Image forming apparatus

Abstract

To reduce interruption of image forming operation due to supply operation of a developer as compared with a case where first supply means and second supply means are individually activated without adjusting activation timing of each other, in an image forming apparatus including first supply means that supplies a developer to at least one developing device of a plurality of developing devices and second supply means that supplies the developer to a remaining developing device of the plurality of developing devices.SOLUTION: An image forming apparatus includes: a plurality of developing devices that accommodate different types of developers from each other; first supply means that supplies a developer to at least one developing device when density of the developer in at least one developing device of the plurality of developing devices is a predetermined value; second supply means that supplies the developer to a remaining developing device when density of the developer in the remaining developing device of the plurality of developing devices is a predetermined value; and control means that controls the first supply means to be activated at the same timing as activation timing of the second supply means.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] The following Patent Document 1 describes an image forming apparatus having first and second developing units, an image density detecting means, a first replenishing means, a ratio detecting means, and a second replenishing means. The first and second developing devices contain two-component developers. The image density detection means detects the density of a reference toner image developed by the first developing device. The first supply means supplies toner to the first developing device based on the image density. The ratio detection means detects the ratio of toner to carrier in the second developing device. The second supply means supplies toner to the second developing device based on the ratio. Furthermore, Patent Document 1 describes that the volume resistivity of the carrier in the first developing unit is set lower than the volume resistivity of the carrier in the second developing unit.

[0003] The following Patent Document 2 describes an electrophotographic apparatus having a plurality of developing units around the same photosensitive member. Furthermore, Patent Document 2 describes that the toner concentration of each developing device is controlled by a different toner concentration control means depending on the color and volume of the toner contained in each developing device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 09-22156 A (Claim 1, Figures 1 and 2) [Patent Document 2] JP 09-190069 A (Claim 1, Figures 1 and 3) Summary of the Invention [Problem to be solved by the invention]

[0005] In an image forming apparatus having a first supply means for supplying developer to at least one of a plurality of developing devices and a second supply means for supplying developer to the remaining developing devices of the plurality of developing devices, the image forming operation being performed is interrupted by the developer supply operation. The present invention provides an image forming device that can reduce the interruption of image forming operations due to developer replenishment operations compared to when the first replenishment means and the second replenishment means are operated individually without adjusting their operating timings. [Means for solving the problem]

[0006] The first aspect of the present invention is a plurality of developing devices containing different types of developers; a first supplying means for supplying developer to at least one of the plurality of developing devices when the concentration of the developer in the at least one developing device reaches a predetermined value; a second supplying means for supplying developer to the remaining developing devices when the developer concentration in the remaining developing devices reaches a predetermined value; a control means for controlling the first supply means to operate at the same time as the second supply means; The image forming apparatus is provided with the above.

[0007] The second aspect of the present invention is a plurality of developing devices containing different types of developers; a first supply means for supplying developer to at least one of the plurality of developing devices when a result of measuring the concentration of the developer in the at least one developing device at a first measurement time reaches a predetermined value; a second supply means for supplying developer to the remaining developing devices when a result of measuring the concentration of developer in the remaining developing devices at a second measurement time different from the first measurement time reaches a predetermined value; a control means for controlling the operation of the first supply means to wait until the second measurement time comes; The image forming apparatus is provided with the above.

[0008] A third aspect of the present invention is the image forming apparatus of the first aspect, The control means is an image forming apparatus that starts the first supply means when the concentration of the developer in the remaining developing device is measured.

[0009] A fourth aspect of the present invention is the image forming apparatus of the second aspect, The control means is an image forming apparatus that starts the first supply means that has been put on standby when the second measurement time comes.

[0010] A fifth aspect of the present invention is the image forming apparatus of the third aspect, The control unit is an image forming apparatus that starts the second supply unit while the first supply unit is in operation.

[0011] A sixth aspect of the present invention is the image forming apparatus according to the fourth aspect, The control unit is an image forming apparatus that starts the second supply unit while the first supply unit is in operation.

[0012] A seventh aspect of the present invention is an image forming apparatus according to the first or second aspect, the predetermined value in the first supply means is a value equal to or greater than a first threshold value, which is an allowable lower limit value that deviates from a first allowable concentration value of the developer in the at least one developing device, the predetermined value in the second supply unit is a value equal to or greater than a second threshold value, which is an allowable lower limit value that deviates from a second allowable concentration value of the developer in the remaining developing device, The control unit is an image forming apparatus that uses, as the first threshold value, a value having a deviation amount that is smaller than the deviation amount of the second threshold value from the second allowable density value.

[0013] The eighth aspect of the present invention is the image forming apparatus of the first or second aspect, The control means is an image forming device that, when the concentration of the developer returns to an allowable concentration value at a stage when the number of replenishments by the first replenishment means does not exceed an upper limit value, retains the result of empty detection, which determines that the developer in at least one developing device is empty, as a determination result that the developer is not empty until the concentration of the developer in the remaining developing devices is measured. [Effects of the Invention]

[0014] According to the image forming device of the first and second means, the image forming operation can be less likely to be interrupted by the developer replenishment operation than when the first replenishment means and the second replenishment means are operated individually without adjusting their operating timings.

[0015] According to the image forming apparatus of the third means, the image forming operation is not interrupted by the first supplying means starting before the developer concentration in the remaining developing devices is measured.

[0016] According to the image forming apparatus of the fourth means, the image forming operation is not interrupted by the first supply means starting before the second measurement time is reached.

[0017] According to the image forming apparatus of the fifth aspect, the operation timing of the first supplying means and the operation timing of the second supplying means at least partially overlap, thereby reducing the time during which the image forming operation is interrupted.

[0018] According to the image forming apparatus of the sixth aspect, the operation timing of the first supplying means and the operation timing of the second supplying means at least partially overlap, thereby reducing the time during which the image forming operation is interrupted.

[0019] According to the image forming apparatus of the seventh aspect, it is possible to prevent a decrease in the development characteristics of at least some of the developing devices due to a delay in the supply of developer from the first supply device to the at least some of the developing devices.

[0020] According to the image forming apparatus of the eighth means, it is possible to reduce the number of interruptions to the image forming operation due to the replacement work of the developer container that contains the developer to be replenished. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a portion relating to developer replenishment of the image forming apparatus of FIG. [Figure 3] FIG. 2 is a block diagram showing a portion relating to control of the image forming apparatus of FIG. 1. [Figure 4] 10 is a flowchart showing the flow of a control operation related to adjustment of the operation timing of the replenishing device. [Figure 5] 1 is a flowchart showing the flow of control operations related to ATC. [Figure 6] 10A and 10B are explanatory diagrams illustrating a state in which a replenishing operation of a replenishing device and an interruption of an image forming operation in a comparative example and an example, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described.

[0023] Embodiment 1 FIG. 1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. In this specification and the drawings, substantially the same components are denoted by the same reference numerals, and redundant explanations of the same components will be omitted in this specification.

[0024] The image forming apparatus 1 is configured as, for example, a printer. As shown in FIG. 1, the image forming apparatus 1 includes a housing 10 in which an image forming unit 20, an intermediate transfer unit 30, a paper feed unit 40, a fixing unit 50, and the like are arranged. The housing 10 has a paper discharge storage section 12 at its top, and an operation display panel section 47 on its top surface. The operation display panel section 47 has a display section that displays information necessary for operations, etc., and an operation section that performs operations necessary for operations, etc.

[0025] The image forming unit 20 is a part that forms a developed image by developing the latent image with a developer. As shown in FIGS. 1 and 2, the imaging section 20 in the first embodiment is made up of four imaging units 21A, 21B, 21C, and 21D.

[0026] Each of the imaging units 21A, 21B, 21C, and 21D has a photosensitive drum 22. Each of the imaging units 21A, 21B, 21C, and 21D creates a developed image on each of the photosensitive drums 22 by electrophotography using a developer of a predetermined color (A, B, C, or D). Examples of the predetermined colors (A, B, C, D) include black, cyan, magenta, and yellow.

[0027] In the image forming section 20, the photosensitive drums 22 in the image forming units 21A, 21B, 21C, and 21D rotate in the directions indicated by the arrows. The outer peripheral surface of each photosensitive drum 22 is charged to a predetermined surface potential by each charging device 23 .

[0028] Thereafter, the charged outer peripheral surface of each photosensitive drum 22 is exposed to light of each color component corresponding to the image information from each latent image forming device 24. As a result, electrostatic latent images of the predetermined color components (A, B, C, D) are distributed and formed on the outer peripheral surface of each photosensitive drum 22. Image information is input from an externally connected device 300 such as an information terminal or a storage medium connected to the image forming apparatus 1.

[0029] Subsequently, the electrostatic latent image formed on the outer peripheral surface of each photosensitive drum 22 is developed with the developer of the corresponding color supplied from each developing device 25A, 25B, 25C, 25D. The developer used is, for example, a two-component developer containing toner and carrier. When the developer is a two-component developer, a toner image made of toner of a predetermined color (A, B, C, D) is obtained as a developed image.

[0030] The developing devices 25 are shown as developing devices 25A, 25B, 25C, and 25D because they differ in that they contain developers containing toners of different colors (A, B, C, and D). Each of the developing devices 25A, 25B, 25C, and 25D has a container for accommodating the developer, and inside the container, a developing roll, an agitating and conveying member, a layer thickness regulating member, and the like (not shown) are arranged. A toner image of a predetermined color (A, B, C, D) is formed on the outer peripheral surface of each photosensitive drum 22 by the developing operation of developing devices 25A, 25B, 25C, 25D.

[0031] In the image forming unit 20 , the toner images of each color formed on each photosensitive drum 22 are transferred to the intermediate transfer unit 30 . In the image forming unit 20, after the transfer, the surface of each photosensitive drum 22 is cleaned by the drum cleaning device 26 in preparation for the next image forming process.

[0032] The intermediate transfer section 30 is a section where toner images of a predetermined color created by the image creating units 21A, 21B, 21C, and 21D of the image creating section 20 are temporarily held on the intermediate transfer belt 31 by primary transfer, and then secondarily transferred onto the paper 9.

[0033] In the intermediate transfer unit 30, an intermediate transfer belt 31 is wound around a plurality of rolls 32a, 32b, 32c, and 32d, and rotates in the direction indicated by the arrow. In the intermediate transfer unit 30 , the toner images of each color on each photosensitive drum 22 are sequentially transferred (primary transfer) onto the outer circumferential surface of the rotating intermediate transfer belt 31 by the primary transfer device 33 . Thereafter, the rotating intermediate transfer belt 31 carries the toner image that has been primarily transferred onto its outer peripheral surface to a secondary transfer position opposite a secondary transfer device 34 .

[0034] In the intermediate transfer unit 30, the toner image that has been primarily transferred onto the outer peripheral surface of the intermediate transfer belt 31 is secondarily transferred onto the paper 9 that is supplied from the paper feed unit 40 by the secondary transfer device . In the intermediate transfer unit 30, the outer peripheral surface of the intermediate transfer belt 31 after the secondary transfer is cleaned by the belt cleaning device 36 in preparation for the next transfer step.

[0035] The paper feed unit 40 is a unit that stores paper 9 on which an image is to be formed, and supplies the paper 9 to a secondary transfer position in the intermediate transfer unit 30. In the paper feed unit 40, a paper feed device 42 feeds the paper 9 one by one from a container 41 that stores the paper 9 toward the secondary transfer position of the intermediate transfer unit 30. A plurality of sets of the container 41 and the delivery device 42 may be provided.

[0036] The paper feed unit 40 is also connected to a paper transport path Tr indicated by a dashed line. The paper transport path Tr is provided to connect the paper feed unit 40 to the paper discharge storage unit 12 via the secondary transfer position of the intermediate transfer unit 30 and the fixing unit 50. The paper transport path Tr is also made up of a predetermined number of transport roll pairs 46a, 46b, 46c, and 46d, paper guide members (not shown), and the like.

[0037] In the paper feed unit 40, the delivery device 42 delivers the paper 9 in the container 41 one by one to the paper transport path Tr. Then, in the paper transport path Tr, the transport roll pair 46b delivers the paper 9 to the secondary transfer position of the intermediate transfer unit 30 in synchronization with the secondary transfer timing. Thereafter, in the intermediate transfer unit 30, the secondary transfer device 34 secondarily transfers the toner image from the intermediate transfer belt 31 onto one side of the paper 9 at the secondary transfer position.

[0038] The fixing unit 50 is a unit that fixes the toner image transferred onto the paper 9 to the paper 9 by heating it under pressure. The fixing unit 50 has a heating rotor 52 and a pressure rotor 53 that rotate in a pressure-contact state inside a housing 51. A fixing processing unit (nip portion) is formed between the heating rotor 52 and the pressure rotor 53, where the paper 9 is introduced and pressurized and heated.

[0039] In the fixing unit 50, the paper 9 sent from the secondary transfer position of the intermediate transfer unit 30 is introduced into the fixing processing unit and passes through it. At this time, in the fixing unit 50, the unfixed toner image on the paper 9 is heated under pressure as it passes through the fixing processing unit, thereby fixing the toner image onto the paper 9 as an image.

[0040] Finally, in the image forming apparatus 1, the paper transport path Tr transports the paper 9 discharged from the fixing unit 50 toward the paper discharge storage unit 12. As a result, the paper 9 on which the image has been formed is stored in the paper discharge storage unit 12. As described above, an operation for forming an image (printing operation) is performed in the image forming apparatus 1. In this way, the image forming apparatus 1 forms an image made of developer (toner) on one side of the paper 9.

[0041] (Configuration for developer replenishment) As shown in FIG. 2, the image forming apparatus 1 includes replenishing devices 6A, 6B, 6C, and 6D. Replenishing devices 6A, 6B, 6C, and 6D are devices that individually replenish developers of colors (A, B, C, and D) corresponding to developing devices 25A, 25B, 25C, and 25D.

[0042] The replenishing devices 6A, 6B, 6C, and 6D include replenishing operating sections 61A, 61B, 61C, and 61D, developer containers 15A, 15B, 15C, and 15D, and developer transport paths 17A, 17B, 17C, and 17D.

[0043] The supply operation units 61A, 61B, 61C, and 61D are each composed of a container drive unit, a developer receiving unit, a developer delivery member, and the like, all of which are not shown. The container driving portion is a portion that drives the driving portion of the developer container 15 to discharge the developer. The developer receiving portion is a portion that receives the developer discharged from the developer container 15. The developer delivery member is a member that delivers the developer in the receiving portion.

[0044] The developer containers 15A, 15B, 15C, and 15D are containers that exclusively store replenishment developers of the respective colors (A, B, C, and D). In the first embodiment, toner is stored as the developer. Developer containers 15A, 15B, 15C, and 15D are detachably mounted in mounting portions 16A, 16B, 16C, and 16D provided in predetermined portions of housing 10. As developer containers 15A, 15B, 15C, and 15D, containers that themselves rotate to feed out developer or containers that have a member inside the container that rotates to feed out developer are used. The developer transport paths 17A, 17B, 17C, and 17D are transport paths that individually transport the developer from the supply operation portions 61A, 61B, 61C, and 61D to the developing devices 25A, 25B, 25C, and 25D.

[0045] When the time for replenishment arrives, replenishment operating units 61A, 61B, 61C, and 61D of the replenishment devices 6A, 6B, 6C, and 6D that are the targets requiring replenishment are activated. At this time, the operated replenishing devices 6A, 6B, 6C, and 6D send out a predetermined amount of developer to the developer transport paths 17A, 17B, 17C, and 17D, respectively. Also, the replenishing operating units 61A, 61B, 61C, and 61D receive the developer in advance from the developer containers 15A, 15B, 15C, and 15D. As a result, the replenishing devices 6A, 6B, 6C, and 6D transport and replenish a predetermined amount of developer to the developing devices 25A, 25B, 25C, and 25D, respectively.

[0046] Further, the supply device 6A, which is one of the supply devices 6A, 6B, 6C, and 6D, operates based on measurement information from the toner concentration measurement unit 65.

[0047] The toner concentration measuring unit 65 measures the toner concentration of the developer contained in the developing device 25A that is the measurement target. The toner concentration measuring unit 65 serves as a first concentration detecting means as an example of a concentration detecting means. If the two-component developer contains non-magnetic toner and magnetic carrier, the toner concentration measuring unit 65 is configured with, for example, a magnetic permeability type TC sensor. The magnetic permeability type TC sensor measures the magnetic permeability of the developer contained in the developing device 25 A. The toner concentration measuring unit 65 obtains the toner concentration from the magnetic permeability of the developer, as will be described later.

[0048] On the other hand, the remaining supply devices 6B, 6C, and 6D among the supply devices 6A, 6B, 6C, and 6D operate based on the measurement information of the toner image density measurement unit 67.

[0049] The toner image density measuring unit 67 measures the density of the reference toner image. The density of the reference toner image is also the density of the amount of developed toner. The toner image density measuring unit 67 serves as a second density detecting unit, which is another example of the density detecting unit. The reference toner image is a toner image for density measurement obtained by developing a specific electrostatic latent image by a developing device to be measured. The reference toner image is formed on the photosensitive drum 22 or transferred from the photosensitive drum 22 to the intermediate transfer belt 31. When measuring the density of a reference toner image made of toner of a chromatic color (color) other than black, the toner image density measuring unit 67 is configured by, for example, a diffuse reflection type development density sensor.

[0050] The toner image density measuring unit 67 measures the density of the reference toner image of each color obtained by development in the development devices 25B, 25C, and 25D to be measured. The toner image density measuring unit 67 also measures the density of the reference toner image primarily transferred from each photosensitive drum 22 to the intermediate transfer belt 31 at a position just before the secondary transfer position.

[0051] Furthermore, the image forming apparatus 1 employs two development control methods, ATC and ADC, to control the developer replenishment operation. ATC is an abbreviation for Auto Toner Concentration Control, and ADC is an abbreviation for Auto Density Control.

[0052] ATC measures the toner concentration in a developing device using a toner concentration measuring unit 65. ATC is a method for controlling the supply of toner based on the toner concentration measurement information so that the toner concentration in the developing device to be supplied is kept constant.

[0053] In the first embodiment, the supply device 6A is configured to be activated when the measurement result of the toner concentration measurement unit 65 becomes a concentration value equal to or greater than a first threshold value. The first threshold value is the lower limit of the allowable amount of deviation from the first allowable concentration value as the toner concentration in the developing device 25A that is the target of ATC. Therefore, replenishing device 6A in the first embodiment operates when the concentration of the developer contained in developing device 25A reaches a predetermined value.

[0054] In the first embodiment, the amount of carrier in a unit volume of developer is estimated from information on magnetic permeability measured by a magnetic permeability type TC sensor in the developability control unit 185, which will be described later. The developer supply operation control unit 186 calculates the weight ratio of toner to carrier from the amount of carrier, and obtains information on toner concentration. Furthermore, in the first embodiment, measurement information from the toner concentration measurement unit 65 is collected in the developability control unit 185. Then, in the first embodiment, the developability control unit 185 determines whether the measurement result from the toner concentration measurement unit 65 is equal to or greater than the first threshold value.

[0055] ADC is a method in which the density of a reference toner image is measured by a toner image density measuring unit 67, and the supply of toner is controlled so that the development characteristics are constant.

[0056] In the first embodiment, when the measurement result of the toner image density measurement unit 67 becomes a density value equal to or greater than the second threshold value, the supply devices 6B, 6C, and 6D are each activated. The second threshold value is the lower limit of the allowable amount of deviation from the second allowable density value as the image density of each reference toner image obtained by developing the reference toner images obtained by developing the reference toner images by the ADC target developing devices 25B, 25C, and 25D. Therefore, the supply devices 6B, 6C, and 6D are activated when the density of each reference toner image reaches a predetermined value. The density of each reference toner image corresponds approximately to the density of the developer contained in the developing devices 25B, 25C, and 25D.

[0057] Furthermore, in the first embodiment, measurement information from the toner image density measurement unit 67 is collected in the developability control unit 185. Then, in the first embodiment, the developability control unit 185 determines whether the measurement result from the toner image density measurement unit 67 is a density value equal to or greater than the second threshold value.

[0058] The toner concentration measurement unit 65 measures the toner concentration at the ATC-compliant concentration measurement time (first measurement time). Specifically, the toner concentration measurement unit 65 always measures the toner concentration while the development device 25A to be measured is in operation. In this case, the ATC-compatible concentration measurement period of the toner concentration measurement unit 65 is when the development device 25A is in operation.

[0059] Furthermore, the toner image density measurement unit 67 measures the toner image density at an ADC-compatible density measurement time (second measurement time). The second measurement time may be any time different from the first measurement time. Specifically, the toner image density measurement unit 67 measures the toner image density when the amount of image formation (print volume: PV) reaches a predetermined threshold. In this case, the ADC-compatible density measurement timing of the toner image density measurement unit 67 is the time when the amount of image formation reaches the predetermined threshold.

[0060] The amount of image formation operations is determined by, for example, the number of sheets of paper 9 on which images are formed, the number of pixels of the formed images, etc. The amount of image formation operations is the cumulative amount from the time when the immediately preceding control operation among various control operations related to the process conditions during image formation executed in the image forming apparatus 1 was completed.

[0061] Furthermore, in the image forming apparatus 1, when the time comes for the supply devices 6A, 6B, 6C, and 6D to operate while an image forming operation is being performed, the image forming operation being performed is interrupted. Furthermore, in the image forming apparatus 1, when the toner image density measurement unit 67 is in the ADC compatible density measurement period while an image forming operation is being performed, the image forming operation being performed is interrupted early in order to allow the operation of forming the reference toner image, which is the measurement target of the toner image density measurement unit 67, to start early.

[0062] For this reason, in the image forming device 1, the operation timing of the supply device 6A, which operates based on the ATC development control method, and the operation timing of the supply devices 6B, 6C, and 6D, which operate based on the ADC development control method, are often performed separately at different times. This can also be said to mean that the time when the image forming operation being performed is interrupted by the supplying operation of supply device 6A and the time when the image forming operation being performed is interrupted by the supplying operation of supply devices 6B, 6C, and 6D are often different from each other.

[0063] Therefore, the image forming apparatus 1 is provided with a control means 18 having a function of controlling and adjusting the operation timing of the supplying device 6A and the operation timing of the supplying devices 6B, 6C, and 6D.

[0064] As shown in FIG. 3, the control means 18 is composed of a central control unit including a development control unit 185 and the like. The central control unit of the control means 18 is a means for controlling the overall operation of the image forming apparatus 1. The control means 18 is composed of an arithmetic processing unit, a memory unit, an input / output unit, etc., which are not shown. Other control units, which will be described later, are also composed in almost the same way.

[0065] The control means 18 performs necessary processing based on the control program and control data stored in the storage unit while the arithmetic processing unit acquires information necessary for control. Then, the control means 18 transmits a signal that controls the operation of the control target that requires control by the arithmetic processing unit or the like. The information necessary for control includes, for example, detection information, input information, and the like.

[0066] As shown in FIG. 3, the control means 18 is connected to a toner density measuring unit 65, a toner image density measuring unit 67, a surface potential measuring unit 68, a communication / input / output unit 192, and the like. This allows the control means 18 to obtain necessary detection information, input information, and the like.

[0067] Of these, the surface potential measuring unit 68 is a unit that measures the surface potential of each photosensitive drum 22 in the imaging units 21A, 21B, 21C, and 21D. The surface potential measuring unit 68 is composed of a known potential sensor, etc. The communication / input / output unit 192 is a unit that communicates with externally connected devices 300 such as information terminals and storage media, and inputs and outputs information.

[0068] Furthermore, the control means 18 is connected to an image processing unit 191, an image forming operation control unit 181, a paper conveyance operation control unit 182, a developer supply operation control unit 186, a display operation control unit 187, etc. This enables the control means 18 to output control signals to necessary control targets, etc.

[0069] The image processing unit 191 is a part that generates an image signal to be formed by performing predetermined processing on image information, etc. input to the image forming apparatus 1. The image processing unit 191 obtains information such as the number of sheets of paper 9 on which an image is to be formed, the number of pixels, etc. The image forming operation control unit 181 is a unit that controls operations related to the image forming unit 20, the intermediate transfer unit 30, and the fixing unit 50. The paper transport operation control unit 182 is a unit that controls operations related to the paper feed unit 40, including the paper transport path Tr. The developer supply operation control unit 186 is a part that controls the operation of (the operating units 61 of) the supply devices 6A, 6B, 6C, and 6D. The display operation control unit 187 is a part that controls the operation related to the operation display panel unit 47.

[0070] The central control unit of the control means 18 also includes a development control unit 185 and an empty detection unit 188 as part of its functions.

[0071] The development control unit 185 is a part that controls operations related to the ATC and ADC control methods. The developability control unit 185 also performs the following control operation as an operation related to the ATC control method: That is, the developability control unit 185 also performs an operation of collecting measurement information from the toner concentration measurement unit 65 and determining whether the measurement result is equal to or greater than the first threshold value. The developability control unit 185 also performs the following control operation as an operation related to the ADC control method: That is, the developability control unit 185 also performs an operation of collecting measurement information from the toner image density measurement unit 67 and determining whether the measurement result is a density value equal to or greater than the second threshold value.

[0072] The empty detector 188 is a part that monitors the remaining amount of toner to be replenished contained in the developer containers 15A, 15B, 15C, and 15D, and as a result of this monitoring, the empty detector 188 is a part that detects when the remaining amount of toner becomes almost zero and the container becomes empty. The empty detection unit 188 obtains necessary information from the development control unit 185 and the like to perform empty detection.

[0073] (Control operation related to adjustment of operation timing of supply device) Next, a control operation for adjusting the operation timing of the supplying device 6A and the operation timing of the supplying devices 6B, 6C, and 6D during the image forming operation will be described.

[0074] In the image forming apparatus 1, as shown in FIG. 4, when an image forming operation (printing operation) is started (S100), the control means 18 determines whether or not it is time to perform ADC-compatible density measurement (S101). S100 and S101 are abbreviations for step 100 and step 101 respectively. This abbreviation shall be the same for other steps hereinafter.

[0075] As the timing for ADC-corresponding density measurement, it is assumed that it is when the amount of image forming operation (printing amount: PV) reaches a predetermined threshold value. As the printing amount PV, the cumulative value of the number of formed images or the number of pixels is applied. The cumulative value in this case is a value accumulated from the time when the immediately preceding control operation regarding the process conditions during image formation ends.

[0076] When it is determined in step 101 that the timing for ADC-corresponding density measurement has arrived, the ongoing printing operation is interrupted (S102). Thereafter, operations related to ADC and operations related to ATC are performed individually (S103).

[0077] <Operations related to ADC> As shown in FIG. 4, for operations related to ADC, first, ADC-corresponding density measurement is performed (S104). For ADC-corresponding density measurement, formation of a reference toner image of the measurement target and measurement of the density of the reference toner image are performed.

[0078] Specifically, after the image forming units 21A, 21B, 21C, 21D operate to form reference toner images of respective colors on the respective photoreceptor drums 22 by the developing devices 25B, 25C, 25D, the reference toner images of respective colors are primarily transferred onto the intermediate transfer belt 31. Next, when the reference toner images of respective colors on the intermediate transfer belt 31 pass through the toner image density measurement unit 67, their respective densities are measured.

[0079] The information measured by the toner image density measurement unit 67 at this time is collected by the developability control unit 185. At this time, in the developability control unit 185, from the measurement information, a deviation amount Db deviating from the second allowable density value as the image density of the reference toner image of each color is calculated. Incidentally, the reference toner images of respective colors at this time are passed through without being secondarily transferred onto the paper 9 at the secondary transfer position, and then removed by the belt cleaning device 36.

[0080] Next, the developability control unit 185 determines whether the density deviation amount Db obtained from the measurement result of the toner image density measurement unit 67 is equal to or greater than the second threshold value (S105). As described above, the second threshold value is the lower limit of the allowable amount of deviation from the second allowable concentration value.

[0081] If it is determined in step 105 that the deviation amount Db is equal to or greater than the second threshold value, a corresponding one of the ADC-compatible replenishing devices 6B, 6C, and 6D is activated (S106). The supply devices 6B, 6C, and 6D are activated when any of the deviation amounts Db reaches or exceeds the second threshold value, thereby supplying a predetermined amount of developer of a predetermined color (B, C, D) to the developing devices 25B, 25C, and 25D, respectively.

[0082] When the relevant replenishing device is activated in step 105 to perform a replenishing operation, ADC-compatible concentration measurement is performed again (S107). In this ADC-compatible density re-measurement, the formation of the reference toner image to be measured in the first ADC-compatible density measurement and the measurement of the density of the reference toner image are carried out again in the same manner. In this case, the developability control unit 185 determines whether the density deviation amount Db obtained from the measurement result of the toner image density measurement unit 67 is less than the second threshold value (S108).

[0083] If it is determined in step 108 that the deviation amount Db is less than the second threshold value, the next operation of potential adjustment control is performed (S109). If the deviation amount Db is less than the second threshold value, it is deemed that the concentration of the developer in the corresponding developing device 25B, 25C, or 25D has returned to the second allowable concentration value by the replenishment operation. In the potential adjustment control operation, the surface potential of the photosensitive drum 22 measured by the surface potential measuring unit 68 is confirmed. The potential adjustment control operation is an operation for making necessary adjustments to potential settings in response to fluctuations in the amount of charge on the toner due to the replenishment of developer, etc. Specifically, it is an operation for making necessary adjustments to the development bias, the charging potential, the latent image potential, etc.

[0084] After the potential adjustment control operation is performed, the printing operation that was interrupted due to the ADC-compatible density measurement and the necessary supply operation is resumed (S110). Finally, it is determined whether the resumed printing operation has been completed (S111). If it is determined that the printing operation has been completed, the entire printing operation is completed.

[0085] When the above-described operation flow occurs, the printing operation being performed is interrupted by the operation of the ADC-compatible density measurement or the operation of the ADC-compatible replenishment device.

[0086] On the other hand, if it is determined in step 101 that it is not time to perform ADC-compatible density measurement, the printing operation in progress is continued without interruption. Also, if it is determined in step 105 that the density deviation amount Db is less than the second threshold, the printing operation in progress is continued without interruption. When the operation flow is as described above, it is determined whether the print operation being executed has ended (S111). If it is determined that the print operation has ended, all of the print operations are terminated.

[0087] In the latter case, the printing operation that is being performed continues without being interrupted by the ADC density measurement operation or the operation of the ADC replenishment device.

[0088] Incidentally, if it is determined in step 108 that the deviation amount Db is not less than the second threshold value but is greater than or equal to the second threshold value, the above-mentioned replenishment operation will not return the concentration of the developer in the corresponding developing device to the second allowable concentration value. In this case, the developability control unit 185 determines whether the number of replenishments by the relevant replenishment device among the replenishment devices 6B, 6C, and 6D is equal to or greater than a threshold value (S112). At this time, the threshold value becomes the upper limit value of the number of repetitions in which the toner in the developer container 15 does not run out and replenishment operation is possible.

[0089] If it is determined in step 112 that the number of replenishments is less than the threshold value, the process returns to the operation of the corresponding replenishment device among the ADC-compatible replenishment devices 6B, 6C, and 6D in step 106. In this case, starting from the replenishment operation in step 106, the operations in steps 107 and 108 are similarly repeated.

[0090] On the contrary, if it is determined in step 112 that the number of replenishments is equal to or greater than the threshold value, the process proceeds to the operation of potential adjustment control in step 109. In this case, further replenishment operations become impossible and are prohibited. Also, in this case, in the empty detection unit 188, it is determined that any one of the developer containers 15B, 15C, and 15D that store the toner of the corresponding color is in a state close to being empty.

[0091] <Operations related to ATC> In operations related to ATC, as shown in FIG. 4, first, the confirmation of the ATC replenishment determination Flag is performed (S120). The ATC replenishment determination Flag is set in the development property control unit 185 when the ATC-compatible density measurement described later is performed.

[0092] (Setting of ATC replenishment determination Flag) Here, the setting of the ATC replenishment determination Flag will be described first.

[0093] In this case, along with the start of the printing operation shown in FIG. 4, the image forming operation for the ATC-compatible color is executed as shown in FIG. 5 (S200). In the first embodiment, the ATC-compatible color is the "A color" which is the color of the developer of the developing device 25A in which ATC development property control is performed.

[0094] When an image forming operation for forming a toner image of this ATC compatible color is performed, density measurement for the ATC compatible color is performed (S201). In the ATC compatible concentration measurement, the toner concentration measuring unit 65 measures the concentration of the developer contained in the developing device 25A that is the measurement target.

[0095] At this time, the information measured by the toner concentration measurement unit 65 is collected in the developability control unit 185. At this time, the developability control unit 185 calculates, from the measurement information, the deviation amount Da that deviates from the first allowable density value as the image density of the developer in the developing device 25A.

[0096] Next, the developability control unit 185 determines whether the deviation amount Da of the density obtained from the measurement result of the toner density measurement unit 65 is equal to or greater than the first threshold value (S202). As described above, the first threshold value is the lower limit of the allowable amount of deviation from the first allowable concentration value.

[0097] If it is determined in step 202 that the deviation amount Da is less than the first threshold value, there is no need to replenish the developing device 25A with developer, and therefore the ATC replenishment determination flag is set to "Flag=0" indicating that replenishment is not required (S203). In this case, the replenishing device 6A is not operated because there is no need to replenish the developer.

[0098] On the other hand, if it is determined in step 202 that the deviation amount Da is equal to or greater than the first threshold value, it is necessary to replenish the developer in the developing device 25A, and therefore the ATC replenishment determination flag is set to "Flag=1" indicating that replenishment is necessary (S204).

[0099] However, in this case, the ATC supply determination flag is simply set to "Flag=1", and the ATC-compatible supply device 6A is not operated. In other words, in this case, the operation of the supply device 6A is put on hold.

[0100] Subsequently, after the ATC replenishment determination flag is set to "Flag=1", the developability control unit 185 checks the empty detection state transition flag set in the empty detection unit 188 (S205). The setting of the blank state transition flag will be described later.

[0101] If the blank state transition flag is "Flag=0" in step 205, which indicates that the blank state is to be transitioned, a storage process is performed to prevent the blank state from being transitioned (S206).

[0102] In this case, the amount of developer in the ATC-compatible developing device 25A is low, and the developer container 15A that stores the developer to be replenished to the developing device 25A is close to empty. However, even in this state, the empty detection unit 188 waits for the developer container 15A to be detected as empty by the above-mentioned storage process.

[0103] As a result, in this case, the developer container 15A is maintained in a state where replacement work for a new one is not performed, and as a result, the printing operation is not interrupted by the replacement work for the developer container 15A.

[0104] On the other hand, if the blank state transition flag is "Flag=1" in step 205, which indicates that it is time to transition the blank state, a storage process is performed to transition the blank state to "Near Empty" (S207). "Near Empty" is a determination item that indicates that the developer container 15A is nearly empty.

[0105] In this case, the empty detector 188 is also on standby for determining that the developer container 15A is empty through the above-described storage process. In this case, however, a warning message or the like is displayed on the operation display panel 47 to notify that the developer container 15A is in the "Near Empty" state. This makes it possible to notify and alert the user that the time to replace the developer container 15A is approaching.

[0106] <Continuation of the operation related to ATC> Here, return to the description of the operation related to ATC shown in FIG. 4.

[0107] If it is determined in step 120 that the ATC supply determination Flag is "Flag = 0", the process proceeds to step S111.

[0108] In this case, since the supply operation by the ATC - corresponding supply device 6A is not necessary, the supply device 6A does not operate. Also in this case, there are two cases regarding the interruption of the printing operation. One is the case where the concentration measurement operation corresponding to ADC and the supply operation of at least one of the supply devices 6B, 6C, 6D are performed as necessary, and the ongoing printing operation is interrupted. The other is the case where the concentration measurement operation and supply operation corresponding to ADC are not performed, and the ongoing printing operation is not interrupted.

[0109] On the other hand, if it is determined in step 120 that the ATC supply determination Flag is "Flag = 1", the ATC - corresponding supply device 6A operates (S121). In this case, when the supply device 6A operates, a predetermined amount of the developer of color A is supplied to the developing device 25A.

[0110] The ATC - corresponding supply device 6A at this time was in a standby state in step 204 shown in FIG. 5. However, the supply device 6A at this time is controlled to start when the concentration measurement corresponding to ADC is performed. Also, it can be said that the supply device 6A at this time is controlled to cancel the standby state and start when the concentration measurement timing corresponding to ADC shown in step 101 arrives.

[0111] When the ATC - corresponding supply device 6A operates and the supply operation is performed, the concentration measurement corresponding to ATC is performed again (S122). In this re-concentration measurement for ATC, the concentration of the developer in the ATC-compatible developing device 25A in the first concentration measurement for ATC shown in FIG. 5 is measured again.

[0112] When this ATC-compatible density re-measurement is performed, the developability control unit 185 determines whether the density deviation amount Da obtained from the measurement result of the toner density measurement unit 65 is less than the first threshold value (S123).

[0113] If it is determined in step 123 that the deviation amount Da is less than the first threshold value, the concentration of the developer in the developing device 25A is restored to the first allowable concentration value by the replenishing operation of the replenishing device 6A.

[0114] In this case, the developability control unit 185 changes the ATC replenishment determination flag to "Flag=0" (S124). That is, at this time, processing is performed assuming that the replenishment operation of the ATC-compatible replenishment device 6A is not required.

[0115] In this case, since the replenishing operation of the replenishing device 6A is being performed, the blank detection state transition flag is set to "Flag=0" in the developability control unit 185 (S125). That is, at this time, it is determined that there is no risk that the developer container 15A that contains the developer to be replenished to the replenishment device 6A will become empty.

[0116] Subsequently, after the processes of steps 124 and 125 are performed, the process proceeds to step S109, where the potential adjustment control operation is performed. In this case, the developer is replenished to the developing device 25A by the operation of the replenishment device 6A, and therefore the above-described potential adjustment control operation is performed in the same manner. In addition, the potential adjustment control operation at this time is performed at the same time when both the ADC-compatible replenishment operation and the ATC-compatible replenishment operation are performed. This combined potential adjustment control operation can shorten the time that the print operation is interrupted compared to when the ADC-compatible replenishment operation and the ATC-compatible replenishment operation are performed separately at different times, and the potential adjustment control operation is performed separately after each replenishment operation is completed.

[0117] After the potential adjustment control operation is performed, the interrupted printing operation is resumed (S110) triggered by ADC-compatible density measurement and a supply operation that is performed as needed. Finally, it is determined whether the resumed printing operation has finished (S111). If it is determined that the printing operation has finished, the entire printing operation is finished.

[0118] In the case of the above-described operation flow, the printing operation being performed is interrupted by the ADC-compatible density measurement operation or the replenishing operation of the ADC-compatible replenishing device. However, in this case, the ATC-compatible supply device 6A performs a supply operation during the interruption.

[0119] Incidentally, if it is determined in step 123 that the deviation amount Da is equal to or greater than the first threshold value, it is determined whether or not the number of times the replenishing device 6A has replenishing is equal to or greater than a threshold value (S126). If it is determined that the number of replenishments is less than the threshold value, the concentration of the developer in developing device 25A will not be restored to the first allowable concentration value. Therefore, in this case, the process proceeds to step 121, where the replenishment operation of replenishment device 6A and the subsequent operations of steps 122 and 123 are repeated in the same manner.

[0120] If it is determined in step 126 that the number of replenishments is equal to or greater than the threshold value, the replenishment operation of the replenishment device 6A is performed. Therefore, in this case, the developability control unit 185 sets the blank state transition flag to "Flag=1" (S127). That is, at this time, it is processed as there is a risk that the developer container 15A that contains the developer to be replenished to the replenishment device 6A may become empty.

[0121] After the operation of step 127 is completed, the process proceeds to step S109, where the potential adjustment control operation is performed, in the same manner as when the operation of step 125 is completed.

[0122] As described above, in image forming apparatus 1, the operation timing of replenishing device 6A and the operation timing of replenishing devices 6B, 6C, and 6D during image forming operation are adjusted.

[0123] Specifically, in the image forming device 1, as conceptually illustrated in the lower part of Figure 6, the operation timing of the ATC-compatible supply device 6A is controlled to operate at the same time as the operation timing of any of the ADC-compatible supply devices 6B, 6C, and 6D. This can also be interpreted as the image forming apparatus 1 controlling the operation of the ATC compatible supply device 6A to wait until the operation time of any of the ADC compatible supply devices 6B, 6C, and 6D.

[0124] The above-mentioned "same time" means that the operation timing of the supply device 6A and the operation timing of any of the supply devices 6B, 6C, and 6D are at least partially simultaneous. Therefore, the above-mentioned "same time" is not limited to the case where the operation timing of the supply device 6A and the operation timing of any of the supply devices 6B, 6C, and 6D coincide, but is used as a phrase that includes the case where they at least partially overlap.

[0125] FIG. 6 shows the following two image forming operations and a supply operation. That is, one is the state of image formation and supplying operations in the A-color image formation unit 21A, which is subjected to ATC developability control, and the other is the state of image formation and supplying operations in the B-color, C-color, and D-color image formation units 21B, 21C, and 21D, which are subjected to ADC developability control. The symbol St in Fig. 6 indicates the start time of the cumulative count of the print amount PV, which corresponds to the density measurement time of the ADC. Also, the symbols t1 to t3 in Fig. 6 indicate the arrival times of the density measurement time of the ADC, that is, the times that have arrived since each start time St.

[0126] FIG. 6 also illustrates a case where the replenishing device 6B is in operation among the ADC-compatible replenishing devices 6B, 6C, and 6D. Interruption A shown in Fig. 6 is the interruption time when the operation is interrupted due to the ATC-compatible A color developer replenishment operation. Interruption B shown in Fig. 6 is the interruption time when the operation is interrupted due to the ADC-compatible B color developer replenishment operation. Interruption B is longer than interruption A because the ADC developability control includes the time required for the reference toner image formation operation and the operation of measuring the density of the reference toner image in addition to the replenishment operation.

[0127] The comparative example shown in the upper part of FIG. 6 is an example in which an ATC-compatible supply device 6A and one ADC-compatible supply device 6B are operated individually without adjusting their operation timings. In the comparative example, the supply device 6A and the supply device 6B may operate completely separately at different times. In this case, the printing operation will be interrupted for the combined time of Interruption A and Interruption B. In this case, the printing operation will also be interrupted twice, at different times: Interruption A and Interruption B.

[0128] Therefore, in the image forming apparatus 1, the image forming operation is less likely to be interrupted by the developer replenishing operation than when the replenishing device 6A and the replenishing devices 6B, 6C, and 6D are operated individually without adjusting their operation timings during the image forming operation. An example of the case where the replenishing devices are operated individually is the comparative example shown in the upper part of FIG.

[0129] More specifically, according to the image forming apparatus 1, as shown in the example at the bottom of Figure 6, the operation timing of the supply device 6A is partially overlapped with the operation timing of the supply device 6B, and the operation timing is the same. As a result, the interruption C of the printing operation at this time is less than the sum of the interruptions A and B, which occur at different times in the comparative example, as shown in the example illustrated at the bottom of Figure 6.

[0130] Furthermore, in the image forming apparatus 1, as shown in the comparative example, the replenishment time of the ATC-compatible replenishment device 6A has already arrived before the density measurement time t1 for the ADC-compatible replenishment device 6A. However, in the image forming apparatus 1, the ATC compatible replenishing device 6A is nevertheless started when the ADC compatible density measurement time t2 arrives and the ADC compatible density is measured.

[0131] This prevents the image forming apparatus 1 from interrupting the printing operation due to the ATC compatible replenishing device 6A starting before the ADC compatible density is measured. That is, in the image forming apparatus 1, interruption of the printing operation at such a time is avoided, and accordingly, interruption of the printing operation due to the developer replenishment operation is reduced.

[0132] Furthermore, in the image forming apparatus 1, the ATC-compatible replenishment device 6A can start immediately when the ADC-compatible density measurement time arrives. This is because the replenishment device 6A does not need to perform the operation of forming a reference toner image required for ADC-compatible density measurement and the operation of measuring the density of that reference toner image. Therefore, in the image forming device 1, when a supply operation by an ADC-compatible supply device 6B or the like is required, the ADC-compatible supply device 6B or the like is started while the ATC-compatible supply device 6A is operating for the supply operation.

[0133] As a result, in the image forming apparatus 1, the operation timing of the ATC-compatible replenishment device 6A and the operation timing of the ADC-compatible replenishment device 6B and the like are at least partially overlapped as illustrated in the example at the bottom of Fig. 6. As a result, in the image forming apparatus 1, the time during which the print operation is interrupted is reduced by the amount of the overlap.

[0134] In addition, when performing ATC developability control, the developability control unit 185 in the image forming apparatus 1 uses, as the first threshold value, a value having a deviation amount that is smaller than the deviation amount of the second threshold value from the second allowable density value. In this case, the small deviation amount as the first threshold value is, for example, the following value. In other words, this value is adjusted to satisfy the condition that the density of the reference toner image developed by the ATC-compatible developing device 25A after the replenishment operation of the ATC-compatible replenishment device 6A that has been put on standby becomes an acceptable density.

[0135] As a result, in the image forming apparatus 1, even if the supply of developer from the ATC-compatible supply device 6A to the ATC-compatible development device 25A is delayed due to standby, the development characteristics of the development device 25A can be prevented from deteriorating. In other words, in this case, the deterioration of the development characteristics of developing device 25A is suppressed compared to when a threshold value having a deviation amount smaller than the deviation amount of the second threshold value from the second allowable density value is not applied as the first threshold value.

[0136] Variant. The present invention is not limited to the configuration exemplified above as Embodiment 1. In other words, the present invention can be modified and altered in various ways without departing from the spirit of the inventions described in the claims. Therefore, the present invention also includes the following modifications, for example.

[0137] In the first embodiment, the image forming apparatus 1 is exemplified as having four developing devices 25. However, the image forming apparatus 1 may have a plurality of developing devices that contain different types (colors, etc.) of developer as the developing devices 25. Therefore, the number of the plurality of developing devices is not limited to four.

[0138] Furthermore, in the first embodiment, the ATC-compliant supply device (an example of the first supply means) is a single supply device 6A, but the ATC-compliant supply device may be a plurality of supply devices.

[0139] Furthermore, in the first embodiment, the ADC-compatible supply devices (an example of the second supply means) are the remaining supply devices 6B to 6D excluding the supply device 6A. However, the ADC-compatible supply devices may be other multiple supply devices or a single supply device.

[0140] As long as the image forming apparatus of the present invention is equipped with a plurality of developing devices, it may be an image forming apparatus that employs a direct transfer method instead of the intermediate transfer unit 30. In this case, the direct transfer method is a transfer method in which the toner image is directly transferred from the photosensitive drum 22 to the paper 9. An image forming apparatus employing the direct transfer method is configured, for example, so that the paper 9 is conveyed by a conveyor belt or the like so as to pass sequentially through the transfer positions of the photosensitive drums 22 of the multiple image forming units 21 .

[0141] (Addendum) (((1))) a plurality of developing devices containing different types of developers; a first supplying means for supplying developer to at least one of the plurality of developing devices when the concentration of the developer in the at least one developing device reaches a predetermined value; a second supplying means for supplying developer to the remaining developing devices when the developer concentration in the remaining developing devices reaches a predetermined value; a control means for controlling the first supply means to operate at the same time as the second supply means; An image forming apparatus comprising: (((2))) a plurality of developing devices containing different types of developers; a first supply means for supplying developer to at least one of the plurality of developing devices when a result of measuring the concentration of the developer in the at least one developing device at a first measurement time reaches a predetermined value; a second supply means for supplying developer to the remaining developing devices when a result of measuring the concentration of developer in the remaining developing devices at a second measurement time different from the first measurement time reaches a predetermined value; a control means for controlling the operation of the first supply means to wait until the second measurement time comes; An image forming apparatus comprising: (((3))) The image forming apparatus according to (((1))), wherein the control unit starts the first supply unit when the concentration of the developer in the remaining developing device is measured. (((4))) The image forming apparatus according to (((2))), wherein the control unit starts the first supply unit that has been put on standby when the second measurement time arrives. (((5))) The image forming apparatus according to (((3))), wherein the control unit starts the second supply unit while the first supply unit is operating. (((6))) The image forming apparatus according to (((4))), wherein the control unit starts the second supply unit while the first supply unit is operating. (((7))) the predetermined value in the first supply means is a value equal to or greater than a first threshold value, which is an allowable lower limit value that deviates from a first allowable concentration value of the developer in the at least one developing device, the predetermined value in the second supply unit is a value equal to or greater than a second threshold value, which is an allowable lower limit value that deviates from a second allowable concentration value of the developer in the remaining developing device, The image forming apparatus according to any one of ((1)) to ((6))), wherein the control means uses as the first threshold a value that is a deviation smaller than the deviation of the second threshold from the second allowable density value. (((8))) The image forming apparatus described in any of (((1))) to (((7))), wherein, when the concentration of the developer returns to an allowable concentration value at a stage when the number of replenishments of the first replenishment means does not exceed an upper limit value, the control means retains the result of empty detection, which determines that the developer in at least one developing device is empty, as a determination result that the developer is not empty until the concentration of the developer in the remaining developing devices is measured.

[0142] According to the image forming apparatuses of (((1))) and (((2))), the image forming operation is less likely to be interrupted by the developer replenishing operation than when the first replenishing means and the second replenishing means are operated individually without adjusting their operating timings. According to the image forming apparatus of (((3))), the image forming operation is not interrupted by the first supplying means starting before the developer concentration in the remaining developing devices is measured. According to the image forming apparatus of (((4))), the first supplying means is started before the second measurement time is reached, and thus the image forming operation is not interrupted. According to the image forming apparatus of (((5))), the operation timing of the first supplying means and the operation timing of the second supplying means at least partially overlap, thereby reducing the time during which the image forming operation is interrupted. According to the image forming apparatus of (((6))), the operation timing of the first supplying means and the operation timing of the second supplying means at least partially overlap, thereby reducing the time during which the image forming operation is interrupted. According to the image forming apparatus of (((7))), it is possible to prevent a decrease in the development characteristics of at least some of the developing devices due to a delay in the supply of developer from the first supply unit to the developing devices. According to the image forming apparatus of (((8))), it is possible to reduce the interruption of the image forming operation due to the work of replacing the developer container that contains the developer to be replenished. [Explanation of symbols]

[0143] 1...Image forming device 6A... Replenishment device (an example of the first replenishing means) 6B, 6C, 6D... Replenishment device (an example of second replenishing means) 25A...developing device (an example of at least one of the developing devices) 25B, 25C, 25D...developing devices (examples of the remaining developing devices of the plurality of developing devices) 185...Development control unit (an example of a control means)

Claims

1. a plurality of developing devices containing different types of developers; a first supplying means for supplying developer to at least one of the plurality of developing devices when the concentration of the developer in the at least one developing device reaches a predetermined value; a second supplying means for supplying developer to the remaining developing devices when the developer concentration in the remaining developing devices reaches a predetermined value; a control means for controlling the first supply means to operate at the same time as the second supply means; An image forming apparatus comprising:

2. a plurality of developing devices containing different types of developers; a first supply means for supplying developer to at least one of the plurality of developing devices when a result of measuring the concentration of developer in the at least one developing device at a first measurement time reaches a predetermined value; a second supply means for supplying developer to the remaining developing devices when a result of measuring the concentration of developer in the remaining developing devices at a second measurement time different from the first measurement time reaches a predetermined value; a control means for controlling the operation of the first supply means to wait until the second measurement time comes; An image forming apparatus comprising:

3. 2. The image forming apparatus according to claim 1, wherein said control means starts said first supply means when the concentration of the developer in said remaining developing device is measured.

4. 3. The image forming apparatus according to claim 2, wherein the control means starts the first supply means that has been put on standby when the second measurement time arrives.

5. 4. The image forming apparatus according to claim 3, wherein the control means starts the second supply means while the first supply means is in operation.

6. 5. The image forming apparatus according to claim 4, wherein said control means starts said second supplying means while said first supplying means is in operation.

7. the predetermined value in the first supply unit is a value equal to or greater than a first threshold value, which is an allowable lower limit value that deviates from a first allowable concentration value of the developer in the at least one developing device, the predetermined value in the second supply unit is a value equal to or greater than a second threshold value, which is an allowable lower limit value that deviates from a second allowable concentration value of the developer in the remaining developing device, 3. The image forming apparatus according to claim 1, wherein the control unit uses, as the first threshold value, a value having a deviation amount smaller than a deviation amount of the second threshold value from the second allowable density value.

8. 3. An image forming apparatus as described in claim 1 or 2, wherein the control means, when the concentration of the developer returns to an allowable concentration value at a stage when the number of replenishments by the first replenishment means does not exceed an upper limit value, retains the result of empty detection, which determines that the developer in at least one developing device is empty, as a determination result that the developer is not empty until the concentration of the developer in the remaining developing devices is measured.

Images