JP2000098730A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an excellent contact developing action and an excellent image forming action corresponding to the fluctuation of the electric resistance of two- component developer to be executed by applying reference voltage to a gap between an image carrier and a developer carrier, calculating the volume resistance value of the two-component developer by measuring a current value and estimating the toner mixing ratio of the two-component developer based on relation among the calculated volume resistance value, a previously defined volume resistance value and a previously defined toner mixing ratio. SOLUTION: By a controller 43, the DC reference voltage for measuring a resistance value is applied to a developing roll 17 from a power source 18 when the volume resistance value of the two-component developer is measured. Besides, the controller 43 is connected to a current value measurement device 44 measuring the current value flowing at that time and the measured current value is inputted to the controller 43. By a central control part 40, the volume resistance value RG of the two-component developer is calculated based on the current value inputted to the controller 43 and the toner mixing ratio is estimated and obtained based on the value RG. Then, when the estimated toner mixing ratio does not satisfy the lower limit toner mixing ratio, a control signal for changing it to a proper value is transmitted to the controller 43.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer using an electrophotographic system, and more particularly to an image forming apparatus having a developing device using a two-component developer composed of a toner and a carrier. It is about.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus using a two-component developer, an electrostatic latent image formed on an image carrier such as a photoconductor is transferred to a developer carrier such as a developing roll. Image formation is performed by developing a toner image with a two-component developer carried and conveyed, and transferring and fixing the toner image on a recording medium such as recording paper.

[0003] In the developing step, a developing bias voltage is applied between the image carrier and the developer carrier, which are arranged opposite to each other at a predetermined interval, and the developer carrier carried on the developer carrier is applied. By transporting the component developer in a state where it is in contact with the image carrier in a development area facing the image carrier,
Only the toner of the two-component developer is electrostatically transferred to and adhered to the electrostatic latent image portion of the image carrier.

[0004]

In the case of such an image forming apparatus, the two-component developer in the developing device may be partially adhered to the surface of the carrier or formed on the surface of the carrier due to its use. As the resin coating layer peels off, the charging ability of the carrier gradually decreases, and as a result, the toner cannot be sufficiently charged due to, for example, frictional charging, and the developing performance also decreases. Will end its life.

As a countermeasure for preventing the deterioration of the carrier and extending the life of the two-component developer, for example, there is a method of increasing the thickness of the resin coat layer. The electric resistance of the two-component developer increases as the thickness increases, and a fringe electric field is easily generated between the developer and the electrostatic latent image (potential) of the image carrier during development.

In order to prevent the resistance of the two-component developer from increasing, it is conceivable to take measures to use a low-resistance material as a coating material for forming the resin coating layer. However, when such a measure is taken, the resistance of the carrier may be too low. In this case, the developing bias formed between the image carrier and the developer carrier due to the application of the developing bias voltage. Current (charge) flows into the carrier due to the strength of the electric field, and the mirror image force of the carrier on the image carrier increases. As a result, the carrier adheres to the latent image area of the image carrier, causing image defects such as white spots. I will.

For this reason, in the development using a two-component developer, it is essential to maintain the resistance of the developer within an appropriate range in order to realize good development. However, the effective resistance of the developer in the actual developing process is determined by the dispersion of the developer, the gap between the image carrier and the developer carrier, the amount of developer transport by the developer carrier, and the like. Since the above factors that determine the effective resistance are different for each image forming apparatus (developing apparatus), even if an appropriate resistance value of the developer is uniformly set, depending on the image forming apparatus to be used. At present, good development cannot be realized, and it is actually difficult to set such a resistance value uniformly in practice.

Japanese Patent Application Laid-Open No. Hei 10-20656 discloses a developing apparatus and an image forming apparatus for preventing adhesion of curia to an image forming body while preventing discharge unevenness and vertical streaks in contact development with a two-component developer. As an apparatus, an insulating portion made of an electrically insulating member in contact with or in proximity to the layer of the two-component developer conveyed to the developer carrier, and a development area or a development area in which the image forming body and the developer carrier are opposed A control electrode having an electrode portion made of a conductive member capable of applying a voltage fixed to an upstream portion, and applying a waveform intermittently having an asymmetrical AC component with respect to a DC component to the developer carrier. There is disclosed a technique in which a voltage is applied and a DC voltage is applied to the electrode portion.

However, in this conventional example, it is not possible to prevent the carrier adhesion caused by the fluctuation of the charging performance (resistance) of the carrier in the two-component developer, and the image forming apparatus or the developing apparatus has If the effective resistance of the two-component developer fluctuates due to the difference in characteristics, there is a possibility that the development characteristics may vary.

[0010] Accordingly, an object of the present invention is to provide a method for controlling the electric resistance of a carrier alone or a two-component developer,
An object of the present invention is to provide an image forming apparatus capable of performing favorable contact development and image formation corresponding to the fluctuation, and capable of forming a stable image without image defects such as white spots due to carrier adhesion.

[0011]

An image forming apparatus according to the present invention, which can achieve the above object, comprises an image carrier, and a latent image forming device for forming an electrostatic latent image on the image carrier in accordance with image information. Using a device and a two-component developer consisting of toner and carrier,
The electrostatic latent on the image carrier is applied with a developing bias voltage applied between the developer carrier and the developer carrying the two-component developer and transporting the developer to a development area facing the image carrier. A developing device having a developing device for contact-developing an image with a two-component developer to form a toner image, a current value flowing by applying a reference voltage between the image carrier and the developer carrier of the developing device; And a resistance measuring means for calculating a volume resistance value of the two-component developer carried on the developer carrying member from the current value, and the volume resistance value obtained by the resistance measuring means is determined in advance. The toner mixing ratio of the two-component developer is predicted from the relationship between the volume resistance value and the toner mixing ratio, and it is determined whether or not the predicted toner mixing ratio satisfies a preset allowable lower limit. Prediction determining means, and the prediction determining means Is intended to and a condition changing means for measuring toner mixing ratio is changed imaging conditions does not meet the allowable lower limit value.

Here, as a means for applying a reference voltage in the resistance measuring means, a bias power supply for applying a developing bias voltage to a developer carrier of a developing device is usually used, but other power supplies are used. Alternatively, a dedicated power supply may be newly provided and used. The toner mixing ratio in the prediction determining means is a value obtained by dividing the toner amount by the total amount of the two-component developer (toner amount + carrier amount) in percentage. Further, the image forming condition in the condition changing means is:
This refers to image forming process conditions that are effective in preventing carrier from adhering to the image carrier based on information on the predicted toner mixing ratio. Image forming step).

In this image forming apparatus, when the developing bias voltage of the developing device is a voltage obtained by superimposing an alternating current on a direct current, the condition changing means lowers the AC duty ratio of the developing bias voltage. Is set to In this case, it is desirable to change the AC duty ratio and to increase the number of dots for increasing the image structure of the thin line.
This is because if the AC duty ratio is lower than before, thin lines tend to be difficult to reproduce, and this is compensated for. Therefore, when writing a thin line,
The writing width of the electrostatic latent image is increased by changing the number of dots (by using an image signal processing technique in a digital machine).

According to such an image forming apparatus, the electrical resistance (volume resistance) of the two-component developer actually used is
Is actually measured, a toner mixing ratio is predicted based on the measured value, and an appropriate image forming condition is set and changed based on the information of the predicted toner mixing ratio. For this reason, even if the resistance of the two-component developer fluctuates (changes) due to some factor, satisfactory contact development and image formation are performed under appropriate conditions corresponding to the fluctuation.

When the toner mixing ratio does not satisfy the lower limit, the AC duty ratio at the developing bias voltage in which the AC is superimposed on the DC is reduced to reduce the potential difference between the carrier and the latent image area of the image carrier. As a result, the charge is less likely to be injected into the carrier from the developing electric field, and as a result, the adhesion of the carrier to the image carrier is greatly suppressed.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a schematic diagram of a color image forming apparatus to which the present invention is applied. In the figure,
Reference numeral 10 denotes a photosensitive drum (image carrier) arranged to rotate in the direction of arrow A. Around the photosensitive drum 10, a charging device 11, a laser writing device (latent image forming device) 12, a developing device 13, a cleaner 14, and the like are provided.

The charging device 11 is a corotron type corona discharger.
A predetermined charging voltage is supplied from a high-voltage power supply (not shown).
The surface of the photosensitive drum 10 is applied with a predetermined charging potential V
_HTo be uniformly charged. Laser writing device
12 is an image signal transmitted from the image signal processing device 15
A laser oscillator such as a semiconductor laser (not shown) based on
The laser beam oscillated from the laser oscillator
The charging table of the photoreceptor drum 10 is determined by a predetermined optical system.
And irradiate it with a predetermined latent image potential V _LFrom
This forms an electrostatic latent image. Image signal processing device 1
5 is a document reading device when the image forming apparatus is a copying machine.
Performs predetermined processing on the document image information
If the image forming device is a printer,
Performs predetermined processing on input image information input from the
U.

The developing device 13 contains any one of four two-component developers G including toners of yellow (Y), magenta (M), cyan (C) and black (K) and a magnetic carrier. Four developing units 13Y, 13M,
13C and 13K are so-called rotary developing devices that are disposed at intervals on a cylindrical support 16 that rotates about a rotation shaft 16a. Further, each developing unit 13
Is a two-component developer G supplied while being stirred.
A developing roller (rotating sleeve in which a magnet roll is disposed) 17 is provided to transport the developing roller to a developing area facing the photosensitive drum 10 while forming a magnetic brush. Further, a developing roll (actually, a rotating sledge) 17 includes:
DC power supply and AC power is a predetermined developing bias voltage from a power supply 18 connected in series V _B is applied. In addition, each developing device 13 replenishes the developer storage section with toner (which may include a carrier) of the two-component developer G at a predetermined timing from a developer replenishing device (not shown). ing.

In the developing device, during development, a predetermined developing device 13 containing a two-component developer G of a color to be developed is opposed to a developing area of the photosensitive drum 10 by driving the support 17 to rotate. Moved. Further, the developing device 13
Is moved to the developing position when the developing roll 17
Are set so as to face the photosensitive drum 10 at a predetermined interval S.

Reference numeral 20 denotes a transfer drum which is arranged so as to rotate in the direction of the arrow B in synchronization with the photosensitive drum 10 in a state in which it abuts on the surface of the photosensitive drum 10. The recording sheet is carried and transported to a transfer position facing the photosensitive drum 10. Further, reference numeral 22 in the drawing denotes a sheet suction device for electrostatically adsorbing the recording sheet P supplied to the surface of the transfer drum 20, and reference numeral 23 denotes the sheet suction device for transferring the recording sheet P from the surface of the transfer drum 20 after the final transfer is completed A paper peeling device 24 for peeling off is a static eliminator that removes electricity from the transfer drum 20.

A transfer device 21 is provided on the back side of a portion (transfer position) of the transfer drum 20 facing the photosensitive drum 10.
Are arranged. The transfer device 21 is a corotron-type corona discharger, to which a transfer bias voltage having a polarity opposite to the charge polarity of the toner of the two-component developer G is applied from a high-voltage power supply (not shown). The toner image on the body drum 10 is electrostatically transferred to recording paper on the transfer belt 20.

The recording paper P sucked and conveyed by the transfer drum 20 is stored in a storage tray 25 for storing the paper P.
From the transfer drum 20 and the sheet suction device 22 at a predetermined timing by the registration roll 28 after being sent out by the feed roll 26 and the paper transport roll 27 and temporarily stopped by the registration roll 28. Has become.

Further, reference numeral 30 denotes a fixing device. The fixing device 30 includes a heating roll 31 and a pressure roll 32, which rotate by pressing.
A fixing process for fixing the toner image by applying heat and pressure by passing the recording paper P after the transfer between the two is performed. A dashed line in FIG. 1 indicates a transport path of the recording paper P.

In this color image forming apparatus, as shown in FIG. 2, the toner mixing ratio is estimated by measuring the volume resistance value of the two-component developer G in the developing device 13,
A control system is provided for performing an operation of changing image forming conditions if necessary according to the toner mixture ratio.

In FIG. 2, reference numeral 40 denotes a central control unit having an arithmetic processing unit, a storage unit, and the like.
Controls the operation of the entire image forming apparatus and executes a control operation according to a control program stored in a storage unit (ROM) (not shown) at a preset time. The central control unit 40 should develop the controller 41 that controls the image signal processing device 15 based on preset signal processing conditions and the drive motor 19 that rotates the (support 16 of) the developing device 13. A driver 42 for controlling according to the color component of the latent image;
The power supply 18 for applying a developing bias voltage to (the developing roller 17 of) 3 is connected to a controller 43 or the like that controls the power supply 18 based on a preset bias condition.

When the volume resistance of the two-component developer G is measured, the controller 43 executes a control operation for applying a DC reference voltage V ₀ for measuring the resistance from the power supply 18 to the developing roll 17. And the current value I _n flowing when the reference voltage V ₀ is applied.
Connected to a current measuring device 44 for measuring
Information of the measured current value I _n is adapted to be inputted at.

Further, the central control unit 40, (resistance measuring means) performs the process of calculating the calculation equation the volume resistivity value R _G of the two-component developer on the basis of the current value I _n, which are input to the controller 43, From the volume resistance value _RG , a toner mixture ratio (TC) is predicted from a collation table or a calculation formula, and the predicted toner mixture ratio (hereinafter, also simply referred to as “predicted toner mixture ratio”) is determined in advance. In accordance with a control program set to perform processing for determining whether or not a toner mixing ratio (hereinafter, also simply referred to as “lower toner mixing ratio”), which is a permissible lower limit, is set (prediction determining means). Works. In addition, the central control unit 40 changes the AC duty ratio of the developing bias voltage to an appropriate value if the predicted toner mixing ratio does not satisfy the lower limit toner mixing ratio. It operates according to a control program set to transmit a control signal to the controller 43 and perform a change process (condition changing means).

In this embodiment, the measurement of the volume resistance value of the two-component developer G and the control operation related thereto are performed when the power of the image forming apparatus main body is turned on, when the preset number of image formation sheets is reached (for example, the cumulative number of sheets). (When the number reaches 2000).

Next, the operation of the color image forming apparatus will be described.

First, an image forming process of a full-color image will be described with reference to FIGS. 1 and 4. When an instruction to start image formation is issued, the rotating photosensitive drum 10 is charged by a charging device 11 with a charging potential V _H. After being uniformly charged, the laser writing device 12 exposes and irradiates a laser beam Bm to form a first-color electrostatic latent image corresponding to image information. At this time, the electrostatic latent image loses its charge due to the irradiation of the laser beam and becomes a predetermined latent image potential _HL . Subsequently, the electrostatic latent image is developed by a developing device (developing device) 13 containing a two-component developer G of a color to be developed.

That is, the development at this time is performed by moving the predetermined developing unit 13 to a position facing the photoreceptor drum 10 and then carrying the two-components carried on the developing roll 17 so as to form a magnetic brush. When the developer G is transported in a state where the developer G is in contact with a developing area facing the photoconductor drum 10 (see FIG. 3), the photoconductor drum 10 and the developing roll
The toner in the two-component developer G is electrostatically transferred to and adheres to the latent image area of the photosensitive drum 10 by the developing electric field formed by the developing bias voltage V _B applied between Done. As a result, the electrostatic latent image is reverse-developed into a toner image, and the first color toner image is sent to a transfer position facing the transfer drum 20 by rotation of the photosensitive drum 10.

On the other hand, in accordance with the timing at which the latent image formation and development are performed, the recording paper P is sent out from the storage tray 25 and then sent to the transfer drum 20 at a predetermined timing by the resilient roll 28. Is adsorbed.

The first color toner image formed on the photosensitive drum 10 is electrostatically transferred by the transfer device 21 to the recording paper P conveyed to the transfer position facing the photosensitive drum 10 by the transfer drum 20. Is done. The residual toner adhered to the photosensitive drum 10 after the transfer is removed by the cleaner 14.

Subsequently, latent image formation of the second and subsequent color components,
Development and transfer are similarly repeated in accordance with the above-described operation contents. At this time, the recording paper P is rotationally conveyed while being attracted to the transfer drum 20, and every time the recording paper P passes through the transfer position,
The toner images of the color components after the color are sequentially transferred so as to be superimposed. As a result, the toner images of the respective colors of yellow (Y), magenta (M), cyan (C) and black (K) are multiplex-transferred onto the recording paper P in a predetermined order.

When the transfer of the final color is completed, the recording paper P is peeled off from the transfer drum 20 by the peeling device 23 and then sent to the fixing device 30 to execute the above-described fixing process. The recording paper P after completion of the fixing is discharged to the outside of the image forming apparatus by the discharge roll 33. Through the above process, a basic full-color image is formed.

Next, the measurement of the volume resistance value of the two-component developer G by the control system and the control operation related thereto will be described with reference to the flowchart shown in FIG.

Here, the case of an image forming apparatus set under the following conditions will be described as an example. First, regarding the settings relating to the image forming conditions, as the two-component developer G,
It is composed of a negatively chargeable toner having a particle diameter of 35 μm and a magnetic carrier having a particle diameter of 50 μm. C
Was set to 8%. Also, the charge potential V _H of the photosensitive drum 10 and -700 V, was -300V a latent image potential V _L. Further, the developing roll 17
Of the gap S between the photosensitive drum 10 and 0.4 mm, it was applied a voltage obtained by superimposing an alternating current to direct current voltage V _B of -560V as the developing bias voltage. Further, the AC duty ratio D of the developing bias voltage was set to, for example, D = 0.65 (FIG. 5A). In the image forming apparatus according to this embodiment, the AC duty ratio D can be arbitrarily changed within a range of 50 to 65%. FIG. 5 shows an AC pulse waveform of the developing bias voltage, and T in the figure indicates one cycle. Accordingly, the AC duty ratio: D is defined as A, which is the duration from the time when the waveform rises from the negative electrode side to the positive electrode side to the time when the waveform again falls to the negative electrode side. Where B is the continuation to the following equation, D = A
/ (A + B). By the way, (A +
B) = T, and T = 100 μsec.

On the other hand, the setting in the measurement and control operations associated therewith of the resistance value of the two-component developer G was from a power source 18 as the reference voltage V ₀ so as to apply a DC -1000 V. The current flowing when the reference voltage was applied was measured using a current monitor provided in the power supply 18. Further, the lower limit toner mixing ratio C.I.
T was 5%. Further, the predicted toner mixture ratio C.I. T is 5
As the image forming condition to be changed when the value is less than%, the AC duty ratio of the developing bias voltage is changed to D = 0.55 (FIG. 5B).

When the central control unit 40 confirms that the preset resistance measurement time has arrived as described above under such condition setting (step: S1).
0), the central processing unit 40 executes the following control operation.

First, when a drive signal is sent to the driver 42, the drive motor 19 is driven, and the developing device (developing device) 13 containing the developer G to be measured faces the photosensitive drum 10 at the developing position. After being moved to (S1
1) A voltage application signal is sent to the controller 43. Thus, the reference voltage V ₀ from the power source 18 is applied to the developing roller (sleeve) 17 of the developing device 13 has moved to the developing position, the current monitor current value I _n (.mu.A) power 18 flowing at that time It is measured (S12).

[0042] Subsequently, the volume resistivity R of the two-component developer G from the current value I _n is supported on the developing roll 17
_G is calculated equation: After being calculated by _{R G = V 0 / I n} (S
13), the toner mixing ratio T. of the two-component developer G is calculated using a collation table or a calculation formula indicating the following relationship between the volume resistance value and the toner mixing ratio based on the calculated volume resistance value _RG . C (%) is predicted (S14).

The relationship between the volume resistance value and the toner mixture ratio at this time is determined based on data (correlation diagram) obtained in advance by a test or the like as shown in FIG. By the way, the calculation formula at this time is the data (straight line) shown in the correlation diagram of FIG.
Linear function formula (y = ax + b) derived from
Is a multiplier of the volume resistance value _RG , and x is the toner mixing ratio T. C, a
Is the inclination of the straight line, and b is the intersection with the vertical axis).

Subsequently, the predicted toner mixture ratio T.R. C is a predetermined lower limit toner mixing ratio T.C. C is determined (S15), and the predicted toner mixture ratio T.C. If C exceeds 5%, it is considered that the electrical resistance of the two-component developer G is normal (sufficient), and the above-described image forming condition (AC duty ratio) is not changed (S16). Conversely, the predicted toner mixture ratio T. If C is less than 5%, the AC duty ratio is changed from D = 0.65 to “D = 0.55” (S
17).

As a result, as shown in FIG. If C is less than 5% and the AC duty ratio is kept at D = 0.65, the number of carriers adhering to the photosensitive drum 10 per A3 size sheet is determined by the toner mixing ratio T.C. As C becomes smaller, it becomes larger, but its AC duty ratio is D = 0.55.
, The number of the attached carriers rapidly decreases. This is because the AC duty ratio is made lower than before so that the carrier and the photosensitive drum 10
It is considered that since the potential difference from the latent image area decreases, it becomes difficult to inject charges into the carrier from the developing electric field, and as a result, the adhesion of the carrier to the photosensitive drum 10 is greatly suppressed.

Therefore, by changing the condition setting, it is possible to prevent carrier adhesion even when the electric resistance of the two-component developer G fluctuates for some reason. Further, such measurement of the resistance value and the control operation related thereto are similarly performed for the two-component developer (the developing device 13 containing the other colors). For this reason, favorable contact development and, consequently, image formation are possible, and stable image formation without image defects such as white spots can be performed.

[Other Embodiments] In the first embodiment, a DC of -1000 V is applied as the reference voltage V ₀ applied at the time of resistance measurement. However, the reference voltage V ₀ is not limited to this. Can be set arbitrarily. However, when the reference voltage V ₀ is set to a value having a large voltage difference, the accuracy of the resistance measurement is improved. However, if a too high voltage is applied, a leak may occur between the reference voltage and the photoconductor. , Preferably set to about -600V to -1200V. Further, the reference voltage V ₀ may be configured to be applied from another power source or a dedicated power source, instead of being applied from the power source 18 for developing bias.

The image forming conditions to be changed when the predicted toner mixing ratio does not satisfy the lower limit toner mixing ratio may be changed, for example, by changing the laser light amount (exposure) of the laser writing device. Amount) to change the potential of the electrostatic latent image to lower the developability, or change the DC component of the developing bias voltage to approach the potential of the electrostatic latent image ( For example, -56
(Change from 0 V to −540 V) to reduce the developability. As a result, the toner mixing ratio is increased. When the AC duty ratio is changed, the change amount may be set to a small value that is 0.7 to 0.9 times the value of the ratio up to that time when the value is “1”.

Further, the developing device 13 is not limited to the rotary type described above, but may be another general two-component developing device. Further, the image forming apparatus itself may form a monochrome image, or may be a color image forming apparatus of another type.

[0050]

As described above, according to the present invention,
Even if the electrical resistance of the two-component developer fluctuates for some reason, good contact development and image formation corresponding to the fluctuation can be performed. In particular, when a voltage obtained by superimposing an alternating current on a direct current is used as the developing bias voltage, when the predicted toner mixing ratio does not satisfy the allowable lower limit value, the ac duty ratio at the developing bias voltage is reduced to thereby reduce the carrier duty. Can be largely suppressed from adhering to the image carrier. Therefore, when an image forming apparatus such as the present invention is used, it is possible to stably form high-quality images without image defects such as white spots.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of an image forming apparatus according to a first embodiment.

FIG. 2 is a block diagram illustrating a configuration of a control system in the image forming apparatus of FIG. 1;

FIG. 3 is a conceptual diagram showing a state when measuring a volume resistance value of a two-component developer.

FIG. 4 is a conceptual diagram illustrating a potential state on a photosensitive drum during image formation.

5A and 5B are waveform diagrams illustrating an example of a setting of an AC duty ratio of a developing bias voltage. FIG.
(B) shows a setting example at the time of change.

FIG. 6 is a flowchart showing an operation procedure of a control system.

FIG. 7 is a correlation diagram showing a relationship between a previously determined volume resistance value (multiplier) of a two-component developer and a toner mixing ratio.

FIG. 8 is a graph showing the results of measuring the relationship between the number of adhered carriers and the toner mixing ratio when the AC duty ratio is set at normal time and at the time of change.

[Explanation of symbols]

Reference Signs List 10: photosensitive drum (image carrier), 12: laser writing device (latent image forming device), 13: developing device, 17: developing roll (developer carrier), 40: central controller (of resistance measuring means) A part, a part of the prediction determining means and the condition changing means), 43...
Controller (part of the condition changing means), 44: current measuring device (part of the resistance measuring means), G: two-component developer.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mutsumi Kikuchi 2274, Hongo, Ebina-shi, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Shino Yokoyama 2274, Hongo, Ebina-shi, Kanagawa Prefecture, Fuji Xerox Co., Ltd. 72) Inventor Akira Yukita 2274 Hongo, Ebina-shi, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd. (72) Inventor Hirohisa Kono 2274, Hongo, Ebina-shi, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd. (72) Inventor Tetsuji Okamoto 2274 Hongo, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Ryuji Hattori 2274 Hongo, Ebina City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. AD06 AD36 BA10 DA20 DA24 DA42 DA57 DB01 DB08 DB22 DB25 EA03 GA13

Claims (2)

[Claims] An image carrier, a latent image forming apparatus for forming an electrostatic latent image on the image carrier in accordance with image information, and a two-component developer including a toner and a carrier are used. An electrostatic latent image on the image bearing member is transferred while a developing bias voltage is applied between the developer bearing member carrying the developer and transporting the developer to a development area facing the image bearing member and the image bearing member. In an image forming apparatus having a developing device that forms a toner image by contact development with a component developer, a current value flowing by applying a reference voltage between the image carrier and the developer carrier of the developing device is measured. A resistance measuring means for calculating a volume resistance value of the two-component developer carried on the developer carrying member from the current value, and a volume resistance value obtained by the resistance measurement means and a predetermined volume resistance From the relationship between the toner value and the toner mixing ratio, the toner Prediction determining means for predicting the mixing ratio and determining whether or not the predicted toner mixing ratio satisfies a preset lower limit; and determining whether the toner mixing ratio predicted by the prediction determining means is lower than the allowable lower limit. An image forming apparatus comprising: condition changing means for changing an image forming condition when a value is not satisfied. 2. The condition changing means, when the developing bias voltage of the developing device is a voltage obtained by superimposing an alternating current on a direct current, is set so as to lower an alternating current duty ratio of the developing bias voltage. The image forming apparatus according to claim 1, wherein: