Patent Publication Number: US-8116662-B2

Title: Development device and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a development device and an image forming apparatus such as a photocopier, a printer, and a facsimile machine with a multicolor electrophotographic method. 
     2. Description of Related Art 
     In a conventional image forming apparatus having a plurality of development devices with a multicolor electrophotographic method, a toner is transferred to a transfer medium in the course of image formation while a toner not transferred to the transfer medium is collected as a waste toner by a cleaning device. The waste toner collected by the cleaning device is mixed of different colors of toners. Consequently, the collected toner is discarded without subjecting to recycling. 
     Generally, a conventional image forming apparatus includes a waste toner container storing a waste toner therein. For example, in a case where the conventional image forming apparatus employs a method using a transfer belt or an intermediate transfer belt in a transfer device, a toner adhered to a surface of such a belt is collected as the waste toner in the waste toner container, causing not only an increase in an amount to the toner to be discarded, but also an increase in difficulty of dealing with such a toner. 
     For example, Japanese Un-examined Patent Application Publication No. 2005-292366 discloses a waste toner container disposed separately from a supply toner container in each of toner cartridges detachably disposed with respect to development units corresponding to respective toner colors so as to reduce the above difficulty. Particularly, a size of each of the toner cartridges is increased, and the development units are disposed to have space therebetween, so that the waste toner expelled from the development unit is stored in the waste toner container disposed separately from the supply toner container in each of the toner cartridges. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a development device includes: a plurality of development units, each of the plural development units including an image carrier carrying a developer image formed by developer, and a cleaning member cleaning the image carrier by removing a waste substance; and a waste substance container or waste substance containers storing the waste substance removed by the cleaning member. A number of the waste substance containers disposed is smaller than a number of development units disposed, and the number of the waste substance containers is greater than or equal to one. 
     According to another aspect of the invention, a development device includes: a plurality of development units, each of the plural development units including an image carrier carrying a developer image formed by developer, and a cleaning member cleaning the image carrier by removing a waste substance; a conveyance member conveying the waste substance removed by each of the plural cleaning members; a waste substance container storing the waste substance conveyed by the conveyance member; and a rotation drive member allowing an end portion of the conveyance member to rotate. 
     According to another aspect of the invention, an image forming apparatus includes: a plurality of development units, each of the plural development units including an image carrier carrying a developer image formed by developer, a transfer medium transferring the developer image thereon, and a cleaning member disposed on a downstream side relative to a contact point between the image carrier and the transfer medium in a rotation direction of the image carrier to clean the image carrier by removing a waste substance; a conveyance member conveying the waste substance removed by each of the plural cleaning members; and a waste substance container disposed to one of the developer units disposed on the most upstream side in a conveyance direction of the transfer medium to store the waste substance conveyed by the conveyance member. 
     Accordingly, the present invention provides a development device and an image forming apparatus capable of reducing a size of the image forming apparatus as a whole by reducing space between each of the development units. 
     Additional features and advantages of the present invention will be more fully apparent from the following detailed description of embodiments, the accompanying drawings and the associated claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the aspects of the invention and many of the attendant advantage thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram illustrating a printer serving as an image forming apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a schematic diagram illustrating a first conveyance member according to the first embodiment of the present invention; 
         FIG. 3  is a schematic diagram illustrating a second conveyance member according to the first embodiment of the present invention; 
         FIG. 4  is a schematic diagram illustrating a coupling state of the first conveyance member and the second conveyance member; 
         FIG. 5  is a schematic diagram illustrating a waste toner container according to the first embodiment of the present invention, 
         FIG. 6  is a schematic diagram illustrating operation in a case where each of toner cartridges is connected to the second conveyance member attached to a development unit; 
         FIG. 7  is a schematic diagram illustrating an attachment state of the toner cartridge and the second conveyance member attached to the development unit; 
         FIG. 8  is a schematic diagram illustrating a joint portion between a waste toner outlet of the second conveyance member and a waste toner collection inlet of the toner cartridge as seen when the toner cartridge is partially cut; 
         FIG. 9  is an enlarged partial view illustrating a vicinity of the waste toner collection inlet of the  FIG. 8 ; 
         FIG. 10  is a schematic diagram illustrating a modification of the first embodiment of the present invention, 
         FIG. 11  is a partial schematic diagram illustrating a vicinity of a waste toner outlet in a second conveyance member according to a second embodiment of the present invention; 
         FIG. 12  is a partial schematic diagram illustrating a vicinity of a waste toner collection inlet of a waste toner container according to the second embodiment of the present invention; 
         FIG. 13  is an enlarged partial view illustrating a joint portion between the waste toner outlet of the second conveyance member and the waste toner collection inlet of a toner cartridge as seen when the toner cartridge is partially cut; 
         FIG. 14A  is a schematic diagram illustrating a driving method of a conveyance flat spiral according to the first embodiment of the present invention; and 
         FIG. 14B  is a schematic diagram illustrating a driving method of a conveyance flat spiral according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, like reference numerals designate identical or corresponding parts throughout the several views. 
     First Embodiment 
     Referring to  FIG. 1 , a printer  1  serving as an image forming apparatus according to a first embodiment of the present invention is illustrated. The printer  1  includes: development units  2   k ,  2   y ,  2   m , and  2   c  corresponding to toners of black, yellow, magenta, and cyan, respectively (hereafter, the toner colors of black, yellow, magenta, and cyan are abbreviated as k, y, m, and c, respectively); toner cartridges  3   k ,  3   y ,  3   m , and  3   c  serving as developer containers storing respective colors of the toner serving as developer; a transfer unit  4  transferring toner images developed on photosensitive drum  21   k ,  21   y ,  21   m , and  21   c  (described later) to a sheet P serving as a transfer medium; exposure units  5   k ,  5   y ,  5   m , and  5   c  forming electrostatic latent images on surfaces of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  with irradiation of light; a sheet feeding cassette  6  storing the sheet P therein and feeding the sheet P in a direction indicated by an arrow “X” shown in  FIG. 1 ; a fixing unit  7  fixing the toner images transferred by the transfer unit  4  to the sheet P; and a sheet conveyance path  8 , in a substantially “S” shape, disposed with respect to a lower frame of the printer  1 . 
     The development units  2   k ,  2   y ,  2   m , and  2   c  are sequentially disposed along the sheet conveyance path  8  from a sheet feeding side to an ejection side of the sheet P in a direction indicated by “Y” shown in  FIG. 1 . The development units  2   k ,  2   y ,  2   m , and  2   c  are integrally formed as a development device  2  and are detachably disposed with respect to the printer  1 . According to the first embodiment of the present invention, only the development unit  2   k  includes a waste toner container  32  (described later) annexed to a toner cartridge  3   k  as illustrated in  FIG. 1 . Since each of the development units  2   k ,  2   y ,  2   m , and  2   c  is substantially similar to one another except for the color of the toner and the waste substance container  32 , the one development unit  2   k  is described as representative of all the development units  2   k ,  2   y ,  2   m , and  2   c  while descriptions of the development units  2   y ,  2   m , and  2   c  are omitted for the sake of simplicity. 
     The development unit  2   k  includes: the photosensitive drum  21   k  serving as an image carrier; a charging roller  22   k  uniformly charging the surface of the photosensitive drum  21   k ; a development roller  23   k  supplying the toner to the photosensitive drum  21   k ; a development blade  24   k  regulating a layer thickness of the toner supplied to the development roller  23   k ; a supply roller  25   k  supplying the toner to the development roller  23   k ; a cleaning blade  26   k  serving as a cleaning member removing a residual toner not transferred to the sheet P and remained on the photosensitive drum  21   k ; and a first conveyance member  27   k  serving as a conveyance member conveying the residual toner removed by the cleaning blade  26   k  as a waste toner. 
     The photosensitive drum  21   k , serving as an organic photosensitive member, includes a conductive support member and a photoconductive layer. In the photosensitive drum  21   k , a charge generation layer and a charge transport layer serving as the photoconductive layers are sequentially laminated on a metal pipe, for example, made of aluminum, serving as the conductive support member. The surface of the photosensitive drum  21   k  is uniformly charged by the charging roller  22   k , and forms the electrostatic latent image thereon with the light irradiated by the exposure unit  5 . 
     The charging roller  22   k  includes a metal shaft and a semi-conductive rubber layer, for example, made of epichlorohydrin rubber. The charging roller  22   k  contacts the photosensitive drum  21   k  with a prescribed pressure amount, and is rotatably driven by rotation of the photosensitive drum  21   k . The charging roller  22   k  is connected with a charging roller power source (not shown) applying the bias voltage of the same polarity as the toner, so that the surface of the photosensitive drum  21   k  is uniformly charged by the bias voltage applied by the charging roller power source. 
     The development roller  23   k  includes a metal shaft and a semi-conductive urethane rubber layer. The development roller  23   k  contacts the photosensitive drum  21   k  with a prescribed pressure amount and supplies the toner to the electrostatic latent image formed on the photosensitive drum  21   k , thereby reversely developing the image. The development roller  23   k  is connected with a development roller power source (not shown) applying the bias voltage of the same polarity as the toner or the reverse polarity to the toner, so that the toner charged by the bias voltage applied from the development roller power source is adhered to the electrostatic latent image on the photosensitive drum  21   k.    
     The development blade  24   k  has, for example, a thickness of 0.08 mm and a length which is substantially the same as a longitudinal direction length of the development roller  22   k . The development blade  24   k  serves as a metal thin plate member regulating the layer thickness of the toner. One end of the development blade  24   k  in a longitudinal direction is secured to a frame (not shown), and another end is disposed in such a manner as to contact the development roller  23   k  with a slight portion of an inner surface in a leading end thereof. 
     The supply roller  25   k  includes a metal shaft and a semi-conductive foam silicone sponge layer. The supply roller  25   k  contacts the development roller  23   k  with a prescribed pressure amount and supplies the toner to the development roller  23   k . The supply roller  25   k  is connected with a supply roller power source (not shown) applying the bias voltage of the same polarity as the toner or the reverse polarity to the toner, so that the toner supplied from a supply toner container  31   k  serving as a developer container included in the toner cartridge  3   k  is supplied to the development roller  23   k  by the bias voltage applied from the supply roller power source. 
     The cleaning blade  26   k  serves as a rubber member made of urethane and is disposed in a position in which one end thereof contacts the photosensitive drum  21   k  with a prescribed pressure amount. A longitudinal direction length of the cleaning blade  26   k  is substantially the same as that of the photosensitive drum  21   k . The cleaning blade  26   k  scrapes the residual toner from the surface of the photosensitive drum  21   k , so that the surface of the photosensitive drum  21   k  is cleaned. The surface of the photosensitive drum  21   k  has a small quantity of a substance adhered thereto from the transfer belt  9  (described later), and the cleaning blade  26   k  scrapes such an adhesion substance from the surface of the photosensitive drum  21   k.    
     The first conveyance member  27   k  conveys the residual toner and the adhesion substance removed by the cleaning blade  26   k  towards a front side in a rotation direction of the photosensitive drum  21   k  in  FIG. 1 . Herein, the residual toner and the adhesion substance are conveyed as the waste toner. The first conveyance member  27   k  is connected to a second conveyance member  28  serving as a conveyance member forming a conveyance path of the waste toner. The waste toner conveyed by the first conveyance member  27   k  is conveyed by the second conveyance member  28  to the waste toner container  32  serving as the waste substance container (described later). The second conveyance member  28  collectively conveys the waste toner conveyed from the first conveyance members  27   k ,  27   y ,  27   m , and  27   c  included in respective development units  2   k ,  2   k ,  2   m , and  2   c  to a direction indicated by an arrow “Z” shown in  FIG. 1 . The first and second conveyance members  27  and  28  serving as the conveyance members are described in detail later. 
     The toner cartridges  3   k ,  3   y ,  3   m , and  3   c  respectively include the supply toner containers  31   k ,  31   y ,  31   m , and  31   c  each of which is a hollow structure. The supply toner containers  31   k ,  31   y ,  31   m , and  31   c  store unused toners of black, yellow, magenta, and cyan, respectively. Among such toner cartridges  3   k ,  3   y ,  3   m , an  3   c , the toner cartridge  3   k  positioned on the most upstream side of the sheet conveyance path  8  has the waste toner container  32  annexed to the supply toner container  31   k . The waste toner container  32 , having independent storage space adjacent to the supply toner container  31   k , stores the waste toner conveyed by the second conveyance member  28 . 
     Each of the development device  2 , the toner cartridges  3   k ,  3   y ,  3   m , and  3   c , and the like is a replaceable unit in the printer  1 . Therefore, in a case where the toner is consumed, or in a case where a component is deteriorated, such a replaceable unit can be replaced. 
     The transfer unit  4  includes: the transfer belt  9  conveying the sheet P with electrostatic absorption of the sheet P thereto; a drive roller (not shown) driving the transfer belt  9  by being rotated by a drive unit (not shown); a tension roller (not shown) forming a pair with the drive roller to tightly stretch the transfer belt  9 ; and the transfer rollers  4 ,  4   y ,  4   m , and  4   c , disposed opposite to the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  with pressure, applying the voltage in such a manner as to transfer the toner images to the sheet P. Each of the transfer rollers  4   k ,  4   y ,  4   m , and  4   c  is connected with a transfer roller power source (not shown) applying the bias voltage of the reverse polarity to the toner, so that the toner images formed on the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  are transferred to the sheet P by the bias voltage applied from the transfer roller power source. 
     Each of the exposure units  5   k ,  5   y ,  5   m , and  5   c  serves as a light emitting diode (LED) head having a light emitting element such as LED and a lens array, for example. The exposure units  5   k ,  5   y ,  5   m , and  5   c  irradiate the surfaces of the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  with the light based on print data input, so that the potential of each of irradiated areas decays, thereby forming the electrostatic latent images on the surfaces of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c.    
     The sheet feeding cassette  6  stores the sheet P therein in a state that a plurality of sheets P are stacked. The sheet feeding cassette  6  is detachably attached in a lower portion of the printer  1 . A sheet feeding unit (not shown) is disposed above the sheet feeding cassette  6 , and includes a hopping roller feeding the sheet P sheet by sheet. The sheet P is fed in the direction “X” shown in  FIG. 1  by the sheet feeding unit and is conveyed to the development device  2  by a conveyance roller (not shown). 
     The fixing unit  7  is disposed on a downstream side of the sheet conveyance path  8  and includes a heat roller  7   a , a pressure roller  7   b , a thermistor (not shown), and a heater (not shown). The heat roller  7   a , for example, includes a hollow cylindrical core metal made of aluminum, a heat-resistant elastic layer made of silicone rubber, and a tube made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). The metal core is coated with the heat-resistant elastic layer, and such an elastic layer is coated with the PFA tube. The metal core includes, for example, a heater such as a halogen lamp therein. The pressure roller  7   b  includes, for example, a core metal made of aluminum, a heat-resistant elastic layer made of silicone rubber coating the core metal therewith, and a PFA tube coating the heat-resistant elastic layer therewith. The pressure roller  7   b  is disposed in such a manner as to form a pressure portion between the pressure roller  7   b  and the heat roller  7   a . The thermistor serves as a temperature detection member detecting the surface temperature of the pressure roller  7   a  and is disposed in the vicinity of the heat roller  7   a  in a non-contact manner. The heater is controlled based on a result of the surface temperature of the heat roller  7   a  detected by the thermistor, so that the surface temperature of the heat roller  7   a  is maintained at prescribed temperature. The toner image transferred to the sheet P passes the pressure portion formed between the pressure roller  7   b  and the heat roller  7   a  maintained at the prescribed temperature, so that the toner image is fixed on the sheet P by application of the heat and pressure. 
     Moreover, the printer  1  includes: a print data input unit, for example, receiving an input of print data from an external device; a display unit including a display device such as a liquid crystal display (LCD) to display a state of the printer  1 ; an operation unit including an input member such as a touch panel to receive a print instruction input from a user; and a central processing unit (CPU) controlling the operation of the printer  1 . 
     According to the printer  1 , the toner image formed by the development device  2  can be transferred to and fixed on the sheet P, and the image based on the print data input can be output to an external unit. Among the toner cartridges  3   k ,  3   y ,  3   m , an  3   c  storing the toner of respective colors, the toner cartridge  3   k  positioned on the most upstream side of the sheet conveyance path  8  has the waste toner container  32  annexed to the supply toner container  31   k . Since the waste toner container  32  has the independent storage space adjacent to the supply toner container  31   k , an adequate amount of the black toner (k) to be used for the development can be stored in the supply toner container  31   k . Moreover, since the waste toner container  32  is annexed to only the toner cartridge  3   k , space between each of the development units can be reduced, thereby allowing a size of the printer  1  as a whole to be reduced or allowing a storage amount of the supply toner to be increased. Moreover, the waste toner container  32  is annexed to the toner cartridge  3   k  storing the most frequently used toner of black among other colors (i.e., yellow, magenta, and cyan), thereby reducing an occurrence of a toner cartridge replacement in a case where an unused toner of less frequently used colors such yellow, magenta, or cyan is remained in the supply toner container  31   y ,  31   m , or  31   c , respectively. 
     Moreover, since the toner cartridge  3   k  is disposed on the most upstream side in the conveyance direction of the sheet P, the toner cartridge  3   k  tends not to be influenced by radiant heat from the fixing unit  7 . 
     Moreover, a top cover  1   a  of the printer  1  includes the exposure units  5   k ,  5   y ,  5   m , and  5   c  disposed toward respective development units  2   k ,  2   y ,  2   m , and  2   c , and is provided with a rotation support member  1   b  rotatably mounted with respect to the printer  1 . The rotation support member  1   b  is disposed on the side near the fixing unit  7 , and the user can open the top cover  1   a  to have access to inside the printer  1 , for example, in a case of replacement of the toner cartridges  3 . The waste toner container  32  is disposed in a farthest position from the rotation support member  1   b  of the top cover  1   a . That is, the waste toner container  32  is disposed to the toner cartridge  3   k  disposed farthest from the rotation support member  1   b , so that the space between each of the development units can be easily reduced, thereby allowing the size of the printer  1  to be reduced or allowing the storage amount of the supply toner to be increased. In other words, the waste toner container  32  is disposed outside the movement range of the exposure units  5 , that is, outside the rotation radius of the exposure units  5 , so that the space between each of the development units can be easily reduced, thereby reducing the size of the printer  1  and increasing the storage amount of the supply toner. 
     Referring to  FIG. 2 , a description is given of conveyance of the waste toner to the waste toner container  32  by the first conveyance members  27   k ,  27   y ,  27   m , and  27   c . Since each of the first conveyance members  27   k ,  27   y ,  27   m , and  27   c  is substantially similar to one another except for the toner color, a description of the first conveyance members  27   k ,  27   y ,  27   m , and  27   c  is given by using a first conveyance member  27  as representative of the conveyance members  27   k ,  27   y ,  27   m , and  27   c . A description of the cleaning blades  26   k ,  26   y ,  26   m , and  26   c  scraping and cleaning the residual toner on the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  is given by using a cleaning blade  26  as representative of the cleaning blades  26   k ,  26   y ,  26   m , and  26   c.    
     As illustrated in  FIG. 2 , the first conveyance member  27  includes: a conveyance path  271  serving as a path in which the waste toner is conveyed; a conveyance spiral coil  272  conveying the waste toner along the conveyance path  271 ; a drive transmission gear  273  transmitting driving force from a drive source (not shown) to the conveyance spiral coil  272 ; and a first waste toner outlet  274  expelling the waste toner conveyed along the conveyance path  271  therefrom. 
     The conveyance path  271  is disposed in a position in which the toner scraped from the photosensitive drum  21  by the cleaning blade  26  is dropped and accumulated, and a longitudinal direction length of the conveyance path  271  is arranged in such a manner as to be substantially the same as that of the cleaning blade  26 . The spiral coil  272  is rotated at a certain circumferential speed in a prescribed rotation direction by the driving force transmitted through the drive transmission gear  273  disposed on an upstream side in a waste toner conveyance direction of the conveyance path  271 . The waste toner is conveyed in the waste toner conveyance direction with the rotation of the conveyance spiral coil  272 . The waste toner conveyed by the rotation of the conveyance spiral coil  272  is expelled from the first waste toner outlet  274  disposed on a downstream side in the waste toner conveyance direction of the conveyance path  271 . 
     Referring to  FIG. 3 , the second conveyance member  28  is illustrated in a schematic diagram. The second conveyance member  28  includes: a conveyance path  281  serving as a path in which the waste toner is conveyed; a conveyance flat spiral  282  conveying the waste toner along the conveyance path  281 ; a drive transmission gear  283  transmitting driving force from a drive power source (not shown) to the conveyance flat spiral  282 ; a spiral deformation prevention bar  284  preventing the conveyance flat spiral  282  from deformation; a second waste toner outlet  285  expelling the waste toner conveyed along the conveyance path  281 ; a waste toner outlet open-close shutter  286  controlling opening and closing of the second waste toner outlet  285 ; an urging spring  287  urging the waste toner outlet open-close shutter  286  in a prescribed direction; and first waste toner inlets  288   k ,  288   y ,  288   m , and  288   c  flowing therein the waste toner expelled from the first waste toner outlet  274 . Herein, the conveyance flat spiral  282 , for example, represents a spiral formed by a wire rod having a flat surface. 
     The conveyance path  281  is formed of a cylindrical pipe member and has a flexion portion having an adequate curvature in a prescribed location. The conveyance flat spiral  282  serves as a spiral coil in a shape of a rectangular cross section, and has a length substantially the same as the longitudinal direction length of the conveyance path  281 . The conveyance flat spiral  282  is disposed inside the conveyance path  281 . The drive transmission gear  283  allowing the conveyance flat spiral  282  to drive is disposed in an end portion on an upstream side in the waste toner conveyance direction of the conveyance path  281 , and obtains the driving force through a drive source (not shown) of the development device  2 , for example, an orthogonal axis transmission gear such as a bevel gear. The spiral deformation prevention bar  284  is disposed in an area inside the conveyance flat spiral  282  corresponding a straight portion of the conveyance path  281 . The spiral deformation prevention bar  284  prevents the conveyance flat spiral  282  from a damage caused by distortion or twist of a certain level or above in a case where the conveyance flat spiral  282  is deformed in a compression direction by resistance of the waste toner to be discarded or friction between the conveyance flat spiral  282  and a conveyance path wall surface. The second waste toner outlet  285  is disposed downward in an end portion on a downstream side in the waste toner conveyance direction of the conveyance path  281 , and the waste toner outlet open-close shutter  286  is urged by the urging spring  287  in a closing direction of the second waste toner outlet  285 . In the straight portion of the conveyance path  281 , each of the first waste toner inlets  288   k ,  288   y ,  288   m , and  288   c  is disposed in a position one level above within a prescribed area, and the first waste toner inlets  288   k ,  288   y ,  288   m , and  288   c  are coupled to the first waste toner outlets  274   k ,  274   y ,  274   m , and  274   c , respectively, so that the waste toner expelled from the first waste toner outlets  274   k ,  274   y ,  274   m , and  274   k  are flown into the second conveyance member  28 . 
     Referring to  FIG. 4 , the first conveyance member  27   c  and the second conveyance member  28  in a coupling state is illustrated in a schematic diagram. Since the first conveyance members  27   k ,  27   y ,  27   m , and  27   c  are substantially similar to one another except for the toner color, a description of the first conveyance members  27   k ,  27   y ,  27   m , and  27   c  is given by using the first conveyance member  27   c  for the development unit  2   c  as representative of the conveyance members  27   k ,  27   y ,  27   m , and  27   c . As illustrated in  FIG. 4 , the first waste toner inlet  288   c  of the second conveyance member  28  is connected to the first waste toner outlet  274   c  of the first conveyance member  27   c . In this way, the second conveyance member  28  is coupled in such a manner as to be positioned one level below with respect to the first conveyance member  27   c , so that the waste toner expelled from the first conveyance member  27  is dropped inside the conveyance path  281  of the second conveyance member  28  by a weight thereof. 
     Referring to  FIG. 5 , the waste toner container  32  is illustrated in a schematic diagram. The waste toner container  32  includes: a frame  321 ; a toner conveyance spiral  322  conveying the waste toner in an inner direction of the storage space; a drive transmission gear  323  transmitting driving force from a drive source (not shown) to the toner conveyance spiral  322 ; a waste toner collection inlet  324  flowing therein the waste toner expelled form the second waste toner outlet  285 ; and a waste toner collection inlet open-close shutter  325  controlling opening and closing of the waste toner collection inlet  324 . 
     The frame  321  includes a body frame  321   a  and a side plate  321   b , and has a waste toner storage space independent from the supply toner container  31   k  therein. The frame  321  may be integrally formed with respect to a frame of the supply toner container  31   k , or may be integrally attached to the frame of the supply toner container  31   k  by a latch engagement, for example. The toner conveyance spiral  322  is rotated at a certain circumferential speed in a prescribed rotation direction by the driving force transmitted through the drive transmission gear  323 . The accumulated waste toner is conveyed in the inner direction of the storage space with the rotation of the toner conveyance spiral  322 . The waste toner collection inlet open-close shutter  325  is urged by an urging spring (not shown) in a closing direction of the waste toner collection inlet  324 . 
     Referring to  FIGS. 6 and 7 , a description is given of operation in a case where each of the toner cartridges  3   k ,  3   y ,  3   m , and  3   c  is connected to the second conveyance member  28  attached to the development units  2   k ,  2   y ,  2   m , and  2   c , and a description is given of a state that the toner cartridges  3   k ,  3   y ,  3   m , and  3   c  are connected to the respective development units  2   k ,  2   y ,  2   m , and  2   k , respectively. 
     As illustrated in  FIG. 6 , in a case where each of the toner cartridges  3   k ,  3   y ,  3   m , and  3   c  is connected to the second conveyance member  28  attached to the development units  2   k ,  2   y ,  2   m , and  2   c , the toner cartridges  3   k ,  3   y ,  3   m , and  3   c  corresponding to the respective development units  2   k ,  2   y ,  2   m , and  2   c  are moved in directions indicated by arrows shown in  FIG. 6 , and the waste toner outlet  285  of the second conveyance member  28  and the waste toner collection inlet  324  of the toner cartridge  3   k  are attached such a manner as to be engaged. Consequently, the toner cartridges  3   k ,  3   y ,  3   m , and  3   c  and the second conveyance member  28  attached to the development units  2   k ,  2   y ,  2   m , and  2   c  are attached as illustrated in  FIG. 7 . 
     Referring to  FIG. 8 , the toner cartridge  3   k  is partially cut to illustrate a joint portion between the waste toner outlet  285  of the second conveyance member  28  and the waste toner collection inlet  324  of the toner cartridge  3   k . A vicinity of the waste toner collection inlet  324  of  FIG. 8  is illustrated in an enlarged partial view of  FIG. 9 . 
     As illustrated in  FIGS. 8 and 9 , when the toner cartridge  3   k  is attached, an end portion  28   a  of the second conveyance member  28  having the waste toner outlet  285  pushes and moves the waste toner collection inlet open-close shutter  325  in an opening direction of the waste toner collection inlet  324 . The waste toner outlet open-close shutter  286  moves in an opening direction of the waste toner outlet  285  with the movement of the waste toner collection inlet open-close shutter  325 . As a result, both of the waste toner outlet  285  and the waste toner collection inlet  324  are open and placed one on another, so that the waste toner can be flown. 
     Now, a description is given of image forming operation of the printer  1 . When the print data is input by the external device, and the image forming operation is begun, the surfaces of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  are discharged by a discharge device (not shown), and surface potentials of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  are averaged between 0 (zero) and −150 V, for example. The charging rollers  22   k ,  22   y ,  22   m , and  22   c  disposed in contact with the surfaces of the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  uniformly charge the surfaces of the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  to approximately −1100 V, for example. 
     The exposure units  5   k ,  5   y ,  5   m , and  5   c  irradiate the surfaces of the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  with the light based on the print data, and the potential of each of the irradiated areas is decayed to, for example, approximately 0 (zero) to −290 V, thereby forming the electrostatic latent images. When each of the electrostatic latent images reaches a position in contact with the development rollers  23   k ,  23   y ,  23   m , and  23   c  by the rotation of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c , the development rollers  23   k ,  23   y ,  23   m , and  23   c  applied with the bias voltage of, for example, approximately −800 V allow the toner to adhere to the electrostatic latent images, thereby forming the toner images. 
     Herein, the supply rollers  25   k ,  25   y ,  25   m , and  25   c  are rotated while frictionally contacting the respective development rollers  23   k ,  23   y ,  23   m , and  23   c  in the development device  2 , so that each surface of the development rollers  23   k ,  23   y ,  23   m , and  23   c  is supplied with a certain amount of the toner. The development blade  24   k ,  24   y ,  24   m , and  24   c  regulate the layer thickness of the toner frictionally charged and supplied to the surfaces of the development rollers  23   k ,  23   y ,  23   m , and  23   c.    
     The tone images formed by adhesion of the toner to the electrostatic latent images on the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  are transferred to the sheet P by the transfer unit  4  at a time at which the sheet P fed from the sheet feeding cassette  6  reaches the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c . The toner image transferred to the sheet P is fixed in the fixing unit by application of the heat and pressure. The sheet P is ejected outside the printer  1  after passing the fixing unit  7 . 
     The cleaning blades  26   k ,  26   y ,  26   m , and  26   c  scrapes the residual toner remained on the surfaces of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  without being transferred to the sheet P in the course of transferring the toner images by the transfer units  4   k ,  4   y ,  4   m , and  4   c  to the sheet P, and the toner adhered to the surfaces of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  by reversely transferring from the sheet P, or an adhesion substance such as sheet dust on the transfer belt  9 . Such toner scraped by the cleaning blades  26   k ,  26   y ,  26   m , and  26   c  is conveyed to and stored in the waste toner container  32  annexed to the toner cartridge  3   k  by first conveyance members  27   k ,  27   y ,  27   m , and  27   c , and the second conveyance member  28 . 
     A description is now given of arrangement of the waste toner storage space of the waste toner container  32  according to the first embodiment of the present invention. Herein, transfer efficiency of the toner image transferred to the sheet P can be determined as a ratio between an amount of the toner adhered by the development rollers  23   k ,  23   y ,  23   m , and  23   c  to the surfaces of the respective photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  and an amount of the toner remained on each of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  without being transferred to the sheet P. Such an amount of the toner remained on each of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  without being transferred to the sheet P is also referred to as a remaining toner amount. According to the first embodiment, however, the transfer efficiency of each of the development units  2   k ,  2   y ,  2   m , and  2   c  is experientially arranged to be 90 percent. Moreover, reverse transfer efficiency of the toner transferred from the sheet P to each of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  can be determined as a ratio between an amount of the toner transferred from each of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c  to the sheet P and an amount of the toner reversely transferred from the sheet P to each of the photosensitive drums  21   k ,  21   y ,  21   m , and  21   c . According to the first embodiment, however, the reverse transfer efficiency is arranged to sequentially decrease to 7 percent, 4 percent, and 1 percent, each time the sheet P passes the development units  2   k ,  2   y ,  2   m , and  2   c . For example, in a case where the toner transferred to the sheet P by the development unit of a first color is reversely transferred in a development unit of a second color, the reverse efficiency is 7 percent. The reverse efficiency of a second round in a development unit of a third color is 4 percent, and a third round in a development unit of a fourth color is 1 percent. 
     Based on the above arrangements, an amount of the waste toner (also referred to as a waste toner amount) with respect to each development unit is calculated. Since the development unit  2   k  is disposed on the most upstream side in the conveyance direction of the sheet P, the toner transferred to the sheet P is not reversely transferred. Therefore, the waste toner amount in the development unit  2   k  is substantially equal to the amount the toner remained on the photosensitive drum  21   k  without being transferred. Since 10 percent of a toner usage amount is not transferred to the sheet P and remained on the photosensitive drum  21   k , the remaining toner amount in the development unit  2   k , that is, the waste toner amount in the development unit  2   k , is expressed as 0.1 Xk (g), where the usage amount of the black toner is Xk (g). 
     The waste toner amount in the development unit  2   y  is substantially equal to a sum of the amount of the toner remained on the photosensitive drum  21   y  without being transferred to the sheet P and the amount of the black toner reversely transferred. Since 10 percent of the toner usage amount is not transferred to the sheet P and remained on the photosensitive drum  21   y , the remaining toner amount in the development unit  2   y  is expressed as 0.1 Xy (g), where the usage amount of the yellow toner is Xy (g). The amount of the black toner reversely transferred is expressed as follows:
 
“Black toner amount on the sheet  P ”×“reverse transfer efficiency”=0.9 Xk× 7%=0.063 Xk (g)
 
Therefore, the waste toner amount in the development unit  2   y  is expressed as (0.1 Xy+0.063 Xy) (g).
 
     The waste toner amount in the development unit  2   m  is substantially equal to a sum of the amount of the toner remained on the photosensitive drum  21   m  without being transferred to the sheet P, the amount of the black toner reversely transferred, and an amount of the yellow toner reversely transferred. Since 10 percent of the toner usage amount is not transferred to the sheet P and remained on the photosensitive drum  21   m , the remaining toner amount is expressed as 0.1 Xm (g), where the usage amount of the magenta toner is Xm (g). The amount of the black toner reversely transferred is expressed as follows:
 
“Black toner amount on the sheet  P ”×“reverse transfer efficiency”=(0.9−0.063) Xk× 4% =0.033 Xk  (g)
 
The amount of the yellow toner reversely transferred is expressed as follows:
 
“Yellow toner amount on the sheet  P ”×“reverse transfer efficiency”=0.9 Xy× 7%=0.063 Xy  (g)
 
Therefore, the waste toner amount in the development unit  2   m  is expressed as (0.1 Xm+0.033 Xk+0.063 Xy) (g).
 
     The waste toner amount in the development unit  2   c  is substantially equal to a sum of the amount of the toner remained on the photosensitive drum  21   c  without being transferred to the sheet P, the amount of the black toner reversely transferred, the amount of the yellow toner reversely transferred, and the amount the magenta toner reversely transferred. Since 10 percent of the toner usage amount is not transferred to the sheet P and remained on the photosensitive drum  21   c , the remaining toner amount is expressed as 0.1 Xc (g), where the usage amount of the cyan toner is Xc (g). The amount of the black toner reversely transferred is expressed as follows:
 
“Black toner amount on the sheet  P ”×“reverse transfer efficiency”=(0.9−0.063−033) Xk× 1%=0.008 Xk  (g)
 
     The amount of the yellow toner reversely transferred is expressed as follows:
 
“Yellow toner amount on the sheet  P ”×“reverse transfer efficiency”=(0.9−0.063) Xy× 4%=0.033 Xy  (g)
 
The amount of the magenta toner reversely transferred is expressed as follows:
 
“Magenta toner amount on the sheet  P ”×“reverse transfer efficiency”=0.9 Xm× 7%=0.063 Xm  (g)
 
Therefore, the waste toner amount in the development unit  2   c  is expressed as (0.1 Xc+0.008 Xk+0.0033Xy+0.063Xm) (g)
 
     Therefore, a total amount of the waste toner during a prescribed period is approximately calculated as follows:
 
Total waste toner amount=(0.204 Xk+ 0.196 Xy+ 0.163 Xm+ 0.1 Xc ) (g)
 
     In a normal usage situation, a usage rate of the black toner is generally higher than that of each of the yellow, magenta, and cyan toners, and the toner cartridge  3   k  is expected to be more frequently replaced compared to the toner cartridges  3   y ,  3   m , and  3   c . Herein, assuming that the usage amount of three toner colors of yellow, magenta, and cyan is Xy=Ym=Xc=aXk (a&lt;1) at a replacement cycle time at which the black toner cartridge  3   k  has consumed Xk (g). In such a situation, a total waste toner amount is approximately calculated as follows:
 
Waste toner amount expelled form the development unit 2 k =0.1 Xk (g)
 
Waste toner amount expelled form the development unit 2 y =(0.1 a+ 0.063) Xk  (g)
 
Waste toner amount expelled form the development unit 2 m =(0.163 a+ 0.033) Xk  (g)
 
Waste toner amount expelled form the development unit 2 c =(0.196 a+ 0.008) Xk  (g)
 
Therefore, the total waste toner amount is approximately calculated as (0.459a+0.204) Xk (g)
 
     According to the approximate calculation above, the waste toner storage space of the waste toner container  32  may be arranged based on anticipation of a toner storage amount of (0.459+0.204)=0.66-fold (i.e., zero point sixty-sixfold) at a maximum with respect to an initial loading amount of the black toner. Herein, in consideration of the small quantity of the adhesion substance from the transfer belt  9  to the surface of the photosensitive drum  21   k , the toner storage amount may be preferably arranged to be 0.7-fold (i.e., zero point sevenfold) with respect to the initial loading amount. Since an amount of the adhesion substance may vary depending on usage environment or condition, the toner storage amount may be arranged appropriately. 
     According to the first embodiment described above, for example, the toner cartridge  3   k  as the replaceable unit of the frequently used black toner is integrally disposed to the waste toner container  32 , so that the space between each of the development units is reduced. Moreover, a storage region for the supply toner can be adequately provided in limited space, and a size of the printer  1  as a whole can be reduced or the loading amount of the supply toner can be increased. According to the first embodiment, since the waste toner container  32  is disposed to only the toner cartridge  3   k  having a short replacement cycle, the printer  1  can be designed with reduction of a waste toner storage region to be provided as the waste toner container  32 . Moreover, the waste toner container  32  is not disposed to the less frequently used toner cartridges  3   y ,  3   m , or  3   c , thereby not only reducing an occurrence of replacing the less frequently used toner cartridge in a case where the unused toner of less frequently used color such yellow, magenta, or cyan is remained therein, but also enhancing usage efficiency of the toner. 
     According to the first embodiment, the waste toner container  32  is disposed to the toner cartridge  3   k  disposed in a position on the most upstream side in the conveyance direction of the sheet P, so that the space between each color of the development devices  2  and the space between each color of the photosensitive drums  21  is reduced. Consequently, the same advantage may be expected by, for example, disposition of the waste toner container  32  to the toner cartridge disposed on the most downstream side in the conveyance direction of the sheet P. However, since components of the fixing unit  7  are disposed adjacent to the most downstream side with respect to the conveyance direction of the sheet P, not only space for disposition of the waste toner container  32  is small on the most downstream side in the conveyance direction of the sheet P, but also the heat generated by the fixing unit  7  is likely to influence on the waste toner stored in the waste toner container  32  in the vicinity of the fixing unit  7 . Therefore, the waste toner container  32  is disposed to the toner cartridge  3   k  disposed in the position on the most upstream side in the conveyance direction of the sheet P according to the first embodiment. 
     According to the first embodiment, the waste toner container  32  is disposed to the toner cartridge  3   k  having the most frequently used toner of black. However, in a case where the usage of the black toner is significantly higher than that of the yellow, magenta, and cyan toner, or in a case where a collection destination of the waste toner needs to be divided, the collection destination may be divided into two, for example, a collection destination for the black toner and a collection destination for the three colors. Herein, a waste toner collection mechanism for the three colors may be independently provided from a waste toner collection mechanism for the black color. 
     According to the first embodiment of the present invention, the second conveyance member  28  is included in the development  2 . However, the present invention is not limited thereto. For example, the second conveyance member  28  may be included in a main body of the printer  1 , and each of the development units  2   k ,  2   y ,  2   m , and  2   c  may be disposed as an independent replaceable unit as illustrated in  FIG. 10 . 
     According to the first embodiment of the present invention, the first conveyance member  27  and the second conveyance member  28  respectively employ the coil spiral and the flat spiral as the conveyance member of the waste toner. The coil spiral may have a shape of round or square (i.e., horizon) in a cross section. According to the first embodiment, the spiral serving as the coil spiral has the round shape in the cross section. However, a spiral to be used may be varied depending on the waste toner amount or conveyance force. 
     Second Embodiment 
     A printer  100  and image forming operation according to a second embodiment are substantially similar to the printer  1  and image forming operation described above according to the first embodiment. Components and configurations of the printer  100  that differ from those of the above embodiment are described, and like components are given the same reference numerals as above and description thereof are omitted for the sake of simplicity. 
     Referring to  FIG. 11 , a vicinity of a waste toner outlet  285  in a second conveyance member  81  is illustrated in a partial schematic diagram. The second conveyance member  81  includes: a conveyance flat spiral  812  conveying a waste toner; and a drive transmission member  813  (including the drive transmission members  813   a ,  813   b ,  813   c ) transmitting driving force from a drive member (described later) to the conveyance flat spiral  812 . Herein, the conveyance flat spiral  812 , for example, represents a spiral formed by a wire rod having a flat surface. 
     In the second conveyance member  81  according to the second embodiment, the drive transmission member  813  is disposed in the vicinity of the waste toner outlet  285  in an end portion on a downstream side in a waste toner conveyance direction unlike the second conveyance member  28  according to the above first embodiment having the drive transmission member disposed in an end portion on an upstream side in the waste toner conveyance direction. 
     The drive transmission member  813   a  includes on a cylindrical surface thereof a spiral rib and a rotation rib each of which has a pitch substantially the same as that of the conveyance flat spiral  812 , and engages with the conveyance flat spiral  812 . A leading end of the conveyance flat spiral  812  does not necessarily have a hook-shaped engagement portion. A side portion of the drive transmission member  813   b  has a rotation transmission protrusion  813   d  engaging with a waste toner collection portion (described later) on the side near the toner cartridge by coupling connection, thereby transmitting the driving force with respect to the drive transmission member  813   a  through an engagement portion such as D-cutting. The drive transmission member  813   c  serving as a fall prevention member made of a PET film, for example, is disposed such that the drive transmission member  813   b  does not fall from the drive transmission member  813   a . One surface of the rotation transmission protrusion  813   d  is formed in a taper shape in such a manner as to rotate in a rotation direction while slidably contacting a rotation transmission protrusion  912   a  (described later) in a case where the rotation transmission protrusion  813   d  collides face to face with the rotation transmission protrusion  912   a  on the side near the toner cartridge in the course of attachment of the toner cartridge. 
     Referring to  FIG. 12 , the vicinity of the waste toner collection inlet  324  of a waste toner container  91  is illustrated in a partial schematic diagram. The waste toner container  91  includes a drive member  916  driving the conveyance flat spiral  812  by connecting with the second conveyance member  81  in the vicinity of the waste toner collection inlet  324 . 
     As illustrated in  FIG. 12 , the waste toner container  91  includes: a drive transmission idle gear  911  transmitting driving force from a driving source (not shown) to a drive transmission gear  912 ; the drive transmission gear  912  transmitting the driving force to the conveyance flat spiral  812  by engagement with the rotation transmission protrusion  813   d  of the second conveyance member  81 ; a slidable post  913  slidably disposed in a rotation axis direction of the drive transmission gear  912 ; an urging spring  914  urging the slidable post  913 ; and a waste toner collection inlet open-close shutter  915  controlling opening and closing of the waste toner collection inlet  324 . 
     The drive transmission idle gear  911  is rotatably driven by the drive member  916  disposed adjacent thereto, and transmits the driving force to the drive transmission gear  912 . The drive transmission idle gear  911  has a spur gear on a circumference surface thereof such that the drive transmission gear  912  is slidable with respect to the rotation axis direction thereof. The drive transmission gear  912  includes the rotation transmission protrusion  912   a  engaging with the rotation transmission protrusion  813   d  of the second conveyance member  81  on a side portion thereof. The drive transmission gear  912  is disposed in such a manner as to be rotatable about an axis of the slidable post  913  capable of sliding in the rotation axis direction by being urged by the urging spring  914 . The drive transmission gear  912  is slidable in a range of a gear teeth width of the spur gear formed in the circumference surface of the drive transmission idle gear  911  disposed adjacent thereto and engaged therewith. The waste toner collection inlet open-close shutter  915  is urged in an opening direction of the waste toner collection inlet  324  through the drive transmission gear  912 . 
     Referring to  FIG. 13 , the toner cartridge  3   k  is partially cut to illustrate a joint portion of the waste toner outlet  285  of the second conveyance member  81  and the waste toner collection inlet  324  of the toner cartridge  3   k  in an enlarged partial view. 
     As illustrated in  FIG. 13 , in a case where the toner cartridge  3   k  is attached, the drive transmission member  813  of the second conveyance member  81  contacts the waste toner collection inlet open-close shutter  915  and the drive transmission gear  912  of the waste toner container  91  and continues to push and move the waste toner collection inlet open-close shutter  915  and the drive transmission gear  912  until the waste toner collection inlet  324  is open. The waste toner outlet open-close shutter  286  moves in an opening direction of the waste toner outlet  285  with the movement of the waste toner collection inlet open-close shutter  915 . Consequently, both of the waste toner outlet  285  and the waste toner collection inlet  324  are open and placed one on another, so that the waste toner can be flown. 
     The conveyance flat spiral  812  included in the second conveyance member  81  is rotated at a certain circumferential speed in a prescribed rotation direction by the driving force transmitted through the drive transmission member  813 , so that waste toner is conveyed to the waste toner outlet  285 . Such waste toner is conveyed from the second conveyance member  81  to the waste toner container  91 . 
     A description is now given of a driving method of the conveyance flat spiral  812 . According to the second embodiment, the drive transmission member  813  transmitting the driving force to drive the conveyance flat spiral  812  is disposed in the vicinity of the waste toner outlet  285  in the end portion on the downstream side in the waste toner conveyance direction unlike the second conveyance member  28  according to the first embodiment having the drive transmission member disposed in the end portion on the upstream side in the waste toner conveyance direction. Herein, a difference between the driving method the conveyance flat spiral  282  according to the first embodiment and the driving method of the conveyance flat spiral  812  according to the second embodiment is described. 
     The driving method of the conveyance flat spiral  282  according to the first embodiment is illustrated in  FIG. 14A  while the driving method of the conveyance flat spiral  812  according to the second embodiment is illustrated in  FIG. 14B . 
     According to the driving method of the conveyance flat spiral  282  of the first embodiment as illustrated in  FIG. 14A , in case where the conveyance flat spiral  282  is rotatably driven in the end portion on the upstream side in the waste toner conveyance direction, the conveyance flat spiral  282  is applied with resistance of the toner or friction between the conveyance flat spiral  282  and a wall surface of the conveyance path  281  towards the upstream side in the waste toner conveyance direction. Herein, in a case where a clearance between an inner diameter of the conveyance path  281  and an outer diameter of the conveyance flat spiral  282  is large, deformation of the conveyance flat spiral  282  in a compression direction causes the conveyance flat spiral  282  continuing to be forcefully rotated to twist gradually, resulting in an increase of risk of damaging the conveyance flat spiral  282 . 
     Therefore, the spiral deformation prevention bar  284  needs to be disposed inside the conveyance flat spiral  282 . Moreover, the conveyance flat spiral  282  is compressively deformed, causing an increase in the possibility of generating a gap from the downstream side in the waste toner conveyance direction of the conveyance flat spiral  282  to the waste toner outlet  285 . 
     According to the driving method of the conveyance flat spiral  812  of the second embodiment as illustrated in  FIG. 14B , on the other hand, in a case where the conveyance flat spiral  812  is rotatably driven in the end portion on the downstream side in the waste toner conveyance direction, the conveyance flat spiral  812  is applied with the resistance of the toner or the friction between the conveyance flat spiral  812  and a wall surface of the conveyance path  811  towards the upstream side in the waste toner conveyance direction. Herein, in a case where a clearance between the inner diameter of the conveyance path  811  and the outer diameter of the conveyance flat spiral  812  is large, the conveyance flat spiral  811  is deformed in a tensile direction, so that the conveyance flat spiral  812  continuing to be forcefully rotated is not twisted. Therefore, the spiral deformation prevention bar  284  of the first embodiment does not need to be disposed inside the conveyance flat spiral  812  of the second embodiment. Moreover, the tensile deformation of the conveyance flat spiral  812  is unlikely to generate the gap from the downstream side in the waste toner conveyance direction of the conveyance spiral  812  to the waste toner outlet  285 . The conveyance flat spiral  812  according to the second embodiment can transmit the rotation in the waste toner direction without having a hook-shape portion at a leading end thereof. 
     That is, in a case where one end of the spiral is secured as considered to be a load applied in the course of conveying the waste toner while another end thereof is rotated, a spiral winding direction of the conveyance flat spiral  282  and the arrangement of the drive transmission member  813  of the conveyance flat spiral  282  are preferably determined in such a manner that an extension direction of the conveyance flat spiral  282  becomes the rotation direction thereof instead of rotating the conveyance flat spiral  282  in the compression direction. In other wards, in a case where the rotation direction of the drive transmission member  813  is secured in one direction, an arrangement of the spiral winding direction of the conveyance flat spiral  282  to be opposite to the spiral winding direction of the second embodiment allows the tensile deformation to be generated in a free end side although the drive transmission member  813  is disposed in the end portion on the upstream side in the waste toner conveyance direction, thereby providing substantially the same advantage as the second embodiment. According to the second embodiment, the drive transmission member  813  is disposed in the end portion on the downstream side in the waste toner conveyance direction, so that the waste toner is conveyed to the waste toner outlet  285  in a case where the amount of the waste toner in the conveyance path  281  is relatively small and the load is not generated in the rotation of the conveyance flat spiral  282 . From such a standpoint, the disposition of the drive transmission member  813  in the end portion on the downstream side in the waste toner conveyance direction has an advantage over that in the end portion on the upstream side in the waste toner conveyance direction. 
     According to the second embodiment described above, the conveyance flat spiral  812  is rotatably driven on the downstream side in the waste toner direction, thereby reducing the twist occurrence of the conveyance flat spiral  812  in operation or the damage and the like caused by the twist in addition to the advantage of the first embodiment. Moreover, since the spiral deformation prevention bar  284  does not need to be disposed, the number of components can be reduced or a shape of the conveyance flat spiral  812  can be simplified. 
     The present invention has been described above with regard to particular embodiments, but the present invention is not limited thereto. For example, according to the first and second embodiments of the present invention described above, the respective printers  1  and  100  are described as the image forming apparatus. However, the present invention is not limited to thereto. The present invention may be applied to, for example, a photocopier, a facsimile machine, a multi-functional peripheral in addition to the printer. As can be appreciated by those skilled in the art, numerous additional modifications and variation of the present invention are possible in light of the above-described teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.