Image forming apparatus

An image forming apparatus includes an image bearing member; developing devices, each of which includes a developer carrying member, having an electrode member, for carrying a developer, and a developer feeding member, having a core metal and a surface foam layer, for supplying the developer to the developer carrying member; a supporting member, supporting the developing devices, for sequentially rotating the developing devices to a developing position; and a controller for executing an operation for reducing non-uniform distributions of the developers in the developing devices on the basis of electrostatic capacities between the electrode members and the core metals, respectively.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image forming apparatus including a plurality of developing devices held by a supporting member.

A full-color image forming apparatus comprising a single image bearing member, and a rotatable supporting member carrying a plurality of developing devices, wherein the developing devices are switched sequentially at predetermined timing to develop an electrostatic latent image formed on a surface of the image bearing member.

As for a method for detecting a remaining amount of the toner in the developing device for the image forming apparatus, there is known an electrostatic capacity detecting type system which obtains information relating to the developer remainder by detecting an electrostatic capacity between the two inter-electrodes provided in the developing device.

In a developing device comprising a developing roller as a toner carrying member and a supplying roller having a foam layer as a toner supplying member, an electrostatic capacity between a core metal of the developing roller and a core metal of the supplying roller is detected to obtain the information relating to the remaining toner amount (Japanese Laid-open Patent Application 2009-9035, for example).

Generally, the developing roller and the supplying roller are placed in a developing chamber in the developing device, and before the initial use of the device, the developer is in the same region as these rollers, or is in a developer chamber separated from the developing chamber by a toner seal.

With an image forming apparatus which can be transported in the state that the developing devices are mounted on the rotatable supporting member, too much toner is on one side (non-uniform distribution) in the developing devices depending on the orientation of attitude of the apparatus during the transportation.

In the case of the developing device having the toner seal in the unused state, a user once takes the device out of the main assembly of the apparatus, and pulls out the toner seal. At this time, the non-uniform distribution of the toner can be corrected.

SUMMARY OF THE INVENTION

In a developing device not having a toner seal, however, the toner seal pulling operation is unnecessary, and therefore, the toner seal pulling operation cannot be expected for the correction of the non-uniform distribution of the toner. In such a case, if the apparatus is operated with the state of the non-uniform distribution of the toner, an image having white void may result in the initial stage after the installation.

Accordingly, it is a principal object of the present invention to provide an apparatus with which the non-uniform distribution of the toner is reduced at the time of initial installation.

According to an aspect of the present invention, there is provided an image forming apparatus comprising an image bearing member for carrying an electrostatic latent image; a plurality of developing devices, each of which includes a developer carrying member, having an electrode member, for carrying a developer and for developing the electrostatic latent image, and a developer feeding member, having a core metal and a surface foam layer, for supplying the developer to said developer carrying member; a supporting member, supporting the developing devices, for sequentially rotating said developing devices to a developing position where the electrostatic latent image is developed; and a controller for executing an operation for reducing non-uniform distributions of the developers in longitudinal directions of said developer feeding members in said developing devices on the basis of electrostatic capacities between said electrode members and said core metals in said developing devices, respectively.

According to the structure, the non-uniform distribution of the toner can be reduced at the time of initial installation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings. Here, the dimensions, the sizes, the materials, the configurations, the relative positional relationships of the elements in the following embodiments and examples are not restrictive to the present invention unless otherwise stated. Therefore, the present invention is not limited to the specific examples which will be described

(Structure of Image Forming Apparatus)

FIG. 1is a schematic illustration of an image forming apparatus according to this embodiment of the present invention. As shown inFIG. 1, the image forming apparatus100comprises a photosensitive drum1as an image bearing member. The photosensitive drum1rotates in a direction of an arrow Rl1Around the photosensitive drum1, there are provided a charging roller2and an exposure device3. A laser beam is outputted from the exposure device3and reaches the exposure position above photosensitive drum1through a reflection mirror4. Then, an electrostatic latent image is formed on the photosensitive drum1.

Opposed to the photosensitive drum1, there is provided a rotary drum50provided with developing devices5(5a,5b,5c,5d) as four developing means. The developing devices5(5a,5b,5c,5d) contain developers including yellow toner, magenta toner, cyan toner and black toner, respectively. Inside structures of the developing devices5are the same, and therefore, in the following description, the suffixes a-d of the reference numerals are omitted, when it is unnecessary to refer to a particular color.

All the developing devices5are mountable to the rotary drum50as the supporting member. The rotary drum50is supported rotatably in the state of carrying the developing devices5, and places a necessary developing device (yellow developing device5a, for example, inFIG. 1) so as to oppose to the photosensitive drum1(developing position C). The rotary drum50is driven and controlled by a controller.

Below the photosensitive drum1, an intermediary transfer belt16as an intermediary transfer member is provided. The intermediary transfer belt16is stretched around a plurality of rollers and is rotated in the direction of R3inFIG. 1. In a primary transfer position B where the intermediary transfer belt16is press-contacted to the photosensitive drum1, the intermediary transfer belt16is sandwiched between a primary transfer roller17and the photosensitive drum1.

One of stretching rollers stretching the intermediary transfer belt16is a secondary transfer opposing roller16b, opposite which a secondary transfer roller18is disposed through the intermediary transfer belt16. The secondary transfer roller18is capable of moving to and away from the intermediary transfer belt16. The position where the secondary transfer roller18moves is a secondary transfer position D. In the secondary transfer position D, as will be described hereinafter, an image is secondary transferred onto a transfer material P fed thereto. The transfer material P after the secondary transfer is fed to a fixing device15.

A cleaning device19is provided at a position downstream of the secondary transfer position D with respect to a moving direction of the intermediary transfer belt16. The cleaning device19is provided with a blade contacted to the intermediary transfer belt16to scrape the toner off the intermediary transfer belt16. Similarly, for the photosensitive drum1, a photosensitive member cleaning device9is provided with at a position downstream of the primary transfer position B with respect to the moving direction of the photosensitive drum1, and the photosensitive member cleaning device9is provided with a blade for scraping the toner off the photosensitive drum1. With such a structure, the untransferred toner is removed.

An image forming operation of the image forming apparatus100will be described.

As shown inFIG. 1, the photosensitive drum1is rotated in the direction of the arrow R1, during which the surface of the photosensitive drum1is charged to a predetermined potential by the charging roller2. In the exposure position A, the photosensitive drum1is exposed to the laser beam in accordance with image signal for each color by the exposure device3and the reflection mirror4. By the exposure the electrostatic latent image is formed on the photosensitive drum1.

The electrostatic latent image formed on the photosensitive drum1is developed in the developing position C by the developing device5into a toner image. Particular one of the developing devices5provided in the developing position C corresponding to the color of the image signal is brought to the developing position C by the rotation of the rotary drum50in the direction of an arrow R2. The order of the colors of the developments is yellow, magenta, cyan and black in this embodiment.

The toner image formed on the photosensitive drum1is transferred onto the intermediary transfer belt16in the primary transfer position B. The toner images are transferred sequentially superimposingly so that a full-color toner image is formed on the intermediary transfer belt16.

The secondary transfer roller18is spaced from the intermediary transfer belt16until the full-color toner image is formed, and is contacted to the intermediary transfer belt16after the full-color toner image is formed. The transfer material P is fed in timed relation with arrival of the formed full-color toner image at the secondary transfer position D.

The secondary transfer roller18and the secondary transfer opposing roller16bcooperate with each other to nip the transfer material P and the intermediary transfer belt16to secondary-transfer the full-color toner image onto the transfer material P. The transfer material P carrying the transferred full-color toner image is fed to the fixing device15.

The fixing device15presses and heats the full-color toner image on the transfer material P to fix the full-color toner image (final image) on the transfer material P.

(Detailed Structure of Developing Device)

Referring toFIG. 2, the developing device5will be described in detail.FIG. 2is an illustration of the developing device during image forming operation. InFIG. 2, the peripheral structures such as the rotary drum50are omitted.

In the developing device5, the toner is accommodated in a developing container21. The developing container21is disposed in a lower opening and includes a developing roller25a developer carrying member opposing the photosensitive drum1. In a position adjacent the developing roller25in the lower part inside the developing container21, a supplying roller24a developer feeding member is provided. An amount of the toner on the supplying roller24is regulated by a regulating blade27as a developer regulating member. The supplying roller24includes an electroconductive core metal24aas a first electrode member, and the developing roller25includes an electroconductive core metal as a second electrode member. A preventing seal26is provided to cover a gap between the developing roller25and the developing container21.

The supplying roller24comprises an electroconductive core metal24ahaving a diameter φ6 (mm), and a foam layer of urethane sponge layer or the like on the electroconductive core metal24a. The urethane sponge layer of this embodiment is a surface foam soft layer including continuous pores. An outer diameter of the supplying roller24is φ15 (mm), and the volume resistivity thereof is approx. 10^8 Ωcm. The surface of the urethane sponge layer has a flow rate of 3.2 liter/min.

The developing roller25includes an electroconductive core metal25ahaving a diameter of φ8 (mm). Around the electroconductive core metal25a, an electroconductive elastic layer comprising silicone rubber is formed. A surface layer of the developing roller25is a rubber layer of acrylic or urethane main assembly. An outer diameter of the developing roller25is φ13 (mm), and a volume resistivity is approx. 10^5 Ωcm.

In order to detect an electrostatic capacity which will be described hereinafter, the developing roller25may be provided with a second electrode member, and the second electrode member may be an electroconductive sleeve which may be provided around the surface of the developing roller25, for example.

In this embodiment, a distance (center-to-center distance) between a center of the electroconductive core metal25aof the developing roller25and a center of the electroconductive core metal24aof the supplying roller24is 13 mm. The surface of the developing roller25bites into the urethane sponge layer of the supplying roller24by 1.0 mm. The depth of 1.0 mm is a difference between the center-to-center distance and one half of a sum of the outer diameters of the supplying roller24and the developing roller25on the line connecting the center of the electroconductive core metal25aand the center of the electroconductive core metal.

The regulating blade27comprises a flexible phosphor bronze metal plate, and one end portion thereof is fixed to the developing container21, and the other end portion which is a free end is contacted to the developing roller25. The free end of the regulating blade27is counter-directional relative to a rotational moving direction of the developing roller25, a smooth surface thereof neighborhood of the free end slides on the surface of the developing roller25.

The description will be made as to an electrostatic capacity measuring method for execution of a detecting sequence for detecting the non-uniform distribution (offset) of the toner.

As shown inFIG. 1, in order to measure the electrostatic capacity, a voltage applying means32for the detection is connected with the electroconductive core metal25a, and a detection circuit31as an electrostatic capacity detecting means is connected with the electroconductive core metal24a. In addition, there are provided a comparator33as comparing means for comparing the electrostatic capacity detected by the detection circuit31with a threshold which will be described hereinafter, and a discriminating means34(detection portion) for discriminating whether or not the non-uniform distribution of the toner has occurred. The result of the discrimination of the discriminating means34is notified by notification means35. A controller36receives the discrimination result of the discriminating means34and controls a notification signal for notifying the user by the notification means35. The voltage applying means32is connected with the voltage control means32afor controlling the voltage.

An AC bias voltage for the electrostatic capacity detection has a frequency of 50 kHz and a peak-to-peak voltage Vpp=200V. In measuring the electrostatic capacity, a predetermined AC bias voltage is applied to the electroconductive core metal25aof the developing roller25, by which an AC voltage is induced in the electroconductive core metal24aof the supplying roller24, and an electrostatic capacity between the core metals is detected from the induced AC voltage.

It will suffice if one of the electroconductive core metal25aand the electroconductive core metal24ais supplied with an AC bias voltage, and the output of the other is detected. Therefore, it is a possible alternative that the AC bias is applied to the electroconductive core metal24a, and the remaining toner amount measurement is effected from the AC voltage induced in the electroconductive core metal25a.

The AC voltage induced in the electroconductive core metal24ais rectified by the detection circuit31. The rectified DC voltage per set or information of a signal of a digitized DC voltage is outputted. The output value is indicative of an electrostatic capacity between the electroconductive core metal25aand the electroconductive core metal, and the electrostatic capacity reflects a toner amount existing between the electroconductive core metal25aand the electroconductive core metal24a.

FIG. 3is a graph showing a relation between the toner amount in the supplying roller24and the electrostatic capacity.FIG. 3shows the results of measurement of the relation between the toner the amount in the urethane sponge layer and the electrostatic capacity between the electroconductive core metal25aof the developing roller25and the electroconductive core metal24aof the supplying roller24. The electrostatic capacity is measured by a LCR meter ZM2354 available from NF Corporation.

As shown inFIG. 3, the electrostatic capacity and the toner amount in urethane sponge layer of the supplying roller24are in a linear relation. From result, it is understood that there is a correlation between the toner amount held in the urethane sponge layer of the supplying roller24and the electrostatic capacity between the supplying roller24and the developing roller25.

A physical situation and the correlation between the difference of the electrostatic capacity of the developing device and the non-uniform distribution of the toner in the container will be considered.

FIG. 4illustrates an attitude difference of the developing device in this embodiment.FIG. 4shows a state of the toner in the developing devices of the image forming apparatus when the longitudinal direction of the developing device (longitudinal direction of the supplying roller24) is perpendicular to the direction of gravity, that is, a disposition attitude of the image forming apparatus.

In the state ofFIG. 4, there are two states of the developing devices (5a,5b,5c,5d), in one of which the urethane sponge layer of the supplying roller24is in the toner, and in the other of which it is out of the toner. More specifically, the urethane sponge layers of the supplying rollers24of the yellow developing device5aand the magenta developing device5bare in the toner over the entire zone in the longitudinal direction. On the other hand, the urethane sponge layers of the supplying roller24of the cyan developing device5cand the black developing device5dis not in the toner.

The plurality of developing devices5of this embodiment are supposed to be shipped in the state that they are mounted on the rotary drum50. During the transportation of the image forming apparatus, a vibration in vertical direction may be imparted thereto, when traveling a bumpy road, for example. In such a case, too, the urethane sponge layers of the supplying roller24of the yellow developing device5aand the magenta developing device5bare in the toner over the entire zone. Therefore, the entire zones of the urethane sponge layers contain the toner.

On the other hand, the urethane sponge layers of the cyan developing device5cand the black developing device5dare not in the toner. In this case, the urethane sponge layers of the supplying rollers24do not contain the toner.

Under such circumstances, there are two cases, in one of which the non-uniform distribution of the toner occurs, and the other of which the non-uniform distribution of the toner does not exists.FIG. 5shows the electrostatic capacities of the developing devices when the non-uniform distribution of the toner does not exist.FIG. 6shows the electrostatic capacities of the developing devices when the non-uniform distribution of the toner exists.

In the normal state, that is, when the non-uniform distribution of the toner does not exist, the electrostatic capacities (therefore the toner contents) of the yellow developing device5aand the magenta developing device5bare equivalent to those in the case that the urethane sponge layers of the supplying rollers24are in the toner. The electrostatic capacities in the cyan developing device5cand the black developing device5dare equivalent to those when the urethane sponge layers therein do not contain the toner.

On the other hand, the description will be made as to the case in which the image forming apparatus is placed vertically, that is, the longitudinal direction of the developing device is parallel with the direction of gravity.FIG. 6shows the results of the measurement of the electrostatic capacities of the developing device under the states of the non-uniform distribution of the toner.

In this state, the longitudinal range in which the urethane sponge layers are in the toner are the same in the yellow developing device5a, the magenta developing device5b, the cyan developing device5cand the black developing device5d. If the vertical vibrations are imparted as when traveling the bumpy road, in such situation, the portions of the urethane sponge layers of the supplying rollers24of the yellow developing device5a, the magenta developing device5b, the cyan developing device5cand the black developing device5dwhich portions are in the respective toner powders, contain the toner powders. Then, the electrostatic capacities and therefore the toner content of the yellow developing device5a, the magenta developing device5b, the cyan developing device5cand black developing device5dare substantially all the same.

Thus, when the developing cartridges are vibrated in the normal attitude in the state that they are mounted to the image forming apparatus, a large difference appears in the electrostatic capacities of the developing devices5, whereas when the vibration is imparted in the vertical attitude, the electrostatic capacities of the developing devices are substantially the same.

(Detecting Method for Non-Uniform Distribution of the Toner)

The description will be made as to a detecting method for a non-uniform distribution of the toner in the developing device in this embodiment.FIG. 7is a flow chart of the detecting sequence for the non-uniform distribution of the toner in this embodiment.

When the main switch is rendered on (S100) in the initial installation of the apparatus, the controller36starts the detecting sequence operation for the non-uniform distribution of the toner, without rotating the supplying roller24and the developing roller25(S101).

The reason for not rotating the supplying roller24and the developing roller25will be described. In this embodiment, the toner amounts contained in the supplying rollers24due to the vibrations are deduced on the basis of the electrostatic capacities. When the supplying roller24or the developing roller25are rotated, the toner contained in the supplying rollers24due to the vibrations or the like is supplied to the developing roller25, and therefore, the possibility that the non-uniform distribution is not detected increases. For this reason, in this embodiment, the supplying roller24and the developing roller25are kept unrotated.

Here, the measurement attitude is as shown by the position E inFIG. 1. In the position E ofFIG. 1, the toner neighborhood the supplying roller24falls by the gravity, and therefore, the influence of the toner density is less. Then, the output of the electrostatic capacity is stabilized.

Then, it is checked whether or not the difference ΔCvn (n=1-6) of the electrostatic capacities≦α (S104). The threshold a can be selected easily by experiment. Specific examples will be described.

FIG. 8shows the electrostatic capacity differences of the developing devices in this embodiment. InFIG. 8, the electrostatic capacity differences of the developing devices in the case that non-uniform distribution of the toner does not exist and in the case that the non-uniform distribution of the toner exist, in this embodiment. The condition of the threshold a in this embodiment will be described.

An upper limit of the threshold a can be determined as a difference between the electrostatic capacity when the urethane sponge layer is filled with the toner and that when the urethane sponge layer is free of the toner. In this embodiment, the difference is 2.9 pF (A inFIG. 8).

The lower limit of the threshold α is determined by a variation of the differences when the same amount of the toner is contained in the urethane sponge layer. The variation of the difference is 0.45 pF (B inFIG. 8) in this embodiment. With these conditions, the threshold α=2.0 in this embodiment. The value of the threshold α is not limited to this.

Referring back toFIG. 7, the detection of the non-uniform distribution of the toner will be described. When difference ΔCvn≦α, the discriminating means34discriminates the occurrence of the non-uniform distribution of the toner (S105), and the controller36executes a reduction sequence operation for the non-uniform distribution of the toner (S106).

In the reduction sequence for non-uniform distribution of the toner, the rotary drum50carrying the developing devices5is rotated for a predetermined time period. By doing so, the toner distribution in the developing device5can be made more uniform with respect to the longitudinal direction.

In addition, when difference ΔCvn≦α, the occurrence of the non-uniform distribution of the toner discriminated at (S105) may be notified to the user by notification means.

When difference ΔCvn>α, on the other hand, it is discriminated that the toner powder is in the normal state (S107), and the image can be formed through a normal sequential operation, and therefore, the apparatus is placed in the stand-by state (S108).

By carrying out the above-described said sequence process, the white void on one side of the image due to the non-uniform distribution of the toner in the initial installation of the apparatus can be avoided beforehand.

As described in the foregoing, the occurrence of the non-uniform distribution can be discriminated by the difference of the electrostatic capacity of the developing device5(5a,5b,5c,5d), by which the toner non-uniform distribution can be reduced at the time of initial installation with a simple and assured structure.

This application claims priority from Japanese Patent Application No. 124318/2011 filed Jun. 2, 2011 which is hereby incorporated by reference.