JPH11143177A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent, in the image forming device equipped with a magnetic- brush electrifier, degradation of electrification performance due to soil of conductive magnetic particles. SOLUTION: The conductive magnetic particles C on the sleeve 7 of the magnetic-brush electrifier 2 which have been soiled due to an image output are collected with a blade 16, fresh conductive magnetic particles C1 which have not been soiled are supplied onto the sleeve 7 from the first storage part 13 of an electrification container 9, and a photoreceptive drum 1 is electrified. This prevents the electrification performance of the magnetic-brush electrifier 2 from degrading due to the conductive magnetic particles C which have been soiled.

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, a facsimile or the like which forms an image by an electrophotographic method, and more particularly to an image forming apparatus in which conductive magnetic particles are brought into contact with the image forming body. The present invention relates to an image forming apparatus provided with a magnetic brush charging device for charging an image.

[0002]

2. Description of the Related Art In a conventional image forming apparatus using an electrophotographic method, a corona charger is frequently used as a means for charging a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. I was In this method, a corona charger is disposed so as to be in non-contact with a photosensitive drum, and the surface of the photosensitive drum is charged to predetermined polarity and potential by exposing the surface of the photosensitive drum to a discharge corona generated by the corona charger.

In recent years, contact charging devices have been put to practical use because they have advantages such as lower ozone and lower power than corona chargers. This is because a charged member to which a voltage is applied is brought into contact with the photosensitive drum to make the surface of the photosensitive drum have a predetermined polarity,
It is charged to a potential.

A contact charging device using a magnetic brush as the charging member is preferably used in terms of charging, contact safety, and the like. In this magnetic brush type contact charging device, the conductive magnetic particles are magnetically constrained and held directly as a magnetic brush on a magnet or a sleeve containing the magnet, and the magnetic brush is stopped or rotated on the surface of the photosensitive drum. The charging of the photosensitive drum is started by bringing it into contact and applying a voltage thereto.

FIG. 7 is a schematic view showing a magnetic brush charging device of a conventional image forming apparatus. The magnetic brush charging device 101 includes a fixed magnet roller 1 in a charging container 102.
03 is provided with a rotatable non-magnetic sleeve 104 containing therein. The magnetic particles C carried by the magnetic force on the sleeve 104 are regulated by the regulating member 105 at an appropriate layer pressure, and then contact the photosensitive drum 100 to perform charging.

In contact charging, a charge injection layer is provided on a photosensitive drum, and a charge member to which a voltage is applied is brought into contact with the photosensitive drum to inject charges into the charge injection layer to cause the surface of the photosensitive drum to have a predetermined polarity. In the charging method, the surface potential of the photosensitive drum is substantially equal to the applied DC voltage (DC bias) regardless of the presence or absence of the AC voltage (alternating bias) superimposed on the charging member. For this reason, since a discharge phenomenon in which charging of the photosensitive drum is performed using a corona charger is not used, ozone is not generated and low-power-consumption charging can be performed.

Further, in recent years, a cleanerless system using the above-described contact charging system has been put into practical use for the purpose of miniaturizing and simplifying the apparatus, or not generating waste toner from the viewpoint of ecology. In this method, a cleaning device for removing transfer residual toner from the surface of a photosensitive drum after transferring a toner image to a transfer material is omitted, and the transfer residual toner is collected by a developing device.

Here, a cleanerless process using a magnetic brush charging device will be briefly described. In this cleanerless process, the polarity of the transfer residual toner entering the charging section of the charging device includes both positive polarity toner and toner whose charging polarity has been inverted due to discharge or the like during transfer. Of these, the positive polarity toner passes through the charging unit while being rubbed by magnetic particles (magnetic brush).

This is because the photosensitive drum surface is normally charged only to a potential slightly lower than the voltage applied to the charging device, so that an electric field is generated in the positive polarity toner which is pressed toward the photosensitive drum. At this time, the image pattern is disturbed to some extent by the rubbing, so that the image pattern is easily collected by the developing device. On the other hand, the toner whose polarity has been reversed generates an electrostatic force in the direction of the charging device, and is once collected in the charging device. Here, the polarity of the toner is normalized again by frictional charging with the magnetic particles, and the toner adheres to the photosensitive drum by electrostatic force toward the photosensitive drum, and is collected by the developing device.

[0010]

However, even in the cleanerless process using the above-described magnetic brush charging device, the charging ability is reduced due to contamination of the magnetic particles by the spent of the toner resin and the like, and a poorly charged image is output. There was a problem that it would.

In view of the above, the present invention provides a method of collecting contaminated conductive magnetic particles carried on a sleeve and supplying new conductive magnetic particles onto the sleeve to prevent the charging performance of the magnetic brush charging means from deteriorating. It is an object of the present invention to provide an image forming apparatus capable of performing the following.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has an image carrier for carrying an image, a surface in which conductive magnetic particles are constrained, and a magnetic field generating means is internally provided. A rotatable sleeve is provided in the charging container, and a regulating means for regulating the carrying amount of the conductive magnetic particles constrained on the sleeve is provided. An image forming apparatus comprising: a magnetic brush charging unit that abuts on a body to charge the image carrier; and a charging bias power supply that applies a charging bias to the sleeve. A collection unit for collecting particles, a storage unit storing uncontaminated conductive magnetic particles supplied on the sleeve, an evaluation unit for evaluating a charging ability of the magnetic brush charging unit, The collection means controls the collection of the conductive magnetic particles on the sleeve based on the charging capability information of the magnetic brush charging means by the charging means, and the contamination from the storage section onto the sleeve is performed. And control means for controlling so as to supply no conductive magnetic particles.

Further, the evaluation means is a current amount measuring means for measuring an amount of current flowing to the sleeve to which a charging bias is applied from the charging bias power supply, and the control means is a current amount measuring means for measuring the current amount. When it is determined that the amount of the supplied current has become equal to or less than a specified value with respect to a preset reference current amount, the collecting means controls the collection of the conductive magnetic particles on the sleeve, and the sleeve from the storage portion. It is characterized in that control is performed to supply the non-contaminated conductive magnetic particles.

Further, the evaluation means is a potential measuring means for measuring a potential on the image carrier, and the control means is
When it is determined that the potential difference by comparison of the potential on the image carrier after the predetermined rotation measured by the potential measuring means has become equal to or greater than a preset reference value, the collecting means determines the conductive magnetic particles on the sleeve. And controlling the supply of the uncontaminated conductive magnetic particles from the storage section onto the sleeve.

Further, the sampling means is a blade which can freely contact and separate from the sleeve.

Further, the magnetic brush charging means also serves as a cleaning means for cleaning the image carrier.

Further, it is characterized in that it is provided with a cleaner means for removing deposits on the surface of the image carrier.

(Operation) According to the structure of the present invention, the contaminated conductive magnetic particles on the sleeve are collected by the collecting means.
By supplying new conductive magnetic particles that are not contaminated from the storage section onto the sleeve, it is possible to prevent the charging performance of the magnetic brush charging unit from being deteriorated due to the contamination of the conductive magnetic particles.

[0019]

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

(Embodiment 1) FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. The image forming apparatus according to the present embodiment uses a magnetic brush type contact charging device as a charging unit for the image carrier, and is a cleanerless system device.

This image forming apparatus includes a photosensitive drum 1 as an image carrier, a magnetic brush charging device 2, a developing device 3, a transfer roller 4, a transport belt 5, a fixing device 6, and the like.

In the present embodiment, the photosensitive drum 1 is a negatively charged organic photosensitive member, and is formed of a first to fifth five photosensitive layers (in order from the bottom) on an aluminum drum base (not shown). (Not shown), and is rotationally driven in a direction of an arrow a at a predetermined process speed.

The lowermost first layer of the photoreceptor layer is a subbing layer, which is a conductive layer having a thickness of 20 μm and provided for smoothing out defects or the like of the drum substrate. The second layer is a positive charge injection preventing layer, which serves to prevent positive charges injected from the drum substrate from canceling out negative charges charged on the surface of the photosensitive drum 1, and is made of an amylan resin and methoxymethylated nylon. This is a 1 μm thick medium resistance layer whose resistance is adjusted to about 10 ⁶ Ω · cm. The third layer is a charge generation layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin.
m, and generate positive and negative charge pairs upon exposure. The fourth layer is a charge transport layer in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor.

Therefore, the negative charges charged on the surface of the photosensitive drum 1 cannot move through this layer (fourth layer), and only the positive charges generated in the third layer (charge generation layer) are transferred to the photosensitive drum 1. Can be transported to the surface. The fifth layer on the outermost surface is a charge injection layer, and is a coating layer of a material in which SnO ₂ ultrafine particles are dispersed as conductive fine particles in a binder of an insulating resin. Specifically, antimony, which is a light-transmitting conductive filler, is doped into an insulating resin to reduce resistance (conductivity).
This is a coating layer of a material in which ultrafine SnO ₂ particles having a particle size of about 0.03 μm are dispersed in a resin by 70% by weight.

The coating solution thus prepared is applied to a thickness of about 3 μm by an appropriate coating method such as dipping coating, spray coating, roll coating, beam coating, etc. And

As shown in FIGS. 1 and 2, the magnetic brush charging device 2 includes a rotatable non-magnetic sleeve 7 having a diameter of 25 mm and a magnet roller 8 fixed inside.
And a fixed magnet roller 8 on the outer peripheral surface of the sleeve 7.
Particles (magnetic carrier) C adhered and held by the magnetic force of
A charging container 9 containing the sleeve 7; and a regulating plate 10 for forming a thin layer of the magnetic particles C on the surface of the sleeve 7.

The sleeve 7 is rotatable with respect to the photosensitive drum 1 in the counter direction (the direction of the arrow b).
From the charging bias power supply S1 (for example,-
By applying a charging bias in which an alternating electric field having a peak-to-peak voltage of 1000 V and a frequency of 1000 Hz is superimposed on a 700 V DC voltage, electric charges from the magnetic particles C are transferred to the photosensitive drum 1
And charged to a potential corresponding to the charging bias.

The sleeve 7 and the charging bias power source S1
Between them, a current amount detection device 11 for detecting a DC current amount flowing through the magnetic particles C on the sleeve 7 and a control device (CPU)
The control device (CPU) 12 controls the supply of the magnetic particles C onto the sleeve 7 based on information on the amount of direct current flowing through the magnetic particles C detected by the current amount detecting device 11 (for details, see FIG. See below).

The thickness of the magnetic particles C is regulated by the regulating plate 10 and is held on the sleeve 7 by magnetic force.
A magnetic brush is formed at a position facing the photosensitive drum 1 and is in contact with the photosensitive drum 1 rotating in the direction of arrow a. The carrying amount of the magnetic particles C on the sleeve 7 is 150 mm /
sec. The gap between the photosensitive drum 1 and the sleeve 7 was set to 0.05 cm.

The charging container 9 has a first storage section 13 for storing new magnetic particles C1 which are not contaminated, and a second storage section 14 for storing used magnetic particles C2 collected from the sleeve 7. . 280 g in the first storage section 13
Is filled with the magnetic particles C1.

In the first storage section 13, a remaining amount detecting sensor 15 for detecting the remaining amount of the magnetic particles C1 is provided.
A scraper 16 that can freely contact and separate from the sleeve 7 is provided above the second storage section 14, and is driven by a drive device (not shown) under the control of the control device (CPU) 12. The scraper 16 is separated from the sleeve 7 during normal image formation, but contacts the sleeve 7 as necessary, and the magnetic particles C
Can be scraped into the second storage section 14.

The magnet roller 8 has four magnetic poles,
The magnetic flux density on the sleeve 7 is 800 gauss each.

The restricting plate 10 is provided by the S1 of the magnet roller 8.
A straight line connecting the S1 pole and the sleeve rotation axis O between the pole (regulation pole) and the N1 pole (main pole), the regulation plate 10 and the sleeve rotation axis O
Are arranged at a position where the angle (hereinafter referred to as θ1) formed by the straight line connecting is 80 °.

The opposite angle θ2 of the S1 pole to the photosensitive drum 1, ie, the straight line connecting the sleeve rotation axis O and the closest position between the photosensitive drum 1 and the sleeve 1, and the straight line connecting the sleeve rotation axis O and the S1 pole. The angle is preferably −10 ° ≦ θ2 ≦ 5 °, with the rotation direction upstream side of the sleeve 7 being the plus side. If the ratio is outside this range, the holding power of the magnetic particles C in the charging nip is insufficient, so that the adhesion of the magnetic particles C to the photosensitive drum 1 increases and the conveying force of the magnetic particles C becomes insufficient. In the present embodiment, θ2 = −
5 °, that is, 5 ° to the downstream side in the rotation direction of the sleeve 7.

The following can be preferably used as the magnetic particles C.

A resin and a magnetic powder such as magnetite are kneaded and molded into particles, or a mixture of this and conductive carbon or the like for adjusting the resistance value. Alternatively, sintered magnetite, ferrite, or those obtained by reducing or oxidizing these to adjust the resistance value. Alternatively, the above-mentioned magnetic particles are coated with a resistance-adjusted coating material (such as phenol resin in which carbon is dispersed) or plated with a metal such as Ni to have an appropriate resistance value.

If the resistance value of the magnetic particles C is too high, the charge cannot be uniformly injected into the photosensitive drum 1 and a fog image due to minute charging failure will result. Conversely, if it is too low, when there is a pinhole on the surface of the photosensitive drum 1, current concentrates on the pinhole and the charging voltage drops, so that the surface of the photosensitive drum 1 cannot be charged. . Therefore, the resistance value of the magnetic particles C is 1 × 10 ⁴
〜1 × 10 ⁷ Ω is desirable. Regarding the magnetic characteristics of the magnetic particles C, it is better to increase the magnetic restraining force in order to prevent the magnetic particles C from adhering to the photosensitive drum 1, and the saturation magnetization is 5%.
0 (A · m ² / kg) or more is desirable. The magnetic particles C used in the present embodiment have a volume average particle size of 30 μm, an apparent density of 2.0 g / cm ³ , a resistance value of 1 × 10 ⁶ Ω, and a saturation magnetization of 5 μm.
8 (A · m ² / kg).

The resistance value of the magnetic particles C was measured by placing 2 g of the magnetic particles C in a metal cell (bottom area: 228 mm ² ) to which a voltage can be applied, applying a load, and applying a voltage of 1 to 1000 V. The volume average particle diameter of the magnetic particles C is indicated by the maximum chord length in the horizontal direction, and the measurement method was calculated by randomly selecting 300 or more magnetic particles by a microscope, measuring the diameter, and taking an arithmetic average. . For the measurement of the magnetic properties of the magnetic particles C, a DC magnetization BH characteristic automatic recording device BHH-50 manufactured by Riken Denshi Co., Ltd. can be used. At this time, the magnetic particles C are filled into a cylindrical container having a diameter (inner diameter) of 6.5 mm and a height of 10 mm under a load of about 2 g, and the magnetic particles C are not moved in the container, and the BH curve is obtained. The saturation magnetization is measured from. The apparent density of the magnetic particles C is JISZ25
041.

The particle size of the magnetic particles C affects charging ability and charging uniformity. That is, if the particle diameter is too large, the contact ratio with the photosensitive drum 1 is reduced, which causes uneven charging. When the particle size is small, both the charging ability and the uniformity are improved, but the adhesion to the photosensitive drum 1 is easily caused. For this reason, the particle diameter of the magnetic particles C is preferably 5 to 100 μm.

As shown in FIGS. 1 and 3, the developing device 4
A component contact developing device (two-component magnetic brush developing device) including a rotatable developing sleeve 20 provided with a magnet roller 21 fixed inside, and a developer T contained in a developing container 22 At 23, a thin layer is coated on the developing sleeve 20 and transported to the developing section. The developing sleeve 20 is 150 mm / s in the direction of arrow c.
It is rotationally driven at a peripheral speed of ec.

The developer T is a two-component developer in which a negatively chargeable toner having an average particle size of 8 μm and a positively chargeable magnetic carrier having an average particle size of 50 μm are mixed at a weight toner concentration of 5%.
The toner used in the present embodiment is a toner manufactured by a polymerization method, and has a spherical shape and very good fluidity than a toner manufactured by a pulverization method usually used in this type of apparatus. The toner density is controlled by an optical toner density sensor (not shown), and toner (not shown) in the toner hopper 24 is supplied by a supply roller 25. The developer T in the developing container 22 is uniformly stirred by the stirring members 26 and 27.

The developing sleeve 20 has a peak-to-peak voltage of -500 V from a developing bias power supply (not shown).
A developing bias in which an alternating electric field of 000 V and a frequency of 2000 Hz is superimposed is applied.

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 by driving means (not shown), and is charged to -700 V by the magnetic brush charging device 2. Then, the laser beam L corresponding to the image signal is irradiated onto the photosensitive drum 1, and the potential on the photosensitive drum 1 at the portion irradiated with the laser beam L is reduced, so that an electrostatic latent image is formed. Then, the portion of the electrostatic latent image irradiated with the laser beam L by the developing device 3 is reversely developed with the toner having the negative polarity, and is transferred to the transfer material P by the transfer roller 4.

The transfer material P on which the toner image has been transferred is transported by the transport belt 5 between the heating roller 6a and the pressure roller 6b of the fixing device 6, where the toner image is thermally fixed on the transfer material P and discharged. .

On the other hand, the transfer residual toner remaining on the photosensitive drum 1 after the above-described image formation is carried on the photosensitive drum 1 and enters the next image forming step. The transfer residual toner is subjected to pattern scraping and polarity normalization by the magnetic brush charging device 2, and is then collected in the developing container 22 by the developing sleeve 20 of the developing device 3 by a fogging potential in a developing process.

In this cleanerless process, as described above, the resistance of the magnetic brush charging device 2 is increased by the adhesion of the resin component of the toner and the external additive to the surface of the magnetic particles C with the image output, thereby increasing the resistance. And fog and ghost images are output.

Therefore, in this embodiment, the magnetic particles C
The charging ability of the magnetic particles C is detected by measuring the resistance of the magnetic particles C with the current amount detecting device 11, and the magnetic particles C on the sleeve 7 are scraped off by the scraper 16 under the control of the control device 12, so that a new one is placed on the sleeve 7. The magnetic particles C are supplied to improve the durability of the magnetic brush charging device 2.

Here, an exchange operation of the magnetic particles C on the sleeve 7 will be described.

The scraper 16 of the second storage section 14 is separated from the sleeve 7 during image formation, but comes into contact with the sleeve 7 as shown in FIG.
When the sleeve 7 is rotated in the direction of the arrow b in this state, the magnetic particles C to which the resin component of the toner, the external additive, and the like have adhered are scraped off by the scraper 16 and fall into the second storage section 14. Then, after new magnetic particles C1 are supplied from the first storage section 13 onto the sleeve 7, the scraper 16 is separated from the sleeve 7, and normal image formation is enabled.

During normal image formation, mixing of the magnetic particles C carried on the sleeve 7 and the magnetic particles C1 stored in the first storage section 13 hardly occurs. This is because the amount of magnetic particles C1 per hour that is regulated by the regulating plate 10 and supplied to the photosensitive drum 1 is substantially equal to the amount of magnetic particles C1 per hour that enters the first storage unit 13. This is because the magnetic particles C on the sleeve 7 are restrained on the sleeve 7 by the magnetic force of the magnet roller 8. For this reason, the magnetic particles C1 in the first storage section 13 are always kept unused except for a part of the magnetic particles C1 on the sleeve 7. Therefore, by peeling off the magnetic particles C on the sleeve 7, new magnetic particles C1 in the first storage section 13 are supplied onto the sleeve 7.

The amount of the magnetic particles C to be scraped off is determined by the number of revolutions of the sleeve 7, but in this embodiment, the sleeve 7 is rotated once while the scraper 16 is in contact. It was possible to replace 80% or more of the sleeve 7 from the drop amount at this time.

Here, a method for detecting the charging ability of the magnetic brush charging device 2 will be described.

As described above, the magnetic brush charger 2 is supplied with a charging bias in which an alternating electric field having a peak-to-peak voltage of 1000 V and a frequency of 1000 Hz is superimposed on a DC voltage of -700 V from the charging bias applying power source S1. The amount of DC current flowing through the magnetic particles C between the power supply S1 and the magnetic brush charging device 2 is detected by the current amount detection device 11.

The current amount detection by the current amount detection device 11 is as follows.
This is performed after image formation when a predetermined number of sheets is exceeded. In this embodiment, the image output is performed every 1500 sheets.

The current amount detection by the current amount detection device 11 is as follows.
In order to accurately measure the resistance of the magnetic particles C, the photosensitive drum 1
It is necessary to make the potential difference of the magnetic particles C with respect to the constant value. Therefore, since the image ratio and the transfer voltage change during image formation, the potential difference from the photosensitive drum 1 during charging is not constant, so that no detection is performed, and the potential on the photosensitive drum 1 is kept constant during non-image formation. Performs current detection. In this embodiment, during non-image formation, the entire surface of the photosensitive drum 1 is exposed by the laser beam L, and the developing bias application power supply (not shown) and the transfer bias application power supply (not shown) are turned off.
The DC current at a constant potential difference from the exposed portion potential to the charging potential was measured.

Then, the control device (CPU) 12 takes in the current amount information detected by the current amount detection device 11 and calculates the ratio of the detected and measured current amount to the reference current. Particle C
To remove the new magnetic particles C1 from the first storage unit 13.
Is controlled to be supplied. In addition, the amount of current after supply is also measured and compared with the value before supply.If the ratio of these two values is within a certain range, and if the charging ability is not improved, it is regarded as a change in the amount of current due to environmental fluctuations Control is performed so as not to supply the particles C1.

When the remaining amount detecting sensor 15 provided in the first storage unit 13 detects that the first storage unit 13 has run out of the magnetic particles C1, the control unit (CPU) 12 controls the subsequent magnetic particles C1. Is controlled not to be exchanged.

FIG. 4 is a diagram showing a change in charging ability according to an image output in this embodiment and a conventional example. The vertical axis of this figure represents the difference between the potential when the photosensitive drum 1 is charged once from the exposed portion potential and the potential when the potential of the photosensitive drum 1 is saturated. Means higher. As is apparent from this figure, when the amount of DC current flowing through the magnetic particles C between the charging bias power supply S1 and the magnetic brush charging device 2 falls below the standard, new magnetic particles C1 are supplied onto the photosensitive drum 1 in the related art. It can be seen that the lowering of the charging ability is significantly improved as compared with the example.

As described above, by detecting the increase in the resistance of the magnetic particles due to the image output and supplying new magnetic particles that have not been contaminated in advance, the output of a poorly charged image is prevented beforehand, and the number of printable images is reduced. It could be greatly extended.

(Embodiment 2) FIG. 5 is a schematic diagram showing the configuration of an image forming apparatus according to the present embodiment. The same members as those in Embodiment 1 are denoted by the same reference numerals, and redundant description is omitted. . The present embodiment has a configuration in which an electrometer 30 for measuring the potential on the photosensitive drum 1 is provided, and other configurations and image forming operations are the same as those in the first embodiment.

In this embodiment, the number of output images is 150
When the number of sheets exceeds zero, a sequence for checking the charging ability of the magnetic brush charging device 2 is performed after the completion of image formation.
That is, the entire surface of the photosensitive drum 1 is irradiated with a laser beam L from an exposure device (not shown), and the potential on the photosensitive drum is attenuated to the exposure portion potential. Then, the exposure by the laser beam L, the developing bias, and the transfer bias are turned off, and the photosensitive drum 1 is rotated while applying a normal charging bias to the magnetic brush charging device 2. At this time, the potentials of the first and third rotations of the photosensitive drum are measured by the electrometer 30, and the control device (CPU) 17 takes in the potential information measured by the electrometer 30, and performs the first and third rotations of the photosensitive drum. When the potential difference of the eyes becomes equal to or more than a specified value, the magnetic particles C on the sleeve 7 are scraped off by the scraper 16, and control is performed so that new magnetic particles C 1 that are not contaminated are supplied from the first storage unit 13.

As described above, also in the present embodiment, similarly to the first embodiment, it is possible to prevent the deterioration of the charging ability due to the contamination of the magnetic particles beforehand and to greatly improve the durability of the magnetic brush charging device 2. Was completed.

(Embodiment 3) FIG. 6 is a schematic side sectional view showing a magnetic brush charging device of an image forming apparatus according to the present embodiment, and the same members as those in Embodiment 1 are denoted by the same reference numerals. Duplicate description will be omitted. In the present embodiment, the above-described first or second embodiment is provided except that the cleaner 31 is provided to remove extraneous matter such as untransferred toner on the surface of the photosensitive drum 1.
Has the same configuration as that of the image forming apparatus.

Even after the adhering matter such as untransferred toner on the surface of the photosensitive drum 1 is removed by the cleaner 31 after the image is formed, the external additive of the toner that has passed through the cleaner 31 is mixed into the magnetic particles C on the sleeve 7. Although the charging ability gradually deteriorates, the magnetic particles C on the sleeve 7 of the magnetic brush charging device 2 are removed by the scraper 16 as in the first and second embodiments.
To supply new non-contaminated magnetic particles C1 onto the sleeve 7 based on the amount of current flowing through the magnetic particles C between the charging bias power supply S1 and the magnetic brush charging device 2 or the potential on the photosensitive drum 1. As a result, a decrease in charging ability due to contamination of magnetic particles was prevented beforehand, and the durability of the magnetic brush charging device 2 was dramatically improved.

[0066]

As described above, according to the present invention,
The contaminated conductive magnetic particles on the sleeve of the magnetic brush charging means by the image output are collected by the collecting means, and the non-contaminated conductive magnetic particles are supplied from the storage section onto the sleeve to charge the image carrier. As a result, deterioration of the charging performance of the magnetic brush charging means due to contamination of the conductive magnetic particles can be prevented, and a good image can be stably formed over a long period of time.

[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 side view showing a magnetic brush charging device of the image forming apparatus according to Embodiment 1 of the present invention.

FIG. 3 is a schematic side view showing a developing device of the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between the number of output images and charging ability according to the first embodiment of the present invention.

FIG. 5 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a schematic side view showing a magnetic brush charging device of the image forming apparatus according to Embodiment 3 of the present invention.

FIG. 7 is a schematic side view showing a magnetic brush charging device of an image forming apparatus in a conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photosensitive drum (image carrier) 2 magnetic brush charging device (magnetic brush charging means) 3 developing device 4 transfer roller 6 fixing device 7 sleeve 8 magnet roller 9 charging container 10 regulating plate (regulating means) 11 current amount detecting device (evaluation) Means, current amount detection means) 12 control device (control means) 13 first storage section (storage section) 14 second storage section 15 remaining amount detection sensor 16 scraper (sampling means) 20 developing sleeve 30 electrometer (evaluation means, potential) Measuring means) 31 cleaner

Claims (6)

[Claims] An image bearing member for carrying an image and a rotatable sleeve having conductive magnetic particles confined on the surface thereof and containing a magnetic field generating means therein are provided in a charging container, and are constrained on the sleeve. A magnetic brush charging unit that has a regulating unit that regulates the amount of the conductive magnetic particles carried, and that contacts the image bearing member with the conductive magnetic particles to which a charging bias is applied to charge the image bearing member; An image forming apparatus comprising: a charging bias power supply for applying a charging bias to the sleeve; a collecting unit for collecting the conductive magnetic particles restrained on the sleeve; and a contamination-free supply supplied to the sleeve. A storage unit for storing conductive magnetic particles, an evaluation unit for evaluating the charging capability of the magnetic brush charging unit, and a charging capability information of the magnetic brush charging unit by the evaluation unit. Control means for controlling the collection of the conductive magnetic particles on the sleeve by the collection means, and controlling the supply of the non-contaminated conductive magnetic particles from the storage section onto the sleeve. An image forming apparatus comprising: 2. The method according to claim 1, wherein the evaluating unit is a current amount measuring unit that measures an amount of current flowing to the sleeve to which a charging bias is applied from the charging bias power supply, and the control unit is configured to measure the amount of current flowing through the sleeve. When it is determined that the amount of the supplied current has become equal to or less than a specified value with respect to a preset reference current amount, the collecting means controls the collection of the conductive magnetic particles on the sleeve, and the sleeve from the storage portion. The image forming apparatus according to claim 1, wherein the control is performed so as to supply the non-contaminated conductive magnetic particles thereon. 3. The evaluation means is a potential measurement means for measuring a potential on the image bearing member, and the control means is provided on the image bearing member after a predetermined rotation measured by the potential measurement means. If it is determined that the potential difference obtained by comparing the potentials is equal to or greater than a preset reference value, the collection unit controls the collection of the conductive magnetic particles on the sleeve and performs the collection from the storage unit onto the sleeve. The image forming apparatus according to claim 1, wherein control is performed to supply conductive magnetic particles that have not been subjected to the control. 4. The image forming apparatus according to claim 1, wherein the collection unit is a blade that can contact and separate from the sleeve. 5. The image forming apparatus according to claim 1, wherein the magnetic brush charging means also serves as a cleaning means for cleaning the image carrier. 6. The image forming apparatus according to claim 1, further comprising a cleaner for removing the deposit on the surface of the image carrier.