JPH02181760A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the generation of developing unevenness due to toner being laminated locally by rotating a photosensitive drum as well as a developing device at the time of setting toner concentration and activating a cleaning device and a destaticizing device therefor. CONSTITUTION:When a toner concentration setting control mode is started by a switching means, a pre-cleaning destaticizing charger and the cleaning means are activated with the rotation of a rotary drum. When the operations of the photosensitive drum and the cleaning means are stabilized, developing bias and a developing motor are activated and the stirring of developer for a prescribed is carried out by a timing means. Then toner concentration detection is carried out by a toner concentration sensor, this data is sampled by CPU, and stored in a nonvolatile memory. Next, when the prescribed time has passed, the stirring of the developer is stopped. Thus toner concentration can be set without generating soiling on the photosensitive drum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that performs development using a two-component developer, such as a facsimile, a printer, and an electrophotographic copying apparatus.

[Prior Art] Conventionally, image forming apparatuses have been widely used that develop an electrostatic latent image with a two-component developer consisting of toner and carrier to form a visible image, and then transfer the cough visible image onto transfer paper. .

In such conventional image forming apparatuses, toner density is set in advance based on the mixing ratio of toner and carrier in a two-component developer, and is used as data for image density control during image formation. Since the toner concentration of the two-component developer is not necessarily constant, when the developer is replaced due to fatigue or the like, the toner concentration of the developer may be set again.

When setting and controlling such toner concentration, a toner concentration sensor provided in the developing device detects the toner concentration based on the mixture ratio of toner and carrier, and work is performed based on the detected data.

A magnetic sensor is generally used as a toner concentration sensor, and magnetically detects the mixing ratio of toner and magnetic carrier.

When setting the toner concentration, it is desirable that the developer be in a stable state; however, if the two-component developer is left for a long time, the amount of charge will be low. In order to keep the amount of charge stable, it is necessary to stir the developer within the developing device. For this reason, toner density setting is performed while the developing device is operating.

When setting the toner at -4 degrees, the photosensitive drum 51 is kept in a stopped state and the developing sleeve 52 is rotated, as shown in Figure 1). a magnetic brush 53 formed on the developing sleeve 23;
In other words, the areas 54.5 before and after the photoreceptor surface of the photoreceptor drum 51 (the area indicated by diagonal lines in the figure) where the spiked developer contacts.
Toner is layered on the photosensitive drum 51, and even if the photosensitive drum 51 is cleaned in a cleaning process, the toner layer is difficult to remove. This toner layer causes band-shaped background stains on the transfer paper during actual copying.This toner layer can be removed by repeating the cleaning process, so if you do not copy until it is removed, the transfer Although background smearing on the paper can be prevented, copying is prohibited until the toner layer is removed, resulting in a corresponding loss of time.

In addition, since the magnetic brush continuously concentrates on a part of the photoconductor drum that is stopped, differences in surface properties may occur due to filming of the drum and other parts of the photoconductor, causing problems on the image and the photoconductor. This causes problems in terms of body lifespan.

When the photosensitive drum 51 is stopped and the developing sleeve 52 is rotated, developer accumulates in the area A above the magnetic brush 53, damaging the inlet seal 56 of the developing device, and causing toner to leak from the damaged portion into the developing device. ! This may cause problems such as scattering outside. This usually occurs because the inlet seal 56 is set assuming that the photosensitive drum 51 is rotating and there is no pool of agent.

Further, in the lower part of the magnetic brush 53, toner gradually falls from the toner layer 55 attached to the photosensitive drum 53 in direction B. In particular, toner and photoreceptor are attracted to each other by intermolecular forces, but because there is no electrical attraction, they tend to fall off easily.

In the method of transferring to a transfer paper fixed to a transfer drum (not shown) that is in contact with the photosensitive drum 51, the toner attached to the photosensitive drum 51 adheres to the film of the transfer drum even when the transfer charger is OFF, causing the transfer. When the transfer paper is attached to the drum, the back side of the transfer paper becomes dirty. It is conceivable to provide a dedicated cleaner for the transfer drum in order to remove dirt from the back of the transfer paper, but this requires extra space and is problematic in terms of cost.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide an image forming apparatus in which toner density can be set without staining a photosensitive drum.

[Means to solve the problem]

The present invention solves the above problem by providing a photosensitive drum that forms an electrostatic latent image in a mode that detects the mixture ratio of toner and carrier and automatically sets toner density based on the detected data.
The problem was solved by an image forming apparatus characterized by operating a cleaning device, a static eliminating device, and a developing device for the photosensitive drum.

[Function] According to the present invention, when setting the toner density, the photosensitive drum is rotated in addition to the developing device, and a cleaning device and a static eliminator for the photosensitive drum are activated.

According to the present invention, the magnetic brush of the developing sleeve of the developing device does not act locally on the photosensitive drum, but acts on the entire photosensitive drum surface, so there is no difference in surface properties, and the cleaning device and the magnetic brush do not act locally on the photosensitive drum. Since the static eliminator is activated, toner is not locally piled up (no toner pools are formed, and toner falling is avoided).

〔Example] The details of the present invention will be explained based on the embodiments shown in the figures.

In FIG. 1, a copying machine as an example of an image forming apparatus utilizing the present invention exposes an image of an original on a contact glass 1 to a photosensitive drum 3 using an exposure optical device 2, and charges the image using a charger 4. An electrostatic latent image is formed on the photosensitive drum 3. The electrostatic latent image is developed into a visible image by a developing device 5, for example, a first developer 5a containing black toner and a second developer 5b containing, for example, three color toners. The visible image is transferred to a transfer paper fixed to a transfer drum 6 under the action of a transfer charger 7.

After the transfer, the photosensitive drum 3 is neutralized by a pre-cleaning static elimination charger 13, cleaned by a cleaning unit 8, and repeats the image forming process from charging.

In the case of color copying, for example, color separated images of three colors are formed on the photosensitive drum 3 and transferred onto transfer paper fixed to the transfer drum 6 in an overlapping manner. Therefore, one color copy can be obtained by rotating the photosensitive drum 3 and the transfer drum 6 three times.

The leading edge of the transfer paper supplied from a paper feed device 9 such as a paper feed cassette is clamped to the transfer drum 6 by a clamp device, and the entire transfer paper is electrostatically brought into close contact with the transfer drum 6 by the action of a transfer charger or the like. Ru. The transfer drum 6 is transferred by a transfer charger 7 and charged by a static electricity removal charger 14 every rotation.
The transfer paper after the transfer is separated from the transfer drum 6, fixed by the fixing device 10, and discharged to the paper discharge tray 1).

The developing device f5 is, for example, as shown in the example of the first developing device 5a.
It is constructed as shown in FIG. A detailed explanation of the second developing device 5b will be omitted, but it is basically the same as the first developing device 5a, except that it has a structure that includes three developing devices for three color toners. They are just different.

In FIG. 2, a developer is housed in a developer casing 21. As shown in FIG. A paddle 22 and a developing sleeve 23 are disposed within the developer casing 21, and the developer drawn up by the paddle 22 is conveyed by the developing sleeve 23.

In the developing sleeve 23, the developer is regulated to a certain layer thickness by a doctor 24 during transportation, and is supplied to the photosensitive drum 3, which is disposed facing the developing sleeve 23 with a predetermined gap, to form a latent image on the photosensitive drum 3. Visualize.

The residual developer in the developing sleeve 23 after development is returned into the developer casing 21. At this time, the developer peeled off from the developing sleeve 23 under the action of the temporary magnetic shield 29 passes through the toner concentration sensor 25 and returns to the position where it is drawn up by the paddle 22 .

A toner hopper 26 is replaceably attached to the developer casing 21. Toner is supplied from the toner hopper 26 into the developer casing 21 by a toner replenishing roller 27. Currently, the toner is agitated and mixed by an agitator 28 in the detector casing 21 and sent to a pumping position of the paddle 22.

The developer casing 21 is provided with an inlet seal portion 30, a separator 31, a pressure relief filter 32, and the like as necessary.

When a replenishment signal is sent from the toner concentration sensor 25, a toner replenishment clutch (not shown) is turned on, the toner replenishment roller 27 rotates, and a seal 33 made of foamed polyurethane or the like, which the toner replenishment roller 27 bites into, turns on the toner replenishment clutch (not shown). The toner is scraped off and falls into the developer casing 21.

A developing bias is applied to the developing sleeve 23.

The toner concentration sensor 25 is arranged at a position between the developing sleeve 23 and the paddle 22 of the developing device casing 21! i! within the detection range! By detecting the fff rate, it is formed as a magnetic sensor that detects the toner concentration at that time.

When the toner concentration sensor 25 provided in the developing device is a magnetic sensor, a change in magnetic flux density due to a change in the mixing ratio of toner and magnetic carrier is detected as a change in toner concentration by a detection section in which a differential transformer is housed. . As shown in FIG. 3, the analog output signal of the magnetic sensor is input to a central control unit (CPU) 37 via an analog/digital conversion circuit (A/D converter) 36, and the control unit controls the toner density setting. Do m.

As shown in FIG. 4, the control device includes an operation section having a numeric keypad, a sheet number display means, etc., a switching means for switching between a normal copying operation control mode and a toner density setting control mode, a toner supply detection means, and a toner density detection means. The central control unit CPU is electrically connected to the developer stirring means, a timing means for setting the stirring time of the developer stirring means, a non-recurring memory means (RAM), and a driver. The driver is a main motor, a developing motor, a toner replenishment clutch for toner replenishment, a cleaning motor for driving a magnetic brush cleaning device that is a cleaning means, and a bias applied to a magnetic brush roller to remove toner from the photoreceptor. Drive control of various outputs such as cleaning bias to control the adsorption force of toner attached to the photoconductor, pre-cleaning static elimination charger to eliminate static from the photoconductor, and development bias to apply bias to the developing roller. do.

Toner concentration setting is performed by detecting toner concentration using a toner concentration sensor while the developer is being stirred, sampling the resulting concentration data by the CPU serving as a sample storage means, and storing it in a non-volatile storage means as threshold data for concentration control. Store.

The toner density setting control will be explained below based on the time charts of FIGS. 5 and 6 and the flowcharts of FIGS. 7 to 10.

In the toner density setting control mode, control is performed based on FIGS. 5 and 7.

First, the toner density setting control mode is set by the switching means shown in FIG. In this mode, normal copying operations are not performed.

From this state, the toner density setting control mode is started by key operation, for example, by pressing down the copy start button on the operation section (step 1).

By starting this toner density setting control mode, the main motor 47 that drives the photosensitive drum 3 is first operated to rotate the photosensitive drum (step 2).
).

As the photosensitive drum rotates, the pre-cleaning static elimination charger is activated, and the cleaning bias and the cleaning motor for driving the cleaning roller are activated to operate the cleaning means (step 3).

After the operations of the photosensitive drum and the cleaning means become stable, the developing bias and developing motor of the developing device are operated to stir the developer (step 4).

At the same time, a timer for measuring the stirring time of the developer is started (step 5).

When the timer is started, the timer is set so that the concentration setting timer operates to determine the stirring stabilization time of the developer. The stirring stabilization time may be about 1 to 3 minutes for both black and white images and color images.

During developer stirring, the CPU samples toner concentration detection data as appropriate. When the timer completes the predetermined time (step 6), the final density sample data is stored in the non-volatile storage means as density control threshold data (D,) in CPtJ (step 7), and the developing bias and developing motor are The agitation of the developer is stopped by stopping the agitation of the developer. (Step 8).

After the agitation of the developer is completed, the cleaning bias and cleaning motor are stopped (step 9), and the pre-cleaning static elimination charger and main motor are stopped, thereby ending the toner density setting control mode (step 10).

After the toner density setting control mode ends, the switching means is returned to its original state, and the state of the image forming apparatus, for example, a copying machine, is returned to the copy operation control mode.

When the copy operation control mode is selected by the switching means shown in FIG. 4, control is performed based on FIG. 8.

The copy operation control mode is started by pressing the copy start button on the operation unit (step 1).

As a result, various parts necessary for the copy operation operate (step 12).

Toner density data (D+1) is sampled during the copying operation (step 13).

The CPU compares the sampled data DX with toner density control threshold data (D,) that has already been set and stored in the non-volatile storage means (step 14).
If D>DX, the toner replenishment clutch is activated and toner is replenished from the toner hopper by the toner replenishment roller (step 15).

Further, if Do <I), the toner replenishment clutch is stopped (step 16).

This makes it possible to control the toner density of the developing device.

After the copying operation is stopped (step 17), the operations of various parts necessary for the copying operation are stopped (step 18).

Although a switch independent of the operation unit was provided as a switching means, for example, double pressing of a special key (operation key not used in normal copy operations) in the operation unit, input of a code number using a numeric keypad, or a combination thereof, etc. It is also possible to provide a mode switching function by using the switching means for other purposes.

Toner end control is performed according to the flow shown in FIG.

Step 21: Start copying in copy operation control mode by pressing the copy start button on the operation panel.
), the parts necessary for the copy operation operate (Step 2
2).

If the toner replenishment clutch is operating continuously during the copy operation control (step 23), the toner replenishment time Tx is measured (step 24).

If the toner hopper runs out of toner, the toner replenishment clutch operates continuously (step 25), so for example, set the time (Tyu) for the toner replenishment clutch to operate continuously per copy, and set it to 10 or more. If the toner replenishment clutch operates continuously (step 26), the measurement of the toner replenishment time is finished and T8 is set to 0 (step 27). Then, the toner end counter Cx is incremented by 1 (step 28).

The toner end counter CX is compared with a preset toner end setting counter C0 (step 29) When LCX becomes equal to or greater than C0, the toner end is determined.

When the toner reaches the end, even if the copy operation is being controlled,
In order to prevent the toner density of the developer from decreasing and the copy image quality to deteriorate, copying operation control is stopped (step 30), a toner end display is lit on the operation panel, etc., and subsequent copying operations are prohibited ( Step 31). Then, the toner end information is stored in the non-volatile storage means (step 32).

Additionally, if the toner replenishment clutch changes from an activated state to a stopped state during copy operation control (steps 23 and 25)
) Stop measuring the toner replenishment time and set the toner replenishment time T,
is set to 0, and the toner end counter CX is also set to 0 (step 33).

Toner end counter CX is toner end setting counter C
If the value is less than 0 (step 29), copy operation control is continued unless copying is stopped (step 34);
If the copying is to be stopped (step 34), the copying operation control is stopped (step 35), and the value of the toner end counter CX at that point is stored in the non-volatile storage means (
In step 36), the toner end count is continuously performed during the next copy.

In the case of toner end recovery mode, control is performed based on the flowchart in FIG. 10 and the time chart in FIG.

When the toner runs out, there is no more toner in the toner hopper, so new toner must be replenished.

Methods for this include, for example, re-dispensing the toner in the cartridge into the toner hopper, or directly putting the toner into the hopper. In this case, the toner supply detection means (Figure 4) detects whether the cartridge is inserted or removed. It is detected that new toner has been supplied by detecting opening/closing of the cover or opening/closing of the cover.

In the embodiment shown in FIG. 4, a switch is used as the toner supply detection means.

First, if it is the toner end state (step 41), then it is detected that new toner has been supplied by the toner supply means, and if it is detected that new toner has been supplied (step 4
2) Start the toner end recovery mode (step 43).

When the toner end recovery mode starts, the main motor that drives the photosensitive drum is first activated to rotate the photosensitive drum, and as the photosensitive drum rotates, the pre-cleaning static elimination charger is activated (step 44).

Further, the cleaning means is operated by operating the cleaning motor that drives the cleaning roller and the cleaning bias (step 45).

After the photosensitive drum and the cleaning means are in a stable operation state, the developing bias and developing motor of the developing device that stirs the developer and transports it to the photosensitive drum are activated (step 46).

After the developer in the developing device reaches a stable agitation state, the CPU samples toner concentration data (DX) (step 47).

The CPU compares the sampled data DX with the toner density control threshold data D0 that has already been set and stored in the non-volatile storage means.Step 4B), Q
o>DX, the toner replenishment clutch is activated and toner is replenished from the toner hopper by the toner replenishment roller (step 49).

At the same time, measurement of toner replenishment recovery time TIX is started (step 50), and toner replenishment recovery time T is started. Compare the toner replenishment recovery time T0 with the toner replenishment recovery time T0 (step 51). If the toner replenishment lunch is still active even after the toner replenishment recovery set time TI has been exceeded, the toner replenishment recovery time measurement is finished and the toner replenishment recovery time is set. The value T+tX of the measuring device is set to O (step 52).

Thereafter, stirring of the developer is stopped by stopping the development motor and the development bias (step 53).

After the agitation of the developer is completed, the cleaning motor and cleaning bias are stopped (step 54), and the pre-cleaning static elimination charger and main motor are stopped (step 55). In this case, even if the toner replenishment recovery setting time is exceeded, Since the toner density data Dx does not reach the toner density control threshold data D0, it is assumed that the toner density is low, and instead of canceling the toner end state, the toner end display is turned on again and the copying operation is prohibited ( Step 56).

This is used in case you set a cartridge that does not contain toner or forget to supply toner.

In step 48, the toner density data DX is D with respect to the toner one-time control threshold data Do.

<D When it becomes X, stop the toner replenishment clutch,
The toner replenishment recovery time is ended, and the value T+tX of the toner replenishment recovery time measuring device is set to O (step 57).
).

After the toner replenishment clutch is stopped, the supplied toner is not sufficiently mixed with the developer, so it is preferable to stir the developer for as long as necessary to stabilize the amount of charge. The developing motor and developing bias are kept in operation for that time. Thereafter, stirring of the developer is stopped by stopping the development motor and the development bias. (Step 58).

After the agitation of the developer is completed, the cleaning motor and cleaning bias are stopped (step 59), and the pre-cleaning charger and main motor are stopped, thereby stopping the rotation of the cleaning means and the photosensitive drum (step 60). Then, in order to release the toner end data stored in the non-volatile storage means, the value of the toner end counter CX is set to O (step 61).

Meanwhile, the toner end display and copy prohibition display displayed on the operation panel, etc. are turned off, and the copy prohibition is canceled (step 6).
2) The copy operation is brought to a normal state and the toner end recovery mode is ended (step 63).

Setting of toner density is automatically performed by selecting the toner density setting mode under the control of the above-mentioned control device.

Automatic setting of toner density and toner end recovery control can be performed by keeping the transfer drum in a non-contact state with respect to the photosensitive drum. This will prevent toner from adhering to the film on the transfer drum, and will also prevent toner from adhering to the back side of the transfer paper. Adhesion can be prevented.

[Effects] According to the present invention, it is possible to prevent background smudges on transfer paper, to eliminate or shorten post-processing after toner concentration setting and toner end recovery, and to prevent uneven development.

Further, according to the present invention, the inlet seal of the developing device can be protected, the life of the photosensitive drum can be extended, and toner scattering can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram of a copying machine that utilizes the present invention, FIG. 2 is a sectional view of a developing device, FIG. 3 is an output circuit diagram of a toner concentration detection means, FIG. 4 is a block diagram of a control device, and FIG. Figure 5 is a time chart of toner density setting control mode, Figure 6 is a time chart of toner end recovery mode, Figures 7~
FIG. 10 is a control flow diagram, and FIG. 1) is an explanatory diagram of the relationship between the photosensitive drum and the developing sleeve when setting the conventional toner density. 3... Photoreceptor 6... Transfer drum 5... Developing device 8... Cleaning device 13... Pre-cleaning charger 23... Developing sleeve (1 other person)

Claims (1)

[Claims] (1) In an image forming apparatus that develops an electrostatic latent image with a two-component developer consisting of toner and carrier to form a visible image and transfers the visible image to transfer paper, the mixing ratio of toner and carrier is adjusted. In a mode in which the toner density is automatically set based on the detected data, a photosensitive drum that forms an electrostatic latent image, a cleaning device for the photosensitive drum, a static eliminator, and a developing device are operated. Features of the image forming device.