JP2000275947A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable reference image density and to always obtain a stable image density without being influenced by variation in optical characteristic due to wear of an image carrier. SOLUTION: This image forming device is constituted by being provided with; an image carrier 1 that can carry a toner image, developing devices 4Y, 4C, 4M and 4BK to form toner images, a toner quantity detection means 50 from which a signal is outputted according to the toner quantity on the reference image formed on the image carrier 1 and at least two adjusting means 61 and 62 where output of the toner quantity detection means 50 to the reference image is adjusted to the desired standard value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a latent image on an image carrier using an electrophotographic system or an electrostatic recording system, visualizing the latent image with a developer, and then transferring the latent image onto a recording material. The present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile, etc., which obtains an image by fixing.

[0002]

2. Description of the Related Art Conventionally, there have been known image forming apparatuses such as a copying machine, a printer, and a facsimile, which use an electrophotographic system or an electrostatic recording system, for example. Also, for example, a color image forming apparatus using an electrophotographic method has been put to practical use.

FIG. 12 shows a schematic configuration of an electrophotographic color image forming apparatus as an example of such an image forming apparatus.

A conventional image forming apparatus shown in FIG. 12 supports a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1 so as to be rotatable in an arrow X direction. For example, when a full-color image formation is performed, at the time of image formation, first, the surface of the photosensitive drum 1 is charged substantially uniformly by a corona charger 2 as a charging unit.
The surface of the photosensitive drum 1 is exposed to a light image E for each of the separated colors by an exposure unit such as a laser beam exposure optical system 3 so that the surface of the photosensitive drum 1 is exposed to the image information of each of the separated colors. To form an electrostatic latent image. Also, the photosensitive drum 1
Is provided with a toner amount detecting means 50 described later.

Along the outer periphery of the photosensitive drum 1, yellow,
Developing devices 4Y, 4C, 4M, and 4Bk for the respective colors containing developers for the respective colors of cyan, magenta, and black (including a so-called toner containing a resin as a base) are provided. By a developing device of a predetermined color corresponding to the electrostatic latent image formed on the photosensitive drum 1 for each of the separated colors,
The toner images of each color are sequentially visualized, and a so-called toner image is formed on the photosensitive drum 1.

For example, when a yellow image is formed, the recording material cassette 7 transfers the yellow toner image from the recording material cassette 7 via the transport system Q in synchronization with the formation of the yellow toner image on the photosensitive drum 1 as described above. It is transported to the transfer device 5, and then
The yellow toner image on the photosensitive drum 1 is electrostatically transferred onto the recording material S supplied to the transfer position where the transfer device 5 and the photosensitive drum 1 are opposed to each other.

The transfer device 5 is a cylindrical transfer / conveying means which is rotated to carry and convey the recording material S, that is, a recording material for adsorbing the recording material S to the opening area of the outer peripheral surface of the transfer drum 5a. As the supporting means, a recording material supporting sheet 5f formed of a dielectric is integrally stretched in a cylindrical shape. The recording material S includes an adsorption charger 5c and the adsorption charger 5c.
The recording material carrying sheet 5f is electrostatically attracted to the recording material carrying sheet 5f by the action of the attracting roller 5g facing c. At the transfer position, the transfer charger 5b is opposed to the photosensitive drum 1 via the transfer drum 5a, and the toner image on the photosensitive drum 1 is electrostatically charged by the action of the transfer charger 5b. Transcribed above.

In this manner, the transfer drum 5a is moved
With the rotation in the direction, for example, a yellow toner image is transferred onto the recording material S as a first color on the photosensitive drum 1,
Similarly, the toner images of each of the separation colors sequentially formed on the photosensitive drum 1 are sequentially transferred with the rotation of the transfer drum 5a, and a full-color unfixed toner image is formed on the recording material S.

When the transfer of, for example, four color toner images is completed, the recording material S is separated from the transfer drum 5a and is conveyed to a heat roller fixing device 9 as a fixing device. In the heat roller fixing device 9, the unfixed toner image on the recording material S is fixed on the recording material S by heat and pressure to become a permanent image.

[0010] Further, the toner remaining on the surface of the photosensitive drum 1 after the transfer step is completed, every time the transfer of the toner image of each color is completed,
After being removed and cleaned by the cleaning device 6, the photosensitive drum 1 is repeatedly used for image formation.

Conventionally, as a developing device, a developing device using a one-component developer containing only a resin-based toner as a developer, or a developing device using a resin-based toner particle and a carrier particle containing a carrier particle as a developer is used. A developing device using a component developer is known.

When the electrostatic latent image on the photosensitive drum 1 reaches the developing position, a developing sleeve 41 as a developer carrier
A developing bias voltage in which DC is superimposed on AC is applied from a developing bias power supply 45 which is a high-voltage power supply, and the developing sleeve 41 is rotationally driven by a driving unit (not shown), and an image of an electrostatic latent image on the photosensitive drum 1 is formed. The toner electrostatically transfers and adheres to the portion. Thus, the electrostatic latent image is visualized to become a toner image.

Conventionally, for example, in an image forming apparatus having the above configuration, the density of the developer (the amount of toner in the developing device when using a one-component developer, or the amount of toner in the developing device when using a two-component developer). There is an image density control device that detects the amount of toner adhering on the photosensitive drum 1 by the amount of reflected light in order to control the ratio of the toner and the carrier, that is, the toner density) to maintain the image density appropriately.

That is, as can be understood from the development view of the photosensitive drum 1 shown in FIG. 13, an area on the photosensitive drum 1 where an image is formed on the recording material S (recording material corresponding portion).
In addition, a predetermined density pattern as a predetermined reference image, a so-called patch latent image which is a latent image of a patch image, is formed under predetermined conditions, and the recording material corresponding portion and the A patch image is formed by performing a developing operation through an area including the patch image, and toner is supplied to the developing devices 4Y, 4C, 4M, and 4Bk such that the amount of reflected toner adhered to the patch image is always constant. .

The image density control device detects the amount of toner adhering on the photosensitive drum 1 and outputs a signal corresponding to the amount of toner (hereinafter referred to as "toner sensor") 50. And control means 60 for receiving the output of the toner sensor 50 and detecting the image density.

More specifically, the toner sensor 50 provided in the image density control device is, for example, an LED that emits near-infrared light.
An optical sensor having a light emitting means as described above and a light receiving means such as a photodiode which is sensitive to the light emitted from the light emitting means. That is, the toner sensor 5
0 indicates that the detection light from the light emitting means is received by the light receiving means via the toner on the photosensitive drum 1 and a signal corresponding to the amount of toner adhering on the photosensitive drum 1 is converted into a voltage signal based on the amount of reflected light. It is configured to output.

For example, in the above-described electrophotographic image forming apparatus, which is a conventional image forming apparatus, the relationship between the amount of applied toner (image density) on the photosensitive drum 1 and the output voltage of the toner sensor 50 is shown in FIG. The relationship is as shown. That is, with respect to the toners of yellow, magenta, and cyan in FIG. 9 (hereinafter, these are simply collectively referred to as “color toners”), when the amount of toner on the photosensitive drum 1 increases, the toner sensor The output voltage value of 50 increases.
Concerning black toner (hereinafter, referred to as “black toner”), the output voltage value of the toner sensor 50 decreases as the amount of toner on the photosensitive drum 1 increases, contrary to the color toner. .

The image density, that is, the amount of toner applied to the latent image on the photosensitive drum 1 changes in accordance with the image signal level, which is the laser output level that determines the image density. Therefore, the output voltage value of the toner sensor 50 changes according to the image signal level. FIG. 10 shows the toner sensor 50 for the image signal level of the color toner and the black toner.
3 shows the relationship between the output voltages. Note that FIG. 10 shows the above relationship for a plurality of image forming apparatuses.

As can be seen from FIG. 10, for the color toner, the image signal level increases and the output voltage of the toner sensor 50 increases as the image density increases. Conversely, for black toner, the output voltage of the toner sensor 50 decreases as the image signal level increases and the image density increases.

Next, the image density control by the image density control device will be described in more detail.

First, at the time of initial setting of the developer, that is, when backup is performed using the initial state of the developer and the photosensitive drum as initial values, the photosensitive drum 1 is removed from the photosensitive drum 1 in a state where toner is not attached. The amount of reflected light from the toner sensor 50
And the toner sensor 50 inputs an output voltage signal to the control means 60 based on the detected value.

The output voltage value of the toner sensor 50 obtained in this way is amplified by an amplifier circuit (not shown) of the control means 60 to obtain a sensor output initial value F1 of the toner sensor 50. For example, when the full range of the output voltage of the toner sensor 50 is 5 V, the output voltage of the toner sensor 50 is amplified to about 2.5 V to 3 V,
It is assumed that the sensor output is an initial value F1.

Subsequently, a patch latent image, which is a latent image of a reference image (patch image) for detecting the image density of, for example, a black image, is placed on the photosensitive drum 1 at a predetermined image signal level set in advance. Form. Thereafter, a developing bias voltage is applied to the developing sleeve 41 under predetermined conditions set in advance, and the developing sleeve 41 is driven to rotate as described above, thereby visualizing the patch latent image formed on the photosensitive drum 1. . Subsequently, a voltage signal output from the toner sensor 50 is input to the control unit 60 based on the reflected light from the patch image to which the toner is attached, amplified, and detected.

An image signal level or the like is set in advance for the patch image formed under the predetermined conditions so as to have a desired target image density, and the output voltage of the toner sensor 50 corresponding to the target image density is set. , A sensor output target value P is set.

Therefore, if the output voltage value of the toner sensor 50 for the formed patch image does not reach the sensor output target value P, the image signal level at the time of forming a patch latent image on the photosensitive drum 1 is determined. Is adjusted, and the output voltage of the toner sensor detected with respect to the patch image density obtained in this manner is set as a sensor output reference value F2.
Input to CPU (Central Processing Unit) connected to 0 and store (backup). The function of the control unit 60 can be naturally included in a form in which the CPU that controls the operation of the image forming unit is included.

The above operation is similarly performed for yellow, magenta, and cyan color toners, respectively.
The sensor output reference value F2 for each color toner image is backed up.

Thereafter, when the image forming apparatus performs the normal image forming operation as described above, as shown in FIG. 13, an area (recording material) where an image is formed on the recording material S on the photosensitive drum 1 is formed. Other than the corresponding portion), a patch image having a desired density corresponding to each color, that is, a patch image having a desired density corresponding to the above-described sensor output reference value F2 is formed. The developing devices 4Y, 4C,
By supplying toner of each color to 4M and 4Bk and controlling each current developer density, an appropriate image density is always obtained.

[0028]

However, in the above-mentioned conventional image forming apparatus, first, at the time of initial setting of the developer,
The toner sensor 50 detects the amount of reflected light from the photosensitive drum 1 to which no toner is attached, amplifies the output of the toner sensor 50 based on the amount of reflected light, and a sensor output initial value F1.
When the output of the toner sensor 50 which is the sensor output initial value F1 fluctuates due to a change in optical properties such as a mirror surface or a rough surface of the surface of the photosensitive drum 1, With the obtained sensor output reference value F2, a desired patch image density cannot be obtained, and it deviates from a set value, so that there is a problem that the control of the image density and the developer density becomes unstable.

Accordingly, it is an object of the present invention to obtain a stable reference image density without being affected by changes in optical properties due to the durability of the image carrier, and to obtain an image capable of always obtaining a stable image density. It is to provide a forming device.

Another object of the present invention is to provide an image forming apparatus which can always obtain a stable image density irrespective of the main body of the image forming apparatus.

[0031]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier capable of carrying a toner image, a developing device for forming the toner image, and a toner amount detecting unit capable of outputting a signal in accordance with a toner amount on a reference image formed on the image carrier And at least two adjusting units for adjusting the output of the toner amount detecting unit for the reference image to a desired reference value.

According to one embodiment of the present invention, one of the at least two adjusting means is configured to calculate the toner amount with respect to the reference image by calculating an output of the toner amount detecting means and the desired reference value. Calculating means for adjusting an output of the means to the desired reference value, one of the at least two adjusting means amplifying an output of the toner amount detecting means for the reference image, and An amplifier circuit for adjusting an output to the desired reference value.

According to another embodiment of the present invention, the output signal of the toner amount detecting means is an output signal initial value which is an output of the toner amount detecting means when the image carrier does not carry the toner image. The at least two adjustment units adjust the output of the toner amount detection unit for the reference image to the desired reference value by adjusting the output signal initial value.

According to another embodiment of the present invention, the image carrier can carry a plurality of color toner images, the reference images are a plurality of reference images of different colors, and the plurality of reference images are different. The toner amounts of the above plurality of colors are detected by a single toner amount detecting unit, and the at least two adjusting units set the outputs of the toner amount detecting units for the plurality of reference images to predetermined reference values, respectively. adjust.

According to a preferred embodiment of the present invention,
The toner amount detection unit is an optical sensor, and detects light reflected from the image carrier and / or the reference image. Preferably, the desired reference value of the output of the toner amount detecting means with respect to the reference image is set in a range in which the sensitivity of the toner amount detecting means with respect to a density change of the reference image is good.

According to another embodiment of the present invention, the image carrier is an electrophotographic photosensitive member.

According to another embodiment of the present invention, there are provided a plurality of the image carriers capable of carrying a toner image, and the toner amount detecting means comprises at least one of the plurality of image carriers.
A signal is output according to the amount of toner on the reference image that has been formed. Preferably, at least one of the plurality of image carriers is an electrophotographic photosensitive member, and at least one of the plurality of image carriers is a transfer member onto which a toner image is transferred from the electrophotographic photosensitive member. is there. Preferably, the toner amount detecting means outputs a signal in accordance with the toner amount on the reference image transferred onto the transfer body.

According to a preferred embodiment of the present invention, during the image forming operation, the toner density is controlled by supplying toner into the developing device so that the output of the toner amount detecting means for the reference image is constant. .

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention.

According to this embodiment, the image forming apparatus is an electrophotographic digital color copying machine. However, the present invention is not limited to this. For example, an electrophotographic or electrostatic recording type printer may be used. It should be understood that the present invention can be applied to any image forming apparatus such as a fax machine and a fax machine. Further, the present invention is naturally applicable to a black monochrome image forming apparatus.

The image forming apparatus of the present embodiment has a digital color image reader section (hereinafter, referred to as an upper section) provided in the upper part of FIG.
Called "leader unit". R) and a digital color printer unit (hereinafter, referred to as a "printer unit") W provided at a lower portion in FIG.

First, the reader unit R will be described.
Is placed on a platen glass 31, and a reflected light image obtained by exposing and scanning the original 31 with an exposure lamp 32 is condensed on a full-color sensor 34 by a lens 33 to obtain a color-separated image signal. Thereafter, the color-separated image signal is subjected to desired image signal processing by a video processing unit (not shown) through an amplifier circuit and the like (not shown) and sent to the printer unit W.

Next, the printer section W will be described. The printer unit W supports a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1 so as to be rotatable in a direction indicated by an arrow X. When an image is formed by the printer unit W, first, the photosensitive drum 1 rotates in the direction of the arrow X, and after the surface of the photosensitive drum 1 is discharged by the pre-exposure lamp 11, the photosensitive drum 1 is transferred to the corona charger 2 as charging means. It is substantially uniformly charged. afterwards,
The surface of the photosensitive drum 1 is exposed to a light image E for each of the separated colors by a laser beam exposure optical system 3 as exposure means, and thus an electrostatic latent image is formed on the photosensitive drum 1.

Here, the laser beam exposure optical system 3
The image signal sent from the reader unit R is input, and this image signal is converted into an optical signal by a laser output unit (not shown). Then, the laser light is reflected by the polygon mirror 3a, and the lens 3b and the mirror 3c are reflected. Is converted into an optical image E that scans the surface of the photosensitive drum 1 linearly (raster scan).

Along the outer periphery of the photosensitive drum 1, yellow,
Developing devices 4Y, 4C, 4M, and 4Bk for the respective colors containing developers for the respective colors of cyan, magenta, and black (including a so-called toner containing a resin as a base) are provided. The electrostatic latent image is visualized by operating a developing device of a predetermined color corresponding to the color of the electrostatic latent image formed on the photosensitive drum 1 for each separation color, and the electrostatic latent image is formed on the photosensitive drum 1 with toner. That is, a so-called toner image is formed.

Here, the developing devices 4Y, 4C, 4
M, 4Bk are eccentric cams 24Y, 24C, 24, respectively.
When an electrostatic latent image according to image information of each separation color is formed on the photosensitive drum 1 by the operations of M and 24Bk, the developing device of the corresponding color alternatively approaches the photosensitive drum 1. Is configured.

The printer unit W is provided with a transfer device 5 so as to face the photosensitive drum 1, and further includes a potential sensor 12, and a transfer device 5 on the photosensitive drum 1 which will be described in detail later. Is provided with a toner amount detecting means (toner sensor) 50 for detecting the amount of toner.

On the other hand, as described above, for example, first, in synchronization with the formation of the yellow toner image on the photosensitive drum 1 according to the yellow image information of the original, the recording material cassette 7
The recording material S is further conveyed to the transfer device 5 via the conveyance system Q, and then the toner image on the photosensitive drum 1 is transferred onto the recording material S supplied to a transfer position where the transfer device 5 and the photosensitive drum 1 face each other. Is electrostatically transferred.

Here, the transfer device 5 carries a recording material and conveys the toner image on the photosensitive drum 1 onto the recording material S to transfer the toner image onto the recording material S. A transfer means, that is, a transfer drum 5a, is provided on the outer peripheral surface opening area of the transfer drum 5a as a recording material holding means for adsorbing the recording material S. The sheet 5f is integrally stretched in a cylindrical shape. As the recording material supporting sheet 5f, a dielectric sheet such as a polycarbonate film is preferably used.

Further, the transfer device 5 includes an adsorption charger 5c for electrostatically adsorbing the recording material S to the recording material carrying sheet 5f.
And a transfer roller 5g facing the photosensitive drum 1 at the transfer position via the transfer drum 5a.

As the transfer drum 5a rotates in the direction of arrow Y, the toner image on the photosensitive drum 1 is transferred to the transfer charger 5b.
Is transferred onto the recording material S carried on the recording material carrying sheet 5f. For example, when the toner image according to the yellow image information is transferred to the recording material S as the first color separation color of the original, which is a full-color image, the transfer drum 5a further rotates, and in the same manner as described above, On the photosensitive drum 1, an electrostatic latent image and a toner image of the subsequent separated colors are formed, and the toner images of the separated colors are sequentially transferred onto the recording material S carried on the recording material carrying sheet 5f. You.

In this manner, a desired number of color images are transferred onto the recording material S which is attracted to the recording material carrying sheet 5f and conveyed with the rotation of the transfer drum 5a. For example, a full-color unfixed toner image is formed.

When a full-color image is formed in the four-color mode, when the transfer of the four-color toner image is completed, the separation claw 8 is formed.
The recording material S is separated from the transfer drum 5a by the action of the separation push-up roller 8b and the separation charger 5h. Thereafter, the recording material S is conveyed to a heat roller fixing device 9 as a fixing device. The unfixed toner image is fixed on the recording material S by heating and pressing by a heating roller 91 and a pressure fixing roller 92 as a fixing rotating body provided in the unit 9 to obtain a permanent image.

Thereafter, the recording material S is discharged to the tray 10. Further, the toner remaining on the surface of the photosensitive drum 1 after the transfer process is removed and cleaned by the cleaning device 6 each time the transfer of the toner image of each color is completed, and the photosensitive drum 1 is repeatedly used for image formation.

The photosensitive drum 1 and the developing device 4 are placed on a recording material carrying sheet 5f formed integrally with the transfer drum 5a.
Y, 4C, 4M, 4Bk, scattering and adhesion of powder (toner, paper powder, etc.) from the cleaning device 6, etc., or toner adhesion at the time of jam of recording material S (paper jam, etc.), and double-sided image formation described later Occasionally, the recording material S may be contaminated due to adhesion of oil or the like.

Therefore, the recording material carrying sheet 5f is separated from the fur brush 14 via the fur brush 14 and the backup brush 15 facing the fur brush 14 via the recording material carrying sheet 5f, and further via the oil removing roller 16 and the recording material carrying sheet 5f. After being cleaned by the operation of the backup brush 17 facing the oil removing roller 16, the image forming process can be performed again. In the image forming apparatus of the present embodiment, such cleaning of the recording material supporting sheet 5f is performed at the time of pre-rotation and post-rotation of the image forming apparatus, and is performed as needed when a jam of the recording material S (paper jam, etc.) occurs. .

Further, the image forming apparatus of the present embodiment operates the transfer drum eccentric cam 25 to operate the cam follower 5i provided integrally with the transfer drum 5a, whereby the recording material carrying sheet 5f and the photosensitive drum 1 are moved. Can be set at predetermined intervals at predetermined timing. For example, when the image forming apparatus is on standby or when the power is off, the distance between the transfer drum 5a and the photosensitive drum 1 is increased, and the rotation of the transfer drum 5a can be made independent of the rotation drive of the photosensitive drum 1.

Further, the image forming apparatus of the present embodiment
In this case, immediately after the recording material S is discharged from the heat roller fixing device 9, the conveyance path switching guide 19 is driven to transfer the recording material S to the vertical path. 20 and once stopped after being guided to the reversing path 21a, and the reversing roller 21b is rotated in the reverse direction, thereby reversing the path 21a.
With the rear end of the recording material S when it is fed to the front, and retreated in the direction opposite to the direction when it is fed, the surface on which the image on the recording material S is formed, that is, It is turned upside down when it is stored in the recording material cassette 7 and stocked in the intermediate tray 22, and then the image is formed on the other surface on which no image is formed by the above-described image forming process.

Next, the developing devices 4Y, 4C, 4M, 4Bk
Will be described. FIG. 12 shows a black developing device 4Bk.
The schematic configuration of is shown. According to the present embodiment, the developing devices 4Y,
Although 4C, 4M, and 4Bk use a two-component developer as a developer, the present invention is not limited to this, and a developing device using a one-component developer can be used as a matter of course. The same applies to the developing devices of other colors, and therefore the description is omitted.

The developing device 4Bk contains, in a developing container 42, a black toner whose main body is a resin and a developer containing carrier particles. At the opening of the developing container 42, a developing sleeve 41 as a developer carrying member that conveys the toner to a position facing the photosensitive drum 1 is provided so as to be exposed outside the developing container 42. Developing container 4
2 is supplied to the developing sleeve 41 by being stirred by the stirring means 43 and 44.
The developer layer thickness regulating member 46 is rotated with the rotation of the arrow 1 in the Z direction.
The amount of application is regulated by this.

A developing bias voltage obtained by superimposing DC on AC is applied to the developing sleeve 41 from a developing bias power supply 45 which is a high-voltage power supply, and toner is electrostatically applied to the image portion of the electrostatic latent image on the photosensitive drum 1. Transfer to and adhere to Thus, the electrostatic latent image is visualized to become a toner image.

As described above, the developing devices 4Y, 4C,
M and 4Bk indicate that the eccentric cam 24 is used only when a corresponding separated color electrostatic latent image is formed on the photosensitive drum 1 and developed.
The photosensitive drum 1 is approached by Y, 24C, 24M, and 24Bk. Therefore, when the electrostatic latent image according to the black image information is formed on the photosensitive drum 1, the black developing device 4Bk approaches the photosensitive drum 1 by the eccentric cam 24Bk, and the electrostatic latent image on the photosensitive drum 1 Is the developing sleeve 4
When the photosensitive drum 1 reaches the developing position where the photosensitive drum 1 and the photosensitive drum 1 face each other, a developing bias voltage in which DC is superimposed on AC is applied to the developing sleeve 41 from the high-voltage power supply 45. The developing sleeve 41 is rotated by a driving device (not shown) in the direction of arrow Z in the figure to visualize the electrostatic latent image on the photosensitive drum 1.

Next, an image density control device of the image forming apparatus according to the present embodiment will be described.

FIG. 3 shows a schematic configuration in the vicinity of the image control device 100 of the present embodiment. The image forming apparatus according to the present exemplary embodiment is configured such that the developer concentration (the ratio of the toner to the carrier in the developing device when a two-component developer is used, that is, the toner concentration; In order to maintain the image density appropriately by controlling the amount of toner, an image density control device 100 is provided which detects the amount of toner adhered on the photosensitive drum 1 by reflection or transmission light amount.

That is, as described above with reference to FIG. 13, the reference image is a predetermined reference image other than the area (recording material corresponding portion) on the photosensitive drum 1 where an image is formed on the recording material S. A predetermined density pattern, a so-called patch latent image, which is a latent image of a patch image, is formed under predetermined conditions, and a developing operation is performed through the area including the recording material corresponding portion and the patch image in the rotation direction of the photosensitive drum 1. Thus, a desired image density control is performed, such as forming a patch image and replenishing the developing container 42 with toner so that the reflected light amount of the toner attached to the patch image is always constant.

The image density control device 100 of this embodiment detects the amount of toner adhering to the photosensitive drum 1 and outputs a signal corresponding to the amount of toner. And control means 60 for inputting the output of 50 and detecting the image density.

The toner sensor 50 included in the image density control device 100 of the present embodiment is the same as the conventional toner sensor 50, and is not limited, but is a light emitting unit which is an LED that can emit near-infrared light. An optical sensor having a light receiving means 52 which is a photodiode having sensitivity to light emitted by the light emitting means, and receives detection light L from the light emitting means 51 via toner on the photosensitive drum 1 The light is received by the means 52 and a signal corresponding to the amount of toner adhering to the photosensitive drum 1 is output as a voltage signal based on the amount of reflected light.

The present inventor examines in detail the operation of the image density device when the surface of the photosensitive drum 1 is changed into an optical property such as light reflection due to the mirror surface or the roughened surface due to durability. The following findings leading to the present invention have been obtained.

FIG. 4 shows that the output voltage of the toner sensor 50 with respect to the photosensitive drum 1 before the toner adheres is changed.
FIG. 4 conceptually shows a state that changes with durability.

Similarly to the above-described conventional example, when the developer and the photosensitive drum 1 are initialized and the developer is backed up, the reflected light amount of the photosensitive drum 1 before the toner is attached is first measured by a toner sensor. Detect at 50.

That is, the line A shown in FIG. 4 shows the output voltage of the toner sensor 50 before the photosensitive drum 1 is durable. In order to standardize the output voltage of the toner sensor 50 when setting the sensor output reference value F2 for the patch image, the raw signal of the toner sensor 50 is converted by an amplifier circuit, which is a first adjusting unit of the control unit 60, The output voltage is amplified by a predetermined width G, and is output as a sensor output reference value F1.
(A).

However, if the surface of the photosensitive drum 1 is mirror-finished after the endurance, the output of the toner sensor 50 rises (up).
For example, at a point b on the line B, the sensor output initial value F
1 (b) indicates a value larger than the sensor output initial value F (a).

When the surface of the photosensitive drum 1 is roughened after the endurance, the output of the toner sensor 50 falls (down).
For example, at a point c on the line C, the sensor output initial value F1
(C) shows a value smaller than the sensor output initial value F (a).

Next, at the time of initial setting of the developer, a patch of each color formed by a predetermined density pattern of yellow, magenta, cyan color toner and black toner is set under predetermined conditions. An image (reference image) is formed on the photosensitive drum 1 and the toner sensor 50
Is used to detect the density of these patch images.

The detected image density of the patch image becomes the image density expected of the patch image, that is, the output voltage of the toner sensor 50 is set to the sensor output target value P for black toner, The image signal level is adjusted so that the sensor output target value P 'for the toner is obtained. The respective output voltage values of the toner sensor 50 corresponding to the image densities of the patch images of the respective colors thus obtained are input and stored (backed up) as a sensor output initial value F2 for each patch image to the CPU connected to the control means 60. I do.

Pa, Pb and Pc in FIG.
The sensor output target value P expected for the black toner patch image before and after the durability of the photosensitive drum 1, that is, at the point a on the line A, the point b on the line B, and the point c on the line C is shown. Similarly, at each of these points, the sensor output target value P ′ expected for the color toner patch image is indicated by Pa ′, Pb ′, and Pc ′, respectively.

As described above, the sensor output target value is set to a predetermined value of P for the black toner and P 'for the color toner. For example, the surface of the photosensitive drum 1 is mirror-finished due to deterioration in durability. (B line), even when the sensor output initial value F1 changes from F1 (a) to F1 (b), the sensor output target value F2 expected for the patch image does not change (for the black toner). P
b = Pa, Pb ′ = Pa ′ for the color toner).

Therefore, when the photosensitive drum 1 is not replaced after the end of the durability of the photosensitive drum 1 and only the replenishment or replacement of the developer is performed, the following problem occurs.

That is, first, the black toner will be described. When the surface of the photosensitive drum 1 is mirror-finished, the density of the actually formed patch image corresponds to the sensor output target value Pb expected for the patch image. Adjust to the concentration,
The output of the toner sensor 50 at that time is referred to as a sensor output reference value F.
In order to set as 2, the image signal level, which is the laser output level for determining the image density, in this embodiment must be greatly changed.

Similarly, when the surface of the photosensitive drum 1 is roughened, the density of the actually formed patch image is adjusted to the density corresponding to the sensor output target value Pc expected for the patch image. In order to set the output of the toner sensor 50 as the sensor output reference value F2, the image signal level must be greatly changed.

FIG. 5 shows the relationship between the image signal level and the image density of the black toner (containing carbon) by the relationship between the image signal level and the output voltage of the toner sensor 50. In FIG. 5, line A represents the relationship between the output of the toner sensor 50 standardized by the sensor output initial value F1 (a) before the endurance of the photosensitive drum 1 and the image signal level, and line B represents the surface of the photosensitive drum 1. The relationship between the output of the toner sensor 50 and the image signal level standardized by the sensor output initial value F1 (b) when the surface is mirror-finished due to durability. Similarly, the C line indicates that the surface of the photosensitive drum 1 is rough due to durability. The case where the surface is formed will be described.

As will be further understood with reference to FIG. 5, when the surface of the photosensitive drum 1 is mirror-finished or roughened due to durability, a predetermined sensor output target value P for the black toner is obtained. Large difference (L
b-La, La-Lc).

FIG. 6 shows the relationship between the image signal level and the image density of the color toner image.
0 is shown in relation to the output voltage. In FIG. 6, line A represents the sensor output initial value F1 before the endurance of the photosensitive drum 1.
The relationship between the output of the toner sensor 50 and the image signal level standardized in (a), and the B line represents the sensor output initial value F1 (b) when the surface of the photosensitive drum 1 is mirror-finished due to durability.
The line C indicates the relationship between the output of the toner sensor 50 and the image signal level standardized in the same manner, and similarly shows the case where the surface of the photosensitive drum 1 is roughened due to durability.

As can be understood from FIG. 6, the color toner is the same as the above-described black toner, and if the surface of the photosensitive drum 1 is mirror-finished or roughened due to durability, A predetermined sensor output target value P '
Large difference (La'-L) in the image signal level for obtaining
b ', Lc'-La').

On the other hand, FIG. 7 shows the developer concentration (the ratio of the toner to the carrier in the developing container 42, that is, the toner concentration because the two-component developer is used in this embodiment. This is the amount of toner in the device.)
The effect on the relationship between the image signal level and the toner sensor 50 is shown for black toner. FIG. 7 shows the characteristics of the output voltage of the toner sensor 50 with respect to the image signal level when the developer concentration changes to 5, 6, and 7 (wt /%: the weight% of the toner with respect to the carrier).

As can be understood from FIG. 7, the sensitivity of the toner sensor 50 to a change in the developer density greatly changes with the image signal level. That is, in the example shown in the drawing, the sensitivity of the toner sensor 50 is higher in the middle range of the image signal level than in the high and low image signal levels. Therefore, it is desirable to control the developer concentration at a stable image signal level with high sensitivity to changes in the developer concentration. This is the same for the color toner, as will be understood with reference to FIG. FIG. 8 shows the relationship between the image signal level and the toner sensor 50 when the developer concentration changes.

Further, as described above with reference to FIG. 9, since the toner sensor 50 has sensitivity to the amount of applied toner (image density) on the photosensitive drum 1, the change in the amount of applied toner (image density) can be prevented. It is desirable to control the image density at a stable image signal level with high sensitivity.

From the above study, the present inventor has found that the optical properties of the surface of the photosensitive drum 1 have changed in accordance with the durability of the photosensitive drum 1.
That is, when the output of the toner sensor 50 is normalized using the sensor output initial value F1 after the amount of reflected light has changed due to, for example, mirroring or roughening, it is equal to the sensor output target value P (P ′) for the patch image. Since the image signal level is largely changed in order to obtain the sensor output initial value F2, the patch image density (toner) which is set in advance so that the sensitivity of the toner sensor 50 to the change in the image density and the developer density is large. Amount) and the patch image density (toner amount) determined by the initial setting,
Toner sensor 50 for changes in image density and developer density
Has been found to decrease the sensitivity.

As a result, it has been found that the density of the patch image is not fixed at the desired density, and that the image density control becomes unstable. Furthermore, during the image formation, it has been found that since the toner supply and the like are performed so that the patch image becomes constant, it is impossible to perform appropriate developer density control.

Therefore, the image forming apparatus according to the present invention is configured to solve the above-mentioned problem. That is, according to the present embodiment, at the time of the initial setting of the developer performed after the endurance of the photosensitive drum 1, the sensor output initial value F1 that fluctuates with the change in the optical properties of the photosensitive drum 1 is adjusted, and the toner sensor 50
The sensor output initial value F1 is controlled to a desired reference value. Further, with this, a patch image (reference image) of each color having a desired density is formed at an image signal level having high sensitivity to changes in image density and developer density, that is, the toner sensor 50 sets a desired reference value. A patch image having a desired density to be output is formed, and a toner sensor 50 for the patch image is formed.
Can be set as the sensor output reference value F2.

More specifically, after the surface of the photosensitive drum 1 is durable, for example, it is mirror-finished or roughened, and the raw output of the toner sensor 50 is controlled by the control means 6 when the developer is initially set.
When the output voltage amplified by the amplifier circuit 61 as the first adjusting means of 0 fluctuates like the B line or the C line shown in FIG. 4, this output voltage is used as the sensor output initial value F1. Instead, the variation from the value of the sensor output initial setting value F1 (a) set before the endurance of the photosensitive drum 1, that is, at the point a of the A line, is calculated as the second adjusting means of the control means 60. It is configured to be calculated by the means 62 (FIG. 3).

That is, for example, when the surface of the photosensitive drum 1 is mirror-finished, the sensor output initial value F1 (b) at the point b on the line B is compared with the sensor output initial value F1 (a) at the point a on the line A. Then, the correction coefficient β is calculated. That is,
At the point b, β = F1 (a) / F1 (b) is calculated,
Β is calculated for the output value F1 (b) at the point b (β × F
1 (b) = F1 (a)), and the value obtained by this calculation, that is, F1 (a) is set as the sensor output initial value.

By calculating a correction coefficient β for the output value of the toner sensor 50, the sensor output initial value F1 (b) after the photosensitive drum 1 has been mirror-finished is used as the sensor output initial value F1 before the endurance of the photosensitive drum 1. (A) can be corrected,
The output of the toner sensor 50 is always the sensor output initial value F1.
The value is corrected to the same value as that standardized using (a). Therefore, the output of the toner sensor 50 is, for example, the output of the toner sensor 50 relating to the black toner is the toner sensor 50 corresponding to the image signal level indicated by the line A in FIG.
Therefore, the actual patch image density does not need to be largely changed when setting the sensor output reference value F2 for the patch image.

Even if the surface of the photosensitive drum 1 is roughened, the output of the toner sensor 50 can be corrected by calculating the correction coefficient β in the same manner. The same applies to the color toner, and the output of the toner sensor 50 for each color (in this embodiment, yellow, cyan, and magenta) can be corrected.

In this embodiment, a single toner sensor is used to control the image density and the developer density of a plurality of colors such as yellow, cyan, magenta, and black. However, a toner sensor 50 is provided for each color. The output of each toner sensor 50 is set in the same manner as described above.
It is also possible to adopt a configuration in which correction is performed so as not to be affected by changes in the optical properties of the photosensitive drum 1.

As described above, the image forming apparatus of this embodiment is
In order to obtain the density of a patch image set to form an image signal level at which the toner sensor 50 shows good sensitivity to changes in image density and developer density, ie, to obtain a sensor output reference value F2, an image signal Since the level does not greatly change, the sensor output initial value F thus set is set.
By performing toner replenishment or the like so that the output of the toner sensor 50 becomes constant in Step 2, it is possible to perform image density control and developer density control with high sensitivity to image density changes and developer density changes.

The image forming apparatus according to the present embodiment also exhibits excellent effects in the following points. That is, FIG.
8 shows the relationship between the image signal level of the color toner and the black toner and the output voltage of the toner sensor 50 for a plurality of image forming apparatuses. As can be understood from FIG. 10, even at the same image signal level, the obtained image density and the amount of applied toner differ depending on the main body of the image forming apparatus. The difference differs depending on the image signal level. Therefore, the output of the toner sensor 50 is an image signal level having sensitivity to the difference of each main body of the image forming apparatus, that is,
By forming a patch image at an image signal level at which the output value of the toner sensor 50 varies, and adjusting the image density, a proper amount of applied toner, that is, a proper toner sensor output value can be obtained.

It should be noted that the function of the control means 60 in the present embodiment may be, for example, a configuration in which the CPU for controlling the operation of the image forming apparatus main body also serves as the function.
For example, the first adjusting means (amplifying circuit 61) and the second adjusting means (arithmetic means 62) may be individually provided, or a part may be included in the CPU.

As described above, according to the image forming apparatus of the present invention, the sensitivity of the toner sensor 50 is always good for changes in image density and developer density without being affected by changes in the optical properties of the photosensitive drum 1. It has become possible to form a patch image having a stable desired image density, and to perform image density control using this patch image. Accordingly, it is possible to reduce variations and fluctuations in image density control, and to obtain a stable output image.

Further, the image forming apparatus of the present invention always uses a patch image having a desired image density which is highly sensitive to a change in the developer density without being affected by a change in the optical properties of the photosensitive drum 1. This makes it possible to control the developer concentration. Therefore, the toner can be replenished as needed in a stable manner, so that the ripple of the density fluctuation can be reduced and a stable output image can be obtained.

Embodiment 2 FIG. 11 shows a schematic configuration of an image forming apparatus of this embodiment. According to the present embodiment, the image forming apparatus is an electrophotographic color image forming apparatus using the intermediate transfer drum 70 as the second image carrier.

In the image forming apparatus of this embodiment, a drum-shaped electrophotographic photosensitive member (photosensitive drum) 1 as a first image carrier is used.
Are rotatable in the direction of arrow X, and the surface of the photosensitive drum 1 is uniformly charged by a corona charger 2 serving as a charging unit.
Thereafter, an electrostatic latent image of each separation color is sequentially formed on the photosensitive drum 1 by exposure E according to image information of each separation color of yellow, magenta, cyan, and black.

For example, when forming from a yellow image, when an electrostatic latent image is formed on the photosensitive drum 1 according to the yellow image information, the developing device rotary 4R is rotated to thereby rotate the developing device rotary 4R. Is arranged at a developing position facing the photosensitive drum 1 to visualize the electrostatic latent image of the yellow image to form a yellow toner image on the photosensitive drum 1.

The yellow toner image formed on the photosensitive drum 1 is a drum-shaped intermediate transfer member that is rotatable in the direction of the arrow V as a second image carrier as the photosensitive drum 1 rotates.
That is, a primary transfer area where the intermediate transfer drum 70 and the photosensitive drum face each other is reached, and a primary transfer charger 7 as a primary transfer unit is provided.
The image is transferred onto the intermediate transfer drum 70 by the operation of 1.

For example, when a full-color image is formed, the above operation is performed for the four separated colors, and a full-color toner image is transferred onto the intermediate transfer drum 70 in a multiplex manner.

On the other hand, in synchronization with the completion of the formation of the full-color toner image on the intermediate transfer drum 70, the recording material S is transferred between the intermediate transfer drum 70 and the secondary transfer roller 72 as the secondary transfer means by the transport belt 73. And is conveyed to the opposing secondary transfer area via.

Thus, the full-color toner image on the intermediate transfer drum 70 is transferred onto the recording material S. afterwards,
The recording material S carrying the unfixed toner image is conveyed to the fixing device 9, and the unfixed toner image is fixed on the recording material S by heat and pressure to become a permanent image.

The cleaning means 6 cleans the surface of the photosensitive drum 1 after the primary transfer, the cleaning means 74 cleans the intermediate transfer drum 70 after the secondary transfer, and the photosensitive drum 1 and the intermediate transfer drum 70 It is repeatedly used for image formation.

The image forming apparatus of the present embodiment has an image density control device 1 having a toner amount detecting means (toner sensor) 50.
00. The toner sensor 50 of the present embodiment is the same as that of the first embodiment. However, in the present embodiment, the output signal which is a voltage signal corresponding to the detected value is detected by detecting the reflected light from the intermediate transfer drum 70. Is output.

Therefore, according to the present embodiment, the photosensitive drum 1
After the patch image formed thereon is primarily transferred onto the intermediate transfer drum 70 by the primary transfer charger 71, the image density is detected by the toner sensor 50.

Since the output voltage of the toner sensor 50 is uniquely determined by the amount of toner applied on the intermediate transfer member, the image density of the patch image on the intermediate transfer drum 70 is detected and the image density and the developer density are determined. Also, in the image forming apparatus of the present embodiment, when the optical properties of the intermediate transfer drum 70 fluctuate, a patch image formed at an image signal level having sensitivity to changes in image density and developer density is formed. In some cases, image density control and developer density control cannot be performed stably.

However, the image forming apparatus of this embodiment is the same as the image density control apparatus 100 of the first embodiment.
By calculating the correction coefficient β and calculating the output of the toner sensor 50 and the correction coefficient β, the output of the toner sensor 50 is always assigned to the sensor output initial value F1 before the optical property of the intermediate transfer drum 70 changes. Can be standardized.

As described above, according to the present invention, a plurality of image carriers,
That is, in the present embodiment, the photosensitive drum 1 and the intermediate transfer drum 70
Also, in the image forming apparatus having the above, the sensitivity of the toner sensor 50 is always good and stable with respect to the change of the image density and the developer density without being affected by the change of the optical property of the image carrier. A patch image can be formed, and image density control can be performed using this patch image. Therefore, variation and fluctuation in image density control can be reduced, and a stable output image can be obtained.

Further, according to the present invention, the patch density of the desired density is always used without being affected by the change in the optical properties of the image carrier, and is highly sensitive to the change of the developer density. Since control can be performed, and toner supply can be stably performed as needed, ripples of density fluctuation can be reduced and a stable output image can be obtained.

[0116]

According to the present invention, an image carrier capable of carrying a toner image, a developing device for forming a toner image, and a toner capable of outputting a signal in accordance with a toner amount on a reference image formed on the image carrier are provided. Since the image sensor has an amount detecting means and at least two adjusting means for adjusting the output of the toner amount detecting means for the reference image to a desired reference value, it is affected by changes in optical properties due to durability of the image carrier. Another object of the present invention is to provide an image forming apparatus capable of obtaining a stable reference image density and constantly obtaining a stable image density. Further, according to the present invention, a stable image density can be always obtained irrespective of the difference in the main body of the image forming apparatus.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram showing a developing device provided in the image forming apparatus according to the present invention.

FIG. 3 is a schematic diagram showing the vicinity of an image density control device according to the present invention.

FIG. 4 is a graph conceptually showing a change in output of a toner sensor due to durability of a photosensitive drum.

FIG. 5 is a graph showing, for black toner, a change in output characteristics of a toner sensor with respect to an image signal level due to durability of a photosensitive drum.

FIG. 6 is a graph illustrating a change in output characteristics of a toner sensor with respect to an image signal level due to durability of a photosensitive drum for a color toner.

FIG. 7 is a graph showing, for a black toner, a change in an output characteristic of a toner sensor with respect to an image signal level for each developer concentration.

FIG. 8 is a graph illustrating a change in output characteristics of a toner sensor with respect to an image signal level according to a developer density for a color toner.

FIG. 9 is a graph showing the output characteristics of the toner sensor with respect to the amount of applied toner.

FIG. 10 is a graph illustrating a change in output characteristics of a toner sensor with respect to an image signal level due to a difference in a main body of the image forming apparatus.

FIG. 11 is a schematic configuration diagram showing another embodiment of the image forming apparatus according to the present invention.

FIG. 12 is a schematic configuration diagram illustrating a conventional image forming apparatus.

FIG. 13 is a development view of the photosensitive drum for explaining a patch image.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 41 developing sleeve 50 toner amount detecting means (toner sensor) 60 control means 61 amplifying circuit (first adjusting means) 62 calculating means (second adjusting means) 100 image density control device

Claims (11)

[Claims] An image carrier capable of carrying a toner image, a developing device for forming the toner image, and a signal output according to a toner amount on a reference image formed on the image carrier. An image forming apparatus comprising: a toner amount detecting unit that obtains toner; and at least two adjusting units that adjust an output of the toner amount detecting unit for the reference image to a desired reference value. 2. One of the at least two adjusting units calculates an output of the toner amount detecting unit for the reference image by calculating an output of the toner amount detecting unit and the desired reference value. Calculating means for adjusting to a reference value, wherein one of the at least two adjusting means amplifies an output of the toner amount detecting means for the reference image;
2. An image forming apparatus according to claim 1, further comprising an amplifier circuit for adjusting an output of said toner amount detecting means to said desired reference value. 3. An output signal of the toner amount detecting means is standardized based on an output signal initial value which is an output of the toner amount detecting means when the image carrier does not carry the toner image. The image according to claim 1, wherein the at least two adjustment units adjust the output of the toner amount detection unit for the reference image to the desired reference value by adjusting the output signal initial value. Forming equipment. 4. The image carrier can carry a plurality of color toner images, the reference image is a plurality of reference images of different colors, and the amount of toner of the plurality of colors on the plurality of reference images is determined. The detection is performed by a single toner amount detecting unit, and the at least two adjusting units adjust the outputs of the toner amount detecting units for the plurality of reference images to predetermined reference values, respectively. Item 4. The image forming apparatus according to item 1, 2 or 3. 5. The image forming apparatus according to claim 1, wherein the toner amount detecting unit is an optical sensor, and detects reflected light from the image carrier and / or the reference image. Image forming apparatus. 6. The desired reference value of the output of the toner amount detecting means for the reference image is set in a range in which the sensitivity of the toner amount detecting means to a change in density of the reference image is good. The image forming apparatus according to claim 1. 7. The image forming apparatus according to claim 1, wherein said image bearing member is an electrophotographic photosensitive member. 8. A plurality of image carriers capable of carrying a toner image, wherein said toner amount detecting means is adapted to detect a toner amount on a reference image formed on at least one of said plurality of image carriers. And outputting a signal.
7. The image forming apparatus according to any one of items 6. 9. At least one of the plurality of image carriers is an electrophotographic photosensitive member, and at least one of the plurality of image carriers is a transfer for transferring a toner image from the electrophotographic photosensitive member. The image forming apparatus according to claim 8, wherein the image forming apparatus is a body. 10. The image forming apparatus according to claim 9, wherein said toner amount detecting means outputs a signal in accordance with a toner amount on a reference image transferred onto said transfer body. 11. An image forming apparatus according to claim 1, wherein during the image forming operation, the image density control is performed by replenishing the developing device with toner so that the output of the toner amount detecting means with respect to the reference image becomes constant. The image forming apparatus according to any one of Items 1 to 10.