JP2005017498A - Image forming apparatus and method for controlling toner concentration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus by which a stable output image is obtained by properly controlling toner concentration by accurately detecting the toner concentration of color developer. <P>SOLUTION: The image forming apparatus possesses a developing device 4 storing toner where a chromatic color is given and a toner concentration detector 44 to detect the toner concentration after developing an electrostatic image by supplying the electrostatic image formed at a photoreceptor 1 with the toner, and when the toner concentration is detected by the toner concentration detector, developing bias voltage having a polarity reverse to that at a developing time is supplied to the developing device is for specified time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an arrangement of a toner density sensor for detecting toner density and a method for detecting toner density, for example, in an electrophotographic color image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art Two-component development systems and apparatuses that use a two-component developer in which toner and a carrier are mixed are widely known in electrophotographic image forming apparatuses.
[0003]
In the two-component development system, the toner density, which is the ratio of the developer toner to the carrier in the developing device, must be kept constant. For this reason, the toner density of the developer in the developing device is constantly measured by the toner density sensor, and the measurement result is compared with a predetermined reference value to replenish the toner.
[0004]
As the toner concentration sensor, a magnetic sensor that captures, as the toner concentration, the magnetic permeability that changes depending on the ratio between the carrier and the toner is widely used. Further, the toner density sensor is generally located at or near the agitating unit in the developing device.
[0005]
Further, in order to stably detect the toner concentration in the developing device, an optical sensor different from the magnetic sensor is opposed to a predetermined position on the outer periphery of the developing roller (developer carrier) to optically obtain the toner concentration. There is an example (for example, patent document 1).
[0006]
[Patent Document 1]
JP-A-3-13978 (FIG. 1, claim (1), page 3, upper left column, line 2 to column 6), page lower left column, line 6 to column 14)
[0007]
[Problems to be solved by the invention]
By the way, a plurality of developing devices are provided in a color copying apparatus and a color printer that form a color image using three color developers corresponding to the three subtractive primary colors and a black developer dedicated to a black image. In general, a plurality of toner density sensors must be provided in accordance with the number of developing devices.
[0008]
Further, in order to reduce the size of the image forming apparatus, when a developing apparatus containing a color developer is a rotary system (hereinafter abbreviated as a revolver system), the position of the developing apparatus corresponding to each color and each color The relative position between the toner concentration sensor and the developer in the developing device changes. For this reason, even if a toner density sensor is provided in each developing device, there is a problem that the output from the toner density sensor does not match the actual toner density.
[0009]
Furthermore, since the developing device is also downsized in accordance with the demand for downsizing of today's image forming apparatuses, there is a problem that the optical density sensor cannot be disposed at a position where the toner density can be detected stably.
[0010]
An object of the present invention is to provide an image forming apparatus capable of obtaining a stable output image by accurately detecting the toner concentration of a color developer and controlling the toner concentration within an appropriate range.
[0011]
[Means for Solving the Problems]
According to the present invention, the electrostatic image is developed by supplying the developer to the electrostatic image formed on the photosensitive member by at least the developing device and containing the developer having a chromatic color. In the image forming apparatus having a developer concentration detecting device for detecting the developer concentration of the developing device later, when the developer concentration detecting device detects the concentration of the developer, An image forming apparatus is characterized in that a developing bias voltage having a polarity opposite to that during development is supplied for a predetermined time.
[0012]
According to the present invention, a predetermined color toner is applied to an electrostatic image corresponding to a chromatic image formed on the photosensitive member, which is opposed to a predetermined position on the outer periphery of the photosensitive member, which holds the latent image. A developing device that supplies and visualizes, and a density of toner that is provided at a predetermined position apart from a developing position where the developing device and the photoconductor face each other, and the concentration of toner contained in the developing device is determined by the reflectance of light. A toner density detecting device that detects the toner density, a charging device that applies a predetermined potential to the photoconductor, a developing bias power supply device that applies a predetermined developing bias voltage to the developing device, and The developing device rotating mechanism for moving the developing device to a predetermined position facing the toner density detecting device, and when the developing device is rotated by the developing device rotating mechanism, to the charging device at a predetermined timing. The supply of the charging output is stopped, there is provided an image forming apparatus characterized by and a control device for reversing the polarity of the developing bias voltage output from the developing bias power supply.
[0013]
Furthermore, the present invention selectively supplies toners of colors corresponding to two or more electrostatic images corresponding to chromatic images to form toner images of two or more colors, and superimposes the toner images. In a toner density control method of an image forming apparatus that outputs an image, an electrostatic image corresponding to an image of a first color is developed by a first developing device that contains toner of a first color, and the first color and The second developing device containing the second color toner is developed so that the electrostatic image corresponding to the second color image can be developed by the second developing device containing the different second color toner. When the electrostatic image is moved to a developable development position, the first developing device is moved to the density detection position opposite to the toner density detection device by the same operation. The charging output is stopped and the polarity of the developing bias voltage is set to the first. The opposite polarity to the time for developing an electrostatic image corresponding to the color of the image, it is intended to provide a toner density control method for an image forming apparatus according to claim.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
FIG. 1 is a schematic diagram for explaining a printer apparatus as an example of an image forming apparatus to which an embodiment of the present invention is applied.
[0016]
A color printer (image forming apparatus) 101 includes a photosensitive member 1 (hereinafter referred to as a photosensitive drum because it is in the form of a drum) that holds an image or character information to be printed.
[0017]
Around the photosensitive drum 1, there are a charging device 2 that applies a predetermined potential to the photosensitive drum 1, a first developing device (for black) 3 that develops an electrostatic image formed on the photosensitive drum 1, A second developing device (for color) 4 that develops an electric image, and a developer image (an image in which an electrostatic image is visualized by the first or second developing device) formed on the photosensitive drum 1 are transferred. An intermediate transfer member (hereinafter referred to as an intermediate transfer belt because it is in the form of a belt) 5 and a photosensitive drum 1 that are temporarily held for transfer to a sheet or the like and that convey the transferred developer image. A cleaning / static discharge device 6 is disposed for removing the developer remaining on the surface of the drum 1 and erasing the potential distribution on the drum 1. The second developing device (hereinafter referred to as a color developing device) 4, which will be described below with reference to FIG. 2, includes three developing units containing three color developers corresponding to the three subtractive primary colors known in the art. Is a revolver system formed integrally.
[0018]
The second developing device includes, for example, a Y developing unit 41 holding a developer in which Y (Yellow, ie, yellow) toner and a carrier are mixed at a predetermined ratio (toner concentration), and C (Cyan, ie, cyan) toner. And a C developing unit 42 holding a developer in which a carrier is mixed at a predetermined ratio (toner concentration), and development in which M (Magenta) toner and carrier are mixed at a predetermined ratio (toner concentration) And an M developing unit 43 holding the agent. Each of the developing units 41 to 43 is formed so as to be rotatable around the central axis of the developing device 4 and is sequentially positioned at a developing position facing the photosensitive drum 1 in response to a request for image output. Further, an optical system that detects the toner density on the surface of the developing roller (developing sleeve surface) of the developing unit containing toner of any color at a predetermined position along the outer periphery of the region where the second developing device 4 is rotated. A toner density sensor (common to each developing unit) 44 is provided.
[0019]
From the space around the photosensitive drum 1 and between the charging device 2 and the black developing device 3, image light (laser beam) L whose light intensity is changed corresponding to an image to be printed or character information. Is irradiated by the exposure device 7.
[0020]
A toner image, which is an electrostatic image developed on the photosensitive drum 1, is transferred to the transfer belt 5 at a position inside the intermediate transfer belt 5 where a developer image on the photosensitive drum 1, that is, a toner image can be transferred. There is provided an intermediate transfer device 8 for providing an electric field for transferring the toner image. Note that the transfer belt 5 is in contact with the photosensitive drum 1 at a predetermined position on the outer periphery of the photosensitive drum 1 by the pressure applied by the intermediate transfer device 8.
[0021]
The toner image transferred on the transfer belt 5 is transferred to a sheet at a predetermined position on the outer periphery of the intermediate transfer belt 5 on the side where the sheet is conveyed via a sheet conveyance system described below. A transfer device 9 is provided that provides an electric field for output.
[0022]
In the above-described image forming apparatus (color printer apparatus) 101, image data is supplied from an external apparatus (not shown) such as a personal computer or an image scanner (image input apparatus), whereby the intensity is modulated based on the image data. The exposure light is irradiated from the exposure device 7 to a predetermined position on the photosensitive drum 1. Thereby, a latent image corresponding to the intensity of the exposure light is formed on the photosensitive drum 1.
[0023]
The latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image by selectively supplying a corresponding color toner from either the black developing device 3 or the color developing device 4 or each. Is done.
[0024]
The toner image developed and attached to the photosensitive drum 1 is conveyed to an intermediate transfer position by rotating the photosensitive drum 1, and is transferred by an intermediate transfer voltage provided from the intermediate transfer device 8. Transferred to the transfer belt 5.
[0025]
The toner image transferred to the transfer belt 5 is transported to a transfer region facing the transfer device 9 by the movement of the belt surface of the transfer belt 5, and is transferred to a sheet supplied to the transfer region at a predetermined timing. Is transferred by a transfer electric field (transfer bias voltage).
[0026]
Sheets (materials to be transferred) are taken out one by one from the first and second sheet cassettes 10a or 10b by the pickup rollers 11a or 11b, and are conveyed in advance through the conveyance path 11 to the aligning roller 12. The paper conveyed to the aligning roller 12 collides with the aligning roller 12 whose rotation has been stopped, so that a non-parallel component, that is, an inclination with respect to the transport direction that may occur when the paper is transported on the transport path 11. It is removed and temporarily stopped. The sheet stopped by the aligning roller 12 is conveyed again toward the transfer position at a predetermined timing with respect to the position of the toner image conveyed by the transfer belt 5. Accordingly, a transfer electric field is provided from the transfer device 9 to the sheet conveyed to the transfer position at a predetermined timing, whereby the toner image conveyed by the transfer belt 5 is transferred. The paper P may be replaced with, for example, a colored paper or a transparent resin sheet according to the user's request.
[0027]
The sheet on which the toner image has been transferred is further conveyed along the conveyance path 11 and guided to the fixing device 13. Predetermined heat is supplied from the fixing device 13 to the paper guided to the fixing device 13, and the toner constituting the toner image is melted and fixed on the paper.
[0028]
The toner (not shown) by the fixing device 1, that is, the paper on which the image output corresponding to the image information is fixed, is sequentially conveyed by the roller 14 to a paper holding portion (tray) 15 that is a part of the exterior cover of the printer device 101. The
[0029]
In this way, a printout (image output) is obtained in which the toner image corresponding to the electrostatic image formed on the photosensitive drum 1 is fixed on the paper.
[0030]
If the supplied image data is color image data, a total of three times until each subtractive color primary toner image is formed for each color component formed on the photosensitive drum 1 by the toner of each color. The image data is developed by the developing units 41 to 43 of each color of the color developing device 4 and sequentially transferred onto the transfer belt 5 so that they are superimposed. Further, when black image formation by the black developing device 3 is also instructed for black enhancement, an image is further formed with black toner based on the black image data, developed, and a color image is formed on the transfer belt 5. Superimposed.
[0031]
When the black developing device 3 is instructed to output only a black image, the exposure device 7 applies light corresponding to the black image data to the photosensitive drum 1 to which a predetermined potential is applied in advance. Exposure light (laser beam) whose intensity is continuously changed is irradiated. As a result, an electrostatic latent image corresponding to the black image data is formed on the photosensitive drum 1.
[0032]
The latent image formed on the photosensitive drum 1 is developed by selectively supplying toner from the black developing device 3.
[0033]
The black toner image formed on the photosensitive drum 1 is transferred to the transfer belt 5 when the photosensitive drum 1 is rotated, and is conveyed to the transfer position by moving the belt surface of the transfer belt 5, and is transferred to a predetermined position. Is transferred to the paper being fed at the timing of the transfer voltage by the transfer voltage provided from the transfer device 9.
[0034]
FIG. 2 is a schematic diagram illustrating an example of a second developing device incorporated in the printer apparatus illustrated in FIG.
[0035]
As shown in FIG. 2, the color developing device (second developing device) 4 holds a developer in which, for example, Y (Yellow, ie, yellow) toner and a carrier are mixed at a predetermined ratio (toner concentration). A Y developing unit 41, a C developing unit 42 holding a developer in which C (Cyan) toner and carrier are mixed at a predetermined ratio (toner density), and M (Magenta) toner and An M developing unit 43 holding a developer mixed with a carrier at a predetermined ratio (toner concentration) is provided. Each of the developing units 41 to 43 is formed so as to be rotatable around the central axis of the developing device 4 and is sequentially positioned at a developing position facing the photosensitive drum 1 in response to a request for image output. Further, an optical system that detects the toner density on the surface of the developing roller (developing sleeve surface) of the developing unit containing toner of any color at a predetermined position along the outer periphery of the region where the second developing device 4 is rotated. A toner density sensor (common to each developing unit) 44 is provided.
[0036]
By the way, in the image forming apparatus 101 in this embodiment, the black developing device 3 is at a fixed position, and can control the toner density and supply the toner by the magnetic sensor type toner supply control method that is the already-invented technology.
[0037]
On the other hand, in the color developing device 4, each of the Y developing unit 41, the M developing unit 42, and the C developing unit 43 is rotated around the central axis and is positioned at a developing position facing the photosensitive drum 1. Therefore, sufficient accuracy is not obtained in the toner replenishment control and toner density control by the magnetic sensor method. For this reason, in the color developing device 4, a method for managing the toner density of each color toner by providing an optical density sensor for detecting the toner density from the reflectance of the toner and the carrier in each color developing unit is proposed. .
[0038]
However, even if an optical density sensor is used, for example, as shown in FIG. 3, the change in toner density of the toner in each color component unit of the color developing device 4 is Y (curve y), M (curve m). In any of the color components of C and C (curve c), it was possible to manage up to a certain number of sheets within the range of the reference value ± 1.0%, but it was recognized that the color components gradually deviated from the management range (within ± 1.0%). .
[0039]
The deviation of the toner density from the management range shown in FIG.
a) Detection error due to contamination of the toner sensor surface,
b) When developing, other color toners are mixed (mixed color),
c) Increased background fog that occurs when the output image is transferred to paper.
d) Internal contamination due to toner flying inside the image forming apparatus (increase in toner scattering depending on the toner density deviating from the reference value),
Cause problems.
[0040]
It is reasonable to consider that the above problems a) to d) are due to the fact that the toner density sensor 44 cannot accurately detect the toner density in each color component developing unit of the color developing device 4. It is reasonable to assume that the color developing device 4 is of a revolver type and is caused by rotating the developing unit of each color and moving it to the developing position.
[0041]
As a method for reducing the toner flying inside the image forming apparatus, the toner itself has characteristics that make it difficult to fly (improvement of toner and carrier), and a fan or the like is installed in the image forming apparatus to fly inside the apparatus. It is conceivable to control the direction of scattering. However, the former increases the cost, and the latter increases the size of the device and increases the cost by using a fan.
[0042]
FIG. 4 illustrates an example of the position of the toner density sensor that detects the toner density and the detection system that processes the output signal from the toner density sensor in each color component developing unit of the color developing device shown in FIG.
[0043]
As shown in FIG. 4, the Y developing unit 41, the M developing unit 42, and the C developing unit 43 of the color developing device 4 are arranged clockwise around the central axis (CW direction). When the unit 41 is opposed to the photosensitive drum 1 at the developing position, the C developing unit 43 is positioned at a toner density measuring position facing the toner density sensor 44. Similarly, when the M developing unit 42 faces the photosensitive drum 1 at the developing position, the Y developing unit 41, and when the C developing unit 43 faces the photosensitive drum 1 at the developing position, the M developing unit 42, respectively. It faces the toner density sensor 44.
[0044]
Therefore, at the toner density detection position facing the toner density sensor 44, for example, the roller that developed the electrostatic image (latent image) on the photosensitive drum 1 is positioned immediately before or two colors before.
[0045]
By the way, in the technique disclosed in Japanese Patent Laid-Open No. 3-13978 as an influence of the toner scattering, the toner density is adjusted at the place where the developer is replaced on the developing sleeve, that is, at the upstream side of the developer conveyance as shown in FIG. In order to detect, it was confirmed that it was difficult to install a toner scattering prevention member such as a seal member installed upstream of the developing sleeve used in the conventional two-component developing device.
[0046]
Therefore, as an improvement, the toner density detection is performed on the downstream side after development with less interference from the scattering prevention member or the like, but the following problems occur.
[0047]
FIGS. 5A and 5B show the toner on the developing roller and the developing sleeve at the developing position defined between the individual developing units and the photosensitive drum of the color developing apparatus described above with reference to FIG. The state of is explained.
[0048]
As shown in FIG. 5A, an arbitrary color developing unit (41 to 43) of the color developing device 4 defines a developer in which a toner and a carrier are mixed at a predetermined ratio between the photosensitive drum 1 and the developer. Developed by developing the developing roller 4n-1 transported to the developing position, the housing 4n-2 that stirs the toner and carrier and holds the developer roller 4n-1 so as to be supplied, and the latent image (electrostatic image). A toner hopper 4n-3 for supplying the toner. Note that the outer peripheral surface of the developing roller 4n-1 is formed on the housing 4n by a predetermined magnetic field from a plurality of magnetic poles 4m-1 to 4m-5 (5 poles in this example) arranged in the developing roller 4n-1. -2 is provided with a developing sleeve 4n-4 that holds a part of the developer contained in -2 and is rotated at a predetermined speed so as to be sequentially replaced at the developing position.
[0049]
That is, the developer conveyed to the developing position facing the photosensitive drum 1 by the developing sleeve 4n-4 provides only the toner to the latent image formed on the photosensitive drum 1 at the developing position, and the developing sleeve. Is returned to the housing 4n-2. The developer returned to the housing 4n-2 is replaced with an unused developer (not developing the latent image) accommodated in the housing, and is again guided to the development position. As a result, the latent images formed on the photosensitive drum 1 are sequentially developed at a predetermined density.
[0050]
Thereafter, when the development with the toner of any color using the development unit located at the development position is completed, the color developing device 4 is rotated for the development with the toner of the next color. Accordingly, a developing unit holding the developer of the next color is positioned in a predetermined order at the developing position facing the photosensitive drum 1. At the same time, the development unit used for development is moved to the toner density detection position facing the toner density sensor 44 immediately before.
[0051]
For example, the toner concentration sensor 44 emits light of a near-infrared wavelength, receives light reflected and returned from the measurement target, and uses the amount of received light as an electric signal corresponding to the reflectance of the measurement target. Output. Therefore, the amount of toner in the developer, that is, the toner concentration can be obtained from the output of the toner concentration sensor 44.
[0052]
By the way, when the development of an arbitrary color is completed, the color developing device 4 is rotated, and when the developing unit 41 or 42 or 43 used for the development immediately before is positioned at the toner density detection position, the toner density sensor 44. The toner density on the surface of the developing roller 4n-3 (developing sleeve 4n-4) opposed to the surface greatly varies depending on the area ratio of the electrostatic image developed immediately before, that is, the toner adhesion amount.
[0053]
Therefore, as described above with reference to FIG. 5A, the direction in which the outer peripheral surface of the photosensitive drum 1 is moved and the direction in which the outer peripheral surface of the developing sleeve is moved are the same direction at the developing position. When the “with method” is used, the toner density on the surface of the developing sleeve at the toner density detection position facing the toner density sensor 44 is, for example, after developing a solid image (solid image, ie, a solid image) and a non-image. There is a problem that the detection result is greatly different after developing a portion (white background) or a very small character image.
[0054]
Even if it is possible to obtain (or predict) the area ratio of the electrostatic image developed immediately before by referring to the image data supplied to the exposure device 7, the developing sleeve 4n-4 is used. As shown in FIG. 5 (b), the developing sleeve 4n-4 is slightly moved from the moment when the supply of the motor pulse to the rotating developing motor is stopped.
[0055]
That is, in the “with method” developing mechanism in which the direction in which the outer peripheral surface of the photosensitive drum 1 is moved and the direction in which the outer peripheral surface of the developing sleeve is moved are the same direction at the developing position, the developing sleeve 4n is more than the developing position. When the toner density on the developing sleeve is detected downstream in the direction in which -4 is rotated, the error is likely to increase, and the fluctuation (degree of error) becomes non-uniform.
[0056]
For example, by providing the developing sleeve or a developing motor for rotating the developing sleeve with a brake mechanism having a large braking force, the degree to which the surface of the developing sleeve is moved by inertial rotation can be suppressed to a certain level, but the cost is low. Increasing is inevitable. In addition, as a problem peculiar to the revolver type developing device, it is advantageous in terms of cost to prepare three sets of brake mechanisms, but the size of the device is large, and one set of brake mechanisms is shared by three developing units. However, the cost is increased due to the complexity of the mechanism.
[0057]
FIG. 6 shows an example of a method for detecting the toner density of the color developing device with high accuracy in order to solve the problem peculiar to the above-described revolver type developing device.
[0058]
As shown in FIG. 6, when the development of a color image of an arbitrary color is completed, first, the surface potential of the photosensitive drum 1 is substantially set to “0” V. That is, the output of the charging device 2 is turned off before each developing unit of the color developing device 4 is rotated.
[0059]
Next, after a predetermined time elapses after the output of the charging device 2 is turned off, the developing unit facing the developing area facing the photosensitive drum 1 is reverse to the normal state (normally “−” in this embodiment, Therefore, a reverse developing bias voltage of “+”) is applied to the developing roller and the developing sleeve. The timing at which the output of the charging device 2 is turned off (charging to the drum 1 is stopped) and the timing at which the polarity of the developing bias voltage is reversed are the size of the photosensitive drum 1, the characteristics of the toner and carrier, or the size of the developing device. Needless to say, it is arbitrarily set according to the above.
[0060]
The toner is transferred from the developing sleeve of the developing unit currently located at the developing position to the photosensitive drum 1 by stopping the charging to the photosensitive drum 1 and applying a reverse developing bias voltage to the developing sleeve. The amount is minimal.
[0061]
As a result, fluctuations in the toner density detected by the toner density sensor 44 at the toner density detection position where the toner density sensor 44 and the developing roller (developing sleeve surface) face each other are reduced.
[0062]
Therefore, as shown in FIG. 7, the toner density of each of the developing units 41 to 43 of the color developing device 4 is Y (curve y), M (curve m), and C (curve c). It is managed within the standard value ± 1.0%.
[0063]
As shown in FIG. 6, the developing sleeve may be slightly rotated while the polarity of the developing bias voltage is reversed and applied for a predetermined time. In this case, the toner density on the developing sleeve exposed at the toner density detection position is less susceptible to the influence of the previous development (image formation), so the toner density on the developing sleeve can be detected more stably. it can.
[0064]
In this way, in the printer device 101 in which the black developing device 3 and the color developing device 4 are provided independently around the photosensitive drum 1, an image of an arbitrary color is developed by the color developing device 4, and then color development is performed. After suppressing the fluctuation of the toner density on the developing sleeve 4n-4 of the developing unit used for the development immediately before the apparatus 4, the toners of the respective colors Y, M and C are guided to the toner density detection position. The toner density in the developing devices 41 to 43 containing the toner can be managed within a certain management range.
[0065]
The present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the scope of the invention when it is implemented. Moreover, each embodiment may be implemented in combination as appropriate as possible, and in that case, the effect of the combination can be obtained. For example, in order to describe the above-described embodiment, an example of the operation of the developing device has been described by taking a color printer as an example. However, a color copying machine (color copy) or a facsimile in which an image reading unit is integrally formed is described. Needless to say, it can also be used for devices.
[0066]
【The invention's effect】
As described above in detail, according to the present invention, the toner density of the color developing device can be accurately detected by a single toner density sensor provided at a predetermined position on the outer periphery of the developing device independently of the developing device. .
[0067]
Accordingly, the amount of toner to be replenished is stabilized, and unwanted toner scattering can be reduced.
[0068]
In addition, a color image having a stable image density can be obtained over a long period of time.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a printer apparatus that is an example of an image forming apparatus to which an embodiment of the invention is applied.
FIG. 2 is a schematic diagram illustrating an example of first and second developing devices incorporated in the printer apparatus shown in FIG.
FIG. 3 is a schematic diagram for explaining a change in toner density in each color component unit of the color developing apparatus shown in FIG. 2;
4 is a schematic diagram for explaining an example of a position of a toner density sensor that detects a toner density in a developing unit of each color component of the color developing device shown in FIG. 2 and a detection system that processes an output signal from the toner density sensor.
FIG. 5 is a schematic diagram illustrating a state of toner on a developing roller and a developing sleeve at a developing position defined between a developing unit for each color component of the color developing device shown in FIG. 4 and a photosensitive drum.
6 is a schematic diagram for explaining an example of a method for detecting the toner density in each developing unit in the color developing apparatus shown in FIG.
7 is a schematic diagram for explaining a change in toner density as a result of controlling the toner density in each color component unit of the color developing device based on the toner density detected by the toner density detecting method shown in FIG. .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Charging device, 3 ... Black developing device (1st developing device), 4 ... Color developing device (2nd developing device), 5 ... Intermediate transfer belt (intermediate transfer body), 7 ... Exposure device, 8 ... intermediate transfer device, 9 ... transfer device, 41 ... Y developing unit, 42 ... M developing unit, 43 ... C developing unit, 44 ... optical toner density sensor, 101 ... image forming apparatus.

Claims (8)

A developing device containing a developer having a chromatic color;
A developer concentration detection device for detecting the concentration of the developer of the developing device after supplying the developer to the electrostatic image formed on the photoreceptor by at least the developing device and developing the electrostatic image;
In an image forming apparatus having
An image forming apparatus, wherein when the developer concentration detecting device detects the developer concentration, a developing bias voltage having a polarity opposite to that during development is supplied to the developing device for a predetermined time. 2. The output of a charging device that applies a predetermined potential to the photosensitive member is stopped before a developing bias voltage having a polarity opposite to that during development is supplied to the developing device. Image forming apparatus. The developing device includes at least two or more developing devices having the same structure formed so as to be rotatable around a rotation axis, and the developer concentration detecting device detects the concentration of the developer in each of the developing devices. The image forming apparatus according to claim 1, wherein the image forming apparatus is shared. A photoreceptor for holding the latent image;
A developing device that is opposed to a predetermined position on the outer periphery of the photoconductor and supplies a predetermined color toner to an electrostatic image corresponding to a chromatic image formed on the photoconductor to be visualized;
A toner concentration detecting device provided at a predetermined position away from a developing position where the developing device and the photosensitive member are opposed to each other, and detecting the concentration of toner contained in the developing device as a light reflectance;
A charging device for applying a predetermined potential to the photoreceptor;
A developing bias power supply device for applying a predetermined developing bias voltage to the developing device;
The developing device rotating mechanism for moving the developing device to a predetermined position facing the toner concentration detecting device when detecting the toner concentration;
When rotating the developing device by the developing device rotating mechanism, the supply of the charging output to the charging device is stopped at a predetermined timing, and the polarity of the developing bias voltage output from the developing bias power supply device is reversed. Equipment,
An image forming apparatus comprising: The developing device includes at least two developing units configured in the same manner, and when one developing unit is positioned at a developing position facing the photoconductor, the other is the toner density detecting device. The image forming apparatus according to claim 4, wherein the image forming apparatus can face a toner density detection position that faces the toner. The developing device includes at least three developing units configured in the same manner, and when the first developing unit is located at a developing position facing the photoconductor, one of the remaining developing devices and the other of the other developing devices. 5. The image forming apparatus according to claim 4, wherein the image forming apparatus is positioned at a toner density detection position associated with the toner density detection apparatus in a predetermined order. 5. The image forming apparatus according to claim 4, wherein supply of the charging output by the charging device is stopped before the developing bias voltage with the polarity reversed is supplied from the developing bias power supply device. An image that selectively supplies toner of a color corresponding to each of two or more electrostatic images corresponding to a chromatic image to form a toner image of two or more colors, and superimposes the toner images to output an image In the toner concentration control method of the forming apparatus,
An electrostatic image corresponding to the first color image is developed by the first developing device containing the first color toner;
A second developing device containing a second color toner different from the first color allows a second developing device containing a second color toner to develop an electrostatic image corresponding to the second color image. When the developing device is moved to a developing position where the second electrostatic image can be developed, the first developing device is moved to the density detecting position opposite to the toner density detecting device by the same operation, and the potential to the photosensitive member is set. The charging output of the charging device to be provided is stopped, and the polarity of the developing bias voltage is opposite to that when developing the electrostatic image corresponding to the image of the first color.
A toner density control method for an image forming apparatus.

Images