JP2001100488A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hybrid type color image forming device which is satisfactorily constituted so that the miniaturization of a device, the increase of an accessing speed and high printing quality free from color slippage may be attained. SOLUTION: The color image forming device 20 is constituted of four developing units 21a, 21b, 21c and 21d for storing different color toner, image carrier drums 22a and 22b, an intermediate transfer belt 25 stretched to be laid between a driving roller 23 and a driven roller 24, cleaners 26a and 26b, electrostatic charging rollers 27a and 27b, laser beam exposure units 28a and 28b, a main power source 29, etc. Respective parts are constituted so that the following relations may be established; Lb=N1×π×D, Lb N2×π×R, and also, Pt=N3×π×R, provided that Lb denotes the peripheral length of the intermediate transfer belt 25, R denotes the diameter of the driving roller 23, D denotes the diameter of each image carrier drum 22a and 22b, Pt denotes a distance between two transfer parts and N1, N2 and N3 denote optional integer numbers. The image carrier drum is exposed with the laser beam 34 through an exposure through-hole of the developing unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus which is small, relatively fast, and hardly causes misregistration of colors to be superimposed.

[0002]

2. Description of the Related Art Conventionally, various electrophotographic color image forming apparatuses as shown in FIGS. 12A to 12F have been proposed and put to practical use. Of these, as shown in FIG. 1A, a tandem-type color image forming apparatus provided with a photosensitive drum 2 for each developing unit 1, that is, using a photosensitive drum for each color, has a disadvantage in terms of speed. Is excellent. Meanwhile, the same figure
As in the case of the photoconductors 3-1 to 3-5 shown in (b) to (f), the color image forming apparatus of another system in which only one photoconductor is used, the overlapping position of each image coincides. In this respect, it is said to be superior to the tandem method. It should be noted that FIG.
The broken line arrow shown in (f) indicates the paper transport path.

FIG. 13 shows a new process for the above various color image forming apparatuses, for example, as disclosed in
FIG. 77286 is a diagram showing a basic structure of an image forming apparatus intermediate between the above-described processes of FIG. 12A and FIGS. 12B to 12F, which can be said to be a hybrid type. .

FIG. 1 shows developers of different colors (color toner A,
C), two developing devices 4 accommodating therein and one photosensitive drum 5
And a second developing unit 9 including two developing units 7 containing developers of different colors (color toners B and D) and one photosensitive drum 8. ,
The intermediate transfer belt 1 is provided along the lower flat portion of the intermediate transfer belt 13 circulating and moving between the driving roller 11 and the driven roller 12 and circulating in the direction of arrow a in the drawing.
An image transfer portion is formed at two locations on the upstream side and the downstream side of No. 3.

In this color image forming apparatus, after the image of the color toner A formed on the photosensitive drum 5 of the first developing unit 6 is transferred to the intermediate transfer belt 13 at the transfer section on the upstream side, the second The image of the color toner B formed on the photosensitive drum 8 of the developing unit 9 is transferred onto the intermediate transfer belt 13 at the downstream transfer section. At the timing when the overlap-transferred toner image circulates again to the upstream transfer portion and the downstream transfer portion, the image of the color toner C of the first developing unit 6 and the color toner of the second developing unit 9 are transferred. The full-color images are formed by superimposing and transferring the images of D, respectively, and the full-color images are transferred to the sheet P at a portion where the transfer roller 14 and the intermediate transfer belt 13 face each other. The four-color superimposed toner image transferred to the paper P is heat-fixed by a fixing unit (not shown).

In order to expose the above-mentioned photosensitive drums 5 and 8, generally, such a color image forming apparatus is provided with a device shown in FIG.
Laser scanner (ROS: Raster Outpu) as shown in FIG.
t Scanner) Laser beam exposure unit 1 using technology
5 are incorporated. A laser beam exposure unit 15 shown in FIG. 1 includes a polygon mirror 17 that deflects a laser beam 16 with an increase in resolution or printing speed.
This has been dealt with by increasing the number of rotations or increasing the frequency of the image clock. Polygon mirror 1 in the same figure
The laser beam 16 ′ reflected by 7 passes through an optical system (fθ lens) 18 to expose the photosensitive surface of a photosensitive member 19 to form an electrostatic latent image.

FIGS. 15A and 15B are views showing a method of mounting the conventional laser beam exposure unit 15. FIG. Same figure
14A and 14B, the same components as those in FIG. 14 are denoted by the same reference numerals as in FIG. FIG. 15A shows the state shown in FIG.
1 shows a form of a laser beam exposure unit 15 incorporated in a tandem type color image forming apparatus shown in FIG. 1. When the laser beam exposure unit 15 is arranged so as to expose from directly above the photosensitive member 19, the photosensitive member 19
It has been known that the displacement of the resist due to the eccentricity of the resist becomes minimum. FIG. 3A also shows a polygon motor 17-1 for driving the polygon mirror 17 to rotate.

FIG. 1B shows an example in which the laser beam exposure unit 15 is arranged horizontally with respect to the photoreceptor 19, and the arrangement of FIG. Is what was being done.

[0009]

However, the hybrid color image forming apparatus shown in FIG. 13 has not yet been put to practical use, and various problems remain to be solved. In particular, the expected improvement was not obtained in terms of color misregistration.

Although the demand for higher resolution of the image to be formed and higher speed of printing is increasing, the polygon mirror is rotated at high speed or the frequency of the image clock is increased as described above. The way to deal with
It is approaching an area that cannot be realized with current device capabilities. Even if it is realized, problems such as an increase in heat generation, noise, and vibration of the polygon motor and an increase in electromagnetic noise due to an increase in the image clock frequency occur.

In order to increase the resolution by lowering the rotation speed of the polygon motor, a dual-beam semiconductor laser (L
D) A two-line parallel simultaneous scanning method of a laser beam using an array has been proposed. However, in the case of adjacent scanning in this method, there is a limitation in the design of the optical system in the sub-scanning direction, and in the case of interlaced scanning, a memory for temporarily holding image information of the intersecting scanning lines is required. Also, in the single beam, the beam passes on the optical axis of the lens, whereas in the dual beam system, each beam passes through a position outside the optical axis of the lens, so that the aberration and shape of the lens (spherical surface, cylindrical surface) , Cylinder surface, etc.) to cause various problems, such as causing image defects.

Furthermore, a tandem type color image forming apparatus using a laser beam exposure unit
From the photoconductor 19 is long, and an error of several tens of μm tends to occur. As described above, if there is an error even if it is about several tens of μm, there occurs a problem that distortion of reduction or enlargement occurs in the main scanning direction (see the direction of arrow X in FIG. 15B). In addition, in the tandem type color image forming apparatus using the laser beam exposure unit, it is very difficult to finely adjust the once mounted laser beam exposure unit. Also, in order to facilitate fine adjustment, an extremely large mounting space had to be taken.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances,
Realize high print quality without downsizing, high speed, color shift,
An object of the present invention is to provide a hybrid color image forming apparatus having a more preferable configuration.

[0014]

The construction of the color image forming apparatus according to the present invention will be described below. The color image forming apparatus of the present invention comprises a first image carrier drum around which two developing devices containing different color developers are arranged, and two developing devices containing other different color developers. A second image carrier drum arranged around and having the same diameter as that of the first image carrier drum is interposed between a driving roller and a driven roller, and is circulated and moved by an intermediate transfer belt. A first color toner image formed on the first image carrier drum is provided along the plane portion of the intermediate transfer belt to form a transfer portion of the intermediate transfer belt. After being transferred to the transfer belt, the second color toner image formed on the second image carrier drum is overlaid on the intermediate transfer belt at the second transfer portion, and is overlaid and transferred. The toner image is circulated again to the first and second transfer portions. A third color toner image and a fourth color toner image respectively formed on the first and second image carrier drums by superimposing to form a full-color image. The peripheral length of the intermediate transfer belt is Lb, the diameter of the drive roller is R, the diameter of the first and second image carrier drums is D, the distance between the first and second transfer units is Pt, When N1, N2, and N3 are arbitrary integers, “Lb = N1 × π × D” and “Lb = N2 × π
× R ”and“ Pt = N3 × π × R ”.

Further, for example, a laser light exposure means for exposing the first or second image carrier drum with laser light is provided, wherein the laser light passes through the developing unit. The corresponding image carrier drum is configured to be exposed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view showing a configuration of a main part of a so-called hybrid type color image forming apparatus according to the first embodiment. As shown in FIG. 1, a main part of the color image forming apparatus 20 includes four developing devices 21 containing toners of different colors as developers.
(21a, 21b, 21c, 21d), the image carrier drum 22 (22a, 22b) arranged in combination with each of the two developing units 21, and the driving roller 23 and the driven roller 24. The intermediate transfer belt 25 circulating between the intermediate transfer belt 25 and a cleaner 26 (2) having a cleaning blade in contact with each image carrier drum 22
6a, 26b), the image carrier drum 2 rather than the cleaner 26
A charging roller 27 (27a, 27b) which is located downstream of the rotation direction 2 and abuts on the image carrier drum 22, and a laser beam exposure unit 28 (28a, 28b) which exposes the peripheral surface of each image carrier drum 22; , A main power supply 29 and the like.

A bias voltage of a negative potential in which alternating current and direct current are superimposed is applied from a bias power supply 32 to the core metal of the developing roller 31 of each developing device 21 (developing devices 21c and 21).
The illustration of the bias power supply 32 of d is omitted). Similarly, a negative bias voltage in which alternating current and direct current are superimposed is applied to each charging roller 27 from another bias power source 33 (the bias power source 33 for the charging roller 27b is not shown).

The two developing units 21a and 21b, one image carrier drum 22a combined with the two developing units 21a and 21b, a cleaner 26a contacting the image carrier drum 22a, and a charging roller 27a are A first image forming unit is formed. Similarly, the two developing devices 21c,
21d, one image carrier drum 22b combined with these two developing units 21c and 21d, and this image carrier drum 22
b, the cleaner 26b and the charging roller 27b are in contact with each other.
A second image forming unit is formed.

The above-mentioned cleaner 26a is used for the image carrier drum 2.
The toner stain remaining on the peripheral surface of 2a is cleaned. The charging roller 27a charges the peripheral surface of the cleaned image carrier drum 22a to a uniform high potential and initializes the same. Then, the laser beam exposure unit 28a corresponding to the first developing unit irradiates the laser beam 34 to the image carrier drum 22a through the exposure light path through hole 35 formed in the second developing unit. .

Thus, the peripheral surface of the image carrier drum 22a charged to a uniform high potential is selectively exposed based on the image data, and the low potential portion whose potential is attenuated by the exposure and the initialization are performed. To form a high-potential portion. The developing device 21a forms (develops) a toner image by transferring the toner to a low potential portion (or a high potential portion) of the electrostatic latent image. The image carrier drum 22 a rotationally conveys the toner image and transfers it to the intermediate transfer belt 25.

The second image forming unit operates in the same manner as described above at the timing when the toner image on the intermediate transfer belt 25 comes into contact with the image carrier drum 22b, and the developing unit 21c The electrostatic latent image on the carrier drum 22b is converted into a toner image (development), and the image carrier drum 22b rotates and conveys the toner image, and transfers the toner image on the intermediate transfer belt 25 in a superimposed manner.

Subsequently, the intermediate transfer belt 25 circulates, and the toner image thus superimposed is transferred to the image carrier drum 2.
1st time again at the timing of coming into contact with 2a
The developing unit 21b turns the electrostatic latent image on the image carrier drum 22a into a toner image, and the image carrier drum 22a rotates and conveys the toner image on the intermediate transfer belt 25. The toner image is further superimposed and transferred onto the superimposed toner image.

Finally, the second image forming unit operates again in synchronization with the timing at which the toner image transferred on the intermediate transfer belt 25 comes into contact with the image carrier drum 22b. Developing unit 21d is an image carrier drum 22b
The upper electrostatic latent image is converted into a toner image, and the image carrier drum 22 b rotates and conveys the toner image, and further superimposes and transfers the toner image on the triple toner image on the intermediate transfer belt 25. The intermediate transfer belt 25 onto which the four color toner images are superimposed and transferred continues the circulating movement to convey the quadruple toner image, and transfers the toner image to the paper P.

FIGS. 2A and 2B are views for explaining the structure of the developing unit 21 in more detail. Figure (a) is the same as Figure (b)
In order to make it easy to understand the comparison, only the image carrier drum 22 and one developing unit 21 which are horizontally arranged as shown in FIG. 1 are taken out and vertically shown, and FIG. FIG. 4 is a plan view showing the inside by removing the upper surface (the right surface in FIG. 4A).

As shown in FIGS. 2A and 2B, the developing device 21 rotatably holds the developing roller 31 at a side opening, and the developing roller 31 has a blade scraper 3 attached thereto.
6. The doctor blade 37 abuts, and the toner supply roller 38 is disposed near the doctor blade 37. The above-described through-hole 35 for the exposure light path is formed substantially at the center of the developing unit 21 so as to penetrate vertically (left and right in FIG. 2A). On both sides of the exposure light path through-hole 35, toner stirring members 39 are provided. A toner supply pipe 41 is connected to one side end of the developing device 21. The toner in the developing unit 21 circulates as shown by arrows a, b, c, and d in the figure while being stirred by the rotation of the toner stirring member 39.

When the two-component developing system is used, the toner and the developing aid are stored in the developing unit 21 and only the toner is supplied from the toner supply pipe 41. FIG.
FIG. 1 is a side sectional view showing an overall configuration of a color image forming apparatus including a main part of the above configuration. The first image forming unit 42 and the second image forming unit 43 described above are arranged at the center of the inside and obliquely below it. A lid 44 is provided at the upper part of the apparatus main body so as to be openable and closable up and down with a support shaft 45 as a fulcrum as shown by a double-headed arrow e in the figure. The front (right side in the figure) of the lid 44 is inclined downward to form a paper discharge tray 46. A paper cassette 47 is accommodated in the lower part of the apparatus main body, and an openable / closable paper feed tray 48 is provided in front of the cassette so as to be openable and closable back and forth as indicated by a double-headed arrow f in the drawing.

The paper cassette 47 has a bottom plate 49 which is urged upward by an unillustrated urging member, in which a large number of sheets P are placed and stored, and a front (right side in the drawing) sheet supply is carried out. The paper port is provided with a separating member 51. A paper feed roller 52 is disposed on the apparatus body side in contact with the separating member 51. Further, another separating member 53 and a sheet feeding roller 54 are provided at a sheet feeding end behind the openable sheet tray 48. Above these, a standby / paper feed roller pair 55 is disposed, and above the drive roller 23 of the intermediate transfer belt 25 is disposed. A transfer roller 56 is disposed in pressure contact with the drive roller 23 via the intermediate transfer belt 25. Transfer roller 56
Is attached to a free end side of an arm 58 rotatably arranged with a support shaft 57 as a fulcrum. The arm 58 is moved rearward by an urging member (not shown),
It is urged to pivot to the side.

A forwardly bent guide plate 59 is provided upright above the pressure contact portion between the transfer roller 56 and the drive roller 23, and a fixing device 61 is provided above the guide plate 59, and a paper discharge is provided above the fixing plate 61. A guide 62 and a paper discharge roller pair 63 are provided. The sheet P to which the quadruple toner image described in FIG. 1 has been transferred is guided by the guide plate 59 in FIG. 3, is carried into the fixing device 61, and the toner image is thermally fixed on the sheet surface, and passes through the sheet ejection guide 62. Then, the discharge tray 4 is driven by the discharge roller pair 63.
6 is discharged with the image face down.

By the way, the above-mentioned intermediate transfer belt 25 is
The driven roller 24 side can be turned to the front position indicated by the two-dot chain line 25 'in the figure with the axis of the drive roller 23 as a fulcrum. The cover 44 is opened upward, the intermediate transfer belt 25 is rotated to the above-described front position, and the first image forming unit 42 and the second image forming unit 43 configured in the image forming unit are
As shown by a double-headed arrow g in the figure, the attachment and detachment can be performed in an oblique direction.

The intermediate transfer belt 25 is formed as a unit. In the unit, a cleaning / charging device 64 (not shown in FIG. 1) is in pressure contact with the driven roller 24 via the intermediate transfer belt 25. The transfer roller 65 (65a, 65b) is provided inside the loop in which the belt 25 circulates.
Are respectively connected to the first image forming unit 4 via the intermediate transfer belt 25.
The second image carrier drum and the image carrier drum of the second image forming unit 43 are in pressure contact with each other.

Four toner tanks 66 are arranged above the rear part of the apparatus main body, and magenta, cyan, yellow, and black toners are stored in these toner tanks 66, respectively. These four toner tanks 66 and four developing units 21 are not shown in FIG. 3, but are shown in FIGS. 2 (a) and 2 (b).
Is connected to the toner supply pipe 41 shown in FIG.

In the color image forming apparatus 20 configured and operated as described above, the optimum relation between the members is prevented in order to prevent the color shift (dot position shift) of the toner image to be transferred in an overlapping manner in each of the developing and transferring steps. To build
The applicant of the present invention has attempted various experiments.

FIG. 4 is a chart of data obtained by such an experiment. The chart shows, from left to right, “photoconductor diameter D”, “belt length Lb”, “belt drive roller diameter R”,
"Photoconductor pitch Pt" is shown. Here, the photoconductor diameter D is the diameter of the image carrier drums 22a and 22b, the belt length Lb is the circumference of the intermediate transfer belt 25, the belt driving roller diameter R is the diameter of the driving roller 23, The pitch Pt is determined from the contact portion between the image carrier drum 22a and the intermediate transfer belt 25 from the image carrier drum 22b to the intermediate transfer belt 2.
5 is the distance to the contact portion (see FIG. 1). The unit of the numerical values in the table is mm.

As shown in FIG.
6mm, 24mm, 30mm, 37mm, 40mm, 5mm
0mm, 60mm, 80mm, 90mm, and 100m
m image carrier drum 22 was prototyped, and a minimum of 25
Intermediate transfer belts 25 of various peripheral lengths Lb between 1.2 mm and a maximum of 565.2 mm are combined, and two transfer sections formed by the intermediate transfer belt 25 and the two image bearing drums 22 are provided. The distance between the belts is set to various distances between a minimum of 62.8 mm and a maximum of 125.6 mm, and the driving roller 23 having a diameter of various sizes between a minimum of 15 mm and a maximum of 50 mm is attached to the intermediate transfer belt 25. Was driven to form an image using A4 size paper, and an image was formed by performing a test. As a result, “photoconductor diameter D = 37 mm” and “belt length Lb = 348.54 m” shown in column h of FIG.
m "," Belt drive roller diameter R = 27.75 mm ",
It was found that the one having the "photoconductor pitch Pt = 87.135 mm" was a preferable configuration.

This can be generally summarized as follows: N1, N2,
Lb = N1 × π × D (1) Lb = N2 × π × R (2) Pt = N3 × π × R (3) It suffices to configure each part so as to satisfy the relational expression.

The above equation (1) allows the electrostatic latent images of the first and second steps to be formed on the same portion on the image carrier drum 22 and makes the angular velocity of the image carrier drum 22 the same. Are shown. Equation (2) is obtained from the first process and the second process.
The figure shows the conditions for the peripheral surface position of the drive roller 23 to be the same during the intermediate transfer in the process, and for the transfer speed to be the same. In Expression (3), the peripheral surface position of the driving roller 23 at the time of transfer by the first image forming unit 42 and the time of transfer by the second image forming unit 43 become the same, and the first image forming unit 42 and the second 2 shows conditions for the transfer speeds of the two image forming units 43 to be the same.

FIG. 5, FIG. 6 and FIG. 7A show examples of a color image forming apparatus relating to the present invention in which the arrangement of each part is different. Each part is configured under the condition that satisfies 2).

By the way, in order to cope with the recent demand for downsizing of the equipment in the market, the laser beam exposure unit 28 for exposing the image carrier drum 22 is also used in the color image forming apparatus of the present invention in order to reduce the size of the internal structure. We have devised the arrangement of That is, as shown in FIGS. 1 and 3, two laser beam exposure units 28a and 28b
Are arranged side by side near the bottom of the apparatus main body, and the first image forming section 42
Instead of arranging the second image forming unit 43 as close as possible, a through hole 35 for an exposure light path is provided, and at least one of the laser beam exposure units 28a of the developing device constituting the other second image forming unit 43 The structure is such that the corresponding image carrier drum 22a is exposed through the exposure light path through hole 35. That is, by this, the exposure light path is secured while securing the developer capacity of the small and thin developing device.

By exposing the through hole 35 for the exposure light path to the center of the movement path of the toner in the developing unit 21 as shown in FIG. 2, the exposure can be performed without obstructing the stirring of the toner. Optical path can be secured.

The laser beam exposure unit 28 can be arranged not only vertically or horizontally but also obliquely like a laser beam exposure unit 67 (67a, 67b) shown in FIG. FIG. 7B is an enlarged view of the laser beam exposure unit 67. As shown in FIG. 7B, the laser beam exposure unit 67 includes an engagement arm 67-1 extending toward the image carrier drum 22 '.
The tip of the engagement arm 67-1 is engaged with the support shaft 68 of the image carrier drum 22 '. Support shaft 6 of image carrier drum 22 '
8 and the tension spring 6 between the adjusting screw 67-2 of the engagement arm 67-1.
9, the image carrier drum 2
2 'is urged in the direction of the laser beam exposure unit 67 as shown by the arrow j in the figure. Alternatively, the laser beam exposure unit 67 is urged in the direction of the image carrier drum 22 '. It is also a preferable configuration to arrange the laser beam exposure unit obliquely in this way.

In any of the above-described color image forming apparatuses, a laser beam exposure unit is used for exposing the image carrier drum, but the laser beam passing through the optical system of the laser beam exposure unit is exposed to the laser beam on the image carrier drum. There are parts that are not imaged. By utilizing this, the laser beam exposure unit can be positioned with respect to the image carrier drum.

FIG. 8A is a diagram showing the relationship between the laser beam exposure unit and the image carrier drum, and FIG. 8B is a diagram showing a measuring device for examining the relationship. Same figure
In the laser beam exposure unit having the structure shown in (a), a laser beam 73 emitted from a laser beam light source 71 and reflected by a polygon mirror 72 is converted into an fθ lens 74.
To form an image on the image carrier drum 75,
The laser beam 73 that has passed through the fθ deflecting units 74-1 and 74-2 of the lens 74 is a portion where no image is formed on the image carrier drum 75.

Therefore, when a continuous line is printed in the main scanning direction indicated by arrow k in FIG.
6 and the non-image-forming portions 76-1 and 76-2 at both ends form a latent image and a non-latent image on the image carrier drum 75, and are transferred to the sheet by development and transfer. The position information of the beam exposure unit can be read. That is, the position adjustment information of the laser beam exposure unit can be calculated based on the position information, and the mounting adjustment of the laser beam exposure unit to a correct position can be performed.

In particular, when there are a plurality of image carrier drums such as a tandem type color image forming apparatus or a hybrid type color image forming apparatus of the present embodiment, the above-described position adjustment causes the image carrier drum opposed to the fθ lens to move. The position of f
Positioning can be performed accurately including the θ characteristic, and thereby, positioning accuracy of each color can be improved.

Further, as shown in FIG.
7 may be used to read the position information. The measuring device 77 shown in FIG. 7B has a structure that can be attached to the mounting portion of the image carrier drum 75 of the device main body, and light receiving element portions are provided at portions corresponding to both ends of the exposure portion of the image carrier drum 75. 77-1 and 77-2. Also in this case, when linear continuous exposure is performed in the main scanning direction, a portion where an image is formed and a portion where no image is formed are formed by the light receiving element unit 77-1 of the measuring device 77,
The position information of the laser beam exposure unit can be easily detected by the detection by 77-2.

By the way, in the present invention, the above-mentioned alignment method is the same, but special measures are taken for the structure itself of the laser beam exposure unit. FIG. 9 is a diagram showing a configuration of a laser beam exposure unit employed in the color image forming apparatus of the present invention. As shown in the figure, the laser beam exposure unit 78 includes two laser light sources 79 (79a, 79b) and a polygon mirror 81.
The number of the reflection surfaces 81-1 is twice the number of the reflection surfaces when the number of the laser light sources is one.

The laser light sources 79a and 79b are mounted at different angles on the horizontal plane with respect to the polygon mirror 81 so that the two laser lights emitted from the laser light sources pass through the same horizontal plane. Laser light is simultaneously emitted from the laser light sources 79a and 79b according to the image data, reflected by the reflection surface 81-1 of the polygon mirror 81, and the fθ lens 82
To form a scanning locus on the image carrier drum 83 in the form of dividing one line.

As described above, by simultaneously scanning one line without increasing the rotation of the polygon mirror,
If the printing speed is the same as the conventional one, it is possible to form a high-resolution image by performing scanning at a higher resolution than the conventional one (in this example, twice the resolution). If the resolution is the same as the conventional one, an image can be formed at a printing speed doubled by the number of laser beams (twice in this example).

In such a color image forming apparatus, a two-component developing method or a one-component developing method can be used as the developing method described above. However, since there are two developing devices for one image carrier drum, It is necessary to prevent a developing device not used for development from participating in the image carrier drum.

As described above, in the case where one image carrier drum has a plurality of developing devices, it has been proposed that a developing device not used for development is separated from the image carrier drum. However, in order to avoid complication of the apparatus, it is not preferable to provide a mechanism for separating the developing device from the image carrier drum.

In the color image forming apparatus of the present invention, the developing device is of a fixed type, and a bias control as described below is performed to prevent color mixing in the multi-color printing process in the "one-drum two-developing-device fixed arrangement". Has solved the above problem.

FIG. 10 is a development characteristic diagram for one-component development and two-component development. In the figure, the DC development start voltage is VTH (1), the carrier pulling start voltage is VTH (2), AC / D
The development start voltage of C superposition is indicated by VTH (3), the selection voltage is indicated by VS, and the non-selection voltage is indicated by VB. Also, AC voltage Vpp
Is 1600V and the DC voltage VD is -600V.

First, the developing devices 21a and 21b shown in FIG.
In the above, during the development by the developing device 21a, the developing device 21b must be in a non-developing state. In the case of one-component development, the AC voltage Vpp of the developing device 21b is turned off, and the non-selection voltage VB <the DC development start voltage VTH (1). Developing device 2
When developing at 1b, the AC voltage Vpp of the developing device 21a is turned off, and the non-selection voltage VB <DC development start voltage VTH (1)
And

In the case of two-component development, the AC voltage Vpp of the developing unit 21b in the non-developing state is turned off in this case as well.
In this case, the carrier pulling start voltage VTH (2) <
It is assumed that the non-selection voltage VB <the DC development start voltage VTH (1).

By controlling the bias voltage as described above, it is possible to prevent color mixing in the multi-color printing process in the one-drum two-developing unit arrangement in which the developing units are fixed. FIG.
(a) shows a timing chart of the bias voltage in the case of the one-component development described above, and (b) shows a timing chart of the bias voltage in the case of the two-component development. In each case, times T1 to T11 indicate a rotation period of the drive motor, times T2 to T6 indicate a development period by the developing device 21a, and times T6 to T10 indicate a development period by the developing device 21b.

[0056]

As described above in detail, according to the present invention, the peripheral length of the intermediate transfer belt is Lb, the diameter of the driving roller is R, and the diameter of each of the first and second image bearing drums is D. , The distance between the first and second transfer portions is Pt, and N1, N2,
And N3 as arbitrary integers, “Lb = N1 × π × D”, “Lb = N2 × π × R” and “Pt = N3 × π × R”
The respective parts are configured so that the following relationship is established, so that the respective parts can be arranged by efficiently using the space inside the apparatus main body while maintaining a high-quality image forming function, thereby reducing the size of the apparatus main body. An easy-to-use color image forming apparatus can be provided.

Since the developing unit is provided with a through hole for an exposure light path to expose the image carrier drum, a plurality of developing units and a plurality of laser beam exposing units can be densely arranged. Thereby, it is possible to further reduce the size of the entire device.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a configuration of a main part of a so-called hybrid type color image forming apparatus according to a first embodiment.

FIGS. 2A and 2B are diagrams for explaining the structure of a developing device of the color image forming apparatus according to the first embodiment in more detail;

FIG. 3 is a side sectional view showing an entire configuration of the color image forming apparatus according to the first embodiment.

FIG. 4 is a table of data obtained by an experiment performed for establishing an optimum relationship between respective members of the color image forming apparatus of the present invention.

FIG. 5 is a diagram (part 1) illustrating an example of a color image forming apparatus according to the present invention in which the arrangement of each unit is different.

FIG. 6 is a diagram (part 2) illustrating an example of a color image forming apparatus according to the present invention in which the arrangement of each unit is different.

FIG. 7A is a diagram (part 3) showing an example of a color image forming apparatus in which the arrangement of each part of the present invention is different, and FIG. 7B is an enlarged view of the laser beam exposure unit.

8A is a diagram showing a relationship between a laser beam exposure unit and an image carrier drum, and FIG. 8B is a diagram showing a measuring device for examining the relationship.

FIG. 9 is a diagram illustrating a configuration of a laser beam exposure unit employed in the color image forming apparatus of the present invention.

FIG. 10 is a development characteristic diagram in the case of one-component development and two-component development.

11A is a timing chart of a bias voltage in the case of one-component development, and FIG. 11B is a timing chart of a bias voltage in the case of two-component development.

12 (a) to 12 (f) are diagrams showing the schematic configuration of various conventional electrophotographic color image forming apparatuses.

FIG. 13 is a diagram showing a basic structure of an image forming apparatus having an intermediate configuration of various conventional color image forming apparatuses.

FIG. 14 shows a conventional ROS (Raster Out) for exposing a photoconductor.
FIG. 3 is a diagram illustrating a configuration of a put scanner).

FIGS. 15A and 15B are diagrams showing a conventional method of mounting a laser beam exposure unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 developing device 2 photoconductor drum 3-1 to 3-5 photoconductor 4, 7 developing device 5, 8 photoconductor drum 6 first developing unit 9 second developing unit 11 drive roller 12 driven roller 13 intermediate transfer belt 14 Transfer roller P Paper 15 Laser beam exposure unit 16 Laser beam 16 'Reflected laser beam 17 Polygon mirror 18 Optical system 19 Photoconductor 20 Color image forming apparatus 21 (21a, 21b, 21c, 21d) Developing device 22 (22a, 22b) ), 22 'image carrier drum 23 drive roller 24 driven roller 25 intermediate transfer belt 26 (26a, 26b) cleaner 27 (27a, 27b) charging roller 28 (28a, 28b) laser beam exposure unit 29 main power supply 31 developing roller 32 , 33 bias power supply 34 laser light 35 exposure light path Through hole 36 Blade scraper 37 Doctor blade 38 Toner supply roller 39 Toner stirring member 41 Toner supply pipe 42 First image forming unit 43 Second image forming unit 44 Cover 45 Support shaft 46 Paper discharge tray 47 Paper cassette 48 Open / close paper feed Tray 49 Bottom plate 51, 53 Separation member 52, 54 Paper feed roller 55 Standby / paper feed roller pair 56 Transfer roller 57 Support shaft 58 Arm 59 Guide plate 61 Fixing device 62 Paper discharge guide 63 Paper discharge roller pair 64 Cleaning / charger 65 (65a, 65b) Transfer roller 66 Toner tank 67 (67a, 67b) Laser beam exposure unit 67-1 Engagement arm 67-2 Adjustment screw 68 Support shaft 71 Laser beam light source 72 Polygon mirror 73 Laser beam 74 fθ lens 74-1 , 74-2 fθ deflecting unit 75 Image carrier Ram 76 imaged portions 76-1 and 76-2 parts 77 measuring device not imaged 77-1 and 77-2 receiving element portion

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeru Shimizu 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Co., Ltd. Tokyo Office (72) Inventor Isao Ebisawa 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Inside the Tokyo Office (72) Inventor Koichi Kamei 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Co., Ltd. (72) Inventor Banzo Tsuzuki 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Yoshinori Uesugi, Inventor Yoshinori Uesugi 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Co., Ltd. Tokyo Office F-term (reference)

Claims (2)

[Claims] 1. A first image carrier drum having two developing devices containing different color developers on its peripheral surface, and two developing devices containing other different color developers on its peripheral surface. A first image carrier drum and a second image carrier drum having the same diameter as the first image carrier drum are arranged between a driving roller and a driven roller, and are circulated and moved to perform first and second transfer. A first color toner image formed on the first image carrier drum is provided along the plane portion of the intermediate transfer belt so as to form a portion. After the transfer, the second color toner image formed on the second image carrier drum is over-transferred onto the intermediate transfer belt at the second transfer portion, and the over-transferred toner image is transferred. Is circulated again to the first and second transfer portions, and A third color toner image and a fourth color toner image formed on each of the second image carrier drums, and a full color image is formed by superimposing and transferring the toner image. , The diameter of the drive roller is R, the diameter of the first and second image carrier drums is D, the distance between the first and second transfer units is Pt, and N
When 1, N2, and N3 are arbitrary integers, "Lb =
N1 × π × D ”and“ Lb = N2 × π × R ”and“ Pt
= N3 × π × R ”. 2. A laser light exposing means for exposing the first or second image carrier drum with a laser beam, wherein the laser beam penetrates the developing unit and exposes the corresponding image carrier drum. The color image forming apparatus according to claim 1, wherein