Patent Publication Number: US-11022914-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-168960 filed Sep. 18, 2019. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to image forming apparatuses. 
     (ii) Related Art 
     An image forming apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2015-225282 includes an image reader, an image processor, a sheet size detector, a photoconductor drum, a photoconductor driver, a charging device, an exposure device, a developing device, a transfer device, a cleaning device, a cleaning driver, an air blower, a temperature-and-humidity detector, a controller, a charger remover, a fixing device, a sheet feeder, and a transport unit. 
     SUMMARY 
     An image forming apparatus includes a revolving member (i.e., a transfer belt) that receives a toner image transferred from a photoconductor while revolving, and that transfers this toner image onto a recording medium. When the revolving member transfers the toner image onto the recording medium, a deposit, such as a discharge product, adheres to the revolving member. When a certain time elapses after the image forming operation is completed, the deposit may increase in adhesive force against the revolving member. Moreover, when the deposit absorbs moisture, it may be difficult to remove the deposit from the revolving member only with a removing member, such as a blade, used for removing the deposit from the revolving member. 
     Aspects of non-limiting embodiments of the present disclosure relate to reducing the deposit remaining on the revolving member, as compared with a case where the deposit is removed from the revolving member by using the removing member alone. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided an image forming apparatus including a revolving member that revolves, a first-transfer member that transfers a toner image onto the revolving member, a second-transfer member that transfers the toner image on the revolving member onto a recording medium, a removing member that is disposed downstream of the second-transfer member and upstream of the first-transfer member in a revolving direction of the revolving member and that removes a deposit adhered on the revolving member, a fixing device that generates heat and that fixes the toner image transferred on the recording medium by the second-transfer member onto the recording medium, a generating member that causes air to flow from the fixing device toward the revolving member, and an executing unit that executes a removal mode including causing the fixing device to generate heat, causing the generating member to operate, causing the revolving member to operate, causing the first-transfer member to operate so as to transfer a cleaning image as a toner image onto the revolving member, and causing the removing member to remove the cleaning image from the revolving member without causing the second-transfer member to transfer the cleaning image onto the recording medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a configuration diagram illustrating relevant components of an image forming apparatus according to a first exemplary embodiment of the present disclosure; 
         FIG. 2  is a configuration diagram illustrating a removing member and other components included in a transfer unit of the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 3  is a perspective view illustrating an image forming unit and the transfer unit of the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 4  is a perspective view illustrating the transfer unit and other components of the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 5  is a perspective view illustrating a belt unit and a fixing device of the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIGS. 6A and 6B  illustrate a process when a removal mode is executed in the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIGS. 7A and 7B  illustrate a process when the removal mode is executed in the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 8  is a block diagram illustrating a control system of a controller included in the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 9  is a flowchart illustrating the flow when the removal mode is executed in the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 10  is a cross-sectional view illustrating a developing device of the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 11  schematically illustrates the configuration of the image forming apparatus according to the first exemplary embodiment of the present disclosure; 
         FIG. 12  is a block diagram illustrating a control system of a controller included in an image forming apparatus according to a second exemplary embodiment of the present disclosure; and 
         FIG. 13  is a flowchart illustrating the flow when the removal mode is executed in the image forming apparatus according to the second exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     First Exemplary Embodiment 
     An example of an image forming apparatus according to a first exemplary embodiment of the present disclosure will now be described with reference to  FIGS. 1 to 11 . In the drawings, an arrow H indicates an up-down direction as a vertical direction of the apparatus, an arrow W indicates a width direction as a horizontal direction of the apparatus, and an arrow D indicates a depth direction as another horizontal direction of the apparatus. 
     Overall Configuration of Image Forming Apparatus 
     As shown in  FIG. 11 , an image forming apparatus  10  includes an image forming unit  12  that forms a toner image by electrophotography, a container  18  that contains recording media P, a controller  28  that controls each component, and an exhaust unit  24 . Moreover, the image forming apparatus  10  includes a transport unit  14  that transports each recording medium P contained in the container  18  along a transport path  16 . The transport unit  14  also inverts the front and rear faces of the recording medium P transported along the transport path  16  by transporting the recording medium P along an inversion path  26 , and transports the recording medium P to the image forming unit  12  again. 
     In the image forming apparatus  10  having this configuration, the toner image formed by the image forming unit  12  is formed onto the front face of the recording medium P transported along the transport path  16 . Furthermore, the recording medium P having the toner image formed thereon is output outside an apparatus body  10   a.    
     In a case where an image is to be formed on the rear face of the recording medium P, the recording medium P having the image formed on the front face thereof is transported along the inversion path  26  so that an image is formed on the rear face of the recording medium P at the image forming unit  12  again, and is output outside the apparatus body  10   a.    
     Image Forming Unit  12   
     As shown in  FIG. 11 , the image forming unit  12  includes multiple toner-image forming units  30  that individually form toner images of respective colors, and also includes a transfer unit  32  that transfers the toner images formed at the toner-image forming units  30  onto the recording medium P. Furthermore, the image forming unit  12  includes a fixing device  34  that fixes the toner images transferred on the recording medium P by the transfer unit  32  onto the recording medium P. 
     Toner-Image Forming Units  30   
     As shown in  FIG. 1 , the multiple toner-image forming units  30  are provided to form toner images of respective colors. In this exemplary embodiment, there are four toner-image forming units  30  provided for yellow (Y), magenta (M), cyan (C), and black (K) colors. In the following description, if the yellow (Y), magenta (M), cyan (C), and black (K) colors are not to be distinguished from one another, Y, M, C, and K added to the reference signs will be omitted. 
     The toner-image forming units  30  for the respective colors basically have identical configurations except for the toners used, and each include a rotating cylindrical image bearing member  40  and a charger  42  that electrostatically charges the image bearing member  40 . Furthermore, each toner-image forming unit  30  includes an exposure device  44  that forms an electrostatic latent image by radiating exposure light onto the electrostatically-charged image bearing member  40 , and also includes a developing device  46  that develops the electrostatic latent image into a toner image by using a developer G that contains a toner. As shown in  FIG. 10 , the developing device  46  includes a developing roller  46   a  that faces the image bearing member  40 , a feeding auger  46   b  that feeds the developer G to the developing roller  46   a , and a stirring auger  46   c  that stirs the developer G. 
     In this configuration, the toner-image forming unit  30  for each color forms an image of that color by using a toner of that color. 
     As shown in  FIG. 1 , the image bearing members  40  for the respective colors are in contact with a revolving transfer belt  50  (to be described in detail later). The toner-image forming units  30  for the yellow (Y), magenta (M), cyan (C), and black (K) colors are arranged in the horizontal direction in this order from upstream in the revolving direction (see an arrow in  FIG. 1 ) of the transfer belt  50 . 
     Transfer Unit  32   
     As shown in  FIG. 1 , the transfer unit  32  includes multiple rollers  58 , a loop roller  56 , the transfer belt  50  that is wrapped around the multiple rollers  58  and the loop roller  56  and that revolves in the direction of the arrow in  FIG. 1 , first-transfer rollers  52 , a removing member  36 , and a second-transfer roller  54 . A second-transfer section NT that transfers the toner images onto the recording medium P is formed between the second-transfer roller  54  and the transfer belt  50 . The configuration of the transfer unit  32  will be described in detail later. 
     Fixing Device  34   
     As shown in  FIG. 1 , the fixing device  34  is disposed downstream of the second-transfer section NT in the transport direction of the recording medium P. The fixing device  34  will be described in detail later. 
     Container  18   
     As shown in  FIG. 11 , the container  18  includes an accommodation member  20  capable of accommodating recording media P and a feed roller  22  that feeds the uppermost one of the recording media P stacked on the accommodation member  20  to the transport path  16 . 
     Transport Unit  14   
     As shown in  FIG. 11 , the transport unit  14  includes multiple transport rollers (not given reference signs) that transport the recording medium P fed from the container  18  along the transport path  16 , and also includes a belt unit  60  that transports the recording medium P having a toner image transferred thereon and delivers the recording medium P to the fixing device  34 . The belt unit  60  will be described in detail later. 
     Furthermore, the transport unit  14  includes multiple transport rollers (not given reference signs) that transport the recording medium P along the inversion path  26  to which the recording medium P passing through the fixing device  34  is delivered in a case where an image is to be formed on the rear face of the recording medium P. In the inversion path  26 , the transport direction of the recording medium P is reversed (i.e., switched back) so that the front and rear faces thereof are inverted. 
     In this configuration, when a toner image is to be formed on the front face of the recording medium P, the transport unit  14  transports the recording medium P fed from the container  18  along the transport path  16 . Then, the second-transfer section NT transfers the toner image onto the front face of the recording medium P, and the fixing device  34  fixes the toner image onto the recording medium P. 
     If a toner image is to be formed also on the rear face of the recording medium P, the transport unit  14  inverts the front and rear faces of the recording medium P by transporting the recording medium P passing through the fixing device  34  along the inversion path  26 . Furthermore, the transport unit  14  causes the recording medium P, whose front and rear faces have been inverted, to merge into the transport path  16 , and transports the recording medium P along the transport path  16 . Then, the second-transfer section NT transfers the toner image onto the rear face of the recording medium P, and the fixing device  34  fixes the toner image onto the recording medium P. 
     Exhaust Unit  24   
     As shown in  FIG. 11 , the exhaust unit  24  is attached to the apparatus body  10   a  such that the air inside the apparatus body  10   a  is discharged outside the apparatus body  10   a . The exhaust unit  24  will be described in detail later. 
     Controller  28   
     As shown in  FIG. 8 , the controller  28  controls each component. The control of each component by the controller  28  will be described later together with the operation. 
     Operation of Overall Configuration 
     In the image forming apparatus  10 , an image is formed as follows. 
     First, the charger  42  for each color shown in  FIG. 1  negatively charges the surface of the image bearing member  40  for that color uniformly with a predetermined potential. Then, the exposure device  44  forms an electrostatic latent image on the electrostatically-charged surface of the image bearing member  40  by radiating exposure light thereto. Consequently, the electrostatic latent image is formed on the surface of the image bearing member  40 . Furthermore, the developing device  46  for that color develops this electrostatic latent image into a visual image as a toner image. The toner images formed on the surfaces of the image bearing members  40  for the respective colors are sequentially transferred onto the transfer belt  50  by the first-transfer rollers  52 . 
     The recording medium P fed from the accommodation member  20  shown in  FIG. 11  to the transport path  16  by the feed roller  22  is fed to the second-transfer section NT where the transfer belt  50  and the second-transfer roller  54  are in contact with each other. At the second-transfer section NT, the recording medium P is transported between the transfer belt  50  and the second-transfer roller  54 , so that the toner images on the transfer belt  50  are transferred onto the surface of the recording medium P. 
     The toner images transferred on the surface of the recording medium P are fixed onto the recording medium P by the fixing device  34 . Then, the recording medium P having the toner images fixed thereon is output outside the apparatus body  10   a.    
     In a case where toner images are to be formed also on the rear face of the recording medium P, the recording medium P having the toner images formed on the front face thereof is transported along the inversion path  26  so that the front and rear faces are inverted, and is transported again to the second-transfer section NT. Then, toner images formed as a result of undergoing a process similar to the above-described process are transferred onto the rear face of the recording medium P. The toner images transferred on the rear face of the recording medium P are fixed onto the recording medium P by the fixing device  34 . Furthermore, the recording medium P having the toner images fixed thereon is output outside the apparatus body  10   a.    
     Configuration of Relevant Components 
     Next, the transfer unit  32 , the fixing device  34 , the belt unit  60  of the transport unit  14 , the exhaust unit  24 , and the controller  28  will be described. 
     Transfer Unit  32   
     As shown in  FIGS. 1 and 4 , the transfer unit  32  includes the multiple rollers  58 , the loop roller  56 , and the transfer belt  50  that is wrapped around the multiple rollers  58  and the loop roller  56  and that revolves in the direction of an arrow G. In a state where the transfer belt  50  is wrapped around the multiple rollers  58  and the loop roller  56 , the transfer belt  50  has a substantially triangular shape with a downward pointing apex, as viewed from the depth direction of the apparatus. The transfer belt  50  is an example of a revolving member. 
     Furthermore, the transfer unit  32  includes the first-transfer rollers  52  that transfer the toner images formed on the image bearing members  40  for the respective colors onto the transfer belt  50  in accordance with a transfer current. Moreover, the transfer unit  32  includes the second-transfer roller  54  that transfers the toner images on the transfer belt  50  onto the recording medium P in accordance with a transfer current, and the removing member  36  that removes a deposit, such as a discharge product, adhered on the transfer belt  50  from the transfer belt  50 . Each first-transfer roller  52  is an example of a first-transfer member, and the second-transfer roller  54  is an example of a second-transfer member. 
     The apex of the transfer belt  50  is looped over the loop roller  56 , and one side (i.e., the right side in the drawings) of the transfer belt  50  in the width direction of the apparatus is looped over a roller  58   a  included in the rollers  58 . One of the multiple rollers  58  is rotationally driven so that the transfer belt  50  rotates in the direction of the arrow G (i.e., in the counterclockwise direction). The image bearing members  40  for the respective colors are in contact with a part of the transfer belt  50  where the peripheral surface thereof faces upward. The image bearing members  40  (i.e., the toner-image forming units  30 ) for the yellow (Y), magenta (M), cyan (C), and black (K) colors are arranged in this order from upstream in the revolving direction of the transfer belt  50 . 
     The first-transfer rollers  52  are disposed opposite the image bearing members  40  of the respective colors with the transfer belt  50  interposed therebetween. Furthermore, the second-transfer roller  54  is disposed opposite the loop roller  56  with the transfer belt  50  interposed therebetween, and the second-transfer section NT that transfers a toner image onto a recording medium P is formed between the second-transfer roller  54  and the transfer belt  50 . 
     The removing member  36  is disposed downstream of the second-transfer section NT and upstream of the first-transfer rollers  52  in the revolving direction (referred to as “belt revolving direction” hereinafter) of the transfer belt  50 , as well as opposite the roller  58   a  with the transfer belt  50  interposed therebetween. As shown in  FIG. 2 , the removing member  36  includes a scraping blade  36   a  whose edge comes into contact with the peripheral surface of the transfer belt  50  to scrape off a deposit adhered to the transfer belt  50 , and also includes a collection box  36   b  that collects the deposit scraped off by the scraping blade  36   a.    
     In this configuration, the removing member  36  removes the deposit adhered to the transfer belt  50 . In other words, the removing member  36  suppresses a partial change in the electrical performance of the transfer belt  50 . Specifically, the removing member  36  functions as a performance maintaining unit that maintains the electrical performance of the transfer belt  50 . 
     Fixing Device  34   
     As shown in  FIG. 1 , the fixing device  34  is disposed below the transfer belt  50  and downstream of the second-transfer section NT in the transport direction (referred to as “medium transport direction” hereinafter) of the recording medium P. Accordingly, as viewed in the width direction of the apparatus, the fixing device  34  is disposed within a range in which the transfer belt  50  is disposed. 
     The fixing device  34  includes a heating roller  34   a  that contains a heat source therein and that is rotated by a driver, and also includes a pressing roller  34   b  that is disposed facing the heating roller  34   a  and that presses the recording medium P having a toner image transferred thereon toward the heating roller  34   a.    
     In this configuration, if the toner image transferred on the recording medium P is to be fixed onto the recording medium P, the peripheral surface of the heating roller  34   a  is increased in temperature to, for example, about 180° C. Then, the rotating heating roller  34   a  and the pressing roller  34   b  rotated by being driven by the heating roller  34   a  nip and transport the recording medium P, so that the fixing device  34  fixes the toner image onto the recording medium P. 
     Belt Unit  60   
     As shown in  FIG. 1 , the belt unit  60  is disposed downstream of the second-transfer section NT and upstream of the fixing device  34  in the medium transport direction. 
     As shown in  FIGS. 1 and 5 , the belt unit  60  includes endless transport belts  62 , a driving roller  64   a  and a driven roller  64   b  around which the transport belts  62  are wrapped, and a suction unit  66  that takes in the air above the transport belts  62  by suction. 
     The multiple transport belts  62  are arranged in the depth direction of the apparatus, and each transport belt  62  has multiple through holes  62   a . The suction unit  66  has a suction fan  66   a  disposed therein. When the suction fan  66   a  is in operation, the suction unit  66  takes in the air above the transport belts  62  by suction so that the recording medium P attaches to the transport belts  62  by suction. 
     In this configuration, the rotationally-driven driving roller  64   a  transmits a rotational force to the transport belts  62 , thereby causing the transport belts  62  to revolve. Furthermore, the suction unit  66  takes in the air above the transport belts  62  by suction so that the belt unit  60  transports the recording medium P while attaching the recording medium P to the transport belts  62  by suction. When the suction fan  66   a  operates in a state where the recording medium P is not being transported, the air around the heating roller  34   a  flows toward the belt unit  60 , as indicated by an arrow A shown in  FIG. 1 . In other words, the suction fan  66   a  in operation causes the air around the heating roller  34   a  to flow toward the transfer belt  50 . 
     Exhaust Unit  24   
     The exhaust unit  24  is disposed opposite the fixing device  34  with the transfer belt  50  interposed therebetween, as viewed from the depth direction of the apparatus, as shown in  FIG. 1 , and is attached to a rear plate  70  of the apparatus body  10   a , as shown in  FIG. 3 . The exhaust unit  24  is an example of a generating member. 
     The exhaust unit  24  includes an exhaust fan  72  and an exhaust duct  74 . The base end of the exhaust duct  74  is connected to the exhaust fan  72 , and the distal end of the exhaust duct  74  is open toward the peripheral surface of the transfer belt  50 . 
     In this configuration, when the exhaust fan  72  is in operation, the exhaust unit  24  takes in the air at the peripheral surface of the transfer belt  50  and causes the air to pass through a filter (not shown). Then, the exhaust unit  24  discharges the air outside the apparatus body  10   a.    
     When the exhaust fan  72  is in operation, the air flows from the heating roller  34   a  of the fixing device  34  toward the transfer belt  50 , as indicated by an arrow B shown in  FIG. 1 . This causes the temperature of the transfer belt  50  to increase. In other words, the heating roller  34   a  and the exhaust unit  24  function as a temperature increasing unit that increases the temperature of the transfer belt  50 . The direction in which the air flows is confirmable by placing dry ice inside the apparatus body  10   a  and checking the direction of flow of white fog produced from the dry ice. 
     Miscellaneous 
     As shown in  FIG. 8 , the image forming apparatus  10  includes a measurement device  80  that measures the time elapsed from when image forming operation for forming an image onto a recording medium P is completed, and also includes a hygrometer  82  that detects a relative humidity within the apparatus body  10   a.    
     The “relative humidity within the apparatus body” is a relative humidity in the region in which the transfer belt  50  is disposed inside the apparatus body  10   a . In detail, the “relative humidity within the apparatus body” is a relative humidity at any location in a region between the peripheral surface of the transfer belt  50  and a position located away from the peripheral surface of the transfer belt  50  by 200 mm, as viewed from the depth direction of the apparatus. In this exemplary embodiment, for example, the hygrometer  82  is disposed below the removing member  36 . 
     Controller  28   
     As shown in  FIG. 8 , the controller  28  receives information from the measurement device  80  and the hygrometer  82  and controls the operation of the exhaust fan  72 , the fixing device  34 , the toner-image forming units  30 , and the transfer unit  32 . The control of each component by the controller  28  will be described later together with the operation. The controller  28  is an example of an executing unit. 
     Operation 
     Next, the operation of the relevant components will be described. In detail, a process in which the controller  28  executes a removal mode by controlling each component to remove a deposit adhered to the transfer belt  50  will be described with reference to a flowchart shown in  FIG. 9 . 
     When image forming operation for forming an image onto a recording medium P is completed, the controller  28  stops the operation of the fixing device  34 , the transport unit  14 , the toner-image forming units  30 , and the transfer unit  32 . Furthermore, when the image forming operation is completed, the measurement device  80  measures the time elapsed from the completion of the image forming operation. 
     In step S 100  shown in  FIG. 9 , the controller  28  determines whether or not the elapsed time measured by the measurement device  80  has passed a threshold time. If the elapsed time has passed the threshold time, the process proceeds to step S 200 . If the elapsed time has not reached the threshold time, the controller  28  determines again in step S 100  whether or not the elapsed time has passed the threshold time. In this exemplary embodiment, the threshold time ranges between 4 hours and 72 hours inclusive, desirably between 5 hours and 10 hours inclusive, and more desirably between 6 hours and 8 hours inclusive in particular. The reason for determining whether or not the elapsed time has reached the threshold time is that, when the elapsed time reaches the threshold time, the adhesive force of a deposit adhered to the transfer belt  50  increases, as compared with a case where the elapsed time has not reached the threshold time. 
     If the power supply of the image forming apparatus  10  is turned off, the controller  28  determines in step S 100  whether or not the elapsed time measured by the measurement device  80  has passed the threshold time from when the power supply is turned on. 
     In step S 200 , the controller  28  determines whether or not the relative humidity measured by the hygrometer  82  when the process proceeds to step S 200  has reached a threshold humidity. If the relative humidity has reached the threshold humidity, the process proceeds to step S 300 . If the relative humidity has not reached the threshold humidity, the controller  28  determines again in step S 100  whether or not the elapsed time has passed the threshold time. The reason for determining whether or not the relative humidity has reached the threshold humidity is that, when the relative humidity reaches the threshold humidity, the adhesive force of a deposit adhered to the transfer belt  50  increases, as compared with a case where the relative humidity has not reached the threshold humidity. 
     If the controller  28  determines in step S 100  that the elapsed time has reached the threshold time from when the power supply is turned on, the controller  28  determines whether or not the relative humidity when the process proceeds from step S 100  to step S 200  has reached the threshold humidity. 
     In step S 300 , the controller  28  causes the exhaust fan  72  and the fixing device  34  shown in  FIG. 1  to operate. With regard to the fixing device  34 , the fixing device  34  operates such that the temperature of the peripheral surface of the heating roller  34   a  becomes equal to the temperature thereof during the image forming operation. 
     The exhaust fan  72  and the fixing device  34  operate in this manner so that the air heated by the heating roller  34   a  flows toward the transfer belt  50  (see the arrow B in  FIG. 1 ), thereby heating the transfer belt  50 . 
     In step S 400 , the controller  28  causes the black toner-image forming unit  30 K and the transfer unit  32  shown in  FIG. 1  to operate. 
     The controller  28  causes the toner-image forming unit  30 K to form a cleaning image as an example of a toner image, causes the transfer belt  50  to revolve, and causes the first-transfer roller  52  to transfer the cleaning image onto the transfer belt  50 . Furthermore, the controller  28  causes a transfer current to flow to the second-transfer roller  54  such that an electric field opposite to that when a toner image is transferred onto a recording medium P is generated. 
     In detail, the toner-image forming unit  30 K forms a dot image as a cleaning image. Furthermore, the first-transfer roller  52  transfers the dot image as a cleaning image onto the transfer belt  50  over an image formation width in which a toner image is formed in the width direction of the transfer belt  50  and over the circumferential length or more of the transfer belt  50  in the circumferential direction of the transfer belt  50 . In other words, the first-transfer roller  52  transfers the dot image as a cleaning image onto the transfer belt  50  such that a part of the transfer belt  50  onto which the cleaning image is transferred first and a part of the transfer belt  50  onto which the cleaning image is transferred last are aligned with each other in the circumferential direction of the transfer belt  50 . The “image formation width” is the maximum width in which an image is formable. The “dot image” is an image constituted of evenly distributed dots. 
     The first-transfer roller  52  transfers the cleaning image onto the transfer belt  50  such that the image density gradually decreases from the part of the cleaning image to be transferred first onto the transfer belt  50  to the part of the cleaning image to be transferred last onto the transfer belt  50 . In other words, the first-transfer roller  52  transfers the cleaning image onto the transfer belt  50  such that the image density gradually decreases from the part of the cleaning image to be scraped off and removed first from the transfer belt  50  by the scraping blade  36   a  to the part of the cleaning image to be scraped off and removed last. In this exemplary embodiment, the image density varies from, for example, 100% to 60%. The image density of the dot image as a cleaning image is measurable by using a spectral densitometer (X-Rite 939 manufactured by X-Rite Inc.). Alternatively, the mass of toner per unit area of the transfer belt  50  may be measured, and the image density may be calculated from this mass. In this exemplary embodiment, a dot image having an image density of 100% is a solid image. 
     Referring to  FIGS. 6A and 6B , the toner-image forming unit  30 K and the transfer unit  32  operate in this manner so that a cleaning image (denoted by G 01  in  FIGS. 6A and 6B ) transferred on the heated transfer belt  50  is transported by the revolving transfer belt  50 . 
     In step S 500 , when the cleaning image G 01  transferred on the transfer belt  50  is removed by the removing member  36 , as shown in  FIGS. 7A and 7B , the revolving transfer belt  50  stops revolving. 
     In detail, the cleaning image G 01  transported by the revolving transfer belt  50  passes through the second-transfer section NT and reaches the removing member  36 . The scraping blade  36   a  of the removing member  36  scrapes off the cleaning image G 01  transported by the transfer belt  50  from the transfer belt  50 . The collection box  36   b  collects the toner constituting the cleaning image G 01  scraped off from the transfer belt  50 . 
     As shown in  FIG. 2 , the scraping blade  36   a  scrapes off the cleaning image G 01  from the transfer belt  50  so that a toner accumulation T 01  occurs in the area where the edge of the scraping blade  36   a  and the transfer belt  50  are in contact with each other. 
     The toner constituting this toner accumulation T 01  acts as an abrasive, so that the deposit adhered to the peripheral surface of the transfer belt  50  is scraped off and removed from the transfer belt  50 . 
     The toner constituting the toner accumulation T 01  falls into the collection box  36   b  and is collected therein as time passes, but the toner of the cleaning image G 01  scraped off from the transfer belt  50  by the scraping blade  36   a  is added as new toner to the toner accumulation T 01 . Accordingly, the toner accumulation T 01  acting as an abrasive is maintained. 
     As mentioned above, the image density gradually decreases from the part of the cleaning image to be scraped off first from the transfer belt  50  by the scraping blade  36   a  to the part of the cleaning image to be scraped off last. In other words, the amount of toner to be scraped off from the transfer belt  50  by the scraping blade  36   a  gradually decreases from the part of the cleaning image to be scraped off first from the transfer belt  50  to the part of the cleaning image to be scraped off last from the transfer belt  50 . Therefore, the toner accumulation T 01  occurs faster than a case where the amount of toner to be scraped off first from the transfer belt  50  by the scraping blade  36   a  is equal to the amount of toner to be scraped off and removed last. 
     Then, when the scraping blade  36   a  scrapes off the entire cleaning image G 01  transferred on the transfer belt  50 , the controller  28  stops the operation of each component and ends the sequential operation. 
     Conclusion 
     As described above, in the image forming apparatus  10 , when the controller  28  executes the removal mode for removing a deposit from the transfer belt  50 , the controller  28  causes the exhaust fan  72  and the fixing device  34  to operate, so that the air heated by the heating roller  34   a  flows toward the transfer belt  50 . Consequently, the transfer belt  50  is heated. With the transfer belt  50  heated, the adhesive force of the deposit adhered to the transfer belt  50  decreases, as compared with a case where the transfer belt  50  is not heated. Therefore, the deposit remaining on the transfer belt  50  may decrease, as compared with a case where the deposit is removed from the transfer belt  50  by the removing member  36  alone. 
     Furthermore, in the image forming apparatus  10 , the deposit remaining on the transfer belt  50  may decrease, as compared with a case where the deposit is removed from the transfer belt  50  by the removing member  36  alone, so that the transfer performance for transferring a toner image from the transfer belt  50  onto a recording medium P may improve. In particular, in a case where the recording medium P used is textured paper, such as embossed paper, having a textured surface, the transfer performance for the toner image to be transferred onto the recording medium P from the transfer belt  50  may improve. In this case, “textured paper” is paper having a textured pattern, and the difference in height of the textured section ranges between, for example, 0.05 mm and 1 mm inclusive. Furthermore, in the image forming apparatus  10 , when the controller  28  determines that the elapsed time from when the image forming operation is completed has reached the threshold time and that the relative humidity within the apparatus body  10   a  is higher than or equal to the threshold humidity, the controller  28  executes the removal mode. By executing the removal mode when the adhesive force of the deposit on the transfer belt  50  increases, the number of times the removal mode is executed may be reduced while the deposit is removed from the transfer belt  50 , as compared with a case where the removal mode is executed regardless of the elapsed time from when the image forming operation is completed and the relative humidity within the apparatus body  10   a . In this case, “when the image forming operation is completed” corresponds to when a toner image is fixed onto the last recording medium P. 
     Furthermore, in the image forming apparatus  10 , the toner accumulation T 01  with a predetermined size may occur faster than in a case where the amount of toner to be scraped off first from the transfer belt  50  by the scraping blade  36   a  is smaller than the amount of toner to be scraped off last. In other words, an abrasive may occur faster than in a case where the amount of toner to be scraped off first from the transfer belt  50  by the scraping blade  36   a  is smaller than the amount of toner to be scraped off last, so that the deposit remaining on the transfer belt  50  may decrease. 
     Furthermore, in the image forming apparatus  10 , the image density gradually decreases from the part of the cleaning image to be removed first from the transfer belt  50  by the removing member  36  to the part of the cleaning image to be removed last. Therefore, the toner accumulation T 01  having a predetermined size may be maintained, as compared with a case where the cleaning image is constituted only of a part of a dot image with an image density to be removed first from the transfer belt  50  and a part of the dot image with an image density to be removed last from the transfer belt  50 , whereby the deposit remaining on the transfer belt  50  may decrease. 
     Second Exemplary Embodiment 
     Next, an example of an image forming apparatus according to a second exemplary embodiment of the present disclosure will be described with reference to  FIGS. 12 and 13 . The second exemplary embodiment will be described while focusing on features different from those of the first exemplary embodiment. 
     Configuration 
     As shown in  FIG. 12 , an image forming apparatus  210  according to the second exemplary embodiment has a storage unit  84  that stores, for example, the sheet type of recording media P accommodated in the accommodation member  20  (see  FIG. 11 ). 
     A controller  228  of the image forming apparatus  210  receives information from the storage unit  84 , the measurement device  80 , and the hygrometer  82 , and controls the operation of the exhaust fan  72 , the fixing device  34 , the toner-image forming units  30 , and the transfer unit  32 . The control of each component by the controller  228  will be described later together with the operation. The controller  228  is an example of an executing unit. 
     Operation 
     Next, a process in which the controller  228  executes the removal mode by controlling each component to remove a deposit adhered to the transfer belt  50  will be described with reference to a flowchart shown in  FIG. 13 . 
     When image forming operation is completed, the measurement device  80  measures the time elapsed from the completion of the image forming operation. Then, in step S 1100  shown in  FIG. 13 , the controller  228  determines whether or not the elapsed time measured by the measurement device  80  has reached a threshold time. If the elapsed time has reached the threshold time, the process proceeds to step S 1200 . If the elapsed time has not reached the threshold time, the controller  228  determines again in step S 1100  whether or not the elapsed time has passed the threshold time. 
     In step S 1200 , the controller  228  determines whether or not the relative humidity measured by the hygrometer  82  when the process proceeds to step S 1200  has reached a threshold humidity. If the relative humidity has reached the threshold humidity, the process proceeds to step S 1300 . If the relative humidity has not reached the threshold humidity, the controller  228  determines again in step S 1100  whether or not the elapsed time has passed the threshold time. 
     In step S 1300 , the controller  228  determines whether or not an image formation command (i.e., a print job) for forming a toner image onto a recording medium P as textured paper having a textured surface is received. In detail, the controller  228  determines whether or not the recording medium P designated by the image formation command is textured paper in accordance with information stored in the storage unit  84 . 
     If the image formation command for forming the toner image onto the recording medium P as textured paper is received, the process proceeds to step S 1400 . If the image formation command for forming the toner image onto the recording medium P as textured paper is not received, the controller  228  determines again in step S 1300  whether or not the image formation command is received. 
     In step S 1400 , the controller  228  causes the exhaust fan  72  and the fixing device  34  shown in  FIG. 1  to operate. With regard to the fixing device  34 , the fixing device  34  operates such that the temperature of the peripheral surface of the heating roller  34   a  becomes equal to the temperature thereof during the image forming operation. 
     In step S 1500 , the controller  228  causes the toner-image forming unit  30 K and the transfer unit  32  shown in  FIG. 1  to operate. 
     The controller  228  causes the toner-image forming unit  30 K to form a cleaning image as an example of a toner image, causes the transfer belt  50  to revolve, and causes the first-transfer roller  52  to transfer the formed cleaning image onto the transfer belt  50 . Furthermore, the controller  228  causes a transfer current to flow to the second-transfer roller  54  such that an electric field opposite to that when a toner image is transferred onto a recording medium P is generated. 
     In step S 1600 , when the cleaning image G 01  transferred on the transfer belt  50  is removed by the removing member  36 , as shown in  FIGS. 7A and 7B , the revolving transfer belt  50  stops revolving. Then, the controller  228  stops the operation of each component and ends the sequential operation. 
     Conclusion 
     As described above, in the image forming apparatus  210 , when the controller  228  receives an image formation command for forming a toner image onto a recording medium P as textured paper, the controller  228  executes the removal mode before image forming operation is executed. Therefore, the number of times the removal mode is executed may be reduced while the transfer performance for the toner image to be transferred onto the textured paper from the transfer belt  50  may be maintained, as compared with a case where the removal mode is executed even when the image formation command for forming the toner image onto the recording medium P is not received. 
     Although specific exemplary embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the above exemplary embodiments. It is obvious to a skilled person that various exemplary embodiments are possible within the scope of the disclosure. For example, in each of the above exemplary embodiments, the removal mode is executed when a predetermined condition is satisfied. Alternatively, for example, a command switch for commanding execution of the removal mode may be provided, such that the removal mode may be executed when the user turns on the command switch. 
     In the above exemplary embodiments, one of the conditions for executing the removal mode is a condition in which the relative humidity within the apparatus body  10   a  becomes higher than or equal to the threshold humidity. Alternatively, the removal mode may be executed regardless of the relative humidity within the apparatus body  10   a . In this case, however, the advantage achieved by setting the relative humidity as one of the conditions for executing the removal mode is not exhibited. 
     Furthermore, in the above exemplary embodiments, the removing member  36  equipped with the scraping blade  36   a  is described as an example of a removing member that removes a deposit from the transfer belt  50 . An alternative example is a removing member equipped with a removing brush. 
     The above exemplary embodiments have been described with reference to the image forming apparatus  10  of a tandem type. Alternatively, an image forming apparatus of a rotary type may be used so long as the image forming apparatus is equipped with a transfer belt or a transfer drum. 
     Furthermore, in the second exemplary embodiment, the removal mode is executed when an image formation command for forming a toner image onto a recording medium P as textured paper having a textured surface is received. Alternatively, the removal mode may be executed when an image formation command for forming a toner image onto a recording medium P is received regardless of the sheet type thereof. 
     Consequently, the number of times the removal mode is executed may be reduced while the transfer performance for the toner image to be transferred onto the recording medium P from the transfer belt  50  may be maintained, as compared with a case where the removal mode is executed even when the image formation command is not received. In this case, however, the advantage achieved when the recording medium P designated for forming a toner image thereon is textured paper having a textured surface is not exhibited. 
     Although not specified in the above exemplary embodiments, the suction fan  66   a  of the belt unit  60  may operate during the removal mode. By causing the suction fan  66   a  to operate, the heat of the heating roller  34   a  may be prevented from traveling away from the transfer belt  50  (see the arrow A in  FIG. 1 ). 
     Furthermore, in the above exemplary embodiments, a cleaning image is formed by using the toner-image forming unit  30 K. Alternatively, a cleaning image may be formed by using a toner-image forming unit  30  for another color, or cleaning images may be formed by using multiple toner-image forming units. 
     Furthermore, in the above exemplary embodiments, the first-transfer roller  52  transfers the cleaning image onto the transfer belt  50  such that the image density gradually decreases from the part of the cleaning image to be transferred first onto the transfer belt  50  to the part of the cleaning image to be transferred last onto the transfer belt  50 . Alternatively, the cleaning image may be another image so long as the image is continuous in the revolving direction of the transfer belt  50 . 
     Furthermore, in the above exemplary embodiments, the first-transfer roller  52  transfers the cleaning image onto the transfer belt  50  such that the image density gradually decreases from the part of the cleaning image to be transferred first onto the transfer belt  50  to the part of the cleaning image to be transferred last onto the transfer belt  50 . Alternatively, the first-transfer roller  52  may transfer the cleaning image onto the transfer belt  50  such that the image density decreases in a stepwise fashion. 
     Furthermore, in the above exemplary embodiments, the dot image is formed as a cleaning image by the toner-image forming unit  30 K. Alternatively, the dot image may be formed as a cleaning image by using a toner-image forming unit  30  for another color. 
     Furthermore, in the second exemplary embodiment, the revolving transfer belt  50  stops revolving in step S 1600 . Alternatively, the print job received in step S 1300  may be executed without stopping the transfer belt  50  from revolving. 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.