JP2000098709A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple-constitution developing device and a simple- constitution image forming device by which an image without fogging whose developing ability is high and in which the electrification amount of toner is stable is formed. SOLUTION: This image forming device is provided with the developing device 4 having a developing sleeve 41 being as the developer carrier and a doctor blade 43 regulating the quantity of developer carried by the sleeve 41 and developing a latent image formed on a photoreceptor 1 by applying vibration bias to the sleeve 41. Then, the blade 43 is electrically grounded through a capacity element. Thus, since a vibration electric field is formed between the sleeve 42 and the blade 43 when the vibration bias is applied, the toner and carrier are stirred between them and the electrification amount of the toner can be increased because the toner is brought into contact with the carrier. Therefore, the image without fogging whose developing ability is high and in which the electrification amount of the toner is stable is obtained.

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, a printer, and the like, and a developing apparatus used for the same. More specifically, the present invention relates to a developing apparatus using a two-component developer composed of a toner and a 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 apparatus is excellent in high-speed responsiveness, and can be used in a copier, a facsimile,
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 a toner and a magnetic carrier is carried on the surface of a developer carrier composed of a non-magnetic developing sleeve in which a magnet is disposed, and the developer carried by a developer regulating member is After regulating the amount, the sheet is transported 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 causes the toner on the developing sleeve to selectively contact or non-contact on the image carrier. It is developed by attaching it.

In recent years, a bias applied to a developing sleeve has been changed to a bias having a periodically changing waveform (hereinafter referred to as a bias).
(AC bias) to form a periodic electric field between the developing sleeve and the image carrier, and a number of developing devices have been proposed and practically used, which have improved the developing capability and the image quality. . According to experiments performed by the present inventors, it was confirmed that the developing capability and image quality were further improved by increasing the AC bias peak-to-peak voltage. Recently, it has been confirmed that the developing ability and the image quality can be further improved by changing the waveform of the AC bias into an asymmetric rectangular wave as shown in FIG.

However, when an AC bias is applied, the developing ability and the image quality can be improved, but the phenomenon that toner adheres to a non-image portion (background portion) of an image carrier (referred to as fogging or background smear). ) Is more likely to occur. This is because, in a developing device using two-component development, the toner and the carrier are frictionally charged by agitating the developer by a stirring means. However, a toner having a low charge amount (hereinafter, a weakly charged toner) is generated. Has been confirmed to be the cause. As a specific example, when the charge amount distribution of the toner is measured by a charge amount measuring device (for example, E-spart analyzer), as shown in FIG. Compared with the developer, the fogging occurred more frequently in the developer having a relatively large distribution near 0 as shown in FIG.

[0005] This is interpreted as follows. Since the weakly charged toner has a small electrostatic adhesion to the carrier, it easily floats in the developer. Further, since the weakly charged toner is less constrained by the electrostatic latent image and the developing bias, the ratio of the weakly charged toner to the non-image portion is considered to increase. Such fogging due to the weakly charged toner is likely to occur when an AC bias is applied to the developing sleeve, and further remarkably occurs when the peak-to-peak voltage of the AC bias is increased. This is presumed to be because the AC bias instantaneously forms a strong electric field, so that floating toner is more likely to be generated.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 8-44177 discloses that a housing having a developing opening and a toner replenishing port is provided. A developer carrying member to which at least a DC developing bias is applied, facing the developing opening of the housing, and a developer agitating means in the developer circulating carrying path. In a developing device, a latent image on the latent image carrier is developed with a two-component developer composed of a toner and a carrier carried on the developer carrier. Auxiliary electrodes are provided to face each other, and an AC bias is applied to one of the developer carrier and the auxiliary electrode, and the auxiliary electrode is the same as a DC bias applied to the developer carrier, 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, by the action of an oscillating electric field formed between the developer carrier and the auxiliary electrode, an electric vibration is given to the developer passing between the developer carrier and the auxiliary electrode, and the existing developer is removed. The toner and the carrier are forcibly once separated from each other, and the replenished new toner is agitated and mixed. Then, the replenished toner is frictionally charged with the carrier, and is controlled to a predetermined charge amount. However, since the developer is filled between the developer carrier and the auxiliary electrode of the developing device, the movement of separating the toner and the carrier due to the electric vibration, and the movement of the new toner to the developer. Cannot be sufficiently stirred and mixed. For this reason, it is insufficient to make all the weakly charged toners have an appropriate charge amount by electric vibration. Further, since an auxiliary electrode and a bias power supply are separately provided, the configuration of the apparatus is complicated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide a fog-free image having a simple structure, a high developing ability and a stable toner charge amount. To provide a developing device and an image forming apparatus for forming the image.

In Japanese Patent Application Laid-Open No. Hei 6-266234, toner is caused to fly 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 so that an electrostatic charge on an image carrier is reduced. In a developing device for attaching to a latent image,
A leveling member that regulates the position of the magnetic pole with respect to the developing region of the magnet included in the developer carrier and the magnitude of the magnetic field and that controls the layer thickness of the developer downstream of the magnetic pole upstream of the developing region is provided. A developing device has been 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 described that toner cloud is easily generated and the developing ability is improved, there is no mention of making the charge amount of the toner appropriate. On the contrary, by generating the toner cloud, scattering of the weakly charged toner is likely to occur,
There is a problem that toner often adheres irregularly to the image as noise.

[0009]

According to a first aspect of the present invention, there is provided an image carrier having a two-component developer comprising a toner and a magnetic carrier, and having an electrostatic latent image formed thereon. A developer carrying member that conveys the developer to the opposite developing area; and a developer regulating member that regulates the amount of the developer carried by the developer carrying member. An image forming apparatus having a developing device for applying an oscillating bias to develop an electrostatic latent image formed on an image bearing member, wherein the developer regulating member is configured to be electrically grounded via a capacitance element. It is characterized by the following.

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

[0011] The invention of claim 3 is the invention according to claim 1 or 2.
In the above image forming apparatus, a switching means for electrically connecting / disconnecting the developer carrier and the developer regulating member is provided.

According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, a toner density detecting means for detecting a toner density in the developing device, and the switching means based on a detection result of the detecting means. Control means for controlling the operation.

According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the control means compares an output value of the toner density detection means with a first threshold value and a second threshold value set in advance. Based on the result, when the output value is equal to or less than the first threshold, the switching unit controls to switch to the connection side, and when the output value is equal to or more than the second threshold, The switching means controls to switch to the cutting side.

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

According to a seventh aspect of the present invention, in the image forming apparatus of the third aspect, a time measuring means for measuring a stop time of the developing device, and an operation of the switching means based on an output result of the time measuring means. And control means for controlling.

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

The developing device 4 includes a developing sleeve 41 as a developer carrier for carrying a two-component developer composed of toner and 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 reservoir 40 for storing the developer, and two screw-shaped stirring members 42 for moving the developer in the developer reservoir 40 while stirring them in opposite directions.

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

Next, the image forming operation of the copying machine will be described. In FIG. 1, the photosensitive member 1 is uniformly charged by the charge from the charging roller 2 while rotating in the direction of the arrow in the drawing, and then irradiated with laser light 31 from an 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 a transfer sheet P conveyed to the surface of the photoreceptor 1 by a sheet feeding device (not shown).
Is transcribed. Transfer paper P on which toner image has been transferred
Is separated from the photoreceptor 1 and subjected to a fixing process by a fixing device 8 and then discharged out of the apparatus. On the other hand, the photoreceptor 1 after the transfer
The untransferred toner is collected and removed by the cleaning device 7. Here, the surface potential of the photoreceptor 1 after exposure is about −100 V in the light-irradiated part and about −800 V in the non-exposed part, and development (reverse development) is performed such that toner adheres to the light-irradiated 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 the magnetic brush is regulated by a doctor blade 43 on the way. Thereafter, the developing sleeve 41 is conveyed to a developing area facing the photoreceptor 1 by rotation in the direction of the arrow in the figure. Then, an electrostatic field is formed between the developing sleeve 41 and the photoconductor 1 by the developing bias applied to the developing sleeve 41, and the toner moves to the latent image on the photoconductor 1 by the electrostatic field, and the toner image is formed. It is formed. Here, the developing sleeve 41 is provided inside the developing sleeve 41 in at least a part of the facing region.
Are provided with magnetic poles for generating a magnetic field such that the magnetic flux density in the vertical direction is larger than the magnetic flux density in the horizontal direction. Thereby, carrier adhesion and carrier scattering to the photoconductor 1 can be prevented, and development efficiency can be ensured.

Next, the toner image formed on the photosensitive member 1 is conveyed to a transfer nip portion which is a portion facing the transfer roller 51 as the photosensitive member 1 rotates. Then, the transfer material P sent by the registration roller pair 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 supply (not shown), and the toner image on the photoconductor 1 is transferred to a transfer material. The transferred image is then fixed by the fixing device 8 and discharged outside the image forming apparatus. Further, the photoconductor 1 after the transfer is cleaned by the cleaning device 7.

In the present embodiment, as a developer, ferrite particles having a maximum magnetization of 60 emu / g are used as a core material, and a carrier whose surface is coated with a silicone resin and a thermoplastic resin colored with carbon black are used. Used as a main component. As the carrier, a carrier obtained by coating a core material of a magnetic substance such as iron powder, ferrite or magnetite with a resin, or a carrier obtained by dispersing magnetite fine powder or the like in a resin (binder) is usually used. The resistance of the carrier is controlled to an appropriate value by the carrier and the binder, and the durability of the carrier is improved.

Next, the developing bar applied to the developing sleeve 41 is
Iias will be described. In FIG. 2, the developing device 4 is used.
4 shows a waveform of a developing bias. In this developing device,
An electric charge for moving the toner from the developing sleeve 41 to the photoconductor 1
And toner from photoconductor 1 to developing sleeve 41
Asymmetrical rectangle where the potential part to be repeated is alternately repeated
Wave bias is applied to the developing sleeve 41 as the developing bias.
Add. The horizontal axis is time, and the vertical axis is the toner heading toward the photoconductor 1.
This is a voltage value with the direction in which the force is received taken upward. Toner
Receiving the maximum force from the developing sleeve 41 toward the photoconductor 1
When the voltage is V₁, Toner is developed from photoconductor 1
The voltage value when receiving the maximum force toward the₀When
Then V₁T is the time₁, V_TwoThe time that will last
t _Two, And the cycle is T. Va in the figure is at the time of the developing bias.
Average value (integral average), and Va = V₀+ (V₁−
V₀) T₁/ T_TwoIt is represented by Here, the normal DC
It is set to about -300 to -900v as in the case of the mouse. What
Contact, t₁/ T × 100 (%) is called a duty ratio.

As described above, in this embodiment, by applying an asymmetric rectangular wave bias as a developing bias to the developing sleeve 41, the movement of the developer becomes active in the developing area, and the developing ability is improved. The detailed portion of the latent image on top of the first image can also be reproduced, and a high-quality image can be obtained. Further, experiments by the present inventors have revealed that the smaller the duty ratio of the asymmetric rectangular wave bias is, the more the effect of improving the image quality is, and the larger the duty ratio is, the more easily the carrier adheres to the photoconductor 1. . This is because the smaller the duty ratio, the less the reversal of the potentials of the photosensitive member 1 and the developing sleeve 41. For this reason, it is desirable to set the duty ratio small, but practically, the bias power supply 4
Since there is a restriction that the waveform is formed in step 5, the setting may be made in consideration of the restriction.

Incidentally, as described above, the developing sleeve 41
When an asymmetric rectangular wave bias is applied to the developing device, an oscillating electric field generated between the developing sleeve 41 and the photosensitive member 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. The same will occur. 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, separation and collision occur repeatedly between the toner and the carrier, and the toner is charged on many portions of the toner surface, so that the average charge amount of the toner can be increased. Thus, 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 study of 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.

Usually, 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) Make the same potential as the developing sleeve 41. (3) Float (electrically insulated). In the case of the above-mentioned (1), which is directly grounded, the developing sleeve 41
There is a possibility that a strong potential difference is generated between the two and the doctor blade 43, and particularly when the gap between the two is narrow, for example, 0.5 mm or less, electric discharge occurs between the two. When the discharge occurs, the toner is removed or scattered, and the quality of an output image is significantly reduced. Further, when the developing sleeve 41 and the doctor blade 43 are set to the same potential as in the above (2), the stirring function by the electric field near the gap therebetween is lost, and the developer is only mechanically stirred by the stirring member. Therefore, particularly when the toner concentration is high, the toner tends to be insufficiently charged, and toner scattering and fogging on the image background are likely to occur. further,
When the doctor blade 43 is in a floating state as in (3), the potential of the doctor blade 43 becomes unstable, so that the movement of the toner is affected by the influence and the charge amount distribution is widened and fogging occurs. In addition, the toner density on the developing sleeve 41 becomes non-uniform, and image density unevenness occurs.

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 between the doctor blade 43 and the developing blade 41 and that the function of stirring the developer is sufficient. A configuration that can be used was adopted.

As shown in FIG. 3, the doctor blade 43 was electrically grounded via the capacitor C1. FIG. 4 illustrates an equivalent circuit of the developing device in this state. Here, assuming that the gap between the doctor blade 43 and the developing sleeve 41 is 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, by controlling the value of the capacitance C1, the potential of the doctor blade 43 can be optimally controlled.

When a developing bias is applied to the developing sleeve 41 in a state in which the potential of the doctor blade 43 is optimally set by the above-described structure, the developing sleeve 41 and the doctor blade 43 are prevented from being discharged without any trouble. And an oscillating electric field is formed between them. This prevents the occurrence of an abnormal image due to discharge or the like, and the oscillating electric field sufficiently exerts the function of stirring the toner and the carrier, so that the average toner charge amount can be increased. Therefore, it is possible to obtain an image having a high developing ability and a stable toner charge amount without fog.

Further, according to the present embodiment, the oscillating electric field is generated by using the developing sleeve 41 and the doctor blade 43 constituting the developing device and by applying the developing bias at the time of development. There is an advantage that the configuration is extremely simple as compared with a configuration in which a power supply is provided.

[Embodiment 2] FIG.
An embodiment in which a switch is provided as switching means for electrically connecting / disconnecting the doctor blade 43 and the doctor blade 43 is shown. FIG. 6 shows an equivalent circuit of the configuration of the present 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 the same as that of the first embodiment, and the same operation and 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 electric potential, so that the stirring function by the oscillating electric field is reduced.

Therefore, by utilizing this, when the charge amount of the toner is large, the switch is closed so that the charge amount does not increase, and when the charge amount of the toner is small, the switch is opened, and the stirring effect by the oscillating electric field is performed. To be generated. Thereby, the charge amount of the toner can be controlled. In this case, the resistance is not necessarily required.

[Embodiment 3] Next, an embodiment in which a toner concentration (mass ratio of toner to developer) detecting means is provided in the developing device 4 and the potential of the doctor blade 43 is controlled according to the detection result. Show. In FIG. 1, a toner concentration sensor 11 as a toner concentration detecting means is provided in a developer reservoir 40 of the developing device 4. Here, one calculated from the change in the magnetic permeability in the developer was used.
For example, any of those obtained from the light transmittance of the developer and 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
This is mainly contact charging with the carrier caused by stirring of the stirring member 43. Therefore, there is a close relationship between the toner density 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 with various particle diameters (toner particle diameter: 6, 7.5, 9 μm, carrier particle diameter: 40, 50, 60 μm) are shown. The relation with the value obtained by dividing the surface area by the total surface area of the carrier is shown. In the graph, the vertical axis indicates the toner charge per unit mass (absolute value), and the horizontal axis indicates 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, the toner hardly separates from the carrier, so that the developing ability is reduced and the image density becomes insufficient. Therefore, in this case, it is not necessary to give an unnecessary stirring action to the developer. On the other hand, the graph shows 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 is small. If the toner charge amount in the developing device is too small, the toner tends to separate from the carrier during development, causing fogging and scattering on the image background. 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 this embodiment,
The toner density sensor 11 detects the toner density,
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 and closing of the switch is controlled in accordance with 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 control means includes a control unit 14 and a switch operation unit 15.
The output from the toner density 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
5 is a small solenoid or the like, which is used to open and close a switch.

FIG. 9 is a flowchart summarizing the operation of the control unit 14. When the value of the toner density is input, it is converted into the ratio S of the total toner surface area to the total carrier surface area according to necessary information such as toner particle diameter and carrier particle diameter. Next, the value S is compared with a first threshold value S1, and if S is equal to or less than S1, the switch is closed to make the doctor blade 43 and the developing sleeve 41 have the same potential. When S is larger than S1, S is compared with a second threshold value S2, and when S is equal to or larger than S2, a switch is opened to provide a 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 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 based on the output result of the toner density sensor 11, and the switch is opened and closed accordingly to control the potential of the doctor blade 43.
The developer agitating action generated between the developer blade and the doctor blade 43 can be controlled. Therefore, even when a large amount of toner is contained, the charge amount of the toner is always kept at a certain level or more, and it is possible to minimize toner scattering and toner adhesion (fogging) to a background portion.

[Embodiment 4] Next, an embodiment in which a humidity detecting means is provided inside the printer and the potential of the doctor blade 43 is controlled according to the detection result will be described. 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 unit is installed at a predetermined location inside the printer.

The humidity sensor 12 detects the humidity inside the image forming apparatus. If the humidity is high, the switch is opened to generate an agitating action by the electric field between the developing sleeve 41 and the doctor blade 43. Is closed to keep the developing sleeve 41 and the doctor blade 43 at substantially the same potential so that an electric stirring action is not generated.

FIG. 10 is a block diagram of a control unit for controlling the above operation. The control device as control means includes a control unit 14 and a switch operation 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 operation unit 15 has the same function as that of the third embodiment.

FIG. 11 is a flowchart for explaining the operation of the control unit 14. When the humidity value H is input, it is compared with a first threshold value H1. If H is equal to or less than H1, the switch is closed and the doctor blade 43 and the developing sleeve 41 are set to the same potential. When H is greater than H1, H is compared with a second threshold value H2. If H is equal to or greater than H2, a switch is opened to provide a 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 the present embodiment, even when the toner charge is predicted to be low in a high humidity environment, the toner charge can be increased by the oscillating electric field. Fogging and scattering can be prevented.

[Embodiment 5] Next, an embodiment will be described in which a timer is provided inside the printer for measuring the stop time of the developing device 4, and the potential of the doctor blade 43 is controlled according to the stop time. In general, as the stop time of the developing device becomes longer, the charge amount of the toner in the developer tends to decrease. This is remarkable when the resistance of the toner or the 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 generate an agitation action by the electric field between the developing sleeve 41 and the doctor blade 43. Is closed to keep the developing sleeve 41 and the doctor blade 43 at substantially the same potential so that an electric stirring action is not generated.
The timer 13 is reset when the developing sleeve 41 or the doctor blade 43 operates, and starts counting time again when the developing sleeve 41 or the doctor blade 43 stops.

FIG. 12 is a block diagram of a control unit for controlling the above operation. The control device as control means includes a control unit 14 and a switch operation 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 operation unit 15. The switch operating section 15 has a function similar to that of the third or fourth embodiment.

FIG. 13 is a flowchart for explaining the operation of the control unit 14. When the output value W of the timer 13 is inputted, it is compared with the threshold value W1. If W is smaller than W1, the switch is closed, and the doctor blade 43 and the developing sleeve 4 are closed.
1 is set to the same potential. If W is equal to or greater than W1, the switch is opened to provide a potential difference between the doctor blade 43 and the developing sleeve 41.

With the above configuration, even when the stopping time of the developing device is long and the toner charge amount is expected to be low,
Since the toner charge amount can be increased by the oscillating electric field, fogging and scattering on the image background portion can be prevented.

[0050]

According to the present invention, when an oscillating bias is applied to the developer carrier, an oscillating electric field due to the bias is formed between the developer carrier and the developer regulating member. Therefore, the toner and the carrier can be agitated between the developer carrier and the developer regulating member. Therefore, the average charge amount of the toner can be increased by contact with the carrier, so that an image having high developing ability and stable toner charge amount without fog can be obtained. Also, since the developer carrier is grounded via a capacitance element, by appropriately selecting the capacitance of the element,
The potential difference between the developer carrier and the developer regulating member can be adjusted. As a result, a discharge that is likely to occur when the potential difference is large is prevented, so that it is possible to prevent a deterioration in the quality of an output image due to the discharge.

Further, since the above-mentioned oscillating electric field is generated by using the developer carrying member and the developer regulating member constituting the developing device and applying the developing bias at the time of development, it is necessary to separately provide an auxiliary electrode and a power supply. There is an excellent effect that the configuration is extremely simple as compared with the simple configuration.

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 present invention, since the potential of the developer regulating means is switched by the switching means, the generation of an oscillating electric field between the developer carrier and the developer regulating means can be controlled. That is, when the toner charge amount is large, the switching unit connects the developer carrier and the developer regulating member, and the potential of the developer regulating unit is set to the same potential as the potential of the developer carrier. As a result, no oscillating electric field is generated between the two, so that the stirring effect of the developer is reduced, and control can be performed so that the toner charge amount does not increase. On the other hand, when the toner charge amount is small, the switching means disconnects the developer carrier and the developer regulating member. This causes the developer to be stirred 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.

In particular, according to the invention of claim 4 or 5, the generation of the oscillating electric field can be automatically controlled in accordance with the toner charge amount estimated from the detection result of the toner density detecting means. effective.

In particular, 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 with humidity.

In particular, 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 according to the stop time of the developing device.

[Brief description of the 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 a 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 a relationship between a toner charge amount and a value obtained by dividing a total toner surface area by a total carrier 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 toner charge amount distribution of a developer.

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 unit 40 developer pool 41 developing sleeve 42 stirring member 43 doctor blade 45 developing Bias power supply 51 Transfer roller

Continued on the front page F term (reference) 2H027 DA14 DA40 DD07 EA05 EC06 EC20 ED09 EE02 EE07 EF06 EF09 2H031 AC30 AD01 BA05 BA09 BC00 CA02 CA09 CA13 DA05 2H073 AA03 BA03 BA06 BA12 BA33 CA03 CA13 2H077 AD02 DA06 AD18 DB36 DA42 EA03 GA02 GA03

Claims (7)

[Claims] A developer carrying member for carrying a two-component developer comprising a toner and a magnetic carrier, and transporting the developer to a developing area opposed to an image carrier on which an electrostatic latent image is formed; A developer regulating member for regulating the amount of developer carried, and applying an oscillating bias having a waveform that changes periodically to the developer carrier to apply an electrostatic latent image formed on the image carrier. An image forming apparatus having a developing device for developing, wherein the developer regulating member is configured to be electrically grounded via a capacitance element. 2. The image forming apparatus according to claim 1, wherein said vibration bias is an asymmetric rectangular wave bias. 3. The image forming apparatus according to claim 1, further comprising switching means for electrically connecting / disconnecting said developer carrier and said developer regulating member. 4. An image forming apparatus according to claim 3, wherein said toner density detecting means detects the toner density in said developing device, and said control means controls the operation of said switching means based on the detection result of said detecting means. An image forming apparatus comprising: 5. The image forming apparatus according to claim 4, wherein the control means compares the output value of the toner density detection means with a first threshold value and a second threshold value set in advance. When the output value is equal to or less than the first threshold, the switching means controls to switch to the connection side, and when the output value is equal to or more than the second threshold, the switching means switches to the disconnection side. An image forming apparatus characterized in that the image forming apparatus is controlled as follows. 6. The 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 an operation of said switching means based on a detection result of said detecting means. The control means, based on the result of comparing the output value of the humidity detection means with a preset third threshold and a fourth threshold, the output value is less than the third threshold Wherein the switching means controls to switch to the connection side when the output value is equal to or greater than the fourth threshold value. apparatus. 7. An image forming apparatus according to claim 3, further comprising: a time measuring means for measuring a stop time of said developing device; and a control means for controlling an operation of said switching means based on an output result of said time measuring means. An image forming apparatus characterized in that: