JP2007079480A - Image forming apparatus and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of enhancing operating ratio when an image is developed by stirring developer containing toner and a carrier by an auger in a developing unit and adhering the toner to an image carrier. <P>SOLUTION: In the image forming apparatus, a development control part 20 performs control for reducing rotation speed of the stirring auger 12b for a prescribed period while newly supplying toner by exhausting the toner in the developing unit 12 by a prescribed amount when prescribed conditions are satisfied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that develops an image by agitating a developer containing toner and a carrier with an auger in a developing device and attaching the toner to an image carrier, and a control method thereof.

  Some electrophotographic image forming apparatuses such as copying machines and printers perform development using a two-component developer containing toner and a carrier. In such an image forming apparatus, the toner and the carrier supplied from a toner cartridge or the like are mixed by stirring with an auger in a developing device to charge the toner. The developing device develops the image by attaching the charged toner conveyed by the carrier to an image bearing member such as a photosensitive drum that has been charged and exposed. The developed image is transferred from the image carrier to a recording medium such as paper and fixed, whereby the image forming apparatus forms an image on the recording medium.

  In such an image forming apparatus, for example, when all the image areas of the formed image formed on the image carrier are continuously formed with few actual image areas to which the toner is actually attached and developed, the unit time If the per-toner consumption is low, the time for the toner to stay in the developing unit becomes long. If the toner is continuously stirred in the developing device for a long time, a phenomenon that the charge amount of the toner abnormally increases or the toner becomes difficult to be charged occurs, and the charging performance of the toner deteriorates. As described above, when the charging performance of the toner deteriorates, fogging, image blurring, and the like may occur, and the image quality of the formed image may be lowered. Therefore, when the average value of the density of the actual image area with respect to all the image areas of the formed image within a predetermined time (image density average value) is equal to or less than a predetermined threshold, a predetermined amount of toner is forcibly discharged from the developing device. However, there is a technique for eliminating the deterioration of the charging performance of the toner by executing a maintenance operation for replacing the toner in the developing device by newly supplying substantially the same amount of toner (see Patent Document 1).

On the other hand, when the image forming apparatus continuously forms an image, the developer is pressed and solidified by continuing the rotation of the auger regardless of whether or not the toner is replaced. The developer in the developing device may not be uniform. If such a problem occurs, the image quality of the formed image may be deteriorated, and it may be impossible to correctly detect the toner density in the developing device. Therefore, in such a case, a maintenance operation is performed in which the rotation of the auger is switched to a low speed for a certain period of time so as to break down the pressed developer and eliminate lumps.
JP-A-11-295976

  However, both of the maintenance operations according to the above-described conventional technique are performed while stopping normal image formation control. That is, normal image formation cannot be performed while toner is replaced and the auger is rotated at a low speed to remove the developer debris. Therefore, execution of such a maintenance operation causes a reduction in the operating rate of the apparatus.

  Further, when the toner is replaced, the rotation of the auger is continued during that time, and the developer is likely to be damped. Further, when the auger is rotated at a low speed to eliminate the lumps, the toner stays in the developing unit during that time, and the charging performance of the toner tends to be deteriorated. That is, these two maintenance operations are in a relationship that increases the necessity for the other maintenance operation.

  The present invention has been made in view of the above circumstances, and one of its purposes is to stir a developer containing toner and a carrier with an auger in a developing device, and to attach the toner to an image carrier. An object of the present invention is to provide an image forming apparatus capable of improving the operating rate when developing an image and a control method thereof.

  In order to solve the above problems, an image forming apparatus according to the present invention develops an image by agitating a developer containing at least a toner and a carrier with an auger in a developing device and attaching the toner to an image carrier. An image forming apparatus for performing control for reducing a rotation time of the auger for a predetermined time while discharging a predetermined amount of toner in the developing unit and supplying new toner when a predetermined condition is satisfied It is characterized by performing.

  Accordingly, the image forming apparatus according to the present invention can shorten the time during which image formation cannot be performed and improve the operation rate by executing two maintenance operations together.

  Further, in the image forming apparatus, the predetermined condition is that an average density of real image regions developed by attaching toner to all image regions of a formed image formed on the image carrier within a predetermined time. The image density average value, which is a value, is not more than a predetermined first threshold value, and the average rotational speed of the auger within a predetermined time is not less than a predetermined threshold value, and the image density average value is When it is equal to or less than a second threshold value different from the first threshold value, the auger rotational speed is kept as it is, and a control is performed to discharge a predetermined amount of toner in the developing device and supply new toner. It is good.

  As a result, the image forming apparatus according to the present invention performs the maintenance operation for replacing the toner alone or in combination with the maintenance operation for reducing the rotation speed of the auger according to the operation state of the apparatus. It is possible to suppress unnecessary maintenance operations.

  Further, in the image forming apparatus, the predetermined condition is that an average density of real image regions developed by attaching toner to all image regions of a formed image formed on the image carrier within a predetermined time. The image density average value, which is a value, is not more than a predetermined threshold, and the average rotation speed of the auger within a predetermined time is not less than a predetermined first threshold, and the average rotation speed is When it is equal to or higher than a second threshold value different from the first threshold value, control for reducing the rotation speed of the auger for a predetermined time without discharging the toner in the developing device may be performed.

  As a result, the image forming apparatus according to the present invention may execute a maintenance operation for reducing the rotation speed of the auger alone or in conjunction with a maintenance operation for replacing toner depending on the operation state of the apparatus. It is possible to suppress unnecessary maintenance operations.

  In the image forming apparatus control method according to the present invention, an image is developed by agitating a developer containing at least a toner and a carrier with an auger in a developing device and attaching the toner to an image carrier. A method of controlling a forming apparatus, wherein when a predetermined condition is satisfied, the rotation speed of the auger is reduced for a predetermined time while discharging a predetermined amount of toner in the developing unit and newly supplying the toner. It is characterized by that.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus according to the embodiment of the present invention includes an image carrier 11, a developing device 12, a transfer unit 13, a fixing device 14, and a development control unit 20.

  The image carrier 11 is, for example, a photosensitive drum and is uniformly charged by a charger (not shown), and carries an electrostatic latent image formed by laser light irradiation or the like on the surface.

  The developing device 12 develops the electrostatic latent image by attaching toner supplied from a toner cartridge T installed in the image forming apparatus to the image carrier 11.

  Specifically, for example, the developing device 12 includes a dispense auger 12a, a stirring auger 12b, and a developing roll 12c. The dispense auger 12 a conveys the toner and carrier supplied from the toner cartridge T into the developing device 12. The stirring auger 12b stirs and charges the toner and the carrier conveyed into the developing device 12 by the dispensing auger 12a by rotation. The developing roll 12 c adheres the charged toner to the image carrier 11. Through these series of operations, the developing device 12 develops the electrostatic latent image on the image carrier 11 to form a toner image.

  Although FIG. 1 shows a case where there is one developing device, the image forming apparatus according to the present embodiment may include a plurality of developing devices. For example, an image forming apparatus that forms a color image using toners of four colors of cyan, magenta, yellow, and black includes a developing device for each color. In this case, development device control by the development control unit 20 described later is performed for each development device.

  The transfer unit 13 includes a transfer roller and the like, and transfers the toner image formed on the image carrier 11 by the developing device 12 to a recording medium such as paper. The transfer unit 13 may include an intermediate transfer member such as a transfer belt. In this case, the toner image formed on the image carrier 11 is first transferred to the intermediate transfer member, and then transferred from the intermediate transfer member to the recording medium.

  The fixing device 14 includes a fixing roller and fixes the toner image transferred by heat, pressure, or the like on the recording medium. Thereby, the image forming apparatus according to the present embodiment forms an image on the recording medium.

  The development control unit 20 includes, for example, a CPU and the like, and controls the operation of each unit in the developing device 12. In particular, in the present embodiment, the development control unit 20 causes the developing device 12 to perform various maintenance operations based on predetermined conditions, for example, every time an image is formed. Hereinafter, the processing executed by the development control unit 20 will be described based on the flowchart of FIG.

  The development control unit 20 first acquires an image density average value D, which is an average value of the density of the actual image area with respect to all the image areas of the formed image within a predetermined time (S1). Specifically, for example, a capacitor (not shown) stores a current due to a signal when the image carrier 11 is irradiated with laser light as an electric charge. Then, the development control unit 20 calculates the density of the actual image area corresponding to the latent image formed on the image carrier 11 by detecting a signal when the electric charge stored in the capacitor is discharged.

  On the other hand, the development control unit 20 can acquire the operation time of the developing device 12 by, for example, counting the rotation driving time of the developing roll 12c. The image density average value D is a value obtained by calculating the above-described average value of the image density within a predetermined time in the operation time. Note that the development control unit 20 may obtain an average image density value as a value representing a moving average by calculating and averaging the image density every time an image is formed.

  Next, the development control unit 20 acquires the average rotation speed V of the stirring auger 12b within a predetermined time (S2). Specifically, the average rotation speed V is a value obtained by calculating an average value of the rotation speeds of the stirring auger 12b within a predetermined time in the operation time of the developing device 12. The development controller 20 may acquire the average rotation speed as a value representing the moving average by acquiring the latest rotation speed value every time an image is formed and calculating the average value.

  Subsequently, the development control unit 20 determines whether the image density average value D acquired by the process of S1 and the average rotation speed V acquired by the process of S2 satisfy a predetermined condition. Specifically, it is determined whether or not a condition that the image density average value D is equal to or less than a predetermined threshold value D1 and the average rotation speed V is equal to or greater than the predetermined threshold value V1 is satisfied (S3). When this condition is satisfied, there is a possibility that the charging performance of the toner has deteriorated to some extent, and that the developer in the developing device 12 has been damaged. In this case, the development control unit 20 temporarily stops the control to form an image, performs a maintenance operation for replacing the toner in the developing device 12, and rotates the stirring auger 12b at a low speed for a predetermined time, thereby supplying the developer. A maintenance operation for eliminating the lumps is executed (S4).

  Specifically, the development control unit 20 executes a maintenance operation for replacing toner as follows, for example. That is, a toner replacement patch image is formed on the image carrier 11 in the same manner as in a normal image forming process. The formed patch image is removed from the image carrier 11 by a cleaning unit (not shown) without being transferred to the recording medium. In this way, the development control unit 20 discharges the toner in the developing device 12. On the other hand, for example, substantially the same amount of toner determined based on the amount of discharged toner is supplied from the toner cartridge T into the developing device 12. Through the above process, the toner in the developing device 12 is replaced with a new one, and the deterioration of the charging performance of the toner is eliminated. For example, the toner may be discharged by another toner discharge mechanism. Further, the supply amount for supplying the toner into the developing device 12 may be determined, for example, by measuring the toner density in the developing device 12.

  In addition to the maintenance operation for replacing the toner, the development control unit 20 executes a maintenance operation for reducing the rotation speed of the stirring auger 12b. As a result, due to vibration, the developer's own weight, etc., the developer that has become lumpy collapses and becomes uniform.

  On the other hand, when the image density average value D is equal to or smaller than the predetermined threshold value D1 and the average rotational speed V is equal to or larger than the predetermined threshold value V1 in the process of S3, the development control unit 20 further determines the image. It is determined whether the density average value D is equal to or less than a predetermined threshold value D2 (S5). In the case of D ≦ D2, the development control unit 20 causes the maintenance operation to replace the toner in the developing device 12 to be executed independently (S6).

  Further, when D> D2 in the process of S5, the development control unit 20 determines whether or not the average rotation speed V is equal to or higher than a predetermined threshold value V2 (S7). When V ≧ V2, the development control unit 20 executes a maintenance operation for reducing the rotation speed of the stirring auger 12b for a predetermined time (S8).

  On the other hand, when none of the determination conditions of S3, S5, and S7 is satisfied, the development control unit 20 determines not to perform any maintenance operation, and ends the process.

  Here, the threshold values D1 and V1 used for the determination in the process of S3 may be different from the threshold values D2 and V2 for determining that each maintenance operation is executed alone. As a result, the respective threshold conditions when deciding to execute two maintenance operations are set relatively gently with respect to the threshold conditions when deciding to execute each maintenance operation independently. can do. Specifically, here, the threshold value D2 satisfies D2 <D1, and the threshold value V2 satisfies V2> V1.

  When each maintenance operation is executed independently, the determination conditions for executing each maintenance operation are usually set to be relatively strict so as not to reduce the operating rate of the apparatus as much as possible. However, since the two maintenance operations are executed together in the present embodiment, the operating rate of the apparatus is not reduced even if the respective determination conditions in this case are set relatively gently. As a result, the image forming apparatus according to the present exemplary embodiment does not decrease the operating rate of the apparatus, and before the problems such as deterioration of the charging performance of the toner and the developer becoming obsolete occur. Maintenance operations can be executed.

  Note that these threshold values D1, V1, D2, and V2 may be changed based on user designation. For example, the threshold is determined based on the user's designation as to whether to prioritize image quality or image formation productivity. Thus, for example, when the user wants to prioritize the image quality, the threshold is determined so that the maintenance operation is executed relatively frequently, and when the user wants to prioritize the productivity of image formation, the execution of the maintenance operation is minimized. The threshold value can be determined so as to be limited.

  Further, when the image forming apparatus according to the present embodiment includes a plurality of developing devices corresponding to a plurality of component colors, these threshold values D1, V1, D2, and V2 are set to the same value for each developing device. Or different values. This makes it possible to vary the frequency of maintenance operations of the developing devices according to, for example, the amount of toner consumed.

  According to the present embodiment described above, by executing the two maintenance operations together, it is possible to reduce the time during which image formation cannot be performed for performing the maintenance operation, and to improve the operation rate.

  In the above description, the average image density value is calculated based on the current based on the signal when the image carrier 11 is irradiated with laser light. However, the average image density value is calculated by other methods. It is good as well. For example, the average image density value can be calculated based on the number of pixels of each component color included in the image data to be formed input to the image forming apparatus.

  Further, instead of the average image density value, it may be determined whether or not to perform the maintenance operation based on a value representing the toner consumption amount at the time of other image formation. Similarly, instead of the average rotation speed of the stirring auger 12b, it may be determined whether or not to perform the maintenance operation based on other values such as a continuous operation time at the normal speed of the stirring auger.

  For example, when the developing device in the image forming apparatus according to the present embodiment includes a plurality of stirring augers, the average rotation speed may be an average value of the rotation speeds of all of the plurality of stirring augers, Of these stirring augers, the average value of the rotational speeds of a predetermined predetermined stirring auger may be used.

1 is a schematic diagram illustrating a partial configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 5 is a flowchart showing an example of a control flow in the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Image carrier, 12 Developer, 12a Dispense auger, 12b Agitation auger, 12c Developing roll, 13 Transfer part, 14 Fixing unit, 20 Development control part

Claims (4)

An image forming apparatus that develops an image by agitating a developer containing at least a toner and a carrier with an auger in a developing device and attaching the toner to an image carrier,
When predetermined conditions are satisfied, control is performed to reduce the rotation speed of the auger for a predetermined time while discharging a predetermined amount of toner in the developing unit and supplying new toner. Forming equipment. The image forming apparatus according to claim 1.
The predetermined condition is that an image density average value, which is an average value of the density of an actual image area developed by attaching toner to the entire image area of the formed image formed on the image carrier within a predetermined time, is determined. The average rotation speed of the auger within a predetermined time is not less than a predetermined first threshold and not less than a predetermined threshold,
When the average image density value is equal to or lower than a second threshold value different from the first threshold value, the toner in the developing device is discharged by a predetermined amount without changing the rotation speed of the auger, and a new toner is obtained. An image forming apparatus that performs control to supply the image. The image forming apparatus according to claim 1.
The predetermined condition is that an image density average value, which is an average value of the density of an actual image area developed by attaching toner to the entire image area of the formed image formed on the image carrier within a predetermined time, is determined. The average rotational speed of the auger within a predetermined time is not less than a predetermined first threshold,
When the average rotation speed is equal to or higher than a second threshold value different from the first threshold value, control is performed to reduce the rotation speed of the auger for a predetermined time without discharging the toner in the developing device. An image forming apparatus. A control method for an image forming apparatus that develops an image by stirring a developer including at least a toner and a carrier with an auger in a developing device and attaching the toner to an image carrier,
An image forming method, wherein when a predetermined condition is satisfied, the rotation speed of the auger is reduced for a predetermined time while discharging a predetermined amount of toner in the developing device and supplying new toner.

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