JP4849105B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine or a combination machine combining two or more of them, and more particularly to a fixing technique for forming a toner image on both sides of a recording sheet.

In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of them, which normally forms a toner image, an electrostatic latent image is usually formed on an image carrier such as a photosensitive member in an exposure process. Then, the electrostatic latent image is developed by a development process to form a visible toner image, and the visible toner image is transferred to a recording medium such as a recording paper by a transfer process, or is temporarily transferred by an intermediate transfer belt or the like. The toner image that is primarily transferred to the body, secondarily transferred from the intermediate transfer body to the recording medium, and thus transferred to the recording medium in the fixing process may be referred to as a recording medium (hereinafter, “ recording paper ” ). ) Can be fixed.

  In the fixing process, it is necessary to fix an unfixed toner image formed on a recording paper to make a permanent image, and a heat fixing method is widely used as the fixing method. In the heat fixing method, generally, a heating roller on the side where an unfixed toner image on the recording paper comes into contact and a pressure roller that conveys the recording paper with the heating roller interposed therebetween are provided, and the heating roller is a predetermined roller. By controlling this temperature, a fixed toner image is formed on the recording paper that has passed between these rollers.

  In electrophotographic image forming apparatuses, it is also widely used to form a fixing toner image on both the front and back sides of a recording sheet in order to save the recording sheet. In the fixing device in the image forming apparatus including the case where image formation is performed on both sides of such recording paper, it is necessary to prevent so-called offset in which toner adheres to the heating roller. This offset includes electrostatic offset in which the unfixed toner is transferred to the heating roller when the heating roller is charged to the opposite polarity to the toner, or the toner is excessively heated by the heating roller to reduce the viscosity, and the unfixed toner is transferred to the heating roller. Low temperature offset that causes heat transfer to the heating roller due to insufficient high temperature offset or insufficient heating by the heating roller and insufficient heat transfer to the interface between the toner and paper and insufficient adhesion between the toner and paper Etc. In an image forming apparatus that forms an image on both sides of a recording sheet, many techniques for suppressing such an offset have been developed.

  For example, Japanese Patent Application Laid-Open No. 8-171304 discloses a method for forming a fixed toner image on both sides of a recording sheet in which offset is prevented without adding special equipment for preventing offset on the heating roller side in contact with the toner image. A suitable fusing device is disclosed. This fixing device forms a latent image on an image forming body, develops the latent image, forms a toner image on the image forming body, transfers the toner image onto a recording sheet, and fixes it. In a fixing device for fixing an unfixed toner image transferred onto a recording paper in an image forming apparatus that forms a fixing toner image on both sides of the recording paper by repeating the paper twice, on the side where the unfixed toner image on the recording paper contacts A heating roller provided, a pressure roller that conveys the recording paper between the heating rollers, a first heating unit that heats the heating roller, a second heating unit that heats the pressure roller, A first surface on which an unfixed toner image is transferred and fixed on a recording paper on which no fixed toner image is formed (hereinafter, the surface of a certain recording paper is the first surface and the back surface of the same recording paper is the second surface) ) Heating in the fixing process The first heating unit is controlled so that the roller is maintained at a predetermined first temperature, and the second heating unit is controlled so that the pressure roller is maintained at a predetermined second temperature. In the fixing process of the second surface, in which the unfixed toner image is transferred and fixed to the other surface of the recording paper on which the fixed toner image is formed, the heating roller is heated to a third temperature higher than the first temperature. Roller temperature control means for controlling the first heating means so as to be held and for controlling the second heating means so that the pressure roller is held at a fourth temperature lower than the second temperature. It is characterized by having.

  According to this fixing device, in the fixing process of the first surface, the heating roller and the pressure roller are held at the first temperature and the second temperature, respectively, as in the case of forming an image only on one surface of the recording paper, for example. In this way, a toner image that is completely fixed in a normal state is formed on one side of the recording paper. Further, in the fixing process on the second surface, the heating roller is held at a third temperature higher than the first temperature on the first surface, so that a fixed toner image is already formed on one surface and is substantially thick. Even if the recording paper becomes defective, the unfixed toner image on the recording paper is completely fixed. In the fixing process of the second surface, the pressure roller is held at a fourth temperature lower than the second temperature of the first surface. Therefore, in the fixing process of the first surface in contact with the pressure roller. The second surface can be fixed without melting the formed fixing toner image again, and an offset in which the molten toner adheres to the pressure roller is prevented. Therefore, it is not necessary to provide the same offset countermeasure equipment on the pressure roller side as on the heating roller side. Further, since the fixing toner image in contact with the pressure roller in the fixing process on the second surface is prevented from being melted again, image disturbance is also prevented.

JP-A-8-171304

  When an image is formed on the second side after the image is formed on the first side of the recording paper, the recording paper is reduced in moisture in the fixing process on the first side and is formed on the first side. Since the sheet passing resistance is high due to the printed image, the heating roller and the pressure roller are easily charged. When the heating roller or pressure roller is charged, electrostatic offset is likely to occur. As a countermeasure, in the fixing process on the second surface, the temperature of the heating roller is set higher than in the fixing process on the first surface, and unfixed toner to be transferred to the heating roller is melted at a higher temperature. Also in the fixing device of Patent Document 1, the heating roller in the fixing process on the second surface is held at a third temperature that is higher than the first temperature on the first surface.

  However, as in the fixing device disclosed in Patent Document 1, if the temperature of the heating roller in the fixing process on the second surface is simply increased above the temperature in the fixing process on the first surface, a high temperature offset may occur. That is, if the temperature of the heating roller on the second surface is raised above the temperature of the heating roller on the first surface, high temperature offset may occur even if electrostatic offset can be suppressed. Further, since the electrostatic offset is caused by static electricity, it is easily affected by the use environment (temperature and humidity) of the image forming apparatus. For this reason, even if the technique disclosed in Patent Document 1 is applied as a countermeasure against electrostatic offset, there is a possibility that the electrostatic offset cannot be suppressed or a high temperature offset may be generated depending on the use environment.

Therefore, the present invention forms a first-surface toner image corresponding to the image to be formed on the first surface of the recording medium, transfers the toner image to the first surface of the recording medium, fixes it with a fixing device, and then fixes the second surface of the recording medium. An image forming apparatus capable of forming a second-surface toner image corresponding to an image to be formed on the second surface, transferring the image on the second surface of the recording medium with both sides reversed, and fixing the image on a fixing device. An object of the present invention is to provide an image forming apparatus capable of satisfactorily fixing the second surface toner image to the second surface of the recording medium while appropriately suppressing electrostatic offset and high temperature offset.

In order to solve the above-described problems, the present invention provides the following image forming apparatus.
An image to be formed on the second surface of the recording medium is formed on the first surface of the recording medium by forming a first surface toner image corresponding to the image to be formed on the first surface, transferring the toner image onto the first surface of the recording medium, fixing the image on the first surface. An image forming apparatus capable of forming a second-surface toner image corresponding to the image on the second surface of a recording medium having both sides reversed by a duplex unit and fixing the image on a second surface of the recording medium,
A detection unit for detecting the temperature and humidity of the use environment of the image forming apparatus;
A controller that controls the temperature of the roller that contacts the unfixed toner in the fixing device,
The control unit is an image forming apparatus that determines a temperature of the roller when the second surface toner image is transferred to the second surface based on the temperature and humidity of the use environment detected by the detection unit.

Here, the roller temperature when transferring the second surface toner image to the second surface of the recording medium is further set to a temperature that suppresses electrostatic offset and high temperature offset of the second surface toner image to the roller. is there. According to this image forming apparatus, the temperature and humidity of the environment in which the image forming apparatus is used are detected, and the temperature of the roller when the second surface toner image is transferred to the second surface is determined based on the temperature and humidity. Is done. As described above, when the temperature of the roller when transferring to the second surface is determined based on the temperature and humidity of the use environment of the image forming apparatus, the temperature is affected by the high temperature offset that is easily affected by the temperature of the use environment and the humidity of the use environment. The easy electrostatic offset can be appropriately suppressed.

Further, the control unit, based on the temperature and humidity of the detected usage environment by the detecting unit, the temperature of the roller when transferring the second surface toner images on the second surface of the recording medium, wherein to be higher than the temperature of the roller when transferring the first surface toner image on the first surface of the recording medium, configured to determine that.

In this way, when the second surface toner image is transferred to the second surface based on the temperature and humidity of the use environment, the temperature of the roller when the first surface toner image is transferred to the first surface is determined. It is determined to be higher than the temperature of the roller. If the temperature of the roller when transferring the second surface toner image to the second surface is determined to be higher than the temperature of the roller when transferring the first surface toner image to the first surface, electrostatic offset is likely to occur. In this case, the unfixed toner transferred to the roller can be melted at a higher temperature, and electrostatic offset can be suppressed. At this time, since the temperature of the roller when the second surface toner image is transferred to the second surface is determined based on the temperature of the use environment, it is possible to suppress the occurrence of the high temperature offset due to the roller temperature becoming too high. it can. As a result, high temperature offset and electrostatic offset can be appropriately suppressed.

Further, when the temperature of the usage environment detected by the detection unit is higher than a predetermined reference temperature, the control unit determines the temperature of the roller when the second surface toner image is transferred to the second surface. The temperature can be determined to be lower than when the temperature is equal to or lower than the reference temperature.

  In this way, since the high temperature offset is likely to occur when the temperature of the use environment is high, the temperature of the roller when transferring to the second surface is less likely to cause the high temperature offset, and the use environment in which the roller temperature can be set high. It is determined to be lower than when the temperature is low. For this reason, the high temperature offset when the usage environment is high can be satisfactorily suppressed. Here, the “predetermined reference temperature” can be determined in advance by experiments or the like in consideration of high temperature offset suppression.

Further, when the humidity of the usage environment detected by the detection unit is lower than a predetermined reference humidity, the control unit determines the temperature of the roller when the second surface toner image is transferred to the second surface. The humidity can be determined to be higher than when the humidity is equal to or higher than the reference humidity.

  In this way, electrostatic offset is likely to occur when the humidity of the usage environment is low, so the roller temperature when transferring to the second surface is less likely to generate electrostatic offset and the roller temperature can be set low. Decide to be higher than when the humidity of the environment is high. For this reason, the electrostatic offset when the usage environment is low can be satisfactorily suppressed. Here, the “predetermined reference humidity” can be determined in advance by experiments or the like in consideration of electrostatic offset suppression.

As described above, according to the present invention, the first surface toner image corresponding to the image to be formed on the first surface of the recording medium is formed, transferred to the first surface of the recording medium, fixed by the fixing device, and recorded. A second-surface toner image corresponding to an image to be formed on the second surface of the medium is formed, transferred to the second surface of the recording medium with both sides reversed by a duplex unit, and fixed by a fixing device. It is possible to provide an image forming apparatus that can satisfactorily fix the toner image on the second surface of the recording medium while appropriately suppressing electrostatic offset and high temperature offset.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

The image forming apparatus according to the embodiment of the present invention will be described below.
[Entire configuration of image forming apparatus]
FIG. 1 shows an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 in FIG. 1 is a so-called four-cycle color image forming apparatus. In the following description, the recording medium is described as recording paper, and the image forming apparatus 10 is described as a full-color copying machine. The image forming apparatus 10 in FIG. 1 can form images on both sides of a recording sheet. The present invention is not limited to the tandem full-color image forming apparatus or the monochrome image forming apparatus, and can form an image as shown below as long as it forms images on both sides of the recording paper. A fixing device in which the temperature of the heating roller in the fixing process on the second surface is higher than that in the fixing process on the first surface can be applied according to the use environment of the forming apparatus.

  The image forming apparatus 10 includes a drum-type photosensitive member 1 (hereinafter referred to as a photosensitive member 1), and a charger 2, a developing device 4, an intermediate transfer belt 6, and a cleaning device 5 are arranged around the drum-type photosensitive member 1 in this order. An image exposure device 3 that performs image exposure on the photosensitive member 1 from between the charger 2 and the developing device 4 is provided, and a recording paper supply unit 9 is provided below the image exposure device 3.

  The photoreceptor 1 is rotationally driven in the clockwise direction in the figure by a photoreceptor drive motor (not shown). A photosensitive member charging voltage is applied to the charger 2 at a predetermined timing from a charging power source (not shown) whose output is variable.

  The developing device 4 has a developing device rack 40 mounted with a black developing device 4K, a cyan developing device 4C, a magenta developing device 4M, and a yellow developing device 4Y. The developing device rack 40 can be driven to rotate counterclockwise in the figure by a driving unit (not shown) including a stepping motor. The developing devices are mounted on the developing device rack 40 in the order of the developing devices 4K, 4C, 4M, and 4Y in the rack rotation direction at equal central angle intervals of 90 degrees.

  Black toner cartridge KC can be replaced with black developer unit 4K, cyan toner cartridge CC with cyan developer unit 4C, magenta toner cartridge MC with magenta developer unit 4M, and yellow toner cartridge YC with yellow developer unit 4Y. It is mounted on. Each developing device is provided with a developing roller (toner carrier roller) 41 for developing the electrostatic latent image on the photoreceptor 1. Each developing roller 41 has an elastic surface layer.

  In addition to the developing roller 41, each developing device includes a toner supply roller that supplies toner to the roller, a toner regulating blade that regulates the layer thickness of the toner supplied from the toner supply roller on the developing roller 41, and the like. Each developing device can reversely develop the electrostatic latent image on the photoreceptor 1 using negatively chargeable toner.

  Each developing device can be arranged at a developing position where the developing device 41 develops the electrostatic latent image on the photoreceptor 1 by rotating the developing device rack 40. The developing roller 41 disposed at the developing position faces the surface of the photosensitive member 1, and a developing bias can be applied from a developing bias power source (not shown) whose output is variable. Further, the developing roller 41 arranged at the developing position can be driven to rotate counterclockwise in the drawing by a developing roller driving motor (not shown). Further, a toner supply bias can be applied to the toner supply roller from a power supply (not shown), and a regulation bias can be applied to the toner regulation blade.

  The intermediate transfer belt 6 is connected to a driving roller 61, a driven counter roller 62 opposite to the driving roller 61, a primary transfer roller 63 disposed opposite to the photosensitive member 1, and a primary transfer roller 63, so that the intermediate transfer belt 6 is attached to the photosensitive member 1. It is wound around a roller group composed of rollers 64 to be brought into contact with each other.

  A primary transfer voltage can be applied to the primary transfer roller 63 from a primary transfer power supply (not shown). The intermediate transfer belt 6 can be rotated counterclockwise by driving the drive roller 61 counterclockwise in the figure by a transfer belt drive motor (not shown).

  A secondary transfer roller 7 is disposed on a portion of the intermediate transfer belt 6 that is wound around the driving roller 61. The secondary transfer roller 7 is brought into contact with and separated from the intermediate transfer belt 6 at a predetermined timing. A secondary transfer voltage can be applied to the secondary transfer roller 7 from a secondary transfer power supply (not shown).

  A cleaning device 65 that removes and cleans paper dust (including secondary transfer residual toner) from a portion of the intermediate transfer belt 6 that is wound around the driven counter roller 62 is disposed. The cleaning device 65 is provided with a cleaning blade for removing paper dust and the like from the intermediate transfer belt 6.

  A fixing device 8 is provided above the secondary transfer roller 7, and a recording paper discharge roller pair R3 and a recording paper discharge tray T are sequentially provided downstream thereof. As will be described in detail later, the fixing device 8 includes a heating roller 81 on the side where the unfixed toner image on the recording paper S contacts, and a pressure roller 82 that conveys the recording paper S between the heating roller 81 and the heating roller 81. Is provided.

  Below the secondary transfer roller 7, a timing roller pair R2 and a guide roller pair Rl for guiding the recording paper S from the recording paper storage unit 9 to the timing roller pair R2 are arranged.

  Further, the image forming apparatus 10 includes a recording paper conveyance path 100 for forming a double-sided image. In the recording paper transport path 100, recording paper transport roller pairs 101, 102, and 103 are arranged. This recording paper conveyance path 100 is used when images are formed on both sides of the recording paper S, and extends behind the recording paper conveyance path from the timing roller pair R2 to the fixing device 8 through the secondary transfer region. The exit continues from the timing roller pair R2 to the recording sheet conveyance path from the pair of timing rollers R2 to the fixing device 8.

  According to the image forming apparatus 10 described above, a toner image on the recording paper S is used using one or more of 4K, 4C, 4M, and 4Y developing devices under the instruction of a control unit (not shown in FIG. 1). Can be formed. An example in which a full color image is formed using four developing devices will be described below.

  First, the developing device rack 40 is rotated by a rack driving unit (not shown) so that the yellow developing device 4Y is disposed at a developing position where the developing roller 41 contacts the photoconductor 1, and the photoconductor 1 is rotated in the clockwise direction in the drawing. The intermediate transfer belt 5 is also rotated. At this stage, the secondary transfer roller 7 is separated from the intermediate transfer belt 6.

  The surface of the rotating photosensitive member 1 is uniformly charged to a predetermined potential by a charger 2 to which a charging voltage is applied from a charging power source, and the charged region is turned from the image exposure device 3 through folding reflection mirrors 31 and 32 to yellow. Image exposure for an image is performed to form a yellow electrostatic latent image, and the latent image is developed by the developing device 4Y to form a yellow toner image. The yellow toner image is primarily transferred onto the intermediate transfer belt 6 by a primary transfer roller 63 to which a primary transfer voltage is applied.

  Further, in the same manner as in the case of forming the yellow toner image, the magenta developing device 4M is arranged at the development position to form a magenta toner image on the photosensitive member 1, and this is transferred onto the intermediate transfer belt 6, and then cyan. The developing unit 4C is arranged at the developing position to form a cyan toner image on the photosensitive member 1, and this is transferred onto the intermediate transfer belt 6, and then the black developing unit 4K is arranged at the developing position and placed on the photosensitive member 1. A black toner image is formed and transferred onto the intermediate transfer belt 6. The formation of each color toner image on the photosensitive member 1 and the primary transfer onto the intermediate transfer belt 6 are performed at the timing when these toner images are superimposed and transferred onto the intermediate transfer belt 6.

  On the other hand, when the recording paper S is pulled out from the recording paper supply unit 9 by the supply roller 91 and supplied to the timing roller pair R2, and the leading edge of the recording paper is detected by a timing sensor (not shown) on the exit side of the timing roller pair R2. Then, the timing roller pair R2 is stopped, and the recording paper S is kept waiting there.

Then, before the multiple toner image on the intermediate transfer belt 6 reaches the secondary transfer roller 7 by the rotation of the intermediate transfer belt 6, the roller 7 is brought into contact with the intermediate transfer belt 6 so that the multiple toner image enters the secondary transfer region. the recording sheet S in the arrival timing is also fed in Thailand timing rollers R2 to the secondary transfer region.

  Thus, the multiple toner image is secondarily transferred onto the recording paper S. The recording paper S to which the multiple toner images have been transferred is fixed on the toner image by the fixing device 8 and discharged to the discharge tray T by the recording paper discharge roller pair R3. Thus, the recording paper S on which a full color image is formed can be obtained.

  The primary transfer residual toner or the like on the photoreceptor 1 is removed and cleaned by the cleaning device 5, and the paper dust or the like (including the secondary transfer residual toner) on the intermediate transfer belt 6 is removed and cleaned by the cleaning device 65.

  In this image forming apparatus 10, when the double-side mode is selected, as described above, the recording paper S that is fixed on one side (first side) and comes out of the fixing device 8 is transferred to the recording paper discharge roller pair R3. Is once conveyed toward the paper discharge tray T, and after the entire recording paper S is discharged from the fixing device 8, the recording paper discharge roller pair R3 is driven in reverse rotation under the instruction of the control unit. Thus, the recording paper S is carried into the recording paper conveyance path 100 and is guided to the timing roller pair R2 by the recording paper conveyance roller pair 101, 102, 103 there. At this time, the recording paper S is guided to the timing roller pair R2 such that the second surface of the recording paper S faces the intermediate transfer belt 6.

  On the other hand, in the same manner as described above, the second surface toner image is formed on the intermediate transfer belt 6 by one or more of the Y, M, C, and K image forming portions, and the timing roller pair R2 has the second toner image. The recording sheet S is carried between the secondary transfer roller 7 and the intermediate transfer belt 6 in synchronization with the surface toner image. Thus, the recording sheet S is transferred with the toner image of the second surface on the second surface thereof, and subsequently passed through the fixing device 8 to fix the toner image. It is discharged to the tray T by the pair R3.

In the image forming apparatus 10 according to the present embodiment, when the duplex mode is selected, the temperature of the heating roller 81 when the toner image is transferred to the second surface of the recording paper is used as the image forming apparatus 10. A fixing device 8 that changes according to the environment (temperature, humidity) and suppresses offset is provided. Hereinafter, the fixing device 8 will be described in detail.

[Configuration of Fixing Device]
FIG. 2 shows a configuration and a control block of the fixing device 8 of the image forming apparatus 10 according to the present embodiment. The control block shown in FIG. 2 shows only the part related to the control of the fixing device 8 in the duplex mode in the control block of the image forming apparatus 10.

  As shown in FIG. 2, the fixing device 8 includes a heating roller 81 on the side where the unfixed toner on the recording sheet S contacts, and a pressure roller 82 that conveys the recording sheet S between the heating roller 81 and the heating roller 81. The fixing roller pair is configured as follows.

  The heating roller 81 is a so-called hard roller in which a surface layer 81A is provided on the surface of a metal core 81B and does not have an elastic layer formed of an elastic material. Such a hard roller has a mirror image force (heating roller). It has a feature that electrostatic offset is likely to occur due to the force that strongly adheres toner to the surface. The heating roller 81 includes an electric heater 83. Electric power is supplied from the heater power supply unit 88 to the electric heater 83. Further, near the surface of the heating roller 81 and on the inlet side of the recording paper S, a temperature sensor (thermistor) that detects the surface temperature of the heating roller 81 (hereinafter sometimes simply referred to as the temperature of the heating roller 81). 84 is provided.

  The pressure roller 82 is obtained by forming, for example, an elastic layer 82C having heat resistance and releasability on the surface of a metal cored bar 82B, and a surface layer 82A is provided on the surface of the elastic layer 82C. Here, the elastic layer 82C is made of silicon rubber. The pressure roller 82 is pressed against the heating roller 81 by a pressing device including a pressing spring (not shown), whereby a pressure nip portion (fixing nip portion) is formed on the heating roller 81 and the pressure roller 82.

  The heating roller 81 can receive a driving force from a motor in the image forming apparatus 10 on which the fixing device 8 is mounted via a transmission mechanism (not shown), and can thereby rotate counterclockwise in the drawing. The pressure roller 82 can be rotated in the clockwise direction in the figure by the rotation of the heating roller 81. A recording sheet detection sensor 85 for determining completion of fixing of the recording sheet S by detecting the recording sheet S is provided on the exit side of the recording sheet S.

  The control block of the image forming apparatus 10 includes a control unit 89 that controls the entire image forming apparatus 10 and a temperature sensor that detects the temperature of the heating roller 81 connected to an input port (not shown) of the control unit 89. 84, a recording paper detection sensor 85, a temperature / humidity sensor 86 and an operation panel 87 provided on the outlet side of the recording paper S, and a heater power supply unit 88 connected to an output port (not shown) of the control unit 89. . Further, other signals are input to the control unit 89 via the input port of the control unit 89, and other signals are output from the control unit 89 via the output port of the control unit 89.

  The temperature / humidity sensor 86 detects the ambient temperature and humidity of the image forming apparatus 10, which is usage environment information of the image forming apparatus 10, and outputs the detected temperature and humidity to the control unit 89. The operation panel 87 outputs a signal indicating, for example, a copy mode (color / monochrome, duplex / single side, recording sheet size, recording sheet type, etc.) to the control unit 89. A command signal from the control unit 89 to the heater power supply unit 88 is either a power supply start signal or a power supply stop signal to the electric heater 83. When the heater power supply unit 88 receives a power supply start signal, it continues to supply power to the electric heater 83 until it receives a power supply stop signal.

  The control unit 89 includes a storage unit configured by a memory or the like, and this storage unit stores a fixing temperature table on a second surface described later. Here, the fixing temperature is defined by the temperature of the heating roller 81.

[Control flow chart of fixing device]
With reference to the flowchart shown in FIG. 3, the control structure of the image forming apparatus 10 according to the present embodiment will be described. Note that the flowchart shown in FIG. 3 shows only a subroutine program relating to temperature control of the heating roller 81 of the fixing device 8. In the following, image formation will be described as a copying operation.

  In step (hereinafter referred to as “S”) 1000, control unit 89 determines whether there is a copy request based on a signal input from operation panel 87. If it is determined that there is a copy request (YES in S1000), the process proceeds to S1010. If not (NO in S1000), the process returns to S1000 and waits until a copy request is detected. If NO in S1000, this process may be terminated.

  In step S1010, the control unit 89 starts temperature control using the fixing temperature α of the first surface (for example, the temperature of the heating roller 81 is 170 ° C.) as a target temperature. When the temperature control is started, the control unit 89 sends a power supply start signal to the electric heater 83 until the signal indicating the temperature of the heating roller 81 input from the temperature sensor 84 to the heater power supply unit 88 exceeds the temperature α. When the temperature α is exceeded, a power supply stop signal to the electric heater 83 is output, and the electric heater 83 is turned on / off. The on / off control is not executed by the control unit 89, but the heater power supply unit 88 and the temperature sensor 84 are connected, and the control unit 89 gives a target temperature to the heater power supply unit 88 and is input from the temperature sensor 84. On the basis of a signal indicating the temperature of the heating roller 81, the heater power supply unit 88 may perform on / off control of power supply to the electric heater 83. Furthermore, instead of the on / off control, for example, feedback control including PI operation may be performed.

  In S1020, control unit 89 detects the temperature of heating roller 81. In S1030, control unit 89 determines whether or not the temperature of heating roller 81 has risen to temperature α. If it is determined that the temperature of heating roller 81 has risen to temperature α (YES in S1030), the process proceeds to S1040. If not (NO in S1030), the process returns to S1020.

  In S1040, control unit 89 starts copying the first side. In S1050, control unit 89 determines whether or not fixing of the first surface has been completed. At this time, if the control unit 89 once detects the recording sheet S based on the signal from the recording sheet detection sensor 85 and then does not detect the recording sheet S, the recording sheet S passes through the fixing device 8 and the first surface. Is determined to have been completed. If it is determined that the fixing of the first surface has been completed (YES in S1050), the process proceeds to S1060. If not (NO in S1050), the process returns to S1050 and waits until it is determined that the fixing of the first surface is completed.

  In S1060, control unit 89 detects the operation mode based on the signal input from operation panel 87. In S1070, control unit 89 determines whether or not the operation mode of image forming apparatus 10 is the duplex mode. If it is determined that the operation mode is the duplex mode (YES in S1070), the process proceeds to S1080. If not (NO in S1080), the process proceeds to S1150.

  In S 1080, the control unit 89 acquires information (temperature and humidity) on the usage environment of the image forming apparatus 10 based on the signal input from the temperature / humidity sensor 86. In S1090, control unit 89 determines fixing temperature β of the second surface. At this time, the control unit 89 determines the fixing temperature of the second surface based on the acquired information (temperature and humidity) of the use environment of the image forming apparatus 10 and the fixing temperature table of the second surface stored in the storage unit. β (temperature of the heating roller 81) is determined. An example of the fixing temperature table on the second surface is shown in the following table.

  As shown in the table, N which is an environment between LL (low temperature and low humidity) environment, HH (high temperature and high humidity) environment, LL environment and HH environment, combining temperature and humidity. The fixing temperature of the second surface is set for each of the -N environments. More specifically, the fixing temperature of the first surface is 170 ° C., and the fixing temperature of the second surface is 190 ° C. under the LL environment, 180 ° C. under the NN environment, and 180 ° under the HH environment. ° C. Here, the temperature and humidity in each environment are such that the LL environment is less than 18 ° C. and the humidity is less than 40%, the NN environment is a temperature of 18 ° C. to less than 27 ° C., and the humidity is 40% to less than 75%. The H-H environment is a temperature of 27 ° C. or higher and a humidity of 75% or higher. Note that these temperature and humidity set values are examples, and the present invention is not limited to these set values.

  In the table, “◯” indicates that a problem in the fixing process has not occurred, “Δ” indicates that a problem within the allowable range occurs in the fixing process, and “X” indicates that a problem outside the allowable range occurs in the fixing process. If it is “◯” or “Δ”, it is determined that there is no problem in the fixing process. As can be seen from this table, the electrostatic offset is disadvantageous (prone to occur) in the LL environment, and is advantageous (not likely to occur) in the HH environment, and the high temperature offset is in the LL environment. It was confirmed that it tends to be advantageous (hard to occur) and disadvantageous (easy to occur) in an H-H environment.

  As shown in the table, for example, if the fixing temperature of the second surface is fixed at 180 ° C., there is no problem in the NN environment and the HH environment, but there is an electrostatic offset in the LL environment. Will occur. If the fixing temperature of the second surface is fixed at 190 ° C. so that no electrostatic offset occurs in the LL environment, high temperature offset occurs in the NN environment and the HH environment. Therefore, the fixing temperature of the second surface is determined according to the use environment (temperature and humidity) of the image forming apparatus 10.

  Further, in the LL environment, electrostatic offset does not occur if the fixing temperature of the second surface is 190 ° C. or higher. However, if the fixing temperature of the second surface is set to 200 ° C. which is 190 ° C. or higher, the temperature is high. An offset will occur. For this reason, the optimum value of the fixing temperature of the second surface in the LL environment is 190 ° C. Under the N-N environment and the H-H environment, the high-temperature offset does not occur if the fixing temperature of the second surface is 180 ° C. or less, but the fixing temperature of the second surface is 170 ° C. which is 180 ° C. or less. If set, electrostatic offset will occur. For this reason, the optimum value of the fixing temperature of the second surface in the NN environment and the HH environment is 180 ° C. Note that these fixing temperature setting values are merely examples, and the present invention is not limited to these setting values.

  In S1100, the control unit 89 determines the fixing temperature β of the second surface (for example, the temperature of the heating roller 81 is 180 ° C. (L-L environment) or 190 ° C. (N-N environment and H-H environment)). Start temperature control using as the target temperature. When the temperature control is started, the control unit 89 sends a power supply start signal to the electric heater 83 until the signal indicating the temperature of the heating roller 81 input from the temperature sensor 84 to the heater power supply unit 88 exceeds the temperature β. When the output exceeds the temperature β, a power supply stop signal to the electric heater 83 is output, and the electric heater 83 is on / off controlled.

  In S 1110, control unit 89 detects the temperature of heating roller 81. In S1120, control unit 89 determines whether or not the temperature of heating roller 81 has risen to temperature β. If it is determined that the temperature of heating roller 81 has risen to temperature β (YES in S1120), the process proceeds to S1130. If not (NO in S1120), the process returns to S1110.

  In S1130, control unit 89 starts copying the second side. In S1140, control unit 89 determines whether or not the fixing of the second surface has been completed. At this time, the control unit 89 once detects the recording sheet S based on the signal from the recording sheet detection sensor 85 and, when the recording sheet S is not detected, similarly to the processing in S1050, the recording sheet S is fixed to the fixing device 8. It is determined that the fixing of the second surface has been completed. If it is determined that fixing of the second surface has been completed (YES in S1140), the process proceeds to S1150. If not (NO in S1140), the process returns to S1140 and waits until it is determined that the fixing of the second surface is completed.

  In S1150, control unit 89 determines whether or not image forming apparatus 10 enters a standby mode based on a signal input from operation panel 87. At this time, for example, if the next request is not input from the operation panel 87 until a predetermined time elapses, the control unit 89 determines to enter the standby mode. If it is determined that the standby mode is entered (YES in S1150), the process proceeds to S1160. If not (NO in S1150), the process returns to S1000.

  In S1100, control unit 89 starts temperature control using the standby temperature (for example, the temperature of heating roller 81 is lower than the fixing temperature of the first surface) as the target temperature.

[Control operation of fixing device]
FIG. 4 showing the change over time of the surface temperature of the heating roller 81 with respect to the operation of the fixing device 8 when the duplex mode of the image forming apparatus 10 according to the present embodiment is selected based on the structure and flowchart as described above. The description will be given with reference.

  Using the operation panel of the image forming apparatus 10, the user performs an operation for requesting double-sided copying, sets the document on the document table, and presses the copy start button (YES in S1000). It is assumed that the time at this time is between time t (1) and time t (2) shown in FIG. As shown in FIG. 4, at this time, the standby mode is set, and the temperature of the heating roller 81 is lower than 170 ° C., which is the fixing temperature α of the first surface. For this reason, temperature control is started at the fixing temperature α of the first surface (S1010), electric power is supplied from the heater power supply unit 88 to the electric heater 83, and the temperature of the heating roller 81 rises. At time t (2), the temperature of the heating roller 81 rises to the fixing temperature α of the first surface (YES in S1030), so that the first surface copying operation is started (S1040).

  When recording sheet S having toner fixed on the first surface is discharged from fixing device 8 (YES in S1050), the operation mode is detected (S1060). Here, since the operation mode is the duplex mode (YES in S1070), the use environment of the image forming apparatus 10 is acquired (S1080). Based on the acquired temperature and humidity and the fixing temperature table of the second surface, which is the above-described table, the fixing temperature β of the second surface is determined (S1090). At this time, the fixing temperature β of the second surface under the LL environment is determined to be 190 ° C., and the fixing temperature β of the second surface under the NN environment and the HH environment is determined to be 180 ° C. ( (When the fixing temperature of the first surface is 170 ° C.)

  At this time, when the fixing temperature of the first surface is 170 ° C., the fixing temperature of the second surface in the LL environment is determined to be 190 ° C. Therefore, in the LL environment, the fixing temperature of the second surface is In the fixing process, neither electrostatic offset nor high temperature offset occurs. Further, since the fixing temperature of the second surface in the NN environment and the HH environment is determined to be 180 ° C., the fixing process of the second surface in the NN environment and the HH environment. No electrostatic offset or high temperature offset occurs.

  Temperature control is started at the fixing temperature β of the second surface (S1100), and power is supplied from the heater power supply unit 88 to the electric heater 83, so that the temperature of the heating roller 81 rises. At time t (3), since the temperature of the heating roller 81 rises to the fixing temperature β of the second surface (YES in S1120), the copying operation of the second surface is started (S1130).

  The recording paper S with the toner fixed on the second surface is discharged from the fixing device 8 (YES in S1140), and the recording paper with the toner fixed on the first surface and the second surface is discharged to the tray T. If the user does not input the next request from operation panel 87, image forming apparatus 10 is determined to enter the standby mode (YES in S1150), and the temperature of heating roller 81 is lowered to the standby temperature (S1160).

  As described above, in the image forming apparatus according to the present embodiment, the fixing temperature of the second surface (the temperature of the heating roller) becomes higher than the fixing temperature of the first surface in accordance with the use environment of the image forming apparatus. Change as follows. For this reason, the electrostatic offset and high temperature offset which are influenced by the use environment can be suppressed, and the image defect resulting from it can be suppressed.

  The embodiment disclosed this time is merely an example, and the present invention is not limited to the embodiment described above. The scope of the present invention is indicated by each claim in the claims after taking into account the description of the detailed description of the invention, and all modifications within the meaning and scope equivalent to the wording described therein are intended. Including.

1 is a diagram illustrating an outline of a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a control block diagram of the image forming apparatus in FIG. 1. 2 is a flowchart of fixing temperature control executed by a control unit in FIG. 1. It is a figure which shows the time change of the surface temperature of a heating roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charger 3 Image exposure apparatus 4 Developing apparatus 5, 65 Cleaning apparatus 6 Intermediate transfer belt 8 Fixing apparatus 10 Image forming apparatus 89 Control part

Claims (3)

An image to be formed on the second surface of the recording medium is formed on the first surface of the recording medium by forming a first surface toner image corresponding to the image to be formed on the first surface, transferring the toner image onto the first surface of the recording medium, fixing the image on the first surface. An image forming apparatus capable of forming a second-surface toner image corresponding to the image on the second surface of a recording medium having both sides reversed by a duplex unit and fixing the image on a second surface of the recording medium,
A detection unit for detecting the temperature and humidity of the use environment of the image forming apparatus;
A controller that controls the temperature of the roller that contacts the unfixed toner in the fixing device,
Wherein, based on the temperature and humidity of the detected usage environment by the detecting unit, the temperature of the first surface of the roller at the time of transfer to the second surface of the recording medium the second surface toner image An image forming apparatus , wherein the temperature is determined to be higher than a temperature of the roller when the toner image is transferred to the first surface of the recording medium . When the temperature of the use environment detected by the detection unit is higher than a predetermined reference temperature , the control unit determines a temperature of the roller when the second surface toner image is transferred to the second surface of the recording medium. 2. The image forming apparatus according to claim 1, wherein the temperature is determined to be lower than when the temperature of the use environment is equal to or lower than the reference temperature . When the humidity of the use environment detected by the detection unit is lower than a predetermined reference humidity , the control unit sets the temperature of the roller when the second surface toner image is transferred to the second surface of the recording medium. The image forming apparatus according to claim 1, wherein the humidity is determined so as to be higher than when the humidity of the use environment is equal to or higher than the reference humidity .

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