JP2007034028A - Fixing device, image forming apparatus, and control method for fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device preventing the damage of an image on a recording medium due to fouling and deterioration in a separation property of the recording medium from an endless belt by avoiding a prescribed amount or more of the fouling from being attached to one recording medium carrying position on the endless belt. <P>SOLUTION: The fixing device 50 is provided with an operation part 90. The arithmetic operation part 90 detects the attached position of foreign matter (adhering position HT of recording paper) attached to the fixing belt 56 and the amount of the foreign matter on the basis of an HP signal from an HP sensor 82 and a foreign matter detecting signal from a foreign matter detecting sensor 61. When the amount of the foreign matter attached to the position exceeds a specified amount, output timing of a drive instruction signal for a pair of registration rollers 63 is changed so that the attaching position of the foreign matter (the adhering position HT of the recording paper) is changed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing a developer image on a recording medium using an endless belt, an image forming apparatus including the fixing device, and a fixing device control method.

  Conventionally, as an image forming apparatus such as a copying machine or a printer, an apparatus using an electrophotographic method is widely known. This electrophotographic image forming apparatus forms not only a monochrome image but also a full color image. There is a device that can. Further, as electrophotographic image forming apparatuses are used in various fields, there is an increasing demand for higher image quality. Here, smoothness of the output image can be cited as one of the factors that determine the image quality, particularly the glossiness of the full-color image. In response to such demands, an image forming method has been proposed in which a color toner image made of a thermoplastic resin is transferred to a recording paper provided with a transparent resin layer made of a thermoplastic resin and fixed. (See, for example, Patent Documents 1 and 2).

  In the image forming method, a belt fixing device has been proposed as a desirable fixing device (see, for example, Patent Document 3). In this belt fixing device, a recording paper carrying an unfixed toner image is hot-pressed by a fixing belt made of a heat-resistant film, and the recording paper is cooled while being in close contact with the fixing belt. As a result, the toner image is solidified and fixed on the recording paper. Then, the recording paper on which the toner image is fixed is peeled off from the fixing belt and discharged to the outside.

  Here, the belt fixing device coagulates with the transparent resin layer together with the transparent resin layer in a state where the toner image is embedded in the transparent resin layer of the recording paper, and the entire surface of the recording paper becomes a smooth surface. A color image having excellent properties can be obtained.

  In addition, as the recording paper having the transparent resin layer, a paper having a resin layer having a thickness of about 10 μm mainly composed of a thermoplastic resin having a glass transition temperature of 358 K or less has been proposed (for example, a patent). Reference 4).

Here, in the belt fixing device, the belt shifting mechanism is arranged so that the contact point between the side edge of the recording paper and the fixing belt is not moved by actively moving the fixing belt in a direction orthogonal to the belt conveyance direction. Is provided. With this mechanism, it is possible to generate a slight deviation in the fixing belt at a predetermined timing so that the recording paper passing portion and the non-passing portion on the fixing belt are not always in the same position. Can be improved (see, for example, Patent Document 5).
Japanese Patent Application Laid-Open No. 64-35542 JP-A-5-216322 JP-A-4-362679 JP 2003-084477 A Japanese Patent Publication No. 07-078658

  However, in the case of the above image forming method, when a recording paper of a standard size is repeatedly used, a phenomenon occurs in which foreign matters such as paper dust and resin components fall on and adhere to the surface of the fixing belt from the end of the recording paper. To do. As a result, the foreign matter adhering to the fixing belt may be transferred to the succeeding recording paper, causing image defects, and the foreign matter adhering to the fixing belt may damage the fixing belt and deteriorate the fixing belt.

  Further, when the foreign matter adheres to and accumulates on the fixing belt, the leading edge position of the recording paper in close contact with the fixing belt may be applied to the position of the accumulated foreign matter. In this case, conveyance separation on the fixing belt may occur. In some cases, the separation property of the recording paper at the part may be significantly reduced.

  An object of the present invention is to prevent a deposit from adhering a predetermined amount or more to one recording medium carrying position on an endless belt, and to prevent image damage on the recording medium due to the deposit and the endless belt. It is an object of the present invention to provide a fixing device capable of preventing deterioration of the separation property of the recording medium, an image forming apparatus including the fixing device, and a control method for the fixing device.

  To achieve the above object, the present invention provides an endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and carries a recording medium on the surface, and a recording medium between the endless belt. Between the fixing roller and the rotating roller, and a pressure roller pressed against the fixing roller across the endless belt so as to form a nip portion for nipping and conveying the sheet. In the fixing device comprising the cooling means, the adhering matter detecting means for detecting adhering matter adhering to the surface of the endless belt, and the output of the adhering matter detecting means There is provided a fixing device comprising a position changing means for changing a recording medium carrying position for carrying a recording medium on a surface.

  To achieve the above object, the present invention provides an endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and carries a recording medium on the surface, and a recording medium between the endless belt. Between the fixing roller and the rotating roller, and a pressure roller pressed against the fixing roller across the endless belt so as to form a nip portion for nipping and conveying the sheet. In the fixing device including the cooling means, the attached matter detecting means for detecting the attached matter attached to the surface of the endless belt, and the recording on the nip portion according to the output of the attached matter detecting means. And a position changing means for changing a recording medium carrying position for carrying the recording medium on the surface of the unsupported belt by controlling the conveyance timing of the medium. To provide a fixing device.

  To achieve the above object, the present invention provides an endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and carries a recording medium on the surface, and a recording medium between the endless belt. Between the fixing roller and the rotating roller, and a pressure roller pressed against the fixing roller across the endless belt so as to form a nip portion for nipping and conveying the sheet. In the fixing device comprising the cooling means, the adhering matter detecting means for detecting adhering matter adhering to the surface of the endless belt, and the speed of the endless belt according to the output of the adhering matter detecting means And a position changing means for changing a recording medium carrying position for carrying the recording medium on the surface of the unsupported belt.

  In order to achieve the above object, the present invention provides an image forming apparatus including any one of the above fixing devices.

  The present invention also provides a method for controlling the fixing device in order to achieve the above object.

  According to the present invention, it is possible to prevent a deposit from adhering to a predetermined amount or more on one recording medium carrying position on the endless belt, and to prevent image damage on the recording medium due to the deposit from the endless belt. It is possible to prevent the recording medium from being deteriorated.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
1 is a longitudinal sectional view showing a configuration of an image forming apparatus including a fixing device according to a first embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of a digital image processing unit 212 in FIG. 1, and FIG. It is a block diagram which shows the structure of the control part 200 of FIG.

  As shown in FIG. 1, the image forming apparatus includes a reader unit R capable of reading a color original in color and a printer unit P capable of forming a color image on a recording sheet by an electrophotographic method.

  The reader unit R includes an automatic document feeder (ADF) 202 that feeds a document to the document table glass 201. A document fed from the automatic document feeder 202 onto the document table glass 201 is illuminated with light from the respective light sources 203 and 204 such as a halogen lamp and a fluorescent lamp through the corresponding reflectors 205 and 206. Reflected light from the illuminated original is imaged on the color CCD 101 mounted on the substrate 211 via the mirrors 207 to 209 and the lens 210. The light sources 203 and 204 and the mirror 207 are accommodated in the carriage 214. The mirrors 208 and 209 are accommodated in the carriage 215. The carriage 214 is moved in the sub-scanning direction at a speed V and the carriage 215 is moved at a speed V / 2. This sub-scanning direction is a direction orthogonal to the electrical scanning (main scanning) direction of the CCD 101. By the movement of the carriage 214 and the carriage 215, the entire surface of the original on the original table glass 201 is scanned (sub-scanning).

  The CCD 101 converts the formed light image into an electrical signal (analog image signal), and this electrical signal is input to the digital image processing unit 212 via the substrate 211. The digital image processing unit 212 converts the electrical signal input from the CCD 101 into a digital signal, performs various processes on the digital signal, and generates C, M, Y, and K signals. The digital image processing unit 212 performs various processes on the image data input via the external I / F 213 to generate C, M, Y, and K signals.

  Specifically, as shown in FIG. 2, the digital image processing unit 212 includes a sample hold unit (clamp & Amp. & S / H & A / D unit) 102 to which an electrical signal (analog image signal) from the CCD 101 is input. Have. The sample hold unit 102 samples and holds the input analog image signal (S / H), and clamps the dark level of the analog image signal to the reference potential. The analog image signal is amplified to a predetermined level, and then converted into a digital image signal, for example, an R, G, B 8-bit digital signal.

  Next, the R, G, and B digital signals are input to the shading unit 103. The shading unit 103 performs shading correction and black correction on the input R, G, and B digital signals. The corrected digital signals of R, G, and B are input to the connecting portion (connecting & MTF correcting & document detecting portion) 104. The joining unit 104 performs joining processing, MTF correction, and document detection processing. When the CCD 101 is a three-line CCD, since the reading positions between the lines are different, the connecting process adjusts the delay amount for each line according to the reading speed, and corrects the signal timing so that the reading positions of the three lines are the same. To do. In the MTF correction, since the reading MTF changes depending on the reading speed and the magnification, the change is corrected. In the document detection process, the document size is detected by scanning the document on the platen glass 201.

  The R, G, and B digital signals whose reading position timing is corrected by the connecting unit 104 are input to the input masking unit 105. The input masking unit 105 corrects the spectral characteristics of the CCD 101 and the spectral characteristics of the light sources 203 and 204 and the reflectors 205 and 206. The R, G, and B digital signals output from the input masking unit 105 are input to a selector 106 that can be switched to an external I / F signal. A signal from an external device is input to the selector 106 via an external I / F (interface) 213. The selector 106 outputs each R, G, B digital signal to the external I / F 213 or a downstream block described later, and outputs a signal input via the external I / F 213 to a downstream block described later. To do.

  The R, G, and B digital signals output from the selector 106 are input to a color conversion unit (color space compression & background removal & LOG conversion unit) 107 and background removal unit 115, respectively. The background removal unit 115 performs background removal on the input R, G, and B digital signals, and the RGB digital signals after the background removal are input to the black character determination unit 116. The black character determination unit 116 determines whether or not the characters in the document are black characters, and generates a black character signal from the document.

  The color conversion unit 107 determines whether the R, G, B digital signals from the selector 106 are signals within a range that can be reproduced by the printer unit P. Here, if the R, G, B digital signals are not within the range reproducible by the printer unit P, the R, G, B digital signals are converted into signals within the range reproducible by the printer unit P. It is corrected so that If each of the R, G, and B digital signals is within a range that can be reproduced by the printer unit P, the signal is not corrected. Then, after background removal processing is performed on the R, G, and B digital signals, the R, G, and B digital signals are converted into C, M, and Y signals by LOG conversion.

  The C, M, and Y signals output from the color conversion unit 107 are delayed by the delay unit 108 to adjust the output timing. The delayed C, M, and Y signals are input to the moire removing unit 109 together with the signal generated by the black character determining unit 116. The moire removing unit 109 removes moire from the input C, M, and Y signals, and each signal after the moire removal is input to the scaling processing unit 110. The scaling processing unit 110 performs scaling processing in the main scanning direction on the input C, M, and Y signals. The C, M, and Y signals subjected to the scaling process are input to a CMYK signal generation unit (UCR & masking & black character reflection unit) 111. The CMYK signal generation unit 111 generates C, M, Y, and K signals from the C, M, and Y signals by UCR processing. The generated C, M, Y, and K signals are corrected to signals suitable for the output of the printer unit P by masking processing, and the determination signals generated by the black character determination unit 116 are C, M, and Y. , K signals are fed back.

  The C, M, Y, and K signals generated by the CMYK signal unit 111 are subjected to density adjustment by the γ correction unit 112 and then input to the filter unit 113. The filter unit 113 performs smoothing or edge processing on the input C, M, Y, and K signals, and outputs the processed C, M, Y, and K signals.

  The C, M, Y, and K signals generated by the digital image processing unit 212 are input to the control unit 200. The control unit 200 sends the input C, Y, M, and K signals to the printer unit P via the printer control I / F 253. The control unit 200 controls the entire image forming apparatus.

  Specifically, as shown in FIG. 3, the control unit 200 includes a CPU 301 that controls the entire image forming apparatus according to a program stored in the memory 303 and executes individual processing. The CPU 301 has I / Fs for connecting the digital image processing unit 212, the external I / F 213, and the printer control I / F 253, and the external I / F 213, the printer control I / F are connected via the I / F. Information for performing control is exchanged with each of F253. Here, the external I / F 213 is an interface for exchanging image data such as image information and code information with an external apparatus such as a facsimile apparatus or a LAN interface apparatus. The printer control I / F 253 is an interface for connecting the CPU 301 and the printer unit P. The printer control I / F 253 includes the C, M, Y, and K signals sent from the digital image processing unit 212 via the CPU 301 and the CPU 301. A control signal for the printer unit P is input.

  Further, the CPU 301 has an I / F for connecting the operation unit 302, and performs corresponding control or processing based on operation information input from the operation unit 302 via the I / F. In addition, information to be displayed on the display panel provided in the operation unit 302 is sent to the operation unit 302 via the I / F.

  The operation unit 302 includes a hard key for inputting information such as operation information by the user and the display panel. Various information such as setting contents and input information is displayed on the display panel. The display panel can display soft keys for inputting information such as operation information.

  As shown in FIG. 1, the printer unit P includes a photoconductor 225 that is driven to rotate in a direction indicated by an arrow A in the drawing. Around the photoconductor 225, a primary charger 221, an exposure device 218, a black developing device 219, a color developing unit 223, a transfer charger 220, a cleaner 222, a static eliminating device 290, and a potential sensor 291 are arranged.

  The primary charger 221 is a charger for charging the surface of the photoreceptor 225 to a uniform potential. The exposure device 218 modulates the laser beam based on the C, M, Y, and K signals input via the printer control I / F 253, and exposes and scans the surface of the photoconductor 225 with the modulated laser beam. . As a result, electrostatic latent images corresponding to C, M, Y, and K colors are formed on the surface of the photosensitive member 225, respectively.

  The black developing device 219 supplies black toner to the photoconductor 225 on which the black electrostatic latent image is formed. As a result, the black electrostatic latent image formed on the photoconductor 225 is visualized as a black toner image. The color developing unit 223 includes three developing devices 223Y, 223M, and 223C for full color development. The developing device 223Y supplies yellow toner to the photoreceptor 225 on which the yellow electrostatic latent image is formed, and visualizes the yellow electrostatic latent image as a yellow toner image. The developing device 223M supplies magenta toner to the photosensitive member 225 on which the magenta electrostatic latent image is formed, and visualizes the magenta electrostatic latent image as a magenta toner image. The developing device 223C supplies cyan toner to the photosensitive member 225 on which the cyan electrostatic latent image is formed, and visualizes the cyan electrostatic latent image as a cyan toner image. When developing each color of C, M, and Y, the developing unit 223 is rotated in the direction indicated by the arrow R in the drawing, and the developing device for the corresponding color is positioned so as to contact the photoconductor 225.

  Each time a toner image is formed on the photoreceptor 225, the toner image is transferred to the intermediate transfer belt 226 by the transfer charger 220. That is, toner images of four colors C, M, Y, and K are superimposed on the intermediate transfer belt 226 and transferred. As a result, a full-color toner image is formed on the intermediate transfer belt 226. Here, the toner remaining on the photosensitive member 225 after the toner image is transferred to the intermediate transfer belt 226 is removed by the cleaner 222 and discharged by the discharging device 290 so as to have a predetermined potential.

  The intermediate transfer belt 226 has a peripheral length that is n (n is an integer) times the outer peripheral length of the photosensitive member 225. Due to the relationship between the peripheral length of the intermediate transfer belt 226 and the outer periphery of the photosensitive member 225, the photosensitive member 225 rotates an integer while the intermediate transfer belt 226 makes one turn, and before the intermediate transfer belt 226 makes one turn. Return to exactly the same state. Therefore, when the four-color toner images are superimposed on the intermediate transfer belt 226 (the intermediate transfer belt 226 rotates four times), color misregistration due to rotation unevenness of the photosensitive member 225 can be avoided.

  Further, the peripheral length of the intermediate transfer belt 226 is set to a length capable of transferring toner images for two images (for two sheets) whose size along the circumferential direction is smaller than a predetermined size. As a result, it is possible to transfer the color toner images for two sheets onto the intermediate transfer belt 226 while the intermediate transfer belt 226 rotates four times to form a color image in which four colors are superimposed. , Productivity is improved.

  The intermediate transfer belt 226 is stretched around a plurality of rollers including the rollers 227, 228, and 229. The roller 227 is a driving roller for driving the intermediate transfer belt 226. The roller 228 is a tension roller that adjusts the tension of the intermediate transfer belt 226. The roller 229 is a backup roller for the secondary transfer roller 231. Between the roller 227 and the roller 228, a reflective sensor 224 that detects the reference position is disposed. The reflective sensor 224 detects a marking such as a reflective tape provided on the edge of the outer peripheral surface of the intermediate transfer belt 226 and outputs an I-top signal. The I-top signal is a signal for instructing the start of image formation. When this signal is input to the exposure device 218, the exposure device 218 emits a laser beam and performs exposure scanning on the photosensitive member 225. To start.

  The secondary transfer roller 231 is driven by the transfer roller attaching / detaching unit 250 so as to contact the intermediate transfer belt 226 and to be detached from the intermediate transfer belt 226. A belt cleaner 232 is provided at a position facing the roller 227 across the intermediate transfer belt 226. The belt cleaner 232 is driven by the belt cleaner attaching / detaching unit 268 so as to come into contact with or separate from the intermediate transfer belt 226. When the belt cleaner 232 comes into contact with the intermediate transfer belt 226, residual toner on the intermediate transfer belt 226 is scraped off by the blade of the belt cleaner 232.

  The toner image formed on the intermediate transfer belt 226 is transferred to the recording paper fed from the cassettes 240 and 241 or the manual paper feed unit 253. Specifically, the recording sheets stored in the cassettes 240 and 241 are picked up by the pickup rollers 238 and 239, and are conveyed toward the registration rollers 255 along the paper feed path by the paper feed roller pairs 237 and 236. Is done. Further, the recording paper loaded on the manual paper feed unit 253 is picked up by the pickup roller 254 and is sent out toward the registration roller 255 through the paper feed roller pair 235. Each of the cassettes 240 and 241 and the manual paper feed unit 253 is provided with recording sheet non-detection sensors 243, 244 and 245 for detecting the presence or absence of the recording sheet. Further, each of the cassettes 240 and 241 and the manual paper feed unit 253 is provided with paper feed sensors 247, 248, and 249 for detecting a pickup failure of the recording paper.

  The recording paper delivered from the cassettes 240 and 241 or the manual paper feed unit 253 is temporarily stopped with its leading end abutted against the registration roller 255 whose driving is stopped. As a result, the skew correction of the recording paper is performed. After this skew correction, the registration roller 255 is driven in accordance with the image formation start timing (transfer timing), and is fed to the nip portion formed between the secondary transfer roller 231 and the intermediate transfer belt 226. At this time, the secondary transfer roller 231 is driven by the transfer roller attaching / detaching unit 250 and is in contact with the intermediate transfer belt 226. The toner image formed on the intermediate transfer belt 226 is transferred onto the fed recording paper at the nip portion. The recording paper on which the toner image is transferred is sent to the fixing device 234 via the conveyance belt 230.

  The fixing device 234 has two pre-fixing chargers 251 and 252 and a pair of fixing rollers 233 that supplement the attractive force of the toner image on the recording paper, and the recording paper is sandwiched and conveyed between the fixing rollers 233. A nip portion is formed. When the recording paper passes through the nip portion, the toner image on the recording paper is heat-pressed and fixed on the recording paper.

  The recording paper that has passed through the fixing device 234 is guided to the paper discharge path 258 or the back surface path 259 by the flapper 257. The recording paper on which image formation has been completed is guided to a paper discharge path 258 by a recording paper flapper 257 and carried into a fixing device 50 described later.

  In the double-side mode in which image formation is performed on both sides of the recording paper, the recording paper on which the image is formed is guided to the back surface path 259 by the flapper 257, and this recording paper is reversed on both sides by each reversing roller 260. It is once transported into the path 261. Next, after the recording paper is conveyed into the double-sided reversing path 261 by the width in the feed direction, the reverse side is driven by the reverse roller 260 and the double-sided path conveying roller 262 so that both sides of the recording sheet face down. The paper is conveyed along the path 263 toward the refeed roller 264.

  The recording paper conveyed toward the paper refeed roller 264 is detected by a paper feed sensor 265 disposed immediately before the paper refeed roller 264. When a predetermined time elapses from this detection time until the leading edge of the recording paper hits the re-feed roller 264 that has stopped driving, the recording paper conveyance operation is temporarily stopped. Thereby, skew correction is performed on the recording paper.

  When the predetermined timing comes after the skew correction, the refeed roller 264 is activated, and the recording paper is conveyed again to the paper feed path with the image forming surface as the back surface. Then, image formation on the back surface of the recording paper is performed in the same procedure as that for image formation on the front surface of the recording paper. The recording paper on which images are formed on both the front and back sides in this way is guided to the paper discharge path 258 by the paper discharge flapper 257 and is carried into the fixing device 50.

  The fixing device 50 is a device for fixing a toner image on the recording paper on the recording paper when the recording paper on which a resin layer is formed (hereinafter referred to as second type recording paper) is used. This type 2 recording paper has a substrate, and a pigment coating layer mainly composed of an adhesive and a pigment is formed on at least one surface of the substrate. A resin layer mainly composed of a thermoplastic resin is formed on the pigment coating layer. The resin layer is a layer mainly composed of a thermoplastic resin and a thermosetting resin. Alternatively, a mixed resin layer in which a thermoplastic resin and a thermosetting resin are mixed may be used. It is good also as a several layer containing the thermoplastic resin layer which has a thermoplastic resin as a main component, and the thermosetting resin layer which has a thermosetting resin as a main component. However, when the resin layer is composed of a plurality of layers, the uppermost layer is composed of a thermosetting resin layer mainly composed of a thermosetting resin. The mixed resin layer, thermoplastic resin layer, and thermosetting resin layer may be combined, but the uppermost layer includes a layer containing a thermosetting resin such as a mixed resin layer or a thermosetting resin layer. It is necessary to. As the thermoplastic resin, a polyester resin, a styrene-acrylic acid ester, a styrene-methacrylic acid ester, or the like can be used, and it is particularly preferable to use a polyester resin.

  A flapper 80, a conveyor belt 87, and a TOP sensor 62 are provided at the entrance of the fixing device 50. The flapper 80 performs a switching operation so as to guide the recording sheet to the bypass 85 when the recording sheet discharged from the printer unit P is a normal recording sheet (a recording sheet that does not need to be subjected to the fixing process by the fixing device 50). Do. The bypass 85 is a path for guiding the recording paper to the paper discharge tray 84. On the other hand, when the recording paper discharged from the printer unit P is the second type recording paper, the switching operation is performed so that the recording paper is guided to the registration roller pair 63 via the conveyance belt 87.

  The registration roller pair 63 is a roller pair for nipping and conveying the second type recording paper at a predetermined timing and sending it to the nip portion between the pressure roller 52 and the fixing belt 56. The fixing belt 56 is stretched around the fixing roller 51, the rotating roller 53, and the tension roller 54. The fixing roller 51 is rotationally driven by a motor (not shown) in a direction indicated by an arrow in the drawing. A predetermined tension is applied to the fixing belt 56 by a tension roller 54, and the fixing belt 56 is held at a substantially constant curvature by the tension.

  The fixing roller 51 is pressed against the pressure roller 52 with a predetermined pressing force with the fixing belt 56 interposed therebetween. The fixing roller 51 has a three-layer structure. Specifically, the fixing roller 51 has a core portion of a hollow pipe, an elastic layer is formed on the surface of the core portion, and a release layer is formed on the elastic layer. The core part is made of an aluminum hollow pipe having a diameter of 44 mm and a thickness of 5 mm, for example. For the core portion having such specifications, the elastic layer is made of, for example, silicon rubber having a JIS-A hardness of 50 degrees and a thickness of 3 mm, and the release layer is made of PFA (tetrafluoroethylene resin) having a thickness of 50 μm. Similar to the fixing roller 51, the pressure roller 52 has a core part of a hollow pipe, and an elastic layer and a release layer formed on the core part.

  A heater 58 for heating the roller is provided in the core portion of the fixing roller 51, and a heater 59 for heating the roller is provided in the core portion of the pressure roller 52. The heaters 58 and 59 are driven and controlled so that the surface temperatures of the fixing roller 51 and the pressure roller 52 become predetermined temperatures, respectively.

  The fixing belt 56 is made of an endless member having a mirror-like release layer formed on the surface (second-type recording paper, a surface in contact with the pressure roller 52). For example, the fixing belt 56 is made of an endless stainless recording paper belt having a thickness of 100 μm, and a release layer made of PFA having a thickness of 10 μm is formed on the surface thereof.

  A cooling fan 55 for cooling the second type recording paper on the fixing belt 56 is disposed on the back side of the fixing belt 56. The cooling fan 55 is positioned between the fixing roller 51 and the tension roller 54 with respect to the conveyance direction of the fixing belt 56. The cooling fan 55 generates an air flow from the back surface to the front surface of the fixing belt 56, and forms a cooling area for cooling the second type recording paper on the fixing belt 56 with respect to the fixing belt 56. That is, when the second type recording paper on the fixing belt 56 passes through the cooling region, the second type recording paper is cooled by the air flow generated by the cooling fan 55.

  A mark representing the home position of the fixing belt 56 is provided on the back surface of the fixing belt 56, and this mark is detected by the HP sensor 82. A foreign matter detection sensor 61 is provided on the surface side of the fixing belt 56. The foreign matter detection sensor 61 is a sensor for detecting the position (position along the fixing belt width direction and its amount (deposition amount)) of the foreign matter attached to the surface of the fixing belt 56. Also, the foreign matter detection sensor 61 is attached to the surface of the fixing belt 56. A cleaner 86 is provided for removing the foreign matter.

  On the downstream side of the fixing belt 56, a cutting cutter 70 that cuts the left and right ends (edges along the transport direction) of the second type recording paper with a predetermined cutting width, and upper and lower ends of the second type recording paper (in the transport direction) A cutter 71 is provided that cuts each edge along the orthogonal direction with a predetermined width. Here, the predetermined cutting width is narrower than the margin area width of the recording paper. The cut recording paper is discharged to the paper discharge tray 83.

  Next, the operation of the image forming apparatus will be described.

  First, when image formation is performed on one side of normal recording paper, normal recording paper is fed from the cassettes 240 and 241 or the manual paper feed unit 253 and is fed to the nip portion between the intermediate transfer belt 226 and the secondary transfer roller 231. It is sent. Then, the toner image formed on the intermediate transfer belt 226 is transferred onto the fed normal recording paper. The normal recording paper to which the toner image is transferred is sent to the fixing device 234 via the conveyance belt 230. In the fixing device 234, the toner image on the normal recording paper is heat-pressed and fixed on the normal recording paper. The normal recording paper after fixing is sent to the fixing device 50 through the paper discharge path 258 by the flapper 257. Here, the normal recording paper is a recording paper that does not require fixing processing by the fixing device 50, and is therefore guided to the bypass 85 by the flapper 80 and discharged to the paper discharge tray 84.

  Similarly, when image formation is performed on both sides of the normal recording paper, the normal recording paper is guided to the bypass 85 by the flapper 80 and discharged to the paper discharge tray 84.

  On the other hand, when image formation is performed using the second type recording paper, the second type recording paper is fed from the cassettes 240 and 241 or the manual feed unit 253, and the second type recording paper is placed on the second type recording paper on the intermediate transfer belt 226. The toner image formed on is transferred. The second type recording paper to which the toner image is transferred is sent to the fixing device 234, and the fixing device 234 performs fixing processing on the second type recording paper. The second type recording paper that has passed through the fixing device 234 is guided to the double-sided reversing path 261 by the flapper 257. Then, the second type recording sheet is reversed using a part of the duplex reversing path 261 and the duplex path 263 and then sent to the fixing device 50 via the discharge path 258. That is, the second type recording paper is sent to the fixing device 50 with its image forming surface facing downward.

  Here, since the second type recording paper is a recording paper subjected to fixing processing by the fixing device 50, the second type recording paper is guided onto the conveying belt 87 by the flapper 80 and passes through the TOP sensor 62. Then, it is conveyed toward the registration roller pair 63. The leading edge of the second type recording paper is temporarily stopped at that position by nipping the leading edge between the registration roller pair 63. At this time, the fixing belt 56 is driven to rotate, and the pressure roller 52 is also driven to rotate. Then, the second type recording paper is sent out toward the nip portion formed between the fixing belt 56 and the pressure roller 52 by the registration roller pair 63 at a predetermined timing.

  Specifically, a recording paper pasting position (recording paper carrying position) HT based on the home position of the fixing belt 56 is defined on the fixing belt 56, and the home position of the fixing belt 56 by the HP sensor 82 is defined. Is detected, the timing at which the recording paper attaching position HT reaches the nip portion between the fixing belt 56 and the pressure roller 52 is calculated. The timing at which the recording paper attaching position HT reaches the nip portion between the fixing belt 56 and the pressure roller 52 is synchronized with the timing at which the leading edge of the second type recording paper reaches the nip portion. The roller pair 63 is driven to rotate, and the second type recording paper is sent out to the nip portion. As a result, the second type recording paper is placed (supported) on the fixing belt 56 such that the front end portion thereof is positioned at the recording paper attaching position HT on the fixing belt 56.

  When the second type recording paper passes through the nip portion between the fixing belt 56 and the pressure roller 52, the second type recording paper and its toner image are heated and pressed by the fixing roller 51 and the pressure roller 52. Further, as described above, since the second type recording paper is carried into the fixing device 50 with its image forming surface facing downward, the image forming surface of the second type recording paper is in close contact with the surface of the fixing belt 56. The As a result, the toner image is buried in the surface of the second type recording paper.

  Here, how the toner image is buried in the surface of the second type recording paper when the second type recording paper P passes through the nip portion will be described with reference to FIG. 4A is a diagram illustrating a state of the second type recording paper P before the second type recording paper P passes through the nip portion, and FIG. 4B is a diagram illustrating the second type recording paper P having passed through the nip portion. FIG. 6 is a diagram illustrating a state of a subsequent second type recording paper P.

  For example, as shown in FIG. 4A, it is assumed that the second type recording paper P is made of a base material P1 on which a transparent resin layer P2 is formed, and a toner image T is fixed on the surface of the transparent resin layer P2. Suppose that When the second type recording paper P in such a state passes through the nip portion, the transparent resin layer P2 and the toner image T of the second type recording paper P are hot-pressed. As a result, as shown in FIG. 4B, the toner image T is embedded in the softened transparent resin layer P2 of the second type recording paper P. At the same time, the second type recording paper P is in close contact with the surface of the fixing belt 56.

  The second type recording paper passes through the cooling region as the fixing belt 56 rotates while being in close contact with the fixing belt 56. In the cooling region, the second type recording paper is forcibly and efficiently cooled by the action of the airflow flowing through the cooling fan 55 and the air duct surrounding it.

  The second type recording paper that is in close contact with the surface of the fixing belt 56 in this manner is sufficiently cooled in the cooling region, and in the region where the curvature of the fixing belt 56 is changed by the rotating roller 53, It is peeled off by (strain).

  The peeled second type recording paper is discharged to the paper output tray 83 after the upper, lower, left and right edges of the second type recording paper are cut to a predetermined width by the cutting cutters 70 and 71, respectively.

  Here, the situation where the second type recording paper from the fixing belt 56 peels will be described with reference to FIGS. FIG. 5 is a diagram schematically illustrating a state where the second type recording sheet is peeled off from the fixing belt 56. FIG. 6 is a diagram illustrating a state in which the foreign matter peeled off from the second type recording paper adheres to the fixing belt 56. FIG. 7 is a diagram schematically showing a state in which the next type 2 recording sheet is peeled off from the fixing belt 56. FIG. 8 is a view showing a state in which the foreign matter peeled off from the second type recording paper is attached to the fixing belt 56. FIG. 9 is a plan view showing a state in which foreign matter has accumulated at the recording paper attaching position HT on the fixing belt 56. FIG. 10 is a diagram showing a distribution state of foreign matters at the recording paper attaching position HT on the fixing belt 56.

  When the recording paper attaching position HT on the fixing belt 56 reaches an area where the curvature of the fixing belt 56 changes by the rotating roller 53, as shown in FIG. The recording paper P starts to peel from the front end portion of the second recording paper P due to its own rigidity from the surface of the fixing belt 56. At this time, as shown in FIG. 6, the leading end portion of the second type recording paper P has a cohesive force of the second type recording paper P and an adhesion force between the fixing belt 56 and the second type recording paper P. Since the resultant force F <b> 1 acts, the foreign matter I <b> 1 in which a minute amount of the resin layer and paper dust are mixed peels from the second type recording paper P and adheres to the recording paper attaching position HT on the fixing belt 56. The fixing belt 56 is rotationally driven with the foreign matter I1 attached thereto.

  In FIG. 7, when there is a recording sheet P ′ following the second type recording sheet, the recording sheet P ′ is placed on the fixing belt 56 so that the leading end thereof is positioned at the recording sheet attaching position HT. Therefore, the leading end portion of the recording paper P ′ and the foreign matter I1 adhering to the fixing belt 56 overlap each other. The recording paper P ′ and the foreign matter I1 pass through the nip portion between the fixing belt 56 and the pressure roller 52 and are cooled in the cooling region.

  When the recording paper pasting position HT on the fixing belt 56 reaches an area where the curvature of the fixing belt 56 changes by the rotating roller 53, the second type recording paper P ′ conveyed in close contact with the surface of the fixing belt 56 is fixed. Peeling is started from the front end portion of the second type recording paper P ′ due to its own rigidity from the surface of the belt 56. At this time, as shown in FIG. 7, the resultant force F2 (> F1) acts on the leading end of the second type recording paper P ′, so that the foreign matter I1 ′ in which a small amount of the resin layer and paper dust are mixed is present. Then, it peels from the second type recording paper P ′ and adheres to the recording paper attaching position HT on the fixing belt 56. Here, the resultant force F2 is the cohesive force of the second type recording paper P ′, the adhesion force between the fixing belt 56 and the second type recording paper P ′, and the adhesion force between the recording paper P ′ and the foreign matter I1. It is a power.

  As a result, as shown in FIG. 8, the foreign matter I1 ′ is superimposed on the foreign matter I1 already adhered on the fixing belt 56 as described above, and the foreign matter obtained by adding both foreign matters I1 and I1 ′ is fixed as the foreign matter I2. It is deposited at the recording paper pasting position HT on the belt 56.

  Thereafter, as shown in FIG. 9, every time the second type recording paper is processed, the foreign matter I accumulates at the recording paper attaching position HT on the fixing belt 56, and the amount thereof increases. Further, as shown in FIG. 10, the foreign matter I on the fixing belt 56 adheres and accumulates on the normal distribution around the recording paper attaching position HT. The distribution width of the foreign matter I is determined by the tolerance of the deviation amount of the conveyance timing by the registration roller pair 63.

  In this way, foreign matter continues to accumulate at the recording paper pasting position HT on the fixing belt 56, and the amount thereof exceeds a predetermined amount.

  Therefore, the present embodiment employs a configuration in which the adhesion positions of foreign matters on the fixing belt 56 are dispersed by changing the adhesion positions of foreign matters on the fixing belt 56 of the fixing device 50.

  This configuration will be described with reference to FIGS. FIG. 11 is a block diagram showing a configuration for realizing control for changing the adhesion position of the foreign matter on the fixing belt 56 of the fixing device 50. FIG. 12 is a timing chart showing the relationship among the HP signal, the drive instruction signal, and the foreign object detection signal. FIG. 13 is a waveform diagram of a foreign object detection signal output from the foreign object detection sensor 61. FIG. 14 is a diagram showing the relationship between the change of the recording paper attaching position HT on the fixing belt 56 and the size of the recording paper.

  Specifically, as shown in FIG. 11, calculation for controlling the drive timing of the registration roller pair 63 based on the HP signal output from the HP sensor 82 and the foreign object detection signal output from the foreign object detection sensor 61. A unit 90 and a drive unit 91 that drives the registration roller pair 63 are provided. Here, when the HP sensor 82 detects the home position mark provided on the back surface of the fixing belt 56, the HP sensor 82 outputs an HP signal. The foreign object detection sensor 61 outputs a foreign object detection signal. The foreign object detection signal is an analog signal having a signal waveform as shown in FIG. 13, for example.

  Based on the HP signal from the HP sensor 82 and the foreign matter detection signal from the foreign matter detection sensor 61, the calculation unit 90 attaches the foreign matter attached on the fixing belt 56 (recording paper pasting position HT) and the foreign matter detection signal. When the amount of foreign matter adhering to the position exceeds a predetermined amount, the output timing of the drive instruction signal to the registration roller pair 63 is changed so as to change the foreign matter attachment position (recording paper attaching position HT). Here, in determining whether or not a foreign matter exceeding a predetermined amount is attached, for example, as shown in FIG. 13, when the level of the foreign matter detection signal becomes a predetermined value 2.6 V or less, the predetermined amount is exceeded. It is determined that a foreign object is attached to the fixing belt 56.

  Prior to the change of the foreign matter attachment position (recording paper attachment position HT), the calculation unit 90 fixes the recording paper on the basis of the changed recording paper attachment position HT without overlapping the attached foreign matter. It is determined whether or not the belt 56 can be pasted, and if possible, the output timing of the drive instruction signal to the registration roller pair 63 so as to change the adhesion position of the foreign matter (recording paper pasting position HT). change. On the other hand, if it is impossible to attach the recording paper on the fixing belt 56 without overlapping the foreign matter with the changed recording paper attaching position HT as a reference, the calculation unit 90 is connected to the fixing belt 56. In order to remove the foreign matter, a drive instruction signal is output to the belt cleaner 86.

  The drive unit 91 drives the registration roller pair 63 when a drive instruction signal for the registration roller pair 63 is input. The belt cleaner 86 is driven when a drive instruction signal is input from the calculation unit 90.

  Here, although the said calculating part 90 is provided independently, it may replace with this and the control part 200 may make it perform the process of this calculating part 90. FIG.

  Next, examples of changing the recording paper attaching position HT and operating the belt cleaner 86 without changing the recording paper attaching position HT will be described.

  For example, assuming that the current recording paper pasting position HT is the recording paper pasting position HT1, the timing at which the recording paper pasting position HT1 reaches the nip portion between the fixing belt 56 and the pressure roller 52 and the leading edge of the second type recording paper. The registration roller pair 63 is rotationally driven at a timing synchronized with the timing at which the portion reaches the nip portion. Specifically, as shown in FIG. 12A, when the time T1 has elapsed from the time when the HP sensor 82 outputs the HP signal, the recording paper attaching position HT1 is between the fixing belt 56 and the pressure roller 52. It is assumed that the timing at which the leading edge of the second type recording paper reaches the nip is synchronized with the timing at which the leading edge of the second type recording paper reaches. That is, the driving instruction signal is output from the arithmetic unit 90 when the time T1 has elapsed from the output time of the HP signal. As a result, the second type recording paper is placed on the fixing belt 56 such that the leading end thereof is positioned at the recording paper attaching position HT1 on the fixing belt 56.

  When the second type recording paper is peeled off from the fixing belt 56, if a foreign matter peeled off from the second type recording paper adheres to the recording paper attaching position HT1 of the fixing belt 56, a foreign matter detection signal is output from the foreign matter detection sensor 61. The output, and the presence, position and amount of the foreign matter are detected based on the foreign matter detection signal. Here, for example, as shown in FIG. 12A, when the recording paper pasting position HT1 reaches the position of the foreign object detection sensor 61 after time TI1 from the output time of the HP signal, the foreign object from the foreign object detection sensor 61 at this time point. The foreign object I1 is detected based on the detection signal.

  When the fixing operation is repeatedly performed with the recording paper pasting position HT1 on the fixing belt 56 as the recording paper pasting position HT, the amount of foreign matter adhering to the recording paper pasting position HT1 on the fixing belt 56 increases. When the amount of foreign matter adhering to the recording paper pasting position HT1 exceeds a predetermined amount, the recording paper pasting position HT1 on the fixing belt 56 is different from the recording paper pasting position HT1, for example, pasting the recording paper The attachment position is changed to HT2. That is, the drive timing of the registration roller pair 63 is changed, the timing when the recording paper attaching position HT2 reaches the nip portion between the fixing belt 56 and the pressure roller 52, and the leading end portion of the second type recording paper to the nip portion. The registration roller pair 63 is rotationally driven at a timing synchronized with the arrival timing.

  For example, as shown in FIG. 12B, the drive instruction signal is output after time T2 (= T1 + α) from the HP signal output time. That is, assuming that the speed of the fixing belt 56 is v, the recording paper pasting position HT2 on the fixing belt 56 is changed to a position shifted by vα downstream from the recording paper pasting position HT1. Foreign matter will adhere to the attachment position HT2. When the recording paper pasting position HT2 reaches the position of the foreign object detection sensor 61 after a time (TI1 + α) from the output time point of the HP signal, the foreign object I2 is detected based on the foreign object detection signal from the foreign object detection sensor 61 at this point. Will be.

  Similarly, when the amount of foreign matter attached to the recording paper pasting position HT2 exceeds a predetermined amount, the recording paper pasting position HT2 is changed to another position.

  Thus, when the amount of foreign matter adhering to the current recording paper pasting position HTn (n ≧ 1) exceeds a predetermined amount, the recording timing on the fixing belt 56 is changed by changing the drive timing of the registration roller pair 63. Since the paper pasting position HTn is changed to another recording paper pasting position HT (n + 1), the position of foreign matter on the fixing belt 56 can be dispersed.

  Here, as shown in FIG. 14, for example, as described above, the recording paper pasting position HT on the fixing belt 56 is changed, and the current recording paper pasting position HT is the position HTn. Assume that the paper pasting position HT is the position HT (n−1),..., And the interval between the recording paper pasting positions is vα. Here, if the amount of foreign matter adhering to the current recording paper pasting position HTn exceeds a predetermined amount, it is necessary to change the current recording paper pasting position HTn to the next recording paper pasting position. However, when the recording paper is pasted on the fixing belt 56 with reference to the next recording paper pasting position changed from the current recording paper pasting position HTn, the recording paper may adhere depending on the size of the recording paper. It may overlap with the foreign object. In this case, the current recording paper pasting position HTn is not changed to the next recording paper pasting position, and the belt cleaner 86 is driven to remove foreign matters adhering to each position on the fixing belt 56. Is done.

  Next, processing of the calculation unit 90 of the fixing device 50 will be described with reference to FIG. FIG. 15 is a flowchart illustrating a processing procedure of the calculation unit 90 of the fixing device 50.

  As shown in FIG. 15, the arithmetic unit 90 first substitutes the previous final value for the foreign matter counter value n indicating what number the current recording paper pasting position HT is in step S1. When the image forming apparatus is used for the first time, the initial value “1” is substituted for the foreign matter counter value n. That is, when the foreign matter counter value n is “1”, it indicates that the current recording paper pasting position HT is the first one.

  Next, in step S2, the calculation unit 90 sets the recording paper size s (length along the circumferential direction of the fixing belt 56) + vα (v: belt speed, as a continuous area on the fixing belt 56 where no foreign matter is attached. α: It is determined whether or not there is an area having a length (the length in the circumferential direction of the fixing belt 56) corresponding to the time when the drive timing of the registration roller pair 63 is delayed in order to change the recording paper pasting position. To do. Here, the continuous area where the foreign matter is not attached on the fixing belt 56 is an area where the recording paper can be pasted so as not to overlap the foreign matter based on the changed recording paper pasting position. For example, when the circumferential length l of the fixing belt 56 and the length s of the recording paper along the circumferential direction of the fixing belt 56 are set and the relationship of the following equation (1) is satisfied, the recording paper size s + vα is provided on the fixing belt 56. It is determined that there is an area (a continuous recording paper pasting area where no foreign matter is attached).

s + vα ≦ l−nvα (1)
If it is determined in step S2 that there is an area having the recording paper size s + vα on the fixing belt 56, the calculation unit 90 determines the current recording paper based on the foreign matter detection signal from the foreign matter detection sensor 61 in step S3. It is determined whether or not the amount of foreign matter adhering to the pasting position exceeds a predetermined amount. Here, if the amount of foreign matter adhering to the current recording paper pasting position does not exceed the predetermined amount, the arithmetic unit 90 returns to step S3. When the amount of foreign matter adhering to the current recording paper pasting position exceeds a predetermined amount, the arithmetic unit 90 determines that the recording paper pasting position needs to be changed, and in step S4, the HP signal Tn + α (α: a constant for delaying the driving of the registration roller pair 63) is substituted into a time Tn from the detection time of the time until the registration roller pair 63 is driven. Here, when the drive timing of the registration roller pair 63 is changed, the gap between the preceding sheet and the succeeding sheet is controlled so as not to collide with the succeeding sheet from the printer unit P. Next, in step S5, the calculation unit 90 substitutes n + 1 for the foreign matter counter value n. And the calculating part 90 returns to said step S2.

  If it is determined in step S2 that there is no region having the recording paper size s + vα on the fixing belt 56, the calculation unit 90 outputs a control signal to the belt cleaner 86 in step S6. As a result, the belt cleaner 86 is driven to come into contact with the fixing belt 56, and the foreign matters at the respective recording paper attaching positions on the fixing belt 56 are removed.

  Next, in step S <b> 7, the arithmetic unit 90 determines that there is no foreign matter exceeding a predetermined value based on the foreign matter detection signal from the foreign matter detection sensor 61 while the fixing belt 56 makes three turns or the fixing belt 56 makes three turns. Wait to detect. Here, the calculation unit 90 detects that there is no foreign matter exceeding a predetermined value based on the foreign matter detection signal from the foreign matter detection sensor 61 while the fixing belt 56 makes three turns or the fixing belt 56 makes three turns. To do. As a result, the calculation unit 90 outputs a control signal so as to separate the belt cleaner 86 from the fixing belt 56 in step S8. As a result, the belt cleaner 86 is driven so as to be separated from the fixing belt 56. And the calculating part 90 returns to said step S2.

  As described above, according to the present embodiment, when a foreign matter adheres to the current recording paper pasting position on the fixing belt 56 in excess of a predetermined amount, the current recording paper pasting position is changed to another recording paper pasting position. Therefore, it is possible to avoid the accumulation of a predetermined amount or more of foreign matter at one recording paper pasting position on the fixing belt 56. As a result, it is possible to prevent image damage on the recording paper due to foreign matter, deterioration of the separation of the recording paper from the fixing belt 56, and the like.

  Further, when the recording paper is pasted on the fixing belt 56 with the recording paper pasting position next to the current recording paper pasting position as a reference, the recording paper is attached to any position of the fixing belt 56. In the case of overlapping with a foreign object, the belt cleaner 86 does not change the current recording paper pasting position to the next recording paper pasting position by the belt cleaner 86 (each recording paper pasting position). ) Is removed. As a result, the overlap between the recording paper and the foreign matter can be prevented in advance, and a significant decrease in the separation of the recording paper from the fixing belt 56 can be avoided. Further, the contact time between the belt cleaner 86 and the fixing belt 56 can be reduced as much as possible, and the life of the fixing belt 56 can be extended.

  In this embodiment, the recording paper pasting position is changed by controlling the drive timing of the registration roller pair 63, but instead, the drive can be temporarily stopped upstream of the registration roller pair 63. A roller may be provided to control the driving timing of this roller. In this case, it is preferable to provide the roller at a position close to the fixing device 50 side.

  Further, when the power is turned on, the above steps S2 and steps S6 to S8 may be executed according to another flow (not shown) in order to determine the removal of foreign matter on the fixing belt 56 or a dirty area. .

  Further, in this embodiment, the foreign matter on the fixing belt 56 is removed by the belt cleaner 86. However, blank recording paper or a blank of the recording paper is used to remove the foreign matter by temporarily interrupting image formation. A portion (unnecessary region) may be placed on the fixing belt 56 so as to overlap the foreign matter adhesion region, foreign matter may be attached to the recording paper, and the foreign matter may be removed from the fixing belt. In order to place the recording paper on the fixing belt 56 so as to overlap the foreign matter, the driving timing of the registration roller pair 63 is changed or the speed of the fixing belt 56 is changed based on the HP sensor 82 and the foreign matter detection sensor 82, respectively. It may be variable.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 16 is a block diagram showing a main part configuration of a fixing device according to the second embodiment of the present invention. FIG. 17 is a timing chart showing the relationship among the HP signal, the drive instruction signal, and the foreign object detection signal. FIG. 18 is a flowchart illustrating a processing procedure of the calculation unit 901 of the fixing device 50. Here, in FIG. 16, the same reference numerals are assigned to the same blocks and the same members as those in the first embodiment.

  The present embodiment is different from the first embodiment in that the recording paper on the fixing belt 56 is pasted by changing the speed of the fixing belt 56 based on the drive timing of the registration roller pair 255 in the printer unit P. It is different in changing the attachment position.

  In the present embodiment, as shown in FIG. 16, the calculation unit 901 generates a drive instruction signal for instructing the speed of the fixing belt 56 (the rotation speed of the fixing roller 51), and the calculation unit 901 generates the driving instruction signal. A drive unit 902 is provided for rotating the fixing roller 51 based on the drive instruction signal.

  Based on the HP signal from the HP sensor 82 and the foreign matter detection signal from the foreign matter detection sensor 61, the calculation unit 901 has a foreign matter attachment position (recording paper attachment position HT) attached to the fixing belt 56 and the foreign matter detection signal. Detect the amount. At this time, if the amount of the foreign matter adhering to the position exceeds a predetermined amount, the speed of the fixing belt 56 (the rotational speed of the fixing roller 51) is instructed so as to change the foreign matter attachment position (recording paper attaching position HT). A drive instruction signal is generated. Here, when the time from the drive start timing of the registration roller pair 255 to the detection of the HP signal of the HP sensor 82 is T, the speed of the fixing belt 56 is varied so as to change the time T. That is, by changing the speed of the fixing belt 56, the adhesion position of the foreign matter (recording paper attaching position HT) can be changed.

  On the other hand, if it is impossible to paste the recording paper on the fixing belt 56 without overlapping the foreign matter on the fixing belt 56, the arithmetic unit 901 removes the foreign matter on the fixing belt 56. A drive instruction signal is output to the belt cleaner 86.

  Here, although the said calculating part 901 is provided independently, it may replace with this and the control part 200 may be made to perform the process of this calculating part 901.

  At present, for example, as shown in FIG. 17A, it is assumed that a time T1 is set as the time from the drive start timing of the registration roller pair 255 until the HP signal of the HP sensor 82 is detected. The recording paper pasting position is HT1. Then, after Ta has elapsed from the HP signal detection time (after T11 has elapsed from the drive start timing of the resist roller pair 255), the foreign matter adhered to the recording paper pasting position HT1 based on the foreign matter detection signal from the foreign matter detection sensor 61. Assume that I1 is detected. The current speed of the fixing belt 56 is v.

  Here, if the amount of the foreign matter I1 adhering to the recording paper pasting position HT1 exceeds a predetermined amount, the recording paper pasting position, that is, the foreign matter adhering position is changed as shown in FIG. . That is, the speed of the fixing belt 56 (the rotational speed of the fixing roller 51) is such that the time from the drive start timing of the registration roller pair 255 to the detection of the HP signal of the HP sensor 82 is from time T1 to time T2 (= T1 + α). ) Is changed to velocity v ′ (<v). As a result, the current recording paper pasting position HT1 is changed to the downstream position HT2. Thereafter, the second type recording paper is placed on the fixing belt 56 so that the leading end thereof is positioned at the recording paper attaching position HT2 on the fixing belt 56. The recording paper pasting position HT2 reaches the position of the foreign matter detection sensor 61 after a time (TI1 + α) from the drive start timing of the registration roller pair 255, and at this time, the foreign matter is detected based on the foreign matter detection signal from the foreign matter detection sensor 61. I2 will be detected.

  Next, processing of the calculation unit 901 of the fixing device 50 will be described with reference to FIG.

  As shown in FIG. 18, the arithmetic unit 901 first substitutes the previous final value for the foreign matter counter value n indicating what number the current recording paper pasting position HT is in step S21. When the image forming apparatus is used for the first time, the initial value “1” is substituted for the foreign matter counter value n. That is, when the foreign matter counter value n is “1”, it indicates that the current recording paper pasting position HT is the first one.

  Next, in step S22, the calculation unit 901 sets the recording paper size s (the length along the circumferential direction of the fixing belt 56) + vα (v: current fixing) as a continuous area on the fixing belt 56 where no foreign matter is attached. There is an area having a length of the belt 56 (α: a time in which the drive timing of the registration roller pair 63 is delayed in order to change the recording paper attaching position) (the circumferential length of the fixing belt 56). It is determined whether or not.

  If it is determined in step S22 that there is a region having the recording paper size s + vα on the fixing belt 56, the calculation unit 901, based on the foreign object detection signal from the foreign object detection sensor 61, in step S23, It is determined whether or not the amount of foreign matter adhering to the pasting position exceeds a predetermined amount. Here, if the amount of foreign matter adhering to the current recording paper pasting position does not exceed the predetermined amount, the computing unit 901 returns to step S23. When the amount of foreign matter adhering to the current recording paper pasting position exceeds a predetermined amount, the arithmetic unit 901 determines that the recording paper pasting position needs to be changed. As a result, in step S24, the arithmetic unit 90 sets the fixing belt so that the time from the drive start timing of the registration roller pair 255 to the detection of the HP signal of the HP sensor 82 is from time T1 to time T2 (= T1 + α). The speed 56 (the rotation speed of the fixing roller 51) is reduced. Next, in step S25, the calculation unit 901 substitutes n + 1 for the foreign matter counter value n. And the calculating part 901 returns to said step S22.

  If it is determined in step S22 that there is no region having the recording paper size s + vα on the fixing belt 56, the calculation unit 901 outputs a control signal to the belt cleaner 86 in step S26. As a result, the belt cleaner 86 is driven to come into contact with the fixing belt 56, and the foreign matters at the respective recording paper attaching positions on the fixing belt 56 are removed.

  Next, in step S <b> 27, the calculation unit 901 has no foreign matter exceeding a predetermined value based on the foreign matter detection signal from the foreign matter detection sensor 61 while the fixing belt 56 makes three turns or the fixing belt 56 makes three turns. Wait to detect. Here, the calculation unit 901 detects that there is no foreign matter exceeding a predetermined value based on the foreign matter detection signal from the foreign matter detection sensor 61 while the fixing belt 56 makes three turns or the fixing belt 56 makes three turns. To do. As a result, the calculation unit 901 outputs a control signal so that the belt cleaner 86 is separated from the fixing belt 56 in step S28. As a result, the belt cleaner 86 is driven so as to be separated from the fixing belt 56. And the calculating part 901 returns to said step S22.

  Thus, when the amount of foreign matter adhering to the current recording paper pasting position HTn (n ≧ 1) exceeds a predetermined amount, the speed of the fixing belt 56 (the rotational speed of the fixing roller 51) is changed, thereby Since the recording paper pasting position HTn on the fixing belt 56 is changed to another recording paper pasting position HTn + 1 that is different, the adhesion positions of foreign matters on the fixing belt 56 can be dispersed.

1 is a longitudinal sectional view illustrating a configuration of an image forming apparatus including a fixing device according to a first embodiment of the present invention. It is a block diagram which shows the structure of the digital image process part 212 of FIG. It is a block diagram which shows the structure of the control part 200 of FIG. (A) is a diagram showing a state of the second type recording paper P before the second type recording paper P passes through the nip portion, and (b) is a second state after the second type recording paper P passes through the nip portion. 4 is a diagram illustrating a state of seed recording paper P. FIG. FIG. 6 is a diagram schematically illustrating a state when the second type recording paper is peeled from the fixing belt 56. FIG. 6 is a diagram illustrating a state in which foreign matter peeled off from the second type recording paper is attached to a fixing belt on 56. FIG. 6 is a diagram schematically showing a state when the next type 2 recording sheet is peeled off from the fixing belt 56. FIG. 6 is a diagram illustrating a state in which foreign matter peeled off from the next type 2 recording paper is attached to a fixing belt 56. 6 is a plan view showing a state in which foreign matter has accumulated at a recording paper attaching position HT on the fixing belt 56. FIG. 6 is a diagram illustrating a distribution state of foreign matters at a recording paper attaching position HT on the fixing belt 56. FIG. 3 is a block diagram illustrating a configuration for realizing control for changing the adhesion position of a foreign substance on the fixing belt 56 of the fixing device 50. FIG. It is a timing chart which shows the relationship between each of a HP signal, a drive instruction | indication signal, and a foreign material detection signal. 6 is a waveform diagram of a foreign object detection signal output from a foreign object detection sensor 61. FIG. FIG. 6 is a diagram illustrating a relationship between a change in a recording paper pasting position HT on the fixing belt 56 and a recording paper size. 6 is a flowchart illustrating a processing procedure of a calculation unit 90 of the fixing device 50. FIG. 6 is a block diagram illustrating a configuration of main parts of a fixing device according to a second embodiment of the present invention. It is a timing chart which shows the relationship between each of a HP signal, a drive instruction | indication signal, and a foreign material detection signal. 6 is a flowchart illustrating a processing procedure of a calculation unit 90 of the fixing device 50.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 Fixing device 51 Fixing roller 55 Cooling fan 56 Fixing belt 61 Foreign matter detection sensor 63,255 Registration roller pair 82 HP sensor 86 Belt cleaner 90,901 Calculation part 200 Control part

Claims (12)

An endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and has a recording medium supported on the surface, and a nip portion for nipping and conveying the recording medium is formed between the endless belt. In a fixing device, comprising: a pressure roller pressed against the fixing roller with the endless belt interposed therebetween; and a cooling unit disposed between the fixing roller and the rotating roller.
An adhering matter detecting means for detecting adhering matter adhering to the surface of the endless belt;
A fixing device comprising: a position changing means for changing a recording medium carrying position for carrying a recording medium on the surface of the unsupported belt according to an output of the adhering matter detecting means. An endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and carries a recording medium on the surface, and a nip portion for nipping and conveying the recording medium is formed between the endless belt In a fixing device, comprising: a pressure roller pressed against the fixing roller with the endless belt interposed therebetween; and a cooling unit disposed between the fixing roller and the rotating roller.
An adhering matter detecting means for detecting adhering matter adhering to the surface of the endless belt;
Position change for changing the recording medium carrying position on the surface of the unsupported belt by controlling the conveyance timing of the recording medium with respect to the nip portion according to the output of the adhering matter detection means And a fixing device. An endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and carries a recording medium on the surface, and a nip portion for nipping and conveying the recording medium is formed between the endless belt In a fixing device, comprising: a pressure roller pressed against the fixing roller with the endless belt interposed therebetween; and a cooling unit disposed between the fixing roller and the rotating roller.
An adhering matter detecting means for detecting adhering matter adhering to the surface of the endless belt;
Position changing means for changing the recording medium carrying position on the surface of the unsupported belt by changing the speed of the endless belt according to the output of the adhering matter detection means. A fixing device.   4. The fixing device according to claim 2, wherein the adhering matter detection means is composed of an optical sensor, and is disposed at a position downstream of the cooling means and upstream of the fixing roller. .   The position changing unit determines whether or not a predetermined amount or more of deposits are attached to the current recording medium carrying position on the surface of the endless belt based on the output of the deposit detection unit, If it is determined that a predetermined amount or more of the deposit is attached to the current recording medium carrying position, the current recording medium carrying position is changed to a recording medium carrying position where the recording medium does not overlap the deposit. The fixing device according to claim 2, wherein the fixing device is a fixed device. Determination means for determining whether or not the size of the continuous region where the deposit on the surface of the endless belt is not adhered is equal to or greater than a predetermined value;
When it is determined by the determining means that the size of the continuous area where the deposit on the surface of the endless belt is not adhered is not greater than a predetermined value, the deposit overlaps with the deposit on the surface of the endless belt. 4. The fixing device according to claim 2, further comprising a deposit removing unit for forcibly supporting the recording medium on the endless belt. A deposit cleaner for removing deposits on the surface of the endless belt;
Determination means for determining whether or not the size of the continuous region where the deposit on the surface of the endless belt is not adhered is equal to or greater than a predetermined value;
When it is determined by the determination means that the size of the continuous region where the deposit on the surface of the endless belt is not adhered is not greater than a predetermined value, the deposit on the surface of the endless belt is removed. The fixing device according to claim 2, further comprising a control unit that operates the deposit cleaner.   The fixing device according to claim 2, wherein the recording medium has a receiving layer made of a thermoplastic resin formed on at least one surface of the recording medium.   An image forming apparatus comprising the fixing device according to claim 1. An endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and carries a recording medium on the surface, and a nip portion for nipping and conveying the recording medium is formed between the endless belt As described above, the control of the fixing device includes: a pressure roller that is pressed toward the fixing roller with the endless belt interposed therebetween; and a cooling unit that is disposed between the fixing roller and the rotating roller. In the method
An adhering matter detecting step of detecting adhering matter adhering to the surface of the endless belt by an adhering matter detecting means;
And a position changing step of changing a recording medium carrying position for carrying the recording medium on the surface of the unsupported belt according to a detection result in the attached matter detecting step. . An endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and carries a recording medium on the surface, and a nip portion for nipping and conveying the recording medium is formed between the endless belt As described above, the control of the fixing device includes: a pressure roller that is pressed toward the fixing roller with the endless belt interposed therebetween; and a cooling unit that is disposed between the fixing roller and the rotating roller. In the method
An adhering matter detecting step of detecting adhering matter adhering to the surface of the endless belt by an adhering matter detecting means;
The recording medium carrying position for carrying the recording medium on the surface of the unsupported belt is changed by controlling the conveyance timing of the recording medium with respect to the nip portion according to the detection result in the adhering matter detection step. And a fixing device control method. An endless belt that is wound around a plurality of rollers including a fixing roller and a rotating roller and has a recording medium supported on the surface, and a nip portion for nipping and conveying the recording medium is formed between the endless belt. As described above, the control of the fixing device includes: a pressure roller that is pressed toward the fixing roller with the endless belt interposed therebetween; and a cooling unit that is disposed between the fixing roller and the rotating roller. In the method
An adhering matter detecting step of detecting adhering matter adhering to the surface of the endless belt by an adhering matter detecting means;
A position changing step for changing a recording medium carrying position for carrying the recording medium on the surface of the unsupported belt by varying the speed of the endless belt according to the detection result of the adhering matter detection step; A fixing device control method comprising:

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