Image forming device

Abstract

To provide an image forming apparatus that can accurately reduce toner fogging when the image forming apparatus is left standing for a long time.SOLUTION: An image forming apparatus comprises: developing devices that each carry developer on a surface of a developer carrier (developing roller) and develop an electrostatic latent image on a surface of an image carrier (photoreceptor drum); and a control unit 5 that controls the developing devices. The control unit 5 has: peripheral environment acquisition means that acquires a peripheral environment of the developing device; left-standing time checking means that checks the time during which the image forming apparatus is left standing; printing rate calculation means that calculates a printing rate; returning means that executes a returning operation of the developing device; returning condition determination means that determines a returning condition; and storage means that stores a tentative parameter related to the returning condition in association with the peripheral environment and the time during which the image forming apparatus is left standing. The returning condition determination means acquires the tentative parameter based on the peripheral environment and the time during which the image forming apparatus is left standing, and determines the returning condition by correcting the tentative parameter based on the printing rate.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a multifunction machine, a printer, or a facsimile machine. [Background technology]

[0002] A developing device is widely used that develops an electrostatic latent image formed on an image carrier by carrying a two-component developer containing toner and carrier on the surface of the developer carrier. The toner, which is charged by friction with the carrier, adheres to the electrostatic latent image on the image carrier, forming a toner image on the image carrier.

[0003] If the charge amount of the toner in the developing device is too high, the toner will not easily separate from the carrier, resulting in a decrease in image density. On the other hand, if the charge amount of the toner in the developing device is too low, non-image areas on the image carrier will become dirty, resulting in a phenomenon known as toner fogging. For this reason, it is necessary to accurately maintain the charge amount of the toner in the developing device during image formation. In particular, if the image forming device has been left in a stopped state for a long period of time, the charge amount of the toner will decrease due to natural discharge. Therefore, it is desirable to perform a recovery operation of the developing device to increase the charge amount of the toner before the image forming device resumes image formation processing.

[0004] Conventionally, known recovery operations for a developing device include a technique for stirring the developer, a technique for adjusting the potential difference between the developer carrier and the image carrier, a technique for forcibly discharging toner from the developing device, etc. Also known as control means for the recovery operation of a developing device are a control means based on the time the image forming apparatus is left unused until it is restored from the previous stopped state (e.g., Patent Document 1), a control means based on the cumulative rotation time and unused time of the developing roller (e.g., Patent Document 2), and a control means based on the ambient environment and unused time of the developing device (e.g., Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-142445 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-156911 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-59153 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-described conventional control means, there is room for improvement in the accuracy of the recovery operation of the developing device in order to reduce toner fogging when the image forming apparatus is left unused for a long period of time.

[0007] Furthermore, although it is conceivable to combine the above-mentioned conventional control means, no specific control content suitable for reducing toner fogging is disclosed.

[0008] The present invention has been made to solve the above-mentioned conventional problems, and aims to provide an image forming apparatus that can accurately reduce toner fogging when the image forming apparatus is left unused for a long period of time. [Means for solving the problem]

[0009] In order to achieve the above object, the image forming apparatus described in the present application is an image forming apparatus comprising a developing device that carries developer on the surface of a developer carrier and develops an electrostatic latent image on the surface of the image carrier, and a control unit that controls the developing device, wherein the control unit comprises a surrounding environment acquisition means that acquires the surrounding environment of the developing device, an idle time measuring means that measures the idle time of the image forming device, a print rate calculation means that calculates the print rate by the image forming device, a recovery means that performs a recovery operation to recover the developing device when the image forming device recovers from a stopped state, a recovery condition determination means that determines the recovery conditions for performing the recovery operation, and a memory means that stores temporary parameters related to the recovery conditions in association with the surrounding environment and the idle time, and the recovery condition determination means acquires the temporary parameters from the memory means based on the surrounding environment acquired by the surrounding environment acquisition means and the idle time measured by the idle time measuring means, and determines the recovery conditions by correcting the acquired temporary parameters based on the print rate calculated by the print rate calculation means.

[0010] Another image forming apparatus described in the present application is an image forming apparatus including a developing device that carries developer on the surface of a developer carrier and develops an electrostatic latent image on the surface of an image carrier, and a control unit that controls the developing device, wherein the control unit includes a surrounding environment acquisition unit that acquires the surrounding environment of the developing device, a left-standby time counting unit that counts the left-standby time of the image forming apparatus, a print rate calculation unit that calculates the print rate of the image forming apparatus, an accumulated rotation time counting unit that counts the accumulated rotation time of the developer carrier, a recovery unit that executes a recovery operation to recover the developing device when the image forming apparatus recovers from a stopped state, and a control unit that controls the recovery operation. and storage means for storing provisional parameters relating to the return conditions in association with the surrounding environment and the standing time, wherein the return condition determination means acquires the provisional parameters from the storage means based on the surrounding environment acquired by the surrounding environment acquisition means and the standing time measured by the standing time measuring means, and determines the return conditions by correcting the acquired provisional parameters based on the print rate calculated by the print rate calculation means and the accumulated rotation time acquired by the accumulated rotation time measuring means.

[0011] Still another image forming apparatus described in the present application is an image forming apparatus including a developing device that carries developer on the surface of a developer carrier and develops an electrostatic latent image on the surface of an image carrier, and a control unit that controls the developing device, wherein the control unit includes a surrounding environment acquisition unit that acquires the surrounding environment of the developing device, a stand-alone time counting unit that measures the stand-alone time of the image forming apparatus, a cumulative rotation time counting unit that measures the cumulative rotation time of the developer carrier, a recovery unit that executes a recovery operation to recover the developing device when the image forming apparatus recovers from a stopped state, a recovery condition determination unit that determines a recovery condition for executing the recovery operation, and a memory that stores temporary parameters related to the recovery conditions in association with the surrounding environment and the stand-alone time. and correction parameter storage means for storing correction parameters for correcting the provisional parameters in association with the accumulated rotation time, and the return condition determination means acquires the provisional parameters from the storage means based on the surrounding environment acquired by the surrounding environment acquisition means and the idle time measured by the idle time measuring means, acquires the correction parameters from the correction parameter storage means based on the accumulated rotation time acquired by the accumulated rotation time measuring means, and determines the return condition by multiplying the acquired provisional parameters by the acquired correction parameters or by correcting the acquired provisional parameters with the acquired correction parameters.

[0012] Further, in the image forming apparatus, the developing device has an agitating member that agitates the developer, and the recovery means performs an agitation operation to cause the agitating member to agitate the developer as the recovery operation, and the recovery condition may be the driving time of the agitating member.

[0013] The image forming apparatus may further include a bias power supply that applies a development bias to the developer carrier, and the recovery means may perform a bias adjustment operation as the recovery operation to adjust the development bias from the bias power supply so that the potential difference between the developer carrier and the image carrier becomes small, and the recovery condition may be the degree of adjustment of the development bias.

[0014] In addition, in the image forming apparatus, the recovery means may perform a forced toner discharge operation to forcibly discharge toner from the developing device as the recovery operation, and the recovery condition may be the amount of toner discharged by the forced toner discharge operation.

[0015] In addition, the image forming apparatus may further include a bias power supply that applies a development bias to the developer carrier, and the developing device may have an agitating member that agitates the developer, and the recovery means may selectively perform, as the recovery operation, one of a stirring operation that causes the agitating member to agitate the developer, a bias adjustment operation that adjusts the development bias by the bias power supply so that the potential difference between the developer carrier and the image carrier becomes small, and a forced toner discharge operation that causes the developing device to forcibly discharge toner, and the recovery conditions may include the driving time of the agitating member, the degree of adjustment of the development bias, and the amount of toner discharged by the forced toner discharge operation. [Effects of the Invention]

[0016] According to the present invention, it is possible to accurately reduce toner fogging that occurs when an image forming apparatus is left unused for a long period of time. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a developing device. [Figure 3] FIG. 2 is a block diagram showing a control unit in the first embodiment. [Figure 4] FIG. 10 is a diagram illustrating an example of an environmental zone table. [Figure 5A] FIG. 10 is a diagram showing an example of a provisional parameter table showing provisional parameters relating to the rotation drive time of the stirring member drive unit. [Figure 5B] FIG. 10 is a diagram showing an example of a temporary parameter table showing temporary parameters relating to the adjustment degree of the development bias; [Figure 5C] FIG. 10 is a diagram showing an example of a temporary parameter table showing temporary parameters related to toner discharge amounts; [Figure 6A] FIG. 10 is a diagram showing an example of a correction parameter table that associates the printing rate with a correction parameter related to the rotation drive time of the stirring member drive unit. [Figure 6B] FIG. 10 is a diagram showing an example of a correction parameter table that associates a printing rate with a correction parameter relating to the degree of adjustment of a development bias; [Figure 6C] FIG. 10 is a diagram showing an example of a correction parameter table that associates a printing rate with a correction parameter relating to a toner discharge amount. [Figure 7] 10 is a flowchart illustrating an example of a processing procedure performed by a control unit. [Figure 8A] 10 is a flowchart illustrating an example of a procedure for determining a return condition for executing a stirring operation. [Figure 8B] 10 is a flowchart illustrating an example of a procedure for determining a restoration condition for executing a bias adjustment operation. [Figure 8C] 10 is a flowchart illustrating an example of a procedure for determining a recovery condition for executing a forced toner discharging operation. [Figure 9] FIG. 10 is a block diagram showing a control unit in the second embodiment. [Figure 10A] FIG. 10 is a diagram showing an example of a correction parameter table that associates the cumulative rotation time of the developing roller with a correction parameter relating to the rotation drive time of the agitation member drive unit. [Figure 10B] FIG. 10 is a diagram showing an example of a correction parameter table that associates the cumulative rotation time of the developing roller with a correction parameter relating to the degree of adjustment of the developing bias. [Figure 10C] FIG. 10 is a diagram showing an example of a correction parameter table that associates the cumulative rotation time of the developing roller with a correction parameter relating to the amount of toner discharged. [Figure 11] FIG. 11 is a block diagram showing a control unit in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] (Embodiment 1) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the same components in the embodiments described below will be designated by the same reference numerals, and redundant descriptions of those components will be omitted.

[0019] -Image forming device- First, the configuration of an image forming apparatus 1 in this embodiment will be described.

[0020] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 1 in embodiment 1. In the drawing, the symbol X indicates the width direction (depth direction), with the X1 direction being the front direction and the X2 direction being the rear direction.

[0021] The image forming apparatus 1 in this embodiment includes a developing device 10, an exposure device 11, a photosensitive drum 13, a cleaner device 14, a charger 15, an intermediate transfer belt device 16, a secondary transfer device 20, a fixing device 17, a sheet transport path 12, a paper feeder 18, and a paper discharge tray 19 (see FIG. 1). The photosensitive drum 13 corresponds to an "image carrier" in the claims. The image forming apparatus 1 forms multicolor and monochrome images on a predetermined sheet according to image data.

[0022] In this embodiment, toners of the colors yellow (Y), magenta (M), cyan (C), and black (K) are used for printing by the image forming apparatus 1. Four developing devices 10, photosensitive drums 13, chargers 15, and cleaner devices 14 are provided for each color, thereby forming image stations P (Pa, Pb, Pc, Pd) for each color.

[0023] The charger 15 uniformly charges the surface of the photosensitive drum 13 to a predetermined potential (for example, approximately -600 V). The exposure device 11 exposes the surface of the photosensitive drum 13 to light to form an electrostatic latent image. The development device 10 develops the electrostatic latent image on the surface of the photosensitive drum 13 to form a toner image on the surface of the photosensitive drum 13. Through this series of operations, a toner image of each color is formed on the surface of each photosensitive drum 13.

[0024] The cleaner device 14 collects residual toner on the surface of the photosensitive drum 13 after development and image transfer.

[0025] The intermediate transfer belt device 16 is disposed above the photosensitive drum 13 and includes an intermediate transfer belt 161, an intermediate transfer belt drive roller 162, an intermediate transfer belt driven roller 163, an intermediate transfer roller 164, and an intermediate transfer belt cleaning device 165.

[0026] The intermediate transfer belt 161 is stretched around an intermediate transfer belt drive roller 162, an intermediate transfer belt driven roller 163, and an intermediate transfer roller 164, and moves in a predetermined direction (the direction of the arrow C in the figure). The toner images of each color formed on the surface of each photosensitive drum 13 are transferred onto the intermediate transfer belt 161 in succession, overlapping each other, to form a color toner image on the surface of the intermediate transfer belt 161.

[0027] The secondary transfer device 20 has a transfer roller 201. The transfer roller 201 forms a nip area between itself and the intermediate transfer belt 161, and the sheet conveyed through the sheet conveying path 12 is sandwiched in this nip area and conveyed. When the sheet passes through the nip area, the toner image on the surface of the intermediate transfer belt 161 is transferred onto the sheet.

[0028] The sheet feeder 18 has a tray for stacking sheets to be used for image formation. The sheet discharge tray 19 is a tray on which sheets on which images have been formed are placed.

[0029] The fixing device 17 heats and melts the toner image transferred onto the sheet, thereby fixing the toner image onto the sheet.

[0030] The sheet transport path 12 includes a main path 121 and a reversing path 122 that branches off from the main path 121 and then rejoins the main path 121. The sheet transport path 12 includes, as the main path 121, a pickup roller 123, pre-registration rollers 125, registration rollers 124, a secondary transfer device 20, a fixing device 17, and a paper discharge roller 126. The sheet transport path 12 also includes a transport roller 127 for transporting paper.

[0031] Pickup roller 123 is provided near the end of paper feeder 18 and is a pickup roller that supplies sheets one by one from paper feeder 18 to sheet transport path 12. Registration roller 124 temporarily holds the sheet being transported from paper feeder 18 and transports the sheet to transfer roller 201 at a timing when the leading edge of the toner image on photosensitive drum 13 and the leading edge of the sheet are aligned. Pre-registration roller 125 assists in facilitating sheet transport. Paper discharge roller 126 discharges the sheet that has passed through fixing device 17 onto paper discharge tray 19.

[0032] In addition to the configuration described above, the image forming apparatus 1 is equipped with a bias power supply 3 that applies a development bias to the developing device 10, an environmental sensor 4 (e.g., a temperature and humidity sensor) that measures the ambient environment of the developing device 10, and a control unit 5 that controls the developing device 10.

[0033] -Developing device- Next, the configuration of the developing device 10 in this embodiment will be described.

[0034] FIG. 2 is a cross-sectional view showing the developing device 10. As shown in FIG.

[0035] The developing device 10 has a developer tank 21, two stirring members 22a and 22b, a developing roller 23, and a regulating member 24 (see FIG. 2). The developing roller 23 corresponds to the "developer carrier" in the claims.

[0036] The developer tank 21 is a container that stores a developer. The developer used is a developer containing non-magnetic toner and a magnetic carrier (two-component developer).

[0037] Stirring members 22a and 22b stir the developer stored in developer tank 21. Although not shown, stirring members 22a and 22b each include a rotation shaft and a spiral blade formed around the rotation shaft. The spiral blade of stirring member 22a rotates to transport the developer stored in developer tank 21 toward the front of the paper in FIG. 2, while the spiral blade of stirring member 22b rotates to transport the developer toward the back of the paper in FIG. 2. In developer tank 21, stirring members 22a and 22b form their own developer transport paths. To divide the internal space of developer tank 21 into two spaces containing stirring members 22a and 22b, respectively, a partition wall is formed between both axial ends (center position) of the rotation shafts of stirring members 22a and 22b. Communication openings for transferring developer are provided in developer tank 21 on the outer side of the partition wall in the rotation shaft direction. With this configuration, as the agitating members 22a and 22b rotate, the developer is agitated and transported so as to circle around the partition wall. The agitation by the agitating members 22a and 22b generates friction between the toner contained in the developer and the magnetic carrier, and this friction charges the non-magnetic toner. The agitating member 22b is disposed near the developing roller 23 and transports the developer to the developing roller 23 while agitating it. The agitating members 22a and 22b rotate by receiving rotational driving force from the agitating member driving unit 25 via gears (not shown).

[0038] The developing roller 23 carries a developer on its surface. The developing roller 23 includes a sleeve portion 231 and a magnetic roll portion 233. The sleeve portion 231 is non-magnetic, cylindrical, and rotatably supported. The sleeve portion 231 receives a rotational driving force from a driving unit (not shown) and rotates in a rotation direction D around a rotation shaft 232.

[0039] The magnetic roll portion 233 is a cylindrical magnet roll that has magnetism and is housed within the sleeve portion 231 so that its peripheral surface faces the inner surface of the sleeve portion 231, and is fixed independently from the sleeve portion 231. In other words, the rotation of the developing roller 23 is carried out by the sleeve portion 231, and the rotation axis 232 of the sleeve portion 231 serves as the rotation axis of the developing roller 23.

[0040] The developing roller 23 forms a nip N with the photosensitive drum 13. At the nip N, a developing bias (for example, about −450 V) is applied to the developing roller 23 by the bias power supply 3. As a result, toner is supplied from the developer carried on the surface of the developing roller 23 to the electrostatic latent image on the surface of the photosensitive drum 13.

[0041] The regulating member 24 is disposed upstream of the nip portion N in the rotation direction D, with a gap provided between it and the circumferential surface of the sleeve portion 231. The regulating member 24 regulates the layer thickness of the developer being transported at a position close to the circumferential surface of the sleeve portion 231 of the developing roller 23.

[0042] -Control Unit- FIG. 3 is a block diagram showing the control unit 5 in the first embodiment.

[0043] The control unit 5, which controls the image forming operation in the image forming apparatus 1, is configured to be able to execute a recovery operation to recover the developing device 10 when the image forming apparatus 1 recovers from a stopped state. In this specification, the "stopped state of the image forming apparatus 1" includes a state in which the power switch is off (main power off, sub power on), and the "recovery of the image forming apparatus 1" includes a case in which the image forming apparatus 1 recovers from a low power consumption state in which the supplied energy is lower than that of a predetermined normal power consumption state, and also includes a case in which the image forming apparatus 1 recovers from a normal power consumption state.

[0044] In this embodiment, the recovery operation of developing device 10 includes an operation to reduce contamination of non-image areas of photosensitive drum 13 (so-called "toner fogging") caused by a decrease in the charge amount of toner when image forming apparatus 1 is left standing for a long time after the previous stop state. The recovery operation of developing device 10 includes an "agitation operation" that causes agitation members 22a and 22b to agitate the developer, a "bias adjustment operation" that adjusts the development bias from bias power supply 3 so that the potential difference between developing roller 23 and photosensitive drum 13 becomes small, and a "forced toner discharge operation" that forcibly discharges toner from developing device 10 by developing the solid latent image formed on the surface of photosensitive drum 13.

[0045] The recovery conditions for executing each recovery operation of the developing device 10 are as follows.

[0046] When the recovery operation of the developing device 10 is an "agitation operation," the recovery condition is the drive time of the agitation members 22a and 22b, specifically, the rotation drive time of the agitation member drive unit 25 that drives the agitation members 22a and 22b to rotate.

[0047] When the recovery operation of the developing device 10 is a "bias adjustment operation," the recovery condition is the adjustment degree of the developing bias. In this embodiment, the adjustment degree of the developing bias is expressed as an adjustment voltage value (hereinafter referred to as "adjustment voltage value") that indicates the adjustment degree.

[0048] When the recovery operation of the developing device 10 is a "forced toner discharge operation," the recovery condition is the amount of toner discharged by the forced toner discharge operation. In this embodiment, the amount of toner discharged is expressed as a numerical value obtained by converting the amount of solid latent image formed on the surface of the photosensitive drum 13 into the number of pages of an A4-sized sheet (hereinafter referred to as "number of solid discharge pages").

[0049] The control unit 5 has a processing unit 50, a data measurement unit 51, a memory unit 52, an input unit 53, and an output unit 54 (see FIG. 3), which are interconnected by a bus line (not shown). The input unit 53 is communicatively connected to the environment sensor 4, and the output unit 54 is communicatively connected to the agitation member driving unit 25, the bias power supply 3, and the image station P.

[0050] The processing unit 50 includes a CPU (Central Processing Unit), etc. The processing unit 50 has a recovery operation switching unit 500 that switches the recovery operation of the developing device 10, an environmental zone determination unit 501 that determines a predetermined environmental zone based on an input from the environmental sensor 4, and a recovery condition determination unit 502 that acquires recovery conditions for executing each recovery operation of the developing device 10.

[0051] In this embodiment, the recovery operation switching unit 500 switches the recovery operation of the developing device 10 in response to an input from the user. In other words, the processing unit 50 of the control unit 5 is configured to selectively execute one of the recovery operations of the developing device 10, namely, the "agitation operation," the "bias adjustment operation," and the "forced toner discharge operation." This makes it possible to selectively execute a recovery operation appropriate for the state of the image forming apparatus 1 when it is restored from a stopped state, thereby accurately reducing toner fogging when the image forming apparatus 1 is left unused for a long period of time.

[0052] The environment zone determination unit 501 and the return condition determination unit 502 will be described in detail later with reference to a flowchart. The return condition determination unit 502 corresponds to the "return condition determination means" in the claims.

[0053] In addition, the processing unit 50 corresponds to the "ambient environment acquisition means" described in the claims, as it acquires measurement values ​​of the ambient environment of the developing device 10 from the environmental sensor 4, and further corresponds to the "returning means" described in the claims, as it instructs the stirring member driving unit 25, the bias power supply 3, and the image station P to perform the return operation.

[0054] The data measuring unit 51 is a software program stored in the ROM of the storage unit 52, and executes each function by being read out under the control of the processing unit 50. The data measuring unit 51 includes an unused time counting unit 510 that counts the unused time, and a print rate calculation unit 511 that calculates the print rate of the image output by the image forming apparatus 1. The unused time counting unit 510 corresponds to the "unused time counting means" set forth in the claims, and the print rate calculation unit 511 corresponds to the "print rate calculation means" set forth in the claims.

[0055] In this specification, the term "left unused time" refers to the time it takes for the image forming apparatus 1 to return to normal operation after being stopped the previous time.

[0056] The printing rate of the image forming apparatus 1 is one of the indicators indicating the state of the image forming apparatus 1 before it is left unused. In this embodiment, the printing rate calculation unit 511 calculates the average printing rate by averaging the printing rates (for example, the ratio of the number of printed pixels to the number of total image pixels) stored for each page of the latest predetermined number of pages (for example, 200 pages).

[0057] The storage unit 52 includes a non-volatile memory such as a read-only memory (ROM) and a volatile memory such as a random access memory (RAM). The storage unit 52 stores a control program 520, an environmental zone table 521, a temporary parameter table group 55, and a correction parameter table group 56. Although not shown, the storage unit 52 also stores which recovery operation the developing device 10 is to execute.

[0058] The control program 520 is stored in the ROM of the storage unit 52. Under the control of the processing unit 50, the control program 520 stored in the ROM is read out and loaded onto the RAM, thereby executing the control program 520. Note that the control program 520 is not limited to the above, and may be read from a recording medium such as an HDD or downloaded from a network such as a LAN (Local Area Network).

[0059] FIG. 4 is a diagram showing an example of the environment zone table 521. As shown in FIG.

[0060] The environmental zone table 521 divides the environment surrounding the developing device 10 into a plurality of environmental zones (zone 1 to zone 8) based on the temperature and humidity around the developing device 10 (see FIG. 4). The item "temperature" in the environmental zone table 521 indicates the temperature conditions around the developing device 10, and the item "humidity" indicates the humidity conditions around the developing device 10. The environmental zone table 521 divides the environmental zones into zone 1 to zone 8 based on the conditions of the items "temperature" and "humidity".

[0061] Fig. 5A is a diagram showing an example of a temporary parameter table 55A indicating temporary parameters related to the rotation drive time of the agitation member drive unit 25. Fig. 5B is a diagram showing an example of a temporary parameter table 55B indicating temporary parameters related to the adjustment degree of the development bias. Fig. 5C is a diagram showing an example of a temporary parameter table 55C indicating temporary parameters related to the toner discharge amount.

[0062] The temporary parameter table group 55 stores temporary parameters related to the recovery conditions for executing each recovery operation of the developing device 10, and is configured to include temporary parameter tables 55A to 55C corresponding to each recovery operation of the developing device 10 (temporary parameter table 55A corresponding to the "agitation operation", temporary parameter table 55B corresponding to the "bias adjustment operation", and temporary parameter table 55C corresponding to the "forced toner discharge operation") (see Figures 5A to 5C). The temporary parameter table group 55 corresponds to the "storage means" recited in the claims.

[0063] The provisional parameter table 55A associates the environmental zone and the storage time with the provisional parameters related to the rotational drive time of the stirring member drive unit 25 (see FIG. 5A). In the present embodiment, the provisional parameters (0, T1, T2, T3) related to the rotational drive time of the stirring member drive unit 25 are values indicating the rotational drive time of the stirring member drive unit 25, and the relationship 0 < T1 < T2 < T3 holds. The item "storage time" in the provisional parameter table 55A indicates the condition of the storage time of the image forming apparatus 1, and the item "environmental zone" indicates the condition of the environmental zone classified by the environmental zone table 521. The provisional parameter table 55A indicates the value of the rotational drive time of the stirring member drive unit 25 corresponding to each condition of the item "storage time" and the item "environmental zone".

[0064] The provisional parameter table 55B associates the environmental zone and the storage time with the provisional parameters related to the degree of adjustment of the developing bias (see FIG. 5B). In the present embodiment, the value (0, V1) of the provisional parameter related to the degree of adjustment of the developing bias is an adjustment voltage value, and the relationship V1 < 0 holds. V1 is, for example, about -50V. The provisional parameter table 55B indicates the adjustment voltage value corresponding to each condition of the item "storage time" and the item "environmental zone".

[0065] The provisional parameter table 55C associates the environmental zone and the storage time with the provisional parameters related to the toner discharge amount (see FIG. 5C). In the present embodiment, the value (yes, no) of the provisional parameter related to the toner discharge amount indicates the presence or absence of forced toner discharge. The provisional parameter table 55C indicates the presence or absence of forced toner discharge corresponding to each condition of the item "storage time" and the item "environmental zone".

[0066] Fig. 6A is a diagram showing an example of a correction parameter table 56A that associates the printing rate with a correction parameter related to the rotation drive time of the agitation member drive unit 25. Fig. 6B is a diagram showing an example of a correction parameter table 56B that associates the printing rate with a correction parameter related to the adjustment degree of the development bias. Fig. 6C is a diagram showing an example of a correction parameter table 56C that associates the printing rate with a correction parameter related to the toner discharge amount.

[0067] The correction parameter table group 56 stores correction parameters for correcting the provisional parameters, and includes correction parameter tables 56A to 56C corresponding to the respective recovery operations of the developing device 10 (correction parameter table 56A corresponding to the "agitation operation", correction parameter table 56B corresponding to the "bias adjustment operation", and correction parameter table 56C corresponding to the "forced toner discharge operation") (see FIGS. 6A to 6C). The correction parameter table group 56 corresponds to the "correction parameter storage means" recited in the claims.

[0068] Correction parameter table 56A associates the printing rate with a correction parameter relating to the rotational drive time of agitation member drive unit 25 (see FIG. 6A). In this embodiment, the value of the correction parameter relating to the rotational drive time of agitation member drive unit 25 is a coefficient. The item "Average printing rate (%)" in correction parameter table 56A indicates the conditions for the average printing rate, and the item "Agitation coefficient" indicates the coefficient by which the value of the provisional parameter relating to the rotational drive time of agitation member drive unit 25 is multiplied when the conditions indicated by the item "Average printing rate (%)" are met.

[0069] Correction parameter table 56B associates the print rate with a correction parameter related to the adjustment degree of the development bias (see FIG. 6B). In this embodiment, the value (0, V2) of the correction parameter related to the adjustment degree of the development bias is an adjustment voltage value, and the relationship V2<0 holds. V2 is, for example, approximately −50 V. The item “Adjustment voltage value (V)” in correction parameter table 56B indicates an adjustment voltage value that is a candidate for replacing the value of the provisional parameter related to the adjustment degree of the development bias when the condition indicated by the item “Average print rate (%)” is satisfied.

[0070] The correction parameter table 56C associates the printing rate with a correction parameter relating to the amount of toner discharged (see FIG. 6C). In this embodiment, the value of the correction parameter relating to the amount of toner discharged is the value of the number of pages discharged. The item "Number of pages discharged" in the correction parameter table 56C indicates the value of the number of pages discharged when forced toner discharge is enabled and when the conditions indicated by the item "Average printing rate (%)" are met.

[0071] Next, the processing procedure of the control unit 5 in the recovery operation of the developing device 10 will be described.

[0072] Fig. 7 is a flowchart showing an example of a processing procedure by the control unit 5. Fig. 8A is a flowchart showing an example of a procedure for determining a return condition for executing a stirring operation. Fig. 8B is a flowchart showing an example of a procedure for determining a return condition for executing a bias adjustment operation. Fig. 8C is a flowchart showing an example of a procedure for determining a return condition for executing a forced toner discharge operation. The series of processes shown in Fig. 7 are executed when the image forming apparatus 1 returns from a stopped state.

[0073] First, in step S1 shown in FIG. 7, the processing unit 50 of the control unit 5 acquires the idle time of the image forming apparatus 1 from the idle time measuring unit 510 of the data measuring unit 51.

[0074] In step S2, the processing unit 50 acquires the measurement value of the surrounding environment of the developing device 10 from the environment sensor 4.

[0075] In step S3, the environment zone determination unit 501 of the processing unit 50 refers to the environment zone table 521 and determines the environment zone based on the measurement values ​​acquired in step S2.

[0076] In step S4 , the processing unit 50 acquires the average printing rate from the printing rate calculation unit 511 of the data measurement unit 51 .

[0077] In step S5, the processing unit 50 refers to the memory unit 52 and determines which recovery operation the developing device 10 will perform. If the recovery operation of the developing device 10 is the "agitation operation," the process proceeds to step S6. If the recovery operation of the developing device 10 is the "bias adjustment operation," the process proceeds to step S7. If the recovery operation of the developing device 10 is the "forced toner discharge operation," the process proceeds to step S8.

[0078] <Stirring operation> 7, the restoration condition determination unit 502 of the processing unit 50 determines the restoration conditions for executing the "agitation operation" as the restoration operation of the developing device 10. Here, the procedure by which the restoration condition determination unit 502 determines the restoration conditions will be described with reference to FIGS. 8A to 8C.

[0079] In step S60 shown in FIG. 8A, the return condition determination unit 502 refers to the provisional parameter table 55A and obtains provisional parameters related to the rotation drive time of the agitation member drive unit 25 based on the environmental zone determined in step S3 and the standing time obtained in step S1.

[0080] In step S61, the restoration condition determination unit 502 refers to the correction parameter table 56A and acquires a correction parameter related to the rotation drive time of the agitation member drive unit 25 based on the average printing rate acquired in step S4.

[0081] In step S62, the return condition determination unit 502 determines the return condition for executing the "agitation operation", i.e., the rotational drive time of the agitation member drive unit 25, by multiplying the value of the temporary parameter obtained in step S60 by the value of the correction parameter obtained in step S61.

[0082] For example, if the value of the temporary parameter acquired in step S60 is T2 and the average printing rate is 8.5%, the value of the correction parameter acquired in step S61 is 1.2, and the rotation drive time of the agitation member drive unit 25 determined in step S62 is the value obtained by multiplying T2 by 1.2.

[0083] 7, the processing unit 50 passes the recovery condition determined in step S62 to the agitation member driving unit 25 to rotate the agitation members 22a and 22b. In this way, the control unit 5 executes the "agitation operation" as a recovery operation of the developing device 10.

[0084] <Bias adjustment operation> 7, the restoration condition determination unit 502 of the processing unit 50 determines the restoration conditions for executing the "bias adjustment operation" as the restoration operation of the developing device 10. Here, a procedure by which the restoration condition determination unit 502 determines the restoration conditions will be described with reference to FIG. 8B.

[0085] In step S70 shown in FIG. 8B, the restoration condition determination unit 502 refers to the temporary parameter table 55B and obtains a temporary parameter related to the degree of adjustment of the development bias based on the environmental zone determined in step S3 and the standing time obtained in step S1.

[0086] In step S71, the restoration condition determination unit 502 refers to the correction parameter table 56B and acquires a correction parameter relating to the degree of adjustment of the development bias based on the average printing rate acquired in step S4.

[0087] In step S72, the return condition determination unit 502 compares the absolute value of the temporary parameter acquired in step S70 with the absolute value of the correction parameter acquired in step S71. If the absolute value of the temporary parameter acquired in step S70 is greater than the absolute value of the correction parameter acquired in step S71, the return condition determination unit 502 sets the value of the correction parameter acquired in step S71 as the return condition (step S73). On the other hand, if the absolute value of the temporary parameter acquired in step S70 is smaller than the absolute value of the correction parameter acquired in step S71, the return condition determination unit 502 sets the value of the temporary parameter acquired in step S70 as the return condition (step S74).

[0088] To summarize steps S72 to S74, the restoration condition determination unit 502 compares the degree of development bias adjustment when the temporary parameters are adopted with the degree of development bias adjustment when the correction parameters are adopted, and sets the value of the temporary parameters or the correction parameters, whichever results in a smaller degree of development bias adjustment, as the restoration condition. This makes it possible to adjust the development bias just right. In this way, the restoration condition determination unit 502 determines the restoration condition for executing the "bias adjustment operation," i.e., the degree of development bias adjustment expressed as an adjustment voltage value.

[0089] For example, if the value of the temporary parameter acquired in step S70 is V1 and the average printing rate is 8.5%, the value of the correction parameter acquired in step S71 is 0, and therefore the adjustment voltage value is 0.

[0090] 7, the processing unit 50 passes the recovery condition determined in step S72 to the bias power supply 3 to adjust the developing bias. In this way, the control unit 5 executes a "bias adjustment operation" as a recovery operation of the developing device 10.

[0091] In step S12, the processing unit 50 executes a "finishing stirring operation" in which the stirring members 22a and 22b are caused to rotate and stir the developer as a finishing process.

[0092] <Forced toner discharge operation> 7, the restoration condition determination unit 502 of the processing unit 50 determines the restoration conditions for executing the "forced toner discharge operation" as the restoration operation of the developing device 10. Here, the procedure by which the restoration condition determination unit 502 determines the restoration conditions will be described with reference to FIG. 8C.

[0093] In step S80, the recovery condition determination unit 502 refers to the temporary parameter table 55C and obtains a temporary parameter related to the amount of toner discharged (whether or not to forcibly discharge toner) based on the environmental zone determined in step S3 and the standing time obtained in step S1.

[0094] In step S81, the restoration condition determination unit 502 determines whether or not forced toner discharge is to be performed based on the provisional parameters acquired in step S80. If forced toner discharge is to be performed, the process proceeds to step S82. On the other hand, if forced toner discharge is not performed, the process proceeds to step S85, where the restoration condition is set to 0. In other words, if forced toner discharge is not performed, the number of pages discharged is 0.

[0095] In step S82, the restoration condition determination unit 502 refers to the correction parameter table 56C and acquires a correction parameter (value of the number of pages of solid discharge) relating to the amount of toner discharged based on the average printing rate acquired in step S4.

[0096] In step S83, the return condition determination unit 502 determines whether the value of the correction parameter acquired in step S82 is greater than 0. If the value of the correction parameter acquired in step S82 is greater than 0, the return condition determination unit 502 sets the value of the correction parameter acquired in step S82 as the return condition (step S84). On the other hand, if the value of the correction parameter acquired in step S82 is 0, the return condition determination unit 502 sets the return condition to 0 (step S85).

[0097] To summarize steps S81 to S85, if forced toner discharge is not performed, the restoration condition determination unit 502 sets the number of solid discharge pages to 0. Under the condition that forced toner discharge is not performed, there is no need to refer to the average printing rate acquired in step S4, and there is no need to acquire a correction parameter related to the amount of toner discharge (value of the number of solid discharge pages). On the other hand, if forced toner discharge is performed, the restoration condition determination unit 502 acquires a correction parameter related to the amount of toner discharge based on the average printing rate acquired in step S4, and sets the value of the correction parameter as the number of solid discharge pages. This allows the developing device 10 to discharge toner neither too much nor too little. In this way, the restoration condition determination unit 502 determines the restoration condition for executing the "forced toner discharge operation," i.e., the amount of toner discharge expressed as the number of solid discharge pages.

[0098] For example, if the value of the temporary parameter acquired in step S80 is valid and the average printing rate is 6.5%, the value of the correction parameter acquired in step S82 is 0, and therefore the number of pages to be discharged is 0.

[0099] Also, for example, if the value of the temporary parameter acquired in step S80 is valid and the average printing rate is 8.5%, the value of the correction parameter acquired in step S82 is 1, and therefore the number of pages to be printed is 1.

[0100] 7, the processing unit 50 passes the recovery condition determined in step S82 to the image station P, forms a solid latent image on the surface of the photosensitive drum 13, and forcibly discharges toner from the developing device 10. In this way, the control unit 5 executes a "forced toner discharge operation" as a recovery operation for the developing device 10.

[0101] In step S13, the processing unit 50 performs a "finishing stirring operation" by rotationally driving the stirring members 22a and 22b.

[0102] The value of the temporary parameter related to the toner discharge amount may be set as the value of the number of pages to be discharged, similarly to the value of the correction parameter related to the toner discharge amount. In this case, the restoration condition determination unit 502 may acquire the correction parameter related to the toner discharge amount based on the average printing rate in each process, and set the smaller value of the temporary parameter or the correction parameter as the number of pages to be discharged.

[0103] In the image forming apparatus 1 described above, the recovery conditions for executing each recovery operation of the developing device 10 are determined taking into consideration not only the environment surrounding the developing device 10 and the time the image forming apparatus 1 has been left unused, but also the print rate, which indicates the state of the image forming apparatus 1 before being left unused. This makes it possible to execute the recovery operation of the developing device 10 under conditions suited to the state of the image forming apparatus 1 when it is restored from a stopped state, and ultimately makes it possible to accurately reduce toner fogging when the image forming apparatus 1 has been left unused for a long period of time.

[0104] It should be noted that the provisional parameter tables 55A to 55C and the correction parameter tables 56A to 56C described above are merely examples of data structures, and what is essential is that the provisional parameters obtained based on the ambient environment of the developing device 10 and the time it has been left unused can be appropriately corrected based on the average printing rate.

[0105] (Embodiment 2) Hereinafter, only the differences between the second embodiment of the present invention and the first embodiment will be described.

[0106] FIG. 9 is a block diagram showing the control unit 5 in the second embodiment.

[0107] In the second embodiment, the data measurement unit 51 of the control unit 5 includes an accumulated rotation time counter 512 that measures the accumulated rotation time of the developing roller 23, instead of the print rate calculation unit 511 in the first embodiment (see FIG. 9). In this specification, the "accumulated rotation time of the developing roller 23" refers to the rotation drive time of the developing roller 23 from the last time the image forming apparatus 1 was stopped until the last time it was restored. The "accumulated rotation time of the developing roller 23" is one of the indicators that indicates the state of the developing device 10 before it was left unused.

[0108] The cumulative rotation time counting unit 512 corresponds to the "cumulative rotation time counting means" in the claims.

[0109] Fig. 10A is a diagram showing an example of a correction parameter table 56D that associates the cumulative rotation time of the developing roller 23 with a correction parameter related to the rotation drive time of the agitation member drive unit 25. Fig. 10B is a diagram showing an example of a correction parameter table 56E that associates the cumulative rotation time of the developing roller 23 with a correction parameter related to the adjustment degree of the development bias. Fig. 10C is a diagram showing an example of a correction parameter table 56F that associates the cumulative rotation time of the developing roller 23 with a correction parameter related to the toner discharge amount.

[0110] In the second embodiment, the correction parameter table group 56 includes correction parameter tables 56D to 56F instead of the correction parameter tables 56A to 56C in the first embodiment.

[0111] Correction parameter table 56D associates the cumulative rotation time of developing roller 23 with correction parameters relating to the rotation drive time of agitation member drive unit 25 (see FIG. 10A). The item "Cumulative rotation time (minutes)" in correction parameter table 56D indicates the condition for the cumulative rotation time of developing roller 23, and the item "Agitation coefficient" indicates a coefficient by which the value of the provisional parameter relating to the rotation drive time of agitation member drive unit 25 is multiplied when the condition indicated by the item "Cumulative rotation time (minutes)" is met.

[0112] The correction parameter table 56E associates the cumulative rotation time of the developing roller 23 with the correction parameter related to the adjustment degree of the developing bias (see FIG. 10B). The item "Adjustment voltage value (V)" in the correction parameter table 56E indicates an adjustment voltage value that is a candidate for replacing the value of the provisional parameter related to the adjustment degree of the developing bias when the condition indicated by the item "Accumulated rotation time (minutes)" is satisfied.

[0113] The correction parameter table 56F associates the cumulative rotation time of the developing roller 23 with correction parameters related to the toner discharge amount (see FIG. 10C). The item "Number of pages discharged" in the correction parameter table 56F indicates the value of the number of pages discharged when forced toner discharge is enabled and the condition indicated by the item "Cumulative rotation time (minutes)" is satisfied.

[0114] The control unit 5 in the second embodiment executes the recovery operation of the developing device 10 in the same procedure as in the first embodiment. The basic procedure is the same as that explained and illustrated in the first embodiment, but the following differences are noted.

[0115] First, in step S4 shown in FIG. 7, the processing unit 50 acquires the accumulated rotation time of the developing roller 23 from the accumulated rotation time counter 512 of the data measuring unit 51.

[0116] Also, in step S61 shown in FIG. 8A, the recovery condition determination unit 502 refers to the correction parameter table 56D and obtains a correction parameter related to the rotation drive time of the agitation member drive unit 25 based on the cumulative rotation time of the developing roller 23 obtained in step S4.

[0117] For example, if the value of the temporary parameter acquired in step S60 is T2 and the cumulative rotation time of the developing roller 23 is 15 minutes, the value of the correction parameter acquired in step S61 is 2.0, and the rotation drive time of the agitation member drive unit 25 determined in step S62 is the value obtained by multiplying T2 by 2.0.

[0118] Also, in step S71 shown in FIG. 8B, the recovery condition determination unit 502 refers to the correction parameter table 56E and obtains a correction parameter related to the degree of adjustment of the development bias based on the cumulative rotation time of the development roller 23 obtained in step S4.

[0119] For example, if the value of the temporary parameter acquired in step S70 is V1 and the cumulative rotation time of the developing roller 23 is 15 minutes, the value of the correction parameter acquired in step S71 is 0, and therefore the adjustment voltage value is 0.

[0120] Also, in step S82 shown in FIG. 8C, the recovery condition determination unit 502 refers to the correction parameter table 56F and obtains a correction parameter related to the toner discharge amount (value of the number of pages discharged) based on the cumulative rotation time of the developing roller 23 obtained in step S4.

[0121] For example, if the value of the temporary parameter acquired in step S80 is valid and the cumulative rotation time of the developing roller 23 is 15 minutes, the value of the correction parameter acquired in step S82 is 0, and therefore the number of pages of solid discharge is 0.

[0122] Also, for example, if the value of the temporary parameter acquired in step S80 is valid and the cumulative rotation time of the developing roller 23 is 30 minutes, the value of the correction parameter acquired in step S82 is 1, and therefore the number of pages to be discharged is 1.

[0123] In the image forming apparatus 1 of the second embodiment, the recovery conditions for executing each recovery operation of the developing device 10 are determined taking into consideration not only the ambient environment of the developing device 10 and the time the image forming apparatus 1 has been left unused, but also the accumulated rotation time of the developing roller 23, which indicates the state of the developing device 10 before being left unused. This makes it possible to execute the recovery operation of the developing device 10 under conditions suitable for the state of the developing device 10 when the image forming apparatus 1 is restored from a stopped state, and ultimately makes it possible to accurately reduce toner fogging when the image forming apparatus 1 has been left unused for a long period of time.

[0124] The provisional parameter tables 55D to 55F and the correction parameter tables 56D to 56F described above are merely examples of data structures, and what is essential is that the provisional parameters obtained based on the ambient environment of the developing device 10 and the time it has been left unused can be appropriately corrected based on the cumulative rotation time of the developing roller 23.

[0125] (Embodiment 3) Hereinafter, only the differences between the third embodiment of the present invention and the first embodiment will be described.

[0126] FIG. 11 is a block diagram showing the control unit 5 in the third embodiment.

[0127] In the third embodiment, the data measurement unit 51 of the control unit 5 includes the printing rate calculation unit 511 described in the first embodiment and the accumulated rotation time counting unit 512 described in the second embodiment (see FIG. 11).

[0128] In the third embodiment, the correction parameter table group 56 includes the correction parameter tables 56A to 56C described in the first embodiment and the correction parameter tables 56D to 56F described in the second embodiment.

[0129] The control unit 5 in the third embodiment executes the recovery operation of the developing device 10 in the same procedure as in the first embodiment. The basic procedure is the same as that explained and illustrated in the first embodiment, but the following differences are noted.

[0130] First, in step S4 shown in FIG. 7, the processing unit 50 acquires the average printing rate from the printing rate calculation unit 511 of the data measurement unit 51, and acquires the accumulated rotation time of the developing roller 23 from the accumulated rotation time counter unit 512.

[0131] 8A, the restoration condition determination unit 502 references the correction parameter table 56A and acquires a correction parameter (hereinafter, for convenience of explanation, referred to as "correction parameter (A)") related to the rotation drive time of the agitation member drive unit 25 based on the average printing rate acquired in step S4. Furthermore, the restoration condition determination unit 502 references the correction parameter table 56D and acquires a correction parameter (hereinafter, for convenience of explanation, referred to as "correction parameter (D)") related to the rotation drive time of the agitation member drive unit 25 based on the cumulative rotation time of the developing roller 23 acquired in step S4.

[0132] In step S62, the return condition determination unit 502 determines the rotation drive time of the agitation member drive unit 25 by multiplying the provisional parameters acquired in step S60 by the correction parameters (A) and (D).

[0133] For example, if the value of the temporary parameter acquired in step S60 is T2 and the average printing rate is 8.5%, the value of the correction parameter (A) acquired in step S61 is 1.2. Similarly, if the cumulative rotation time of the developing roller 23 is 15 minutes, the value of the correction parameter (D) acquired in step S61 is 2.0. Therefore, the rotation drive time of the agitation member drive unit 25 determined in step S62 is the value obtained by multiplying T2 by (1.2 * 2.0 = 2.4).

[0134] 8B, the restoration condition determination unit 502 references the correction parameter table 56B to obtain a correction parameter (hereinafter, for convenience of explanation, referred to as "correction parameter (B)") relating to the adjustment degree of the developing bias based on the average printing rate obtained in step S4. Furthermore, the restoration condition determination unit 502 references the correction parameter table 56E to obtain a correction parameter (hereinafter, for convenience of explanation, referred to as "correction parameter (E)") relating to the adjustment degree of the developing bias based on the accumulated rotation time of the developing roller 23 obtained in step S4.

[0135] In step S72, the return condition determination unit 502 compares the absolute value of the temporary parameter acquired in step S70 with the absolute value of the correction parameter (B) and the absolute value of the correction parameter (E). If the absolute value of the temporary parameter acquired in step S70 is greater than the absolute value of the correction parameter (B) and greater than the absolute value of the correction parameter (E), the return condition determination unit 502 sets the value of the correction parameter (B) or the correction parameter (E), whichever has the smaller absolute value, as the return condition (step S73). On the other hand, if the absolute value of the temporary parameter acquired in step S70 is smaller than the absolute value of the correction parameter (B) and smaller than the absolute value of the correction parameter (E), the return condition determination unit 502 sets the value of the temporary parameter acquired in step S70 as the return condition (step S74).

[0136] To summarize steps S72 to S74 in the third embodiment, the restoration condition determination unit 502 compares the adjustment degree of the development bias when the provisional parameters are adopted, the adjustment degree of the development bias when the correction parameter (B) is adopted, and the adjustment degree of the development bias when the correction parameter (E) is adopted, and sets the value that gives the smallest adjustment degree of the development bias among the provisional parameters, the correction parameter (B), and the correction parameter (E) as the restoration condition. This makes it possible to adjust the development bias just right.

[0137] For example, if the value of the temporary parameter acquired in step S70 is V1 and the average printing rate is 8.5%, the value of the correction parameter (B) acquired in step S71 is 0. Similarly, if the cumulative rotation time of the developing roller 23 is 60 minutes, the value of the correction parameter (E) acquired in step S71 is V2. Therefore, the adjustment voltage value is 0.

[0138] 8C, the restoration condition determination unit 502 references the correction parameter table 56C to obtain a correction parameter related to the amount of toner discharge (hereinafter, for convenience of explanation, referred to as "correction parameter (C)") based on the average printing rate obtained in step S4. Furthermore, the restoration condition determination unit 502 references the correction parameter table 56F to obtain a correction parameter related to the amount of toner discharge (hereinafter, for convenience of explanation, referred to as "correction parameter (F)") based on the cumulative rotation time of the developing roller 23 obtained in step S4.

[0139] In step S83, the return condition determination unit 502 determines whether the value of the correction parameter (C) and the value of the correction parameter (F) are both greater than 0. If the value of the correction parameter (C) and the value of the correction parameter (F) are both greater than 0, the return condition determination unit 502 sets the smaller value of the correction parameter (C) or the correction parameter (F) as the return condition (step S84). On the other hand, if at least one of the value of the correction parameter (C) and the value of the correction parameter (F) is 0, the return condition determination unit 502 sets the return condition to 0 (step S85).

[0140] To summarize steps S83 to S85 in the third embodiment, when forced toner discharge is enabled, the restoration condition determination unit 502 sets the smaller value of the correction parameter (C) or the correction parameter (F) as the number of pages for solid discharge. This allows the developing device 10 to discharge toner neither too much nor too little.

[0141] For example, if the value of the temporary parameter acquired in step S80 is Yes and the average printing rate is 6.5%, the value of the correction parameter (C) acquired in step S82 is 0. Similarly, if the cumulative rotation time of the developing roller 23 is 40 minutes, the value of the correction parameter (F) acquired in step S82 is 1. Therefore, the number of solid discharge pages is 0.

[0142] Also, for example, if the value of the temporary parameter acquired in step S80 is Yes and the average printing rate is 8.5%, the value of the correction parameter (C) acquired in step S82 is 1. Similarly, if the cumulative rotation time of the developing roller 23 is 60 minutes, the value of the correction parameter (F) acquired in step S82 is 2. Therefore, the number of solid discharge pages is 1.

[0143] In the image forming apparatus 1 of the third embodiment, the recovery conditions for executing each recovery operation of the developing device 10 are determined by taking into consideration not only the surrounding environment of the developing device 10 and the time the image forming apparatus 1 has been left unused, but also the print rate indicating the state of the image forming apparatus 1 before being left unused and the cumulative rotation time of the developing roller 23 indicating the state of the developing device 10 before being left unused. This makes it possible to execute the recovery operation of the developing device 10 under conditions suited to the state of the image forming apparatus 1 and the state of the developing device 10 when the image forming apparatus 1 is restored from a stopped state, and ultimately makes it possible to accurately reduce toner fogging when the image forming apparatus 1 is left unused for a long period of time.

[0144] As described above, the present invention is applicable to any of the cases where the recovery operation of the developing device 10 is the "agitation operation," the "bias adjustment operation," and the "forced toner discharge operation."

[0145] Furthermore, the values ​​in the provisional parameter tables 55A to 55C and the correction parameter tables 56A to 56F in each of the above embodiments are merely examples, and may be set in advance as described above, or may be calculated each time based on predetermined conditions.

[0146] Furthermore, the processing procedures of the control unit 5 in each of the above embodiments are merely examples, and the order of the processing shown in the flowcharts may be changed within the scope of the gist of the present invention.

[0147] The above-described embodiments and examples are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments and examples, but should be defined based on the claims. Furthermore, all modifications within the meaning and scope of the claims are included. [Explanation of symbols]

[0148] 1. Image forming device 10 Developing device 13 Photosensitive drum 21 Developer tank 22a, 22b stirring members 23 Developing roller 25 Agitator drive unit 3 Bias power supply 4 Environmental Sensors 5. Control section 50 Processing section 500 Return operation switching unit 501 Environmental Zone Judgment Unit 502 Return condition determination unit 51 Data Measurement Section 510 Idle time measurement section 511 Print rate calculation section 512 Accumulative rotation time counter 52 Storage section 521 Environmental Zone Table 53 Input section 54 Output section 55 Provisional Parameter Tables 55A~55F Provisional Parameter Table 56 Correction parameter tables 56A~56F Correction parameter table P Image Station

Claims

1. a developing device having a rotatable developer carrier that carries a developer on its surface and that develops the electrostatic latent image on the surface of the image carrier; a control unit that controls the developing device, The control unit a surrounding environment acquisition unit for acquiring the surrounding environment of the developing device; an idle time counting unit that counts the idle time of the image forming apparatus; a printing rate calculation unit for calculating a printing rate by the image forming apparatus; a recovery unit that performs a recovery operation to recover the developing device when the image forming apparatus recovers from a stopped state; an accumulated rotation time measuring means for measuring an accumulated rotation time, which is a rotational driving time of the developer carrier from the last stopped state of the developing device to the last restored state; a return condition determination means for determining a return condition for executing the return operation; a storage means for storing a provisional parameter relating to the recovery condition in association with the surrounding environment and the standing time; a bias power supply that applies a development bias to the developer carrier; The return condition determination means acquiring the provisional parameters from the storage means based on the ambient environment acquired by the ambient environment acquisition means and the unused time measured by the unused time measuring means, and correcting the acquired provisional parameters based on the print rate calculated by the print rate calculation means and the accumulated rotation time acquired by the accumulated rotation time measuring means, thereby determining the restoration condition; the restoring unit performs, as the restoring operation, a bias adjusting operation of adjusting the developing bias from the bias power supply so as to reduce a potential difference between the developer carrier and the image carrier; The recovery condition is the degree of adjustment of the developing bias. An image forming apparatus comprising:

2. a developing device having a rotatable developer carrier that carries a developer on its surface and that develops the electrostatic latent image on the surface of the image carrier; a control unit that controls the developing device, The control unit a surrounding environment acquisition unit for acquiring the surrounding environment of the developing device; an idle time counting unit for counting the idle time of the image forming apparatus; a recovery unit that performs a recovery operation to recover the developing device when the image forming apparatus recovers from a stopped state; an accumulated rotation time measuring means for measuring an accumulated rotation time, which is a rotational driving time of the developer carrier from the last stopped state of the developing device to the last restored state; a return condition determination means for determining a return condition for executing the return operation; a storage means for storing a provisional parameter relating to the recovery condition in association with the surrounding environment and the standing time; a bias power supply that applies a development bias to the developer carrier; a correction parameter storage means for storing a correction parameter for correcting the provisional parameter in association with the cumulative rotation time, The return condition determination means acquires the provisional parameters from the storage means based on the surrounding environment acquired by the surrounding environment acquisition means and the standing time measured by the standing time measuring means, acquires the correction parameters from the correction parameter storage means based on the accumulated rotation time acquired by the accumulated rotation time measuring means, and determines the return condition by multiplying the acquired provisional parameters by the acquired correction parameters or correcting the acquired provisional parameters with the acquired correction parameters; the restoring unit performs, as the restoring operation, a bias adjusting operation of adjusting the developing bias from the bias power supply so as to reduce a potential difference between the developer carrier and the image carrier; The recovery condition is the degree of adjustment of the developing bias. An image forming apparatus comprising:

Images