JP4770221B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus having a plurality of developing units for storing toner and an image forming method thereof.

  In electrophotographic image forming apparatuses that use toner to form images, such as printers, copiers, and facsimile machines, it has been proposed to use a plurality of developing units that store toner of the same color. Yes. For example, the image recording apparatus described in Patent Document 1 (corresponding to the “image forming apparatus” in the present specification) is an image recording apparatus in which a plurality of developing devices can be mounted, and the developing devices having different toner colors are mounted. In addition to being usable as a color printer, it can be used as a single-color printer by mounting a developing device of the same toner color.

  In this image recording apparatus, a developing device mounted in a predetermined position is preferentially used. However, when the remaining amount of toner in the developing device is reduced to a predetermined value, the developing device is switched to another developing device. In another aspect of the image recording apparatus, when there are a plurality of usable developing devices, the one having the oldest mounting time is preferentially used.

Japanese Patent Laying-Open No. 2003-316106 (FIG. 4)

  In the above-described conventional image forming apparatus, the order of use is automatically determined by the mounting position on the apparatus regardless of the state of each developing device. Such a mode of use is not necessarily suitable for forming an image with good image quality and efficiency. For example, even when the remaining toner amount of one developing device decreases to a predetermined value and the timing for switching the developing device comes, depending on the position of the developing device to be used next, it takes a long time to switch and image formation Throughput may be reduced. Further, depending on the state of the developing device after switching, there may be a case where good image quality cannot be maintained. However, in such an image forming apparatus, the criteria for selecting a developing device used for an image forming operation have not been sufficiently studied so far.

  The present invention has been made in view of the above problems, and an object of the present invention is to stably and efficiently form an image with good image quality in an image forming apparatus having a plurality of developing devices and an image forming method thereof.

In order to achieve the above object, the image forming apparatus according to the present invention is configured to be capable of mounting N (N is an integer of 3 or more) developing devices that store toner, and is capable of developing around a predetermined rotation axis. The rotary and the developing rotary are rotated to selectively position the developing device mounted on the developing rotary at a predetermined developing position, and an image forming operation for forming an image with the toner stored in the developing device is executed. Control means, and the control means includes M (M is an integer less than or equal to 2 and less than N) developing devices that store toner of the same color and can form an image with a desired image quality. When mounted next to each other on the developing rotary, the developing unit located on the most downstream side in the rotation direction of the developing rotary among the developing units is first positioned at the developing position and the image Toward the developing device in the most upstream side from the developing device starts the formation operation, executes the image forming operation while switching the developing unit adjacent in order, moreover, continuously using one of the developing device When the number of images formed in a predetermined number has reached a predetermined number and there is an image to be formed next, the developing device located adjacent to the upstream side of the developing device in the rotational direction of the developing rotary is moved to the developing position. Then, the developing device is switched, and the next image is formed using the developing device moved to the developing position by the switching .

The image forming method according to the present invention is configured to be capable of mounting N (N is an integer greater than or equal to 3) developing devices for storing toner, and an image forming method including a developing rotary that is rotatable about a predetermined rotation axis. In the image forming method in the apparatus, in order to achieve the above object, the toners of the same color that are mounted next to each other on the developing rotary are stored and can be formed with an intended image quality. Among the number of developing devices (M is an integer of 2 or more and less than N), the developing device located on the most downstream side in the rotation direction of the developing rotary is first positioned at a predetermined developing position, and the most upstream side from the developing device. A step of sequentially switching adjacent developing units toward the developing unit located in the image forming unit, and each time one developing unit is positioned at the developing position, the toner is stored in the developing unit. And an image forming step of forming one of the number of continuously formed image using the developing device reaches a predetermined number, and when there is an image to be formed next is the in the rotation direction of the developing rotary The developing device is switched by moving the developing device adjacent to the upstream side of the developing device to the developing position, and the image forming process is executed using the developing device moved to the developing position by the switching, and the next It is characterized by forming an image .

According to these aspects of the invention, the developing unit to be used first is disposed adjacently located image formation ready at the desired image quality (hereinafter, simply referred to as "Available") the same color to each other This is the most downstream of the M developing units storing the toner . From the viewpoint of this developing device, there can be a developing device that can be used at a position adjacent to the upstream side in the rotation direction of the developing rotary. Therefore, the rotation amount of the developing rotary necessary for switching from the developing device in use to the next usable developing device can be minimized, and a decrease in throughput due to switching can be suppressed. In addition, each developing device can be used effectively by switching the developing devices from the most downstream side to the most upstream side in order. As a result, according to the present invention, an image with good image quality can be formed stably and efficiently.

The present invention, each of the developing devices is achieved a particularly remarkable effect Oite the equipment is obtained by storing the toner of the same color to each other. This is because such an apparatus can continuously form a larger number of images while maintaining a predetermined image quality by using the developing device while switching.

  Switching of the developing device can be performed as follows, for example. That is, when the number of images continuously formed using one developing device reaches a predetermined number and there is an image to be formed next, an upstream adjacent position of the developing device in the rotation direction of the developing rotary The developing device is moved to the developing position to switch the developing device, and the next image is formed using the developing device moved to the developing position by the switching. When the number of formed images reaches a predetermined number, the developing device is switched, and a new image is formed using a new developing device, so that the image quality can be maintained satisfactorily. Further, the amount of movement in the rotation direction of the developing rotary can be minimized by switching to the upstream adjacent position developing device.

  It should be noted that when there is no developing device in the upstream adjacent position in the rotation direction of the developing rotary as viewed from the developing device used for the image forming operation, and when viewed from the developing device used for the image forming operation, It is desirable not to switch the developing device when the developing device in the upstream adjacent position in the rotation direction is not usable. Thereby, the fluctuation | variation of image quality can be suppressed. Even if there is a developing device that can be used at a position different from the above position, it takes a long time to switch to the developing device. Therefore, in such a case, it is desirable to continue using the developing device that has been used until then without switching. If one developer is continuously used, the image quality gradually deteriorates. However, since such image quality deterioration gradually proceeds, the image quality does not change abruptly.

Here, as to whether or not each developing device can be used, for example, information regarding the usage history of the developing device that changes with the use of each developing device is updated and stored, and the information is set to a predetermined threshold value. Judgment can be made based on whether or not it has been reached . As such information, for example, the remaining amount of toner of the developing device, the rest time after the use in the previous image forming operation is completed, and the like can be used. If the remaining amount of toner is reduced, there is a high possibility that an image defect such as that a desired image density cannot be obtained or blur occurs. On the other hand, a developing device having a sufficient remaining amount of toner has a low probability of occurrence of such an image defect and can be suitably used for an image forming operation. Further, in a developing device having a long rest time, there is a risk of density unevenness due to being left for a long time, but in a developing device having a short rest time, there is no concern.

  FIG. 1 is a view showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. As will be described later, the apparatus 1 is an image forming apparatus in which four developing devices are mounted to form an image. In a state where developing devices storing different color toners are attached, a full color image using these developing devices and a monochrome image using one of these developing devices can be formed. Further, in a state where a developing device that stores toner of the same color is mounted, it functions as an image forming apparatus dedicated to monochrome images of the toner color. In the following, an embodiment in which the present invention is applied to an image forming apparatus dedicated to monochrome images and equipped with four developing units each storing black toner will be described.

  In this image forming apparatus 1, when an image forming command is given to the main controller 11 from an external device such as a host computer, the engine controller 10 controls each part of the engine unit EG in accordance with the command from the main controller 11. An image forming operation is executed, and a monochrome image corresponding to an image signal given from an external device is formed on the sheet S.

  In the engine unit EG, the photosensitive member 22 is provided to be rotatable in the arrow direction D1 in FIG. A charging unit 23, a rotary developing unit 4 and a cleaning unit 25 are arranged around the photosensitive member 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes the toner remaining on the surface of the photosensitive member 22 after the primary transfer, and collects it in a waste toner tank provided inside. The photosensitive member 22, the charging unit 23, and the cleaning unit 25 integrally constitute the photosensitive member cartridge 2, and this photosensitive member cartridge 2 is detachably attached to the main body of the apparatus 1 as a whole.

  Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 22 charged by the charging unit 23. The exposure unit 6 exposes the light beam L onto the photosensitive member 22 in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4. The developing unit 4 is configured as a support frame 40 that is rotatably provided around a rotation axis that is orthogonal to the paper surface of FIG. To 4Kd, and a rotary drive (not shown) for rotating them integrally. The developing unit 4 is controlled by the engine controller 10. Based on the control command from the engine controller 10, the developing unit 4 is rotationally driven in the direction D4 in FIG. 1, and the developing cartridges 4Ka to 4Kd are selectively brought into contact with the photosensitive member 22 or have a predetermined value. When positioned at a predetermined developing position facing each other with a gap, toner is applied to the surface of the photosensitive member 22 from the developing roller 44 provided in the developing cartridge. As a result, the electrostatic latent image on the photosensitive member 22 is developed with the toner in the developing cartridge positioned at the developing position.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 that is stretched over a plurality of rollers 72 to 75, and a drive unit that rotates the roller 73 to rotate the intermediate transfer belt 71 in a predetermined rotation direction D2. Yes. Then, the transfer unit 7 transfers the black toner image formed on the photosensitive member 22 onto the intermediate transfer belt 71 and is taken out one by one from the cassette 8 to the secondary transfer region TR2 along the transport path F. Secondary transfer is performed on the conveyed sheet S.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing of feeding the sheet S to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. S is sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet S on which the monochrome image is thus formed is conveyed to the discharge tray portion 89 provided on the upper surface portion of the apparatus main body via the fixing unit 9, the pre-discharge roller 82 and the discharge roller 83. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reversal position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is conveyed in the direction of the arrow D3 along the reverse conveyance path FR. Then, the sheet is again placed on the transport path F before the gate roller 81. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 71 in the secondary transfer region TR2 is first transferred. It is the opposite surface. In this way, images can be formed on both sides of the sheet S.

  A cleaner 76 is disposed in the vicinity of the roller 75. The cleaner 76 can be moved toward and away from the roller 75 by an electromagnetic clutch (not shown). Then, the blade of the cleaner 76 abuts on the surface of the intermediate transfer belt 71 that is stretched over the roller 75 while moving to the roller 75 side, and the toner that remains on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Remove.

  A density sensor 60 is disposed in the vicinity of the roller 75. The density sensor 60 is provided to face the surface of the intermediate transfer belt 71 and measures the image density of the toner image formed on the outer peripheral surface of the intermediate transfer belt 71 as necessary. Based on the measurement result, this apparatus adjusts the operating conditions of each part of the apparatus that affects the image quality, for example, the developing bias applied to each developing cartridge, the intensity of the light beam L, and the like.

  The density sensor 60 is configured to output a signal corresponding to the image density of a region of a predetermined area on the intermediate transfer belt 71 using, for example, a reflection type photosensor. The CPU 101 can detect the image density of each part of the toner image on the intermediate transfer belt 71 by periodically sampling the output signal from the density sensor 60 while rotating the intermediate transfer belt 71.

  Further, as shown in FIG. 2, each of the developing cartridges 4Ka to 4Kd is provided with memories 91 to 94 for storing data relating to the manufacturing lot and usage history of the developing cartridge, the remaining amount of the built-in toner, and the like. Further, each of the developing cartridges 4Ka to 4Kd is provided with wireless communication devices 49Ka, 49Kb, 49Kc, and 49Kd. Then, if necessary, these selectively communicate with the wireless communication device 109 provided on the main body side in a non-contact manner, and data is transmitted between the CPU 101 and each of the memories 91 to 94 via the interface 105. Various information such as consumable management for the developing cartridge is managed by sending and receiving. In this embodiment, non-contact data transmission / reception is performed using electromagnetic means such as wireless communication. However, a connector is provided on the main body side and each developing cartridge side, and the connector is mechanically fitted. By doing so, you may make it mutually transmit / receive data.

  In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112, and reference numeral 117 denotes a calculation result in the CPU 111 and other information. It is a RAM that temporarily stores data. Reference numeral 106 is a ROM for storing a calculation program executed by the CPU 101, control data for controlling the engine unit EG, and the like. Reference numeral 107 is a RAM for temporarily storing calculation results in the CPU 101 and other data. is there.

  Each developing device is used in order along the rotation direction D4 of the rotary developing unit 4, and is switched to a developing device located upstream one of the currently used developing devices as necessary. Shall. By doing so, the developing device can be switched in the image forming operation only by rotating the rotary developing unit 4 by 90 degrees in the rotation direction. However, which developing unit is to be used first is determined in advance. Here, the developing device 4Ka is used first, but is not limited to this.

  FIG. 3 is a diagram showing a stop position of the rotary developing unit. As shown in FIG. 3, the rotary developing unit 4 can be positioned and stopped at (a) the home position and (b) the image forming position. FIG. 3B shows an example of the image forming positions. Actually, there are four image forming positions corresponding to each of the four developing devices and having angles different from each other by 90 degrees. To do. Among these, the home position is a standby position of the rotary developing unit 4 when no image signal is given to the apparatus. At this home position, as shown in FIG. 3A, the developing rollers 44a, 44b, 44c and 44d provided in the developing units are all separated from the photosensitive member 22.

  In the state where the rotary developing unit 4 is stopped at the image forming position, the developing roller 44a provided in one of the developing devices (the developing device 4Ka in the example of FIG. 3B) is connected to the photosensitive member 22. Opposed. In this state, the electrostatic latent image formed on the surface of the photoconductor 22 can be visualized with toner stored in the developing device 4Ka (image forming operation). That is, the position of the developing device 4Ka in FIG. 3B corresponds to the “developing position” in the present invention.

  On the other hand, in the developing device 4Kd at a position downstream of the developing device 4Ka in the rotation direction of the rotary developing unit 4 (hereinafter referred to as “access position”), a wireless communication device 49d provided in the developing device 4Kd includes The main body side wireless communication device 109 is disposed opposite to the main body side wireless communication device 109. For this reason, the memory provided in the developing device 4Kd can be accessed by wireless communication from the CPU 101. In this state, information on the usage status of the developing device stored in the memory is updated (update operation).

  As described above, the developing position and the access position are arranged so that the other developing device is positioned at the access position in a state where the developing device mounted on the rotary developing unit 4 is positioned at the developing position. As a result, while the image forming operation is executed on the one hand, the memory updating operation can be executed on the other hand, and the processing time can be shortened.

  Next, the rank classification of the developing devices in this embodiment will be described in detail. In this embodiment, the life rank of the developing device is determined based on the remaining amount of toner in each developing device and the total rotation time of the developing roller 44 provided in the developing device, and according to the life rank of each developing device. The mode of the image forming operation is changed. This is because the deterioration of the developing device progresses as the developing device is used, and the image quality when the image is formed using the developing device gradually changes.

  FIG. 4 is a diagram showing rank classification of the developing devices. The deterioration of image quality due to the life of the developing device is caused not only when the remaining amount of toner decreases, but also due to the deterioration of the characteristics of the remaining toner. In other words, good image quality cannot be obtained if the remaining amount of toner is small, and even if a sufficient amount of toner remains in the developing device, good image quality will not be obtained if the toner is deteriorated. I can't get it. The total rotation time of the developing roller is a value indicating the degree of deterioration of the toner. When the value reaches a predetermined value (for example, 10,000 seconds), even if the remaining amount of toner is sufficient, The toner is likely to be deteriorated, and it can be said that the developing device is not suitable for use.

  In this embodiment, as shown in FIG. 4, when the remaining amount of toner is 5% or more of the initial amount and the developing roller rotation time is less than 70% of the predetermined value, the developing device is ranked 1. When image formation is performed using a rank 1 developer, the remaining amount of toner is sufficient and the degree of deterioration is slight, so that the necessary and sufficient image density does not occur due to insufficient density or blurring. It is expected to be obtained. On the other hand, when the remaining amount of toner is less than 1% of the initial amount or when the developing roller rotation time exceeds the predetermined value, the developing device is ranked 3. Rank 3 developers are no longer suitable for use in image forming operations. Further, in the middle of both ranks, that is, the toner remaining amount is 1% or more and less than 5% of the initial amount, and the developing roller rotation time is less than the predetermined value, or the toner remaining amount is 1% or more of the initial amount. When the developing roller rotation time is 70% or more and less than 100% of the predetermined value, the developing device is ranked 2. When image formation is performed using a rank 2 developing device, although image formation is possible, image defects such as insufficient density and blurring may occur. That is, rank 2 is a state in which an image can be formed, but the image quality may be deteriorated in some way. It should be noted that the rank to which each developing device belongs is preferably displayed on a display display (not shown) as needed.

In this way, the life rank of the developing device is ranked into three ranks: rank 1 that can form an image with a predetermined quality, rank 3 that is not suitable for use, and rank 2 that is positioned between them. The state of the device can be divided into three stages:
(I) A state where at least one developing device of rank 1 is mounted. In this state, a rank 1 developer can be used to form an image with the desired image quality;
(Ii) A state in which there is no rank 1 developer and at least one rank 2 developer is installed. In this state, it is possible to form an image using a rank 2 developer, but the desired image quality may not be obtained;
(Iii) A state in which only a rank 3 developer is mounted. In this state, the expected image quality can no longer be expected.

  Further, even in a rank 1 or 2 developing device, if the unused state continues for a long time, a phenomenon in which periodic density unevenness occurs in an image in an initial stage of image formation performed thereafter (in this specification, This phenomenon is sometimes referred to as “banding phenomenon”. Such density unevenness is caused by the fact that the toner is left on the developing roller, and the developing roller provided in the developing device is used before the image forming operation. It can be solved by rotating a predetermined amount. Therefore, in this embodiment, an operation of rotating a developing device provided in each developing device by a predetermined amount (this operation is referred to as “stirring operation” in this specification) is performed as necessary. Yes. More specifically, for each developing device, a pause time from the end of use in the last executed image forming operation and preparation operation to the present is measured, and the pause time is predetermined. When the value is reached, a flag indicating that a stirring operation is required for the developing device is set. The pause time can be defined as, for example, the elapsed time from when the rotation of the developing roller 44 provided in the developing device is stopped to the present time. For the developing device in which this flag is set, the stirring operation is executed at the timing described later, and the occurrence of the neglected banding phenomenon is suppressed. When the stirring operation is executed, the flag is reset.

  Furthermore, as the developing device is used, its deterioration progresses and the image density fluctuates. Therefore, it may be necessary to change the operating conditions of each part of the apparatus when the image forming operation is performed using the developing device. Therefore, in this embodiment, when the information indicating the life of the developing device described above, that is, when either the remaining toner amount or the developing roller rotation time reaches a predetermined threshold, the operating conditions of the developing device are readjusted. A flag indicating that an operation (density control operation) for controlling the image density to a predetermined density is necessary is set. For the developing device in which this flag is set, the density control operation is executed at a timing described later. As a result, fluctuations in image density are suppressed. When the density control operation is executed, the flag is reset.

  There is not only one threshold value for the remaining toner amount and the developing roller rotation time that triggers the execution of the density control operation. That is, when the remaining amount of toner and the developing roller rotation time reach a certain threshold value and the density control operation is performed, the next threshold value is newly set. When the remaining amount of toner or the developing roller rotation time reaches the new threshold value, the density control operation is executed again. In this way, by repeatedly performing the density control operation a plurality of times while one developing device is attached to the apparatus and has reached the end of its life, it is possible to change the characteristics of the developing device over time. Correspondingly, the image quality can be maintained stably.

  Further, information indicating the state of the developing device, such as the remaining amount of toner and the developing roller rotation time, is stored in a storage unit provided in the developing device (for example, a non-volatile memory 91 provided in the developing device 4Ka). In addition, the CPU 101 can be configured to read / write the information as necessary. By doing so, information about each developing device is attached to the developing device itself, and when the developing device is once removed and remounted, or a developing device used in another apparatus is mounted. Even in this case, the state of each developing device can be appropriately managed.

  In this specification, in order to make a developing device usable for image formation, processing operations performed on the developing device prior to use for image forming operation are collectively referred to as “preparation operation”. And The stirring operation and concentration control operation described here are both included in the “preparation operation”.

  FIG. 5 is a flowchart showing an image forming operation in this embodiment. In this apparatus, an image forming operation starts when an image forming command is given from an external apparatus (step S101). In this image forming operation, first, it is determined whether or not a usable developing device is attached to the developing unit 4 (step S102). Here, the “usable” developing device is a developing device that has a life rank of 1 and does not require a preparatory operation before the image forming operation is performed. In a state where such a developing device is mounted, an image corresponding to the image formation command can be formed with a desired quality and without delay.

  If there is at least one developing device that can be used, it is confirmed where the developing device is located on the developing unit 4 (step S103). If two or more usable developing devices are arranged adjacent to each other, the developing device located on the most downstream side in the rotation direction D4 of the developing unit 4 is moved and positioned to the developing position (step S104). . Subsequently, an image for one page is formed using the developing device (step S105).

  If the formation of all the images to be formed is completed, that is, if only one image is to be formed (step S106), the developing unit 4 is returned to the home position and the image forming operation is completed (step S106). S116). On the other hand, if there is an image to be formed next, the image is continuously formed. Prior to that, whether the number of images continuously formed by the developing device currently used has reached a predetermined number. It is determined whether or not (step S107). If the predetermined number (here, 8) has not been reached, the process returns to step S105 to form the next image. When the predetermined number has been reached, it is determined whether there is a next developing device that can be switched and used (step S108). If there is a next developing device, the rotary developing unit 4 is rotated 90 degrees to develop. While the next developer is positioned at the development position (step S109), if there is no next developer, the developer is not switched, and all the remaining images to be formed are in use. (Step S115).

  The determination criteria in step S108 are as follows. When a developing device in the upstream adjacent position of the developing device currently in use in the rotation direction of the developing unit 4 is usable, the developing device can be used as the next developing device. The determination result in this case is “YES”. In all other cases, “NO” is set. For example, if the developing device currently in use is the developing device 4Ka and the developing device 4Kb in the upstream adjacent position can be used, the determination result in step S108 is “YES”. On the other hand, if the developing device 4Kb in the upstream adjacent position of the developing device 4Ka currently in use is not usable, the determination result in step S108 is, even if there is a developing device that can be used in another position. “NO”.

  If there is a usable developing device at a position adjacent to the upstream side of the developing device currently in use, the newly usable developing device can be moved to the developing position only by rotating the developing unit 4 by 90 degrees. Therefore, the developing device can be switched without reducing the image forming throughput. In addition, since the developing unit to be used next can have a life rank of 1 and can be used without performing a preparatory operation, the quality of the formed image can be maintained well.

  By switching the developing device in a series of image forming operations, the following effects can be obtained. If one developing device is continuously used, the ratio of old toner increases around the developing roller in the developing device, and the image quality gradually decreases. During this time, in other developing units, since the toner is left on the surface of the developing roller 44, the banding phenomenon tends to occur. On the other hand, when the developing unit 4 is rotated to switch the developing device, the toner in the developing device is agitated and uniformed, and the image quality can be maintained. In addition, by not biasing the developing devices to be used, it is possible to suppress the occurrence of the leaving banding phenomenon in each developing device.

  On the other hand, if the developing device in the upstream adjacent position of the developing device currently in use is not usable, the image quality greatly fluctuates before and after switching when the image is formed using the developing device. There is a possibility that. Even if the usable developing device is located at a position other than the position adjacent to the upstream side of the currently used developing device, the developing unit 4 needs to be rotated 180 degrees or more in order to switch to the developing device. Switching takes time and causes a reduction in throughput. Therefore, in these cases, the developing device is not switched and the currently used developing device is used continuously.

  The operation when there is no usable developer in step S102 is as follows. If none of the developing units mounted on the developing unit 4 is immediately usable, an alternative developing unit is searched for. That is, it is determined whether or not there is one that has a life rank 1 but requires a preparatory operation prior to the image forming operation (S110), and if necessary, the necessary preparatory operation is performed on the developing device (step S113). ), The developer is positioned at the development position to form the required number of images (steps S114 and S115).

  If there is no service life rank 1, search for service life rank 2. In this embodiment, the user can set in advance whether to allow or prohibit the image forming operation using the life rank 2 developing device. When a rank 2 developer is used, the quality of the formed image may be reduced. Prohibiting image formation in this state can prevent the image quality from deteriorating, but the toner in the developing device cannot be used up effectively. On the other hand, if image formation can be performed while allowing a slight deterioration in image quality, the toner can be used up effectively. Which is emphasized depends on the user, but if the user can select whether or not to use the rank 2 developing device, the apparatus can be properly used according to the user's preference.

  If the user has set to permit use of the rank 2 developer (step S111), if there is a rank 2 developer, the image forming operation is performed using the rank 2 developer (steps S112 to S115). In this case, since it is considered that the user has accepted the image quality degradation to some extent, it is not always necessary to perform the preparation operation prior to the image forming operation. On the other hand, if the user is set to prohibit the use of the rank 2 developing device and if there is no rank 2 developing device, the operation is terminated. That is, no image is formed in this case. In such a case, it is desirable to notify an error message that an image cannot be formed to the external device and the user who have given the image formation command to the device by some method.

  FIG. 6 is a diagram showing the transition of the developing unit when four developing devices can be used. When all four developing devices can be used, the concept of “the most downstream” and “the most upstream” in the rotation direction of the developing unit 4 does not exist in principle between the developing devices. In this case, the developing device 4Ka that is predetermined to be used first is handled as a developing device located on the “most downstream side” for convenience. That is, in the image forming operation in this case, the developing device 4Ka is first moved and positioned at the developing position (step S104 in FIG. 5). When a predetermined number of images are formed using the developing device 4Ka, the developing unit 4 rotates 90 degrees, and the next developing device 4Kb in the adjacent position upstream of the developing device 4Ka is newly set at the developing position. Positioning is performed (step S109). At this time, the information content of the memory 91 provided in the developing device 4Ka that has moved from the development position to the access position is updated. That is, the new toner remaining amount obtained by subtracting the amount of toner consumed by the image forming operation from the remaining toner amount stored in the memory 91 and the integrated value of the developing roller rotation time stored in the memory 91 Each new integrated value obtained by adding the developing roller rotation time in the image forming operation is written in the memory 91.

  Similarly, the developing device is switched every time the number of images formed by one developing device reaches a predetermined number, and when the required number of images has been formed, the developing unit 4 is returned to the home position (step S106). , S116). In FIG. 6, after the image formation by the developing device 4Kd and the memory update to the developing device, the developing unit 4 is returned to the home position. However, depending on the number of images to be formed, the developing device 4Ka is subsequently reconnected. In some cases, the operation is terminated without forming an image by using it or conversely using the developing device 4Kd.

  FIG. 7 is a diagram showing the transition of the developing unit when three developing devices can be used. When there are three developing devices that can be used in the developing unit 4 to which four developing devices can be mounted, the three developing devices are naturally arranged adjacent to each other. Here, a case where three developing devices 4Ka, 4Kc, and 4Kd can be used will be described, but the concept is the same in other combinations.

  In this case, the developing device 4Ka is used first in the original order, but in this embodiment, the developing device 4Kc located on the most downstream side in the rotation direction D4 of the developing unit 4 among the three developing devices. Will be used first. That is, the developing unit 4 at the home position is rotated 315 degrees to move the developing device 4Kc to the developing position (step S104 in FIG. 5). After the image formation by the developing device 4Kc is thus performed, the developing unit 4 is rotated by 90 degrees, and the developing devices are switched to the upstream side one by one (step S109). When the number of images formed using the most upstream developing device 4Ka reaches a predetermined number (step S107), there is no usable developing device upstream (step S108). For this reason, the developing device 4Ka currently in use is used for forming the remaining image (step S115).

  If the developing units are used in the original order, that is, in the same sequence as when four developing units are used, the switching of the developing unit 4Ka to the developing unit 4Kc requires the rotation of the developing unit 4 by 180 degrees. It becomes. Since such rotational movement takes time, the throughput of image formation is reduced. In contrast, in the present embodiment, the rotation amount of the developing unit 4 during image formation is always 90 degrees, and a high throughput can be obtained by minimizing the time required for switching. Moreover, each developing device in a usable state can be used effectively.

  FIG. 8 is a diagram showing the transition of the developing unit when two adjacent developing devices can be used. Here, it is assumed that the developing devices 4Ka and 4Kd can be used. In this case as well, the developing device 4Ka should be used first, but in this embodiment, the developing device 4Kd on the downstream side is used first. Therefore, even in this case, the rotation amount of the developing unit 4 during image formation is always 90 degrees.

  FIG. 9 is a diagram showing the transition of the developing unit when two developing devices at symmetrical positions are usable. Here, it is assumed that the developing devices 4Kb and 4Kd are in a usable state. In this case, there is no developer that can be used in the adjacent position upstream from any developer. Therefore, in this case, the developing device is not switched, and a necessary number of images are formed by using the first selected developing device. Whichever may be selected as the developing device to be used first, it is desirable to select the developing device that has not been used in the previous image forming operation. This is because each developer can be used more effectively by doing so. As described above, by using a developing device that has not been used in the previous image forming operation, two developing devices are used alternately. As a result, it is possible to avoid the occurrence of density unevenness (abandonment banding phenomenon) due to one developer being left for a long time, and to prevent the apparatus from falling into a situation requiring a preparatory operation. The Therefore, the apparatus can be maintained in a state where an image can be formed with a good image quality for a longer period of time. As a result, in this embodiment, an image can be formed without delay in response to the image formation command, and good image quality can be obtained.

  As described above, in this embodiment, when there are two or three developing devices mounted adjacent to each other on the developing unit 4, the developing device located on the most downstream side in the rotation direction of the developing unit 4 among them. Is first used to perform an image forming operation. Then, whenever the number of formed images reaches a predetermined number, the required number of images is formed while switching to the developing unit located at the upstream adjacent position. Therefore, in this embodiment, it is possible to form a small number of images to a large number of images with good quality and stably. Further, each developing device can be used effectively from the developing device located on the most downstream side to the developing device located on the most upstream side.

  Further, since the developing devices are switched between adjacent developing devices during image formation, the developing devices can be switched in a short time, and an image can be formed with high throughput. Further, by not biasing the developing devices to be used, it is possible to suppress the occurrence of the neglected banding phenomenon, and it is possible to suppress the execution frequency of the preparation operation while obtaining stable image quality.

  As described above, this embodiment corresponds to the case where N = 4, M = 2, or 3 in the present invention. In this embodiment, the rotary developing unit 4 and the engine controller 10 function as “developing rotary” and “control means” of the present invention, respectively.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the above embodiment is an image forming apparatus dedicated to monochrome images equipped with four developing devices for storing black toner, but full-color image formation with developing devices for storing different color toners. Even in the case of an apparatus, an operation sequence based on the present invention can be employed when an image is formed using some of the developing devices.

  In the above embodiment, for each developing device, whether or not the developing device can be used is determined based on a combination of parameters of the remaining toner amount, the developing roller rotation time, and the rest time. However, the present invention is not limited to this. However, these parameters or other parameters indicating the usage history of the developing device may be used alone or in appropriate combination to determine whether or not the developing device can be used.

  In the above embodiment, the four developing cartridges 4Ka to 4Kd having the same shape are used. However, developing cartridges having different shapes may be used. In the above embodiment, the present invention is applied to a so-called rotary type image forming apparatus in which the rotary developing unit 4 is arranged for one photoconductor 22. The present invention can also be applied to an elevator type image forming apparatus in which a developing cartridge moves up and down and develops with each developing cartridge.

  Further, the present invention is not limited to the configuration of the above-described embodiment. For example, the present invention is also applied to an apparatus including a transfer medium (transfer drum, transfer sheet, etc.) other than the intermediate transfer belt, and also to other image forming apparatuses such as a copying machine and a facsimile machine. The invention can be applied.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. The figure which shows the stop position of a rotary image development unit. The figure which shows rank division of a developing device. 6 is a flowchart showing an image forming operation in this embodiment. FIG. 6 is a diagram illustrating a transition of a developing unit when four developing devices can be used. The figure which shows the transition of the image development unit when three developing devices can be used. FIG. 6 is a diagram illustrating a transition of a developing unit when two adjacent developing devices can be used. FIG. 4 is a diagram illustrating a transition of a developing unit when a developing device at a symmetrical position is usable.

Explanation of symbols

  4 ... Rotary developing unit (developing rotary), 4Ka, 4Kb, 4Kc, 4Kd ... Developing device, 10 ... Engine controller (control means), 22 ... Photoconductor, 44a, 44b, 44c, 44d ... Developing roller

Claims (7)

A developing rotary configured to be capable of mounting N (N is an integer of 3 or more) developer storing toner, and rotatable about a predetermined rotation axis;
Control means for rotating the developing rotary to selectively position a developing unit mounted on the developing rotary at a predetermined developing position and to form an image with toner stored in the developing unit; With
The control means stores M (M is an integer less than or equal to 2 and less than N) developing devices adjacent to each other on the developing rotary in a state where toner of the same color is stored and an image can be formed with a desired image quality. Of the developing devices, the developing device located on the most downstream side in the rotation direction of the developing rotary is first positioned at the developing position to start the image forming operation and from the developing device to the most. The image forming operation is executed while sequentially switching the adjacent developing devices toward the developing device on the upstream side , and
When the number of images continuously formed using one developing device reaches a predetermined number and there is an image to be formed next, it is in the upstream adjacent position of the developing device in the rotation direction of the developing rotary. An image forming apparatus characterized in that the developing device is switched by moving the developing device to the developing position, and the next image is formed using the developing device moved to the developing position by the switching. . When there is no developing device at the upstream adjacent position in the rotation direction of the developing rotary as viewed from the developing device used for the image forming operation, the control means does not perform the switching and continues the developing device in use. the image forming apparatus according to claim 1 to be used. When the developing unit at the upstream adjacent position in the rotation direction of the developing rotary is not in a state capable of forming an image with the desired image quality as viewed from the developing unit used for the image forming operation, The image forming apparatus according to claim 1 , wherein the developing device in use is continuously used without switching. Storage means for updating and storing information on the usage history of the developing device that changes with use of each of the developing devices;
The control unit determines whether or not the developing device is capable of forming an image with the desired image quality based on whether or not the information read from the storage unit has reached a predetermined threshold value. Item 4. The image forming apparatus according to any one of Items 1 to 3 . The image forming apparatus according to claim 4 , wherein the control unit is in a state in which an image can be formed with the desired image quality in a developing device having a remaining amount of toner exceeding a predetermined value. 5. The control device according to claim 4 , wherein the developing unit in which the pause time after the end of use in the previous image forming operation is less than a predetermined time is in a state in which an image can be formed with the desired image quality. The image forming apparatus described in 1. In an image forming method in an image forming apparatus configured to be capable of mounting N (N is an integer of 3 or more) developer storing toner, and including a developing rotary that is rotatable about a predetermined rotation axis,
M developers (M is an integer less than or equal to 2 and less than N) that are adjacent to each other on the development rotary and store toners of the same color and are capable of forming an image with a desired image quality. Among them, the developing device located on the most downstream side in the rotation direction of the developing rotary is first positioned at a predetermined developing position, and the adjacent developing devices are sequentially arranged from the developing device toward the developing device located on the most upstream side. A process of switching to
An image forming step of forming an image with toner stored in the developing device each time one developing device is positioned at the developing position ;
When the number of images continuously formed using one developing device reaches a predetermined number and there is an image to be formed next, it is in the upstream adjacent position of the developing device in the rotation direction of the developing rotary. The developing device is switched by moving the developing device to the developing position, and the image forming process is executed using the developing device moved to the developing position by the switching to form the next image. An image forming method.

Images