JPH06337567A - Color image forming device - Google Patents

Abstract

PURPOSE:To miniaturize a color image forming device of a type that toner images are superposed on a photosensitive medium, to realize high speed development and to obtain a full color image excellent in the stability of image quality in the device. CONSTITUTION:Developing devices 1a to 1d respectively storing two-component developer having the same electrostatic charging polarity and provided with a magnetic brush type developer carrier 6 electrostatically supplying and recovering toner 4 to/from a toner carrier 2 are used; and the plural developing devices 1a to 1d are arranged in order of developed color from an upstream side in the rotating direction of the toner carrier 2, and set to freely advance to and retreat from the surface of the toner carrier 2. A voltage impressing means 7 is provided between the developer carrier 6 in the developing devices 1a to 1d and the toner carrier 2; and a control means 8 is provided, which actuates the developing devices 1a to 1d and the voltage impressing means 7 so that toner supply may be immediately started by the developing device of the succeeding stage to the toner recovering surface of the toner carrier 2 just after starting toner recovery by the developing device at the preceding stage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to form a plurality of toner images of plural colors on a photosensitive medium by repeating a series of steps of charging, image exposure and development on the photosensitive medium, and then superimposing the toner images. The present invention relates to a color image forming apparatus that collectively transfers toner images onto a recording medium.

[0002]

2. Description of the Related Art The following two types of color image forming apparatuses using electrophotography are known, roughly classified from the viewpoint of superimposing toner images. One is that, as disclosed in JP-A-57-119378, etc., a toner image formed on a photosensitive medium is sequentially transferred for each color onto a recording sheet held on a transfer drum, and then, on the recording sheet. It is a device that superimposes toner images, and the other is
As disclosed in Japanese Unexamined Patent Publication No. 56-144452, it is a device for superposing toner images of a plurality of colors on a photosensitive medium and transferring the superposed toner images collectively onto a transfer sheet. However, in the former device, a transfer drum for temporarily holding the recording paper at the time of transfer is required, so that the device becomes large in size, and the position of superimposition of each toner image easily shifts, and the number of toner colors is small. There is a problem that the recording time of an image becomes longer as the number increases. On the other hand, the latter device has an advantage that the above-mentioned problems of the former can be solved to some extent, but on the other hand, since the developing devices must be arranged around the photosensitive medium by the number of different toner colors, the device cannot be downsized sufficiently. There is also a problem that the toner image previously formed on the photosensitive medium is disturbed by the subsequent development, or toner of a different color is mixed to cause color mixing.

Therefore, for the purpose of further downsizing the apparatus and preventing color mixture, a plurality of developers having different toner colors and charging characteristics are housed in the same developing unit to selectively extract a predetermined developer. By doing each color development,
A color image forming apparatus for superposing a toner image on a photosensitive medium has been proposed (Japanese Patent Laid-Open No. 58-50548).
JP-A-60-189775). In such an apparatus, the developers of different colors are accommodated in the same developing unit to reduce the number of developing units (for example, when forming a color image of two colors, only one developing unit is required). Miniaturize, and at the time of development, select and extract only a predetermined developer by appropriately changing and adjusting the conditions of the applied voltage between the developing device and the photosensitive medium and the conditions of the latent image of the photosensitive medium. It is intended to develop the image.

[0004]

However, the color image forming apparatus proposed above has the following problems. That is, since a plurality of developers (toners) having different charging characteristics are stored in one developing device, when the charging state changes due to internal or external factors, they are mixed with each other in the developing device or during development. Mixing may cause color mixing. In addition, since the toner images having different charging polarities are superposed, the toner images on the photosensitive medium lack stability and image quality is easily deteriorated, and it is necessary to charge the superposed toner images to a constant polarity prior to transfer. Yes The development process is complicated. In addition, control of applied voltage and image exposure for selectively extracting a predetermined developer for development is complicated.

Further, in the above-mentioned JP-A-60-189775, a common toner carrier (developing roll) is provided for a plurality of developing devices, and toner from each developing device is once layered on the toner carrier. An example of an apparatus that develops a latent image on a photosensitive medium after it is formed is disclosed (see FIG. 6 and the like). However, this device completely scrapes off the residual toner formed on the toner carrier with the cleaning blade when the next toner color is developed, and the applied voltage between the toner carrier and the developing unit is completely removed. Since the next toner cannot be supplied onto the toner carrier until after the switching, the developing process takes a long time, especially when a full-color image is formed by four color toners.

Therefore, it is an object of the present invention to provide a color image forming apparatus of the type in which toner images are superposed on a photosensitive medium, the size of the apparatus can be reduced, and simple and high-speed development can be performed. An object of the present invention is to provide a color image forming apparatus capable of obtaining a full-color image having no image distortion and excellent in image quality stability.

[0007]

As shown in FIGS. 1 and 2, a color image forming apparatus according to the present invention includes a common toner from a plurality of developing devices (1) containing a two-component developer for each toner color. The toner (4) conveyed for each color to the developing area (A) of the photosensitive medium (3) through the carrier (2) is developed to superimpose toner images of a plurality of colors on the photosensitive medium (3). After that, assuming a color image forming apparatus that collectively transfers the superposed toner images onto a recording medium (5), two-component developers having the same charging polarity are stored as the plurality of developing devices (1). And a developing device (1) equipped with a magnetic brush type developer carrier (6) for electrostatically supplying and recovering each toner of the two-component developer to the toner carrier (2).
a, 1b, 1c, 1d), a plurality of developing devices (1a to 1d) are arranged in the order of developing colors from the upstream side in the rotational direction of the toner carrier (2), and at the same time with respect to the surface of the toner carrier (2). It is installed so that it can move back and forth freely, and each developing device (1
A voltage applying means (7) for applying a voltage for forming a predetermined electric field is provided between the developer carrying member (6) and the toner carrying member (2) in a to d), and the developing device ( Immediately after the toner collection by the developing device (1a) is started immediately after the toner collection by the developing device (1b) is started to the toner collecting surface (2a) of the toner carrier (2). d) and a control means (8) for operating the voltage applying means (7) are provided.

Further, in the above-mentioned technical means, the apparatus of the present invention is such that, as shown in FIG. 3, the intervals (L ₁ , L ₂ , L ₃ ) between the developer carrying members (6) are the closest surface portions. 10 mm
As described above, it is preferably about 15 to 30 mm. When this distance is less than 10 mm, the magnetic brush is not normally formed due to the influence of the magnetic force of the adjacent developer carrier, and the toner layer cannot be formed uniformly and satisfactorily on the toner carrier. This interval (L ₁ , L ₂ ,
It is desirable that L ₃ ) be equidistant from each other.

In the apparatus of the present invention, in the above technical means, the toner carrier (2) is a drum-shaped toner carrier, and the radius r ₁ (mm) of the drum-shaped toner carrier (2). ) And the radius r ₂ (mm) of the developer carrying member are as follows: [{2 (r ₁ + r ₂ ) × π} / (n-1)]-2r ₂ > 1
0, r ₂ > 5 (wherein n represents the number of the development carrier) is a value satisfying. Here, in the former relational expression, the left side is the center point (p,
p) part that almost indicates the distance between [{2 (r ₁ + r ₂ ) × π}
/ (N-1)] minus the radius (2r ₂ ) of the two adjacent developer carrying members, that is, the distance between the developer carrying members is approximately shown. Therefore, the value on the left side is a suitable distance (1) between the developer carrying members (6) described above.
It is shown that it may be larger than 0 mm). The latter relational expression shows that the radius of the developer carrier is at least 5
It shows that it is larger than mm. If the radius of the developer carrier is 5 mm or less, the efficiency of toner supply to the toner carrier (2) will be poor.

Further, in the apparatus of the present invention, in the above technical means, as shown in FIG. 9, the photosensitive medium (3) is a photosensitive belt, and the radius r of the drum-shaped toner carrier (2) is r.
₁ (mm) is the relational expression 2r ₁ <R × (1 / k), (wherein R
Is a value satisfying the peripheral length (mm) of the photosensitive belt, and k is the total number of driving points and driven points. Here, in the above relational expression, the left side shows the diameter of the developer carrying member, and this shows the length of one side when it is stretched (equally divided) on the driving roll or the driven roll of the photosensitive belt. It is shown that it is smaller than the value on the right side. Therefore, when the radius of the drum-shaped toner carrier is a value that does not satisfy the above relational expression, it may not be possible to arrange the carrier around the photosensitive belt, which may hinder the configuration of the apparatus itself. .

Further, the apparatus of the present invention is characterized in that, in the above technical means, the toner carrier (2) is a belt-shaped toner carrier as shown in FIG.
In the case of the belt-shaped toner carrier, the shape of the portion of the photosensitive medium facing the developing area A can be made smaller than that of the drum-shaped one, so that the selection range of the arrangement position with respect to the photosensitive medium is widened, and the belt-shaped toner carrier is used. It is possible to orderly arrange a plurality of developing devices in one row along one side of the carrier.

Further, the apparatus of the present invention is characterized in that, in the above technical means, the circumferential length of the belt-shaped toner carrier is equal to or less than the circumferential length of the drum-shaped or belt-shaped photosensitive medium. If this condition is not satisfied, the device will become large.

[0013]

According to the above technical means, since the toner carrier for developing the latent image on the photosensitive medium is commonly used, the space for the developing section for the photosensitive medium can be saved and the developing device of the preceding stage can be used. The residual toner from the toner carrier by the toner carrier and the toner supply to the toner carrier by the next-stage developing device are electrostatically carried out almost simultaneously by the magnetic brush type developer carrier, so that the toner layer on the toner carrier is The formation efficiency can be improved, and development of a plurality of colors can be speedily performed.

Further, the magnetic brushes of the developer carrying member are used only when the developers having the same charge polarity are used and stored in the developing device for each color, or when the toner is supplied from the developer carrying member to the toner carrying member and collected. Since the toner carrier is brought into contact with the toner carrier, a clear full-color image free from color mixture and image disturbance and excellent in image quality stability can be obtained by a simple developing process.

Moreover, since the form and size of the toner carrier and the arrangement conditions and size of the developer carrier are set appropriately, space can be saved and effective use can be made in the developing section.
The size of the device can be reduced.

[0016]

EXAMPLES The present invention will be described in more detail below with reference to examples. Embodiment 1 FIGS. 1 and 2 show a color image forming apparatus according to a first embodiment of the present invention. FIG. 1 is a schematic structural view showing the overall structure thereof, and FIG. FIG.

In this embodiment, the drum-shaped photosensitive medium 3 is used.
Charger 10, laser optical system 1 for image exposure around
1. Toner carrier 2 in the developing section and a plurality of developing devices 1a to 1
d, a transfer charger 12, a cleaning device 13, and a static eliminator (erase lamp) 14 are installed in this order, and a conveying means 15 for conveying the recording medium 5 between the photosensitive medium 3 and the transfer charger 12. A fixing device 16 for fixing the toner image transferred onto the recording medium 5 is provided and the main part thereof is configured.

The toner carrier 2 is in the shape of a drum and is made of an organic photosensitive material such as OPC. The drum-shaped toner carrier 2 is provided in the developing area A of the photosensitive drum 3.
Are installed facing each other at a predetermined distance and are rotated in the direction of the arrow.

Each of the developing devices 1a to 1d is a magnetic brush type developing device which is composed of a casing 20 for accommodating a developer and a sleeve rotatably provided at an opening at the tip thereof and in which a magnet roll is installed. The main part is composed of the agent carrier 6. The developer carrying member 6 is not particularly limited as long as it has a structure capable of carrying a developer by forming a magnetic brush on the surface thereof. Inside the casing 20, a supply member for supplying the developer to the developer carrying member 6, a developer stirring member, and the like, which are not shown, are provided.

The plurality of developing units 1a to 1d are arranged along the periphery of the toner carrier 2 from the upstream side in the direction of rotation in the order of development color, and are also arranged on the surface of the toner carrier 2 by driving means (not shown). Is installed so that it can move back and forth in the direction of arrow X-Y. Here, each developing device moves in the arrow X direction so that the tip of the magnetic brush 21 contacts the surface of the toner carrier 2 only when the toner is supplied and collected, and otherwise retracts in the Y direction and retracts. It is supposed to do.

The developer accommodated in each developing unit is a two-component developer composed of non-magnetic toner and magnetic carrier, and is separately accommodated in each developing unit for each toner color. In this embodiment, the developing device 1a has a yellow color,
Magenta for the developing device 1b, cyan for the developing device 1c, and developing device 1
Although the black two-component developer is stored in d and the development is sequentially performed in this toner color order, the development color order is not limited to this. The two-component developer has the same charge polarity, and in this embodiment, the toner is negatively charged for each color.

In this developing section, a predetermined voltage is applied from the voltage applying means 7 to the toner carrier 2 and the developer carrier 6 of each developing device. In particular, a constant voltage is always applied to the toner carrier 2 and two kinds of voltages (one is zero level) are switched and applied to one developer carrier 6 by the switch 22.

Further, the timing of the advancing / retreating movement of the developing device 1 and the switching of the voltage applied to the developer carrying member 6 are controlled by the control means 8 such as a CPU. In the control means 8, particularly, immediately after the toner recovery by the developing device of the previous stage (for example, the developing device 1a) is started, the developing device (1b) of the next stage with respect to the toner collecting surface 2a of the toner carrier 2 is started. It is set to control the operation of the developing device 1 and the voltage applying means 7 so that the toner supply by the method is immediately started. This makes it possible to realize higher speed development. This control can be performed using, for example, a rotation pulse signal of the toner carrier 2.
In addition, it can be performed while directly detecting the passage time of the toner collecting surface by an optical sensor or the like.

In the present embodiment, the photosensitive medium 3 has a drum diameter of 180 mm, and the toner carrier 2 has a diameter of 50 m.
m, the developer carrier 6 has a diameter of 20 mm. Further, the developer carrying members 6 are arranged at equal intervals of 15 mm.

According to the apparatus of this embodiment, a color image is formed as follows.

First, the surface of the photosensitive medium 3 is uniformly charged to -850 V by the charger 10, and then the laser optical system 11 irradiates the laser beam 11a whose pulse width is modulated according to the image information to perform image exposure. Then, the latent image of the first color is formed on the photosensitive medium 3. At this time, the potential of the latent image part is −
It is set to 50V.

Almost at the same time when the latent image of the first color is formed, based on the control signal from the control means 8, FIG.
, The first color yellow developer in the developing device 1a is supplied to the developer carrying member 6 to form the magnetic brush 21 on the carrying member 6, and the developing device 1a is moved from the retracted position B to the magnetic brush. The tip end of 21 is moved forward to a position where it contacts the surface of the toner carrier 2.

At this time, a DC voltage of -150V is applied to the toner carrier 2 and a voltage of -300V is applied to the developer carrier 6 from the voltage applying means 7, whereby the negatively charged toner 4a is formed by the potential difference. Due to the electric field, the toner is transferred to the side of the toner carrier 2 via the magnetic brush 21, and a uniform thin toner layer of the toner 4a of the first color is formed on the carrier 2.

When the toner layer formed on the toner carrier 2 is conveyed to the developing area A of the photosensitive medium 3, the toner 4 formed by the potential difference between the toner carrier 2 and the latent image portion.
Due to the electric field that electrostatically attracts a from the carrier 2 to the photosensitive medium 3 side, only the toner corresponding to the latent image portion of the photosensitive medium 3 flies and adheres, and development is performed. As a result, the first-color toner image 40a is formed on the photosensitive medium 3.

The photosensitive medium 3 on which the toner image 40a of the first color is formed is charged by the charger 10 while holding the toner image.
Are uniformly charged to form a latent image of the second color.
In this embodiment, after the formation of the second latent image, all are the same as -8.
It is charged to 50 V, and the charging condition at this time is appropriately set depending on the type of the photosensitive medium, the toner, the capacity of the charger, and the like. After charging, image exposure of the second color is performed by the laser optical system 11, and a latent image of the second color is formed on the photosensitive medium 3.

On the other hand, while the latent image of the second color is being formed, the voltage applied to the developer carrying member 6a is switched to the 0V side by the switch 22a based on the control signal from the control means 8. As a result, the toner 4a remaining on the toner carrier 2 without being involved in the development is removed by the toner carrier 2
Is electrostatically attracted to the developer carrying member 6 side by an electric field formed by the potential difference between the developer carrying member 6a and the developer carrying member 6a, and at the same time electrostatically captured by the magnetic brush and collected in the casing of the developing device 1a. (Fig. 4b).

When the toner recovery by the developing device 1a is started, a toner recovery surface 2a without residual toner appears on the toner carrier 2, and the second color magenta by the developing device 1b appears on the toner recovery surface. The supply of the developer is immediately started. That is, as shown in FIG. 4B, similarly to the developing device 1a, the developing device 1b moves forward from the retracted position B to the toner carrier 2 side based on the control signal from the control means 8, and at the same time, carries the developer. A voltage of −300V is applied to the body 6b from the voltage applying means 7 by the operation of the switch 22b to form the magnetic brush 21. As a result, the toner 4b of the second color is supplied to the toner collecting surface 2a and a uniform toner thinness is obtained. A layer is formed.

When the developing device 1a finishes collecting the residual toner 4a, as shown in FIG.
a is moved backward and returned to the retracted position B, and the voltage application to the developer carrying member 6a is released by the operation of the switch 22a. Further, the developer carrying member which is not involved in the supply and recovery of the toner is in a floating state or in the same potential state as the toner carrying body.

When the second-color toner layer formed on the toner carrier 2 is conveyed to the developing area A of the photosensitive medium 3, the photosensitive medium is subjected to an electric field due to a potential difference as in the case of the first color. The toner image 40b of the third color selectively fly and adheres to the latent image portion of the toner image No. 3 and is used for development, whereby a toner image 40b of the second color is formed on the photosensitive medium 3 so as to overlap the toner image 40a of the first color. (Fig. 4c).

Next, the photosensitive medium 3 is recharged by the charging device 10 to form a latent image of the third color while holding the superimposed toner images of the first color and the second color. On the other hand, when the development of the second color is completed, based on the control signal from the control means 8, in the developing device 1b, the toner carrier 2
At the same time as the collection of the toner 4b remaining on the top is started,
The supply of the third color cyan developer by the developing device 1c is started to the toner collecting surface. Further, the developing device 1b moves to the retracted position B when the toner collection is completed.

Similarly, after that, a series of steps of charging, image exposure, and development (including supply and recovery of toner by the developing device 1c and the developing device 1d) are repeated, so that the third image is formed on the photosensitive medium 3. The color toner image and the fourth color toner image are sequentially superimposed. The toner collected in each developing device is reused after being agitated with the developer in the casing.

In this way, four color full-color toner images are formed on the photosensitive medium 3. Then, the superposed toner images are collectively transferred onto the recording paper 5, which is a recording medium, by the transfer charger 12, and thereafter, the fixing device 1 is used.
It is heated and fixed by 6 and output to the outside of the apparatus. A color image is obtained through the above steps.

Photosensitive medium 3 after the toner images have been collectively transferred
After the surface thereof is cleaned by the cleaning device 13 and the residual charges are removed by the static eliminator 14, the next color image forming cycle is started.

When the relationship between the gap between the developer carrying members and the uniformity of the toner layer formed on the toner carrying member was examined using the apparatus of this embodiment, the results shown in FIG. 5 were obtained. Was obtained. As is clear from this result, it was confirmed that a uniform toner layer can be stably obtained at a constant level when the distance between the developer carrying members exceeds 10 mm. In this embodiment, the distance between the developer carrying members is 15
It was set to mm.

Further, when the relationship between the radius r ₂ of the developer carrying member and the toner supply efficiency to the toner carrying member was examined using the apparatus of this embodiment, the results shown in FIG. 6 were obtained.
From this result, the radius of the developer carrier is at least 10 mm from the viewpoint that the toner can be efficiently supplied to the toner carrier.
It is understood that the above is necessary.

Although a DC voltage is applied to the toner carrier 2 in this embodiment, a DC voltage superimposed with AC may be applied as long as it does not disturb the toner image on the photosensitive medium 3. Further, an electrode member as shown in Japanese Patent Application Laid-Open No. 3-113474 may be provided in the developing area of the toner carrier 2 and the photosensitive medium 3 and the development may be performed while forming the toner cloud. Such a configuration change can be similarly made in the following embodiments.

Embodiment 2 FIGS. 7 to 9 show a color image forming apparatus according to the second embodiment of the present invention. This embodiment has the same configuration as that of the first embodiment except that a belt-shaped toner carrier 30 is applied as the toner carrier 2 and a plurality of developing devices are arranged along one side of the belt-shaped toner carrier. It is a thing. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The belt-shaped toner carrier 30 comprises a belt 31.
Is stretched around the driving roll 32 and the driven rolls 33 and 34, and is rotated in the arrow direction by three-point support. In the case of the belt-shaped toner carrier 30, the peripheral length (the length of the belt 31) needs to be equal to or less than the peripheral length of the photosensitive medium 3, and in this embodiment, it is set to 330 mm. Since the photosensitive medium 3 is a drum having a diameter of 180 mm, its peripheral length is 180π.

Each of the developing devices 1a to 1d has the same structure as that of the first embodiment, but one of the belt-shaped toner carrier 30 is used.
The rows are arranged neatly in a vertical line along the sides, which makes installation and design simple. In addition, each of the developer carrying members 6 in these developing devices has a diameter of 20 mm, and the intervals between the carrying members 6 are all set to 15 mm.

In the apparatus of this embodiment, as in the case of the first embodiment, the four color toner images can be superposed on the photosensitive medium 3 by repeating a series of steps of charging, image exposure and development. Then, after that, the superposed toner images are collectively transferred onto the recording medium 5 to form a full-color image. In addition, each developing device 1a
In (d) to (d), the toner is efficiently supplied to and collected from the belt-shaped toner carrier 30 according to the same operation principle as in the first embodiment.

Embodiment 3 FIG. 9 shows a color image forming apparatus according to the third embodiment of the present invention. The apparatus of this embodiment has the same configuration as that of the first embodiment except that a belt-shaped photosensitive medium 40 is applied as the photosensitive medium 3.

The belt-shaped photosensitive medium 50 is constructed so that the photosensitive belt 51 is stretched around a driving roll 52 and driven rolls 53 and 54, and is rotated in the arrow direction by three-point support. The peripheral length of the belt-shaped photosensitive medium 50 is 480 m.
It is set to m. By applying such a belt-shaped photosensitive medium, the installation allowable range of the toner carrier 2 is widened, and it is easier to downsize the apparatus.

In the apparatus of such an embodiment, as in the case of the first embodiment, by repeating a series of steps of charging, image exposure and development, four color toner images are superposed on the belt-shaped photosensitive medium 50. After that, the superposed toner images are collectively transferred onto the recording medium 5 to form a full-color image. Further, in each of the developing devices 1a to 1d, the toner is efficiently supplied and collected according to the same operation principle as that of the first embodiment.

Embodiment 4 FIG. 10 shows a color image forming apparatus according to the fourth embodiment of the present invention. In this embodiment, the toner carrier 2
A belt-shaped toner carrier 30 is used as the photosensitive medium 3, and a belt-shaped photosensitive medium 50 is used as the photosensitive medium 3.

The toner carrier 30 is the second embodiment.
Then, as the belt-shaped photosensitive medium 50, the one having the same configuration as that in Example 3 was used. Also with such a configuration, it is easier to reduce the size of the device.

In the apparatus of this embodiment, as in the case of the first embodiment, the four color toner images are superposed on the belt-shaped photosensitive medium 50 by repeating a series of steps of charging, image exposure and development. After that, the superposed toner images are collectively transferred onto the recording medium 5 to form a full-color image. Further, in each of the developing devices 1a to 1d, the toner is efficiently supplied and collected according to the same operation principle as that of the first embodiment.

[0052]

As described above, in the color image forming apparatus of the present invention, the size of the apparatus can be reduced, and development of a plurality of colors can be performed easily and at high speed. It is possible to obtain a clear full-color image that is stable and has excellent image quality stability.

[Brief description of drawings]

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

FIG. 2 is an enlarged view of a main part showing a developing unit in the apparatus of FIG.

FIG. 3 is a schematic diagram for explaining sizes and arrangement conditions of a toner carrier and a developer carrier.

FIG. 4 is an explanatory diagram showing an operating state in a developing process.

FIG. 5 is a characteristic diagram showing a relationship of uniformity between a developer carrying member and a toner layer.

FIG. 6 is a characteristic diagram showing the relationship between the waveform of the developer carrier and the efficiency of toner supply to the toner carrier.

FIG. 7 is a schematic configuration diagram of a color image forming apparatus according to a second embodiment of the invention.

FIG. 8 is an enlarged view of a main part showing a developing unit in the apparatus of FIG.

FIG. 9 is a schematic configuration diagram of a color image forming apparatus according to a third embodiment of the invention.

FIG. 10 is a schematic configuration diagram of a color image forming apparatus according to a fourth embodiment of the invention.

[Explanation of symbols]

1a, 1b, 1c, 1d ... Developing device, 2 ... Toner carrier,
3 ... Photosensitive medium, 4 ... Toner, 5 ... Recording medium, 6 ... Magnetic brush type developer carrier, 7 ... Voltage applying means, 8 ... Control means, 20 ... Belt-shaped toner carrier, 50 ... Belt-shaped photosensitive medium, a ... developing area, a radius of r ₁ ... drum-shaped toner carrier, r2 ... radius of the developer carrying member.

 ─────────────────────────────────────────────────── (72) Inventor Haruyuki Namba, 2274 Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor, Yasuki Yamauchi 2274, Hongo Ebina City, Kanagawa, Fuji Xerox Co., Ltd. 72) Inventor Jun Abe, 2274 Hongo, Ebina, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd. (72) Koichiro Shinohara, 2274, Hongo, Ebina City, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd. (72) Inventor, Takuto Tanaka Kanagawa Fuji Xerox Co., Ltd., 2274 Hongo, Ebina City, Japan (72) Inventor Takahide Inoue 2274 Hongo, Ebina City, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd.

Claims (6)

[Claims] 1. A photosensitive medium is developed by developing toner with each color conveyed from a plurality of developing devices containing two-component developer for each color of toner to a developing area of the photosensitive medium through a common toner carrier. In a color image forming apparatus that superimposes toner images of a plurality of colors and then transfers the superposed toner images to a recording medium at a time, a two-component developer having the same charge polarity is stored as each of the plurality of developing devices. Then, a developing device equipped with a magnetic brush type developer carrier for electrostatically supplying and recovering each toner of the two-component developer to the toner carrier is used. Are arranged in the order of developing colors from the upstream side in the rotation direction of the toner, and are installed so as to move back and forth with respect to the surface of the toner carrier, and a predetermined electric field is provided between the developer carrier and the toner carrier in each developing device. A voltage applying means for applying a voltage for generating the voltage is provided, and immediately after the toner recovery by the developing device in the previous stage is started, the toner supply by the developing device in the next stage is immediately started to the toner recovery surface of the toner carrier. A color image forming apparatus is provided with control means for operating the developing device and the voltage applying means. 2. The color image forming apparatus according to claim 1, wherein the interval between the developer carrying members is 10 mm or more at the closest surface portion. 3. The toner carrier is a drum-shaped toner carrier, and the radius r ₁ of the drum-shaped toner carrier.
(Mm) and the radius r ₂ (mm) of the developer carrying member are the following relational expressions: [{2 (r ₁ + r ₂ ) × π} / (n-1)]-2r ₂ > 1
The color image forming apparatus according to claim 1, wherein the color image forming apparatus has a value satisfying 0, r ₂ > 5 (wherein, n represents the number of the development carrier). 4. The photosensitive medium is a photosensitive belt, and the radius r ₁ (mm) of the drum-shaped toner carrier is 2r ₁ <R × (1 / k), where R is The color image forming apparatus according to claim 1, wherein the peripheral length (mm) of the photosensitive belt (k) represents a total number of driving points and driven points). 5. The color image forming apparatus according to claim 1, wherein the toner carrier is a belt-shaped toner carrier. 6. The color image forming apparatus according to claim 5, wherein the peripheral length of the belt-shaped toner carrier is less than or equal to the peripheral length of the drum-shaped or belt-shaped photosensitive medium.