Patent Publication Number: US-9835985-B2

Title: Image forming apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to an image forming apparatus including a cleaning device for cleaning a surface of a member-to-be-cleaned. 
     Conventionally, as disclosed in Japanese Laid-Open Patent Application (JP-A) 2013-57703, a cleaning device for cleaning an intermediary transfer belt, in which a first unit for removing a toner by using a positive bias voltage and a second unit for removing the toner by using a negative bias voltage are provided has been provided. In this cleaning device, each of the first unit and the second unit includes a brush roller for attracting the toner deposited on an intermediary transfer belt and a collecting roller for collecting the toner attracted to the brush roller. Further, each of the first unit and the second unit includes a scraping blade for scraping the deposited toner off the collecting roller and a screw for feeding the toner scraped off the collecting roller by the scraping blade to an outside of the cleaning device. 
     The cleaning device disclosed in JP-A 2013-57702 had a constitution in which each of the first unit and the second unit was provided with the screw. For this reason, there is a need to ensure a space for placement of these (plurality of) screws and there is a need to provide a motor, a gear and the like for driving these screws, so that reduction of part (component) costs and downsizing of the cleaning device are hindered. Therefore, it would be considered that a deposited matter such as the toner is scraped off by the plurality of scraping members. In this case, when one of the scraping members is disposed below the other scraping member, the toner scraped by the other scraping member drops on the one of the scraping members, and therefore it would be considered that their positions are shifted in a horizontal direction. In the case where the toner scraped off by the plurality of scraping members disposed as described above is intended to be fed by a single feeding member, for example, it would be considered that a wall surface of a container covering the cleaning device is inclined and is used for feeding the toner. That is, a deposited matter scraped by the plurality of scraping members is collected on the feeding member by using the inclined wall surface. 
     However, in the case where such a constitution is employed, there is a possibility that the deposited matter scraped by the two (first and second) scraping members is deposited on the wall surface of the container. Then, when the deposited matter is further deposited on the deposited matter which has already been deposited, the deposited matter clogs inside the cleaning device, so that the deposited matter scraped off the roller cannot collected on the feeding member. In this case, there is a liability that the cleaning device is contaminated with the deposited matter which overflowed from the cleaning device. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided an image forming apparatus for forming an image with a toner, comprising: a movable member-to-be-cleaned on which the toner is deposited; a first cleaning unit configured to remove the toner deposited on the member-to-be-cleaned, the first cleaning unit including a first attracting member, a first rotatable member and a first blade member, wherein the first attracting member contacts the member-to-be-cleaned while rotating and is supplied with a voltage of a first polarity to attract the toner deposited on the member-to-be-cleaned, wherein the first rotatable member contacts the first attracting member to move the toner from the first attracting member thereto, wherein the first blade member contacts the first rotatable member at a first contact portion and scrapes a deposited matter off the first rotatable member with rotation of the first rotatable member, and the toner scraped off by the first blade member drops by gravitation at a first position in a neighborhood of the first contact portion, a second cleaning unit configured to remove the toner deposited on the member-to-be-cleaned, the second cleaning unit including a second attracting member, a second rotatable member and a second blade member, wherein the second attracting member contacts the member-to-be-cleaned while rotating and is supplied with a voltage of a second polarity to attract the toner deposited on the member-to-be-cleaned, wherein the second rotatable member contacts the second attracting member to move the toner from the second attracting member thereto, wherein the second blade member contacts the second rotatable member at a second contact portion and scrapes a deposited matter off the second rotatable member with rotation of the second rotatable member, and the toner scraped off by the second blade member drops by gravitation at a second position in a neighborhood of the second contact portion; and a feeding member configured to feed the toner dropped from the first position and the second position in a direction of a rotational axis thereof, wherein the feeding member rotates around the rotational axis and is provided vertically below the first position and the second position, and wherein the feeding member is disposed such that vertical lines passing through the first position and the second position cross the feeding member. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structural view showing an image forming apparatus according to First Embodiment of the present invention. 
         FIG. 2  is a schematic view showing a position of a control patch formed on an intermediary transfer belt in First Embodiment. 
         FIG. 3  is a sectional view showing a secondary transfer unit and a cleaner unit in First Embodiment. 
         FIG. 4  is a perspective view showing the cleaner unit in First Embodiment. 
         FIG. 5  is a sectional view for illustrating an operation of the cleaner unit in First Embodiment. 
         FIG. 6  is a schematic view showing a positional relationship between a cleaning blade and a feeding screw in First Embodiment. 
         FIG. 7  is a schematic view showing a polarity distribution of a toner deposited on a secondary transfer belt. 
         FIG. 8  is a sectional view showing a cleaner unit in Comparison Example. 
         FIG. 9  is a sectional view for illustrating a phenomenon grooving in the cleaner unit in Comparison Example. 
         FIG. 10  is a sectional view showing a cleaner unit according to Second Embodiment of the present invention. 
         FIG. 11  is a sectional view showing a principal part of the cleaner unit in Second Embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     With reference to the drawings, image forming apparatuses according to First and Second Embodiments of the present invention will be described. In the following description, on the basis of a point of sight of the image forming apparatus from a front side ( FIG. 1 ), an up-down direction and a left-right direction are shown. 
     First Embodiment 
     [Image Forming Apparatus] 
     An image forming apparatus  100  according to First Embodiment is, as shown in  FIG. 1 , a color image forming apparatus of an electrophotographic type. The image forming apparatus  100  includes stations Pa, Pb, Pc and Pd as image forming portions for forming toner images of 4 colors of yellow (Pa), magenta (Pb), cyan (Pc) and black (Pd). The image forming apparatus  100  is a tandem image forming apparatus of an intermediary transfer type in which these stations Pa, Pb, Pc and Pd are disposed along an intermediary transfer belt  7 . 
     In the following, a constitution of the stations will be described using the station Pa for yellow as an example. Other stations Pb, Pc and Pd have the same constitution as the constitution of the station Pa except for the colors of the toners, and therefore, will be omitted from description. The station Pa includes a photosensitive drum  1  rotating along a feeding direction of the intermediary transfer belt  7 , and includes a charging portion  2 , an exposure portion  3 , a developing portion  4 , a primary transfer portion T 1 , a cleaning portion  6  and the like which are provided along a rotational direction of the photosensitive drum  1 . 
     The photosensitive drum  1  as an image bearing member is electrically charged uniformly at a surface thereof by the charging portion  2 . The exposure portion  3  includes a light-emitting portion subjected to light emission control correspondingly to an image signal by a control device  50  provided in an apparatus main assembly and a mirror portion for guiding laser light from the light-emitting portion to the photosensitive drum  1  to scan the surface of the photosensitive drum  1  with the laser light. On the surface of the photosensitive drum  1 , surface electric charges are removed by the laser light emitted from the exposure portion  3  and an electrostatic latent image is formed. 
     The developing portion includes a developing sleeve rotating while carrying the toner on a surface thereof, and the electrostatic latent image on the photosensitive drum  1  is visualized (developed) as a toner image by the toner supplied from the developing sleeve to the photosensitive drum  1 . A primary transfer portion T 1  is formed as a nip between the photosensitive drum  1  and a primary transfer roller  5  opposing the photosensitive drum  1  via the intermediary transfer belt  7 . The primary transfer roller  5  is connected with an unshown high-voltage output substrate, and a primary transfer bias voltage is applied thereto. The toner image carried on the photosensitive drum  1  is urged and transferred by the primary transfer bias voltage from the photosensitive drum  1  onto the intermediary transfer belt  7 . A residual toner or the like which passes through the primary transfer portion T 1  and which remains on the photosensitive drum  1  is removed by the cleaning portion  6  including a cleaning blade, so that the surface of the photosensitive drum  1  is again in a state in which the toner image is capable of being carried thereon. Such a toner image forming process is also performed at other stations Pb, Pc and Pd in parallel, so that associated toner images are transferred onto the intermediary transfer belt  7  so as to be superposed on the yellow toner image, and thus a full-color toner image is formed. 
     The intermediary transfer belt  7  as an image bearing member for carrying and feeding the toner image is an endless belt disposed so as to extend through the primary transfer portions T 1  of the 4 stations Pa, Pb, Pc and Pd which are disposed in a horizontal direction. The intermediary transfer belt  7  is supported at the primary transfer portions T 1  and is extended around a driving roller  8 , a tension roller  20 , a stretching roller  22  and an inner secondary transfer roller  23 . 
     The intermediary transfer belt  7  is rotationally driven in a predetermined feeding direction (clockwise direction) by the driving roller  8  driven by an unshown driving device. The tension roller  20  is provided slidably (movably) in a direction of urging the intermediary transfer belt  7  toward an outer peripheral surface side and is urged by an urging (pressing) spring  21  connected with each of both end portions thereof, so that a proper tension is applied to the intermediary transfer belt  7 . The inner secondary transfer roller  23  sandwiches the intermediary transfer belt  7  and a secondary transfer belt  176  between itself and an outer secondary transfer roller  172  of a secondary transfer unit  17  described later, so that a secondary transfer portion T 2  is formed between the intermediary transfer belt  7  and the secondary transfer belt  176 . Downstream of the secondary transfer portion T 2 , an intermediary transfer belt cleaning portion  10  for collecting the toner or the like which passes through the secondary transfer portion T 2  and which remains on the surface of the intermediary transfer belt  7  is provided. 
     Of the 4 stations pa, Pb, Pc and Pd, in a side downstream of the most downstream station Pd with respect to the feeding direction of the intermediary transfer belt  7 , a sensor unit  29  for reading a control patch (registration patch) for correcting color misregistration is provided. The sensor unit  29  includes a detecting portion  29   a  for detecting the control patch formed on the surface of the intermediary transfer belt  7 . Incidentally, a portion of the intermediary transfer belt  7  opposing the detecting portion  29   a  is supported by the stretching roller  22 . 
     The sensor unit  29  is, as shown in  FIG. 2 , constituted by arranging side portion sensors  291  and  293  provided on both sides with respect to a widthwise direction of the intermediary transfer belt  7  and a central portion sensor  292  provided at a widthwise central portion, in the widthwise direction of the intermediary transfer belt  7 . The sensor unit  29  reads control patches formed at  3  positions corresponding to the side portion sensors  291  and  293  and the central portion sensor  292 , and detects occurrence or non-occurrence of deviation of transfer positions by the 4 stations Pa, Pb, Pc and Pd. These control patches are formed in a region between the toner images to be transferred onto a recording material P at the secondary transfer portion T 2 . In other words, the control patches are formed between a region (first region) where a toner image (“IMAGE  1 ”) to be transferred onto a first recording material P 1  ( FIG. 3 ) is formed and a region (second region) where a toner image (“IMAGE  2 ”) to be transferred onto a second recording material P 2  is formed. However, the first recording material P 1  refers to a preceding one of the recording materials P and P which successively pass through the secondary transfer portion T 2 , and the second recording material P 2  refers to the recording material passing through the secondary transfer portion T 2  subsequently to the first recording material P 1 . 
     The control device  50  as a control means provided in the apparatus main assembly not only causes the stations Pa, Pb, Pc and Pd to form the control patches but also monitors an inside state (occurrence or non-occurrence of positional deviation of transfer positions) by a feed-back signal sent from the sensor unit  29 . In the case where the positional deviation of the toner images is detected, the control device  50  sends an instruction to correct the positional deviation to the associated station. As a result, the inside state is automatically monitored and appropriately corrected without causing a user to perform a positional deviation correcting operation, and therefore, the image forming apparatus  100  is maintained in a state in which productivity is high. 
     Incidentally, a constitution in which a density sensor capable of detecting a density of density patches is provided as the sensor unit  29  and density correction is made by forming the density patches prepared at predetermined gradation levels separately from the control patches prepared for the purpose of correcting the color misregistration may also be added. Further, a detection position by the detecting portion  29   a  is not limited to the above-described position and the number, but the patches may also be disposed at, e.g., two positions which are symmetrical with respect to the widthwise direction. 
     The image forming apparatus  100  includes, in addition to the above-described 4 stations and intermediary transfer belt  7 , accommodating portions  12 , a feeding portion  11 , a registration adjusting portion  13 , the secondary transfer unit  17 , the cleaner unit  18 , a fixing portion  15 , a discharge tray  16  and the like as shown in  FIG. 1 . 
     The recording material P (such as paper or an OHP sheet) staked in each of the accommodating portions  12  is fed by the feeding portion  11  through the inside of the apparatus main assembly and is subjected to correction of oblique movement by the registration adjusting portion  13 . 
     At the secondary transfer portion T 2 , the toner images are transferred from the intermediary transfer belt  7  onto the recording material P fed from the registration adjusting portion  13 . The recording material P passed through the secondary transfer portion T 2  is attracted to a pre-fixing feeding belt  14  provided with a suction fan, and then is fed to the fixing portion  15 . The recording material P is heated and pressed by being sandwiched between a fixing roller pair of the fixing portion  15 , so that an image fixed on the recording material P can be obtained. The recording material P passed through the fixing portion  15  is fed to a discharging feeding portion and is discharged to a discharge tray  16  exposed to an outside of the apparatus main assembly. In the case of double-sided printing or the like, when an image is formed on a back surface, the recording material P passed through the fixing portion  15  is fed again toward the secondary transfer portion T 2  in a state in which the recording material P is turned upside down by an unshown reverse feeding portion. Then, the image is formed on the back surface of the recording material P, and thereafter, the recording material P passes through the fixing portion  15  and the discharging feeding portion, and then is discharged on the discharge tray  16 . 
     [Secondary Transfer Unit] 
     The secondary transfer unit  17  for forming the secondary transfer portion T 2  between itself and the intermediary transfer belt  7  will be described. The secondary transfer unit  17  is, as shown in  FIG. 1 , disposed between the registration adjusting portion  13  and the pre-fixing feeding belt  14  in a left-right direction. The secondary transfer unit  17  is accommodated, together with the cleaner unit  18  described later, inside a casing  192  detachably mounted in the apparatus main assembly of the image forming apparatus  100 . The casing  192  extends along the widthwise direction (front-rear direction of the apparatus main assembly) of the intermediary transfer belt  7  and is formed to open upwardly. 
     The secondary transfer unit  17  is, as shown in  FIG. 3 , constituted by winding the secondary transfer belt  176  which is an endless belt member around a driving roller  171 , the outer secondary transfer roller  172 , a separation roller  173  and a tension roller  174 . The driving roller  171 , the outer secondary transfer roller  172 , the separation roller  173  and the tension roller  174  are not only disposed in parallel to the inner secondary transfer roller  23  but also rotatably supported by the casing  192  at both end portions with respect to an axial direction. 
     The secondary transfer belt T 2  is formed as the nip between the intermediary transfer belt  7  and the secondary transfer belt  176  which are sandwiched between the inner secondary transfer roller  23  and the outer secondary transfer roller  172 . At the secondary transfer portion T 2 , the recording material P is fed leftwardly in a state in which the recording material P is sandwiched between the intermediary transfer belt  7  and the secondary transfer belt  176 . Accordingly, the secondary transfer belt  176  is a transfer feeding belt for feeding the recording material P while sandwiching the recording material P between itself and the intermediary transfer belt  7 . 
     The outer secondary transfer roller  172  is grounded, and on the other hand, the inner secondary transfer roller  23  is connected with the high-voltage output substrate and is supplied with a negative bias voltage. In this embodiment, toner particles of the toner images and the control patches which are carried on the intermediary transfer belt  7  are charged to the negative polarity, and therefore in accordance with an electrostatic bias at the secondary transfer portion T 2 , the toner particles are moved from the intermediary transfer belt  7  toward the secondary transfer belt  176 . As a result, not only the toner images are secondary-transferred onto the recording material P passing through the secondary transfer portion T 2 , but also the control patches are transferred onto the secondary transfer belt  176  between the recording materials P successively passing through the secondary transfer portion T 2 . The toner of the control patches transferred on the secondary transfer belt  176  is collected by the cleaner unit  18  as described later. 
     The driving roller  171  is rotationally driven by an unshown driving motor, and feeds the secondary transfer belt  176 . The secondary transfer belt  176  is fed leftwardly in an upper side and is fed rightwardly in a lower side where the cleaner unit  18  is disposed. A feeding speed of the secondary transfer belt  176  is controlled so as to be substantially the same as the feeding speed of the intermediary transfer belt  7  at the secondary transfer portion T 2 . The tension roller  174  is urged by a tension spring  175  which is an elastic member and urges (presses) the intermediary transfer belt  7 , so that the secondary transfer belt  176  is maintained in a state in which the secondary transfer belt  176  has a proper tension. The separation roller  173  disposed downstream of the outer secondary transfer roller  172  with respect to the feeding direction of the secondary transfer belt  176  is constituted so as to be capable of separating the recording material P from the secondary transfer belt  176  by curvature (separation), and delivers the recording material P to the pre-fixing feeding belt  14 . 
     [Cleaner Unit] 
     Next, the cleaner unit  18  as a cleaning device for cleaning the secondary transfer belt  176  as a member-to-be-cleaned will be described. The cleaner unit  18  is, as shown in  FIG. 3 , the cleaning device of an electrostatic brush type in which a positive polarity cleaning set  18 P and a negative polarity cleaning set  18 N which are used for cleaning the surface of the secondary transfer belt  176  by using an electrostatic bias, and a feeding screw  188  are provided. The image forming apparatus  100  is provided with an unshown toner collecting container, and the deposited matter removed from the surface of the secondary transfer belt  176  is finally accommodated in the toner collecting container. 
     The positive polarity cleaning set  18 P includes a brush roller  181  as a first attracting member, a bias roller  182  as a first collecting member and a cleaning blade  183  as a first scraping member. The brush roller  181  which is a brush member (fur brush roller) is constituted by, e.g., planting electroconductive brush fibers  181   b  in a cylindrical core portion  181   a  formed of a metal material ( FIG. 5 ). This brush roller  181  contacts a lower surface of the secondary transfer belt  176  and sandwiches the secondary transfer belt  176  between itself and an opposing roller  184  provided in an inner peripheral surface side of the secondary transfer belt  176 . The bias roller  182  which is a roller member is disposed in a lower-right side of the brush roller  181  in contact with the brush roller  181 . The cleaning blade  183  contacting a lower-right portion of the bias roller  182  at a free end portion  183   a  thereof is disposed under the bias roller  182 . 
     Each of the brush roller  181  and the bias roller  182  is connected with the high-voltage output substrate (not shown) of the apparatus main assembly, and is supplied with a bias voltage of the same polarity (positive polarity in this embodiment). This bias voltage is set so that the bias voltage for the bias roller  182  is higher than the bias voltage for the brush roller  181 . The opposing roller  184  as a first grounding member has electroconductivity, and is grounded and maintained at ground potential. 
     The negative polarity cleaning set  18 N includes a brush roller  185  as a second attracting member, a bias roller  186  as a second collecting member and a cleaning blade  187  as a second scraping member. The brush roller  185  which is a brush member (fur brush roller) is constituted by, e.g., planting electroconductive brush fibers  185   b  in a cylindrical core portion  185   a  formed of a metal material ( FIG. 5 ). This brush roller  185  contacts the lower surface of the secondary transfer belt  176  at a position downstream of the positive-side brush roller  181 , and sandwiches the secondary transfer belt  176  between itself and the driving roller  171  of the secondary transfer unit  17 . The bias roller  186  which is a roller member is disposed in a lower-left side of the brush roller  185  in contact with the brush roller  185 . The cleaning blade  187  contacting a lower-right portion of the bias roller  186  at a free end portion  187   a  thereof is disposed under the bias roller  186 . 
     Each of the brush roller  185  and the bias roller  186  is connected with the high-voltage output substrate (not shown) of the apparatus main assembly, and is supplied with a bias voltage of the opposite polarity (negative polarity in this embodiment) to the polarity of the above-described brush roller  181 . This bias voltage is set so that the bias voltage for the bias roller  186  is higher than the bias voltage for the brush roller  185 . The driving roller  171  of the secondary transfer unit  17  has electroconductivity, and is grounded and maintained at ground potential. That is, the driving roller  171  not only constitutes a part of the secondary transfer unit  17  but also is provided as a second grounding member corresponding to the negative polarity cleaning set  18 N. 
     The brush rollers  181  and  185  and the bias rollers  182  and  186  are, as shown in  FIG. 4 , disposed in parallel to each other and extend in the widthwise direction of the secondary transfer belt  176 . The brush rollers  181  and  185  and the bias rollers  182  and  186  are rotatably supported at both end portions with respect to the axial direction by a front side plate  193  and a rear side plate  194  of the casing  192 . At one end portion (front side) with respect to the axial direction, a driving force transmitting portion G consisting of gears  195   a  and  195   b  rotating integrally with the brush rollers  181  and  185  and gears  196   a  and  196   b  rotating integrally with the bias rollers  182  and  186  is provided. The brush rollers  181  and  185  and the bias rollers  182  and  186  are rotationally driven via the driving force transmitting portion G by an unshown driving motor. 
     The positive side brush roller  181  and the negative side brush roller  185  rotate counterdirectionally (counterclockwise) to the rotational direction of the secondary transfer belt  176  as shown in  FIG. 5 . The positive side bias roller  182  rotates codirectionally (clockwise) with the positive side brush roller  181  at an opposing portion therebetween. The negative side bias roller  186  rotates counterdirectionally to the rotational direction of the negative side brush roller  185 . Accordingly, the two bias rollers  182  and  186  are rotationally driven from above toward below in opposite directions to each other in a side close to the other bias roller. 
     The positive side cleaning blade  183  contacts the bias roller  182  from below in a state in which the free end portion  183   a  thereof faces counterdirectionally to the rotational direction of the bias roller  182  (i.e., extends in an upper right direction). The negative side cleaning blade  187  positioned at the upper right of the cleaning blade  183  contacts the bias roller  186  from below in a state in which the free end portion  187   a  thereof faces counterdirectionally to the rotational direction of the bias roller  186  (i.e., extends in an upper left direction). Accordingly, the two cleaning blades  183  and  187  are disposed in an inverted V-shape as seen from the front side. These cleaning blades  183  and  187  are supported by the casing  192  via an unshown blade stay in a state in which the cleaning blades are positioned so that contact pressures of their free end portions with the bias rollers  182  and  186  are a predetermined pressure. 
     The feeding screw  188  as a feeding member for feeding the deposited matter scraped off by the cleaning blades  183  and  187  is disposed at a position below the free end portions  183   a  and  187   a  of these blades, and is accommodated inside a feeding groove  189  constituting a part of the casing  192 . The feeding groove  189  is, as shown in  FIG. 6 , partly surrounded by feeding walls  189   a  and  189   b  each standing substantially in the vertical direction at the bottom of the casing  192 , and is formed in a U-shape in cross section and extends in parallel to the bias rollers  182  and  186 . As seen from above, an axial center (line) of the feeding screw  188  is positioned between an axial center (line) of the bias roller  182  and an axial center (line) of the bias roller  186 . Accordingly, a space between the bias rollers  182  and  186  which are disposed and spaced from each other in a direction (left-right direction) crossing their axial centers is configured to overlap with the feeding screw  188  as seen from above. 
     The feeding screw  188  includes a shaft (axis) portion  188   a  and a helical blade portion  188   b  formed at an outer peripheral surface of the shaft portion  188   a , and is rotatably supported by the casing  192  at both end portions thereof with respect to the axial direction. The feeding screw  188  is connected with an unshown driving device in one side (front side) with respect to the axial direction, and is rotationally driven in a direction of feeding the deposited matter toward the other side (rear side) with respect to the axial direction. In the rear side of the feeding groove  189 , an unshown opening through with the feeding walls are connected with the toner collecting container. 
     A positional relationship between the feeding screw  188  and the cleaning blades  183  and  187  will be described using  FIG. 6 . As described above, the feeding screw  188  is disposed inside the feeding walls  189   a  and  189   b  which oppose each other with an interval W 2  larger than a diameter W 1  of the blade portion  188   b  with respect to the left-right direction (W 2 &gt;W 1 ). 
     The free end portions  183   a  and  187   a  of the cleaning blades  183  and  187  are formed in a substantially rectangular shape, for example, and contact the bias rollers  182  and  186  at edges (end portions) A 1  and A 2  in one side of the free end portions  183   a  and  187   a . Edges B 1  and B 2  which are the other ones of the edges (end portions) of the free end portions  183   a  and  187   a  and which are opposite from the edges A 1  and A 2  with respect to a blade thickness direction are positioned between the edges A 1  and A 2  with respect to the left-right direction. Accordingly, the edges B 1  and B 2  are the end portions in sides where the deposited matters scraped off at the edges A 1  and A 2  drop. 
     These edges B 1  and B 2  in the sides where the scraped deposited matters drop are disposed so as to overlap with the feeding screw  188  as seen from above. That is, both of a distance D 1  between the edge B 1  and an axial (shaft) center O 1  of the feeding screw  188  with respect to the left-right direction and a distance D 2  between the edge B 2  and the axial center O 1  with respect to the left-right direction are set so as to be smaller than a radius r 1  of the blade portion  188   b  (D 1 &lt;r 1 , D 2 &lt;r 1 ). 
     The shape of the free end portions of the cleaning blades  183  and  187  is not limited to the rectangular shape, but may also be another shape such as a single edged knife shape. In this case, the end portions of the free end portions in the sides where the deposited matters drop refer to positions where the deposited matters scraped off the bias rollers  182  and  186  are capable of dropping in the vertical direction. 
     [Cleaning of Secondary Transfer Belt] 
     The cleaner unit  18  constituted as described above cleans the secondary transfer belt  12  by the positive polarity cleaning set  18 P and the negative polarity cleaning set  18 N and feeds the deposited matters toward the toner cleaning container by the feeding screw  188 . The positive side brush roller  181  and the negative side brush roller  185  remove the deposited matters such as the toners deposited on the surface of the secondary transfer belt  176  by electrostatic depositing forces by the bias voltages and a mechanical scraping force. The brush roller  181  to which the positive bias voltage is applied principally collects the negatively charged toner, and the brush roller  185  to which the negative bias voltage is applied principally collects the positively charged toner. 
     In this embodiment, the toner images formed by the respective stations Pa, Pb, Pc and Pd and the toner particles of the control patches are negatively charged. For this reason, most of the toner particles deposited on the secondary transfer belt  176  at the secondary transfer portion T 2  are charged to the negative polarity as shown in a graph of  FIG. 7 . Accordingly, most of the deposited matter deposited on the secondary transfer belt  176  are attracted to the positive side brush roller  181 . The deposited matter, such as the toner particles into which positive electric charges are injected by the positive side brush roller  181 , which is not attracted to the bias roller  181  is attracted to the negative side brush roller  182 . 
     The deposited matters attracted to the brush rollers  181  and  185  are collected by the bias rollers  182  and  186  to which the bias voltages which are higher than the bias voltages applied to the brush rollers  181  and  185  are applied. The deposited matters collected by the bias rollers  182  and  186  are scraped off by the edges A 1  and A 2  of the cleaning blades  183  and  187  and are temporarily deposited on ridges (end surfaces) of the free end portions  183   a  and  187   a . Then, the deposited matters overflowing from the edges B 1  and B 2  which are end portions of the ridges drop by gravitation and reach the feeding screw  188 . Then, the deposited matters are fed toward the rear side with rotation of the feeding screw  188 , and are collected in the toner collecting container. 
     The positive side brush roller  181  rotates in a rightward direction in a side (contact portion) where the roller  181  contacts the bias roller  182  ( FIG. 5 ). Further, the bias roller  182  contacts a lower right portion of the brush roller  181 , and therefore a tangential direction of the core portion  181   a  at the contact portion extends in an upper right direction and thus passes through above the free end portion  187   a  of the negative side cleaning blade  187 . Accordingly, at least a part of the toner which scatters due to flicking or the like of the brush fibers a the contact portion reaches the free end portion  187   a  of the cleaning blade  187  as indicated by a broken line of an arrow in  FIG. 5 . 
     Comparison Example 
     A cleaner unit  18 A as Comparison Example with the cleaner unit  18 A of First Embodiment will be described with reference to  FIGS. 8 and 9 . This cleaner unit  18 A is different from the cleaner unit  18  of First Embodiment in that a deposited matter scraped off by a negative side cleaning blade  187 A is guided to the feeding screw  188  by an inclined wall  192 A provided as a part of a casing  192 . Other constitutions are the same as those of the above-described cleaner unit  18 , and therefore, members similar to those in First Embodiment are represented by the same reference numerals or symbols and will be omitted from description. 
     A negative side bias roller  186 A of the cleaner unit  18 A is rotationally driven codirectionally (clockwise) to the brush roller  185  at their opposing portion. The cleaning blade  187 A contacts a lower right portion of the bias roller  186 A in a state in which a free end portion thereof faces toward an upper right direction so as to extend counterdirectionally to the rotational direction of the bias roller  186 A. For this reason, the free end portion of the cleaning blade  187 A positions in a right side spaced from a right end portion of the feeding screw  188 . The casing  192  includes the inclined wall  192 A which extends from below the free end portion of the cleaning blade  187 A toward a lower left direction and which is connected with the feeding groove  189 . Accordingly, an upper surface of the inclined wall  192 A is a movement path along which the deposited matter scraped off the bias roller  186 A by the cleaning blade  187 A slides down in the lower left direction by gravitation. 
     In the cleaner unit  18 A, the deposited matter collected by the negative side brush roller  185  slides down along the inclined wall  192 A after dropping on the inclined wall  192 A. Then, the deposited matter which reached the feeding groove  189  is fed by the feeding screw  188  and is collected in the toner collecting container. However, by an adhesiveness of a substance (such as a wax) contained in the deposited matter, a part of the deposited matter is deposited on the wall surface of the inclined wall  192  ( FIG. 9 ) in some cases. 
     In this way, when the deposited matter scraped by the cleaning blade  187 A drops on the deposited matter deposited on the wall surface, an amount of the deposited matter deposited on the wall surface increases. Thus, when a space between the cleaning blade  187 A and the casing  192  is clogged with the deposited matter, the deposited matter is not collected by the feeding screw  188  and remains inside the casing  192 , and thus finally overflows from the inside of the casing  192 . That is, in the case where the deposited matter scraped off by the cleaning blade  187 A is guided by the wall surface of the inclined wall  192 A or the like, there is a possibility that a state in which the inside of the cleaner unit  18 A is clogged with the deposited matter is formed (toner clogging). When such a toner clogging generates, there is a liability that the toner clogging leads to improper cleaning such that the secondary transfer belt  176  is contaminated with the deposited matter which overflowed from the cleaner unit  18 A. 
     Effect of this Embodiment 
     The cleaner unit  18  in this embodiment attracts not only the negatively charged deposited matter such as the toner particles to the positive side brush roller  181  but also the positively charged deposited matter to the negative side brush roller  185 . As a result, not only the control patches transferred onto the secondary transfer belt  176  at the secondary transfer portion T 2  but also the deposited matter deposited on the secondary transfer belt  176  can be collected efficiently. Further, the constitution in which the feeding screw  188  was provided below the free end portions  183   a  and  187   a  of the cleaning blades  183  and  187  and the deposited matters collected by the positive polarity cleaning set  18 P and the negative polarity cleaning set  18 N were fed by the single feeding member was employed. For this reason, compared with a constitution in which two feeding members are provided correspondingly to the two cleaning sets ( 18 P and  18 N), respectively, it is possible to reduce not only a size of the cleaning device but also part costs. 
     Incidentally, in the case where the feeding member for feeding the deposited matters scraped off the plurality of cleaning blades is provided, as in the cleaner unit  18 A of Comparison Example, there is a liability that the improper cleaning generates by the deposition of the deposited matter on the wall surface of the casing  192  or the like. The cleaner unit  18  in this embodiment is disposed so that the edges B 1  and B 2 , of the free end portions  183   a  and  187   a  of the cleaning blades  183  and  187 , in sides where the scraped deposited matters drop overlap with the feeding screw  188  as seen from above. That is, the constitution in which the deposited matters dropped from the free end portions  183   a  and  187   a  of the cleaning blades  183  and  187  directly drop on the feeding screw  188  is employed. As a result, the deposition of the deposited matters scraped by the cleaning blades  183  and  187  on a portion other than the feeding groove  189  can be suppressed, so that it is possible to prevent generation of the improper cleaning. Thus, the cleaner unit  18  is capable of not only efficiently collecting the deposited matter in a limited space but also achieving a good cleaning performance for a long term. 
     Further, the constitution in which most of the deposited matter deposited on the secondary transfer belt  176  is collected by the positive side brush roller  181  and the toner in a slight amount which is scattered from the brush roller  181  reaches the negative side bias roller  186  was employed. As a result, even in the case where an amount of the toner attracted to the negative side brush roller  185  is extremely small, the toner is supplied in a very small amount to the negative side bias roller  186 . Then, particles, of an external additive or the like contained in the toner, which are smaller in particle size than the toner particles enter a gap between the bias roller  186  and the cleaning blade  187  and thus lowers a friction coefficient between the bias roller  186  and the cleaning blade  187 . As a result, an excessive frictional force is prevented from generating between the bias roller  186  and the cleaning blade  187 , so that a problem such as turning-up or the like of the cleaning blade  187  can be prevented. 
     Modified Embodiment 
     In the above-described cleaner unit  18 , in place of the negative polarity cleaning set  18 N, a blade member  38  ( FIG. 3 ) contacting the secondary transfer belt  176  may also be provided. This blade member  38  contacts the secondary transfer belt  176  in a state in which a free end portion thereof extends counterdirectionally to the feeding direction (arrow R direction) of the secondary transfer belt  176  in the upper left direction. In this case, an end portion of the free end portion of the blade member  38  in a side where the deposited matter drops may preferably be disposed so as to overlap with the feeding screw  188  as seen from above. As a result, the deposited matters scraped by the cleaning blade  183  and the blade member  38  can be dropped on the feeding screw  188  without being deposited on the wall surface or the like of the casing  192 . That is, the cleaner unit in this modified embodiment is, similarly as in the above-described case where the negative polarity cleaning set  18 N is provided, capable of not only efficiently collecting the deposited matter in the limited space but also achieving the good cleaning performance for the long term. 
     Second Embodiment 
     A cleaner unit  28  (cleaning device) in Second Embodiment will be described. The cleaner unit  28  is different from the cleaner unit  18  of First Embodiment in rotational directions of the bias rollers and arrangements of the cleaning blades. Other constitutions are the same as those of the above-described cleaner unit  18 , and therefore members similar to those in First Embodiment are represented by the same reference numerals or symbols and will be omitted from description. 
     [Cleaner Unit] 
     The cleaner unit  28  in this embodiment includes, as shown in  FIG. 10 , a positive polarity cleaning set  28 P, a negative polarity cleaning set  28 N and a feeding screw  188 . The positive polarity cleaning set  28 P includes a brush roller  181 , a bias roller  282  rotating in a contact state with the brush roller  181 , and a cleaning blade  283  contacting the bias roller  282  at a free end portion  283   a  thereof. The brush roller  181  and the bias roller  282  are connected with a high-voltage output substrate through contacts provided at end portions thereof with respect to the axial directions and are supplied with positive bias voltages, and the positive bias voltage applied to the bias roller  282  is set so as to be higher than the positive bias voltage applied to the brush roller  181 . The negative polarity cleaning set  28 N includes a brush roller  185 , a bias roller  286  rotating in a contact state with the brush roller  185 , and a cleaning blade  287  contacting the bias roller  286  at a free end portion  287   a  thereof. The brush roller  185  and the bias roller  286  are connected with a high-voltage output substrate through contacts provided at end portions thereof with respect to the axial directions and are supplied with negative bias voltages, and the negative bias voltage applied to the bias roller  282  is set so as to be higher (in absolute value) than the negative bias voltage applied to the brush roller  181 . The feeding screw  188  is accommodated inside the feeding groove  189  formed as a part of the casing  192  and is disposed below the free end portions  283   a  and  287   a  of the cleaning blades  283  and  287 . The feeding screw  188  is rotationally driven by an unshown driving source and feeds the deposited matters dropped on the feeding groove  189  to the rear side. At a rear side position of the feeding groove  189 , an unshown opening is provided, and the feeding groove  189  is connected with the toner collecting container (bottle) through the opening. 
     The positive side bias roller  282  is, as shown in  FIG. 11 , rotationally driven in the counterclockwise direction. The positive side brush roller  181  is rotationally driven in a direction (counterclockwise direction) opposite to the feeding direction (arrow roller direction in  FIG. 10 ) of the secondary transfer belt  176  at the contact portion, and therefore, the bias roller  282  and the brush roller  181  are rotated at the contact portion in opposite directions in which these rollers rub against each other. Further, the negative side bias roller  286  is rotationally driven in the clockwise direction which is codirectional at the contact portion with the rotational direction of the negative side brush roller  185  which is rotationally driven in the counterclockwise direction. Accordingly, the bias rollers  182  and  186  are rotationally driven from below toward above in opposite directions to each other in a side close to the other bias roller. 
     The positive side cleaning blade  283  and the negative side cleaning blade  287  are, as shown in  FIG. 11 , disposed between the positive side bias roller  282  and the negative side bias roller  286  with respect to the left-right direction. These cleaning blades  283  and  287  contact the bias rollers  282  and  296 , respectively, in a state in which the free end portions  283   a  and  287   a  of thereof extend downwardly and counterdirectionally to the rotational directions of the bias rollers  282  and  286 , respectively. Accordingly, of the free end portions  283   a  and  287   a , edges A 3  and A 4  in sides where the free end portions  283   a  and  287   a  contact the bias rollers  282  and  296 , respectively, are end portions in sides where the scraped deposited matters drop by gravitation. These cleaning blades  283  and  287  are supported on a left side surface and a right side surface of a blade supporting member  197  formed in a substantially inverted U-shape in cross section, and are fixed to the casing  192  via the blade supporting member  197 . 
     Next, a positional relationship between the feeding screw  188  and the cleaning blades  283  and  287  will be described. The feeding screw  188  is disposed inside feeding walls  189   a  and  189   b  opposing each other with an interval W 4  larger than a diameter W 3  of the blade portion  188   b  with respect to the left-right direction (W 4 &gt;S 3 ). As seen from above, an axial center (line) O 2  of the feeding screw  188  is positioned between an axial center (line) of the bias roller  282  and an axial center (line) of the bias roller  286 . Accordingly, a space between the bias rollers  282  and  286  which are disposed and spaced from each other in a direction (left-right direction) crossing their axial centers is configured to overlap with the feeding screw  188  as seen from above. 
     The edge A 3  of the positive side cleaning blade  283  is spaced leftwardly from the axial center O 2  of the feeding screw  188  by a distance D 3  in the left-right direction. Further, the edge A 4  of the negative side cleaning blade  287  is in a position spaced rightwardly from the axial center O 2  by a distance D 4  in the left-right direction. These edges A 3  and A 4  are disposed so as to overlap with the feeding screw  188  as seen from above. In other words, the distances D 3  and D 4  from the edges A 3  and A 4  to the axial center O 2  are set so as to be smaller than a radius r 2  of the blade portion  188   b  (D 3 &lt;r 2 , D 4 &lt;r 2 ). 
     In this embodiment, the two cleaning blades  283  and  287  are disposed in an inclined manner so that the cleaning blades  283  and  287  are somewhat increased, in a distance therebetween with respect to the left-right direction, downwardly, but positions and contact angles of the edges A 3  and A 4  may also be appropriately changed so long as the drop of the scraped deposited matters is not hindered. For example, the cleaning blades  283  and  287  may also be parallel to each other, or the distance between the cleaning blades  283  and  287  with respect to the left-right direction may also be somewhat increased upwardly. 
     Effect of this Embodiment 
     The cleaner unit  28  constituted as described above is capable of efficiently collecting the deposited matters scraped off the secondary transfer belt  176  by the brush roller  181  to which the positive bias voltage is applied and the brush roller  185  to which the negative bias voltage is applied. Further, the constitution in which the feeding screw  188  was provided below the free end portions  283   a  and  287   a  of the cleaning blades  283  and  287  and the deposited matters collected by the positive polarity cleaning set  28 P and the negative polarity cleaning set  28 N were fed by the single feeding screw  188  was employed. For this reason, it is possible to reduce not only a size of the cleaning device but also part costs. 
     In such a constitution, the cleaner unit  28  in this embodiment was disposed so that the edges A 3  and A 4 , of the free end portions  283   a  and  287   a  of the cleaning blades  283  and  287 , which are end portions in sides where the scraped deposited matters drop overlap with the feeding screw  188  as seen from above (in plan view). That is, the constitution in which the deposited matters scraped off the bias rollers  282  and  286  at the edges A 3  and A 4  directly drop on the feeding screw  188  was employed. As a result, the deposition of the deposited matters scraped by the cleaning blades  283  and  287  on a portion other than the feeding groove  189  can be suppressed, so that it is possible to prevent generation of the improper cleaning. That is, the cleaner unit  28  is capable of not only efficiently collecting the deposited matter in a limited space but also achieving a good cleaning performance for a long term. 
     Further, the cleaning blade  283  and  287  and the blade supporting member  197  are disposed using a space between the two bias rollers  282  and  296  which are disposed and spaced from each other in the left-right direction. For this reason, compared with First Embodiment, there is no need to ensure a space, at a position below the bias rollers  282  and  296 , for placement of the cleaning blades and a supporting member for supporting the cleaning blades, so that the cleaning device can be made compact with respect to the up-down direction. 
     Other Embodiments 
     In the above-described First and Second Embodiments, the cleaning device for cleaning the secondary transfer belt  176  was described, but a cleaning device for cleaning another member of the image forming apparatus may also be used in the present invention. For example, a device (such as the intermediary transfer belt cleaning portion  10 ) for cleaning the intermediary transfer member, such as the intermediary transfer belt, as the member-to-be-cleaned may also be constituted similarly as in the case of the cleaner unit  18 . 
     In the above-described First and Second Embodiments, the constitution in which the two bias rollers are rotated in the opposite directions to each other was described as an example, but a constitution in which their rotational directions are the same may also be employed. In this case, it is preferable that each of the cleaning blades is contacted to the associated bias roller in a state in which the free end portion thereof faces counterdirectionally to the rotational direction of the bias roller. Further, of the free end portions of the cleaning blades, end portions (edges) in sides where the scraped deposited matters drop are disposed at positions which overlap with the feeding screw (feeding member) as seen from above, so that it is possible to obtain effects similar to those of the above-described First and Second Embodiments. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2015-133804 filed on Jul. 2, 2015, which is hereby incorporated by reference herein in its entirety.