JP2004317960A - Toner concentration control method for two-component developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner concentration control method to effectively avoid trouble such as the lowering of toner concentration, the lowering of image density, the jumping of carrier, image irregularity caused by the irregularity of toner concentration, and the erroneous detection of the depletion of toner, which are caused when a large quantity of toner is consumed because of outputting an image whose image ratio is high. <P>SOLUTION: In the toner concentration control method, the toner concentration of the two-component developer composed of toner and magnetic carrier and filling up a developing device is detected according to the output of a magnetic permeability sensor, and the toner is supplied to the developing device from a supplied toner storage container attached to the developing device when the output thereof exceeds a fixed level. In the method, toner is supplied according to the output value of the sensor and the output rise change rate (ΔV/ΔT) of the sensor. After the toner is supplied, only the stirring action of the developer is performed without performing an image forming cycle for a fixed time in accordance with the output rise change rate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００４８】
実施例１
センサ出力値において、基準レベルを２Ｖ、ＴＥレベルを３Ｖに設定すると同時に、センサ出力上昇変化率（ΔＶ／ΔＴ）の閾値を６ｍＶ／秒に設定し、該変化率（ΔＶ／ΔＴ）がこの閾値以上でトナー補給を行い、且つエージングを５分間行い、該閾値以下の変化値でトナー補給が行われる場合には、エージングを行わないように設定した。尚、出力変化値が６ｍＶ／秒は、Ａ０紙での画像形成において、約３０％の画像比率の画像を最大濃度で出力するときのトナー消費量に匹敵する。
【００４９】
上記の条件で、Ａ０紙を使用し、画像比率１００％のベタ画像を最大濃度で連続して出力したところ、安定にトナー濃度の制御が行うことができ、トナーエンプティの誤検知や画像濃度の低下、キャリア飛びなどの不都合も生じなかった。
【００５０】
実施例２
センサ出力上昇変化率（ΔＶ／ΔＴ）の閾値を１３ｍＶ／秒（Ａ０紙で画像比率５０％に対応）及び４ｍＶ／秒（Ａ０紙で画像比率１５％に対応）に設定し、エージング時間を以下のように設定した。
１３ｍＶ／秒以上： ６分
１３ｍＶ／秒未満４ｍＶ／秒以上： ４分
４ｍＶ／秒未満： ２分
【００５１】
さらに、出力上昇変化率（ΔＶ／ΔＴ）が１３ｍＶ／秒以上でトナー補給を行うように設定するとともに、センサ出力値については、実施例１と全く同様に設定した。
【００５２】
上記の制御条件を採用し、Ａ０紙について、画像比率１００％、５０％、２５％、１５％及び６％の画像出力を、それぞれ連続して行った。何れの場合も、安定にトナー濃度の制御が行うことができ、トナーエンプティの誤検知や画像濃度の低下、キャリア飛びなどの不都合も生じなかった。
【００５３】
比較例１
出力上 昇変化率（ΔＶ／ΔＴ）に関する設定を全く行わなかった以外は実施例１と同様の制御条件を設定し、画像比率１００％のベタ画像を最大濃度で連続して出力したところ、トナーエンプティの誤検知や画像濃度の低下、キャリア飛びなどの不都合がしばしば生じた。
【００５４】
【発明の効果】
本発 明によれば、ベタ画像のように、画像比率の高い画像出力により、多量のトナーが消費されたときにも、トナー濃度の低下や、画像濃 度の低下、キャリア飛び、トナー濃度ムラによる画像ムラ、トナーエンプティの誤検知などを有効煮回避し、安定してトナー濃度の制御を行うことができる。
【図面の簡単な説明】
【図１】本発明方法の実施に使用される現像器の構造を示す側断面図。
【図２】図１の現像器の平面断面図。
【図３】透磁率センサの出力値と時間との関係を示す図。
【符号の説明】
７：感光体ドラム
９：現像器
２１：パドル
２２：スパイラル
２３：現像ロール
２５：透磁率センサ
２８：補給用ローラ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for controlling a toner concentration of a two-component developer used for image formation by electrophotography such as a copying machine, a facsimile, a laser printer, and the like.
[0002]
[Prior art]
In electrophotography, the surface of a photoreceptor is uniformly charged to a predetermined polarity, and then image exposure is performed by light irradiation based on predetermined document information to form an electrostatic charge image. An image is formed, the toner image is transferred to a predetermined sheet, and the toner image is fixed on the sheet by heating and pressing with a fixing roller, thereby forming an image. After the transfer of the toner image, the surface of the photoreceptor is cleaned by a cleaning blade or the like to remove the remaining toner, and if necessary, the charge is removed by light irradiation or the like, and the next image forming process is performed.
[0003]
As a developer used for developing an electrostatic image in such an image forming process, a two-component magnetic developer composed of a toner and a magnetic carrier (for example, ferrite or iron powder) is typical.
[0004]
The two-component magnetic developer is filled in a developing device having, for example, a developing roller with a built-in magnet having a large number of magnetic poles (disposed at a position facing the photoconductor) and a stirring and conveying member. Provided for development. That is, the toner is charged to a predetermined polarity by stirring and friction mixing between the toner and the magnetic carrier by the conveying member, and the developer is supplied onto the developing roller. The developing roller forms a magnetic brush containing charged toner. The magnetic brush is conveyed to a developing area (a portion facing the photoconductor), and the charged toner in the magnetic brush is transferred onto the photoconductor using electrostatic force. By attaching the toner to the electrostatic latent image portion, development of the electrostatic latent image, that is, formation of a toner image is performed. In this case, the magnetic carrier in the magnetic brush is not consumed by the development, but is recovered as it is, and is again used by being mixed with the toner in the developing device, but the toner is consumed by the development. Therefore, a replenishing toner container such as a hopper or a cartridge for replenishing toner is attached to the developing device, and when the toner concentration in the developing device drops below a certain value, the replenishing toner container is , The toner is supplied.
[0005]
The control of the toner concentration as described above is generally performed using a magnetic permeability sensor that generates an output voltage in proportion to the concentration of the magnetic carrier. That is, when the output voltage of the sensor exceeds a certain level (toner replenishing voltage), the toner replenishment is performed by replenishing the toner. If the output voltage does not decrease to the constant toner replenishing voltage even by the toner replenishment, It is configured to emit a signal indicating that the toner is empty. Various methods for controlling the toner concentration using such a magnetic permeability sensor have been proposed (for example, see Patent Documents 1 to 3).
[0006]
[Patent Document 1]
JP-A-1-131585 [Patent Document 2]
JP-A-9-73222 [Patent Document 3]
JP 2001-215788 A
[Problems to be solved by the invention]
However, in the toner density control method using the magnetic permeability sensor as described above, when an image having a high image ratio is continuously output at a high density, when a large amount of toner is consumed per unit time, There are still insufficient points to perform stable concentration control, and improvements are required.
That is, in the case of an image output with an image ratio as low as about 6%, stable control is performed by the sensor output voltage so that a constant reference level of toner density is maintained. In the case of outputting the image data, the amount of toner consumption per unit time increases, so that there is a problem that toner supply from a hopper or the like cannot keep up with toner consumption. For example, when an image having an extremely high image ratio, such as a solid image having an image ratio of 100%, is continuously output at a high density, toner supply cannot keep up and the toner density extremely decreases. As a result, the sensor output sharply increases. In addition, when the toner consumption position (that is, the development area) and the sensor position are separated from each other, there is a time lag before the developer whose toner concentration has decreased reaches the sensor position. In some cases, the voltage level rises sharply, and in some cases, exceeds a voltage level indicating toner empty. As a result, the toner concentration of the developer is extremely reduced, causing inconvenience such as carrier jump.
[0009]
Even if the output level of the sensor is returned to a fixed reference level after the toner concentration of the developer is extremely reduced, a larger amount of toner than usual is supplied in a short time. In some cases, the toner density may be high and low, and if the developer is not agitated to some extent, the sensor output may not be stable, and the toner may be erroneously detected by the image forming operation immediately after toner replenishment. Occurs. Further, even if the toner empty is not erroneously detected, the sensor output is unstable, so that it is difficult to perform normal toner density control. Further, if the toner density in the developer is not uniform, problems such as image unevenness may occur. Will happen.
[0010]
The toner density control methods described in Patent Documents 1 to 3 described above cannot address the above-described problem that occurs when a large amount of toner is consumed as described above.
[0011]
Accordingly, an object of the present invention is to solve problems such as a decrease in toner density caused when a large amount of toner is consumed in a short time, a decrease in image density, carrier jump, image unevenness due to toner density unevenness, and erroneous detection of toner empty. An object of the present invention is to provide a method for controlling a toner concentration in a two-component developer which can be effectively avoided.
[0012]
[Means for Solving the Problems]
According to the present invention, the toner concentration of a two-component developer that is composed of a toner and a magnetic carrier and is filled in a developing device is detected by the output of a magnetic permeability sensor, and the output is set to a preset toner supply voltage. A toner concentration control method for replenishing toner into the developing device from a replenishing toner storage container attached to the developing device until the output voltage drops to the toner replenishing voltage when
A rate of change in output rise (ΔV / ΔT) of the magnetic permeability sensor per fixed time is measured, and even when the rate of change in output rises exceeds a certain threshold value, the toner is output until the sensor output value drops to the toner supply voltage Replenish,
When the output rise change rate (ΔV / ΔT) exceeds the threshold value, the next image forming step is not performed, and after the toner supply is stopped, aging for performing only the developer stirring operation for a certain period of time is performed.
If the sensor output value does not decrease to the toner supply voltage at the time when a predetermined time has elapsed from the start of toner supply, a toner concentration control method for a two-component developer is provided, wherein a signal of a toner empty is issued. You.
[0013]
That is, in the present invention, it is an important feature that the output rise change rate (ΔV / ΔT) of the sensor is used as a parameter for toner density control. That is, in the control using only the sensor output value, when an image having a high image ratio is output at a high density, a large amount of toner is consumed. Therefore, the above-described various problems (an extremely low toner density, a variation in the toner density, In addition, a decrease in image density, carrier jump, erroneous detection of toner empty, and the like resulting from these are caused. In particular, when the sensor position is apart from the toner consumption position, there is a time lag between the toner density at the time of toner consumption and the sensor output. However, in the present invention, the above-described problem can be effectively solved because the rate of change in output of the sensor (ΔV / ΔT) is used as a control parameter in addition to the sensor output value.
[0014]
That is, when the sensor output value exceeds a predetermined toner supply voltage, toner supply is performed until the output value decreases to the toner supply voltage (so-called density control in a normal mode), but the output rise change rate (ΔV / If ΔT) exceeds a certain level, an image having a high image ratio is continuously output at a high density, and a large amount of toner is consumed in a short time. Therefore, at this time, toner supply is started regardless of the sensor output value. Further, the next image forming cycle is not performed (if the image forming cycle is being performed continuously, the execution of the image forming is interrupted or stopped when the current image forming cycle is completed). Run time, aging. As a result, the toner density can follow the rapid consumption of a large amount of toner, and the occurrence of density unevenness caused by replenishing a large amount of toner in a short time can be effectively avoided. Further, erroneous detection of toner empty can be prevented, the sensor output can be stabilized, and inconveniences such as uneven image density, reduced image density, and carrier skipping can be effectively eliminated during the subsequent image forming cycle. be able to.
[0015]
Note that, even when toner is supplied in accordance with the detected value of the output rise change rate (ΔV / ΔT), toner supply is performed until the sensor output value falls below the toner supply voltage (the toner supply voltage has been reached). At this point, toner supply is stopped). In this case, if the output rise change rate (ΔV / ΔT) exceeds a certain level when the sensor output value is lower than the toner supply voltage, the sensor output immediately exceeds the toner supply voltage, as described above. There is no problem even if toner is replenished based on the output rise change rate.
[0016]
In both cases of toner replenishment in the normal mode and toner replenishment based on the output rise change rate, if the sensor output value does not decrease to the toner replenishment voltage after a certain period of time has elapsed from the start of toner replenishment, the toner empty A signal is issued, prompting the user to replace the toner container, for example.
[0017]
In the present invention, the control based on the rate of change in output rise (ΔV / ΔT) is specifically performed by setting a constant threshold value according to a sensor or the like to be used, and when the threshold value is exceeded, Set to perform aging.
[0018]
In the present invention, it is also possible to set a plurality of threshold values for the output rise change rate (ΔV / ΔT), and it is preferable that the higher the threshold level, the longer the aging execution time is set. . That is, since the higher the rate of change in the recognized output rise is, the higher the image ratio is, the higher the image ratio is output. By adjusting the aging time by setting a plurality of threshold values as described above, for example, Even when a solid image having a ratio of 100% is output at a high density, the above-described problem can be effectively avoided.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 showing the structure of a developing device used for carrying out the method of the present invention (FIG. 1 is a diagram showing a side section of the developing device together with a photosensitive drum, and FIG. 2 is a plan sectional view of the developing device). The developing device 9 indicated as a whole is provided in the image forming apparatus together with the photosensitive drum 7 and is arranged near the photosensitive drum 7. Although not shown in FIG. 1, a main charger, an exposure optical system, a transfer device, and a cleaning device are provided around the photoconductor drum 7 together with the developing device 9. That is, the main charger, the exposure optical system, the developing device 9, the transfer device, and the cleaning device are located in this order along the rotation direction of the photosensitive drum 7.
[0020]
At the time of image formation, the surface of the photosensitive drum 7 is uniformly charged to a predetermined polarity by the main charger, and then the surface of the photosensitive drum 7 is irradiated with laser light or the like by an optical system based on predetermined image information. (Image exposure), an electrostatic latent image is formed due to a decrease in the potential of the light irradiation unit. The electrostatic latent image formed on the photosensitive drum 7 is developed by a developer filled in the developing unit 9 and a toner image is formed by attaching the toner image to a portion where the potential is reduced. This toner image is transferred onto transfer paper introduced between the transfer device and the photosensitive drum 7. The transfer paper onto which the toner image has been transferred is introduced into a fixing device provided in the image forming apparatus, and after the toner image is fixed on the surface of the transfer paper by heat and pressure, is discharged outside the image forming apparatus. Is done. After the transfer of the toner image, the toner remaining on the surface of the photosensitive drum 7 is removed by the cleaning device, and if necessary, the charge is removed. One cycle of image formation is completed, and the next image formation cycle is performed. Become.
[0021]
The developing device 9 includes a paddle 21, a spiral 22, and a developing roll 23 in a housing indicated by 20, and is filled with a two-component developer composed of a mixture of a toner and a magnetic carrier such as ferrite or iron powder. .
[0022]
The paddle 21 and the spiral 22 extend parallel to each other and are provided so as to convey the developer in directions opposite to each other (in this example, the paddles 21 and the spiral 22 rotate in directions opposite to each other). Provided). A central portion between the spiral 22 and the paddle 21 is partitioned by a partition wall 24, so that the developer is circulated and conveyed while being mixed by the spiral 22 and the paddle 21. Further, a magnetic permeability sensor 25 is provided on a wall of the housing 20 located near the spiral 22 so that the toner density can be detected from an output value proportional to the carrier density.
[0023]
The developing roll 23 has a magnet inside and transports the developer in the form of a magnetic brush. The developing roll 23 extends parallel to and adjacent to the paddle 21, and passes through an opening formed in the housing 20. To face the photosensitive drum 7. A guide plate 26 is provided at an upper portion between the paddle 21 and the developing roll 23 so that the developer can be smoothly supplied from the paddle 21 to the developing roll 23. An ear cutting blade 27 is provided with a certain clearance from the developing roll 23, and the blade length of the magnetic brush is adjusted by the blade 27.
[0024]
That is, the developer including the toner and the magnetic carrier is circulated and conveyed between the spiral 22 and the paddle 21 while being mixed and stirred by the spiral 22 and the paddle 21. By this mixing and stirring, the toner and the carrier are frictionally charged to a predetermined polarity, and the developer is supplied onto the developing roll 23 in the transport path by the paddle 21. The developer forms a magnetic brush on the developing roll 23, and the spike length is adjusted by a blade 27 to be supplied to a developing area (an area facing the photosensitive drum 7) to perform development.
[0025]
The development is performed by a method known per se, for example, by applying a predetermined developing bias between the developing roll 23 and the photosensitive drum 7 to remove the charged toner in the magnetic brush from the latent image portion of the photosensitive drum (for example, The development is performed by adhering to the (potential-lowering portion). At this time, the developer magnetic brush on the developing roll 23 and the surface of the photosensitive drum 7 may be in contact or non-contact. The toner and the magnetic carrier not consumed by the above-described development are collected by the developing roll 23 in the form of a magnetic brush and reused.
[0026]
Incidentally, the toner concentration in the developer needs to be maintained within a certain range, for example, about 3 to 6% by weight in order to form an appropriate image. Is consumed, and the toner concentration gradually decreases. When the toner concentration is extremely reduced, not only the image density is reduced, but also carrier jump occurs. To this end, the developing device 9 is provided with a toner hopper H, and toner is supplied from the toner hopper H.
[0027]
A replenishing roller 28 is provided in the toner hopper H. The replenishing roller 28 is configured to interlock with the magnetic permeability sensor 25 via a controller 29. Further, a stirring plate 30 is provided in the toner hopper H, and the toner is supplied into the developing device 9 through the supply roller 28 under stirring. The toner supply position by the supply roller 28 is normally set on the downstream side in the developer transport direction with respect to the detection unit D by the sensor 25.
[0028]
To maintain the toner density in a certain range, toner density control is performed using the magnetic permeability sensor 25. In the present invention, control based on sensor output voltage (control in normal mode) and sensor output are performed as follows. The toner density is controlled by the control based on the rate of change of increase (ΔV / ΔT).
[0029]
Referring to FIG. 3 showing the relationship between the output voltage value of sensor 25 and time, this output voltage value is proportional to the carrier density, and the output value increases as the toner density decreases. That is, by measuring this output value over time, control in the normal mode by the output voltage and control by the output change rate are performed.
[0030]
(Control in normal mode)
The control in the normal mode is basically performed in the same manner as in the related art. For such control, generally, the toner supply voltage (hereinafter, may be referred to as a reference level) and the reference level may be higher. Two thresholds, that is, a high second toner supply voltage (hereinafter sometimes referred to as a TE level) are set.
[0031]
The reference level (toner replenishment voltage) is an output value corresponding to a toner density that can form a stable image even with a small amount of toner consumption, and is set to 2 V in the example of FIG.
[0032]
Further, when the toner is consumed at a TE level (second supply voltage) higher than that, the image density becomes unstable, and there is a possibility that a carrier jump may occur. Therefore, the image forming cycle is stopped and the toner is supplied. 3 is higher than the reference level, and is set to 3 V in the example of FIG.
It should be noted that the output values of the above-mentioned reference level and replenishment level naturally vary depending on the sensitivity of the sensor used, and the above-mentioned numerical values (2 V, 3 V) are merely examples.
[0033]
That is, in the normal mode, basically, when the sensor output voltage (output value) exceeds the reference level, the replenishing roller 28 is driven via the controller 29 to perform toner replenishment. At this time, the image forming cycle can be executed as it is. For example, when the image forming cycle is continuously executed, the image forming cycle can be executed subsequently.
[0034]
Then, when the sensor output value does not decrease to the reference level when a certain period of time has elapsed since toner replenishment, a toner empty signal is issued to urge replacement of the toner hopper H. Further, when the sensor output value decreases to the reference level when a certain time has elapsed since the toner supply, the toner supply is stopped.
[0035]
Further, in the normal mode, if the sensor output value exceeds the TE level despite toner supply, the image forming cycle is stopped and toner supply is performed. That is, in this case, when the image forming cycle is being performed continuously, after the image forming cycle at the time when the TE level is exceeded is completed, the subsequent image forming cycle is interrupted.
[0036]
(Control by output change rate)
By the way, the density adjustment in the normal mode using only the sensor output value cannot cope with a case where images having a high image ratio are continuously output. That is, the detection unit D by the sensor 25, and the toner consumption unit (developing area), there is a distance L ₂ at a minimum (see FIG. 2). Therefore, there is a time lag between the toner density detected by the sensor 25 and the toner density in the toner consuming unit. Therefore, when an image with a high image ratio, for example, a solid image with an image ratio of 100% is output, a large amount of toner is rapidly consumed and the timing of toner replenishment is delayed. The level greatly exceeds the level, resulting in a remarkable decrease in toner density and image density. In some cases, the level may exceed the TE level, resulting in carrier skipping and the like. Also, even if the output value is returned to the reference level by toner replenishment, a large amount of toner replenishment that follows a large amount of toner consumption causes uneven toner density, and the sensor output becomes unstable, and in some cases, the sensor output becomes unstable. In some cases, erroneous detection of toner empty may occur.
[0037]
However, in the present invention, in addition to the control in the normal mode based on the sensor output value, the above-described inconvenience is effectively avoided by performing the toner density control based on the rate of change in sensor output increase (ΔV / ΔT). be able to.
[0038]
Specifically, the output rise change rate (ΔV / ΔT) is measured together with the sensor output value, and when this change rate (ΔV / ΔT) exceeds a certain threshold, regardless of the sensor output value described above. , Toner supply, and the image forming cycle is stopped. That is, after the image forming cycle at the time when the rate of change (ΔV / ΔT) exceeds a certain threshold is completed, execution of the next image forming cycle is not performed. The rate of change (ΔV / ΔT) corresponds to the amount of toner consumption. The greater the rate of change (ΔV / ΔT), the greater the amount of toner consumption. This is because it is output in a typical manner. By performing toner replenishment at such a change rate (ΔV / ΔT), it is possible to avoid that the output value greatly exceeds the reference level or further exceeds the TE level, and it is possible to significantly reduce the toner density and the like. Therefore, it is possible to effectively avoid problems such as a reduction in image density or a carrier jump.
[0039]
When toner replenishment is performed based on the output change rate (ΔV / ΔT), aging is performed according to the change rate. In this aging, only the developer is stirred and transported in a state where the toner is not supplied and the image forming cycle is stopped. For example, only the spiral 22 and the paddle 21 in the developing device 9 are driven to stir the developer. This is performed by circulating the developer through the developing device 9. By such aging, even when a large amount of toner is replenished, there is no density unevenness, a constant toner density can be secured, and erroneous detection of toner empty can be prevented.
[0040]
The above-mentioned aging is preferably performed for a longer time as the output increase change rate (ΔV / ΔT) is higher. That is, the higher the rate of change (ΔV / ΔT), the larger the image ratio, and the larger the amount of toner that is supplied as a result of the rapid consumption of a large amount of toner. Therefore, a plurality of thresholds can be set separately from the above-described threshold for toner replenishment, and the aging time after toner replenishment for the threshold can be set. As a result, an image having a remarkably high image ratio such as a solid image is continuously output at a high density, and an image having a relatively high image ratio (for example, a mixture of a photographic image and a character image). ) Can be dealt with effectively without unnecessary aging time until a high density is output. For example, when the change rate (ΔV / ΔT) is equal to or less than a certain value, the aging time can be set to zero, that is, the aging is not performed.
[0041]
Note that the output rise change rate (ΔV / ΔT) as described above is preferably measured by setting ΔT to be relatively long (for example, about 250 msec when 30 images can be output per minute). This is because if the rate of change (ΔV / ΔT) is measured with ΔT set to a short time, the fluctuation becomes large and the measurement becomes unstable.
[0042]
As described above, after aging is performed after toner replenishment, the image forming cycle is restarted.
[0043]
In the present invention, toner replenishment in the normal mode and the output rise change rate can be performed continuously by, for example, continuously rotating the replenishing roller 28 as long as a constant amount of toner is replenished in a unit time. Alternatively, the replenishment roller 28 may be rotated intermittently and intermittently.
[0044]
【Example】
Hereinafter, the present invention will be described based on examples.
[0045]
A large digital copier manufactured by Kyocera Mita was modified, and a magnetic permeability sensor was attached as shown in FIG. The sensitivity of this magnetic permeability sensor is 1 V / 1% (the output value changes by 1 V for a 1% change in toner density).
The developer charged in the developing device was a mixture of a positively charged toner and a ferrite carrier, and the initial toner concentration was set at 5% by weight.
[0046]
The amount of toner falling from the toner hopper was 5 to 10 g / min.
[0047]
Further, when an image is formed on A0 paper, the relationship between the image ratio and the toner consumption when outputting at the highest density is as follows.

[0048]
Example 1
In the sensor output value, the reference level is set to 2 V and the TE level is set to 3 V. At the same time, the threshold value of the sensor output increase change rate (ΔV / ΔT) is set to 6 mV / sec, and the change rate (ΔV / ΔT) is set to this threshold value. As described above, the toner is replenished and the aging is performed for 5 minutes. When the toner replenishment is performed with a change value equal to or less than the threshold value, the aging is not performed. The output change value of 6 mV / sec is equivalent to the amount of toner consumed when an image having an image ratio of about 30% is output at the maximum density in image formation on A0 paper.
[0049]
Under the above conditions, when a solid image having an image ratio of 100% is continuously output at the maximum density using A0 paper, the toner density can be stably controlled, and erroneous toner empty detection and image density There were no inconveniences such as lowering and carrier jump.
[0050]
Example 2
The threshold values of the rate of change in sensor output increase (ΔV / ΔT) are set to 13 mV / sec (corresponding to an image ratio of 50% for A0 paper) and 4 mV / sec (corresponding to an image ratio of 15% for A0 paper). It was set as follows.
13 mV / sec or more: 6 minutes less than 13 mV / sec 4 mV / sec or more: 4 minutes less than 4 mV / sec: 2 minutes
Further, the toner supply was set so that the output increase change rate (ΔV / ΔT) was 13 mV / sec or more, and the sensor output value was set exactly the same as in the first embodiment.
[0052]
Using the above control conditions, image output of A0 paper with image ratios of 100%, 50%, 25%, 15% and 6% was continuously performed. In any case, the toner density can be stably controlled, and there were no problems such as erroneous detection of toner empty, a decrease in image density, and carrier jump.
[0053]
Comparative Example 1
The same control conditions as in Example 1 were set except that no setting was made for the rate of increase in output (ΔV / ΔT), and a solid image having an image ratio of 100% was continuously output at the maximum density. Inconveniences such as erroneous detection of empty, reduction in image density, and carrier skipping often occurred.
[0054]
【The invention's effect】
According to the present invention, even when a large amount of toner is consumed due to an image output with a high image ratio, such as a solid image, a decrease in the toner density, a decrease in the image density, carrier skipping, and uneven toner density. This effectively avoids image unevenness and erroneous detection of toner empty, thereby stably controlling the toner density.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing the structure of a developing device used for carrying out the method of the present invention.
FIG. 2 is a plan sectional view of the developing device of FIG.
FIG. 3 is a diagram showing a relationship between an output value of a magnetic permeability sensor and time.
[Explanation of symbols]
7: Photoreceptor drum 9: Developing device 21: Paddle 22: Spiral 23: Developing roll 25: Magnetic permeability sensor 28: Supply roller

Claims (3)

The toner concentration of the two-component developer, which is composed of toner and a magnetic carrier and is filled in the developing device, is detected by the output of the magnetic permeability sensor, and when the output exceeds a preset toner supply voltage, A toner concentration control method for replenishing toner into the developing device from a replenishing toner container attached to the developing device until the output voltage decreases to the toner replenishing voltage;
A rate of change in output rise (ΔV / ΔT) of the magnetic permeability sensor per fixed time is measured, and even when the rate of change in output rises exceeds a certain threshold value, the toner is output until the sensor output value drops to the toner supply voltage Replenish,
When the output rise change rate (ΔV / ΔT) exceeds the threshold value, the next image forming step is not performed, and after the toner supply is stopped, aging for performing only the developer stirring operation for a certain period of time is performed.
If the sensor output value does not decrease to the toner supply voltage at a point in time when a predetermined time has elapsed from the start of toner supply, a toner empty control signal is issued, and a toner density control method for a two-component developer is provided. 2. The toner density according to claim 1, wherein a second supply voltage higher than the toner supply voltage is set, and when the sensor output value exceeds the second supply voltage, the image forming cycle is stopped and toner supply is performed. Control method. 2. The toner density control method according to claim 1, wherein a plurality of threshold values are set for the output rise change rate, and the aging execution time is set longer as the level of the threshold value exceeding the recognized output rise change rate is higher. 3. .

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