Patent Publication Number: US-8971748-B2

Title: Image forming apparatus

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention contains subject matter related to Japanese Patent Application JP 2012-280133 filed in the Japanese Patent Office on Dec. 21, 2012, the entire contents of which being incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrophotographic image forming apparatus. 
     2. Description of the Related Art 
     Conventionally, there has been known an image forming apparatus having an endless belt as an intermediate transfer body or a conveying belt. Examples of such image forming apparatus include the one which has a cleaner adapted to remove toner and/or the like remaining on the belt. As an example of such cleaner, there is known a cleaner having a cleaning blade which has elasticity and whose end portion abuts the belt so as to remove the toner from the belt. 
     The problem with the image forming apparatus having such a cleaning blade is that blade burr will be caused due to the deformation of the cleaning blade in the rotating direction of the belt. To solve such a problem, there is proposed an image forming apparatus in which a measure is implemented to prevent the blade burr from being formed. 
     For example, Japanese Unexamined Patent Application Publication No. 2004-157532 describes an image forming apparatus in which if the cleaning blade and the like are new, or if the temperature and humidity inside or outside the apparatus meet a predetermined condition, a lubricant will be coated onto the belt. 
     Further, Japanese Unexamined Patent Application Publication No. 2005-77579 describes an image forming apparatus in which if the temperature detected by a temperature detector is equal to or higher than a predetermined value, image forming operation will be stopped. 
     SUMMARY OF THE INVENTION 
     However, in the image forming apparatus described in Japanese Unexamined Patent Application Publication No. 2004-157532, if the cleaning blade and the like are new, or if the temperature and humidity inside or outside the apparatus meet a predetermined condition, the lubricant will be coated onto the belt even if the possibility of occurrence of the blade burr is actually low. 
     Further, in the image forming apparatus described in Japanese Unexamined Patent Application Publication No. 2005-77579, if the temperature detected by the temperature detector is equal to or higher than a predetermined temperature, the image forming operation will be stopped even if the possibility of occurrence of the blade burr is actually low. 
     In other words, in the image forming apparatuses described in Japanese Unexamined Patent Application Publication No. 2004-157532 and Japanese Unexamined Patent Application Publication No. 2005-77579, the measure for preventing blade burr will be implemented upon detecting an environment under which the blade is susceptible to burr, even in the case where such measure is actually not necessary to be implemented. 
     In view of the aforesaid problems, it is an object of the present invention to provide an image forming apparatus capable of implementing the measure for preventing blade burr at appropriate time. 
     To solve the aforesaid problems, an image forming apparatus according to an aspect of the present invention includes a belt, a steering mechanism, a cleaning blade, a timer, an adjuster and a controller. 
     The belt is an endless belt, the steering mechanism is adapted to correct deviation of the belt, the cleaning blade is adapted to abut the belt so as to clean the belt, the timer is adapted to clock the time necessary for the steering mechanism to correct the deviation of the belt, the adjuster is adapted to adjust the abutting state between the belt and the cleaning blade, and the controller is adapted to control the operation of the adjuster based on the time clocked by the timer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view schematically showing an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  is a view showing a secondary transfer section of the image forming apparatus; 
         FIG. 3  is a perspective view showing a steering mechanism of the image forming apparatus; 
         FIG. 4  is a block diagram showing a control system of the image forming apparatus; 
         FIG. 5  is a view for explaining the position of a side portion of a secondary transfer belt detected when performing steering control; 
         FIG. 6  is a scatter plot showing the relationship between operation time of the image forming apparatus and belt position transition time; 
         FIG. 7  is a view showing cleaning belts formed on the secondary transfer belt when performing blade abutting stabilization control; and 
         FIG. 8  is a flowchart showing the operation of the image forming apparatus when forming image. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An image forming apparatus  1  according to an embodiment of the present invention will be described below with reference to  FIGS. 1 to 8 . Note that, in  FIGS. 1 to 8 , like components are denoted by like reference numerals. 
     [Configuration Example of Image Forming Apparatus] 
     First, the image forming apparatus  1  will be briefly described below with reference to  FIG. 1 . 
       FIG. 1  is a cross-sectional view schematically showing the image forming apparatus  1  according to the embodiment of the present invention. 
     As shown in  FIG. 1 , the image forming apparatus  1  is adapted to form an image on a sheet based on electrophotographic technology. The image forming apparatus  1  is a tandem type color image forming apparatus, in which four colors of toner, which are yellow (Y), magenta (M), cyan (C), and black (Bk), are superimposed one on top of another. The image forming apparatus  1  includes a document conveying section  10 , a plurality of sheet accommodating sections  20 , an image reading section  30 , an image forming section  40 , an intermediate transfer belt  50 , a secondary transfer section  60 , and a fixing section  80 . 
     The document conveying section  10  includes a document feeding table  11  on which a document G is set, a plurality of rollers  12 , a conveying drum  13 , a conveying guide  14 , a document ejecting roller  15 , and a document receiving tray  16 . The document G set on the document feeding table  11  is conveyed page by page to a reading position of the image reading section  30  by the plurality of rollers  12  and the conveying drum  13 . The conveying guide  14  and the document ejecting roller  15  eject the document G conveyed by the plurality of rollers  12  and the conveying drum  13  to the document receiving tray  16 . 
     The image reading section  30  reads the image of the document G conveyed by the document conveying section  10  or the image of a document placed on a platen  31 , and creates image data. To be specific, the image of the document G is irradiated by a lamp L. The light reflected from the document G is guided to a first mirror unit  32 , a second mirror unit  33  and a lens unit  34  in that order, so as to form an image on a light receiving surface of an image pickup device  35 . The image pickup device  35  photoelectrically converts the light incident thereon and outputs a prescribed image signal. The image signal outputted by the image pickup device  35  is A/D converted to thereby create image data. 
     The image reading section  30  has an image reading control section  36 . The image reading control section  36  performs various processing, such as shading correction, dither processing, compression and/or the like, on the image data created by the A/D conversion, and stores the resultant data in a RAM  103  of a controller  100  (see  FIG. 4 ). Incidentally, the image data is not limited to the data outputted from the image reading section  30 , but may also be data received from an external device (such as a personal computer, another image forming apparatus or the like) connected to the image forming apparatus  1 . 
     The plurality of sheet accommodating sections  20  are arranged in the lower portion of the main body of the apparatus, and the number of the sheet accommodating sections  20  is determined according to the sizes and/or kinds of sheets. The sheet is fed by a sheet feeding section  21  and conveyed to a conveying section  23 , and is then conveyed to the secondary transfer section  60  (which is the transfer position) by the conveying section  23 . Further, a manual sheet feeding section  22  is arranged in the vicinity of the sheet accommodating sections  20 . A specialty sheet, such as a sheet of a size not accommodated in the sheet accommodation section  20 , a tag sheet having a tag, an OHP sheet or the like, is sent to the transfer position from the manual sheet feeding section  22 . 
     The image forming section  40  (as an adjuster of the present embodiment) and the intermediate transfer belt  50  are arranged between the image reading section  30  and the sheet accommodating section  20 . The image forming section  40  has four image forming units  40 Y,  40 M,  40 C,  40 K for forming a toner image of yellow (Y), a toner image of magenta (M), a toner image of cyan (C), and a toner image of black (K). 
     To be specific, the first image forming unit  40 Y forms a toner image of yellow, the second image forming unit  40 M forms a toner image of magenta, the third image forming unit  40 C forms a toner image of cyan, and the fourth image forming unit  40 K forms a toner image of black. Since the four image forming units  40 Y,  40 M,  40 C,  40 K have the same configuration, only the first image forming unit  40 Y will be described herein. 
     The first image forming unit  40 Y has a drum-like photoreceptor  41 , a charging section  42  arranged around the photoreceptor  41 , an exposure section  43 , a developing section  44 , and a cleaning section  45 . The photoreceptor  41  is rotated by a drive motor (not shown). The charging section  42  applies electric charges to the photoreceptor  41  so that the surface of the photoreceptor  41  is evenly charged. The exposure section  43  performs an exposure operation on the surface of the photoreceptor  41  based on the image data read from the document G or the image data transmitted from the external device, to thereby form an electrostatic latent image on the photoreceptor  41 . 
     The developing section  44  causes yellow toner to adhere to the electrostatic latent image formed on the photoreceptor  41 . Thus, a toner image of yellow is formed on the surface of the photoreceptor  41 . Incidentally, the developing section  44  of the second image forming unit  40 M causes the magenta toner to adhere to the photoreceptor  41  of the second image forming unit  40 M, the developing section  44  of the third image forming unit  40 C causes the cyan toner to adhere to the photoreceptor  41  of the third image forming unit  40 C, and the developing section  44  of the fourth image forming unit  40 K causes the black toner to adhere to the photoreceptor  41  of the fourth image forming unit  40 K. 
     The cleaning section  45  removes the toner remaining on the surface of the photoreceptor  41 . 
     The toner adhering to the photoreceptor  41  is transferred to the intermediate transfer belt  50  (which is an example of an intermediate transfer body). The intermediate transfer belt  50  is an endless belt wrapped around a plurality of rollers. The intermediate transfer belt  50  is driven by a drive motor (not shown) to rotate in a direction opposite to the rotation (moving) direction of the photoreceptor  41 . 
     In the intermediate transfer belt  50 , four primary transfer sections  51  are arranged in positions facing the respective photoreceptors  41  of the four image forming units  40 Y,  40 M,  40 C,  40 K. Each primary transfer section  51  applies a voltage having a polarity opposite to that of toner to the intermediate transfer belt  50 , to thereby transfer the toner adhering on the photoreceptor  41  to the intermediate transfer belt  50 . 
     Thus, by rotationally driving the intermediate transfer belt  50 , four toner images respectively formed by the four image forming units  40 Y,  40 M,  40 C,  40 K are sequentially transferred to the surface of intermediate transfer belt  50 . Consequently, a toner image of yellow, a toner image of magenta, a toner image of cyan, and a toner image of black are superimposed on the intermediate transfer belt  50  to thereby form a color image. 
     Further, a belt cleaning device  53  faces the intermediate transfer belt  50 . The belt cleaning device  53  is adapted to clean the surface of the intermediate transfer belt  50 , which has completed the transfer of the toner image to the sheet. 
     The secondary transfer section  60  is arranged near the intermediate transfer belt  50  and on the downstream side of the conveying section  23  in the sheet conveying direction. The secondary transfer section  60  causes the sheet conveyed by the conveying section  23  to contact the intermediate transfer belt  50 , so that the toner image formed on the outer surface of the intermediate transfer belt  50  is transferred to the sheet. The secondary transfer section  60  has a secondary transfer belt  67  and a cleaning blade  65  adapted to remove the toner adhering on the secondary transfer belt  67 . The secondary transfer section  60  will be described later in more detail. 
     The fixing section  80  is arranged on the sheet ejection side of the secondary transfer section  60 . The fixing section  80  presses and heats the sheet to fix the transferred toner image to the sheet. The fixing section  80  is configured by, for example, a pair of fixing members which are an upper fixing roller  81  and a lower fixing roller  82 . The upper fixing roller  81  and the lower fixing roller  82  are arranged in a state where they are brought into pressure contact with each other, so that a fixing nip is formed as a pressure-contact portion between the upper fixing roller  81  and the lower fixing roller  82 . 
     A heater is provided within the upper fixing roller  81 . A roller portion of the upper fixing roller  81  is heated by the heat radiated from the heater. The heat of the roller portion of the upper fixing roller  81  is transferred to the sheet, and thereby the toner image on the sheet is heat-fixed. 
     The sheet is conveyed to pass through the fixing nip in a state where the surface having the toner image transferred thereto by the secondary transfer section  60  (i.e., the surface to be subjected to the fixing process) faces the upper fixing roller  81 . Thus, when the sheet passing through the fixing nip is pressed by the upper fixing roller  81  and the lower fixing roller  82 , it is heated by the roller portion of the upper fixing roller  81 . 
     A switching gate  24  is arranged on the downstream side of the sheet conveying direction of the fixing section  80 . The switching gate  24  switches the conveying path of the sheet having passed through the fixing section  80 . In other words, when ejecting sheet with the image side facing up in the case of performing one-sided image formation, the switching gate  24  will cause the sheet to go straight ahead. Therefore, the sheet is ejected by a pair of sheet ejecting rollers  25 . Further, when ejecting the sheet with the image side facing down in the case of performing one-sided image formation, or when performing two-sided image formation, the switching gate  24  will guide the sheet downward. 
     Further, when ejecting sheet with the image side facing down, the sheet is guided downward by the switching gate  24  and then reversed and conveyed upward by a sheet reversing and conveying section  26 . Therefore, the reversed sheet is ejected by the pair of sheet ejecting rollers  25 . 
     When performing two-sided image formation, the sheet is guided downward by the switching gate  24  and then reversed by the sheet reversing and conveying section  26  and sent to the transfer position again by a sheet re-feeding path  27 . 
     Alternatively, a post-processing device may be arranged on the downstream side of the pair of the sheet ejecting rollers  25 , wherein the post-processing device is adapted to perform folding processing, stapling processing and/or the like on the sheet. 
     [Secondary Transfer Section] 
     Next, the secondary transfer section  60  will be described below with reference to  FIG. 2 . 
       FIG. 2  is a view showing the secondary transfer section  60 . Note that, in  FIG. 2 , the sheet to be conveyed by the secondary transfer belt  67  is donated by letter “S”, and the sheet conveying direction is indicated by arrow “A”. Further, in a plane parallel to the surface of the secondary transfer belt  67 , the direction perpendicular to the sheet conveying direction is donated by letter “B”. 
     As shown in  FIG. 2 , the secondary transfer section  60  includes a secondary transfer roller  61 , a secondary transfer roller  61 , a drive roller  62 , a steering roller  63 , a driven roller  64 , the cleaning blade  65 , a lubricant brush  66 , the secondary transfer belt  67  (as an example of the belt of the present invention), and a steering mechanism  68  (see  FIG. 3 ). 
     The secondary transfer roller  61  is brought into pressure contact with a secondary transfer counter roller  52  through the secondary transfer belt  67  and the intermediate transfer belt  50 . The nip portion where the secondary transfer roller and the intermediate transfer belt  50  come into contact with each other is the transfer position where the toner image formed on the outer surface of the intermediate transfer belt  50  is transferred to the sheet S. 
     The secondary transfer belt  67  is wrapped around the secondary transfer roller  61 , the drive roller  62 , the steering roller  63  and the driven roller  64 , and is adapted to be able to rotate either in a first rotating direction in which the sheet is caused to be conveyed along the conveying direction A or in a second rotating direction opposite to the first rotating direction. 
     The drive roller  62  is rotated by a roller drive section (see  FIG. 4 ). In the present embodiment, a stepping motor is used as the driving source of the roller drive section  90 . The driving force generated by the rotation of the drive roller  62  is transmitted to the secondary transfer roller  61 , the steering roller  63  and the driven roller  64  through the secondary transfer belt  67 . Thus, the secondary transfer roller  61 , the steering roller  63  and the driven roller  64  rotate along with the drive roller  62 . Due to being driven by the drive roller  62 , the secondary transfer belt  67  rotates to convey the sheet which has guided to the transfer position by guide members  23 A,  23 B of the conveying section  23 . 
     The secondary transfer belt  67  is an example of the belt of the present invention. The secondary transfer belt  67  has toner adhered thereto for forming a pattern to adjust color registration or forming a cleaning pattern. When forming images on both sides of the sheet, since one side (front surface) of the sheet on which an image has been first formed contacts the secondary transfer belt  67 , there is a possibility that the toner of the image formed on the one side of the sheet might adhere to the secondary transfer belt  67 . Also, when forming an image over the entire area of the sheet (i.e., when performing a so-called “full bleed printing”), there is a possibility that the toner might adhere to the secondary transfer belt  67 . The toner adhering to the secondary transfer belt  67  is removed by the cleaning blade  65 . 
     The cleaning blade  65  is a substantially rectangular plate-like member formed of an elastic material such as a rubber, a resin or the like. The cleaning blade  65  has two long side portions opposite to each other in the transversal direction and two short side portions opposite to each other in the longitudinal direction. 
     One long side portion forms an abutting portion  65   a  that abuts the surface of the secondary transfer belt  67 . The secondary transfer belt  67  rotates in a state where the abutting portion  65   a  abuts the secondary transfer belt  67 , so that the toner adhering on the surface of the secondary transfer belt  67  is removed by the abutting portion  65   a.    
     The other long side portion is fixed to a blade fixing portion  69 . The drive roller  69  is fixed to a blade drive mechanism  91  (see  FIG. 4 ). In the present embodiment, a stepping motor is used as the driving source of the blade drive mechanism  91 . According to the instruction of the controller  100  (see  FIG. 4 ), the blade drive mechanism  91  drives the cleaning blade  65  so that the cleaning blade  65  is moved close to or away from the secondary transfer belt  67 . 
     The lubricant brush  66  has a rotating shaft extending in the same direction as the rotating shafts of the rollers  61 ,  62 ,  63 ,  64 , and faces the secondary transfer roller  61  through the secondary transfer belt  67 . The lubricant brush  66  is connected to a brush drive section  92  (see  FIG. 4 ). In the present embodiment, a stepping motor is used as the driving source of the brush drive section  92 . According to the instruction of the controller  100  (see  FIG. 4 ), the brush drive section  92  drives the lubricant brush  66  to rotate. The lubricant brush  66  is sliding-contacted with a lubricant block (not shown) formed of a solid lubricant to scrape off the lubricant, so that the scraped lubricant adheres to the surface of the brush. Further, the lubricant brush  66  contacts the secondary transfer belt  67 , so that the lubricant adhering to the lubricant brush  66  is coated on the secondary transfer belt  67 . 
     [Steering Mechanism] 
     Next, the steering mechanism  68  will be described below with reference to  FIGS. 2 and 3 .  FIG. 3  is a perspective view of the steering mechanism  68 . Note that, in  FIG. 3 , the conveying direction in which the secondary transfer belt  67  conveys the sheet is indicated by arrow “A”, and in a plane parallel to the surface of the secondary transfer belt  67 , the direction perpendicular to the sheet conveying direction is donated by letter “B”. 
     When rotating, the secondary transfer belt  67  is predisposed to deviate to either side in the width direction of the secondary transfer belt  67  depending on the assembly attitude of the rollers  61 ,  62 ,  63 ,  64 , the distortion of the secondary transfer section  60  itself, and/or the like. Such a predisposition causes color drift of the toner image transferred to the sheet. To solve such a problem, the image forming apparatus  1  of the present embodiment is provided with the steering mechanism  68  adapted to periodically read the position of the secondary transfer belt  67  in the width direction and correct the deviation or meandering of the secondary transfer belt  67 . Incidentally, the width direction of the secondary transfer belt  67  is identical to the direction B. 
     The steering mechanism  68  of the present embodiment includes the steering roller  63 , a position detector  70  (see  FIG. 3 ), and a steering drive section  93  (see  FIG. 4 ). 
     One end portion of the steering roller  63  in the direction B is connected to the steering drive section  93 . In the present embodiment, a stepping motor is used as the driving source of the steering drive section  93 . According to the instruction of the controller  100  (see  FIG. 4 ), the steering drive section  93  tilts the other end portion of the steering roller  63  in the direction B. 
     The position detector  70  includes three photosensors  71 , a movable portion  72 , and a biasing member  73 . 
     The movable portion  72  has a roller portion  74  which contacts a side portion of the secondary transfer belt  67  in the direction B (note that sometimes the “side portion of the secondary transfer belt  67  in the direction B” is simply referred to as “side portion” hereinafter). The movable portion  72  is supported by a supporting member  75  provided in the image forming apparatus  1  so that it can move in the direction B. The roller portion  74  rotates with the rotation of the secondary transfer belt  67 . 
     The biasing member  73  is a spring-like member with one end portion thereof connected to the movable portion  72  and the other end portion thereof connected to the supporting member  75 . The biasing member  73  biases the movable portion  72  so that the roller portion  74  contacts the side portion of the secondary transfer belt  67  in the direction B. 
     Each photosensor  71  is a reflective photosensor having a light-emitting portion (not shown) and a light-receiving portion (not shown), wherein the light-emitting portion is adapted to emit light and the light-receiving portion is adapted to receive light. A reflecting (not shown) is provided at a predetermined place located in the lower portion of the movable portion  72 . When receiving light, the light-receiving portion outputs a detection signal to the controller  100  (see  FIG. 4 ). 
     [Configuration of Control System of Image Forming Apparatus] 
     A control system of the image forming apparatus  1  will be described below with reference to  FIG. 4 . 
       FIG. 4  is a block diagram of the control system of the image forming apparatus  1 . 
     As shown in  FIG. 4 , the image forming apparatus  1  includes the controller  100 . The controller  100  is connected to a communication section  108 , the document conveying section  10 , the sheet accommodating section  20 , the image reading section  30 , the image forming section  40  and the secondary transfer section  60  through a system bus  107 . 
     The controller  100  controls the operation (driving) of the document conveying section  10 , the sheet accommodating section  20 , the image reading section  30 , the image forming section  40  and the secondary transfer section  60  connected thereto. In other words, the controller  100  controls the entire image forming apparatus  1 . The controller  100  includes a CPU (central processing unit)  101 , a ROM (Read Only Memory)  102  for storing program(s) executed by the CPU  101  and the like, and a RAM (Random Access Memory)  103  used as work area of the CPU  101 . Incidentally, a programmable ROM capable of erasing the data electrically stored therein, for example, is used as the ROM  102 . 
     The communication section  108  is adapted to receive, through a communication line, job information sent from a PC (personal computer)  120 , which is the aforesaid external device. The received job information is transmitted to the controller  100  through the system bus  107 . 
     Incidentally, although the present embodiment is described based on an example in which a personal computer is used as the external device, the present invention is not limited to such example, but various other devices, such as a facsimile device or the like, can be used as the external device. 
     During the rotation of the secondary transfer belt  67 , the controller  100  performs steering control every predetermined timing. 
     The steering control will be described below with reference to  FIG. 5 .  FIG. 5  is a view for explaining the position of the side portion of secondary transfer belt  67  detected when performing the steering control. When performing the steering control, the controller  100  detects the position of the secondary transfer belt  67  based on the detection signal outputted from the photosensors  71  of the position detector  70 . For example, the controller  100  detects, based on the detection signal, whether or not the side portion of the secondary transfer belt in the direction B is located at any one of predetermined positions P 2  to P 5  as shown in  FIG. 5 . 
     Next, based on the detected position of the secondary transfer belt  67 , the controller  100  controls the operation of the steering drive section  93  to tilt the steering roller  63  to correct the deviation or meandering of the secondary transfer belt  67 . For example, the controller  100  controls the operation of the steering drive section  93  to tilt the steering roller  63  so that the side portion of the secondary transfer belt  67  is located at either the position P 3  or the position P 4 . 
     To be specific, the controller  100  controls the operation of the steering drive section  93  so that when the side portion of the secondary transfer belt  67  is located at the position P 3  , the side portion of the secondary transfer belt  67  will be moved to the position P 4 ; and when the side portion of the secondary transfer belt  67  is located at the position P 4 , the side portion of the secondary transfer belt  67  will be moved to the position P 3 . Further, the controller  100  controls the operation of the steering drive section  93  so that when the side portion of the secondary transfer belt  67  is located at the position P 5 , the side portion of the secondary transfer belt  67  will be moved to the position P 4 ; and when the side portion of the secondary transfer belt  67  is located at the position P 2 , the side portion of the secondary transfer belt  67  will be moved to the position P 3 . 
     Thus, the side portion of the secondary transfer belt  67  can be situated close to a design ideal position (i.e., a design center) which is the boundary between the position P 3  and the position P 4 . 
     Further, the controller  100  clocks the time necessary for the steering control, i.e., the time necessary to perform one position transition (note that sometimes such time is referred to as “belt position transition time” hereinafter) every time it performs the steering control, and stores the result in the ROM  102  or RAM  103 . 
     Further, the controller  100  conducts a blade abutting stabilization control. The blade abutting stabilization control is a control for stabilizing the abutting state between the secondary transfer belt  67  and the cleaning blade  65 . The controller  100  determines whether or not it is necessary to conduct the blade abutting stabilization control based on the belt position transition time. 
     Here, the relationship between the belt position transition time and the abutting state between the secondary transfer belt  67  and the cleaning blade  65  is described below with reference to  FIG. 6 . 
       FIG. 6  is a scatter plot showing the relationship between operation time of the image forming apparatus  1  and belt position transition time. 
     The term “stable period” indicated in  FIG. 6  is a period in which the friction between the cleaning blade  65  and the secondary transfer belt  67  is relatively small, and therefore the abutting state between the cleaning blade  65  and the secondary transfer belt  67  is stable. In the stable period, variation in belt position transition time is small. Further, in the stable period, good cleaning effect caused by the cleaning blade  65  can be expected. 
     The term “stable period” indicated in  FIG. 6  is a period in which the friction between a portion of the cleaning blade  65  and the secondary transfer belt  67  is larger compared with the stable period, and therefore the abutting state between the cleaning blade  65  and the secondary transfer belt  67  is slightly unstable. 
     For example, if the friction between a portion of the cleaning blade  65  in the direction B and the secondary transfer belt  67  becomes large, such portion of the cleaning blade  65  will slightly bound on the surface of the secondary transfer belt  67  to cause so-called “bounding”. 
     Thus, pressing force for the cleaning blade  65  to press the secondary transfer belt  67  differs between the portion of the cleaning blade  65  where the bounding occurs and the other portion of the cleaning blade  65 . Thus, a difference in belt tension is caused between a portion of the secondary transfer belt  67  which abuts the portion of the cleaning blade  65  where the bounding occurs and the other portion of secondary transfer belt  67  which abuts the other portion of the cleaning blade  65 . Thus, since the transition of the belt position can not be smoothly performed, the belt position transition time may be longer compared with the stable period. 
     Thus, a variation in belt position transition time ranging from 0.5 to 3 seconds is observed in the metastable period. However, in the metastable period, the cleaning effect of the cleaning blade  65  does not drop to a level that may cause cleaning failure. 
     The term “unstable period” indicated in  FIG. 6  is a period in which the friction between almost the entire cleaning blade  65  and the secondary transfer belt  67  is larger compared with the metastable period, and the bounding of the cleaning blade  65  becomes deteriorated, so that the abutting state between the cleaning blade  65  and the secondary transfer belt  67  is unstable. 
     In the unstable period, the difference in belt tension becomes large with the deterioration of the bounding of the cleaning blade  65 . Thus, in the unstable period, the belt position transition time may become further longer compared with the metastable period. 
     Thus, a variation in belt position transition time ranging from 0.5 to 9 seconds is observed in the unstable period. Further, in the unstable period, the cleaning effect of the cleaning blade  65  is not sufficient, and cleaning failure occurs. 
     To solve such problem, in the metastable period, which is a period before the unstable period, the controller  100  determines that it is necessary to perform the blade abutting stabilization control, and performs the blade abutting stabilization control. To be specific, the controller  100  calculates standard deviation and 3σ based on the belt position transition time stored in the ROM  102  or the RAM  103 , and determines, if the last stored belt position transition time falls within the range of 3σ, that it is necessary to perform the blade abutting stabilization control. 
     Incidentally, if it is intended to increase the number of data stored in the ROM  102  or the RAM  103  so as to increase the accuracy of the determination, a predetermined number of data (for example, 200 pieces of pseudo belt position transition time) may be stored in the ROM  102  or the RAM  103 . Further, the determination of whether or not it is necessary to perform the blade abutting stabilization control may also be executed when the number of data of the belt position transition time stored exceeds the predetermined number of data. 
     Next, the blade abutting stabilization control performed by the controller  100  will be described below with reference to  FIG. 7 .  FIG. 7  is a view showing cleaning belts formed on the secondary transfer belt  67  when performing the blade abutting stabilization control. In  FIG. 7 , the sheet is indicated by letter “S”, and the conveying direction of the sheet conveyed to the secondary transfer belt  67  is indicated by arrow “A”. 
     When performing the blade abutting stabilization control, the controller  100  controls the operation of the image forming section  40  to form a cleaning belt (i.e., a cleaning pattern) on the secondary transfer belt  67 , wherein the cleaning belt has a predetermined shape. 
     The cleaning belt is a rectangular pattern formed for supplying an external additive (which has the same function as a lubricant) between the cleaning blade  65  and the secondary transfer belt  67 , and is formed by a toner that contains the external additive. The cleaning belt is formed on the surface of the secondary transfer belt  67  after the image has been transferred to the sheet. In the case where the image is continuously formed, as shown in  FIG. 7 , the cleaning belt is formed between the sheets continuously conveyed. 
     In  FIG. 7 , the cleaning belt CP 1  is a cleaning belt formed when the blade abutting stabilization control is not performed (i.e., in the normal time). The cleaning belt CP 2  and cleaning belt CP 3  are each a cleaning belt formed when the blade abutting stabilization control is performed. The cleaning belt CP 2  is formed so that the area thereof is substantially twice as large as the area of the cleaning belt CP 1 . Further, the cleaning belt CP 3  is formed as two cleaning belts CP 1  aligned side by side. In other words, the toner amount necessary for forming the cleaning belt CP 2  or the cleaning belt CP 3  is larger than the toner amount necessary for forming the cleaning belt CP 1  (which is a predetermined amount of toner). Thus, when performing the blade abutting stabilization control, the amount of the external additive supplied to between the cleaning blade  65  and the secondary transfer belt  67  is larger compared with the normal time. 
     When a large amount of the external additive is supplied to between the cleaning blade  65  and the secondary transfer belt  67 , the friction between the cleaning blade  65  and the secondary transfer belt  67  is reduced. Thus, the abutting state between the cleaning blade  65  and the secondary transfer belt  67  can be adjusted, and therefore blade burr can be restrained, and occurrence of bounding can be suppressed. 
     Incidentally, when performing the blade abutting stabilization control, the controller  100  may also control the operation of the image forming section  40  to either form the cleaning belt CP 2  only or form the cleaning belt CP 3  only, instead of alternately forming the cleaning belt CP 2  and the cleaning belt CP 3 . 
     The operation of the image forming apparatus  1  when forming image will be described below with reference to  FIG. 8 .  FIG. 8  is a flowchart showing the operation of the image forming apparatus  1  when forming image. 
     First, when the communication section  108  receives job information, or when the user operates an operation unit (not shown) of the image forming apparatus  1 , the controller  100  will control the operation of each section including the roller drive section  90  according to the job information or the user&#39;s operation to rotate the secondary transfer belt  67  (step S 1 ). 
     Next, the controller  100  controls the operation of the steering drive section  93  to perform the belt steering control (step S 2 ). 
     Next, the controller  100  determines whether or not it is necessary to perform the blade abutting stabilization control (step S 3 ). 
     If it is determined that it is necessary to perform the blade abutting stabilization control (YES in step S 3 ), the controller  100  will performs the blade abutting stabilization control (step S 4 ). While if it is determined that it is not necessary to perform the blade abutting stabilization control (NO in step S 3 ), the controller  100  will move the processing to step S 5 . 
     The controller  100  determines, based on the job information or the operation inputted to the operation unit, whether or not the image of the final page has been formed (step S 5 ). If it is determined that the image of the final page has been formed, the controller  100  will terminate the operation executed when forming image; while if it is determined that the image of the final page has not been formed, the controller  100  will return the processing to step S 1 . 
     Here, occurrence of bounding can be considered as a sign of the blade burr. As described above, the belt position transition time varies according to occurrence of bounding. In the image forming apparatus  1  of the present embodiment, whether or not it is necessary to perform the blade abutting stabilization control is determined based on the belt position transition time. In other words, the blade abutting stabilization control (i.e., the formation of the cleaning belts CP 2 , CP 3  in the present embodiment), which is a measure to prevent the blade burr, can be performed based on the sign of the blade burr. Thus, it is possible to perform the blade abutting stabilization control at appropriate time. 
     Described above is an embodiment to which the present invention is applied. It is to be understood that the present invention is not limited to the aforesaid embodiment, and various modifications can be made without departing from the spirit and scope of the present invention. 
     For example, the present invention includes a configuration in which a reference transition time previously calculated based on a simulation or an experiment is stored in the ROM  102 , and the controller  100  compares the last clocked belt position transition time with the reference transition time to determine whether or not it is necessary to perform the blade abutting stabilization control. In such a case, if the clocked belt position transition time exceeds the reference transition time, the controller  100  will determine that it is necessary to perform the blade abutting stabilization control. 
     Further, instead of the image forming section  40 , the blade drive mechanism  91  may be used as the adjuster. In such a case, when performing the blade abutting stabilization control, the controller  100  controls the operation of the blade drive mechanism  91  to move the cleaning blade  65  so that the value of the force for the cleaning blade  65  to press secondary transfer belt  67  is larger than that in the normal time (which is a predetermined value). Thus, it is possible to cause the cleaning blade  65  to press the secondary transfer belt  67  more strongly than the normal time to thereby suppress the occurrence of bounding and restrain the burr of the cleaning blade  65 . 
     Further, the brush drive section  92  may also be used as the adjuster. In such case, when performing the blade abutting stabilization control, the controller  100  controls the operation of the brush drive section  92  to increase the lubricant coated onto the secondary transfer belt  67  compared with the normal time to thereby adjust the abutting state between the cleaning blade  65  and the secondary transfer belt  67 . To be specific, when performing the blade abutting stabilization control, the controller  100  controls the operation of the brush drive section  92  so that the rotation number in a predetermined period becomes larger than that of the normal time. Thus, the coating amount of the lubricant is larger than the coating amount of the normal time (a predetermined amount), and therefore the friction between the cleaning blade  65  and the secondary transfer belt  67  is reduced. Thus, the abutting state between the cleaning blade  65  and the secondary transfer belt  67  can be adjusted, and therefore occurrence of bounding can be suppressed, and blade burr can be restrained. 
     Further, the roller drive section  90  may also be used as the adjuster. In such case, when performing the blade abutting stabilization control, the controller  100  controls the operation of the roller drive section  90  to rotate the secondary transfer belt  67  in a direction opposite to the direction when forming the image on the sheet. By rotating the secondary transfer belt  67  in opposite direction, the cleaning blade  65  caused due to the normal rotation of the secondary transfer belt  67  can be restored to its original shape. Thus, the abutting state between the cleaning blade  65  and the secondary transfer belt  67  is adjusted, and thereby the subsequent occurrence of bounding and blade burr can be suppressed. 
     Further, although the present embodiment is described based on an example in which the present invention is applied to the secondary transfer section  60 , the present invention may also be applied to the intermediate transfer belt  50 , the conveying belt for conveying the sheet, and/or the like.