JP2008216932A - Fixing device, and image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for fixing a toner image on a recording material by passing the recording material through a fixing nip formed by abutting a heating member with a pressure member and capable of flexibly coping with a change in the temperature of the pressure member during a fixing operation, thereby steadily providing a satisfactory fixing characteristics. <P>SOLUTION: A heat absorbing member is disposed so as to be freely brought into contact with or separated from the surface of the pressure belt forming the fixing nip between the heat roller and the pressure belt. A fixing unit is warmed up with the heat absorption member separated (step S101 to S104). If consecutive printing is carried out thereafter such that sheets are consecutively conveyed at very short time intervals (step S105), a fixing process is performed with the heat absorption member kept separated, thereby preventing the temperature of the pressure belt from decreasing excessively. If a non-consecutive printing is carried out such that sheets are intermittently conveyed, the fixing process is performed with the heat absorption member kept in contact with the pressure belt (step S106), thereby preventing overheat of the pressure belt. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device, an image forming apparatus, and an image forming method for feeding a recording material to a fixing nip formed by contact of a heating member and a pressure member to fix a toner image on the recording material. is there.

  In an image forming apparatus that forms an image on a recording material using toner, such as a copying machine, a printer, and a facsimile machine, the toner image is permanently applied on the recording material by heating and pressurizing the recording material to which the toner image has been transferred. It has become established. A general configuration of a fixing device used for such a purpose is to form a fixing nip by bringing a heating member and a pressure member heated to a predetermined fixing temperature into contact with each other, and a recording material is formed in the fixing nip. It is to send through. In an apparatus having such a configuration, it is important to give a necessary and sufficient amount of heat to the toner and fuse it to the recording material, and the recording material is required not to be overheated. This is because if the temperature of the recording material becomes too high, the surface of the recording material is damaged by the so-called blister phenomenon, or the glossiness of the surface changes and affects the image quality.

  In order to solve such a problem, for example, in the fixing device described in Patent Document 1, the pressure belt is configured to be freely separated from and contacted with the heat fixing roll, and pressure is applied except when the fixing operation is performed. By separating the belt from the heat-fixing roll, a fixing nip is formed only when the recording material is fed to prevent the temperature of the pressure belt from rising. In the fixing device described in Patent Document 2, overheating of the lower fixing roller is prevented by bringing a heat radiation roller into contact with the lower fixing roller corresponding to the pressure member.

Japanese Patent No. 3612976 (FIG. 4) JP-A-8-179642 (FIGS. 1 and 3)

  When the temperature control is not positively performed on the pressure member, the surface temperature of the pressure member greatly varies depending on the mode of transport of the recording material. For example, when a large number of recording materials are continuously fed, the temperature of the pressure member is kept at a relatively low temperature because the recording materials are deprived of heat. On the other hand, when the recording material is intermittently fed, the temperature of the pressure member decreases while the recording material passes through the fixing nip, but the temperature rises when the recording material passes. Turn to. Then, when the next recording material reaches the fixing nip, the temperature is lowered again, so that the temperature of the pressure member greatly varies with time. In particular, in recent years, a reduction in the heat capacity of the fixing device has been demanded in order to reduce power consumption. However, the reduction in the heat capacity of the pressure member causes a greater temperature fluctuation.

  However, in the fixing device described in Patent Document 1, the state where the fixing nip is formed is maintained during the fixing operation, whereas in the fixing device described in Patent Document 2, the heat radiation roller is always in contact. In the prior art described in each patent document, the mode of the fixing operation is fixed. For this reason, the conventional technique has a problem in that it cannot cope with the temperature fluctuation of the pressure member during such a fixing operation and a good fixing characteristic cannot be obtained.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a fixing device and an image for fixing a toner image on a recording material by feeding the recording material to a fixing nip formed by contact between a heating member and a pressure member. In a forming apparatus and an image forming method, an object is to provide a technique that can flexibly cope with a temperature change of a pressure member during a fixing operation and stably obtain good fixing characteristics.

  In order to achieve the above object, the fixing device according to the present invention includes a heating member that has been heated to a predetermined fixing temperature, a pressure member that contacts the heating member to form a fixing nip, and a surface of the pressure member And a heat absorbing member that contacts the surface of the pressure member and absorbs the heat of the surface, and passes a recording material having a toner image formed on the surface to the fixing nip. Thus, as a fixing operation for fixing the toner image on the recording material, a contact fixing operation in which the recording material is passed through the fixing nip while the heat absorbing member is in contact with the pressure member; The separation fixing operation of feeding the recording material to the fixing nip in a state where the heat absorbing member is separated from the pressurizing member can be selectively performed.

  In order to achieve the above object, the image forming apparatus according to the present invention includes an image forming unit that forms a toner image and transfers the toner image to the surface of the recording material, a heating member heated to a predetermined fixing temperature, and the heating member. A pressure member that forms a fixing nip by contact, and the toner image is fixed on the recording material by passing the recording material onto which the toner image has been transferred by the image forming means to the fixing nip; A fixing unit that performs a fixing operation to be performed, and the fixing unit is configured to be able to come into contact with and separate from the surface of the pressure member, and a heat absorbing member that contacts the surface of the pressure member and absorbs heat of the surface. The fixing operation includes a contact fixing operation in which the recording material is fed to the fixing nip in a state where the heat absorbing member is in contact with the pressure member, and the heat absorption from the pressure member. State where the members are separated It is characterized by performing the spaced fixing operation for Tsuoku the recording material to the fixing nip selectively.

  Further, in order to achieve the above object, the image forming method according to the present invention applies an image forming operation in which a toner image is formed and transferred onto the surface of a recording material, and a pressure member is applied to a heating member heated to a predetermined fixing temperature. A fixing operation for fixing the toner image on the recording material by passing the recording material on which the toner image has been transferred to the fixing nip that is in contact with the recording material; A contact fixing operation for feeding the recording material to the fixing nip in a state where a heat absorbing member that absorbs heat of the surface is in contact with the surface of the member, and a state in which the heat absorbing member is separated from the pressure member A separation fixing operation for feeding the recording material to the fixing nip is selectively performed.

  In the invention configured as described above, the fixing operation in a state where the heat absorbing member is brought into contact with the pressure member and the fixing operation in a state where the heat absorbing member is not brought into contact with the pressure member, that is, separated. Various types of fixing operations can be performed. Of these, in the contact fixing operation performed in a state where the heat absorbing member is in contact with the pressure member, the heat absorbing member takes the heat of the pressure member, thereby suppressing the temperature rise of the pressure member or reducing the temperature. It is done. Further, in the separation fixing operation performed in a state in which the heat absorbing member is separated from the pressure member, the fixing failure of the toner due to insufficient heat amount can be prevented by not lowering the temperature of the pressure member more than necessary. In the present invention, by making these two types of fixing operations executable, it is possible to flexibly cope with temperature fluctuations of the pressure member in the fixing operation and stably obtain good fixing characteristics. It has become.

  In the image forming apparatus configured as described above, for example, a temperature detection unit that detects the temperature of the pressure member surface, and the contact fixing operation and the separation fixing operation based on the detection result by the temperature detection unit Control means for selecting one of these and causing the fixing means to execute may be further provided. By doing so, it becomes possible to select an appropriate fixing operation in accordance with the actually measured surface temperature of the pressure member.

  More specifically, for example, the control unit selects the contact fixing operation if the surface temperature of the pressure member detected by the temperature detection unit is higher than a predetermined temperature, while the surface temperature is the predetermined temperature. If it is lower than the temperature, the separation fixing operation can be selected. By doing so, it is possible to prevent the temperature of the pressure member from becoming too high or too low.

  As another method, for example, the contact fixing operation and the separation fixing operation based on a time interval from when one recording material passes through the fixing nip until the next recording material reaches the fixing nip. One of the above may be selected, and a control unit that causes the fixing unit to execute may be further provided. As described above, the temperature of the pressure member varies according to the timing at which the recording material passes through the fixing nip. The mode of the fluctuation depends on the time interval from when the recording material passes through the fixing nip until the next recording material reaches the fixing nip. Therefore, the fixing operation to be executed is selected according to this time interval. By doing so, the temperature fluctuation of the pressure member can be suppressed.

  More specifically, for example, the control unit selects the contact fixing operation when the time interval is longer than a predetermined time, and selects the separation fixing operation when the time interval is shorter than the predetermined time. can do. By doing so, it is possible to prevent the temperature of the pressure member from becoming too high or too low.

  As another method, for example, a control unit that selects one of the contact fixing operation and the separation fixing operation based on the length of the recording material along the moving direction of the recording material and causes the fixing unit to execute the selected one. May be further provided. The mode of temperature fluctuation of the pressure member also depends on the length of time that the recording material passes through the fixing nip. Therefore, by selecting the fixing operation to be executed according to the length of this time or the length of the recording material related thereto, the temperature fluctuation of the pressure member can be suppressed.

  More specifically, for example, the control unit selects the contact fixing operation when the length is shorter than a predetermined length, and selects the separation fixing operation when the length is longer than the predetermined length. can do. By doing so, it is possible to prevent the temperature of the pressure member from becoming too high or too low.

  FIG. 1 is a diagram showing a configuration example of an image forming apparatus to which the present invention can be preferably applied. FIG. 2 is a diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of yellow (Y), magenta (M), cyan (C) and black (K) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory and the like, the main controller MC gives a control signal to the engine controller EC, and based on this, the engine controller EC The controller EC controls each part of the device such as the engine unit EG and the head controller HC to execute a predetermined image forming operation, and responds to an image forming command on a sheet as a recording material such as a copy sheet, a transfer sheet, a sheet, and an OHP transparent sheet. The image to be formed is formed.

  In the housing main body 3 of the image forming apparatus, an electrical component box 5 containing a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided. An image forming unit 2, a transfer belt unit 8, and a paper feed unit 7 are also disposed in the housing body 3. In FIG. 1, a secondary transfer unit 12, a fixing unit 13 and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feed unit 7 is configured to be detachable from the housing body 3. The paper feeding unit 7 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 2 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan) and 2K (for black) that form a plurality of images of different colors. In FIG. 1, since the image forming stations of the image forming unit 2 have the same configuration, only some of the image forming stations are denoted by reference numerals for convenience of illustration, and the reference numerals are omitted for other image forming stations. To do.

  Each image forming station 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. Each photosensitive drum 21 is connected to a dedicated drive motor and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction thereof. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. When the color mode is executed, the toner images formed by all the image forming stations 2Y, 2M, 2C, and 2K are superimposed on the transfer belt 81 provided in the transfer belt unit 8 to form a color image. When the monochrome mode is executed, only the image forming station 2K is operated to form a black monochrome image.

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface of the photosensitive drum 21 at the charging position, and is driven to rotate as the photosensitive drum 21 rotates. The charging roller is connected to a charging bias generator (not shown). The charging roller is supplied with the charging bias from the charging bias generator and is charged at the charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other. The surface of 21 is charged to a predetermined surface potential.

  The line head 29 includes a plurality of light emitting elements arranged in the axial direction of the photosensitive drum 21 (a direction perpendicular to the paper surface of FIG. 1), and is disposed to face the photosensitive drum 21. Then, light is emitted from these light emitting elements toward the surface of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image on the surface.

  The developing unit 25 has a developing roller 251 on which toner is carried. The charged toner is developed at a developing position where the developing roller 251 and the photosensitive drum 21 come into contact with each other by a developing bias applied to the developing roller 251 from a developing bias generator (not shown) electrically connected to the developing roller 251. Moves from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed on the surface thereof is visualized.

  The toner image made visible at the developing position is conveyed in the rotational direction D21 of the photosensitive drum 21, and then is transferred to the transfer belt 81 at a primary transfer position TR1 where the photosensitive belt 21 comes into contact with the transfer belt 81 described later in detail. Primary transcription.

  A photoreceptor cleaner 27 is provided in contact with the surface of the photoreceptor drum 21 downstream of the primary transfer position TR1 and upstream of the charging unit 23 in the rotation direction D21 of the photoreceptor drum 21. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to remove the toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and an arrow D81 illustrated in FIG. And a transfer belt 81 that is circulated in the direction (conveyance direction). Further, four transfer belt units 8 are arranged on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations 2Y, 2M, 2C, and 2K when the cartridge is mounted. Primary transfer rollers 85Y, 85M, 85C and 85K. Each of these primary transfer rollers is electrically connected to a primary transfer bias generator (not shown).

  When the color mode is executed, as shown in FIG. 1, the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations 2Y, 2M, 2C, and 2K, so that the transfer belt 81 is moved to the image forming station 2Y. The primary transfer position TR1 is formed between each photosensitive drum 21 and the transfer belt 81 by being pushed and brought into contact with the photosensitive drum 21 included in each of 2M, 2C, and 2K. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85Y or the like at an appropriate timing, the toner images formed on the surface of each photosensitive drum 21 are respectively transferred to the corresponding primary transfer positions. Transfer is performed on the surface of the transfer belt 81 in TR1. That is, in the color mode, the single color toner images of the respective colors are superimposed on the transfer belt 81 to form a color image.

  In this image forming apparatus which is a so-called tandem image forming apparatus, the primary transfer position where the toner image is primarily transferred from the photosensitive drum 21 to the transfer belt 81 is different for each image forming station. That is, the yellow image forming station 2Y, the magenta image forming station 2M, the cyan image forming station 2C, and the black image forming station 2K are arranged in this order along the moving direction D81 of the transfer belt 81.

  On the other hand, when executing the monochrome mode, among the four primary transfer rollers, the primary transfer rollers 85Y, 85M, and 85C are separated from the image forming stations 2Y, 2M, and 2C that face each other, and the primary transfer rollers corresponding to the black color are used. By bringing only 85K into contact with the image forming station 2K, only the monochrome image forming station 2K is brought into contact with the transfer belt 81. As a result, the primary transfer position TR1 is formed only between the primary transfer roller 85K and the image forming station 2K. Then, by applying a primary transfer bias to the primary transfer roller 85K from the primary transfer bias generator at an appropriate timing, a black toner image formed on the surface of the photosensitive drum 21 provided in the image forming station 2K is obtained. A black and white image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed on the downstream side of the black primary transfer roller 85K and on the upstream side of the driving roller 82. The downstream guide roller 86 is common to the primary transfer roller 85K and the black photosensitive drum 21 (K) at the primary transfer position TR1 formed by the primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station 2K. It is configured to contact the transfer belt 81 on the tangent line.

  The paper feed unit 7 includes a paper feed cassette 77 capable of stacking and holding sheet-like recording materials (hereinafter simply referred to as “sheets”), and a pickup roller 79 for feeding sheets one by one from the paper feed cassette 77. A paper feed unit is provided. The sheet fed from the sheet feeding unit by the pickup roller 79 is adjusted in sheet feeding timing by the registration roller pair 80, and then the drive roller 82 and the secondary transfer roller 121 abut along the sheet guide member 15. Paper is fed to the secondary transfer position TR2.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). Then, the sheet on which the image is secondarily transferred is guided to the fixing unit 13 by the sheet guide member 15, and the fixing unit 13 heats and pressurizes the toner transferred onto the sheet to make the toner image permanent on the sheet. To settle. The structure of the fixing unit 13 will be described in detail later. The sheet that has undergone the fixing process by the fixing unit 13 is conveyed to a paper discharge tray 4 provided on the upper surface of the housing body 3.

  The drive roller 82 circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the drive roller 82, and secondary transfer is omitted by grounding through a metal shaft. A conductive path of a secondary transfer bias supplied from the bias generation unit via the secondary transfer roller 121 is used. Thus, by providing the driving roller 82 with a rubber layer having high friction and shock absorption, image quality deterioration caused by transmission of the impact to the transfer belt 81 when the sheet enters the secondary transfer position TR2. Can be prevented.

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt 81 after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are integrally formed with the blade facing roller 83.

  In this image forming apparatus, the photoconductive drum 21, the charging unit 23, the developing unit 25, and the photoconductive cleaner 27 of each of the image forming stations 2Y, 2M, 2C, and 2K are integrated into a unit as a cartridge. The cartridge is configured to be detachable from the apparatus main body. Each cartridge is provided with a nonvolatile memory for storing information related to the cartridge. Data communication is performed between the engine controller EC and each cartridge. Thus, information about each cartridge is transmitted to the engine controller EC, and information in each memory is updated and stored. Based on these pieces of information, the usage history of each cartridge and the lifetime of consumables are managed.

  The electrical configuration of each part in this apparatus will be described in more detail with reference to FIG. In this embodiment, the main controller MC, the head controller HC, and each line head 29 are configured as separate blocks, and are connected to each other via a communication line to exchange signals with each other as described below. Yes.

  When an image formation command is given from the external device to the main controller MC, the main controller MC transmits a control signal for starting the engine unit EG to the engine controller EC. Further, the image processing unit 100 provided in the main controller MC performs predetermined signal processing on the image signal included in the image formation command, and generates image data for each toner color.

  On the other hand, upon receiving the control signal, the engine controller EC starts initialization and warm-up of each part of the engine unit EG such as the image forming stations 2Y, 2M, 2C and 2K, the transfer belt unit 8, and the fixing unit 13. When these are completed and the image forming operation can be executed, the engine controller EC outputs a synchronization signal that triggers the start of the image forming operation to the head controller HC that controls each line head 29. In addition, in communication between the engine controller EC and the head controller HC, various control parameters for controlling the line head 29 are exchanged.

  The head controller HC is provided with a head control module 400 that controls the line head 29 provided in each of the image forming stations 2Y, 2M, 2C, and 2K, and a head-side communication module 300 that manages data communication with the main controller MC. It has been. On the other hand, the main communication module 200 is also provided in the main controller MC. A request signal for requesting image data is transmitted from the head side communication module 300 to the main side communication module 200. On the other hand, image data is transmitted from the main communication module 200 to the head communication module 300 in response to the request signal.

  The head side communication module 300 gives the received image data to the head control module 400. The head control module 400 generates a lighting control signal for each toner color from the supplied image data, and applies it to each of the line heads 29 provided in the image forming stations 2Y, 2M, 2C, and 2K corresponding to each toner color. Output. In the line head 29, each light emitting element is turned on according to the lighting control signal, so that the surface of the charged photosensitive drum 21 is exposed to form an electrostatic latent image corresponding to the image data.

  FIG. 3 is a diagram showing the structure of the fixing unit in this image forming apparatus. The fixing unit 13 incorporates a heating element such as a halogen heater and has a heating roller 131 that is temperature-controlled to a predetermined fixing temperature and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. ing. More specifically, the heating roller 131 is a roller in which a resin-made surface layer 1313 having elasticity and heat resistance such as silicon rubber is provided on the surface of a metal pipe 1312 having a heater 1311 therein. The heater 1311 is, for example, a halogen heater and has a heat generation amount of about several hundred to 1000 W. The surface layer 1313 is made of a resin having elasticity and heat resistance. For example, a surface of a silicon rubber layer coated with a fluororesin such as PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) is used. Can do.

  A temperature sensor 1314 made of, for example, a thermistor for detecting the surface temperature of the heating roller 131 is in contact with the surface of the heating roller 131. The output of the temperature sensor 1314 is input to the engine controller EC. The engine controller EC controls the energization of the heater 1311 based on the output of the temperature sensor 1314, thereby changing the surface temperature of the heating roller 131 to a predetermined fixing temperature ( For example, it is adjusted to about 200 degrees Celsius. In addition to the thermistor illustrated here, for example, a sensor that detects the temperature in a non-contact manner may be used for temperature detection of the heating roller.

  The pressure unit 132 includes two rollers 1321 and 1322, a pressure belt 1323 stretched between them, and a heat absorbing roller 1324 that can freely come into contact with the surface of the pressure belt 1323. And. A fixing nip formed by the heating roller 131 and the pressure belt 1323 is formed by pressing the belt tension surface stretched by the two rollers 1321 and 1322 on the surface of the pressure belt 1323 against the peripheral surface of the heating roller 131. It is comprised so that FN can be taken widely. The sheet to which the toner image has been transferred and sent from the secondary transfer position TR2 is conveyed along the conveyance path F in the direction Df, and is discharged through the fixing nip FN. At this time, heat and pressure are applied to the toner in the fixing nip FN to fix the toner image on the sheet. A separation plate 133 is provided behind the fixing nip FN in the sheet conveyance direction Df for separating the sheet from the heating roller 131 and preventing the sheet from being wound around the roller.

  Further, in the fixing unit 13, a heat absorbing member 1324 that can be separated and contacted by a driving mechanism (not shown) is provided on the surface of the pressure belt 1323. The heat absorbing member 1324 is a roller formed of a material having high heat conductivity. As such a material, for example, a metal such as copper or aluminum can be used. In a state where such a heat absorbing member 1324 is in contact with the surface of the pressure belt 1323, the heat of the pressure belt 1323, which has become a high temperature due to the heat from the heating roller 131, is taken away by the heat absorbing member 1324, and thus The surface temperature of 1323 decreases. Further, in the state where the heat absorbing member 1324 is separated from the pressure belt 1323, the heat radiation from the pressure belt 1323 is only natural heat radiation. In FIG. 3, arrows attached to the respective rollers 131 and the like indicate the respective rotation directions.

  Next, three embodiments of the fixing operation executed by the fixing unit 13 configured as described above will be described. In this apparatus, the engine controller EC controls the fixing unit 13 based on a control program prepared in advance, and when an image formation command is given from the outside, the engine controller EC executes the program, thereby the fixing unit 13 13 executes a predetermined fixing operation.

  FIG. 4 is a flowchart showing the fixing operation of the first embodiment. In this embodiment, when an image formation command is given from an external device, the heat absorbing member 1324 is separated from the pressure belt 1323 (step S101), and rotation of each roller 131 provided in the fixing unit 13 is started ( In step S102), warm-up is started to raise the temperature of the heating roller 131 to the fixing temperature (step S103).

  When the warm-up is completed (step S104), it is determined whether the print job to be executed based on the image formation command is a continuous print operation for continuously forming images of a plurality of pages (step S105). When the print job is a continuous print operation, the sheet is passed through the fixing nip FN while the heat absorbing member 1324 is separated, and the toner image is fixed. On the other hand, if this is not the case, that is, if the print job forms only one image or forms a plurality of images at relatively long intervals, the heat absorbing member 1324 is brought into contact with the pressure belt 1323. Then, the fixing process is performed (step S106). The reason for this will be described below.

  FIG. 5 is a view showing temperature fluctuations of the pressure belt in the first embodiment. When the print job is a continuous print operation, the heat absorbing member 1324 is held in a state of being separated from the pressure belt 1323 as shown in FIG. The plurality of sheets pass through the fixing nip FN one after another at a slight time interval T1, but at this time, the temperature of the heating roller 131 is adjusted by the engine controller EC, so that it is maintained at a substantially constant temperature. On the other hand, in the pressure belt 1324 having no temperature adjusting means such as a heater, the surface temperature is drastically lowered because heat is taken away by the sheets passing one after another, and a certain temperature difference from the heating roller 131 is obtained. It becomes almost constant while keeping Accordingly, the surface temperature of the pressure belt 1323 is kept at a relatively low temperature during the fixing process. For this reason, sheet damage and image quality deterioration due to a blister phenomenon and a change in glossiness can be suppressed, and good fixing characteristics can be obtained.

  At this time, if the heat absorbing member 1324 is kept in contact with the pressure belt 1323, the heat of the pressure belt 1323 is taken away by both the sheet and the heat absorbing member 1324, and therefore, this is shown by the one-dot chain line in FIG. As such, the surface temperature is greatly reduced. As described above, if the temperature of the pressure belt 1323 is too low, the toner may not be sufficiently melted to cause fixing failure, or a large amount of heat generated by the heater 1311 may be required, resulting in a reduction in energy efficiency. Therefore, when the fixing process is continuously performed in this way, it is desirable that the heat absorbing member 1324 be separated from the pressure belt 1323. Furthermore, it is desirable that the heat generation amount of the heater 1311 and the heat capacities of the heating roller 131 and the pressure belt 1323 be designed so that a necessary and sufficient temperature can be obtained when performing the fixing process continuously.

  On the other hand, as shown in FIG. 5B, when the print job is a discontinuous printing operation and the fixing process is intermittently performed, the time interval T2 through which the sheet passes is long. Therefore, if the heat absorbing member 1324 is not brought into contact, the surface temperature of the pressure belt 1323 once lowered due to the passage of the sheet rises again during a period in which the sheet does not pass, and as a result, as shown by the one-dot chain line in FIG. The surface temperature of 1323 fluctuates greatly and changes at a relatively high temperature. When the heat absorbing member 1324 is brought into contact in such a case, the temperature of the pressure belt 1323 decreases due to the contact with the heat absorbing member 1324 as shown by the solid line in FIG. It becomes possible to suppress.

  Returning to FIG. 4, the description of the fixing operation will be continued. As described above, the heat absorbing member 1324 is separated from the pressure belt 1323 in the case of continuous printing operation, and the heat absorbing member 1324 is in contact with the pressure belt 1323 in the case of non-continuous printing operation. Then, the fixing process for the required number of sheets is executed. When all the printing operations are completed (step S107), the control target temperature of the heating roller 131 is changed to a standby temperature lower than the fixing temperature (step S108), and the heat absorbing member 1324 is separated from the pressure belt 1323. The fixing operation is finished (step S109). By doing so, it is possible to suppress heat from escaping from the heating roller 131, and to suppress unnecessary heat generation and power consumption in the standby state.

  As described above, in the fixing operation of this embodiment, the mode of the fixing operation is varied according to the time interval between sheets fed to the fixing nip FN. That is, in the case of a continuous printing operation in which fixing processing is continuously performed on a plurality of sheets at short time intervals, the fixing processing is performed in a state where the heat absorbing member 1324 is separated from the pressure belt 1323. By doing this, it is possible to prevent the temperature of the pressure belt 1323 from increasing and to prevent the temperature from being excessively lowered, so that good fixing characteristics can be stably obtained. Further, in the case of a non-continuous printing operation in which the sheet is intermittently passed, the temperature increase of the pressure belt 1323 when the sheet is not passed is suppressed by keeping the heat absorbing member 1324 in contact with the pressure belt 1323. As a result, good and stable fixing characteristics can be obtained.

  Note that the threshold of the sheet passing time interval for selecting the fixing process in which state should be comprehensively determined in consideration of the heat capacity of the heating roller 131 and the pressure belt 1323, the heat absorption amount of the sheet, and the like. It is.

  FIG. 6 is a flowchart showing the fixing operation of the second embodiment. In this embodiment, whether or not the heat absorbing member 1324 is brought into contact with the pressure belt 1323 is determined according to the length of the sheet to be subjected to the fixing process. Except for this point, the fixing operation is the same as that of the first embodiment. That is, the operations in steps S201 to S204 and S207 to S209 in the second embodiment (FIG. 6) are the same as the operations in steps S101 to S104 and S107 to S109 in the first embodiment (FIG. 4).

  In this embodiment, when the length of the sheet in the transport direction Df is equal to or longer than a predetermined length (hereinafter, such a sheet is referred to as “long paper”), the heat absorbing member 1324 is separated from the pressure belt 1323. Fixing process is performed in the state. On the other hand, when the length of the sheet is shorter than the predetermined length (hereinafter, such a sheet is referred to as “short paper”), the fixing process is performed with the heat absorbing member 1324 in contact with the pressure belt 1323. The reason for this will be described below.

  FIG. 7 is a view showing temperature fluctuations of the pressure belt in the second embodiment. When the sheet is long paper, the heat absorbing member 1324 is held in a state of being separated from the pressure belt 1323 as shown in FIG. Since the sheet, which is a long sheet, passes through the fixing nip FN over a long time T3, the surface temperature of the pressure belt 1323 also greatly decreases. If the heat absorbing member 1324 is kept in contact at this time, the temperature of the pressure belt 1323 may be excessively lowered as shown by the alternate long and short dash line in FIG. If the heat absorbing member 1324 is separated, the temperature of the pressure belt 1323 continues to decrease during the period T5 during which the sheet passes, and the temperature decrease stops during the period T4 from when the sheet passes until the next sheet arrives. The temperature rises. Thereby, it is possible to stably obtain good fixing characteristics by preventing a large temperature drop.

  On the other hand, when the sheet is short paper, the sheet is fed to the fixing nip with the heat absorbing member 1324 in contact with the pressure belt 1323 as shown in FIG. 7B. Since the period T5 during which the short paper passes through the fixing nip FN is short and the heat absorption amount is small, the temperature drop during this period is small. Therefore, if the heat absorbing member 1324 is not brought into contact, the surface temperature of the pressure belt 1323 changes in a relatively high state, as shown by a one-dot chain line in FIG. On the other hand, in this embodiment, the surface temperature of the pressure belt 1323 can be kept lower by bringing the heat absorbing member 1324 into contact therewith. Further, since the amount of heat absorbed by the sheet is small, the temperature of the pressure belt 1323 does not drop too much due to the contact of the heat absorbing member 1324.

  As described above, in the fixing operation of this embodiment, the mode of the fixing operation is varied according to the length of the sheet that is fed to the fixing nip FN. That is, when the fixing process is performed on the long paper, the fixing process is performed with the heat absorbing member 1324 separated from the pressure belt 1323. By doing this, it is possible to prevent the temperature of the pressure belt 1323 from increasing and to prevent the temperature from being excessively lowered, so that good fixing characteristics can be stably obtained. Further, when the sheet is short paper, the heat absorption member 1324 is brought into contact with the pressure belt 1323, thereby suppressing the temperature rise of the pressure belt 1323 and obtaining good and stable fixing characteristics. it can.

  Next, a third embodiment of the fixing operation according to the present invention will be described. In this embodiment, the mode of the fixing operation varies depending on the surface temperature of the pressure belt 1323, not the sheet length and the passage time interval. In order to make this possible, in this embodiment, the structure of the fixing unit is partially modified from the above embodiment.

  FIG. 8 is a view showing the structure of a fixing unit for realizing the fixing operation of the third embodiment. In the fixing unit 13a, a temperature sensor 1325 for detecting the surface temperature of the pressure belt 1324 is provided, and a sheet detection sensor for detecting the passage of the sheet on the conveying path F at a position upstream of the fixing nip FN. 1326 is provided. Since the other configuration is the same as that of the above-described apparatus (FIG. 3), the same configuration as the configuration of FIG.

  Note that the sheet detection sensor 1326 only needs to be able to grasp in advance the timing at which the sheet reaches the fixing nip FN, and is not necessarily provided immediately before the fixing nip FN. In this sense, for example, when a sensor for detecting the passage of the sheet is provided at a position upstream of the secondary transfer position TR2 such as the vicinity of the gate roller 80, the detection output may be used. This is because the sheet conveyance speed is known, and the timing at which the sheet reaches the fixing nip FN can be estimated from the output of such a sensor.

  FIG. 9 is a flowchart showing the fixing operation of the third embodiment. Of the fixing operation in this embodiment, the operation until the warm-up is completed is the same as in the first and second embodiments. That is, the operations in steps S301 to S304 in FIG. 9 correspond to the operations in steps S101 to S104 in the first embodiment (FIG. 4). Thereafter, in this embodiment, based on the output of the sheet detection sensor 1326, the process waits until the time when the leading edge of the sheet reaches the fixing nip FN or a certain time before that (step S305). At this time, if the surface temperature of the pressure belt 1323 detected by the temperature sensor 1325 is equal to or higher than a predetermined temperature, the heat absorption member 1324 is brought into contact with the pressure member 1323 to perform the fixing process (steps S306 and S307). By doing so, the surface temperature of the pressure member 1323 is lowered, and deterioration of the fixing characteristics due to the high temperature is prevented. On the other hand, when the surface temperature of the pressure belt 1323 is lower than the predetermined temperature when the sheet reaches the fixing nip FN, the fixing process is performed without contacting the heat absorbing member 1323. By doing so, it is possible to suppress poor fixing due to the temperature of the pressure belt 1323 being excessively lowered by the contact of the heat absorbing member 1324.

  As described above, in this embodiment, the mode of the fixing operation is varied based on the temperature detection result of the pressure belt 1323. More specifically, when the temperature of the pressure belt 1323 is equal to or higher than a predetermined temperature when the sheet reaches the fixing nip FN, the heat absorbing member 1324 is brought into contact with the pressure member 1323 to perform the fixing process. Good fixing characteristics are obtained by suppressing the temperature of the pressure belt 1323. On the other hand, when the temperature of the pressure belt 1323 is lower than the predetermined temperature when the sheet reaches the fixing nip FN, the temperature of the pressure belt 1323 is excessively lowered by performing the fixing process with the heat absorbing member 1323 separated. Fixes poor fixing.

  As described above, in each of the above embodiments, the fixing unit 13 functions as the “fixing device” and the “fixing unit” of the present invention. The heating roller 131, the pressure belt 1323, and the heat absorbing member 1324 function as the “heating member”, “pressure member”, and “heat absorbing member” of the present invention, respectively.

  In each of the above embodiments, each of the image forming stations 2Y, 2M, 2C, and 2K functions as the “image forming unit” of the present invention, and the engine controller EC functions as the “control unit” of the present invention. . Further, the temperature sensor 1325 in the third embodiment functions as the “temperature detection means” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the fixing operation of each of the above embodiments, the heat absorbing member 1324 is separated from the pressure belt 1323 during the warm-up to shorten the warm-up time. For this reason, for example, as shown in FIG. 5A, the temperature of the pressure belt 1323 immediately after the start of the fixing operation tends to increase. In order to avoid this, for example, before the sheet reaches the fixing nip FN after the warm-up, the heat absorbing member 1324 is brought into contact with the pressure belt 1323 for a predetermined time to adjust the surface temperature of the pressure belt 1323. You may make it do.

  Further, the fixing unit of each of the above embodiments has a structure in which the fixing nip FN is formed by bringing the pressure belt 1323 stretched over a plurality of rollers into contact with the heating roller 131. As a “pressure member” of the invention, a roller-shaped pressure roller may be provided and brought into contact with the heating roller.

  In each of the above embodiments, after the fixing process is completed, the control target temperature of the heating roller 131 is set to the standby temperature, thereby reducing both standby power consumption and shortening the rise time in the next fixing operation. However, instead of this, after the fixing process is completed, the heater may be cut off and the temperature of the heating roller may not be adjusted. This is particularly effective in further reducing power consumption in an apparatus using a fixing unit having a small heat capacity.

  Further, the heat absorbing member 1234 in each of the above embodiments is a metal roller-like member having a high thermal conductivity, and has a structure in which heat is released from the roller to the surrounding atmosphere by natural heat dissipation, but the material and shape of the heat absorbing member Is not limited to this. For example, a heat sink having heat radiating fins may be provided in order to enhance the heat radiating effect to the outside, or a heat pipe that transports heat away from the pressure belt and dissipates it further may be provided as the heat absorbing member.

  In the third embodiment, the sheet on the conveyance path F is detected and the temperature of the pressure belt is detected in accordance with the sheet conveyance timing. However, the pressure is applied regardless of the sheet conveyance timing. The temperature of the belt may be detected, and the separation / contact of the heat absorbing member may be controlled according to the detection result.

  Furthermore, in the above-described embodiment, the present invention is applied to a tandem type color image forming apparatus using YMCK four-color toner, but the application target of the present invention is not limited to this. Image forming apparatus with different color types and number of colors, such as an image forming apparatus that has only an image forming station and forms a monochrome image, and a rotary developing type image forming apparatus in which a plurality of developing devices are mounted on a rotatable developing rotary. The present invention can also be applied to.

1 is a diagram illustrating a configuration example of an image forming apparatus to which the present invention can be preferably applied. FIG. 2 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. FIG. 3 is a diagram illustrating a structure of a fixing unit in the image forming apparatus. 6 is a flowchart illustrating a fixing operation according to the first embodiment. The figure which shows the temperature fluctuation of the pressure belt in 1st Embodiment. 9 is a flowchart showing a fixing operation according to the second embodiment. The figure which shows the temperature fluctuation of the pressure belt in 2nd Embodiment. FIG. 10 is a diagram illustrating a structure of a fixing unit for realizing a fixing operation according to a third embodiment. 10 is a flowchart illustrating a fixing operation according to a third embodiment.

Explanation of symbols

  2Y, 2M, 2C, 2K ... Image forming station (image forming means), 13 ... Fixing unit (fixing device, fixing means), 131 ... Heating roller (heating member), 1323 ... Pressure belt (pressure member), 1324 ... endothermic member, 1325 ... temperature sensor (temperature detection means), EC ... engine controller (control means)

Claims (9)

A heating member heated to a predetermined fixing temperature;
A pressure member that forms a fixing nip in contact with the heating member;
A heat absorbing member configured to be freely separated from and abutting against the surface of the pressure member, and abutting the surface of the pressure member to absorb the heat of the surface;
As a fixing operation for fixing the toner image on the recording material by passing a recording material having a toner image formed on the surface thereof to the fixing nip, the heat absorbing member is brought into contact with the pressure member. A contact fixing operation for feeding the recording material to the fixing nip in a state, and a separation fixing operation for feeding the recording material to the fixing nip with the heat absorbing member separated from the pressure member. A fixing device characterized in that it is configured to be executable. Image forming means for forming a toner image and transferring it to the surface of the recording material;
A heating member that has been heated to a predetermined fixing temperature; and a pressure member that contacts the heating member to form a fixing nip, and the recording material onto which the toner image has been transferred by the image forming means is transferred to the fixing nip. Fixing means for executing a fixing operation for fixing the toner image on the recording material by passing the toner image on the recording material;
The fixing unit is configured to be freely contactable with the surface of the pressure member, and further includes a heat absorbing member that contacts the surface of the pressure member and absorbs heat of the surface.
As the fixing operation, a contact fixing operation in which the recording material is fed to the fixing nip while the heat absorbing member is in contact with the pressure member, and a state in which the heat absorbing member is separated from the pressure member. And an image forming apparatus that selectively performs a separation fixing operation for feeding the recording material to the fixing nip. Temperature detecting means for detecting the temperature of the pressure member surface;
The image forming apparatus according to claim 2, further comprising: a control unit that selects one of the contact fixing operation and the separation fixing operation based on a detection result by the temperature detection unit and causes the fixing unit to execute the operation.   The control unit selects the contact fixing operation if the surface temperature of the pressure member detected by the temperature detection unit is higher than a predetermined temperature, and the separation fixing operation if the surface temperature is lower than the predetermined temperature. The image forming apparatus according to claim 3, wherein the image forming apparatus is selected.   One of the contact fixing operation and the separation fixing operation is selected based on a time interval from when one recording material passes through the fixing nip to when the next recording material reaches the fixing nip, The image forming apparatus according to claim 2, further comprising a control unit that causes the fixing unit to execute.   6. The image according to claim 5, wherein the control unit selects the contact fixing operation if the time interval is longer than a predetermined time, and selects the separation fixing operation if the time interval is shorter than the predetermined time. Forming equipment.   The control unit according to claim 2, further comprising a control unit that selects one of the contact fixing operation and the separation fixing operation based on a length of the recording material along a moving direction of the recording material and causes the fixing unit to execute the selected one. Image forming apparatus.   The image according to claim 7, wherein the control unit selects the contact fixing operation when the length is shorter than a predetermined length, and selects the separation fixing operation when the length is longer than the predetermined length. Forming equipment. An image forming operation for forming a toner image and transferring it to the surface of the recording material;
Fixing for fixing the toner image onto the recording material by feeding the recording material onto which the toner image has been transferred to a fixing nip in which a pressure member is brought into contact with a heating member heated to a predetermined fixing temperature. Perform actions, and
As the fixing operation, a contact fixing operation of passing the recording material to the fixing nip in a state where a heat absorbing member that absorbs heat of the surface is brought into contact with the surface of the pressure member; An image forming method comprising: selectively performing a separation fixing operation of feeding the recording material to the fixing nip in a state where the heat absorbing member is separated.

Images