Image forming apparatus and toner supply control method in image forming apparatus

Abstract

To provide an image forming apparatus and a toner supply control method in the image forming apparatus configured to supply two kinds of toner with one driving source, and to supply the two kinds of toner with good balance.SOLUTION: According to an image forming apparatus (10), when at least one of cumulative required supply times (Tz[X]) of two kinds of toner becomes a threshold (Ta) for toner supply or more, supply of one toner (α) is performed. The supply of the one toner (α) is performed over a cumulative required supply time (Tz[α]) of the one toner (α) and with a continuous supply allowed time Ton as an upper limit. Subsequently, supply of the other toner (β) is performed according to a cumulative required supply time (Tz[β]) of the other toner (β) and the current cumulative required supply time (Tz[α]) of the one toner (α), or the supply of the one toner (α) is resumed, or supply of both kinds of toner (α and β) is brought into a stopped state.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus and a toner supply control method in the image forming apparatus, and more particularly to an image forming apparatus and a toner supply control method in the image forming apparatus that performs color image formation processing by an electrophotographic system. [Background technology]

[0002] This type of image forming apparatus generally has four developing devices for developing four colors: yellow (Y), magenta (M), cyan (C), and black (K). Each developing device consumes toner during development, and to compensate for this toner consumption, toner is replenished to each developing device. This toner replenishment is performed by a toner replenishment device, and some toner replenishment devices are configured to replenish two of the four colors using a single (common) drive source and the other two colors using a separate drive source. This configuration reduces the number of drive sources, thereby reducing the cost (price) of the entire image forming apparatus, including the toner replenishment device. However, since each drive source selectively replenishes two colors of toner, it cannot simultaneously replenish the two colors. Therefore, it is important that each drive source replenishes the two colors of toner it is responsible for in a well-balanced manner.

[0003] For example, Patent Document 1 discloses a technology in which the amount of a first developer to be supplied to a first developing device is calculated, and the amount of a second developer to be supplied to a second developing device is calculated, and a first drive time for driving a first developer supply member responsible for supplying the first developer and a second drive time for driving a second developer supply member responsible for supplying the second developer are allocated according to the ratio between the calculated amounts of the first and second developers, and the first and second developer supply members are selectively driven according to the allocated times. The technology disclosed in Patent Document 1 is said to reduce developer concentration fluctuations, thereby reducing, for example, the inconvenience of the developer concentration in one of the first and second developing devices being high and the developer concentration in the other being insufficient. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-48201 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, in the technology disclosed in Patent Document 1, a first drive time for driving a first developer supply member responsible for supplying the first developer and a second drive time for driving a second developer supply member responsible for supplying the second developer are allocated according to the ratio between the amount of first developer to be supplied to a first developing device and the amount of second developer to be supplied to a second developing device. That is, at least a process (calculation) for calculating the ratio and a process for allocating the first drive time and the second drive time according to the ratio are performed. The toner supply procedure, including these processes, is quite complex, and requires a means, such as a CPU, with appropriate capabilities (performance). This leads to higher costs (prices) for the entire image forming apparatus, which in turn hinders the cost reduction of the entire image forming apparatus that would be achieved by reducing the number of drive sources.

[0006] Therefore, the present disclosure aims to provide a novel technology for an image forming device configured to replenish two types of toner using a single drive source and a toner replenishment control method for the image forming device, which is capable of replenishing the two types of toner in a well-balanced manner in an extremely simple and straightforward manner. [Means for solving the problem]

[0007] To achieve this object, the present disclosure includes a first disclosure relating to an image forming apparatus and a second disclosure relating to a toner replenishment control method in an image forming apparatus.

[0008] The first disclosure is an image forming apparatus for performing an image forming process using an electrophotographic method, and includes a first container, a first supply member, a second container, a second supply member, a drive source, a drive control means, a discharge means, and an accumulation means. The first container contains a first toner. The first supply member supplies the first toner contained in the first container to a first developing means. The second container contains a second toner. The second supply member supplies the second toner contained in the second container to a second developing means. The drive source selectively drives the first supply member and the second supply member. The drive control means controls the drive source. The discharge means derives a first required replenishment time and a second required replenishment time based on image data used in the image forming process. The first required replenishment time is the time required to supply the first toner to compensate for the amount of first toner consumed by the first developing means. The second required replenishment time is the replenishment time of the second toner required to make up for the consumption of the second toner by the second developing means. The accumulating means accumulates the shortage of the actual replenishment time of the first toner by the first replenishment member relative to the first required replenishment time each time an image formation process is performed, and obtains a first accumulated time that is the accumulated value of the shortage. In addition, the accumulating means accumulates the shortage of the actual replenishment time of the second toner by the second replenishment member relative to the second required replenishment time each time an image formation process is performed, and obtains a second accumulated time that is the accumulated value of the shortage.

[0009] Here, when at least one of the first cumulative time and the second cumulative time is equal to or greater than a predetermined first threshold, the drive control means identifies the first cumulative time or the second cumulative time equal to or greater than the first threshold as the one-side cumulative time and identifies the first supply member or the second supply member associated with the one-side cumulative time as the one-side cumulative time. The drive control means then drives the one-side supply member for the one-side cumulative time and up to the predetermined second threshold, and then stops driving the one-side supply member. Furthermore, the drive control means controls the drive source to drive the other supply member of the first or second supply member that is not the one-side supply member, or to redrive the one-side supply member, or to stop both the one-side supply member and the other supply member without driving them, depending on the other-side cumulative time that is not the one-side cumulative time of the first or second cumulative time and the current one-side cumulative time. In particular, when the other supply member is driven, the other supply member is driven for the other-side cumulative time and up to the second threshold. Furthermore, when the one-side supply member is driven again, the one-side supply member is driven for the current one-side cumulative time with the second threshold value as the upper limit.

[0010] When both the first accumulated time and the second accumulated time are equal to or greater than the first threshold value, the drive control means specifies the longer of the first accumulated time and the second accumulated time as one accumulated time.

[0011] Furthermore, in this first disclosure, a first toner concentration detection means and a second toner concentration detection means may be further provided. The first toner concentration detection means detects the concentration of a first toner contained in the developer in the first developing means, and the second toner concentration detection means detects the concentration of a second toner contained in the developer in the second developing means. Then, when both the first cumulative time and the second cumulative time are equal to or greater than a first threshold and the first cumulative time and the second cumulative time are the same length, the drive control means specifies the first cumulative time or the second cumulative time corresponding to the lower of the concentration detection value by the first toner concentration detection means or the concentration detection value by the second toner concentration detection means as one cumulative time.

[0012] The second threshold value in the first disclosure is preferably equal to or greater than the first required replenishment time when the print rate for the first toner based on the image data is 50% and equal to or less than the first required replenishment time when the print rate is 90%. In other words, the second threshold value is preferably equal to or greater than the second required replenishment time when the print rate for the second toner based on the image data is 50% and equal to or less than the second required replenishment time when the print rate is 90%.

[0013] In addition, it is preferable that the drive control means controls the drive source so that, when at least one of the first accumulated time and the second accumulated time reaches or exceeds a predetermined third threshold, the image forming process is interrupted and the first supply member is driven for the first accumulated time and the second supply member is driven for the second accumulated time, i.e., forced supply is performed. Note that the third threshold is a value greater (corresponding to a longer time) than the first and second thresholds.

[0014] A second disclosure of the present disclosure is a toner replenishment control method for an image forming apparatus that performs an electrophotographic image formation process, the method including a drive control step, a deriving step, and an accumulation step. The image forming apparatus includes a first container, a first supply member, a second container, a second supply member, and a drive source. The first container contains a first toner. The first supply member replenishes the first toner contained in the first container to a first developing unit. The second container contains a second toner. The second supply member replenishes the second toner contained in the second container to a second developing unit. The drive source selectively drives the first supply member and the second supply member. The drive control step controls the drive source. The deriving step derives a first required replenishment time and a second required replenishment time based on image data used in the image formation process. The first required replenishment time is the replenishment time of the first toner required to compensate for the amount of first toner consumed by the first developing unit. The second required replenishment time is the replenishment time of the second toner required to make up for the consumption of the second toner by the second developing means. Furthermore, in the accumulation step, the shortage of the actual replenishment time of the first toner by the first replenishment member relative to the first required replenishment time is accumulated each time an image formation process is performed, to obtain a first accumulated time which is the accumulated value of the shortage. In addition, in the accumulation step, the shortage of the actual replenishment time of the second toner by the second replenishment member relative to the second required replenishment time is accumulated each time an image formation process is performed, to obtain a second accumulated time which is the accumulated value of the shortage.

[0015] In the drive control step, if at least one of the first cumulative time and the second cumulative time is equal to or greater than a predetermined first threshold, the first cumulative time or the second cumulative time equal to or greater than the first threshold is identified as the one-side cumulative time, and the first supply member or the second supply member associated with the one-side cumulative time is identified as the one-side cumulative time. Then, in the drive control step, the one-side supply member is driven for the one-side cumulative time and up to the predetermined second threshold, and then the drive of the one-side supply member is stopped. Furthermore, in the drive control step, the drive source is controlled to drive the other supply member of the first supply member or the second supply member that is not the one-side supply member, or to drive the one-side supply member again, or to stop both the one-side supply member and the other supply member without driving them, depending on the other-side cumulative time of the first cumulative time or the second cumulative time that is not the one-side cumulative time and the current one-side cumulative time. In particular, when the other supply member is driven, the other supply member is driven for the other-side cumulative time and up to the second threshold. Furthermore, when the one-side supply member is driven again, the one-side supply member is driven for the current one-side cumulative time with the second threshold value as the upper limit. [Effects of the Invention]

[0016] According to the present disclosure, two types of toner, a first toner and a second toner, can be replenished in a well-balanced manner in a much simpler and more straightforward manner than the technology disclosed in the aforementioned Patent Document 1. This is extremely beneficial for an image forming apparatus configured to reduce costs by replenishing two types of toner with a single drive source. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram schematically illustrating the internal configuration of an image forming apparatus according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a perspective view of the toner supply device in the first embodiment. [Figure 3] FIG. 3 is a perspective cross-sectional view of the toner supply device in the first embodiment. [Figure 4] FIG. 4 is a diagram for explaining the operation of the toner supply device in the first embodiment. [Figure 5] FIG. 5 is a diagram showing an example of the relationship between printing timing and toner replenishment timing in the first embodiment. [Figure 6] FIG. 6 is a diagram for explaining an example of a toner supply procedure in the first embodiment. [Figure 7] FIG. 7 is a diagram for explaining another example of a toner supply procedure in the first embodiment. [Figure 8] FIG. 8 is a block diagram showing the electrical configuration of the image forming apparatus according to the first embodiment. [Figure 9] FIG. 9 is a flowchart showing the flow of the toner supply control task in the first embodiment. [Figure 10] FIG. 10 is a flowchart showing a part of the toner supply process in the first embodiment. [Figure 11] FIG. 11 is a flowchart showing the flow of another part of the toner supply process in the first embodiment. [Figure 12] FIG. 12 is a flowchart showing the flow of the remaining part of the toner supply process in the first embodiment. [Figure 13] FIG. 13 is a diagram conceptually showing the configuration of a forced replenishment threshold table in the second embodiment of the present disclosure. [Figure 14] FIG. 14 is a diagram conceptually showing the configuration of a threshold coefficient table in the third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] [First Example] The first embodiment of the present disclosure will be described using an image forming apparatus 10 shown in FIG. 1 as an example.

[0019] Image forming apparatus 10 according to the first embodiment is a so-called multifunction peripheral (MFP) having multiple functions such as a copy function, a printer function, an image scanner function, and a fax function. FIG. 1 is a view showing the internal configuration of image forming apparatus 10 installed in a usable state, as viewed from the front side of image forming apparatus 10. That is, the up-down direction in FIG. 1 corresponds to the up-down direction of image forming apparatus 10. The left-right direction in FIG. 1 corresponds to the left-right direction of image forming apparatus 10. Furthermore, the front side of the paper surface of FIG. 1 corresponds to the front of image forming apparatus 10. The back side of the paper surface of FIG. 1 corresponds to the rear of image forming apparatus 10.

[0020] An image reading unit 12 serving as an image reading means is provided at the top of the image forming apparatus 10. The image reading unit 12 performs image reading processing, reading an image of an original (not shown) and outputting two-dimensional read image data corresponding to the image of the original. To this end, the image reading unit 12 has a document table 14 on which the original is placed. The document table 14 is formed of a transparent material such as glass in a roughly rectangular flat plate shape, and is provided with both main surfaces aligned horizontally. An image reading unit 16 is provided below the document table 14. Although not described in detail, the image reading unit 16 includes a light source, a mirror, a lens, a line sensor, etc., and has a linear image reading position Pr on the top surface of the document table 14 that extends along the front-to-rear direction of the image forming apparatus 10. Furthermore, a drive mechanism (not shown) is provided below the document table 14 for moving (scanning) the image reading position Pr of the image reading unit 16 along the left-to-right direction of the image forming apparatus 10. That is, with a document placed on document table 14, the image reading position Pr of image reading unit 16 is moved by a drive mechanism, and the image of the document is read by a so-called fixed reading method. The front-to-rear direction of image forming apparatus 10 is called the main scanning direction, and the left-to-right direction of image forming apparatus 10 is called the sub-scanning direction.

[0021] An automatic document feeder (ADF) 18 is provided above the document table 14, and also serves as a document pressing cover for pressing down a document placed on the document table 14. The automatic document feeder 18 is provided so as to be able to switch between a state in which the top surface of the document table 14 is exposed to the outside and a state in which the top surface of the document table 14 is covered. For this reason, the automatic document feeder 18 is coupled to the main body (housing) of the image forming apparatus 10 via an appropriate movable support member such as a hinge (not shown). Note that FIG. 1 shows a state in which the automatic document feeder 18 covers the top surface of the document table 14. The automatic document feeder 18 performs its original function when it is in a state in which it covers the top surface of the document table 14 as shown in FIG. 1.

[0022] The automatic document feeder 18 has a document placement tray 20. Documents, specifically sheet-like documents, can be placed on this document placement tray 20, and in particular, multiple documents can be placed in a stack. Although a detailed explanation will be omitted, the automatic document feeder 18 takes in the documents placed on the document placement tray 20 one by one (one by one) and transports them through a document transport path 22 within the automatic document feeder 18. Along the way, the document passes through an image reading position Pr, or more precisely, the image reading position Pr is fixed. This allows the image of the document to be read, and the document is read using a so-called flow reading method. The document is then discharged to a document discharge tray 24.

[0023] An image forming unit 26 is provided below the image reading unit 12 as an image forming means. This image forming unit 26 is responsible for image formation processing, i.e., printing, that forms an image based on appropriate image data such as the above-mentioned scanned image data on a sheet-like image recording medium (not shown), such as paper. This printing is performed using a known electrophotographic method. The image forming unit 26 also employs a tandem method to perform color printing.

[0024] Specifically, the image forming unit 26 has four process units (sometimes referred to as "image forming stations") 28, 28, . . . serving as monochromatic toner image forming means for individually forming monochromatic toner images (not shown) of a plurality of different colors, e.g., four colors: yellow, magenta, cyan, and black. The image forming unit 26 also has an exposure device 30, . . . serving as exposure means for performing the exposure required for forming the monochromatic toner images by each of the process units 28, 28, . . . The image forming unit 26 further has a transfer unit 34, . . . serving as transfer means. The transfer unit 34 has an intermediate transfer belt 32 (sometimes referred to as a "primary transfer belt") to which each monochromatic toner image formed by each of the process units 28, 28, . . . is sequentially transferred, and the toner images transferred to the intermediate transfer belt 32 are then transferred onto a sheet of paper. The image forming unit 26 also has a fixing device 36, . . . serving as fixation means for fixing the toner images transferred onto the sheet of paper. In addition, the image forming section 26 has a toner supply device 37 for supplying toner (not shown) to each of the developing devices 50, 50, . . . (to be described later) of each of the process units 28, 28, .

[0025] First, the transfer unit 34 will be described in detail. In addition to the intermediate transfer belt 32 described above, the transfer unit 34 has a drive roller 38 that rotates the intermediate transfer belt 32, and a driven roller 40 that stretches the intermediate transfer belt 32 together with the drive roller 38. The transfer unit 34 also has four intermediate transfer rollers (sometimes called "primary transfer rollers") 42, 42, ... provided at positions corresponding to the process units 28, 28, ... on the inside of the intermediate transfer belt 32, and a transfer roller (sometimes called "secondary transfer roller") 44 as a transfer member.

[0026] The intermediate transfer belt 32 is tensioned between a drive roller 38 and a driven roller 40. The drive roller 38 receives a driving force from a motor serving as an intermediate transfer belt driving unit (not shown) and rotates, for example, counterclockwise in FIG. 1 . Accordingly, the intermediate transfer belt 32 rotates (circularly moves) in the same direction, and the driven roller 40 also rotates in the same direction. A lower region 32a of the intermediate transfer belt 32 between the drive roller 38 and the driven roller 40 is tensioned along the horizontal direction, and the process units 28, 28, ... are arranged opposite this horizontally tensioned region 32a. The region 32a of the intermediate transfer belt 32 where the process units 28, 28, ... are arranged is called the intermediate transfer region. In this intermediate transfer region 32a, the intermediate transfer belt 32 moves from the left to the right of the image forming apparatus 10, i.e., moves along the sub-scanning direction.

[0027] The intermediate transfer belt 32 is a flexible endless belt made of synthetic resin (such as polyimide or polycarbonate) appropriately blended with a conductive material such as carbon black. Although not described in detail, the driven roller 40 also has a slack prevention function that prevents the intermediate transfer belt 32 from slackening by applying an appropriate tension to the intermediate transfer belt 32.

[0028] The process units 28 are disposed below the intermediate transfer region 32a of the intermediate transfer belt 32 at regular intervals along the direction of movement of the intermediate transfer belt 32 in the intermediate transfer region 32a, i.e., along the sub-scanning direction. As described above, each process unit 28 forms a single-color toner image of one of four colors, yellow, magenta, cyan, and black, on the intermediate transfer belt 32. Although not apparent from the figures including FIG. 1, the process units 28 are disposed in the order of yellow, magenta, cyan, and black, from upstream to downstream in the direction of movement of the intermediate transfer belt 32 in the intermediate transfer region 32a (from left to right in FIG. 1). However, this order is merely an example and is not limiting. The process units 28 have the same structure except that they form single-color toner images of different colors on the intermediate transfer belt 32.

[0029] Each process unit 28 includes a photosensitive drum 46, a charging device 48, a developing device 50, a cleaning device 52, a charge removing device (not shown), and the like.

[0030] The photosensitive drum 46 is an image carrier that carries an electrostatic latent image and a monochrome toner image, which will be described later, and has a cylindrical substrate formed of a conductive material such as aluminum. Although not shown, the substrate is grounded, and a photosensitive layer is formed on its surface (outer periphery). The photosensitive drum 46 is disposed in the intermediate transfer region 32a so that the surface of the substrate abuts against the outer surface of the intermediate transfer belt 32, and rotates by receiving a driving force from a motor (not shown) serving as a drum driving means. The photosensitive drum 46 rotates clockwise in FIG. 1 at a speed that matches the moving speed of the intermediate transfer belt 32.

[0031] The charging device 48 is a charging means that charges the surface of the photosensitive drum 46 to a predetermined potential. The surface of the photosensitive drum 46, charged to a predetermined potential by the charging device 48, is exposed by the exposure device 30, and the exposed area of ​​the surface of the photosensitive drum 46 drops to a potential close to ground potential (0 V). The exposure device 30 is provided below the row of process units 28, 28, ... and exposes the surface of the photosensitive drum 46 of each process unit 28 from below, i.e., irradiates the surface of the photosensitive drum 46 with light in a manner corresponding to the image data to be printed. As a result, an electrostatic latent image whose surface potential changes according to the image data to be printed is formed on the surface of the photosensitive drum 46. Note that the exposure device 30 is, for example, a laser scanning unit having a laser diode (not shown) as a light source and a polygon mirror as a deflection means. However, instead, an LED unit having an LED array in which LEDs are arranged as a light source may be used as the exposure device 30.

[0032] The developing device 50 is a developing means that develops the electrostatic latent image formed on the surface of the photosensitive drum 46. Specifically, the developing device 50 has a developer storage chamber 50a, which stores developer containing toner. The developer stored in the developer storage chamber 50a is agitated by agitators 50c and 50d provided in the developer storage chamber 50a. As a result, the toner contained in the developer is frictionally charged, and the developing device 50 develops the electrostatic latent image on the photosensitive drum 46 with this charged toner. In other words, the electrostatic latent image formed on the photosensitive drum 46 is visualized as a monochromatic toner image by the toner contained in the developer stored in the developing device 50 (developer storage chamber 50a). The developer is a two-component developer that contains a carrier in addition to the toner. The toner is a non-magnetic material, and the carrier is a magnetic material. Further, below the developer storage chamber 50a, a toner concentration sensor 50b is provided as a toner concentration detection means for detecting the concentration of toner (mass ratio of toner to carrier) T / D contained in the developer in the developer storage chamber 50a. This toner concentration sensor 50b is a so-called magnetic permeability sensor, and by measuring the magnetic permeability of the developer, it detects the bulk density of the carrier contained in the developer, and thus detects the toner concentration T / D.

[0033] The monochromatic toner image visualized by development by the developing device 50 is transferred from the surface of the photosensitive drum 46 to the outer surface of the intermediate transfer belt 32 at the contact position between the surface of the photosensitive drum 46 and the outer surface of the intermediate transfer belt 32, a process known as intermediate transfer (primary transfer). To achieve this, an intermediate transfer roller 42 is provided facing the photosensitive drum 46 across the intermediate transfer belt 32. The intermediate transfer roller 42 is provided with its outer surface (outer periphery) in contact with the inner surface of the intermediate transfer belt 32 and rotates by receiving a driving force generated by the rotation of the intermediate transfer belt 32, i.e., rotates counterclockwise in FIG. 1. A predetermined intermediate transfer voltage is applied to the intermediate transfer roller 42 from an intermediate transfer power source (not shown), thereby forming a transfer electric field between the surface of the photosensitive drum 46 and the outer surface of the intermediate transfer belt 32. The monochromatic toner image on the photosensitive drum 46 is transferred onto the intermediate transfer belt 32 by the action of this transfer electric field.

[0034] In this manner, four single-color toner images of yellow, magenta, cyan, and black are individually formed on the intermediate transfer belt 32. Then, these four single-color toner images are superimposed on each other to form a color toner image on the intermediate transfer belt 32.

[0035] The (color) toner image formed on the intermediate transfer belt 32 is transferred to paper at a transfer nip Nt, which is the contact point between the intermediate transfer belt 32 and a transfer roller 44. Specifically, the transfer roller 44 is positioned opposite the drive roller 38 across the intermediate transfer belt 32, and is positioned so as to press the intermediate transfer belt 32 against the drive roller 38. The transfer roller 44 rotates by receiving a driving force from the rotation of the intermediate transfer belt 32, i.e., clockwise in FIG. 1 . Then, a transfer bias current having the same polarity as the charge polarity of the toner is applied to the drive roller 38 from a transfer bias power supply (not shown). This forms a transfer electric field between the intermediate transfer belt 32 and the transfer roller 44, i.e., at the transfer nip Nt. In this state, when paper passes through the transfer nip Nt, the toner image on the intermediate transfer belt 32 is transferred to the paper.

[0036] The cleaning device 52 is a cleaning means that removes residual toner from the photosensitive drum 46 after a single-color toner image has been transferred from the photosensitive drum 46 onto the intermediate transfer belt 32. The static eliminator (not shown) is a static eliminator that removes static electricity from the photosensitive drum 46 after the residual toner has been removed by the cleaning device 52. After the static electricity has been removed by this static eliminator, the process from charging by the charging device 48 onwards is repeated.

[0037] The fixing device 36 is provided downstream of the transfer nip Nt in the transport direction of the paper transported along a paper transport path 54, which will be described later. As described above, the fixing device 36 fixes the toner image on the paper to the paper, more specifically, by heating and melting the toner image and then pressing it, thereby fixing (thermally fixing) the toner image to the paper. To this end, the fixing device 36 has a heating belt 56, a heating roller 58, a fixing roller 60, a pressure roller 62, etc.

[0038] The heating belt 56 is a flexible, endless belt made of a synthetic resin (e.g., polyimide or polycarbonate) with high thermal conductivity. The heating belt 56 is stretched between a heating roller 58 and a fixing roller 60. The heating roller 58 has a cylindrical base (thermal conductive layer) with high thermal conductivity and a heat source disposed therein. The heat source is a lamp heater such as a halogen lamp, and is heated by receiving heating power from a heater power supply (not shown). The fixing roller 60 is a cylindrical roller member having a core and an elastic layer covering the core. The heating roller 58 and the fixing roller 60 extend parallel to each other and are inscribed within the heating belt 56. The fixing roller 60 receives driving force from a motor (not shown) serving as a heating belt driving means and rotates, for example, counterclockwise in FIG. 1 . Accordingly, the heating belt 56 rotates (circularly moves) in the same direction as the fixing roller 60, and the heating roller 58 also rotates in the same direction as the fixing roller 60.

[0039] The pressure roller 62 is a cylindrical roller member and includes a core metal, an elastic layer covering the core metal, and a release layer covering the elastic layer. The pressure roller 62 is positioned opposite the fixing roller 60 across the heating belt 56, and presses the heating belt 56 between the pressure roller 62 and the fixing roller 60. That is, the pressure roller 62 is positioned so as to extend along the rotational axis of the fixing roller 60, in other words, so as to extend along the rotational axis of the heating belt 56. The pressure roller 62 rotates by receiving a driving force generated by the rotation of the heating belt 56, that is, clockwise in FIG. 1. The fixing nip Nf, where the pressure roller 62 presses the heating belt 56, is located in the paper transport path 54, which will be described later. When paper passes through the fixing nip Nf, the toner image on the paper is heated and melted, and then pressed against the paper, thereby being fixed to the paper.

[0040] Although detailed description including illustrations will be omitted, the fixing device 36 has a temperature sensor for detecting the surface temperature (fixing temperature) of the heating belt 56. Based on the detection result from this temperature sensor, the heating temperature of the heating roller 58 by the heat source described above is controlled, and thus the surface temperature of the heating belt 56 is controlled. A thermistor is used as the temperature sensor, for example, but is not limited to this. Alternatively, the fixing device 36 may be configured without the heating belt 56, with the fixing roller 60 also serving as the heating roller 58, and the direct contact portion between the fixing roller 60 and the pressure roller 62 serving as the fixing nip portion Nf.

[0041] The toner supply device 37 supplies toner to each of the developing devices 50, 50, ..., more specifically, to the developer storage chamber 50a of each developing device 50. That is, when each developing device 50 performs development, the toner in the developer storage chamber 50a of each developing device 50 is consumed. To make up for this toner consumption, the toner supply device 37 supplies toner to the developer storage chamber 50a of each developing device 50. This toner supply device 37 will be described in detail later, but the toner supply device 37 is fitted with four toner cartridges 100, 100, ... containing toner corresponding to the four colors mentioned above.

[0042] Furthermore, below image forming unit 26, in other words, at the bottom of image forming apparatus 10, there is provided paper feed unit 64 as a paper feed means. Paper feed unit 64 has paper feed cassette 66, which can store multiple sheets of paper in a stack. Paper feed unit 64 also has pickup roller 68. Paper feed unit 64 uses pickup roller 68 to pick up sheets of paper stored in paper feed cassette 66 one by one, and supplies the sheets to paper transport path 54, which will be described next.

[0043] The paper transport path 54 is provided so as to extend from the paper feed unit 64 through the transfer nip Nt and the fixing nip Nf to the paper discharge outlet 72 for the paper discharge tray 70. A plurality of transport rollers (strictly speaking, roller pairs) 74, 74, ... are provided at appropriate positions on the paper transport path 54 for transporting paper along the paper transport path 54 from the paper feed unit 64 toward the paper discharge outlet 72. Of the transport rollers 74, 74, ..., the transport roller 74a, which is provided upstream of the transfer nip Nt in the paper transport direction on the paper transport path 54 and closest to the transfer nip Nt, is a registration roller (sometimes called a "paper stop roller") for timing the passage of the paper through the transfer nip Nt. Among the transport rollers 74, 74, the transport roller 74b provided at the most downstream side in the paper transport direction on the paper transport path 54, i.e., provided near the paper discharge port 72, is a paper discharge roller for discharging paper to the paper discharge tray 70 through the paper discharge port 72. The paper discharge tray 70 is provided between the image reading unit 12 and the image forming unit 26, and is provided in the so-called internal space, but is not limited to this.

[0044] In addition, a reversing conveying path 76 for double-sided printing is provided within the image forming apparatus 10. This reversing conveying path 76 is a conveying path that takes in paper that has once passed through the fixing nip portion Nf, i.e., paper after printing, and supplies the paper for printing again. That is, the paper taken in by the reversing conveying path 76 is supplied again to the paper conveying path 54 via the reversing conveying path 76, and more specifically, is supplied to the upstream side of the registration rollers 74a. As a result, the paper supplied to the upstream side of the registration rollers 74a is in a reversed state. Then, printing is performed on this reversed paper, achieving so-called double-sided printing. Conveying rollers 78 are also provided at appropriate positions on the reversing conveying path 76.

[0045] Furthermore, a manual feed tray 80 is provided on the right side of the image forming apparatus 10. A plurality of sheets of paper can be placed in a stack on this manual feed tray 80. When this manual feed tray 80 is designated as the paper supply source, the paper feed unit 64 supplies the paper from the manual feed tray 80 to the paper transport path 54 one sheet at a time.

[0046] Furthermore, the paper feed unit 64 may have an optional paper feed cassette (not shown). This optional paper feed cassette is provided below the paper feed cassette 66. When the optional paper feed cassette is specified as the paper supply source, the paper feed unit 64 supplies paper from the optional paper feed cassette one sheet at a time to the paper transport path 54. An optional transport roller 82 for supplying paper from the optional paper feed cassette to the paper transport path 54 is provided at an appropriate position.

[0047] Next, toner supply device 37 will be described in detail with reference to Figures 2 to 4. Figure 2 is a perspective view of toner supply device 37 as seen from diagonally above the front right. Figure 3 is a cross-sectional view of the toner supply device as seen from diagonally above the front right at a slightly different angle from that in Figure 2. Figure 4 is a diagram illustrating the transmission path of rotational force from drive source 110, which will be described later.

[0048] The toner supply device 37 provided in the image forming apparatus 10 according to the first embodiment has two supply devices, a first supply device 37a and a second supply device 37b. Of these, the first supply device 37a is responsible for supplying toner of two colors, yellow and magenta. To this end, the first supply device 37a includes a toner cartridge 100 (hereinafter sometimes referred to as the "yellow toner cartridge 100[Y]") as a storage section for yellow toner that contains yellow toner, a toner cartridge 100 (hereinafter sometimes referred to as the "magenta toner cartridge 100[M]") as a storage section for magenta toner that contains magenta toner, a first supply motor 110a that is a driving source 110 for supplying toner from the toner cartridges 100[Y], 100[M] to the corresponding developing devices 50, and internal supply paths 104[Y], 104[M] that guide toner from the toner cartridges 100[Y], 100[M] to the corresponding developing devices 50, respectively. The toner cartridges 100[Y], 100[M], first supply motor 1100a, and internal conveying paths 104[Y], 104[M] are attached to the main body of the image forming device 10, but the toner cartridges 100[Y], 100[M] are attached to the main body of the image forming device 10 in a manner that allows them to be easily detached and attached so that they can be replaced when the toner inside them runs out.

[0049] On the other hand, the second supply device 37b is responsible for supplying toner of two colors, cyan and black. To this end, the second supply device 37b includes a toner cartridge 100 (hereinafter sometimes referred to as the "cyan toner cartridge 100[C]") as a cyan toner storage unit that stores cyan toner, a toner cartridge 100 (hereinafter sometimes referred to as the "black toner cartridge 100[K]") as a black toner storage unit that stores black toner, a second supply motor 110b that is a drive source 110 for supplying toner from the toner cartridges 100[C] and 100[K] to the corresponding developing devices 50, and internal supply paths 104[C] and 104[K] that guide toner from the toner cartridges 100[C] and 100[K] to the corresponding developing devices 50, respectively. The toner cartridges 100[C], 100[K], second supply motor 110b, and internal conveying paths 104[C], 104[K] are attached to the main body of the image forming device 10, but the toner cartridges 100[C], 100[K] are attached to the main body of the image forming device 10 in a manner that allows them to be easily detached and replaced when the toner inside them runs out.

[0050] Each toner cartridge 100 is provided with a transporting and replenishing member (auger screw) 102 that transports the toner contained in the toner cartridge 100 forward while stirring it (FIG. 3). A first gear 116 is attached to the front end of each transporting and replenishing member 102 (FIG. 2), and when rotational force from the corresponding drive source 110 is transmitted to the first gear 116, the transporting and replenishing member 102 rotates. As this transporting and replenishing member 102 rotates, the toner contained in the toner cartridge 100 is transported forward and sent to the internal replenishing path 104 via a discharge port 118 provided at the front of the toner cartridge 100. A replenishing member (screw feeder) 106 is provided in each internal replenishing path 104 that is provided to correspond to the discharge port 118 of each toner cartridge 100. Each supply member 106 is also provided at its end (left end) with a second gear 120 that receives rotational force from the corresponding drive source 100. The second gear 120 receives rotational force from the drive source 110 and rotates at a constant speed, thereby discharging toner supplied from each toner cartridge 100 via each discharge outlet 118 from the supply port 108 at a constant speed (Vs[X]). The toner discharged from this supply port 108 is replenished to the developer storage chamber 50a of the corresponding developing device 50 via an external supply path (not shown). Note that, because black toner is consumed in greater quantities than toners of other colors, the black toner cartridge 100[K] may be larger in size than the other toner cartridges 100.

[0051] Furthermore, in the first embodiment, the supply member 106 is provided between the internal supply path 104 and the supply port 108, but the supply member 106 may be eliminated, and the internal supply path 104 may be configured so that the discharge port 118 is located directly above the supply port 108. In this case, the toner in the toner cartridge 100 is replenished to the developer accommodating chamber 50a by rotating the transport and supply member 102.

[0052] Here, the first supply device 37a in the first embodiment selectively drives either the supply member 106 for the yellow toner cartridge 100[Y] (yellow supply member 106[Y]) and the conveying and supply member 102 in the yellow toner cartridge 100[Y] (yellow conveying and supply member 102[Y]), or the supply member 106 for the magenta toner cartridge 100[M] (magenta supply member 106[M]) and the conveying and supply member 102 in the magenta toner cartridge 100[M] (magenta conveying and supply member 102[M]), using a common (single) drive source, the first supply motor 110a. That is, the first supply motor 110a selectively drives the yellow supply member 106[Y] and the yellow conveying and supply member 102[Y], or the magenta supply member 106[M] and the magenta conveying and supply member 102[M]. In other words, the first supply motor 110a cannot simultaneously drive the yellow supply member 106[Y] and the yellow transport supply member 102[Y], and the magenta supply member 106[M] and the magenta transport supply member 102[M].

[0053] To explain in more detail with reference to Figure 4, a drive gear 112a is provided on the rotating shaft 111a of the first supply motor 110a (note that in Figure 4, the first supply motor 110a is omitted from the illustration so that the arrangement of the drive gear 112a can be seen). The drive gear 112a is connected to a yellow gear train 121[Y] that transmits rotational force to a first gear 116 (yellow first gear 116[Y]) attached to the yellow transport and supply member 102[Y] and a second gear 120 (yellow second gear 120[Y]) attached to the yellow supply member 106[Y], and a magenta gear train 121[M] that transmits rotational force to a first gear 116 (magenta first gear 116[M]) attached to the magenta transport and supply member 102[M] and a second gear 120 (magenta second gear 120[M]) attached to the magenta supply member 106[M]. The yellow gear train 121[Y] and the magenta gear train 121[M] are each provided with a one-way clutch (not shown) that transmits rotational force in one direction. Here, the one-way clutch provided in the yellow gear train 121[Y] transmits rotational force to the yellow gear train 121[Y] when the drive gear 112a of the first supply motor 110a rotates in a predetermined direction R1 (counterclockwise in FIG. 4), but is arranged so as not to transmit rotational force to the yellow gear train 121[Y] when the drive gear 112a rotates in a direction R2 (clockwise in FIG. 4) opposite to the predetermined direction R1. Similarly, the one-way clutch provided in the magenta gear train 121[M] is arranged so as not to transmit rotational force to the magenta gear train 121[M] when the drive gear 112a rotates in one direction R1, which is the predetermined direction, but to transmit rotational force to the magenta gear train 121[M] when the drive gear 112a rotates in the other direction R2, which is the direction opposite to the one direction R1. In other words, when the first supply motor 110a (its drive gear 112a) rotates in one direction R1, the yellow supply member 106[Y] and the yellow transport supply member 102[Y] are driven, thereby supplying yellow toner to the developer storage chamber 50a of the yellow developing device 50.When the first supply motor 110a rotates in the other direction R2, the magenta supply member 106[M] and the magenta transporting and supplying member 102[M] are driven, thereby supplying magenta toner to the developer storage chamber 50a of the magenta developing device 50. Note that Fig. 4 is a diagram illustrating the main parts of the first supply device 37a. The first supply motor 110a is, for example, a stepping motor, but is not limited to this.

[0054] Similarly, in the second supply device 37b in the first embodiment, either the supply member 106 for the cyan toner cartridge 100[C] (cyan supply member 106[C]) and the conveying and supply member 102 in the cyan toner cartridge 100[C] (cyan conveying and supply member 102[C]), or the supply member 106 for the black toner cartridge 100[K] (black supply member 106[K]) and the conveying and supply member 102 in the black toner cartridge 100[K] (black conveying and supply member 102[K]), is driven by a common (single) drive. The second supply motor 110b selectively drives the cyan supply member 106[C] and the yellow supply member 102[Y], and the black supply member 106[K] and the black supply member 102[K]. In other words, the second supply motor 110b cannot simultaneously drive the cyan supply member 106[C] and the cyan supply member 102[c] and the black supply member 106[K] and the black supply member 102[K].

[0055] In addition, the rotating shaft 111b of the second supply motor 110b is provided with a drive gear 112b similar to that provided on the rotating shaft 111a of the first supply motor 110a (note that in Figure 4, the rotating shaft 111b and drive gear 112b of the second supply motor 110b are not visible as they are blocked by the second supply motor 110b). The drive gear 112b of the second supply motor 110b also forms a transmission path that transmits rotational force to the first gear 116 (cyan first gear 116[C]) attached to the cyan transporting and supplying member 102[C] and the second gear 120 (cyan second gear 120[c]) attached to the cyan transporting and supplying member 106[C], and is connected to a cyan gear train having a one-way clutch in the transmission path, and a black gear train having a one-way clutch in the transmission path that transmits rotational force to the first gear 116 (black first gear 116[K]) attached to the black transporting and supplying member 102[K] and the second gear (black second gear) attached to the black supplying member 106[K]. Similarly to the first supply motor 110a, when the second supply motor 110b (drive gear 112b) rotates in one direction R1, the cyan supply member 106[C] and the cyan transporting and supply member 102[C] are driven, and when the drive gear 112b rotates in the other direction R2, the black supply member 106[K] and the black transporting and supply member 102[K] are driven, thereby supplying the corresponding toner. Note that the second supply motor 110b is also, like the first supply motor 110a, for example, a stepping motor, but is not limited to this.

[0056] As described above, each supply member 106 rotates at a constant speed, supplying toner to the developer storage chamber 50a of the corresponding developing device 50 at a constant speed (Vs[X]). This toner supply speed Vs[X] (X is an index representing one of Y, M, C, and K) is set to a value that prevents the toner from being supplied in clumps and ensures a sufficient mixing time for the supplied toner to be charged as intended. The toner supply speed Vs[X] of the toner supply device 37 in the first example is expressed as the amount of toner that can be supplied per unit time, and its value is, for example, 0.2 g / s. This value can be determined experimentally, and the supply device 37 in the first example drives the supply member 106 (and the transporting and supplying member 102) so that 0.2 g of toner is supplied per second from the supply port 108 (and the discharge port 118). The amount of toner supplied by toner supply device 37 during toner image formation can be controlled (adjusted) by the driving time of drive source 110 that drives supply member 106 (and conveying and supplying member 102). Next, the amount of toner consumed in forming a toner image Qc[X] will be described.

[0057] The amount of toner consumed Qc[X] can be calculated based on the size of the paper on which the toner image is formed and the print rate Rp[X]. Here, the actual amount of toner consumed when forming a toner image with an A4-size paper and a print rate Rp[X] (the ratio of the area of ​​the toner image to the paper size) of 5% was determined from experimental results to be 0.013 g per sheet of paper. Because the amount of toner consumed Qc[X] is correlated with the print rate Rp[X], when the paper size is A4 and the print rate Rp[X] is 100%, the amount of toner consumed Qc[X] can be predicted to be 0.26 g per sheet of paper by proportional calculation, since the amount of toner consumed Qc[X] when the paper size is A4 and the print rate Rp[X] is 0.013 g when the print rate Rp[X] is 5%. As such, since the toner consumption amount Qc[X] can be predicted from the value of the print rate Rp[X], it can be seen that the amount of toner replenished by the toner replenishment device 37 can be determined based on the print rate Rp[X]. Note that the print rate Rp[X] is calculated by converting it to A4 size. Therefore, for example, if the print rate Rp[X] is 100% for A3 size, since the area of ​​A3 is twice that of A4, it is converted to 200%, or the equivalent of two A4 sheets. From here on, however, unless otherwise specified, the paper size will be assumed to be A4 size. Furthermore, this toner consumption amount Qc[X] is also common (the same) for all four colors.

[0058] Next, the CPM (pages per minute) representing the printing speed of the image forming apparatus 10 in the first embodiment is, for example, 35. Therefore, the printing time (paper passing time) Tp (=1 / CPM), which is the time required to print one sheet of paper, is approximately 1.71 seconds. In other words, when forming an A4-sized toner image with a printing rate Rp[X] of 100%, 0.26 g of toner needs to be replenished. However, since the toner replenishment speed Vs[X] per unit time of the replenishment device 37 is 0.2 g / s, the time (driving time) required to replenish 0.26 g of toner is 1.3 seconds, and toner replenishment can be completed within the time required to print one sheet.

[0059] Now, focusing on the first supply device 37a, as described above, the first supply motor 110a selectively drives the yellow supply member 106[Y] and the magenta supply member 106[M], i.e., the supply of yellow toner and the supply of magenta toner are selectively performed. For example, if the yellow coverage rate Rp[Y] and magenta coverage rate Rp[M] for printing on one sheet of paper are 5% and 5%, respectively, i.e., if the yellow toner consumption Qc[Y] is 0.013 g and the magenta toner consumption Qc[M] is also 0.013 g, then the drive time of the yellow supply member 106[Y] required to replenish the consumed yellow toner, i.e., the required yellow toner replenishment time Ts[Y] (=Qc[Y] / Vs[Y]), is 0.065 seconds, and the drive time of the magenta supply member 106[M] required to replenish the consumed magenta toner, i.e., the required magenta toner replenishment time Ts[M] (=Qc[M] / Vs[M]), is also 0.065 seconds. In other words, a total of 0.13 seconds is required to replenish the consumed yellow and magenta toners during printing. This 0.13 seconds is shorter than the printing time Tp per sheet of paper, which is approximately 1.71 seconds. This means that all of the yellow and magenta toner consumed during printing can be replenished within the printing time Tp per sheet of paper, in other words, while printing is being performed on one sheet of paper.

[0060] In contrast, if the yellow coverage rate Rp[Y] for printing on one sheet of paper is 100% (solid yellow) and the magenta coverage rate Rp[M] is 100% (solid magenta), i.e., if the yellow toner consumption Qc[Y] is 0.26 g and the magenta toner consumption Qc[M] is also 0.26 g, the replenishment time Ts[Y] required to replenish the consumed yellow toner is 1.3 seconds, and the replenishment time Ts[M] required to replenish the consumed magenta toner is also 1.3 seconds. In other words, a total of 2.6 seconds is required to replenish the consumed yellow and magenta toners during printing. This 2.6 seconds is longer than the printing time Tp per sheet of paper, which is approximately 1.71 seconds. This means that it is not possible to replenish all of the yellow and magenta toner consumed during printing within the printing time Tp per sheet of paper, i.e., while printing is being performed on one sheet of paper, or in other words, replenishment is not possible in time.

[0061] Therefore, it is important to drive the yellow supply member 106[Y] and the magenta supply member 106[M] in an appropriate balance according to the required yellow toner replenishment time Ts[Y] and the required magenta toner replenishment time Ts[M], specifically, the cumulative required yellow toner replenishment time Tz[Y] and the cumulative required magenta toner replenishment time Tz[M]. The cumulative required yellow toner replenishment time Tz[Y] is the cumulative value of the shortfall obtained by subtracting the actual driving time of the yellow supply member 106[Y] (yellow toner replenishment time) from the required yellow toner replenishment time Ts[Y]. The cumulative required magenta toner replenishment time Tz[M] is the cumulative value of the shortfall obtained by subtracting the actual driving time of the magenta toner replenishment member 106[M] from the required magenta toner replenishment time Ts[M]. These cumulative required replenishment times Tz[Y] and Tz[M] are calculated every time printing is performed.

[0062] Therefore, in the first embodiment, for example, when the cumulative required replenishment time Tz[Y] of yellow toner becomes equal to or greater than the toner replenishment threshold value Ta, which is a predetermined first threshold, the yellow replenishment member 106[Y] is driven, i.e., yellow toner is replenished. This yellow toner replenishment is performed over the cumulative required replenishment time Tz[Y], with the upper limit set to the allowable continuous replenishment time Ton, which is a predetermined second threshold. That is, when the cumulative required replenishment time Tz[Y] is equal to or less than the allowable continuous replenishment time Ton, yellow toner replenishment is performed over the cumulative required replenishment time Tz[Y]. On the other hand, when the cumulative required replenishment time Tz[Y] exceeds the allowable continuous replenishment time Ton, yellow toner replenishment is performed over the allowable continuous replenishment time Ton, and then the replenishment is temporarily stopped. In other words, the replenishment of yellow toner is temporarily stopped before the replenishment of yellow toner over the cumulative required replenishment time Tz[Y] is completed. Then, after a predetermined replenishment stop time Toff has elapsed, replenishment of yellow toner is resumed on the condition that the cumulative required replenishment time Tz[M] of the other toner, magenta toner, is less than the toner replenishment threshold Ta. This replenishment of yellow toner continues until the cumulative required replenishment time Tz[Y] of the yellow toner becomes 0 (zero), or more precisely, until it becomes 0 or less. In short, yellow toner is replenished intermittently in a pattern that follows a replenishment duty (Ton:Toff) that is a combination of the continuous replenishment allowable time Ton and the replenishment stop time Toff.

[0063] Similarly, when the cumulative required replenishment time Tz[M] of magenta toner exceeds the toner replenishment threshold Ta, the magenta replenishment member 106[M] is driven, i.e., magenta toner is replenished. This replenishment of magenta toner is performed over the cumulative required replenishment time Tz[M], with the allowable continuous replenishment time Ton as its upper limit. In particular, when the cumulative required replenishment time Tz[M] exceeds the allowable continuous replenishment time Ton, magenta toner is replenished intermittently in a pattern conforming to the replenishment duty described above, provided that the cumulative required replenishment time Tz[Y] of the other toner, yellow toner, is less than the toner replenishment threshold Ta.

[0064] Furthermore, when both the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner are equal to or greater than the toner replenishment threshold Ta, the toner associated with the longer of the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner (i.e., the toner in greater need of replenishment) is replenished first. In other words, the replenishment of one toner α is performed over the cumulative required replenishment time Tz[α] (α; an index representing Y or M) of the one toner α, with the continuous replenishment allowable time Ton as an upper limit, as described above. In other words, the replenishment of one toner α is performed over the cumulative required replenishment time Tz[α] or the continuous replenishment allowable time Ton. Then, the other toner β is replenished. The replenishment of this other toner β is also performed over the cumulative required replenishment time Tz[β] (β; an index representing M or Y) of the other toner β, with the continuous replenishment allowable time Ton as an upper limit. Thereafter, depending on the current cumulative required replenishment time Tz[α] of one toner α and the current cumulative required replenishment time Tz[β] of the other toner β, the replenishment of one toner α is resumed, or the replenishment of the other toner β is resumed, or both the replenishment of one toner α and the replenishment of the other toner β are stopped.

[0065] That is, according to the first embodiment, when at least one of the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner exceeds the toner replenishment threshold Ta, one of the toners α corresponding to the cumulative required replenishment time Tz[Y] of yellow toner or the cumulative required replenishment time Tz[M] of magenta toner that has exceeded the toner replenishment threshold Ta is replenished. This replenishment of one of the toners α is performed for the cumulative required replenishment time Tz[α] of the one of the toners α, with the allowable continuous replenishment time Ton as the upper limit. Thereafter, depending on the cumulative required replenishment time Tz[β] of the other toner β and the current cumulative required replenishment time Tz[α] of the one of the toners α, the replenishment of the other toner β is performed, or the replenishment of one of the toners α is resumed, or the replenishment of both toners is stopped. In particular, when the other toner β is replenished, the replenishment of the other toner β is performed for the cumulative required replenishment time Tz[β] of the other toner β, with the allowable continuous replenishment time Ton as the upper limit. When the replenishment of one toner α is resumed, after a predetermined replenishment stop time Toff has elapsed, the replenishment of the one toner α is resumed for the current cumulative required replenishment time Tz[α] of the one toner α, with the allowable continuous replenishment time Ton as the upper limit. When the cumulative required replenishment time Tz[β] of the other toner β is equal to or less than the toner replenishment threshold Ta and the current cumulative required replenishment time Tz[α] of the one toner α is also equal to or less than the toner replenishment threshold Ta, the replenishment of both toners α and β is stopped.

[0066] The toner replenishment threshold Ta is set to an appropriate value, such as 1 second, so that toner replenishment is not performed too frequently, in other words, so that toner replenishment is performed as necessary and frequently as necessary. The continuous replenishment allowable time Ton is preferably set to a value greater than or equal to the required replenishment time Ts[X] when the print rate Rp[X] is 50% and less than or equal to the required replenishment time Ts[X] when the print rate Rp[X] is 90%, and more preferably set to a value greater than or equal to the required replenishment time Ts[X] when the print rate Rp[X] is 75% and less than or equal to the required replenishment time Ts[X] when the print rate Rp[X] is 85%, such as 1 second. This continuous replenishment allowable time Ton of 1 second corresponds to the required replenishment time Ts[X] when the print rate Rp[X] is approximately 77%. The supply stop time Toff is set to a value approximately 1 / 20 to 1 / 5 of the continuous supply allowable time Ton, for example, 0.1 seconds, which corresponds to 1 / 10 of the continuous supply allowable time Ton. The specific values ​​of the toner supply threshold Ta, continuous supply allowable time Ton, and supply stop time Toff are merely examples and are not limited to these values.

[0067] Furthermore, if both the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner are equal to or greater than the toner replenishment threshold value Ta, and if the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner are the same length, the toner concentration detection value T / D[Y] by the toner concentration sensor 50b of the yellow developing device 50 and the toner concentration detection value T / D[M] by the toner concentration sensor 50b of the magenta developing device 50 are compared with each other. Then, the toner corresponding to the smaller value (lower toner concentration T / D) of the toner concentration detection value T / D[Y] of yellow toner and the toner concentration detection value T / D[M] of magenta toner is replenished preferentially. From this point onwards, when both the cumulative required replenishment time Tz[Y] of the yellow toner and the cumulative required replenishment time Tz[M] of the magenta toner are equal to or greater than the toner replenishment threshold value Ta, the toner corresponding to the longer cumulative required replenishment time Tz[Y] of the yellow toner or the cumulative required replenishment time Tz[M] of the magenta toner is replenished first as a priority.

[0068] Furthermore, when both the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner are equal to or greater than the toner replenishment threshold Ta, and the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner are equal to each other, and the toner concentration detection value T / D[Y] of yellow toner and the toner concentration detection value T / D[M] of magenta toner are equal to each other, the toner replenishment of the predetermined side, for example, yellow toner, is prioritized. From this point on, the same as when both the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner are equal to or greater than the toner replenishment threshold Ta, and the toner replenishment of the longer of the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner is prioritized. It should be noted that the supply of magenta toner may be given priority over the supply of yellow toner.

[0069] For example, consider a case where printing is performed continuously with a yellow coverage rate Rp[Y] of 100% and a magenta coverage rate Rp[M] of 100%. In this case, as shown in FIG. 5, printing on one sheet of paper is repeated with a printing time Tp of 1.71 seconds as a cycle. In contrast, yellow toner and magenta toner are replenished alternately with a continuous replenishment allowable time Ton of 1 second as a cycle, which is completely asynchronous with the printing. As mentioned above, the continuous replenishment allowable time Ton of 1 second corresponds to the required replenishment time Ts[X] when the printing rate Rp[X] is approximately 77%. By alternating between yellow toner and magenta toner replenishment with this continuous replenishment allowable time Ton as a cycle, the replenishment of yellow toner and magenta toner is performed in an extremely good (exquisite) balance. This maintains a good balance between the toner concentration T / D[Y] in the developer storage chamber 50a of the yellow developing device 50 and the toner concentration T / D[M] in the developer storage chamber 50a of the magenta developing device 50, thereby maintaining a good density balance in the image (output image) finally formed on the paper. Note that Figure 5 shows an example in which priority is given to replenishment of magenta toner.

[0070] The replenishment procedure for yellow toner and magenta toner shown in Fig. 5 will be described with reference to Fig. 6, taking into account their respective cumulative required replenishment times Tz[X] (Tz[Y] and Tz[M]). Fig. 6 shows an example in which the cumulative required replenishment time Tz[Y] for yellow toner immediately before a job instructing printing is accepted is 0 seconds, and the cumulative required replenishment time Tz[M] for magenta toner is also 0 seconds, and replenishment of magenta toner is given priority.

[0071] As shown in FIG. 6, when the first page is printed, the cumulative required replenishment time Tz[M] for magenta toner is 1.3 seconds, and the cumulative required replenishment time Tz[Y] for yellow toner is also 1.3 seconds. More specifically, the magenta coverage rate Rp[M] and the yellow coverage rate Rp[Y] are derived based on the image data (pixel data) used to print the first page. The required replenishment time Ts[M] for magenta toner is then derived based on the magenta coverage rate Rp[M], and the required replenishment time Ts[Y] for yellow toner is then derived based on the yellow coverage rate Rp[Y]. The cumulative required replenishment time Tz[M] for magenta toner is then updated based on the derived required replenishment time Ts[M] for magenta toner, and the cumulative required replenishment time Tz[Y] for yellow toner is then updated based on the derived required replenishment time Ts[Y] for yellow toner. As a result, the cumulative required replenishment time Tz[M] for magenta toner becomes 1.3 seconds, calculated by adding the required replenishment time Ts[M] for magenta toner of 1.3 seconds corresponding to the magenta print rate Rp[M] of 100% to the value of 0 seconds before the update.The cumulative required replenishment time Tz[Y] for yellow toner becomes 1.3 seconds, calculated by adding the required replenishment time Ts[Y] for yellow toner of 1.3 seconds corresponding to the yellow print rate Rp[Y] of 100% to the value of 0 seconds before the update.

[0072] The updated cumulative required replenishment time Tz[M] (=1.3 s) for magenta toner and the cumulative required replenishment time Tz[Y] (=1.3 s) for yellow toner are both greater than or equal to the toner replenishment threshold Ta (=1 s). Therefore, one of the magenta and yellow toners is replenished first, with the magenta toner being replenished first, as described above. This magenta toner replenishment is carried out over the cumulative required replenishment time Tz[M] for the magenta toner, with the allowable continuous replenishment time Ton (=1 s) as the upper limit, i.e., over the allowable continuous replenishment time Ton of 1 s. As a result, the cumulative required replenishment time Tz[M] for magenta toner becomes 0.3 s (=1.3 s - 1 s). Meanwhile, the cumulative required replenishment time Tz[Y] for yellow toner remains at 1.3 s.

[0073] After the magenta toner is replenished, the other toner, yellow toner, is replenished. This yellow toner replenishment is performed over the cumulative required replenishment time Tz[Y] of the yellow toner, with the continuous replenishment allowable time Ton as the upper limit, i.e., over the continuous replenishment allowable time Ton of 1 s. Meanwhile, while the yellow toner is being replenished, the first page is printed and the second page is printed. That is, the first page is printed from the start of yellow toner replenishment until 0.71 s (= Tp - 1 s) has elapsed, and after 0.71 s has elapsed, the second page is printed. Therefore, the cumulative required replenishment time Tz[Y] of yellow toner at the time the first page is printed is 0.59 s (= 1.30 s - 0.71 s). Note that the cumulative required replenishment time Tz[M] of magenta toner at the time the first page is printed remains at 0.3 s.

[0074] Then, when the second page is printed, the cumulative required replenishment time Tz[M] for magenta toner is updated to 1.6 seconds (= 0.3 seconds + 1.3 seconds), and the cumulative required replenishment time Tz[Y] for yellow toner is updated to 1.89 seconds (= 0.59 seconds + 1.3 seconds). At this time, yellow toner replenishment continues. Then, 0.29 seconds (= 1 second - 0.71 seconds) have passed since the start of printing the second page, and the yellow toner replenishment, which took 1 second, ends. At this point, the cumulative required replenishment time Tz[Y] for yellow toner is 1.6 seconds (= 1.89 seconds - 0.29 seconds), and the cumulative required replenishment time Tz[Y] for magenta toner remains at 1.6 seconds.

[0075] That is, when the 1-second yellow toner replenishment is completed, the cumulative required magenta toner replenishment time Tz[Y] (=1.6 seconds) is equal to or greater than the toner replenishment threshold Ta (=1 second), so the replenishment of the magenta toner is resumed. This magenta toner replenishment is carried out over the cumulative required magenta toner replenishment time Tz[M], with the continuous replenishment allowable time Ton (=1 second) as the upper limit, i.e., over the continuous replenishment allowable time Ton of 1 second. As a result, the cumulative required magenta toner replenishment time Tz[M] becomes 0.6 seconds (=1.6 seconds - 1 second). Meanwhile, the cumulative required yellow toner replenishment time Tz[Y] remains at 1.6 seconds.

[0076] When the magenta toner supply is completed, the cumulative required yellow toner supply time Ts[Y] (=1.6 s) is equal to or exceeds the toner supply threshold Ta (=1 s), so the yellow toner supply is resumed. After this, the magenta toner and yellow toner are supplied alternately in the same manner.

[0077] Comparing the cumulative required replenishment time Tz[M] for magenta toner and the cumulative required replenishment time Tz[Y] for yellow toner during this process, the difference between the two (=|Tz[M]-Tz[Y]|) is a maximum of 1 second. This difference (time) of 1 second corresponds to an extremely small amount of toner, 0.2 g. This means that the replenishment of magenta toner and yellow toner is carried out in an extremely good balance, maintaining a good density balance in the output image.

[0078] In FIG. 6, the time enclosed by the short dashed line adds up to 1 s, which is the continuous replenishment allowable time Ton. In FIG. 6, the time enclosed by the long dashed line adds up to 1.71 s, which is the printing time Tp per sheet of paper. That is, after one of magenta toner and yellow toner is replenished for the continuous replenishment allowable time Ton, the other of magenta toner and yellow toner is replenished for the continuous replenishment allowable time Ton, which means that the replenishment target transitions (switches) as shown by the arrow in FIG. 6. This transition of the replenishment target occurs asynchronously with the printing state.

[0079] While the above description has been given with respect to the first supply device 37a, i.e., the selective supply of yellow toner and magenta toner, the second supply device 37b, i.e., the selective supply of cyan toner and black toner, is performed in a similar manner. In other words, the selective supply of cyan toner and black toner is performed in an extremely well-balanced manner, and a good density balance is maintained on the output image.

[0080] As can be seen from Figure 6, each time printing is performed with a yellow coverage rate Rp[Y] of 100% and a magenta coverage rate Rp[M] of 100%, the cumulative required replenishment time Tz[Y] for yellow toner and the cumulative required replenishment time Tz[M] for magenta toner both increase. If these cumulative required replenishment times Tz[Y] for yellow toner and Tz[M] for magenta toner increase excessively, the replenishment of yellow toner and magenta toner will not be able to keep up, respectively, and the amount of yellow toner and magenta toner used for development will be insufficient. As a result, poor image quality, such as a decrease in density, will occur in the output image.

[0081] To avoid this, when the cumulative required replenishment time Tz[X] of any color of toner exceeds a predetermined third threshold, a forced replenishment threshold Tb, printing is interrupted and forced replenishment is performed for all colors of toner over the cumulative required replenishment time Tz[X]. However, if forced replenishment is performed too frequently, printing will be interrupted accordingly, resulting in reduced productivity. Therefore, it is important to appropriately determine the forced replenishment threshold Tb, which is the criterion for determining whether to perform forced replenishment. In the first embodiment, the forced replenishment threshold Tb is, for example, 5 seconds. The specific value of the forced replenishment threshold Tb is merely an example and is not limited thereto. However, it is assumed that the forced replenishment threshold Tb is greater than the aforementioned toner replenishment threshold Ta and the continuous replenishment allowable time Ton.

[0082] Next, a case where printing is performed consecutively with the yellow printing rate Rp[Y] being 0% and the magenta printing rate Rp[M] being 100% will be described with reference to Fig. 7. Fig. 7 shows an example where the cumulative required replenishment time Tz[M] of magenta toner immediately before a job instructing printing is accepted is 0 seconds, and the cumulative required replenishment time Tz[Y] of yellow toner is less than the toner replenishment threshold Ta.

[0083] As shown in FIG. 7, when the first page is printed, the cumulative required replenishment time Tz[M] of magenta toner is 1.3 seconds. Then, magenta toner is replenished. This magenta toner replenishment is performed over the cumulative required replenishment time Tz[M] of magenta toner, with the maximum continuous replenishment time Ton (=1 second) as the upper limit. In other words, it is performed over the continuous replenishment time Ton of 1 second. As a result, the cumulative required replenishment time Tz[M] of magenta toner becomes 0.3 seconds (=1.3 seconds - 1 second). In contrast, although not shown, the cumulative required replenishment time Tz[Y] of yellow toner remains below the toner replenishment threshold Ta, as described above.

[0084] Then, after the replenishment of magenta toner is stopped for the aforementioned replenishment stop time Toff (=0.1 s), the replenishment of magenta toner is resumed. This replenishment of magenta toner continues until the cumulative required replenishment time Tz[M] of the magenta toner reaches 0, that is, for 0.3 s. Thereafter, the replenishment of magenta toner is stopped until printing of the second page begins, that is, until 0.31 s (=1.71 s-1 s-0.1 s-0.3 s) has elapsed. (This 0.1 s stop time is set when the cumulative required replenishment time Tz[Y] of the free yellow toner is less than the toner replenishment threshold Ta, that is, when there is no need to switch the rotation direction of the first replenishment motor 110a from the other direction R2 to the one direction R1. This simplifies the determination process of the control program for the first replenishment motor 110a.)

[0085] Then, when the second sheet is printed, the cumulative required replenishment time Tz [M] of magenta toner becomes 1.3 seconds again. After this, magenta toner is replenished in the same manner.

[0086] 7, when printing is performed continuously with a yellow coverage rate Rp[Y] of 0% and a magenta coverage rate Rp[M] of 100%, the cumulative required replenishment time Tz[M] of magenta toner does not exceed 1.3 seconds, i.e., it does not increase excessively. Therefore, the aforementioned forced replenishment is not performed, and productivity is maintained.

[0087] 7, the time enclosed by the short dashed line is the time required for one replenishment of magenta toner, i.e., the allowable continuous replenishment time Ton (=1 s). In addition, the total time enclosed by the long dashed line in FIG. 7 is 1.71 s, which is the printing time Tp per sheet of paper.

[0088] FIG. 8 is a block diagram showing the electrical configuration of the image forming apparatus 10. As shown in FIG. 8, the image forming apparatus 10 includes a control unit 200. The image reading unit 12, the automatic document feeder 18, the image forming unit 26, and the paper feed unit 64 are connected to the control unit 200 via a bus 202. The control unit 200 is also connected to an operation unit 204, an auxiliary storage unit 206, a communication unit 208, and the like via the bus 202. The image forming apparatus 10 includes various other elements, but illustrations and descriptions of elements not directly related to the gist of the present disclosure will be omitted here. The image reading unit 12, the automatic document feeder 18, the image forming unit 26, and the paper feed unit 64 are as described above. In particular, the image forming unit 26 includes a first supply motor 110a and a second supply motor 110b.

[0089] The control unit 200 is a control means that controls the entire image forming apparatus 10. To this end, the control unit 200 has a computer, such as a CPU 200a, as a control execution means. The control unit 200 also has a main memory unit 200b as a main memory means that can be directly accessed by the CPU 200a. The main memory unit 200b includes, for example, a ROM and a RAM (not shown). The ROM stores a control program (firmware) for controlling the operation of the CPU 200a. The control program includes a toner replenishment control program (described later). The RAM provides a working area and a buffer area when the CPU 200a executes processes in accordance with the control program.

[0090] The operation unit 204 has a display with a touch panel (not shown). The display with a touch panel is a component that integrally combines a touch panel as an example of an operation reception means that can receive operations by a user (not shown) and a display as an example of a display means that displays various information. In addition to the display with a touch panel, the operation unit 204 also has appropriate light-emitting means such as an LED (not shown) and appropriate hardware switches such as a push button (not shown).

[0091] The auxiliary storage unit 206 is an example of an auxiliary storage means. That is, the auxiliary storage unit 206 appropriately stores various data such as the above-mentioned scanned image data and jobs. The auxiliary storage unit 206 includes, for example, a hard disk drive (not shown). In addition, the auxiliary storage unit 206 may include a rewritable nonvolatile memory such as a flash memory.

[0092] The communication unit 208 is an example of a communication means. That is, the communication unit 208 is responsible for two-way communication processing via a LAN line (not shown). The communication unit 208 may be connected to the LAN line by wire or wirelessly. The communication unit 208 is also responsible for two-way communication processing via a public switched telephone network (not shown).

[0093] As described above, according to the first embodiment, particularly the first replenishment device 37a, when at least one of the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner exceeds the toner replenishment threshold Ta, the first replenishment device 37a replenishes one of the toners α corresponding to the cumulative required replenishment time Tz[Y] of yellow toner or the cumulative required replenishment time Tz[M] of magenta toner that has exceeded the toner replenishment threshold Ta. This replenishment of one of the toners α is performed for the cumulative required replenishment time Tz[α] of the one of the toners α, up to the allowable continuous replenishment time Ton. Subsequently, depending on the cumulative required replenishment time Tz[β] of the other toner β and the current cumulative required replenishment time Tz[α] of the one of the toners α, the other toner β is replenished, or the replenishment of one of the toners α is resumed, or the replenishment of both toners α and β is stopped. The second replenishment device 37b also replenishes toner in a similar manner.

[0094] To achieve this toner replenishment, the CPU 200a executes a toner replenishment control task in accordance with the toner replenishment control program described above. The flow of this toner replenishment control task is shown in Figure 9. The toner replenishment control task is executed in response to the acceptance of a job that instructs the execution of printing. The job referred to here includes jobs in the printer function, copy function, and fax function (fax reception function).

[0095] According to this toner supply control task, the CPU 200a first performs an initial check in step S1. In this initial check, the CPU 200a references the history information of the previous job and checks the cumulative required replenishment time Tz[X] of each toner at the current time (at the start of the toner supply control task). The job history information is stored, for example, in the auxiliary storage unit 206. Then, the CPU 200a proceeds to step S3.

[0096] In step S3, the CPU 200a sets the variable n, which indicates the number of sheets to be printed, to its initial value of 1. Then, in the following step S5, the CPU 200a expands (analyzes) the image data to be used for printing the nth sheet. Furthermore, in the following step S7, the CPU 200a derives the printing rate Rx[X] for each toner based on the image data expanded in step S5. Then, in the following step S9, the CPU 200a starts printing the nth sheet, and then proceeds to step S11. Note that the printing started in step S9 is performed by a printing task separate from the toner replenishment control task. A detailed description of this printing task, including illustrations, will be omitted.

[0097] In step S11, the CPU 60a derives the required replenishment time Ts[X] (=Qc[X] / Vs[X]) for each toner. In deriving this required replenishment time Ts[X], the consumption amount Qc[X] of each toner is used, and this consumption amount Qc[X] is calculated based on, for example, a relational expression between the print rate Rp[X] and the consumption amount Qc[X] for each toner. Alternatively, the consumption amount Qc[X] may be calculated based on a lookup table that summarizes the relationship between the print rate Rp[X] and the consumption amount Qc[X] for each toner. After executing step S11, the CPU 200a proceeds to step S13.

[0098] In step S13, the CPU 200a adds the necessary replenishment time Ts[X] of each toner calculated in step S11 to the current cumulative necessary replenishment time Tz[X] of that toner, sets the resulting value as the new cumulative necessary replenishment time Tz[X], i.e., updates the cumulative necessary replenishment time Tz[X]. Then, the CPU 200a proceeds to step S15.

[0099] In step S15, the CPU 200a compares the cumulative required replenishment time Tz[X] of each toner with the forced replenishment threshold Tb to determine whether the cumulative required replenishment time Tz[X] of each toner is less than the forced replenishment threshold Tb. If the cumulative required replenishment time Tz[X] of any toner is equal to or greater than the forced replenishment threshold Tb (S15: NO), the CPU 200a proceeds to step S17. On the other hand, if the cumulative required replenishment time Tz[X] of all toners is less than the forced replenishment threshold Tb (S15: YES), the CPU 200a proceeds to step S19, which will be described later.

[0100] In step S17, the CPU 200a starts the above-mentioned forced replenishment and ends the toner replenishment control task. Note that the forced replenishment is performed by a forced replenishment task separate from the toner replenishment control task. A detailed description of this forced replenishment task, including illustrations, will be omitted. Also, when the forced replenishment starts, printing is interrupted. Then, when the forced replenishment ends, printing is resumed.

[0101] On the other hand, if the process proceeds from step S15 to step S19, the CPU 200a compares the cumulative required replenishment time Tz[X] of each toner with the toner replenishment threshold Ta in step S19 to determine whether the cumulative required replenishment time Tz[X] of each toner is less than the toner replenishment threshold Ta. If the cumulative required replenishment time Tz[X] of any toner is equal to or greater than the toner replenishment threshold Ta (S19: NO), the CPU 200a proceeds to step S21. On the other hand, if the cumulative required replenishment time Tz[X] of all toners is less than the toner replenishment threshold Ta (S19: YES), the CPU 200a proceeds to step S23, which will be described later.

[0102] In step S21, the CPU 200a executes a toner supply process to supply toner. This toner supply process will be described in detail later. After completing this toner supply process, the CPU 200a advances the process to step S23.

[0103] In step S23, the CPU 200a determines whether all printing according to the job has been completed. If all printing according to the job has been completed (S23: YES), the CPU 200a ends the toner supply control task. On the other hand, if all printing according to the job has not been completed, the CPU 200a proceeds to step S25. Then, in step S25, the CPU 200a increments the value of the variable n, which represents the number of printed sheets, and returns the process to step S5.

[0104] Next, the toner supply process will be described with reference to Figures 10 to 12. Note that Figures 10 to 12 show the flow of the toner supply process for the first supply device 37a, but the toner supply process for the second supply device 37b is also performed in a similar manner.

[0105] According to this toner replenishment process, first, in step S101, the CPU 200a resets and starts a timer (not shown) for measuring the printing time Tp per sheet of paper (strictly speaking, the printing time Tp including (or subtracting) the processing time of the toner replenishment control task, including the toner replenishment process). This timer is, for example, a software timer configured by the CPU 200a, but it may also be a hardware timer configured by hardware elements such as an RTC (Real-Time Clock). After executing step S101, the CPU 200a proceeds to step S103.

[0106] In step S103, the CPU 200a compares the cumulative required replenishment time Tz[Y] of the yellow toner with the cumulative required replenishment time Tz[M] of the magenta toner to determine whether they are equivalent to each other. If they are equivalent to each other (S103: YES), the CPU 200a proceeds to step S105. On the other hand, if they are not equivalent to each other (S103: NO), the CPU 200a proceeds to step S113, which will be described later.

[0107] In step S105, the CPU 200a compares the toner concentration detection value T / D[Y] of the yellow toner with the toner concentration detection value T / D[M] of the magenta toner to determine whether they are equivalent to each other. If they are equivalent to each other (S105: YES), the CPU 200a proceeds to step S107. On the other hand, if they are not equivalent to each other (S105: NO), the CPU 200a proceeds to step S109, which will be described later.

[0108] In step S107, the CPU 200a designates the yellow toner as the replenishment target α, i.e., identifies the yellow toner as the aforementioned one of the toners α. At the same time, the CPU 200a designates the magenta toner as the replenishment target β, i.e., identifies the magenta toner as the aforementioned other toner β. The CPU 200a then proceeds to step S115, which will be described later.

[0109] In contrast, when the CPU 200a proceeds from step S105 to step S109, it determines in step S109 whether the detected toner concentration value T / D[Y] of yellow toner is less than the detected toner concentration value T / D[M] of magenta toner. If the detected toner concentration value T / D[Y] of yellow toner is less than the detected toner concentration value T / D[M] of magenta toner (S109: YES), the CPU 200a proceeds to step S107. On the other hand, if the detected toner concentration value T / D[Y] of yellow toner is greater than the detected toner concentration value T / D[M] of magenta toner (S109: NO), the CPU 200a proceeds to step S111, which will be described later.

[0110] In step S111, the CPU 200a designates yellow toner as the supply target β, i.e., identifies the yellow toner as the other toner β. At the same time, the CPU 200a designates magenta toner as the supply target α, i.e., identifies the magenta toner as the one toner α. The CPU 200a then proceeds to step S115, which will be described later.

[0111] Furthermore, when the CPU 200a proceeds from step S103 to step S113, it determines in step S113 whether the cumulative required replenishment time Tz[Y] of yellow toner is longer than the cumulative required replenishment time Tz[M] of magenta toner. If the cumulative required replenishment time Tz[Y] of yellow toner is longer than the cumulative required replenishment time Tz[M] of magenta toner (S113: YES), the CPU 200a proceeds to step S107. On the other hand, if the cumulative required replenishment time Tz[Y] of yellow toner is shorter than the cumulative required replenishment time Tz[M] of magenta toner (S113: NO), the CPU 200a proceeds to step S111.

[0112] In step S115, the CPU 200a resets a counter for counting the replenishment time Td of the toner to be replenished, that is, sets the count value to an initial value of 0. Then, the CPU 200a advances the process to step S117.

[0113] In step S117, the CPU 200a compares the count value of the counter for counting the replenishment time Td with the allowable continuous replenishment time Ton to determine whether the replenishment time Td is shorter than the allowable continuous replenishment time Ton. If the replenishment time Td is shorter than the allowable continuous replenishment time Ton (S117: YES), the CPU 200a proceeds to step S119. On the other hand, if the replenishment time Td is equal to or longer than the allowable continuous replenishment time Ton (S117: NO), the CPU 200a proceeds to step S129, which will be described later.

[0114] In step S119, the CPU 200a drives the first supply motor 110a so that the supply of one toner, a, is performed over a predetermined supply unit time ΔT. The supply unit time ΔT here is a time that is sufficiently shorter than the continuous supply allowable time Ton (=1 s), for example, 0.1 s. After executing step S119, the CPU 200a proceeds to step S121.

[0115] In step S121, the CPU 200a subtracts the replenishment unit time ΔT from the current cumulative required replenishment time Tz[α] of one toner α, sets the subtracted value as the new cumulative required replenishment time Tz[α], that is, updates the cumulative required replenishment time Tz[α]. Then, the CPU 200a proceeds to step S123.

[0116] In step S123, the CPU 200a subtracts the replenishment unit time ΔT from the count value of the counter for counting the replenishment time Td described above, and sets the value after the subtraction as a new count value, that is, updates the count value of the replenishment time Td. Then, the CPU 200a proceeds to step S125.

[0117] In step S125, the CPU 200a determines whether the time measured by the timer described above has not yet elapsed the printing time Tp per sheet of paper, i.e., whether the printing time Tp has not yet elapsed. If the printing time Tp has not yet elapsed (S125: YES), the CPU 200a proceeds to step S127. On the other hand, if the printing time Tp has elapsed (S125: NO), the CPU 200a ends the toner supply process.

[0118] In step S127, the CPU 200a determines whether the current cumulative required replenishment time Tz[α] of one toner α is equal to or less than 0. If the current cumulative required replenishment time Tz[α] of one toner α is not equal to or less than 0 (S127: NO), the CPU 200a returns the process to step S117. On the other hand, if the current cumulative required replenishment time Tz[α] of one toner α is equal to or less than 0 (S127: YES), the CPU 200a proceeds to step S129.

[0119] In step S129, the CPU 200a compares the cumulative required replenishment time Tz[β] of the other toner β with the toner replenishment threshold Ta to determine whether the cumulative required replenishment time Tz[β] is equal to or greater than the toner replenishment threshold Ta. If the cumulative required replenishment time Tz[β] is less than the toner replenishment threshold Ta (S129: NO), the CPU 200a proceeds to step S131. In step S131, the CPU 200a waits for the replenishment stop time Toff, and then returns the process to step S115. On the other hand, if the cumulative required replenishment time Tz[β] is equal to or greater than the toner replenishment threshold Ta (S129: YES), the CPU 200a proceeds to step S133.

[0120] In step S133, the CPU 200a resets the counter described above for counting the replenishment time Td of the toner to be replenished, and then proceeds to step S135. Then, in step S135, the CPU 200a compares the count value of the replenishment time Td measured by the counter with the allowable continuous replenishment time Ton to determine whether the replenishment time Td is less than the allowable continuous replenishment time Ton. If the replenishment time Td is equal to or greater than the allowable continuous replenishment time Ton (S135: NO), the CPU 200a returns the process to step S115. On the other hand, if the replenishment time Td is less than the allowable continuous replenishment time Ton (S135: YES), the CPU 200a proceeds to step S137.

[0121] In step S137, the CPU 200a drives the first supply motor 110a so that the other toner β is supplied for the above-mentioned supply unit time ΔT. Thereafter, the CPU 200a advances the process to step S139.

[0122] In step S139, the CPU 200a subtracts the replenishment unit time ΔT from the current cumulative required replenishment time Tz[β] of the other toner β, sets the subtracted value as the new cumulative required replenishment time Tz[β], that is, updates the cumulative required replenishment time Tz[β]. Then, the CPU 200a proceeds to step S141.

[0123] In step S141, the CPU 200a subtracts the replenishment unit time ΔT from the count value of the replenishment time Td measured by the counter described above, and sets the value after the subtraction as a new count value, i.e., updates the count value of the replenishment time Td. Then, the CPU 200a proceeds to step S143.

[0124] In step S143, the CPU 200a determines whether the time measured by the timer described above has not yet elapsed the printing time Tp per sheet of paper, i.e., whether the printing time Tp has not yet elapsed. If the printing time Tp has not yet elapsed (S143: YES), the CPU 200a proceeds to step S145. On the other hand, if the printing time Tp has elapsed (S143: NO), the CPU 200a ends the toner supply process.

[0125] In step S145, the CPU 200a determines whether the current cumulative required replenishment time Tz[β] of the other toner β is equal to or less than 0. If the current cumulative required replenishment time Tz[β] of the other toner β is not equal to or less than 0 (S145: NO), the CPU 200a returns the process to step S135. On the other hand, if the current cumulative required replenishment time Tz[β] of the other toner β is equal to or less than 0 (S147: YES), the CPU 200a returns the process to step S115.

[0126] Thus, according to this first embodiment, particularly the first replenishment device 37a, when at least one of the cumulative required replenishment time Tz[Y] of yellow toner and the cumulative required replenishment time Tz[M] of magenta toner exceeds the toner replenishment threshold Ta, one of the toners α corresponding to the cumulative required replenishment time Tz[Y] of yellow toner or the cumulative required replenishment time Tz[M] of magenta toner that has exceeded the toner replenishment threshold Ta is replenished. This replenishment of one of the toners α is performed for the cumulative required replenishment time Tz[α] of the one of the toners α, up to the allowable continuous replenishment time Ton. Thereafter, depending on the cumulative required replenishment time Tz[β] of the other toner β and the current cumulative required replenishment time Tz[α] of the one of the toners α, the other toner β is replenished, or the replenishment of one of the toners α is resumed, or the replenishment of both toners α and β is stopped. The second replenishment device 37b also replenishes toner in a similar manner.

[0127] That is, according to the first embodiment, unlike the technology disclosed in the aforementioned Patent Document 1, which requires complex processing such as calculating the ratio between the amount of the first developer to be supplied to the first developing device and the amount of the second developer to be supplied to the second developing device, and allocating the first drive time and the second drive time according to that ratio, the first embodiment does not require such complex processing, in other words, it is possible to replenish two types of toner, α and β, in a well-balanced manner using a single drive source in an extremely simple and easy manner. This is extremely beneficial for a configuration such as the first embodiment, which aims to reduce the overall cost of the image forming apparatus 10 by replenishing two types of toner, α and β, using a single drive source.

[0128] In the first embodiment, the CPU 200a that executes step S11 of the toner supply control task, i.e., the CPU 200a that derives the required replenishment time Ts[X] for each toner, is an example of the derivation means of the present disclosure. The CPU 200a that executes step S13 of the toner supply control task, i.e., the CPU 200a that updates the cumulative required replenishment time Tz[X] for each toner, is an example of the accumulation means of the present disclosure. Furthermore, the first and second supply motors 110a and 110b, which are drive sources, are driven under the control of the CPU 200a, and the CPU 200a that controls the first and second supply motors 110a and 110b is an example of the drive control means of the present disclosure.

[0129] [Second Example] Next, a second embodiment of the present disclosure will be described.

[0130] In the first embodiment, a common forced replenishment threshold Tb was used for each toner, and the forced replenishment threshold Tb was constant, but in the second embodiment, an individual forced replenishment threshold Tb[X] is used for each toner. In addition, in the second embodiment, the forced replenishment threshold Tb[X] for each toner is set (changed) based on the average printing rate Ra[X], which is the average value of the printing rates Rp[X] for each toner on the most recent N sheets.

[0131] That is, as mentioned above, frequent forced replenishment results in corresponding interruptions to printing, resulting in reduced productivity. On the other hand, if forced replenishment is performed too late, there is a risk of image quality defects, such as reduced density, occurring in the output image. Furthermore, if the amount of toner replenished through forced replenishment is excessively large, the replenished toner may not be sufficiently charged, i.e., may be insufficiently charged, resulting in uneven charging and the formation of a toner image in areas on the paper where a toner image would not normally be formed, resulting in another image quality defect known as fogging. Furthermore, if the amount of toner replenished through forced replenishment is excessively large, there is a risk that the replenished toner may scatter outside the developing device 50 (its housing). Therefore, it is essential that forced replenishment be performed at the appropriate time.

[0132] Therefore, in the second embodiment, as described above, an individual forced replenishment threshold Tb[X] is used for each toner, and the forced replenishment threshold Tb[X] for each toner is set based on the average printing rate Ra[X], which is the average value of the printing rates Rp[X] for each toner on the most recent N sheets. For this purpose, a forced replenishment threshold table 300 as shown in Fig. 13 is provided. The forced replenishment threshold table 300 is incorporated into the toner replenishment control program.

[0133] According to this forced replenishment threshold table 300, for each toner, if the average print rate Ra[X] for the most recent N sheets is 5% or less, a value of 5.0 seconds is set as the forced replenishment threshold Tb[X]. If the average print rate Ra[X] is greater than 5% but less than 10%, a value of 4.5 seconds is set as the forced replenishment threshold Tb[X]. If the average print rate Ra[X] is greater than 10% but less than 25%, a value of 4.0 seconds is set as the forced replenishment threshold Tb[X]. If the average print rate Ra[X] is greater than 25% but less than 40%, a value of 3.5 seconds is set as the forced replenishment threshold Tb[X]. If the average print rate Ra[X] is greater than 40% but less than 60%, a value of 3.0 seconds is set as the forced replenishment threshold Tb[X]. If the average printing rate Ra[X] is greater than 60% and less than 80%, the forced replenishment threshold Tb[X] is set to a value of 2.0 s, and if the average printing rate Ra[X] is greater than 80%, the forced replenishment threshold Tb[X] is set to a value of 2.0 s.

[0134] That is, the lower the average print rate Ra[X] of the most recent N sheets, the longer the time set as the forced replenishment threshold Tb[X], and the higher the average print rate Ra[X] of the most recent N sheets, the shorter the time set as the forced replenishment threshold Tb[X]. In other words, an appropriate forced replenishment threshold Tb[X] is set for each toner according to the average print rate Ra[X] of the most recent N sheets. As a result, forced replenishment is performed for each toner at an appropriate timing according to the average print rate Ra[X] of the most recent N sheets.

[0135] The value of N is, for example, 5. If the value of N is too large, the timing of forced replenishment may be delayed, which may result in the aforementioned poor image quality. Also, if the value of N is too small, forced replenishment may be performed too frequently, which may result in a decrease in productivity. In consideration of these factors, the value of N is derived as 5. However, the value of N is not limited to 5, and may be arbitrarily changed.

[0136] In the second embodiment, the toner replenishment control task described above is also executed. Specifically, in the initial check in step S1, the cumulative required replenishment time Tz[X] for each toner at the current time point is confirmed, and the average print rate Ra[X] for the most recent N sheets is also confirmed. Then, at an appropriate stage after step S7 but before step S15, the average print rate Ra[X] for the most recent N sheets is recalculated, i.e., updated, and the forced replenishment threshold value table 300 is referenced to identify the forced replenishment threshold value Tb[X] corresponding to the updated average print rate Ra[X]. The identified forced replenishment threshold value Tb[X] is then used as a comparison target for the cumulative required replenishment time Tz[X] in step S15.

[0137] Thus, according to the second embodiment, for each toner, forced replenishment is performed at an appropriate timing according to the average printing rate Ra[X] of the most recent N sheets. This reduces the frequency of forced replenishment, maintains high productivity, prevents image quality defects such as a decrease in density of the output image and fogging, and further prevents the replenished toner from scattering outside the developing device 50 (its housing).

[0138] [Third Example] Next, a third embodiment of the present disclosure will be described.

[0139] This third embodiment is based on the first embodiment. In this third embodiment, for each toner, a threshold coefficient γ[X] corresponding to the toner concentration detected by the toner concentration sensor 50b is multiplied by the forced replenishment threshold Tb, and the resulting multiplied value γ[X]·Tb is used as a comparison target for the cumulative required replenishment time Tz[X]. For this purpose, a threshold coefficient table 400 such as that shown in FIG. 14 is provided. The threshold coefficient table 400 is incorporated into the toner replenishment control program.

[0140] According to this threshold coefficient table 400, for each toner, if the toner concentration detection value T / D[X] is 5.0 wt% or less, a value of 0.75 is used as the threshold coefficient γ[X] to multiply the forced replenishment threshold Tb. In this case, the multiplication value γ[X]·Tb, which is used to compare the cumulative required replenishment time Tz[X], is smaller than the forced replenishment threshold b, making it easier to perform forced toner replenishment. If the toner concentration detection value T / D[X] is greater than 5.0 wt% and less than or equal to 5.5 wt%, a value of 1.00 is used as the threshold coefficient γ[X] to multiply the forced replenishment threshold Tb. In this case, the multiplication value γ[X]·Tb, which is used to compare the cumulative required replenishment time Tz[X], is equivalent to the forced replenishment threshold Tb. Furthermore, if the detected toner concentration value T / D[X] is greater than 5.5 wt% and less than 6.5 wt%, a value of 1.25 is used as the threshold coefficient γ[X] to multiply the forced replenishment threshold Tb. In this case, the multiplied value γ[X]·Ta, which is used to compare the cumulative required replenishment time Tz[X], is greater than the forced replenishment threshold Tb, making it more difficult to perform forced toner replenishment. The appropriate value for toner concentration T / D is, for example, 6.0 wt%.

[0141] Furthermore, if the detected toner concentration value T / D[X] is greater than 6.5 wt% and less than or equal to 7.0 wt%, the forced replenishment threshold value Tb is multiplied by the threshold coefficient γ[X] of 1.00. In this case, the multiplied value γ[X]·Tb, which is used to compare the cumulative required replenishment time Tz[X], is equivalent to the forced replenishment threshold value Tb. If the detected toner concentration value T / D[X] is greater than 7.0 wt%, the threshold coefficient [X] is multiplied by the forced replenishment threshold value Tb of 0.75. In this case, the multiplied value γ[X]·Tb, which is used to compare the cumulative required replenishment time Tz[X], is smaller than the forced replenishment threshold value Tb, making it easier for toner to be forced to be replenished.

[0142] That is, when the toner concentration detection value T / D[X] is 5.0 wt% or less, that is, when the toner concentration T / D is excessively lower than its appropriate value, the forced replenishment threshold Tb is corrected so that forced toner replenishment is facilitated. When the toner concentration T / D is excessively low, there is a risk of a decrease in the density of the output image and uneven stirring of the developer. To avoid these problems, the forced replenishment threshold Tb is corrected so that forced toner replenishment is facilitated.

[0143] Furthermore, even when the toner concentration detection value T / D[X] exceeds 7.0 wt%, that is, when the toner concentration T / D is excessively higher than its appropriate value, the forced replenishment threshold Tb is corrected to facilitate forced toner replenishment. If the toner concentration T / D is excessively high, there is a risk that the toner in the developing device 50 (developer storage chamber 50a) will scatter outside the developing device 50 or that the fogging phenomenon described above will occur. To avoid these problems, the forced replenishment threshold Tb is corrected to facilitate forced toner replenishment.

[0144] When the toner concentration detection value T / D[X] is greater than 5.5 wt% and less than 6.5 wt%, that is, when the toner concentration T / D is approximately an appropriate value, the forced replenishment threshold Tb is corrected to make forced toner replenishment less likely. When the toner concentration T / D is approximately an appropriate value, there is almost no risk of problems occurring, such as when the toner concentration T / D is excessively high or excessively low. Therefore, in order to further improve productivity, the forced replenishment threshold Tb is corrected to make forced toner replenishment less likely.

[0145] In the third embodiment, the toner replenishment control task described above is also executed. Specifically, in the initial check in step S1, the current cumulative required replenishment time Tz[X] for each toner is confirmed, and the detected toner concentration value T / D[X] for each toner is also confirmed. Then, in step S1, or at an appropriate stage after step S1 but before step S15, the threshold coefficient table 400 is referenced to identify the threshold coefficient γ[X] corresponding to the detected toner concentration value T / D[X] for each toner. The identified threshold coefficient γ[X] is then multiplied by the forced replenishment threshold value Tb, and the resulting product γ[X]·Tb is used as the comparison target for the cumulative required replenishment time Tz[X] in step S15.

[0146] Thus, according to the third embodiment, for each toner, the product γ[X]·Tb of the threshold coefficient γ[X] corresponding to the toner concentration detection value T / D[X] and the forced replenishment threshold Tb is compared with the cumulative required replenishment time Tz[X]. This prevents problems caused by excessively high or low toner concentration T / D for each toner, while further improving productivity.

[0147] Although the third embodiment is based on the first embodiment, it may also be based on the second embodiment. In this case, for each toner, the product γ[X]·Tb[X] of the threshold coefficient γ[X] and the forced replenishment threshold Tb[X] is compared with the cumulative required replenishment time Tz[X].

[0148] [Other application examples] The above-described examples are specific examples of the present disclosure and do not limit the technical scope of the present disclosure. The present disclosure can also be applied to aspects other than these examples.

[0149] For example, the developer is not limited to a two-component developer, but may be a one-component developer that does not contain a carrier. However, the third embodiment is premised on a two-component developer.

[0150] Furthermore, in each embodiment, the paper size is A4 size, but the paper size is not limited to A4 size.

[0151] Furthermore, in each embodiment, an image forming apparatus 10 employing a tandem-type color image forming unit 26 has been given as an example, but the present disclosure can also be applied to an image forming apparatus employing a rotary-type color image forming unit.

[0152] Additionally, although the image forming apparatus 10 in each embodiment is a multifunction machine, the present disclosure can also be applied to image forming apparatuses other than the multifunction machine, such as a dedicated printer, a dedicated copier, or a dedicated fax machine.

[0153] The present disclosure is not limited to the form of an image forming apparatus, but can also be provided in the form of a method for controlling toner replenishment in an image forming apparatus. [Explanation of symbols]

[0154] 10... Image forming device 26... Image forming unit 37 ... Toner supply device 37a … 1st supply device 37b…Second supply device 50... Developing device 50a ... Developer chamber 50b ... Toner density sensor 100... Toner cartridges 106 ... Supply parts 110a ... First supply motor 110b ... Second supply motor 200 ... Control section 200a...CPU 200b… Main memory Qc[X] … Consumption amount Rp[X] … Printing rate Ta: Toner replenishment threshold Tb: Threshold for forced replenishment Toff…Supply stop time Ton: Allowable continuous supply time Ts[X] … Required supply time Tz[X] … Cumulative required replenishment time

Claims

1. An image forming apparatus that performs image formation processing by an electrophotographic method, a first storage section in which a first toner is stored; a first supply member that supplies the first toner contained in the first container to the first developing means; a second storage section in which a second toner is stored; a second supply member that supplies the second toner contained in the second container to the second developing means; a drive source that selectively drives the first supply member and the second supply member; a drive control means for controlling the drive source; a derivation means for deriving a first required replenishment time, which is a replenishment time of the first toner required to compensate for the consumption of the first toner consumed by the first developing means, and a second required replenishment time, which is a replenishment time of the second toner required to compensate for the consumption of the second toner consumed by the second developing means, based on image data provided for the image forming process; and an accumulating means for accumulating a shortage of the actual replenishment time of the first toner by the first replenishment member relative to the first required replenishment time each time the image forming process is performed, to obtain a first accumulated time which is an accumulated value of the shortage, and for accumulating a shortage of the actual replenishment time of the second toner by the second replenishment member relative to the second required replenishment time each time the image forming process is performed, to obtain a second accumulated time which is an accumulated value of the shortage, an image forming apparatus, wherein the drive control means, when at least one of the first cumulative time and the second cumulative time is equal to or greater than a predetermined first threshold, identifies the first cumulative time or the second cumulative time that is equal to or greater than the first threshold as one cumulative time, identifies the first supply member or the second supply member related to the one cumulative time as one supply member, drives the one supply member for the one cumulative time with a predetermined second threshold as an upper limit, and then stops driving the one supply member, and further controls the drive source to drive the other supply member, of the first supply member and the second supply member that is not the one supply member, for the other cumulative time with the second threshold as an upper limit, or drive the one supply member for the one cumulative time with the second threshold as an upper limit, or stop driving either the one supply member or the other supply member without driving them, depending on the other cumulative time that is not the one cumulative time among the first cumulative time and the second cumulative time and the one cumulative time.

2. 2. The image forming apparatus according to claim 1, wherein when both the first cumulative time and the second cumulative time are equal to or greater than the first threshold value, the drive control unit specifies the longer of the first cumulative time and the second cumulative time as the one cumulative time.

3. a first toner concentration detecting means for detecting the concentration of the first toner contained in the developer in the first developing means; and a second toner concentration detecting means for detecting the concentration of the second toner contained in the developer in the second developing means; 3. The image forming apparatus according to claim 2, wherein when both the first cumulative time and the second cumulative time are equal to or greater than the first threshold value and the first cumulative time and the second cumulative time are the same length, the drive control means specifies the first cumulative time or the second cumulative time corresponding to the lower of the concentration detection value by the first toner concentration detection means and the concentration detection value by the second toner concentration detection means as the one cumulative time.

4. 2. The image forming apparatus according to claim 1, wherein the second threshold value is a value that is greater than or equal to the first required replenishment time when the printing rate for the first toner based on the image data is 50% and less than or equal to the first required replenishment time when the printing rate is 90%.

5. 2. The image forming apparatus according to claim 1, wherein the drive control means controls the drive source to interrupt the image forming process and drive the first supply member for the first cumulative time and the second supply member for the second cumulative time when at least one of the first cumulative time and the second cumulative time is equal to or greater than a predetermined third threshold.

6. 1. A toner replenishment control method for an image forming apparatus that performs image formation processing by an electrophotographic method, comprising: the image forming apparatus, a first storage section in which a first toner is stored; a first supply member that supplies the first toner contained in the first container to the first developing means; a second storage section in which a second toner is stored; a second supply member that supplies the second toner contained in the second container to the second developing means; and a drive source that selectively drives the first supply member and the second supply member, a drive control step of controlling the drive source; a derivation step of deriving a first required replenishment time, which is a replenishment time of the first toner required to compensate for the consumption of the first toner consumed by the first developing means, and a second required replenishment time, which is a replenishment time of the second toner required to compensate for the consumption of the second toner consumed by the second developing means, based on image data provided for the image forming process; and an accumulating step of accumulating a shortage of the actual replenishment time of the first toner by the first replenishment member relative to the first required replenishment time each time the image forming process is performed to obtain a first accumulated time which is an accumulated value of the shortage, and accumulating a shortage of the actual replenishment time of the second toner by the second replenishment member relative to the second required replenishment time each time the image forming process is performed to obtain a second accumulated time which is an accumulated value of the shortage, In the drive control step, when at least one of the first cumulative time and the second cumulative time is equal to or greater than a predetermined first threshold, the first cumulative time or the second cumulative time that is equal to or greater than the first threshold is identified as one cumulative time, and the first supply member or the second supply member related to the one cumulative time is identified as one supply member, and the one supply member is driven for the one cumulative time with a predetermined second threshold as an upper limit, and then the drive of the one supply member is stopped, and further, depending on the other cumulative time that is not the one cumulative time among the first cumulative time and the second cumulative time and the one cumulative time, the other supply member that is not the one supply member, of the first supply member and the second supply member, is driven for the other cumulative time with the second threshold as an upper limit, or the one supply member is driven for the one cumulative time with the second threshold as an upper limit, or neither the one supply member nor the other supply member is driven but stopped, controlling the drive source.

Images