JP4645253B2 - 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 that store toner of the same color 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 decreases 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 according to the mounting position on the apparatus. 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. Further, in the above prior art, since a specific developing device is used preferentially, some of the developing devices are left unused for a long time. When this is formed, density unevenness may occur.

  Thus, in this type of apparatus, it is necessary to fully consider in what manner each developing device should be used. However, in such an image forming apparatus, the criteria for selecting and using the developing device used for the image forming operation have not been sufficiently studied so far.

  The present invention has been made in view of the above problems, and an image forming apparatus having a plurality of developing units that store toner of the same color and an image forming method thereof stably and efficiently form an image with good image quality. The purpose is to do.

An image forming apparatus according to the present invention is an image forming apparatus that forms an image on a recording material in response to an external image forming command . A positioning means for selectively moving and positioning the developing device to a predetermined developing position, and an image forming operation for forming an image with toner stored in the developing device positioned at the developing position. An image forming unit that executes the image forming unit, and a first main surface of the recording material is conveyed to a predetermined transfer position, and an image formed by the image forming unit is transferred to the one main surface, and then the other of the recording material and a transfer means for transferring another image formed by said image forming means to convey the main surface to said transfer position to said other main surface, upon receiving the image formation command, use at the time The positioning of the developing device in the positioning unit is confirmed, and the mode of the positioning operation of the developing unit by the positioning unit is determined based on the result and the content of the image forming command, and the determined mode is The image forming operation is executed by the image forming means while the developing device is switched for each predetermined number of image forming sheets by the positioning means, and the content of the image forming instruction is to form a plurality of images by the image forming means. The positioning means is estimated based on the content of the image forming command, and the image forming means is configured in a manner according to a length of an interval time provided between forming each of the plurality of images in the image forming means. A positioning operation is performed, and the positioning means retracts the developing device located at the developing position and is different from the developing device. Switching of the developing device for positioning the image device at the developing position is executed as necessary during the interval time, and the content of the image forming operation is to form an image on one side of the recording material. At that time, only the switching from the developing device at the developing position to the adjacent developing device at the upstream adjacent position can be executed, while the content of the image forming operation forms an image on both sides of the recording material. If it is, the positioning means can switch to a developing device other than the adjacent developing device .

Also, the image forming method according to the present invention is a recording material according to an image forming command from the outside by an image forming apparatus having positioning means configured to be capable of mounting a plurality of developing devices that store toner of the same color. an image forming method for forming an image on, in order to achieve the above object, a positioning step of moving and positioning the selectively predetermined developing position developing unit mounted on the front Symbol positioning means is positioned in the developing position An image forming process for performing an image forming operation for forming an image with toner stored in the developing device, and when the image forming command is received, an arrangement in the positioning unit of the developing device that can be used at that time is arranged. A mode of the positioning operation of the developing unit by the positioning unit is determined based on the result and the content of the image formation command. In executing the developing device wherein the image forming operation while switching the every predetermined number of image formation by said positioning means, the content of the image formation command, when those should form a plurality of images, the image formation command The positioning step is performed in a manner according to the length of the interval time provided between forming each of the plurality of images, which is estimated based on the content of the image, and the developer located at the development position is retracted and the Switching of the developing device for positioning a developing device different from the developing device at the developing position is executed as necessary during the interval time, and the content of the image forming operation forms an image on one side of the recording material. If it is to be performed, only switching from the developing device at the developing position at that time to the adjacent developing device at the upstream adjacent position is executed. That one, when the content of the image forming operation in which images are formed on both sides of the recording material is characterized in that to perform the switching of the the adjacent developing unit other than the developing device.

In the invention configured as described above, the developing device used for image formation is not uniformly determined, but in a mode according to the content of the given image forming command and the arrangement of the usable developing device in the positioning means. The developing device is positioned at the developing position, and an image is formed while switching the developing device every predetermined number of image forming sheets . Therefore, it is possible to maintain good image quality and improve the efficiency of image formation.

For example, the content of the image formation command is, when those should form a plurality of images by said image forming means, said positioning means, said estimated based on the content of the image formation instruction, the in the image forming means The positioning operation can be performed in a manner corresponding to the length of the interval time provided while forming each of the plurality of images. In an image forming operation with a long interval time, the degree of freedom with respect to movement and switching of the developing device is high. On the other hand, in an image forming operation with a short interval time, operations that can be performed during that time are limited. Accordingly, by changing the mode of the positioning operation according to the length of the interval time, it is possible to use the developing device efficiently according to the progress of each image forming operation.

  For example, after transporting one main surface of the recording material to a predetermined transfer position and transferring the image formed by the image forming means to the one main surface, the other main surface of the recording material is used as necessary. In the apparatus further comprising a conveying unit that conveys the surface to the transfer position and transfers another image formed by the image forming unit to the other main surface, the positioning unit records the plurality of images on the recording side. The mode of the positioning operation can be made different depending on whether it is formed on one side of the material or on both sides of the recording material.

  This apparatus is an image forming apparatus capable of so-called double-sided printing. In such an apparatus, the length of the image formation interval inevitably differs between the case where a plurality of images are formed on one side of different recording materials and the case where the images are formed on both sides of the recording material. Accordingly, by changing the mode of the positioning operation in each case, it is possible to use the developing device efficiently according to the progress of each image forming operation.

  For example, the positioning unit retreats the developing device located at the developing position and switches the developing device that positions a developing device different from the developing device at the developing position as needed during the interval time. In addition, when the content of the image forming operation is to form an image on one side of the recording material, switching from the developing device at the developing position at that time to the adjacent developing device at the upstream adjacent position is performed. It may be possible to execute only. When a plurality of images are formed on one side of different recording materials (so-called single-sided printing), each image can be formed with only a small interval for separating the images. In addition, the throughput of image formation can be increased by reducing the interval. In such a case, higher throughput can be obtained by permitting only switching to the adjacent developing device that can be completed in a short time.

  Further, when the content of the image forming operation is to form an image on both sides of the recording material, the positioning means may be able to execute switching to a developing device other than the adjacent developing device. When images are formed on both sides of a single recording material, it is necessary to invert the recording material after the image is formed on one side of the recording material. Inevitably requires a longer interval than. Therefore, in this case, it may be possible to execute a switching operation that takes more time. By allowing such switching, each developing device can be used more efficiently.

Further, not all the developing devices that can be always mounted are mounted on the positioning means, and not all the mounted developing devices can be used in the same manner. For example, there are cases where some of the developing devices are not installed or the toner is out. A full-color image forming apparatus cannot form a full-color image unless all the toner colors constituting the full-color image are prepared, but at least one can be used in an apparatus in which each developing device stores toner of the same color. With a simple developing device, a monochrome image can be formed with the desired quality. Accordingly, in each of the image forming apparatuses having the above-described configurations, the control unit determines whether or not the developing unit can be used based on information on the usage history of each developing unit mounted on the positioning unit. Preferably, the positioning means positions only the developing device determined to be usable at the developing position when the image forming operation is executed.

  By doing so, it is possible to form an image with good image quality if at least one usable developing device is installed, and a developing device that is not suitable for use is used for image forming operation. An inferior image is not formed.

  FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus to which the present invention can be applied. 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. 1, and is configured as a cartridge that is detachable with respect to the support frame 40, and includes four developing cartridges 4Ka that contain black toner. 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 apparatus, data is transmitted and received in a non-contact manner 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. Thus, data transmission / reception may be performed mutually.

  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 image forming apparatus will be described in detail. In this apparatus, 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 an image is displayed according to the life rank of each developing device. The mode of the 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 apparatus, 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 apparatus, 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. . 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”.

  Next, three embodiments of the image forming operation in this image forming apparatus will be described. The basic configuration of the image forming operation in these three embodiments is as described above, but the developing device to be used and the mode of switching the developing device are different for each embodiment. Hereinafter, each embodiment will be described in order.

(First embodiment)
In the first embodiment of the image forming operation in the image forming apparatus according to the present invention, the number of images to be formed is read from the content of the image forming command given from the external device, and the switching operation sequence of the developing devices according to the number of images. To change.

  FIG. 5 is a flowchart showing the image forming operation of the first 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). Next, it is determined whether the number of images to be formed specified by the image formation command is larger or smaller than a predetermined number (for example, 8) (step S104), and the subsequent operation differs depending on the determination result.

  First, a case where the number of images to be formed exceeds a predetermined number will be described. When the same developing device is continuously used to form a large number of images, the image quality gradually deteriorates due to a decrease in the remaining amount of toner in the developing device and bias in the developing device. Further, the time for which the other developing devices are not used is lengthened, and the possibility of causing a leaving banding phenomenon in those developing devices is increased. Therefore, when the number of images to be formed is large, it is desirable to use a plurality of developing devices while switching them as much as possible. Therefore, in this embodiment, when the number of images to be formed exceeds a predetermined number, the developing device is switched during the formation of those images.

  Specifically, if two or more usable developing devices are disposed 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 above-described developing position ( Step S105). Subsequently, an image for one page is formed using the developing device (step S106). If there is only one developing device that can be used, and if there are a plurality of developing devices that are not adjacent to each other, use the one that has the longest pause time. It shall be formed. This is to prevent the neglected banding phenomenon.

  If the formation of all the images to be formed has been completed (step S107), after updating the information in the memory of each developing device, the developing unit 4 is returned to the home position and the image forming operation is completed (step S117). ). Here, since only one of the images exceeding the predetermined number is formed, those images are continuously formed. Prior to that, the images continuously formed by the currently used developing device are formed. It is determined whether or not the number has reached the predetermined number (step S108). If the predetermined number has not been reached, the process returns to step S106 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 S109). 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 S110), if there is no next developer, the developer is not switched, and all the remaining images to be formed are in use. (Step S116).

  The criterion in step S109 is 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 S109 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 S109 is, even if there is a usable developing device 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 devices, since the toner is left on the surface of the developing roller 44, the neglected banding phenomenon is likely 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.

  Next, a case where the number of images to be formed specified by the image formation command is equal to or less than a predetermined number in step S104 will be described. When the number of images to be formed is small, there is almost no deterioration in image quality by continuing to use the same developing device, and the formation of those images can be completed in a relatively short time. There is little influence on the developer. Therefore, in this case, the developing device is not switched, and only the first selected developing device is used. However, in order to prevent biasing of the developing devices to be used, when there are a plurality of usable developing devices, regardless of the arrangement, the longest rest time after being used first is the longest. A developing device is selected.

  The developing device thus selected is moved to the developing position (step S115), and a necessary number of images are formed using the developing device (step S116). After the completion, the developing unit 4 is moved to the home position. The image forming operation ends.

  The operation when there is no usable developing device 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 (S111), and if necessary, the necessary preparatory operation is performed on the developing device (step S114). ), The developer is positioned at the development position to form a required number of images (steps S115 and S116).

  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 S112), if there is a rank 2 developer, the image forming operation is performed using the rank 2 developer (steps S113 to S116). 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 two adjacent developing devices can be used. Here, it is assumed that the developing devices 4Ka and 4Kd can be used. If all the developing devices are usable, the developing device 4Ka should be used first, but in this example, the developing device 4Kd on the downstream side of the two usable developing devices is used first. Will be. Thus, after a predetermined number of images are formed by the developing device 4Kd, the developing unit 4 is rotated 90 degrees. As a result, the upstream developing device 4Ka newly moves to the developing position, while the developing device 4Kd moves to the access position. In this state, the information content of the memory 94 provided in the developing device 4Kd is updated while forming an image using the developing device 4Ka. 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 94 and the integrated value of the developing roller rotation time stored in the memory 94 New integrated values obtained by adding the developing roller rotation time in the image forming operation are respectively written in the memory 94. When all the remaining images are formed by the developing device 4Ka, the developing unit 4 is further rotated 90 degrees. Then, after the information content of the memory 91 provided in the developing device 4Ka is updated, the developing unit 4 returns to the home position.

  FIG. 7 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. As the developing device to be used first, the developing device that has not been used in the previous image forming operation is selected. In the example of FIG. 7, the developing device 4Kb is used.

  Thereafter, when a new image formation command is given, the developing unit 4Kb that has not been used first is used. 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.

  Also, if the number of images to be formed is less than a predetermined number, regardless of the number and arrangement of the developing devices that can be used, the developing device that has the longest pause time is used. Since no switching is performed, the developing unit 4 also moves as shown in FIG. 7 in this case.

  If there are three usable developing devices, the number of units that can be attached to the developing unit 4 is four, so that the three developing devices are naturally arranged adjacent to each other. Accordingly, in this case, if the number of images to be formed exceeds a predetermined number, the three developing devices are used while switching in order from the downstream one. If the number of images to be formed is equal to or less than a predetermined number, the one with the longest pause time among the three developing devices is used.

  As described above, in this embodiment, when the number of images to be formed exceeds a predetermined number, the developer is used while being switched. On the other hand, when the number is less than the predetermined number, the switching is not performed and the pause time is longest. Select one developer and use it. Therefore, the use of the developing devices is not biased, and an image with good and stable image quality can be formed while using each developing device effectively. Further, since the switching of the developing device is performed between the developing device currently in use and the developing device located adjacent to the upstream side thereof, it can be switched in a short time, thereby preventing a decrease in image forming throughput. it can.

(Second Embodiment)
In the second embodiment of the image forming operation in the image forming apparatus according to the present invention, the image forming command given from the external apparatus forms an image on both sides of the sheet S or only on one side of the sheet S. The development unit 4 is configured to move differently depending on whether an image is formed. When a plurality of images are formed on different sheets, each sheet can be sent to the secondary transfer region TR2 one after another, so that these images are subjected to a slight amount of time for separating the images from each other. It can be formed continuously with only an interval. In addition, image formation throughput can be increased in this way. However, when forming images on both sides of the sheet, it is necessary to transfer the image to one side of the sheet in the secondary transfer region TR2 and then turn the sheet over and transport it to the secondary transfer region TR2. For this reason, it is necessary to provide a longer interval between two images to be transferred on both sides of one sheet than when an image is formed only on one side of the sheet.

  FIG. 8 is a diagram schematically showing how the sheet is conveyed. When images are formed on both surfaces of one sheet S1, as shown in FIG. 8A, first, one surface S1a of the sheet S1 is sent to the secondary transfer region TR2 along the conveyance path FF. Next, the sheet S1 that has passed through the secondary transfer region TR2 is conveyed along the reverse conveyance path FR (FIG. 8B). Thereafter, the other surface S1b of the sheet S1 is fed into the secondary transfer region TR2 and an image is transferred from the intermediate transfer belt 71 (FIG. 8C).

  In this way, a certain free time occurs between the time when one surface S1a of the sheet S1 passes through the secondary transfer region TR2 and the time when the other surface S1b reaches the secondary transfer region TR2. This idle time is a time required for reversing the sheet S1 determined by the conveyance speed of the sheet S1 and the length of the reversal conveyance path FR, and it is not easy in terms of the configuration of the apparatus to shorten this time. On the other hand, when considering a case where an image is transferred to the sheet S2 following the sheet S1, the above-described free time after the sheet S1 passes through the secondary transfer region TR2 than shown in FIG. 8D. The next sheet S2 can be fed into the secondary transfer region TR2 at shorter time intervals.

  In other words, in the image forming apparatus having such a configuration, the time required for sequentially feeding both surfaces of one sheet to the secondary transfer region TR2 is shorter than when two sheets are sequentially fed to the secondary transfer region TR2. Will increase. Therefore, in this embodiment, by utilizing the idle time, the developer is switched, so that the apparatus can be used efficiently without reducing the image forming throughput. That is, in this embodiment, a single-sided printing mode in which an image is formed only on one side of a sheet and a double-sided printing mode in which an image is formed on both sides of a sheet can be executed as operation modes. The switching sequence of the developing unit 4 is different.

  FIG. 9 is a flowchart showing the image forming operation of the second embodiment. In this embodiment, it is determined whether the operation mode to be executed is the single-sided printing mode or the double-sided printing mode based on the image formation command given from the external device (step S203). Processing is different. First, the operation in the single-sided printing mode (steps S201 to S210) is basically the same as the operation in the first embodiment (steps S101 to S110 in FIG. 5) except for the determination of the operation mode (step S203). The same. In FIG. 9, the operation when there is no usable developing device (steps S102 and S111 to S116 in FIG. 5) is omitted, but the same processing as in the first embodiment may be performed. .

  When the operation mode is the double-sided printing mode, a developing device that has been used first and has the longest rest time is selected from the available developing devices and moved to the developing position (step S211). As in the case of the first embodiment, an image for one page is formed using this developing device (step S212), and if all the images to be formed have been formed, the operation is ended. (Step S213). Further, images are formed using the same developing device until the number of images continuously formed by the developing device currently in use reaches a predetermined number (step S214).

  The operation when the number of images formed by the developing device reaches a predetermined number is different from that in the first embodiment and the single-sided printing mode. That is, in the double-sided printing mode, if there is a usable developing device at any position on the developing unit 4, not only the upstream adjacent position of the developing device currently in use, the switching to the developing device is performed. (Steps S215 and S216). As described above, in the double-sided printing mode, a relatively large interval is provided between the two images to be transferred on both sides of one sheet. Therefore, since the developing unit 4 can be rotated and moved by more than 90 degrees during this interval, the throughput of image formation is reduced even if the developing unit is switched to a position other than the upstream adjacent position. There is no. Further, by doing so, each developing device can be used more efficiently. In this case, it is desirable that the developer switching timing is such that when the image to be transferred is formed on the first surface of one sheet, the number of image formation reaches the “predetermined number”. For example, every time the developing device is switched, the “predetermined number” can be alternately switched between odd and even.

  FIG. 10 is a timing chart showing the operation of each unit in the single-sided printing mode. FIG. 11 is a timing chart showing the operation of each unit in the duplex printing mode. Here, it is assumed that the developing device 4Ka is used first. Here, the fact that the image forming operation is being executed using the developing device is represented by the application of the developing bias to the developing device. In the single-sided printing mode, as shown in FIG. 10, one side S1a, S2a,... Of each different sheet passes through the secondary transfer region TR2 at regular intervals. This interval is relatively short as long as the sheets do not overlap each other. Therefore, the period when the developing device is not used is also short, and it is necessary to complete the switching of the developing device in a short time.

  On the other hand, in the double-sided printing mode, as shown in FIG. 11, one side S1a, S2a of each sheet passes through the secondary transfer region TR2, and then the other side S1b, S2b reaches the secondary transfer region TR2. There is a relatively long interval to do. By rotating the developing unit 4 during this interval, it is possible to switch to a developing device at a position other than the adjacent position.

  As described above, in this embodiment, when the single-sided printing mode in which the interval between the formation of a plurality of images is relatively short is executed, only switching from the currently used developing device to the developing device at the upstream adjacent position is performed. On the other hand, when executing the double-sided printing mode, the development at a position other than the adjacent position is performed by utilizing a relatively long interval between two images to be transferred on each side of one sheet. Switching to a container is also allowed. By doing so, each developing device can be used efficiently without reducing the throughput in accordance with the operation mode of the apparatus.

  In addition, when the developing device is switched in the double-sided printing mode of this embodiment, and there is a usable developing device in the upstream adjacent position of the developing device currently in use, naturally, to the developing device. May be switched. If there is a developer that can be used at the upstream adjacent position, an image to be transferred is formed on the rear surface of one sheet, and then an image to be transferred is formed on the first surface of the next sheet. It may be permissible to switch to the developing unit during the shorter interval.

(Third embodiment)
In the third embodiment of the image forming operation in the image forming apparatus according to the present invention, the movement of the developing unit 4 varies depending on the size of the sheet specified by the image forming command given from the external device. This type of image forming apparatus is required to support sheets of various sizes. When forming images corresponding to sheets of different sizes, it is ideal to apply different image forming operation sequences for each sheet size from the viewpoint of throughput. However, this makes the control of each part complicated. In particular, when the length of the sheet along the sheet conveyance direction is not one type, when the repetition cycle of the operation sequence is adjusted to the sheet size, for example, the rotation speed of the intermediate transfer belt 71 can be changed for each sheet size. In some cases, it is difficult to realize such control due to the structure of the apparatus. Therefore, it is more realistic to prepare one type or several types of operation sequences according to the standard sheet size and apply the operation sequence corresponding to the closest size to sheets of other sizes. .

  In this embodiment, the operation sequence is configured with the Japanese Industrial Standard A4 version as the standard size, and the same operation sequence is used so that the B5 version slightly shorter than this and the legal size sheet slightly longer than this can be supported. Yes. It should be noted that loading of sheets of different sizes into the cassette 8 may be performed by the user as needed, or a separate manual insertion tray may be provided, or sheets of different sizes may be loaded in advance. The cassette may have a plurality of stages.

  FIG. 12 is a flowchart showing the image forming operation of the third embodiment. In this embodiment, when an image formation command is given from the outside (step S301), the arrangement of each developing device mounted in the developing unit 4 is confirmed (step S302), and then the paper size designated by the image formation command is determined. Is confirmed (step S303). Here, the subsequent operation (steps S306 to S311) when the paper size is the standard size A4 is the same as the operation in the first embodiment described above.

  FIG. 13 is a timing chart showing the operation of each part when the paper is a standard size. Since the operation of each part of the apparatus is configured in accordance with a standard size sheet, the repetition cycle Tcyc is necessary and sufficient for the sheet of the size to pass through the secondary transfer region TR2 sequentially with a slight space between each other. Length. Corresponding to this interval, there is an interval time t1 when the developing device is not used, and the developing device can be switched using this time. Since the switching in this case needs to be completed in a short time, the object of switching is limited to the developing unit at the upstream adjacent position. For example, when the developing device 4Ka is used first and the developing device 4Kb located adjacent to the upstream side can be used, the developing unit 4 becomes ready when the number of images formed by the developing device 4Ka reaches a predetermined number. It is rotated 90 degrees and switched to the developing device 4Kb.

  Returning to FIG. 12, the description of the image forming operation is continued. When the paper size is B5 size shorter than the standard size, the restriction that the developing device switching target is the developing device at the upstream adjacent position is removed, and switching to another developing device is permitted. (Step S304). Further, the developing device to be used first is the developing device having the longest pause time after the end of the previous use among the usable developing devices. The subsequent operations are basically the same as in the case of the standard size. However, as described above, since the restriction on the switching target is eliminated, as in the case of the duplex printing mode in the second embodiment, other than the upstream adjacent position. There may be a case where switching to the developing device at the position is performed.

  FIG. 14 is a timing chart showing the operation of each part when the paper size is short. In this case, the repetition period Tcyc of the operation sequence is the same as that for the standard size. However, since the sheet size is short, an interval time t2 that is longer than that in the case of the standard size occurs. Accordingly, during this time, the developing unit 4 can be rotated more than 90 degrees. For example, the developing unit 4 can be rotated 180 degrees to switch from the developing device 4Ka to the developing device 4Kb.

  Returning to FIG. 12 again, the operation when the paper size is the legal size will be described. In this case, since the sheet is long, the interval between the formation of one image and the formation of the next image is shorter than in the case of the standard size. As a result, there is no time margin for switching the developing devices. Therefore, in this case, an image is formed without switching the developing device. That is, the developer having the longest rest time is selected from the usable developing devices and moved to the developing position (step S312), and a necessary number of images are formed using the developing device (step S313). When the image formation is completed, the developing unit 4 is returned to the home position after the memory of the used developing device is updated (step S314).

  FIG. 15 is a timing chart showing the operation of each part in the case of a long paper size. Even in this case, the repetition period Tcyc of the operation sequence is constant. As a result of the increase in the sheet size, the interval time t3 becomes shorter than in the case of the standard size. In order to suppress a decrease in throughput, in this case, the developer is not switched, and the first selected developer (here, developer 4Ka) is used to the end. When a series of images corresponding to one image formation command is formed and then an image corresponding to a newly received image formation command is formed, a developing device other than the developing device 4Ka can be used.

  Thus, in this embodiment, the mode of switching the developing unit 4 is changed according to the sheet size specified by the image formation command. By doing so, the same operation sequence can be applied to sheets of different sizes, and the control can be prevented from becoming complicated. Further, by appropriately selecting and switching the developing devices corresponding to the difference in sheet size, it is possible to form an image using each developing device efficiently.

(Summary)
As described above, in the first embodiment of the image forming operation in this image forming apparatus, the mode of selecting and switching the developing device changes according to the number of images to be formed corresponding to the image forming command. Further, in the second embodiment of the image forming operation in this image forming apparatus, the mode of selecting and switching the developing device varies depending on whether an image is formed on one side of the sheet or on both sides. Further, in the third embodiment of the image forming operation in this image forming apparatus, the mode of selecting and switching the developing device changes according to the sheet size specified by the image forming command. According to these embodiments, it is possible to stably form an image with good image quality, and it is possible to use each developing device efficiently.

  As described above, in each of the above embodiments, the rotary developing unit 4 functions as the “positioning unit” of the present invention. The engine unit EG functions as the “image forming unit” of the present invention. Further, the rollers 81, 82, etc. constituting the transport path F and the reverse transport path FR function as a “transport means” of the present invention. In the present embodiment, the sheet S corresponds to a “recording material”.

  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, in the image forming command given to the actual image forming apparatus, the number of images to be formed, whether double-sided / single-sided, and the sheet size are designated. Therefore, if each of the above embodiments is not implemented individually but in combination with each other, various image forming commands can be handled.

  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.

FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus to which the present invention can be applied. 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 illustrating an image forming operation according to the first embodiment. FIG. 4 is a diagram illustrating a transition of a developing unit when an adjacent developing device can be used. FIG. 4 is a diagram illustrating a transition of a developing unit when a developing device in a symmetric position is usable. The figure which shows the mode of sheet conveyance typically. 9 is a flowchart showing an image forming operation of the second embodiment. 6 is a timing chart showing the operation of each unit in the single-sided printing mode. 6 is a timing chart showing the operation of each unit in the duplex printing mode. 10 is a flowchart illustrating an image forming operation according to a third embodiment. 6 is a timing chart showing the operation of each part when the paper is a standard size. 6 is a timing chart showing the operation of each unit when the paper size is short. 6 is a timing chart showing the operation of each unit when the paper size is long.

Explanation of symbols

  4 ... Rotary developing unit (positioning means), 4Ka, 4Kb, 4Kc, 4Kd ... Developing unit, 81, 82, 83 ... Roller (conveying means), EG ... Engine part (image forming means), S ... Sheet (recording material)

Claims (3)

In an image forming apparatus that forms an image on a recording material in accordance with an image formation command from the outside,
A positioning unit configured to be able to mount a plurality of developing units that store toner of the same color, and to selectively move and position the developing unit to a predetermined developing position;
An image forming means for performing an image forming operation for forming an image with toner stored in a developing device positioned at the developing position;
After conveying one main surface of the recording material to a predetermined transfer position and transferring the image formed by the image forming means to the one main surface, the other main surface of the recording material is conveyed to the transfer position. Transporting means for transferring another image formed by the image forming means to the other main surface ,
Upon receiving the image formation command, the positioning of the developing device that can be used at that time is confirmed in the positioning unit, and the positioning unit positioning operation by the positioning unit based on the result and the content of the image formation command The image forming operation is performed by the image forming unit while switching the developing device for each predetermined number of image forming sheets by the positioning unit in the determined mode .
When the content of the image forming command is to form a plurality of images by the image forming unit, the positioning unit is estimated based on the content of the image forming command. Performing the positioning operation in a manner according to the length of the interval time provided between forming each of the images,
The positioning means retreats the developing device positioned at the developing position and executes switching of the developing device that positions a developing device different from the developing device at the developing position as necessary during the interval time, Moreover,
When the content of the image forming operation is to form an image on one side of the recording material, only switching from the developing device at the developing position to the adjacent developing device at the upstream adjacent position at that time can be executed. While
When the content of the image forming operation is to form an image on both sides of the recording material, the positioning means can execute switching to a developing device other than the adjacent developing device. An image forming apparatus. Based on the information about the use history of each developing device is mounted in front Symbol positioning means determines whether or not it is possible using the developing device, the positioning means, when the image forming operation is executed, The image forming apparatus according to claim 1, wherein only a developing device determined to be usable is positioned at the developing position. In an image forming method for forming an image on a recording material in accordance with an image forming command from the outside by an image forming apparatus having a positioning unit configured to be capable of mounting a plurality of developing units that store toner of the same color.
A positioning step of selectively moving and positioning the developing device mounted on the positioning means to a predetermined developing position;
An image forming step of performing an image forming operation for forming an image with toner stored in a developing device positioned at the developing position;
Upon receiving the image formation command, the positioning of the developing device that can be used at that time is confirmed in the positioning unit, and the positioning unit positioning operation by the positioning unit based on the result and the content of the image formation command The image forming operation is executed while switching the developing device for each predetermined number of image forming sheets by the positioning means in the determined mode .
When the content of the image formation command is to form a plurality of images, the length of the interval time provided between forming each of the plurality of images, which is estimated based on the content of the image formation command The positioning step is performed in a mode according to
Retreating the developing device located at the developing position and positioning a developing device different from the developing device at the developing position, if necessary during the interval time, and
When the content of the image forming operation is to form an image on one side of the recording material, only switching from the developing device at the developing position to the adjacent developing device at the upstream adjacent position at that time is executed. on the other hand,
When the content of the image forming operation is to form an image on both sides of the recording material, switching to a developing device other than the adjacent developing device is executed .

Images