JP2001318493A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a defective image from occurring by detecting the reduction of the electrified potential of a photoreceptor drum. SOLUTION: A computational toner consumption is calculated by a controller 33 based on image ratio information from an image ratio detecting sensor 32, and also, the actual toner consumption is calculated by the controller 33 based on the driving time of a supply roller 28, and in the case of deciding that a difference between the computational toner consumption and the actual toner consumption is larger than a prescribed value, it can be judged that the electrified potential of the photoreceptor drum 1 becomes lower than the set value, so that magnetic particles of a magnetic brush electrifier 2 are prevented from sticking to the photoreceptor drum 1, so that the occurrence of the defective image is prevented.

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, a printer and a facsimile which forms an image by an electrophotographic system or an electrostatic recording system. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus of an electrophotographic type or an electrostatic recording type, an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric and other charged members are charged to a predetermined polarity and potential. As a charging means, a corona charger has been generally used conventionally. In this method, a corona charger is disposed opposite to an image carrier (hereinafter, referred to as a photoconductor) in a non-contact manner, and the photoconductor surface is exposed to a corona emitted from the corona charger to charge the photoconductor surface to a predetermined polarity and potential. Things.

In recent years, a voltage (charging bias) has been applied to a photoreceptor as a member to be charged because it has advantages such as low ozone and low power as compared with the non-contact type corona charger described above. 2. Description of the Related Art A contact-type charging device that contacts a charging member (contact charging member) to charge a photoreceptor surface to a predetermined polarity and potential has been put to practical use. In particular, a roller charging type apparatus using a conductive roller (charging roller) as a charging member is preferably used in terms of charging stability.

Further, a magnetic brush charging member (hereinafter, referred to as a magnetic brush charger) having a magnetic brush in which magnetic particles are magnetically bound to the surface of a charging roller as a magnetic particle carrier is used as the contact charging member. A charging device of a magnetic brush charging type in which a magnetic brush of a charging device is brought into contact with a photoreceptor is preferably used in terms of stability. The magnetic brush charger is provided with a magnetic brush formed by directly constraining conductive magnetic particles to a magnet or magnetically on a sleeve containing a magnet,
The magnetic brush is stopped or rotated to contact the photoconductor, and a voltage is applied to the photoconductor to start charging the photoconductor. In addition, a conductive fiber formed into a brush shape (fur brush charging member, charging fur brush), a conductive rubber blade formed of conductive rubber in a blade shape (charging blade), and the like are also preferably used as the contact charging member. Have been.

The charging mechanism (charging mechanism, charging principle) of the contact charging includes a corona charging system and a charge injection (direct charging) system.

[0006] The corona charging system is a system in which the surface of the photoconductor is charged with a discharge product due to a corona discharge phenomenon occurring in a minute gap between the contact charging member and the photoconductor. Since corona charging has a certain discharge threshold value for the contact charging member and the photoconductor, it is necessary to apply a voltage higher than the charging potential to the contact charging member. Although the amount of generation is not so small as compared with the corona charger, a discharge product is generated.

On the other hand, the charge injection charging system charges the surface of the photoconductor by injecting charge directly from the contact charging member to the photoconductor. More specifically, the charge is directly injected into the surface of the photoreceptor without contacting the surface of the photoreceptor with a medium-resistance contact charging member and without causing a discharge phenomenon, that is, basically without using discharge. Therefore, even if the applied voltage to the contact charging member is equal to or lower than the discharge threshold, the photosensitive member can be charged to a potential corresponding to the applied voltage. Although this charge injection charging system does not involve the generation of ions, since it is charge injection charging, the contact property of the contact charging member to the photoreceptor greatly affects the charging property. Therefore, it is necessary to form the contact charging member more densely, and to adopt a configuration in which there is a large difference in speed from the photoconductor and the photoconductor is contacted more frequently. The charger can perform stable charging.

[0008] The charge injection charging by the magnetic brush charger is as follows.
It can be seen that it is equivalent to a series circuit of a resistor and a capacitor. In an ideal charging process using a magnetic brush charger, the capacitor is charged while a certain area of the photoreceptor surface is in contact with the magnetic brush (charging nip x peripheral speed of the photoreceptor), and the potential on the photoreceptor surface is applied voltage Is almost the same as

In recent years, as a contact charging method, an injection charging method has been proposed in which a voltage is applied to a conductive contact member to inject electric charges into trap levels on the surface of the photoreceptor to perform contact charging of the photoreceptor. ing. In the injection charging method, when a photoconductor having a surface layer (charge injection layer) in which conductive fine particles are dispersed on a normal organic photoconductor or an amorphous silicon photoconductor is used, the bias applied to the contact charging member is reduced. It is possible to obtain a charged potential substantially equal to the DC component on the photoreceptor surface. The above injection charging method is not only less environmentally dependent but also does not use discharge, so that the voltage applied to the contact charging member is sufficient to be substantially equal to the photoconductor potential, and has the advantage of not generating ozone. It is possible to perform charging with low ozone and low power consumption.

In recent years, the size of an image forming apparatus has been reduced. However, it is difficult to reduce the size of an image forming apparatus such as charging, exposure, development, transfer, fixing, and cleaning by simply reducing the size of each unit. There was a limit to the overall miniaturization of the device. Further, the transfer residual toner (residual developer) on the photoreceptor after the transfer is collected by a cleaning unit (cleaner) to become waste toner, but it is preferable that the waste toner does not come out from the viewpoint of environmental protection.

Therefore, in recent years, the cleaning device (cleaner) has been removed, and the transfer residual toner on the photoconductor has been removed from the photoconductor by "development simultaneous cleaning" by the developing device, and has been collected and reused by the developing device. Practical use of the "cleanerless process" image forming apparatus has been made. Simultaneous development cleaning refers to a fog removal bias (a fog removal potential difference (hereinafter referred to as a potential difference between a DC voltage applied to the developing means and a surface potential of the photoreceptor) at the time of development after the next step. ,
This is a method of collecting by fog removal bias). According to this method, since the transfer residual toner is collected by the developing means and used in the subsequent steps, the waste toner is eliminated,
Maintenance work can be reduced.

[0012] Further, since there is no need for a cleaner, there is a great advantage in terms of space, and the size of the image forming apparatus can be greatly reduced. Further, when the charging device of the photoconductor is a contact charging device, the transfer residual toner is once collected by a charging member of the contact charging device that is in contact with the photoconductor, and is discharged again onto the photoconductor, thereby causing the developing device to Can be recovered.

[0013]

By the way, in a cleaner-less image forming apparatus using the above-described cleaning at the same time as cleaning by simultaneous development and use, the transfer residual toner is transferred to the magnetic brush charger. When the external additives of the developer or the fragments of the toner adhere to the surfaces of the magnetic particles in the magnetic brush charger little by little, the electric resistance gradually increases. For this reason, sufficient charging is not performed while passing through the charging nip where the magnetic brush and the photoconductor are in contact, and as a result, the charging potential (photoconductor potential) decreases.

In the case where the charging potential is reduced, in a reversal developing system, when the charging potential is reduced, the difference from the developing bias is reduced.
The developer adheres to the image-receiving portion on the photoconductor, and so-called fogging occurs.

In addition, a potential difference occurs between the charging sleeve of the magnetic brush charger and the surface of the photoreceptor, and the contact resistance between the magnetic brush and the surface of the photoreceptor is higher than the electric resistance of the charging sleeve and the photoreceptor. Is big. For this reason, as shown in FIG. 9, the potential between the charging sleeve and the surface of the photoconductor has a large voltage drop at the contact interface between the magnetic brush and the surface of the photoconductor.
Magnetic particles adhere to the photoreceptor surface. Then, when the magnetic particles attached to the photoreceptor are collected in the developing device, the toner tribo is fluctuated and causes an image defect. Further, even when the transfer device and the fixing device are not collected by the developing device, the magnetic particles may damage the transfer device and the fixing device and shorten their life.

Accordingly, it is an object of the present invention to provide an image forming apparatus capable of preventing magnetic particles from adhering to a photoreceptor and obtaining a good image.

[0017]

In order to achieve the above object, the present invention provides an image carrier and magnetic particles carried on a magnetic particle carrier, which are brought into contact with the image carrier, by applying a charging bias. Charging means for charging the image carrier; exposure means for exposing the charged image carrier to form an electrostatic latent image; developing the electrostatic latent image with a developer to form a developer image; Developing means for forming an image, and transfer means for transferring the developer image to a transfer material, after transferring the developer image to the transfer material, the transfer residual developer remaining on the image carrier, In the image forming apparatus, which is once collected in the magnetic particles, is discharged from the magnetic particles and is collected again by the developing unit,
Image ratio detecting means for detecting an image ratio of the developer image to an image forming region on the image carrier, and developer consumption detecting means for detecting an amount of developer consumed for forming the developer image; Calculating the calculated amount of developer consumption based on the image ratio detection information input from the image ratio detection means, and calculating the calculated amount of developer consumption based on the developer consumption detection information input from the developer consumption detection means. Control means for calculating a developer consumption amount by forming the developer image, and detecting a decrease in the charged potential of the image carrier based on the calculated developer consumption amount and the developer consumption amount; It is characterized by having.

When the difference between the calculated consumption amount of the developer and the consumption amount of the developer exceeds a predetermined value, the control means lowers the charging potential of the image bearing member below a predetermined value. It is characterized in that control is performed so that the image formation of the developer image is stopped upon judging that the image formation has been performed.

Further, the developer consumption detecting means is a developer replenishing member for replenishing the developer to the developing means, and the control means is configured to control the developer consumption based on a driving time of the developer replenishing member. Is calculated.

An image carrier, and charging means for contacting the magnetic particles carried on the magnetic particle carrier with the image carrier and charging the image carrier by applying a charging bias;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; developing means for developing the electrostatic latent image with a developer to visualize it as a developer image; and And a transfer unit for transferring the developer image onto the transfer material. After transferring the developer image onto the transfer material, the transfer residual developer remaining on the image carrier is once collected into the magnetic particles. In an image forming apparatus that discharges from the developing unit and collects the developer again, a density detecting unit that detects a density of the developer by the developing unit, and a charging operation of the image carrier by the charging unit during non-image formation. While performing the developing operation by the developing unit, the density detecting unit detects the density of the developer, and before and after performing the charging operation and the developing operation, the density detecting unit detects the density of the developer. Concentration when performing each Knowledge information is input, the developer concentration before and after the charging operation and the developing operation is calculated from the input density detection information, and the calculated developing operation before and after the charging operation and the developing operation is performed. Control means for detecting a decrease in the charged potential of the image carrier based on the difference in the agent concentration.

When the difference between the calculated developer concentration before and after the charging operation and the developing operation exceeds a predetermined value, the control means sets the charging potential of the image carrier to a predetermined value. The image forming apparatus is characterized in that it is determined that the developer image has been lowered, and control is performed to stop the image formation of the developer image.

In addition, a magnetic field having at least a portion of a surface having conductivity is provided between the image bearing member and the developing means so as to be close to the image bearing member along the rotation direction of the image bearing member. Means for applying the same bias to the magnetic field generating means as the developing bias applied to the developing means.

Further, the image carrier is an electrophotographic photosensitive member having a charge injection layer in which conductive fine particles are dispersed in an insulating binder.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus of the present embodiment is an electrophotographic process type,
This is a laser beam printer with a cleaner-less process, which has a magnetic brush charging device of a charge injection charging system.

The image forming apparatus includes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) 1, a magnetic brush charging device 2 around the photosensitive member, and an exposure device (not shown) as an electrostatic latent image forming means. , A developing device 3, a transfer roller 4, and a conductive brush 5. Further, a fixing device 6 is provided downstream of the transfer nip portion N formed between the photosensitive drum 1 and the transfer roller 4 in the transport direction of the transfer material P.

The photosensitive drum 1 is driven to rotate at 150 mm / sec in the direction of arrow a by a driving means (not shown). As the photosensitive drum 1, a commonly used organic photosensitive member or the like can be used. Preferably, the photosensitive drum 1 has a surface layer having a material having a resistance of 10 ² to 10 ¹⁴ Ω · cm on the organic photosensitive member. When an amorphous silicon photoreceptor or the like is used, charge injection charging can be realized, which is effective in preventing ozone generation and reducing power consumption. Further, the chargeability can be improved. Therefore, in the present embodiment, as shown in FIG.
The following first to fifth five layers 1b, 1c, 1d, 1e, and 1 are formed on an aluminum drum base 1a having a diameter of 30 mm.
The photosensitive drum 1 provided with f in order from the bottom (inside) was used.

The first layer is an undercoat layer 1b having a thickness of about 20 provided for smoothing out defects or the like of the drum base 1a.
μm conductive layer. The second layer is a positive charge injection preventing layer 1c, which serves to prevent positive charges injected from the drum substrate 1a from canceling out negative charges charged on the surface of the photosensitive drum 1, and comprises an amylan resin and methoxymethylated nylon. Thickness adjusted to about 10 ⁶ Ω · cm
It is a medium resistance layer of μm. The third layer is a charge generation layer 1d, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates a positive and negative charge pair upon exposure. The fourth layer is a charge transport layer 1e in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, negative charges charged on the surface of the photosensitive drum 1 cannot move through this layer, and only positive charges generated in the charge generating layer 1d can be transported to the surface of the photosensitive drum 1.

The fifth layer is a charge injection layer 1f, which is a coating layer of a material in which SnO ₂ particles are dispersed in a binder of an insulating resin. Specifically, antimony which is a light-transmitting insulating filler is doped into an insulating resin to reduce the resistance (conductivity) of SnO ₂ particles having a particle size of about 0.03 μm by 70% by weight with respect to the resin. It is a coating layer of the material that was applied. The thus prepared coating liquid is applied to a thickness of about 3 μm by an appropriate coating method such as a dipping coating method, a spray coating method, a roll coating method, and a beam coating method, and the charge injection layer 1 is formed.
f. The electric resistance value of the charge injection layer 1f is 1 × 10 ^10, which is a condition that sufficient chargeability and image deletion do not occur.
A 1 × 10 ¹⁴ Ω · cm, in the present embodiment, the surface resistance using a photosensitive drum 1 of 1 × 10 ¹¹ Ω · cm.

As shown in FIG. 3, the magnetic brush charging device 2 includes a charging container 7 and a magnet roller 8 fixed inside.
, A charging sleeve 9 made of a rotatable non-magnetic material (for example, stainless steel), magnetic particles 10 carried on the charging sleeve 9 and in contact with the photosensitive drum 1 to inject electric charge, and a magnetic sleeve 10 9 has a regulating blade 11 made of a non-magnetic material (for example, stainless steel) for coating the surface with a uniform thickness.

The charging sleeve 9 is driven to rotate in the direction of the arrow (clockwise) at a peripheral speed of 225 mm / sec in the present embodiment in the same rotational direction as the photosensitive drum 1. The regulating blade 11 has a gap of 900 μm with the surface of the charging sleeve 9.
It is arranged to become. A part of the magnetic particles 10 in the charging container 7 is magnetically constrained on the outer peripheral surface of the charging sleeve 9 by the magnetic force of the magnet roller 8, and the magnetic brush 10
a. The magnetic brush 10 a rotates together with the charging sleeve 9 in the same direction as the charging sleeve 9 with the rotation of the charging sleeve 9. At this time, the layer thickness of the magnetic brush 10a is regulated to a uniform thickness by the regulating blade 11. Since the thickness of the regulating layer of the magnetic brush 10a is larger than the gap between the opposing gaps between the charging sleeve 9 and the photosensitive drum 1, the magnetic brush 10a is
A nip portion having a predetermined width is formed on and contacts the photosensitive drum 1 at a position where the photosensitive drum 1 faces the photosensitive drum 1. This contact nip is the charging nip M.

Accordingly, the photosensitive drum 1 is rubbed in the charging nip M by the magnetic brush 10a which rotates as the charging sleeve 9 rotates. In this case, in the charging nip portion M, the rotation direction of the photosensitive drum 1 and the rotation direction of the magnetic brush 10a are opposite to each other, and the relative movement speed is increased. Further, a predetermined charging bias is applied to the charging sleeve 9 and the regulating blade 11 from a charging bias applying power source 12. In the case of the present embodiment, the bias is such that the AC component is superimposed on the DC component. Then, the photosensitive drum 1 and the charging sleeve 9 are driven to rotate, and a predetermined charging bias is applied from a charging bias applying power supply 12, so that the peripheral surface of the photosensitive drum 1 is uniformly charged to a predetermined negative potential by injection charging. Is subjected to contact charging treatment.

The magnet roller 8 has an N pole (main pole) of about 900 gauss at 10 ° upstream from the closest position of the charging sleeve 9 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. It is desirable that the main pole has an angle (θ) with the closest position within a range of 20 ° upstream of the rotation direction of the photosensitive drum 1 to 10 ° downstream of the rotation direction of the photosensitive drum 1, and preferably 15 ° upstream of the rotation direction of the photosensitive drum 1. ° to 0 °. Thus, when the photosensitive drum 1 is located downstream in the rotation direction, the magnetic particles 1
0 is attracted, and the magnetic particles 10 are more likely to stay on the charging nip M downstream of the photosensitive drum 1 in the rotation direction. It becomes worse and stagnation tends to occur.

The charge injection and charging to the photosensitive drum 1 by the magnetic brush 10a is performed by a resistor R such as an equivalent circuit shown in FIG.
And a capacitor C in series. In the case of such a circuit, the resistance value of the resistor R is r, the capacitance of the photosensitive drum 1 is Cp, the voltage applied from the charging bias application power supply 12 is Vo, and the charging time (a certain area on the surface of the photosensitive drum 1 is charged nip) Assuming that the time of passing through the section M) is To,
The surface potential Vd of the photosensitive drum 1 is represented by the following equation (1).

Vd = Vo (1−exp (To / (Cp · r))) Expression (1) The DC component of the charging bias (DC + AC) applied from the charging bias applying power source 12 to the charging sleeve 9 is required. The same value as that of the surface potential of the photosensitive drum 1 was set to -700 V in the present embodiment. The AC component of the charging bias at the time of image formation (at the time of image formation) is represented by the peak-to-peak voltage Vpp.
Is preferably 100 to 2000 V, particularly preferably 300 to 1200 V. When the peak-to-peak voltage Vpp is 100 V or less, the effect of improving the charging uniformity and the rise of the potential is thin, and the effect is 2,000 V.
Above, retention of the magnetic particles 10 and adhesion to the photosensitive drum 1 are deteriorated. AC component frequency is 100-5000H
z, particularly preferably 500 to 2000 Hz. 100Hz
In the following, the effect of improving the adhesion of the magnetic particles 10 to the photosensitive drum 1 and improving the uniformity of charge and the rise of the potential becomes thin, and the effect of improving the uniformity of charge and the rise of the potential becomes difficult even at 5000 Hz or more. . The AC waveform may be a rectangular wave, a triangular wave, a sine wave, or the like. In the present embodiment, the peak-to-peak voltage Vpp of the AC voltage of the charging bias during image formation is 700 V, and the magnetic particles 10
The peak-to-peak voltage Vpp of the AC voltage of the charging bias at the time of discharging the mixed toner was set to 0V.

In the present embodiment, the magnetic particles 10 used are those obtained by reducing a sintered ferromagnetic material (ferrite). Alternatively, a resin and a ferromagnetic material powder are kneaded and formed into particles. It is also possible to use a material obtained by mixing conductive carbon or the like for adjusting the resistance value, or a material subjected to a surface treatment. The magnetic particles 10 serve to satisfactorily inject charges into trap levels on the surface of the photosensitive drum 1,
The magnetic particles 10 caused by the concentration of the charging current on defects such as pinholes generated on the photosensitive drum 1
In addition, it must have a role of preventing the photosensitive drum 1 from being energized and destroyed.

Therefore, the resistance value of the magnetic particles 10 is 1 × 10
⁴ to 1 × 10 ⁹ Ω, preferably 1 × 10 ⁹ Ω
More preferably, it is ⁴ to 1 × 10 ⁷ Ω. If the resistance value of the magnetic particles 10 is less than 1 × 10 ⁴ Ω, pinhole leakage tends to occur. If the resistance value exceeds 1 × 10 ⁹ Ω, good charge injection tends to be difficult. In order to control the resistance value within the above range, the volume resistance value of the magnetic particles 10 is preferably 1 × 10 ⁴ to 1 × 10 ⁹ Ω · cm, and particularly preferably 1 × 10 ⁴ to 1 × 10 ^7. More preferably, it is Ω · cm. In this embodiment, the resistance value is 1
× 10 ⁶ Ω · cm magnetic particles 10 were used.

The volume resistance value of the magnetic particles 10 was measured using a measuring device shown in FIG. This measuring device fills the cell 13 with the magnetic particles 10, and arranges the main electrode 14 and the upper electrode 15 so as to be in contact with the filled magnetic particles 10.
A voltage was applied during that time, and the volume resistance value of the magnetic particles 10 was measured from the current value flowing at that time.

The measurement conditions at this time were as follows: the contact area S of the magnetic particles 10 filled with the cell 13 in an environment of a temperature of 23 ° C. and a humidity of 65% was 2 cm ² , the thickness d was 1 mm, the load on the upper electrode 15 was 10 kg, The applied voltage is 100V. In the figures, 16a and 16b are insulators, 17 is a guide ring, 1
8 is an ammeter, 19 is a voltmeter, and 20 is a constant voltage device.

The peak in the measurement of the average particle size and the particle size distribution of the magnetic particles 10 is preferably in the range of 5 to 100 μm to prevent the deterioration of electrification due to the contamination of the particle surface and to adhere the magnetic particles 10 to the surface of the photosensitive drum 1. It is preferable from the viewpoint of prevention. The average particle diameter of the magnetic particles 10 is indicated by the maximum chord length in the horizontal direction. The measuring method is to randomly select 300 or more magnetic particles by a microscope, measure the diameter of the particles, and take the arithmetic average.

In the present embodiment, the developing device 3 uses, as a developer, a mixture of a highly releasable spherical non-magnetic toner produced by a polymerization method and a magnetic carrier (magnetic particles for development, a developing carrier). The developer is held on a developing sleeve (developer carrier) as a magnetic brush layer by a magnetic force, is conveyed to a developing section, and is brought into contact with the surface of the photosensitive drum 1 to develop an electrostatic latent image as a toner image. This is a reversal developing device of a brush contact developing type.

In the developing device 3 shown in FIG. 6, a developing container 21 and a developing sleeve 22 as a developer carrier
Is a magnet (magnet roller) as a magnetic field generating means fixedly arranged in the developing sleeve 22; 24 and 25 are developer conveying screws; and 26 is a developing device for forming a thin layer of developer on the surface of the developing sleeve 22. Agent layer thickness regulating blade,
T is a two-component developer accommodated in the developing container 21 and includes a non-magnetic toner (hereinafter, referred to as toner) t and a magnetic carrier c.
Are mixed. The toner t is supplied to the toner supply unit 27.
Is supplied into the developing container 21 by the driving of the supply roller 28.

The developing sleeve 22 has a closest distance (gap) of about 5 to the photosensitive drum 1 at least during development.
The developer is arranged so as to have a thickness of 00 μm, and is set so that a thin layer of the developer T carried on the outer surface of the developing sleeve 22 is brought into contact with the surface of the photosensitive drum, thereby developing the electrostatic latent image on the photosensitive drum 1. Further, the developing sleeve 22 is driven at a predetermined rotation speed in a direction indicated by an arrow (counterclockwise) around the inside of a magnet (magnet roller) 23 inside. The developer T on the surface of the developing sleeve 22 is conveyed with the rotation of the developing sleeve 22, and is regulated to a layer thickness by a developer layer thickness regulating blade 26 to be formed into a predetermined layer thickness.

A predetermined developing bias in which a DC component and an AC component are superimposed is applied to the developing sleeve 22 from a developing bias applying power source 29. The development characteristics in the present embodiment are as follows:
If the difference between the charged potential of the photosensitive drum 1 and the DC component value of the developing bias is 200 V or less, fogging occurs. If the difference is 350 V or more, the magnetic carrier c adheres to the photosensitive drum 1. Was -400V.
The AC component has a peak-to-peak voltage of 1500 V and a frequency of 3000.
Hz rectangular wave. When the toner density of the developer T in the developing container 21 is detected by density detecting means (not shown) and decreases to a predetermined lower limit density, the toner is supplied from the toner replenishing unit 27 by driving the supply roller 28 as a developer replenishing member. When the toner T is supplied to the developer T in the container 21,
The toner supply is controlled so that the toner concentration of the developer T in the developing container 21 is always kept within a predetermined allowable range.

A transfer roller 4 serving as a transfer means contacts the surface of the photosensitive drum 1 with a predetermined pressing force to form a transfer nip N, and a transfer bias (a polarity opposite to that of the toner (positive Gender bias)
At the transfer nip N, the toner image on the surface of the photosensitive drum 1 is transferred onto the transfer material P.

The conductive brush 5 is in contact with the photosensitive drum 1 between the transfer roller 4 and the magnetic brush charging device 2, and has a polarity (positive polarity) opposite to the charging polarity of the photosensitive drum 1 from a bias power supply 31. At the same time as the surface potential of the photosensitive drum 1 immediately before charging by the magnetic brush charging device 2, the transfer residual toner on the photosensitive drum 1 after the transfer is opposite in polarity to the charged polarity of the photosensitive drum 1 ( (Positive polarity) to facilitate collection by the magnetic brush 10a of the magnetic brush charging device 2.

Further, in the present embodiment, an image ratio detecting sensor (for example, a video counter) 32 for detecting the image ratio of the surface of the photosensitive drum 1 at the time of image formation (image formation) is provided. The (CPU) 33 detects the image ratio based on the detection information input from the image ratio detection sensor 32, and can calculate the calculated consumption of the toner c from the image ratio. Further, the control device (CPU) 33 can detect the operation time of the supply roller 28 and calculate the actual consumption amount of the toner c from the supply of the toner c into the developing container 21. In the present embodiment, the control device (CPU) 33 calculates the amount of toner c calculated based on the detection information from the image ratio detection sensor 32 and the detection information of the operation time of the supply roller 28. The image forming (image forming) operation is controlled based on the actual consumption amount of the toner c (the details will be described later).

Next, an image forming operation of the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate in the direction of arrow a (clockwise) by driving means (not shown), and is charged to −700 V by the magnetic brush charging device 2. Then, an exposure L by a laser beam corresponding to an image signal input from an exposure device (not shown) is given onto the photosensitive drum 1, and the potential on the photosensitive drum 1 decreases due to a decrease in the potential of the exposed portion. An electrostatic latent image is formed. Then, the electrostatic latent image is reversely developed with the developer T (toner c) formed in a thin layer on the surface of the developing sleeve 22 of the developing device 3, and is visualized as a toner image. The developing characteristics of the present embodiment are as follows. When the difference between the DC component value of the charging potential and the DC component value of the developing bias is 200 V or less, fogging occurs, and when the difference is 350 V or more, the developing carrier adheres to the photosensitive drum 1. The DC component value of the bias was -400V.

When the toner image on the photosensitive drum 1 reaches the transfer nip N, the transfer material P such as paper in the paper cassette 34 is fed to the paper feed roller 3 at the timing.
5 and is transported to the transfer nip N by the transport rollers 36 and the like. Then, the transfer nip portion N is transferred by the transfer roller 4 to which a transfer bias having a polarity (positive polarity) opposite to that of the developer T (toner c) is applied from the transfer bias power supply 32.
The toner image on the photosensitive drum 1 is transferred by the electrostatic force generated between the photosensitive drum 1 and the transfer roller 4 to the transfer material P transported to the photosensitive drum 1. Then, the transfer material P on which the toner image has been transferred
Is conveyed to the fixing device 6, and the toner image is heated and pressed to the transfer material P by a fixing nip between the fixing roller 6a and the pressure roller 6b, thermally fixed, and then discharged to the outside, thereby completing a series of image forming operations. I do.

The untransferred toner remaining on the surface of the photosensitive drum 1 without being transferred is charged by the conductive brush 5 to which a bias having a polarity (positive polarity) opposite to the charging potential of the photosensitive drum 1 is applied from a bias power supply 33. Then, the toner is mixed with the magnetic brush 10a on the surface of the charging sleeve 9 at the charging nip M and temporarily collected. By the way, in the above-mentioned transfer residual toner, positive and negative polarities are often mixed due to peeling discharge at the time of transfer. The transfer residual toner having the mixed polarity reaches the magnetic brush charging device 2 and is transferred to the magnetic brush 10.
a and is temporarily collected. The transfer residual toner is taken into the magnetic brush 10 a by applying an AC component from the charging bias power supply 12 to the charging sleeve 9.
Due to the oscillating electric field effect between the charging sleeve 9 and the photosensitive drum 1, it can be more effectively performed.

The transfer residual toner (recovered developer) taken into the magnetic brush 10a is discharged to the photosensitive drum 1 with its polarity all being negatively charged. The untransferred toner (discharged toner) discharged onto the photosensitive drum 1 with the same polarity is collected by the developing sleeve 22 of the developing device 3 at the developing position by the simultaneous cleaning with development by the fog removing bias at the time of development. The simultaneous development and recovery of the transfer residual toner is performed when the image area in the rotation direction is
When the length is longer than the circumference, the image forming process is performed simultaneously with other image forming processes such as charging, exposure, development, and transfer.
As a result, the transfer residual toner is collected in the developing device 3 and used after the next step, so that waste toner can be eliminated. Further, there is a great advantage in terms of space, and the size of the image forming apparatus can be significantly reduced.

Further, by using a highly releasable spherical toner produced by a polymerization method as the toner c of the developer T, the amount of transfer residual toner can be reduced, and the toner is discharged from the magnetic brush 10a. The recoverability of the toner (the discharged toner) into the developing device 3 can be improved. In the present embodiment, the use of the developing device 3 of the two-component contact developing system improves the recoverability of the toner discharged from the magnetic brush 10a to the developing device 3.

When an image is formed (image formed) by the image forming apparatus of the present embodiment, if the charging potential of the photosensitive drum 1 is -700 V and the developing bias to the developing sleeve 22 is -400 V, the photosensitive drum toner amount of the image portion of the first surface is 0.60 mg / cm ^2, the toner amount of the non-image portion was 0 mg / cm ^2. However, the transfer residual toner is mixed into the magnetic brush 10a, and the external additive of the developer or the fragments of the toner adhere to the magnetic particles little by little, so that the electric resistance gradually increases and the chargeability deteriorates. .
Thus, the amount of toner image portion when the charge potential drops to -550V is 0.65 mg / cm ^2, the toner amount of the non-image portion becomes 0.15 mg / cm ^2, fogging occurs. Therefore, when an A4 size image with an image ratio of 10% is formed, the toner consumption per image is 37.8 mg when the charging potential is -700 V, and one image when the charging potential is -550 V. The toner consumption per unit is 126 mg, and 88.2 mg due to the occurrence of fog.
Toner was consumed in excess.

As described above, in the magnetic brush charging device 2 according to the present embodiment, when the potential difference between the charging bias from the charging bias applying power supply 12 and the charging potential on the surface of the photosensitive drum 1 exceeds 150 V, the magnetic brush charging device 2 Particle adhesion begins to occur.

Therefore, in the present embodiment, at the time of image formation (image formation), the control device (CPU) 33 calculates the image ratio from the detection information of the image portion and the non-image portion detected by the image ratio detection sensor 32, From the calculated image ratio, a toner consumption amount on a calculation value at which fogging does not occur is calculated. Further, the control device 33 detects the operation time of the supply roller 28 at the time of image formation (image formation), and based on this detection information, the toner replenishing unit 27.
To calculate the amount of toner supplied into the developing container 21, that is, the actual amount of toner consumption.

The control device 33 includes an image ratio detection sensor 32
And the toner replenishing unit 27 on the calculated value that does not generate fog calculated from the image ratio based on the detection information from
The difference from the actual toner consumption calculated from the operation time information from is calculated. When the difference between the two is smaller than a predetermined value (for example, up to 88.2 mg per A4 size image), the control device 33 executes an image forming (image forming) operation as usual, and the difference between the two is predetermined. When it is determined to be larger than the value (for example, 88.2 mg per A4 size image)
Is determined to have exceeded the threshold value), it is determined that the charged potential of the photosensitive drum 1 has fallen below a preset value (-550 V in the present embodiment), and control is performed to stop the image forming (image forming) operation.

As described above, in the present embodiment, the control device 3
The difference between the toner consumption on the calculated value calculated in step 3 and the actual toner consumption is 88.2 m per A4 size image.
By stopping the image forming (image forming) operation when the value exceeds g, fogging can be prevented, and the potential difference between the charging bias and the charging potential can be prevented from becoming 150 V or more. As a result, it is possible to prevent magnetic particles from adhering to the surface of the photosensitive drum 1 and obtain a good image.

The determination of the difference between the ideal toner consumption amount and the actual toner consumption amount by the control device 33 is performed not every single image but every several tens of sheets. The difference from the calculated toner amount increases, and the image forming (image forming) operation can be stopped accurately so that the magnetic particles do not adhere to the surface of the photosensitive drum 1.

Second Embodiment FIG. 7 is a schematic configuration diagram showing an image forming apparatus according to a second embodiment of the present invention. Members having the same functions as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and overlapping descriptions will be omitted.

This image forming apparatus has a toner concentration detecting sensor 37 for detecting the toner concentration in the developer T filled in the developing container 21.
PU) 33 detects the toner density based on the toner density detection information input from the toner density detection sensor 37. In this embodiment, the image formation (image formation) is temporarily stopped during the image formation (image formation) operation, and the development is performed when the charging and the development operation of the surface of the photosensitive drum 1 are performed without performing the exposure. The controller 33 detects the toner density in the developer T based on the toner density detection information from the toner density detection sensor 37, and when it is determined that the amount of change in the detected toner density exceeds a predetermined value, the photosensitive drum 1 Is determined to have fallen below a preset value (−550 V in the present embodiment), and control is performed to stop the image forming (image forming) operation.

Specifically, when there is almost no change in the toner density, that is, when there is no fog, the charging potential is a predetermined -700 V as in the first embodiment. When the controller 33 determines that the toner concentration has decreased from the initial 10% to 9.6% and has exceeded a predetermined value (change amount), the image forming (image forming) operation is stopped. At this time, 900 mg of the toner was consumed in 20 seconds, fog occurred, and the charging potential was lowered to -550V.

As described above, in the present embodiment, the toner density in the developer T when the charging and the developing operation of the surface of the photosensitive drum 1 are performed without performing the exposure is detected by the toner density detection sensor 37. The control device 33 detects the change based on the information, and stops the image forming (image forming) operation when it is determined that the detected amount of change in the toner density exceeds a predetermined value, thereby preventing the occurrence of fog. And
Since the potential difference between the charging bias and the charging potential can be prevented from becoming 150 V or more, it is possible to prevent the magnetic particles from adhering to the surface of the photosensitive drum 1 and obtain a good image.

<Embodiment 3> In the image forming apparatus according to each of the above-described embodiments, if a large number of images are formed in which the toner region is concentrated on a specific portion in the thrust direction, the magnetic brush corresponding to the portion is formed. Magnetic brush 10 of charging device 2
Deterioration of the magnetic particles 10 forming a is accelerated, and the charged potential of the photosensitive drum 1 is locally reduced. In this case, fogging occurs only in a portion where the charged potential is lowered, and thus the toner consumption due to fogging is small.

Therefore, in this embodiment, as shown in FIG. 8, a plate-shaped magnet 40 covered with a conductor 39 such as aluminum is provided on the upper cover 38 of the developing sleeve 22 of the developing device 3 with the photosensitive drum 1. They were arranged so as to be close to each other. The magnet 40 is located on the upstream side of the developing position A facing the developing sleeve 22 with respect to the rotation direction of the photosensitive drum 1.
And close. The magnet 40 is formed along the longitudinal direction of the developing sleeve 22. The same developing bias as the developing bias applied to the developing sleeve 22 from the developing bias application power supply 29 is applied to the conductor 39. Other configurations of the developing device 3 and the configuration of the image forming apparatus are described in Embodiment 2.
Is the same as

As described above, when the charging potential of the photosensitive drum 1 locally decreases, magnetic particles adhere to the photosensitive drum 1, and the magnetic particles move to the developing position A facing the developing sleeve 22 as the photosensitive drum 1 rotates. Move. At this time, the magnetic particles on the photosensitive drum 1 are attracted by the magnetic force of the magnet 40 and adhere to the surface of the conductor 39 on the magnet 40.

When the total amount of magnetic particles adhering to the photosensitive drum 1 exceeds a certain amount, the magnetic particles fill the gap between the conductor 39 and the photosensitive drum 1. As a result, the photosensitive drum 1 is recharged to the DC value of the developing bias applied to the conductor 39 (−400 V in the present embodiment). When the area charged by the developing bias on the photosensitive drum 1 passes through the developing position A, fogging that is darker than fogging that occurs when the charging potential is reduced causes toner consumption to increase.

Then, the controller 33 detects a change in the toner density in the developer T based on the toner density detection information from the toner density detection sensor 37 shown in FIG. Adhesion to the surface can be detected. When the attachment of the magnetic particles to the surface of the photosensitive drum 1 is detected, the image forming (image forming) operation is stopped.

As described above, in the present embodiment, even when the toner consumption due to fog is small during normal image formation, the adhesion of the magnetic particles to the surface of the photosensitive drum 1 can be detected. By stopping the (imaging) operation, occurrence of an image defect can be prevented.

Although the conductor 39 is not grounded in the present embodiment, the conductor 39 may be grounded.

Although each of the above embodiments is an image forming apparatus for forming a monochrome image, the present invention can be applied to an image forming apparatus capable of forming a full-color image.

[0072]

As described above, according to the first aspect of the invention, the toner consumption is calculated from the calculated value calculated from the image ratio detected by the image ratio detection means and the operation information of the developer supply means. If it is determined that the difference from the actual toner consumption is larger than a predetermined value, it can be determined that the charging potential of the image carrier has dropped below the set value, and thus the adhesion of the magnetic particles to the image carrier is preliminarily determined. And the occurrence of image defects can be prevented.

According to the present invention, the toner concentration in the developer when the image carrier is charged and the developing operation is performed without performing the exposure is detected by the toner concentration detecting means. When it is determined that the amount of change in the toner density exceeds a predetermined value, it can be determined that the charging potential of the image carrier has fallen below the set value, so that the magnetic particles are prevented from adhering to the image carrier. As a result, it is possible to prevent image defects from occurring.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a layer configuration of a photosensitive drum.

FIG. 3 is a schematic configuration diagram illustrating a magnetic brush charging device of the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an equivalent circuit between a magnetic brush charging device and a photosensitive drum.

FIG. 5 is a diagram showing a measuring device for measuring a resistance value of magnetic particles.

FIG. 6 is a schematic configuration diagram illustrating a developing device of the image forming apparatus according to the first embodiment of the present invention.

FIG. 7 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention.

FIG. 8 is a schematic configuration diagram showing a developing device of the image forming apparatus according to Embodiment 3 of the present invention.

FIG. 9 is a diagram illustrating a potential between a charging sleeve and a photosensitive drum of an image forming apparatus according to a conventional example.

[Explanation of symbols]

Reference Signs List 1 photosensitive drum (image carrier) 2 magnetic brush charging device (charging device) 3 developing device (developing device) 4 transfer roller (transfer device) 6 fixing device 9 charging sleeve (magnetic particle carrier) 10 magnetic particles 10a magnetic brush 22 Developing sleeve (developer carrier) 28 Supply roller (developer consumption detecting means, developer replenishing member) 32 Image ratio detecting sensor (image ratio detecting means) 33 Control device (control means) 37 Toner density detecting sensor (density detecting Means) 39 Conductor 40 Magnet (Magnetic field generating means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyuki Komiya 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Shuichi Kadota 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Kenichi Shibuya 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H003 AA02 BB11 CC04 DD08 DD14 2H027 DA02 DA09 DA32 DD07 DE04 DE05 DE07 EA01 EA18 EC06 ED03 ED08 EF09 EK03 2H077 AA37 AC04 AC16 AD06 AD35 DA02 DA10 DA12 DA42 DA51 DA59 DB12 DB21 EA03

Claims (7)

[Claims] An image bearing member; a charging unit configured to contact magnetic particles supported on the magnetic particle bearing member with the image bearing member and charge the image bearing member by applying a charging bias; Exposure means for exposing the image carrier to form an electrostatic latent image, developing means for developing the electrostatic latent image with a developer to visualize it as a developer image, and applying the developer image to a transfer material Transfer means for transferring, after transferring the developer image to the transfer material, after once recovering the transfer residual developer remaining on the image carrier to the magnetic particles, it can be discharged from the magnetic particles and discharged In an image forming apparatus for re-collecting by a developing unit, an image ratio detecting unit for detecting an image ratio of the developer image to an image forming area on the image carrier, and a developer consumed for forming the developer image Developer consumption detecting means for detecting the amount of the developer, Calculating the calculated amount of developer consumption based on the image ratio detection information input from the image ratio detection means, and calculating the development amount based on the developer consumption detection information input from the developer consumption detection means. Control means for calculating a developer consumption amount by forming a developer image, and detecting a decrease in the charged potential of the image carrier based on the calculated developer consumption amount and the developer consumption amount. An image forming apparatus, characterized in that: 2. When the difference between the calculated consumption amount of the developer and the consumption amount of the developer exceeds a predetermined value, the control unit lowers the charging potential of the image carrier below a predetermined value. The image forming apparatus according to claim 1, wherein it is determined that the image formation has been completed, and control is performed to stop the image formation of the developer image. 3. The developer consumption detecting means is a developer replenishing member for replenishing the developer to the developing means, and the control means is configured to control a developer consumption based on a driving time of the developer replenishing member. The image forming apparatus according to claim 1, wherein is calculated. 4. An image bearing member, charging means for bringing magnetic particles carried on a magnetic particle bearing member into contact with the image bearing member, and charging the image bearing member by applying a charging bias; Exposure means for exposing the image carrier to form an electrostatic latent image, developing means for developing the electrostatic latent image with a developer to visualize it as a developer image, and applying the developer image to a transfer material Transfer means for transferring, after transferring the developer image to the transfer material, after once recovering the transfer residual developer remaining on the image carrier to the magnetic particles, it can be discharged from the magnetic particles and discharged An image forming apparatus for re-collecting by the developing unit; a density detecting unit for detecting a density of the developer by the developing unit; a charging operation of the image carrier by the charging unit during non-image formation; While performing the developing operation, the density The density detection of the developer is performed by the informing means, and before and after the charging operation and the developing operation are performed, the density detection information when the density detection of the developer is performed by the density detection means is input. Calculating the developer concentration before and after the charging operation and the developing operation from the input density detection information, and based on the difference between the calculated developer concentration before and after the charging operation and the developing operation. And control means for detecting a decrease in the charged potential of the image carrier. 5. When the difference between the calculated developer concentration before and after the charging operation and the developing operation exceeds a predetermined value, the control unit changes the charging potential of the image carrier to a predetermined value. 5. The image forming apparatus according to claim 4, wherein the image forming apparatus controls the image forming of the developer image to be stopped when the image forming apparatus determines that the developer image has decreased. 6. A magnetic field generator having at least a portion of a surface having conductivity, between the image bearing member and the developing means and in the vicinity of the image bearing member along a rotation direction of the image bearing member. 6. The image forming apparatus according to claim 1, wherein a unit is arranged, and the same bias as a developing bias applied to the developing unit is applied to the magnetic field generating unit. 7. The image bearing member according to claim 1, wherein the image bearing member is an electrophotographic photosensitive member having a charge injection layer in which conductive fine particles are dispersed in an insulating binder. 7. The image forming apparatus according to claim 5 or 6.