Patent Publication Number: US-9841719-B2

Title: Image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2015-233380 filed on Nov. 30, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an image forming apparatus that forms a toner image and prints the toner image on a paper sheet. 
     Conventionally, there is known an image forming apparatus that develops, by using a developing device, an electrostatic latent image into a toner image and transfers (prints) the toner image on a paper sheet. In such an image forming apparatus, for example, in order to suppress contamination inside the apparatus with scattering toner that scatters inside the apparatus, a fan that collects the scattering toner is provided. 
     SUMMARY 
     An image forming apparatus according to one aspect of the present disclosure is provided with a printing portion, a waste toner collection portion, a current detection portion, a fan, and a control portion. The printing portion forms a toner image and prints the toner image on a paper sheet. The waste toner collection portion includes a motor and a conveyance member that is driven by the motor, and conveys, by using the conveyance member, waste toner generated at the time of formation of the toner image by the printing portion, thereby to collect the waste toner in a waste toner container. The current detection portion is to detect a motor current value that is a value of an electric current flowing through the motor. The fan sucks in scattering toner that scatters inside the image forming apparatus and discharges the scattering toner to outside the apparatus. The control portion controls driving of the fan. Further, in driving the fan, based on an output of the current detection portion, the control portion detects a value of the motor current value, and sets rotation speed of the fan so that the larger said detected value of the motor current value, the higher the rotation speed of the fan. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an image forming apparatus according to one embodiment of the present disclosure. 
         FIG. 2  is a diagram showing a configuration of a waste toner collection portion of the image forming apparatus according to the one embodiment of the present disclosure. 
         FIG. 3  is a diagram showing a configuration of a fan installed in the image forming apparatus according to the one embodiment of the present disclosure. 
         FIG. 4  is a diagram showing a hardware configuration of the image forming apparatus according to the one embodiment of the present disclosure. 
         FIG. 5  is a diagram for explaining setting of rotation speed of the fan performed in the image forming apparatus according to the one embodiment of the present disclosure. 
         FIG. 6  is a diagram for explaining control data (first data) used for the setting of rotation speed of the fan performed in the image forming apparatus according to the one embodiment of the present disclosure. 
         FIG. 7  is a diagram for explaining control data (second data) used for the setting of rotation speed of the fan performed in the image forming apparatus according to the one embodiment of the present disclosure. 
         FIG. 8A  is a diagram for explaining the setting of rotation speed of the fan performed in the image forming apparatus according to the one embodiment of the present disclosure (a diagram in a case where a scattering level is highest). 
         FIG. 8B  is a diagram for explaining the setting of rotation speed of the fan performed in the image forming apparatus according to the one embodiment of the present disclosure (a diagram in a case where the scattering level is intermediate). 
         FIG. 8C  is a diagram for explaining the setting of rotation speed of the fan performed in the image forming apparatus according to the one embodiment of the present disclosure (a diagram in a case where the scattering level is lowest). 
         FIG. 9  is a flow chart for explaining a flow of a setting process of setting the rotation speed of the fan performed in the image forming apparatus according to the one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     &lt;Outline of Image Forming Apparatus&gt; 
     As shown in  FIG. 1 , an image forming apparatus  100  of this embodiment is provided with a printing portion  4  that includes a paper feed portion  1 , an image forming portion  2 , and a fixing portion  3 . The printing portion  4  includes a paper sheet conveyance path  40  on which a plurality of conveyance roller pairs  41  are provided, conveys a paper sheet along the paper sheet conveyance path  40 , and, based on image data of an image to be printed, forms a toner image. Further, the printing portion  4  prints (transfers) the toner image on the paper sheet being conveyed and ejects the paper sheet thus printed. That is, the printing portion  4  executes a printing job. Printing encompasses a series of operations in which a toner image formed by an electrophotographic process is transferred on a paper sheet and then is fixed thereon. 
     The paper feed portion  1  includes a pick-up roller  11  and a paper feed roller pair  12 . Further, the paper feed portion  1  supplies a paper sheet housed in a paper sheet cassette  13  to the paper sheet conveyance path  40 . 
     The image forming portion  2  is divided into mechanism portions  20 Bk,  20 Y,  20 C, and  20 M that correspond to colors of black (Bk), yellow (Y), cyan (C), and magenta (M), respectively. Each of the mechanism portions  20 Bk,  20 Y,  20 C, and  20 M has one each of a photosensitive drum  21 , a charging device  22 , a developing device  23 , and a cleaner  24  and forms a toner image of one of the colors corresponding thereto. Furthermore, the image forming portion  2  includes an exposure device  30  for forming an electrostatic latent image on a surface of the photosensitive drum  21 . The above-described image forming portion  2  adopts a configuration capable of forming color images of the four colors of black, yellow, cyan, and magenta. A configuration, however, may be adopted that is provided with one of the mechanism portions  20 Bk,  20 Y,  20 C, and  20 M, thus being capable of forming a single color image. 
     The developing device  23  houses developing toner, and the toner inside the developing device  23  is consumed at the time of formation of a toner image and thus is to be decreased in quantity. For this reason, toner containers TC that house replenishing toner are mounted in the image forming apparatus  100 . 
     The image forming portion  2  further includes an intermediate transfer belt  25 , a primary transfer roller  26 , and a secondary transfer roller  27 . The intermediate transfer belt  25  is laid under tension over a driving roller  28  and a driven roller  29 . On a surface of the intermediate transfer belt  25 , toner images of the respective colors (toner images formed on the surface of each of the photosensitive drums  21 ) are primarily transferred. Then, the toner images transferred on the surface of the intermediate transfer belt  25  are secondarily transferred on a paper sheet. 
     The fixing portion  3  includes a heating roller  31  and a pressing roller  32 . The heating roller  31  has a built-in heat generation source. The pressing roller  32  is in pressure contact with the heating roller  31 . Further, when a paper sheet enters between the heating roller  31  and the pressing roller  32 , the fixing portion  3  heats and presses the paper sheet (fixes a toner image on the paper sheet). 
     The image forming apparatus  100  is provided also with an image reading portion  5 . The image reading portion  5  reads an original document and generates image data of the original document thus read. For example, based on the image data of the original document generated at the image reading portion  5 , the printing portion  4  executes a printing job. 
     Here, at the time of formation of a toner image by the printing portion  4 , waste toner (toner to be discarded) is generated. For example, when forming a toner image (when supplying toner from the developing device  23  to the photosensitive drum  21 ), concurrently therewith, the printing portion  4  also performs, by using the cleaner  24 , cleaning of the surface of the photosensitive drum  21 . Although there is no particular limitation, the cleaner  24  is a resinous blade or brush and comes in contact with the surface of the photosensitive drum  21  to scrape off toner remaining on the surface of the photosensitive drum  21 . In this manner, a part of the toner supplied from the developing device  23  to the photosensitive drum  21  that remains on the surface of the photosensitive drum  21  without being transferred on a paper sheet is removed. Further, the part of the toner removed by the cleaner  24  refers to waste toner. 
     In order to collect waste toner generated at the time of formation of a toner image, the image forming apparatus  100  is provided with a waste toner collection portion  6  (see  FIG. 2 ). As shown in  FIG. 2 , the waste toner collection portion  6  includes a waste toner conveyance path  61 , a collection screw  62  that is provided on the waste toner conveyance path  61 , a collection motor  63  (for example, a stepping motor) for causing the collection screw  62  to rotate by transmitting a driving force thereto, and so on. The collection screw  62  corresponds to a “conveyance member”, and the collection motor  63  corresponds to a “motor”. 
     The waste toner collection portion  6  receives waste toner removed by the cleaner  24  and conveys, by causing the collection screw  62  to rotate, the waste toner along the waste toner conveyance path  61 . The waste toner conveyance path  61  is linked to a mounting space of a waste toner container  60 . The waste toner conveyed along the waste toner conveyance path  61 , therefore, reaches the mounting space of the waste toner container  60 . When the waste toner reaches the mounting space of the waste toner container  60 , the waste toner drops from the waste toner conveyance path  61 , and in this manner, waste toner is accumulated in the waste toner container  60 . 
     Although not shown, a configuration also may be adopted in which a cleaner for cleaning the surface of the intermediate transfer belt  25  is provided, and toner (toner to be discarded) remaining on the surface of the intermediate transfer belt  25  is removed through cleaning by the cleaner. In this case, the toner removed from the surface of the intermediate transfer belt  25  also is collected as waste toner in the waste toner container  60  (conveyed by the waste toner collection portion  6 ). 
     At the time of formation of a toner image by the printing portion  4 , toner scatters inside the image forming apparatus  100 . When toner has scattered inside the apparatus, there occurs an inconvenience such as contamination inside the apparatus (for example, the toner adheres to a pre-printed paper sheet, causing smudges on the paper sheet). To prevent this, in the image forming apparatus  100 , a fan  7  (see  FIG. 3 ) for collecting scattering toner that scatters inside the apparatus is installed. Scattering toner collected by the fan  7  is discarded. That is, scattering toner also is waste toner. 
     For example, as shown in  FIG. 3 , the fan  7  is installed on a back cover CV of the image forming apparatus  100 . Furthermore, inside the apparatus, a suction duct  71  that extends from a position in a vicinity of the image forming portion  2  to an installation position of the fan  7  is provided. Further, the fan  7  sucks in scattering toner that scatters in the vicinity of the image forming portion  2  and discharges the scattering toner from inside the apparatus to outside the apparatus via a filter  72 . Then, the scattering toner discharged to outside the apparatus is accumulated in a collection box  70  that is installed on an outer side of the back cover CV. 
     &lt;Hardware Configuration of Image Forming Apparatus&gt; 
     As shown in  FIG. 4 , the image forming apparatus  100  is provided with a control portion  110 . The control portion  110  includes a CPU  111 , an image processing portion  112 , and a storage portion  113 . The image processing portion  112  is formed of an ASIC or the like and performs, with respect to image data, various types of image processing (enlargement/reduction, density conversion, data format conversion, and so on). The storage portion  113  is formed of, for example, a ROM and a RAM and stores control programs and data. Further, based on the control programs and data stored in the storage portion  113 , the control portion  110  controls a printing operation of the printing portion  4  (the paper feed portion  1 , the image forming portion  2 , and the fixing portion  3 ) and a reading operation of the image reading portion  5 . 
     Furthermore, the collection motor  63  is connected to the control portion  110 . The control portion  110  controls driving of the collection motor  63 , thereby to perform switching between rotation of the collection screw  62  and a stop of the rotation thereof. That is, the control portion  110  controls a collection operation of the waste toner collection portion  6 . A minimum value of a driving current (minimum driving current value) for the collection motor  63  is predetermined. 
     When the printing portion  4  is forming a toner image (when toner is being supplied from the developing device  23  to the photosensitive drum  21 ), the control portion  110  controls the waste toner collection portion  6  to collect waste toner. For example, when starting a printing job by the printing portion  4  (when starting formation of a toner image), the control portion  110  controls the collection screw  62  to rotate (starts collection of waste toner by the waste toner collection portion  6 ). In a printing job, upon a start of supplying (feeding) a paper sheet to the paper sheet conveyance path  40 , formation of a toner image (including formation of an electrostatic latent image) is started. 
     Then, upon completion of the printing job, the control portion  110  controls the collection screw  62  to stop from rotating (completes collection of waste toner by the waste toner collection portion  6 ). Alternatively, a configuration may be adopted in which at timing after a lapse of a given length of time from completion of a printing job, the collection screw  62  is stopped from rotating. 
     Not only at the time of executing a printing job, but also at the time of executing a calibration process, a toner forcible discharge process, or the like, a toner image is formed by the printing portion  4 . Further, also at this time, the control portion  110  controls the waste toner collection portion  6  to collect waste toner. For example, in a calibration process, in order to correct a density or a color deviation of an outputted image, a toner image for calibration is formed. In a toner forcible discharge process, in order to replace toner inside the developing device  23  with fresh toner (reduce deteriorated toner), a solid toner image is formed. 
     Here, a current detection portion  64  for detecting a magnitude of an electric current flowing through the collection motor  63  (hereinafter, referred to as a motor current value) is connected to the collection motor  63 . For example, the current detection portion  64  includes a current detection resistance that is connected to the collection motor  63 . An output of the current detection portion  64  is received by the control portion  110 . Then, based on the output of the current detection portion  64 , the control portion  110  detects the motor current value of the collection motor  63 . The motor current value detected by the control portion  110  based on the output of the current detection portion  64  is used for driving control of the fan  7 . A detail thereof will be described later. 
     The fan  7  having a fan motor also is connected to the control portion  110 . The control portion  110  controls driving (rotation and a stop of the rotation) of the fan  7 . For example, when having started collection of waste toner by the waste toner collection portion  6  (when the collection motor  63  has been brought to a constant speed state), the control portion  110  sets a value of rotation speed (a rotation speed) of the fan  7  and starts driving of the fan  7  at said set value of the rotation speed. At this time, based on the motor current value of the collection motor  63 , the control portion  110  sets the value of the rotation speed of the fan  7 . A detail thereof will be described later. 
     A minimum value of the rotation speed (minimum rotation speed) of the fan  7  is predetermined. For example, when the motor current value of the collection motor  63  is equal to the minimum driving current value, the rotation speed of the fan  7  is set to the minimum rotation speed. 
     A temperature and humidity detection portion  8  also is connected to the control portion  110 . The temperature and humidity detection portion  8  includes a temperature sensor  81  and a humidity sensor  82 . The temperature sensor  81  and the humidity sensor  82  correspond to a “temperature detection portion” and a “humidity detection portion”, respectively. 
     The temperature and humidity detection portion  8  is installed on an exterior cover (not shown) of the image forming apparatus  100 . For example, in order to avoid an influence of heat generation by the fixing portion  3 , an installation position of the temperature and humidity detection portion  8  is set to be away from the fixing portion  3 . Further, based on an output of the temperature and humidity detection portion  8 , the control portion  110  detects temperature and humidity (relative humidity) at a periphery of the image forming apparatus  100 . The temperature and humidity detected by the control portion  110  based on the output of the temperature and humidity detection portion  8  is used for driving control of the fan  7 . A detail thereof will be described later. The temperature and humidity detection portion  8  may be installed in a vicinity of the image forming portion  2  (inside the apparatus). That is, a configuration may be adopted in which based on temperature and humidity inside the apparatus, driving control of the fan  7  is performed. 
     &lt;Driving Control of Fan&gt; 
     A quantity of waste toner generated varies depending on a toner image formation condition (job execution condition). For example, in a job performed using a high number of printing dots per page, compared with a job performed using a low number of printing dots per page, a quantity of toner supplied from the developing device  23  to the photosensitive drum  21  (toner consumed) is increased, and thus a quantity of toner removed by the cleaner  24  is increased accordingly, as a result of which a quantity of waste toner also is increased. With the quantity of waste toner increased, a quantity of waste toner collected by the waste toner collection portion  6  (waste toner conveyed by the collection screw  62 ) is increased. 
     Moreover, in the job performed using a high number of printing dots per page, compared with the job performed using a low number of printing dots per page, a quantity of scattering toner inside the apparatus (toner to be sucked in and discharged by the fan  7 ) also is increased. That is, when a quantity of waste toner collected by the waste toner collection portion  6  is large, it follows that a quantity of scattering toner inside the apparatus is large. 
     With the quantity of scattering toner inside the apparatus increased, an inconvenience of causing contamination inside the apparatus becomes likely to occur. Hence, in a case where a quantity of scattering toner inside the apparatus is large, preferably, the scattering toner is collected immediately. For this reason, in driving the fan  7 , the control portion  110  judges whether a quantity of scattering toner inside the apparatus is large or small and sets a value of the rotation speed of the fan  7  so that the larger the quantity of scattering toner, the higher the rotation speed of the fan  7  (drives the fan  7  at said set value of the rotation speed). 
     Whether a quantity of scattering toner inside the apparatus is large or small can be judged based on the motor current value of the collection motor  63 . For example, in a case where a quantity of waste toner collected by the waste toner collection portion  6  is large (that is, in a case where a quantity of scattering toner inside the apparatus is large), a load of the collection motor  63  becomes large, so that the motor current value is increased. 
     With this as a basis, in driving the fan  7 , based on an output of the current detection portion  64 , the control portion  110  detects a value of the motor current value. When the value of the motor current value detected based on the output of the current detection portion  64  is large, it can be said that a quantity of scattering toner inside the apparatus is large. Then, the control portion  110  sets the rotation speed of the fan  7  so that the larger the motor current value, the higher the rotation speed. Thus, the larger a quantity of scattering toner inside the apparatus, the higher the rotation speed of the fan  7  becomes. 
     For example, as shown in  FIG. 5 , a gradient (ratio) of a variation (an amount of increase) in rotation speed of the fan  7  with respect to a variation (an amount of increase) in motor current value of the collection motor  63  is predetermined (gradient Δt=Δy/Δx). Further, based on the predetermined gradient, the control portion  110  determines a value of the rotation speed of the fan  7  corresponding to the value of the motor current value detected based on the output of the current detection portion  64 , and sets said determined value as the rotation speed of the fan  7 . 
     By the way, under a high humidity environment, a water absorption quantity of toner is increased, and under a low humidity environment, the water absorption quantity of toner becomes less than that in the high humidity environment. With the water absorption quantity of toner increased, the toner becomes less likely to scatter, and thus a quantity of scattering toner is decreased. Hence, even when the same toner image formation condition (number of printing dots per page or the like) is used, there occurs a difference in quantity of scattering toner generated between a case where a toner image is formed under a high humidity environment and a case where a toner image is formed under a low humidity environment. That is, in the case where a toner image is formed under a high humidity environment, compared with the case where a toner image is formed under a low humidity environment, a quantity of scattering toner inside the apparatus is decreased. 
     Hence, in driving the fan  7 , based on an output of the current detection portion  64 , the control portion  110  detects the motor current value, and moreover, based on an output of the temperature and humidity detection portion  8 , the control portion  110  also detects temperature and humidity at a periphery of the image forming apparatus  100  or inside the apparatus (hereinafter, referred to simply as temperature and humidity). Then, based on the motor current value and the temperature and humidity, the control portion  110  sets the rotation speed of the fan  7 . 
     Control data  200  for selling the rotation speed of the fan  7  based on the motor current value and temperature and humidity in this manner is predetermined and stored in the storage portion  113  (see  FIG. 4 ). The control data  200  includes first data  201  and second data  202 . 
     As shown in  FIG. 6 , the first data  201  is data obtained by categorizing levels of a scattering degree, which indicates a likelihood of generation of scattering toner that varies depending on temperature and humidity, into a plurality of scattering levels and predetermining values of temperature and humidity corresponding to the plurality of scattering levels, respectively. In  FIG. 6 , the levels of the scattering degree are identified by different types of hatching. 
     Although there is no particular limitation, the levels of the scattering degree are categorized into three stages. That is, the levels of the scattering degree are categorized into three stages of a highest level (a level at which scattering toner is most likely to be generated), a lowest level (a level at which scattering toner is least likely to be generated), and an intermediate level between the highest level and the lowest level. While, here, a description is given of an example in which the levels of the scattering degree are categorized into three stages, the levels of the scattering degree may be categorized into two stages or four or more stages. 
     For example, in a case of a temperature of lower than 30° C., the highest level is achieved at a humidity range of not lower than 0% and lower than 70%, the intermediate level is achieved at a humidity range of not lower than 70% and lower than 75%, and the lowest level is achieved at a humidity range of not lower than 75%. Furthermore, in a case of a temperature of not lower than 30° C., the highest level is achieved at a humidity range of not lower than 0% and lower than 50%, the intermediate level is achieved at a humidity range of not lower than 50% and lower than 75%, and the lowest level is achieved at a humidity range of not lower than 75%. 
     As shown in  FIG. 7 , the second data  202  is data obtained by predetermining values of the gradient (the gradient of a variation in rotation speed of the fan  7  with respect to a variation in motor current value of the collection motor  63 ) corresponding to the plurality of scattering levels, respectively. Here, the values of the gradient corresponding to the plurality of scattering levels, respectively, are set to be larger as the scattering degree becomes higher in level. That is, the value of the gradient corresponding to the highest level is set to be largest (see  FIG. 8A ). The value of the gradient corresponding to the intermediate level is set to have a magnitude between the value of the gradient corresponding to the highest level and the value of the gradient corresponding to the lowest level (see  FIG. 8B ). The value of the gradient corresponding to the lowest level is set to be smallest (see  FIG. 8C ). 
     For example, the value of the gradient corresponding to the highest level is set to “1”, the value of the gradient corresponding to the intermediate level is set to “0.5”, and the value of the gradient corresponding to the lowest level is set to “0”. Magnitudes of the gradient corresponding to the plurality of scattering levels, respectively, can be changed. 
     Further, in driving the fan  7 , based on an output of the temperature and humidity detection portion  8 , the control portion  110  detects present values of temperature and humidity. Subsequently, based on the first data  201 , the control portion  110  determines a level of the scattering degree corresponding to the present values of temperature and humidity. Upon determining the level of the scattering degree corresponding to the present values of temperature and humidity, the control portion  110  recognizes said determined level of the scattering degree as a subject level (a present level of the scattering degree). For example, in a case of using the first data  201  shown in  FIG. 6 , when a present value of temperature is 20° C. and a present value of humidity is 50%, the subject level is the highest level, and when a present value of temperature is 20° C. and a present value of humidity is  90 %, the subject level is the lowest level. 
     Furthermore, based on the second data  202 , the control portion  110  determines a value of the gradient (the gradient of a variation in rotation speed of the fan  7  with respect to a variation in motor current value of the collection motor  63 ) corresponding to the subject level. For example, in a case of using the second data  202  shown in  FIG. 7 , when the subject level is the highest level, the value of the gradient is “1”, and when the subject level is the lowest level, the value of the gradient is “0”. That is, the higher a level of the scattering degree (the more likely toner is to scatter), the larger a value of the gradient determined by the control portion  110 . 
     After that, based on the value of the gradient corresponding to the subject level, the control portion  110  determines a value of the rotation speed of the fan  7  corresponding to a value of the motor current value (this can be determined based on, for example, a linear function expression y=ax+b). Then, the control portion  110  sets said determined value as the rotation speed of the fan  7 . 
     As a result, as shown in  FIG. 8A  to  FIG. 8C , a comparison between a case where the motor current value has a small value (denoted as a current value A 1 ) and a case where the motor current value has a large value (denoted as a current value A 2 ) indicates that the rotation speed of the fan  7  is larger in the case where the motor current value has a large value. In a case, however, where the subject level is the lowest level (a case where the gradient is 0), regardless of a magnitude of the motor current value, the same value is set as the rotation speed of the fan  7 . For example, when the subject level is the lowest level, the rotation speed of the fan  7  is fixed to the predetermined minimum rotation speed. 
     Furthermore, a comparison between a case of having a high level of the scattering degree and a case of having a low level of the scattering degree indicates that, even when the same value is used as the motor current value, the rotation speed of the fan  7  is larger in the case of having a high level of the scattering degree. That is, the control portion  110  performs setting so that the larger a value of the motor current value detected based on an output of the current detection portion  64  and the higher a level of the scattering degree determined based on an output value of the temperature and humidity detection portion  8  (the lower the humidity), the larger a value set as the rotation speed of the fan  7  (the higher the rotation speed of the fan  7 ). 
     Here, when a lapse of time from a start of driving the fan  7  has reached a prescribed length of time (a dozen or so seconds to several tens of seconds), the control portion  110  detects, based on an output of the current detection portion  64 , a value of the motor current value and also detects, based on an output of the temperature and humidity detection portion  8 , values of temperature and humidity, upon which, based on the value of the motor current value and values of temperature and humidity at that point in time, the control portion  110  resets the rotation speed of the fan  7 . Then, the control portion  110  performs control so that the fan  7  is driven at a reset value of the rotation speed (switches the rotation speed of the fan  7 ). In a case, however, where a job has been completed (a case where the fan  7  has been stopped from being driven) before the lapse of time from a start of driving the fan  7  reaches the prescribed length of time, resetting of the rotation speed of the fan  7  (switching of the rotation speed of the fan  7 ) is not performed. A configuration also may be adopted in which after the rotation speed of the fan  7  has been reset, every time a lapse of time from resetting performed last time reaches a prescribed length of time, resetting of the rotation speed of the fan  7  is performed. 
     Alternatively, when the number of paper sheets printed from a start of driving the fan  7  has reached a prescribed number (a dozen or so paper sheets to several tens of paper sheets), the control portion  110  detects, based on an output of the current detection portion  64 , a value of the motor current value and also detects, based on an output of the temperature and humidity detection portion  8 , values of temperature and humidity, upon which based on the value of the motor current value and values of temperature and humidity at that point in time, the control portion  110  resets the rotation speed of the fan  7 . Then, the control portion  110  performs control so that the fan  7  is driven at a reset value of the rotation speed. In a case, however, where a job has been completed (a case where the fan  7  has been stopped from being driven) before the number of paper sheets printed from a start of driving the fan  7  reaches the prescribed number, resetting of the rotation speed of the fan  7  (switching of the rotation speed of the fan  7 ) is not performed. A configuration also may be adopted in which after the rotation speed of the fan  7  has been reset, every time the number of paper sheets printed from resetting performed last time reaches a prescribed number, resetting of the rotation speed of the fan  7  is performed. 
     With reference to a flow chart shown in  FIG. 9 , the following describes a flow of driving control of the fan  7 . The flow chart shown in  FIG. 9  starts when collection of waste toner by the waste toner collection portion  6  is started. 
     At Step S 1 , based on an output of the temperature and humidity detection portion  8 , the control portion  110  detects present values of temperature and humidity. Furthermore, at Step S 2 , based on an output of the current detection portion  64 , the control portion  110  detects a value of the motor current value of the collection motor  63 . Step S 1  and Step S 2  may be reversed in order. 
     At Step S 3 , the control portion  110  determines that one of the plurality of scattering levels which corresponds to the present values of temperature and humidity. That is, the control portion  110  determines a subject level. Furthermore, at Step S 4 , the control portion  110  determines a value of the gradient (the gradient of a variation in rotation speed of the fan  7  with respect to a variation in motor current value of the collection motor  63 ) corresponding to the subject level. After that, at Step S 5 , based on the value of the gradient corresponding to the subject level, the control portion  110  determines a value of the rotation speed of the fan  7  corresponding to the value of the motor current value (the current value detected at Step S 2 ) and sets said determined value as the rotation speed of the fan  7 . Then, at Step S 6 , the control portion  110  performs control so that the fan  7  is driven at the value of the rotation speed set based on the value of the gradient corresponding to the subject level. 
     At Step S 7 , the control portion  110  judges whether or not a stop condition is satisfied. When a job presently being executed (formation of a toner image) is completed, the control portion  110  judges that the stop condition is satisfied. Alternatively, after a lapse of a given length of time from completion of a job presently being executed, the control portion  110  judges that the stop condition is satisfied. Further, in a case where the control portion  110  judges that the stop condition is satisfied, a transition is made to Step S 8 . Upon the transition to Step S 8 , the control portion  110  performs control so that the fan  7  is stopped from being driven. 
     In a case where, at Step S 7 , the control portion  110  judges that the stop condition is not satisfied, a transition is made to Step S 9 . Upon the transition to Step S 9 , the control portion  110  judges whether or not a prescribed condition is satisfied. When a lapse of time from a start of driving the fan  7  (a lapse of time from setting of the rotation speed of the fan  7  performed last time) has reached a prescribed length of time, the control portion  110  judges that the prescribed condition is satisfied. Alternatively, when the number of paper sheets printed from a start of driving the fan  7  (the number of paper sheets printed from setting of the rotation speed of the fan  7  performed last time) has reached a prescribed number, the control portion  110  judges that the prescribed condition is satisfied. 
     In a case where, at Step S 9 , the control portion  110  judges that the prescribed condition is satisfied, a transition is made to Step S 1  (resetting of the rotation speed of the fan  7  is performed). On the other hand, in a case where, at Step S 9 , the control portion  110  judges that the prescribed condition is not satisfied, a transition is made to Step S 7  (it is judged whether or not the stop condition is satisfied). 
     As described above, in the image forming apparatus  100  of this embodiment, the control portion  110  sets the rotation speed of the fan  7  so that the larger the motor current value, the higher the rotation speed. Here, when a quantity of waste toner including scattering toner is increased and thus a quantity of waste toner to be collected at the waste toner collection portion  6  (a quantity of waste toner to be conveyed by the collection screw  62 ) is increased, a load of the collection motor  63  becomes large, so that the motor current value is increased. That is, in this configuration, when a quantity of scattering toner is large, the rotation speed of the fan  7  is set to be higher, and thus collection capability (capability of sucking in and discharging scattering toner) of the fan  7  is enhanced. This can suppress occurrence of an inconvenience in which, in a case where a quantity of scattering toner is large, the scattering toner cannot be collected completely, causing contamination inside the apparatus. 
     The rotation speed of the fan  7  is set so that the larger the motor current value, the higher the rotation speed, and it follows that the rotation speed of the fan  7  is set so that the smaller the motor current value, the lower the rotation speed. That is, in a case where a quantity of scattering toner is small, the rotation speed of the fan  7  becomes low. This can suppress power consumption of the fan  7 . When the rotation speed of the fan  7  becomes low, however, the collection capability of the fan  7  is degraded. Even so, it is when a quantity of scattering toner is small that the rotation speed of the fan  7  becomes low. Hence, even when the rotation speed of the fan  7  becomes low and thus the collection capability of the fan  7  is degraded, scattering toner inside the apparatus can be collected to a sufficient degree. 
     Furthermore, in this embodiment, in driving the fan  7 , based on an output of the temperature and humidity detection portion  8 , the control portion  110  detects present values of temperature and humidity and determines that one of the plurality of scattering levels (the highest level, the intermediate level, and the lowest level) which corresponds to the present values of temperature and humidity as a subject level. Then, based on a value of the gradient corresponding to the subject level, the control portion  110  determines a value of the rotation speed of the fan  7  corresponding to a value of the motor current value detected based on an output of the current detection portion  64  and sets said determined value as the rotation speed of the fan  7 . According to this configuration, a comparison between a case of having a high level of the scattering degree and a case of having a low level of the scattering degree indicates that, even when the same value is used as the motor current value, the rotation speed of the fan  7  is larger in the case of having a high level of the scattering degree. Thus, even when an installation environment (temperature and humidity) of the image forming apparatus  100  changes to bring about a state where scattering toner is likely to be generated, it is possible to suppress occurrence of an inconvenience in which scattering toner cannot be collected completely, causing contamination inside the apparatus. Furthermore, in the case of having a low level of the scattering degree, the rotation speed of the fan  7  becomes lower than that in the case of having a high level of the scattering degree, and thus power consumption of the fan  7  can be further suppressed. 
     Furthermore, in this embodiment, a value of the gradient corresponding to one of the plurality of scattering levels having the lowest level of the scattering degree (lowest level) is set to 0. That is, when a level of the scattering degree is lowest, regardless of the motor current value, the rotation speed of the fan  7  is set to the minimum rotation speed. According to this configuration, power consumption of the fan  7  can be further suppressed. 
     Furthermore, in this embodiment, when a lapse of time from a start of driving the fan  7  has reached a prescribed length of time, the control portion  110  resets the rotation speed of the fan  7  to a reset value and performs control so that the fan  7  is driven at said reset value of the rotation speed. Alternatively, when the number of paper sheets printed from a start of driving the fan  7  has reached a prescribed number, the control portion  110  resets the rotation speed of the fan  7  to a reset value and performs control so that the fan  7  is driven at said reset value of the rotation speed. According to this configuration, after driving of the fan  7  has been started, when a quantity of scattering toner is decreased, the rotation speed of the fan  7  can be set to be lower, and when a quantity of scattering toner is increased, the rotation speed of the fan  7  can be set to be higher. 
     The embodiment disclosed herein is to be construed in all respects as illustrative and not limiting. The scope of the present disclosure is indicated by the appended claims rather than by the foregoing description of the embodiment, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.