JP2006337869A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive developing device capable of obtaining a stable high-quality image by controlling a developing condition according to environmental variation on the periphery without using a humidity sensor, and an image forming apparatus equipped with the developing device. <P>SOLUTION: The developing device includes: a developing roller 1 for supplying toner to an image carrier; a developing housing 2 for turnably holding and housing the developing roller 1; a toner replenishing means 3 for replenishing the developing housing 2 with the toner; a stirring means 4 for stirring the toner of developer supplied from the toner replenishing means 3 and conveyed to the developing roller 1; and a control means 5 for controlling the developing condition according to a peeling discharge current just after peeling a medium to be recorded (P) to which a toner image is transferred to and which is conveyed from a transfer conveying means 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a developing device and an image forming apparatus including the developing device.
More specifically, a developing device that supplies toner to an electrostatic latent image on an image carrier in an image forming process of an electrophotographic method and visualizes the image, and an electrophotographic image forming process that includes the developing device. The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a complex machine for forming a toner recording image.

In a conventional developing device and a copying machine, a facsimile machine, a printer, or the like of an image forming apparatus provided with the developing device, a photosensitive drum or a photosensitive member as an image carrier in an image forming process of an electrophotographic method A developing device that supplies toner while making contact with a belt or maintaining a minute interval to visualize a latent image is known.
The humidity in the air in the installation environment of the image forming apparatus has a great influence on the image quality to be formed. That is, for example, the triboelectric charging ability of toner in the developing device is more affected by humidity than temperature. For example, if high temperature and high humidity with low frictional charging capability and high temperature and low humidity with high frictional charging capability are controlled in the same way, density deficiency and background stains will occur at high temperature and low humidity.
In addition, various influences occur in the finally obtained image depending on the moisture content of the transfer paper.
Conventionally, the humidity is measured by measuring the current value flowing into the back plate of the transfer electrode or the back plate of the separation electrode, and by this data, the transfer power source, the separation power source, and the development bias of the developing device are controlled, There is known a high-voltage power supply control device for an image forming apparatus that eliminates the environment dependency of a transfer electrode, a separation electrode, and the like without providing a humidity sensor in the image forming apparatus (see Patent Document 1).
A corona charger facing a part of the transfer paper passing through the transfer section on the downstream side of the transfer section in the transfer paper conveyance direction, an AC power source for applying an AC voltage to the corona charger, and corona charging DC current detection device that detects the DC current flowing between the AC power supply and the transfer paper via the device, and the DC current flowing between the transfer belt and the support roller are detected, and based on the detection results of each DC current Therefore, a control unit that changes the setting of the output current of the transfer power supply is provided so that the transfer current flowing to the photoconductor side at the transfer unit is kept constant in consideration of the current generated when the transfer paper is separated from the photoconductor. A transfer device that can obtain more stable transfer performance and separation performance with respect to environmental fluctuations and the like by performing constant current control with higher reliability is known (see Patent Document 2).
When adjusting the exposure amount that determines the image forming conditions, the potential of the image carrier on which the electrostatic latent image is formed by writing exposure with the LD as the writing light source is the same at each position of the potential detecting means and the developing device. Without a shift. By setting a value that cancels out this deviation as a target value for adjustment performed by the value detected by the potential detection means, the developing device can form an image under appropriate image forming conditions. The time from the exposure to the photoreceptor to the detection of the surface potential by the potential sensor is short, and even if the temperature change or the change of the photoreceptor with time occurs, the exposure amount adjustment based on the detection of the potential sensor, and An image forming apparatus that appropriately performs process control such as toner density adjustment is also known (see Patent Document 3).

In the image forming apparatus disclosed in Patent Document 4, first, the developer agitation is started in the developing unit simultaneously with the driving of the photosensitive member, and the charging charger is turned on until the dark part potential of the photosensitive member detected by the potential sensor enters the target area. Operate and set the potential. An intermediate potential latent image pattern (also used as a P sensor pattern for toner density adjustment) is formed, the potential of the latent image pattern is set to a target intermediate potential by adjusting LD exposure, and a development bias voltage is set. The toner is attached to the P sensor pattern with the set bias, and the toner adhesion amount is detected by the P sensor in order to obtain the toner density control reference value. The setting of image forming conditions can be shortened by combining the pattern, and the optimal setting of image forming conditions such as charging, exposure, development conditions, toner density control reference value, etc. can be completed in a short time, which is inconvenient for the user. And stable image quality can be formed.
In an image forming apparatus having a transfer material transport unit that electrostatically attracts and transports a transfer material, a surface on which an unfixed image of the transfer material is formed immediately after the transfer material is peeled off from the transfer material transport unit The charge generation means is provided in a non-contact facing manner only on the surface opposite to the surface, and the charge generation means charges on the transfer material surface on the opposite side to the surface on which the unfixed image is formed. And a transfer material generated when the transfer material is peeled off from the transfer conveyance belt so as to have a grounded electrode to be opposed to the charge generating means on the surface side on which the non-fixed image is formed. There is also known an image forming apparatus that can prevent the peeling electrification of the image, prevent the image forming medium from scattering on the transfer material, prevent the discharge pattern of the image forming medium from being generated, and obtain a high-quality image (patent) Reference 5).
In addition, there is also a technique that controls a bias of transfer or development by measuring a current flowing in a case portion of a transfer device or a separator facing the photoconductor (see Patent Document 1).
However, this current varies depending on the amount of image, that is, the ratio of the area occupied by the toner image on the photoreceptor.
Since the toner is made of an insulating resin, the amount of current increases when the amount of images is large. For this reason, the formed image is not stable unless the image amount is constant.

In addition, there is a type that performs toner replenishment control of the developing device using a temperature sensor in the fixing device (see Patent Document 3 and Patent Document 4).
However, the triboelectric charging ability of the toner in the developing device is more affected by humidity than temperature. If humidity is not taken into consideration, high temperature and high humidity with low frictional charging capability and high temperature and low humidity with high frictional charging capability are the same control, resulting in insufficient density and background stains at high temperature and low humidity. .
Furthermore, in order to reduce transfer paper peeling discharge and to suppress image dust, there is also an electrode provided on the back side of the transfer paper in a non-contact facing manner at a position immediately after the transfer paper is peeled on the transfer material conveying means (Patent Document). 5).
However, the transfer paper is electrostatically attracted to the transfer material conveying means, and the charge increases due to the peeling discharge that occurs when the transfer paper is peeled off. If the charge is excessively accumulated on the transfer paper, the charge is discharged to the electrically grounded conveying member or casing, and the toner image is disturbed at that time. The image dust is suppressed by providing an electrode near the position where the peeling discharge is performed to release the electric charge accumulated on the transfer paper. Since the peeling discharge of the transfer paper is an electrostatic phenomenon, it varies depending on the surrounding environment and the moisture content of the transfer paper. Therefore, the current flowing through the electrode also varies depending on the surrounding environment and the moisture content of the transfer paper.
JP 7-84469 A JP-A-8-339127 JP 2000-330345 A JP 2001-312109 A Japanese Patent No. 3257080

In a conventional developing device and an image forming apparatus equipped with the developing device, in order to obtain a stable image by controlling the developing conditions according to environmental fluctuations, etc., the ambient environmental conditions are set using a humidity sensor. Since the measurement has to be performed, there is a problem that the cost is increased and the quality of the formed image is also lowered.
Therefore, an object of the present invention is to solve such problems. That is, it is possible to provide a low-cost developing device that obtains a stable and high-quality image by controlling development conditions according to environmental changes without using a humidity sensor, and an image forming apparatus including the developing device. With the goal.

In order to achieve the object, the present invention according to claim 1 is configured to rotate freely to supply toner to an electrostatic latent image on an image bearing member upon receipt of toner from a toner replenishing means to form a toner image. A developing roller, a developing housing that houses the developing roller, a stirring unit that stirs the toner in the developing housing, and a transfer conveying unit that conveys a recording medium onto which the toner image on the image carrier is transferred. A peeling discharge current measuring means for measuring a peeling discharge current immediately after peeling off the recording medium; and a control means for controlling development conditions based on the value of the peeling discharge current measured by the peeling discharge current measuring means. It is characterized by doing.
According to a second aspect of the present invention, in the developing device according to the first aspect, the electrode member includes an acute-angle shaped portion at a tip facing a separation point between the transfer conveying unit and the recording medium.
According to a third aspect of the present invention, in the developing device according to the first or second aspect, the control unit controls a toner replenishment amount by the toner replenishing unit.
According to a fourth aspect of the present invention, in the developing device according to the first, second, or third aspect, the control unit controls a stirring time of the developer toner by the stirring unit.
According to a fifth aspect of the present invention, there is provided an image forming apparatus for forming a toner recorded image in an image forming process of an electrophotographic method, wherein the image forming unit forms a toner recorded image on a recording medium, and the image forming unit is disposed in the image forming unit. Item 5. The developing device according to Item 1, 2, 3, or 4 is provided.

According to the present invention, it is possible to provide a low-cost developing device that obtains a stable and high-quality image by controlling the developing conditions according to the surrounding environmental change without using a humidity sensor.
Further, it is possible to provide a developing device which has a higher static elimination effect, obtains a stable and high-quality image by controlling the developing conditions in accordance with the surrounding environmental change without using a humidity sensor, and further provides a low cost. Can be done.
Further, it has become possible to provide a low-cost developing device that can control the stirring time of the toner under the developing conditions according to the surrounding environmental change without using a humidity sensor and obtain a stable high-quality image.
Another object of the present invention is to provide a low-cost image forming apparatus capable of forming a stable, high-quality toner-recorded image free of background stains by controlling development conditions according to environmental changes without using a humidity sensor. Can be done.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
FIG. 1 is a configuration explanatory diagram of a developing device 0 and an image forming apparatus 50 including the developing device 0 according to an embodiment of the present invention.
FIG. 2 is an enlarged view for explaining a main part of the image forming apparatus 50.
FIG. 3 is a graph for explaining the characteristics of the peeling discharge current according to the time (seconds) and the current value in the image forming apparatus 50.
In FIG. 1, a developing device 0 that supplies toner in an electrophotographic image forming process to visualize a latent image is a surface of a photosensitive drum that is an image carrier 51a that is rotationally driven in the direction of arrow (A). A developing roller 1 that transports and supplies toner while being in contact with 51a ₁ or maintaining a small interval, a developing housing 2 that holds and holds the developing roller 1 rotatably, and a toner in the developing housing 2 Toner replenishing means 3 for replenishing, agitating means 4 for agitating the developer toner replenished from the toner replenishing means 3 and conveyed to the developing roller 1, and a recording medium (P) to which the toner image is transferred and conveyed Control means 5 for controlling the development conditions based on the peeling discharge current immediately after peeling from the transfer conveying means 10.
The control unit 5 may also serve as a unit that is disposed downstream of the transfer conveyance unit and measures the peeling discharge current of the recording medium.
As described above, the development conditions are controlled based on the value of the peeling discharge current immediately after the recording medium is peeled off from the transfer conveying means, so the development conditions are controlled according to the surrounding environmental changes without using a humidity sensor. Thus, it is possible to provide a low-cost developing device 0 that obtains a stable and high-quality image.

The image forming apparatus 50 includes a developing device 0 and forms a toner recording image on a recording sheet as a recording medium (P), and is positioned below the image forming section 51 to form the image. A recording medium feeding unit 52 that feeds the recording medium (P) to the printing unit, a paper discharge tray 53 that stores the recording medium on which the toner recording image is formed by the image forming unit 51, and the image forming unit 51. A document image reading device 54 that reads a document image of a document (O) placed above the document.
The image forming apparatus 50 is a copying machine that employs an N / P developing method, which is a reverse developing method, to form a recorded image of toner.
That is, after the surface 51a ₁ of the image carrier 51a is uniformly negatively charged to about −900 (V) by the charging device 51b, the document (O) placed on the contact glass 54a of the document image reading device 54. The signal read from the image memory 54b storing image information such as the above is replaced with an electrostatic latent image of about −50 (V) by the laser beam 51c ₁ of the latent image forming apparatus 51c.
Further, a recorded image of the toner is formed by the negatively charged nonmagnetic toner.
The developing device 0 is a two-component developing device. In the developing housing 2, non-magnetic toner is contained in a carrier made of a magnetic material so as to have a predetermined concentration at a predetermined ratio.
The developing device 0 includes a developing roller 1 (developing roller 1a and developing roller 1b) that applies toner in the developer to the surface of the image carrier 51a, a developing doctor 6 that regulates the amount of developer on the developing roller 1a, and a developer. Stirring means 4 (stirring member 4a, stirring member 4b, stirring member 4c) and the like for stirring the toner.
The developing device 0 is rotationally driven by a developing motor as a driving source 7.

The toner replenishing means 3 is arranged on the right side of the developing housing 2 as shown, and gradually replenishes toner sent from a toner cartridge (not shown) into the developing housing 2 by a toner replenishing roller 3a.
The toner supply of the toner supply means 3 is rotationally controlled by the toner supply clutch 3b so that only the shortage is supplied according to the developer concentration in the developing housing 2.
The toner replenished in the developing housing 2 is stirred with the carrier by the stirring member 4a, the stirring member 4b, and the stirring member 4c, adheres to the carrier, and is negatively charged.
The negatively charged toner is attracted to the magnets constituting the developing roller 1a and the developing roller 1b and adheres to the developing roller 1a and the developing roller 1b.
The toner attached on the developing roller 1a is conveyed to the developing doctor 6 by the rotation of the developing roller 1a and the developing roller 1b, and after being regulated to a predetermined amount, reaches the developing area of the image carrier 51a.
About −550 (V) is supplied to the developing roller 1a and the developing roller 1b from a developing bias power source (not shown), and only the negatively charged toner in the developer moves to the electrostatic latent image. Become.

The recording medium is conveyed from the paper feeding cassette 52a of the recording medium feeding unit 52 from the direction of the arrow (B) shown in the drawing, and is temporarily stopped with the leading end in contact with the registration roller pair 51d.
In accordance with the movement timing of the toner image formed on the surface of the image carrier 51a, the recording medium is fed from the registration roller pair 51d, and is driven to rotate by the arrow (C) in the transfer conveyance means 10 as shown in FIG. Thus, the toner image formed on the surface of the image carrier 51a is transferred to the recording medium.
The transfer belt 11 is made of a material in which rubber has a medium resistance. The transfer belt 11 is provided with a driving roller 11a, a driven roller 11b, and a bias roller 11c on the inner side.
The bias roller 11c is connected to the transfer high-voltage power supply 11d, is applied with a transfer bias, and is controlled so that the current flowing to the image carrier 51a side is constant.
The recording medium to which the toner image has been transferred is charged by the peeling discharge received from the transfer bell 11 by the electrode member 12 provided downstream of the transfer belt 11.
The electrode member 12 is made of a thin metal plate, and the tip thereof is installed so as to face the separation point between the transfer belt 11 and the recording medium.
The shape of the tip of the electrode member 12 facing the separation point between the transfer belt 11 and the recording medium has an acute-angled portion 12a as shown in FIG. Furthermore, a high quality image can be obtained.

Residual toner adhering to the surface of the transfer belt 11 after separating the recording medium is collected by the transfer belt cleaning device 11f.
After that, the toner image is heated and fixed on the recording medium by heating and pressing of the heating roller 51e ₁ and the pressure roller 51e ₂ of the fixing device 51e, and is discharged to the paper discharge tray 53 and stored by the paper discharge roller pair 51f. Is done.
Residual toner or the like adhering to the surface of the image carrier 51a that has not been transferred to the recording medium is collected by the brush roller 51g ₁ and the cleaning blade 51g ₂ of the image carrier cleaning device 51g.
Thereafter, the surface of the image carrier 51a is neutralized by a neutralizing lamp 51h which is a neutralizing unit.
The electrode member 12 provided on the downstream side of the transfer belt 11 of the transfer conveying means 10 is grounded, and an ammeter (peeling discharge current measuring means) 12b is provided therebetween. The ammeter 12 b measures the peeling discharge current of the recording medium separated from the transfer belt 11.
The characteristics of the peeling discharge current are shown in FIG. At the time of low humidity (solid line (A), humidity: 20% RH), the amount of current is the largest, and at the time of high humidity (dotted line (B), humidity: 70% RH), almost no current flows. When the humidity is low, since the electrostatic adsorption force between the recording medium and the transfer belt 11 is the strongest, a large amount of peeling discharge current is measured.

The (+) side current shown in FIG. 3 is a current that flows because the transfer belt 11 is charged with a positive charge due to peeling from the recording medium and a negative charge is induced in the electrode member 12.
The peeling discharge current of the recording medium is a current on the (−) side. This peeling discharge current varies depending on the type of recording medium.
As the recording medium has a higher resistance, for example, an insulating resin sheet such as an OHP sheet has a larger maximum current value.
Further, the maximum value of the peel discharge current varies depending on the size of the recording medium and the paper passing direction. The maximum value of current increases as the width of the recording medium becomes larger than the width of the electrode member 12. For this reason, the peeling discharge current flowing from the electrode member 12 to the ammeter 12b is counted by the control means 5 for a time corresponding to one recording medium.
Further, the control means 5 integrates the current on the (−) side, and divides the integrated current amount by the recording paper size coefficient (area ratio of recording paper size).
In the control means 5, when the value of the current amount is equal to or less than the predetermined value (a), it is determined that the surrounding environment is high humidity, and the developing conditions of the developing device 0 are controlled.
When the humidity is high, the charging ability of the toner is reduced. Therefore, compared with the low humidity, the amount of toner replenished at one time is reduced, and the toner is replenished in a number of times.
Specifically, the control means 5 controls the toner replenishment amount of the toner replenishing means 4 into the developing housing 2 so that the rotation connection of the toner replenishing clutch 3b is made many times in a short time.
In addition, when the humidity is high, a sufficient toner charging time is ensured by setting the toner stirring time longer than usual during image formation. Specifically, the control unit 5 controls to extend the rotation time of the developing motor of the drive source 7 after the end of the image forming job.
Therefore, even when the toner charging capability at high humidity becomes low, the toner can be sufficiently charged, and a stable high-quality toner image free from background stains can be formed.

FIG. 4 is a flowchart for explaining the operation of the main part of the developing device 0 according to the embodiment of the present invention.
In FIG. 4, the developing device 0 uses the control means 5 to control the developing conditions according to the surrounding environmental fluctuations without using a humidity sensor as follows, and obtain a stable high quality image. Yes.
First, the amount of current is calculated from the peeling discharge current that flows from the electrode member 12 to the ammeter 12b (step 1). It is determined whether the value of the current amount is equal to or less than a predetermined value (a) (step 2). If the value of the current amount is equal to or greater than the predetermined value (a) in (Step 2), a normal toner replenishing operation is performed (Step 3) and the process is terminated.
However, if the value of the current amount is equal to or less than the predetermined value (a) in (Step 2), the toner replenishment amount of the toner replenishing means 4 is set to a large number of times in the rotational connection of the toner replenishment clutch 3b for a short time. The toner supply operation at high humidity is performed (step 4), and the process ends at the end.

FIG. 5 is a flowchart for explaining another operation of the main part of the developing device 0 according to another embodiment of the present invention.
The developing device 0 obtains a stable high-quality image by controlling the developing conditions according to the surrounding environmental fluctuations without using a humidity sensor by the control means 5 as follows.
First, the amount of current is calculated from the peeling discharge current flowing from the electrode member 12 to the ammeter 12b (step 11). It is determined whether the value of the current amount is equal to or less than a predetermined value (a) (step 12). If the current value is equal to or greater than the predetermined value (a) in (Step 12), the process ends.
However, if the value of the current amount is equal to or smaller than the predetermined value (a) in (Step 12), the rotation driving time of the developing motor of the driving source 7 after the end of the image forming job is extended, and the toner is formed during image formation. An operation is performed in which the agitation time is set longer than usual and sufficient time for the toner to be charged is provided (step 13), and the process ends at the end.
According to this, even when the toner charging capability at high humidity becomes low, the toner can be sufficiently charged, and a stable and high-quality toner image free from background stains can be formed. .
Therefore, an image forming apparatus provided with a low-cost developing device 0 that can form a stable and high-quality toner image free of background stains by controlling the developing conditions according to the surrounding environmental fluctuations without using a humidity sensor. 50 can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a developing device and an image forming apparatus including the developing device according to an embodiment of the present invention. It is a block diagram of an example of a peeling discharge current measuring means. It is a graph explaining the characteristic of peeling discharge current. 6 is a flowchart for explaining the operation of the main part of the developing device according to the embodiment of the present invention. It is a flowchart explaining other operation | movement of the principal part of the image development apparatus which shows the embodiment of this invention.

Explanation of symbols

0 Developing device 1 Developing roller,
1a Development roller,
1b developing roller 2 developing housing 3 toner replenishing means,
3a Toner supply roller,
3b Toner supply clutch 4 Stirring means,
4a stirring member,
4b stirring member,
4c stirring member 5 control means 6 developing doctor 7 drive source 10 transfer conveying means 11 transfer belt,
11a Driving roller,
11b driven roller,
11c bias roller,
11d transfer high voltage power supply,
11f Transfer belt cleaning device 12 Electrode member,
12a acute angle shape part,
12b Ammeter 50 Image forming apparatus 51 Image forming unit,
51a image carrier,
51a ₁ surface,
51b charging device,
51c latent image forming device,
51c ₁ laser beam,
51d Registration roller pair,
51e fixing device,
51e ₁ heating roller,
51e ₂ pressure roller,
51f discharge roller pair,
51g image carrier cleaning device,
51g ₁ brush roller,
51g ₂ cleaning blade,
51h Static elimination lamp 52 Recording medium feeding section,
52a paper feed cassette 53 paper discharge tray 54 document image reading device,
54a contact glass,
54b Image memory

Claims (5)

  A rotatable developing roller that receives toner replenishment from the toner replenishing means and supplies the toner to the electrostatic latent image on the image carrier to form a toner image, a developing housing that houses the developing roller, and the development An exfoliation discharge current for measuring an exfoliation discharge current immediately after the recording medium is exfoliated from an agitation unit for agitating the toner in the housing and a transfer conveyance unit for conveying the recording medium to which the toner image on the image carrier is transferred A developing apparatus comprising: a measuring unit; and a control unit that controls a developing condition based on a value of the peeling discharge current measured by the peeling discharge current measuring unit.   The developing device according to claim 1, wherein the electrode member includes an acute-angled portion at a tip that faces a separation point between the transfer conveyance unit and the recording medium.   3. The developing device according to claim 1, wherein the control unit controls a toner replenishment amount by a toner replenishing unit. 4.   4. The developing device according to claim 1, wherein the control unit controls a stirring time of the developer toner by the stirring unit.   An image forming apparatus for forming a toner recorded image in an image forming process of an electrophotographic method, wherein the image forming unit forms a toner recorded image on a recording medium, and the image forming unit is disposed in the image forming unit. Or an image forming apparatus comprising the developing device according to 4.

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