JP2015215540A - Fixation device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device and an image forming apparatus that are capable of preventing the excessive temperature rise in a non-sheet passing area on a fixation surface side member when allowing continuous passing of sheets having a smaller width than that of a maximally wide paper that can pass a fixation nip.SOLUTION: An image forming apparatus 1 includes: a fixation roller 61 provided on a fixation surface side of a sheet S having a toner image formed thereon; a pressure roller 64 that forms, in pressure contact with the fixation roller 61, a fixation nip NP for sandwiching and conveying the sheet S; halogen heaters 62 and 63 for heating the fixation roller 61; an external heating roller 65 for providing/receiving heat to/from the pressure roller 64; and a control section 100 that adjusts the provision/reception of heat by the external heating roller 65 so that the temperature of a non-sheet passing area as an area not in contact with the sheet S in the fixation roller 61 heated by the halogen heaters 62 and 63 is less than a first temperature (e.g., 250°C) when a prescribed image formation condition is satisfied.

Description

  The present invention relates to a fixing device and an image forming apparatus.

  In general, an image forming apparatus (printer, copier, facsimile, etc.) using an electrophotographic process technology generates an electrostatic latent image by irradiating (exposing) a charged photoconductor with a laser beam based on image data. Form. Then, by supplying toner from the developing device to the photosensitive member (image carrier) on which the electrostatic latent image is formed, the electrostatic latent image is visualized to form a toner image. Further, the toner image is directly or indirectly transferred to a sheet, and then heated and pressed to fix it, thereby forming an image on the sheet.

  The fixing device for fixing the toner image as described above is formed by a fixing surface side member such as a fixing roller or a fixing belt and a back surface side supporting member such as a pressure roller or a pressure belt that is pressed against the fixing surface side member. There is a heat-fixing type fixing device that heats and pressurizes a sheet on which a toner image has been transferred through the fixing nip.

  Patent Document 1 discloses a heating roller having a heating unit, a pressure roller that presses the heating roller, an external heating roller that comes into contact with the pressure roller, a detection unit that detects the quality of the recording paper to be fixed, and a detection unit. In accordance with this detection result, there has been proposed a fixing device that includes a control unit that controls to automatically set the surface temperature of the outer heating roller to the first temperature or the second temperature.

  Patent Document 2 discloses a rotatable heating rotator heated by a heating source, a pressure member that forms a nip portion through which a recording material is nipped and conveyed between the heating rotators, A heating rotator and a blowing means for blowing air to at least one non-sheet passing portion of the pressure member, and detecting the amount of power supplied to the heating source immediately before the blowing operation of the blowing means is started, thereby passing the paper A configuration in which the temperature rise rate of the non-sheet-passing portion (edge) through which the recording material of the smallest possible width does not pass is recognized, and air is blown by the blowing means by setting the air flow rate according to the edge temperature rise rate Has been proposed.

  Further, Patent Document 3 includes a plurality of heating units, and each detects temperatures of a fixing unit that fixes a toner image on a sheet and a plurality of portions corresponding to the plurality of heating units in the fixing unit. There has been proposed a fixing device having a plurality of temperature detection means and a control means for independently controlling the plurality of heating means based on the temperature detection signals of the plurality of temperature detection means.

JP 2007-25540 A JP2013-117551A JP-A-10-228206

  By the way, in the fixing device of the heat fixing method as described above, when fixing is performed by continuously passing a small size paper having a width smaller than the maximum width paper that can be passed through the fixing nip, A so-called non-sheet passing portion temperature rise phenomenon occurs in which the surface temperature of the non-sheet passing region of the fixing surface side member (the region of the surface of the fixing surface side member that does not contact the small size paper) excessively increases.

  This is because when small-size paper is continuously passed, in the non-sheet passing area where the paper does not pass, heat is partially accumulated by the amount of heat lost by the small-size paper. If the surface temperature of the non-sheet-passing region rises excessively, it will cause hot offset and thermal deterioration of the components of the fixing device. When the occurrence of hot offset is specifically described, in order to fix the entire area of the maximum width sheet (for example, A4 landscape sheet), the temperature in the sheet width direction of the fixing surface side member is equal to or greater than the sheet width of the sheet. It is necessary to. However, when small-size paper (for example, A4) is continuously passed, the temperature of the fixing surface side member rises excessively in the non-paper-passing area, and does not pass through the paper-passing area (area that contacts the small-size paper). There is a temperature difference between the paper passing area. Therefore, when a large size paper (for example, B4) having a width larger than that of the small size paper is passed next, a hot offset occurs in a portion corresponding to the non-paper passing area of the fixing surface side member, and the image quality is remarkably deteriorated. I was letting. Further, not only hot offset occurs, but also the conveyance of the paper becomes unstable due to the temperature difference between the paper passing area and the non-paper passing area, which may cause problems such as image misalignment and looseness. An excessive temperature rise in the non-sheet passing region is particularly remarkable in the fixing surface side member in which the heat capacity is reduced by thinning, for example, in order to save energy.

  The techniques described in Patent Documents 1 and 3 are not intended to prevent an excessive temperature rise in the non-sheet passing region of the fixing surface side member, and therefore do not have a configuration for that purpose.

  In addition, as in the technique described in Patent Document 2, the configuration in which the air is blown to the non-sheet passing region of the fixing surface side member by the blowing unit aims at energy saving, cost saving, and space saving of the fixing device. There was a problem that it was not preferable from the viewpoint of. In addition, a configuration using a plurality of heaters with different heat distribution (for example, a heater that heats only the sheet passing area of the fixing surface side member and a heater that heats only the non-sheet passing area of the fixing surface side member) is also conceivable. Similar to the technique described in Patent Document 2, there is a problem that the fixing device is not preferable from the viewpoint of energy saving, cost saving, and space saving.

  The present invention can prevent an excessive temperature rise in the non-sheet passing region of the fixing surface side member when continuously feeding a sheet having a width smaller than the maximum width sheet that can be passed through the fixing nip. An object of the present invention is to provide a fixing device and an image forming apparatus.

The fixing device according to the present invention includes:
A fixing surface side member disposed on the fixing surface side of the paper on which the toner image is formed;
A back-side support member that forms a fixing nip for nipping and transporting the paper in a state of being pressed against the fixing surface-side member;
A heating unit for heating the fixing surface side member;
A heat exchanging part that exchanges heat with the back side support member;
When a predetermined image forming condition is satisfied, the heat exchange is performed so that a temperature of a non-sheet passing region which is a region not in contact with the sheet among the fixing surface side member heated by the heating unit is lower than a first temperature. An adjustment unit for adjusting the transfer of heat in the unit;
It is characterized by providing.

  An image forming apparatus according to the present invention includes the fixing device.

  According to the present invention, when a predetermined image forming condition is satisfied, heat transfer by the heat exchange unit is adjusted such that the temperature of the non-sheet passing region of the fixing surface side member is lower than the first temperature. Accordingly, when a sheet having a width smaller than the maximum width sheet that can be passed through the fixing nip is continuously passed, an excessive temperature rise in the non-sheet passing region of the fixing surface side member can be prevented.

1 is a diagram schematically showing an overall configuration of an image forming apparatus in the present embodiment. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus according to the present embodiment. FIG. 2 is a diagram schematically illustrating a configuration of a fixing unit of the image forming apparatus according to the present embodiment. 3 is a flowchart showing a control operation of the image forming apparatus in the present embodiment.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 shows a main part of the control system of the image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 transfers the toner images of Y (yellow), M (magenta), C (cyan), and K (black) formed on the photosensitive drum 413 to the intermediate transfer belt 421 (primary transfer). Then, after superposing four color toner images on the intermediate transfer belt 421, the toner images are transferred to the paper S (secondary transfer) to form an image.

  Further, in the image forming apparatus 1, the photosensitive drums 413 corresponding to the four colors of YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and the respective color toner images are sequentially transferred to the intermediate transfer belt 421 in one step. Tandem system is adopted.

  As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100 (" It functions as an “adjustment unit”.

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program corresponding to the processing content from the ROM 102 and develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program. At this time, various data stored in the storage unit 72 is referred to. The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 100 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Do. For example, the control unit 100 receives image data transmitted from an external device, and forms an image on the paper S based on the image data (input image data). The communication unit 71 is composed of a communication control card such as a LAN card, for example.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

  The automatic document feeder 11 transports the document D placed on the document tray by a transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on a document tray all at once.

  The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like in accordance with a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on the input image data, and image forming units 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component. Etc.

  The Y component, M component, C component, and K component image forming units 41Y, 41M, 41C, and 41K have the same configuration. For convenience of illustration and explanation, common constituent elements are denoted by the same reference numerals, and Y, M, C, or K are added to the reference numerals when distinguished from each other. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has an undercoat layer (UCL) and a charge generation layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube) having a drum diameter of 80 mm, for example. It is a negatively charged organic photoconductor (OPC) in which a generation layer (CTL) and a charge transport layer (CTL) are sequentially stacked. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges by exposure by the exposure device 411. The charge transport layer consists of a material in which a hole transport material (electron donating nitrogen-containing compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The control unit 100 controls a drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413, so that the photosensitive drum 413 rotates at a constant peripheral speed.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 is, for example, a two-component developing type developing device, and forms a toner image by visualizing the electrostatic latent image by attaching toner of each color component to the surface of the photosensitive drum 413.

  The drum cleaning device 415 includes a drum cleaning blade that is slidably contacted with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face a roller 423B (hereinafter referred to as “backup roller 423B”) disposed on the downstream side of the driving roller 423A in the belt traveling direction. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photoconductive drum 413 are primarily transferred onto the intermediate transfer belt 421 in sequence. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet S. Specifically, a toner image is applied by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper S (the side in contact with the secondary transfer roller 424). Is electrostatically transferred to the paper S. The sheet S to which the toner image is transferred is conveyed toward the fixing unit 60.

  The belt cleaning unit 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller is adopted. Also good.

  The fixing unit 60 includes an upper fixing unit 60A having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) of the paper S, and the back surface (surface opposite to the fixing surface) of the paper S. A lower fixing unit 60B having a rear side support member to be disposed is provided. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the paper S is formed.

  The fixing unit 60 fixes the toner image on the paper S by heating and pressurizing the paper S on which the toner image is secondarily transferred and conveyed at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F may be provided with an air separation unit that separates the sheet S from the fixing surface side member or the back surface side support member by blowing air. Details of the fixing unit 60 will be described later.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on basis weight, size, etc. is stored for each preset type. . The conveyance path unit 53 includes a plurality of conveyance roller pairs such as registration roller pairs 53a.

  The sheets S stored in the sheet feed tray units 51 a to 51 c are sent one by one from the top and are conveyed to the image forming unit 40 by the conveyance path unit 53. At this time, the registration roller portion provided with the registration roller pair 53a corrects the inclination of the fed paper S and adjusts the conveyance timing. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one side of the sheet S at a time, and a fixing process is performed in the fixing unit 60. The sheet S on which the image has been formed is discharged out of the apparatus by a discharge unit 52 having a discharge roller 52a.

  Next, the configuration of the fixing unit 60 will be described with reference to FIG. FIG. 3 is a diagram schematically illustrating the configuration of the fixing unit 60. The fixing unit 60 and the control unit 100 function as a fixing device. The fixing unit 60 and the control unit 100 may be configured as a unit and attached to the image forming apparatus 1, or may be separately incorporated in the image forming apparatus 1 and function as a fixing device. .

  The upper fixing unit 60A includes a fixing roller 61 that is a fixing surface side member (roller fixing method). The fixing roller 61 includes a halogen heater 62, 63 (functioning as a “heating unit” of the present invention) built in the center, a core metal formed in a cylindrical shape from aluminum, iron, copper, or an alloy thereof, and a core. A heat-resistant elastic body, which is located on the outer surface of gold and formed from silicon rubber, fluorine rubber or the like, and a fluorine resin such as PFA (perfluoroalkoxy) or PTFE (polytetrafluoroethylene) coated with the heat-resistant elastic body It is comprised from the release layer formed from. In the present embodiment, in order to save energy of the fixing unit 60, the heat capacity of the fixing roller 61 is reduced by reducing the thickness (wall thickness) of the fixing roller 61 to, for example, 5 [mm], that is, by reducing the thickness. Yes.

  The halogen heaters 62 and 63 are configured using, for example, one of 1300 [W] and one of 500 [W]. The halogen heaters 62 and 63 are supplied with electric power from a commercial power source (not shown) and heat the entire fixing roller 61 from the inside by radiant heat to raise the temperature of the outer peripheral surface of the fixing roller 61. In the axial direction of the halogen heaters 62 and 63 (in the direction perpendicular to the plane of FIG. 3), the heat generation amount (radiation heat amount) on both ends of the halogen heaters 62 and 63 is larger than the heat generation amount on the center side. A position where the amount of generated heat is the largest exists on both ends of the halogen heaters 62 and 63. The amount of heat generated by the halogen heaters 62 and 63 increases proportionally as the amount of power supplied increases.

  Drive control of the halogen heaters 62 and 63 (for example, on / off of heat generation, amount of heat generation, etc.) is performed by the control unit 100. The control unit 100 controls the surface temperature of the fixing roller 61 by controlling the amount of power supplied to the halogen heaters 62 and 63 (that is, the amount of heat generated by the halogen heaters 62 and 63). Specifically, the control unit 100 performs on / off control of power supply to the halogen heaters 62 and 63 using a switching control element (not shown). As the switching control element, a semiconductor switching element, a transistor, a thyristor, a triac, and other switching means (means for turning on / off a part of an electric circuit) can be used.

  In the present embodiment, the control unit 100 includes an on state in which power is supplied to the halogen heaters 62 and 63 and an off state in which power is not supplied. The supply of electric power to the halogen heaters 62 and 63 is controlled based on an on / off pattern of a half-wave unit with a predetermined duty ratio corresponding to the amount of electric power to be supplied to (half cycle duty control). This half cycle duty control makes it possible to finely adjust the power supplied to the halogen heaters 62 and 63. Therefore, when the power supply is simply on / off controlled, the temperature ripple is large near the set temperature of the fixing roller 61. The problem of becoming can be avoided. In addition, the occurrence of a so-called inrush current, in which a large current flows instantaneously at the start of power supply, suppresses the occurrence of flicker (lighting equipment connected to a commercial power source that supplies power to the halogen heaters 62 and 63 flickers, etc. Occurrence) can be suppressed. Note that details of controlling power supply (lighting) by an on / off pattern in a half-wave unit with a predetermined duty ratio are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2011-187238, 9-80961, and 2006-72235. It is described in the gazette.

  The fixing roller 61 contacts the paper S on which the toner image is formed, and heat-fixes the toner image on the paper S in a fixing allowable temperature range (for example, 165 to 220 [° C.]). The allowable fixing temperature range is a temperature at which a heat amount necessary for melting the toner on the paper S can be supplied, and varies depending on the paper type of the paper S on which an image is formed.

  The lower fixing unit 60B includes a pressure roller 64 that is a back side support member, and an external heating roller 65 (functioning as the “heat exchange unit” of the present invention) (roller pressure method). The pressure roller 64 includes, for example, a metal core made of stainless steel, a rubber roller made of a foam of silicon rubber located on the outer peripheral surface of the metal core, and a release formed from a PFA tube covering the outer peripheral surface of the rubber roller. It consists of a mold layer.

The pressure roller 64 is urged by an urging member (not shown) and is brought into pressure contact with the fixing roller 61 with a predetermined fixing load (for example, 2650 [N]). In this way, a fixing nip NP for nipping and transporting the paper S is formed between the fixing roller 61 and the pressure roller 64. The contact pressure (surface pressure) between the fixing roller 61 and the pressure roller 64 in the fixing nip NP is, for example, 30.67 [N / cm ² ].

  The outer heating roller 65 contacts the pressure roller 64 and heats the surface of the pressure roller 64. As a result, the heat from the outer heating roller 65 is indirectly supplied to the paper S passing through the fixing nip NP. By controlling the surface temperature (set temperature) of the pressure roller 64 to a predetermined temperature (for example, 160 [° C.]), it is possible to prevent the occurrence of fixing failure in the paper S passing through the fixing nip NP. The outer heating roller 65 includes a halogen heater 66 built in the center and a cylindrical member formed in a cylindrical shape from aluminum, iron, copper, or an alloy thereof, and is compared with the fixing roller 61 and the pressure roller 64. And it is formed small.

  The halogen heater 66 is configured by using, for example, one of 300 [W]. The halogen heater 66 is supplied with electric power from a commercial power source (not shown) and heats the entire outer heating roller 65 from the inside by radiant heat to raise the temperature of the outer peripheral surface of the outer heating roller 65. The amount of heat generated by the halogen heater 66 increases proportionally as the amount of power supplied increases.

  The drive control of the halogen heater 66 (for example, on / off of heat generation, amount of heat generation, etc.) is performed by the control unit 100. The control unit 100 controls the surface temperature of the outer heating roller 65 and thus the pressure roller 64 by controlling the amount of power supplied to the halogen heater 66 (that is, the amount of heat generated by the halogen heater 66). Specifically, the control unit 100 performs on / off control of power supply to the halogen heater 66 using a switching control element (not shown).

  The control unit 100 controls a drive source (drive motor) (not shown) to rotate the pressure roller 64 in the arrow R2 direction (counterclockwise direction). Drive control of the drive motor (for example, rotation on / off, peripheral speed, etc.) is performed by the control unit 100. The peripheral speed of the pressure roller 64 is set to 460 [mm / s], for example.

  When the pressure roller 64 is driven and rotated in the direction of the arrow R2, the fixing roller 61 is driven to rotate in the direction of the arrow R1 (clockwise direction). Further, the outer heating roller 65 rotates following the direction of the arrow R3 (clockwise direction). When the sheet S is fixed, the peripheral speed of the fixing roller 61 is equal to the peripheral speed of the pressure roller 64 (for example, 460 [mm / s]).

  As described above, in the fixing unit 60, the upper fixing unit 60A and the lower fixing unit 60B fix the unfixed toner image on the sheet S by conveying the sheet S while heating and pressing at the fixing nip NP. .

  By the way, when the sheet S having a width smaller than the maximum width sheet S that can be passed through the fixing nip NP is continuously passed and fixing is performed, the non-sheet passing region (the fixing roller 61) of the fixing roller 61 is executed. The surface temperature of the surface not contacting the sheet S) increases excessively (non-sheet passing portion temperature increase phenomenon). For example, the surface temperature of the sheet passing area of the fixing roller 61 (area of the surface of the fixing roller 61 that contacts the sheet S) is suppressed to 180 [° C.], while the surface temperature of the non-sheet passing area of the fixing roller 61 is The temperature rises to 230 [° C]. This is because, when the small-sized paper S is continuously passed, in the non-paper passing area where the paper S does not pass, the heat is partially accumulated as much as there is no heat removal by the paper S. If the surface temperature of the non-sheet-passing region rises excessively (for example, up to 250 [° C.]), it will lead to the occurrence of hot offset and thermal deterioration of the components of the fixing unit 60.

  The occurrence of the hot offset will be described in detail. In order to fix the entire area of the maximum width sheet S (for example, A4 landscape sheet), the sheet width direction of the fixing roller 61 (the direction orthogonal to the conveyance direction of the sheet S). Is required to be equal to or higher than the paper width of the paper S. However, when a small-size sheet (for example, A4: 210 × 297 [mm]) is continuously passed, the temperature of the fixing roller 61 is excessively increased in the non-sheet passing area, and the sheet passing area and the non-sheet passing sheet. There is a temperature difference between the areas. Therefore, when a sheet S (for example, B4: 257 × 364 [mm]) having a width larger than that of the small-sized sheet S is passed next, a hot offset occurs in a portion corresponding to the non-sheet passing area of the fixing roller 61. As a result, there is a problem that the image quality is remarkably lowered. Further, not only hot offset occurs, but also the conveyance of the paper S becomes unstable due to the temperature difference between the paper passing area and the non-paper passing area, which may cause problems such as image misalignment and looseness. An excessive temperature rise in the non-sheet passing region is particularly noticeable in the fixing roller 61 having a reduced heat capacity as in the present embodiment.

  Therefore, in the present embodiment, the control unit 100 stops the heat generation operation of the halogen heater 66 included in the outer heating roller 65 when the sheet S having a small sheet width is continuously fed and fixing is performed ( Fever off). As a result, the temperature of the pressure roller 64 is lowered by the amount of heat supply from the outer heating roller 65, and heat generated in the non-sheet passing area of the fixing roller 61 due to heat conduction is removed via the pressure roller 64. It becomes easy to move to the heating roller 65. In other words, the outer heating roller 65 receives heat conducted from the non-sheet passing region through the pressure roller 64 in the fixing roller 61 heated by the halogen heaters 62 and 63. Therefore, an excessive temperature rise in the non-sheet passing region of the fixing roller 61 can be prevented. For example, when the heating operation of the halogen heater 66 is not stopped (heating is turned on), the surface temperature of the non-sheet passing area of the fixing roller 61 rises to 230 [° C.], while the heating operation of the halogen heater 66 is stopped. The surface temperature of the non-sheet passing area of the fixing roller 61 can be suppressed to 215 [° C.]. In the present embodiment, in the axial direction of the halogen heaters 62 and 63 (perpendicular to the paper surface in FIG. 3), the heat generation amount on both ends of the halogen heaters 62 and 63 is larger than the heat generation amount on the center side. The temperature in the non-sheet passing area of the fixing roller 61 tends to be higher than the temperature in the sheet passing area. Therefore, even if there is no supply of heat from the external heating roller 65, the heat S is conducted from the non-sheet passing area of the fixing roller 61 to the sheet passing area, and as a result, the sheet S having a small sheet width is continuously passed. In this case, the amount of heat supplied to the paper S is not greatly reduced, and the fixing property of the paper S can be ensured.

  Next, the operation of the image forming apparatus 1 in the present embodiment will be described with reference to the flowchart of FIG. Note that the process shown in FIG. 4 is executed every time one image forming process corresponding to a print job is executed, for example.

  First, the control unit 100 determines whether or not a predetermined image forming condition (that is, a condition that the surface temperature of the non-sheet passing area of the fixing roller 61 may excessively increase) is satisfied (step S100). The predetermined image forming condition is that the sheet width of the sheet S is a predetermined length (more specifically, the length between the positions where the halogen heaters 62 and 63 are respectively present at both ends in the axial direction and the amount of generated heat is the largest. It is a condition that it is less than (a). The control unit 100 acquires the sheet width of the sheet S by referring to the sheet information set in the print job when the execution of the image forming process for the sheet S is started or when the sheet S is fed. As a result of the determination, when the predetermined image forming condition is not satisfied (step S100, NO), the control unit 100 executes the heat generation operation of the halogen heater 66 included in the outer heating roller 65 so as to heat the pressure roller 64. (Step S120). When the process of step S120 is completed, the image forming apparatus 1 ends the process in FIG.

  On the other hand, when the predetermined image formation condition is satisfied (step S100, YES), the control unit 100 determines whether the number of images formed in continuous image formation processing in the print job is less than a predetermined number (for example, 1000 [sheets]). It is determined whether or not (step S140). In the determination process in step S140, it is confirmed that the sheet S having a small sheet width is continuously passed to a certain extent and the fixing process is executed, and the surface temperature of the non-sheet passing area of the fixing roller 61 is excessively increased. This is done to reliably detect the occurrence of the phenomenon. If the result of determination in step S140 is that the number of formed images is less than the predetermined number (step S140, YES), the process transitions to step S120. And the control part 100 performs the heat_generation | fever operation | movement of the halogen heater 66 which the outer heating roller 65 has so that the pressurization roller 64 may be heated.

  On the other hand, if the number of formed images is equal to or greater than the predetermined number (step S140, NO), the control unit 100 stops the heat generation operation of the halogen heater 66 included in the outer heating roller 65 so as not to heat the pressure roller 64 ( Step S160). As a result, the temperature of the pressure roller 64 is lowered by the amount of heat supply from the outer heating roller 65, and heat generated in the non-sheet passing area of the fixing roller 61 due to heat conduction is removed via the pressure roller 64. It becomes easy to move to the heating roller 65. Therefore, an excessive temperature rise in the non-sheet passing region of the fixing roller 61 can be prevented. When the process of step S160 is completed, the image forming apparatus 1 ends the process in FIG.

  In the flowchart, the determination process in step S140 is not necessarily provided. When the determination process of step S140 is not provided, the heat generation operation of the halogen heater 66 is stopped earlier than when the determination process is provided. Therefore, it is possible to reliably prevent the surface temperature of the non-sheet passing region of the fixing roller 61 from excessively rising and to reduce the power consumption of the halogen heater 66.

  In the above flowchart, the example in which the predetermined image forming condition is that the paper width of the paper S is less than the predetermined length has been described. However, the fixing surface side in the paper width direction orthogonal to the transport direction of the paper S has been described. It may be a condition that the temperature on both ends of the member is equal to or higher than a predetermined temperature (for example, 230 [° C.], corresponding to the “second temperature” of the present invention). The temperature at both end portions of the fixing surface side member can be detected by a known temperature detecting means provided near the both end portions. Of course, the predetermined image forming conditions include the condition that the sheet width of the sheet S is less than the predetermined length, and the temperature at both ends of the fixing surface side member in the sheet width direction is equal to or higher than the predetermined temperature. It may be a thing. That is, when the sheet width of the sheet S is less than the predetermined length and the temperature at both ends of the fixing surface side member in the sheet width direction is equal to or higher than the predetermined temperature, the predetermined image forming condition is satisfied.

  In the above flowchart, the control unit 100 stops the heat generation operation of the halogen heater 66 included in the outer heating roller 65 when a predetermined image forming condition is satisfied and the number of images formed is equal to or larger than the predetermined number. Although described, the present invention is not limited to this. For example, the control unit 100 may control the amount of power supplied to the halogen heater 66 so that the amount of heat generated by the halogen heater 66 is smaller than when the predetermined image forming condition is not satisfied. In this case, the surface temperature of the pressure roller 64 is lowered to a temperature (for example, 50 [° C.]) lower than the temperature (for example, 160 [° C.]) when the predetermined image forming condition is not satisfied. As a result, the heat generated in the non-sheet passing area of the fixing roller 61 moves to the outer heating roller 65 via the pressure roller 64 without being stored in the non-sheet passing area. In short, the heat transfer by the outer heating roller 65 may be adjusted with the pressure roller 64 so that the temperature of the non-sheet passing region of the fixing roller 61 does not rise excessively.

  As described above in detail, in the present embodiment, the image forming apparatus 1 includes the fixing roller 61 disposed on the fixing surface side of the sheet S on which the toner image is formed, and the sheet in a state of being pressed against the fixing roller 61. A pressure roller 64 that forms a fixing nip NP that holds and conveys S, a halogen heater 62 and 63 that heats the fixing roller 61, and an outer heating roller 65 that transfers heat between the pressure roller 64. When the predetermined image forming condition is satisfied, the temperature of the non-sheet passing region that is a region not in contact with the sheet S in the fixing roller 61 heated by the halogen heaters 62 and 63 is a first temperature (for example, 250 [° C.]). The control unit 100 adjusts the transfer of heat by the external heating roller 65 so as to be less than.

  According to the present embodiment configured as described above, when the predetermined image forming condition is satisfied, the heat of the outer heating roller 65 is adjusted so that the temperature of the non-sheet passing region of the fixing roller 61 is lower than the first temperature. Delivery is coordinated. More specifically, the heat transfer by the external heating roller 65 is adjusted by stopping the heat generation operation of the halogen heater 66, and the heat generated in the non-sheet passing area of the fixing roller 61 is stored in the non-sheet passing area. Instead, it moves to the outer heating roller 65 via the pressure roller 64. Accordingly, when the paper S having a width smaller than the maximum width of the paper S that can pass through the fixing nip NP is continuously passed, an excessive temperature rise in the non-paper passing area of the fixing roller 61 can be prevented. it can.

  In the above embodiment, the example in which the heat generation amount at the both end portions of the halogen heaters 62 and 63 is larger than the heat generation amount at the central portion side is described, but the present invention is not limited to this. For example, the amount of heat generated at both ends of the halogen heaters 62 and 63 may be smaller than the amount of heat generated at the center or may be the same as the amount of heat generated at the center.

  In the above embodiment, the fixing nip NP has been described with respect to the example in which the upper fixing unit 60A is configured by the roller fixing method including only the fixing roller 61, but the present invention is not limited thereto. For example, the fixing nip NP may be configured by a belt fixing system in which the upper fixing unit 60A includes a heating roller and a fixing belt in addition to the fixing roller 61.

  In the above embodiment, the example in which the lower fixing unit 60B includes the pressure roller 64 has been described, but the present invention is not limited to this. For example, the lower fixing unit 60B may be configured by a belt pressing method having a heating roller and a pressure belt in addition to the pressure roller 64.

  In the above embodiment, the example in which the fixing roller 61 includes the two halogen heaters 62 and 63 has been described. However, the present invention is not limited to this. For example, the fixing roller 61 may incorporate one or three or more halogen heaters.

  Moreover, although the said embodiment demonstrated the example in which the external heating roller 65 incorporated the one halogen heater 66, this invention is not limited to this. For example, the outer heating roller 65 may incorporate a plurality of halogen heaters.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Operation display part 21 Display part 22 Operation part 30 Image processing part 40 Image forming part 50 Paper conveyance part 60 Fixing part 60A Upper fixing part 60B Lower fixing part 61 Fixing rollers 62, 63, 66 Halogen heater 64 Pressure roller 65 External heating roller 71 Communication unit 72 Storage unit 100 Control unit 101 CPU
102 ROM
103 RAM
NP fixing nip

Claims (7)

A fixing surface side member disposed on the fixing surface side of the paper on which the toner image is formed;
A back-side support member that forms a fixing nip for nipping and transporting the paper in a state of being pressed against the fixing surface-side member;
A heating unit for heating the fixing surface side member;
A heat exchanging part that exchanges heat with the back side support member;
When a predetermined image forming condition is satisfied, the heat exchange is performed so that a temperature of a non-sheet passing region which is a region not in contact with the sheet among the fixing surface side member heated by the heating unit is lower than a first temperature. An adjustment unit that adjusts the transfer of heat by the unit;
A fixing device comprising:   The fixing device according to claim 1, wherein the image forming condition includes a condition that a sheet width of the sheet is less than a predetermined length. In the axial direction of the heating unit, the heating value on both ends of the heating unit is larger than the heating value on the center side of the heating unit,
The fixing device according to claim 2, wherein the predetermined length is a length between positions that are respectively present on both end sides of the heating unit and that generates the largest amount of heat.   The image forming condition includes a condition that a temperature on an end portion side of the fixing surface side member in a sheet width direction orthogonal to a conveyance direction of the sheet is equal to or higher than a second temperature. The fixing device according to any one of the above.   5. The fixing device according to claim 2, wherein the image forming condition includes a condition that a number of images formed in an image forming process on the sheet is a predetermined number or more. The heating unit receives power supply and heats the fixing surface side member,
The adjustment unit includes an on state where the power is supplied and an off state where the power is not supplied, and a half wave having a predetermined duty ratio corresponding to the amount of power to be supplied to the heating unit. The fixing device according to claim 1, wherein supply of the electric power to the heating unit is controlled based on an on / off pattern of a unit.   An image forming apparatus comprising the fixing device according to claim 1.

Images