BACKGROUND

[0001] An imaging apparatus with a developing device may develop an electrostatic latent image of an image carrier using a developer that contains a toner and a carrier. In the developing device, the toner and the carrier which are mixed at a given ratio are supplied in response to the consumption amount of the toner consumed in accordance with a printing operation of the imaging apparatus. The developer is discharged by overflow depending on the amount of the supplied carrier.

BRIEF DESCRIPTION OF DRAWINGS

[0002] FIG. 1 is a schematic diagram of an example imaging apparatus.

[0003] FIG. 2 is a schematic cross-sectional view of an example developing device.

[0004] FIG. 3 is a diagram illustrating a toner-and-carrier (TC) sensor and an admix auger of the developing device.

[0005] FIG. 4 is a schematic diagram illustrating an example functional configuration of the imaging apparatus.

[0006] FIG. 5 is a graph illustrating an example waveform output by the TC sensor.

[0007] FIG. 6 is a graph illustrating an example waveform output by the TC sensor.

[0008] FIG. 7 is a diagram illustrating an example waveform output by the TC sensor.

[0009] FIG. 8 is a graph of a relationship between a value obtained from the output waveform of the TC sensor and a developer amount inside the example developing device.

[0010] FIG. 9 is a graph of a relationship between the TC sensor output value and the developer amount stored in the example developing device. [0011] FIG. 10 is a graph of a relationship between density of a toner image and a charge amount of a developer, according to an example.

[0012] FIG. 11 is a flowchart illustrating operations of an example carrier supply method.

[0013] FIG. 12 is a graph of a relationship between the TC sensor output value and a toner and carrier mixing ratio, according to an example.

[0014] FIG. 13 is a flowchart illustrating operations of an example carrier supply method.

[0015] FIG. 14 is a flowchart illustrating operations of an example carrier supply method.

DETAILED DESCRIPTION

[0016] In a developing device that uses a two-component developer containing a toner and a carrier as a developer, a trickle discharge method may be adopted in order to extend the life of the developer. According to the trickle discharge method, a new carrier is supplied to a developer storage unit and an old developer is discharged from a developer discharge unit to the outside of the developer storage unit during a toner supply operation. The trickle discharge method is also referred to as a trickle development method or an auto developer refill (ADR). In the present disclosure, the "developer" indicates a developer containing both a toner and a carrier.

[0017] In the ADR, in order to suppress a deterioration in the charging performance of the carrier, the toner and the carrier are stored inside a toner cartridge at a given ratio, while being mixed, and new carrier is supplied at a given ratio along with the toner during a toner supply operation. Then, the deterioration of the charging performance of the carrier is suppressed by discharging the deteriorated carrier to the outside of the developing device by the amount of the supplied carrier.

[0018] Incidentally, in the ADR, the carrier is supplied at a given ratio in response to the toner consumption amount regardless of the actual deterioration of the developer. In the ADR, since the carrier supply amount is determined in accordance with a printing operation with a high load, the carrier may be forcibly replaced even when the carrier is not yet deteriorated. Thus, the carrier may be unnecessarily replaced. In one aspect of the present disclosure, it is possible to suitably detect the decrease and deterioration of the developer and supply the carrier with reduced waste, and thereby reduce cost.

[0019] Hereinafter, an example imaging apparatus will be described with reference to the drawings. In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. For ease of understanding, the drawings may be partially simplified or exaggerated and the dimensional ratios and the like are not limited to those described in the drawings.

[0020] With reference to FIG. 1 , an example imaging apparatus 1 may form a color image by using four colors of magenta, yellow, cyan, and black, designated by the letters “C”, “M”, “Y”, and “K”, respectively. The imaging apparatus 1 includes a conveying device 10 which conveys a print medium (e.g., a sheet of paper) 3, image carriers (e.g., photoconductor drums) 20M, 20Y, 20C, and 20K having surfaces (peripheral surfaces) on which electrostatic latent images are formed, developing devices 30M, 30Y, 30C, and 30K which develop the electrostatic latent images to form respective toner images, a transfer device 40 onto which the toner images are layered to form a single composite toner image (or layered toner image) to be subsequently transferred to the print medium 3, a fixing device 50 which fixes the composite toner image to the print medium 3, a discharge device 60 which discharges the print medium 3, and a controller (or control unit) 70. The example imaging apparatus 1 is an imaging apparatus including a two-component development type developing device.

[0021] An example of the print medium 3 is a sheet (e.g., sheet of paper). The conveying device 10 conveys the print medium 3 on which an image is to be formed, along a conveyance route 11 . The print medium 3 is initially in a cassette 12 in a stacked state, and is picked up and conveyed by a feeding roller 13. The conveying device 10 conveys the print medium 3 to reach a transfer nip portion 14 along the conveyance route 11 at a timing in which the toner image to be transferred to the print medium 3 reaches the transfer nip portion 14.

[0022] The image carriers 20M, 20Y, 20C, and 20K may be referred to as electrostatic latent image carriers or photoconductor drums. The image carriers 20M, 20Y, 20C, and 20K forms electrostatic latent images for forming a magenta toner image, a yellow toner image, a cyan toner image, and a black toner image, respectively. The example configurations of the respective image carriers 20M, 20Y, 20C, and 20K are similar, and for ease of understanding, the image carrier 20M will be described as a representative image carrier, to describe features that are equivalent or similar in each of the image carriers 20M, 20Y, 20C, and 20K.

[0023] The developing device 30M, a charging roller 22M, an exposure unit 23, and a cleaning unit 24M are provided adjacent the image carrier 20M. Additionally, the developing devices 30Y, 30C, and 30K, corresponding charging rollers, corresponding exposure units 23, and corresponding cleaning units are also respectively provided adjacent the image carriers 20Y, 20C, and 20K in a similar manner.

[0024] The charging roller 22M charges the outer peripheral surface of the image carrier 20M to a predetermined potential. The charging roller 22M rotates to follow the rotation of the image carrier 20M. The exposure unit 23 exposes the outer peripheral surface of the image carrier 20M having been charged by the charging roller 22M, according to an image to be formed on the print medium 3. Consequently, a potential of a portion exposed by the exposure unit 23 on the surface of the image carrier 20M changes so that an electrostatic latent image is to be formed. The cleaning unit 24M cleans the developer remaining on the outer peripheral surface of the image carrier 20M.

[0025] The developing device 30M develops the electrostatic latent image formed on the image carrier 20M by the developer supplied from the developer storage unit 21 M storing a magenta developer so as to form a magenta toner image. The developing device 30Y develops the electrostatic latent image formed on the image carrier 20Y by the developer supplied from the developer storage unit 21 Y storing a yellow developer so as to form a yellow toner image. The developing device 30C develops the electrostatic latent image formed on the image carrier 20C by the developer supplied from the developer storage unit 21 C storing a cyan developer so as to form a cyan toner image. The developing device 30K develops the electrostatic latent image formed on the image carrier 20K by the developer supplied from the developer storage unit 21 K storing a black developer so as to form a black toner image. The example configurations of the developing devices 30M, 30Y, 30C, and 30K are similar, and the developing device 30M will be described as a representative developing device to describe features that are equivalent or similar in each of the developing devices 30M, 30Y, 30C, and 30K.

[0026] The developing device 30M includes a developing roller 31 M which carries the developer on the image carrier 20M. In the developing device 30M, a two-component developer containing a toner and a carrier is used as the developer. In the developing device 30M, the toner and the carrier are adjusted and mixed and stirred to a targeted mixing ratio and the toner is dispersed to achieve an optimal charge amount in the developer. In the developing device 30M, the developer is carried on the developing roller 31 M. Then, the developer is conveyed to a position facing the image carrier 20M following a rotation of the developing roller 31 M, and the toner in the developer carried on the developing roller 31 M is transferred to the electrostatic latent image formed on the outer peripheral surface of the adjacent image carrier 20M so as to develop the electrostatic latent image.

[0027] The transfer device 40 conveys the toner images formed by the developing devices 30M, 30Y, 30C, and 30K to the transfer nip portion 14. The transfer device 40 includes a transfer belt 41 , suspension rollers 44, 45, 46, and 47 that support the transfer belt 41 , primary transfer rollers 42M, 42Y, 42C, and 42K, and a secondary transfer roller 43. The toner image is primarily transferred from each of the image carriers 20M, 20Y, 20C, and 20K to the transfer belt 41 . The transfer belt 41 extends between the primary transfer rollers 42M, 42Y, 42C, and 42K and the respective image carriers 20M, 20Y, 20C, and 20K, to carry out a primary transfer by which the individual the toner images developed are layered onto the transfer belt 41 to form the composite toner image (or layered toner image). The transfer belt 41 further extends between the secondary transfer roller 43 and the suspension roller 47, to carry out a secondary transfer by which the composite toner image is transferred from the transfer belt 41 to the print medium 3 the transfer nip portion 14.

[0028] The transfer belt 41 is an endless belt which moves in a circulating manner along the outer peripheries of the suspension rollers 44, 45, 46, and 47. For example, the suspension roller 47 is a drive roller and the suspension rollers 44, 45, and 46 are driven rollers which rotate in a following manner by the rotational driving of the suspension roller 47. The primary transfer rollers 42M, 42Y, 42C, and 42K are arranged to press against the respective image carriers 20M, 20Y, 20C, and 20K from the inner peripheral side of the transfer belt 41 . For example, the secondary transfer roller 43 is disposed in parallel to the suspension roller 47 with the transfer belt 41 interposed therebetween and is provided to press the suspension roller 47 from the outer peripheral side of the transfer belt 41. The secondary transfer roller 43 forms the transfer nip portion 14 between the transfer belt 41 and the secondary transfer roller so as to transfer the toner image from the transfer belt 41 to the print medium 3.

[0029] The fixing device 50 conveys the print medium 3 to pass through a fixing nip portion for heating and pressing the print medium so that the toner image is attached to the print medium 3, so as to fix the toner image to the print medium 3. The fixing device 50 includes a heating roller 52 which heats the print medium 3 and a pressing roller 54 which rotates while pressing the heating roller 52. For example, the heating roller 52 and the pressing roller 54 are formed in a substantially cylindrical shape and a heat source such as a halogen lamp may be provided inside the heating roller 52. The fixing nip portion is provided between the heating roller 52 and the pressing roller 54 and the toner image is melted and fixed to the print medium 3 when the print medium 3 is conveyed to pass through the fixing nip portion.

[0030] The discharge device 60 includes discharge rollers 62 and 64 which discharge the print medium 3 to which the toner image is fixed by the fixing device 50 to the outside of the imaging apparatus 1 .

[0031] The controller (e.g., control unit) 70 is an electronic control unit of the imaging apparatus 1 including a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like. The control unit 70 performs various controls in the operation of the imaging apparatus 1. In the control unit 70, various kinds of control are performed by loading a program stored in the ROM, in the form of data and instructions, onto the RAM and executing the program using the CPU. The control unit 70 may include a plurality of electronic control units or singular electronic control unit. The control unit 70 controls respective units of the imaging apparatus 1 .

[0032] FIG. 2 is a schematic cross-sectional view of the developing device 30M. The example developing device 30M includes the developing roller 31 M, a housing 32M, a supply auger 33M, an admix auger 34M, and a layer thickness regulation member 35M. The housing 32M includes a developing chamber 36M therein. The developing roller 31 M, the layer thickness regulation member 35M, and the developer are stored in the developing chamber 36M. The housing 32M has an opening at a position where the developing roller 31 M faces the image carrier 20M and the toner inside the developing chamber 36M is supplied from the opening to the image carrier 20M.

[0033] The developing roller 31 M faces the image carrier 20M and carries the developer stored in the housing 32M. The developing roller 31 M rotates around a rotation axis A1 in a rotation direction D1 to convey the developer. The rotation axis A1 of the developing roller 31 M extends in parallel to a rotation axis A2 of the image carrier 20M (for example, extends in a direction orthogonal to the view of FIG. 2). The developing roller 31 M develops the electrostatic latent image of the image carrier 20M by transferring the carried developer to the electrostatic latent image at a developing area 37M. The developing area 37M is an area where the developing roller 31 M faces the image carrier 20M.

[0034] The example developing roller 31 M includes a developing sleeve 311 M which forms a surface layer of the developing roller 31 M and a magnet 312M which is disposed inside the developing sleeve 311 M. The developing sleeve 311 M is, for example, a cylindrical member formed of non-magnetic metal. The magnet 312M is fixed to, for example, a shaft 313M fixed to the housing 32M. The developer is carried on the surface of the developing sleeve 311 M by the magnetic force of the magnet 312M.

[0035] The supply auger 33M and the admix auger 34M stir a magnetic carrier and a non-magnetic toner that form the developer so as to frictionally charge the carrier and the toner. The supply auger 33M is disposed in, for example, a first conveyance path 381 M disposed below the developing roller 31 M in the developing chamber 36M. The admix auger 34M is disposed in a second conveyance path 382M formed at a position adjacent to the first conveyance path 381 M.

[0036] FIG. 3 is a schematic view of an enlarged cross-section of the admix auger 34M. The example developing device 30M may include a magnet 80 which is attached to the admix auger 34M and a toner-and-camer (TC) sensor 81 which is disposed at a position facing the admix auger 34M. As an example, the magnet

80 is a cleaning member that cleans the developer remaining in the TC sensor 81 using a magnetic force. The TC sensor 81 detects, for example, the density of the developer stored in the developing device 30M. For example, the TC sensor

81 is a magnetic permeability sensor that detects the ratio of toner and carrier from the magnetic permeability of the developer.

[0037] With reference to FIG. 4, the example imaging apparatus 1 according to the present disclosure includes the TC sensor 81 , a toner supply unit (or toner supply device) 82 which supplies the toner to the developing device 30M, a carrier supply unit (or carrier supply device) 83 which supplies the carrier to the developing device 30M, and a developer discharge unit (or developer discharge device) 84 which discharges the developer from the developing device 30M. The example imaging apparatus 1 further includes a developer amount calculation unit (or developer amount calculation device) 85 which calculates the amount of the developer of the developing device 30M, an image density detection unit (image density detection device) 86 which detects the density of the toner image, and a storage unit (storage device) 87 which stores various information in the imaging apparatus 1. The controller (or control unit 70) controls at least one of the toner supply unit 82, the carrier supply unit 83, the developer discharge unit 84, the developer amount calculation unit 85, and the image density detection unit 86.

[0038] With reference to FIGS. 5, 6, and 7, the TC sensor 81 detects the mixing ratio of the toner and the carrier of the developer stored in the developing device 30M as the output waveform of magnetic permeability. FIG. 5 illustrates a waveform output of the TC sensor 81 when the developing device 30M contains a first amount of the developer, FIG. 6 illustrates a waveform output of the TC sensor 81 when the developing device 30M contains a second amount of the developer, which is greater than the first amount, and FIG. 7 illustrates a waveform output of the TC sensor 81 when the developing device 30M contains a third amount of the developer, which is greater than the second amount. As an example, the first amount is 230 g, the second amount is 260 g, and the third amount is 290 g.

[0039] In FIGS. 5 to 7, the output waveform of the TC sensor 81 varies in response to the amount of the developer stored in the developing device 30M. For example, the output value of the TC sensor 81 increases and a size of a shoulder S of the output waveform widens as the amount of the developer increases. When the size of the shoulder S of the output waveform varies, the average value of the output value indicated by the output waveform of the TC sensor 81 varies. Consequently, it is conceivable to obtain the amount of the developer of the developing device 30M from the average value per cycle of the output waveform of the TC sensor 81 .

[0040] The amount of the developer stored in the developing device 30M is obtained by using the maximum value, the minimum value, and the average value of the output waveform of the TC sensor 81. For example, given a first difference Va between the maximum value and the average value of the output waveform of the TC sensor 81 and a second difference Vb between the average value and the minimum value of the output waveform of the TC sensor 81 , an example of a relationship between the differences represented by Va/Vb and the amount of the developer stored in the developing device 30M is plotted in the graph of FIG. 8.

[0041] In FIG. 8, the value of (or ratio) Va/Vb decreases as the amount of the developer stored in the developing device 30M increases. Additionally, based on FIGS. 8 and 9, a ratio of a first difference (the value of Va) between the maximum value and the average value with respect to a second difference (the value of Vb) between the average value and the minimum value decreases as the amount of the developer increases in the output waveform (the output value) of the TC sensor 81 . Additionally, the average value increases and the difference (the value of Vb) between the average value and the minimum value increases as the amount of the developer increases.

[0042] Additionally, the amplitude of the output waveform of the TC sensor 81 increases as the amount of the developer stored in the developing device 30M increases. However, since the change in the value of (or ratio) VaA/b according to the amount of the developer stored in the developing device 30M is greater than the change in the amplitude of the output waveform according to the amount of the developer stored in the developing device 30M, the value of VaA/b may be used more suitably to calculate the amount of the developer.

[0043] The example developer amount calculation unit 85 compares the output waveform detected by the TC sensor 81 with a previously stored output waveform to calculate the amount of the developer stored in the developing device 30M. The previously stored output waveform indicates, for example, the output waveform stored in the storage unit 87. The developer amount calculation unit 85 may calculate the maximum value, the average value, and the minimum value of the output waveform detected by the TC sensor 81 and may calculate the amount of the developer from the calculated maximum, average, and minimum values.

[0044] For example, the developer amount calculation unit 85 may calculate the maximum value, the average value, and the minimum value when the voltage value indicated by the output waveform detected by the TC sensor 81 is within a given range. As an example, the developer amount calculation unit 85 may calculate the value of (the first difference) Va which is the difference between the maximum value and the average value and the value of (the second difference) Vb which is the difference between the average value and the minimum value, and may additionally calculate the amount of the developer from the first difference Va and the second difference Vb calculated as described above. As a specific example, the developer amount calculation unit 85 may calculate the value of VaA/b from the output waveform detected by the TC sensor 81 using the first difference Va and the second difference Vb, and may calculate the amount of the developer from the value of Va/Vb using, for example, a relationship shown in FIG. 8.

[0045] The image density detection unit 86 detects, for example, the charging performance of the developer stored in the developing device 30M. Incidentally, the density of the toner image varies in response to the charging performance of the developer under the same potential condition. The image density detection unit 86 includes an optical image density sensor which detects deterioration of the developer stored in the developing device 30M and detects the density of the toner image formed at a given potential by the optical image density sensor.

[0046] FIG. 10 is a graph showing an example relationship of the density of the toner image to the charge amount (Q/M) of the developer. The density of the toner image is correlated with the charge amount Q/M of the developer. The charge amount Q/M indicates the ratio between the charged charge amount (Q) and the mass (M) of the developer. As shown in FIG. 10, the charge amount of the developer and the density of the toner image have a substantially linear relationship. Namely, the charge amount of the developer increases as the density of the toner image decreases and the charge amount of the developer decreases as the density of the toner image increases. For example, the image density detection unit 86 may detect the deterioration of the developer (the decrease in the charge amount) by detecting the density of the toner image formed based on a given potential and calculating the charge amount of the developer using the relationship shown in FIG. 10.

[0047] The image density detection unit 86 may detect the density of the toner image when the mixing ratio of the toner and the carrier detected by the TC sensor 81 is within a given range and the amount of the developer calculated by the developer amount calculation unit 85 is within a predetermined range. The image density detection unit 86 may determine that the developer (the carrier) inside the developing device 30M is deteriorated, for example, when the detected density of the toner image is equal to or greater than a predetermined given image density. The given image density may be, for example, the density within the range of the target image density (Tgt) ± 0.15 or the density of the target image density + 0.15.

[0048] The carrier supply unit 83 determines the carrier supply amount to be supplied to the developing device 30M in response to, for example, the amount of the developer calculated by the developer amount calculation unit 85. Further, the carrier supply unit 83 may calculate a supply operation time based on the determined supply amount, to supply the carrier to the developing device 30M during the next printing operation. The carrier supply unit 83 supplies, for example, a determined supply amount of the carrier to the developing device 30M. [0049] The carrier supply unit 83 may supply the carrier to the developing device 30M when the amount of the developer calculated by the developer amount calculation unit 85 decreases by a given amount. As an example, the carrier supply unit 83 may determine the carrier supply amount from the difference between a reference value R0 and the ratio of differences Va/Vb calculated by the developer amount calculation unit 85. The reference value R0 may be suitably changed or may be set as a predetermined value.

[0050] As an example, the reference value R0 is set to the ratio VaA/b when initializing the developing device 30M by setting-up the imaging apparatus (for example, during the initial installation of the imaging apparatus) or when replacing the developing device 30M. According to examples, the carrier supply unit 83 supplies the carrier to the developing device 30M when the value of VaA/b is greater than the reference value R0. The carrier supply unit 83 may supply the carrier to the developing device 30M when the difference between the value of VaA/b and the reference value R0 is greater than a predetermined value. Accordingly, the carrier can be reliably supplied when the amount of the developer inside the developing device 30 decreases.

[0051] According to examples, the carrier supply unit 83 determines the carrier supply amount when the density of the toner image detected by the image density detection unit 86 is equal to or greater than a given image density. The carrier supply unit 83 may determine the carrier supply amount in response to the difference between the density of the toner image detected by the image density detection unit 86 and the given image density. The carrier supply unit 83 supplies the carrier to the developing device 30M, for example, when the deterioration of the developer (caused by the deterioration of the carrier) is detected by the image density detection unit 86 (the optical image density sensor). Since the carrier supply unit 83 is operated as described above, the carrier can be reliably supplied to the developing device 30M when the density of the toner image increases so that the developer (the carrier) is deteriorated.

[0052] With reference to FIG. 11 , an example method for supplying the carrier to the developing device according to the present disclosure, will be described. The operations illustrated in FIG. 11 show an example of a method of supplying the carrier in response to the amount of the developer contained in the developing device 30M and, may be operated for example, by the control of the control unit (or controller) 70.

[0053] At operation S11 , it is determined whether or not Q/M patch creation (Q/M patch creation sequence) is being executed. The Q/M patch may be, for example, a toner patch for controlling the density of the toner image or may be created before the printing operation is performed. At operation S11 , the method proceeds to operation S12 when it is determined that the Q/M patch creation is being executed and ends when it is determined that the Q/M patch creation is not being executed.

[0054] Next, the TC sensor 81 measures the magnetic permeability of the developer stored inside the developing device 30M and determines whether or not the output value TC which is a voltage value obtained from the magnetic permeability is within a given range. At operation S12, it is determined whether or not the output value TC is greater than (target value Tgt - target value Tgt x 10%), namely, 0.9 Tgt, with further reference to FIG. 12. At operation S13, it is determined whether or not the output value TC is less than (target value Tgt + target value Tgt x 10%), namely, 1.1 Tgt. Accordingly, it may be determined whether or not the toner and carrier mixing ratio of the developer stored in the developing device 30M is within ±1 % of the target value.

[0055] When the output value TC is greater than 0.9 Tgt and less than 1.1 Tgt, it is determined that the toner and carrier mixing ratio is within a predetermined range and the method proceeds to operation S15. When the output value TC is 0.9 Tgt or less, the method ends. On the other hand, when the output value TC is 1.1 Tgt or more, it is determined that the toner and carrier mixing ratio is not within a predetermined range and the toner supply unit 82 supplies the toner to the developing device 30M at operation S 14, and the method ends.

[0056] At operation S15, the developer amount calculation unit 85 calculates the maximum value, the average value, and the minimum value from the output waveform of the TC sensor 81. At operation S16, the developer amount calculation unit 85 calculates the ratio VaA/b which is a ratio between the first difference Va corresponding to the difference between the maximum value and the average value, and the second difference Vb corresponding to the difference between the average value and the minimum value from the maximum value, the average value, and the minimum value calculated as described above. At operation S17, the carrier supply unit 83 determines whether or not the difference between the ratio VaA/b and the reference value R0 is positive.

[0057] At operation S17, when the difference between the ratio VaA/b and the reference value R0 is positive, that is, the value of VaA/b is greater than the reference value R0, the method proceeds to operation S18. On the other hand, when the ratio VaA/b is equal to or less than the reference value R0, then the method ends. At operation S18, it is determined whether or not the difference between the value of VaA/b and the reference value R0 is greater than a predetermined value.

[0058] FIG. 11 illustrates an example in which the predetermined value for the reference value R0 is 0.2. A state in which the difference between the ratio of differences VaA/b and the reference value R0 is 0.2 indicates a state in which the amount of the developer inside the developing device 30 is decreased by 20g from a given value as an example. However, the predetermined value is not limited to 0.2 and can be suitably changed. At operation S18, the method proceeds to operation S19 when the difference between the value of VaA/b and the reference value R0 is greater than the predetermined value and the method ends when the difference is the predetermined value or less. At operations S17 and S18, it is determined whether or not the value of (VaA/b) is relatively large and whether or not the amount of the developer inside the developing device 30 has decreased, and the method proceeds to operation S19 when it is determined that the amount of the developer has decreased.

[0059] In operation S19, the carrier supply unit 83 calculates the carrier supply amount with respect to the developing device 30M. The carrier supply amount may be calculated based on the following reference equation, as an example.

((Va/Vb) - R0) 0.1 x 10 = carrier supply amount

[0060] At operation S20, the carrier supply unit 83 calculates the carrier supply operation time from the calculated carrier supply amount. At operation S21 , the carrier supply unit 83 supplies the carrier to the developing device 30M during the calculated supply operation time at the time of the next printing operation. Then, the method ends.

[0061] With reference to FIG. 13, an example operation of supplying the carrier to the developing device according to a modified example will be described. Some operations illustrated in FIG. 13 correspond to the same operations described with reference to FIG. 11 , and overlapping description may be omitted. Operations S31 to S36 in FIG. 13 are respectively identical to the operations S11 to S16 of FIG. 11.

[0062] At operation S36, the carrier supply unit 83 calculates the ratio VaA/b, and subsequently determines whether or not the value of Va/Vb is within ±20% of the reference value R0 after calculating Va/Vb at operation S37. Namely, the carrier supply unit 83 determ ines whether or not the value of Va/Vb is between 0.8 x reference value R0 and 1 .2 x reference value R0.

[0063] At operation S37, when the carrier supply unit 83 determines that the value of Va/Vb is between 0.8 x reference value R0 and 1.2 x reference value R0, the method proceeds to operation S38. When the carrier supply unit 83 determines that the value of Va/Vb is outside the range of 0.8 x reference value R0 to 1.2 x reference value R0, the method ends.

[0064] At operation S38, the image density detection unit 86 detects the density of the toner image OD and determines whether or not the density OD is greater than a given image density OD_UL. As shown in FIG. 10, for example, the given image density OD_UL may be the density of target image density Tgt + 0.15 or other values. In this way, the image density detection unit 86 determines whether or not the density OD is greater than the given image density OD_UL, so as to determine whether or not the developer (namely, the carrier) is deteriorated. [0065] At operation S38, when it is determined that the density OD is no greater than the given image density ODJJL, the method ends. On the other hand, when it is determined that the density OD is greater than the given image density OD_UL, the method proceeds to operation S39 so that the carrier supply unit 83 calculates the carrier supply amount from the deviation (the difference) between the density OD and the given image density OD_UL and determines the carrier supply amount. At operation S40, the carrier supply unit 83 supplies a determined supply amount of the carrier to be supplied to the developing device 30M during the next printing operation. Then, the method ends.

[0066] With reference to FIG. 14, an example method of supplying the carrier to the developing device according to another modified example will be described. Hereinafter, description that is redundant with respect to the description of the operations illustrated in FIG. 11 or FIG. 13 may be omitted. The operations S51 to S56 are respectively identical to the operations S11 to S16 illustrated in FIG. 11. At operation S56, the carrier supply unit 83 calculates the ratio VaA/b, and subsequently determines whether or not the value of Va/Vb is greater than 0.8 x reference value R0 at operation S57.

[0067] At operation S57, when it is determined that the value of VaA/b is greater than 0.8 x reference value R0, then the method proceeds to operation S58, and ends when it is determined that the value of VaA/b is no greater than 0.8 x reference value R0. At operation S58, the carrier supply unit 83 determines whether the value of VaA/b is less than 1 .2 x reference value R0.

[0068] At operation S58, when it is determined that the value of VaA/b is less than 1.2 x reference value R0, then the method proceeds to operation S59, and when it is determined that the value of VaA/b is no less than 1 .2 x reference value R0, then the method proceeds to operation S62.

[0069] At operation S58, when it is determined that the value of VaA/b is no less than 1 .2 x reference value R0, that is, the value of VaA/b is 1 .2 x reference value RO or more, then the operations S62, S63, and S64 are performed assuming that the amount of the developer inside the developing device 30 decreases. According to examples, the operations S62, S63, and S64 may be respectively identical to the operations S19, S20, and S21 illustrated in FIG. 11. At operation S64, the carrier supply unit 83 supplies the carrier to the developing device 30M during the next printing operation, and the method ends.

[0070] At operation S58, when it is determined that the value of VaA/b is less than 1.2 x reference value R0, the operations S59, S60, and S61 are performed. For example, the operations S59, S60, and S61 are respectively identical to the operations S38, S39, and S40 illustrated in FIG. 13. In this case, in operation S59, it is determined whether or not the developer (the carrier) is deteriorated similarly to operation S38 of the diagram of FIG. 13. At operation S61 , when it is determined that the developer is deteriorated, the carrier supply unit 83 supplies a supply amount of the carrier determined at operation S60, to the developing device 30M during the next printing operation and the method ends.

[0071] Various operations and effects of the example imaging apparatus 1 will be described. In the example imaging apparatus 1 , the developer amount calculation unit 85 calculates the amount of the developer stored in the developing device 30M, by comparing the output waveform detected by the TC sensor 81 with a previously stored output waveform and the carrier supply unit 83 determines the carrier supply amount in response to the calculated amount of the developer. Thus, since the amount of the developer stored in the developing device 30M is calculated by the developer amount calculation unit 85 using the output waveform of the TC sensor 81 and the carrier supply amount is determined based on the amount of the developer, a suitable amount of the carrier can be supplied at a suitable timing by the carrier supply unit 83.

[0072] As described above, the imaging apparatus 1 may include the image density detection unit 86 and the image density detection unit 86 may include the optical image density sensor that detects the deterioration of the developer stored in the developing device 30M. Then, the carrier supply unit 83 may supply the carrier to the developing device 30M when the deterioration of the developer is detected by the optical image density sensor. In this case, the deterioration of the developer (caused by the deterioration of the carrier), can be detected from the density of the toner image detected by the optical image density sensor and the carrier can be supplied when the deterioration is detected, so as to supply the carrier at a suitable timing.

[0073] The carrier supply unit 83 may supply the carrier to the developing device 30M when the amount of the developer calculated by the developer amount calculation unit 85 decreases by a given amount, so as to supply the carrier at a more suitable timing in response to the decrease in the amount of the developer.

[0074] The developer amount calculation unit 85 may calculate the maximum value, the average value, and the minimum value of the voltage value indicated by the output waveform detected by the TC sensor 81 and calculate the amount of the developer stored in the developing device 30, based on the calculated maximum, average, and minimum values. In this case, the maximum value, the average value, and the minimum value of the output waveform of the TC sensor 81 can be effectively used when calculating the amount of the developer stored.

[0075] The developer amount calculation unit 85 may calculate the maximum value, the average value, and the minimum value when the voltage value indicated by the output waveform detected by the TC sensor 81 is within a given range, so as to calculate the amount of the developer stored under a suitable condition.

[0076] The developer amount calculation unit 85 may calculate the first difference Va which is the difference between the maximum value and the average value and the second difference Vb which is the difference between the average value and the minimum value, and calculate the amount of the developer from the first difference Va and the second difference Vb. Accordingly, the ratio Va/Vb correlated with the amount of the developer stored, may be calculated based on the maximum value, the average value, and the minimum value.

[0077] The developer amount calculation unit 85 may calculate the value of Va/Vb from the output waveform detected by the TC sensor 81 using the first difference Va and the second difference Vb and the carrier supply unit 83 may determine the carrier supply amount from the difference between the value of Va/Vb and the reference value RO. In this case, the carrier supply amount can be determined from the ratio Va/Vb indicating the amount of the developer stored in the developing device 30M.

[0078] The reference value R0 may be the value of Va/Vb when initializing the developing device 30M, for example when installing the imaging apparatus 1 or when replacing the developing device 30M. Since the amount of the developer is suitable and the state of the carrier is suitable when installing the imaging apparatus 1 or replacing the developing device 30M, the value of Va/Vb in this suitable state can be set as the reference value R0.

[0079] The carrier supply unit 83 may supply the carrier to the developing device 30M when the value of Va/Vb is greater than the reference value R0. In this case, when the value of Va/Vb exceeds the reference value R0 and the amount of the developer decreases, the carrier can be supplied to the developing device 30M.

[0080] The carrier supply unit 83 may supply the carrier to the developing device 30M when the difference between the value of Va/Vb and the reference value R0 is greater than a predetermined value, so as to determine whether or not to supply the carrier, with greater accuracy.

[0081] The carrier supply unit 83 may calculate the supply operation time from the determined supply amount and supply the carrier to the developing device 30M during the next printing operation. Accordingly, the carrier supply operation time may be calculated so that the carrier is supplied selectively during the calculated supply operation time at the time of the next printing operation, so as to supply a suitable amount of the carrier to the developing device 30M, and at a suitable timing.

[0082] The developing device 30M may include an admix auger 34M which stirs the developer and the TC sensor 81 may be disposed at a position facing the admix auger 34M, so as to more accurately measure the amount of the developer stored in the developing device 30M.

[0083] The image density detection unit 86 may detect the deterioration of the developer by detecting the density of the toner image formed based on a given potential and calculating the charge amount of the developer and the carrier supply unit 83 may determine the carrier supply amount when the density of the toner image detected by the image density detection unit 86 is a given image density or more. In this case, the deterioration state of the developer can be detected by the image density detection unit 86 and the carrier supply amount is determined when the deterioration state is detected, so as to more reliably supply the carrier in response to the deterioration.

[0084] The image density detection unit 86 may detect the density of the toner image when the mixing ratio of the toner and the carrier detected by the TC sensor 81 is within a given range and the amount of the developer calculated by the developer amount calculation unit 85 is within a predetermined range, so as to determine with greater accuracy whether or not the carrier is deteriorated.

[0085] The carrier supply unit 83 may determine the carrier supply amount in response to the difference between the density of the toner image detected by the image density detection unit 86 and a given image density and may supply the carrier to the developing device 30M during the next printing operation. In this case, the deterioration state of the developer can be measured using the difference of the density of the toner image and the carrier can be supplied in response to the measured deterioration state of the developer, so as to supply a suitable amount of the carrier at a more accurate timing.

[0086] As described above, in the present specification, various examples of the imaging apparatus have been described. However, the imaging apparatus according to the present disclosure is not limited to the above-described example and can be further modified. In the description above, an example of detecting the amount of the developer from the output waveform of the TC sensor 81 and an example of detecting the deterioration state of the developer from the density of the toner image detected by the image density detection unit 86 have been described. At least one of these examples may be used when determining the failure of the imaging apparatus.

[0087] For example, when the supply of the carrier is repeated by the carrier supply unit 83 in a given period of time, the imaging apparatus may output an alarm prompting the replacement of the unit of the developing device 30M, for example when an unintended decrease in the amount of the carrier has occurred. Further, when the supply of the carrier is repeated by the carrier supply unit 83 for a given time and the accumulated value of the carrier supply operation time is equal to or greater than a threshold value, it may be determined that the carrier inside the carrier supply unit 83 has decreased below a threshold (for example, when the carrier supply unit is empty or almost empty). An alarm of that effect may be output.

[0088] The imaging apparatus may determine that the developer in the developing device 30M is excessively discharged or consumed when the value of Va/Vb within a specific time after the carrier supply unit 83 supplies the carrier does not decrease from that of the case before the supply of the carrier. Then, the replacement of the developing device 30M may be prompted by an alarm indicating a state in which the developer is excessively discharged or the developer is excessively consumed. Further, the imaging apparatus may handle the increase in charge of the developer by combining the drain operation of the toner inside the developing device 30M with the operation of detecting the charge amount.

[0089] The imaging apparatus 1 may include a plurality of carrier supply units 83 for respective colors or may include a single carrier supply unit 83. When the single carrier supply unit 83 is provided, the supply of the carrier to each of the developing device 30M, the developing device 30Y, the developing device 30C, and the developing device 30K may be switched via a clutch. In some examples, a single carrier supply unit 83 is provided so as to reduce the cost or inhibit an increase in the cost of the imaging apparatus 1 . In addition, the imaging apparatus may output an alarm prompting the supply of the highly charged carrier when the deterioration of the charging performance of the carrier (deterioration of the developer) is detected a plurality of times within a given period.

[0090] It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail is omitted.