recent years, there are image forming apparatuses capable of forming full-color (natural color) images. In such a full-color image forming apparatus, in fact, it is not frequently used to form a full-color image, and is used to form a monochrome (monochrome color) image such as a document. There are many. In consideration of such a difference in usage frequency, many general full-color image forming apparatuses have a monochrome image forming speed higher than a full-color image forming speed.

  Here, a general full-color image forming apparatus has a configuration in which images of four colors of yellow, magenta, cyan, and black are temporarily transferred to a transfer belt so as to overlap each other, and then secondarily transferred to a predetermined sheet and fixed. There are many things. Each color image is formed by a separate device (photosensitive member or developing device corresponding to each color).

  Therefore, assuming this configuration and disposing a black image forming apparatus in the vicinity of the secondary transfer position to the paper, the speed at which a monochrome image (first sheet) is output is set to a full color image (one). There is a conventional image forming apparatus that is faster than the output speed of the first sheet (see Patent Document 1).

Also, two first and second transfer belts are provided, and a yellow image and a magenta image are formed and transferred onto the first transfer belt, and a cyan image and a black image are transferred onto the second transfer belt. Conventionally, after transferring the image of the first transfer belt to the second transfer belt, the image of the first transfer belt is transferred to the second transfer belt, and then the images of all colors are transferred from the second transfer belt to the sheet at once. There is an image forming apparatus (see Patent Document 2). Since this image forming apparatus can form a monochrome image by using only the second transfer belt, a monochrome image can be formed at a higher speed than an image forming apparatus having only one transfer belt.
JP 2002-148896 A JP 2001-1000048 A1

  However, in the conventional image forming apparatus described in Patent Document 1, since each color image is formed by a separate device (a photoreceptor or a developing device corresponding to each color), the transfer belt includes these devices. It will be extended for a long time in the direction of arrangement. This configuration is often used in a general conventional full-color image forming apparatus. For this reason, the transfer belt is required to have a precise mechanism for suppressing the meandering and deflection.

  When a transfer belt that requires such a precise mechanism is driven at a higher speed for the formation of monochrome images, the mechanism for suppressing the meandering and bending is higher than the high precision required for the formation of full-color images. However, a particularly high accuracy is required, and a mechanism for suppressing wear is also required. Since such a mechanism becomes expensive, there is a problem that the manufacturing cost of the image forming apparatus is increased.

  The conventional image forming apparatus described in Patent Document 2 does not require a precise mechanism for suppressing meandering or bending of the transfer belt as compared with an apparatus having only one transfer belt, but the first transfer. A precise mechanism for realizing accurate transfer from the belt to the second transfer belt is required, and there is a problem that the apparatus becomes large because the transfer mechanism is complicated.

  Accordingly, an object of the present invention is to form a monochrome image at a higher speed than when a multicolor image such as a full color is formed, and to suppress the meandering and deflection of the transfer belt with a simple configuration, with particularly high accuracy. The present invention provides an image forming apparatus that is not required.

A first invention is an image forming apparatus capable of forming an image having a plurality of colors and an image having only one of the plurality of colors,
A plurality of latent image carriers capable of carrying latent images respectively corresponding to the plurality of colors;
A plurality of developing means capable of visualizing the latent image by applying a predetermined developer to each of the plurality of latent image carriers;
If the to the plurality of images having a color is formed, a first intermediate transfer belt, wherein the developer to the plurality of latent image bearing member is transferred to visualized image provided by the plurality of developing means,
A first driving means for rotating the first intermediate transfer belt when an image having the plurality of colors is to be formed ;
If the to image having only one color is formed, the developer in predetermined one of the corresponding plurality of latent image carrier by predetermined one of said plurality of developing means A second intermediate transfer belt to which a visualized image is transferred,
When an image having only one color is to be formed, a second driving unit that rotates the second intermediate transfer belt so that the peripheral speed is higher than the peripheral speed when the first intermediate transfer belt rotates. When,
When an image having a plurality of colors is to be formed, an image transferred to the first intermediate transfer belt is formed on a predetermined recording medium and output , and an image having only one color is to be formed And an output means for forming and outputting the image transferred to the second intermediate transfer belt on the recording medium .

According to a second invention, in the first invention,
The second intermediate transfer belt has a smaller peripheral length than the first intermediate transfer belt.

According to a third invention, in the first invention,
The second driving unit stops driving the second intermediate transfer belt while the first intermediate transfer belt is rotated by the first driving unit.

According to a fourth invention, in the first invention,
The second intermediate transfer belt is characterized in that a black image is transferred as an image having only one color.

According to a fifth invention, in the first invention,
When an image having a plurality of colors is formed, the plurality of latent image carriers are held on the first intermediate transfer belt by pressing the first intermediate transfer belt against the corresponding plurality of latent image carriers. A plurality of first primary transfer rollers for transferring an image on the body;
When the images having the plurality of colors are formed, the positions of the plurality of primary transfer rollers are moved to positions where the first intermediate transfer belt is pressed against the corresponding plurality of latent image carriers, respectively. When the image having only the image is formed, the positions of the plurality of first primary transfer rollers are moved to positions where the first intermediate transfer belt is separated from the corresponding latent image carriers by a predetermined distance. First position changing means ;
When an image having only one color is formed, the second intermediate transfer belt is brought into pressure contact with a predetermined one of the corresponding plurality of latent image carriers by pressing the second intermediate transfer belt. A second primary transfer roller for transferring an image on a predetermined one of the latent image carriers,
When an image having only one color is formed, the second primary transfer roller is positioned at a position where the second intermediate transfer belt is pressed against a predetermined one of the corresponding latent image carriers. When the image having the plurality of colors is formed, the second intermediate transfer belt is moved a predetermined distance from a predetermined one of the plurality of latent image carriers. And a second position changing means for moving the position of the second primary transfer roller to a position to be separated .

According to a sixth invention, in the first invention,
The output means includes
When an image having a plurality of colors is formed, the image on the first intermediate transfer belt is transferred to the recording medium by pressing the first intermediate transfer belt against the recording medium, and only the one color is transferred. A first secondary transfer roller that separates the first intermediate transfer belt from the recording medium,
When an image having only one color is formed, the image on the second intermediate transfer belt is transferred to the recording medium by pressing the second intermediate transfer belt against the recording medium, and the plurality of colors are transferred. A second secondary transfer roller that separates the second intermediate transfer belt from the recording medium.
And fixing means for fixing the image transferred to the recording medium.

  According to the first invention, in addition to the first intermediate transfer belt used when an image having a plurality of colors is formed, the second used when an image having only one color is formed. An intermediate transfer belt is provided, and the second intermediate transfer belt is driven by the second driving means so that its peripheral speed is higher than that of the first intermediate transfer belt. As a result, when an image having only one color (for example, a monochrome image) is formed at a higher speed than an image having a plurality of colors (for example, a full color image), it is possible to suppress meandering or bending of the transfer belt with a simple configuration No special high accuracy is required.

  According to the second invention, since the circumference of the second intermediate transfer belt is smaller than the circumference of the first intermediate transfer belt, the meandering and deflection of the second intermediate transfer belt even when the second intermediate transfer belt is driven at high speed. In order to suppress this, a particularly high accuracy is not required.

  According to the third aspect, since the driving of the second intermediate transfer belt by the second driving unit is stopped while the first intermediate transfer belt is driven, an image having a plurality of colors is formed. In this case, power consumption is reduced.

  According to the fourth aspect of the invention, the second intermediate transfer belt transfers a black image, so that a frequently used monochrome image such as a general document can be formed at high speed. The configuration does not require a particularly high accuracy in order to suppress the meandering and deflection of the transfer belt.

According to the fifth aspect of the present invention, the plurality of first primary transfer rollers used when an image having a plurality of colors is formed have the first position change when an image having only one color is formed. Since it is separated by a predetermined distance by the means, it is possible to prevent the operation when an image having only one color is formed. Further, the second primary transfer roller used when an image having only one color is formed is separated by a predetermined distance by the second position changing unit when an image having a plurality of colors is formed. Therefore, it is possible to prevent the operation when an image having a plurality of colors is formed.

According to the sixth aspect , the first secondary transfer roller used when an image having a plurality of colors is formed is the first intermediate transfer belt when an image having only one color is formed. Is separated from the recording medium, and the second secondary transfer roller used when an image having only one color is formed records the second intermediate transfer belt when an image having a plurality of colors is formed. Since they are separated from the medium, it is possible not to disturb each other's operation.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
<1. Overall configuration of image forming apparatus and full color image forming operation>
FIG. 1 is a side view simply showing the structure of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus outputs a sheet Pb on which a full color or monochrome image is formed on a sheet Pa based on image data given from outside the apparatus. Therefore, the image forming apparatus includes an exposure unit 20, photosensitive drums 12a to 12d, developing devices 13a to 13d, toner cartridges 23a to 23d, a full-color intermediate transfer belt 11 for forming a full-color image, A full-color secondary transfer roller 14, a full-color primary transfer roller, a fixing unit 21 including a heating roller (also referred to as a fixing roller) and a pressure roller, a paper separating roller 16, a paper discharge tray 18, and a monochrome image And a mechanism for forming. The operation of the full-color primary transfer roller and the mechanism for forming a monochrome image will be described in detail later with reference to FIG. In FIG. 1, the sheet conveyance path is indicated by a one-dot chain line.

  This image forming apparatus forms an image based on image data corresponding to each hue of four colors including black (K) and subtractive mixed primary colors cyan (C), magenta (M), and yellow (Y). I do. For example, the image forming apparatus is provided with a photosensitive drum 12a, a developing device 13a, a charging roller, and a cleaning unit for forming a black image, and the same three-color image forming is performed. Configurations (photosensitive drums 12b to 12d, developing devices 13b to 13d, and the like) are provided. These components are arranged in a line as shown in FIG. 1 along the moving direction of the full-color intermediate transfer belt 11. In FIG. 2 described later, the charging roller for forming a black image is shown as a charging roller 26a, and the cleaning unit is shown as a cleaning unit 25a.

  The charging roller is a contact-type charger that uniformly charges the surfaces of the photosensitive drums 12a to 12d, which are image carriers, to a predetermined potential. In this embodiment, the charging roller is used as a charging device. However, the charging device to be used is not limited to the charging roller. For example, a fur brush, a magnetic brush, or a corona wire is used. As long as it gives a desired charging potential to the photosensitive member, such as a sawtooth or ion generator, it can be used.

  The exposure unit 20 which is a laser beam scanning device includes a semiconductor laser, a polygon mirror 15, a plurality of reflection mirrors, and the like, and modulates based on image data corresponding to black, cyan, magenta, and yellow hues. Each of the four laser beams thus applied is irradiated onto the surfaces of the corresponding photosensitive drums 12a to 12d. As a result, electrostatic latent images based on image data corresponding to the hues of black, cyan, magenta, and yellow are formed on the surfaces of the photosensitive drums 12a to 12d.

  The toner cartridges 23a to 23d are detachably attached near the upper portions of the developing devices 13a to 12d, and store toner that is a developer corresponding to a hue of black, cyan, magenta, or yellow.

  The developing devices 13a to 13d supply toner to the surfaces of the photosensitive drums 12a to 12d on which the electrostatic latent images are formed, and visualize the electrostatic latent images into toner images that are developer images. Specifically, the developing devices 13a to 13d receive toner corresponding to the hue from a supply port (not shown) of the toner cartridges 23a to 23d mounted on the upper portion, and the hue formed on the photosensitive drums 12a to 12d by the toner. The electrostatic latent image corresponding to 1 is visualized as a toner image corresponding to the hue of black, cyan, magenta, or yellow. The cleaning unit 17 removes and collects toner remaining on the surfaces of the photosensitive drums 12a to 12d after development and image transfer.

  The full-color intermediate transfer belt 11 is stretched between a driving roller and a driven roller to form a loop-shaped movement path as shown in FIG. The outer peripheral surface of the full-color intermediate transfer belt 11 faces the photosensitive drum 12d, the photosensitive drum 12c, the photosensitive drum 12b, and the photosensitive drum 12a. It rotates so as to face the body drums 12a to 12d. A full-color primary transfer roller is disposed at a position facing each of the photoconductive drums 12a to 12d with the full-color intermediate transfer belt 11 interposed therebetween. In FIG. 2 to be described later, a full-color primary transfer roller for forming a black image of each color constituting a full-color image is shown as a full-color primary transfer roller 101.

  When a full-color image is formed, the primary transfer roller for full color has a reverse polarity to the charging polarity of the toner in order to transfer the toner image carried on the surface of the photosensitive drums 12a to 12d onto the intermediate transfer belt 11 for full color. A primary transfer bias for full color, which is a constant voltage of polarity, is applied. At the same time, the full-color primary transfer roller is pressed against the inner peripheral surface of the full-color intermediate transfer belt 11 by a mechanism described later. As a result, the toner images corresponding to the respective hues formed on the photosensitive drums 12 a to 12 d are transferred so as to be sequentially superimposed on the outer peripheral surface of the full-color intermediate transfer belt 11, and are transferred onto the outer peripheral surface of the full-color intermediate transfer belt 11. A full color toner image is formed.

  The toner image transferred to the outer peripheral surface of the full-color intermediate transfer belt 11 in this way is conveyed to a position facing the full-color secondary transfer roller 14 by the rotation of the full-color intermediate transfer belt 11. The full-color secondary transfer roller 14 is in pressure contact with the outer peripheral surface of the full-color intermediate transfer belt 11 whose inner peripheral surface is in contact with the peripheral surface of the driving roller during image formation at a predetermined nip pressure. The full-color secondary transfer roller 14 is separated from the outer peripheral surface of the full-color intermediate transfer belt 11 by a predetermined position changing mechanism (not shown) during monochrome image formation.

  The paper fed by the paper separating roller 16 that pulls out the paper Pa one by one from the paper feed cassette that stores the paper Pa passes when it passes between the full-color secondary transfer roller 14 and the full-color intermediate transfer belt 11. A high voltage having a polarity opposite to the charging polarity of the toner is applied by the full-color secondary transfer roller 14. As a result, a full-color toner image is transferred from the outer peripheral surface of the full-color intermediate transfer belt 11 to the surface of the paper. Of the toner adhering to the full-color intermediate transfer belt 11, the toner remaining on the full-color intermediate transfer belt 11 without being transferred onto the sheet is cleaned so as to come into sliding contact with the driven roller in order to prevent color mixing. Collected by the unit 25a.

  The sheet on which the toner image, which is a full-color image, has been transferred is guided to the fixing unit 21 and is heated and pressurized by passing between a heating roller and a pressure roller that constitute the fixing unit 21. By the operation of the fixing unit 21, the toner image is firmly fixed on the surface of the paper. The paper Pb on which the toner image is fixed is discharged onto the paper discharge tray 18 by a paper discharge roller.

  The full color image forming operation as described above is performed by a plurality of drive units including an electric motor and gears (not shown) and a control unit that controls these drive units. The function of the control unit is a sensor (not shown). And a microcomputer that receives information such as an operation input unit. The monochrome image forming operation is substantially the same as described above, but the intermediate transfer belt, the primary transfer roller, the secondary transfer roller, and the like used are different. Hereinafter, the configuration and operation for forming a monochrome image will be described with reference to FIG.

<2. Configuration and operation for monochrome image formation>
FIG. 2 is a side view showing a configuration in the vicinity of the photoconductor 12a for forming a black image. More specifically, FIG. 2A is a side view showing the arrangement of each component when forming a full-color image. FIG. 2B is a side view showing the arrangement of each component when a monochrome image is formed.

  In FIG. 2, the paper transport path is indicated by a dotted line. The full-color intermediate transfer belt 11 and the full-color secondary transfer roller 14 shown in FIG. 2 have been described above. The function of the full-color primary transfer roller 101 has been described above, and the position changing mechanism will be described next.

  As shown in FIG. 2, the full-color primary transfer roller 101 is rotatably attached to one end of the support rod 102 so as to rotate in the direction opposite to the rotation direction of the photosensitive member 12a. The support rod 102 is rotatably attached around the rotation shaft 103 (clockwise or counterclockwise in the figure) so as to be orthogonal to the drive motor rotation shaft 103 including the gear mechanism. The support rod 102 and the rotating shaft 103 constitute a position changing mechanism 100 a for the full-color primary transfer roller 101.

  Therefore, when the drive motor rotating shaft 103 rotates counterclockwise by a predetermined angle, the full-color primary transfer roller 101 is brought into pressure contact with the inner peripheral surface of the full-color intermediate transfer belt 11, whereby the photoconductor 12 a becomes full-color. 2 is pressed against the outer peripheral surface of the intermediate transfer belt 11 (the state shown in FIG. 2A). In this case, the outer peripheral surface of a monochrome intermediate transfer belt 211 described later is separated from the photoconductor 12a. In this state, a full-color image can be formed as described above.

  Further, when the drive motor rotating shaft 103 rotates clockwise by a predetermined angle, the full-color primary transfer roller 101 is separated from the inner peripheral surface of the full-color intermediate transfer belt 11, so that the full-color intermediate transfer roller 101 is separated from the photoreceptor 12 a. The outer peripheral surface of the transfer belt 11 is separated (for example, about 3 to 10 mm) (the state shown in FIG. 2B). In this case, the outer peripheral surface of the monochrome intermediate transfer belt 211 is pressed against the photoconductor 12a as described later. In this state, a monochrome image can be formed.

  The mechanism for forming cyan, magenta, and yellow images is also provided with the same primary transfer roller for full color and its position changing mechanism as described above, and performs the same operation as the primary transfer roller 101 for full color. Next, a monochrome image forming mechanism that is not provided in the mechanism for forming these cyan, magenta, and yellow images, but provided only in the mechanism for forming black images will be described.

  Referring to FIG. 2A, the outer peripheral surface of the monochrome intermediate transfer belt 211 is separated from the photoreceptor 12a (for example, about 3 to 10 mm) by the monochrome primary transfer roller 201. The monochrome primary transfer roller 201 is rotatably attached to one end of a movable iron core of a solenoid 220 having a known structure via a compression coil spring. At this time, the solenoid 220 (excitation coil thereof) is not energized. In this embodiment, the solenoid is used. However, the present invention is not limited to this, and a known mechanism for bringing the monochrome primary transfer roller 201 into and out of contact with the photoreceptor 12a can be used. Alternatively, a cam mechanism or the like may be used.

  Next, when the solenoid 220 (excitation coil) is energized by the control operation of the control unit described above, one end of the movable iron core is moved forward by a predetermined distance to the solenoid 220 (substantially to the right in FIG. 2A). Moving. As a result, as shown in FIG. 2B, the position of the monochrome primary transfer roller 201 is moved, so that the outer peripheral surface of the monochrome intermediate transfer belt 211 is in pressure contact with the photoreceptor 12a. Therefore, the solenoid 220 functions as a position changing unit for the monochrome primary transfer roller 201.

  The monochrome intermediate transfer belt 211 is stretched between the monochrome primary transfer roller 201 and the driving roller 203, and a driven roller provided at a predetermined position shown in FIG. 202 is press-contacted, and a driven roller 204 provided at a predetermined position is press-contacted to the outer peripheral surface thereof. The driven roller 204 is provided so as to contact only an area (non-image forming area) other than an area where an image is to be formed on the outer peripheral surface of the monochrome intermediate transfer belt 211.

  When a monochrome image is formed, the monochrome primary transfer roller 201 has a polarity opposite to the toner charging polarity in order to transfer the toner image carried on the surface of the photosensitive drum 12a onto the monochrome intermediate transfer belt 211. A primary transfer bias having a constant voltage of 1 is applied. In this state, the primary transfer roller for monochrome 201 is pressed against the inner peripheral surface of the intermediate transfer belt for monochrome 211, so that the toner image corresponding to black (in the monochrome image) formed on the photosensitive drum 12a is an intermediate for monochrome. The image is transferred onto the outer peripheral surface of the transfer belt 211, and a monochrome toner image is formed on the outer peripheral surface of the monochrome intermediate transfer belt 211.

  When forming a monochrome image, the peripheral speed (rotational speed) of the photosensitive drum 12a is larger than when forming a full-color image (a black image of each color) (for example, a full-color image is formed). In order to obtain a predetermined peripheral speed twice as high as the case). Accordingly, the peripheral speed (moving speed) of the monochrome intermediate transfer belt 211 determined according to the peripheral speed of the photosensitive drum 12a is larger than the peripheral speed of the full-color intermediate transfer belt 11 (for example, a full-color image is formed). The predetermined peripheral speed is set to about twice that of the case. Thus, even when the monochrome intermediate transfer belt 211 is driven at a higher speed than the full-color intermediate transfer belt 11, the peripheral length (belt length) thereof is considerably shorter than that of the full-color intermediate transfer belt 11. A particularly high accuracy is not required to suppress meandering or deflection.

  The toner image transferred to the outer peripheral surface of the monochrome intermediate transfer belt 211 as described above is conveyed to a position facing the monochrome secondary transfer roller 214 by the rotation of the monochrome intermediate transfer belt 211. The monochrome secondary transfer roller 214 is pressed against the outer peripheral surface of the monochrome intermediate transfer belt 211 whose inner peripheral surface is in contact with the peripheral surface of the driving roller 203 at a predetermined nip pressure during monochrome image formation. The monochrome secondary transfer roller 214 is separated from the outer peripheral surface of the monochrome intermediate transfer belt 211 by a predetermined position changing mechanism (not shown) during full color image formation.

  As in the case of forming the full-color image described above, the paper Pa to be fed passes through between the monochrome secondary transfer roller 214 and the monochrome intermediate transfer belt 211. A high voltage of reverse polarity is applied by the monochrome secondary transfer roller 214. As a result, a toner image, which is a monochrome image, is transferred from the outer peripheral surface of the monochrome intermediate transfer belt 211 to the surface of the sheet.

  The sheet on which the toner image, which is a monochrome image, is transferred is guided to the fixing unit 21, and the toner image is firmly fixed on the surface of the sheet by the operation of the fixing unit 21. The paper Pb on which the toner image is fixed is discharged onto the paper discharge tray 18.

  When a monochrome image is formed as described above, a mechanism for forming a full color image, that is, the photosensitive drums 12b to 12d, the developing devices 13b to 13d, the full color intermediate transfer belt 11, and the full color secondary transfer roller. 14 and the full-color primary transfer roller are stopped based on the control of the control unit, and are held at a predetermined gap (3 to 10 mm) from the photoconductors 12a to 12d.

  When a full-color image is formed, the mechanism for forming a monochrome image, that is, the monochrome intermediate transfer belt 211, the monochrome primary transfer roller 201, the driving roller 203, and the monochrome secondary transfer roller 214 are the above-described control units. The operation is stopped based on this control, and is held at a predetermined gap (3 to 10 mm) from the photoreceptor 12a. By stopping the operation in this manner, power consumption during full-color image formation can be suppressed, and meandering of the monochrome intermediate transfer belt 211 that is not pressed against the photoreceptor 12a is prevented.

<3. Effect>
As described above, the present image forming apparatus operates a monochrome image faster than a full-color image by operating the mechanism for forming the monochrome image at a higher speed than the mechanism for forming a full-color image. When a monochrome image is formed, the monochrome intermediate transfer belt 211 shorter than the full-color intermediate transfer belt 211 is used, and the full-color intermediate transfer belt 211 is not used. Even when a monochrome image is formed at high speed, a particularly high accuracy is not required to suppress meandering or deflection of the transfer belt.

<4. Modification>
The image forming apparatus according to the above embodiment has a configuration capable of forming a monochrome (black and white) image and a full color (natural color) image. Even with a configuration capable of forming a monochrome image other than black, the same effects as described above can be obtained.

  In the image forming apparatus according to the above-described embodiment, the full-color intermediate transfer belt 11 is stretched between the driving roller and the driven roller to form a loop-shaped moving path as shown in FIG. The intermediate transfer belt 211 is stretched between the monochrome primary transfer roller 201 and the driving roller 203 to form a movement path as shown in FIG. 2, but these movement paths are appropriately changed. Alternatively, the full-color intermediate transfer belt 11 and the monochrome intermediate transfer belt 211 may be driven by a driving unit including a known control device such as a computer and a known driving device other than the driving roller and a driving motor (not shown). Good.

  In the image forming apparatus according to the above-described embodiment, the monochrome intermediate transfer belt 211 shorter than the full-color intermediate transfer belt 211 is used, but the same length as the full-color intermediate transfer belt 211 or somewhat longer than that. The monochrome intermediate transfer belt 211 is used, and the same effects as described above can be obtained. This is because the full-color intermediate transfer belt 211 is high in order to suppress meandering and deflection so as not to cause color misregistration between the colors because the images are formed so that the respective colors are sequentially superimposed along the moving direction. Although accuracy is required, the monochrome intermediate transfer belt 211 does not cause a problem of color misregistration, and so high accuracy is not required. Therefore, even when driven at a high speed, a relatively simple configuration may be used. Because it can.

  In the image forming apparatus according to the above-described embodiment, the position of the monochrome primary transfer roller 201 on which the monochrome intermediate transfer belt 211 is stretched is determined according to whether the monochrome image is formed or the full color image is formed. However, it is not necessary that the monochrome intermediate transfer belt 211 is stretched over the monochrome primary transfer roller 201, and a known position changing mechanism other than the solenoid 220 is used as the position changing means. May be. For example, the monochrome primary transfer roller 201 is not covered with the monochrome intermediate transfer belt 211, and the inner circumference of the monochrome intermediate transfer belt 211 is the same as the arrangement position of the full-color primary transfer roller 101 for forming a full-color image. The position changing means may be provided by a component corresponding to a drive motor having a support rod 102 and a rotating shaft 103. Further, as the position changing unit of the full-color primary transfer roller 101, a known position changing mechanism other than the above-described configuration may be used. For example, the position changing unit may be configured by a component corresponding to the solenoid 220. The position changing means is not necessarily provided for each color, and may be a mechanism for changing the positions of a plurality of or all full-color primary transfer rollers of each color.

1 is a side view simply showing the structure of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a side view showing a configuration in the vicinity of a photoconductor for forming a black image in the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Intermediate transfer belt for full color 12a-12d ... Photoconductor drum 13a-13d ... Developing device 14 ... Secondary transfer roller for full color 15 ... Polygon mirror 16 ... Paper separation roller 18 ... Paper discharge tray 20 ... Exposure unit 21 ... Fixing unit 23a to 23d ... toner cartridge 25a ... cleaning unit 26a ... charge roller 100a ... position changing mechanism 101 ... full color primary transfer roller 102 ... support rod 103 ... rotary shaft 201 ... monochrome primary transfer roller 202 ... driven roller 203 ... drive roller 211 ... Intermediate transfer belt for full color 211 ... Intermediate transfer belt for monochrome 214 ... Secondary transfer roller for monochrome 220 ... Solenoid Pa, Pb ... Paper

Claims (6)

An image forming apparatus capable of forming an image having a plurality of colors and an image having only one of the plurality of colors,
A plurality of latent image carriers capable of carrying latent images respectively corresponding to the plurality of colors;
A plurality of developing means capable of visualizing the latent image by applying a predetermined developer to each of the plurality of latent image carriers;
If the to the plurality of images having a color is formed, a first intermediate transfer belt, wherein the developer to the plurality of latent image bearing member is transferred to visualized image provided by the plurality of developing means,
A first driving means for rotating the first intermediate transfer belt when an image having the plurality of colors is to be formed ;
If the to image having only one color is formed, the developer in predetermined one of the corresponding plurality of latent image carrier by predetermined one of said plurality of developing means A second intermediate transfer belt to which a visualized image is transferred,
When an image having only one color is to be formed, a second driving unit that rotates the second intermediate transfer belt so that the peripheral speed is higher than the peripheral speed when the first intermediate transfer belt rotates. When,
When an image having a plurality of colors is to be formed, an image transferred to the first intermediate transfer belt is formed on a predetermined recording medium and output , and an image having only one color is to be formed An image forming apparatus comprising: an output unit configured to form and output an image transferred to the second intermediate transfer belt on the recording medium .   The image forming apparatus according to claim 1, wherein the second intermediate transfer belt has a circumferential length smaller than that of the first intermediate transfer belt.   2. The second drive unit stops driving the second intermediate transfer belt while the first intermediate transfer belt is rotated by the first drive unit. 3. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the second intermediate transfer belt transfers a black image as an image having only one color. When an image having a plurality of colors is formed, the plurality of latent image carriers are held on the first intermediate transfer belt by pressing the first intermediate transfer belt against the corresponding plurality of latent image carriers. A plurality of first primary transfer rollers for transferring an image on the body;
When the images having the plurality of colors are formed, the positions of the plurality of primary transfer rollers are moved to positions where the first intermediate transfer belt is pressed against the corresponding plurality of latent image carriers, respectively. When the image having only the image is formed, the positions of the plurality of first primary transfer rollers are moved to positions where the first intermediate transfer belt is separated from the corresponding latent image carriers by a predetermined distance. First position changing means ;
When an image having only one color is formed, the second intermediate transfer belt is brought into pressure contact with a predetermined one of the corresponding plurality of latent image carriers by pressing the second intermediate transfer belt. A second primary transfer roller for transferring an image on a predetermined one of the latent image carriers,
When an image having only one color is formed, the second primary transfer roller is positioned at a position where the second intermediate transfer belt is pressed against a predetermined one of the corresponding latent image carriers. When the image having the plurality of colors is formed, the second intermediate transfer belt is moved a predetermined distance from a predetermined one of the plurality of latent image carriers. The image forming apparatus according to claim 1, further comprising: a second position changing unit that moves the position of the second primary transfer roller to a position to be separated . The output means includes
When an image having a plurality of colors is formed, the image on the first intermediate transfer belt is transferred to the recording medium by pressing the first intermediate transfer belt against the recording medium, and only the one color is transferred. A first secondary transfer roller that separates the first intermediate transfer belt from the recording medium,
When an image having only one color is formed, the image on the second intermediate transfer belt is transferred to the recording medium by pressing the second intermediate transfer belt against the recording medium, and the plurality of colors are transferred. A second secondary transfer roller that separates the first intermediate transfer belt from the recording medium;
The image forming apparatus according to claim 1, further comprising: a fixing unit that fixes the image transferred onto the recording medium.

Images