Patent Publication Number: US-6704528-B1

Title: Image forming apparatus having detachable cleaning unit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus using an electrophotographic process such as a copying machine, a printer, a facsimile telegraph, etc. 
     2. Related Background Art 
     For example, the construction of an image forming apparatus using an intermediate transfer member is adopted in an image forming apparatus having a full color or multiplex image forming function in many cases. 
     In this image forming apparatus, component color toner images corresponding to plural color component images of a full color image or a multiplex image as an object are sequentially formed on a first image bearing member such as an electrophotographic photosensitive member, an electrostatic recording dielectric, etc. by suitable image forming process means. These component color toner images are sequentially superimposed and transferred to the intermediate transfer member as a second image bearing member being generally of a rotary belt type by a primary transfer portion. Thus, a full color image and a multiplex toner image corresponding to the full color image and the multiplex image as an object are synthesized and formed on the intermediate transfer member. The toner image synthesized and formed on this intermediate transfer member is transferred to a transfer material by a secondary transfer portion. This transfer material is guided to a fixing portion and the image is fixed so that a full color image forming object is obtained. 
     Here, the image forming apparatus adopting an intermediate transfer belt as the second image bearing member (intermediate transfer member) will be explained with reference to FIG.  11 . FIG. 11 shows the image forming apparatus with an intermediate transfer unit  120  and a cleaner unit  112  as centers, and shows only one of plural image forming portions. 
     Component color toner images corresponding to plural color component images formed on an image bearing member  101  are sequentially superimposed and transferred by a primary transfer portion T 1  nipped between the image bearing member  101  and a primary transfer opposite roller  102 . Thus, a full color image as an object is formed on an intermediate transfer belt  103 . This full color image on the intermediate transfer belt  103  is collectively transferred to a transfer material P by a secondary transfer portion T 2  formed by a secondary transfer roller  118  and a secondary transfer opposite roller  105 . The full color image is then fixed by an unillustrated fixing portion so that a full color forming object is obtained. 
     The intermediate transfer unit  120  is composed of the primary transfer opposite roller  102 , the intermediate transfer belt  103 , rollers of three shafts for supporting the intermediate transfer belt  103 , i.e., a drive roller  104 , the secondary transfer opposite roller  105 , and a tension roller  106  as a movable roller. The intermediate transfer unit  120  can be detachably attached to an apparatus main body. 
     Tensile force of the intermediate transfer belt  103  is constantly maintained by pressurizing a bearing  107  of the swingable tension roller  106  by a compressing spring  108 . 
     The cleaner unit  112  is arranged around the intermediate transfer belt  103  and cleans toner not transferred in the secondary transfer but left as the residual transfer remaining on the intermediate transfer belt  103 . The cleaner unit  112  has a cleaning blade  111  abutting on the intermediate transfer belt  103 , and a cleaner container  110  for containing the remaining toner removed by the cleaning blade  111 . The cleaning blade  111  is retained by the cleaner container  110 . A backup roller  109  is arranged in an opposite portion of the cleaning blade  111 . The cleaner unit  112  and the backup roller  109  are fixed to the apparatus main body or the intermediate transfer unit  120 . 
     Japanese Patent Application Laid-open No. 5-289426 discloses a cleaning blade arranged such that the cleaning blade is opposed to a tension roller for tensioning a photosensitive belt. A photosensitive member unit having first and second casing members is disclosed more particularly. A shaft of a drive roller for driving the photosensitive belt and a shaft of an exposure roller for supporting an exposure position of the photosensitive belt are assembled into the first casing member. A charger for charging the photosensitive belt and a cleaning blade for cleaning the photosensitive belt are assembled into the second casing member. 
     Further, it is also disclosed that a shaft of the tension roller is guided to an elongated hole formed in the first casing member and is also guided to an elongated hole formed in the second casing member. 
     However, the following problems exist in the above conventional example since the cleaner unit  112  of the intermediate transfer belt  103  is fixed to the main body or the intermediate transfer unit  120 . 
     (1) The tension roller  106  for maintaining the tensile force of the intermediate transfer belt  103  constant and a roller for controlling the deviation of the belt are movable to make an alignment adjustment. Therefore, the position of a surface of the intermediate transfer belt  103  is also changed in accordance with the positions of the movable rollers. In such a case, the cleaning blade  111  does not abut against the intermediate transfer belt  103  depending on the position of the surface of the intermediate transfer belt  103 , and hence the cleaning blade  111  does not fulfil its role as a cleaner. Further, the backup roller  109  is required in the opposite portion of the cleaning blade  111  so that the number of parts is increased and the construction becomes complicated. 
     (2) When the cleaner unit  112  is fixed to the intermediate transfer unit  120  and when one of the intermediate transfer belt  103  and the cleaner unit  112  is exchanged by life, etc., both the units must be simultaneously exchanged, which is not economical and efficient. 
     In the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 5-289426, the tension roller is displaced in two directions and these two directions are not perpendicular to each other at any time. Accordingly, when the tension roller is displaced, abutting positions of the tension roller and a tip of the cleaning blade abutting through the photosensitive belt are changed. Namely, an abutting angle of the cleaning blade on the photosensitive belt and an inroad amount of the cleaning blade tip are changed. Therefore, there is a fear of generation of a cleaning defect in which toner passes through the cleaning blade, etc. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image forming apparatus for preferably maintaining a contact state of a cleaning member and a belt member and able to prevent the generation of a cleaning defect even when a roller for supporting the belt member is moved. 
     The other objects of the present invention will become apparent by reading the following detailed explanation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a main sectional view schematically showing the entire construction of an image forming apparatus; 
     FIG. 2 is a perspective view showing the construction of a tension roller of the present invention; 
     FIG. 3 is a cross-sectional view showing the relation of an intermediate transfer unit and a cleaner unit in the present invention; 
     FIG. 4 is a perspective view showing the relation of the intermediate transfer unit and the cleaner unit in the present invention; 
     FIG. 5 is a side view showing a method for attaching and detaching the cleaner unit of the present invention; 
     FIG. 6 is a side view showing the method for attaching and detaching the cleaner unit of the present invention; 
     FIG. 7 is a side view showing the method for attaching and detaching the cleaner unit of the present invention; 
     FIG. 8 is a top view showing the cleaner unit of the present invention; 
     FIG. 9 is a main sectional view schematically showing the entire construction of an image forming apparatus using a photosensitive belt unit in a second embodiment of the present invention; 
     FIG. 10 is a main sectional view schematically showing the entire construction of an image forming apparatus using a transfer belt unit in a third embodiment of the present invention; and 
     FIG. 11 is a main sectional view showing a conventional example. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will next be described with reference to the drawings. 
     First Embodiment 
     [Description of Entire Image Forming Apparatus] 
     The entire construction of a color image forming apparatus will first be schematically explained with reference to FIG.  1 . FIG. 1 is a view for explaining the entire construction of a laser beam printer in one mode of the color image forming apparatus. 
     As shown in FIG. 1, the color laser beam printer is constructed by, an image forming portion having image bearing members  1  ( 1 Y,  1 M,  1 C,  1 K) and color developing devices, and an intermediate transfer member. The image bearing member  1  is rotated at a constant speed every each color of Y(yellow), M(magenta), C(cyan) and Bk(black). The intermediate transfer member retains a color image developed by the image forming portion and multiplexed and transferred, and further transfers the color image to a transfer material  2  as a recording material fed from a feeding portion. The transfer material  2  having the transferred color image is next conveyed to a fixing portion  38  and the color image is fixed to the transfer material  2 . Thus, the transfer material  2  is discharged to a discharge portion  44  on an upper face of the image forming apparatus by discharge rollers. The above color developing device of each of the four colors is individually detachably attached to a printer main body. 
     The construction of image forming means of the above image forming apparatus will next be explained sequentially in detail. 
     [Image Bearing Member] 
     An image bearing member (photosensitive drum)  1  is constructed integrally with a container  3  of a holder of the developing device. A developing unit  4  is detachably supported by the printer main body and can be easily exchanged in accordance with life of the image bearing member  1 . The image bearing member (photosensitive drum)  1  in this embodiment is coated with an organic photoconductive layer outside an aluminum cylinder, and is rotatably supported by the container  3  of the holder of the image bearing member  1 . Driving force of an unillustrated drive motor is transmitted to one rear end of the image bearing member in FIG. 1 so that the image bearing member  1  is rotated in the counterclockwise direction in FIG. 1 in accordance with an image forming operation. 
     [Charging Means] 
     Charging means  5  uses an injection charging method in which a surface of the image bearing member  1  is uniformly charged by an applied voltage of a charging sleeve through a charging agent. 
     [Exposure Means] 
     The above image bearing member  1  is exposed from a scanner portion  6 . Namely, when an image signal is given to a laser diode, this laser diode irradiates image light corresponding to the image signal to a polygon mirror  6   a . This polygon mirror  6   a  is rotated at a high speed by a scanner motor. The image light reflected on the polygon mirror  6   a  selectively exposes the surface of the image bearing member  1  rotating at a constant speed through an imaging lens  6   b  so that an electrostatic latent image is formed on the image bearing member. 
     [Developing Means] 
     Developing means is constructed by four developing devices  4 Y,  4 M,  4 C,  4 K able to develop the respective colors of yellow, magenta, cyan and black to visualize the above electrostatic latent image. In the respective developing devices  4 Y,  4 M,  4 C,  4 K of the four colors, sleeves  3 YS,  3 MS,  3 CS,  3 KS are arranged in positions each opposed to the image bearing member  1  at small intervals with respect to the image bearing member  1 , and a visual image is formed by the toner of each color on the image bearing member  1 . 
     The developer  4  of each color feeds the toner within the container by a feeding mechanism, and coats an outer circumference of the sleeve  3 S rotating in the clockwise direction in FIG. 1 with mixing powder of the (nonmagnetic) toner and a (magnetic) developer. Thereafter, the toner within the powder is developed in accordance with the electrostatic latent image of the image bearing member  1 . 
     [Intermediate Transfer Member Unit] 
     An intermediate transfer unit  13  has an intermediate transfer member  18  as a belt member, a drive roller  14  for tensioning the intermediate transfer member  18 , a secondary transfer opposite roller  15  and a tension roller  16 . The intermediate transfer member  18  is rotated in the clockwise direction in FIG. 1 in synchronizm with a peripheral speed of the image bearing member  1  to multiplex and transfer the toner image on the image bearing member  1  visualized by each developing device at the time of a color image forming operation. The transfer member  2  is nipped and conveyed by the multiplexed and transferred intermediate transfer member  18  and a secondary transfer roller  22  to which a voltage is applied. Thus, the color toner images on the intermediate transfer member are simultaneously multiplexed and transferred to the transfer member  2 . 
     The intermediate transfer member  18  in this embodiment is formed by a resin belt having about 1000 mm in circumferential length, and is tensioned by three shafts of the drive roller  14 , the secondary transfer opposite roller  15  and the tension roller  16 . The intermediate transfer member  18  is loaded by a spring  19  at each of both ends of the tension roller  16  so that a changing amount of the circumferential length of the intermediate transfer member  18  can be absorbed even when the circumferential length of the intermediate transfer member  18  is changed by temperature and humidity within the main body or by variation per hour. This intermediate transfer member  18  is supported by the main body with the drive roller as a fulcrum, and the driving force of an unillustrated drive motor is transmitted to one rear end of the drive roller in FIG.  1 . Thus, the intermediate transfer member  18  is rotated in the clockwise direction in FIG. 1 in accordance with the image forming operation. Further, this intermediate transfer member  18  can be attached to be easily detached in a rightward direction in FIG.  1 . 
     [Feeding Portion] 
     A feeding portion feeds the transfer material  2  to the image forming portion. The feeding portion is mainly constructed by a cassette  7  for containing plural sheets of transfer material  2 , a pickup roller  8 , a feeding roller  9 , a retard roller  10  for double feed prevention, a feeding guide  11  and a registration roller  12 . When an image is formed, the pickup roller  8  is rotated in accordance with the image forming operation, and separates and feeds the transfer materials  2  within the cassette  7  one by one. The transfer material  2  is guided by a guide plate  11  and reaches the registration roller  12  via a conveying roller. While the image forming operation is performed, the registration roller  12  performs a non-rotating operation and a rotating operation in a predetermined sequence. In the non-rotating operation, the transfer material  2  is at rest and is on standby. In the rotating operation, the transfer material  2  is conveyed toward the intermediate transfer member. Positions of the image and the transfer material  2  are aligned with each other by the registration roller  12  at the time of a transfer process as the next process. 
     [Transfer Portion] 
     A transfer portion is constructed by a swingable transfer roller  22 . The transfer roller  22  is constructed by winding a metallic shaft by a medium-resistance foam elastic material, and can be moved upward and downward in FIG.  1  and is operated. While toner images of the four colors are formed on the above intermediate transfer member  18 , i.e., until the toner images on the intermediate transfer member  18  reach the secondary transfer portion, the transfer roller  22  is located downward and is separated from the intermediate transfer member  18  as shown by a dotted line in FIG. 1 so as not to disturb these images. Thereafter, the transfer roller  22  is located by an unillustrated cam member in an upward position shown by a solid line in FIG. 1, i.e., is pressed against the intermediate transfer member  9  through the transfer member  2  by a predetermined pressure in synchronizm with transfer timing of a color image onto the transfer material  2 . At this time, a bias voltage is simultaneously applied to the transfer roller  22 , and the toner images on the intermediate transfer member  18  are transferred to the transfer material  2 . Here, since the intermediate transfer member  18  and the transfer roller  22  are respectively operated, the transfer process is performed in the transfer material  2  nipped by both the intermediate transfer member  18  and the transfer roller  22 . Simultaneously, the transfer material  2  is conveyed at a predetermined speed in a leftward direction in FIG.  1  and is sent to the fixing device in the next process. 
     [Intermediate Transfer Member Cleaning Unit] 
     An intermediate transfer member cleaning unit  23  is constructed by a cleaning blade  24 , a pressurizing spring  29  for pressing the cleaning blade  24  against the intermediate transfer member  18 , and a cleaner container  27  for retaining these members. 
     A material of the cleaning blade  24  is urethane rubber and is formed on a metallic plate  26 . A shaft  25  retained by the cleaner container  27  is set to a center of rotation, and the cleaning blade  24  is pressed against the intermediate transfer member  18  by the pressurizing spring  29  at a predetermined angle (counter abutting). Therefore, the cleaning blade  24  can uniformly abut against the intermediate transfer member  18 . The tension roller  16  as a backup roller is arranged in an opposite portion of the cleaning blade  24  so that the cleaning blade  24  can abut against the intermediate transfer member  18  by a predetermined abutting pressure. At a portion in which this cleaning blade  24  abuts against the intermediate transfer member  18 , the toner is scraped off from the intermediate transfer member  18  and the intermediate transfer member  18  is cleaned. 
     As will be described later, the tension roller can be moved in only one direction to increase or decrease tension of the belt. 
     The waste toner scraped off by the cleaning blade  24  is collected in the cleaner container  27  and is then sent and collected in a waste toner box  37  separately arranged within the main body by a screw  28  arranged in a lowermost portion of the cleaner container  27 . This screw  28  is rotated in its conveying direction by the driving force of an unillustrated drive motor transmitted to one rear end of the screw  28  in FIG.  1 . 
     [Fixing Portion] 
     The toner image formed by the above developing means is transferred onto the transfer material  2  through the intermediate transfer member  18 . The fixing portion  38  fixes the transferred toner image to the transfer material  2 . As shown in FIG. 1, the fixing portion  38  is constructed by a fixing roller  39  for heating the transfer material  2 , and a pressure roller  40  for making the transfer member  2  come in press contact with the fixing roller  39 . Each of these rollers is a hollow roller and an unillustrated heater is arranged within each of these rollers. Each of these rollers is rotated and simultaneously conveys the transfer material  2 . Namely, the transfer material  2  retaining the toner image is conveyed by the fixing roller  39  and the pressure roller  40 , and is heated and pressurized so that the toner is fixed to the transfer material  2 . 
     [Image Forming Operation] 
     The image forming operation of the image forming apparatus having the above construction will next be explained. 
     First, the pickup roller  8  shown in FIG. 1 is rotated and one transfer material  2  within the sheet feed cassette  7  is separated and conveyed to the registration roller  12 . 
     Each of the image bearing member  1  and the intermediate transfer member  18  is rotated at a peripheral speed V (hereinafter referred to as a process speed) in the direction of an arrow shown in FIG.  1 . 
     When a peripheral arbitrary point of the intermediate transfer member in FIG. 1 reaches an S-position in FIG. 1, the image bearing member  1  having a surface uniformly charged by the charging means is exposed by a laser beam in an E-position in FIG. 1 so that an image is formed. A distance from the exposure position E of the image bearing member  1  to a contact portion T 1  with the intermediate transfer member  18  in the counterclockwise direction is equal to a distance from the S-point of the intermediate transfer member  18  in FIG. 1 to the contact portion T 1 . Accordingly, after a period of time has elapsed, a write starting point E of the image and the point S on the intermediate transfer member  18  are in conformity with each other in a position of the contact portion T 1 . Namely, the image is formed in the counterclockwise direction on the intermediate transfer member  18  with the S-point as an image tip. 
     1: Formation of a Yellow Image 
     A laser beam of a yellow image is irradiated by a scanner portion  6 Y so that a yellow latent image is formed on an image bearing member  1 Y. Simultaneously, a yellow developing device  4 Y is operated and a voltage having the same polarity as a charging polarity of the image bearing member  1 Y and approximately having the same electric potential as the image bearing member  1 Y is applied to the yellow developing device  4 Y such that a yellow toner is attached to the latent image on the image bearing member  1 Y. Thus, the yellow toner is developed. Simultaneously, the yellow toner image on the image bearing member  1 Y is primarily transferred to an outer circumference of the intermediate transfer member  18  in a primary transfer position T 1 Y in the downstream of a developing portion. At this point, the intermediate transfer member  18  performs a primary transfer operation by applying a voltage having characteristics reverse to those of the above yellow toner to a primary transfer roller arranged on a back surface of the intermediate transfer member  18 . 
     When the formed image has a size of A 3  having 420 mm in length, the image is formed from a peripheral S-point of the intermediate transfer member  18  to a point L 1 . 
     2: Formation of a Magenta Image 
     When one peripheral point S (a tip of the yellow image) of the intermediate transfer member  18  next reaches the position of an S′-point in FIG. 1, the irradiation of a laser beam of a magenta image is similarly started by a scanner portion  6 M. Thus, similar to the yellow image, a magenta toner image is developed in a latent image on an image bearing member  1 M. The magenta toner image on the image bearing member  1 M is transferred onto the intermediate transfer member  18  in a primary transfer position T 1 M. 
     3: Formation of a Cyan Image 
     When one peripheral point S (tips of the yellow and magenta images) of the intermediate transfer member  18  next reaches the position of a point S″ in FIG. 1, the irradiation of a laser beam of a cyan image is similarly started by a scanner portion  6 C. Thus, similar to the magenta image, a cyan toner image is developed in a latent image on an image bearing member  1 C. The cyan toner image on the image bearing member  1 C is superimposed and transferred onto the yellow and magenta toner images on the intermediate transfer member  18  in a primary transfer position TiC. 
     4: Formation of a Black Image 
     When one peripheral point S (tips of the yellow, magenta and cyan images) of the intermediate transfer member  18  next reaches the position of a point S′″ in FIG. 1, the irradiation of a laser beam of a black image is similarly started by a scanner portion  6 K. Similar to the cyan image, a black toner image is developed in a latent image on an image bearing member  1 K. The black toner image on the image bearing member  1 K is further superimposed and transferred onto the intermediate transfer member  18  in a primary transfer position T 1 K. 
     As mentioned above, the latent image formation and the development are performed in the order of yellow, magenta, cyan and black, and the toner is transferred to the intermediate transfer member  18  in each of the primary transfer positions T 1 Y, T 1 M, T 1 C and T 1 K. Thus, a full color image constructed by the toners of four kinds of yellow, magenta, cyan and black is formed on a surface of the intermediate transfer member  18 . 
     The transfer material  2  on standby in the above registration roller begins to be synchronously conveyed before the black toner is completely transferred to the intermediate transfer member  18 , i.e., before the primary transfer of the black toner of the fourth color is completed and before an image tip S of the intermediate transfer member  18  forming the full color image thereon reaches a secondary transfer portion T 2 . When the image of each of the above four colors is formed on the intermediate transfer member  18 , the transfer roller  22  is on standby downward and does not come in contact with the intermediate transfer member  18 . This transfer roller  22  is simultaneously moved upward by an unillustrated cam, and the transfer material  2  comes in press contact with the secondary transfer portion T 2  of the intermediate transfer member  18 . Simultaneously, a bias voltage having characteristics reverse to those of the toner is applied to the transfer roller  22 . Thus, the four colors of the full color image on the intermediate transfer member  18  are simultaneously transferred to the transfer material  2 . The transfer material  2  passing through the secondary transfer portion T 2  is separated from the intermediate transfer member  18  and is conveyed to the fixing portion  38  and the toner is fixed. Thereafter, the transfer material  2  is discharged onto a discharge tray  44  in an upper portion of the main body through discharge roller pairs  41 ,  42 ,  43  such that an image face of the transfer material  2  is directed downward. Thus, the image forming operation is terminated. 
     FIG. 2 is a perspective view of a tension giving mechanism portion of the intermediate transfer belt unit  13  in an embodiment of the present invention. Reference numeral  50  designates a tension bearing rotatably fitted onto a shaft  16   a  of the tension roller  16 . Similar to the conventional example, a compressing spring  19  is attached by a predetermined pressure between an end face  50   b  of the tension bearing  50  and a wall face  51   b  of a frame  51 . A material of the tension bearing  50  is formed by using a conductive polyacetal resin as in the conventional example so that the tension roller is electrically connected to the ground. Similar to the conventional example, a tensioner  17  and the shaft  16   a  of the tension roller  16  are slidably rotated, but a load applied to an inner wall of a bearing portion of the tensioner  17  is reduced and there is almost no wearing on an inner wall face. In contrast to this, the inner wall  50   a  of the tension bearing  50  and the tension roller shaft  16   a  are worn as in the conventional example, but there is no change in the position relation of the tensioner  17  and the tension roller  16 , and there is also no change in the relative position relation of the tension roller  16  and the blade  24 . An attachment size of the compressing spring  19  is slightly changed by this wearing, but no belt is slipped by a reduction in pressure due to a changing amount of this attachment size. 
     The conductive polyacetal resin is used in the material of the tension bearing. However, for example, similar effects can also be obtained even when an oil-impregnating sintering material of iron and copper groups is used. 
     Further, the intermediate transfer unit  13  has both side plates arranged on both end sides of the intermediate transfer member  18  in a thrust direction and respectively securely supporting both end portions of rotating shafts of the drive roller  14  and the secondary transfer opposite roller  15 . After the intermediate transfer unit is moved downward in FIG.  1  and after the intermediate transfer belt is separated from each photosensitive drum, the intermediate transfer unit can be detachably attached to the apparatus main body from an X-direction in FIG.  1 . The tensioners  17 ,  17 ′ are supported by elongated holes formed in the above both side plates through the rotating shaft  16   a  of the tension roller  16 . A longitudinal direction of each of the elongated holes formed in the both side plates is approximately equal to a direction in which the intermediate transfer belt is tensioned by the tension roller  16  (compression spring  19 ). 
     A central construction of the present invention will next be described in detail by using FIGS. 3 to  8 . 
     As shown in FIG. 3, the intermediate transfer belt  18  is tensioned by three shafts of the drive roller  14 , the secondary transfer opposite roller  15  and the tension roller  16 . The tension roller  16  is pressurized by a spring pressure of the compression spring  19  so that a change in circumferential length of the intermediate transfer belt  18  due to change in temperature and humidity within the main body or variation per hour is absorbed. Further, the driving force of an unillustrated drive motor is transmitted to one rear end of the drive roller  14  in FIG. 3 so that the intermediate transfer belt  18  is rotated at a predetermined peripheral speed in the clockwise direction in FIG. 3 in accordance with an image forming operation. 
     The cleaning blade  24  for cleaning the intermediate transfer belt  18  is arranged in an opposite portion of the above tension roller  16  in the above cleaner container  27 . The cleaning blade  24  is retained such that the cleaning blade  24  abuts against the intermediate transfer belt  18  by a predetermined angle with a swinging shaft  25  as a center of rotation (counter abutting). The above cleaning blade  24  abuts against the intermediate transfer belt  18  by a predetermined abutting pressure by the compression spring  29 . The above cleaning blade  24  is also fixed to a blade retaining plate  26 . 
     As shown by the perspective view of FIG. 4, bosses  20 ,  20 ′ for positioning a cleaner unit  23  are arranged in two places of the intermediate transfer member unit  13 . The above bosses  20 ,  20 ′ are formed integrally with bearing members  17 ,  17 ′ in both end portions of the above tension roller  16 . An axial line  0  of the tension roller shaft  16   a  and a line  0 ′ connecting axial lines of the above both bosses  20 ,  20 ′ are maintained in parallel at any time even when the above tension roller  16  is moved. A round elongated hole  21  is formed in one portion of the rear tensioner  17 ′ in FIG. 4, and a screw drive input portion  34  of the above cleaner unit  23  is fitted into this round elongated hole  21 . When the above cleaner unit  23  is set, the round elongated hole  21  functions as a detent. A front detent member  30  in FIG. 4 is arranged in the above cleaner unit  23 . This detent member  30  is positioned in one portion of the above front tensioner  17  in FIG.  4 . Further, the above bosses  20 ,  20 ′ are respectively fitted into positioning grooves  31 ,  31 ′ formed in the above cleaner unit  23 , and the above cleaner unit  23  can be positioned in the above intermediate transfer member unit  13  by latches  32 ,  32 ′. 
     In a method for setting the above cleaner unit  23 , as shown in FIGS. 5 to  7  (front views) and FIG. 8 (top view), the cleaner unit  23  is inserted into the main body from the front in a separating state in a direction perpendicular to a paper conveying direction. The cleaner unit  23  is inserted until the cleaner unit  23  comes in contact with an unillustrated hitting portion in a rear portion of the above intermediate transfer member unit  13 . In an inserted state, a lever  36  arranged in the above cleaner unit  23  is gripped and rotated about a waste toner conveying screw shaft and is pushed upward until the above latches  32 ,  32 ′ are respectively engaged with the above bosses  20 ,  20 ′. When the cleaner unit  23  is conversely taken out, the above latches  32 ,  32 ′ are released by the lever  36  also serving as a latch release lever so that the above cleaner unit  23  is set to the separating state and is pulled out forward. 
     The waste toner collected by the above cleaning blade  24  is conveyed forward by a waste toner conveying screw  28  arranged in a lowermost portion of the cleaner container  27 . The waste toner then drops and is collected from a connecting portion of the above cleaner container  27  and a waste toner bottle  37  into this waste toner bottle  37 . The above waste toner conveying screw  28  is rotated by the driving force of an unillustrated drive motor transmitted to a drive input portion  34  at one rear end of the conveying screw  28 . 
     A drive source of the above waste toner conveying screw  28  is set to a fixing drive source, and thus the number of motors can be reduced so that the structure is simplified. 
     The cleaner unit  23  is separated from the intermediate transfer unit by the above lever  36 , and is guided by a rail member arranged on a side of the main body of the apparatus, and can be detachably attached to the apparatus main body in a Y-direction in FIG.  4 . 
     When lives of the intermediate transfer belt  18  and the cleaner unit  23  are not in conformity with each other, it is inefficient to simultaneously exchange both the units. Accordingly, both units are detachably constructed. 
     Second Embodiment 
     The above construction is not limited to the intermediate transfer belt, but is also effective with respect to a photosensitive belt and a transfer belt. 
     FIG. 9 is a view of a full color image forming apparatus using a photosensitive belt in a second embodiment of the present invention. Image formation of this image forming apparatus will next be explained. As shown in FIG. 9, a cassette  7  for stacking and containing plural sheets of transfer material  2  is detachably mounted to the image forming apparatus and the transfer materials  2  are fed by a pickup roller  8 . The fed transfer materials  2  are separated from each other one by one by a retard roller pair  9 ,  10  and are conveyed to a registration roller pair  12  by a conveying roller  45 . When the transfer material  2  is conveyed, the rotation of the registration roller is stopped and skew feed of the transfer material  2  is corrected by making the transfer material  2  hit against a nip portion of the registration roller. As shown in FIG. 9, developing cartridges  59 Y,  59 M,  59 C,  59 K of four colors of cyan, magenta, yellow and black are arranged in parallel with each other. Optical scanning systems  6 Y,  6 M,  6 C,  6 K corresponding to the respective developing cartridges are arranged. A latent image is formed on a photosensitive belt  61  by an image signal every color, and a toner image formed by each developing cartridge is laminated so that a full color toner image is formed. Here, in the construction of a photosensitive belt unit  63 , the photosensitive belt  61  is tensioned by three shafts of a drive roller  14 , a transfer opposite roller  64  and a tension roller  16 , and tensile force is given to the photosensitive belt  61  by pressurizing the tension roller  16  by a compression spring  19 . Thereafter, the transfer material  2  is sent out to a transfer roller  22  at a predetermined timing and the toner image on the photosensitive belt  61  is transferred onto the transfer material  2  and is fixed by a fixing device  38 . Thereafter, the transfer material  2  is discharged and stacked onto a discharge tray  44  by discharge roller pairs  41 ,  42 ,  43 . 
     In this embodiment, similar to the first embodiment, a cleaner unit  23  is fixedly positioned in a tensioner  17 . Thus, an abutting angle of a cleaning blade on the belt, an inroad amount of a cleaning blade tip with respect to the belt, etc. can be maintained. Accordingly, preferable cleaning performance can be maintained and an output image of high quality can be obtained. 
     Third Embodiment 
     The cleaning performance can also be maintained by a similar construction in a full color image forming apparatus using a transfer belt in a third embodiment. FIG. 10 is a view of such a full color image forming apparatus using the transfer belt in the third embodiment of the present invention. Image formation of this image forming apparatus will be explained. 
     First, as shown in FIG. 10, a cassette  7  for stacking and containing plural sheets of transfer material  2  is detachably mounted to the image forming apparatus. The transfer materials  2  are fed by a pickup roller  8  and are separated from each other one by one by a retard roller pair  9 ,  10  and are conveyed to a registration roller pair  12 . When the transfer material  2  is conveyed, the rotation of the registration roller is stopped and skew feed of the transfer material  2  is corrected by making the transfer material  2  hit against a nip portion of the registration roller. In the case of a four-drum full color system, process cartridges  4 Y,  4 M,  4 C,  4 K of four colors of cyan, magenta, yellow and black including image bearing members are arranged in parallel with each other as shown in FIG.  10 . Optical scanning systems  6 Y,  6 M,  6 C,  6 K are respectively arranged with respect to the process cartridges. A toner image is formed on the image bearing member by an image signal every color. Thereafter, each toner image is sequentially transferred onto the transfer material  2  conveyed on a transfer belt  70 . At this point, a primary transfer opposite roller  64  is arranged in every color. The transfer material  2  is sent out onto the transfer belt  70  at a predetermined timing. The toner image on each image bearing member is sequentially superimposed and transferred onto the transfer material  2  and is fixed by a fixing device  38 . Thereafter, the transfer material  2  is discharged and stacked onto a discharge tray  44  by discharge roller pairs  41 ,  42 ,  43 . 
     Here, in a transfer belt unit  71 , the transfer belt  70  is tensioned by three shafts of a drive roller  14 , a roller  72  and a tension roller  16 . Tensile force is given to the transfer belt  61  by pressurizing the tension roller  16  by a compressing spring  19 . 
     In this embodiment, similar to the first and second embodiments, preferable cleaning performance can be maintained and an output image of high quality can be obtained by fixedly positioning the cleaner unit  23  in the tensioner  17 . 
     In the above embodiments, description was made of a belt member surface cleaned by the cleaning blade. However, the present invention is not limited to this case, but can also be applied when a cleaning brush is used. Further, the tension roller is used as an opposite roller of the cleaning blade. However, the present invention is not limited to this case, but can also be applied when an alignment roller for adjusting deviation of the belt member in a direction perpendicular to a moving direction by moving one end side of a rotating shaft of the roller is used as the opposite roller. 
     As explained above, in accordance with the present invention, the cleaning unit is positioned in a retaining member for retaining a roller. Accordingly, an abutting condition (abutting angle, etc.) of the cleaning member on the belt member is maintained even when the roller retained by the retaining member is moved. Therefore, a cleaning defect can be prevented. 
     Further, it is not necessary to separately arrange an opposite member of the cleaning member so that the image forming apparatus can be made compact and can be simplified and reduced in cost.