JP3524398B2 - Image forming device - Google Patents

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 facsimile and a printer and a developing apparatus used for the same, and more specifically, to a developing apparatus using a two-component developer composed of toner and magnetic carrier. And an image forming apparatus using the developing device.

[0002]

2. Description of the Related Art An image forming apparatus using a two-component developing device is excellent in high-speed compatibility and is suitable for copying machines, facsimiles,
It has been put to practical use as many products such as printers. In a two-component developing device, a two-component developer composed of toner and a magnetic carrier is carried on the surface of a developer carrier composed of a non-magnetic developing sleeve having a magnet arranged therein, and the developer carried by a developer regulating member is After the amount is regulated, the sheet is conveyed to a developing area facing the image carrier on which the electrostatic latent image is formed.
In the developing area, a bias is applied to the developing sleeve to form an electric field between the image carrier and the developing sleeve, and the electric field selectively causes the toner on the developing sleeve to contact or non-contact with the image carrier. It is attached and developed.

Further, in recent years, a bias applied to a developing sleeve is a bias having a waveform which changes periodically (hereinafter, referred to as
By using AC bias), a large number of developing devices have been proposed and put into practical use, in which a periodic electric field is formed between the developing sleeve and the image carrier to achieve improvement in developing ability and image quality. . According to the experiments by the inventor, it was confirmed that the developing ability and the image quality are further improved by increasing the peak-to-peak voltage of the AC bias. Further, recently, it has been confirmed that the developing ability and the image quality can be further improved by making the waveform of the AC bias into an asymmetrical rectangular wave as shown in FIG.

However, when the AC bias is applied, the developing ability and the image quality can be improved, but on the other hand, the phenomenon in which toner adheres to the non-image portion (background portion) of the image bearing member (called fog or background stain). ) Is likely to occur. This is because in a developing device using two-component development, the toner and the carrier are frictionally charged by stirring the developer by a stirring means. It has already been confirmed that the cause is. As a specific example, when the charge amount distribution of the toner is measured by a charge amount measuring device (for example, a trade name E-spart analyzer), a developer that does not have much distribution near the charge amount 0 as shown in A of FIG. Compared with the above, the developer with a relatively large distribution around 0 as shown by B in FIG.

This is interpreted as follows. Since the weakly charged toner has a small electrostatic adhesion to the carrier, it tends to float in the developer. Further, since the weakly charged toner is less restricted by the electrostatic latent image and the developing bias, it is considered that the weakly charged toner adheres to the non-image portion more frequently. The fogging due to the weakly charged toner is likely to occur when an AC bias is applied to the developing sleeve, and more significantly occurs when the peak-to-peak voltage of the AC bias is increased. It is presumed that this is because the AC bias instantaneously forms a strong electric field, so that the floating toner is more likely to be generated.

In order to solve such a problem, Japanese Unexamined Patent Publication No. 8-44177 discloses that "a housing having a developing opening and a toner replenishing opening is provided, and the developing opening and the toner replenishing opening in the housing are provided. A developer circulating and conveying path is provided between the developer circulating means and the developing means, and a developer carrying member to which at least a DC developing bias is applied is disposed facing the developing opening of the housing, and the developer stirring means is provided in the developer circulating and conveying path. In a developing device so that the latent image on the latent image carrier is developed with a two-component developer composed of toner and carrier carried by the developer carrier. Auxiliary electrodes arranged opposite to each other are provided, and an AC bias is applied to one of the developer carrying member and the auxiliary electrode, and the same DC bias applied to the developer carrying member is applied to the auxiliary electrode. Or, the toner toward the auxiliary electrode side has proposed a developing device "which is characterized in that so as to apply a DC bias to be electrostatic attraction. In this developing device, due to the action of the oscillating electric field formed between the developer carrier and the auxiliary electrode, the developer passing between the developer carrier and the auxiliary electrode is electrically vibrated so that the existing developer The toner and the carrier are forcibly separated once, and the replenished new toner is agitated and mixed, so that the replenished toner is frictionally charged with the carrier and controlled to a predetermined charge amount. However, since the developer is filled between the developer carrier of the developing device and the auxiliary electrode, the movement of separating the toner and the carrier due to electric vibration and the development of the new toner Cannot be sufficiently mixed with stirring. For this reason, it is not sufficient to make all the weakly charged toner have an appropriate charge amount by the electric vibration. Further, since the auxiliary electrode and the bias power source are separately provided, the structure of the device is complicated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an image having a simple structure, a high developing ability and a stable toner charge amount and no fog. To provide a developing device and an image forming apparatus for forming a sheet.

In Japanese Patent Laid-Open No. 6-266234, toner is ejected from a two-component developer layer carried on a developing sleeve having a small diameter of 5 to 15 mm under an oscillating electric field to electrostatically charge the image carrier. In a developing device that attaches to a latent image,
The position of the magnetic pole of the magnet contained in the developer carrying member with respect to the developing region and the magnitude of the magnetic field are regulated, and a leveling regulating member for regulating the layer thickness of the developer is provided downstream of the magnetic pole on the upstream side of the developing region. A developing device is proposed in which a DC bias is applied to the tip of the leveling regulating member. In this publication, the developer on the developing sleeve is laid down on the developing sleeve by the leveling regulating member, and an alternating electric field is applied between the electrode at the tip of the leveling regulating member and the developing sleeve. Although it is said that the toner cloud is easily generated and the developing ability is improved, there is no mention of making the toner charge amount appropriate. On the contrary, by generating a toner cloud, scattering of weakly charged toner easily occurs,
There arises a problem that toner often adheres irregularly to the image as noise.

[0009]

In order to achieve the above object, the invention of claim 1 is an image carrier on which a two-component developer comprising a toner and a magnetic carrier is carried and an electrostatic latent image is formed. A developer carrying member that conveys to the opposing developing area and a developer regulating member that regulates the amount of the developer carried on the developer carrying body are provided, and a waveform that changes periodically is provided on the developer carrying body. In an image forming apparatus having a developing device for developing an electrostatic latent image formed on an image carrier by applying a vibration bias, the developer regulating member is electrically grounded via a capacitive element. It is characterized by.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the vibration bias is an asymmetric rectangular wave bias.

The invention of claim 3 is the same as claim 1 or 2.
In the image forming apparatus, the switching means for electrically connecting / disconnecting the developer carrying member and the developer regulating member is provided.

According to a fourth aspect of the invention, in the image forming apparatus according to the third aspect, the toner concentration detecting means for detecting the toner concentration in the developing device, and the switching means based on the detection result of the detecting means. A control means for controlling the operation is provided.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the control means compares the output value of the toner density detecting means with a preset first threshold value and second preset threshold value. Based on the result, the switching means controls to switch to the connection side when the output value becomes equal to or lower than the first threshold value, and when the output value becomes equal to or higher than the second threshold value, It is characterized in that the switching means controls to switch to the disconnection side.

According to a sixth aspect of the invention, in the image forming apparatus according to the third aspect, the humidity detecting means for detecting the humidity inside or near the image forming apparatus, and the switching means based on the detection result of the detecting means. And a control means for controlling the operation of, the control means, based on the result of comparing the output value of the humidity detection means with the preset third threshold value and the fourth threshold value, the output value When the output value is equal to or less than the third threshold value, the switching means is controlled to switch to the connection side, and when the output value is equal to or greater than the fourth threshold value, the switching means is controlled to switch to the disconnection side. It is characterized by that.

According to a seventh aspect of the invention, in the image forming apparatus according to the third aspect, the operation of the switching means is controlled based on the time measuring means for measuring the stop time of the developing device and the output result of the time measuring means. A control means for controlling is provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] An embodiment in which the present invention is applied to an electrophotographic laser printer (hereinafter referred to as a printer) which is an image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of a printer according to this embodiment. Drum-shaped organic photoconductor as an image carrier (OP
C) A charging roller 2 as a charging device, an exposure device (not shown) that irradiates the laser light 31 around the developing device 1, and a developing device that supplies toner to form an electrostatic latent image on the photoconductor 1 into a toner image. 4, a transfer roller 51 as a transfer device that transfers the toner image on the surface of the photoconductor 1 onto the transfer paper P,
A cleaning device 7 that removes residual toner from the surface of the photoconductor 1 is provided. Further, a fixing device 8 for fixing the toner image transferred on the transfer paper P is provided.

The developing device 4 includes a developing sleeve 41 as a developer carrying member for carrying a two-component developer composed of toner and a magnetic carrier, and a developer regulating member for regulating the amount of the developer on the developing sleeve 41. Doctor blade 43
And a developer pool 40 for storing the developer, and two screw-shaped stirring members 42 for moving the developer in the developer pool 40 in the opposite directions while stirring.

The developing sleeve 41 is a cylindrical member composed of a non-magnetic conductive member, and is provided with a plurality of fixed magnets inside and rotates in the direction of the arrow (counterclockwise) in the figure. Further, the developing sleeve 41 is provided with a developing bias power source 45.
The developing bias is applied from. This developing bias will be described in detail later. The doctor blade 43 is made of a rigid conductive material such as metal and has a gap of 0.2 to 1.0 mm from the developing sleeve 41.
In addition, the tolerance is set to an accuracy of 0.1 mm or less. This doctor blade will also be described in detail later.

Next, the image forming operation of the copying machine will be described. In FIG. 1, the photoconductor 1 is uniformly charged by the charge from the charging roller 2 while rotating in the direction of the arrow in the figure, and then is irradiated with the laser beam 31 from the exposure device to form an electrostatic latent image. This electrostatic latent image is developed by the developing device 4 to form a toner image as a visible image. The toner image developed by the developing device 4 is transferred onto the transfer paper P conveyed to the surface of the photoconductor 1 by a paper feeding device (not shown) and transferred onto the transfer roller 51.
Transcribed by Transfer paper P on which the toner image is transferred
Is separated from the photoconductor 1, subjected to a fixing process by the fixing device 8, and then discharged to the outside of the machine. On the other hand, the photoconductor 1 after transfer
The untransferred toner is collected and removed by the cleaning device 7. Here, the surface potential of the photoconductor 1 after exposure is about −100 v in the light irradiation part and −800 v in the non-exposure part, and development (reverse development) is performed so that toner adheres to the light irradiation part. .

On the surface of the developing sleeve 41, a developer is carried in a brush shape (hereinafter referred to as a magnetic brush) by a magnetic field formed by an internal fixed magnet, and the amount of this magnetic brush is regulated by a doctor blade 43 on the way. After that, the developing sleeve 41 is rotated in the direction of the arrow in the drawing to be conveyed to the developing area facing the photoconductor 1. Then, the developing bias applied to the developing sleeve 41 forms an electrostatic field between the developing sleeve 41 and the photoconductor 1, and the electrostatic field causes the toner to move to a latent image on the photoconductor 1 to form a toner image. It is formed. Here, inside the developing sleeve 41, the developing sleeve 41 is provided in at least a part of the opposing region.
Is provided with a magnetic pole for forming a magnetic field such that the magnetic flux density in the vertical direction is higher than the magnetic flux density in the horizontal direction. As a result, carrier adhesion to the photoconductor 1 and carrier scattering can be prevented, and the development efficiency can be ensured.

Next, the toner image formed on the photoconductor 1 is conveyed to the transfer nip portion, which is a portion facing the transfer roller 51, as the photoconductor 1 rotates. Then, the transfer material P sent by the pair of registration rollers 9 is supplied to the transfer nip portion in synchronization with the rotation of the photoconductor 1. And
A transfer bias is applied to the transfer roller 4 by a power source (not shown), and the toner image on the photoconductor 1 is transferred to the transfer material. The transferred image is then fixed by the fixing device 8 and discharged to the outside of the image forming apparatus. Further, the photoconductor 1 after the transfer is cleaned by the cleaning device 7.

In this embodiment, as a developer, a carrier having ferrite particles having a maximum magnetization of 60 emu / g as a core material, the surface of which is coated with a silicone resin, and a thermoplastic resin colored with carbon black are used. A mixture of a toner containing as a main component was used. The carrier is usually a magnetic core material such as iron powder, ferrite, or magnetite coated with a resin, or a dispersion of magnetite fine powder in a resin (binder). The resistance of the carrier is controlled to an appropriate value by the or binder, and the durability of the carrier is improved.

Next, a developing bar applied to the developing sleeve 41.
I will explain about Ias. 2 is used in the developing device 4.
The waveform of the developing bias is shown. In this developing device,
An electric charge for moving the toner from the developing sleeve 41 to the photosensitive member 1.
And toner from the photoconductor 1 to the developing sleeve 41
An asymmetrical rectangle in which the potential part to be caused is alternately repeated
The developing sleeve 41 is marked with the wave bias as the developing bias.
Add The horizontal axis is time, and the vertical axis is toner toward the photoconductor 1.
It is a voltage value with the direction of receiving force taken upward. Toner
Receives the maximum force from the developing sleeve 41 toward the photoconductor 1
The voltage when₁, Toner from photoconductor 1
The voltage value at the time of receiving the maximum force toward the valve 41 is V₀When
And then V₁Is the time t lasts₁, V₂The time that
t ₂, And the cycle is T. In the figure, Va is the developing bias
Inter-average value (integrated average), Va = V₀+ (V₁−
V₀) T₁/ T₂It is represented by. Here, a normal DC bypass
Like asus, it is set to about -300 to -900v. Na
Oh, t₁/ T × 100 (%) is called a duty ratio.

As described above, in the present embodiment, by applying the asymmetrical rectangular wave bias as the developing bias to the developing sleeve 41, the movement of the developer becomes active in the developing area to improve the developing ability, and The detailed portion of the latent image on 1 can be reproduced, and a high quality image can be obtained. In addition, experiments by the present inventors have revealed that the smaller the duty ratio of the asymmetrical rectangular wave bias, the better the effect of improving the image quality, and the larger the duty ratio, the easier the carrier adhesion to the photoconductor 1 occurs. . This is because the smaller the duty ratio is, the less the reversal of the electric potential between the photoconductor 1 and the developing sleeve 41 is. Therefore, it is desirable to set the duty ratio small, but in practice, the bias power supply 4
Since there is a constraint of waveform formation in No. 5, it may be set in consideration of it.

By the way, as described above, the developing sleeve 41
When an asymmetrical rectangular wave bias is applied to the developing device, an oscillating electric field generated between the developing sleeve 41 and the photoconductor 1 is also generated between the developing sleeve 41 and the doctor blade 43 made of a conductive material due to the configuration of the developing device. It will occur similarly. When an oscillating electric field is generated between the developing sleeve 41 and the doctor blade 43, the toner and the carrier, which tend to be charged with different polarities, move differently. As a result, the toner and the carrier are repeatedly separated and collided with each other, and many parts of the toner surface are charged, so that the average toner charge amount can be increased. In this way, the oscillating electric field between the developing sleeve 41 and the doctor blade 43 has a stirring function of stirring the toner and the carrier.

However, according to the research conducted by the present inventors, it has been clarified that the image quality is greatly affected by the potential of the doctor blade 43 even in the above configuration.

Normally, the potential of the doctor blade 43 is
It is set to one of the following. (1) The potential is set to 0 (ground). (2) The potential is the same as that of the developing sleeve 41. (3) Float state (electrically insulated state). In the case of direct grounding in (1) above, the developing sleeve 41
A strong potential difference is generated between the doctor blade 43 and the doctor blade 43, and discharge may occur between the two in particular when the gap between them is narrow, for example, 0.5 mm or less. When the electric discharge occurs, the toner may come off or scatter, and the quality of the output image may be significantly deteriorated. Further, when the developing sleeve 41 and the doctor blade 43 have the same potential as in the above (2), the stirring function due to the electric field near the gap between them is lost, and the developer is mechanically stirred only by the stirring member. Therefore, when the toner density is particularly high, the charge tends to be insufficient, and toner scattering and fogging on the image background portion are likely to occur. further,
As shown in (3), when the doctor blade 43 is in a floating state, the potential of the doctor blade 43 becomes unstable, and the movement of the toner is affected by the spread of the charge amount distribution, causing fog. In addition, the toner density on the developing sleeve 41 becomes non-uniform, resulting in uneven image density.

Therefore, in the present embodiment, the potential of the doctor blade 43 is controlled to a potential that does not cause a problem such as discharge with the developing sleeve 41 and has a sufficient stirring function for the developer. Adopted a configuration that can.

As shown in FIG. 3, the doctor blade 43 was electrically grounded via the capacitor C1. An equivalent circuit of the developing device in this state is shown in FIG. Here, if the gap between the doctor blade 43 and the developing sleeve 41 is regarded as one capacitor Cd, the potential of the doctor blade 43 becomes Cd / (C1 + Cd) times the potential of the developing sleeve 41 due to the presence of the capacitor C1. Become.
Therefore, the potential of the doctor blade 43 can be optimally controlled by controlling the value of the capacitance C1.

When a developing bias is applied to the developing sleeve 41 in a state where the potential of the doctor blade 43 is optimally set by the above-mentioned structure, the developing sleeve 41 and the doctor blade 43 do not cause any trouble such as discharge. An oscillating electric field is formed between and. As a result, the occurrence of an abnormal image due to discharge or the like is prevented, and the oscillating electric field sufficiently exhibits the stirring function of the toner and the carrier, so that the average toner charge amount can be increased. Therefore, it is possible to obtain a fog-free image having a high developing ability and a stable toner charge amount.

Further, according to this embodiment, the developing sleeve 41 and the doctor blade 43 constituting the developing device are used, and the oscillating electric field is generated by applying the developing bias at the time of development. Therefore, the auxiliary electrode is separately provided. Moreover, there is an advantage that the configuration is extremely simple as compared with the configuration in which the power source is provided.

[Second Embodiment] FIG. 5 shows a developing sleeve 41.
2 shows an embodiment in which a switch is provided as a switching means for electrically connecting / disconnecting the doctor blade 43. FIG. 6 shows an equivalent circuit of the configuration of this embodiment.
As shown in FIGS. 5 and 6, the developing sleeve 41 and the doctor blade 43 are electrically connected via a switch and a resistor. When the switch is opened in this state, the configuration is similar to that of the first embodiment, and the same operation / effect can be obtained. On the other hand, when the switch is closed, the developing sleeve 41 and the doctor blade 43 have substantially the same potential, so that the stirring function by the oscillating electric field becomes small.

Therefore, by utilizing this, when the toner charge amount is large, the switch is closed so that the charge amount does not rise, and when the toner charge amount is small, the switch is opened to cause the stirring effect by the oscillating electric field. To generate. Thereby, the charge amount of the toner can be controlled. In this case, the resistance is not always necessary.

[Embodiment 3] Next, an embodiment in which the developing device 4 is provided with a toner concentration (toner mass ratio to the developer) detecting means and the potential of the doctor blade 43 is controlled according to the detection result will be described. Show. In FIG. 1, a toner concentration sensor 11 as a toner concentration detecting means is installed in the developer reservoir 40 of the developing device 4. Here, the one calculated from the change of the magnetic permeability in the developer is used, but the other known ones as the toner concentration detecting means,
For example, any type such as a type obtained from the light transmittance of the developer or the reflectance of the toner image developed on the photoconductor 1 may be used.

Here, the charging of the toner in the developing device is as follows.
The contact charging with the carrier is mainly caused by the stirring of the stirring member 43. Therefore, there is a close relationship between the toner concentration and the toner charge amount. In the graph of FIG. 7, the toner charge amount and the total toner amount when the toner and the carrier are combined in various particle sizes (toner particle size: 6, 7.5, 9 μm, carrier particle size: 40, 50, 60 μm) The relationship between the surface area divided by the total surface area of the carrier is shown. In the graph, the vertical axis represents the toner charge amount (absolute value) per unit mass, and the horizontal axis represents the value obtained by dividing the total toner surface area by the total carrier surface area. Thus, it can be seen that the relationship is almost inversely proportional.

As can be seen from the graph, when the ratio of the total surface area of the toner to the total surface area of the carrier is small, that is, when the toner concentration is low, the probability that the toner comes into contact with the carrier increases, and the charge amount of the toner increases. I understand. If the toner charge in the developing device is too large,
At the time of development, it becomes difficult for the toner to separate from the carrier, the developing ability decreases, and the image density becomes insufficient. Therefore, in this case, it is not necessary to give an excessive stirring action to the developer. On the other hand, from the graph, it can be seen that when the ratio of the total surface area of the toner to the total surface area of the carrier is large, that is, when the toner concentration is high, the charge amount of the toner becomes small. If the toner charge amount in the developing device is too small, the toner easily separates from the carrier during development, causing fog or scattering on the image background portion. Therefore, in this case, it is effective to increase the charge amount of the toner by giving a greater stirring action to the developer.

From the above, in the present embodiment,
The toner concentration sensor 11 detects the toner concentration,
The potential of the doctor blade 43 is changed based on the detection result. Specifically, the configuration shown in the second embodiment is adopted, and the opening / closing of the switch is controlled based on the detection result of the toner density.

FIG. 8 is a block diagram of a control system for controlling the operation of the above configuration. The control device as a control means is composed of a control unit 14 and a switch operating unit 15.
The output from the toner concentration sensor 11 is read by the control unit 14, and after performing necessary arithmetic processing and judgment, the result is output to the switch operating unit 15. Switch operating part 1
A small solenoid or the like is used for 5, and the switch is opened and closed by it.

FIG. 9 is a flowchart summarizing the operation of the control unit 14. When the toner concentration value is input, it is converted into a ratio S of the total toner surface area to the total carrier surface area according to necessary information such as the toner particle diameter and the carrier particle diameter. Next, the value S is compared with the first threshold value S1, and if S is S1 or less, the switch is closed and the doctor blade 43 and the developing sleeve 41 are made to have the same potential. When S is larger than S1, S is compared with the second threshold value S2, and when S is S2 or more, the switch is opened to establish the potential difference between the doctor blade 43 and the developing sleeve 41. If neither condition is met, the switch state does not change. It is desirable that the two threshold values S1 and S2 have the same value or S1 <S2.

As described above, the ratio of the total surface area of the toner and the carrier is estimated from the output result of the toner concentration sensor 11, and the switch is opened / closed accordingly to control the potential of the doctor blade 43, thereby developing the developing sleeve 41.
The stirring action of the developer generated between the doctor blade 43 and the doctor blade 43 can be controlled. Therefore, even when a large amount of toner is contained, it is possible to always maintain the toner charge amount at a certain level or more, and minimize toner scattering and toner adhesion (fog) to the background portion.

[Embodiment 4] Next, an embodiment will be described in which humidity detecting means is provided inside the printer and the potential of the doctor blade 43 is controlled according to the detection result. In general,
When the humidity is high, the charge amount of the toner tends to decrease, and when the humidity is low, the charge amount of the toner tends to increase. Therefore, in the present embodiment, in order to correct this, as shown in FIG. 1, a humidity sensor 12 as a humidity detecting means is installed at a predetermined location inside the printer.

The humidity sensor 12 detects the humidity inside the image forming apparatus. When the humidity is high, the switch is opened to cause a stirring action by the electric field between the developing sleeve 41 and the doctor blade 43, and when the humidity is low, the switch is activated. Is closed to keep the developing sleeve 41 and the doctor blade 43 at substantially the same potential so as not to cause an electric stirring action.

FIG. 10 is a block diagram of a control unit for controlling the above operation. The control device as a control means is composed of a control unit 14 and a switch operating unit 15. The output from the humidity sensor 12 is read by the control unit 14,
After performing necessary arithmetic processing and judgment, the result is output to the switch operating unit 15. The switch operating unit 15 has the same function as that of the third embodiment.

FIG. 11 is a flow chart for explaining the operation of the control unit 14. When the humidity value H is input, it is compared with the first threshold value H1, and if H is H1 or less, the switch is closed and the doctor blade 43 and the developing sleeve 41 are made to have the same potential. When H is larger than H1, H is compared with the second threshold value H2, and when H is H2 or more, the switch is opened to establish the potential difference between the doctor blade 43 and the developing sleeve 41. If neither condition is met, the switch state does not change. It is desirable that the two thresholds H1 and H2 have the same value or H1 <H2.

As described above, according to this embodiment, even when the toner charge amount is predicted to be low in a high humidity environment, the toner charge amount can be increased by the oscillating electric field. Prevents fogging and scattering.

[Embodiment 5] Next, an embodiment will be described in which a timer means for timing the stop time of the developing device 4 is provided inside the printer and the potential of the doctor blade 43 is controlled according to the stop time. Generally, when the developing device is stopped for a long time, the amount of charge of the toner in the developer tends to decrease. This is remarkable when the resistance of the toner or carrier is low. Therefore, in the present embodiment, in order to correct this, as shown in FIG. 1, a timer 13 as a time measuring means is installed at a predetermined position inside the printer.

When the time measured by the timer 13 exceeds a preset threshold value, the switch is opened to cause the stirring action by the electric field between the developing sleeve 41 and the doctor blade 43, and when the time is less than the threshold value, the switch is activated. Is closed to keep the developing sleeve 41 and the doctor blade 43 at substantially the same potential so as not to cause an electric stirring action.
The timer 13 is reset when the developing sleeve 41 or the doctor blade 43 operates, and restarts the time counting when they stop.

FIG. 12 is a block diagram of a control unit for controlling the above operation. The control device as a control means is composed of a control unit 14 and a switch operating unit 15. The output from the timer 13 is read by the control unit 14, and after performing necessary arithmetic processing and judgment, the result is output to the switch operating unit 15. The switch actuating unit 15 has the same function as that in the third or fourth embodiment.

FIG. 13 is a flow chart for explaining the operation of the control unit 14. When the output value W of the timer 13 is input, it is compared with a threshold value W1 and if W is less than W1, the switch is closed, and the doctor blade 43 and the developing sleeve 4
1 is brought to the same potential. If W is W1 or more, the switch is opened to establish the potential difference between the doctor blade 43 and the developing sleeve 41.

With the above configuration, even when it is predicted that the developing device is stopped for a long time and the toner charge amount is low,
Since the toner charge amount can be increased by the oscillating electric field, fogging and scattering to the image background portion can be prevented.

[0050]

According to the present invention, when a vibration bias is applied to the developer carrying member, an oscillating electric field due to the bias is also formed between the developer carrying member and the developer regulating member. Therefore, the toner and the carrier can be agitated between the developer carrying member and the developer regulating member. Therefore, since the average toner charge amount can be increased by contact with the carrier, it is possible to obtain a fog-free image with a high developing ability and a stable toner charge amount. Further, since the developer carrying member is grounded via the capacitive element, by properly selecting the capacitance of the element,
The potential difference between the developer carrying member and the developer regulating member can be adjusted. As a result, the discharge that is likely to occur when the potential difference is large is prevented, so that the quality of the output image can be prevented from being deteriorated by the discharge.

Further, since the oscillating electric field is generated by applying the developing bias at the time of developing by using the developer carrying member and the developer regulating member constituting the developing device, it is necessary to separately provide the auxiliary electrode and the power source. It has an excellent effect that it is an extremely simple structure as compared with the simple structure.

In particular, according to the invention of claim 2, the developing ability and the image cortex can be further improved.

In particular, according to the third aspect of the invention, since the potential of the developer regulating means is switched by the switching means, it is possible to control the generation of an oscillating electric field between the developer carrier and the developer regulating means. That is, when the toner charge amount is large, the developer carrying member and the developer regulating member are connected by the switching means so that the potential of the developer regulating means becomes the same potential as the potential of the developer carrying body. As a result, an oscillating electric field is not generated between the two, so that the stirring action of the developer can be reduced and the toner charge amount can be controlled so as not to increase. On the other hand, when the toner charge amount is small, the developer carrying member and the developer regulating member are cut by the switching means. As a result, a stirring action of the developer is generated by the oscillating electric field, so that the toner charge amount can be increased. Thus, there is an excellent effect that the generation of the oscillating electric field can be controlled according to the toner charge amount.

Particularly, according to the invention of claim 4 or 5, it is excellent in that the generation of the oscillating electric field can be automatically controlled according to the toner charge amount estimated from the detection result of the toner concentration detecting means. effective.

Particularly, according to the image forming apparatus of claim 6,
There is an excellent effect that the generation of the oscillating electric field can be automatically controlled according to the toner charge amount that changes depending on the humidity.

Particularly, according to the image forming apparatus of claim 7,
There is an excellent effect that the generation of the oscillating electric field can be automatically controlled according to the toner charge amount that changes depending on the stop time of the developing device.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of a waveform of an AC bias applied to a developing sleeve of the developing device of the image forming apparatus.

FIG. 3 is a schematic configuration diagram of the developing device.

FIG. 4 is an equivalent circuit diagram of the developing device.

FIG. 5 is a schematic configuration diagram of a developing device according to a second embodiment.

FIG. 6 is an equivalent circuit diagram of the developing device.

FIG. 7 is a graph showing the relationship between the toner charge amount and the total toner surface area divided by the carrier total surface area.

FIG. 8 is a system block diagram of a developing device according to a third embodiment.

FIG. 9 is a flowchart relating to system control of the developing device.

FIG. 10 is a system block diagram of a developing device according to a fourth embodiment.

FIG. 11 is a flowchart relating to system control of the developing device.

FIG. 12 is a system block diagram of a developing device according to a fifth embodiment.

FIG. 13 is a flowchart relating to system control of the developing device.

FIG. 14 is an explanatory diagram of a charge amount distribution of toner of a developer.

[Explanation of symbols]

1 photoconductor 2 charging roller 4 Developing device 7 Cleaning device 8 fixing device 9 Registration roller pair 11 Toner density sensor 12 Humidity sensor 13 timer 14 Control unit 15 Switch operating part 40 developer pool 41 Development sleeve 42 Stirrer 43 doctor blade 45 Development bias power supply 51 transfer roller

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-54962 (JP, A) JP-A-11-143211 (JP, A) JP-A-8-190277 (JP, A) JP-A-8- 123193 (JP, A) JP-A-8-30093 (JP, A) JP-A-7-175318 (JP, A) JP-A-7-168426 (JP, A) JP-A-6-242673 (JP, A) JP-A-6-222656 (JP, A) JP-A-6-95481 (JP, A) JP-A-6-27807 (JP, A) JP-A-3-114089 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 13/06-13/095 G03G 15/06-15/095

Claims (7)

(57) [Claims] 1. A developer carrying member carrying a two-component developer composed of toner and a magnetic carrier and carrying it to a developing area facing an image carrying member on which an electrostatic latent image is formed, and the developer carrying member. A developer regulating member that regulates the amount of the carried developer, and a vibration bias having a waveform that changes periodically is applied to the developer carrying member to form an electrostatic latent image formed on the image carrying body. An image forming apparatus having a developing device for developing, wherein the developer regulating member is electrically grounded via a capacitive element. 2. The image forming apparatus according to claim 1, wherein the vibration bias is an asymmetrical rectangular wave bias. 3. The image forming apparatus according to claim 1, further comprising switching means for electrically connecting / disconnecting the developer carrying member and the developer regulating member. 4. The image forming apparatus according to claim 3, further comprising: a toner density detecting means for detecting a toner density in the developing device; and a control means for controlling the operation of the switching means based on the detection result of the detecting means. An image forming apparatus comprising: 5. The image forming apparatus according to claim 4, wherein the control unit compares the output value of the toner density detection unit with a preset first threshold value and second preset threshold value, and When the output value becomes equal to or lower than the first threshold value, the switching means controls to switch to the connection side, and when the output value becomes equal to or higher than the second threshold value, the switching means switches to the disconnection side. An image forming apparatus that is controlled as described above. 6. An image forming apparatus according to claim 3, wherein humidity detecting means for detecting humidity inside or near the image forming apparatus, and control means for controlling operation of the switching means based on a detection result of the detecting means. And the control means, based on the result of comparing the output value of the humidity detection means with a preset third threshold value and a fourth threshold value, the output value is less than or equal to the third threshold value. When the output value is equal to or greater than the fourth threshold value, the switching unit controls the switching unit to switch to the connection side, and the switching unit controls to switch to the disconnection side. apparatus. 7. The image forming apparatus according to claim 3, further comprising a time measuring means for measuring a stop time of the developing device, and a control means controlling an operation of the switching means based on an output result of the time measuring means. An image forming apparatus characterized by the above.