JP5910940B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine. Specifically, a toner image obtained by developing a latent image on a latent image carrier with a two-component developer is finally formed on a recording material. The present invention relates to an image forming apparatus that performs image formation by transferring to the above.

  A two-component developer containing toner and carrier (hereinafter simply referred to as “developer”) used in an electrophotographic image forming apparatus is circulated and conveyed along a developer circulation conveyance path in a developing device (developing means). As a result, the toner is dispersed in the developer and the toner is charged. During the image forming operation, the developer is continuously circulated and conveyed in the developing device. When the toner in the developer is consumed by the image formation, the consumed toner is replenished by the toner replenishing means.

  In general, the toner replenishing operation is controlled so that the toner density of the developer in the developing device is detected by a toner density sensor, and the toner is replenished so that the difference value between the detection result and the target toner density becomes small. Many toner concentration sensors are of the magnetic permeability type that detects the magnetic permeability of the developer having a high correlation with the toner concentration. In the case of a magnetic density toner density sensor, even if the developer has the same toner density, the sensor output value changes when the density of the developer present in the detection region changes. If this is the case, erroneous detection of toner density occurs. In many cases, toner replenishment control is performed by detecting the toner density during image forming operation in which the developer in the developing device is circulated and transported. Know the toner density.

  During the period from the end of the image forming operation to the next image forming operation (hereinafter referred to as “leaving period”), from the viewpoint of preventing the deterioration of the developer and reducing the power consumption, the circulation of the developer is stopped. . When the circulation conveyance is stopped, the air taken into the developer during the circulation conveyance is released, the volume of the developer is reduced, and the developer density is increased. Therefore, at the initial stage of the image forming operation performed after a relatively long standing period, the developer density is higher than expected, and the toner density is erroneously detected to be low. As a result, a larger amount of toner than the original toner is replenished, and a large amount of insufficiently charged toner is generated in the developer in the developing device, which easily causes problems such as background contamination and toner scattering. In addition, during the leaving period, the charge of the toner that has been frictionally charged by the circulatory conveyance is gradually removed, so that the toner existing in the developing device from before the toner replenishment is also in a state where the charge amount has dropped. Therefore, in the initial stage of the image forming operation performed after a relatively long standing period, problems such as background stains and toner scattering are likely to occur.

  In Patent Document 1, a difference value between the output value of the toner density sensor measured during the warm-up operation prior to the image forming operation after being left and the output value before being left is calculated, and this difference value is calculated from a predetermined value. Is also large, an image forming apparatus is disclosed in which the toner density reference value (target toner density) is increased. Since the output value of the toner density sensor becomes higher than the original value, it is possible to suppress a situation where toner is excessively replenished after being left.

  Further, when a certain period (for example, a period until the image formation of 50 sheets is completed) after the image forming operation is started after being left, the developer density is restored to the assumed value, and the output value of the toner density sensor Indicates the correct toner density. For this reason, if the changed toner density reference value is continuously used even after the fixed period has elapsed, the actual toner density becomes lower than the target toner density, and the image density becomes light. Therefore, in the image forming apparatus of Patent Document 1, in the image forming operation after being left, the toner supply is performed using the changed toner density reference value until the predetermined period elapses, and after the predetermined period elapses, the change is performed. The toner is replenished by returning to the previous toner density reference value.

  In Patent Document 2, when the difference between the output value of the toner density sensor during warm-up after power-on and the output value immediately before power-off is greater than a predetermined value, it is consumed by image formation. An image forming apparatus is disclosed that supplies a replenishment amount of toner corresponding to the amount of toner to be supplied. In this image forming apparatus, even if an erroneous detection of the toner concentration sensor occurs due to an increase in developer density during the leaving period from when the power is turned off to when it is next turned on, the remaining period is a quantitative replenishment. The output value of the density sensor is not used for toner supply control. Therefore, it is possible to suppress a situation where the toner is excessively replenished after being left.

  However, in the image forming apparatus disclosed in Patent Document 1, after a certain period of time has elapsed since the image forming operation was started after being left, the toner density is replenished by returning to the toner density reference value before the change. Therefore, at the timing when the toner density reference value is returned, the toner replenishment operation greatly fluctuates, and the toner density in the developer is temporarily changed greatly. Therefore, there arises a problem that a large change occurs in the image density before and after the timing for returning the toner density reference value.

  Further, in the image forming apparatus of Patent Document 2, in the quantitative replenishment performed during the image forming operation after the leaving period, the toner replenishment amount is an average toner consumption amount per copy of the image forming apparatus (for example, , The toner amount corresponding to (solid image) of about 6% per A4 size copy. For this reason, if the actual toner consumption consumed by the image forming operation deviates significantly from the average toner consumption, the toner concentration in the developer deviates significantly from the target toner concentration, and the appropriate image density Cannot form an image.

  The present invention has been made in view of the above background, and an object of the present invention is to maintain an appropriate toner concentration in an image forming operation after a leaving period and to suppress background contamination and toner scattering while suppressing image density. It is an object of the present invention to provide an image forming apparatus capable of suppressing the fluctuation of the image.

To achieve the above object, the present invention is formed on a latent image carrier, latent image forming means for forming a latent image on the latent image carrier based on image information, and the latent image carrier. A developing device that develops a latent image using a two-component developer containing toner and a carrier, a toner replenishing unit that replenishes toner in the developing device, and a toner concentration in the two-component developer in the developing device Toner density detecting means for detecting toner, and toner density control means for executing normal toner density control for controlling the toner replenishing operation by the toner replenishing means based on the comparison result between the detection result by the toner density detecting means and the target toner density in the image forming apparatus having the bets, the toner density control means, when starting the next image forming operation after completion of the previous image forming operation after a predetermined unused period, or to start an image forming operation of said next The special toner density control is executed until a predetermined special toner density control end time is reached, and the normal toner density control is executed after the special toner density control is finished. A toner consumption index value indicating a toner consumption amount consumed in image formation based on the image information is calculated, and if the calculated toner consumption index value is equal to or less than a specified value, the previous image forming operation based on the detection result of the toner concentration detecting means in controlling the toner supply operation, when the calculated toner consumption index value exceeds the specified value, waiting for the arrival of the predetermined special toner density control end time And the special toner supply control is terminated.

In the present invention, in the special toner density control performed before executing the normal toner density control, when the toner consumption amount in the next image forming operation is small (when the toner consumption amount index value is equal to or less than the specified value). The toner replenishing operation is controlled based on the detection result by the toner density detecting means during the previous image forming operation. Therefore, since it is not used for the detection result by the toner density detection means during the next image forming operation, even if the developer density increases due to being left to cause false detection, the toner supply operation based on the erroneous detection result Therefore, the toner is not replenished excessively. Further, when the toner consumption is small, the change in the toner density in the developer is small. Therefore, it is assumed that the predetermined special toner density control is completed for a certain period after the start of the next image forming operation. Even if the amount of toner replenishment becomes small or when toner replenishment is not performed, a situation in which the image density is largely insufficient during that period does not occur.

Here, when the toner consumption in the next image forming operation after being left is large, the present inventor does not detect the actual toner concentration in the developer even if a large amount of toner is supplied due to erroneous detection by the toner concentration detecting means. Was not so high, and new knowledge was obtained that stains on the surface and toner scattering were less likely to occur. In other words, a large amount of toner is replenished due to erroneous detection of the toner density detection means, and the background stain or toner scattering is likely to occur when an image forming operation with less toner consumption is performed in the next image forming operation after being left. When an image forming operation that consumes a large amount of toner is executed, background stains and toner scattering are less likely to occur.

Therefore, in the special toner density control of the present invention, based on this new knowledge, when the toner consumption is large (when the toner consumption index value exceeds the specified value), the developer density increases due to leaving it and the false detection. Even in such a situation, the special toner density control is terminated and the normal toner density control is executed. As a result, even when the next image forming operation is executed with a toner consumption amount that greatly exceeds the average toner consumption amount per image, the toner replenishment amount is the same as that of the image forming apparatus of Patent Document 2 described above. Compared with the case of fixed replenishment fixed at an average toner consumption per sheet, the actual toner density in the developer can be made to follow the target toner density, and an image can be formed with an appropriate image density. It becomes possible to do.

  As described above, according to the present invention, it is possible to obtain an excellent effect that image density fluctuations can be suppressed while maintaining an appropriate toner density in an image forming operation after a leaving period and suppressing background contamination and toner scattering.

1 is a schematic configuration diagram illustrating a main part of a copier according to an embodiment. FIG. 2 is an explanatory diagram illustrating a configuration of a first developing device in the copier. 6 is a flowchart illustrating a flow of special toner replenishment control that is executed when power is turned on or when returning from a standby mode in the embodiment.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic copying machine as an image forming apparatus will be described.
The copying machine of this embodiment is a two-color digital image forming apparatus by reversal development that forms an image based on image information read by a scanner or image information input from an external device such as a personal computer on a recording material such as paper. It is. Specifically, a first color toner image and a second color toner image are formed on a surface of a photosensitive member as a latent image carrier so as to overlap each other, and these toner images are collectively put on a recording material. Transcript. The present invention is not limited to the copying machine according to the following embodiments, and can be widely applied to various types of image forming apparatuses.

First, a basic configuration of the copying machine according to the present embodiment will be described.
FIG. 1 is a schematic configuration diagram showing the main part of the copying machine according to the present embodiment.
The photoconductor 1 of the present copying machine is formed by sequentially laminating a charge generation layer and a charge transport layer on the peripheral surface of a drum-shaped conductive substrate, and is rotatably supported. It is driven to rotate in a constant direction at 250 [mm / sec]. A first image forming unit for forming a first color toner image and a second image forming unit for forming a second color toner image around the photoconductor 1 in the direction of movement of the photoconductor surface. They are arranged side by side.

  The first image forming unit includes a first charging device 2A for uniformly charging the surface of the photoreceptor 1 and a first toner on the surface of the photoreceptor 1 based on image information such as a document image signal read by the scanner. A first exposure device (not shown) that irradiates writing light L1 for forming a first electrostatic latent image for an image, and a first electrostatic latent image is developed with a first color toner to form a toner image. The first developing device 3A. In this embodiment, a case where black toner is used as the first color toner will be described as an example.

  The second image forming unit performs photosensitivity based on the second charging device 2B that uniformly charges the surface of the photoreceptor 1 on which the first color toner image is formed, and image information such as an original image signal read by the scanner. A second exposure device (not shown) that irradiates writing light L2 for forming a second electrostatic latent image for the second toner image on the surface of the body 1, and the second electrostatic latent image as a second color toner. And a second developing device 3B that forms a toner image by developing the toner image. In the present embodiment, a case where red toner is used as the second color toner will be described as an example.

  In addition, a transfer device 4 is provided around the photoconductor 1 to transfer the first color toner image and the second color toner image formed on the surface of the photoconductor 1 to a recording paper P as a recording material in a lump. ing. The transfer device 4 sandwiches a recording sheet P fed from a sheet feeding unit (not shown) between a transfer belt 4c stretched around support rollers 4a and 4b and the surface of the photosensitive member 1, and supports the support roller 4a. On the other hand, a voltage having a polarity opposite to the normal charging polarity of the toner is applied to transfer the toner image on the photoreceptor onto the recording paper P. The recording paper P to which the toner image has been transferred is conveyed to a fixing device (not shown) while being carried on the transfer belt 4c of the transfer device 4, and the toner image is recorded and fixed to P by heat and pressure.

  Further, around the photosensitive member 1, there is a cleaning device 5 for removing toner remaining on the surface of the photosensitive member after the transfer by a cleaning blade 5a and a cleaning brush 5b, and the surface of the photosensitive member 1 in preparation for the next image formation. A static elimination device 6 made of an LED for removing electric charges is also arranged.

  The first developing device 3 </ b> A in this embodiment includes a first developing roller that is a developer carrying member in a developing case that is opened at a position facing the surface of the photoreceptor 1. The surface of the first developing roller faces the surface of the photoreceptor 1 with a predetermined distance through the opening of the developing case. A two-component developer composed of a magnetic carrier and toner is accommodated in the developing case of the first developing device 3A. The first developing roller is rotationally driven by a driving unit (not shown) in a state where a developer is carried on the outer peripheral surface by a magnetic field generating unit arranged inside the first developing roller. Then, the developer carried on the first developing roller rises in a brush shape by the action of a magnetic field in the developing region facing the surface of the photoreceptor 1 and contacts the surface of the photoreceptor 1.

  On the other hand, the second developing device 3B according to the present embodiment includes a second developing roller that is a developer carrying member in a developing case that is opened at a position facing the surface of the photoreceptor 1. The surface of the second developing roller faces the surface of the photoreceptor 1 with a predetermined distance through the opening of the developing case. In the developing case of the second developing device 3B, a one-component developer made of nonmagnetic toner not containing a magnetic carrier is accommodated. The second developing roller is rotationally driven by a driving unit (not shown) with toner carried on the outer peripheral surface. The toner layer formed on the second developing roller passes through the developing area in a non-contact state with respect to the surface of the photoreceptor 1.

  In the present embodiment, a non-contact developing method is employed as a developing method of the second developing device 3B so that the first color toner image formed in the first image forming unit is not disturbed by the rubbing of the developer or the like. However, a contact development method may be adopted. When adopting the contact development method, for example, a developing roller having an elastic layer made of a general rubber material such as silicon rubber, NBR rubber, EPDM rubber, urethane rubber on the surface of a metal core metal, It may be used as the second developing roller.

FIG. 2 is an explanatory diagram showing the configuration of the first developing device 3A in the present embodiment.
The first developing device 3A includes two conveying screws 32 for circulating and conveying a developer composed of a magnetic carrier and toner in the developing case. The first developing device 3 </ b> A includes a doctor 33 as a developer regulating member that regulates the amount of developer that is transported to the developing region by regulating the developer supplied onto the first developing roller 31. The first developing device 3A includes a toner concentration sensor 36 as a toner concentration detecting unit that detects the toner concentration in the developer in the developing case. As the toner concentration sensor 36, a general magnetic permeability sensor is used.

  Further, the first developing device 3A in the present embodiment is provided with a toner bottle unit 34 as a toner replenishing means in which a toner bottle containing replenishing toner is set. The toner bottle unit 34 includes a toner transport mylar 35 for transporting the replenishment toner in the toner bottle to the developing case. By rotating the toner transport mylar 35 in the clockwise direction in the figure, the replenishment toner in the toner bottle can be sent out to the developing case, and by controlling the rotational driving time of the toner transport mylar 35, The amount of toner to be replenished to the developer can be adjusted.

The toner replenishment control (normal toner replenishment control) during the normal operation of the present embodiment is performed as follows.
At a predetermined timing during the image forming operation (for example, timing when the recording paper P passes through the transfer region), the toner density sensor 36 detects the toner density and acquires the sensor output value Vt. Then, a difference value between the sensor output value Vt and a toner density reference value Vref which is a target toner density stored in advance is calculated, and the sensor output value Vt exceeds the toner density reference value Vref (detected toner). When the density is lower than the target toner density), the toner transport mylar 35 is driven to rotate and a toner supply operation is executed.

Next, the special toner replenishment control executed when the power is turned on or when returning from the standby mode, which is a characteristic part of the present invention, will be described.
Here, a case where the special toner replenishment control is executed when the power is turned on or when returning from the standby mode is taken as an example. However, if it is time to start the image forming operation after a relatively long standing period, There is no limitation when returning from the standby mode.

FIG. 3 is a flowchart showing the flow of special toner replenishment control that is executed when the power is turned on or when returning from the standby mode in the present embodiment.
In the present embodiment, the toner density sensor 36 before the main power is turned off or before the transition to the standby mode (the state where the power supply to a predetermined device is stopped and the image forming operation is stopped while the main power is on). Sensor output value Vt0 is held in a storage device (non-volatile memory) (not shown). When the power is turned on or when returning from the standby mode, first, predetermined processing for image forming operation such as warm-up of the fixing device is executed (S1). However, in this embodiment, the warm-up operation of the first developing device 3A (the operation of rotating the two conveying screws 32) is not executed. The rotation driving of the conveying screw 32 of the first developing device 3A is started in accordance with the start of the image forming operation.

  When the pre-processing is completed in this way, an image forming operation is started (S2). First, the first recording sheet P is passed through and an operation for forming an image is performed (S3). . Then, as in the case of the normal toner replenishment control, for example, the toner density is detected by the toner density sensor 36 at the timing when the recording paper P passes the transfer area (S4). In this embodiment, the number of pixels of the first image is counted based on the image information, and the image is an image occupation rate per unit area (image area area of the recording paper P) based on the number of pixels. The area ratio S is calculated (S5).

  Thereafter, it is determined whether or not the calculated image area ratio S is equal to or less than a specified value (25% in the present embodiment) (S6). In this determination, if it is determined that it is not less than 25% (No in S6), the previous sensor output value Vt0 held in the non-volatile memory (before the main power is turned off or before shifting to the standby mode) Is updated to the sensor output value Vt acquired in step S4, and the normal toner supply control for controlling the toner supply operation based on the difference value between the sensor output value Vt and the toner density reference value Vref. (S10).

  As described above, when forming an image with an image area ratio that is not less than 25%, that is, an image with a large amount of toner consumption that exceeds 25%, as described above, Misdetection that the leaving period before returning from the standby mode is long, the developer density in the first developing device 3A is increased, and the sensor output value Vt acquired in step S4 does not indicate the original toner concentration. Even if the result is, the toner is not replenished excessively by the toner replenishment control (normal toner replenishment control) based on the sensor output value Vt indicating the erroneous toner density, and the background stain or the toner scattering is not caused.

  Subsequently, when it is determined in step S6 that the image area ratio S is 25% or less (Yes in S6), the sensor output value Vt acquired in step S4 is then stored in the nonvolatile memory. It is determined whether or not the value is greater than a predetermined value (0.2 [V] in the present embodiment) above the previous sensor output value Vt0 held at (S7). In this determination, if it is determined that the sensor output value Vt does not exceed the previous sensor output value Vt0 by a specified value or more (No in S7), the previous sensor output value held in the nonvolatile memory. Vt0 is updated to the sensor output value Vt acquired in step S4, and the process shifts to normal toner supply control for controlling the toner supply operation based on the difference value between the sensor output value Vt and the toner density reference value Vref (S10). ).

  As described above, when the sensor output value Vt does not exceed the previous sensor output value Vt0 by 0.2 [V] or more, the sensor output value Vt acquired in step S4 described above causes background stains and toner scattering. This does not include an error that causes excessive toner replenishment. Therefore, even if the toner replenishment control (normal toner replenishment control) based on the sensor output value Vt acquired in step S4 is performed, background stains and toner scattering are not caused.

  Subsequently, if it is determined in step S7 that the sensor output value Vt exceeds the previous sensor output value Vt0 by 0.2 [V] or more (Yes in S7), then, It is determined whether the number N of sheets that have passed since the start of the image forming operation has reached nine (S8). In this determination, if it is determined that the number of sheets N has reached nine (Yes in S8), the previous sensor output value Vt0 held in the nonvolatile memory is obtained as the sensor output value acquired in step S4. Vt is updated to normal toner supply control for controlling the toner supply operation based on the difference value between the sensor output value Vt and the toner density reference value Vref (S10).

  The developer in the first developing device 3A is sufficiently agitated by the conveying screw 32 when the number N of sheets passing after the start of the image forming operation reaches nine. For this reason, even if the number N of sheets passed reaches 9, the sensor output value Vt exceeds the previous sensor output value Vt0 by 0.2 [V] or more, which means that the sensor output value Vt is no longer neglected. It can be said that this is not an error due to the result of the increase in developer density during the period but an actual toner density. Therefore, in this embodiment, the toner concentration of the developer in the first developing device 3A can be corrected to the target toner concentration by shifting to the normal toner replenishment control in this case.

  On the other hand, if it is determined in step S8 that the sheet passing number N has not reached nine (No in S8), the image forming operation has a toner consumption amount in which the image area ratio S is 25% or less. Since a small image is formed and the sensor output value Vt includes an error due to an increase in developer density during the leaving period, the previous sensor output value Vt0 held in the nonvolatile memory The sensor output value Vt acquired in step S4 is not updated. Thus, the toner replenishing operation is controlled based on the difference value between the previous sensor output value Vt0 and the toner density reference value Vref (S9). As a result, even if the sensor output value Vt acquired in step S4 is a result of erroneous detection that does not indicate the original toner concentration, the toner supply control based on the sensor output value Vt indicating the incorrect toner concentration causes Will not be replenished excessively, and background stains and toner scattering will not occur.

The toner replenishing operation performed during the first image forming operation when the power is turned on or when returning from the standby mode is performed by the previous sensor output value Vt0 and the toner density reference value Vref held in the nonvolatile memory. Is controlled based on the difference value.
Further, when the main power is turned off or when shifting to the standby mode, the count value of the number N of sheets that have passed since the start of the image forming operation is cleared.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A latent image carrier such as the photosensitive member 1; a latent image forming unit such as a first exposure device that forms a latent image on the latent image carrier based on image information; and a latent image formed on the latent image carrier. A developing device such as a first developing device 3A that develops an image using a two-component developer containing toner and a carrier; a toner replenishing means such as a toner bottle unit 34 that replenishes toner in the developing device; Toner density detecting means such as a toner density sensor 36 for detecting the toner density in the two-component developer in the developing device, a detection result (sensor output value Vt) by the toner density detecting means, and a target toner density (toner density reference value) In an image forming apparatus having a toner density control unit such as a control unit (not shown) that executes normal toner density control for controlling a toner supply operation by the toner supply unit based on a comparison result with Vtref). The toner density control means executes the special toner density control from the start of the image forming operation until the predetermined special toner density control end time comes, and executes the normal toner density control after the special toner density control is finished. In the special toner density control, a toner consumption index value such as an image area ratio S indicating the toner consumption consumed in image formation based on the image information is calculated based on the image information, and the calculated toner When the consumption index value is equal to or less than the specified value (S ≦ 25%), the detection result (sensor output value Vt0) by the toner density detection unit during the image forming operation performed before the start of the image forming operation is obtained. If the calculated toner consumption index value exceeds the specified value, the special toner concentration control end value is not waited for and the special toner concentration control value is calculated. Characterized by terminating the toner replenishment control.
According to this, as described above, it is possible to suppress fluctuations in the image density while maintaining an appropriate toner density in the image forming operation after the leaving period and suppressing background contamination and toner scattering.
In particular, in a wide image forming apparatus (wide machine) capable of printing A2 size or larger, the main scanning of the developing device is larger than an image forming apparatus in which the print width (length in the main scanning direction of the image area) is A3 size or less. The direction dimension is large. For this reason, the developer circulation conveyance path is long, and it takes time for the supplied toner to be sufficiently mixed with the developer in the developing device to obtain a sufficient charge amount. Therefore, background contamination and toner scattering are likely to occur. Therefore, this aspect is particularly useful for wide machines.
Further, in the conventional image forming apparatus, the toner density is detected while the developing device is warmed up before the image forming operation after the leaving period, and the toner is excessively replenished after being left by using the detection result. Was to suppress. The warm-up operation of the developing device is performed in parallel with the warm-up operation of the fixing device for the purpose of shortening the first print time. Both the warm-up operation of the developing device and the warm-up operation of the fixing device consume a large amount of power. Therefore, a large amount of power is consumed for each image forming operation after the leaving period, and such a large amount of power is consumed. A large-capacity power supply is needed to cover the consumption of energy. In particular, in the case of a wide image forming apparatus (wide machine) capable of printing of A2 size or larger, it is necessary to start up a large fixing device in a short time, and the load torque of the developing device is large. The problems of power consumption and power supply capacity are more serious than general image forming apparatuses of A3 size or smaller. The special toner density control of this aspect does not require the developing device to warm up prior to the image forming operation. Therefore, problems of power consumption and power supply capacity can be reduced as compared with a conventional image forming apparatus that requires a warm-up operation of the developing device.

(Aspect B)
In the aspect A, the predetermined special toner density control end time is a time when an image forming operation of a predetermined operation amount is performed after the image forming operation is started (a time when the number N of sheets to be passed reaches 9). Etc.).
As a result, after the detection result (sensor output value Vt) by the toner density detection means during the image forming operation does not include an error due to the increase in developer density during the leaving period, the development in the first developing device 3A is performed. The toner concentration of the agent can be maintained at the target toner concentration with high accuracy.

(Aspect C)
In the above aspect A or B, the predetermined special toner density control end timing includes the detection result by the toner density detecting means during the image forming operation and the above-mentioned during the image forming operation performed before the start of the image forming operation. It includes a time when the difference from the detection result by the toner density detection means becomes equal to or less than a specified value.
According to this, when the detection result (sensor output value Vt) by the toner density detecting means during the image forming operation does not include an error that causes excessive toner replenishment to cause background contamination or toner scattering. The normal toner replenishment control can be performed to maintain the toner concentration of the developer in the first developing device 3A at the target toner concentration with high accuracy.

(Aspect D)
In any one of the aspects A to C, the toner consumption index value is an image area ratio S of an image formed based on the image information.
According to this, it is possible to grasp the toner consumption consumed by image formation based on the image information with high accuracy from the image information.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2A 1st charging device 2B 2nd charging device 3A 1st developing device 3B 2nd developing device 4 Transfer device 5 Cleaning device 6 Static elimination device 31 Developing roller 32 Conveying screw 33 Doctor 34 Toner bottle unit 35 Toner conveying mylar 36 Toner Concentration sensor

Japanese Patent No. 3537116 Japanese Patent No. 3817366

Claims (4)

A latent image carrier;
Latent image forming means for forming a latent image on the latent image carrier based on image information;
A developing device that develops the latent image formed on the latent image carrier using a two-component developer including a toner and a carrier;
Toner replenishing means for replenishing toner into the developing device;
Toner concentration detecting means for detecting the toner concentration in the two-component developer in the developing device;
In an image forming apparatus having a toner concentration control means for executing normal toner density control for controlling a toner replenishing operation by the toner replenishing means based on a comparison result between a detection result by the toner density detecting means and a target toner density.
When the toner density control means starts the next image forming operation after a predetermined period after the previous image forming operation is finished, the predetermined special toner density control end time is started after the start of the next image forming operation. The special toner density control is executed until the toner arrives, and the normal toner density control is executed after completion of the special toner density control.
In the special toner density control, a toner consumption index value indicating a toner consumption amount consumed in image formation based on the image information is calculated based on the image information, and the calculated toner consumption index value is equal to or less than a specified value. the, if based on the detection result by the toner concentration detection means in the previous image forming operation by controlling the toner supply operation, the calculated toner consumption index value exceeds the predetermined value, the predetermined special An image forming apparatus characterized in that the special toner replenishment control is terminated without waiting for the toner density control end time to arrive. The image forming apparatus according to claim 1.
The predetermined special toner density control end timing includes a timing when an image forming operation of a predetermined operation amount is performed after the start of the next image forming operation. The image forming apparatus according to claim 1 or 2,
The predetermined special toner density control end timing is defined by the difference between the detection result by the toner density detection means during the next image forming operation and the detection result by the toner density detection means during the previous image forming operation. An image forming apparatus including a time when the value becomes less than or equal to a value. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the toner consumption index value is an image area ratio of an image formed based on the image information.

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