JP2003131438A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of accurately adjusting image forming conditions that affect an image finally formed on a recording medium. SOLUTION: In the image forming device 100 that forms a toner image and finally fixes the toner image to a recording medium, thereby forming on the recording medium an image composed of the fixed toner image, a toner patch 20 at the intermediate rate of area is formed. When a toner patch 20 is newly formed, the toner patch 20 is formed at the high rate of area in comparison with the previous rate in the case that a toner patch 20 previously measured by an ADC sensor 10 is higher than a target density.

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 used in an electrophotographic copying machine or printer.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image is formed on a photosensitive member by scanning the photosensitive member with an exposure beam modulated according to an image signal, and the electrostatic latent image is developed with toner. An image forming apparatus is known in which a toner image is formed on the photoconductor, and the toner image is finally transferred and fixed on a recording medium to form an image of the fixed toner image on the recording medium. ing. In such an image forming apparatus, the density of the image formed on the recording medium is set to a predetermined reference density (target density) due to the environmental conditions (temperature / humidity) of the apparatus and changes over time of members constituting the apparatus. )
It may shift in a darker or lighter direction. Therefore, a toner patch for image density detection is formed in a non-image area on an image carrier such as a photoconductor or an intermediate transfer belt, and the density of the toner patch is adjusted to ADC (Auto density).
control) sensor and refers to a gradation correction table that corrects the gradation of the input image signal, corrects the gradation of the image signal so that the density of the toner patch becomes the target density, or By correcting the light amount of the exposure beam, image forming conditions that affect the image finally formed on the recording medium are adjusted.

[0003]

Here, the gradation gradient (γ characteristic curve) represented by the gradation correction table in the toner patch of the target density and the gradation in the toner patch deviated to a density other than the target density. Gradient inclinations represented by the correction table are different from each other. However, in the conventional image forming apparatus, since the correction is performed by referring to the gradation correction table with the toner patch of the target density, the gradation correction of the input image signal cannot be performed accurately, so that the final image is not corrected. It is difficult to accurately adjust the image forming conditions that affect the image formed on the recording medium.

In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus capable of accurately adjusting image forming conditions that finally affect an image formed on a recording medium.

[0005]

An image forming apparatus of the present invention that achieves the above object forms a toner image, and finally fixes the toner image on a recording medium to fix the toner image on the recording medium. In an image forming apparatus for forming an image consisting of, a patch forming means for forming a toner patch having a predetermined area ratio, a patch density measuring means for measuring the density of the toner patch, and a toner measured by the patch density measuring means. Image forming condition adjusting means for adjusting image forming conditions that affect the image finally formed on the recording medium according to the density of the patch, and the patch forming means has an area ratio of the toner patch to be formed. Is changed under a predetermined condition to form a toner patch having the changed area ratio.

Here, the patch forming means forms a toner patch having a halftone area ratio, and when forming the toner patch this time, the density of the toner patch previously measured by the patch density measuring means is measured. It is preferable to form a toner patch having an area ratio higher than that of the previous time and a toner patch having an area ratio lower than that of the previous time when the toner density exceeds the target density.

Further, the image forming apparatus forms an electrostatic latent image on the photosensitive member by scanning the photosensitive member with an exposure beam modulated according to an image signal, and the electrostatic latent image is formed into a toner image. A toner image is formed by developing with a developing device that holds a developer containing a mixture of toner and carrier inside and develops the electrostatic latent image with the toner in the developer. The patch forming means forms a toner patch having a predetermined halftone area ratio,
It is also a preferred embodiment that when the toner in the developing device is reduced below a predetermined level, or when a state correlated with this is generated, the process shifts to the formation of a toner patch with a predetermined high area ratio. .

Furthermore, the patch forming means is provided with a sensor for measuring the ratio of toner to carrier in the developing device, and the patch forming means determines a predetermined value when the sensor detects that the toner ratio has decreased below a predetermined value. It is also preferable to shift to the formation of a toner patch having a high area ratio.

Further, the patch forming means includes a toner tank and a sensor for detecting that the toner tank is empty, and a toner replenishing means for replenishing the toner in the toner tank to the developing device. Alternatively, when it is detected by the sensor that the toner tank is empty, the process may shift to the formation of a toner patch having a predetermined high area ratio.

Further, the image forming condition adjusting means adjusts the light quantity of the exposure beam, and the patch forming means receives the light quantity of the exposure beam which is equal to or more than a predetermined light quantity. Alternatively, the process may be shifted to the formation of a toner patch having a predetermined high area ratio.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

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

The image forming apparatus 100 shown in FIG. 1 includes four photoconductors corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K) from the right side of FIG. 1Y, 1M, 1C and 1K are arranged side by side in a straight line, and around these photoconductors 1Y, 1M, 1C and 1K, chargers 2Y, 2M, 2C and 2K and developing units 3Y and 3M,
3C and 3K and transfer devices 4Y, 4M, 4C and 4K are arranged. An electrostatic latent image is formed on the photoconductors 1Y, 1M, 1C, 1K by scanning with an exposure beam modulated according to an image signal. Developing devices 3Y, 3M, 3
C and 3K develop the electrostatic latent image with the toner in the developer in which the toner and the carrier are mixed.

Further, in the image forming apparatus 100, toners for accommodating yellow (Y), magenta (M), cyan (C) and black (K) toners in the developing units 3Y, 3M, 3C and 3K. The toner in the toner tanks 5Y, 5M, 5C and 5K and the toner in the toner tanks 5Y, 5M, 5C and 5K is developed by the developing device 3
Toner supply motor 6 for supplying Y, 3M, 3C and 3K
ATC (Aut) for measuring the ratio of toner to carrier in Y, 6M, 6C, 6K (corresponding to an example of toner replenishing means in the present invention) and developing units 3Y, 3M, 3C, 3K.
o Toner concentration Con
toner sensor 7Y, 7M, 7C, 7K and toner remaining amount sensor 11Y, 11M, 11C, 11 for detecting that the toner tanks 5Y, 5M, 5C, 5K have become empty.
K and are provided.

Further, the image forming apparatus 100 has an arrow A
The intermediate transfer belt 8 that is driven in the direction, the drive roll 9,
ADC (Auto Density Control)
The sensor 10 is provided. The ADC sensor 10 is
The density of the toner patch 20 formed on the intermediate transfer belt 8 is detected, and corresponds to an example of the patch density detecting means according to the present invention.

The image forming apparatus 100 also includes a charger 2
Photoconductors 1Y, 1 charged by Y, 2M, 2C, 2K
A raster scanning device (hereinafter referred to as ROS) 30 that writes an electrostatic latent image on M, 1C, and 1K, and a controller 40 are provided. The controller 40 has a gradation correction table LUT 41. Further, the controller 40, in cooperation with the developing devices 3Y, 3M, 3C, 3K, plays the role of a patch forming means for forming a toner patch having a predetermined area ratio according to the present invention, and is intended to be formed. The area ratio of the toner patch 20 is changed under a predetermined condition to form the toner patch 20 having the changed area ratio.

Further, the image forming apparatus 100 includes an ADC.
A gradation control unit 50 that adjusts image forming conditions that finally affect an image formed on a recording medium (not shown) according to the density of the toner patch 20 measured by the sensor 10.
(One example of the image forming condition adjusting means according to the present invention) is provided. When adjusting the image forming conditions, the gradation control unit 50 corrects the gradation of the print image represented by the input image signal by referring to the gradation correction table LUT 41, and outputs the corrected image data. To do.

Further, the image forming apparatus 100 has a ROS 3
LD light amount control unit 6 for adjusting the light amount of the exposure beam from 0
0 (another example of the image forming condition adjusting means according to the present invention) is provided.

Further, the image forming apparatus 100 is provided with a TC controller 70. The TC control unit 70 regulates the maximum stacking amount by adjusting the transfer amount of each color toner to each electrostatic latent image by each developing device 3Y, 3M, 3C, 3K according to the measurement result by the ADC sensor 10. To do.

The image forming apparatus 100 configured as described above.
Scans the photoconductors 1Y, 1M, 1C, 1K with an exposure beam that is modulated according to the print image represented by the image signal to form an electrostatic latent image on the photoconductors 1Y, 1M, 1C, 1K. And then form those electrostatic latent images with yellow (Y), magenta (M), cyan (C), black (K)
To develop a color toner image on the photoconductors 1Y, 1M, 1C, and 1K, and finally transfer and fix the color toner image on the recording medium to fix the toner image on the recording medium. Is used to form a color image. In this image forming apparatus 100, image forming conditions that affect the image finally formed on the recording medium are adjusted as described below.

The image forming apparatus 100 forms the toner patch 20 having a halftone area ratio. When forming the toner patch 20 this time, the density of the toner patch 20 measured last time exceeds the target density. When it is lower than or equal to the lower limit, a toner patch having a higher area ratio than the previous time and a toner patch having a lower area ratio than the previous time are respectively formed. Hereinafter, description will be made with reference to FIG.

FIG. 2 is a graph of an ideal gradation correction table and a corrected gradation correction table in the image forming apparatus shown in FIG.

The abscissa of FIG. 2 shows the image data Cin for forming the toner patch 20, and the ordinate shows the image output level of the ADC sensor 10 for the toner patch 20 formed corresponding to the image data Cin. Indicates Cout.
Graph A shown in FIG. 2 is a graph of an ideal gradation correction table at the target density. On the other hand, the graph B is a graph in which the image output level Dout larger than the ideal image output level Dout in the graph A is output because the density of the toner patch 20 changes in the dark direction due to the environmental conditions of the apparatus. is there. Here, the image data C of the graph A for forming the toner patch 20 having the halftone area ratio is shown.
The gradation gradient (angle α) at in (value P) is smaller than the gradation gradient (angle β) at graph B. Also,
The gradient of the gradation in the image data Cin (value Q) for forming the toner patch 20 in the highlight region of the graph B is the same as the gradient of the gradation in the value P of the graph A (angle α). From these graphs A and B, when forming the toner patch 20 this time, if the density of the toner patch 20 measured last time exceeds the target density, if the toner patch 20 having a higher area ratio than the previous time is formed, The gradation correction can be performed with high accuracy by using the graph A of the ideal gradation correction table at the target density.

FIG. 3 is a diagram showing a graph for correcting the gradation correction table at a predetermined density.

FIG. 3 shows a graph C for correcting the gradation correction table at the target density. Also,
A graph D for correcting the gradation correction table at a density higher than the target density and a graph E for correcting the gradation correction table at a density lower than the target density are shown. Here, the horizontal axis of FIG. 3 indicates the current density value RADC from the ADC sensor 10 to the target density value RADC.
Represents the difference value ΔRADC, and the vertical axis represents the correction amount (ΔLUT) for correcting the gradation correction table, which corresponds to the difference value ΔRADC. The slope of the graph D at a density higher than the target density is smaller than the slope of the graph C at the target density. On the other hand, the slope of the graph E at a density lower than the target density is the graph C at the target density.
Greater than the slope of. From the graphs C and D, when forming the toner patch 20 this time, if the previously measured density of the toner patch 20 exceeds the target density, the same correction amount can be obtained by forming the toner patch 20 having a higher area ratio than the previous time. (ΔLUT) is enough. From the graphs C and E, when the toner patch 20 is formed this time and the previously measured density of the toner patch 20 is lower than the target density,
It can be seen that the same correction amount (ΔLUT) can be obtained by forming the toner patch 20 having a lower area ratio than the previous time.

Further, in the image forming apparatus 100 of this embodiment, as described above, the toner tanks 5Y, 5M, 5C,
5K and toner remaining amount sensor 11Y, 1 for detecting that these toner tanks 5Y, 5M, 5C, 5K have become empty
1M, 11C, 11K are provided, and when it is detected that one of the toner remaining amount sensors 11Y, 11M, 11C, 11K or a plurality of toner remaining amount sensors has emptied the toner tank. , And shift to the formation of a toner patch with a predetermined high area ratio. This will be described below with reference to FIGS. 4 and 5.

FIG. 4 is a diagram showing the relationship between the remaining toner amount and the output of the remaining toner amount sensor.

The horizontal axis represents the toner remaining amount value, and the vertical axis represents the output value of one of the toner remaining amount sensors 11Y, 11M, 11C and 11K. The output value of the toner remaining amount sensor increases as the toner remaining amount decreases. Here, when the toner becomes empty, a value Tex indicating that the toner is exhausted from the toner remaining amount sensor
Is output.

FIG. 5 is a diagram showing the relationship between the toner remaining amount sensor output and the image data Cin.

The horizontal axis represents the output value of the toner remaining amount sensor,
The vertical axis represents the value (0 to 255) of the image data Cin.
When the toner becomes empty, the value T
ex is output. Then, the value of the image data Cin is set to a large value, whereby the process shifts to the formation of a toner patch having a predetermined high area ratio.

FIG. 6 is a graph in the case where the exposure beam light amount is controlled based on the output value of the ADC sensor of the toner patch having a halftone area ratio when the remaining amount of toner is low.

The horizontal axis of FIG. 6 shows the image data Cin,
The vertical axis represents the image output level Dout of the ADC sensor 10 for the toner patch 20 having a halftone area ratio formed corresponding to the image data Cin. Here, the graph A in FIG. 6 is an ideal graph in which the target density is set. Further, the graph B shows that the image output level Dou in the ideal graph A is due to the decrease in the toner remaining amount.
7 is a graph before correction in which an image output level Dout smaller than t is output. Further, in order to bring the graph B closer to the ideal graph A, the graph C is such that the image output level Dout in the image data Cin (value P) representing the halftone area ratio matches the value on the graph A. 5 is a graph obtained by correcting the light quantity of the exposure beam. However, the portion of the graph C in the highlight region (high density region) exceeding the value P exceeds the ideal value of the graph A. Therefore, the highlight area is overcorrected.

FIG. 7 is a graph when the amount of exposure beam light is controlled based on the output value of the ADC sensor of a toner patch having a predetermined high area ratio when the amount of remaining toner is low.

The graph C'shows the image output level Dou in the image data Cin (value Q) representing a predetermined high area ratio.
9 is a graph obtained by correcting the light amount of the exposure beam so that t matches the value on graph A. By correcting in this way, the portion of the graph C ′ in the highlight region can be made closer to the ideal graph A.
Therefore, the highlight area is corrected with high accuracy.

Further, the image forming apparatus 100 of the present embodiment.
In addition, when the exposure beam is adjusted to a light amount equal to or higher than a predetermined light amount (LD light amount upper limit value), the process shifts to the formation of a toner patch having a predetermined high area ratio. Below, FIG.
This will be described with reference to FIG.

FIG. 8 is a graph showing the light quantity value of the exposure beam with respect to the output value of the ADC sensor.

The horizontal axis of FIG. 8 represents the output value RADC of the ADC sensor 10, and the vertical axis represents the light quantity value (LD light quantity value) of the exposure beam. The value LDup is the upper limit value of the LD light amount value. Here, the toner patch 20 is formed with a fixed LD light quantity value, and the LD light quantity value is uniquely obtained from the measurement value obtained by measuring the toner patch 20 with the ADC sensor 10. The toner patch 20 formed by the LD light amount value may be measured by the ADC sensor 10 to obtain the measured value, and the difference from the previous LD light amount value may be corrected to obtain the LD light amount value.

FIG. 9 is a diagram showing the relationship between the LD light amount value obtained in FIG. 8 and the image data Cin.

The horizontal axis represents the LD light amount value, and the vertical axis represents the value (0 to 255) of the image data Cin. Here, in response to the LD light amount value reaching the upper limit value LDup, the value of the image data Cin is set to a large value, whereby the process shifts to the formation of a toner patch having a predetermined high area ratio.

FIG. 10 is a gradation reproduction characteristic diagram when the LD light quantity value is less than the upper limit value.

The horizontal axis of FIG. 10 represents the image data Cin, and the vertical axis thereof represents the toner patch 20 of the ADC sensor 10 having the halftone area ratio formed corresponding to the image data Cin.
The image output level Dout for Here, the graph A is an ideal graph in which the target density is set. Further, the graph B is a graph before correction in which the image output level Dout smaller than the image output level Dout in the ideal graph A is output due to the decrease in the LD light amount. Further, the graph C is a graph that is corrected with the image data Cin (value P) representing the halftone area ratio as the center in order to bring the graph B closer to the ideal graph A. Here, the corrected graph C is almost ideal until near the halftone, but the part in the highlight region is excessively corrected.

FIG. 11 is a gradation reproduction characteristic diagram when the LD light amount value is the upper limit value.

In this embodiment, the LD light quantity value is the upper limit value LD.
In response to the up status, the process shifts to the formation of the toner patch 20 having a predetermined high area ratio. Since the density of the toner patch 20 is measured by the ADC sensor and the density control is performed based on the measurement result, the portion in the highlight region can be brought close to the ideal graph A.

Further, the image forming apparatus 100 of the present embodiment.
Is one of the developing units 3Y, 3M, 3C, 3K
When the amount of toner in one or a plurality of developing units decreases below a predetermined level, the process shifts to the formation of a toner patch having a predetermined high area ratio. This will be described below with reference to FIGS. 12 and 13.

FIG. 12 is a diagram showing the relationship between the toner density and the output of the toner density sensor (ATC sensor).

When the toner concentration is high, the output value from the ATC sensor is low, and the ATC sensor becomes lower as the toner concentration decreases.
The output value from the sensor is high. In addition, in FIG. 12,
A value TC, which is output from the ATC sensor and indicates a toner concentration decrease determination level for determining whether the toner concentration has decreased
th is shown.

FIG. 13 is a diagram showing the relationship between the output value of the ATC sensor and the image data Cin.

A value TCt indicating the toner density decrease determination level
In response to h becoming the upper limit value LDup, the value of the image data Cin is set to a large value, whereby the process shifts to the formation of a toner patch having a predetermined high area ratio. The following description is omitted because it is the same as the case when the remaining amount of toner is low as shown in FIGS. 6 and 7 described above, but the highlight region is corrected with high accuracy. Here, the example in which the toner in the developing device is reduced to the predetermined amount or less has been described, but even if a state having a correlation with this is generated, the process shifts to the formation of a toner patch of a predetermined high area ratio. By doing so, the accuracy of density correction can be improved.

In this embodiment, the toner tank 5Y,
An example in which the process shifts to the formation of a toner patch of a predetermined high area ratio when it is detected that one or more toner tanks of 5M, 5C, and 5K are empty is described. If any one or a plurality of toner tanks among the tanks 5Y, 5M, 5C, and 5K is empty, and the density is maintained by controlling the light amount of the exposure beam or the gradation control in such a toner density lowered state. When the toner concentration is restored from the lowered toner concentration state to the high toner concentration state by mounting a new toner tank (toner cartridge), it is necessary to greatly change the control state of the light amount of the exposure beam or the gradation control. In particular, when the toner concentration is reduced to the limit state, the amount of change is extremely large, and the control performance immediately after recovery of the toner concentration is unavoidable. Therefore,
Immediately after the toner density is recovered, the light amount control of the exposure beam is changed to a correction value from a predetermined light amount instead of the control based on the correction amount from the normal fully open light amount, and gradation control is not corrected (through).
The correction amount is suppressed to be small by performing the correction from the state of. By doing so, it is possible to improve the density correction accuracy immediately after the recovery of the toner density.

Further, the accuracy of the density correction can be further improved by considering the environment correction and the deterioration correction for the predetermined light amount or gradation control amount immediately after the toner density recovery.

Further, in the present embodiment, when the toner patch having the halftone area ratio is formed, and the toner patch previously measured by the ADC sensor 10 exceeds the target density when forming the toner patch this time, Although the explanation has been given mainly on the example of forming a toner patch having a higher area ratio than A,
When the toner patch measured last time by the DC sensor 10 is lower than the target density, a toner patch having a lower area ratio than the previous time may be formed, and the present invention is not limited to these, and the present invention is not limited to the above. In adjusting the image forming condition means that affects the image formed on the recording medium, the area ratio of the toner patch to be formed is changed under a predetermined condition to form the toner patch having the changed area ratio. Anything will do.

[0052]

As described above, according to the image forming apparatus of the present invention, it is possible to accurately adjust the image forming conditions that affect the image finally formed on the recording medium.

[Brief description of drawings]

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

2A and 2B are a graph of an ideal gradation correction table and a graph of a corrected gradation correction table in the image forming apparatus shown in FIG.

FIG. 3 is a diagram showing a graph for correcting a gradation correction table at a predetermined density.

FIG. 4 is a diagram illustrating a relationship between a remaining toner amount and a remaining toner amount sensor output.

FIG. 5 is a diagram showing a relationship between a toner remaining amount sensor output and image data Cin.

FIG. 6 is a graph when the exposure beam light amount is controlled based on the ADC sensor output value of a toner patch having a halftone area ratio when the toner remaining amount is low.

FIG. 7 is a graph when the amount of exposure beam light is controlled based on the output value of the ADC sensor of a toner patch having a predetermined high area ratio when the amount of remaining toner is low.

FIG. 8 is a graph showing a light amount value of an exposure beam with respect to an output value of an ADC sensor.

9 is an LD light amount value and image data Ci obtained in FIG.
It is a figure which shows the relationship of n.

FIG. 10 is a gradation reproduction characteristic diagram when the LD light amount value is less than the upper limit value.

FIG. 11 is a gradation reproduction characteristic diagram when the LD light amount value is the upper limit value.

FIG. 12 is a diagram showing a relationship between a toner concentration and an output of a toner concentration sensor (ATC sensor).

FIG. 13 is a diagram showing a relationship between an output value of an ATC sensor and image data Cin.

[Explanation of symbols]

1Y, 1M, 1C, 1K photoconductor 2Y, 2M, 2C, 2K charger 3Y, 3M, 3C, 3K developing device 4Y, 4M, 4C, 4K transfer device 5Y, 5M, 5C, 5K toner tanks 6Y, 6M, 6C, 6K Toner supply motor 7Y, 7M, 7C, 7K ATC sensor 8 Intermediate transfer belt 9 drive roll 10 ADC sensor 11Y, 11M, 11C, 11K Toner level sensor 20 color toner patch 30 ROS (raster scanning device) 40 controller 41 Look-up table LUT 50 gradation control section 60 LD light quantity control unit 70 TC control unit 100 image forming apparatus

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yama ▲ Saki ▼ Naoya             Fuji Zero, 2274 Hongo, Ebina City, Kanagawa Prefecture             Co., Ltd. Ebina Office (72) Inventor Masahiro Gazuma             Fuji Zero, 2274 Hongo, Ebina City, Kanagawa Prefecture             Co., Ltd. Ebina Office F-term (reference) 2H027 DA09 DD02 DE02 EA02 EA18                       EB04

Claims (6)

[Claims] 1. An image forming apparatus for forming an image of a fixed toner image on a recording medium by forming a toner image and finally fixing the toner image on the recording medium, the toner having a predetermined area ratio. A patch forming unit for forming a patch, a patch density measuring unit for measuring the density of the toner patch, and an image finally formed on a recording medium according to the density of the toner patch measured by the patch density measuring unit. Image forming condition adjusting means for adjusting an image forming condition having an influence, wherein the patch forming means changes the area ratio of the toner patch to be formed under a predetermined condition to obtain the toner patch having the changed area ratio. An image forming apparatus characterized by being formed. 2. The patch forming means forms a toner patch having a halftone area ratio, and in forming the toner patch this time, when the density of the toner patch previously measured by the patch density measuring means is changed, 2. The image according to claim 1, wherein a toner patch having an area ratio higher than that of the previous time and a toner patch having an area ratio lower than that of the previous time are respectively formed when the target density is higher or lower than the target density. Forming equipment. 3. The image forming apparatus forms an electrostatic latent image on the photoconductor by scanning the photoconductor with an exposure beam modulated according to an image signal, and the electrostatic latent image is formed by a toner. A toner image is formed by developing with a developing device that holds a developer composed of a mixture of toner and carrier inside and develops the electrostatic latent image with the toner in the developer. The patch forming means forms a toner patch having a predetermined halftone area ratio, and when the toner in the developing device is reduced to a predetermined amount or less, or a state correlated with this occurs. In some cases, the process shifts to the formation of a toner patch having a predetermined high area ratio.
The image forming apparatus described. 4. A sensor for measuring a ratio of toner to a carrier in the developing device is provided, and the patch forming unit determines a predetermined value when the sensor detects that the toner ratio has decreased to a predetermined value or less. The image forming apparatus according to claim 1, wherein the image forming apparatus is for forming a toner patch having a high area ratio. 5. A toner tank, a sensor for detecting that the toner tank is empty, and a toner replenishing means for replenishing the toner in the toner tank to the developing device. The image forming apparatus according to claim 1, wherein when the sensor detects that the toner tank is empty, the process shifts to forming a toner patch having a predetermined high area ratio. 6. The image forming condition adjusting means adjusts a light quantity of the exposure beam, and the patch forming means receives the light quantity of the exposure beam adjusted to a predetermined light quantity or more. The image forming apparatus according to claim 1, wherein the image forming apparatus shifts to forming a toner patch having a predetermined high area ratio.