Patent Publication Number: US-7715773-B2

Title: Cleaning device, fixing device, and image forming apparatus

Description:
CROSS REFERENCE 
   This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2006-058903 filed in Japan on Mar. 6, 2006, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a cleaning device for cleaning a surface of a body by intermittently feeding a cleaning belt in compressive contact with the surface. The invention also relates to a fixing device including a fixing roller as a body to be cleaned. The invention further relates to an image forming apparatus including such a fixing device. 
   An image forming apparatus for electrophotographic image formation includes a fixing device with a pair of fixing rollers. One of the fixing rollers is a heating roller heated to a temperature at which toner can melt. The other fixing roller is a pressing roller in compressive contact with the heating roller. While a recording medium such as paper having a toner image transferred to it is passing between the fixing rollers, the fixing device heats and presses the medium so as to fix the image on the medium. 
   While the recording medium is passing between the fixing rollers, part of the toner transferred to the medium sticks to the cylindrical surfaces of the rollers. The toner on the roller surfaces would dirty or spoil the following recording media passing between the fixing rollers. Therefore, the fixing device is fitted with cleaning devices for removing the toner on the roller surfaces. 
   In recent years, it has been demanded that image forming apparatus perform image formation at higher speed and accordingly feed recording media at higher speed. When recording media pass at higher speed between the fixing rollers of an image forming apparatus, larger amounts of toner stick to the cylindrical surfaces of the rollers. The cleaning devices fitted to the fixing device of the apparatus need to remove large amounts of toner on the roller surfaces reliably over a long time. 
   As disclosed in JP-2003-107952A, a conventional cleaning device includes a cleaning belt called a web sheet, which may be made of woven cloth. The cleaning belt is wound on an unwinder and can be fed intermittently from it via a cleaning position, where the belt is brought into compressive contact with the cylindrical surface of a fixing roller. The fed belt is then wound up by a winder. The cleaning belt is impregnated with a cleaning agent such as silicon oil. 
   Such a cleaning device can also be applied as a device for cleaning a dirty surface of a part of a device other than the fixing device of image forming apparatus. 
   As the cleaning belt is wound up repeatedly, its portion remaining on the unwinder decreases, so that a trailing end portion of it becomes unable to be held reliably by the unwinder. The unwinder may include a delivery roller, the cylindrical surface of which is wound with the cleaning belt. If the portion of the cleaning belt that remains on the delivery roller becomes shorter than the circumference of the roller, no sufficient tension can be applied to the belt, so that the belt cannot come into compressive contact with the fixing roller in the cleaning position. This results in insufficient cleaning. If the belt portion on the delivery roller becomes shorter than the roller circumference, a trailing end portion of the cleaning belt becomes loose. The loose belt portion may come into contact with other parts of the apparatus than the fixing roller, so that the parts may be dirtied with the cleaning agent with which the cleaning belt is impregnated, and/or their functions may lower. 
   Another conventional cleaning device counts the rotations of the delivery roller of an unwinder or the wind-up roller of a winder. Based on the number of rotations of the roller, the cleaning device determines the length of the portion of a cleaning belt that is wound on the roller. Before a trailing end portion of the cleaning belt becomes unable to be held reliably on the unwinder, the user is prompted to replace the belt. 
   However, the relation between the number of rotations of the delivery or wind-up roller and the length of the belt portion wound on the roller varies with the number of turns of the wound belt portion. Besides, because the cleaning belt is flexible, the relation between the number of rotations and the length of the wound belt portion is not always equal even if the number of turns is equal. In particular, because the wind-up roller is wound with a portion of the cleaning belt to which toner has stuck, it is impossible to accurately determine the relation between the number of rotations of this roller and the length of the belt portion wound on the roller. 
   Accordingly, it is impossible to accurately detect the length of the wound portion of the cleaning belt of a conventional cleaning device. This prevents the user from being prompted to replace the cleaning belt at the proper time. If the belt replacement is delayed, the body to be cleaned cannot be cleaned sufficiently, and the cleaning agent may dirty other bodies and lower their functions. If the belt replacement is too early, the cleaning belt is thrown away with a long portion of it remaining unused. This results in a high running cost. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to provide a cleaning device, a fixing device, and an image forming apparatus each of which detects between the unwinder and the cleaning position an end point on the cleaning belt that is near to the trailing end of the belt in order to prompt the user to replace the belt at a proper time before the belt end becomes unable to be held reliably on the unwinder, so that the belt on the unwinder can be used without a too long or too short end portion of it remaining unused. 
   The present invention comprises a cleaning belt, an unwinder, a winder, and a detector. The unwinder is wound with the cleaning belt. The winder winds up the cleaning belt intermittently from the unwinder along a path leading past a cleaning position where the belt is brought into contact with a body to be cleaned. The detector is fitted in a detecting position on the path between the unwinder and the cleaning position. The cleaning belt has an end point set on it near its trailing end and associated with the detecting position. When detecting the end point, the detector outputs a detection signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic sectional side view of an image forming apparatus according to a first embodiment of the present invention; 
       FIG. 2  is a sectional view of the fixing device of the image forming apparatus; 
       FIG. 3  is a plan view of a trailing end portion of a web sheet used for the cleaning device of the image forming apparatus; 
       FIG. 4  shows the structure of the cleaning device in detail; 
       FIG. 5  is a block diagram of the control unit of the image forming apparatus; 
       FIG. 6A  is a plan view of a trailing end portion of a web sheet used for a cleaning device according to a second embodiment of the present invention; and 
       FIG. 6B  is a plan view of a trailing end portion of a web sheet used for a cleaning device according to a third embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Preferred embodiments of the present invention will be described below in detail with reference to the drawings. 
     FIG. 1  is a schematic sectional side view of an image forming apparatus  100  according to a first embodiment of the present invention. The image forming apparatus  100  includes an image reading unit  200 , an image forming unit  300 , and a paper feeding unit  400 . 
   The image reading unit  200  includes an ADF (automatic document feeder)  201 , a first document platform  202 , a second document platform  203 , a first mirror base  204 , a second mirror base  205 , a lens  206 , and a CCD (charge coupled device)  207 . The CCD  207  might be replaced by another image sensor. 
   The ADF  201  feeds documents one after one from a document tray  211  via the second document platform  203  to a discharge tray  212 . The rear edge of the ADF  201  is supported pivotably in such a manner that the ADF can cover the top of the first document platform  202 . By raising the front edge of the ADF  201  so as to expose the first document platform  202 , it is possible to place a document manually on this platform. 
   The document platforms  202  and  203  are a hard glass plate. 
   The mirror bases  204  and  205  are supported horizontally movably under the document platforms  202  and  203 . The speed at which the second mirror base  205  moves is ½ of the speed at which the first mirror base  204  moves. The first mirror base  204  carries a light source and a first mirror. The second mirror base  205  carries a second mirror and a third mirror. 
   The image on a document being fed by the ADF  201  can be read with the first mirror base  204  stopping under the second document platform  203 . The light source on the first mirror base  204  under the second document platform  203  radiates light to the front side of the document passing over this platform. The light reflected by this side of the document is then reflected by the first mirror on the first mirror base  204  toward the second mirror base  205 . 
   The image on a document placed on the first document platform  202  can be read with the mirror bases  204  and  205  moving horizontally under this platform. The light source on the first mirror base  204  moving under the first document platform  202  radiates light to the front side of the document on this platform. The light reflected by this side of the document is then reflected by the first mirror on the first mirror base  204  toward the second mirror base  205 . 
   Whether the ADF  201  is used or not, the light reflected by the front side of the document is incident on the CCD  207  via the second and third mirrors on the second mirror base  205  and the lens  206 , with the optical path length constant. 
   The CCD  207  outputs an electric signal in proportion to the quantity of light reflected by the front side of the document. The electric signal is input as image data into the image forming unit  300 . 
   The image forming unit  300  includes a photosensitive drum  31 , a charging device  32 , an exposure device  33 , a developing device  34 , a transfer belt  35 , a cleaner  36 , and a fixing device  37 , which form parts of an image former  30 . 
   The photosensitive drum  31  has a photosensitive layer formed on its cylindrical surface and rotates clockwise in  FIG. 1 . The charging device  32  charges the drum surface uniformly to a preset electric potential. The charging device  32  may be either a non-contact type charging device with a charger or a contact type charging device with a roller or a brush. 
   The exposure device  33  irradiates the cylindrical surface of the photosensitive drum  31  with light based on image data. Photoconduction in the photosensitive layer of the drum  31  forms an electrostatic latent image on the irradiated surface of the drum  31 . The exposure device  33  scans the drum surface axially of the drum  31  with a laser beam modulated with image data. Alternatively, the exposure device  33  might be replaced by an exposure device having an array of ELs, LEDs, or other light emitting devices. 
   The developing device  34  supplies the cylindrical surface of the photosensitive drum  31  with toner to make the electrostatic latent image visible. 
   The transfer belt  35  forms a loop around rollers under the photosensitive drum  31  and has a resistance between about 1×10 9  and 1×10 13  Ω·cm. A transfer roller  35 A is supported inside the transfer belt  35  and keeps it in compressive contact with the cylindrical surface of the photosensitive drum  31 . A transfer voltage is applied to the transfer roller  35 A. The toner image on the photosensitive drum  31  is transferred to a sheet of paper passing between the drum and the transfer belt  35 . 
   The cleaner  36  removes the toner remaining on the portion of the drum surface from which the toner image has been transferred. 
   The fixing device  37  includes a heating roller  37 A and a pressing roller  37 B. The heating roller  37 A has a heater fitted in it for heating it to a temperature at which the toner on this roller can melt. The pressing roller  37 B is biased for compressive contact with the heating roller  37 A at a preset pressure. While a sheet of paper having a toner image transferred to it is passing between the rollers  37 A and  37 B, the fixing device  37  heats and presses the sheet so as to fix the image fast on the sheet. After passing through the fixing device  37 , the sheet of paper is discharged to a delivery tray  38 , which is fitted on one side of the image forming apparatus  100 . 
   The paper feeding unit  400  includes paper feeding cassettes  401 - 404  and a manual feed tray  405 . Each of the paper feeding cassettes  401 - 404  holds sheets of paper of a size. The manual feed tray  405  supports a sheet of paper of size or quality for less frequent use. 
   The paper feeding unit  400  feeds sheets of paper one after one from one of the paper feeding cassettes  401 - 404  or the manual feed tray  405 . A sheet of paper fed from the paper feeding unit  400  is conveyed through a paper conveying passage  10  to the image former  30 . The paper conveying passage  10  includes a first conveying passage  11 , a second conveying passage  12 , a third conveying passage  13 , a fourth conveying passage  14 , and a fifth conveying passage  15 . 
     FIG. 2  shows the structure of the fixing device  37 . The fixing device  37  includes a pair of fixing rollers, which are the heating roller  37 A and the pressing roller  37 B, heater lamps  371 ,  372 ,  374 , and  376 , an external heating roller  373 , a thermister  375 , a cleaning device  1 , and release nails  377  and  378 . 
   A sheet of paper conveyed along conveying guides  11 A- 11 C through the first conveying passage  11  has a toner image transferred to its front side. The conveyed sheet passes with its front side up between the heating roller  37 A and the pressing roller  37 B. 
   The heater lamps  371  and  372  are fitted in the heating roller  37 A. The heater lamp  374  is fitted in the external heating roller  373 . The cylindrical surfaces of the heating rollers  37 A and  373  are kept in compressive contact with each other. The heater lamps  371  and  372  and the external heating roller  373  heat the heating roller  37 A to a preset temperature of about 180-200 degrees C., at which the toner can melt. The thermister  375  senses the surface temperature of the heating roller  37 A. 
   The heater lamp  376  is fitted in the pressing roller  37 B and heats it to a temperature of about 150 degrees C. The pressing roller  37 B is biased toward the heating roller  37 A so that the cylindrical surfaces of these rollers can come into compressive contact with each other. 
   After the sheet of paper passes between the heating roller  37 A and the pressing roller  37 B, one of the release nails  377  and  378  releases the sheet from the cylindrical surface of the adjacent roller  37 A or  37 B if the sheet follows the surface. 
   While passing between the heating roller  37 A and the pressing roller  37 B, the sheet of paper is heated and pressed, so that the toner image transferred to it penetrates into it under pressure while melting with heat. After the sheet of paper passes between these rollers  37 A and  37 B, its temperature lowers, so that the toner image on the sheet hardens and is fixed fast on it. 
   While the sheet of paper is passing between the heating roller  37 A and the pressing roller  37 B, part of the toner that has not been fixed, paper dust, etc. on the sheet stick to the cylindrical surface of the heating roller  37 A. 
   The cleaning device  1  includes a web sheet  2  as a cleaning belt, a delivery roller  3 , a wind-up roller  4 , a pressure roller  5 , tension rollers  6  and  7 , and a detector  20 . The web sheet  2  is a belt of woven or unwoven cloth. The delivery roller  3  and the wind-up roller  4  are supported in an unwinder and a winder respectively. The web sheet  2  moves along the sheet path leading from the unwinder past the tension roller  6 , the pressure roller  5 , and the tension roller  7  in order to the winder. 
   The cylindrical surface of the delivery roller  3  is wound with a preset number of turns of the web sheet  2 , which has not been used. The wind-up roller  4  winds up a used portion of the web sheet  2  on its cylindrical surface. The pressure roller  5  presses the web sheet  2  against the cylindrical surface of the heating roller  37 A in a cleaning position P. The tension rollers  6  and  7  apply a preset tension to the web sheet  2  moving along the sheet path. 
   The web sheet  2  is kept in compressive contact with the cylindrical surface of the heating roller  37 A over a nip width N at the cleaning position P. Every time a preset number of sheets of paper have passed between the heating roller  37 A and the pressing roller  37 B, the wind-up roller  4  turns by a preset angle, winding up a preset length of the web sheet  2 . While the web sheet  2  is sliding on the cylindrical surface of the heating roller  37 A, the sheet removes toner, paper dust, etc. from the surface. 
   While the wind-up roller  4  is rotating to wind up the web sheet  2 , the delivery roller  3  rotates. The portion of the web sheet  2  that is wound on the wind-up roller  4  is equal in length to the portion of this sheet that is unwound from the delivery roller  3 . 
   The trailing end of the web sheet  2  is not fixed to the cylindrical surface of the delivery roller  3 . When the number of turns of the web sheet  2  on the delivery roller  3  is more than one, the trailing end of this sheet is held fixedly between the sheet and the cylindrical surface of this roller. This results in sufficient tension acting on the web sheet  2  over the sheet path, which leads from the delivery roller  3  past the cleaning position P to the wind-up roller  4 . 
   When the number of turns of the web sheet  2  on the delivery roller  3  is less than one, the trailing end of this sheet is not held between the sheet and the cylindrical surface of this roller but can move freely. This results in no sufficient tension acting on the web sheet  2 . In addition, this may bring a trailing end portion of the web sheet  2  into contact with the heating roller  37 A and other parts in the fixing device  37 . The contact of the web sheet  2  may cause malfunction of the apparatus. The web sheet  2  is impregnated with silicon oil or another cleaning agent, which improves its cleaning function. The cleaning agent dirties the parts in contact with the web sheet  2 . 
   Therefore, it is necessary to detect whether the number of turns of the web sheet  2  on the delivery roller  3  is small or not when the number is more than one. If the number is small, the web sheet  2  needs to be replaced. 
     FIG. 3  is a plan view of a trailing end portion of the web sheet  2 . The sheet end portion has an opening  8  as the detection part of the present invention. The opening  8  is formed in a zone extending longitudinally of the web sheet  2  and near one edge of it. The zone has a width W 1  in the lateral directions W across the web sheet  2 . The trailing edge of the opening  8 , which is upstream in the wind-up direction S, is spaced a distance LS 1  from the trailing end of the web sheet  2 . 
     FIG. 4  shows the structure of the cleaning device  1  in detail. As stated already, the cleaning device  1  includes a detector  20 , which is fitted on the sheet path between the delivery roller  3  and the tension roller  6 . The detector  20  detects the opening  8  in the web sheet  2  and outputs a detection signal. 
   The detector  20  includes a pair of terminals  21  and  22 , a presser  23 , a power source  24 , and a voltmeter  25 . The terminals  21  and  22  are connected to the power source  24  and the voltmeter  25  respectively and positioned on both sides of the web sheet  2 . The elasticity of the presser  23  biases the terminal  22  toward the terminal  21  to keep the two terminals in compressive contact with the web sheet  2 . The terminals  21  and  22  are positioned in the zone of width W 1  of the web sheet  2 . 
   The presser  23  may be a coil spring, which biases the terminal  22  toward the terminal  21 . The power source  24  applies a preset voltage to the terminal  21 . The voltmeter  25  measures the voltage applied to the terminal  22 . 
   When the opening  8  in the web sheet  2  is not positioned between the terminals  21  and  22 , the sheet insulates the terminals, so that the voltmeter  25  detects no voltage. When the opening  8  is positioned between the terminals  21  and  22 , they are connected electrically, so that the voltmeter  25  detects the voltage applied to the terminal  22 . When the voltmeter  25  detects a voltage equal to or higher than a reference value, it outputs a detection signal. Thus, the detector  20  detects the opening  8  by means of the voltmeter  25 . 
   The detector  20  is positioned at a distance LW 2  from the position where the web sheet  2  leaves the cylindrical surface of the delivery roller  3 . The distance LS 1  ( FIG. 3 ) between the trailing end of the web sheet  2  and the trailing edge of the opening  8  is longer than the sum of the distance LW 2  and the circumferential length LR of the delivery roller  3 . 
   When the detector  20  detects the opening  8 , at least one turn of the web sheet  2  remains on the delivery roller  3 . Accordingly, with sufficient tension acting on the web sheet  2 , it is possible to detect that a short portion of the sheet remains on the delivery roller  3 . 
     FIG. 5  shows the control unit  50  of the image forming apparatus  100 , which is the controller of the present invention. The control unit  50  includes a CPU  51 , a ROM  52 , a RAM  53 , and a display controller  54 . The detection signal from the voltmeter  25  is input via an interface  54  to the CPU  51 . The display controller  55  is connected to a display  56 , which is fitted on an outer surface of the image forming apparatus  100 . 
   In accordance with the program written in the ROM  52 , the CPU  51  can output the display data for a message prompting the user to replace the web sheet  2 . When a detection signal is input to the CPU  51 , the CPU outputs the display data to the display controller  55 . Based on the display data, the display controller  55  displays the prompting message on the display  56 . 
   The prompting message might be replaced by the number of sheets on which images can be formed by the time the web sheet  2  is replaced. This number is the number of sheets that pass through the fixing device  37  by the time the cylindrical surface of the heating roller  37 A is in such a dirty limit condition that the surface can be cleaned by the unused portion of the web sheet  2 . This number may be a preset value or a value calculated from the average image concentration in the image formation performed by the image forming apparatus  100 . 
   Thus, while sufficient tension is acting on the web sheet  2 , with at least one turn of the sheet remaining on the delivery roller  3 , it is possible to prompt the user to replace the sheet. Before the web sheet  2  is replaced, a trailing end portion of it does not move freely. This keeps the apparatus from being dirtied and prevents its malfunction. 
   Because the opening  8  in the web sheet  2  is detected between the delivery roller  3  and the cleaning position P in the sheet path, the opening is prevented from reaching this position before the sheet is replaced. Accordingly, the cylindrical surface of the heating roller  37 A is cleaned reliably until the web sheet  2  is replaced. 
     FIGS. 6A and 6B  are plan views of trailing end portions of web sheets  2 A and  2 B used for cleaning devices according to a second embodiment and a third embodiment respectively of the present invention. 
   With reference to  FIG. 6A , the web sheet  2 A has openings  8 A- 8 D formed as detection parts in a zone extending in the wind-up direction S and having the width W 1 . The openings  8 A- 8 D are spaced in the wind-up direction S. The dimensions of the openings  8 A- 8 D in the wind-up direction S are larger toward the trailing end of the web sheet  2 A. Accordingly, the time taken by the detector  20  to detect each of the openings  8 A- 8 D is longer toward the trailing end of the web sheet  2 A. 
   From the differences between the times during which detection signals are input from the voltmeter  25  to the CPU  51 , the CPU can determine which of the openings  8 A- 8 D is being detected by the detector  20 . It depends on the length of the unused portion of the web sheet  2 A which of the openings  8 A- 8 D is being detected by the detector  20 . The CPU  51  displays different messages on the display  56  depending on which of the openings  8 A- 8 D is being detected by the detector  20 . The messages for the openings  8 A- 8 D can be stored in a memory area of the ROM  52 . 
   The urgency in a message prompting the user to replace the web sheet  2 A is greater for the opening  8 D than for the opening  8 C, greater for the opening  8 C than for the opening  8 B, and greater for the opening  8 B than for the opening  8 A. Alternatively, the CPU  51  might display the number of sheets on which images can be formed by the time the web sheet  2 A is replaced. This number of sheets is smaller for the opening  8 D than for the opening  8 C, smaller for the opening  8 C than for the opening  8 B, and smaller for the opening  8 B than for the opening  8 A. 
   With reference to  FIG. 6B , the web sheet  2 B has openings  81 A- 81 E formed as detection parts in a zone extending in the wind-up direction S and having the width W 1 . The dimensions of the openings  81 A- 81 E in the wind-up direction S are equal. A memory area of the RAM  53  may be allotted for a counter, which the CPU  51  causes to count the number of times detection signals are input from the detector  20  to the CPU. According to the count from the counter, the CPU  51  displays the different degrees of urgency in the messages prompting the user to replace the web sheet  2 B. Alternatively, according to the count, the CPU  51  might display different numbers of sheets on which images can be formed by the time the web sheet  2 B is replaced. 
   The openings  81 A- 81 E in the web sheet  2 B are spaced at intervals shorter toward the trailing end of the sheet. This makes it possible to gradually shorten the intervals at which the display on the display  56  changes. 
   As shown in  FIG. 6A  and stated already, the web sheet  2 A has four openings  8 A- 8 D arrayed in the wind-up direction S. When one of the last three openings  8 B- 8 D is detected by the detector  20 , one of the first three openings  8 A- 8 C may reach the cleaning position P. If any of the openings  8 A- 8 C stopped in the cleaning position P, the cylindrical surface of the heating roller  37 A would be cleaned insufficiently. 
   The detection of each of the first three openings  8 A- 8 C by the detector  20  enables the CPU  51  to recognize the position of the opening in the sheet path, that is, the distance between the current position of the opening and the cleaning position P. Because the turns of the web sheet  2 A on the wind-up roller  4  are equal in length, the CPU  51  can calculate from the number of turns of the sheet on this roller the distance each of the openings  8 A- 8 C has moved. With reference to  FIG. 4 , if each of the openings  8 A- 8 C moves a distance ranging between LW 1  minus LW 2  (LW 1 −LW 2 ) and LW 1  minus LW 2  plus N (LW 1 −LW 2 +N) after detected by the detector  20  while the wind-up roller  4  is winding up the web sheet  2 A, this roller is kept rotating until it further winds up the sheet by a length equal to or longer than N. This prevents the openings  8 A- 8 C from stopping in the cleaning position P. 
   The distance LS 2  between the trailing end of the web sheet  2 A and the first opening  8 A is shorter than the sum of the circumferential length LR of the delivery roller  3  and the distance LW 1 . The distance LW 1  is the length of the portion of the sheet path that extends between the cleaning position P and the position where the web sheet  2 A leaves the cylindrical surface of the delivery roller  3 . The first opening  8 A does not reach the cleaning position P before the detector  20  detects the last opening  8 D between the cleaning position and the position where the web sheet  2 A leaves the cylindrical surface of the delivery roller  3 . 
   As stated already, the web sheet  2  wound on the delivery roller  3  is impregnated with silicon oil or another cleaning agent, which may affect the detection of the opening  8  by the detector  20 . Therefore, a web sheet  2  impregnated with no cleaning agent might alternatively be wound on the delivery roller  3  and supplied with a cleaning agent between the detector  20  and the cleaning position P. For example, the tension roller  6  might supply the cleaning agent, so that the apparatus could avoid being large in size. This applies to the web sheets  2 A and  2 B as well. 
   The detector  20  would not be limited to what detects the electric connection between the terminals  21  and  22 . The detector  20  might be replaced by a contact type sensor on condition that it would not damage the surfaces of the web sheet  2 . Alternatively, the detector  20  might be replaced by a non-contact sensor such as an optical sensor. 
   The detection part is not limited to the opening  8 . If the detector  20  were an optical sensor, a sheet different in light reflectance or transmittance from the material for the web sheet  2  might be stuck as a detection part on the web sheet. This applies to the web sheets  2 A and  2 B as well. 
   Another cleaning device identical with the cleaning device  1  may be provided for the pressing roller  37 B. A cleaning device according to the present invention can be used with not only the fixing device of an image forming apparatus but also another device having a part that should be cleaned with a cleaning belt. 
   It should be considered that the foregoing descriptions of the embodiments are illustrative in all respects and not restrictive. The scope of the present invention is defined by the appended claims, not by the embodiments, and intended to include meanings equivalent to those of the elements of the claims and all modifications in the claims.