JPH09134044A - Color electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, without being affected by an irregularity in the electrostatic characteristic of the photoreceptor of each of image forming units, a color image which is stable all the time, to make halftone reproducibility high, and to facilitate maintenance, in a color electrophotographic device having four image-forming units. SOLUTION: The four image-forming units 1B, 1Y, 1M, and 1C, each of which has a charge roller, the photoreceptor 9, a developing roller 19 and so on and forms a toner image whose color is different from those of the others are placed into an image forming position 50 in order, a patch image is formed onto the photoreceptor 9 of each of the image forming units and transferred to an intermediate transfer belt 32, and the density of each patch image is detected by a toner concentration sensor 61. Then, conditions for latent-image formation in each image forming unit are determined, and a toner image in each color is formed using the determined conditions.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a color printer,
The present invention relates to a color electrophotographic device used in a color copying machine, a color fax machine, or the like.

[0002]

2. Description of the Related Art Generally, in order to form a color image using an electrophotographic method, a method of forming a color image by superposing toner images of yellow, magenta, cyan and black on a transfer material is used. ing. As a method of forming this color image, toner images of respective colors are sequentially formed on one photoconductor, and the toner images are sequentially superposed on the transfer belt.
Next transfer, and then secondary transfer to paper collectively at a time, and toner image of each color is sequentially formed on one photoconductor, and the toner images are sequentially superposed on a transfer drum around which paper is wound. A transfer drum system and a plurality of image forming units are arranged side by side to form a toner image of each color by parallel processing,
A tandem system in which this toner image is transferred in parallel onto a transfer material conveyed by a belt is generally used.

On the other hand, for the purpose of improving the maintainability and downsizing of the color electrophotographic apparatus, for example, JP-A-7-3 is used.
Japanese Patent Laid-Open No. 6246 proposes a method in which toner images of respective colors are sequentially formed using a rotating image forming unit including four photoconductors, and the toner images are sequentially superposed on a transfer belt. FIG. 14 is an overall configuration diagram of a conventional color electrophotographic apparatus, and the configuration and operation will be described below with reference to the drawings.

As shown in FIG. 14, four sets of fan-shaped image forming units 1Y, 1M, 1C, 1 for yellow, magenta, cyan and black are provided at the center of the color electrophotographic apparatus.
B is arranged in an annular shape and constitutes an image forming unit group. Since each image forming unit is composed of the same constituent members except for the developer, the black image forming unit will be described and the other colors will be omitted to simplify the description. Note that the same numbers are given to the same portions of each color image forming unit, and when it is necessary to distinguish each color, the characters indicating each color are given to the reference numerals.

As shown in FIG. 15, the black image forming unit 1B includes an organic photoconductor 9 based on phthalocyanine, a charging roller 10 for negatively charging the photoconductor 9, and a toner 2.
5B, a developing hopper 14 for accommodating 5B, a rotatable developing roller 19 made of aluminum, a developing bias power source 20 for applying a bias to the developing roller 19, a toner made of a urethane material for supplying the toner of the developing hopper 14 to the developing roller 19. A supply roller 21, a toner layer regulation blade 22 that regulates the toner layer thickness on the developing roller 19, a cleaner 27 that cleans the toner remaining on the surface of the photoconductor 9 after transfer, and a photoconductor cover that protects the photoconductor 9. It is composed of 28 etc. In FIG. 15, the photoconductor cover 28 is shown in an open state for image formation. The toner 25B is black non-magnetic one-component toner. The surface of the photoconductor 9 is exposed by the exposure signal light 13 from the laser.

Next, the configuration of the printer section will be described with reference to FIG. Image forming units 1B, 1 arranged in an annular shape
Y, 1M, and 1C are supported by a support (not shown), and are driven by a moving motor 30 which is a moving means controlled by a control circuit 29 as a whole, and an arrow around a cylindrical fixed shaft 31. It can be rotated in any direction. Each of the image forming units 1B, 1Y, 1M, 1C is moved to and positioned at an image forming position 50 facing a transfer roller 33 for supporting an intermediate transfer belt 32 described later. The support of the image forming units 1B, 1Y, 1M, 1C is provided with means (not shown) for detecting that each image forming unit has moved to the image forming position 50, and the movement of each image forming unit is completed. A signal corresponding to the completion of movement is transmitted to the control circuit 29 each time.

The laser exposure device 3 generates an exposure signal light 13 by a laser beam modulated by a signal input to the printer section. The exposure signal light 13 passes through the optical path formed between the image forming units 1B and 1C of FIG. 5 and is reflected and is irradiated on the photoconductor 9 of the image forming unit at the image forming position 50 to form a latent image. In the state of FIG. 14, it acts on the black image forming unit 1B.

The intermediate transfer belt 32 is made of an endless belt-shaped film of semiconductive urethane having a thickness of 100 μm as a base material, and is wound around a transfer roller 33 and a stainless steel roller 34 each having urethane foam formed around the film. Thus, the photoconductor 9 can move as it rotates. The transfer roller 33 is in light contact with the photoconductor 9 of the image forming unit 1B via the intermediate transfer belt 32. The transfer roller 3 is attached to the roller 34 via the intermediate transfer belt 32.
A second transfer roller 35 having the same configuration as that of No. 3 is lightly pressed so as to be driven and rotatable. A sheet conveying path is formed in the nip portion where the intermediate transfer belt 32 and the second transfer roller 35 are in pressure contact with each other, and the sheet is conveyed from the sheet feeding section 36. The belt cleaner unit 40 includes a belt cleaner and cleans the intermediate transfer belt. The fixing device 44 fixes the toner image on the paper after transfer, and the discharge roller 45 discharges the paper after fixing.

[0009]

Generally, in a color electrophotographic apparatus, it is necessary to provide a stable color image output.
The color balance of colors (balance of toner adhesion amount) is important. For example, if the toner adhesion amount of any one color is reduced, the color reproduction range of the color image is greatly reduced, and the color balance of the secondary colors and the tertiary colors is lost. For this reason,
The image forming process of each color is required to have temporal stability and environmental stability that are several times those of a monochrome electrophotographic apparatus. In order to maintain these stability, conventionally, a photoconductor potential sensor is provided around the photoconductor to monitor the potential of the photoconductor and the density of the toner image formed on the photoconductor using the toner image density sensor. A method of maintaining stability over time and environmental stability by monitoring the image quality and controlling the image forming conditions from the outputs of these sensors has been used.

In the conventional color electrophotographic apparatus described in JP-A-7-36246, since the four image forming units each have a photoconductor, the electrostatic characteristics (potential characteristics) of the four photoconductors are The variation is one factor that hinders image stabilization. For this reason, conventionally, it is necessary to provide a photoconductor potential sensor and a toner image density sensor in each of the four image forming units, resulting in a large increase in cost and complication of the configuration, and impairing maintainability of the image forming unit. Had the problem.

Further, in the color electrophotographic apparatus, the halftone reproduction characteristic (gradation reproduction characteristic: γ characteristic) of each color is important. 2 per unit pixel, like a black and white electrophotographic device
If the value is white or black, halftone reproducibility is not required. However, in the color electrophotographic apparatus, since a signal of about 32 to 256 gradations is sent to the unit pixel in the signal system, linearity of image density reproducibility for this multiple gradations is required. To enhance this linearity, the halftone reproducibility (γ characteristic) of each color must be a gradual γ characteristic that does not have a sudden change point. However, in general, this gradual γ characteristic is in a relationship contradictory to the stability of the electrophotographic image forming process. That is, there is a problem in that if an attempt is made to obtain a gentle γ characteristic, the electrophotographic image forming process tends to be unstable, and if an attempt is made to obtain stability, a steep γ characteristic is likely to occur.

Further, each of the four image forming units is filled with a fixed amount of toner of four colors so that a fixed number of sheets can be printed. However, in color printing, the toner consumption of the four colors greatly differs depending on the print sample, so that it is necessary to replace only a specific image forming unit. Even when the image forming unit of only one color is replaced in this manner, conventionally, before the apparatus is restarted, the initial operation check of all four image forming units and the image forming unit image forming condition setting, that is, the so-called initializing operation is performed. However, there is a problem that it takes a lot of time to perform the initialization operation. Immediately after the specific image forming unit is replaced, the toner charge amount of the replaced image forming unit is different from the toner charge amount of the image forming unit that has been conventionally mounted. There is a problem that transfer defects are likely to occur.

The present invention has been made to solve the above-mentioned problems of the prior art, and has a color having four image forming units each having a charging means, an electrostatic image carrier, a developing means and a cleaning means. In the electrophotographic device,
It is possible to always obtain a stable color image without being affected by the variations in the electrostatic characteristics of the four electrostatic image bearing members (photoconductors), the halftone reproducibility of the color image is high, and the maintenance is easy. Aims to provide a simple and inexpensive color electrophotographic apparatus.

[0014]

To achieve the above object, the color electrophotographic apparatus of the present invention comprises (1) a charging means, an electrostatic image carrier, and a developing means having toners of different colors. Four movable image forming units each having a cleaning unit and forming toner images of different colors on the electrostatic image carrier, and (2) the electrostatic image carrier at a predetermined transfer position. Transfer means for transferring the toner image on the body to the transfer material, (3) density detecting means for detecting the toner image density on the transfer material, and (4) image exposure at a predetermined exposure position corresponding to the transfer position. And (5) the entire image forming unit group so that the four image forming units are sequentially positioned at image forming positions corresponding to the exposure position and the transfer position, respectively. And a moving means for rotating and moving the image. A latent image forming condition is formed by forming a patch image using an image forming unit located at the final position, transferring the patch image to the transfer material, and detecting the density of the transferred patch image by the density detecting means. To form different color toner images by using the determined latent image forming conditions, and transfer the formed toner images to the transfer material while aligning the positions thereof to form a color image. Do.

In the above structure, it is preferable that the latent image forming condition to be determined is the irradiation intensity of laser exposure on the electrostatic image carrier. Alternatively, it is preferable that the latent image forming condition to be determined is the grid voltage of the charging means of the electrostatic image carrier.

Further, another color electrophotographic apparatus of the present invention comprises (1) a charging means, an electrostatic image carrier, a developing means having toners of different colors, and a cleaning means. Four movable image forming units for forming toner images of different colors on the electrostatic image carrier,
(2) transfer means for transferring the toner image on the electrostatic image carrier to a transfer material at a predetermined transfer position, (3) density detecting means for detecting the toner image density on the transfer material, and (4) ) Laser exposure means for performing image exposure at a predetermined exposure position corresponding to the transfer position, and (5) the four image forming units, respectively.
An image forming unit located at the image forming position, the moving unit rotating the entire image forming unit group so as to sequentially position the image forming position corresponding to the exposure position and the transfer position. A unit is used to form N (N> 2) patch images P _{1 to} P _N having different optical densities by changing the image forming conditions of the image forming unit, and then the patch images are transferred to the transfer material. transferred to above, determining the image forming condition by each patch image density which is transferred is detected by said density detecting means detects the difference (P _m -P _m-1) of the optical density adjacent each patch image Then, toner images of different colors are formed under the determined image forming conditions, and the formed toner images are superposed and transferred on the transfer material in position to form a color image.

In the above arrangement, the image forming condition to be determined is
The irradiation pulse width time of the laser light is preferable. Alternatively, the image forming condition to be determined is preferably the developing bias of the developing device. Further, it is preferable that the algorithm of the image forming condition to be determined differs depending on the image quality switching mode.

Further, according to still another color electrophotographic apparatus of the present invention, (1) charging means, an electrostatic image carrier, and
Four movable image forming units, each having a developing unit having a different color toner and a cleaning unit, for forming a toner image of a different color on the electrostatic image carrier, and (2) a predetermined image forming unit. Transfer means for transferring the toner image on the electrostatic image carrier to the transfer material at the transfer position; (3) density detecting means for detecting the toner image density on the transfer material; and (4) on the transfer material. Of the toner layer surface potential, (5) laser exposure means for performing image exposure at a predetermined exposure position corresponding to the transfer position, and (6) the four image forming units, respectively. In order to sequentially position the image forming positions corresponding to the exposure position and the transfer position,
A moving unit that rotates and moves the entire image forming unit group, and after the toner image is formed by the image forming unit located at the image forming position, the toner image is transferred to the transfer material, The image forming conditions are determined by detecting the toner image density and the toner layer surface potential, and the toner images of different colors formed by using the determined image forming conditions are superimposed and transferred on the transfer material. Then, a color image is formed.

In the above structure, it is preferable that the transfer condition from the transfer material to the final printing target is determined by detecting the surface potential of the toner layer on the transfer material.

Further, according to still another color electrophotographic apparatus of the present invention, (1) a charging means, an electrostatic image carrier, and
Four movable image forming units, each having a developing unit having a different color toner and a cleaning unit, for forming a toner image of a different color on the electrostatic image carrier, and (2) a predetermined image forming unit. Transfer means for transferring the toner image on the electrostatic image carrier to a transfer material at the transfer position, (3) density detecting means for detecting the toner image density on the transfer material, and (4) the transfer position. Laser exposure means for performing image exposure at a corresponding predetermined exposure position, and (5) each of the four image forming units is sequentially positioned at an image forming position corresponding to the exposure position and corresponding to the transfer position. A moving means for rotating the entire image forming unit group, and (6) a detecting means for detecting an image forming pattern of the image forming unit at a position other than the image forming position. Image forming unit Image forming unit is formed, and then the image forming unit is rotationally moved by the moving unit, and the image forming condition is determined by detecting the image forming pattern by the detecting unit, and the determined image forming condition is used. Toner images of different colors are formed, and the formed toner images are superposed and transferred on the transfer material in position to form a color image.

In the above arrangement, it is preferable that the detecting means is a toner density sensor for detecting the toner density on the electrostatic image carrier. Alternatively, the detection means is preferably a surface potential sensor that detects the surface potential of the electrostatic image carrier.

Further, according to still another color electrophotographic apparatus of the present invention, (1) a charging means, an electrostatic image carrier, and
(4) four movable image forming units having developing means having different color toners and cleaning means and forming toner images of different colors on the electrostatic image carrier, and (2) the image Image forming unit attachment / detachment detecting means for detecting attachment / detachment of the forming unit; (3) transfer means for transferring the toner image on the electrostatic image carrier to a transfer material at a predetermined transfer position; and (4) the transfer material. Density detection means for detecting the upper toner image density, (5) laser exposure means for performing image exposure at a predetermined exposure position corresponding to the transfer position, and (6) the four image forming units respectively for the exposure. A moving unit for rotating and moving the entire image forming unit group so as to sequentially position the image forming unit corresponding to the position and the image forming position corresponding to the transfer position. Judged image shape Only the unit is moved to the image forming position, a toner image is formed by using the image forming unit, and then the image forming unit image forming condition is determined and detected by detecting the toner image density by the density detecting unit. Toner images of different colors are formed under the above-mentioned image forming conditions, and the formed toner images are superposed and transferred on the transfer material in position to form a color image.

In each of the above structures, it is preferable that at least a part of the optical element for scanning the laser beam of the exposing means is provided in the vicinity of the center of rotation of the rotational movement of the image forming unit group.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) A first embodiment of a color electrophotographic apparatus according to the present invention.
Embodiments will be described with reference to FIGS. 1 and 2. FIG. 1 is a sectional view showing the overall constitution of the first embodiment of the color electrophotographic apparatus of the present invention, and FIG. 2 is a sectional view showing the detailed constitution of the image forming unit in FIG. In FIG. 1, four sets of fan-shaped image forming units 1Y, 1M, 1C, and 1B of yellow, magenta, cyan, and black are arranged in an annular shape in the center of the color electrophotographic apparatus, and the image forming unit group is formed. Are configured. Each of the image forming units 1Y, 1M, 1C, and 1B is composed of the same member except for the developer, so the black image forming unit 1B will be described for simplification of description, and other colors will be described. Omit it. In addition, each color image forming unit 1
For Y, 1M, 1C, and 1B, the same numbers are given to the same parts, and when it is necessary to distinguish each color, the letters showing the respective colors are given to the reference numerals.

As shown in FIG. 2, the black image forming unit 1B includes an organic photoconductor 9 based on phthalocyanine, a charging roller 10 for negatively charging the photoconductor 9, and a toner 2.
The developing hopper 14 for accommodating 5B, the rotatable developing roller 19 made of aluminum, the developing bias power source 20 for applying a bias to the developing roller 19, the urethane material for supplying the toner of the developing hopper 14 to the developing roller 19, and the like. The toner supply roller 21, the toner layer regulating blade 22 that regulates the toner layer thickness on the developing roller 19, the cleaner 27 for cleaning the toner remaining on the surface of the photoconductor 9 after transfer, and the photoconductor 9 are protected. Photoconductor cover 28 for
And so on. In FIG. 2, the photoconductor cover 28 is shown in an open state for image formation. The surface of the photoconductor 9 is exposed by the exposure signal light 13 from the laser.

The organic photoreceptor 9 has a diameter of 30 mm and is rotated in the direction of arrow A in the figure at a peripheral speed of 100 mm / s. The developing roller 19 has a diameter of 20 mm and a peripheral speed of 100 mm /
It is rotated in the arrow B direction by s. The toner 25B is a black non-magnetic one-component toner, which is obtained by dispersing a pigment which is a colorant, a charge control agent, a fixing improving agent and the like in a polyester resin and adding a toner surface modifier. Inside the developing hopper 14, the black non-magnetic one-component toner 25B is
It is filled with 0g and prints 50% of A4 blackening rate.
It is set to output 00 sheets.

The image forming unit 1 configured as described above.
The operation of Y, 1M, 1C, and 1B will be described with reference to FIG. The charging roller 10 moves the photoconductor 9 to -70.
The photosensitive member 9 is charged to 0 V, and the exposure signal light 13 from the laser is applied to the photosensitive member 9 to form an electrostatic latent image. At this time, the overall exposure potential of the photoconductor 9 was −100V, for example. The surface of the photoconductor 9 is opposed to the developing roller 19 which carries the non-magnetic one-component toner 25B and rotates in the same direction as the photoconductor 9 at a constant speed. By the developing bias power source 20, the developing roller 19
In addition, the DC voltage of -500V is 750V (0 to pea
k), a superposed sine wave AC voltage having a frequency of 2 KHz is applied. As a result, a negative-positive inverted toner image is formed only on the image portion on the photoconductor 9.

Next, the configuration of the printer section will be described with reference to FIG. Image forming units 1B, 1 arranged in an annular shape
Y, 1M, and 1C are supported by a support (not shown), and are driven by a moving motor 30 controlled by a control circuit 29 as a whole to rotate around a cylindrical fixed shaft 31 in the arrow direction. It is possible. The image forming units 1B, 1Y,
1M and 1C are moved to and positioned at an image forming position 50 facing a transfer roller 33 for supporting an intermediate transfer belt 32 described later. The image forming position 50 is the exposure signal light 1
It is also the exposure position by 3. Image forming unit 1B, 1
Each of the image forming units 1Y, 1Y,
Means (not shown) for detecting that 1M, 1C, 1B have moved to the image forming position 50 is provided, and each time the movement of each image forming unit 1Y, 1M, 1C, 1B is completed, the movement is completed. The signal is transmitted to the control circuit 29.

The laser exposure device 3 generates the exposure signal light 13 by the laser beam modulated by the signal input to the printer section. The exposure signal light 13 passes through the optical path formed between the black and cyan image forming units 1B and 1C shown in FIG. 1, and passes through the transparent window 4 opened in a part of the fixed shaft 31 to the inside of the shaft 31. Is incident on the optical correction member 65, which is a cylindrical lens, is reflected and is irradiated on the photoconductor 9 of the image forming unit (for example, 1B) at the image forming position 50, and a latent image is formed on the surface of the photoconductor 9. Form.
In the state of FIG. 1, it acts on the black image forming unit 1B. The control device 51 controls the laser power of the laser exposure device 3, and can control the laser power from 0.15 mw to 0.30 mw in 0.01 mw steps on the surface of the electrostatic image carrier 9.

The optical path from the laser exposure device 3 to the optical correction member 65 is a fan-shaped image forming unit (for example, 1).
B and 1C), the area occupied by the image forming unit groups 1B, 1Y, 1M, and 1C is hardly wasted. Further, since the optical correction member 65 is provided in the central portion of the image forming unit groups 1B, 1Y, 1M, 1C, it has a simple and highly reliable configuration and the like. Conventionally, all the optical correction is performed in the exposure apparatus 3, and a simple plane mirror is installed inside the fixed shaft 31 to change the direction of the laser beam. On the other hand, by providing the optical correction member 65 in the central portion of the image forming unit groups 1B, 1Y, 1M, 1C as in the present embodiment, optical correction can be performed near the image forming position. Therefore, it is possible to increase the accuracy of the positional deviation of the laser beam at the imaging position and the beam shape. Although a cylindrical lens is used as the optical correction member 65 here, the same effect can be obtained by using a cylinder mirror or the like. Further, since the optical path is set so that the reflection surface of the optical correction member 65 faces downward, there is an effect that dust and the like in the device hardly adheres.

The intermediate transfer belt 32 is formed of a film such as an endless belt-shaped semiconductive urethane base material having a thickness of 100 μm. It is wound and movable in the direction of arrow C. Transfer roller 33
Is lightly pressed against the photoconductor 9 of the image forming unit 1B via the intermediate transfer belt 32. A conductive belt running stabilizing member 62 made of, for example, metal is in contact with the inner circumference of the intermediate transfer belt 32 and is grounded to the main body. The reflective toner concentration sensor 61 is for detecting the toner concentration on the intermediate transfer belt 32, and is provided so as to face the belt running stabilizing member 62 with the intermediate transfer belt 32 interposed therebetween. The belt running stabilizing member 62 stabilizes the running of the intermediate transfer belt 32 and, at the same time, keeps the distance between the toner density sensor 61 and the intermediate transfer belt 32 constant and reduces the variation in the output of the toner density sensor 61. The transfer roller 33 is attached to the roller 34 via the intermediate transfer belt 32.
The second transfer roller 35 having the same configuration as the above is lightly pressed so as to be driven to rotate. A sheet conveying path is formed in the nip portion where the intermediate transfer belt 32 and the second transfer roller 35 are in pressure contact with each other, and the sheet is conveyed from the sheet feeding section 36. The belt cleaner unit 40 includes a belt cleaner and cleans the intermediate transfer belt 32. The fixing device 44 fixes the toner image on the paper after transfer, and the discharge roller 45 discharges the paper after fixing.

The operation of the first embodiment of the color electrophotographic apparatus of the present invention constructed as above will be described. When the power of the color electrophotographic apparatus is turned on, the entire apparatus first performs an initialization operation, and after the initialization is completed, the color printing operation starts. First, the initialization operation will be described. As an example, as shown in FIG. 1, the black image forming unit 1B is used at the image forming position 5
The operation when it is positioned at 0 will be described.

The laser exposure device 3 presets 2.0 mw as the reference light for the black patch image.
The laser light of is output to the image forming unit 1B, the operation of the image forming unit 1B is started, and a patch image with a size of 20 × 30 mm is formed using black toner. The image forming speed of the image forming unit 1B (equal to the peripheral speed of the photoconductor 9) and the moving speed of the intermediate transfer belt 32 are set to be the same, and at the same time when the image is formed, the transfer roller 33 acts at the same time. The black patch image is transferred to the intermediate transfer belt 32, and the transferred patch image density is detected by the toner density sensor 61.

Here, the detected toner concentration is a predetermined value (for example, 1.3 for black).
If it is higher than 0), the initialization operation of the black image forming unit 1B is finished, the yellow image forming unit 1Y is moved to the image forming position 30 by the moving motor 30, and the initialization operation is performed similarly to the black image forming unit 1B. I do. On the other hand, when the detected toner concentration is lower than the specified value 1.30, a predetermined signal to that effect is transmitted to the control circuit 51, the laser power is increased by one step (for example, 2.1 mw), and the The steps of patch image creation, transfer, and toner density detection are repeated until the specified value is reached. If the toner density does not reach the specified value even when the laser power reaches the maximum value, the apparatus main body side outputs a replacement instruction signal for the black image forming unit 1B.

In this way, the image forming units 1B, 1
In the order of Y, 1M, and 1C, the specified values are yellow 1.20, magenta 1.25, and cyan 1.25, respectively.
Performs initialization operation. In the case of the above specific numerical example,
The determined laser powers are 2.2 mw, 2.0 mw, and 2.0 in the order of black, yellow, magenta, and cyan.
It was mw and 2.3 mw. In this way, the initialization operation of the entire color electrophotographic apparatus is completed.

Next, in the color printing operation, the black image forming unit 1B is used to form a black image with a laser power of 2.2 mw corresponding to the black determined by the initialization, and the toner image is formed. Is transferred to 32. Next, the image forming unit group 1B,
1Y, 1M, 1C are entirely driven by the moving motor 30,
It is integrally rotated in the direction of arrow D in FIG. The yellow image forming unit 1Y rotates exactly 90 degrees, stops at the position where the yellow image forming unit 1Y reaches the image forming position 50, and the yellow image forming unit 1Y is positioned. Each image forming unit 1B, 1
Since the portions of Y, 1M, and 1C other than the photoconductor 9 are located inside the rotation arc of the tip of the photoconductor 9, the intermediate transfer belt 32 may not contact the image forming units 1B, 1Y, 1M, and 1C. Absent.

As in the case of the black image forming unit 1B, the laser exposure device 3 uses the laser power of 2.0 mw in response to the yellow signal and the yellow image forming unit 1 has a laser power of 2.0 mw.
The exposure signal light 13 is output to Y to form and transfer a yellow toner image. At this time, the writing timing of the yellow exposure signal light 13 is controlled so that the next yellow toner image positionally matches the previously transferred black toner image on the intermediate transfer belt 32. During this time, the second transfer roller 35 and the cleaner unit 40 are slightly apart from the intermediate transfer belt 32, and do not affect the black toner image on the intermediate transfer belt 32.

The same operation as above is performed with a laser power of 2.0 mw for the magenta image forming unit 1M and with a laser power of 2.3 mw for the cyan image forming unit 1.
Do with. On the intermediate transfer belt 32, toner images of four colors are superposed so as to be aligned with each other, and a color image is formed. After the last transfer of the cyan toner image, the second transfer roller 35 acts to match the timing and feed the paper feed unit 3.
The toner images of four colors are collectively transferred onto the paper sent from the printer 6. The toner image transferred to the paper is fixed by the fixing device 44. The sheet is then discharged to the outside of the apparatus via the discharge roller 45. The color image obtained in this way is
The maximum image density is always stable, and a stable color image can always be obtained even after continuous operation of the apparatus and after replacement of the individual image forming unit 1B, 1Y, 1M or 1C during continuous operation.

As described above, in the first embodiment, the patch image on the intermediate transfer belt 32 is detected and the laser irradiation intensity is determined. Therefore, the four image forming units 1B, 1Y, 1
Even if the photoconductors 9 of M and 1C have variations in electrostatic characteristics, one toner density sensor 61 on the intermediate transfer belt 32 can always obtain a stable color image of the maximum image density. . Further, by making the toner concentration specified value changeable by the user, it is possible to easily adjust the color image to a desired color balance.

In the first embodiment, when the toner density does not reach the specified value, the laser power is increased by one step. However, the difference between the specified value and the detected toner density is detected and the difference is calculated. Depending on the number of laser power increases, the initialization time can be shortened. Further, since the specified value of the toner density used in the first embodiment does not go through the fixing step, it differs from the final image density of the printed matter, and the appropriate value changes depending on the toner material used. Therefore, it is not limited to the numerical examples in the first embodiment.

Further, in the first embodiment, when the specified value is exceeded in the initial operation, the initialization operation of the image forming unit is terminated at that time, but the laser power is set to 1
By repeating the steps of stepwise descending, patch image creation, transfer, and toner density detection until the value falls below the specified value, the reproducibility in the shadow area of the color image is improved and more accurate image density control is performed. It is possible.

(Second Embodiment) Next, a second embodiment of the color electrophotographic apparatus of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 3 is a sectional view showing the overall configuration of the second embodiment of the color electrophotographic apparatus of the present invention, and FIG. 4 is a sectional view showing the detailed configuration of the image forming unit in FIG. In each of the drawings, members given the same reference numerals as those in the first embodiment are substantially the same, and the description thereof will be omitted.

In the color electrophotographic apparatus according to the second embodiment, the belt running stabilizing member 6 in the first embodiment is used.
Instead of 2, the intermediate transfer belt running stabilizing roller 63 formed of a conductive roller made of metal or the like is used as the intermediate transfer belt 32.
It is in contact with the inner wall of and is rotatably installed. Also,
Inside the image forming units 2Y, 2M, 2C, and 2B for each color, instead of the charging roller 10, a scorotron charger 11 is provided.
Is provided. The scorotron charger 11 is the photoconductor 9
As shown in FIG. 4, the central part of the corona wire is connected to a constant voltage power source (not shown) of -5 KV, and the grid is further connected to 10 V from -500V to -700V. Constant voltage power supply 12 that can be changed in steps
Is connected.

Next, the second color electrophotographic apparatus of the present invention will be described.
The color image forming operation in the embodiment will be described.
As in the case of the first embodiment, when the power of the color electrophotographic apparatus is turned on, the entire apparatus first performs the initialization operation, and after the initialization is completed, the color printing operation starts. First, the initialization operation will be described. As an example, the operation when the black image forming unit 2B is positioned at the image forming position 50 will be described.

The scorotron charger 11 charged the photosensitive member 9 to a constant potential of -550V with a wire voltage of -5KV and a grid voltage of -550V. The surface of the photoconductor 9 is opposed to the developing roller 19 which carries the black non-magnetic one-component toner 25B and rotates in the same direction as the photoconductor 9 at a constant speed. The developing bias power source 20 supplies the developing roller 19 with a DC voltage of -450V of 500V (0 to peak),
A rectangular wave alternating voltage with a frequency of 1 KHz was applied. As a result, faint toner adhesion was observed on the photoconductor 9. Next, this toner image was transferred onto the intermediate transfer belt 32, and its density was detected by the toner density sensor 61, and it was 0.13.

Here, the detected toner concentration is a predetermined value (for example, 0.0 for black).
If it is lower than 7), the initialization operation of the black image forming unit 2B is completed, the yellow image forming unit 2Y is moved to the image forming position 50 by the moving motor 30, and the initialization operation is performed similarly to the black image forming unit 2B. I do. On the other hand, when the detected toner density is higher than the specified value 0.07, the signal is transferred to the grid voltage control circuit 12 to increase the grid voltage by one step (for example, −560V), and the patch image is created again. The steps of transfer, toner concentration detection, and so on are repeated until the specified value is reached. In addition, the grid voltage has a maximum value (for example, -700).
If the toner density does not reach the specified value even when the voltage becomes V), the apparatus main body side outputs a replacement instruction signal for the black image forming unit 2B.

In this way, the image forming units 2B, 2
In the order of Y, 2M, and 2C, the specified values are yellow 0.10, magenta 0.10, and cyan 0.10.
Performs initialization operation. In the case of the above specific numerical example,
The determined grid voltages are -590V, -570V, -55 in the order of black, yellow, magenta, and cyan.
It was 0V and -550V. In this way, the initialization operation of the entire color electrophotographic apparatus is completed.

Next, in the color printing operation, a black image forming unit 2B is used to form a black image with a grid voltage of -590V determined by the initialization, and the toner image is transferred to the intermediate transfer belt 32. . The image forming unit groups 2B, 2Y, 2M and 2C are wholly driven by the moving motor 30 and integrally rotated in the direction of arrow D in FIG. The yellow image forming unit 2Y rotates exactly 90 degrees, stops at the position where the yellow image forming unit 2Y reaches the image forming position 50, and the yellow image forming unit 2Y is positioned. Photoreceptor 9 of image forming unit 2B, 2Y, 2M, 2C
Since the other portions are located inside the rotation arc of the tip of the photoconductor 9, the intermediate transfer belt 32 is not included in the image forming unit 2.
There is no contact with B, 2Y, 2M and 2C.

Similarly to the black image forming unit 2B unit, the exposure signal light 13 is output to the yellow image forming unit 1Y by the grid voltage of -570V by the signal corresponding to yellow to form the yellow toner image. Transfer is performed. At this time, the writing timing of the yellow exposure signal light 13 is controlled so that the next yellow toner image positionally matches the previously transferred black toner image on the intermediate transfer belt 32. During this time, the second transfer roller 35 and the cleaner unit 40 are slightly apart from the intermediate transfer belt, and do not affect the black toner image on the intermediate transfer belt 32.

The same operation as described above is performed with a grid voltage of −550V for the magenta image forming unit 1M and with a grid voltage of −5V for the cyan image forming unit 1C.
It is performed at 50V. On the intermediate transfer belt 32, toner images of four colors are superposed so as to be aligned with each other, and a color image is formed. After the final transfer of the cyan toner image, the toner images of four colors are collectively transferred onto the paper fed from the paper feed section 36 at the same timing by the action of the second transfer roller 35. The toner image transferred onto the sheet is fixed by the fixing device 4
It is fixed by 4. The sheet is then discharged to the outside of the apparatus via the discharge roller 45. The transfer residual toner remaining on the intermediate transfer belt is cleaned by the action of the cleaner unit 40 to prepare for the next image formation.

As described above, in the second embodiment, the patch image on the intermediate transfer belt 32 is detected and the charger grid voltage is determined. Therefore, the four image forming units 1B, 1
Even if each of the Y, 1M, and 1C photoconductors 9 has a variation in electrostatic characteristics, one toner density sensor 61 on the intermediate transfer belt 32 always causes toner adhesion to a non-image portion, so-called fogging. You can get no image.

In the second embodiment, when the toner density exceeds the specified value, the grid voltage is increased by one step. However, the difference between the specified value and the detected toner density is detected,
The initialization time can be shortened by determining the number of grid voltage increases according to the difference. Further, when detecting a low toner density on the intermediate transfer belt 32, the intermediate transfer belt 32 before the toner is transferred is detected.
It is possible to perform highly accurate control in a shorter time by previously detecting the density of 1 and determining the number of grid voltage increases based on this density variation. Further, before forming a patch image for density detection, a solid image is formed by using an image forming unit of another color, and the solid image is transferred onto the transfer belt 32, which is used as the background of the patch image. It is also possible to stabilize the output of the sensor 61. Further, the output of the density sensor 61 can be stabilized by providing a white background portion for patch detection on the end portion of the intermediate transfer belt 32.

Further, in the second embodiment, when the patch density is equal to or lower than the specified value during the initial operation, the initializing operation of the image forming unit is finished at that time, but the grid voltage is lowered until it reaches the specified value or more. This makes it possible to enhance the highlight reproducibility of a color image.

(Third Embodiment) Next, a third embodiment of the color electrophotographic apparatus of the present invention will be described with reference to FIGS.
This will be described with reference to FIGS. FIG. 5 is a sectional view showing the overall constitution of the third embodiment of the color electrophotographic apparatus of the present invention, and FIG. 6 is a sectional view showing the detailed constitution of the image forming unit in FIG. FIG. 7 is a perspective view showing a patch image forming method according to the third embodiment.
FIG. 8 is a graph showing the densities of patch images formed on the surface of the photoconductor 9 in this embodiment. Since the members designated by the same reference numerals as those of the first embodiment shown in FIGS. 1 and 2 are substantially the same, the description thereof will be omitted.

The irradiation pulse width control circuit 52 shown in FIG.
The irradiation pulse width of the laser light of the laser exposure device 3 is controlled. In the third embodiment, the laser exposure device 3 has 6
It has a resolution of 00 × 600 dpi and its laser beam diameter is 1 / e ² and is 55 μm in the main scanning direction and 70 μm in the sub scanning direction.
m. The irradiation pulse width control circuit 52 can control the laser irradiation time up to 64 divisions with 2 pixels of 600 dpi in the laser beam main scanning direction as one unit. That is, the laser irradiation time has 64 modes from t ₁ to t _64, and the 64th mode is 2 pixel laser full irradiation (overall exposure). Generally, the image forming unit 1B,
The toner image densities formed by 1Y, 1M, and 1C show a tendency of rising to the right as the irradiation time increases. The third embodiment utilizes this characteristic to enhance the gradation reproducibility of an image.

Next, the third color electrophotographic apparatus of the present invention will be described.
The color image forming operation of the embodiment will be described.
When the color electrophotographic device is turned on, the entire device
First, the initialization operation is performed, and after the initialization is completed, the color printing operation is started. First, the initialization operation will be described. As an example, as shown in FIG. 5, the operation when the black image forming unit 1B is positioned at the image forming position 50 will be described with reference to FIG.

The charging roller 10 moves the photosensitive member 9 to -70.
It is charged to a constant potential of 0V. Next, the control circuit 51 irradiates the photosensitive member 9 with eight kinds of exposure signal light 13 pulse-width modulated to form eight kinds of latent patch image images. This patch image latent image forming method is shown in FIG. In FIG.
The photoconductor 9 inside the image forming unit 1B is rotated in the direction of the arrow in the figure, and the exposure signal light 13 is irradiated onto the surface of the photoconductor 9 while scanning as shown in the figure. As a result, a patch image as shown in the figure is formed on the end of the photoconductor 9.

The surface of the photoconductor 9 is opposed to a developing roller 19 which carries a black non-magnetic one-component toner 25B and rotates in the same direction as the photoconductor 9 at a constant speed. The developing bias power source 20 applies to the developing roller 19 a DC voltage of -500 V superposed with a rectangular wave AC voltage of 750 V (0 to peak) and a frequency of 3 KHz. As a result, eight types of patch images having different image densities are observed on the photoconductor 9. Let the densities of the patch images be P _{1 to} P ₈ .

Next, the patch image is actually transferred onto the intermediate transfer belt 32 shown in FIG.
The 1, was detected the P ₈ from the concentration P _1, FIG. 8
The results were as shown in (a) and (b). The densities P _{1 to} P ₈ of the patch images are 0.08 and 0.0, respectively.
8, 0.10, 0.32, 0.85, 1.32, 1.3
It was 3, 1.32. Next, the adjacent difference of image density, calculating the P _m -P _m-1, 0.00,0.0
2, 0.22, 0.63, 0.47, 0.01, -0.
01.

Here, the difference P _m − measured from the difference (for example, 0.10) specified in advance on the apparatus main body side.
The point where P _m-1 becomes large is detected. In this case, the points of difference 0.02 and 0.22 and 0.47 and 0.
01 to have been P ₃ and P ₆ is a point. This P ₃
, And P ₆ are set as the minimum and maximum image density areas, respectively,
By storing the laser irradiation times t ₃ and t ₆ at this time and setting the irradiation time width of the laser light to the full range at the time of gradation reproduction as shown in FIG. 8B, the black image forming unit Initialization of 1B is completed. Similarly, when the irradiation time widths of the respective laser beams are determined in the order of the image forming units 1B, 1Y, 1M, and 1C, black is t ₃ and t ₆ , yellow is t ₂ and t ₇ , and magenta is t.
₂ and t ₇ , and cyan became t ₃ and t ₇ . In this way, the initialization operation of the entire color electrophotographic apparatus is completed.

Next, in the color printing operation, a black image is formed on the intermediate transfer belt 32 by using the black image forming unit 1B for the laser irradiation times t ₃ and t ₆ determined by the initialization. Transcribe. The image forming unit groups 1B, 1Y, 1M, and 1C are wholly driven by the moving motor 30 and integrally rotated in the direction of arrow D in FIG. The yellow image forming unit 1Y rotates exactly 90 degrees, stops at the position where the yellow image forming unit 1Y reaches the image forming position 50, and the yellow image forming unit 1Y is positioned.

As in the case of the black image forming unit 1B, the exposure signal light 13 is output to the yellow image forming unit 1Y at the laser irradiation times t ₂ and t ₃ based on the signal corresponding to yellow. A yellow toner image is formed and transferred. At this time, the writing timing of the yellow exposure signal light 13 is controlled so that the next yellow toner image positionally matches the previously transferred black toner image on the intermediate transfer belt 32. The same operation as above is performed for the magenta image forming unit 1M by the laser irradiation times t ₂ and t ₇ , and for the cyan image forming unit 1C by the laser irradiation times t ₃ and t ₇ . On the intermediate transfer belt 32, toner images of four colors are superposed so as to be aligned with each other, and a color image is formed.

After transferring the last cyan toner image, the second
By the action of the transfer roller 35, the toner images of four colors are collectively transferred onto the paper fed from the paper feed unit 36 at the same timing. The toner image transferred onto the paper is fixed by the fixing device 44.
Is fixed by After that, the paper is discharged to the outside of the apparatus via the discharge roller 45. The color image thus obtained has high gradation reproducibility, and in particular, the gradation reproducibility is greatly improved in the highlight part (light density part) and the shadow part. Further, although the gradation reproducibility has largely changed with the passage of time and environmental changes, according to the third embodiment of the color electrophotographic apparatus of the present invention, a stable color image can always be obtained.

Next, an algorithm for detecting points in the shadow portion of the black image forming unit 1B will be described. In the case of detecting points in the shadow portion, 1 is added to the number of points in the third embodiment. That is, P ₆
Was changed to P ₇ , and the point of the highlight part was imaged as P ₃ . As a result, the solid image of the black image was stabilized against changes over time and changes in the environment. In this way, by changing the gradation correction algorithm for black and the gradation correction algorithm for color toner, it is possible to set the optimum image forming condition for the print image pattern. For example, it is possible to reduce the gradation reproducibility of black for a document image by using the same black and color algorithms as for a photographic image and attach importance to stability as described above.

As described above, according to the third embodiment, the upper and lower limits of the laser irradiation pulse width time are determined by using the density difference of the patch image on the intermediate transfer belt 32. The gradation reproducibility of the shadow area has been dramatically improved, and the image stability in the halftone area has also been improved. Further, by using patches at three or more places (eight places in the third embodiment), the upper and lower limits of the laser irradiation time can be determined at once.

In the third embodiment, the irradiation time width of the laser light is determined by using the density difference, but the same effect can be obtained by using the differential value of the optical density with respect to the laser light irradiation time. Further, the number of divisions of the laser irradiation time is 64 and the number of patches is 8. However, if the number of divisions and the number of patches appropriate for the color electrophotographic apparatus are determined in consideration of the memory of the apparatus main body and the accuracy at the time of initialization. Good. Further, the detection error can be reduced by detecting the density variation of the specific patch image in advance and determining the specified difference.

(Fourth Embodiment) Next, a fourth embodiment of the color electrophotographic apparatus of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 6 is a sectional view showing a detailed configuration of an image forming unit in the fourth embodiment of the color electrophotographic apparatus of the present invention. The configuration of the fourth embodiment is different from that of the image forming unit as shown in FIG.
Since the configuration is substantially the same as that of the first embodiment shown in FIG. 1, its description is omitted.

As shown in FIG. 6, a developing bias power source 69 is connected to the developing roller 19. The output of the developing bias power source 69 has a DC component of -400V to -600V.
The voltage can be changed in steps of 10 V, and a constant AC component is superimposed on this DC component.

Next, the fourth color electrophotographic apparatus of the present invention will be described.
The color image forming operation of the embodiment will be described.
When the color electrophotographic device is turned on, the entire device
First, the initialization operation is performed, and after the initialization is completed, the color printing operation is started. First, the initialization operation will be described. As an example, the operation when the black image forming unit 1B is positioned at the image forming position 50 as shown in FIG. 1 will be described with reference to FIG.

The charging roller 10 moves the photosensitive member 9 to -70.
It is charged to a constant potential of 0V. Next, 2
The exposure signal 13 having a size of 0 × 10 mm is irradiated at five places at intervals of 0.2 seconds (at intervals of 20 mm on the electrostatic image carrier). The surface of the photoconductor 9 is opposed to the developing roller 19 which carries the black non-magnetic one-component toner 25B and rotates in the same direction as the photoconductor 9 at a constant speed. A developing bias power source 69 synchronizes with the latent image on the developing roller 19, and the DC component is -420V, -440V, -46 at intervals of 0.2 seconds.
Switching is performed in the order of 0 V, -480 V, and -500 V, and a voltage in which a rectangular wave AC voltage having a voltage of 750 V (0 to peak) and a frequency of 3 KHz is superimposed is applied to this DC component. As a result, five types of patch images having different image densities are observed on the photoconductor 9. Let the densities of the patch images be P _{1 to} P ₅ .

Next, this patch image is actually transferred onto the intermediate transfer belt 32 shown in FIG.
When the densities P ₁ to P ₅ are detected by ₁ , the respective image densities are 1.02, 1.15, 1.25,
It was 1.32 and 1.32. Next, the adjacent difference of image density, calculating the _{P m -P m-1, 0.13} ,
It becomes 0.10, 0.07, 0.00.

Here, the difference P _m − measured from the difference (for example, 0.05) specified on the apparatus body side in advance.
The point where P _m-1 becomes large is detected. In this case, it was P ₄ which is the point between the difference of 0.07 and 0.00. This P ₄ is set as the maximum image density portion, the developing bias at this time (for example, −480 V) is stored, and this developing bias value is set as the developing bias value of the black image forming unit 1B. This completes the initialization of the black image forming unit 1B. Similarly, when the developing bias values of the image forming units 1B, 1Y, 1M, and 1C are determined in this order, black is -480.
V and yellow were -440V, magenta was -440V, and cyan was -460V. In this way, the initialization operation of the entire color electrophotographic apparatus is completed.

Next, in the color printing operation, the black image forming unit 1B is used to form a black image by the developing bias -480V determined by the initialization, and the toner image is transferred to the intermediate transfer belt 32.
The image forming unit groups 1B, 1Y, 1M, and 1C are wholly driven by the moving motor 30 and integrally rotated in the direction of arrow D in FIG. The yellow image forming unit 1Y rotates exactly 90 degrees, stops at the position where the yellow image forming unit 1Y reaches the image forming position 50, and the yellow image forming unit 1Y is positioned.

As in the case of the black image forming unit 1B, the exposure signal light 13 is output to the yellow image forming unit 1Y by the developing bias -440V based on the signal corresponding to yellow, and the yellow toner image is formed. Formation and transfer. At this time, on the intermediate transfer belt 32,
The writing timing of the yellow exposure signal light 13 is controlled so that the next yellow toner image is positionally aligned with the previously transferred black toner image. The same operation as described above is performed for the magenta image forming unit 1M with the developing bias of -440V and for the cyan image forming unit 1C with the developing bias of -460V. On the intermediate transfer belt 32, toner images of four colors are superposed so as to be aligned with each other, and a color image is formed.

After the final cyan toner image is transferred, the second
By the action of the transfer roller 35, the toner images of four colors are collectively transferred onto the paper fed from the paper feed unit 36 at the same timing. The toner image transferred onto the paper is fixed by the fixing device 44.
Is fixed by After that, the paper is discharged to the outside of the apparatus via the discharge roller 45. The transfer residual toner remaining on the intermediate transfer belt is cleaned by the action of the cleaner unit 40 to prepare for the next image formation.

As described above, according to the fourth embodiment, since the DC value of the developing bias value is determined using the density difference of the patch image on the intermediate transfer belt 32, the gradation reproduction of the shadow portion in the color image is reproduced. Remarkably improves the image stability and also improves the image stability in the halftone region. In the fourth embodiment, the development bias value is determined by using the density difference, but the same effect can be obtained by using the differential value of the optical density with respect to the development bias. Also, although the number of patches is 5,
An appropriate number of patches for the color electrophotographic apparatus may be determined in consideration of the memory of the apparatus main body and the accuracy at the time of initialization.

(Fifth Embodiment) Next, a fifth embodiment of the color electrophotographic apparatus of the present invention will be described with reference to FIGS.
Description will be given with reference to 0. FIG. 9 is a sectional view showing the overall constitution of the fifth embodiment of the color electrophotographic apparatus of the present invention, and FIG. 10 is a sectional view showing the detailed constitution of the image forming unit in FIG. In each of the drawings, members given the same reference numerals as those in the first embodiment are substantially the same, and the description thereof will be omitted.

As shown in FIG. 9, the configuration of the fifth embodiment is similar to the configuration of the first embodiment shown in FIG.
A second transfer bias power supply 37 for applying a transfer bias to the transfer roller 35 and a surface potential sensor 64 for measuring the potential on the intermediate transfer belt 32 in a non-contact manner are provided. The bias voltage of the second transfer bias power supply 37 is +50.
It is switched between 0V and + 1000V. FIG.
As shown in 0, a developing bias power source 66 is connected to the developing roller 19. The DC component of the bias voltage of the developing bias power source 66 is fixed at -500V, and the amplitude value (0 to peak) of the AC component is variable from -300V to -800V in steps of 50V. The waveform is a sine wave, and the frequency is 2 KHz.

Next, the fifth color electrophotographic apparatus of the present invention will be described.
The color image forming operation in the embodiment will be described.
As in the case of the first embodiment, when the power of the color electrophotographic apparatus is turned on, the entire apparatus first performs the initialization operation, and after the initialization is completed, the color printing operation starts. First, the initialization operation will be described. As an example, the operation when the black image forming unit 1B is positioned at the image forming position 50 will be described.

The charging roller 10 moves the photosensitive member 9 to -70.
It is charged to a constant potential of 0V. Next, 2
The exposure signal 13 having a size of 0 × 10 mm is emitted. The surface of the photoconductor 9 is replaced with black non-magnetic one-component toner 25B.
Is opposed to a developing roller 19 that carries the toner and rotates at the same speed in the same direction as the photosensitive member 9. The developing bias power source 66 applied to the developing roller 19 an alternating current component of 500V. As a result, a patch image was observed on the photoconductor 9.

Next, this patch image was actually transferred onto the intermediate transfer belt 32, and its density was detected by the toner density sensor 61, and it was 1.25. here,
When the detected toner density is higher than a predetermined specified value (for example, 1.35 in the case of black),
The initializing operation of the black image forming unit 1B is completed, the yellow image forming unit 1Y is moved to the image forming position 50 by the moving motor 30, and the initializing operation is performed similarly to the black image forming unit 1B. On the other hand, when the detected toner density is lower than the specified value 1.35, a signal to that effect is transmitted to the developing bias power source 66 to increase the developing bias amplitude value by one step (for example, 550V).
Then, the steps of patch image creation, transfer, and toner density detection are repeated until the specified value is reached. If the toner concentration does not reach the specified value even when the amplitude value reaches the maximum value, the apparatus main body side outputs a black image forming unit 1B replacement instruction signal.

In this way, the image forming units 1B, 1
In the order of Y, 1M, and 1C, the specified values are yellow 1.30, magenta 1.30, and cyan 1.35, respectively.
Performs initialization operation. In the case of the above specific numerical example,
The determined amplitude values are black, yellow, magenta,
600V, 550V, 550V, 600 in the order of cyan
V. In this way, the initialization operation of the entire color electrophotographic apparatus is completed.

Next, in the color printing operation, the black image forming unit 1B is used to form a black image by the developing bias 600V determined by the initialization, and the toner image is transferred to the intermediate transfer belt 32. Next, the image forming unit groups 1B, 1Y, 1M, and 1C are wholly driven by the moving motor 30 and integrally rotated in the direction of arrow D in FIG. The image forming unit 1Y rotates exactly 90 degrees, stops at the position where the image forming unit 1Y reaches the image forming position 50, and the image forming unit 1Y is positioned.

As in the case of the black image forming unit 1B, the exposure signal light 13 is output to the yellow image forming unit 1Y in response to the yellow signal, and the developing bias 550 is output.
By V, a yellow toner image is formed and transferred. At this time, the writing timing of the yellow exposure signal light 13 is controlled so that the next yellow toner image positionally matches the previously transferred black toner image on the intermediate transfer belt 32.

The same operation as described above is performed with a developing bias of 550 V for the magenta image forming unit 1M and with a developing bias of 600 V for the cyan image forming unit 1C. On the intermediate transfer belt 32, toner images of four colors are superposed so as to be aligned with each other, and a color image is formed. At this time, when the surface potential sensor 64 detects the surface potential of the toner layer of a solid image formed by superimposing three colors of yellow, magenta, and cyan on the intermediate transfer belt 32, the toner excluding the potential of the intermediate transfer belt 32 itself is detected. The layer surface potential was -65 V on average. After the final transfer of the cyan toner image, the toner images of four colors are collectively transferred onto the paper fed from the paper feed section 36 at the same timing by the action of the second transfer roller 35. At this time, the second
The voltage applied to the transfer roller 35 is +500 V and +
It is switched to 1000V, and +10 when the toner layer surface potential is lower than the main body specified value (for example, -80V).
00V is applied, and + 500V is applied when the voltage is equal to or higher than the specified value. In the case of the above specific numerical value example, the toner layer surface potential was −65 V, so the voltage applied to the second transfer roller 35 was set to +500 V. Next, the toner image transferred onto the paper is fixed by the fixing device 44. The sheet is then discharged to the outside of the apparatus via the discharge roller 45. The transfer residual toner remaining on the intermediate transfer belt is cleaned by the cleaner unit 4.
It is cleaned by the action of 0 to prepare for the next image formation.

As described above, in the fifth embodiment, the toner density and the toner layer potential on the intermediate transfer belt 32 are detected and the amplitude value of the developing bias and the secondary transfer voltage are determined. Was stabilized, and it was possible to prevent the secondary transfer failure due to the change in the toner charge amount with the lapse of time. Further, this effect was also effective for secondary transfer failure that occurs immediately after the replacement of a specific image forming unit.

In the fifth embodiment, the toner density on the intermediate transfer belt 32 is detected and the developing bias amplitude value is determined. It is also possible to use it as a container condition. Further, the toner layer surface potential sensor 64 on the intermediate transfer belt 32 is preferably installed as close to the secondary transfer roller as possible in order to improve the measurement accuracy.

(Sixth Embodiment) Next, a sixth embodiment of the color electrophotographic apparatus of the present invention will be described with reference to FIGS.
1 will be described. FIG. 11 is a sectional view showing the configuration of the sixth embodiment of the color electrophotographic apparatus of the present invention. In each of the drawings, members given the same reference numerals as those in the first embodiment are substantially the same, and the description thereof will be omitted. Since the configuration is substantially the same as that of the first embodiment shown in FIG. 1, its description is omitted.

In the color electrophotographic apparatus according to the sixth embodiment shown in FIG. 11, the control device 51 controls the laser power of the laser exposure device 3 to 0.15 mw on the surface of the photoconductor (electrostatic image carrier) 9. From 0.01 to 0.30 mw
It is possible to control in mw steps. Further, instead of the toner density sensor 61 on the intermediate transfer belt 32 in the first embodiment shown in FIG. 1, the toner density on the image forming units 1B, 1Y, 1M, 1C rotated by the moving motor 30 is detected. A toner concentration sensor 67 is provided for this purpose. Here, if the toner density sensor 67 is set to the image forming position 5
If it is provided at a position where the image forming unit (for example, 1B) in 0 and the intermediate transfer belt 32 are in contact with each other, the toner image is disturbed as the image forming unit 1B rotates. Therefore, it is provided at a position different from the image forming position 50 (for example, near the bottom of the apparatus), and is attached at a position slightly deviated from the perpendicular of the photoconductor 9 of the image forming unit (for example, 1C). That is, in the sixth embodiment, the density of the patch image is detected by moving the image forming units 1B, 1Y, 1M, 1C without transferring the patch image to the intermediate transfer belt 32. .

Image forming unit 1 configured as described above
The operation of B, 1Y, 1M, and 1C will be described with reference to FIG. As in the case of the first embodiment, the charging roller 10 charges the photoconductor 9 to −700 V, and the photoconductor 9 is irradiated with the exposure signal light 13 from the laser to form an electrostatic latent image. At this time, the overall exposure potential of the photoconductor 9 was −100V. The surface of the photoconductor 9 is opposed to the developing roller 19 which carries the black non-magnetic one-component toner 25B and rotates in the same direction as the photoconductor 9 at a constant speed. The developing roller 19 is supplied with −500V by the developing bias power source 20.
DC voltage of 750V (0 to peak), frequency 2KHz
The sine wave AC voltage was superimposed and applied. As a result, a negative-positive inverted toner image is formed only on the image portion on the photoconductor 9.

The operation of the sixth embodiment of the color electrophotographic apparatus of the present invention constructed as above will be described. When the power of the color electrophotographic apparatus is turned on, the entire apparatus first performs an initialization operation, and after the initialization is completed, the color printing operation starts. First, the initialization operation will be described. As an example, the operation when the black image forming unit 1B is positioned at the image forming position 50 as shown in FIG. 11 will be described.

The laser exposure device 3 outputs a laser beam of 2.0 mw as the reference light of the black patch image to the image forming unit 1B, the operation of the image forming unit 1B is started, and the size of the black toner is 20. × 30
mm patch image formation is performed. After the formation of the patch image, the image forming unit 1B is moved from the image forming position 50 to the bottom of the apparatus, for example, and the patch image density is detected by the toner density sensor 67.

Here, the detected toner density is a predetermined value (for example, 1.3 for black).
If it is higher than 0), the initialization operation of the black image forming unit 1B is finished, the yellow image forming unit 1Y is moved to the image forming position 50 by the moving motor 30, and the initialization operation is performed similarly to the black image forming unit 1B. I do. On the other hand, when the detected toner concentration is lower than the specified value 1.30, a signal to that effect is transmitted to the control circuit 51 to increase the laser power by one step (for example,
2.1 mw). At the same time, the image forming unit 1B is moved to the image forming position 50 again, and patch image formation, transfer,
The toner concentration detection process is repeated until the specified value is reached. If the toner density does not reach the specified value even when the laser power reaches the maximum value, the apparatus main body side outputs a replacement instruction signal for the black image forming unit 1B.

In this way, the image forming units 1B, 1
In the order of Y, 1M, and 1C, the specified values are yellow 1.20, magenta 1.25, and cyan 1.25, respectively.
Performs the initialization operation of the image forming unit. In the case of the above specific numerical example, the determined laser power is 2.2 mw in the order of black, yellow, magenta, and cyan.
It was 2.0 mw, 2.0 mw, and 2.3 mw. In this way, the initialization operation of the entire color electrophotographic apparatus is completed.

Next, in the color printing operation, a black image is formed by using the black image forming unit 1B with a laser power of 2.2 mw determined by the initialization, and this toner image is transferred to the intermediate transfer belt 32. . Next, the image forming unit groups 1B, 1Y, 1M, and 1C are wholly driven by the moving motor 30 and integrally rotated in the direction of arrow D in FIG. The yellow image forming unit 1Y rotates exactly 90 degrees, stops at the position where the yellow image forming unit 1Y reaches the image forming position 50, and the yellow image forming unit 1Y is positioned. Since the portions of the image forming units 1B, 1Y, 1M, and 1C other than the photoconductor 9 are located inside the rotation arc of the tip of the photoconductor 9, the intermediate transfer belt 32 is disposed in the image forming units 1B, 1Y, 1M, and 1C. Never come into contact with.

As in the case of the black image forming unit 1B, the laser exposure device 3 uses the laser power of 2.0 mw to generate the yellow image forming unit 1 in response to the yellow signal.
The exposure signal light 13 is output to Y to form and transfer a yellow toner image. At this time, the writing timing of the yellow exposure signal light 13 is controlled so that the next yellow toner image positionally matches the previously transferred black toner image on the intermediate transfer belt 32. During this time, the second transfer roller 35 and the cleaner unit 40 are slightly apart from the intermediate transfer belt, and do not affect the toner on the intermediate transfer belt.

The same operation as above is performed with a laser power of 2.0 mw for the magenta image forming unit 1M and with a laser power of 2.3 m for the cyan image forming unit 1C.
Do with w. On the intermediate transfer belt 32, toner images of four colors are superposed so as to be aligned with each other, and a color image is formed. After the final transfer of the cyan toner image, the four transfer toner images are collectively transferred onto the paper fed from the paper feed section 36 at the same timing by the action of the second transfer roller 35. The toner image transferred to the paper is fixed by the fixing device 44. After that, the paper is discharged to the outside of the apparatus via the discharge roller 45. The transfer residual toner remaining on the intermediate transfer belt is cleaned by the action of the cleaner unit 40,
Prepare for the next image formation.

As described above, in the sixth embodiment, the image forming units 1B, 1Y, 1M, 1 are arranged at positions other than the image forming position 50.
Since the toner density on C is detected and the laser irradiation intensity is determined, it is possible to always obtain a stable color image having the maximum image density. Moreover, since it is not necessary to transfer the patch image to the transfer belt 32, the initial operation can be completed in a short time. Further, in the sixth embodiment, the toner density sensor 67 is provided in addition to the image forming position 50, but the surface potential sensor of the photoconductor 9 can be attached.
Further, by combining the photoconductor surface potential sensor and the toner density sensor 61 on the intermediate transfer belt 32 used in the first embodiment, the variation correction of the photoconductor 9 and the halftone reproduction control of the color image are performed. It is also possible to do simultaneously.

In the sixth embodiment, the image forming position 5
At the time of detection other than 0, the image forming units 1B, 1Y, 1
Although M and 1C are not driven, the drive mechanism for the image forming units 1B, 1Y, 1M, and 1C is provided at a position other than the image forming position 50, and the image forming power supply terminal is further installed to perform the initialization operation and the color operation. The image operation and the image operation can be performed in parallel. Such a configuration is effective for a copying machine that requires high-speed printing or a printer that prints a large number of sheets.

(Seventh Embodiment) Next, a seventh embodiment of the color electrophotographic apparatus of the present invention will be described with reference to FIGS. 12 is a sectional view showing the entire constitution of the seventh embodiment of the color electrophotographic apparatus of the present invention, and FIG. 13 is a sectional view showing the detailed constitution of the image forming unit in FIG. Since the seventh embodiment has almost the same configuration as the third embodiment, only the differences will be described and the description of the substantially same parts will be omitted.

As shown in FIGS. 12 and 13, in the color electrophotographic apparatus according to the seventh embodiment, the image forming unit 1 is added to the color electrophotographic apparatus according to the third embodiment.
B, 1Y, 1M, 1C image forming unit attachment / detachment sensor 6
8 is provided, and the presence or absence of the image forming unit of each color and the color thereof can be recognized.

Next, the seventh embodiment of the color electrophotographic apparatus of the present invention
The color image forming operation in the embodiment will be described.
In the color electrophotographic apparatus according to each of the above embodiments,
Usually four independent image forming units 1B, 1Y, 1M,
1C is operated to perform color printing. However, four image forming units 1B, 1Y, 1M, 1C
When a phenomenon such as running out of toner or insufficient image density occurs in any one of them, the apparatus body side outputs a replacement instruction signal for the image forming unit and replaces the corresponding image forming unit. As an example, the operation when the black image forming unit 1B is replaced will be described.

The image forming unit 1B immediately after the replacement is an annular upper portion (for example, the yellow image forming unit 1 in FIG. 12).
Y position). The image forming unit 1B is moved to the image forming position 50,
Initialize only. By the charging roller 10,
The photoconductor 9 is charged to a constant potential of -700 V, and the photoconductor 9 is irradiated with eight types of exposure signal light 13 controlled by the pulse width modulation circuit 52 to form eight types of patch image latent images. The surface of the photoconductor 9 is opposed to the developing roller 19 which carries the black non-magnetic one-component toner 25B and rotates in the same direction as the photoconductor 9 at a constant speed. The developing bias power source 20 applies to the developing roller 19 a DC voltage of -500 V superposed with a rectangular wave AC voltage of 750 V (0 to peak) and a frequency of 3 KHz. As a result, eight types of patch images having different image densities are observed on the photoconductor 9. Hereinafter, as in the case of the third embodiment, the densities of the patch images are set to P _{1 to} P ₈ .

Next, when this patch image is transferred onto the intermediate transfer belt 32 and the densities P ₁ to P ₈ are detected by the toner density sensor 61, the respective image densities are
0.07, 0.10, 0.33, 0.67, 1.02,
They are 1.32, 1.33, and 1.32. Next, the adjacent difference of image density, calculating the P _m -P _m-1,
0.03, 0.23, 0.34, 0.35, 0.30,
It becomes 0.01 and -0.01.

Here, the difference P _m − measured from the difference (for example, 0.10) specified in advance on the apparatus main body side.
The point where P _m-1 becomes large is detected. In this case, the points of difference 0.03 and 0.23 and 0.30 and 0.
01 to have been P ₂ and P ₆ is a point. This P ₂
And P ₆ are defined as the minimum and maximum image density portions, the laser irradiation times t ₂ and t ₆ at this time are stored, and the irradiation time width of this laser light is set as the dynamic range at the time of gradation reproduction. , The initialization of the black image forming unit 1B is completed.

Next, in the color printing operation, a black image is formed using the black image forming unit 1B using the laser irradiation times t ₂ and t ₆ determined by the initialization, and the toner image is transferred to the intermediate transfer belt 32. Transfer to. The image forming unit groups 1B, 1Y, 1M, and 1C are wholly driven by the moving motor 30 and integrally rotated in the direction of arrow D in FIG. The yellow image forming unit 1Y rotates exactly 90 degrees, stops at the position where the yellow image forming unit 1Y reaches the image forming position 50, and the yellow image forming unit 1Y is positioned.

The irradiation pulse width control circuit 52 controls the image forming unit 1Y at the laser irradiation times t ₂ and t ₃ based on the signal corresponding to yellow which is set before the black image forming unit 1B is replaced. Exposure signal light 13
Is output to form and transfer a yellow toner image. At this time, the writing timing of the yellow signal light is controlled so that the next yellow toner image positionally matches the previously transferred black toner image on the intermediate transfer belt 32. The same operation as above is performed for the magenta image forming unit 1M by the laser irradiation times t2 and t7.
Further, the laser irradiation time t3 and t7 is applied to the cyan image forming unit 1C. On the intermediate transfer belt 32, the toner images of four colors are superposed so as to be in good positional alignment to form a color image.

After the final transfer of the cyan toner image, the toner images of four colors are collectively transferred onto the paper fed from the paper feed section 36 at the same timing by the action of the second transfer roller 35. The toner image transferred to the paper is fixed by the fixing device 44. After that, the paper is discharged to the outside of the apparatus via the discharge roller 45. The transfer residual toner remaining on the intermediate transfer belt is cleaned by the action of the cleaner unit 40,
Prepare for the next image formation.

As described above, according to the seventh embodiment, attachment / detachment of the image forming units 1B, 1Y, 1M, 1C is detected,
By initializing only the detached image forming unit, it is possible to replace the image forming unit during the continuous printing operation in a short time, and restart it in a short time without unnecessary initialization.

[0110]

As described above, the color electrophotographic apparatus of the present invention has the charging means, the electrostatic image carrier, the developing means having the toners of different colors, and the cleaning means, respectively. Four image forming units, which form toner images of different colors on the electrophotographic image carrier, are transferred by a predetermined transfer position for transferring the toner image on the electrostatic image carrier to a transfer material by a moving unit and a laser exposure unit. The patch image is formed by using the image forming unit located at the image forming position, which is sequentially positioned at the image forming position corresponding to the predetermined exposure position for image exposure, and the patch image is transferred to the transfer material. The latent image forming condition is determined by detecting the density by means of the density detecting means, toner images of different colors are formed using the decided latent image forming condition, and the formed toner image is formed on the transfer material. Align and stack Transferred, and is configured to perform color image formation. Therefore, even if the electrostatic image carrier (photoreceptor) of each image forming unit has variations in electrostatic characteristics, one latent image forming condition suitable for each electrostatic image carrier is obtained by one density detection unit. It is possible to obtain a stable color image with a maximum image density.

Further, as a latent image forming condition, the irradiation intensity of laser exposure to the electrostatic image carrier or the grid voltage of the charging means of the electrostatic image carrier is adjusted to control the control circuit of the conventional color electrophotographic apparatus. The color electrophotographic apparatus of the present invention can be obtained relatively easily by simply changing

Further, another color electrophotographic apparatus of the present invention has a charging means, an electrostatic image carrier, a developing means having toners of different colors, and a cleaning means, respectively. Four image forming units that form toner images of different colors on the body are subjected to image exposure by a predetermined transfer position where the toner image on the electrostatic image carrier is transferred to the transfer material by the moving means and the laser exposure means. The image is positioned at the image forming position by sequentially arranging it at the image forming position corresponding to the predetermined exposure position to be formed, forming a patch image using the image forming unit located at the image forming position, transferring the patch image to the transfer material. By using the image forming unit, the optical density is changed by changing the image forming condition of the image forming unit N (N> 2)
After forming the individual patch images P _{1 to} P _N , the patch images are transferred onto a transfer material, the transferred patch image densities are detected by the density detecting means, and the difference between the adjacent optical densities of the patch images is detected. The image forming conditions are determined by detecting (P _m −P _m−1 ), toner images of different colors are formed using the determined image forming conditions, and the formed toner images are transferred onto the transfer material. It is configured so that the color images are formed by aligning the positions with and transferring the images. Therefore, the gradation reproducibility of the highlight portion and the shadow portion in the color image is improved step by step, and the image stability in the halftone area is improved. Further, since the gradation reproducibility is excellent over time and environmental changes, it is possible to always obtain a stable color image.

Further, by adjusting the irradiation pulse width time of the laser beam or the developing bias of the developing means as the image forming condition, the present invention can be relatively easily performed only by changing the control circuit of the conventional color electrophotographic apparatus. It is possible to obtain a color electrophotographic device. Further, by changing the algorithm of the image forming condition depending on the image quality switching mode, it is possible to use the optimum image forming condition according to the print image pattern.

Further, still another color electrophotographic apparatus of the present invention has a charging means, an electrostatic image carrier, a developing means having toners of different colors, and a cleaning means. Four image forming units, which form toner images of different colors on the carrier, are exposed at a predetermined transfer position where the toner image on the electrostatic image carrier is transferred to the transfer material by the moving means and by the laser exposing means. The image forming unit located at the image forming position forms a toner image, then the toner image is transferred to the transfer material, and the toner image density on the transfer material is increased. And the toner layer surface potential are respectively detected by the density detecting means and the surface potential detecting means to determine the image forming condition, and the toner images of different colors formed by using the determined image forming condition are transferred. Transferred superimposed in alignment on wood, it is configured to perform color image formation. Therefore, the image density in the color image is stable, and it is possible to prevent the secondary transfer failure due to the change in the toner charge amount with the lapse of time. In particular, it is effective for preventing the secondary transfer failure that occurs immediately after the image forming unit is replaced.

Further, by detecting the surface potential of the toner layer on the transfer material and determining the transfer condition from the transfer material to the final print target, the optimum image forming conditions are used according to the print image pattern. You can

Further, still another color electrophotographic apparatus of the present invention has a charging means, an electrostatic image carrier, a developing means having toners of different colors, and a cleaning means. Four image forming units, which form toner images of different colors on the carrier, are exposed at a predetermined transfer position where the toner image on the electrostatic image carrier is transferred to the transfer material by the moving means and by the laser exposing means. The image forming unit is sequentially positioned at a position other than the image forming position corresponding to the predetermined exposure position for performing image formation, an image forming pattern is formed using the image forming unit located at the image forming position, and the image forming unit is formed by the image forming pattern detecting means. The image forming conditions are determined by detecting the image pattern, toner images of different colors are formed using the determined image forming conditions, and the formed toner images are aligned and superposed on the transfer material. Turning And it is configured to perform color image formation. Therefore, since it is not necessary to transfer the image forming pattern to the transfer body, the initialization operation of each image forming unit can be completed in a short time.

Further, by using a toner concentration sensor for detecting the toner concentration on the electrostatic image bearing member or a surface potential sensor for detecting the surface potential of the electrostatic image bearing member as the detecting means, the conventional color electrophotographic apparatus can be used. The color electrophotographic apparatus of the present invention can be relatively easily obtained only by providing these detecting means and changing the control circuit.

Further, still another color electrophotographic apparatus of the present invention has a charging means, an electrostatic image carrier, a developing means having toners of different colors, and a cleaning means. Four image forming units, which form toner images of different colors on the carrier, are exposed at a predetermined transfer position where the toner image on the electrostatic image carrier is transferred to the transfer material by the moving means and by the laser exposing means. The image forming unit is determined to have been attached / detached by the image forming unit attachment / detachment detecting means when any of the image forming units is attached / detached, and the image forming unit is attached / detached at a position other than the image forming position corresponding to the predetermined exposure position. To the image forming position, a toner image is formed using the image forming unit, and the image forming unit image forming condition is determined by detecting the toner image density by the density detecting means. Toner images of different colors are formed using the determined image forming conditions, and the formed toner images are superimposed and transferred on a transfer material at positions to form a color image. . Therefore, since only the detached image forming unit is initialized, it is possible to replace the image forming unit during the continuous printing operation in a short time and restart it in a short time without performing unnecessary initialization.

Further, by providing at least a part of the optical element for scanning the laser beam of the exposure means in the vicinity of the center of rotation of the rotational movement of the image forming unit group, it is simple and has high positional accuracy. An optical system can be obtained, and positional deviation at the image forming position of the laser beam and collapse of the beam shape can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the overall configuration of a first embodiment of a color electrophotographic apparatus of the present invention.

FIG. 2 is a sectional view showing a detailed configuration of an image forming unit according to the first embodiment.

FIG. 3 is a sectional view showing an overall configuration of a second embodiment of a color electrophotographic apparatus of the present invention.

FIG. 4 is a sectional view showing a detailed configuration of an image forming unit according to a second embodiment.

FIG. 5 is a sectional view showing the overall configuration of a third embodiment of the color electrophotographic apparatus of the present invention.

FIG. 6 is a sectional view showing a detailed configuration of an image forming unit according to a third embodiment.

FIG. 7 is a perspective view showing a method for forming a patch image on a photoconductor according to each embodiment of the present invention.

FIG. 8A is a graph showing a relationship between a laser irradiation time and a gradation reproduction curve in the third embodiment, and FIG. 8B is a graph showing a correction method thereof.

FIG. 9 is a sectional view showing the overall configuration of a fifth embodiment of the color electrophotographic apparatus of the present invention.

FIG. 10 is a sectional view showing a detailed configuration of an image forming unit according to a fifth embodiment.

FIG. 11 is a sectional view showing the overall configuration of a sixth embodiment of the color electrophotographic apparatus of the present invention.

FIG. 12 is a sectional view showing the overall configuration of a seventh embodiment of the color electrophotographic apparatus of the present invention.

FIG. 13 is a sectional view showing a detailed configuration of an image forming unit in a seventh embodiment.

FIG. 14 is a sectional view showing the overall structure of a conventional color electrophotographic apparatus.

FIG. 15 is a sectional view showing a detailed configuration of a conventional image forming unit.

[Explanation of symbols]

 1Y: Yellow image forming unit 1M: Magenta image forming unit 1C: Cyan image forming unit 1B: Black image forming unit 3: Laser exposure device 5: Mirror 9: Organic photoconductor 13: Signal light 19: Developing roller 20: Development bias power supply 25: Non-magnetic one-component toner 32: Intermediate transfer belt 35: Second transfer roller 51: Irradiation intensity control circuit 52: Irradiation pulse width control circuit 61: Toner concentration sensor 64: Surface potential sensor 65: Optical Correction member 66: Development bias power supply 67: Toner density sensor 68: Image forming unit attachment / detachment sensor 69: Development bias power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akinori Toyota, 1006, Kadoma, Kadoma, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Hiroshi Komagine, 1006, Kadoma, Kadoma, Osaka

Claims (14)

[Claims] (1) A charging unit, an electrostatic image carrier, a developing unit having toners of different colors, and a cleaning unit, each of which has a different color on the electrostatic image carrier. Four movable image forming units for forming the toner image, (2) transfer means for transferring the toner image on the electrostatic image carrier to a transfer material at a predetermined transfer position, and (3) the transfer Density detection means for detecting the density of the toner image on the material, (4)
Laser exposure means for performing image exposure at a predetermined exposure position corresponding to the transfer position, and (5) each of the four image forming units is provided at an image forming position corresponding to the exposure position and corresponding to the transfer position. A moving unit that rotates and moves the entire image forming unit group so that the patch images are formed by using the image forming units located at the image forming position, and the patch images are formed on the transfer material. The latent image forming condition is determined by detecting the density of the transferred patch image by the density detecting means, and toner images of different colors are formed using the determined latent image forming condition. A color electrophotographic apparatus that forms a color image by transferring the formed toner image on the transfer material while aligning the positions thereof. 2. The color electrophotographic apparatus according to claim 1, wherein the latent image forming condition to be determined is an irradiation intensity of laser exposure on the electrostatic image bearing member. 3. The color electrophotographic apparatus according to claim 1, wherein the latent image forming condition to be determined is the grid voltage of the charging means of the electrostatic image carrier. 4. A charging means, an electrostatic image carrier, a developing means having toners of different colors, and a cleaning means, each of which has a different color on the electrostatic image carrier. Four movable image forming units for forming the toner image, (2) transfer means for transferring the toner image on the electrostatic image carrier to a transfer material at a predetermined transfer position, and (3) the transfer Density detection means for detecting the density of the toner image on the material, (4)
Laser exposure means for performing image exposure at a predetermined exposure position corresponding to the transfer position, and (5) each of the four image forming units is provided at an image forming position corresponding to the exposure position and corresponding to the transfer position. Moving means for rotating and moving the entire group of image forming units so as to sequentially position the image forming unit, and changing the image forming condition of the image forming unit by using the image forming unit located at the image forming position. After forming N (N> 2) patch images P _{1 to} P _N having different optical densities, the patch images are transferred onto the transfer material, and the transferred patch image densities are detected by the density detecting means. The difference between the adjacent optical densities of the detected patch images (P _m −
P _m-1 ) to detect the image forming condition, and form toner images of different colors using the determined image forming condition,
A color electrophotographic apparatus for forming a color image by transferring the formed toner image on the transfer material while aligning the positions thereof. 5. The color electrophotographic apparatus according to claim 4, wherein the image forming condition to be determined is an irradiation pulse width time of laser light. 6. The color electrophotographic apparatus according to claim 4, wherein the image forming condition to be determined is a developing bias of the developing means. 7. The color electrophotographic apparatus according to claim 5, wherein the algorithm of the image forming condition to be determined differs depending on the image quality switching mode. 8. (1) Each has a charging unit, an electrostatic image carrier, a developing unit having a toner of a different color, and a cleaning unit, and different colors are provided on the electrostatic image carrier. Four movable image forming units for forming the toner image, (2) transfer means for transferring the toner image on the electrostatic image carrier to a transfer material at a predetermined transfer position, and (3) the transfer Density detection means for detecting the density of the toner image on the material, (4)
Surface potential detection means for detecting the surface potential of the toner layer on the transfer material, (5) laser exposure means for performing image exposure at a predetermined exposure position corresponding to the transfer position, and (6) the four image forming units. And a moving means for rotating the entire image forming unit group so as to sequentially position the image forming units corresponding to the exposure position and the image forming position corresponding to the transfer position, respectively. After the toner image is formed by the image forming unit, the toner image is transferred to the transfer material, and the image forming condition is determined by detecting the toner image density and the toner layer surface potential on the transfer material. A color electrophotographic apparatus for forming a color image by transferring toner images of different colors formed by using image forming conditions, onto the transfer material in a positionally aligned manner. 9. The color electrophotographic apparatus according to claim 8, wherein the transfer condition from the transfer material to the final print target is determined by detecting the surface potential of the toner layer on the transfer material. 10. (1) Each has a charging unit, an electrostatic image carrier, a developing unit having a toner of a different color, and a cleaning unit, each having a different color on the electrostatic image carrier. Four movable image forming units for forming the toner image, (2) transfer means for transferring the toner image on the electrostatic image carrier to a transfer material at a predetermined transfer position, and (3) the transfer Density detection means for detecting the density of the toner image on the material,
(4) laser exposure means for performing image exposure at a predetermined exposure position corresponding to the transfer position, and (5) an image corresponding to the exposure position and corresponding to the transfer position of the four image forming units, respectively. Moving means for rotationally moving the entire image forming unit group so as to be sequentially positioned at the forming position,
(6) a detection means for detecting an image forming pattern of the image forming unit at a position other than the image forming position, wherein the image forming pattern is formed by the image forming unit located at the image forming position, and then, After the image forming unit is rotationally moved by the moving unit, the image forming condition is determined by detecting the image forming pattern by the detecting unit, and toner images of different colors are formed by using the determined image forming condition. A color electrophotographic apparatus that forms a color image by transferring the formed toner image on the transfer material while aligning the positions thereof. 11. The color electrophotographic apparatus according to claim 10, wherein the detection unit is a toner density sensor that detects a toner density on the electrostatic image bearing member. 12. The color electrophotographic apparatus according to claim 10, wherein the detection unit is a surface potential sensor that detects a surface potential of the electrostatic image carrier. 13. (1) Each has a charging unit, an electrostatic image carrier, a developing unit having toner of a different color, and a cleaning unit, and different colors are provided on the electrostatic image carrier. Four movable image forming units for forming the toner image, (2) image forming unit attachment / detachment detecting means for detecting attachment / detachment of the image forming unit, and (3) electrostatic image carrying at a predetermined transfer position. Transfer means for transferring the toner image on the body to the transfer material, (4) density detecting means for detecting the toner image density on the transfer material, and (5) image exposure at a predetermined exposure position corresponding to the transfer position. And (6) the four image forming units are arranged so as to sequentially position the four image forming units respectively at the image forming positions corresponding to the exposure position and the transfer position. Moving means for rotating and moving the image, Only the image forming unit determined to be attached / detached by the image forming unit attachment / detachment detecting unit is moved to the image forming position, a toner image is formed using the image forming unit, and then the toner image density is detected by the density detecting unit. The image forming unit image forming conditions are determined by the above, toner images of different colors are formed by using the determined image forming conditions, and the formed toner images are superposed by aligning the positions on the transfer material. A color electrophotographic device that transfers and transfers color images. 14. An optical element for scanning a laser beam of said exposure means is provided at least partly in the vicinity of the center of rotation of the rotational movement of said image forming unit group.
14. The color electrophotographic apparatus according to any one of 1 to 13.