JP2005316223A - Image density control unit and image forming apparatus provided with the same, and image density control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize image density, by simply and appropriately controlling toner replenishment to stabilize the toner density, regardless of the changes in the environment, such as humidity and temperature, and deterioration of photoreceptor drum with the lapse of time. <P>SOLUTION: The image density controller unit comprises an image carrier (1), an electrostatic charging means (2) for electrostatically charging the image carrier, an exposure means (3) for forming an electrostatic latent image on the image carrier, a developing means (5) for forming a sensible image by developing the electrostatic latent image by a two-component developer, an image density detecting means (21) for detecting the density of the developed image on the image carrier, a toner density detecting means (22) of the developing means, and a toner replenishing means (20) of the developing means. The controller unit has a control means (25) for applying a prescribed development bias to the electrostatic latent image for a specified time, in a state of holding the surface potential of the image carrier at 0V by the electrostatic charging means, to which a DC voltage of 0V and a prescribed AC voltage are applied, and developing the image and controlling the toner replenishment, according to the density of the developed image read by the image density detecting means and the toner concentration detected by the toner concentration detecting means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image density control apparatus that stabilizes an image density by appropriately controlling a toner density of a developing device, an image forming apparatus including the image density control apparatus, and an image density control method.

  Conventionally, in image forming apparatuses (printers, copiers, facsimiles, multifunction machines, etc.), the image density becomes unstable due to environmental changes such as ambient humidity and temperature, and deterioration of the developer and the photosensitive drum over time. Undesirable phenomena such as missing images and fog may occur. Therefore, as one of the measures for stabilizing the image density, a method of appropriately controlling toner supply in consideration of various influential factors has been adopted.

For example, an image carrier uniformly charged to a predetermined surface potential is developed by a potential difference between the surface potential and a developing bias, and toner is replenished according to the density value of the developed image and the cumulative usage amount of the developer. An image forming apparatus that controls the image is known (for example, see Patent Document 1). This technique is intended to minimize toner density fluctuation by performing toner replenishment control in accordance with the density value of the developed image and the cumulative usage amount of the developer.
Japanese Patent Laid-Open No. 2001-183876 (paragraph 32, FIG. 1)

  By the way, in the technique as described in Patent Document 1, although the deterioration with time (cumulative usage amount) of the developer is taken into consideration, the change in the toner density due to the environmental change in the developing device, the time of the photosensitive drum, and the like. The toner replenishment is controlled according to the density value of the developed image including the influence of the fluctuations without considering the fluctuations in the surface potential of the photosensitive drum due to the deterioration and the environmental change. Therefore, since toner replenishment control is performed based on an index in which many such influential factors are reflected at once, there is a problem that accurate and appropriate control is difficult.

  The present invention has been made on the basis of such knowledge, and it is possible to easily and appropriately control toner replenishment regardless of environmental changes such as humidity and temperature and deterioration of the developer and the photosensitive drum over time. It is an object of the present invention to provide an image density control apparatus, an image forming apparatus including the image density control apparatus, and an image density control method.

  In order to solve such a problem, the image density control device according to the present invention uniformly charges the surface of the image carrier and the image carrier in a state where a predetermined voltage is applied. A charging unit; an exposure unit that exposes a uniformly charged image carrier according to image information to form an electrostatic latent image according to the image information; and at least a carrier in a state where a predetermined developing bias is applied. Developing means for developing and developing an electrostatic latent image with a developer comprising toner, image density detecting means for detecting the density of the developed image on the image carrier, and detecting the toner density in the developing means And a toner replenishing unit for replenishing toner to the developing unit, and the surface potential of the image carrier is held at 0 V by a charging unit to which a DC voltage of 0 V and a predetermined AC voltage are applied. In the state where A bias is applied for a certain period of time, the developing means directly develops the potential difference between the surface potential and the developing bias, and the density of the developed image read by the image density detecting means and the toner density detected by the toner density detecting means Accordingly, a control unit that controls toner supply by the toner supply unit is provided.

  According to this, since the developed image read by the image density detecting means is formed in a state where the surface potential of the image carrier is maintained at 0 V, the influence of environmental change and deterioration with time on the image carrier is all eliminated, and development is performed. Only the influence of environmental change and deterioration with time in the means is reflected. Therefore, by correcting the toner density detected by the toner density detecting means in accordance with the density of the developed image read by the image density detecting means, the influence of the environmental change and deterioration with time of the developing means is reduced. Toner replenishment can be controlled. Therefore, regardless of environmental changes such as humidity and temperature and aging of the developer and the photosensitive drum, toner replenishment can be easily and appropriately controlled to stabilize the developing ability of the developing means.

  According to a second aspect of the present invention, the control means determines an operation amount for changing the toner density in the developing means in accordance with the density of the developed image read by the image density detecting means, and sets the operation amount to a plurality. According to the divided operation amount, the toner supply by the toner supply unit can be controlled stepwise.

  As a result, toner replenishment is controlled based on the division operation amount divided into minute values, so that the occurrence of under-toner or over-toner can be prevented instantaneously, and thin lines in the image can be prevented from being blurred or thin. be able to.

  According to a third aspect of the present invention, the control means determines an operation amount provided with a predetermined variation limit for changing the toner density in the developing means according to the density of the developed image read by the image density detecting means. The toner supply by the toner supply means can be controlled according to the operation amount.

  As a result, toner replenishment can be controlled so that the fluctuation of the toner density in the developing means is within a predetermined range, so that occurrence of under toner or over toner can be prevented in advance, and carrier adhesion, fogging or toner scattering can be prevented. can do.

  Further, according to the image density control apparatus of the present invention, as shown in claim 4, the image carrier, charging means for uniformly charging the surface of the image carrier with a predetermined voltage applied thereto, and charging uniformly The image bearing member is exposed to light according to image information to form an electrostatic latent image according to the image information, and a developer composed of at least a carrier and toner in a state where a predetermined developing bias is applied. Developing means for developing and developing the electrostatic latent image, image density detecting means for detecting the density of the developed image on the image carrier, toner density detecting means for detecting the toner density in the developing means, and development A developer deterioration detecting means for detecting deterioration of the developer in the means with time, a temperature / humidity detecting means for detecting the ambient temperature / humidity of the developing means, and a toner replenishing means for supplying toner to the developing means. The DC voltage and the predetermined AC voltage are marked A predetermined developing bias is applied to the developing means for a predetermined time while the surface potential of the image carrier is held at 0 V by the charging means, and the developing means directly develops with the potential difference between the surface potential and the developing bias. The density of the developed image read by the image density detection means, the deterioration with time of the developer detected by the developer deterioration detection means, the ambient temperature and humidity detected by the temperature and humidity detection means, and the toner density detected by the toner density detection means Accordingly, a control unit that controls toner supply by the toner supply unit is provided.

  According to this, since the developed image read by the image density detecting means is formed in a state where the surface potential of the image carrier is maintained at 0 V, the influence of environmental change and deterioration with time on the image carrier is all eliminated, and development is performed. Only the influence of environmental change and deterioration with time in the means is reflected. For this purpose, the density of the developed image read by the image density detection means, the state of developer deterioration with time detected by the developer deterioration detection means, and the ambient temperature detected by the temperature / humidity detection means are detected by the toner density detection means. By correcting according to the humidity, it is possible to control the replenishment of toner while reducing the influence of environmental changes and deterioration with time of the developing means. Therefore, regardless of environmental changes such as humidity and temperature and deterioration with time of the developer and the photosensitive drum, toner replenishment can be controlled easily and appropriately with high accuracy to stabilize the toner density.

  According to another aspect of the present invention, the control means adjusts the toner density in the developing means according to the density of the developed image read by the image density detecting means, the time-degraded state of the developer, and the temperature and humidity around the developing means. An operation amount to be changed can be determined, and toner supply by the toner supply means can be controlled stepwise in accordance with a divided operation amount obtained by dividing the operation amount into a plurality of operations.

  As a result, toner replenishment is controlled based on the division operation amount divided into minute values, so that the occurrence of under-toner or over-toner can be prevented instantaneously, and thin lines in the image can be prevented from being blurred or thin. be able to.

  According to a sixth aspect of the present invention, the control means sets the toner density in the developing means in accordance with the density of the developed image read by the image density detecting means, the state of deterioration of the developer with time, and the temperature and humidity around the developing means. It is possible to adopt a configuration in which an operation amount provided with a predetermined variation limit for changing is determined, and toner replenishment by the toner replenishing means is controlled according to the operation amount.

  As a result, the control of the toner density in the developing unit can be limited within a predetermined range, so that the occurrence of under toner or over toner that causes the toner density in the developing unit to be outside the allowable range can be prevented, and carrier adhesion or fogging can be prevented. Alternatively, toner scattering can be prevented.

  Furthermore, as shown in claim 7, the image forming apparatus of the present invention is configured to include the image density control device according to any one of claims 1 to 6.

  Further, according to the image density control method of the present invention, as shown in claim 8, an image carrier is applied by applying a DC voltage of 0 V and a predetermined AC voltage to an image carrier for carrying an electrostatic latent image on the surface. A charging step for maintaining the surface potential of the body at 0 V, and applying a predetermined developing bias in a state where the surface potential of the image carrier is maintained at 0 V, and developing with a developer composed of at least a carrier and a toner. A developing step for forming the image, an image density detecting step for detecting the density of the developed image, a toner concentration detecting step for detecting the toner concentration of the developer, and a density of the developed image and a toner concentration detecting step detected in the image density detecting step And a toner replenishment control step for controlling toner replenishment to the developer based on the toner density detected in step (a).

  Further, according to the image density control method of the present invention, as shown in claim 9, an image carrier is applied by applying a DC voltage of 0 V and a predetermined AC voltage to an image carrier for carrying an electrostatic latent image on the surface. A charging step for maintaining the surface potential of the body at 0 V, and applying a predetermined developing bias in a state where the surface potential of the image carrier is maintained at 0 V, and developing with a developer composed of at least a carrier and a toner. A developing step for forming the image, an image density detecting step for detecting the density of the developed image, a toner concentration detecting step for detecting the toner concentration of the developer, a developer deterioration detecting step for detecting a time-degraded state of the developer, Temperature / humidity detection process for detecting the temperature and humidity around the developer, the density of the developed image detected in the image density detection process, the toner density detected in the toner density detection process, and the developer detected in the developer deterioration detection process A structure having at degraded condition, and a toner supply control process on the basis of the detected temperature and humidity to control the toner replenishment to the developer in the temperature and humidity detection process.

  As described above, according to the present invention, regardless of environmental changes such as humidity and temperature and deterioration with time of the developer and the photosensitive drum, toner replenishment can be controlled easily and appropriately to stabilize the toner density, and further, the image density Can be stabilized. In particular, since toner replenishment is controlled based on a developed image formed with the surface potential of the image carrier held at 0 V, it is possible to eliminate all the effects of environmental changes and deterioration with time on the image carrier.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view showing an image forming apparatus according to the present invention. The image forming apparatus scans the photosensitive drum 1 around the photosensitive drum 1 with a charging roller 2 for uniformly charging the imaging surface of the photosensitive drum 1 and an exposure light beam on the imaging surface of the photosensitive drum 1. The electrostatic latent image on the image forming surface of the photosensitive drum 1 is visualized by an LSU (laser scanning unit) 3 which is an exposure means for forming an electrostatic latent image and a developer composed of at least a carrier and toner. A developing device 5 having a developing roller 4 for forming a developed image, a transfer roller 6 for transferring a toner image formed on the image forming surface of the photosensitive drum 1 onto a recording paper, and a photosensitive drum 1 A cleaning blade 7 for cleaning the image surface is provided, and after the recording paper in the paper feeding unit 8 is fed between the photosensitive drum 1 and the transfer roller 6, the fixing paper 9 is passed through the fixing unit 9. Discharged. The image forming apparatus further includes an original reading unit 11 for copying and facsimile transmission.

  In the image forming apparatus, in order to stabilize the image density, it is necessary to sufficiently agitate the developer in the developing device 5 to uniformize the toner density distribution and to optimize the toner density. . Therefore, the image forming apparatus includes an image density control unit (image density control apparatus) 12 for stabilizing toner density by controlling toner replenishment simply and appropriately.

  FIG. 2 is a block diagram showing details of an image density control unit in the image forming apparatus shown in FIG. As shown in FIG. 1, the image density controller 12 includes a photosensitive drum (image carrier) 1, a charging roller (charging means) 2, an LSU (exposure means) 3, and a developing device (developing means) 5. The charging roller 2 applies a DC voltage of 0 V and a predetermined AC voltage to the photosensitive drum 1 to maintain the surface (image forming surface) potential at 0 V. The developing unit 5 A predetermined developing bias is applied with the surface potential held at 0 V, and development is performed with a developer composed of a carrier and toner to form a toner band (developed image).

  Further, the image density control unit 12 includes a toner bottle (toner replenishing means) 20a for storing toner to be supplied to the developing device 5, a toner bottle driving motor 20b for driving the toner bottle, and a photo for detecting the density of the toner band. A sensor (image density detecting means) 21, a toner density sensor (toner density detecting means) 22 for detecting the toner density in the developing device 5, and an agitating screw 23a that conveys the developer in the developing device 5 while being agitated by rotation. And a paddle 23b, a developing stirring motor 23c for driving them, and a temperature / humidity sensor (temperature / humidity detecting means) 24 for detecting the temperature / humidity around the developing device 5. Here, the rotation time of the developing stirring motor 23c that drives the stirring screw 23a is measured by the timer 26, thereby functioning as a developer deterioration detecting unit that detects the deterioration of the developer in the developing device 5 with time. The microcomputer (control unit) 25 measures the toner band density detected by the photosensor 21, the toner density detected by the toner density sensor 22, and the rotation time of the developing stirring motor 23 c by the timer 26. The toner supply to the developer in the developing device 5 is controlled based on the deterioration with time and the temperature / humidity detected by the temperature / humidity sensor 24.

  FIG. 3 is a conceptual diagram showing a charged state of the surface of the photosensitive drum when a toner band is formed in the image forming apparatus shown in FIGS. FIG. 3A shows the charged state of the surface of the photosensitive drum according to the present invention, and FIG. 3B shows the case of the prior art for comparison.

  In the case of the prior art, as shown in FIG. 3B, the potential Vl of the toner band forming portion on the surface of the photosensitive drum 1 is affected by the fluctuation of the laser power of the LSU 3 for exposure, the photosensitive drum 1 and The charging roller 2 may fluctuate under the influence of environmental changes and changes with time. As a result, when the potential difference ΔV (= Vb−Vl) between the potential Vl of the toner band forming portion and the developing bias potential Vb varies, it becomes difficult to form a stable toner band by the developing device 5.

  On the other hand, in the case of the present invention, as shown in FIG. 3A, the potential Vl of the toner band forming portion on the surface of the photosensitive drum 1 is kept at 0 V, so the potential Vl of the toner band forming portion and the developing bias are maintained. The potential difference ΔV (= Vb) with respect to the potential Vb is determined by the developing bias potential Vb, and a stable toner band can be formed. At this time, with respect to the voltage applied to the charging roller 2 to the photosensitive drum 1, the DC voltage is set to 0 V (OFF) and the AC voltage is set to a predetermined value. Thereby, excess charges on the photosensitive drum 1 can be removed, and the surface potential of the photosensitive drum 1 can be stably maintained at 0V.

  FIG. 4 is a graph showing an outline of a toner density changing method by the image density control unit shown in FIG. In this graph, the vertical axis represents the toner density sensor output (V), the horizontal axis represents the toner density detection value (%) in the developing device 5 by the toner density sensor, and the relationship between these values is shown for each control voltage (5.0 V, 6 0.0V, 7.0V, 8.0V, 9.0V). Here, a case where a developer having an initial toner concentration of 8% is used will be described.

  First, the microcomputer 25 rotates the stirring screw 23a in the developing device 5 immediately after putting the developer into the developing device 5, and initially sets the sensor output to 2.5 V (toner replenishment operation control voltage). Set the control voltage. In this embodiment, since the initial toner density is 8%, the initial control voltage is 7.0V. When the toner replenishment control is started, the microcomputer 25 sets the operation amount (usually “the operation amount determined according to the density of the toner band”), “degradation state of developer over time” to the initial adjustment value (7.0 V). The control voltage of the toner density sensor is determined by adding the “operation amount determined according to the temperature” and “the operation amount determined according to the temperature and humidity around the developing device 5”, and the determined new voltage is determined. Input the control voltage. As a result, the sensor output changes, but the microcomputer 25 keeps the sensor output at 2.5 V by driving the toner bottle and supplying toner to the developing device 5.

  For example, the operation amount of the control voltage determined in accordance with the density of the toner band detected by the photo sensor 21, the deterioration with time of the developer detected by the developer deterioration detection sensor 23, and the temperature and humidity detected by the temperature / humidity sensor 24. In the case of +2.0 V, the microcomputer 25 changes the input value of the control voltage from 7.0 to 9.0 (see the arrow in the figure). This change in the control voltage corresponds to + 2% of the toner density correction amount in the developing device 5 (that is, the toner density increases from 8% to 10%). Therefore, when the sensor output becomes larger than 2.5V due to the change of the control voltage to 9.0V, the microcomputer 25 drives the toner bottle to keep the sensor output at 2.5V. The toner is supplied to the developing device 5 until the detected value of the toner density in the developing device 5 reaches 10%.

  Here, the microcomputer 25 does not necessarily need to directly change the input value of the control voltage from 7.0 to 9.0, and the operation amount + 2.0V is divided into a plurality of operation amounts (for example, + 0.1V). The toner supply can be controlled step by step, and the toner supply can be controlled stepwise by repeatedly executing until the total operation amount becomes + 2.0V. In addition, in order to set the upper limit and the lower limit of the toner density after the change, it is also possible to set a variation limit of the operation amount of the control voltage in advance (for example, within the range of the control voltage 6.0V to 9.0V).

  As another method, it is possible to adjust the toner density by changing the toner density sensor output by changing the control voltage to a constant value. However, the sensor for the toner density as shown in FIG. When there is a region where the output sensitivity is reduced (in the figure, the region where the sensor output is about 0.3 V or less and about 4.2 V or more), the control voltage is set in a region where the sensor sensitivity is relatively good as described above. The method of changing is effective.

  FIG. 5 is a diagram illustrating an example of the operation amount of the control voltage of the toner concentration sensor determined according to the time-degraded state of the developer and the temperature and humidity around the developing device.

  As shown in FIG. 5A, the operation amount of the control voltage of the toner density sensor can be determined by the rotation time of the stirring screw in the developing device 5 after the start of use of the developer. The rotation time of the stirring screw in the developing device 5 reflects the state of deterioration of the developer with time. Here, the amount of operation is increased as the deterioration of the developer proceeds (that is, the rotation time of the stirring screw becomes longer). Increase. Further, as shown in FIG. 5B, the operation amount of the control voltage of the toner density sensor can be determined by the temperature and humidity around the developing device 5. Here, the operation amount tends to decrease as the temperature increases, while the operation amount tends to decrease as the humidity increases.

  The control voltage of the toner density sensor as described above can be determined in consideration of only the operation amount determined according to the density of the toner band. The influence of the environmental change of the device 5 and the change of the developer over time is reflected in the control voltage in a mixed state. Therefore, by further considering the operation amount determined according to the time-deteriorated state of the developer and the operation amount determined according to the temperature and humidity around the developing device 5, the environmental change of the developing device 5 and the change of the developer with time Can be reflected in the control voltage in more detail, and the target toner density can be realized in a shorter time. Here, the deterioration state of the developer with time and the temperature and humidity around the developing device 5 are shown as preferred examples, but the present invention is not limited to this, and various factors related to environmental changes and changes over time can be considered. .

  FIG. 6 is a flowchart showing an operation of toner replenishment control in the image density control unit shown in FIG. First, a toner band is formed by the developing device 5 with the surface potential of the photosensitive drum 1 held at 0 V by the charging roller 2 (ST101). Next, the density of the formed toner band is detected by the photosensor 21 (ST102).

  Therefore, it is determined whether or not the detected toner band density exceeds a preset target density (ST103). If the density exceeds the target density (toner density is high), the toner determined accordingly is determined. The control voltage is reduced by a small amount based on the division operation amount of the control voltage of the density sensor (ST104). As a result, when the toner in the developing device 5 is consumed after being printed on the recording paper, the toner density is decreased by a small amount. On the other hand, when the target density is not exceeded (toner density is low) in ST103, it is determined whether or not the detected density of the toner band is less than a preset target density (ST105), and less than the target density. (Toner density is low), the control voltage is slightly increased based on the divided operation amount of the control voltage of the toner density sensor determined accordingly (ST106). As a result, when toner is supplied to the developing device 5 during printing thereafter, the toner density increases by a small amount. However, in ST103, when the density of the toner band is the same as the target density, the control voltage is not changed.

  Next, temperature / humidity correction is performed to determine the operation amount of the control voltage of the toner density sensor based on the temperature / humidity around the developing device 5 (ST107). Further, the stirring screw in the developing device 5 after the start of use of the developer is executed. Developer deterioration correction for determining the operation amount of the control voltage of the toner density sensor according to the rotation time is executed (ST108). Therefore, the final control voltage operation amount after the temperature / humidity correction and the developer deterioration correction are adjusted so as to be within a preset range of fluctuation of the operation amount (ST109). As a result, the final control voltage is determined (ST110), but the toner is replenished or the toner is consumed by the determination of the control voltage, and the toner density in the developing device 5 actually reaches the target density. This is after printing on a predetermined number of recording sheets. Therefore, a predetermined number of prints are executed until the photosensor can detect the net toner density in the developing device 5 (ST111). Thereafter, the process returns to ST101 and the above-described series of steps are repeatedly executed.

  According to the image density control device, the image forming apparatus including the image density control method, and the image density control method of the present invention, toner replenishment can be performed easily and easily regardless of environmental changes such as humidity and temperature, and deterioration of the developer and the photosensitive drum over time. It is possible to stabilize the toner density by controlling it appropriately, and further to stabilize the image density, and to provide an image density control device that stabilizes the image density by appropriately controlling the toner density of the developing device, and the same It is useful as an image forming apparatus and an image density control method.

Schematic sectional view showing an image forming apparatus according to the present invention. 1 is a block diagram showing details of an image density control unit in the image forming apparatus of FIG. 1 is a conceptual diagram showing a charged state of the surface of a photosensitive drum when a toner band is formed in the image forming apparatus of FIG. FIG. 2 is a graph showing an outline of a toner density changing method by the image density control unit of FIG. The figure which shows an example of the operation amount of the control voltage of a toner density sensor FIG. 2 is a flowchart showing an operation of toner replenishment control by the image density control unit of FIG.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller (charging means)
3 LSU
5 Developer (Developing means)
20a Toner bottle 21 Photosensor (image density detecting means)
22 Toner density sensor (toner density detection means)
23 Developer deterioration detection sensor (Developer deterioration detection means)
24 Temperature / humidity sensor (temperature / humidity detection means)
25 Microcomputer (control means)

Claims (9)

An image carrier, charging means for uniformly charging the surface of the image carrier with a predetermined voltage applied thereto, and exposing the uniformly charged image carrier in accordance with image information. An exposure unit that forms an electrostatic latent image in accordance with the developing unit, a developing unit that develops and visualizes the electrostatic latent image with a developer including at least a carrier and toner in a state where a predetermined developing bias is applied, and the image Image density detecting means for detecting the density of the developed image on the carrier, toner density detecting means for detecting the toner density in the developing means, and toner supplying means for supplying toner to the developing means. ,
A predetermined developing bias is applied to the developing unit for a predetermined time while the surface potential of the image carrier is held at 0 V by the charging unit to which a DC voltage of 0 V and a predetermined AC voltage are applied, and the developing The toner replenishing means is directly developed in a potential difference state between the surface potential and the developing bias by means, and the density of the developed image read by the image density detecting means and the toner density detected by the toner density detecting means An image density control apparatus comprising control means for controlling toner replenishment.   The control unit determines an operation amount for changing the toner density in the developing unit according to the density of the developed image read by the image density detection unit, and a divided operation amount obtained by dividing the operation amount into a plurality of The image density control apparatus according to claim 1, wherein the toner supply by the toner supply unit is controlled stepwise according to the control.   The control unit determines an operation amount provided with a predetermined variation limit for changing the toner density in the developing unit in accordance with the density of the developed image read by the image density detection unit, and the operation amount The image density control apparatus according to claim 1, wherein toner supply by the toner supply unit is controlled according to the control. An image carrier, charging means for uniformly charging the surface of the image carrier with a predetermined voltage applied thereto, and exposing the uniformly charged image carrier in accordance with image information. An exposure unit that forms an electrostatic latent image in accordance with the developing unit, a developing unit that develops and visualizes the electrostatic latent image with a developer including at least a carrier and toner in a state where a predetermined developing bias is applied, and the image Image density detecting means for detecting the density of the developed image on the carrier, toner density detecting means for detecting the toner density in the developing means, and developer deterioration for detecting deterioration with time of the developer in the developing means Detecting means, temperature / humidity detecting means for detecting the ambient temperature / humidity of the developing means, and toner replenishing means for replenishing toner to the developing means,
A predetermined developing bias is applied to the developing unit for a predetermined time while the surface potential of the image carrier is held at 0 V by the charging unit to which a DC voltage of 0 V and a predetermined AC voltage are applied, and the developing The developer is directly developed with the potential difference between the surface potential and the developing bias by the means, the density of the developed image read by the image density detecting means, the deterioration state of the developer with time detected by the developer deterioration detecting means, and the temperature and humidity detection An image density control apparatus comprising control means for controlling toner replenishment by the toner replenishing means in accordance with the ambient temperature and humidity detected by the means and the toner density detected by the toner density detecting means.   The control means changes the toner density in the developing means according to the density of the developed image read by the image density detecting means, the time-degraded state of the developer, and the temperature and humidity around the developing means. 5. The image density control apparatus according to claim 4, wherein toner operation by the toner replenishing unit is controlled in a stepwise manner according to a divided operation amount obtained by dividing the operation amount into a plurality of operation amounts.   The control means changes the toner density in the developing means according to the density of the developed image read by the image density detecting means, the time-degraded state of the developer, and the temperature and humidity around the developing means. 5. The image density control apparatus according to claim 4, wherein an operation amount provided with a predetermined variation limit is determined, and toner supply by the toner supply means is controlled in accordance with the operation amount.   An image forming apparatus comprising the image density control device according to claim 1. A charging step of applying a DC voltage of 0 V and a predetermined AC voltage to the image carrier for carrying the electrostatic latent image on the surface to maintain the surface potential of the image carrier at 0 V;
A developing step of applying a predetermined developing bias in a state where the surface potential of the image carrier is maintained at 0 V, and developing with a developer composed of at least a carrier and a toner to form a developed image;
An image density detection step for detecting the density of the developed image;
A toner concentration detection step of detecting a toner concentration of the developer;
And a toner replenishment control step for controlling toner replenishment to the developer based on the density of the developed image detected in the image density detection step and the toner concentration detected in the toner concentration detection step. . A charging step of applying a DC voltage of 0 V and a predetermined AC voltage to the image carrier for carrying the electrostatic latent image on the surface to maintain the surface potential of the image carrier at 0 V;
A developing step of applying a predetermined developing bias in a state where the surface potential of the image carrier is maintained at 0 V, and developing with a developer composed of at least a carrier and a toner to form a developed image;
An image density detection step for detecting the density of the developed image;
A toner concentration detection step of detecting a toner concentration of the developer;
A developer deterioration detecting step for detecting a time-dependent deterioration state of the developer;
A temperature and humidity detection step for detecting the temperature and humidity around the developer;
The density of the developed image detected in the image density detection process, the toner density detected in the toner density detection process, the deterioration with time of the developer detected in the developer deterioration detection process, and the temperature detected in the temperature and humidity detection process And a toner replenishment control step of controlling toner replenishment to the developer based on humidity.