JP2002031937A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent static charging unevenness or lowering of charging performance because massive transfer residual toner flaws into a contact type electrostatic charging member at a time, with regard to an image forming device of the contact charging arrangement/cleaner less system. SOLUTION: This image forming device, provided with static charging means cleaning mode for ejecting incorporated toner from contact type charging means 2, controls charging means cleaning condition, by detecting density of the toner image on the image carrier 1 being ejected in the charging means cleaning mode by a density detecting means 81.

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, etc., which forms an image by an electrophotographic method or the like.

More particularly, the present invention relates to an image forming apparatus of a contact charging type and a cleanerless system.

[0003]

2. Description of the Related Art Corona Charging For example, in a conventional image forming apparatus using an electrophotographic method, a corona charger is frequently used as a means for charging a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier. .

[0004] In this method, a corona charger is arranged to face a photosensitive drum in a non-contact manner, and the surface of the photosensitive drum is charged to a predetermined polarity and potential by exposing the surface of the photosensitive drum to a discharge corona generated by the corona charger. It is.

[0005] Contact charging In recent years, it has advantages such as lower ozone and lower power than corona chargers.
Has been put to practical use.

In this method, a charging member to which a voltage is applied is brought into contact with the photosensitive drum to charge the surface of the photosensitive drum to a predetermined polarity and potential. A contact charging device using a magnetic brush as the charging member is preferably used in terms of charging, contact stability, 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.

In the 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 so that the surface of the photosensitive drum has 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.

[0008] Cleanerless system Further, in recent years, a so-called cleanerless system has been put into practical use for the purpose of reducing the size and simplification of the apparatus, or not generating waste toner from the viewpoint of ecology.

In this method, the cleaning device for removing the transfer residual toner from the surface of the photosensitive drum after the transfer of the toner image onto the transfer material is omitted, and the transfer residual toner is cleaned by the developing device at the same time as the development.

The simultaneous cleaning with development is a method in which a small amount of toner remaining on the photosensitive drum after transfer is collected by a fogging bias at the time of development after the next step. According to this method, the transfer residual toner is collected and used after the next step, so that waste toner can be eliminated and troublesome maintenance can be reduced. In addition, there is a great advantage in terms of space, and the size can be significantly reduced.

In a multicolor image forming apparatus having a plurality of photosensitive drums, an intermediate transfer member is provided, and the transfer residual toner on the photosensitive drum is transferred to the intermediate transfer member and collected by a cleaning device for the intermediate transfer member. However, since there is no need to provide a cleaning device for each photosensitive drum, the size of the device can be reduced.

In order to improve the cleaning efficiency, it is very effective to use a toner having an excellent releasability, such as a toner produced by a polymerization method.

By adopting such a photosensitive drum cleaner-less system in the above-described contact charging system, a small-sized,
It is possible to obtain an image forming apparatus which is simple, generates no ozone, consumes low power, and generates no waste toner.

[0014]

By the way, in the image forming apparatus using the above-mentioned contact charging system, when the image formation is repeated, toner particles as a developing material are mixed into the contact charging member (for example, conductive magnetic particles). There are many things to do.

Normally, the electric resistance of the toner particles is relatively high, so that if the toner particles are mixed into the contact charging member, the resistance of the whole or a part of the contact charging member will increase. As a result, there has been a problem that the photosensitive drum as a member to be charged cannot be charged to a desired potential, or charging unevenness occurs, resulting in image defects.

This problem is particularly problematic in an image forming apparatus having no cleaning device for removing residual toner from the photosensitive drum, that is, a so-called cleaner-less image forming apparatus, in which a large amount of residual toner is transferred to the contact charging member. Notably, this was caused by mixing.

On the other hand, since the transfer residual toner is present in the form in which the previous image is left as it is, when the toner passes through the contact charging member as it is, the charge potential of only the residual image portion is reduced, or the transfer potential for the next image formation is reduced. Exposure is interrupted, affecting the next development process as it is, causing a phenomenon (hereinafter, referred to as ghost) that the image portion becomes lighter or darker on the next image.

Therefore, a cleaner-less image provided with a brush-like uniformizing member for uniformly dispersing the transfer residual toner having the image shape as it is on the photosensitive drum, and a simple cleaning member using the bias effect temporarily. A forming device has been proposed.

Further, by optimizing the contact conditions of the contact charging member with the photosensitive drum and the charging sequence, the transfer residual toner is once collected in the charging container, and then discharged to the photosensitive drum by a potential action to develop the developing device. Also, there has been proposed a cleaner-less image forming apparatus that collects the image with an intermediate transfer member.

However, in the above-described cleaner-less image forming apparatus, ideally, the contact charging member scrapes off the photosensitive drum at the contact portion, and 100% of the transfer residual toner collected in the charging container is discharged onto the photosensitive drum again. However, if images having a high image ratio are continuously formed or transfer efficiency is reduced, the amount of toner to be collected becomes excessive and may be accumulated without being able to be completely discharged.

When such accumulated toner is present in the charging container, when the vibration is applied, a large amount of accumulated toner is taken into the contact charging member at once, and the chargeability is remarkably reduced, and fogging and ghosting are prevented. Cause. In particular, in the case of the magnetic brush charging system, a phenomenon occurs in which a large amount of magnetic particles leak to the photosensitive drum. The deficiency of the magnetic particles also causes a decrease in the chargeability, and the leaked magnetic particles may be mixed into the developing device, thereby deteriorating the image and adversely affecting the toner remaining amount detecting means.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing uneven charging and a reduction in charging performance due to a large amount of untransferred toner mixed into a contact charging member at once. .

[0023]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) an image carrier for carrying an image; contact charging means for contacting the image carrier and charging the image carrier;
Information writing means for forming an electrostatic latent image on the image carrier, developing means for developing the electrostatic latent image to form a toner image, transfer means for transferring the toner image to a transfer material, A density detecting unit for detecting a toner image density on the image carrier, wherein the developing unit collects the toner remaining on the image carrier after the transfer unit transfers the toner image to the transfer material. An image forming apparatus that also serves as a cleaning unit that includes a charging unit cleaning mode for discharging mixed toner from the contact charging unit, and detects the density of the toner image on the image carrier discharged in the charging unit cleaning mode. An image forming apparatus for detecting the charging unit cleaning conditions by detecting the charging unit cleaning condition.

(2) an image carrier for carrying an image; contact charging means for contacting the image carrier and charging the image carrier;
Information writing means for forming an electrostatic latent image on the image carrier, developing means for developing the electrostatic latent image to form a toner image, and transferring the toner image formed on the image bearing member Transfer means for transferring to a material, transfer material holding means for holding the transfer material, transfer material holding means cleaning means for collecting toner on the transfer material holding means, and detecting the toner image density on the transfer material holding means A charging unit cleaning mode for discharging mixed toner from the contact charging unit, and detecting the density of the toner image discharged in the charging unit cleaning mode by the density detecting unit. And an image forming apparatus for controlling the charging unit cleaning condition.

(3) an image carrier for carrying an image; contact charging means for contacting the image carrier and charging the image carrier;
Information writing means for forming an electrostatic latent image on the image bearing member, developing means for developing the electrostatic latent image to form a toner image, and a toner image formed on the image bearing member; A second image carrier to be transferred next, a secondary transfer unit for secondary transferring the toner image primarily transferred to the second image carrier to a transfer material, and a second image carrier remaining on the second image carrier In an image forming apparatus including a second image carrier cleaning unit for collecting toner and a density detection unit for detecting the density of a toner image on the second image carrier, charging for discharging mixed toner from the contact charging unit is performed. An image forming apparatus comprising a cleaning unit mode, wherein the density detecting unit detects the density of the toner image discharged in the charging unit cleaning mode, and controls the charging unit cleaning condition.

(4) The image forming apparatus according to (1), (2) or (3), wherein the control of the cleaning condition of the charging means is control of the cleaning time of the charging means.

(5) In the image forming apparatus described in (1), (2) or (3), the control of the cleaning condition of the charging unit is a voltage control applied to the charging unit at the time of cleaning the charging unit. Image forming apparatus.

(6) In the image forming apparatus according to any one of (1) to (5), the information writing means for forming an electrostatic latent image on the image carrier is an exposure means. Image forming device.

[Operation] That is, a charging unit cleaning mode for discharging mixed toner from the contact charging unit is provided, and the density of the toner image discharged in the charging unit cleaning mode is detected by the density detection unit. By controlling the charging time, it is possible to prevent uneven charging and a reduction in charging performance due to an excessive amount of toner mixed in the charging device, a reduction in productivity due to a time required for the charging member cleaning mode, and a A large amount of reused toner is collected and developed at a time, so that image fogging and roughness, and contamination of the transfer means by toner that cannot be collected by the developing device can be minimized.

[0031]

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

Embodiment 1 (1) Example of Image Forming Apparatus FIG. 1 is a schematic structural model diagram showing an image forming apparatus according to the present embodiment. The image forming apparatus of the present embodiment is a laser beam printer using an electrophotographic process, and uses a magnetic brush type contact charging device as a charging unit of the image carrier.
It is also a cleanerless system device.

A is a laser beam printer as an image forming apparatus according to the present embodiment, and B is an image reading device (image scanner) mounted on the laser beam printer A.

A) Image Reading Apparatus B In the image reading apparatus B, reference numeral 20 denotes a fixed platen glass, which is placed on the upper surface of the platen glass 20 with the original G to be copied facing downward. A document pressure plate (not shown) is placed on the top and set.

Reference numeral 21 denotes an image reading unit in which a document irradiation lamp 21a, a short focus lens array 21b, a CCD sensor 21c and the like are arranged.

When the copy button (not shown) is pressed, the image reading unit 21 moves from the home position on the right side of the platen glass 20 to the left side along the lower surface of the platen glass 20 when the copy button (not shown) is pressed. When it reaches a predetermined end point of reciprocation, it is driven backward and returned to the initial home position. Image reading unit 21
In the forward movement driving process, the downward image surface of the placed and set original G on the original platen glass 20 is sequentially illuminated and scanned by the original irradiation lamp 21a from the right side to the left side, and the original surface reflected light of the illumination scanning light Is short focus lens array 21
By b, an image is incident on the CCD sensor 21c.

The CCD sensor 21c includes a light receiving unit, a transfer unit, and an output unit (not shown). The light signal is converted into a charge signal in the light receiving unit, and the transfer unit sequentially outputs the signal in synchronization with a clock pulse. The charge signal is converted to a voltage signal at the output unit, amplified, reduced in impedance, and output. The analog signal thus obtained is converted into a digital signal by well-known image processing and output to a laser beam printer (image forming apparatus) A.

That is, the image reading device B photoelectrically reads the image information of the document G as a time-series electric digital pixel signal (image signal).

B) Printer A In the laser beam printer A, reference numeral 1 denotes a photosensitive drum as an image carrier. Photosensitive drum 1 of this embodiment
Is a negatively chargeable OPC photosensitive member having a charge injection layer on the surface. This photoconductor will be described in detail in section (2).

The photosensitive drum 1 is driven to rotate at a predetermined peripheral speed (process speed) in the clockwise direction indicated by an arrow about a central support shaft. In the case of the present embodiment, the nip portion a receives a uniform charging process of -700V. The contact charging means 2 in this embodiment is a magnetic brush charging device (injection charger). The charging device 2 will be described in detail in section (3).

Then, the uniformly charged surface of the photosensitive drum 1 is modulated in accordance with the image signal output from the exposure device (laser scanning device) 3 and output from the image reading device B to the laser beam printer A side. By performing the scanning exposure L with the laser light on the exposed portion b, an electrostatic latent image corresponding to the image information of the document G photoelectrically read by the image reading device B is sequentially formed on the photosensitive drum 1. The exposure device 3 will be described in detail in section (4).

The electrostatic latent image formed on the photosensitive drum 1 is sequentially developed as a toner image at a developing site c by the developing device 4 and is reversely developed in this embodiment. Developing device 4 of this embodiment
Is a two-component contact developing system. The developing device 4 will be described in detail in section (5).

On the other hand, the transfer material P such as paper stored in the paper cassette 5 is fed one by one by the paper feed roller 6,
At a predetermined timing, the sheet is fed to a transfer portion (transfer nip portion) d which is a press contact portion between the photosensitive drum 1 and a transfer roller 8 as a transfer unit by a registration roller 7. Transfer roller 8
At a predetermined control timing, a transfer bias (positive in this embodiment) having a polarity opposite to the charge polarity of the toner is applied from a power supply (not shown), and the photosensitive drum is transferred to the transfer material P nipping and transferring the transfer portion d. 1 are sequentially transferred.

The transfer material P to which the toner image has been transferred through the transfer portion d is sequentially separated from the surface of the photosensitive drum 1, spliced by the transfer device 10 and transferred to the fixing device 11, where the toner image is thermally fixed. Then, the image data is output from the paper discharge roller 12 to a paper discharge tray 13 outside the apparatus as an image formed product (copy, print).

After the transfer, the remaining toner on the surface of the photosensitive drum 1 is transferred to the auxiliary charging portion e, which is the contact portion between the photosensitive drum 1 and the auxiliary charging fur brush 9, by the subsequent rotation of the photosensitive drum 1.
The developer is carried to the developing site c via the charged site a and the exposed site b, and is collected by the developing device 4 by the simultaneous development cleaning (cleanerless process). This cleanerless process will be described in detail in section (6).

(2) Photosensitive Drum 1 As the photosensitive drum 1 as an image carrier, a commonly used organic photoreceptor or the like can be used. Preferably, the resistance is 10 ⁹ to 10 on the organic photoreceptor. ^When a material having a surface layer having a material of ¹⁴ Ω · cm or an amorphous silicon photoreceptor 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.

The photosensitive drum 1 used in this embodiment is
As shown in the schematic diagram of the layer structure in FIG. 2, a negatively chargeable organic photoreceptor provided with a charge injection layer 1f on the surface and having a diameter of 30 m
m on a drum base 1a made of aluminum having a photosensitive layer composed of first to fifth five layers 1b to 1f in order from the bottom, and has a predetermined process speed (for example, 100 mm).
/ Sec).

The first layer 1b is a subbing layer and has a thickness of 20 μm provided to smooth defects and the like of the drum base 1a.
m of the conductive layer.

Second layer 1c: a positive charge injection preventing layer, which serves to prevent the positive charge injected from the drum substrate 1a from canceling out the negative charge charged on the surface of the photosensitive drum 1; It is a 1 μm thick medium resistance layer whose resistance is adjusted to about 10 ⁶ Ω · cm by methylated nylon.

Third layer 1d: a charge generation layer, 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 to light.

Fourth layer 1e: 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 the fourth layer 1e, and only the positive charges generated in the third layer (charge generation layer) 1d are transferred to the surface of the photosensitive drum 1. Can be transported.

Fifth layer 1f: 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.

More specifically, ultra-fine SnO ₂ fine particles having a particle size of about 0.03 μm obtained by doping an insulating resin with antimony as a light-transmitting conductive filler to make the resistance low (conducting) are applied to the resin by 70%. It is a coating layer of a material dispersed by weight percent.

The coating solution thus prepared is applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coating method, beam coating method, etc. 1f.

(3) Magnetic Brush Charging Device 2 FIG. 3 is a schematic structural diagram of the magnetic brush charging device 2 in the present embodiment.

The magnetic brush charging device 2 has a rotatable outer diameter 16 having a fixed magnet roller 41 provided therein.
mm non-magnetic and conductive charging sleeve (electrode sleeve)
A conductive magnetic particle (magnetic carrier) 42 attached and held as a magnetic brush on the outer peripheral surface of the charging sleeve 40 by the magnetic force of the magnet roller 41;
A charging container 43 containing the magnetic particles 42 and the magnetic particles 42 and a regulating blade 44 for forming a thin layer of the magnetic brush of the magnetic particles 42 on the surface of the charging sleeve 40 are provided.

The magnetic brush of the magnetic particles 42 adhered and held on the outer peripheral surface of the charging sleeve 40 is in contact with the surface of the photosensitive drum 1. In this embodiment, the nip width formed by the magnetic brush of the magnetic particles 42 with respect to the photosensitive drum 1 is approximately 6 mm.
It was adjusted to become.

The charging sleeve 40 is rotatable with respect to the photosensitive drum 1 in the counter direction. In this embodiment, the charging sleeve 40 is rotated at 150 mm / sec with respect to the process speed of the photosensitive drum 1 of 100 mm / sec. As a result, the surface of the photosensitive drum 1 is evenly rubbed by the magnetic brush of the magnetic particles 42 adhered and held on the outer peripheral surface of the charging sleeve 40 at the charging portion a. Then, by applying a charging bias to the charging sleeve 40 from a charging bias power supply 45, charges are transferred from the magnetic particles 42 of the magnetic brush to the photosensitive drum 1.
And the surface of the photosensitive drum 1 is charged to a potential corresponding to the charging bias. As the rotation speed of the charging sleeve 40 increases, the uniformity of charging tends to be improved.

The magnetic particles 42 have an average particle size of 10 to
100 μm, candy magnetization 20-250 emu / cm ³ ,
It is preferable that the resistance is 1 × 10 ² to 1 × 10 ¹⁰ Ω · cm. Considering that the photosensitive drum 1 has an insulation defect such as a pinhole, a resistance of 1 × 10 ⁶ Ω · cm or more is used. Is preferred. In order to improve the charging performance, it is better to use one having as small a resistance as possible. In this embodiment, the average particle diameter is 25 μm and the saturation magnetization is 200 μm.
Magnetic particles 4 having emu / cm ³ and a resistance of 5 × 10 ⁶ Ω · cm
2 was used.

The resistance value of the magnetic particles 42 is 228
After putting 2 g of the magnetic particles 42 in a metal cell of mm ² ,
A measurement was performed by applying a load of 6.6 kg and applying a voltage of 100 V.

The magnetic particles 42 may be composed of a resin carrier formed by dispersing magnetite as a magnetic material in a resin and dispersing carbon black for conductivity and resistance adjustment, or a magnetite simple substance surface such as ferrite. A material whose resistance has been adjusted by an oxidation or reduction treatment or a material whose surface has been adjusted by coating the surface of a single magnetite such as ferrite with a resin may be used.

FIG. 4 shows the relationship between the amplitude of the applied bias and the charging potential when a rectangular alternating voltage (AC voltage) Vpp is applied to the charging sleeve 40 of the magnetic brush charging device 2 at a frequency of 1000 Hz. By increasing the amplitude, the difference between the DC (direct current) component of the applied bias and the charged potential is reduced. The applied DC bias is -700
V.

More specifically, assuming that the DC component of the bias applied to the charging sleeve 40 of the magnetic brush charging device 2 is Vdc, and the surface potential of the charged photosensitive drum 1 at this time is Vs, When the contrast ΔV = | Vdc−Vs | becomes approximately 40 V or less, the uniformity of charging is improved.

Therefore, in the present embodiment, the bias obtained by superimposing a rectangular alternating voltage of 800 V at a frequency of 1000 Hz on a DC voltage of -700 V is applied to the sleeve 40 of the magnetic brush charging device 2 to achieve good charging performance. Could be obtained.

(4) Exposure Apparatus 3 FIG. 5 is a schematic structural diagram of an exposure apparatus 3 of a laser beam scanning exposure system. The exposure device 3 controls the photosensitive drum 1
When the laser scanning exposure L is performed on the charged surface of the solid-state laser device, first, the solid-state laser device 25 is turned on and off at a predetermined timing by the light emission signal generator 24 based on the input image signal (O).
N / OFF). Then, the laser light emitted from the solid-state laser element 25 is collimated by a collimator lens system 26.
Is converted into a substantially parallel light beam, and is further scanned in the direction of arrow g by the rotating polygon mirror 22 rotating at high speed in the direction of arrow f, and the photosensitive drum 1 is scanned by the f-θ lens group 23.
An image is formed in a spot on the surface. An exposure distribution for one image scan is formed on the surface of the photosensitive drum 1 by such laser scanning L. Further, by scrolling the photosensitive drum 1 vertically by a predetermined amount for each scan, the photosensitive drum 1
An exposure distribution according to the image signal is obtained on the surface.

That is, the light of the solid-state laser element 25 whose ON / OFF light emission is controlled in accordance with the image signal is scanned on the uniformly charged surface of the photosensitive drum 1 by the rotating polygon mirror 22 rotating at a high speed. An electrostatic latent image corresponding to the scanning exposure pattern is sequentially formed on one surface.

(5) Developing Device 4 FIG. 6 is a schematic structural diagram of a two-component contact developing device (two-component magnetic brush developing device) which is the developing device 4 of the present embodiment. In this figure, reference numeral 14 denotes a developing sleeve which is driven to rotate in the direction of the arrow h, 15 denotes a magnet roller fixedly disposed in the developing sleeve 14, 16/16 denotes a stirring screw, and 17 denotes a thinner of the developer T on the surface of the developing sleeve 14. A regulating blade for forming a layer, 18 is a developing container, and 19 is a toner hopper for replenishment.

At least at the time of development, the developing sleeve 14 has an interval of about 5
The thickness is set to be 00 μm, and is set so that development can be performed in a state where the thin layer Ta of the developer T formed on the surface of the developing sleeve 14 is in contact with the photosensitive drum 1.

The developer T used in this embodiment is a two-component developer composed of the toner t and the magnetic carrier C. Toner t
Used is a negatively charged toner having an average particle diameter of 6 μm manufactured by a pulverization method and externally added with 1% by weight of titanium oxide having an average particle diameter of 20 nm. The carrier C has a saturation magnetization of 205 emu / cm ³ . A magnetic carrier having an average particle size of 35 μm was used. A mixture of the toner t and the carrier C at a weight ratio of 6:94 was used as the developer T.

Here, the electrostatic latent image on the surface of the photosensitive drum 1 is
A developing process of developing the toner by the two-component magnetic brush method using the developing device 4 and a circulation system of the developer T will be described. First, the developer T pumped by the magnetic pole N3 with the rotation of the developing sleeve 14 is regulated by the regulating blade 17 arranged perpendicular to the developing sleeve 14 in the process of being transported to the magnetic pole S2 to the magnetic pole Nl. Sleeve 14
A thin layer Ta of the developer T is formed thereon. When the developer thin layer Ta is conveyed to the magnetic pole S1, ears are formed by the magnetic force, and come into contact with the surface of the photosensitive drum 1. The electrostatic latent image on the surface of the photosensitive drum 1 is developed by the spike-shaped developer, and then the developer on the developing sleeve 14 is returned into the developing container 18 by the repulsive magnetic fields of the magnetic poles N3 and N2.

A direct current (DC) voltage and an alternating current (AC) voltage are applied to the developing sleeve 14 from a power source S2. In this embodiment, a DC voltage of -500V and a frequency of 2000H
An AC voltage having a peak-to-peak voltage of 1500 V was applied at z.

In general, in the two-component developing method, when an AC voltage is applied, the developing efficiency increases, and the image becomes high quality.
Conversely, there is a problem that fogging easily occurs.
For this reason, by providing a potential difference between the DC voltage normally applied to the developing device 4 and the surface potential of the photosensitive drum 1,
The fog is prevented.

The toner concentration (mixing ratio with the carrier) of the developer T in the developing container 18 gradually decreases as the toner is consumed for developing the electrostatic latent image. When the toner concentration of the developer T in the developing container 18 is detected by a detection unit (not shown) and decreases to a predetermined allowable lower limit concentration, the toner T is replenished from the toner hopper 19 for replenishment to the developer T in the developing container 18. Then, toner replenishment control is performed such that the toner concentration of the developer T in the developing container 18 is agitated and dispersed by the agitating screws 16, 16 so that the toner concentration is always kept within a predetermined allowable range.

(6) Cleanerless Process At the transfer portion d, the transfer residual toner remains on the photosensitive drum 1 after the transfer of the toner image onto the transfer material P (after the transfer material separation). In the case of the cleanerless process, basically, the transfer residual toner on the photosensitive drum 1 is carried to the developing part c via the charged part a and the exposed part b by the subsequent rotation of the photosensitive drum 1 and developed. The device 4 collects and reuses the cleaning at the same time as the development.

However, if the transfer residual toner is brought into contact with the magnetic brush of the magnetic brush charging device 2 as it is and passes through the charging portion a, a ghost occurs as described above.
Even when the transfer residual toner passes on the upstream side in the rotation direction of the photosensitive drum 1 of the magnetic brush in contact with the photosensitive drum 1, in most cases, the shape of the previous image is kept, and the magnetic brush charging device 2 under appropriate charging conditions is maintained. In the setting of, there was no such thing as being uniformly dispersed.

For this reason, the transfer residual toner that has reached the charged portion a with the rotation of the photosensitive drum 1 is charged with the charged magnetic brush device 2.
It is necessary to capture the history of the previous image by taking it into the magnetic particles 42 of the above. At this time, when the DC voltage is applied to the charging sleeve 40 of the charging magnetic brush device 2, the toner is not sufficiently taken into the magnetic particles 42, but when the alternating voltage is applied to the charging sleeve 40, Due to the vibration effect caused by the electric field between the magnetic brush device 2 and the charged magnetic brush device 2, the toner is relatively easily taken into the magnetic particles 42.

However, there is a case where it is very difficult to take in the toner into the magnetic particles 42 of the magnetic brush device 2 depending on the charge amount of the transfer residual toner that has reached the charged portion a.
That is, as long as the transfer residual toner is charged, the potential difference between the charged magnetic brush device 2 and the photosensitive drum 1 and the mirroring force between the toner and the photosensitive drum 1 have a great effect on the capturing performance.

With respect to the voltage applied to the magnetic brush charging device 2,
Ideally, the surface potential of the photosensitive drum 1 passing therethrough is ideally charged equally, but in practice, the contact portion between the magnetic brush of the magnetic brush charging device 2 and the photosensitive drum 1 also has a width. For this reason, even if it is eventually charged to almost the same potential,
Since sufficient charge has not been obtained in the initial stage of passing through the contact part,
There is a potential difference between the magnetic brush charging device 2 and the photosensitive drum 1 there.

In this embodiment, since the DC voltage of the magnetic brush charging device 2 is set to -700 V, in the region where the surface potential of the photosensitive drum 1 is lower at the initial stage of passing through the contact portion, the positively charged toner is Although the toner is easily taken in the direction of the brush charging device 2, the negatively charged toner is not taken in.

Further, even if the amount of charge of the transfer residual toner is extremely large and the mirror force with the photosensitive drum 1 is too large, the toner remains on the photosensitive drum 1.

Therefore, it is desirable that the transfer residual toner is positively charged, although the toner is originally a negatively chargeable toner. However, the effect of being forcibly scraped off by the magnetic brush of the magnetic brush charging device 2 can be expected if the absolute value of the charge amount is sufficiently small even if the battery is not positively charged.

Actually, the charge polarity of the transfer residual toner is often reversed due to the peeling discharge at the time of transfer. However, even if the transfer efficiency is the same, the charge amount distribution of the transfer residual toner greatly differs depending on the transfer current. Further, if the developer is used for a long period of time, the developer itself deteriorates and the transfer efficiency decreases, so that the ratio of the toner remaining on the photosensitive drum 1 while being negatively charged increases.

Therefore, it is preferable to have a means for increasing the transfer current or charging the transfer residual toner to the opposite polarity.
For this reason, in the present embodiment, as shown in FIGS.
In the rotation direction of the photosensitive drum 1, between a transfer portion d which is a contact portion between the transfer roller 8 and the photosensitive drum 1, and a charged portion a which is a contact portion between the magnetic brush of the magnetic brush charging device 2 and the photosensitive drum 1. Then, an auxiliary charging fur brush 9 made of rayon was placed in contact with the photosensitive drum 1 and a bias of +500 V was applied from the power supply 51. “e” denotes an auxiliary charging portion which is a contact portion between the auxiliary charging fur brush 9 and the photosensitive drum 1. In this embodiment, the auxiliary charging fur brush 9
Are attached to the magnetic brush charging device 2.

Since a bias of +500 V is applied to the auxiliary charging fur brush 9, the transfer residual toner carried from the transfer portion d to the auxiliary charging portion e becomes
The transfer residual toner of the positive polarity passes through the auxiliary charging portion e, and the transfer residual toner of the negative polarity is temporarily captured by the auxiliary charging fur brush 9, is discharged, and is sent out onto the photosensitive drum 1 again. At this time, if toner accumulates on the surface of the fur brush 9 without applying a bias or the like for positively sending the photosensitive drum 1 to the photosensitive drum 1, the limit of the amount of toner is reached, and the discharged toner successively starts. It is returned onto the photosensitive drum 1.

Accordingly, the toner entering the charged portion a, which is the contact portion between the magnetic brush of the magnetic brush charging device 2 and the photosensitive drum 1, is limited to the toner having the opposite polarity to the charging polarity, or the toner having a low charge amount after being discharged. The magnetic particles are substantially collected by the magnetic particles 42 of the magnetic brush charging device 2. Thus, at this point, the history of the previous image is lost, and the direct cause of the ghost is removed.

Also, once the transfer residual toner is collected by the magnetic particles 42 of the magnetic brush charging device 2 and is still positively charged, the relationship between the potential difference between the magnetic brush of the magnetic brush charging device 2 and the photosensitive drum 1 becomes As mentioned above,
The transfer residual toner accumulates in the magnetic particles 42 without being discharged, and depends on the resistance value of the toner. However, if a predetermined amount or more of toner is mixed into the magnetic brush charging device 2, even when the alternating voltage is superimposed, the toner is charged. Performance will be reduced.

Further, even if the toner is discharged onto the photosensitive drum 1 by the centrifugal force of the magnetic particles 42 or the like, the toner is not collected by the developing device 4 and remains in the non-image area unless it has a proper negative charge. I will.

Therefore, once the toner particles are taken into the magnetic particles 42, the toner particles are turned into regular negatively charged toners to complete a long-term stable cleanerless process for the first time. This can be realized by setting a combination in which the frictional charging series of the toner and the magnetic particles 42 is closer to the negative polarity for the toner. In the present embodiment, a negative toner using polyester as a binder resin was used as the magnetic particles 42 in which the surface of a single magnetite such as ferrite was coated with a resin and the resistance was adjusted.

However, if images having a high image ratio are continuously formed, or if the transfer efficiency is reduced due to durability, the discharge of toner in the charging device during a normal image forming operation may be insufficient. There is.

Therefore, in the image forming sequence of the image forming apparatus, when the image forming apparatus is not forming an image while the image forming apparatus is not forming an image, the charging means (the charging means () which positively discharges the mixed toner from the contact charging device 2 onto the photosensitive drum 1 It has already been proposed that by performing the "charging member) cleaning mode", the toner contamination state of the contact charging device 2 is always maintained at or below an allowable level to maintain the charging performance.

More specifically, in the image forming sequence of the image forming apparatus, during the so-called pre-rotation process for preparing for image formation, during the so-called post-rotation process during the transition from the end of image formation to the standby state, or continuously. When image formation is not being performed (during non-image formation), such as during a so-called inter-paper stroke between recording materials (transfer materials) when the images are formed, the voltage applied to the contact charging device 2 is reduced. The potential difference ΔV is provided between the photosensitive drum 1 and the contact charging device 2 by performing adjustment or the like, and the high-resistance toner mixed in the contact charging device 2 is positively discharged onto the photosensitive drum 1 by the potential difference. The toner is collected at the development site c.

For example, the AC component (Vac) of the charging bias applied to the magnetic brush charging device 2 is cut off, and the DC component (Vdc) of the charging bias applied to the charging sleeve 40 is cut off.
The toner contained in the magnetic brush is electrically discharged by a potential difference between the magnetic brush and the surface potential (Vd) when the photosensitive drum 1 is charged.

Here, the AC component of the charging bias (Va
The reason for cutting off c) is to lower the surface potential (Vd) by lowering the chargeability to the photosensitive drum 1 and increase the potential difference ΔV (Vdc−Vd) of the toner discharge.
Further, since the transfer residual toner mixed into the magnetic brush layer of the magnetic particles 42 has a uniform charge (negative toner) due to friction with the magnetic particles 42, the potential difference ΔV
To move (discharge) onto the photosensitive drum 1.

In the present invention, as the cleaning means for the contact charging device (contact charging member), any means can be used as long as it can discharge mixed toner from the contact charging device. For example, a method of adjusting and discharging a DC component (Vdc) of a charging bias applied to the magnetic brush charging device 2,
There is a method of adjusting the separation distance between the magnetic brush charging device 2 and the photosensitive drum 1 and discharging.

However, since the amount of the transfer residual toner collected in the charging device 2 depends on the image ratio and the transfer efficiency to be formed as described above, the length and frequency of the charging unit cleaning mode can be appropriately adjusted. It was difficult to set.

That is, the charging means cleaning mode is lengthened for sufficient cleaning, and the output capability of the image forming apparatus main body for image formation is reduced if frequent cleaning is performed.
If the image forming ability is not reduced so much, the discharge will be insufficient.

Therefore, in this embodiment, a density sensor 81 (FIGS. 1 and 3) for detecting the density of the toner image on the surface of the photosensitive drum 1 is provided between the charging device 2 and the developing device 4. The density sensor 81 irradiates light from the light emitting unit 81a such as an LED to the surface of the photosensitive drum 1, and receives reflected light of the irradiated light from the surface of the photosensitive drum 1 at a light receiving unit 81b such as a photoelectric conversion element. Is input to the control circuit (CPU) 100. The control circuit 100 calculates and detects the density of the image on the surface of the photosensitive drum 1 based on the input electric conversion signal information of the received light amount.

Reference numeral 101 denotes a driver of a charging bias application power supply 45 for the charging sleeve 40.
0 controls the power supply 45 via the driver 101.

In the charging means cleaning mode, the control circuit 100 cuts off the AC component (Vac) of the power supply 45 via the driver 101 and charges the photosensitive drum 1 with the DC component (Vdc) of the charging bias applied to the charging sleeve 40. The toner difference in the magnetic brush is actively positively discharged by the potential difference between the surface potential (Vd) and the surface potential (Vd).

Thus, the control circuit 100 activates the density sensor 81 in the charging unit cleaning mode, and measures the density (toner amount) of the toner discharged from the magnetic brush charging device 2 to the surface of the photosensitive drum 1. If the value is less than the predetermined value, the charging unit cleaning mode is terminated, and the process returns to normal image formation. If it is more than the predetermined value,
Further, the charging unit cleaning mode is continued. When the value falls below a predetermined value, the charging unit cleaning mode is terminated, and the process returns to normal image formation.

As in the present embodiment, a charging unit cleaning mode for discharging mixed toner from the charging unit 2 is provided. The density detecting unit 81 detects the density of the toner image discharged in the charging unit cleaning mode. By controlling the cleaning conditions, it is possible to prevent uneven charging and a reduction in charging performance due to excessive toner mixed in the charging device 2, and minimize a reduction in productivity due to the time required for the charging unit cleaning mode. Was able to be suppressed.

In this embodiment, whether or not to continue the charging unit cleaning mode is determined according to the value of the density sensor 81. However, the frequency of the charging unit cleaning mode is controlled according to the value of the density sensor 81. The effect of the present invention can be obtained by controlling the cleaning condition of the charging means by another method.

Note that the present invention is not limited to the above-described embodiments, and a configuration in which these are appropriately combined is also possible.

[Embodiment 2] This embodiment is an example in which the problem caused by excessive discharge toner in the "charging means cleaning mode" is solved. A description will be given by omitting parts similar to those in the first embodiment.

When a large amount of mixed toner is discharged at a time in the charging unit cleaning mode, the following problems occur. In other words, a large amount of reused toner is collected and developed by the developing device 4 at one time, and the image is fogged and rusted by the development, and the transfer unit 8 is stained by the toner that cannot be recovered by the developing device 4. And so on.

For this reason, it is desirable to limit the amount of toner discharged at a time. Therefore, in this embodiment, the density sensor 81 is activated in the charging member cleaning mode, and the density (toner amount) of the toner discharged from the magnetic brush charging device 2 to the surface of the photosensitive drum 1 is measured. The value of Vdc applied to 40 is reduced to limit the amount of discharged toner.

As in the present embodiment, a charging unit cleaning mode for discharging mixed toner from the charging unit 2 is provided, and the density of the toner image discharged in the charging unit cleaning mode is detected by the density detecting unit 81. By controlling the cleaning conditions, it is possible to prevent uneven charging and deterioration of charging performance due to excessive toner mixed in the charging device 2, and a large amount of reused toner is collected in the developing device 4 at a time. In addition, it was possible to minimize the fogging and roughness of the image due to the development, and to minimize the contamination of the transfer unit by toner that cannot be collected by the developing device.

[Embodiment 3] The image forming apparatus of this embodiment shown in FIG. 7 has four image forming units (image forming stations).
Are sequentially arranged and the image forming process is performed independently in each image forming unit,
This is a four-color tandem-type color printer that sequentially superimposes four colors of toner images formed by each image forming unit on a transfer material in one pass to synthesize and form a full-color toner image.

The image reading apparatus B has a function of reading and separating a full-color original. In printer body A, I
II, III and IV are first to fourth four image forming units arranged in tandem from the right to the left. In this example, the first image forming unit I is a yellow image forming unit, the second image forming unit II is a magenta image forming unit, and a third image forming unit.
III is a cyan image forming unit, and the fourth image forming unit is a black image forming unit.

First to fourth image forming units I, II, III, IV
All are electrophotographic image forming mechanisms of a magnetic brush charging system, a reversal developing system, and a cleanerless system as in the printer of the first embodiment (FIG. 1), and an electrophotographic photosensitive drum 1 as an image carrier and a magnetic brush A charging device 2, an exposure device (laser scanning device) 3 as an image information writing device,
A developing device 4 is provided.

The developing device 4 of the first image forming unit I is a developing device having a yellow toner as a developer, and the developing device 4 of the second image forming unit II is a developing device having a magenta toner as a developer. Developing device 4 of third image forming unit III
Denotes a developing device having a cyan toner as a developer;
The developing device 4 of the image forming section IV is a developing device having a black toner as a developer.

Reference numeral 8 denotes first to fourth image forming units I, II, and III.
A transfer belt device disposed substantially horizontally in the left-right direction across the image forming units below the IV, and having an endless transfer belt 31 as a transfer material holding means between a driving roller 32 and a driven roller 33; And the photosensitive drum 1 in the direction of arrow i.
Is driven to rotate at a peripheral speed substantially equal to the rotational peripheral speed. A transfer charging blade 34 is provided inside the transfer belt 31, and the ascending belt portion of the transfer belt 31 is brought into contact with the lower surface of the photosensitive drum 1 of each of the image forming units I, II, III, and IV by the transfer charging blade 34.

In this embodiment, a transfer belt 31 made of a polyimide resin having a thickness of 75 μm was used. The material of the transfer belt 31 is not limited to a polyimide resin. In addition, for example, a polycarbonate resin, a polyethylene terephthalate resin, a polyvinylidene fluoride resin, a polyethylene naphthalate resin, a polyether ether ketone resin, a polyether Plastics such as sulfone resins and polyurethane resins, and fluorine-based and silicon-based rubbers can be suitably used. Also, the thickness is not limited to 75 μm, and a thickness of about 25 to 2000 μm, preferably about 50 to 150 μm is suitably used. Further, the transfer charging blade 34 has a resistance of 1 × 10 ⁵ to
1 × 10 ⁷ Ω, 2 mm thick and 306 mm long were used.

The image forming operation in each of the image forming units I, II, III and IV is the same. However, on the surface of the photosensitive drum 1 of the first image forming unit I, an image exposure corresponding to a yellow component image of a full-color original read color-separated by the image reading device B is performed to form an electrostatic latent image thereof. You. Image exposure corresponding to the magenta component image is performed on the surface of the photosensitive drum 1 of the second image forming section II to form an electrostatic latent image thereof. Third
The image exposure corresponding to the cyan component image is performed on the surface of the photosensitive drum 1 of the image forming unit III to form an electrostatic latent image thereof.
Image exposure corresponding to the black component image is performed on the surface of the photosensitive drum 1 of the fourth image forming section IV to form an electrostatic latent image thereof.

Then, the developing device 4 reversely develops the electrostatic latent image on the photosensitive drum 1 of the first image forming section I as a yellow toner image. The electrostatic latent image on the photosensitive drum 1 of the second image forming section II is reversely developed by the developing device 4 as a magenta toner image. The electrostatic latent image on the photosensitive drum 1 of the third image forming unit III is reversely developed by the developing device 4 as a cyan toner image. The electrostatic latent image on the photosensitive drum 1 of the fourth image forming section IV is reversely developed by the developing device 4 as a black toner image.

On the other hand, the transfer material P as a recording material loaded and stored in the paper feed cassette 5 is fed out one by one by the paper feed roller 6 and fed, and passes through a path of the registration roller 7 to perform predetermined control. At the timing, the sheet is fed onto the ascending side belt of the transfer belt 31 of the transfer belt device 8. A predetermined transfer bias is applied to each transfer charging blade 34 from a transfer bias application power source (not shown) at a predetermined control timing.

The transfer material P fed onto the transfer belt 31 as a transfer material holding means is electrostatically attracted and held on the belt surface, and the first to fourth image forming units are rotated with the rotation of the transfer belt 31.
I, II, III, and IV transfer sections are sequentially transported, and a first transfer section transfers a yellow toner image on the photosensitive drum 1 surface of the first image forming section I, and a second transfer section transfers a yellow toner image. The transfer of the magenta toner image on the photosensitive drum 1 surface of the image forming unit II, the transfer of the cyan toner image on the photosensitive drum 1 surface of the third image forming unit III in the third transfer unit, and the transfer of the fourth toner image on the fourth transfer unit. The superimposed transfer of the toner image is performed four times due to the transfer of the black toner image on the photosensitive drum 1 surface of the image forming unit IV. That is, each transfer charging blade 54 charges the reverse polarity of the toner from the back surface of the transfer material P. In this embodiment,
A transfer was performed by applying a transfer bias of 15 μA to each transfer charging blade 34 under constant current control. Thus, the toner image on the side of the rotating photosensitive drum 1 is sequentially electrostatically transferred to the surface of the transfer material P passing through each transfer portion in order. As a result, a desired full-color toner image is synthesized and formed on the transfer material surface.

The image formation of the toner images in each of the image forming units I to IV is performed in synchronization with each other in a predetermined manner.
Are transferred to the same transfer material P conveyed by the transfer belt device 8 so as to be aligned at predetermined positions and sequentially overlap.

The transfer material conveyed by the transfer belt 31 and having passed through the final fourth transfer portion is separated from the transfer belt 31 and introduced into the heat fixing device 11, where the unfixed full-color toner image on the transfer material surface is formed. The image is fixed as a permanent fixed image by heat and pressure, and is output from the paper discharge roller 12 to a paper discharge tray 13 outside the apparatus as an image formed product (copy, print).

Now, such a full-color image forming apparatus has a problem different from the mono-color image forming apparatus shown in the first embodiment.

That is, there is a problem of retransfer in the multiple transfer system in which a plurality of different color toners are sequentially superimposed and transferred as in the present embodiment. This is because, after the transfer of the first color, the toner of the first color is re-transferred onto the photosensitive drum of the second color, though very slightly, due to physical and electrostatic factors at the time of the transfer of the second color. Things. The retransferred toner is once collected by the charging device 2 together with the untransferred toner. Here, in a system similar to the first embodiment in which the toner mixed in the charging device 2 is discharged in the “charging unit cleaning mode” and collected by the developing device 4, re-transfer toner of a different color is mixed in the developing device 4. Becomes This is, of course, undesirable because it causes a change in the tint of the output image.

Therefore, in the present embodiment, in the "charging means cleaning mode" in which the amount of toner discharged from the charging device 2 onto the photosensitive drum 1 is larger than that in image formation, the discharged toner is not collected by the developing device 4 and the transfer belt 31 is not recovered. The image is transferred to the upper side and collected by the transfer belt cleaning device 82.

Now, as described above, the four image forming units I
Each of the image forming units I, II, II, III, and IV has the same configuration as in the first embodiment in the present configuration in which the toner mixed into the transfer belt 31 is discharged in the charging unit cleaning mode and collected by the transfer belt cleaning device 82. The same control can be performed by providing a density sensor between the III / IV charging device 2 and the developing device 4.

However, in this embodiment, each of the image forming units I and II
A density sensor was not provided for III and IV, and a density sensor 81 was provided in front of the transfer belt cleaning device 82.
The charging unit cleaning mode is set for each of the image forming sections I and I.
In I, III, and IV, the timing of the discharge position on the transfer belt 31 for each color is shifted, and the density of the discharged toner of each color is measured. For each color, that is, for each image forming unit I, II, and I
It is determined whether or not to continue the charging unit cleaning mode for each of II and IV.

In this embodiment, the object of the present invention is achieved, and even in an image forming apparatus including four image forming units I, II, III, and IV, the cleaning condition of the charging means can be controlled by one density sensor 81. it can.

Of course, the density sensor 81 can be used for other controls such as control of image density and phase adjustment of four stations.

[Embodiment 4] FIG. 8 is a schematic structural diagram of an example of a color printer using an intermediate transfer member. The description of the same parts as those of the color printer of FIG. 7 will be omitted.

Reference numeral 35 denotes an endless intermediate transfer belt serving as a second image bearing member.
3. The rotating peripheral speed of the photosensitive drum 1 suspended in the direction of arrow i by suspending between the backup rollers 36 and passing over the image forming units below the first to fourth image forming units I, II, III, and IV. Is driven to rotate at substantially the same peripheral speed as. A transfer charging blade 34 is provided inside the intermediate transfer belt 35, and the transfer charging blade 3
At 4, the ascending-side belt portion of the intermediate transfer belt 35 is brought into contact with the lower surface of the photosensitive drum 1 of each of the image forming units I, II, III, and IV.

Then, the yellow toner image on the photosensitive drum 1 surface of the first image forming unit I is transferred to the surface of the rotating intermediate transfer belt 35 in the first transfer unit, and the second toner image is transferred to the second transfer unit in the second transfer unit. The transfer of the magenta toner image on the photosensitive drum 1 surface of the image forming unit II, the transfer of the cyan toner image on the photosensitive drum 1 surface of the third image forming unit III in the third transfer unit, and the transfer of the fourth toner image on the fourth transfer unit. The superimposed transfer (primary transfer) of the toner image is performed four times because of the transfer of the black toner image on the surface of the photosensitive drum 1 of the image forming unit IV.
5, a full-color toner image is synthesized and formed.

Reference numeral 83 denotes a transfer roller as a secondary transfer means, which presses against the backup roller 36 with the intermediate transfer belt 35 interposed therebetween to form a secondary transfer nip. The transfer material P of the sheet cassette 5 is placed in the secondary transfer nip.
Is fed at a predetermined control timing, so that the full-color toner image on the surface side of the intermediate transfer belt 35 is collectively transferred (secondarily transferred) to the surface of the transfer material P. The transfer material P that has exited the secondary transfer nip is separated from the intermediate transfer belt 35 and introduced into the heat fixing device 11, where the unfixed full-color toner image on the transfer material surface is fixed as a permanently fixed image by heat and pressure. The paper is output from the paper discharge roller 12 to a paper discharge tray 13 outside the apparatus as an image formed product (copy, print).

In this embodiment, each of the image forming units I, II, III, IV
Is provided with a density sensor 81 in front of the intermediate transfer belt cleaning device 82. The charging unit cleaning mode is set for each of the image forming sections I, II, and III.
In IV, the timing of the discharge position on the transfer belt 31 for each color is shifted, and the density of the discharged toner of each color is measured. For each color, that is, for each image forming unit I, II, III, and IV
It is determined every time whether or not the charging unit cleaning mode is continued.

In this embodiment, the object of the present invention is achieved. Further, even in an image forming apparatus including four image forming units I, II, III, and IV, the cleaning condition of the charging means can be controlled by one density sensor 81. it can.

Of course, the density sensor 81 can be used for other controls such as control of image density and phase adjustment of four stations.

[Others] 1) Although an organic photosensitive member was used as an image carrier in each of the embodiments, the present invention is not limited to this as long as cleanerlessness can be achieved. For example, there is no problem with an amorphous silicon photosensitive member.

2) The contact charging device is a sleeve rotating type magnetic brush charging device in each embodiment, but it is a matter of course that a different type of magnetic brush charging device may be used. Of course, a contact charging device other than a magnetic brush charging device using a contact charging member such as a charging roller or a fur brush may be used.

3) The image carrier may be an electrostatic recording dielectric. In this case, after the dielectric surface is primary-charged uniformly to a predetermined polarity / potential, the image bearing member is charged with a static elimination needle head and an electron gun. An electrostatic latent image of image information is written and formed by selectively removing charge by a charge removing unit.

[0138]

As described above, according to the present invention, in an image forming apparatus of a contact charging type / cleanerless system, uneven transfer or charging due to a large amount of untransferred toner mixed into a contact charging member at a time. Performance degradation can be prevented, and the intended purpose is well achieved.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of a layer structure of a photoreceptor.

FIG. 3 is a schematic diagram of the configuration of a magnetic brush charging device.

FIG. 4 is a diagram showing a relationship between an alternating voltage applied to a magnetic brush charging device and a charging potential;

FIG. 5 is a schematic diagram of an exposure apparatus.

FIG. 6 is a schematic model diagram of a developing device.

FIG. 7 is a schematic diagram illustrating a configuration of an image forming apparatus according to a third embodiment.

FIG. 8 is a schematic model diagram of another image forming apparatus.

[Explanation of symbols]

1. photosensitive drum, 2. contact charging device, 3. exposure device, 4. developing device, 5. paper cassette, 8. transfer device, 9, auxiliary charging fur brush, 10. fixing Device, 81 ··· Density sensor, 82 Cleaning device for transfer belt or intermediate transfer belt, 35 ··· Intermediate transfer belt

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H003 AA01 AA12 BB11 CC04 DD00 DD03 DD14 2H027 DA06 DA09 DA10 DA39 DE01 DE07 EA01 EA03 EA09 EA18 EC06 EC09 ED03 ED24 ED27 HB19 2H032 AA05 BA02 BA07 BA11 BA17 AC23 AD31 DA02 DA31 DA47 DB12 GA04

Claims (6)

[Claims] An image carrier for carrying an image; contact charging means for contacting the image carrier to charge the image carrier; and information writing means for forming an electrostatic latent image on the image carrier. Developing means for developing the electrostatic latent image to form a toner image;
Transfer means for transferring the toner image to a transfer material; and density detecting means for detecting the density of the toner image on the image carrier, wherein the developing means transfers the toner image to the transfer material by the transfer means. An image forming apparatus also serving as a cleaning unit for collecting the toner remaining on the image carrier after the charging, wherein a charging unit cleaning mode for discharging mixed toner from the contact charging unit is provided, and the charging unit is discharged during the charging unit cleaning mode. An image forming apparatus for detecting the density of the toner image on the image carrier by the density detecting means and controlling the cleaning condition of the charging means. 2. An image carrier for carrying an image, contact charging means for contacting the image carrier and charging the image carrier, and information writing means for forming an electrostatic latent image on the image carrier. Developing means for developing the electrostatic latent image to form a toner image;
Transfer means for transferring the toner image formed on the image bearing member to a transfer material, transfer material holding means for holding the transfer material,
An image forming apparatus comprising: a transfer material holding unit cleaning unit that collects toner on the transfer material holding unit; and a density detection unit that detects a toner image density on the transfer material holding unit. An image forming apparatus comprising: a charging unit cleaning mode for discharging the toner; a density of the toner image discharged in the charging unit cleaning mode is detected by the density detection unit to control the charging unit cleaning condition. 3. An image carrier for carrying an image, contact charging means for contacting the image carrier and charging the image carrier, and information writing means for forming an electrostatic latent image on the image carrier. Developing means for developing the electrostatic latent image to form a toner image;
A second image carrier on which the toner image formed on the image bearing member is primarily transferred, and a secondary image carrier on which the toner image primarily transferred on the second image carrier is secondarily transferred to a transfer material. Transfer means,
An image forming apparatus comprising: a second image carrier cleaning means for collecting toner remaining on the second image carrier; and a density detecting means for detecting a toner image density on the second image carrier. A charging unit cleaning mode for discharging mixed toner from the charging unit, wherein a density of the toner image discharged in the charging unit cleaning mode is detected by the density detection unit, and the charging unit cleaning condition is controlled. Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the control of the cleaning condition of the charging unit is a control of a cleaning time of the charging unit. 5. An image forming apparatus according to claim 1, wherein the control of the cleaning condition of the charging unit is a voltage control applied to the charging unit at the time of cleaning the charging unit. 6. An image forming apparatus according to claim 1, wherein said information writing means for forming an electrostatic latent image on said image carrier is an exposure means.