JPH0611935A - Image forming device - Google Patents

Abstract

PURPOSE:To accurately detect density in the whole optical density area using amplifiers for amplifying outputs of a density sensor, and varying the amplification factor of each amplifier when necessary. CONSTITUTION:The light emitting element 91 of a density sensor 9 emits light toward a toner image (not shown in Figure) having predetermined gradation. The light reflected at the toner image is received by a light receiving element 92, which in turn outputs a signal proportional to the quantity of the light received. This output is amplified by an amplifier 81 and is further amplified by amplifiers 82, 83. The amplifiers 82, 83 have different amplification factors. A switch 13 selects either of the amplifiers 82, 83 so that an optimum output proportional to the density of the toner image is available.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image.

[0002]

2. Description of the Related Art Conventionally, as one of image forming apparatuses,
An electrophotographic copying machine is used.

Such a copying apparatus, as shown in FIG.
It is provided with a photosensitive drum (image carrier) 1 which is rotatably supported, and the photosensitive drum 1 is rotationally driven in the direction of the arrow by a driving device (not shown).

Around the photosensitive drum 1, a primary charging device (charging means) 2 for sequentially charging the surface of the photosensitive drum 1 to a uniform potential and an electrostatic latent image by exposing the surface of the photosensitive drum 1 are exposed. An exposure device (exposure means) 3 that forms a toner image, a rotary developing device (developing means) 4 that develops the electrostatic latent image to form a toner image (visible image), and a toner image transfer material (described later).
A transfer device 5 for transferring the image to the upper side and a cleaning device (cleaning means) 6 for removing the residual toner on the surface of the photosensitive drum 1 are provided.

The transfer device 5 also includes a transfer drum 50 that is rotatably supported, and the transfer drum 50 rotates in the direction of the arrow in the figure. As shown in FIG. 36, the transfer drum 50 has a cylindrical transfer base 501, and a PE is provided on the transfer base 501.
A dielectric sheet 502 such as T or PVDF is attached. Then, on the surface of the transfer drum 50, the transfer material P
Are held electrostatically or mechanically.

As shown in FIG. 35, a transfer charger 52 is disposed inside the transfer drum 50 so as to face the photosensitive drum 1 with the transfer drum 50 interposed therebetween, and is formed on the photosensitive drum 1. The formed toner image is transferred onto the transfer material P. Further, a pair of separation chargers 53, 53 are arranged inside and outside the transfer drum 50 so as to discharge the transfer material P after transfer. further,
A separation claw 56 is provided at a position facing the surface of the transfer drum 50, and the tip of the separation claw 56 is located at the end of the transfer.
The transfer material P is separated from the transfer drum 50 by coming into contact with the surface of 0. Further, a cleaning device 54 is arranged so as to face the transfer drum 50, and the surface of the transfer drum 50 is cleaned after the transfer is completed.

The transfer material P separated from the transfer drum 50 passes through the fixing device 7 so that the toner image is fixed.

On the other hand, the rotary developing device 4 is, for example, yellow toner, magenta toner, cyan toner, and black toner (hereinafter referred to as “Y toner”, “M toner”, “C toner”, and “BK toner”, respectively). 4) four developing devices 4a, 4b, 4c, 4 for individually storing the four color toners
d, and a substantially cylindrical developing device supporter 410 that holds the four developing devices 4a to 4d and is rotatably supported.
It consists of and.

The rotary developing device 4 includes a developing device support 41.
By rotating 0 in the direction of the arrow in the drawing, the desired developing device 4a ...
4d is conveyed to a position facing the surface of the photosensitive drum 1, the electrostatic latent image on the surface of the photosensitive drum 1 is developed, and the developing device support 410 rotates once, so that so-called full-color development for four colors can be performed. Is configured.

The photosensitive drum 1 has a photosensitive layer provided on a conductive substrate which is an image carrier, and the exposure device 3 is composed of a light emitting element such as a laser or an LED.

In the image forming apparatus having the above structure,
When the transfer material P is fed by a feeding device (not shown), it is held in a state of being wound around the surface of the transfer drum 50.

Then, the primary charging device 2 charges the surface of the rotating photosensitive drum 1 to a uniform potential, and the exposure device 3
Image exposure based on image information of the first color (for example, yellow color) is performed at a predetermined timing to form an electrostatic latent image of the first color. At this time, the developing device 4a is being conveyed to a position facing the surface of the photosensitive drum 1.
The electrostatic latent image on the surface is developed and visualized by the developing device 4a.

The visualized toner image is rotated to a position facing the transfer drum 50 as the photosensitive drum 1 is rotated, and the transfer charger 52 is activated to transfer it to the transfer material P on the transfer drum 50. To be done. On the other hand, the photosensitive drum 1
The toner remaining on the surface is cleaned by the cleaning device 6, and the photosensitive drum 1 is ready for the next image formation.

When a second-color electrostatic latent image is formed on the surface of the photosensitive drum 1, the rotary developing device 4 is rotationally driven, and the developing device 4b is conveyed to a position facing the surface of the photosensitive drum 1. There is. Then, on the surface of the photosensitive drum 1, 2
The toner image of the second color is formed on the surface of the transfer material P on which the toner image of the first color has already been transferred.

In this way, when the toner images of all colors have been transferred to the surface of the transfer material P, the separation chargers 53, 53, etc. are activated, and the transfer material P is separated from the transfer charger 52. Then, the toner on the surface of the transfer material P is fixed by the fixing device 7, and the image formation is completed.

Next, the density detecting sensor 9 will be described.

At a position facing the photosensitive drum 1, FIG.
As shown in FIG. 3, a concentration detecting sensor (concentration detecting means) 9 is provided, and the concentration detecting sensor 9 is connected to a concentration calculating device and a control device (not shown).

As shown in FIG. 37, the density detecting sensor 9 has a light emitting element 91, a light receiving element 92, and a holder 93 for supporting them. The light emitting element 91 is formed of an LED, an incandescent bulb, or the like,
The surface of the object to be measured (the surface of the photosensitive drum in the above-mentioned conventional example) is irradiated with light. The light receiving element 92 is a photodiode, a phototransistor, a CD.
It is formed of S or the like, receives light emitted from the light emitting element 91 and reflected on the surface of the object to be measured, and outputs a signal according to the received light amount.

At the time of density detection, the exposure device 3 and the developing device 4 are activated, and a toner image for density detection is formed on the surface of the photosensitive drum 1.

Next, when the light emitting element 91 irradiates the toner image with light, the light is reflected by the toner image, and the reflected light is received by the light receiving element 92. Then, the light receiving element 92 outputs a signal according to the amount of received light.
At this time, since the amount of reflected light changes according to the density of the toner image, the amount of light received by the light receiving element 92 also changes according to the density of the toner image. Therefore, the light receiving element 92 generates a signal corresponding to the density of the toner image.

Further, a density calculating device (not shown) calculates the density of the toner image based on the output signal of the light receiving element 92. The controller determines whether or not the density is a predetermined value, and if it is not the predetermined value, the density of the toner image is made appropriate by controlling the latent image potential, the developing bias, and the like. to correct.

Such control is performed for each color toner. FIG. 38 shows the relationship between the output of the density detecting sensor 9 and the toner density for all the Y, M, C, and BK toners. As shown in this figure, the output of the Y, M, and C toners also increases with an increase in the toner concentration, which means that the amount of reflected light of these toners increases as the concentration increases. Because. Further, the output characteristics of the BK toner are such that the sensor output decreases as the toner concentration increases, but this uses carbon because it absorbs the irradiation light for concentration detection,
In addition, the amount of absorption increases as the toner concentration increases.

Incidentally, in FIG. 35, the concentration detecting sensor 9
Is provided so as to face the photosensitive drum 1, but there is also one provided so as to face the transfer drum 50 as shown in FIG. In such a type, the density of the toner image for density detection transferred on the transfer drum 50 is detected.

[0024]

By the way, in order to perform accurate density calculation using the output of the density detecting sensor 9 as described above, the sensor output width (hereinafter, referred to as "dynamic It is desirable to increase the "range") so that even slight changes in toner concentration can be detected.

As a method for increasing the dynamic range in this way, A. Method of amplifying output of concentration detecting sensor 9 by an amplifier B. There is a method (details will be described later) of selecting the sensor output when the toner density is 0 so as to have an appropriate value.

However, both methods have problems. The problem will be described below with reference to FIGS. 40 and 41.
explain.

FIGS. 40 (a) and 40 (b) show an amplifier when the density of a certain color toner image is detected by the density detecting sensor 9 and its output is amplified by the method A. It is a graph showing the relationship between the output and the optical density of the toner image. Note that FIG. 40 (b) shows the output of an amplifier having a larger amplification factor than that of FIG. 40 (a).

In the case of FIG. 40 (a), the optical density is 0.1-0.1%.
Up to 0.8, the output of the amplifier is sufficiently changed and the dynamic range is wide, so that accurate concentration detection can be performed, but when the concentration is 0.8 or more, there is little change and sufficient detection cannot be performed.

In the case of FIG. 40 (b), the concentration is 0.8
Even with the above, the output of the amplifier is sufficiently changed, so that accurate detection can be performed, but when the concentration is 0.6 or less, the output of the amplifier is saturated and accurate detection cannot be performed.

That is, as shown in FIGS. 40 (a) and 40 (b),
No matter which amplification factor is selected for the amplifier, there is a problem in that it is not always possible to perform accurate density detection in all optical density regions.

Next, the method B will be described in detail with reference to FIG.

Since the Y, M, and C toners change with the same tendency as shown in FIG. 38, in FIG. 41,
The Y and C toners are omitted, and only the output characteristics of the M toner and the BK toner are shown.

In this figure, the output characteristics of three sets of M and BK toners are shown. These are the output characteristics when the output when there is no toner image is changed to A, B and C, respectively. This is to compare the changes in. Also, these A,
B and C represent sensor outputs when the toner image is not formed on the surface of the object to be measured, and are values that change depending on the reflectance of the surface of the object to be measured (hereinafter, simply referred to as “reflectance”). . If the reflectance is high, the output of the density detecting sensor 9 is large, and if the reflectance is low, the output of the density detecting sensor 9 is small.

Here, looking only at the BK toner,
It can be seen that the dynamic range of BK toner widens in the order of A, B, and C. In the case of C, the density can be accurately detected. However, on the other hand, the dynamic range of M toner is narrowing,
The density of the M toner cannot be detected accurately.

On the other hand, in the case of A, which can accurately detect the density of M toner, on the contrary, the density of BK toner cannot be accurately detected. Therefore, it is practically impossible to accurately detect the concentrations of both BK and M toners on an object to be measured having a predetermined reflectance without using an amplifier or the like.

In the state B, the dynamic range of any toner has the same width, but the dynamic range in this case cannot detect the density, and therefore the density of any toner is detected. Can not be done accurately.

By the way, as shown in FIG. 42, this reflectance decreases with the number of sheets printed by the photosensitive drum 1,
There is also a problem that it hinders accurate toner concentration detection.
Especially when the toner image for density measurement is halftone,
The surface of the photosensitive drum 1 is easily affected, and accurate density detection is extremely difficult. As a result, there is a problem in that accurate concentration control cannot be performed.

This is an object to be measured, for example, the photosensitive drum 1.
This is because if images are repeatedly formed on the surface, the surface of the photosensitive drum 1 becomes rough due to contact with the transfer material P or the like, and the surface becomes rough.

On the other hand, in order to avoid such a problem, particularly in a full-color image forming apparatus, a toner image for the base is first formed on the surface of the photosensitive drum, and the toner image for density measurement is formed on the toner image for the base. Is formed, and the reflectance of the toner image for density measurement is measured to avoid the influence of the surface roughness of the photosensitive drum.

However, in such a method, the toner image for the base is always formed regardless of whether or not the surface of the photosensitive drum is rough, so that there is a problem that the toner is wastefully consumed.

On the other hand, the position where the density detecting sensor 9 is arranged is, as described above, a position facing the photosensitive drum 1 or
For example, there is a position facing the transfer drum 50.

However, since the primary charging device 2, the rotary developing device 4 and the like must be arranged around the photosensitive drum 1 as described above, the density detecting sensor 9 is further provided around the photosensitive drum 1. The problem is that it is difficult in space.

Further, the consumable parts such as the photosensitive drum 1 and the developing device are housed in one case to form a process cartridge,
In the case where they are replaceable, if the density detecting sensor 9 is provided around the photosensitive drum 1, the density detecting sensor 9 needs to be attached to the housing. In such a case, the density detection sensor 9 must be replaced with the replacement of the photosensitive drum 1 and the like. However, since the density detecting sensor 9 is not a consumable part, there is a problem that the replacement of the density detecting sensor 9 is useless and the process cartridge becomes expensive.

Further, when the density detecting sensor 9 is provided so as to face the transfer drum 50 to measure the toner density on the transfer drum 50, a toner image for density detection remains on the transfer drum 50, and a normal image is formed. There is also a problem that the back surface of the transfer material P is soiled during formation. Further, similarly to the above-described photosensitive drum, when the surface of the transfer drum 50 is roughened, the amount of received light in the density detecting sensor 9 is reduced, and there is also a problem that accurate density detection cannot be performed.

On the other hand, with the recent development of color DTP, the colors of characters have come to be used other than black such as green and red. In such a case, Y, M, C,
Characters of a desired color are obtained by appropriately multi-transferring BK toner. In the following description, a character obtained by mixing two color toners is referred to as a “two color character”, a character obtained by mixing three color toners is referred to as a “three color character”, and a four color toner is used. Characters obtained by mixing are called "four-color characters". Also, they are collectively referred to as "multicolored characters". Further, a character formed with only one color toner is referred to as a "monochromatic character".

However, when a multi-color character is formed by the color image forming apparatus using the non-magnetic one-component toner described in the conventional example, the thickness of the character becomes thicker than that of the single-color character, and the image There was a problem of degrading quality.

The reason for this is not clear, but it is considered as follows. That is, if the exposure amount is the same when forming a single-color character and when forming a two-color character, the amount of toner forming a single-color character is the same as the toner amount of the first color in the two-color character. That is, the amount of toner when forming a two-color character is twice the amount of toner when forming a single-color character. Therefore, when the toner is melted in the fixing step, the larger the amount of the toner is, the more the toner spreads widely on the surface of the transfer material, and as a result, the two-color character having a large amount of toner becomes thicker.

Incidentally, FIGS. 43 and 44 schematically show the sectional shape of the toner attached to the surface of the photosensitive drum 1. Here, FIGS. 43 and 44 (a) show the cross-sectional shape of a single-color character, and FIG. 44 (b) shows the cross-sectional shape of a two-color character.

By the way, as shown in FIGS. 43 and 44, the toner of the character image developed by the conventionally known jumping developing method, in which the non-magnetic one-component toner is used to develop in a non-contact manner, the central portion is raised. It has a cross-sectional shape. Therefore, an object of the present invention is to provide an image forming apparatus that solves these problems.

[0050]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first invention is an image carrier on which a toner image is formed, and an image carrier formed on the image carrier. In an image forming apparatus equipped with a transfer material holding means for holding a transfer material on which the formed toner image is transferred, and a density detecting means for detecting the density of the toner image, an output signal from the density detecting means is amplified. It is characterized by comprising an amplifying unit and an amplification factor changing unit for changing the amplification factor of the amplification unit according to the detected concentration.

In this case, the density detecting means is provided at a position facing the image carrier to detect the density of the toner image for density detection formed on the image carrier. May be.

Further, the density detecting means is provided at a position facing the transfer material holding means, and detects the density of the toner image for density detection transferred on the transfer material holding means. Good.

Further, the image forming conditions may be optimally controlled according to the output signal from the density detecting means.

Furthermore, the image carrier has a charging means for charging the surface of the image carrier to a uniform potential, a developing means for forming a toner image on the surface of the image carrier, and The process cartridge may be configured with at least one of cleaning means for cleaning the surface of the image carrier.

On the other hand, a second invention is a transfer material holding means for holding an image carrier on which toner images of respective colors are formed and a transfer material on which the toner images formed on the image carrier are transferred. And a density detecting means for detecting the density of the toner image for density detection,
In an image forming apparatus including, when the output value of the density detecting means when a toner image is not formed is within a predetermined range, while forming a toner image for density detection on the surface of the image carrier, A density control unit for forming a base toner image and a toner image for density detection on the surface of the image carrier when the output value is not within a predetermined range.
It is characterized by

In this case, the density detecting means is provided at a position facing the image carrier to detect the density of the toner image for density detection formed on the image carrier. May be.

Further, the density detecting means is provided at a position facing the transfer material holding means, and detects the density of the toner image for density detection transferred onto the transfer material holding means. Good.

Further, the density detecting means includes a light emitting means for irradiating a predetermined amount of light and a light receiving means for receiving the reflected light, and detects the density of the toner image based on the received light amount. , May be done.

Furthermore, in the image forming apparatus for forming a color image on the image carrier by exposing and developing the image forming means, the image forming means is for detecting the density on the image carrier. A transfer target formed of a plurality of regions having different reflectances while forming a toner image; and a density detecting unit provided to face the transfer target, the transfer target being provided on the transfer target. It is also possible to detect the density of the toner image for density detection transferred to the.

Further, density control means for controlling image forming conditions in the image forming means based on the detection result from the density detection means may be provided.

Further, among the areas having different reflectances on the surface of the transferred material, at least two of them have a reflectance difference of 70.
% Or more.

Further, among the areas having different reflectances on the surface of the image carrier, a toner image for density detection using yellow, magenta, and cyan toners is formed in an area having a smaller reflectance, A toner image for density detection with black toner may be formed in a large area of.

Further, the transfer target may be a transfer material holding means which is provided so as to face the image bearing member and holds the transfer material.

Furthermore, the transfer target may be a transfer material onto which the color image on the image carrier is transferred.

On the other hand, a third aspect of the invention is directed to an image carrier, an image forming means for forming a toner image on the image carrier by exposing and developing, and an image carrier facing the image carrier. And a transfer material holding means for holding the transfer material, wherein the toner image formed on the image carrier is transferred onto the transfer material. A toner image for density detection is formed on a carrier, a transfer material for density detection for transferring the toner image for density detection, and the transfer material for density detection is conveyed to the transfer material holding means. And a carrying means for holding the transfer material on the transfer material holding means, and a density detecting means provided so as to face the carrying path of the density detecting transfer material on which the toner image is formed to detect the density of the toner image for density detecting. And are provided.

In this case, the image forming conditions in the image forming means may be controlled based on the detection result from the density detecting means.

Further, the density detecting transfer material may have a plurality of regions having different reflectances.

Further, an image carrier, and an exposing means for forming an electrostatic latent image by irradiating the image carrier with light.
Developing means for adhering toner of a prescribed color to the electrostatic latent image to form a toner image of the prescribed color on the image carrier, and transfer means for transferring the toner image formed by the developing means onto a transfer material. By repeating the process of exposing by the exposing means, developing by the developing means, and transferring by the transferring means a plurality of times, multiple toner images of different colors are transferred onto the transferring material to obtain a desired image on the transferring material. In the image forming apparatus for forming the image of the color, the exposure amount of the exposure unit when the multiple transfer is performed is controlled to be smaller than the exposure amount when the multiple transfer is not performed, the exposure amount control unit, May be provided.

Furthermore, the developing means may contain a non-magnetic one-component developer.

Further, the exposure amount control means may be a light emission time controller for controlling the time for which the exposure means emits light.

Further, the exposure amount control means may be a light emission brightness controller for controlling the brightness of the light emitted from the exposure means.

[0072]

Embodiments of the present invention will be described below with reference to the drawings. The same parts as those shown in FIGS. 35 to 44 are designated by the same reference numerals, and the description thereof will be omitted.

First, an embodiment of the first invention will be described with reference to FIGS. 1 to 6.

Here, FIG. 1 is a block diagram showing the configuration of the concentration detecting sensor 9, the amplifying device 8 and the like used in this embodiment, and FIG. 2 is a circuit diagram thereof.

The density detecting sensor (density detecting means) 9 is
It is provided so as to face the photosensitive drum (image carrier) 1, and a toner image for density measurement is formed on the photosensitive drum 1 by a developing device or the like. Also,
As shown in FIGS. 1 and 2, the density detecting sensor 9 has a light emitting element 91 and a light receiving element 92. Light emitted from the toner image and reflected by the toner image is received by the light receiving element. The light is received by 92 and a current signal according to the amount of received light is generated.

On the other hand, the light receiving element 92 of the density detecting sensor 9 is connected to the amplifying device (amplifying means) 8. The amplification device 8 includes an amplifier 81 that amplifies the output of the light receiving element 92, and amplifiers 82 and 83 that further differentially amplify the output of the amplifier 81.

As shown in detail in FIG. 2, the amplifier 81 has an operational amplifier 81a as a differential amplifier and a resistor 81R, and outputs a signal having an output characteristic as shown in FIG. It has become so. The resistor 81
R converts the current signal from the light receiving element 92 into a voltage signal and determines the amplification factor of the operational amplifier 81a.

The amplifiers 82 and 83 are the operational amplifier 8
2a, 83a, constant voltage power supplies 82V, 83V, resistor 82
R, 83R, respectively. Of these, the constant voltage power supply 82V outputs the voltage V ₀ shown in FIG.
The voltage V ₁ shown in FIG. 3 is output from the constant voltage power supply 83V, and the amplification ranges of the amplifiers 82 and 83 are A and B in FIG.
Are different. Also, the operational amplifier 8
The amplification factors of 2a and 83a are determined by the resistors 82R and 83R.
Resistor 83 is set so that the area A in the inside becomes the optimum output range.
R is set so that the area of B in FIG. 3 becomes the optimum output range.

Further, these amplifiers 82 and 83 have
A switch (amplification factor changing means) 13 is connected so that the output can be selected. Then, the outputs of the amplifiers 82 and 83, which are appropriately selected, are used for the concentration detection, and the result is used for the concentration control.

Next, the operation of this embodiment will be described with reference to FIGS. 4 and 5. Here, FIG. 4 is a flow chart showing the flow of the density control in this embodiment,
Further, FIG. 5 is a diagram showing a toner image formed at the time of density detection.

First, at the time of density detection, charging, exposure, and development are performed, so that toner images L1, L2, L3, L4, L5, L6, L7, for density detection as shown in FIG.
L8 is formed on the photosensitive drum 1 (FIG. 4, S1). The toner images L1 to L8 have an optical density of 0.
1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.
It consists of an image with 8 tones of 3,1.5.

Next, the density detecting sensor 9 sequentially measures the toner densities of these images, and from each measurement result,
The optical density of the toner image to be measured is determined (S
2).

When it is judged that the output signal is the output in the range A shown in FIG. 3, that is, when the optical density is 0.1,
Toner images L1 to L targeting 0.3, 0.5, and 0.7
In the case of 4, the output of the amplifier 82 for measuring low concentration is selected by the switch 13 (S3). Further, when it is determined that the output signal is the output in the range B shown in FIG. 3, that is, in the case of the toner images L5 to L8 whose optical densities are 0.9, 1.1, 1.3 and 1.5, respectively. The output of the amplifier 83 for measuring high concentration is selected by the switch 13 (S4).

6 (a) and 6 (b) show the output of the amplifier 82 and the output of the amplifier 83, respectively.
Both outputs have a wide dynamic range and can accurately detect density.

The output thus selected is converted into density by means not shown (S5), and image forming conditions such as charging potential and developing bias are controlled by a conventionally known method (S6).

As a result, an output having a wide dynamic range can be obtained as shown in FIGS. 6 (a) and 6 (b), and accurate density detection can be performed in all optical density regions.

In the above-described embodiment, the number of amplifiers switched by the switch 13 is two (82, 83), but needless to say, it is not limited to this and may be three or more.

Regarding the amplification range, it is not always necessary to have a plurality of tables such as converting the output of the concentration detecting sensor 9 into the concentration, and further, the configuration of the amplifier is the same as that of this embodiment. It goes without saying that various conventionally known configurations can also be used.

Further, although the number of images for image detection formed on the photosensitive drum 1 is eight in the above-mentioned embodiment, it is not limited to this and may be larger. However, if the number of images is large, more accurate control can be performed, but on the other hand, the control time becomes longer and the toner consumption amount also increases. Therefore, it is generally preferable to form about 4 to 8 images, and the optical density of the images is preferably in the range of 0.1 to 1.5.

Next, another embodiment of the present invention will be described with reference to FIGS. Here, FIG. 7 is a block diagram showing an outline of the present embodiment, and FIG. 8 is a circuit diagram of the present embodiment. FIG. 9 is a flow chart for explaining the operation of this embodiment.

Also in this embodiment, the light receiving element 92 is connected to the amplifier 81, and the amplifier 81 is connected to the amplifier (amplifying means) 800. The amplifier 800 includes a variable resistor (amplification factor changing means) as an amplification factor adjusting unit.
801 is connected, and the amplification factor is adjusted. Further, a variable power source 802 as an offset adjusting section is connected to the amplifier 800 so as to adjust the amplification range.

Next, the operation of this embodiment will be described with reference to FIG.

First, on the photosensitive drum 1, charging, exposure,
By performing the development, the images L1, L2, L3, L4, L5, L6 for density detection similar to those in the above-described embodiment are obtained.
L7 and L8 are formed (S11).

Next, the density detecting sensor 9 sequentially measures the toner densities of these images, and from each measurement result,
The optical density of the toner image to be measured is determined (S
12).

For the toner images L1 to L4, the output value of the variable power source 802 is set to V1 and the value of the variable resistor 801 is set to R1. Thereby, the amplification range and the amplification factor of the amplifier 800 are set to the optimum ones.

For toner images L5 to L8, the output value of the variable power source 802 is set to V2 and the value of the variable resistor 801 is set to R2. As a result, the amplifier 8
The amplification range and amplification rate of 00 are set to the optimum ones.

The output thus obtained is converted into density by means not shown (S15), and image forming conditions such as charging potential and developing bias are controlled by a conventionally known method (S16).

As a result, by adjusting the amplification factor and offset of the amplifier 800 between the case of measuring a low-density toner image and the case of measuring a high-density toner image, accurate adjustment from low density to high density is possible. The concentration can be detected.

By varying the amplification factor and offset of the amplifier, it is possible to accurately measure the toner concentration with one amplifier. Therefore, the number of required amplifiers can be reduced, and a device with lower cost can be provided.

Further, in the present embodiment, even when the number of divisions is increased, it is sufficient to change the amplification factor adjustment and the offset adjustment by the required number, and it is not necessary to add a new amplifier.

Further, another embodiment of the present invention will be described with reference to FIGS.

In the figure, a photosensitive drum (image carrier) 1, a primary charging device (charging means) 2, a cleaning device (cleaning means)
6, and the developing device (developing means) 14 are integrally housed in the housing 10 to form a process cartridge. The developing device 14 includes developing devices 14a, 14b, 14c and 14d that store toners of respective colors, and these developing devices 14a to 14d are selectively moved to positions close to the photosensitive drum 1. It has become.

The transfer device 15 is equipped with a transfer drum (transfer material holding means) 60 rotatably supported.
The transfer drum 60 is adapted to rotate in the direction of the arrow by a driving device (not shown). The transfer drum 60 is
As shown in FIG. 11, it has a transfer substrate 601, and an elastic layer 602 is attached to the surface of the transfer substrate 601. A dielectric sheet 603 is attached to the surface of the elastic layer 602.

A density detecting sensor 9 is provided at a position facing the surface of the transfer drum 60 so that the density of the toner image transferred onto the transfer material P on the transfer drum 60 can be measured. It has become. The density detecting sensor 9 has the same configuration as that of the sensor described above, and the image forming conditions are controlled by the algorithm shown in FIG. 4 or 9.

As a result, by detecting the density of the toner image transferred on the transfer drum 60 and controlling the image forming conditions, a stable image can be obtained without maintenance by a service person.

Since the optimum amplification factor and amplification range are selected according to the density of the image to be detected, accurate density control can be performed.

By adopting a process cartridge structure in which members that need to be periodically replaced are integrally provided, maintenance which was conventionally performed by a service person can be performed by the user replacing the process cartridge.

The density detecting sensor 9 is the transfer drum 6
Since it is provided so as to face 0, it is not necessary to provide it in the process cartridge, so that it is possible to prevent the cost of the process cartridge from increasing.

Further, even when the process cartridge is replaced, it is possible to prevent the density of the printed image and the tint of the color image from changing.

In the above-mentioned embodiment, since the dielectric sheet 603 is supported by the elastic layer 602, it is hard to be deformed by use, and the conventional dielectric sheet needs to be replaced every tens of thousands of prints. On the other hand, it is possible to provide an apparatus that can withstand several hundreds of thousands to 1 million sheets of printing, does not need to be replaced until the life of the apparatus main body, and, together with the process cartridge, does not require maintenance.

Next, an embodiment of the second invention will be described with reference to FIGS.

FIG. 12 is a vertical cross-sectional view showing the structure of the copying apparatus (image forming apparatus) according to the present embodiment, in which the periphery of the photosensitive drum (image carrier) 1 is the same as in the above-described embodiments. Primary charging device (charging means) 2, exposure device (exposure means) 3,
A developing device (developing means) 14 and the like are arranged so as to form an image corresponding to a document on the surface of the photosensitive drum 1. Further, after a full-color toner image is formed on the photosensitive drum 1, the transfer material P is conveyed by a transfer material holding means such as a conveying roller, and the toner images are collectively transferred onto the transfer material P. It is supposed to be done.

On the other hand, at the time of density measurement, a toner image for density detection is formed on the photosensitive drum 1, and the density detection sensor (density detection means) 9 is, as shown in FIG. It is provided so as to face the surface of the photosensitive drum 1.

This density detecting sensor 9 is similar to that of the above-described embodiment, and has a light emitting element (light emitting means) 91 for emitting a predetermined amount of light and a light receiving element (light receiving means) 92 for receiving the reflected light. The light quantity received by the light receiving element 92, that is, the reflectance of the object to be measured is measured. When the object to be measured is a toner image, this reflectance is proportional to the density of the toner image, and as a result, the density of the toner image is measured.

The mounting angle between the light emitting element 91 and the light receiving element 92 is 30 to 6 which enables the reflectance to be measured most efficiently.
It is desirable to set it to 0 degree (Fig. 13).

The density detecting sensor 9 is connected to the density control device (density control means) 11 and the display panel 12, and the density control device 11 detects the roughness of the surface of the photosensitive drum 1. The density is detected by.

Next, the density control device 11 will be described in detail with reference to FIG.

The accuracy of the density detection performed by the density detection sensor 9 is affected by the surface roughness of the photosensitive drum 1, as described in detail in the conventional art. Therefore, in the control of the present embodiment, the roughness of the surface of the photosensitive drum 1 is measured as the reflectance by the density detection sensor 9, and the limit value (limit reflectance) at which the density detection can be accurately performed is used as a criterion for determination. There is. This limit value changes depending on the required stability of the image density and the configuration of the sensor, but for convenience, the limit value is set to I _Th.
The following description will be given (see FIG. 42).

First, the density control device 11 operates the photosensitive drum 1
The density detection sensor 9 with no image formed on it
Is started, and the reflectance I _{Ph of the} surface of the photosensitive drum 1 is measured (S20). Next, the magnitude of the measured reflectance I _Ph and the predetermined limit value I _Th are compared (S21).

When I _Ph ≧ I _Th , it is determined that the surface of the photosensitive drum 1 is not rough and the density detection can be normally performed, and the density control device 11 causes the exposure device 3 and the developing device 1 to operate.
4 is activated to form a toner image for density measurement of the first color (hereinafter, simply referred to as “patch”) on the photosensitive drum 1 (S22). Then, the density detecting sensor 9 is activated again, and the reflectance I _Y of this patch is measured (S23).
Next, based on this measurement result, the density of the patch is calculated by the basic equation of D _Y = −log (I _Y / I _Ph ) (S2
4).

Then, the density controller 11 uses this value D _Y.
Based on the above, the image forming conditions such as the latent image potential and the developing bias are changed to control so that the image density becomes optimum (S2
5). Hereinafter, similarly, density control is performed for other colors.
Note that the order of the colors of the patches for which the density detection is performed may be arbitrary.

On the other hand, when I _Ph <I _Th , it is determined that the surface of the photosensitive drum 1 is rough and the density cannot be normally detected. In this case, the density control device 11 first uses the display panel 12 to notify the user of the abnormality of the photosensitive drum 1 and the necessity of replacement (S26).

Next, a background toner image (hereinafter referred to as "background patch") is formed on the photosensitive drum 1 using BK toner (S27). Then, the reflectance I of this base patch
_BK is measured (S28). Next, a patch is created on the base patch using Y toner (S29). At this time, the cleaning blade 6a is kept in an OFF state apart from the photosensitive drum 1. Then, the reflectance I _YBK of the patch formed on the base patch of this BK toner is measured (S30). Next, based on this measurement result, the patch density is calculated by the basic equation of D _Y = _−log (I _YBK / I _Ph ) (S3
1).

Then, the density controller 11 uses this value D _Y.
Based on the above, the image forming conditions such as the latent image potential and the developing bias are changed to control so that the image density becomes optimum (S2
5). Similarly, the densities of the patches of other colors are measured and the density is controlled. Note that the order of the colors of the patches for which the density detection is performed may be arbitrary.

As a result, when the surface of the photosensitive drum 1 is rough, a background patch is formed and then density detection is performed. Therefore, the patch density can be accurately measured without being affected by the surface of the photosensitive drum 1.

The background patch is formed by the photosensitive drum 1.
This is limited to the case where the surface of R is roughened to a predetermined level or more, so that the toner consumption associated with the formation of the base patch can be minimized.

The relationship between the color of the patch and the irradiation light of the light emitting element 91 will be described. When the color of the patch absorbs the irradiation light, a monochromatic light source or an optical filter is used for the light emitting element 91. Then, irradiation light having a relationship with the color of the patch is irradiated so that the irradiation light is not absorbed by the patch, and the color of the toner used for the base patch has the same color or reflectance of the irradiation light. You can use the expensive one.

When the color of the patch reflects the irradiation light, light of the same color as that of the patch is irradiated, and toner of a color having a complementary color relationship with the color of the irradiation light is used for the base patch. If the toner has a low reflectance or a low reflectance, good detection is possible.

Further, the irradiation light is Y, like near infrared light.
If the light is reflected by any of the M and C toners, it is preferable that the toners used for the combination of the patch and the base patch have a large difference in reflectance. Therefore,
When controlling the density of the Y, M, and C toners, the BK toner may be used as the base patch. When controlling the density of the BK toner,
Any one of Y, M, and C toners may be used for the base patch.

On the other hand, the amount of consumption of each toner is measured by counting the lighting time of the exposure device 3 for each toner, and the toner with the smallest consumption is used as the base patch. As a result, uneven toner consumption can be prevented. A conventionally known method for detecting the remaining toner amount may be used for this toner consumption detection.

Next, another embodiment of the present invention will be described with reference to FIG.

In this embodiment, a transfer drum (transfer material holding means) 50 is provided in the vicinity of the photosensitive drum 1. With the transfer material P held on the surface of the transfer drum 50, each color toner image is held. Are sequentially formed on the photosensitive drum 1 and transferred, and finally a full-color image is formed on the transfer material P.

Further, the density detecting sensor 9 is provided at a position facing the transfer drum 50. The patch formed on the photosensitive drum 1 is once transferred onto the transfer drum 50, and then the density of the patch is measured. It is designed to measure. The other configurations and operations are the same as those of the above-described embodiment.

That is, the density control device 11 first activates the density detecting sensor 9 in a state where an image is not formed on the photosensitive drum 1 and the transfer drum 50, and sets the reflectance I _{Ph of the} surface of the transfer drum 50. It measures (FIG. 14, S20).
Next, the measured reflectance I _Ph and a predetermined limit value I
The size is compared with _Th (S21).

When I _Ph ≧ I _Th , it is determined that the surface of the transfer drum 50 is not rough and the density detection can be normally performed, and the density control device 11 causes the exposure device 3, the developing device 14, etc. To start forming a patch of the first color on the photosensitive drum 1. This patch is transferred onto the transfer drum 50 by the transfer charger 52, and a patch is formed on the transfer drum 50 (S22). Then, the density detecting sensor 9 is activated again, and the reflectance I _Y of this patch is measured (S23). Next, based on this measurement result, the density of the patch is calculated by the basic equation of D _Y = −log (I _Y / I _Ph ) (S2
4).

Then, the density controller 11 uses this value D _Y.
Based on the above, the image forming conditions such as the latent image potential and the developing bias are changed to control so that the image density becomes optimum (S2
5). Hereinafter, similarly, density control is performed for other colors.
Note that the order of the colors of the patches for which the density detection is performed may be arbitrary.

On the other hand, when I _Ph <I _Th , it is determined that the surface of the transfer drum 50 is rough and the density cannot be normally detected. In this case, the concentration controller 11
First, the display panel 12 is used to inform the user of the abnormality of the transfer drum 50 and the necessity of replacement (S26).

Next, a base patch is formed on the photosensitive drum 1 by using BK toner, and is transferred onto the transfer drum 50 (S27). Then, the reflectance I _BK of the background patch of the background BK toner is measured (S28). Next, a patch using Y toner is transferred onto the base patch (S29). Then, the reflectance I _YBK of the patch formed on the base patch of this BK toner is measured (S3).
0). Next, based on this measurement result, the patch density is calculated by the basic equation of D _Y = _−log (I _YBK / I _Ph ) (S3
1).

Then, the density control device 11 uses this value D _Y.
Based on the above, the image forming conditions such as the latent image potential and the developing bias are changed to control so that the image density becomes optimum (S2
5). Similarly, the densities of the patches of other colors are measured and the density is controlled. Note that the order of the colors of the patches for which the density detection is performed may be arbitrary.

The surface of the transfer drum 50 also becomes rough with the number of printed sheets, like the above-mentioned photosensitive drum. According to this embodiment, even if the surface of the transfer drum 50 is rough, the influence of the surface of the transfer drum 50 is large. The density of the patch can be accurately measured without being affected.

The background patch is prepared by the transfer drum 5
Only when the surface of 0 is roughened more than a predetermined value, it is possible to minimize the toner consumption associated with the formation of the base patch.

As a result, even if the surface of the transfer drum 50 is rough, the reflectance can be accurately measured without being affected by the surface of the transfer drum 50.

The background patch is created by the transfer drum 5
Only when the surface of 0 is roughened more than a predetermined value, it is possible to minimize toner consumption.

The relationship between the patch color and the irradiation light of the light emitting element 91 will be described. When the patch color absorbs the irradiation light, a monochromatic light source is used for the light emitting element 91 or an optical filter is used. Then, irradiation light having a relationship with the color of the patch is irradiated so that the irradiation light is not absorbed by the patch, and the color of the toner used for the base patch has the same color or reflectance of the irradiation light. You can use the expensive one.

When the color of the patch reflects the irradiation light, light of the same color as that of the patch is irradiated, and toner of a color that has a complementary color relationship with the color of the irradiation light is used for the base patch. If the toner has a low reflectance or a low reflectance, good detection is possible.

Further, the irradiation light is Y, like near-infrared light.
If the light is reflected by any of the M and C toners, it is preferable that the toners used for the combination of the patch and the base patch have a large difference in reflectance. Therefore,
When controlling the density of the Y, M, and C toners, the BK toner may be used as the base patch. When controlling the density of the BK toner,
Any one of Y, M, and C toners may be used for the base patch.

On the other hand, the amount of consumption of each toner is measured by, for example, counting the lighting time of the exposure device 3 for each toner, and the toner with the smallest consumption is used as the base patch. As a result, uneven toner consumption can be prevented. A conventionally known method for detecting the remaining toner amount may be used for this toner consumption detection.

Next, an embodiment of the third invention will be described with reference to FIGS.

FIG. 16 is a vertical sectional view showing the structure of the copying machine according to this embodiment. An image forming unit such as an exposure device 3 is provided above the photosensitive drum (image carrier) 1, and the light L emitted from the exposure device 3 is supplied to the high speed motor 32.
After being reflected by the polygon mirror 31 which is rotationally driven at high speed, transmitted through the lens 33, further reflected by the folding mirror 34, the photosensitive drum 1 is irradiated with the reflected light. Then, a color image is formed on the photosensitive drum 1 by the same method as the conventional example (FIG. 35).

Further, at a position facing the photosensitive drum 1,
A transfer drum (transfer material holding means) 50 to which a gripper 57 is attached is provided to transfer the transfer material P to the transfer drum 5.
The color image on the photosensitive drum 1 is transferred onto the transfer material P while being held at 0.

On the other hand, the cassette 1 is provided below the copying machine.
7 is provided, and a large number of transfer materials P are stored in the cassette 17. The transfer material P is taken out of the cassette 17 by the pickup roller 18 and conveyed to the transfer drum 50.

A density detecting sensor (density detecting means) 9 is provided so as to face the transfer drum 50.
The density of the toner image transferred onto the transfer drum 50 is detected during density detection.

This density detection sensor 9 is connected to a density control device (density control means) 11, and the density control device 11 uses the signals from the density detection sensor 9 to form image forming conditions in the image forming means. To control.

Next, the structure of the transfer drum will be described with reference to FIGS. 17 and 18. Here, FIG. 17 is a perspective view showing the surface structure of the transfer drum 50 and the positional relationship with the density detecting sensor 9, and FIG. 18 is a view showing the surface structure of the transfer drum 50.

In this embodiment, on the surface of the transfer drum 50, a region 503 is formed by a sheet having a low reflectance, and a region 504 is formed by a sheet having a high reflectance. Of these, the region 504 having a high reflectance is set so as not to affect the transfer of a normal image.
It is formed in the non-image forming portion (FIG. 18).

The reflectance is described below. The relationship between the optical density D and the reflectance R is as follows.

10 ^−R = 1−10 ^−D Therefore, the reflectance R can be obtained by measuring the optical density D with the density detecting sensor 9.

In this example, the reflectance of the color laser copier paper sold by Canon Sales Co., Ltd. is set to 100%, and other reflectances are standardized. And here, 20% or less is a small reflectance, 7
0% or more will be referred to as high reflectance.

The difference between the reflectance of the region 503 and the reflectance of the region 504 depends on the structure of the device, but is 50% or more, preferably 70% or more, and a good result is obtained.

Next, the operation of the present embodiment when measuring the concentration will be described.

First, the exposure device 3 and the developing device 4 are activated based on a predetermined signal, and a patch of BK toner is formed at a predetermined position on the photosensitive drum 1. The patch is transferred to the area 505 on the transfer drum 50, and the density is detected by the density detecting sensor 9. At this time,
The toner remaining on the photosensitive drum 1 is cleaned by the cleaning device 6
Then, the photosensitive drum 1 is ready for forming a new patch. After the end of the density detection, the surface of the transfer drum 50 is also cleaned by the cleaning device 54.

Next, a patch of Y toner is formed on the photosensitive drum 1, and the patch is transferred to the area 506 on the transfer drum 50. The density of this patch is also detected by the density detecting sensor 9.

Similarly, patches are formed for the M and C toners, and the densities of the patches are detected.

Then, based on these detection results, the image forming conditions are changed to the optimum ones, and the density control is performed. The order of density detection may be arbitrary.

As a result, the BK toner patch is formed in the region 504 having a high reflectance, and the Y, M, and C patches are formed.
Since the patch made of toner is formed in the region 503 having a low reflectance, the dynamic range of the density detection sensor 9 can be widened for any toner (FIG. 19), and therefore the density control can be accurately performed. You can

In the embodiment described above, the area 5
03 is formed of a sheet having a small reflectance, and the region 504 is formed of a sheet having a large reflectance. However, it is not limited to this, and the magnitude relation of the reflectance between the region 503 and the region 504 may be reversed. .

It is desirable that the transfer efficiencies of the sheets in the regions 503 and 504 are the same, but if they are different, the difference in the transfer efficiencies should be measured in advance and corrected in the density control. Good.

Next, another embodiment of the present invention will be described with reference to FIGS. Here, FIG.
Is the surface structure of the transfer drum 50 and the density detecting sensor 9
FIG. 21 is a perspective view showing the positional relationship with the, and FIG. 21 is a view showing the surface structure of the transfer drum 50.

In this embodiment, the density detecting sensor 9 is used.
Is movably supported in the direction of arrow a along the surface of the transfer drum 50, and is configured to move forward by a driving unit (not shown). When detecting the density of the BK toner patch, it is held at the position facing the area 514, and when detecting the density of the patch of another color, it is held at the position facing the area 513. ing.

The surface of the transfer drum 50 is formed of a region 513 having a low reflectance and a region 514 having a high reflectance, so that the region 514 having a high reflectance does not affect the transfer of a normal image. It is formed in the non-image forming portion at the end of the transfer drum 50 (FIG. 21).

Although the difference between the reflectance of the region 513 and the reflectance of the region 514 depends on the structure of the device, 50% or more, preferably 70% or more, a good result is obtained.

Next, the operation of the present embodiment when measuring the concentration will be described.

First, the exposure device 3 and the developing device 4 are activated based on a predetermined signal, and a patch of BK toner is formed at a predetermined position on the photosensitive drum 1. The patch is transferred to the area 515 on the transfer drum 50, and the density is detected by the density detecting sensor 9. At this time,
The toner remaining on the photosensitive drum 1 is cleaned by the cleaning device 6
Then, the photosensitive drum 1 is ready for forming a new patch. After the end of the density detection, the surface of the transfer drum 50 is also cleaned by the cleaning device 54.

Next, a patch of Y toner is formed on the photosensitive drum 1, and the patch is transferred to the area 516 on the transfer drum 50. The density of this patch is also detected by the density detecting sensor 9.

Thereafter, similarly, patches are formed for the M and C toners, and their densities are detected.

Then, based on these detection results, the image forming condition is changed to the optimum one, and the density control is performed. The order of density detection may be arbitrary.

As a result, the patch of BK toner is formed in the area 514 having a high reflectance, and the Y, M, C
Since the patch made of toner is formed in the area 513 having a low reflectance, the dynamic range of the density detecting sensor 9 can be widened for any toner.
Therefore, the concentration control can be accurately performed.

In this embodiment, the areas 513 and 514 are also used.
However, both are formed to be long in the circumferential direction of the transfer drum 50. Therefore, in any of the regions 513 and 514, it is possible to form a plurality of patches having different gradations at the same time, and even in that case, the density detection of the plurality of patches is carried out by the density detection held in one place. It can be performed by the sensor 9. That is, the density of a plurality of patches formed in the area 513 or the area 514 can be detected in a short time of one rotation of the transfer drum 50, and accurate density control can be performed in a short time.

In the embodiment described above, the area 5
13 is formed of a sheet having a small reflectance, and the region 514 is formed of a sheet having a large reflectance. However, the present invention is not limited to this, and the magnitude relation of the reflectance between the region 513 and the region 514 may be reversed. .

It is desirable that the transfer efficiencies of the sheets in the areas 513 and 514 are the same, but if they are different, the difference in the transfer efficiencies should be measured in advance and corrected during density control. Good.

Further, in the above-mentioned embodiment, the density detecting sensor 9 is moved along the surface of the transfer drum 50, but it is not limited to this, and as shown in FIG. And two density detection sensors 9 are provided at positions facing the area 514 and B, respectively.
The densities of the K toner patch and the patches of other colors may be detected by a dedicated density detection sensor. As a result, the BK and Y, M, and C toner densities can be detected simultaneously, so that the time required for the density detection can be shortened by one color. Further, a device for driving the concentration detecting sensor 9 is not required, and the structure is relatively simple.

Further, in the above-described embodiment, a plurality of regions 503, 5 having different reflectances are formed on the surface of the transfer drum 50.
04 or regions 513 and 514 are provided, but needless to say, this is not the only option. That is, the surface of the transfer drum 50 is formed of a sheet having a low reflectance, and Y,
It is also possible to form patches with the M and C toners and measure the densities thereof, and use the transfer material (transferred material) P having a large reflectance to measure the BK toner density. On the contrary, the surface of the transfer drum 50 may be formed of a sheet having a high reflectance, and the transfer material P having a low reflectance may be used. At this time, the transfer drum 50
The difference in reflectance between the transfer material and the transfer material depends on the device configuration,
Good results are obtained at 50% or more, preferably at 70% or more.

Further, when the surface of the transfer drum 50 is formed by a sheet having neither a large reflectance or a small reflectance as shown in FIG. 44B, a transfer material having a plurality of regions having different reflectances ( It is also possible to hold the (transfer target) on the transfer drum 50 to form a patch and detect the density of the patch. That is, by using a transfer material having a reflectance region suitable for detecting the density of each toner (see FIG. 23,
(FIG. 24), and the density detection may be performed on it. As a result, a wide dynamic range can be obtained for each toner.

Furthermore, the transfer material having a plurality of regions having different reflectances is not limited to being used, and a plurality of transfer materials having different reflectances may be used. By forming the patch on the transfer material in this manner, it is not necessary to attach toner to the transfer drum 50, and as a result, it is not necessary to clean the surface of the transfer drum 50 by the cleaning device 54. Further, the cleaning operation can prevent the surface of the transfer drum 50 from being damaged.

It is desirable that there is no difference in the transfer efficiency between the area where the patches of Y, M and C toners are formed and the area where the patches of BK toners are formed. However, if there is a difference in transfer efficiency between these areas, the difference may be measured in advance and corrected during density control.

Next, regarding one embodiment of the fourth invention,
It will be described with reference to FIG. FIG. 25 is a vertical cross-sectional view showing the structure of the copying apparatus according to this embodiment. First, the structure will be described. The same parts as those shown in FIG. 35 and the like are designated by the same reference numerals and the description thereof will be omitted. An image forming unit such as an exposure device 3 is provided around the photosensitive drum (image carrier) 1, and a toner image is formed by exposing and developing the photosensitive drum 1. .

A cassette 17 in which a large number of transfer materials P are stored is arranged at the lower left of the photosensitive drum 1, and the transfer materials P are sequentially taken out by a pickup roller 18.

Further, above the cassette 17, a tray 21 on which a patch transfer material (concentration detecting transfer material) 20 made of polyethylene terephthalate (PET) is placed is arranged, and the patch transfer material 20 is provided. Are picked up by a pickup roller (conveying means) 23. The pickup roller 23 is supported by a driving means (not shown) so as to move in a direction indicated by an arrow in the figure, and moves downward when the transfer material 20 for the patch is taken out, and moves upward in other cases. Is configured to.

Further, at the right end portion of the tray 21, there is provided a swingingly supported transport switching means (transport means) 22, which is indicated by an arrow in the figure by a drive means (not shown). The transfer material for patch 2 is driven by
The transport route of 0 is switched.

The pickup roller 18, pickup roller 23, and conveyance switching means 22 are driven by a predetermined signal, and a toner image which is not for normal density detection is formed on the photosensitive drum 1. In this case, the pickup roller 18 is driven and the pickup roller 23 is held at a position where it does not contact the patch transfer material 20, so that only the transfer material P is further transferred to the transfer drum (transfer material holding). Means) 50. On the other hand, when a toner image (patch) for density detection is formed on the photosensitive drum 1, the pickup roller 23
Is held at a position in contact with the transfer material for patch 20 and is driven, and the transfer switching means 22 is driven, and the pickup roller 18 is not driven, so that only the transfer material for patch 20 is further transferred by the pair of transfer rollers 28. It is adapted to be conveyed toward the drum 50.

On the other hand, a gripper 57 is attached to the transfer drum 50, and the transfer material P or the patch transfer material 20 is attached.
It is designed to hold the edges of.

At the position in contact with the surface of the transfer drum 50, the suction roller 70 is supported, and the transfer drum 5
Inside the 0, a suction charger 71 is arranged so as to face the suction roller 70. This adsorption charger 71
Is designed to charge the dielectric sheet 502,
The transfer material P or the patch transfer material 20 is electrostatically attracted to the transfer drum 50.

A separating claw 73 having the same function as the separating claw 56 is disposed between the transfer drum 50 and the tray 21, and is normally held at a position where it does not contact the surface of the transfer drum 50. , Transfer material for patch 20 to transfer drum 50
The transfer drum 50 is contacted only when it is separated from. A guide 27, rollers 24, etc. are arranged between the separating claw 73 and the tray 21,
The transfer material for patch 20 is conveyed onto the tray 21. Further, a roller-shaped cleaning device 25 is arranged above the guide 27, and the surface of the patch transfer material 20 conveyed on the guide 27 is cleaned.

On the other hand, the cleaning device 54 for cleaning the surface of the transfer drum 50 is movably supported.
The surface of the transfer drum 50 is selectively cleaned. In addition, so as to face each other with the transfer drum 50 interposed therebetween,
A pair of sheet static eliminators 72, 72 are provided so as to neutralize the dielectric sheet 502.

Further, a density detecting sensor (density detecting means) 9 is provided so as to face the transfer drum 50,
When the density is detected, the density of the patch transferred on the transfer drum 50 is detected. The image forming conditions in the image forming means are controlled based on the signal from the density detecting sensor 9.

Next, the operation at the time of density detection in this embodiment will be described.

When a predetermined signal is sent at the time of density detection, the exposure device 3, the developing device 14 and the like are activated in the same manner as in the above-described embodiment, and a patch for density detection is formed on the photosensitive drum 1.

On the other hand, the transport switching means 22 is driven by a driving means (not shown) to switch the transport path so that the patch transfer material 20 is transported to the transfer drum 50. Further, the pickup roller 23 moves downward and is driven to rotate, so that the patch transfer material 20 placed on the tray 21 is taken out from the tray 21. The transfer material for patch 20 thus taken out is further transferred to the transport roller 2
8 is conveyed, and the edge thereof is held by the gripper 57 of the transfer drum 50.

The transfer drum 50 is rotationally driven, and at the same time, the attraction charger 71 is activated, so that the patch transfer material 20 is electrostatically attracted to the surface of the transfer drum 50. The transfer material for patch 20 is accompanied by the rotation of the transfer drum 50.
Although it comes into contact with the surface of the photosensitive drum 1, the transfer charger 52 is activated at this time, so that the density detection patch formed on the photosensitive drum 1 is transferred onto the patch transfer material 20. In this manner, patches of each color are sequentially formed on the photosensitive drum 1, and the patches are sequentially transferred on the patch transfer material 20.

The density detecting sensor 9 is provided so as to face the conveyance path of the patch transfer material 20.
The densities of these patches are detected by the density detection sensor 9.

After detecting the density of each color, the separation charger 5
3, 53 are activated, and the transfer material for patch 20 is discharged. At the same time, the separation claw 73 moves so as to separate the patch transfer material 20, and the gripper 57 releases the holding of the patch transfer material 20.
It is separated from the transfer drum 50 and conveyed along the guide 27 to the tray 21. At this time, the separation claw 56 is not activated. Further, the transport switching means 22 switches the transport path so that the transfer material for patch 20 can be stored without delay.

As a result, the density detecting patch is formed on the patch transfer material 20 and is not formed on the transfer drum 50. Therefore, there is no possibility that the back surface of the transfer material P, which is electrostatically attracted to the surface of the transfer drum 50 during normal image formation, is contaminated by the density detection patch (toner).

Although the patch transfer material 20 is made of polyethylene terephthalate (PET) in the above-mentioned embodiments, it is not limited to this, and is excellent in abrasion resistance and releasability from toner. If necessary, for example, polyvinylidene fluoride (PVdF) may be used, or fluorinated ethylene propylene copolymer (FEP) or
It may be formed of polycarbonate, polyurethane or the like. However, it is preferable to use a material that is of the same quality as the transfer drum 50 and does not change the transfer efficiency.

Although the cleaning of the transfer material for patch 20 is carried out by the cleaning device 25 in the above-mentioned embodiment, the cleaning device is not limited to this, and the cleaning device 54 may be used together.

Further, in the above-mentioned embodiment, the cleaning device 25 has a roller shape, but needless to say, it is not limited to this, and a so-called fur brush may be used, or a blade-shaped cleaning device may be used. A device may be used.

Furthermore, in the above-described embodiment, the copying machine using the hollow cylindrical shape as the transfer drum 50 has been described, but it goes without saying that the copying machine is not limited to this and any type may be used. A transfer drum may be used.

As an example, another type of transfer drum 150 will be described with reference to FIG.

The transfer drum 150 is composed of a conductive support base 150a, an elastic layer 150b formed of urethane foam, silicone rubber foam or the like, and a sheet 150c covering the surface thereof.

The transfer drum of this type has a simpler internal structure and is less expensive than the transfer drum 50 having a hollow cylindrical shape, and since it is not hollow, it is strong in strength and the sheet 150c is not easily deformed. There are advantages. Therefore, by using such a transfer drum 150 in the above-described embodiment, it is possible to obtain a copying apparatus having further excellent performance.

Next, another embodiment will be described with reference to FIG.

In this embodiment, the density detecting sensor 9 is provided above the guide 27, and detects the density of the density detecting patch formed on the patch transfer material 20 conveyed on the guide 27. Is configured.

Generally, the transfer material P or the transfer material for patch 20 is used.
Is conveyed near the density detection sensor 9, and an unfixed toner image is formed on the transfer material P or the patch transfer material 20. Therefore, there is a possibility that unfixed toner is scattered and adheres to the density detection sensor 9 as the transfer material P moves, and the detection accuracy of the density detection sensor 9 is reduced. However, according to the present embodiment, the unfixed toner image passes near the density detection sensor 9 only during density detection, and this does not occur during normal image formation. There is no fear that the detection accuracy of the sensor 9 will decrease.

Further, the density detecting sensor 9 is the transfer drum 5
Since the toner image is not opposed to 0, even if the transfer material P on the transfer drum 50 is deviated from the normal position due to conveyance failure during normal image formation, the toner image formed on the transfer drum 50 is transferred to the density detection sensor 9. Since there is no contact, it is possible to avoid contamination of the density detecting sensor 9.

In the above-described embodiment, the density detecting sensor 9 is one, but it is not limited to this, and a plurality of density detecting sensors 9 may be provided and a plurality of gradations of a plurality of colors may be provided on the patch transfer material 20. The density may be detected at the same time by forming a patch.

The patch transfer material 20 described above includes
The density may be detected by using the material having the regions having different reflectances as described in FIGS. 23 and 24 and by the density detection method described in those figures. As a result, accurate density detection can be performed.

Next, an embodiment of the fifth invention will be described with reference to FIGS. 28 to 32. Here, FIG.
It is a longitudinal cross-sectional view showing the structure of the copying apparatus of the present embodiment. The structure of the copying apparatus in this embodiment is the same as that of the copying apparatus described above, except for the light emission time controller (exposure amount control means) 29, and the description of the same parts will be omitted.

In this embodiment, a light emission time controller 29 is connected to the exposure device 3 and determines the length of time (exposure time) during which the exposure device 3 irradiates light when forming multicolor characters. , It is designed to be shorter than the case of forming a single color character.

Next, the operation of this embodiment will be described with reference to FIG.

In this embodiment, first, image information is input to the light emission time controller 29 (S30). Then, the light emission time controller 29 determines whether or not it is a monochrome character based on this image information (S31). In the case of monochromatic characters, the exposure time (exposure amount) of the exposure device 3 is set to A1 (S3
2), a latent image is formed on the photosensitive drum (image carrier) 1 (S33). The latent image formed in this manner is developed by the method described above (S34), and the monochromatic character is transferred onto the transfer material P (S35).

On the other hand, in the case of a two-color character, the exposure time (exposure amount) of the exposure device (exposure means) 3 is set to A2 (S4).
2) The exposure amount is made smaller than that when forming a single color. As a result, as shown in FIG. 30, the absolute value Vl of the potential of the electrostatic latent image formed on the photosensitive drum 1 becomes large. Here, FIG. 30 shows the relationship between the exposure amount and the absolute value of the potential of the electrostatic latent image.

Then, an electrostatic latent image is formed on the photosensitive drum 1 (S43). The latent image thus formed is developed by the developing device (developing means) 4 by the method described above (S44), and one-color characters are transferred to the transfer material P held on the transfer drum (transfer means) 60. Is done (S4
5). At this time, since the absolute value of the potential of the electrostatic latent image becomes large as described above, the toner amount becomes small as shown in FIG. Here, FIG. 31 shows the absolute value of the potential of the electrostatic latent image on the photosensitive drum 1, the toner image formed on the electrostatic latent image by development, and further transferred onto the transfer material P. The relationship between the toner amount and the toner amount of the toner image is shown.
Therefore, when forming a two-color image, the amount of toner for one color is smaller than when forming a single-color image.

Further, the same steps (S42 to S45) are repeated for the other color, whereby a two-color character is formed on the transfer material P.

Thus, when forming a two-color character, the toner amount of one color is made smaller than the toner amount of a single-color character, so that the single-color character and the multi-color character can have the same thickness. FIG. 32 shows an experimental result in the case of forming a two-color character according to this example, in which the vertical axis represents the thickness of the two-color character and the horizontal axis represents the exposure amount A2. There is. In addition, L1 is the thickness of the fixed image of a single color character,
Q1 indicates the exposure amount of the exposure device 3 when forming an electrostatic latent image of monochromatic characters.

In the case of forming a two-color character, the exposure time may be controlled to be about 80% of that in the case of forming a single-color character.

By the way, conventionally, the exposure time of the exposure device 3 is controlled according to the density of the original image, and the so-called pulse width modulation (PWM) is used as the control method (FIG. 45).

That is, the density signal (analog signal) of the original image is converted into a density signal of 256 gradations, and in the pulse width modulation, a pulse having a width corresponding to this density signal is output, and this pulse causes the exposure device 3 to operate. It has been started and its exposure time has been changed. The irradiation area on the photosensitive drum 1 also changes according to this exposure time, and the toner adhesion amount also changes accordingly, so that an image corresponding to the density of the original image is finally formed.

Therefore, by changing the exposure time of the exposure apparatus 3 by utilizing such a function,
The single-color characters and the multi-color characters may have the same thickness.

That is, in the case of forming a monochrome character,
As the density signal for the pulse width modulation, a 256-step maximum density signal is sent to determine the exposure time of the exposure device 3. on the other hand,
When forming a two-color character, for example, the exposure time of the exposure device 3 is set using a density signal of 204 steps. In addition, the density signal of 153 steps is used when forming a three-color character, and the density signal of 102 steps is used when forming a four-color character.

Thus, when forming a two-color character, the toner amount for one color is smaller than the toner amount for a single-color character, so that the single-color character and the multi-color character can have the same thickness.

The charging polarity of the toner used in the above embodiments may be either positive or negative.

The developing system may be either a regular developing system or a reversal developing system.

Further, in the above-mentioned embodiment, the transfer drum 6
It is assumed that the transfer material P is held on the transfer material P and the toners of the respective colors are multiply transferred to the transfer material P. However, it is not limited to this, and a full color image is formed on the intermediate transfer material by using the intermediate transfer material. After that, it may be collectively transferred to the transfer material P.

Next, another embodiment of the present invention will be described with reference to FIG.
3 and FIG. 34.

In this embodiment, a light emission brightness controller (exposure amount control means) 291 is connected to the exposure apparatus 3,
The light emission brightness of the exposure device 3 is changed according to the number of colors of toner forming characters. For example, when a two-color character is formed, the emission brightness is controlled to be about 80% of that when a single-color character is formed.

As a result, it is possible to make the thicknesses of the monochromatic character and the multicolor character equal.

As means for controlling the emission brightness,
The circuit shown in FIG. 34 was used.

[0237]

As described above, according to the first aspect of the present invention, the amplification factor changing means changes the amplification factor of the amplification means in accordance with the detected concentration, so that the dynamic range is widened, and therefore all the optical elements can be used. The density can be accurately detected in the density region.

Further, when the image carrier is integrated with the charging means and the like to form a process cartridge, the density detecting means is provided so as to face the transfer material holding means so that the density can be changed even when the process cartridge is replaced. There is no need to replace the detection means. Therefore, it is possible to keep the cost of the process cartridge low, while not hindering the original effect of the process cartridge, which is improvement of maintenance. Furthermore, a stable image can be obtained even when the process cartridge is replaced.

On the other hand, according to the second aspect of the present invention, the density control means determines whether the surface on which the toner image for density detection is formed is rough or not. The density is detected after the toner image is formed. Therefore, the density can be accurately detected without being affected by the roughness of the surface on which the toner image is formed.

Further, since the toner image for the base is formed only when the surface is rough, it is possible to minimize the toner consumption associated with the formation.

On the other hand, according to the third aspect of the invention, for any toner, it is possible to accurately detect the density by widening the dynamic range of the density detecting means.

Further, according to the fourth invention, the toner image for density detection is transferred onto the transfer material for density detection and is not transferred onto the transfer drum or the like. Therefore, the transfer drum and the like are not contaminated.

Furthermore, according to the fifth aspect of the invention, when a multicolor character is formed, the toner amount is reduced, so that the thickness of the multicolor character and the thickness of the single color character are substantially equal. Therefore, the image quality can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a concentration detection sensor 9, an amplification device 8 and the like used in an embodiment of the first invention.

FIG. 2 is a circuit diagram of FIG.

FIG. 3 is a diagram showing output characteristics of an amplifier 81.

FIG. 4 is a flowchart showing a flow of density control in one embodiment of the first invention.

FIG. 5 is a diagram showing a toner image formed during density detection.

6A is a diagram showing an output characteristic of an amplifier 82, and FIG. 6B is a diagram showing an output characteristic of an amplifier 83.

FIG. 7 is a block diagram showing an outline of another embodiment of the first invention.

8 is a circuit diagram of FIG. 7.

FIG. 9 is a flowchart showing a flow of concentration control in another embodiment of the first invention.

FIG. 10 is a vertical sectional view of a copying apparatus showing an outline of still another embodiment of the first invention.

FIG. 11 is a sectional view showing a detailed structure of a transfer drum.

FIG. 12 is a vertical cross-sectional view showing the structure of a copying apparatus according to an embodiment of the second invention.

FIG. 13 is a diagram showing a detailed structure of a concentration detecting sensor 9.

FIG. 14 is a flowchart showing a flow of density control in one embodiment of the second invention.

FIG. 15 is a vertical sectional view showing the structure of a copying apparatus according to another embodiment of the second invention.

FIG. 16 is a vertical cross-sectional view showing the structure of a copying apparatus according to an embodiment of the third invention.

17 is a perspective view showing the surface structure of the transfer drum 50 and the positional relationship with the density detection sensor 9. FIG.

FIG. 18 is a diagram showing a surface structure of a transfer drum 50.

FIG. 19 is a diagram for explaining the effect of the embodiment of FIG.

20 is a perspective view showing another example of the surface structure of the transfer drum 50 and the positional relationship with the density detection sensor 9. FIG.

FIG. 21 is a diagram showing another example of the surface structure of the transfer drum 50.

22 is a perspective view showing still another example of the surface structure of the transfer drum 50 and the positional relationship with the density detecting sensor 9. FIG.

FIG. 23 is a diagram showing a structure of a transfer material.

FIG. 24 is a diagram showing a structure of a transfer material.

FIG. 25 is a vertical sectional view showing the structure of a copying apparatus according to an embodiment of the fourth invention.

FIG. 26 is a view showing the structure of a transfer drum 150.

FIG. 27 is a vertical sectional view showing the structure of a copying apparatus according to another embodiment of the fourth invention.

FIG. 28 is a vertical cross-sectional view showing the structure of a copying apparatus according to an embodiment of the fifth invention.

FIG. 29 is a flow chart for explaining the operation of the fifth embodiment of the invention.

FIG. 30 is a diagram showing the relationship between the exposure amount and the absolute value of the electrostatic latent image potential.

FIG. 31 is a diagram showing the relationship between the amount of toner on the transfer material and the absolute value of the potential of the electrostatic latent image.

FIG. 32 is a diagram showing an experiment result when a two-color character is formed.

FIG. 33 is a vertical sectional view showing the structure of a copying apparatus according to another embodiment of the fifth invention.

FIG. 34 is a circuit diagram of a light emission brightness controller 291.

FIG. 35 is a vertical sectional view showing the structure of a conventional copying apparatus.

FIG. 36 is a sectional view showing the structure of a transfer drum.

FIG. 37 is a sectional view showing the structure of a concentration detecting sensor.

FIG. 38 is a diagram showing the relationship between the output of the density detecting sensor and the toner density.

FIG. 39 is a vertical cross-sectional view showing another conventional example.

FIG. 40 is a diagram showing the relationship between the amplified output of the density detecting sensor and the toner density.

FIG. 41 is a diagram for explaining a conventional problem.

FIG. 42 is a diagram for explaining a conventional problem.

FIG. 43 is a cross-sectional view showing a cross-sectional shape of a monochrome character.

FIG. 44 (a) is a cross-sectional view showing a cross-sectional shape of a monochrome character, (b)
Is a cross-sectional view showing a cross-sectional shape of a two-color character.

FIG. 45 is a longitudinal sectional view showing the structure of a copying apparatus according to an embodiment of the fifth invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging means (primary charging device) 3 Exposure means (exposure device) 4 Developing means (rotary developing device) 5 Transfer device 6 Cleaning means (cleaning device) 7 Fixing device 8 Amplifying means ( Amplification device 9 Density detection means (sensor for density detection) 11 Density control means (density control device) 12 Display panel 13 Amplification factor changing means (switcher) 14 Developing means (developing device) 15 Transfer device 17 Cassette 20 For density detection Transfer material (transfer material for patch) 21 Tray 22 Conveying means (conveyance switching means) 23 Conveying means (pickup roller) 29 Exposure amount control means (light emission time controller) 50 Transfer material holding means (transfer drum) 60 Transfer material holding means (Transfer drum) 81 Amplifier 82 Amplifier 91 Light emitting means (light emitting element) 92 Light receiving means (light receiving element) 291 Exposure amount control means Emission luminance control unit) 800 amplifying means (amplifier) 801 amplification factor changing means (variable resistor) P material to be transferred (transfer material)

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical indication location G03G 15/08 115 9222-2H 15/16 (72) Inventor Tetsuya Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo No. Canon Inc. (72) Inventor Naoki Enomoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Mashiro Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Akihiko Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Haruo Fujii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 72) Inventor Hiroshi Sasame 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (22)

[Claims] 1. An image carrier on which a toner image is formed, a transfer material holding means for holding a transfer material on which the toner image formed on the image carrier is transferred, and the density of the toner image is detected. In the image forming apparatus including the density detecting unit, an amplifying unit that amplifies the output signal from the density detecting unit, and an amplification factor changing unit that changes the amplification factor of the amplification unit according to the detected density An image forming apparatus comprising: 2. The density detecting means is provided at a position facing the image carrier to detect the density of a toner image for density detection formed on the image carrier. The image forming apparatus according to claim 1. 3. The density detecting means is provided at a position facing the transfer material holding means, and detects the density of a toner image for density detection transferred onto the transfer material holding means. The image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 1, wherein the image forming condition is optimally controlled according to the output signal from the density detecting unit. 5. The image carrier has a charging means for charging the surface of the image carrier to a uniform potential, a developing means for forming a toner image on the surface of the image carrier, and the image carrier. The image forming apparatus according to claim 3, wherein the process cartridge is configured with at least one of cleaning means for cleaning the surface of the holding body. 6. An image carrier on which a toner image of each color is formed, a transfer material holding unit for holding a transfer material on which the toner image formed on the image carrier is transferred, and a density detection unit. In an image forming apparatus provided with a density detecting means for detecting the density of a toner image, when the output value of the density detecting means when a toner image is not formed is within a predetermined range, the image carrier surface And a density control unit for forming a toner image for density detection on the surface of the image carrier and forming a toner image for density detection and a toner image for density detection on the surface of the image carrier when the output value is not within a predetermined range. An image forming apparatus characterized by the above. 7. The density detecting means is provided at a position facing the image carrier, and detects the density of a toner image for density detection formed on the image carrier. The image forming apparatus according to claim 6. 8. The density detecting means is provided at a position facing the transfer material holding means, and detects the density of a toner image for density detection transferred onto the transfer material holding means. The image forming apparatus according to claim 6. 9. The density detecting means comprises a light emitting means for emitting a predetermined amount of light and a light receiving means for receiving the reflected light, and detects the density of the toner image based on the received light amount. The image forming apparatus according to claim 6, wherein 10. An image forming apparatus for forming a color image on an image carrier by exposing and developing the image forming means, wherein the image forming means forms a toner image for density detection on the image carrier. And a transfer-receiving body formed of a plurality of regions having different reflectances, and a density detecting means provided facing the transfer-receiving body,
An image forming apparatus comprising: and detecting the density of a toner image for density detection transferred onto the transfer target. 11. The image forming apparatus according to claim 10, further comprising a density control unit that controls an image forming condition in the image forming unit based on a detection result from the density detecting unit. 12. The difference between the reflectances of at least two of the areas on the surface of the transferred body having different reflectances is 70% or more, and the difference is 70% or more. The image forming apparatus described. 13. A toner image for density detection using yellow, magenta, and cyan toners is formed in a region having a small reflectance among regions having different reflectances on the surface of the image carrier, and a large reflectance is obtained. The image forming apparatus according to any one of claims 10 to 12, wherein a toner image for density detection with black toner is formed in the area. 14. The transfer material holding means, which is provided so as to face the image bearing member and holds the transfer material, according to any one of claims 10 to 13. The image forming apparatus according to item 1. 15. The image forming apparatus according to claim 10, wherein the transfer target is a transfer material onto which a color image on the image carrier is transferred. . 16. An image carrier, an image forming means for forming a toner image on the image carrier by exposure and development, and a transfer material provided opposite to the image carrier. An image forming apparatus comprising: a transfer material holding means for holding the toner image formed on the image carrier, wherein the toner image formed on the image carrier is transferred onto the transfer material. For forming a toner image for toner, and a transfer material for density detection for transferring the toner image for density detection, and the transfer material for density detection are conveyed to the transfer material holding means, and the transfer material holding means Transporting means for holding the
An image forming apparatus comprising: a density detecting unit that is provided so as to face a conveyance path of the density detecting transfer material on which the toner image is formed and that detects the density of the density detecting toner image. . 17. The image forming apparatus according to claim 16, wherein the image forming condition in the image forming unit is controlled based on the detection result from the density detecting unit. 18. The image forming apparatus according to claim 16, wherein the density detecting transfer material has a plurality of regions having different reflectances. 19. An image carrier, exposure means for forming an electrostatic latent image by irradiating the image carrier with light, and a toner of a prescribed color is adhered to the electrostatic latent image to form an electrostatic latent image. The developing device includes a developing unit that forms a toner image of a prescribed color on the image carrier, and a transfer unit that transfers the toner image formed by the developing unit onto a transfer material. An image forming apparatus for forming an image of a desired color on a transfer material by repeating the process of developing and transferring by the transfer means a plurality of times to multiple-transfer toner images of different colors onto the transfer material. An image forming apparatus comprising: an exposure amount control unit that controls the exposure amount of the exposure unit to be smaller than the exposure amount when multiple transfer is not performed. 20. The image forming apparatus according to claim 19, wherein the developing means stores a non-magnetic one-component developer. 21. The image according to claim 19, wherein the exposure amount control means is a light emission time controller that controls a time for which the exposure means emits light. Forming equipment. 22. The light emission brightness controller for controlling the brightness of light emitted from the exposure means, wherein the exposure amount control means is a light emission brightness controller. Image forming apparatus.