JPH06222676A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a compact, inexpensive device and to prevent the movement of a magnetic particle to a photosensitive drum by carrying out a magnetic brush development, where the development is carried out under the application of an oscillating electric field, applying a DC element after the application of an AC element by the use of an AC voltage common to electrification and development, and stopping the AC voltage after the stop of the DC voltage element. CONSTITUTION:By rotating the photosensitive drum 10 and then a cylinder 22 at peripheral speed 1.2-2.0 time higher than that of the photosensitive drum 10, a magnetic brush is formed on a layer of magnetic particles 21 carried while sticking to a cylinder 22. The magnetic brush is carried in the direction of the rotation of the cylinder 22, and comes into contact with the photosensitive layer of the photosensitive drum 10 and slides against it. When electrification is started, an AC element is first applied between the cylinder 22 and the photosensitive drum 10 and, after a voltage between the peaks of the AC element reaches a prescribed value, a DC element is increased to a prescribed potential. When the electrification is stopped, the DC element is first decreased, and then the AC element is decreased after the elapse of a proper time.

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 an electrophotographic copying machine or an electrostatic recording apparatus, which utilizes an electrostatic transfer process for transferring after charging, image exposing and developing on an image forming body. Regarding

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a corona charger has generally been used for charging an image forming body such as a photosensitive drum. This corona charger applies a high voltage to the discharge wire to generate a strong electric field around the discharge wire to perform gas discharge, and the charged ions generated at that time are adsorbed to the image forming body to charge. Done.

Since the corona charger used in such a conventional image forming apparatus can be charged without mechanical contact with the image forming body, it is said that the image forming body is not damaged during charging. Have advantages. However, since this corona charger uses a high voltage, there is a risk of electric shock or leakage, and ozone generated by gas discharge is harmful to humans, which shortens the life of the image forming body. Had. Further, the charging potential of the corona charger is unstable because it is strongly affected by temperature and humidity. Further, the corona charger generates noise due to high voltage, which causes electrophotographic image formation as a communication terminal or an information processing device. This is a major drawback when using the device.

Many drawbacks of such corona chargers are:
The cause is that gas discharge is involved in charging.

Therefore, a magnet body is included as a charging device capable of charging the image forming body without causing high-pressure gas discharge like a corona charger and without mechanically damaging the image forming body. A charging device in which conductive magnetic particles are adsorbed on a cylindrical carrier to form a magnetic brush, and the surface of an image forming body is rubbed with the magnetic brush to perform charging is disclosed in Japanese Patent Application Laid-Open No. 2000-242242. 59-133569, JP-A-4-218
No. 73 and Japanese Patent Laid-Open No. 4-116674.

[0006]

In the image forming apparatus using the charging device disclosed in the above publication, magnetic particles are used for both the charging device and the developing device, and a bias voltage is applied to perform charging and development. It is being appreciated. At that time, the charging power source and the developing power source were used separately. Against this background, an AC bias that moves charges through a magnetic brush is applied during charging, while an AC bias that moves toner through the magnetic brush without moving charges such as discharge is required during development. These A
This is because it was difficult to set the same C bias condition. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus in which these power sources are commonly used and which is compact, low-cost, and capable of stable and uniform charging and development.

[0007]

An object of the present invention is to charge magnetic particles on a carrier to form a magnetic brush, and to place the magnetic brush on the carrier under an oscillating electric field to charge an image forming body. In the forming apparatus, magnetic brush development is performed in which the development is performed under an oscillating electric field, and the resistance of the developing magnetic particles is higher than that of the charging magnetic particles by using an AC voltage common to the charging and the development. And an image forming apparatus that performs magnetic brush development in which development is performed under an oscillating electric field, and a common AC voltage is used for charging and development, and a DC component is applied after an AC component is applied. The image forming apparatus to be used, and the magnetic brush development which develops under an oscillating electric field in the development are performed, and the DC voltage component is stopped by using the AC voltage common to the charging and development. After it achieved by 3 invention-of the image forming apparatus characterized by stopping the alternating voltage.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, both a charging device and a developing device using magnetic particles of an image forming apparatus are applied as a bias voltage in a form in which a DC component and an AC component are superposed, but a common power source is used. It is characterized by using a common constant-voltage power supply for the balance, especially for the AC component, and this has the effect of achieving compactness and cost reduction. Further, it is characterized in that the order of applying and stopping the bias voltage of the direct current component and the alternating current component in the charging device and the developing device is made proper, thereby preventing adhesion of magnetic particles to the image forming body. It is a thing.

That is, regarding the charging device, the bias voltage applied between the carrier for charging the magnetic particles (charging sleeve) and the image forming member is sufficient to inject charges into the magnetic brush.
In order to perform uniform charging of the image forming body, it is preferable to superimpose an AC component on a DC component. However, when the direct current component and the alternating current component of the bias voltage are simultaneously started and stopped at the time of starting and stopping the charging, a high potential difference is momentarily generated between the image forming body and the magnetic brush, so that the magnetic particles are generated in the image forming body. Move to adhere. In order to prevent this, in the present invention, the AC component is applied at the start of charging, and then the DC component is applied, and when the charging is stopped, the application of the DC component is stopped and then the application of the AC component is stopped.

Also in the developing device, particularly in the case of performing non-contact development, a direct current component and an alternating current component are provided between the carrier for carrying magnetic particles and toner or one component magnetic developer (developing sleeve) and the image forming body. By superimposing the above, the flying property of the toner is enhanced and the developing performance is improved. However, in the development as well as in the charging, when the DC component and the AC component of the bias voltage are simultaneously started and stopped at the start and stop of the development, a high potential difference is momentarily generated between the image forming body and the magnetic brush. The resulting magnetic particles move and adhere to the image forming body. In order to prevent this, in the present invention, the AC component is applied after the development is started, the AC component is applied, and the DC component is stopped when the development is stopped, and then the AC component is stopped.

[0011]

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

FIG. 1 is a sectional view showing the outline of the construction of an electrostatic recording apparatus which is an image forming apparatus of the present invention. In the figure,
Reference numeral 10 is an image forming body that rotates in the direction of the arrow (clockwise) (-).
A photosensitive drum made of charged OPC is provided with a charging device 20, an exposure unit 12, a developing device 30, a transfer roller 13, a cleaning device 50, and the like, which will be described later, on which image light L from the exposure device enters, on its peripheral portion. ing.

The basic operation of the copy process of this embodiment is as follows.
When a copy start command is sent from an operation unit (not shown) to a control unit (not shown), the control unit controls the photosensitive drum.
10 starts rotating in the direction of the arrow. As the photosensitive drum 10 rotates, the peripheral surface of the photosensitive drum 10 is uniformly charged by a charging device 20 described later and passes through. An image is written on the photoconductor drum 10 by the image writing device such as a laser beam in the exposure unit 12 to form an electrostatic latent image corresponding to the image.

In the developing device 30, a resistance higher than that of the magnetic particles used in the charging device 20 is 10 ¹² Ω · cm, preferably 10 ¹⁴ Ω · cm.
After the above-mentioned two-component developer composed of magnetic particles and toner or one-component magnetic toner is agitated by the agitating screws 33A and 33B, it is attached to the outer circumference of the developing sleeve 31 which is outside the magnet sleeve 32 and rotates. Then, a magnetic brush of developer is formed, and an AC bias voltage common to the AC voltage of the oscillating electric field applied to the charging device 20 is applied to the developing sleeve 31 so that the developing sleeve 31 does not contact in the developing area facing the photoconductor drum 10. Alternatively, contact reversal development is performed to form a toner image.

In the image forming apparatus of the present embodiment, the bias power supply 60 for charging and developing is applied by superimposing an individual DC power supply of constant voltage on the AC power supply 64 of common constant voltage V _AC . A constant-voltage DC power source 24 is superposed on, and a constant-voltage DC power source 34 is superposed on for development. These DC power supply 24, 34 each of a predetermined voltage V _c, the ON / OFF switching between 0V and V _D is possible. The common AC power supply 64 is a constant voltage power supply to prevent the charging and developing DC power supplies 24 and 34 from changing due to ON / OFF operations.

From the paper feed cassette 40, the recording papers P are delivered one by one by a first paper feed roller 41. The fed recording paper P is sent onto the photosensitive drum 10 by the second paper feed roller 42 which operates in synchronization with the toner image on the photosensitive drum 10. Then, by the action of the transfer roller 13, the toner image on the photoconductor drum 10 is transferred onto the recording paper P and separated from the photoconductor drum 10. The recording paper P on which the toner image has been transferred is sent to the fixing device 81 via the conveying means 80, is nipped by the heat fixing roller and the pressure bonding roller, melted and fixed, and then discharged outside the device. A photoconductor drum 10 that rotates with the toner remaining without being transferred to the recording paper P.
The surface of 1 is scraped off and cleaned by a cleaning device 50 having a blade 51 and the like, and stands by for the next image recording.

FIG. 2 is a sectional view showing an embodiment of the charging device 20 of the present invention used in the electrostatic recording apparatus of FIG. In the figure, 21 is a magnetic particle, and spherical ferrite particles coated so as to have conductivity are used. In addition, conductive magnetic resin particles obtained by pulverizing the magnetic particles and a resin as main components after thermal smelting can also be used. The outer shape is a true sphere and the particle size is 50μ to ensure good charging.
It is adjusted to m and a specific resistance of 10 ⁵ Ω · cm, and the frictional charge amount with the toner is −5 μC / g under the condition that the toner concentration is 1%. The preferable resistance of the magnetic particles is 10 ³ to 10 ⁸ Ω · cm.

Reference numeral 22 is a cylinder which is a carrier for carrying magnetic particles 21 formed of non-magnetic and conductive metal such as aluminum, and 23 is a columnar magnet disposed inside the cylinder 22. As shown in FIG. 3, the S pole and the N pole are magnetized so that the cylindrical surface has 700 gauss on the peripheral surface, and the cylinder 22 is rotatable with respect to the fixed magnet 23. Further, the magnet 23 may rotate as a magnetic pole having an equal pole. The cylinder 22 is opposed to the photoconductor drum 10 in the opposite direction to the movement direction of the photoconductor drum 10, but is rotated in the same direction at a peripheral speed of 0.2 to 2.0 times.

The photosensitive drum 10 comprises a conductive base material 10b and a photosensitive body layer 10a covering the surface thereof, and the conductive base material 10b is grounded.

Reference numeral 60 denotes an AC power source common to the developing device 30 for applying a bias voltage between the cylinder 22 and the conductive substrate 10b.
The cylinder 22 is grounded via the bias power source 60, which is a bias power source in which 54 and the charging DC power source 24 are superposed.

The DC component V _C of the bias power source is a DC component set to the same value as the voltage to be charged, and is a power source for superimposing an AC bias voltage, which is provided between the cylinder 22 and the photosensitive drum 10. Although it depends on the size of the gap, the charging voltage charged on the photosensitive drum 10, and the like, the gap is maintained between 0.1 and 5 mm, and is approximately the same as the voltage to be charged, V _C (-500 to -10).
The DC component of 00V), V as peak-to-peak voltage (V _pp)
By supplying an AC bias voltage on which an AC component of _AC (200 to 3500 V) frequency of 0.3 to 10 KHz is superimposed through a protective resistor, a preferable charging condition could be obtained. By applying an AC bias voltage, an oscillating electric field can be formed and uniform charging can be obtained.

The bias power source 60 performs constant voltage control for the DC component and constant voltage control for the AC component, and the control unit (not shown) independently turns on and off the DC component and the AC component, respectively.
You can do it. Further, it is preferable that the ON / OFF operation continuously changes the applied voltage, not instantaneously. Specifically, it is preferable that the time is about 1 to 500 msec in order to prevent the magnetic particles from adhering to the image forming body.

Reference numeral 25 denotes a casing forming a storage portion for the magnetic particles 21, the cylinder 22 and the magnet 23 are arranged in the casing 25, and a regulation plate 26 is provided at the outlet of the casing 25. The thickness of the layer of magnetic particles 21 attached to the cylinder 22 and carried out is regulated. The gap between the regulation plate 26 and the cylinder 22 is such that the transport amount of the magnetic particles 21, that is, the existing amount of the magnetic particles on the cylinder 22 in the developing region is 10 to 200 mg / cm.
Adjusted to ² . The existing amount is an average value of the contact area of the magnetic brush. Photoconductor drum 10 and cylinder
The gap with 22 is connected by 21 layers of magnetic particles whose thickness is regulated. The stirring plate 27 is a rotating body having a plate-shaped member that corrects the bias of the magnetic particles 21 around the axis.

Next, the operation of the charging device 20 described above will be described.

The photosensitive drum 10 is rotated in the direction of the arrow in advance, and then the cylinder 22 is rotated simultaneously or with a slight delay at the peripheral speed of 1.2 to 2.0 times the peripheral speed of the photosensitive drum 10 in the same direction as the arrow. Then, the layer of the magnetic particles 21 attached and conveyed to the cylinder 22 will be a photosensitive drum on the cylinder 22 due to the magnetic lines of force of the magnet 23.
Magnetically connected at a position facing 10 to form a kind of brush-like, so-called magnetic brush is formed. Then, the magnetic brush is conveyed in the rotating direction of the cylinder 22 and comes into contact with and slides on the photosensitive layer 10a of the photosensitive drum 10. The rubbing operation of the magnetic brush is preferably performed before the DC component of the charging bias is applied.

More preferably, it is preferable to apply an AC component from an AC power source common to the developing device 30. Cylinder
When a voltage is applied to 22 and a potential difference is generated between the photosensitive drum 10 and the photosensitive drum 10, magnetic particles are easily attached to the photosensitive drum 10.

At this time, the cylinder 22 is rotated in advance and the magnetic brush rubs against it, so that the adhesion can be prevented. It is considered that the transfer of electric charges is facilitated and the potential difference is reduced, so that the adhesion of magnetic particles is reduced.

At the start of charging, the cylinder 22 and the photosensitive drum 10
As shown in FIG. 3, first, the AC component is applied between and, and the peak-to-peak voltage of the AC component reaches a predetermined value V _AC , immediately or after an appropriate time d (c1) elapses. The DC component is increased from 0V to a predetermined potential V _C. By shifting the application timing of the DC component in this way, it was possible to prevent the magnetic particles from moving and adhering to the photosensitive drum 10 at the start of charging. The rising time t _c1 associated with the ON operation shown in FIG. 3 is preferably 1 to 500 msec.

Furthermore, in order to prevent the adhesion of magnetic particles,
Before the charging, the charge of the image forming body is set to about 0 in advance by the static elimination lamp 14.
It is preferable to eliminate the charge to V.

As described above, by applying the AC bias voltage between the cylinder 22 and the photoconductor drum 10, charges are injected onto the photoconductor layer 10a through the conductive magnetic particles 21 to perform charging. . In this case, since the bias voltage is a bias voltage in which an AC component is superimposed on a DC component, the efficiency of charge injection from the magnetic brush that accompanies the movement of charges and the discharge phenomenon is improved. Charging can be performed.

The results of changing the frequency and voltage of the AC voltage component applied to the cylinder 22 in the above embodiment are shown in FIG.

In FIG. 4, the shaded area with vertical lines is the area where dielectric breakdown is likely to occur, the shaded area is shaded with uneven charging, and the area without shade is stable. This is a preferable range in which electrostatic charging is obtained. As is clear from the figure, the preferable range changes slightly depending on the change of the AC voltage component. The waveform of the AC voltage component is not limited to a sine wave, and may be a rectangular wave or a triangular wave. Also, in FIG. 4, the low-frequency region of 300 Hz or less, which is shaded, is
This is the range where uneven charging occurs due to the low frequency.

Next, when the charging is stopped, as shown in FIG. 3, the direct current component is first lowered to approximately 0 V, and after a suitable time d (c2) has elapsed, the alternating current component is reduced. In this way, the AC component was reduced after the potential difference between the magnetic brush and the photoconductor drum 10 was eliminated, and therefore it was possible to prevent the magnetic particles from moving and adhering to the photoconductor drum 10 when the charging bias was stopped. The fall time t _C2 associated with the OFF operation shown in FIG. 3 is preferably 1 to 500 msec.

Further, in order to prevent the magnetic particles from adhering, it is preferable that the potential of the image forming body is previously discharged to about 0 V by the discharging lamp 14 even after the charging bias is stopped. By doing so, it is possible to prevent a potential difference from being generated between the photosensitive member which is the image forming body and the cylinder 22, and to prevent the magnetic particles from being attached to the image forming body.

After the charging bias is stopped, the rubbing operation of the magnetic brush is stopped. This stop is performed before or simultaneously with the stop of the photosensitive drum 10.

In this embodiment, the charge eliminating lamp 14 was not used,
It is also possible to charge the image-forming body potential by applying an alternating current component of the bias voltage and then applying a direct current component, or by stopping the direct current component and then stopping the alternating current component.

When the cylinder 22 is retracted or the magnetic poles of the magnet 23 are rotated so that the NS direction is parallel to the tangent line of the facing portion of the photoconductor drum 10, the ears of the magnetic brush move to the photoconductor drum 10 by the horizontal magnetic field. Since the magnetic brush is parallel to the tangential direction of the facing portion and the tip of the magnetic brush is separated from the photoconductor drum 10, it can be brought out of contact with the image forming body. As a result, it is possible to prevent the photoreceptor from being deteriorated or changed when it is left.

It is desirable that the operation of separating the magnetic brush from the photoconductor is performed after the application of the DC and AC biases is stopped. It is possible to prevent the phenomenon in which the magnetic particles move to the photoconductor when a potential difference occurs between the photoconductor and the cylinder 22.

The ON / OFF of the bias voltage at the time of starting / stopping the rotation of the cylinder 22 is delayed at the start,
In the case of stopping, it is preferable to do it early. The start / stop of the rotation of the photoconductor drum 10 is not particularly limited, but the start of the rotation of the photoconductor drum 10 starts earlier than the start of the rotation of the cylinder 22 of the charging device, and the start of the rotation stops late when the charging is stopped to shorten the charging time. It is preferable because When the image forming apparatus causes a paper jam or the like to start / stop the operation, it is preferable to perform the same as above.

Further, the charging device 20 described above also serves as a cleaning device for cleaning the residual toner on the photoconductor drum 10 by making the DC component of the output bias voltage the same as the charging polarity of the residual adhered toner. You can also do it. Further, the voltage of the DC component of the bias power source 24 can be changed so that it can be used as a device for controlling the temperature and humidity of the photoconductor and the potential fluctuation due to repetition to be constant.

Further, in the present invention, the magnet is contained in the cylinder as the magnetic particle carrier, but the cylinder may be omitted and the magnetic particles may be directly attached to the magnet roll to form the magnetic brush. .

Next, the developing device 30 will be described.

Reference numeral 60 denotes a bias power source for applying a bias voltage to the developing sleeve 31, and the developing sleeve 31 is grounded via the bias power source 60.

The bias power source 60 is a power source for supplying an AC bias voltage obtained by superimposing an AC component V _AC common to the charging device 20 on a DC component V _D set to a slightly lower value than the charging voltage.
Although it depends on the size of the gap Dd between the developing sleeve 31 and the photosensitive drum 10, the developing conditions for developing the photosensitive drum 10, and the like, when the gap Dd is held at 0.1 to 5 mm, it is more than the voltage to be charged by 50. -200V lower -500V to -1,000V DC component, AC voltage bias between peak value voltage (V _PP ) 200 to 3,500V and frequency 0.3 to 10KHz superposed AC bias voltage through protection resistor R As a result, favorable developing conditions could be obtained. The bias power source 60 performs constant voltage control for the DC component and constant voltage control for the AC component.

The developer is composed of a carrier having a ferrite core as a core and an insulating resin coating therearound, and a toner T containing polyester as a main material and a pigment according to a color, a charge control agent, silica, titanium oxide and the like. Things
In the non-contact development, the developer is regulated by the layer forming rod on the developing sleeve 31 to have a layer thickness of 300 to 800 μm, and is conveyed to the developing area.

The gap D _d between the developing sleeve 31 and the photosensitive drum 10 in the developing area is 0.4 to larger than the layer thickness (developer).
The thickness of 1.0 mm is applied between the developing sleeve 31 and the photoconductor drum 10 by superimposing the AC component V _AC and the DC bias voltage V _D common to the charging device 20, and V _D and the charging potential of the photoconductor. Since the charge of V _H and the toner T are of the same polarity (negative), the toner T, which has been given the opportunity to be separated from the carrier by V _AC , does not adhere to the V _H portion having a higher insulation value than V _D. , adhered toner amount corresponding to the potential difference lower V _L portion of the absolute value of the potential from V _D to image exposure is made visualized (reversal development) is carried out.

At the start of development, the AC component is first applied between the developing sleeve 31 and the photosensitive drum 10 as shown in FIG. 3, and the peak-to-peak voltage of the AC component reaches a predetermined value V _AC. After a suitable time d (D1) has elapsed, the DC component is increased from 0 V to a predetermined potential V _D. By shifting the application timing of the DC component in this way, it was possible to prevent the magnetic particles from moving and adhering to the photosensitive drum 10 at the start of development. Here, the rise time t _c1 associated with the ON operation is 1 to
It is preferably 500 msec. When the development is stopped, first, the direct current component is lowered to about 0 V, and then the alternating current component is reduced immediately or after an appropriate time d (D2) has elapsed. In this way, the AC component was reduced after the potential difference between the magnetic brush and the photoconductor drum 10 was eliminated, so that it was possible to prevent the magnetic particles from moving and adhering to the photoconductor drum 10 when the developing bias was stopped. The resistance of the magnetic particles is 10 ³ to 10 ⁸ Ωcm as a charger and 10 ¹² Ωcm as the magnetic particles of the developer, preferably 10 ¹⁴ Ωcm or more, so that the common AC voltage condition is satisfied. Could be used.

[0048]

According to the present invention, since the photosensitive drum is charged by directly injecting the electric charge through the magnetic brush, the bias voltage can be lowered and the generation of ozone can be prevented. Further, since the charging power source and the developing power source in which the DC component and the AC component are superimposed are made common, a compact and low-cost image forming apparatus is provided. Furthermore, in the step of starting the application of the bias voltage, the application of the direct current component is performed subsequently to the application of the alternating current component, and in the step of stopping the application of the bias voltage, the application of the alternating current component is continued after the stop of the application of the direct current component. By stopping, the movement of magnetic particles to the photosensitive drum was prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an outline of the configuration of an electrostatic recording device of the present invention.

FIG. 2 is a sectional view showing an embodiment of the charging device of the present invention.

FIG. 3 is a time chart of starting and stopping application of a bias voltage according to the present invention.

FIG. 4 is a charging characteristic diagram when a frequency of an AC voltage component is changed.

[Explanation of symbols]

 10 Photoconductor drum 20 Charging device 21 Magnetic particles (charging device) 22 Carrier (charging roller, cylinder) 23 Magnet 24 DC bias power supply (for charging) 30 Developing device 31 Developing sleeve 32 Magnet sleeve 33 Stirring screw 34 DC bias power supply (For development) 60 bias power supply 64 AC bias power supply

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masakazu Fukuchi 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Inventor Shizuo Morita 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Invention Noriyuki Hiroshi Nomori 2970 Ishikawa-cho, Hachioji City, Tokyo Konica Stock Company

Claims (3)

[Claims] 1. An image forming apparatus for charging an image forming body by supplying magnetic particles onto a carrier to form a magnetic brush, and placing the magnetic brush on the carrier under an oscillating electric field.
In the image development, magnetic brush development is carried out under an oscillating electric field during development, and the resistance of the developing magnetic particles is higher than that of the charging magnetic particles by using an alternating voltage common to the charging and developing. apparatus. 2. An image forming apparatus for charging an image forming body by supplying magnetic particles onto a carrier to form a magnetic brush, and placing the magnetic brush on the carrier under an oscillating electric field.
An image forming apparatus characterized by performing magnetic brush development for development under an oscillating electric field during development, and using an AC voltage common to the charging and development, and applying an AC component and then a DC component. 3. An image forming apparatus for charging an image forming body by supplying magnetic particles onto a carrier to form a magnetic brush, and placing the magnetic brush on the carrier under an oscillating electric field.
An image forming apparatus, characterized in that magnetic brush development is carried out under an oscillating electric field during development, and an alternating voltage common to the charging and developing is used to stop the alternating voltage after stopping the direct voltage component.