Developing device, image forming device, toner replenishing method, and program

Abstract

To provide a developing device which offers extended life of a developing unit while suppressing image problems, and to provide an image forming device, toner replenishing method, and program.SOLUTION: A developing device disclosed herein comprises a control unit 11 configured to control replenishment of toner by a replenishment unit (toner bottle TB) in such a way that toner density detected by a detection unit (TCR censor SE1) matches a target level. The control unit 11 changes the target level according to the level of deterioration of developer when replacing the replenishment unit upon detection of the "toner empty" state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a developing device, an image forming apparatus, a toner supply method, and a program. [Background technology]

[0002] Electrophotographic image forming apparatuses are known in the art. In an electrophotographic image forming apparatus, first, an image carrier (photoreceptor) having a photoconductive material is uniformly charged by a charging means. Next, the surface of the image carrier is exposed to light by an exposure means, and an electrostatic latent image is formed by a potential difference. Next, the electrostatic latent image is converted into a toner image by a developing device and transferred to a transfer material such as paper. After that, the toner image is fixed to the transfer material using heat, pressure, etc., thereby forming an image on the transfer material.

[0003] In the above configuration, when the toner bottle (TB) is replaced after the toner is empty, forced toner replenishment is performed. This attempts to bring the toner concentration (Tc) in the developing unit closer to the target value. Under normal conditions, the toner concentration increases as the replenished toner is absorbed into the developer in the developing unit, and the forced toner replenishment operation is completed when the toner concentration reaches the target value.

[0004] However, in a configuration without a sub-hopper, toner emptying is determined based on changes in toner concentration, resulting in a significant drop in toner concentration when the toner is empty. To restore the toner concentration to the target value from that state, a large amount of toner must be rapidly replenished. This often leads to image problems such as powder smoke and fogging. Furthermore, increased toner consumption in the toner bottle shortens the life of the toner bottle and the developing device.

[0005] Furthermore, in recent years, developing units have become smaller, faster, and less expensive, resulting in less mixing capacity. As a result, the replenished toner cannot be absorbed into the developer in the developing unit, and the toner concentration may not increase beyond a certain level. This makes image problems such as dust smoke and fogging more likely to occur. Furthermore, if this condition continues, a low abnormality in the TCR sensor, which detects the toner concentration of the developer in the developing unit, will be displayed. This may lead to the developer unit being replaced before its lifespan is reached. This condition becomes more likely as the unit's lifespan increases (the amount of carrier in the developer is consumed increases).

[0006] To solve the above problem, a configuration has been disclosed in which a predetermined amount of toner is replenished based on the detected voltage value when the toner end is detected, thereby canceling the toner end state (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-296891 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the configuration described in Patent Document 1, toner is replenished at a predetermined amount, which differs from the actual state and can result in a large error from the target toner density, which can lead to problems such as unnecessary image noise (powder smoke, fogging, uneven density, etc.) and unnecessary toner consumption.

[0009] SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device, an image forming apparatus, a toner supply method, and a program that can extend the life of a developing unit while suppressing the occurrence of image problems. [Means for solving the problem]

[0010] The invention described in claim 1 has been made to achieve the above object, A developing device comprising: a developing unit that develops an electrostatic latent image formed on an image carrier using a two-component developer consisting of toner and a carrier; a replaceable supply unit that supplies toner to the developing unit; and a detection unit that detects the toner concentration of the developer in the developing unit, wherein the developing device detects that the toner concentration of the supply unit is empty when the toner concentration detected by the detection unit becomes equal to or lower than a predetermined value, a control unit that controls the supply of toner by the supply unit so that the toner concentration detected by the detection unit reaches a target value; The control unit changes the target value in accordance with the degree of deterioration of the developer when the supply unit is replaced in response to detection of the toner empty state.

[0011] The invention described in claim 2 is the developing device described in claim 1, The control unit changes the target value to a value lower than that during image formation in accordance with the degree of deterioration of the developer.

[0012] The invention described in claim 3 is the developing device described in claim 2, The control unit is characterized in that the greater the degree of deterioration of the developer, the lower the target value is changed to.

[0013] The invention described in claim 4 is the developing device described in claim 2, The control unit is characterized in that, after the toner concentration detected by the detection unit reaches the changed target value, the control unit returns the target value to the value at the time of image formation.

[0014] The invention described in claim 5 is the developing device described in claim 4, The control unit is characterized in that after the toner concentration detected by the detection unit reaches the changed target value and a predetermined number of sheets are printed, the control unit returns the target value to the value at the time of image formation.

[0015] The invention described in claim 6 is the developing device described in claim 4, The control unit returns the target value to the value at the time of image formation in a stepwise manner.

[0016] The invention described in claim 7 is the developing device described in claim 1, The control unit calculates the degree of deterioration of the developer as the ratio of the amount of replenished toner to the amount of toner required at the time of replenishment, and determines that the degree of deterioration of the developer is greater as the ratio of the amount of replenished toner is greater.

[0017] The invention described in claim 8 is the developing device described in claim 1, The control unit calculates the degree of deterioration of the developer as the percentage of time during which the toner concentration detected by the detection unit is lower than the target value, and determines that the greater the percentage of time during which the value is lower than the target value, the greater the degree of deterioration of the developer.

[0018] The invention described in claim 9 is the developing device described in claim 1, The control unit changes the target value in accordance with the degree of deterioration of the developer and at least one of the number of sheets that can be printed and the number of replaced supply units.

[0019] The invention described in claim 10 is In the image forming apparatus, an image forming unit that forms an image on a sheet; The image forming unit includes: an image carrier; a developing device according to any one of claims 1 to 9, which supplies a developer to the electrostatic latent image formed on the image carrier to form a toner image; The present invention is characterized by comprising:

[0020] The invention described in claim 11 is A toner supply method for a developing device, comprising: a developing unit that develops an electrostatic latent image formed on an image carrier using a two-component developer consisting of toner and a carrier; a replaceable supply unit that supplies toner to the developing unit; and a detection unit that detects the toner concentration of the developer in the developing unit, wherein the toner supply unit is detected as empty when the toner concentration detected by the detection unit becomes equal to or lower than a predetermined value, a control step of controlling the supply of toner by the supply unit so that the toner concentration detected by the detection unit reaches a target value; The control step is characterized in that, when the supply unit is replaced due to detection of the toner empty state, the target value is changed in accordance with the degree of deterioration of the developer.

[0021] The invention described in claim 12 is a computer for a developing device comprising: a developing unit that develops an electrostatic latent image formed on an image carrier using a two-component developer consisting of toner and a carrier; a replaceable supply unit that supplies toner to the developing unit; and a detection unit that detects the toner concentration of the developer in the developing unit, the computer detecting that the toner concentration of the supply unit is empty when the toner concentration detected by the detection unit becomes equal to or lower than a predetermined value; the toner concentration detecting unit is caused to function as a control unit that controls the supply of the toner by the supply unit so that the toner concentration detected by the detection unit reaches a target value; The control unit is a program that changes the target value in accordance with the degree of deterioration of the developer when the supply unit is replaced upon detection of the toner empty. [Effects of the Invention]

[0022] According to the present invention, it is possible to extend the life of the development unit while suppressing the occurrence of image problems. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2]FIG. 2 is a functional block diagram showing a control structure of the image forming apparatus according to the present embodiment. [Figure 3] FIG. 2 is a diagram illustrating a schematic configuration of an imaging cartridge. [Figure 4] 6 is a flowchart illustrating an example of control of the image forming apparatus according to the present embodiment. [Figure 5] 10 is an example of a graph showing the relationship between the number of sheets that can be printed and the deterioration degree r of the developer. [Figure 6] FIG. 10 is a diagram showing an example of a change in the target value of a TCR sensor. [Figure 7] 10 is a flowchart showing an example of control of the image forming apparatus according to Modification 1. [Figure 8] 10 is a flowchart showing an example of control of the image forming apparatus according to Modification 2. [Figure 9] 10 is a flowchart showing an example of control of the image forming apparatus according to Modification 3. [Figure 10] 10 is a flowchart showing an example of control of the image forming apparatus according to Modification 4. [Figure 11] FIG. 10 is a diagram showing another example of a change in the target value of the TCR sensor. [Figure 12A] FIG. 10 is a diagram showing an example of an output value of a TCR sensor when the degree of deterioration of a developer is small. [Figure 12B] FIG. 10 is a diagram showing an example of an output value of a TCR sensor when the degree of deterioration of a developer is large. [Figure 13] FIG. 10 is a diagram showing the relationship between the percentage of time during which the output value of the TCR sensor is lower than the target value and the deterioration degree of the developer. [Figure 14] 10 is an example of a graph showing the relationship between the number of sheets that can be printed and the deterioration degree ru of the developer. [Figure 15] 10 is a flowchart showing an example of control of the image forming apparatus 1 using the deterioration degree ru. [Figure 16] 10 is an example of a graph showing the relationship between the value of the DC component (Vdc) of the developing bias applied to the developing roller and the amount of toner adhered to the intermediate transfer belt. [Figure 17]10 is an example of a graph showing the relationship between the deterioration degree of a developer and the output value of an AIDC sensor. [Figure 18] 10 is an example of a graph showing the relationship between the stirring time of a development unit and the output value of a TCR sensor. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0025] As shown in Figures 1 and 2, the image forming apparatus 1 of this embodiment includes a control unit 11, an image forming unit 12, a memory unit 13, an operation panel 14, a detection unit 15, and a communication unit 16.

[0026] The control unit 11 includes a CPU, RAM, ROM, etc. The CPU first reads out various processing programs stored in the ROM and loads them into the RAM in response to an operation signal input from the operation unit 142 or an instruction signal received by the communication unit 16. Next, the CPU comprehensively controls the operation of the image forming apparatus 1 in cooperation with the various programs loaded into the RAM.

[0027] The image forming unit 12 forms an image made up of four colors, Y, M, C, and K, on ​​a sheet of paper in accordance with the pixel values ​​of the four colors of each pixel of the image-processed original image. 1, the image forming unit 12 includes an imaging cartridge 20, an exposure unit 30, an intermediate transfer belt 40, a primary transfer roller 50, a secondary transfer roller 60, a fixing unit 70, a cleaning unit 80, etc. The imaging cartridge 20, the exposure unit 30, and the primary transfer roller 50 are provided for each of the colors Y, M, C, and K. Toner bottles TB containing replenishment developer are arranged above the intermediate transfer belt 40 for each of the colors Y, M, C, and K.

[0028] The imaging cartridges 20 are arranged in series (tandem) along the belt surface of the intermediate transfer belt 40, and form images of the respective colors Y, M, C, and K. The imaging cartridges 20 have the same configuration except for the colors of the images they form. As shown in FIGS. 1 and 3, each imaging cartridge 20 includes an image carrier unit 21 and a developing unit 22. The image carrier unit 21 includes an image carrier 21a, a charging unit 21b, and a cleaning unit 21c.

[0029] When forming an image, the image forming unit 12 first charges the image carrier 21a using the charging unit 21b. Then, a light beam emitted from the exposure unit 30 is scanned over the image carrier 21a based on the original image to form an electrostatic latent image. Next, the developing unit 22 supplies a color material such as toner to develop the image. As a result, an image (toner image) is formed on the image carrier 21a. The images formed on the image carriers 21a are sequentially superimposed and primarily transferred onto the intermediate transfer belt 40 by the respective primary transfer rollers 50. As a result, images of each color are formed on the intermediate transfer belt 40. The intermediate transfer belt 40 is wound around multiple rollers and rotates. A cleaning unit 80 removes color material remaining on the image carriers 21a after the primary transfer.

[0030] Paper is fed from paper feed tray TR1 to image forming unit 12 in time with the image on the rotating intermediate transfer belt 40 reaching the position of secondary transfer roller 60. Secondary transfer roller 60 is one of a pair of rollers, one of which presses against intermediate transfer belt 40 and the other of which wraps around intermediate transfer belt 40. Image forming unit 12 performs secondary transfer of the image from intermediate transfer belt 40 onto paper by the pressure of secondary transfer roller 60. Image forming unit 12 then transports the paper to fixing unit 70 for fixing, and ejects the paper to paper ejection tray T3 via paper ejection roller R1. The fixing process involves applying heat and pressure to the paper using fixing roller 70a to fix the image to the paper. Cleaning unit 80 removes residue (such as residual toner) remaining on intermediate transfer belt 40 after secondary transfer. The residue removed by cleaning unit 80 is collected and stored in waste toner box B1 located below cleaning unit 80.

[0031] The developing unit 22 develops the electrostatic latent image formed on the image carrier 21a using a two-component developer consisting of toner and carrier. That is, the developing unit 22 functions as a developing section of the present invention. A developing unit 22 is provided for each color. Each developing unit 22 develops the electrostatic latent image using a developer containing toner of a different color. 1, each developing unit 22 is provided with a toner bottle TB that supplies toner to the developing unit 22. The toner bottle TB (supply unit) is provided so as to be replaceable.

[0032] The developing unit 22 includes two transport rollers 22a and 22b and a developing roller 22c.

[0033] The two transport rollers 22a and 22b are rotatably installed in the developing unit 22. The two transport rollers 22a and 22b agitate and circulate the two-component developer in the developing unit 22.

[0034] Developing roller 22c is disposed substantially above transport roller 22a. Developing roller 22c has a plurality of magnetic poles for transporting the developer disposed therein. Developing roller 22c has a freely rotatable cylindrical member disposed on the outer periphery of the plurality of magnetic poles. The developing roller 22c receives the developer from the transport roller 22a. The developing roller 22c transports the developer, which has been regulated to a target amount by the regulating unit RE, to the nip formed between the developing roller 22c and the image carrier 21a. As a result, the latent image formed on the image carrier 21a is visualized with toner. At this time, a developing bias is applied to the nip to cause the toner to fly to the image carrier 21a. The developing bias is a high voltage that combines a DC component of -200V to 900V with an AC component of a square wave or sine wave with a frequency of 3 to 7 kHz and a Vpp of 1 to 3 kVpp.

[0035] A TCR sensor SE1 is disposed below the transport roller 22b. The TCR sensor SE1 detects the ratio of toner to carrier (toner concentration Tc) in the developer in the developing unit 22. That is, the TCR sensor SE1 functions as a detection unit of the present invention. The developing device of the present invention includes at least a developing unit 22, a toner bottle TB, a TCR sensor SE1, and a control unit 11. The developing device supplies a developer to an electrostatic latent image formed on an image carrier 21a to form a toner image.

[0036] The control unit 11 controls the supply of toner from the toner bottle TB so that the toner concentration Tc detected by the TCR sensor SE1 becomes the target value. Specifically, the control unit 11 compares the output value of the TCR sensor SE1 with a predetermined target value while the developing unit 22 is in operation. If the output value is lower than the target value, the control unit 11 causes toner to be supplied. The output value of the TCR sensor SE1 is the toner concentration Tc detected by the TCR sensor SE1. The control unit 11 detects that the toner bottle TB is empty of toner when the toner concentration Tc detected by the TCR sensor SE1 becomes equal to or less than a predetermined value. When the toner bottle TB is replaced due to detection of toner empty, the control unit 11 changes the target value in accordance with the degree of deterioration of the developer.

[0037] When the control unit 11 detects that the toner in the toner bottle TB is empty, it causes the display unit 141 to display a screen instructing the user to replace the toner bottle TB. This allows the user to replace the toner bottle TB. When the detection unit 15 detects that the toner bottle TB has been replaced, the control unit 11 causes toner to be replenished so that the output value of the TCR sensor SE1, which has become lower than the target value, approaches the target value.

[0038] The storage unit 13 is a non-volatile storage means configured by a hard disk drive (HDD), a solid state drive (SSD), etc. The storage unit 13 stores various programs, various setting data, etc. in a manner that allows the control unit 11 to read and write the data.

[0039] The operation panel 14 includes a display unit 141 that displays various information to the user, and an operation unit 142 that accepts operation inputs from the user. The display unit 141 is configured with a color liquid crystal display or the like. The display unit 141 displays an operation screen or the like in accordance with a display control signal input from the control unit 11. The operation screen or the like includes, for example, various setting screens, various buttons, and the operating status of each function. The display unit 141 also displays a screen for instructing the user to replace the toner bottle TB. The operation unit 142 includes a touch panel provided on the screen of the display unit 141 and various hard keys arranged around the screen of the display unit 141. When a button displayed on the screen is pressed with a finger, a touch pen, or the like, the operation unit 142 first detects the X and Y coordinates of the pressed point of force as a voltage value. Next, the operation unit 142 outputs an operation signal associated with the detected position to the control unit 11. Note that the touch panel is not limited to a pressure-sensitive type and may be, for example, an electrostatic type or an optical type. Furthermore, when a hard key is pressed, the operation unit 142 outputs an operation signal associated with the pressed key to the control unit 11. The user can operate the operation unit 142 to make settings related to image formation, issue paper transport instructions, and stop the device. Settings related to image formation include, for example, image quality settings, magnification settings, application settings, output settings, and paper settings.

[0040] The detector 15 detects that the toner bottle TB has been replaced with a new one.

[0041] The communication unit 16 has a communication IC, a communication connector, etc., and is an interface that connects the image forming apparatus 1 to a communication network. The communication unit 16 transmits and receives various information to and from external devices connected to the communication network using a predetermined communication protocol under the control of the control unit 11. The communication unit 16 can also input and output various information via USB.

[0042] Next, the control of the image forming apparatus 1 according to this embodiment will be described with reference to the flowchart of Fig. 4. The control of Fig. 4 is started when the control unit 11 detects that the toner bottle TB is empty of toner.

[0043] First, the control unit 11 determines whether or not the detection unit 15 has detected replacement of the toner bottle TB (step S101). When the control unit 11 determines that replacement of the toner bottle TB has been detected (step S101: YES), the process proceeds to the next step S102. On the other hand, when the control unit 11 determines that replacement of the toner bottle TB has not been detected (step S101: NO), the process proceeds to step S107.

[0044] In step S102, the control unit 11 determines whether the deterioration degree r of the developer is 2 or more (r>2). When the control unit 11 determines that the deterioration degree r of the developer is 2 or more (step S102: YES), the process proceeds to the next step S103. On the other hand, when the control unit 11 determines that the deterioration degree r of the developer is not equal to or greater than 2 (step S102: NO), the process proceeds to step S104.

[0045] Figure 5 is an example graph showing the relationship between the number of pages used and the degree of developer deterioration r. The horizontal axis represents the number of pages used, and the vertical axis represents the degree of deterioration r. The degree of deterioration r is calculated by dividing the "actual amount of toner replenished" by the "amount of toner required at the time of replenishment." The required amount of toner is calculated from the output value of the TCR sensor SE1. The control unit 11 determines that the greater the proportion of replenished toner, the greater the degree of developer deterioration r. As shown in Figure 5, the degree of deterioration r increases as the number of pages used increases. When the number of pages used is low, the replenished toner is directly absorbed into the developer in the developing unit 22, so the amount of replenished toner is approximately the same as the amount of required toner. On the other hand, as the number of pages used increases, the developer deteriorates and the replenished toner is less easily absorbed into the developer in the developing unit 22. As a result, some of the replenished toner scatters, soiling the interior of the machine or adhering to the white background of the image. As a result, the toner concentration Tc of the developer in the developing unit 22 does not reach the target value, and additional toner must be replenished. That is, the greater the number of sheets that can be printed, the greater the amount of toner required for replenishment, and therefore the greater the deterioration degree r. As described above, the control unit 11 calculates the deterioration degree r of the developer as the ratio of the amount of replenished toner to the amount of toner required at the time of replenishment, and determines that the greater the ratio of the amount of replenished toner, the greater the deterioration degree r of the developer.

[0046] In step S103, the control unit 11 changes the target value of the TCR sensor SE1 to a value 1.5% lower than the normal value (during image formation), and then proceeds to step S107.

[0047] In step S104, the control unit 11 determines whether the deterioration degree r of the developer is 1.5 or more (r>1.5). When the control unit 11 determines that the deterioration degree r of the developer is 1.5 or more (step S104: YES), the process proceeds to the next step S105. On the other hand, when the control unit 11 determines that the deterioration degree r of the developer is not 1.5 or more (step S104: NO), the process proceeds to step S106.

[0048] In step S105, the control unit 11 changes the target value of the TCR sensor SE1 to a value 1% lower than that during image formation, and then proceeds to step S107.

[0049] In step S106, the control unit 11 changes the target value of the TCR sensor SE1 to a value 0.5% lower than that during image formation, and then proceeds to step S107.

[0050] As described above, in steps S103, S105, and S106, the control unit 11 changes the target value of the TCR sensor SE1 to a value lower than that during image formation. That is, the control unit 11 changes the target value of the TCR sensor SE1 to a value lower than that during image formation in accordance with the deterioration degree r of the developer. Specifically, if the degradation level r is less than 1.5, the target value of the TCR sensor SE1 is changed to a value 0.5% lower than that during image formation. If the degradation level r is 1.5 or greater but less than 2, the target value of the TCR sensor SE1 is changed to a value 1% lower than that during image formation. If the degradation level r is 2 or greater, the target value of the TCR sensor SE1 is changed to a value 1.5% lower than that during image formation. In this way, the control unit 11 changes the target value of the TCR sensor SE1 to a lower value as the deterioration degree r of the developer increases.

[0051] FIG. 6 shows an example of the change in the target value of the TCR sensor SE1. The horizontal axis represents the number of sheets that can be printed, and the vertical axis represents the target value of the TCR sensor SE1. The solid line L10 represents the target value during image formation (normal operation). In the example shown in FIG. 6, the target value during image formation is also changed to a lower value in accordance with the deterioration of the developer when the number of sheets that can be printed exceeds a predetermined value (see symbol F). The dashed line L11 represents the target value when the toner bottle TB is replaced when the degree of deterioration of the developer is determined to be 1.5 or greater but less than 2. The dashed line L12 represents the target value when the toner bottle TB is replaced when the degree of deterioration of the developer is determined to be 2 or greater. In the example shown in FIG. 6, the target value when the toner bottle TB is replaced is changed to a value lower than that during image formation depending on the degree of deterioration of the developer. Specifically, the dashed line L11 represents a value 1% lower than that during image formation, and the dashed line L12 represents a value 1.5% lower than that during image formation. That is, the more sheets are used, the lower the changed target value becomes. Note that the target value is lowered only from the time the toner bottle TB is replaced until a predetermined number of sheets are printed, and after the predetermined number of sheets are printed, the target value is returned to the target value at the time of image formation. That is, after the toner concentration Tc detected by the TCR sensor SE1 reaches the changed target value and the predetermined number of sheets are printed, the control unit 11 returns the target value to the value at the time of image formation.

[0052] By lowering the target value of the TCR sensor SE1, the amount of toner replenished during recovery can be reduced. It also reduces the amount of toner that cannot be absorbed into the developer in the development unit 22. Adjusting the amount of change in the target value according to the degree of developer deterioration allows for adjustments based on the actual state of the developer. This makes it possible to more effectively prevent image noise (powder smoke, fogging, etc.) and contamination of the developer and machine. Lowering the target value of the TCR sensor SE1 also makes it easier for the toner concentration Tc to return to the target value, reducing false detections of problems. This prevents unnecessary replacement of developers that are nearing the end of their life.

[0053] In step S107, the control unit 11 starts to supply toner.

[0054] Next, the control unit 11 determines whether the output value of the TCR sensor SE1 (the toner concentration Tc detected by the TCR sensor SE1) has returned to (reached) the target value (step S108). When the control unit 11 determines that the output value of the TCR sensor SE1 has returned to the target value (step S108: YES), the process proceeds to the next step S109. On the other hand, when the control unit 11 determines that the output value of the TCR sensor SE1 has not returned to the target value (step S108: NO), it repeats the process until the output value returns to the target value.

[0055] In step S109, the control unit 11 ends the toner replenishment associated with the replacement of the toner bottle TB. At this time, the control unit 11 performs a process to return the target value of the TCR sensor SE1 to the value at the time of image formation. That is, after the toner concentration Tc detected by the TCR sensor SE1 reaches the changed target value, the control unit 11 returns the target value to the value at the time of image formation.

[0056] As described above, the image forming apparatus 1 according to this embodiment includes the control unit 11 that controls the supply of toner by the supply unit (toner bottle TB) so that the toner concentration detected by the detection unit (TCR sensor SE1) reaches the target value. When the supply unit is replaced due to detection of empty toner, the control unit 11 changes the target value according to the degree of deterioration of the developer. Therefore, the image forming apparatus 1 according to this embodiment can control toner replenishment according to the actual state of the developer. Therefore, it is possible to suppress image problems such as dust smoke and fogging while maintaining a compact and low-cost device. Furthermore, it is possible to reduce the number of times the developing unit 22 needs to be replaced due to the output of the TCR sensor SE1 not reaching its target. Therefore, the life of the developing unit 22 can be extended.

[0057] Furthermore, the control unit 11 changes the target value to a value lower than that during image formation depending on the degree of deterioration of the developer. Specifically, the control unit 11 changes the target value to a lower value as the degree of deterioration of the developer increases. Therefore, toner replenishment can be limited according to the actual degree of developer deterioration. This can prevent image problems such as powder smoke and fogging. It can also reduce the number of times the developing unit 22 needs to be replaced due to the output of the TCR sensor SE1 not reaching its target. This can extend the life of the developing unit 22.

[0058] Furthermore, after the toner concentration detected by the detection unit reaches the changed target value, the control unit 11 returns the target value to the value at the time of image formation. Specifically, after the toner concentration detected by the detection unit reaches the changed target value and a predetermined number of sheets are printed, the control unit 11 returns the target value to the value at the time of image formation. Therefore, it is possible to supply toner appropriately for image formation, and therefore it is possible to form an appropriate image.

[0059] Furthermore, the control unit 11 calculates the deterioration degree of the developer as the ratio of the amount of replenished toner to the amount of toner required at the time of replenishment, and determines that the greater the ratio of the amount of replenished toner, the greater the deterioration degree of the developer. Therefore, the degree of deterioration of the developer can be calculated appropriately, which allows the actual state of the developer to be grasped more accurately, thereby more reliably preventing image problems such as powder smoke and fogging.

[0060] Although the present invention has been specifically described above based on the embodiments thereof, the present invention is not limited to the above embodiments and can be modified within the scope of the present invention.

[0061] (Variation 1) For example, in the above embodiment, the target value of the TCR sensor SE1 is changed to a value lower than that during image formation in accordance with the deterioration degree r of the developer, but this is not limited to this. For example, if the deterioration degree r of the developer is small, the current state may be maintained (the target value may remain the same as that during image formation). Hereinafter, the control of the image forming apparatus 1 according to the first modification will be described with reference to the flowchart of FIG.

[0062] First, the control unit 11 determines whether or not the detection unit 15 has detected replacement of the toner bottle TB (step S201). When the control unit 11 determines that replacement of the toner bottle TB has been detected (step S201: YES), the process proceeds to the next step S202. On the other hand, if the control unit 11 determines that replacement of the toner bottle TB has not been detected (step S201: NO), the process proceeds to step S204.

[0063] In step S202, the control unit 11 determines whether the deterioration degree r of the developer is large or not. When the control unit 11 determines that the deterioration degree r of the developer is large (step S202: YES), the process proceeds to the next step S203. On the other hand, when the control unit 11 determines that the deterioration degree r of the developer is not large (step S202: NO), the process proceeds to step S204. In Modification 1, for example, if the deterioration degree r is 1.5 or more, it is determined that the deterioration degree of the developer is large. On the other hand, if the deterioration degree r is less than 1.5, it is determined that the deterioration degree of the developer is not large.

[0064] In step S203, the control unit 11 sets the target value of the TCR sensor SE1 to be lower than that during image formation. In Modification 1, for example, if the deterioration degree r is 1.5 or more (step S202: YES), the target value of the TCR sensor SE1 is set to -1% of the value at the time of image formation. On the other hand, if the deterioration degree r is less than 1.5 (step S202: NO), the target value of the TCR sensor SE1 is left as it was at the time of image formation.

[0065] Next, the control unit 11 starts to supply toner (step S204).

[0066] Next, the control unit 11 determines whether the output value of the TCR sensor SE1 (the toner concentration Tc detected by the TCR sensor SE1) has returned to the target value (step S205). When the control unit 11 determines that the output value of the TCR sensor SE1 has returned to the target value (step S205: YES), the process proceeds to the next step S206. On the other hand, when the control unit 11 determines that the output value of the TCR sensor SE1 has not returned to the target value (step S205: NO), it repeats the process until the output value returns to the target value.

[0067] In step S206, the control unit 11 ends the toner supply.

[0068] As described above, according to the first modification, when the deterioration degree r of the developer is small, the current state can be maintained.

[0069] (Variation 2) In the above embodiment, the target value is changed according to the degree of deterioration of the developer, but this is not limiting. For example, the target value may be changed according to the degree of deterioration of the developer and the number of sheets that can be printed. The control of the image forming apparatus 1 according to the second modification will be described below with reference to the flowchart of FIG.

[0070] First, the control unit 11 determines whether or not the detection unit 15 has detected replacement of the toner bottle TB (step S301). When the control unit 11 determines that replacement of the toner bottle TB has been detected (step S301: YES), the process proceeds to the next step S302. On the other hand, if the control unit 11 determines that replacement of the toner bottle TB has not been detected (step S301: NO), the process proceeds to step S308.

[0071] In step S302, the control unit 11 determines whether the durable number of sheets of the developer exceeds 50,000 (durable number of sheets>50,000). When the control unit 11 determines that the durable number of sheets of the developer exceeds 50,000 (step S302: YES), the process proceeds to the next step S303. On the other hand, when the control unit 11 determines that the durable number of sheets of the developer does not exceed 50,000 (step S302: NO), the process proceeds to step S308.

[0072] The processing in steps S303 to S310 is the same as the processing in steps S102 to S109 in FIG. 4, and therefore a description thereof will be omitted.

[0073] As described above, in Modification 2, the target value of the TCR sensor SE1 can be changed taking into consideration the number of pages that the developer can print in addition to the degree of deterioration of the developer. This allows the target value of the TCR sensor SE1 to be changed further in accordance with the actual deterioration of the developer.

[0074] (Variation 3) The target value may also be changed according to the degree of deterioration of the developer and the number of replaced toner bottles TB. Hereinafter, the control of the image forming apparatus 1 according to the third modification will be described with reference to the flowchart of FIG.

[0075] First, the control unit 11 determines whether or not the detection unit 15 has detected replacement of the toner bottle TB (step S401). When the control unit 11 determines that replacement of the toner bottle TB has been detected (step S401: YES), the process proceeds to the next step S402. On the other hand, if the control unit 11 determines that replacement of the toner bottle TB has not been detected (step S401: NO), the process proceeds to step S408.

[0076] In step S402, the control unit 11 determines whether the number of times the toner bottle TB has been replaced exceeds five (number of times the toner bottle TB has been replaced > 5). When the control unit 11 determines that the number of times the toner bottle TB has been replaced exceeds five times (step S402: YES), the process proceeds to the next step S403. On the other hand, if the control unit 11 determines that the number of times the toner bottle TB has been replaced does not exceed five times (step S402: NO), the process proceeds to step S408.

[0077] The processing in steps S403 to S410 is the same as the processing in steps S102 to S109 in FIG. 4, and therefore a description thereof will be omitted.

[0078] As described above, in Modification 3, the target value of the TCR sensor SE1 can be changed taking into consideration the number of times the toner bottle TB has been replaced as well as the degree of deterioration of the developer. This allows the target value of the TCR sensor SE1 to be changed further in accordance with the actual deterioration of the developer.

[0079] (Variation 4) The target value may also be changed according to the degree of deterioration of the developer, the number of sheets that can be printed, and the number of replaced toner bottles TB. Hereinafter, the control of the image forming apparatus 1 according to the fourth modification will be described with reference to the flowchart of FIG.

[0080] First, the control unit 11 determines whether or not the detection unit 15 has detected replacement of the toner bottle TB (step S501). When the control unit 11 determines that replacement of the toner bottle TB has been detected (step S501: YES), the process proceeds to the next step S502. On the other hand, if the control unit 11 determines that replacement of the toner bottle TB has not been detected (step S501: NO), the process proceeds to step S509.

[0081] In step S502, the control unit 11 determines whether the durable number of sheets of the developer exceeds 50,000 (durable number of sheets>50,000). When the control unit 11 determines that the durable number of sheets of the developer exceeds 50,000 (step S502: YES), the process proceeds to the next step S503. On the other hand, when the control unit 11 determines that the durable number of sheets of the developer does not exceed 50,000 (step S502: NO), the process proceeds to step S509.

[0082] In step S503, the control unit 11 determines whether the number of times the toner bottle TB has been replaced exceeds five (number of times the toner bottle TB has been replaced > 5). When the control unit 11 determines that the number of times the toner bottle TB has been replaced exceeds five times (step S503: YES), the process proceeds to the next step S504. On the other hand, if the control unit 11 determines that the number of times the toner bottle TB has been replaced does not exceed five times (step S503: NO), the process proceeds to step S509.

[0083] The processing in steps S504 to S511 is the same as the processing in steps S102 to S109 in FIG. 4, and therefore a description thereof will be omitted.

[0084] As described above, in Modification 4, the target value of the TCR sensor SE1 can be changed in consideration of the deterioration degree r of the developer, the number of pages the developer can print, and the number of times the toner bottle TB has been replaced. This allows the target value of the TCR sensor SE1 to be changed further in accordance with the actual deterioration of the developer.

[0085] That is, as shown in the above-mentioned modified examples 2 to 4, the target value may be changed depending on the degree of deterioration of the developer and at least one of the number of sheets that can be printed and the number of replaced toner bottles TB. This makes it possible to grasp the actual state of the developer from multiple angles and adjust the target value, thereby more reliably suppressing image problems such as powder smoke and fogging.

[0086] (Other variations) For example, in the above embodiment, after the toner concentration reaches the changed target value, the target value is immediately returned to the value at the time of image formation, but this is not limiting. For example, when returning the target value to the value at the time of image formation, the target value may be returned in stages.

[0087] FIG. 11 shows another example of the change in the target value of the TCR sensor SE1. The horizontal axis represents the number of sheets that can be printed, and the vertical axis represents the target value of the TCR sensor SE1. The solid line L20 represents the target value during image formation (normal operation). In the example shown in FIG. 11, the target value during image formation is also changed to a lower value in accordance with the deterioration of the developer when the number of sheets that can be printed exceeds a predetermined value (see symbol F). The dashed line L21 represents the target value when the toner bottle TB is replaced when the degree of deterioration r of the developer is determined to be 1.5 or greater but less than 2. The dashed line L22 represents the target value when the toner bottle TB is replaced when the degree of deterioration r of the developer is determined to be 2 or greater. In the example shown in FIG. 11, the target value when the toner bottle TB is replaced is changed to a value lower than that during image formation depending on the degree of deterioration r of the developer. Specifically, the dashed line L21 indicates a value that is 1% lower than that during image formation, and the dashed line L22 indicates a value that is 1.5% lower than that during image formation. That is, the higher the number of pages of durability, the lower the target value after the change. The target value is lowered only from the time the toner bottle TB is replaced until a predetermined number of pages have been printed. After the predetermined number of pages have been printed, the target value is returned to the target value used during image formation. At this time, the target value is not immediately returned to the target value used during image formation, but is returned gradually. That is, the target value is kept at an intermediate value for a predetermined time, and then returned to the target value used during image formation. That is, when returning the target value to the value used during image formation, the control unit 11 returns the target value gradually. This prevents a large amount of toner from being replenished at once, and allows an appropriate amount of toner to be replenished. This makes it possible to more effectively compensate for deterioration in mixing performance and further suppress increases in dust smoke and toner scattering. In the example shown in FIG. 11, one step is inserted during the process of returning the target value used during image formation. However, this is not limited to this. That is, multiple steps may be inserted during the process. As described above, when the control unit 11 returns the target value to the value during image formation, it does so in stages, preventing a large amount of toner from being replenished at once and allowing an appropriate amount of toner to be replenished. This makes it possible to further compensate for deterioration in stirring performance and further suppress increases in powder smoke and toner scattering.

[0088] In the above embodiment, the degree of deterioration of the developer is calculated as the ratio of the amount of replenished toner to the amount of toner required at the time of replenishment, but this is not limited to this. For example, the degree of deterioration of the developer may be calculated as the proportion of time during which the toner concentration is lower than the target value.

[0089] 12A and 12B show the difference in the output value of the TCR sensor SE1 depending on the degree of developer deterioration. The horizontal axis represents mixing time, and the vertical axis represents the output value (toner concentration Tc) of the TCR sensor SE1. FIG. 12A shows an example of a case where the degree of deterioration is low. In the example shown in FIG. 12A, the output value G2 of the TCR sensor SE1 fluctuates around the target value G1. This indicates that the output value G2 of the TCR sensor SE1 is well controlled according to the target value G1. FIG. 12B shows an example of a case where the degree of deterioration is high. In the example shown in FIG. 12B, the output value G2 of the TCR sensor SE1 is often lower than the target value G1. In the state shown in FIG. 12B, the replenished toner is not easily absorbed into the developer, so the output value G2 of the TCR sensor SE1 maintains the target value G1 for a short period of time. When the degree of deterioration is low, the replenished toner is absorbed directly into the developer, and the output value G2 of the TCR sensor SE1 is approximately the same as the target value G1. On the other hand, as the degree of deterioration increases, it becomes more difficult for the replenished toner to be absorbed into the developer in the developing unit 22. As a result, some of the replenished toner scatters, soiling the inside of the machine or adhering to the white parts of images. As a result, the time during which the toner concentration Tc (output value G2 of the TCR sensor SE1) of the developer in the developing unit 22 does not reach the target value G1 becomes longer, and the percentage of time during which the value is lower than the target value G1 increases. In other words, the greater the degree of deterioration of the developer, the more difficult it becomes for the replenished toner to be absorbed into the developer, and the percentage of time during which the value is lower than the target value G1 increases.

[0090] Figure 13 is a diagram showing the relationship between the percentage of time the output value of the TCR sensor SE1 is lower than the target value and the degree of deterioration of the developer. The horizontal axis represents the degree of deterioration, and the vertical axis represents the percentage of time the output value of the TCR sensor SE1 is lower than the target value (target Tc). As shown in Figure 13, as the degree of deterioration increases, the percentage of time the output value of the TCR sensor SE1 is lower than the target value increases. Therefore, the control unit 11 first calculates the deterioration degree ru of the developer as the proportion of time during which the toner concentration Tc detected by the TCR sensor SE1 is lower than the target value. Next, the control unit 11 determines that the deterioration degree ru of the developer is greater the greater the proportion of time during which the toner concentration is lower than the target value. This makes it possible to determine the deterioration degree of the developer using the proportion of time during which the toner concentration is lower than the target value. This makes it possible to properly grasp the actual state of the developer.

[0091] FIG. 14 is an example of a graph showing the relationship between the number of pages used and the degree of developer deterioration ru. The horizontal axis represents the number of pages used, and the vertical axis represents the degree of deterioration ru. The degree of deterioration ru is the percentage of time during which the output value of the TCR sensor SE1 is lower than the target value. The degree of deterioration ru is "0" when the output value of the TCR sensor SE1 is always higher than the target value, and "1" when the output value is always lower than the target value. The percentage of time during which the output value of the TCR sensor SE1 is lower than the target value increases as the number of pages used increases. When the number of pages used is low, the degree of developer deterioration is low and the replenished toner is absorbed directly into the developer, so the output value of the TCR sensor SE1 is approximately the same as the target value. In other words, the percentage of time during which the output value of the TCR sensor SE1 is lower than the target value (the degree of deterioration ru) decreases. On the other hand, as the number of pages used increases, it becomes more difficult for the replenished toner to be absorbed into the developer in the development unit 22. As a result, some of the replenished toner may scatter, soiling the interior of the machine or adhering to the white background of the image. As a result, the time during which the toner concentration Tc of the developer in the developing unit 22 does not reach the target value becomes longer, and the percentage of time during which the value is lower than the target value becomes larger. In other words, the more sheets the developer prints, the more difficult it becomes for the replenished toner to be absorbed into the developer, and therefore the percentage of time during which the value is lower than the target value (the degree of deterioration ru) becomes larger.

[0092] Next, the control of the image forming apparatus 1 using the deterioration degree ru will be described with reference to the flowchart of FIG.

[0093] First, the control unit 11 determines whether or not the detection unit 15 has detected replacement of the toner bottle TB (step S601). When the control unit 11 determines that replacement of the toner bottle TB has been detected (step S601: YES), the process proceeds to the next step S602. On the other hand, if the control unit 11 determines that replacement of the toner bottle TB has not been detected (step S601: NO), the process proceeds to step S608.

[0094] In step S602, the control unit 11 determines whether the durable number of sheets of the developer exceeds 50,000 (durable number of sheets>50,000). When the control unit 11 determines that the durable number of sheets of the developer exceeds 50,000 (step S602: YES), the process proceeds to the next step S603. On the other hand, if the control unit 11 determines that the durability of the developer does not exceed 50,000 sheets (step S602: NO), the process proceeds to step S608.

[0095] In step S603, the control unit 11 determines whether the deterioration degree ru of the developer is 0.8 or more (ru>0.8). When the control unit 11 determines that the deterioration degree ru of the developer is 0.8 or more (step S603: YES), the process proceeds to the next step S604. On the other hand, when the control unit 11 determines that the deterioration degree ru of the developer is not equal to or greater than 0.8 (step S603: NO), the process proceeds to step S605.

[0096] In step S604, the control unit 11 changes the target value of the TCR sensor SE1 to a value 1.5% lower than the normal value (during image formation), and then proceeds to step S608.

[0097] In step S605, the control unit 11 determines whether the deterioration degree ru of the developer is equal to or greater than 0.5 (ru>0.5). When the control unit 11 determines that the deterioration degree ru of the developer is 0.5 or more (step S605: YES), the process proceeds to the next step S606. On the other hand, if the control unit 11 determines that the deterioration degree ru of the developer is not equal to or greater than 0.5 (step S605: NO), the process proceeds to step S607.

[0098] In step S606, the control unit 11 changes the target value of the TCR sensor SE1 to a value 1% lower than that during image formation, and then proceeds to step S608.

[0099] In step S607, the control unit 11 changes the target value of the TCR sensor SE1 to a value 0.5% lower than that during image formation, and then proceeds to step S608.

[0100] As described above, in steps S604, S606, and S607, the control unit 11 changes the target value of the TCR sensor SE1 to a value lower than that during image formation. That is, the control unit 11 changes the target value of the TCR sensor SE1 to a value lower than that during image formation in accordance with the deterioration degree ru of the developer. Specifically, if the degradation degree ru is less than 0.5, the target value of the TCR sensor SE1 is changed to a value 0.5% lower than that during image formation. If the degradation degree ru is 0.5 or more but less than 0.8, the target value of the TCR sensor SE1 is changed to a value 1% lower than that during image formation. If the degradation degree ru is 0.8 or more, the target value of the TCR sensor SE1 is changed to a value 1.5% lower than that during image formation. In this way, the control unit 11 changes the target value of the TCR sensor SE1 to a lower value as the deterioration degree ru of the developer increases.

[0101] The processing in steps S608 to S610 is the same as the processing in steps S107 to S109 in FIG. 4, and therefore a description thereof will be omitted.

[0102] As described above, the target value of the TCR sensor SE1 can be changed taking into consideration the number of pages that the developer can print in addition to the degree of deterioration ru of the developer. This allows the target value of the TCR sensor SE1 to be changed further according to the actual deterioration of the developer.

[0103] Further, for example, the degree of deterioration of the developer may be calculated using the amount of toner adhered to the intermediate transfer belt 40 relative to Vdc. Vdc is the value of the DC component of the developing bias applied to the developing roller 22c. FIG. 16 is an example of a graph showing the relationship between the value of the DC component (Vdc) of the development bias applied to the development roller 22c and the amount of toner adhesion on the intermediate transfer belt 40. The horizontal axis represents Vdc. The vertical axis represents the amount of toner adhesion on the intermediate transfer belt 40 (amount of toner adhesion on the belt). The solid line L31 represents the case where the degree of developer deterioration is small. The dashed line L32 represents the case where the degree of developer deterioration is large. In the example shown in FIG. 16, when compared at the same Vdc, the value is larger when the degree of developer deterioration is large (dashed line L32) than when the degree of developer deterioration is small (solid line L31). This is because, as the developer deteriorates, the charge amount of the toner decreases, and therefore, even when the same Vdc is applied, the greater the degree of developer deterioration, the greater the amount of toner adhesion on the intermediate transfer belt 40. As described above, the degree of developer deterioration can be determined using the amount of toner adhesion on the intermediate transfer belt 40 relative to Vdc.

[0104] Further, for example, the degree of deterioration of the developer may be calculated using the voltage value of the bare surface of the intermediate transfer belt 40. FIG. 17 is an example of a graph showing the relationship between the degree of developer deterioration and the output value of the AIDC sensor. The AIDC sensor detects the voltage value of the bare belt surface (without toner attached) of the intermediate transfer belt 40. Therefore, the output value of the AIDC sensor is the voltage value of the bare belt surface of the intermediate transfer belt 40. The horizontal axis of FIG. 17 represents the degree of developer deterioration. The vertical axis represents the output value of the AIDC sensor (bare belt surface output). In the example shown in FIG. 17, the output value of the bare belt surface increases as the degree of developer deterioration increases. This is because the amount of fogging is greater when the degree of developer deterioration is high compared to when it is low, and therefore a greater amount of toner adheres even when no toner is attached. As described above, the degree of developer deterioration can be determined using the voltage value of the bare belt surface of the intermediate transfer belt 40.

[0105] Further, for example, the degree of deterioration of the developer may be calculated using the height of the peak of the output value of the TCR sensor SE1 when a predetermined amount of toner is replenished or the time required to reach the peak. FIG. 18 is an example of a graph showing the relationship between the stirring time of the developing unit 22 and the output value of the TCR sensor SE1. The horizontal axis represents the stirring time of the developing unit 22. The vertical axis represents the output value of the TCR sensor SE1 (toner concentration Tc detected by the TCR sensor SE1). The solid line L41 represents the case where the degree of developer deterioration is low. The dashed line L42 represents the case where the degree of developer deterioration is high. Tc1 in the figure represents the peak output value of the TCR sensor SE1 when the degree of developer deterioration is low. Tc2 in the figure represents the peak output value of the TCR sensor SE1 when the degree of developer deterioration is high. T1 in the figure represents the time at which the output value of the TCR sensor SE1 reaches its peak when the degree of developer deterioration is low. T2 in the figure represents the time at which the output value of the TCR sensor SE1 reaches its peak when the degree of developer deterioration is high. The output value of the TCR sensor SE1 when a predetermined amount of toner is replenished increases when the replenished toner reaches the vicinity of the TCR sensor SE1. Thereafter, the output value of the TCR sensor SE1 stops at a value corresponding to the amount of replenishment and maintains that value. As shown in FIG. 18, when the degree of developer deterioration is high, the slope of the increase in the output value of the TCR sensor SE1 is smaller than when the degree of developer deterioration is low. Therefore, the time to reach the peak of the output value of the TCR sensor SE1 (T2 in the figure) is delayed. Also, when the degree of developer deterioration is high, the peak of the output value of the TCR sensor SE1 (Tc2 in the figure) is lower than when the degree of developer deterioration is low. In other words, when the degree of developer deterioration is high, the peak of the output value is lower and it takes longer to reach the peak than when the degree of developer deterioration is low. This is because as the degree of developer deterioration increases, the time it takes for toner to be absorbed into the developer decreases and the amount absorbed decreases. As described above, the degree of developer deterioration can be determined using the height of the peak of the output value of the TCR sensor SE1 when a predetermined amount of toner is replenished or the time it takes to reach the peak.

[0106] In addition, the detailed configuration and operation of each device constituting the image forming apparatus can be modified as appropriate without departing from the spirit of the present invention. [Explanation of symbols]

[0107] 1. Image forming device 11 Control section 12 Image forming unit 20 Imaging cartridge 21 Image carrier unit 21a Image carrier 21b Charging part 21c Cleaning Department 22 Development unit (development section) 22a, 22b Conveyor rollers 22c developing roller SE1 TCR sensor (detection part) RE Regulation Department 30 Exposure section 40 Intermediate transfer belt 50 Primary transfer roller 60 Secondary transfer roller 70 Fixing unit 70a Fuser roller 80 Cleaning Department 13 Storage section 14 Operation panel 141 Display section 142 Operation section 15. Detection unit 16 Communications Department TB Toner bottle (supply part) TR1 input tray R1 Paper ejection roller B1 Waste Toner Box

Claims

1. A developing device comprising: a developing unit that develops an electrostatic latent image formed on an image carrier using a two-component developer consisting of toner and a carrier; a replaceable supply unit that supplies toner to the developing unit; and a detection unit that detects the toner concentration of the developer in the developing unit, wherein the developing device detects that the toner concentration of the supply unit is empty when the toner concentration detected by the detection unit becomes equal to or lower than a predetermined value, a control unit that controls the supply of toner by the supply unit so that the toner concentration detected by the detection unit reaches a target value; The developing device, wherein the control unit changes the target value in accordance with a degree of deterioration of the developer when the supply unit is replaced upon detection of the toner empty.

2. 2. The developing device according to claim 1, wherein the control unit changes the target value to a value lower than that during image formation in accordance with a degree of deterioration of the developer.

3. 3. The developing device according to claim 2, wherein the control section changes the target value to a lower value as the degree of deterioration of the developer increases.

4. 3. The developing device according to claim 2, wherein the control unit returns the target value to the value at the time of image formation after the toner concentration detected by the detection unit reaches the changed target value.

5. The developing device according to claim 4, wherein the control unit returns the target value to the value at the time of image formation after printing a predetermined number of sheets after the toner concentration detected by the detection unit reaches the changed target value.

6. 5. The developing device according to claim 4, wherein the control unit returns the target value in stages when returning the target value to the value at the time of image formation.

7. The developing device according to claim 1, characterized in that the control unit calculates the degree of deterioration of the developer as a ratio of the amount of replenished toner to the amount of toner required at the time of replenishment, and determines that the degree of deterioration of the developer is greater the greater the ratio of the amount of replenished toner.

8. The developing device according to claim 1, characterized in that the control unit calculates the degree of deterioration of the developer as the percentage of time during which the toner concentration detected by the detection unit is lower than the target value, and determines that the degree of deterioration of the developer is greater the greater the percentage of time during which the toner concentration is lower than the target value.

9. 2. The developing device according to claim 1, wherein the control unit changes the target value in accordance with the degree of deterioration of the developer and at least one of the number of sheets that can be printed and the number of replaced supply units.

10. an image forming unit that forms an image on a sheet; The image forming unit includes: an image carrier; a developing device according to any one of claims 1 to 9, which supplies a developer to the electrostatic latent image formed on the image carrier to form a toner image; An image forming apparatus comprising:

11. A toner supply method for a developing device, comprising: a developing unit that develops an electrostatic latent image formed on an image carrier using a two-component developer consisting of toner and a carrier; a replaceable supply unit that supplies toner to the developing unit; and a detection unit that detects the toner concentration of the developer in the developing unit, wherein the toner supply unit is detected as empty when the toner concentration detected by the detection unit becomes equal to or lower than a predetermined value, a control step of controlling the supply of toner by the supply unit so that the toner concentration detected by the detection unit reaches a target value; The toner supply method is characterized in that the control step changes the target value in accordance with a degree of deterioration of the developer when the supply unit is replaced upon detection of the toner empty state.

12. a computer for a developing device comprising: a developing unit that develops an electrostatic latent image formed on an image carrier using a two-component developer consisting of toner and a carrier; a replaceable supply unit that supplies toner to the developing unit; and a detection unit that detects the toner concentration of the developer in the developing unit, the computer detecting that the toner concentration of the supply unit is empty when the toner concentration detected by the detection unit becomes equal to or lower than a predetermined value; the toner concentration detecting unit is caused to function as a control unit that controls the supply of the toner by the supply unit so that the toner concentration detected by the detection unit reaches a target value; The control unit changes the target value in accordance with a degree of deterioration of the developer when the supply unit is replaced upon detection of the toner empty.

Images