Image forming device

Abstract

This prevents water vapor inside the device from condensing on the photosensitive drum, thereby reducing the negative impact on print quality. [Solution] The image forming device 1 has a process cartridge 67 that can be attached to the main body housing 3, an exposure unit that exposes the photosensitive drum 61 to form an electrostatic latent image, a fixing unit 8 that has a heater 81A and fixes the developer image to a sheet, and a control unit 100 that controls the process cartridge 67, exposure unit, and fixing unit 8 and performs printing, and the control unit 100 executes count value acquisition control that acquires a count value C that changes depending on the number of sheets printed by fixing the developer image to a sheet by the fixing unit 8, and preparatory rotation control that rotates the photosensitive drum 61 and developing roller 71 without forming an electrostatic latent image on the photosensitive drum 61 when the process cartridge 67 is attached to the main body housing 3, and switches between executing the preparatory rotation control for a first period or a second period that is longer than the first period based on the count value C.

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus in which a process cartridge having a photosensitive drum is mounted in a main body housing. [Background technology]

[0002] Conventionally, as described in Patent Document 1, for example, some image recording devices are provided with an exhaust fan to exhaust water vapor, which is generated inside the device when paper containing moisture is thermally fixed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-57647 Summary of the Invention [Problem to be solved by the invention]

[0004] In so-called laser printers such as the image recording device described in Patent Document 1, the cartridge having the photosensitive drum may be replaced after printing on multiple sheets of paper and leaving water vapor trapped inside. If the newly installed cartridge is stored at a temperature lower than the temperature inside the image recording device, for example, at room temperature, the water vapor inside the image recording device may condense on the photosensitive drum after installation, which can have a negative impact on print quality.

[0005] An object of the present invention is to provide an image forming apparatus that can prevent water vapor inside the apparatus from condensing on a photosensitive drum and can prevent adverse effects on print quality. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, an image forming apparatus of the present invention includes a process cartridge mountable to a main body housing, the process cartridge having a main body housing, a photosensitive drum, and a developing roller that contacts the photosensitive drum to supply developer, an exposure unit that exposes the photosensitive drum to light to form an electrostatic latent image, a fixing unit that has a heater and fixes the developer image to a sheet, and a control unit that controls the process cartridge, the exposure unit, and the fixing unit to perform printing. The control unit performs count value acquisition control that acquires a count value that changes depending on the number of sheets printed by fixing the developer image to a sheet by the fixing unit, and preparatory rotation control that rotates the photosensitive drum and the developing roller without forming an electrostatic latent image on the photosensitive drum when the process cartridge is mounted to the main body housing, and switches between performing the preparatory rotation control for a first period and a second period longer than the first period based on the count value.

[0007] In the image forming apparatus of the present invention, when a process cartridge is attached to the main body housing, the control unit performs preparatory rotation control, which rotates the photosensitive drum and the developing roller without forming an electrostatic latent image on the photosensitive drum. Meanwhile, the control unit also performs count value acquisition control, which acquires a count value that changes depending on the number of printed sheets by fixing the developer image to the sheet using the fixing unit. Therefore, when a large number of printed sheets is produced and there is a lot of water vapor inside the main body housing, the count value becomes relatively large. When the process cartridge is installed, the control unit switches between executing preparatory rotation control for a first period or a second period longer than the first period based on the count value. This makes it possible to execute preparatory rotation control for a second period longer than the normal first period when there is a risk of condensation forming on the photosensitive drum due to a large amount of water vapor. By performing preparatory rotation control for such a relatively long period, the photosensitive drum can be warmed and its temperature increased, thereby suppressing condensation. As a result, the adverse effects of condensation on printing can be suppressed.

[0008] In addition, in the count value acquisition control, the control unit may increase the count value according to the number of sheets printed, and when the heater is stopped, may decrease the count value every time a first predetermined period has elapsed.

[0009] When the heater of the fixing unit is stopped, the temperature inside the housing drops and the amount of water vapor decreases. In response to this, in the present invention, in a configuration in which the count value is increased according to the number of sheets printed, while the heater is stopped, the control unit decreases the count value every first predetermined period to change the conditions for determining whether condensation has occurred, thereby enabling appropriate control.

[0010] Furthermore, when the count value reaches a predetermined upper limit, the control unit may not change the count value even when printing is performed.

[0011] When the control unit increases the count value in accordance with the number of printed sheets as described above, if the count value becomes too large, even if the heater is stopped, it can take longer than necessary for the count value to fall below the threshold value, which can be a problem. In the present invention, the control unit sets an upper limit on the count value, preventing the count value from becoming too large even when printing is performed, thereby avoiding the above problem.

[0012] In addition, the control unit may control the heater to set the fixing unit to a standby temperature lower than the fixing temperature during a period from the end of printing until a second predetermined period has elapsed, and may not increase or decrease the count value when the fixing unit is controlled to be at the standby temperature.

[0013] When the fixing unit is at a standby temperature that is lower than the normal fixing temperature, there is little change in the temperature inside the housing. In response to this, in the present invention, when the fixing unit is at the standby temperature, the control unit does not change the counter value until the second predetermined period has elapsed after printing is completed, and does not change the conditions for determining whether condensation has occurred, thereby enabling appropriate control.

[0014] In addition, in the count value acquisition control, the control unit may make the amount of change in the count value when printing is performed at a first conveying speed larger than the amount of change in the count value when fixing is performed at a second conveying speed that is slower than the first conveying speed.

[0015] When the transport speed during printing is low, the amount of heat generated and the amount of water vapor generated are relatively small. In response to this, in the present invention, the control unit increases the amount of change in the count value during high-speed transport compared to low-speed transport, thereby making it possible to adjust the count value appropriately.

[0016] Furthermore, the image forming apparatus may further have a fixing temperature sensor that detects the temperature of the fixing unit, and the control unit may set a start value for starting the change in the count value when printing is performed, depending on the temperature detected by the fixing temperature sensor when the count value is initialized.

[0017] In the present invention, by providing a fixing temperature sensor that detects the temperature of the fixing unit, the starting value of the count value that changes as described above can be set based on the temperature inside the main body housing obtained from the fixing temperature sensor, and appropriate control can be performed using that starting value. [Effects of the Invention]

[0018] According to the present invention, it is possible to prevent water vapor inside the device from condensing on the photosensitive drum, thereby suppressing adverse effects on print quality. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is an external view of an image forming apparatus according to a first embodiment of the present invention. [Figure 2] 1 is a cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. [Figure 3] FIG. 2 is a horizontal cross-sectional view showing the structure of the duct portion. [Figure 4] FIG. 2 is an explanatory diagram showing the relationship between a motor, a transmission, and a control unit for driving each member of the image forming apparatus. [Figure 5] 10 is a flowchart showing a process relating to preparatory rotation control executed by a control unit. [Figure 6] 10 is a flowchart illustrating a process executed by a control unit to extend or shorten an execution period of count value acquisition control. [Figure 7] 10 is a flowchart illustrating a process executed by a control unit to extend or shorten an execution period of power saving mode control of the fixing unit. [Figure 8] 10 is a table showing the correlation between the initial fixing temperature of the fixing unit and the start value of the count value. DETAILED DESCRIPTION OF THE INVENTION

[0020] <Image forming device overview> An embodiment of the present invention will be described with reference to the drawings. In the following description of each figure, directions will be described based on the direction of a user when using the image forming apparatus. That is, in FIG. 1, the right side of the page is the "front side," the left side of the page is the "rear side," the back side of the page is the "right side," and the front side of the page is the "left side." The up-down direction of the page is the "up-down direction."

[0021] <Main body> 1 and 2, the main body housing 3 of the image forming apparatus 1 covers the image forming unit 5 (described in detail later) and the main frame 7. The main body housing 3 has a front cover 3A, a rear cover 3B, a side cover 3C, and a top cover 3D.

[0022] The front cover 3A, rear cover 3B, side cover 3C and top cover 3D are made of resin such as PS (polystyrene) or ABS (acrylonitrile butadiene styrene).

[0023] The front cover 3A is swingably attached to the main frame 7 and forms the outer wall surface on the front side of the image forming apparatus 1. The front cover 3A can be opened and closed by swinging forward. When the front cover 3A is open, the front cover 3A functions as part of a paper feed tray on which sheets to be transported to the image forming unit 5 are placed.

[0024] The rear cover 3B is assembled and fixed to the main frame 7 or the rear frame 9, and forms the rear outer wall surface of the image forming apparatus 1. The side cover 3C is assembled and fixed to the main frame 7. The side cover 3C forms the outer wall surface by connecting the front cover 3A and the rear cover 3B, and covers the main frame 7, etc.

[0025] The top cover 3D is assembled and fixed to the main frame 7, and constitutes the upper outer wall of the image forming apparatus 1. A discharge tray 3E on which sheets on which image formation has been completed are placed is provided on the front side of the top cover 3D.

[0026] <Image forming section> The image forming unit 5 forms an image on a sheet such as paper. As shown in FIG. 2, the image forming unit 5 is an electrophotographic unit having a process cartridge 67, an exposure unit 4, a fixing unit 8, etc. The process cartridge 67 has a photosensitive drum 61, a charger 62, a transfer roller 63, a developing roller 71, a supply roller 72, a container 74 that contains developer, and an agitator 75 that rotates within the container 74, and is configured to be detachable from the main body casing 3.

[0027] That is, the surface of the rotationally driven photosensitive drum 61 is uniformly charged by the charger 62 and exposed to laser light from the exposure unit 4, thereby forming an electrostatic latent image based on image data on the photosensitive drum 61. The agitator 75 rotates in the container 74, agitating the developer in the container 74 and transporting it toward the developing roller 71. The supply roller 72 rotates in contact with the developing roller 71, thereby supplying the developer discharged from the container 74 by the agitator 75 to the developing roller 71. The developing roller 71 carries the developer on its surface as it rotates. The developer carried on the developing roller 71 is then supplied to the photosensitive drum 61, thereby visualizing the electrostatic latent image and forming a developer image on the photosensitive drum 61. The supplied sheet is then transported between the photosensitive drum 61 and the transfer roller 63, whereby the developer image on the photosensitive drum 61 is transferred to the sheet.

[0028] The process cartridge 67 may be structured as two separate cartridges: a drum cartridge including the photosensitive drum 61, the charger 62, the transfer roller 63, etc., and a developer cartridge including the developing roller 71, the supply roller 72, the storage section 74, the agitator 75, etc. In this case, the drum cartridge and the developer cartridge may be configured to be detachably attached to the main body casing 3 in an integrated state.

[0029] The fixing unit 8 heats the developer transferred onto the sheet to fix the developer onto the sheet. Specifically, the fixing unit 8 has a heating unit 81, a pressure unit 82, and the like.

[0030] The heating unit 81 is disposed on one side of the conveying path Lo for the sheet discharged from the process cartridge 67, and heats the developer. The heating unit 81 is a cylindrical roller, and is heated by a heater 81A. The pressure unit 82 is disposed on the other side of the conveying path Lo, and applies pressure to the sheet by sandwiching it between itself and the heating unit 81. Note that "one side of the conveying path Lo" corresponds to the inner side of the conveying path Lo in the image forming apparatus 1, and "the other side of the conveying path Lo" corresponds to the outer side of the conveying path Lo in the image forming apparatus 1.

[0031] The fixing unit 8 further includes a fixing temperature sensor 81 B for acquiring the temperature of the heating unit 81 .

[0032] <Main frame, rear frame, connecting frame> The main frame 7 supports each device that constitutes the image forming unit 5. The outside of the main frame 7 is covered with a side cover 3C. The rear frame 9 is located outside the transport path Lo, and also functions as a guide portion that guides the transport of the sheet transported along the transport path Lo. The outside of the rear frame 9 is covered with a rear cover 3B.

[0033] The outside of the main frame 7 or the rear frame 9 refers to the side of the main frame 7 or the rear frame 9 opposite the image forming unit 5. The main frame 7 and the rear frame 9 are made of resin such as ABS (acrylonitrile butadiene styrene).

[0034] The connecting frame 11 is disposed on the front side and supports from below the exposure unit 4. The connecting frame 11 is made of metal such as SPCC (cold rolled steel plate).

[0035] <Duct section> In this embodiment, a duct section 15 is provided on the outer wall surface of the main body housing 3, i.e., on the rear cover 3B, as a structure for ventilating the inside of the image forming apparatus 1. As shown in Fig. 3, the duct section 15 is a pipe section through which air flows that protrudes rearward from the rear cover 3B and extends along the rear cover 3B, and is in communication with the space inside the main body housing 3. That is, the duct section 15 is in communication with the space inside the main body housing 3 on the pressurizing section 82 side with respect to the conveying path Lo (see Fig. 2). The duct section 15 extends horizontally across the entire width of the rear cover 3B.

[0036] 3, duct portion 15 communicates at one widthwise end with space A between main frame 7 and side cover 3C, and in the region from one widthwise end to the other widthwise end with the space inside main body housing 3 so as to directly face rear frame 9. In this example, duct portion 15 is integrally molded with rear cover 3B.

[0037] 3, the rear frame 9 is provided with at least one communication passage 9A that connects the duct portion 15 side of the rear cover 3B to the space B in which the fixing unit 8 is disposed. In other words, the duct portion 15 communicates with the space B via the communication passage 9A.

[0038] The heating unit 81 of the fixing unit 8 has a cylindrical roller extending in the width direction. Therefore, in this example, multiple communication paths 9A are provided along the width direction. In other words, the duct unit 15 communicates with the space B over a range corresponding to the range from one end of the roller to the other end in the longitudinal direction.

[0039] <External communication port> 3, an external communication port 15A is provided at one end of the duct portion 15 in the extension direction, i.e., on the space A side (see also FIGS. 1 and 2). The space inside the duct portion 15 communicates with the outside of the main body housing 3 via the external communication port 15A.

[0040] The external communication port 15A is provided at a corner where two mutually perpendicular outer wall surfaces of the main body housing 3 intersect, i.e., at a corner 3F where the side cover 3C and the rear cover 3B are connected. The other end of the duct portion 15 in the extension direction is closed.

[0041] The opening direction D1 of the external communication port 15A is parallel to the horizontal direction and intersects with the extension direction D2 of the duct portion 15 so that the angle θ1 formed with the extension direction D2 is an obtuse angle. The opening direction D1 of the external communication port 15A is the main direction of air flowing through the external communication port 15A. Specifically, the opening direction D1 coincides with a direction perpendicular to an imaginary plane including the outer edge of the external communication port 15A.

[0042] <Axial flow fan and louver> An axial fan 17, whose axis direction is parallel to the opening direction D1, is disposed in the external communication port 15A. The axial fan 17 generates an airflow that draws in air from the space A and the duct portion 15 and expels it to the outside. The axial fan 17 is a fan (see JIS B 0132 No. 1012, etc.) through which air passes along the rotation axis.

[0043] The external communication port 15A is configured like an armor window by being provided with at least one strip-shaped louver 15B. Note that the air flowing out from the external communication port 15A is discharged downward by the louver 15B, but the "main flow direction" means the "main flow direction" when the louver 15B is not provided.

[0044] <Main parts of the embodiment> The main feature of this embodiment is the control of extending or shortening the execution duration of preparatory rotation control (described in detail later). That is, in a so-called laser printer such as image forming apparatus 1, the process cartridge 67 may be replaced after printing multiple sheets and water vapor has accumulated inside. If the newly installed process cartridge 67 is stored at a temperature lower than the temperature inside the image forming apparatus 1, for example, at room temperature, the water vapor inside the image forming apparatus 1 may condense on the photosensitive drum 61 after installation, which may adversely affect print quality.

[0045] In this example, as described above, an axial fan 17 is provided in exhaust duct 15 to exhaust air from space A. However, there are cases where exhaust by axial fan 17 is effective only in a part of the water vapor generation area, or where the capacity of axial fan 17 is relatively insufficient, and in such cases, condensation is particularly likely to occur. Also, depending on the image forming apparatus 1, an exhaust fan such as axial fan 17 may not be provided.

[0046] Therefore, in this embodiment, as a countermeasure against the adverse effects of water vapor, the preparatory rotation control is executed for a longer period than usual to suppress condensation. The details of this will be explained below in order.

[0047] <Preparatory rotation control> First, the preparatory rotation control will be described. Fig. 4 shows the relationship between the motor, transmission, and control unit for driving each member of the image forming apparatus 1. In Fig. 4, the image forming apparatus 1 of this embodiment has a motor M, a drive train GM, a transmission 9, and a control unit 100 provided within the main body housing 3.

[0048] The motor M is a drive source for supplying drive force to the photosensitive drum 61, the developing roller 71, the supply roller 72, the agitator 75, etc., and is connected to the photosensitive drum 61 via a drive train GM. The motor M is also connected to the developing roller 71, etc. via a transmission 9.

[0049] The drive train GM is a drive train equipped with multiple gears for transmitting the driving force of the motor M to the photosensitive drum 61, and is connected to the motor M and the photosensitive drum 61. In other words, the photosensitive drum 61 is connected to the motor M at a fixed gear ratio.

[0050] The transmission 9 transmits the driving force of the motor M to the developing roller 71, and can switch the peripheral speed ratio of the developing roller 71 to the photosensitive drum 61 between a first peripheral speed ratio less than 1 and a second peripheral speed ratio greater than or equal to 1. Specifically, the developing roller 71, the supply roller 72, and the agitator 75 are connected via predetermined gears and configured to rotate simultaneously at a predetermined gear ratio. The driving force of the motor M is input via the transmission 9 to rotate the developing roller 71, etc., so that the peripheral speed of the developing roller 71, specifically the peripheral speed ratio to the photosensitive drum 61, can be switched by the transmission 9.

[0051] The control unit 100 includes a CPU, RAM, ROM, input / output circuits, etc., and has the function of controlling the motor M and the transmission 9. The control unit 100 also controls the process cartridge, exposure unit, and fixing unit 8 by known methods to perform printing. In detail, the control unit 100 also has the function of applying a voltage (bias) to the developing roller 71, etc., and the function of controlling the exposure unit 4, the heating unit 81, and the pressure unit 82 of the fixing unit 8, etc. In particular, the control unit 100 adjusts the fixing unit 8 to a target temperature by controlling the energization of the heater 81A based on the detection result of the fixing temperature sensor 81B.

[0052] When a process cartridge is attached to the main body housing 3, the control unit 100 is capable of executing preparatory rotation control, which rotates the photosensitive drum 61 and the developing roller 71 without forming an electrostatic latent image on the photosensitive drum 61, and image formation control, which forms an electrostatic latent image on the photosensitive drum 61. The photosensitive drum 61 and the developing roller 71 rotate so that their circumferential surfaces move in the same direction at the contact portion, but in the preparatory rotation control, the control unit 100 controls the motor M and the transmission 9 by a known method, so that the circumferential speed of the developing roller 71 is faster than the circumferential speed of the photosensitive drum 61.

[0053] <Details of control by the control unit> An example of the process executed by the control unit 100 to avoid the adverse effects of water vapor described above will be described with reference to the flowcharts of Figures 5, 6, and 7. The processes shown in Figures 5, 6, and 7 are performed simultaneously in parallel by the control unit 100 using a well-known method similar to the "multitasking" often performed in a computer OS, for example.

[0054] <Preparatory rotation control> FIG. 5 is a flowchart showing the contents of the preparatory rotation control.

[0055] First, in S200, it is determined whether or not there is a history of installation and removal of the process cartridge 67. Specifically, it is determined whether or not the front cover 3A has been opened or closed, which is performed when the process cartridge 67 is installed or replaced. If the front cover 3A has not been opened or closed, the determination is No, and the process proceeds to S230, which will be described later.

[0056] In S210, it is determined whether the count value C is equal to or greater than a predetermined threshold value. That is, in this embodiment, as will be described in S45 below, the count value C, which is counted up by the control unit 100 each time printing on a sheet is completed, is used as a determination criterion for determining whether the execution duration T can be extended or shortened. The threshold value is, for example, 100. If the count value C is less than the threshold value, a "No" determination is made, and the process proceeds to S230. In S230, the execution duration of the preparatory rotation control described above is set to a first period. The first period is, for example, 6 to 7 seconds.

[0057] If the count value C is equal to or greater than the threshold, a Yes determination is made in S210, and the process proceeds to S220. In S220, the duration of the preparatory rotation control is set to a second period, which is longer than the first period. The second period is, for example, one minute. Thereafter, the process proceeds to S63.

[0058] As described above, control unit 100 switches between executing the preparatory rotation control for a first period or a second period longer than the first period based on count value C. When S220 or S230 is completed, control unit 100 transitions to a standby state in which it controls heater 81A so that heating unit 81 reaches a predetermined standby temperature, and ends this flow.

[0059] <Count value acquisition control> 6 is a flowchart showing the contents of the count value acquisition control that extends or shortens the execution duration T of the preparatory rotation control. As will be described in detail later, this count value acquisition control is a control for acquiring a count value C that changes depending on the number of sheets printed by fixing a developer image onto a sheet by the fixing device 8.

[0060] First, in S3, it is determined whether the count value at this time is "0000." This count value C is initialized to "0000" when the image forming apparatus 1 is turned on from a power-off state, or when it enters a deep sleep state in power-saving mode (see S340, etc., described later). In S3, it is determined whether the count value C is "0000."

[0061] If the count value C is not "0000", a "No" determination is made, and the process proceeds to S15, which will be described later. If the count value C is "0000", a "Yes" determination is made, and the process proceeds to S6. In S6, the control unit 100 determines a start value for starting the change of the count value C, depending on the initial fixing temperature of the fixing unit 8 detected by the fixing temperature sensor 81B. In this case, the control unit 100 determines the start value of the count value C, for example, using the table shown in FIG. 8.

[0062] In this example of FIG. 8, if the initial fixing temperature is less than 50°C, the starting value of the count value C is set to 0. If the initial fixing temperature is equal to or greater than 50°C and less than 70°C, the starting value of the count value C is set to 10. That is, the count value C starts at 10 for control purposes, and the count increase / decrease process described below starts from this value. Similarly, if the initial fixing temperature is equal to or greater than 70°C and less than 100°C, the starting value of the count value C is set to 20. If the initial fixing temperature is equal to or greater than 100°C and less than 130°C, the starting value of the count value C is set to 30. If the initial fixing temperature is equal to or greater than 130°C and less than 150°C, the starting value of the count value C is set to 50. If the initial fixing temperature is 150°C or greater, the starting value of the count value C is set to 80.

[0063] When S6 is finished, the process moves to S15, which will be described later.

[0064] In S15, it is determined whether the heater 81A of the heating unit 81 is operating and not controlled to be stopped at this time. If the heater 81A is operating, a Yes determination is made, and the process proceeds to S23, which will be described later. If the heater 81A is stopped, a No determination is made, and the process proceeds to S18.

[0065] In S18, it is determined whether a predetermined period, which is an example of a first predetermined period, has elapsed since the determination in S15. The predetermined period is, for example, several seconds to 10 seconds. If the predetermined period has not elapsed, the determination is No and the process returns to S15. If the predetermined period has elapsed, the determination is Yes and the process proceeds to S21.

[0066] In S21, r (where r>0) is subtracted from the count value C. Then, the process proceeds to S23.

[0067] In S23, it is determined whether the heating unit 81 is being controlled to reach the standby temperature. In this embodiment, the control unit 100 controls the heater 81A to a predetermined standby temperature from the time printing ends until the first time period has elapsed (see S320, described later). If the heating unit 81 is at the standby temperature, the determination is Yes, and the process proceeds to S25. In S25, the count value C is not added or subtracted, and the value is maintained as is, and the process proceeds to S27, described later.

[0068] If the heating unit 81 has not reached the standby temperature in S23, a No determination is made, and the process proceeds to S27. In S27, it is determined whether image formation, i.e., printing, has started. Printing refers to fixing a developer image on a sheet. If printing has not started, a No determination is made, and the process returns to the aforementioned S3. If printing has started, a Yes determination is made, and the process proceeds to S28.

[0069] In S28, the heating unit 81 is controlled to a predetermined fixing temperature. Then, the process proceeds to S29. The fixing temperature is a temperature for fixing the developer image on the sheet.

[0070] In S29, after printing is started in S27, it is determined whether printing of one page has been completed. If printing of one page has been completed, the determination is Yes, and the process proceeds to S30.

[0071] In S30, during printing, i.e., image formation, it is determined whether the sheet was transported in the fixing device 8 at a high speed, which is an example of a first transport speed, or at a low speed, which is an example of a second transport speed. That is, in the image forming apparatus 1 of this embodiment, the transport speed is switchable, and the transport modes include a high-speed mode in which the sheet is transported at the high speed, and a low-speed mode in which the sheet is transported at a speed slower than the high speed, for example, about half the speed. In the low-speed mode, the control unit 100 performs control using a known method so that the fixing temperature is lower than in the high-speed mode. In S30, it is determined whether image formation was performed by transport in this high-speed mode.

[0072] If image formation is performed in the low-speed mode, S30 is judged as No, and the process proceeds to S31. In S31, q (where q>0) is added to the count value C as an example of the amount of change in the count value, and the process proceeds to S36 described below.

[0073] If image formation is performed in the high-speed mode instead of the low-speed mode, a Yes determination is made in S30, and the process proceeds to S32. In S32, p, which is an example of a value greater than q, is added to the count value C as an example of the amount of change in the count value, and the process proceeds to S36.

[0074] In S36, it is determined whether the count value C exceeds a predetermined upper limit value Cmax. If it is equal to or less than Cmax, the determination is No, and the process proceeds to S41, which will be described later. If it exceeds Cmax, the determination is Yes, and the process proceeds to S39.

[0075] In S39, the value of the count value C is set to Cmax, and then the process proceeds to S41.

[0076] In S41, it is determined whether or not all printing that started in S27 has finished. If printing has not finished, the determination is No and the process returns to the above-mentioned S28. If printing has finished, the determination is Yes and this flow ends.

[0077] <Power saving mode control> 7 is a flowchart showing the power-saving mode. The power-saving mode control is a control for reducing power consumption when printing is not in progress. This flow is executed when printing is completed, i.e., when the determination in S41 above is Yes.

[0078] First, in S300, it is determined whether a predetermined first time has elapsed since printing ended. The first time is, for example, one minute and is an example of a second predetermined period. If the first time has not elapsed, S300 is determined as No and the process proceeds to S320, where the control unit 100 controls the heater 81A so that the heating unit 81 reaches a standby temperature lower than the fixing temperature. After S320, this flow ends. On the other hand, if the first time has elapsed, S300 is determined as Yes and the process proceeds to S310, where the control unit 100 stops the heater 81A. Note that this stopped state of the heater 81A is a so-called sleep state, in which the heater 81A is stopped but the control unit 100 is operating. After S310, the process proceeds to S330.

[0079] In S330, it is determined whether a second time has elapsed since the heater 81A was stopped in S310. The second time is, for example, one minute. If the second time has not elapsed, S330 is determined as No and this flow ends. On the other hand, if the second time has elapsed, S330 is determined as Yes and the flow proceeds to S340, where the control unit 100 stops the heater 81A and enters a so-called deep sleep state in which part of the control unit 100 is also stopped. After S340, the flow proceeds to S350.

[0080] In S350, the count value C is cleared to 0000. Then, this flow ends.

[0081] <Effects of the embodiment> As described above, in the image forming apparatus 1 of this embodiment, when the process cartridge 67 is attached to the main body housing 3, the control unit 100 performs preparatory rotation control to rotate the photosensitive drum 61 and the developing roller 71 without forming an electrostatic latent image on the photosensitive drum 61. Meanwhile, the control unit 100 also performs count value acquisition control to acquire a count value C, which changes depending on the number of printed sheets by fixing a developer image to a sheet using the fixing unit. Therefore, when a large number of printed sheets is printed and there is a lot of water vapor inside the main body housing 3, the count value C becomes relatively large. When the process cartridge 67 is installed, the control unit 100 switches between executing the preparatory rotation control for a first period or a second period longer than the first period based on the count C value. This allows the preparatory rotation control to be executed for a second period longer than the normal first period if there is a risk of condensation on the photosensitive drum 61 due to a large amount of water vapor. By performing the preparatory rotation control for such a relatively long period, the photosensitive drum 61 can be warmed and its temperature increased, thereby suppressing condensation. As a result, the adverse effects of condensation on printing can be suppressed.

[0082] Furthermore, while heater 81A of fixing unit 8 is stopped, the temperature inside main body housing 3 drops, and the amount of water vapor decreases. In response to this, in this embodiment, in a configuration in which count value C is increased according to the number of printed sheets, while heater 81A of fixing unit 8 is stopped, control unit 100 decreases count value C in S21 every time a first predetermined period elapses, thereby changing the conditions for determining whether condensation has occurred, thereby enabling appropriate control.

[0083] Furthermore, when the control unit 100 increases the count value C in accordance with the number of printed sheets as described above, if the count value C becomes too large, it may take longer than necessary for the count value to fall below the threshold, even if the heater 81A of the fixing unit 8 is stopped. In this embodiment, the control unit 100 sets an upper limit on the count value C in S39, thereby preventing the count value C from becoming too large and avoiding the above-mentioned problem.

[0084] Furthermore, when the fixing unit 8 is at a standby temperature that is lower than the normal fixing temperature, there is little change in the temperature inside the main body housing 3. In response to this, in this embodiment, when the fixing unit 8 is at the standby temperature, the control unit 100 does not change the counter value in S25 until the second predetermined period has elapsed after printing is completed, and does not change the conditions for determining whether condensation has occurred, thereby enabling appropriate control.

[0085] Furthermore, when the transport speed during printing is low, the amount of heat generated and the amount of water vapor generated are relatively small. In response to this, in this embodiment, the control unit 100 makes the amount of change in the count value C during transport in high-speed mode larger than during transport in low-speed mode in S31 and S32, thereby making it possible to make the count value C appropriate.

[0086] Furthermore, in this embodiment, particularly when a fixing temperature sensor that detects the temperature of the fixing unit 8 is provided, the starting value of the count value C that changes as described above with reference to Figure 8 can be set based on the temperature inside the main body housing 3 obtained from the fixing temperature sensor, and appropriate control can be performed using that starting value.

[0087] <Modification> The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the spirit and technical concept of the present invention. Such modifications will be described below in order.

[0088] (1) Variations in cartridge installation judgment Note that the determination of whether the process cartridge 67 is attached in S42 above may be performed by other methods besides the above. That is, as indicated by the dashed line in Fig. 2, the process cartridge 67 may have a memory 201 (IC) that can be read by the reading unit 202 when the process cartridge 67 is attached, and the control unit 100 may acquire the reading result by the reading unit 202. Then, if the control unit 100 determines based on the reading result that the stored contents of the memory 201 have changed, the control unit 100 determines that the process cartridge 67 has been attached, i.e., that it has been replaced with a different process cartridge.

[0089] At that time, if the control unit 100 determines that the installed process cartridge 67 is the same as before, the time for the preparatory rotation control described above is not extended. This is because there may be cases where the process cartridge 67 is temporarily removed and then re-installed due to jam clearance, etc. In this case, the temperature of the photosensitive drum 61 has risen and the possibility of condensation occurring is low, so extension is not necessary, thereby shortening the time until printing.

[0090] (2) Other Furthermore, although the above has been explained using the example of a direct transfer method in which a developer image from a photosensitive member is transferred to a sheet during image formation processing, an intermediate transfer method may also be used in which a developer image from a photosensitive member is transferred to a transfer belt, and the developer image on the transfer belt is then transferred to a sheet that is transported separately.

[0091] In the above embodiment, the count value C is configured to be incremented each time printing is performed from the value at the start of processing (see S31 and S32 in Figure 6), but it may also be configured to set the value at the start of processing to a predetermined positive value and decrement it each time printing is performed.

[0092] Furthermore, the flowcharts shown in Figures 5, 6, and 7 do not limit the present invention to the procedures shown in the above flows, and steps may be added or deleted or the order may be changed within the scope that does not deviate from the spirit and technical idea of ​​the invention.

[0093] In addition to the above, the methods according to the above embodiments and modifications may be used in appropriate combination.

[0094] Although not specifically illustrated, the present invention can be implemented with various modifications within the scope of the invention. [Explanation of symbols]

[0095] 1. Image forming device 3 Main unit housing 4 Exposure section 5 Image forming unit 8 Fixing unit 61 Photosensitive drum 62 Charger 63 Transfer roller 67 Process cartridge 71 Developing roller 100 control section C Count value T Execution duration X sensor detection temperature

Claims

1. A main body housing; a process cartridge that is mountable to the main body casing and that has a photosensitive drum and a developing roller that contacts the photosensitive drum to supply a developer; an exposure unit that exposes the photosensitive drum to light to form an electrostatic latent image; a fixing device having a heater and fixing the developer image on the sheet; a control unit for controlling the process cartridge, the exposure unit, and the fixing unit to perform printing; and The control unit a count value acquisition control for acquiring a count value that changes depending on the number of sheets printed by fixing a developer image on the sheet by the fixing device; a preparatory rotation control for rotating the photosensitive drum and the developing roller without forming an electrostatic latent image on the photosensitive drum when the process cartridge is attached to the main body housing; Run The image forming apparatus is characterized in that, based on the count value, switching is performed between executing the preparatory rotation control for a first period and executing the preparatory rotation control for a second period longer than the first period.

2. The control unit In the count value acquisition control, the count value is increased in accordance with the number of sheets printed, and when the heater is stopped, the count value is decreased every time a first predetermined period elapses.

2. The image forming apparatus according to claim 1, wherein:

3. The control unit When the count value reaches a predetermined upper limit, the count value is not changed even when printing is performed.

3. The image forming apparatus according to claim 2.

4. The control unit controlling the heater so that the fixing unit has a standby temperature lower than a fixing temperature during a period from the end of printing until a second predetermined period has elapsed; When the fixing unit is controlled to reach the standby temperature, the count value is not increased or decreased.

2. The image forming apparatus according to claim 1, wherein:

5. The control unit In the count value acquisition control, a change amount of the count value when printing is performed at a first transport speed is made larger than a change amount of the count value when printing is performed at a second transport speed slower than the first transport speed.

2. The image forming apparatus according to claim 1, wherein:

6. a fixing temperature sensor for detecting the temperature of the fixing unit; The control unit When the count value is initialized, a start value is set for starting the change of the count value when printing is performed in accordance with the temperature detected by the fixing temperature sensor.

2. The image forming apparatus according to claim 1, wherein:

Images