JPH0830105A - Image forming device - Google Patents

Abstract

PURPOSE:To achieve the miniaturization of a developing device while maintaining high image quality by using magnetic carrier which satisfies a specific relationship among an amount of developer, a process speed and the length of a developer carrier and whose magnitude of magnetization is lower than or equal to a specific value. CONSTITUTION:A magnet 29 is fixed inside a developing sleeve 25 and has a development magnetic pole S1 opposite a developing part 26. A magnetic brush of developer is formed by a development magnetic field that the development magnetic pole S1 generates at the developing part 26, and this magnetic brush comes into contact with a photosensitive drum 3 to develop a dot- distributed electrostatic latent image. At this time, the nap of the magnetic carrier and toner sticking to the surface of a developing sleeve are transferred to the part where the electrostatic latent image is exposed, and they are used for developing the image. As the magnetic carrier the device uses one which satisfies the relationship of Z<=2PL, wherein the amount of developer is Z (g), a process speed is P(cm/sec), and the length of the developer carrier in the longitudinal direction is L (cm), and whose magnitude of the magnetization in a magnetic field of 1000G is 100emu/cm<3>.

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 or a printer, equipped with a developing device for developing an electrostatic latent image formed by electrophotography or electrostatic recording. .

[0002]

2. Description of the Related Art Conventionally, various dry developing methods have been proposed and put into practical use. The dry development method is
When roughly classified, it is divided into a one-component developing method and a two-component developing method.

Most of the one-component developing methods are non-contact methods, but a typical method is a one-component jumping developing method using magnetic toner. This developing method can obtain a high-quality image with a simple structure, but cannot obtain a color image because the toner contains a magnetic material. The one-component developing method using a non-magnetic toner can obtain a color image and can realize a low-cost and small-sized developing device, but it is difficult to apply the toner onto the developing sleeve, and the elastic blade is used. Currently, it is coated, and it lacks stability and durability.

On the other hand, in the two-component developing method, toner is conveyed by a magnetic carrier, but since a non-magnetic toner can be used, a color image can be obtained and the image quality is high.

[0005]

However, in the two-component developing method, it is necessary to control the toner concentration of the developer (ratio of the weight of the toner to the weight of the developer) to be constant and to maintain the uniform toner concentration. Therefore, it is necessary to replenish the toner based on the signal from the toner concentration sensor, stir the replenished developer, and convey it. For this reason, usually, two screws are used for stirring and carrying. Therefore, under the present circumstances, the size of the developing device is inevitably large.
The amount of developer is generally about 400 to 600 g,
As compared with the one-component developing method, the developing container becomes larger by the amount of carrier. As described above, there is a problem that the image forming apparatus provided with the developing device for carrying out the two-component developing method becomes larger than the developing device for carrying out the one-component developing method.

Therefore, an object of the present invention is to provide an image forming apparatus by the two-component developing method, which can achieve downsizing of the developing device while maintaining high quality image quality.

[0007]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A developer having toner and a magnetic carrier is conveyed to a developing section by a developer carrier, and a developing magnetic pole of a magnet arranged inside the developer carrier forms a developing magnetic field in the developing section,
In an image forming apparatus equipped with a developing device that develops an electrostatic latent image formed on the image carrier by bringing a magnetic brush of the developer into contact with the image carrier, the amount of the developer is Z (g) and the process speed is Is P (cm / sec) and the length in the longitudinal direction of the developer carrier is L (cm), the relationship of Z ≦ 2PL is satisfied, and the strength of magnetization is 1 in a magnetic field of 1000 G.
The image forming apparatus is characterized by using a magnetic carrier of 00 emu / cm ³ or less.

It is preferable that only one agitating / conveying member is used in the developing device.

The amount of the developer is preferably 150 g or less.

The electrostatic latent image formed on the image bearing member is preferably a dot distribution electrostatic latent image.

The image carrier is an electrophotographic photosensitive member, and the electrophotographic photosensitive member is exposed with a light beam modulated by a pulse-width-modulated signal corresponding to the light and shade of a recorded image to produce a dot distribution electrostatic image. It is preferable to form a latent image.

A vibration bias voltage is preferably applied to the developer carrying member.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

FIG. 2 is a schematic diagram showing an example of an electrophotographic color printer to which the present invention can be applied. This printer has an electrophotographic photosensitive drum 3 that rotates in the direction of the arrow.
Around the photosensitive drum 3, a charging device 4, a rotary developing device 1 having developing devices 1M, 1C, 1Y, 1BK, a discharging device 10 for transfer, a cleaning means 12, and a photosensitive drum 3 above the drawing. Arranged laser beam scanner LS
An image forming unit including the above is provided.

Each developing device supplies a two-component developer containing toner particles and carrier particles to the photosensitive drum 3. The developer of the developing device 1M is magenta toner, and the developing device 1C is
The developer of 1 contains cyan toner, the developer of the developing device 1Y contains yellow toner, and the developer of the developing device 1BK contains black toner.

The semiconductor laser incorporated in the scanner LS is controlled according to the input image signal and emits a laser beam.

The sequence of the entire color printer will be briefly described by taking the case of the full color mode as an example. First, the photosensitive drum 3 is uniformly charged by the charger 4. Next, scanning exposure is performed by the laser light L modulated by the magenta image signal, a dot distribution electrostatic latent image is formed on the photosensitive drum 3, and this latent image is fixed by the magenta developing device 1M which is fixed at the developing position in advance. Reverse development is performed.

On the other hand, the transfer material such as paper taken out from the cassette CS and advanced through the paper feed roller 6 is held by the gripper 7 of the transfer drum 9 and is brought into contact with the contact roller 8.
Is electrostatically wound around the transfer drum 9. The transfer drum 9 is rotating in the direction of the arrow in the figure in synchronization with the photosensitive drum 3, and the magenta image developed by the magenta developing device 1M is transferred to the transfer material by the transfer charger 10 at the transfer portion. The transfer drum 9 continues to rotate and is ready for transfer of an image of the next color (cyan in FIG. 1).

The photosensitive drum 3 is cleaned by the cleaning means 12, is charged again by the charger 4, and is exposed as described above by the laser beam L modulated by the next cyan image signal to obtain an electrostatic latent image. Is formed. During this time, the developing device 1 is rotated so that the cyan developing device 1C is fixed at a predetermined developing position and reverse development of the dot distribution electrostatic latent image corresponding to cyan is performed to form a cyan visible image.

Subsequently, when the transfer of the four color images (toner images) for the yellow image signal and the black image signal is completed by the above steps, the transfer material is
The electricity is removed by the inner and outer chargers 13 and 14, the gripper 7 is released, the toner is separated from the transfer drum 9, and the toner is sent to a fixing device (hot pressure roller fixing device) 17. The fixing device 17 fixes the visible images of four colors that are overlaid on the transfer material.

In this way, a series of full-color print sequences is completed, and a required full-color print image is formed.

In FIG. 3, the semiconductor laser device 102 is shown.
Is connected to a laser driver 500, which is a light emission signal generator that sends a light emission signal (drive signal) for generating a laser beam, and blinks in response to the light emission signal of the laser driver 500. The laser light flux L emitted from the laser element 102 is made into substantially parallel light by the collimator lens system 103.

The polygon mirror, that is, the rotary polygon mirror 104 rotates in the direction of arrow B at a constant speed to scan the parallel light emitted from the collimator lens system 103 in the direction of arrow C. The f-θ lens group 100 provided in front of the rotary polygon mirror 104 images the laser light flux L deflected by the rotary polygon mirror 104 on the surface to be scanned, that is, the photosensitive drum 3 in a spot shape, and the scanning speed thereof. Is constant on the surface to be scanned.

By the scanning exposure of the photoconductor with the laser beam L, a dot distribution electrostatic latent image is formed on the photoconductor 3.

Each of the developing devices carries out reversal development in which the toner charged to the same polarity as the charging polarity of the charger 4 is attached to the bright portion potential portion of the latent image, so that the toner on the photosensitive drum 3 is attached to the laser beam L. Expose the area to be exposed.

In this embodiment, since the PWM (pulse width modulation) method is used to perform multi-valued recording in which the minimum recording unit is one pixel, the PWM method will be briefly described with reference to FIGS. FIG. 4 is a circuit block diagram showing an example of the pulse width modulation circuit, and FIG. 5 is a timing chart showing the operation of the pulse width modulation circuit.

In FIG. 4, 401 is a TTL latch circuit for latching an 8-bit digital image signal, and 402 is T.
A level converter for converting the TL logic level into a high-speed ECL logic level, and a D / A converter 403 for converting the ECL logic level into an analog signal. Reference numeral 404 is an ECL comparator for generating a PWM signal, 405 is a level converter for converting an ECL logic level into a TTL logic level,
406 is a clock oscillator that oscillates the clock signal 2f,
Reference numeral 407 denotes a triangular wave generator that generates a substantially ideal triangular wave signal in synchronization with the clock signal 2f, and 408 denotes the clock signal 2f.
1 is divided by 2 to generate the image clock signal f 1
/ 2 frequency divider. As a result, the clock signal 2f has a cycle twice that of the image clock signal f.
In order to operate the circuit at high speed, ECL logic circuits are arranged everywhere.

The operation of the circuit having such a configuration is further shown in FIG.
The timing chart will be described. The signal a indicates the clock signal 2f and the signal b indicates the image clock signal f, which are associated with the image signal as shown in the drawing. Also,
Also in the triangular wave generator 407, in order to maintain the duty ratio of the triangular wave signal at 50%, the triangular wave signal c is generated after the clock signal 2f is once divided by 1/2. Further, the triangular wave signal c is converted to the ECL level (0 to -1V) and becomes the triangular wave signal d.

On the other hand, the image signal is 00h (white) to FFh.
Up to (black), for example, 256 gradation levels change. The symbol "h" indicates hexadecimal notation. The image signal e indicates an ECL voltage level obtained by D / A converting some image signal values. For example, the first pixel indicates the highest density pixel level FFh, the second pixel indicates the intermediate tone level 80h, the third pixel indicates the intermediate tone level 40h, and the fourth pixel indicates the intermediate tone level 20h. The comparator 404 compares the triangular wave signal d and the image signal e to generate a PWM signal having a pulse width (time length) T, t ₂ , t ₃ , t _4, etc. according to the pixel density to be formed. The pulse width corresponding to the low density pixel becomes narrower. Then, this PWM signal is converted to the TTL level of OV or 5V and becomes the PWM signal f, which is the laser driver circuit 50.
Input to 0.

By changing the exposure time per pixel in accordance with the PWM signal value thus obtained, it is possible to obtain 256 gradations with one pixel.

Incidentally, h in FIG. 5 shows the laser beam exposure area shape of the photosensitive member corresponding to each drive pulse width. The area shape of each dot latent image also substantially corresponds to this exposure area shape.

In FIG. 5, the signal waveforms a to g are time on the horizontal axis, and h is the distance in the beam scanning direction on the horizontal axis.

Next, referring to FIG. 1, each developing device 1 for visualizing the dot distribution electrostatic latent image formed on the photosensitive drum 3
M to 1BK will be described.

Each developing device is provided with a developing container 18, a toner storage chamber R2 is formed above the developing chamber R1 inside the developing container 18, and a replenishment toner (non-magnetic toner) is provided in the toner storage chamber R2. ) 20 are housed. In addition,
A replenishment roller 21 is provided in the toner storage chamber R2, and a replenishment toner 20 in an amount commensurate with the toner consumed in the development is dropped and replenished into the development chamber R1 via the replenishment roller 21.

On the other hand, the developing chamber R1 contains the developer 22 in which the toner particles and the magnetic carrier particles are mixed.

As the toner, a known toner obtained by adding a colorant, a charge control agent and the like to a binder resin can be used, and a toner having a volume average particle diameter of 5 to 15 μm can be preferably used. Here, as the volume average particle diameter of the toner, for example, one measured by the following measuring method is used.

A Coulter counter T is used as a measuring device.
A-II type (manufactured by Coulter) is used, an interface (manufactured by Nikkaki) that outputs a number average distribution and a CX-i personal computer (manufactured by Canon) are connected, and the electrolyte is 1% Nacl using primary sodium chloride. Prepare the aqueous solution.

The measuring method is as follows:
0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) as a dispersant is added to 150 ml,
Further, 0.5 to 50 mg of the measurement sample is added.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and a particle size distribution of particles of 2 to 40 μm was obtained by using the above Coulter counter TA-II type with an aperture of 100 μm as an aperture. To determine the volume distribution. With these volume distributions obtained,
The volume average particle size of the sample is obtained.

On the other hand, as the magnetic carrier, those having magnetic particles coated with an extremely thin resin are preferably used, and the average particle diameter is preferably 5 to 70 μm. The average particle size of the carrier is shown by the maximum chord length in the horizontal direction, and the measurement method is a microscope method in which 300 or more carriers are randomly selected, the diameters of the carriers are measured, and the arithmetic mean is taken to obtain the carrier particle size of this example. And

As shown in FIG. 1, an agitating / conveying member 23 is housed in the developing chamber R1. By the rotational driving of the stirring / transporting member 23, the developer 22 in the developing chamber R1 is stirred and transported in the longitudinal direction of the developing sleeve 25. By the stirring operation of the stirring / transporting member 23, the toner particles are charged with a polarity for developing the latent image by friction with the magnetic carrier particles.

An opening is provided in a portion of the developer container 18 which is close to the photosensitive drum 3, and a non-magnetic developing sleeve 25 which is a developer carrier such as aluminum or non-magnetic stainless steel is provided in the opening.

The developing sleeve 25 rotates in the direction of the arrow b, and carries the developer in which the toner and the carrier are mixed in the developing section 26. The magnetic brush of the developer carried on the developing sleeve 25 comes into contact with the photoconductor 3 rotating in the arrow a direction at the developing section 26, and the electrostatic latent image is developed at the developing section 26.

An oscillating bias voltage in which a DC voltage is superimposed on an AC voltage is applied from the power supply 27 to the developing sleeve 25. The dark portion potential (non-exposed portion potential) and the light portion potential (exposed portion potential) of the latent image are located between the maximum value and the minimum value of the vibration bias potential. As a result, an alternating electric field whose direction changes alternately is formed in the developing section 26. In this alternating electric field, the toner and the carrier violently vibrate, and the toner sticks to the photosensitive drum 3 corresponding to the latent image by shaking off the electrostatic restraint on the developing sleeve and the carrier.

The difference between the maximum value and the minimum value of the vibration bias voltage (peak-to-peak voltage) is preferably 1 to 5 kV, and the frequency is preferably 1 to 10 kHz. A rectangular wave, a sine wave, a triangular wave, or the like can be used as the waveform of the vibration bias voltage.

The DC voltage component has a value between the dark portion potential and the light portion potential of the latent image, but the dark portion potential is closer to the dark portion potential than the absolute minimum light portion potential. It is preferable for preventing the fog toner from adhering to the potential region.

The minimum gap between the developing sleeve 25 and the photosensitive drum 3 (this minimum gap position is inside the developing section 26) is preferably 0.2 to 1 mm.

As shown in FIG. 1, the developing sleeve 25
A developer layer thickness regulating blade 28 is disposed so as to face the above, and the developing sleeve 25 regulates the layer thickness of the two-component developer carried and conveyed to the developing section 26. The amount of the developer regulated by the blade 28 and conveyed to the developing unit 26 is determined by the height of the developer formed on the sleeve surface of the magnetic brush of the developer formed by the magnetic field in the developing unit by the developing magnetic pole S1 described later. It is preferable that the amount is 1.2 to 3 times the minimum gap value between the developing sleeve and the photosensitive drum with 3 removed.

A roller-shaped magnet 2 is provided in the developing sleeve 25.
9 is fixedly arranged. The magnet 29 has a developing magnetic pole S1 facing the developing section 26. A magnetic brush of developer is formed by the developing magnetic field formed by the developing magnetic pole S1 in the developing unit 26, and the magnetic brush comes into contact with the photosensitive drum 3 to develop the dot-distributed electrostatic latent image. At this time, the toner attached to the brush (brush) of the magnetic carrier and the toner attached to the surface of the developing sleeve instead of the brush are transferred to the exposed portion of the electrostatic latent image and developed.

The intensity of the developing magnetic field by the developing magnetic pole S1 on the surface of the developing sleeve 25 (the magnetic flux density in the direction perpendicular to the developing sleeve surface) preferably has a peak value of 500 to 2000 gauss.

In this example, in addition to the developing magnetic pole S1 of the magnet, there are N1, N2, N3 and S2 poles.

With this configuration, as in the conventional case, the developer drawn up by the N2 pole by the rotation of the developing sleeve 25 is conveyed from the S2 pole to the N1 pole, and is regulated by the developer layer thickness regulating blade 28 in the middle thereof. , Forming a thin layer of developer.
Then, the developer that has risen in the magnetic field of the developing magnetic pole S1 develops the electrostatic latent image on the photosensitive drum 3. Then N3 pole, N2
The developer on the developing sleeve 25 falls into the developing chamber R1 due to the repulsive magnetic field between the poles. The developer dropped into the developing chamber R1 is agitated and conveyed by the agitating and conveying member 23.

When the above problems were investigated using such a developing device, the developing device was downsized and the stirring characteristics were found to be such that the process speed P (cm / sec) and the length L (cm) in the longitudinal direction of the developing sleeve. , And the amount of developer (g)
It turned out that it depends greatly on the relationship of. Table 1 below shows the relationship between the process speed, the length in the longitudinal direction of the developing sleeve, and the amount of the developer measured by the above-mentioned apparatus, and the evaluation of miniaturization and stirring characteristics.

[0054]

[Table 1]

It is natural that the smaller the amount of the developer is, the better the downsizing of the developing device is. However, the stirring property is particularly excellent in downsizing because one stirring and conveying member is used in this embodiment. If the amount of the developer is too large, the stirring and feeding cannot be sufficiently performed.

It can be seen from Table 1 that if the amount of the developer is smaller than the value of 2PL, which is twice the value obtained by multiplying the process speed by the length in the longitudinal direction of the developing sleeve, the stirring characteristics can be sufficiently satisfied. Especially when the amount of developer is 150g
When it is less than the above, the size of the developing device becomes small and the stirring characteristics are excellent. The amount of developer is the product of the process speed and the longitudinal length of the developing sleeve, which is 2
In other words, less than twice is the relationship between the developer amount per unit length in the longitudinal direction and the process speed. The amount of developer per unit length in the longitudinal direction is involved in stirring, and the amount of developer increases as the process speed increases. That is, if the amount of the developer per unit length in the longitudinal direction of the developing sleeve is not more than an appropriate amount corresponding to the process speed, it has satisfactory stirring characteristics and can be downsized.

However, when the amount of the developer is small, the durability of the developer tends to deteriorate. This deterioration is a phenomenon in which pressure is applied to the toner due to shear in the developing device, the external additive externally added to the toner is embedded in the toner, the fluidity deteriorates, and the image deteriorates. Therefore, when the amount of the developer is reduced, the number of times of use is increased even with the same number of durable sheets, and the deterioration of the developer is aggravated. Therefore, in this embodiment, the strength of carrier magnetization is weakened to prevent deterioration.

For measuring the magnetic characteristics of the magnetic carrier, a DC magnetization BH characteristic automatic recording apparatus BHH manufactured by Riken Denshi Co., Ltd.
-50 can be used. At this time, the diameter (inner diameter)
The carrier is filled in a cylindrical container having a height of 6.6 mm and a height of 10 mm with a load of about 2 kg, and the strength of the magnetization is measured while the carrier does not move in the container.

First, since the developing magnetic pole S1 has a magnetic flux density peak value of 1000 gauss on the developing sleeve surface in the direction normal to the developing sleeve surface, a magnetic force (magnetic flux density) of 1000 is used. When the magnetization value of the carrier in the case of Gauss and the density of the magnetic brush in the developing part were examined, the smaller the σ ₁₀₀₀ , the denser the ears. The image quality is correspondingly improved. Further, since the share in the developing device is also magnetic, the durability is improved by reducing the strength of magnetization of the carrier. Table 2 below shows the evaluation of the initial image quality and the durable image quality when the magnetization intensity was changed.

[0060]

[Table 2]

The process speed at this time is 4 cm / s.
ec, the length of the developing sleeve in the longitudinal direction is 21 cm, and the amount of the developer is 150 g. However, if the magnetization of the carrier is small, the density of the ears of the magnetic brush becomes dense and the initial image quality is improved. Further, the durability is also improved. Process speed is 8 cm / sec, length of developing sleeve is 30c
When the amount of the developer was 400 g and the amount of the developer was 400 g, the same results as in Table 2 were obtained. If the amount of the developer per unit length in the longitudinal direction of the developing sleeve is small corresponding to the process speed, the durability characteristics will be disadvantageous. If the amount of the developer per unit length in the longitudinal direction of the developing sleeve corresponding to the process speed is the same, the evaluation in Table 2 is the same.

As described above, it is twice the product of the process speed and the length of the developing sleeve in the longitudinal direction.
The amount of developer is less than the value of PL, and the strength of magnetization is 1
By using a magnetic carrier having a density of 00 emu / cm ³ or less, it is possible to achieve downsizing of the developing device that satisfies the stirring characteristics, suppress deterioration of the developer, and maintain high image quality for a long time. In this embodiment, since one agitating / conveying member is used, further miniaturization is excellent.

In this embodiment, a pulse width modulated digital latent image is used. Generally, even in an analog image, if the density of the magnetic brush is rough, the roughness will occur.
When a dot latent image is formed, the image is more significantly deteriorated due to missing dots or the like. Since a pulse-width-modulated digital latent image forms a very high-definition latent image, a technique for densely packing the magnetic brush and improving durability as in this embodiment is essential.

The magnetic carrier is made of ferrite and has a periodic table of IA, IIA, IIIA, IVA, V.
A, IB, IIB, IIIB, IVB, VIB, VIIB, VIIIB
It contains at least one element selected from the group. For example, Ni-Zn based, Li based, Li-Zn
System, Mn-Cu system ferrite can be used. σ
The magnitude of d can be adjusted, for example, by appropriately adjusting the composition. Of course, the material of the carrier is not limited to the above.

The present invention can also be applied to the one that expresses gradation by the dither method.

Next, another embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. The present embodiment is a printer in which four process units are juxtaposed along a horizontally extending transfer belt 9. The paper fed from the cassette CS is registered by the paper feed roller 6 and fed onto the transfer belt 9. The transfer belt 9 conveys the paper to the first station. In the first station, the photosensitive drum 3M is uniformly charged by the primary charger 4M, and then the LED (M
L) forms a latent image. Then, the latent image is developed by the magenta developing device 1M. In the transfer section, a transfer brush 10M is provided on the opposite side of the transfer belt 9 to the photosensitive drum 3M, and a transfer voltage is applied, so that the toner on the photosensitive drum 3M is transferred onto the conveyed paper.

Thereafter, in the same manner, images are formed on cyan, yellow, and black, and the images are multiple-transferred onto paper, and the fixing device 17 is used.
Is established by. On the other hand, the transfer residual toner remaining on the photosensitive drum without being transferred is not a cleaner member in this embodiment, and so-called cleanerless is adopted in which it is collected by the developing device.

As the developing device, the developing device shown in FIG. 1 of the above-mentioned embodiment is used. The carrier of the developer is 70 emu / cm ³ in a magnetic field of 1000 G. In this embodiment, the process speed is 4 cm / sec and the length of the developing sleeve in the longitudinal direction is 21 cm. The amount of developer is 1
20 g is used, which satisfies the requirements of the present invention.
As the toner, a toner produced by a polymerization method is used, and since the toner produced by the polymerization method is spherical, the releasability from the photosensitive drum is good and the transfer efficiency is improved. Therefore, the cleanerless structure of this embodiment is realized.

Also according to this embodiment, it is possible to realize a small-sized printer capable of maintaining high image quality.

[0070]

As is apparent from the above description, in the image forming apparatus according to the present invention, the amount of the developer is Z (g), the process speed is P (cm / sec), and the longitudinal direction of the developer carrier is When the length is L (cm), Z ≦ 2PL and the magnetization intensity is 100e in a magnetic field of 1000G.
By using a magnetic carrier of mu / cm ³ or less,
It is small and can maintain high image quality.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a developing device of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram showing a laser color printer which is an example of an image forming apparatus according to the present invention.

FIG. 3 is an explanatory diagram of a laser beam scanner that can be used in the present invention.

FIG. 4 is an explanatory diagram of a PWM circuit.

FIG. 5 is an explanatory diagram of a signal waveform of the PWM method.

FIG. 6 is an explanatory diagram showing a laser color printer which is another embodiment of the image forming apparatus according to the present invention.

[Explanation of symbols]

 3 Photosensitive Drum (Image Bearing Body) 23 Stirring / Conveying Member 25 Developing Sleeve (Developer Bearing Body) 26 Developing Section 29 Magnet S1 Developing Magnetic Pole

Claims (6)

[Claims] 1. A developing magnetic field in which a developer having toner and a magnetic carrier is conveyed to a developing section by a developer carrier, and a developing magnetic pole of a magnet arranged inside the developer carrier forms in the developing section. In an image forming apparatus equipped with a developing device for bringing a magnetic brush of developer into contact with the image carrier to develop the electrostatic latent image formed on the image carrier, the amount of developer is Z (g), Process speed is P (cm /
sec), the length in the longitudinal direction of the developer carrying member is L (c
m), the relationship of Z ≦ 2PL is satisfied, and 10
The strength of magnetization is 100 emu / cm ³ in a magnetic field of 00G.
An image forming apparatus using the following magnetic carrier. 2. The image forming apparatus according to claim 1, wherein only one agitating / conveying member is used in the developing device. 3. The image forming apparatus according to claim 1, wherein the amount of the developer is 150 g or less. 4. The image forming apparatus according to claim 1, wherein the electrostatic latent image formed on the image carrier is a dot distribution electrostatic latent image. 5. The image bearing member is an electrophotographic photosensitive member,
4. The dot distribution electrostatic latent image is formed by exposing the electrophotographic photosensitive member with a light flux modulated by a pulse width modulated signal corresponding to the density of a recorded image. One of the image forming devices. 6. The image forming apparatus according to claim 1, wherein a vibration bias voltage is applied to the developer carrying member.