Patent Publication Number: US-8989619-B2

Title: Image forming apparatus having transfer belt contact and separating mechanism interfering with removable unit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2012-061300, filed on Mar. 17, 2012, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine combining several of the functions of these apparatuses, particularly to an image forming apparatus including an image carrier removably installed therein. 
     2. Description of the Related Art 
     In an image forming apparatus such as a copier or a printer, in some cases an image carrier such as a photoconductor drum is removably (i.e., replaceably) installed in the body of the image forming apparatus. The image carrier such as a photoconductor drum may be a component of a process cartridge such that, when the process cartridge in the body of the image forming apparatus is replaced with a new process cartridge, the image carrier is also replaced with a new image carrier. 
     Further, the image forming apparatus may be configured such that a transfer member of a transfer device is contactable with and separable from the image carrier, and that the transfer member is brought into contact with the image carrier in a normal image forming operation and is separated from the image carrier in, for example, replacement of the image carrier. In this type of image forming apparatus, the image carrier is replaced when the transfer member is separated therefrom. This configuration therefore reduces the possibility of the image carrier and the transfer member interfering with each other and damaging respective surfaces thereof in replacement work. 
     According to this configuration, however, an operator may mistakenly operate the image forming apparatus with the transfer member separated from the image carrier after the completion of the replacement work of the image carrier. In such a case, the image forming apparatus may fail to form a normal image, or may fail to normally feed a recording medium. 
     SUMMARY OF THE INVENTION 
     The present invention describes a novel image forming apparatus that, in one example, includes an image carrier, a transfer member, a contact and separation mechanism, and a removable unit. The image carrier is configured to be removably installed in the image forming apparatus to carry a toner image. The transfer member is configured to come into contact with the image carrier to transfer the toner image from the image carrier onto a surface of one of the transfer member and a recording medium fed to a position between the transfer member and the image carrier. The contact and separation mechanism is configured to move the transfer member relative to the image carrier to bring the transfer member into contact with the image carrier, and is configured to move the transfer member relative to the image carrier to separate the transfer member from the image carrier. The removable unit is configured to be removably installed in the image forming apparatus from the same direction as an installation direction of the image carrier to be disposed proximal of the image carrier and the transfer member in the installation direction, and is configured to at least partially overlap the image carrier and the transfer member as viewed in the installation direction. The removable unit interferes with the contact and separation mechanism and is prevented from being installed in the image forming apparatus in a state in which the transfer member is separated from the image carrier by the contact and separation mechanism. 
     The contact and separation mechanism may include a lever configured to be rotated to bring the transfer member into contact with the image carrier, and configured to be rotated to separate the transfer member from the image carrier. When the transfer member is separated from the image carrier, the lever may be rotated to a position at which the lever interferes with the removable unit. When the transfer member is in contact with the image carrier, the lever may be rotated to a position at which the lever does not interfere with the removable unit. 
     The image forming apparatus may further include a detector configured to detect a state in which the removable unit is installed in the image forming apparatus. The image forming apparatus may be prevented from operating when the detector detects that removable unit is not installed in the image forming apparatus. 
     The image forming apparatus may further include a cleaning device configured to remove untransferred toner remaining on the image carrier as waste toner and a transport tube configured to transport the waste toner discharged by the cleaning device. The removable unit may include a waste toner collecting container configured to store the waste toner. The waste toner collecting container may be brought into contact with the transport tube when installed in the image forming apparatus, and may be separated from the transport tube when removed from the image forming apparatus. 
     The image forming apparatus may further include a drive gear configured to transmit drive force. The transport tube may include an outlet configured to discharge the waste toner and a shutter member configured to open and close the outlet. The waste toner collecting container may include a pressing member configured to press the shutter member of the transport tube and open the outlet in accordance with the installation of the waste toner collecting container into the image forming apparatus, a transport member configured to transport the waste toner stored in the waste toner collecting container, and a gear configured to mesh with the drive gear in accordance with the installation of the waste toner collecting container into the image forming apparatus to transmit the drive force to the transport member. 
     The present invention further describes another novel image forming apparatus that, in one example, includes an image carrier, a transfer member, a contact and separation mechanism, and a removable unit. The image carrier is configured to be removably installed in the image forming apparatus to carry a toner image. The transfer member is configured to come into contact with the image carrier to transfer the toner image from the image carrier onto a surface of one of the transfer member and a recording medium fed to a position between the transfer member and the image carrier. The contact and separation mechanism is configured to move the transfer member relative to the image carrier to bring the transfer member into contact with the image carrier, and is configured to move the transfer member relative to the image carrier to separate the transfer member from the image carrier. The removable unit is configured to be removably installed in the image forming apparatus from the same direction as an installation direction of the image carrier to be disposed proximal of the image carrier and the transfer member in the installation direction, and is configured to at least partially overlap the image carrier and the transfer member as viewed in the installation direction. The contact and separation mechanism brings the transfer member into contact with the image carrier in accordance with installation of the removable unit into the image forming apparatus, and separates the transfer member from the image carrier in accordance with removal of the removable unit from the image forming apparatus. 
     The image forming apparatus may further include a detector configured to detect a state in which the removable unit is installed in the image forming apparatus. The image forming apparatus may be prevented from operating when the detector detects that the removable unit is not installed in the image forming apparatus. 
     The image forming apparatus may further include a cleaning device configured to remove untransferred toner remaining on the image carrier as waste toner and a transport tube configured to transport the waste toner discharged by the cleaning device. The removable unit may include a waste toner collecting container configured to store the waste toner. The waste toner collecting container may be brought into contact with the transport tube when installed in the image forming apparatus, and may be separated from the transport tube when removed from the image forming apparatus. 
     The image forming apparatus may further include a drive gear configured to transmit drive force. The transport tube may include an outlet configured to discharge the waste toner and a shutter member configured to open and close the outlet. The waste toner collecting container may include a pressing member configured to press the shutter member of the transport tube and open the outlet in accordance with the installation of the waste toner collecting container into the image forming apparatus, a transport member configured to transport the waste toner stored in the waste toner collecting container, and a gear configured to mesh with the drive gear in accordance with the installation of the waste toner collecting container into the image forming apparatus to transmit the drive force to the transport member. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the advantages thereof are 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 diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  is a diagram illustrating an image forming unit included in the image forming apparatus; 
         FIG. 3  is a schematic perspective view illustrating a process cartridge included in the image forming unit; 
         FIG. 4  is a schematic diagram illustrating a state in which an intermediate transfer belt is separated from photoconductor drums in the image forming units; 
         FIG. 5  is a schematic diagram illustrating a state in which a waste toner collecting container interferes with an intermediate transfer belt contact and separation mechanism; 
         FIG. 6  is a schematic diagram illustrating a state in which the intermediate transfer belt is in contact with a photoconductor drum; 
         FIG. 7  is a schematic diagram illustrating a state in which the waste toner collecting container is installed in the body of the image forming apparatus; 
         FIG. 8  is a schematic diagram illustrating a state in which the intermediate transfer belt is in contact with four photoconductor drums; and 
         FIGS. 9A and 9B  are schematic diagrams of a second embodiment of the present invention, illustrating a process of installing the waste toner collecting container in the image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In describing the embodiments illustrated in the drawings, specific terminology is adopted for the purpose of clarity. However, the disclosure of the present invention is not intended to be limited to the specific terminology so used, and it is to be understood that substitutions for each specific element can include any technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of the present invention will be described in detail. In the following, redundant description of parts once described will be simplified or omitted. 
     With reference to  FIG. 1 , description will first be given of the overall configuration and operation of an image forming apparatus according to an embodiment of the present invention. An image forming apparatus illustrated in  FIG. 1  is a tandem-type color copier having an apparatus body  1  including a document feeder  3 , a document reader  4  including a contact glass  5 , a writing unit  2 , sheet feeding units  7  each including a sheet feed roller  8 , a registration roller pair  9 , process cartridges  15 K,  15 Y,  15 M, and  15 C respectively including photoconductor drums  11 K,  11 Y,  11 M, and  11 C and charging rollers  12 K,  12 Y,  12 M, and  12 C, development devices  13 K,  13 Y,  13 M, and  13 C, primary transfer bias rollers  14 K,  14 Y,  14 M, and  14 C, an intermediate transfer belt  17 , a secondary transfer bias roller  18 , an intermediate transfer belt cleaning device  19 , a fixing device  20 , and a waste toner collecting container  30 . 
     The document feeder  3  feeds a document D to the document reader  4 . The document reader  4  reads image information of the document D. The writing unit  2  emits beams of laser light based on the input image information. Each of the sheet feeding units  7  stores a recording medium P, such as a transfer sheet. The registration roller pair  9  serves as a timing roller pair which adjusts the timing of feeding the recording medium P. The photoconductor drums  11 K,  11 Y,  11 M, and  11 C serve as image carriers on which toner images of black, yellow, magenta, and cyan colors are formed. The charging rollers  12 K,  12 Y,  12 M, and  12 C serve as charging devices which charge respective outer circumferential surfaces of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C. The development devices  13 K,  13 Y,  13 M, and  13 C develop electrostatic latent images formed on the photoconductor drums  11 K,  11 Y,  11 M, and  11 C, to thereby form toner images. The primary transfer bias rollers  14 K,  14 Y,  14 M, and  14 C superimpose and transfer the toner images formed on the photoconductor drums  11 K,  11 Y,  11 M, and  11 C onto the recording medium P. The intermediate transfer belt  17  serves as a transfer member having an outer circumferential surface onto which the toner images of the plurality of colors are superimposed and transferred. The secondary transfer bias roller  18  transfers the color toner images on the intermediate transfer belt  17  onto the recording medium P. The intermediate transfer belt cleaning device  19  cleans the intermediate transfer belt  17 . The fixing device  20  fixes the unfixed images on the recording medium P. The waste toner collecting container  30  stores collected waste toner. 
     Description will now be given of a normal color image forming operation performed by the image forming apparatus. Image forming processes performed on the photoconductor drums  11 K,  11 Y,  11 M, and  11 C may be referred to  FIG. 2 , in which the photoconductor drums  11 K,  11 Y,  11 M, and  11 C are designated as a photoconductor drum  11 . 
     The document D on a document table of the document feeder  3  is first fed in the direction of arrow A in  FIG. 1  by feed rollers of the document feeder  3 , and is placed onto the contact glass  5  of the document reader  4 . Then, the image information of the document D placed on the contact glass  5  is optically read by the document reader  4 . 
     Specifically, the document reader  4  scans the image of the document D on the contact glass  5 , while irradiating the document D with light emitted from an illuminating lamp thereof. The light reflected by the document D is imaged by a color sensor through mirrors and lenses. Color image information of the document D is read by the color sensor for each of color-separated light beams of RGB (i.e., red, green, and blue), and thereafter is converted into electrical image signals. Further, on the basis of the color-separated image signals of RGB, an image processor performs processing, such as color conversion, color correction, and spatial frequency correction, to obtain color image information of the black, yellow, magenta, and cyan colors. 
     The image information of the black, yellow, magenta, and cyan colors is transmitted to the writing unit  2 . Then, as illustrated in  FIG. 2 , beams of laser light L based on the image information of the respective colors are emitted from the writing unit  2  to the respective photoconductor drums  11 K,  11 Y,  11 M, and  11 C. 
     Meanwhile, the four photoconductor drums  11 K,  11 Y,  11 M, and  11 C rotate counterclockwise in  FIG. 1 . The outer circumferential surface of each of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C is first uniformly charged at a position facing the corresponding one of the charging roller  12 K,  12 Y,  12 M, and  12 C serving as a charging device. That is, a charging process is performed. Thereby, a charging potential is formed on each of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C. Thereafter, the charged outer circumferential surface of each of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C reaches a laser light irradiation position. 
     Beams of laser light corresponding to the image signals of the respective colors are emitted from four not-illustrated light sources of the writing unit  2 , and pass different light paths corresponding to the respective color components of black, yellow, magenta, and cyan. That is, an exposure process is performed. 
     The beam of laser light corresponding to the black component is directed to the outer circumferential surface of the leftmost photoconductor drum  11 K in  FIG. 1 . In this process, the beam of laser light corresponding to the black component is deflected by a not-illustrated high-speed rotating polygon mirror to scan the photoconductor drum  11 K along the rotation axis thereof, i.e., in a main scanning direction. Thereby, an electrostatic latent image corresponding to the black component is formed on the photoconductor drum  11 K charged by the charging roller  12 K. 
     Similarly, the beam of laser light corresponding to the yellow component is directed to the outer circumferential surface of the second leftmost photoconductor drum  11 Y in  FIG. 1 , to thereby form an electrostatic latent image corresponding to the yellow component. Further, the beam of laser light corresponding to the magenta component is directed to the outer circumferential surface of the third leftmost photoconductor drum  11 M in  FIG. 1 , to thereby form an electrostatic latent image corresponding to the magenta component. Further, the beam of laser light corresponding to the cyan component is directed to the outer circumferential surface of the fourth leftmost photoconductor drum  11 C in  FIG. 1 , to thereby form an electrostatic latent image corresponding to the cyan component. 
     Thereafter, the outer circumferential surfaces of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C formed with the electrostatic latent images of the respective colors reach respective positions facing the development devices  13 K,  13 Y,  13 M, and  13 C. Then, toners of the respective colors are supplied onto the photoconductor drums  11 K,  11 Y,  11 M, and  11 C by the development devices  13 K,  13 Y,  13 M, and  13 C, to thereby develop the latent images on the photoconductor drums  11 K,  11 Y,  11 M, and  11 C. That is, a development process is performed. 
     After the development process, the outer circumferential surfaces of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C reach respective positions facing the intermediate transfer belt  17  serving as a transfer member. At the positions, the primary transfer bias rollers  14 K,  14 Y,  14 M, and  14 C are disposed to be in contact with the inner circumferential surface of the intermediate transfer belt  17 . At the positions of the primary transfer bias rollers  14 K,  14 Y,  14 M, and  14 C, the toner images of the respective colors formed on the photoconductor drums  11 K,  11 Y,  11 M, and  11 C are sequentially superimposed and transferred onto the intermediate transfer belt  17 . That is, a primary transfer process is performed. 
     After the primary transfer process, the outer circumferential surface of each of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C reaches a position facing a cleaning blade  15   a  illustrated in  FIG. 2 , which is a cleaning device included in the corresponding one of the process cartridges  15 K,  15 Y,  15 M, and  15 C. Then, untransferred toner remaining on the outer circumferential surface is collected by the cleaning blade  15   a . That is, a cleaning process is performed. 
     Thereafter, the outer circumferential surface of each of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C reaches and is discharged by a not-illustrated discharging device. Thereby, a series of image forming processes on the photoconductor drums  11 K,  11 Y,  11 M, and  11 C is completed. 
     Meanwhile, the intermediate transfer belt  17  having (i.e., carrying) the toner images of the respective colors superimposed and transferred thereto from the photoconductor drums  11 K,  11 Y,  11 M, and  11 C rotates clockwise in  FIG. 1 , and reaches a position facing the secondary transfer bias roller  18 . At the position facing the secondary transfer bias roller  18 , the color toner images carried on the intermediate transfer belt  17  are transferred onto the recording medium P. That is, a secondary transfer process is performed. 
     Thereafter, the intermediate transfer belt  17  reaches a position facing the intermediate transfer belt cleaning device  19 , and untransferred toner adhering to the outer circumferential surface of the intermediate transfer belt  17  is collected by the intermediate transfer belt cleaning device  19 . Thereby, a series of transfer processes on the intermediate transfer belt  17  is completed. 
     Meanwhile, the recording medium P is fed to a secondary transfer nip formed between the intermediate transfer belt  17  and the secondary transfer bias roller  18  from one of the sheet feeding units  7  via rollers such as the registration roller pair  9 . Specifically, from one of the sheet feeding units  7  storing the recording medium P, the recording medium P is fed by the corresponding sheet feed roller  8 , and is guided toward the registration roller pair  9  by not-illustrated feeding guide members. The recording medium P then reaches the registration roller pair  9 , and is fed toward the secondary transfer nip with appropriate timing. 
     Then, a full-color image is transferred onto the recording medium P, and the recording medium P is guided to the fixing device  20  by a feed belt. In the fixing device  20 , the full-color image is fixed on the recording medium P at a nip formed between a fixing belt and a pressure roller included in the fixing device  20 . After the fixing process, the recording medium P with the image is discharged (i.e., output) outside the apparatus body  1  by a sheet discharge roller pair, thereby completing a series of processes of the image forming operation. 
     With reference to  FIGS. 2 and 3 , an image forming unit included in the image forming apparatus will now be described in detail. The image forming apparatus of the present embodiment includes four image forming units for the respective colors, which are substantially similar in structure.  FIGS. 2 and 3 , therefore, illustrate components of one of the image forming units without the alphabetical suffixes K, Y, M, and C. 
     As illustrated in  FIG. 2 , the image forming unit includes the photoconductor drum  11 , the charging roller  12 , the development device  13 , the cleaning blade  15   a , a transport screw  15   b , a transport tube  15   c , and a lubricant supply device  16 . The photoconductor drum  11  serves as an image carrier. The charging roller  12  serves as a charging device which charges the photoconductor drum  11 . The development device  13  develops an electrostatic latent image formed on the photoconductor drum  11 , and includes a development roller  13   a , a supply roller  13   b , a doctor blade  13   c , and a mixing member  13   d . The cleaning blade  15   a  serves as a cleaning device which collects untransferred toner remaining on the photoconductor drum  11 . The lubricant supply device  16  supplies a lubricant onto the photoconductor drum  11 , and includes a lubricant supply roller  16   a , a solid lubricant  16   b , a holder  16   e , and a compression spring  16   c.    
     In the present embodiment, the photoconductor drum  11 , the charging roller  12 , the cleaning blade  15   a , and the lubricant supply device  16  included in the components of the image forming unit are integrated as the process cartridge  15  configured as a removable unit installable in and removable from the apparatus body  1 . Further, the development device  13  is configured as a unit separated from the process cartridge  15  and independently installable in and removable from the apparatus body  1 . 
     Similarly to the image forming units for the respective colors, the process cartridges  15 K,  15 Y,  15 M, and  15 C for the respective colors are also substantially similar in structure. Each of the process cartridges  15 K,  15 Y,  15 M, and  15 C has an exterior as illustrated in  FIG. 3 . In  FIG. 3 , a reference numeral  15   d  denotes a later-described shutter member, and arrow B indicates the direction of installing the process cartridge  15  in the apparatus body  1  (hereinafter referred to as the installation direction). 
     In the present embodiment, the photoconductor drum  11  serving as an image carrier is a negatively charged organic photoconductor including a drum-shaped conductive support member and a plurality of layers, such as photosensitive layers, provided around an outer circumferential surface of the support member. Although illustration is omitted, the photoconductor drum  11  includes an insulating under layer, a photosensitive charge generating layer, a photosensitive charge transporting layer, and a protective surface layer sequentially laminated around the outer circumferential surface of the conductive support member serving as a base layer. The conductive support member of the photoconductor drum  11  serving as a base layer may be made of a conductive material having volume resistivity of approximately 10 10  Ωcm or less. 
     The charging roller  12  serving as a charging device is a roller including a conductive core bar forming a shaft portion and a medium-resistance elastic layer covering an outer circumferential surface of the core bar. The charging roller  12  is disposed to be in contact with the photoconductor drum  11  at a position downstream of the lubricant supply device  16  in the rotation direction of the photoconductor drum  11 . Further, the charging roller  12  is supplied with a predetermined charging bias voltage by a not-illustrated power supply unit provided to the apparatus body  1 , to thereby uniformly charge the outer circumferential surface of the photoconductor drum  11  facing the charging roller  12 . In the present embodiment, the charging roller  12  is kept in contact with the photoconductor drum  11 . Alternatively, the charging roller  12  may be configured to face the photoconductor drum  11  such that the charging roller  12  is separated from the photoconductor drum  11  with a slight gap formed therebetween. 
     In the development device  13 , the development roller  13   a  is disposed to be in contact with the photoconductor drum  11  to form a development area (i.e., development nip) therebetween. The development device  13  contains toner T serving as a one-component developer, and develops the electrostatic latent image formed on the photoconductor drum  11 , to thereby form a toner image. Specifically, as illustrated in  FIG. 2 , the development device  13  of the present embodiment employs a one-component development system, and includes the development roller  13   a  serving as a developer carrier, the supply roller  13   b , the doctor blade  13   c  serving as a layer thinning member, and the mixing member  13   d.    
     The thus-configured development device  13  operates as follows. A part of the toner T supplied to and contained in the development device  13  is first carried by the supply roller  13   b , and then is frictionally charged at a portion of the supply roller  13   b  pressed against the development roller  13   a . Thereafter, the toner T moves onto and is carried by the development roller  13   a , and is uniformly spread into a relatively thin layer at a position facing the doctor blade  13   c . The toner T then reaches the development area corresponding to the position at which the development roller  13   a  is in contact with the photoconductor drum  11 . At this position, the toner T is attracted to the latent image on the photoconductor drum  11  by a development electric field generated in the development area. In the present embodiment, the development roller  13   a  is kept in contact with the photoconductor drum  11 . Alternatively, the development roller  13   a  may be configured to face the photoconductor drum  11  such that the development roller  13   a  is separated from the photoconductor drum  11  with a slight gap formed therebetween. 
     The cleaning blade  15   a  disposed downstream of the lubricant supply device  16  in the rotation direction of the photoconductor drum  11  is made of a rubber material, such as urethane rubber, and is kept in contact with the outer circumferential surface of the photoconductor drum  11  with predetermined pressure at a predetermined angle. Thereby, deposits such as untransferred toner adhering to the photoconductor drum  11  are mechanically scraped off and collected into the process cartridge  15 . The toner collected in the process cartridge  15  is transported, as waste toner, toward the waste toner collecting container  30  illustrated in  FIG. 7  by the transport screw  15   b . As illustrated in  FIG. 7 , the transport tube  15   c  of the process cartridge  15  including therein the transport screw  15   b  is connected to the waste toner collecting container  30  installed in the apparatus body  1 . 
     The deposits adhering to the photoconductor drum  11  include, in addition to the untransferred toner, paper dust arising from the recording medium P, such as a sheet, discharge products produced on the photoconductor drum  11  in discharge of the charging roller  12 , and an additive added to the toner, for example. Further, the cleaning blade  15   a  of the present embodiment also functions as a layer thinning blade with which the lubricant supplied to the photoconductor drum  11  by the lubricant supply roller  16   a  is spread in a relatively thin layer. 
     In the lubricant supply device  16 , the lubricant supply roller  16   a  is a brush roller which slides over the photoconductor drum  11  and the solid lubricant  16   b . Further, the holder  16   e  holds the solid lubricant  16   b , and the compression spring  16   c  serves as a biasing device which biases the solid lubricant  16   b  and the holder  16   e  toward the lubricant supply roller  16   a . The thus-configured lubricant supply device  16  supplies the lubricant to the photoconductor drum  11 , and the lubricant supplied to the photoconductor drum  11  is spread into a relatively thin layer by the cleaning blade  15   a  disposed downstream of the lubricant supply device  16  in the rotation direction of the photoconductor drum  11 . 
     With reference to  FIGS. 4 to 8 , the configuration and operation of the image forming apparatus of the present embodiment will be described in detail.  FIG. 4  is a schematic diagram illustrating a state in which the intermediate transfer belt  17  is separated from the four photoconductor drums  11 K,  11 Y,  11 M, and  11 C.  FIG. 5  is a schematic diagram illustrating a state in which the intermediate transfer belt  17  is separated from the four photoconductor drums  11 K,  11 Y,  11 M, and  11 C, and the waste toner collecting container  30  is interfering with a later-described contact and separation mechanism.  FIG. 6  is a schematic diagram illustrating a state in which the intermediate transfer belt  17  is in contact with the photoconductor drum  11 K for forming a monochromatic image.  FIG. 7  is a schematic diagram illustrating a state in which the waste toner collecting container  30  is installed in the apparatus body  1  of the image forming apparatus.  FIG. 8  is a schematic diagram illustrating a state in which the intermediate transfer belt  17  is in contact with the four photoconductor drums  11 K,  11 Y,  11 M, and  11 C. For the sake of simplicity,  FIGS. 4 ,  6 , and  8  illustrate a cam  52  as being in contact not with a shaft portion but with a roller portion of the primary transfer bias roller  14 K. 
     As described above, the photoconductor drum  11  serving as an image carrier is removably installed in the apparatus body  1  of the image forming apparatus as one of the components of the process cartridge  15 . Specifically, when a not-illustrated main cover of the apparatus body  1  in  FIG. 1  is open, each of the process cartridges  15 K,  15 Y,  15 M, and  15 C for the respective colors is installed in the apparatus body  1  toward a distal side in a direction perpendicular to the drawing plane, or is removed from the apparatus body  1  toward a proximal side in the direction perpendicular to the drawing plane. The process cartridge  15  is installed in the apparatus body  1  in the direction of arrow B in  FIG. 3  along a not-illustrated guide rail provided to the apparatus body  1 , to thereby determine the position of the process cartridge  15  in the apparatus body  1 . 
     Further, as described above, in the color image forming operation, the intermediate transfer belt  17  serving as a transfer member comes into contact with the photoconductor drums  11 K,  11 Y,  11 M, and  11 C to transfer the toner images carried on the photoconductor drums  11 K,  11 Y,  11 M, and  11 C onto the outer circumferential surface of the intermediate transfer belt  17 . In the present embodiment, the intermediate transfer belt  17  serving as a transfer member and a plurality of rollers form an intermediate transfer unit, in which the intermediate transfer belt  17  is stretched around and supported by the rollers. The intermediate transfer unit is also removably (i.e., replaceably) configured to be installed in the apparatus body  1  from the same direction as the installation direction of the process cartridge  15 . 
     The image forming apparatus of the present embodiment includes a contact and separation mechanism which moves the intermediate transfer belt  17  relative to the photoconductor drum  11 K to cause the intermediate transfer belt  17  to come into contact with or separate from the photoconductor drum  11 K. 
     Specifically, the contact and separation mechanism includes a rotary shaft  53 , cams  52 , and a lever  51 . The rotary shaft  53  extends in the lateral direction in  FIGS. 5 and 7 , i.e., the direction perpendicular to the drawing plane in  FIGS. 1 ,  4 , and  6  (hereinafter referred to as the depth direction). The cams  52  are provided to opposed end portions of the rotary shaft  53  in the depth direction, and come into contact with the shaft portion of the primary transfer bias roller  14 K. The lever  51  is provided on the front side of the rotary shaft  53  in the depth direction. When the lever  51  is rotated on the front side in the depth direction, the cams  52  rotate together with the lever  51  around the rotary shaft  53 . Accordingly, the primary transfer bias roller  14 K vertically moves, causing the intermediate transfer belt  17  to come into contact with or separate from the photoconductor drum  11 K. 
     Specifically,  FIGS. 4 and 5  illustrate a state in which the primary transfer bias roller  14 K is moved downward by the contact and separation mechanism to separate from the photoconductor drum  11 K, and thereby the photoconductor drum  11 K for forming a monochromatic image is separated from the intermediate transfer belt  17  as well as the photoconductor drums  11 Y,  11 M, and  11 C for forming a color image. In such a state, the process cartridges  15 K,  15 Y,  15 M, and  15 C including the four photoconductor drums  11 K,  11 Y,  11 M, and  11 C are partially or fully replaced (i.e., removed and reinstalled) as necessary. This configuration prevents a situation in which the photoconductor drums  11 K,  11 Y,  11 M, and  11 C in contact with the intermediate transfer belt  17  are removed from and reinstalled in the apparatus body  1 , making the photoconductor drums  11 K,  11 Y,  11 M, and  11 C and the intermediate transfer belt  17  rub against each other and damaging the respective surfaces. 
     Meanwhile,  FIGS. 6 and 7  illustrates a state in which the primary transfer bias roller  14 K is moved upward by the contact and separation mechanism to come into contact with the photoconductor drum  11 K via the intermediate transfer belt  17 , and thereby the photoconductor drum  11 K for forming a monochromatic image is in contact with the intermediate transfer belt  17 . Such a state results from operation of the lever  51  after, for example, the operation of removing and reinstalling the photoconductor drums  11 K,  11 Y,  11 M, and  11 C in the separated state illustrated in  FIGS. 4 and 5 . In this state, the image forming operation in a monochrome mode (i.e., print mode for performing the image forming operation with only the toner of the black color) is performed. 
     If a full-color mode (i.e., print mode for performing the image forming operation with the toners of the four colors) is selected, the primary transfer bias rollers  14 Y,  14 M, and  14 C for forming a color image are moved upward by a drive control of a not-illustrated second contact and separation mechanism, to bring the intermediate transfer belt  17  into contact with the photoconductor drums  11 Y,  11 M, and  11 C for forming a color image, as illustrated in  FIG. 8 . 
     As described above, in the present embodiment, the control of the second contact and separation mechanism is set such that the image forming apparatus in the initial state waiting for a print mode command, such as a post-warm-up state or a standby state, is placed in the monochrome mode, as illustrated in  FIGS. 6 and 7 . Alternatively, the control of the second contact and separation mechanism may be set such that that the image forming apparatus in the initial state is placed in the full-color mode, as illustrated in  FIG. 8 . In such a case, the image forming apparatus may be configured such that the four primary transfer bias rollers  14 K,  14 Y,  14 M, and  14 C are vertically moved in an interlocking manner by a not-illustrated connecting plate, and that the intermediate transfer belt  17  is brought into contact with or separated from the four photoconductor drums  11 K,  11 Y,  11 M, and  11 C in accordance with the operation of rotating the lever  51 . 
     As illustrated in  FIGS. 5 and 7 , the waste toner collecting container  30  is installed in the image forming apparatus of the present embodiment. The waste toner collecting container  30  is a removable unit in which the untransformed toner discharged by the cleaning blade  15   a  and the intermediate transfer belt cleaning device  19  is collected as waste toner. 
     The waste toner collecting container  30  serving as a removable unit is removably installed in the apparatus body  1  of the image forming apparatus from the same direction as the installation direction of the process cartridge  15  including the photoconductor drum  11 . Further, the waste toner collecting container  30  is disposed proximal of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C and the intermediate transfer belt  17  in the installation direction parallel to the depth direction. As illustrated in  FIG. 4 , for example, the waste toner collecting container  30  is formed to at least partially overlap the photoconductor drums  11 K,  11 Y,  11 M, and  11 C and the intermediate transfer belt  17 , as viewed in the installation direction parallel to the depth direction. Due to such positional relationship, the process cartridges  15 K,  15 Y,  15 M, and  15 C including the photoconductor drums  11 K,  11 Y,  11 M, and  11 C and the intermediate transfer belt  17  are prevented from being installed in or removed from the apparatus body  1 , unless the waste toner collecting container  30  is removed from the apparatus body  1 . 
     Further, in the present embodiment, when the intermediate transfer belt  17  is separated from the photoconductor drum  11 K by the contact and separation mechanism, as illustrated in  FIGS. 4 and 5 , the waste toner collecting container  30  is dimensioned to interfere with the contact and separation mechanism, and thus is prevented from being installed in the apparatus body  1  of the image forming apparatus. Specifically, when the intermediate transfer belt  17  is separated from the photoconductor drum  11 K, the lever  51  is rotated to a position at which the lever  51  interferes with a projection  30   a  of the waste toner collecting container  30 . Meanwhile, when the intermediate transfer belt  17  is in contact with the photoconductor drum  11 K, the lever  51  is rotated to a position at which the lever  51  does not interfere with the waste toner collecting container  30 . 
     That is, in the separated state as illustrated in  FIGS. 4 and 5 , if the waste toner collecting container  30  is moved in the direction of arrow C in  FIG. 5  to install the waste toner collecting container  30  in the apparatus body  1 , the projection  30   a  interferes with the lever  51 , preventing the waste toner collecting container  30  from being installed in the apparatus body  1 . In this case, the not-illustrated main cover provided on the front side of the apparatus body  1  in the installation direction is prevented from being closed, thereby preventing the image forming apparatus from operating. Accordingly, the image forming operation is not performed in the separated state of the intermediate transfer belt  17 . That is, the present configuration prevents the image forming operation from being mistakenly executed in the separated state of the intermediate transfer belt  17  in, for example, replacement work of the process cartridge  15 . 
     Meanwhile, in the contact state as illustrated in  FIGS. 6 and 7 , the projection  30   a  does not interfere with the lever  51 , allowing the waste toner collecting container  30  to be fully installed in the apparatus body  1  in the direction of arrow C in  FIG. 7 . In this state, therefore, the image forming operation is executed. 
     In the present embodiment, in accordance with the installation or removal the waste toner collecting container  30  in or from the apparatus body  1 , the waste toner collecting container  30  is brought into contact with or separated from the transport tube  15   c  which transports the waste toner, as illustrated in  FIGS. 5 and 7 . Specifically, a pin  30   c  serving as a pressing member is provided to an upper portion of the waste toner collecting container  30  to rise in the installation direction. Meanwhile, a leading end portion of the transport tube  15   c  is formed with an outlet  15   c   1 , and has a shutter member  15   d  provided therein and having a bottom portion formed with an opening to open and close the outlet  15   c   1 . In accordance with the installation of the waste toner collecting container  30  into the apparatus body  1 , the pin  30   c  serving as a pressing member presses the shutter member  15   d  disposed at the outlet  15   c   1  of the transport tube  15   c , thereby opening the outlet  15   c   1 . That is, the opening of the shutter member  15   d  and the outlet  15   c   1  overlap. At the same time, an inlet  30   b  formed in an upper portion of the waste toner collecting container  30  communicates with the outlet  15   c   1  of the transport tube  15   c , allowing the waste toner to flow into the waste toner collecting container  30  from the transport tube  15   c.    
     As described above, in the present embodiment, the outlet  15   c   1  of the transport tube  15   c  is closed by the shutter member  15   d  in the state in which the waste toner collecting container  30  is not fully installed in the apparatus body  1 , as illustrated in  FIG. 5 . Further, the outlet  15   c   1  of the transport tube  15   c  is opened by the shutter member  15   d  in the state in which the waste toner collecting container  30  is fully installed in the apparatus body  1 , as illustrated in  FIG. 7 . When the waste toner collecting container  30  is not installed in the apparatus body  1 , therefore, the waste toner is prevented from leaking from the transport tube  15   c.    
     Further, the waste toner collecting container  30  also includes a not-illustrated internal transport member and a gear  30   d . The transport member transports the waste toner stored in the waste toner collecting container  30 . The gear  30   d  is provided to a shaft portion of the transport member to transmit drive force to the transport member. In accordance with the installation of the waste toner collecting container  30  into the apparatus body  1  of the image forming apparatus, the gear  30   d  meshes with a drive gear  62  provided to the apparatus body  1  of the image forming apparatus, as illustrated in  FIG. 7 . Accordingly, in the present embodiment, the gear  30   d  does not mesh with the drive gear  62  when the waste toner collecting container  30  is not fully installed in the apparatus body  1 , as illustrated in  FIG. 5 . Consequently, erroneous operation of the waste toner collecting container  30  is prevented. 
     Further, as illustrated in  FIGS. 5 and 7 , the present embodiment includes an installation sensor  65  serving as a detector that detects the state in which the waste toner collecting container  30  is installed in the apparatus body  1 . The image forming apparatus is prevented from operating when the installation sensor  65  serving as a detector detects that the waste toner collecting container  30  is not installed in the apparatus body  1 . 
     Specifically, when the waste toner collecting container  30  is not fully installed in the apparatus body  1 , as illustrated in  FIG. 5 , a movable portion  65   a  of the installation sensor  65  is not in contact with the waste toner collecting container  30 , or is in contact with but insufficiently pressed against the waste toner collecting container  30 . The image forming apparatus is prevented from performing the image forming operation when this state is detected. Meanwhile, when the waste toner collecting container  30  is fully installed in the apparatus body  1 , as illustrated in  FIG. 7 , the movable portion  65   a  of the installation sensor  65  is in contact with and sufficiently pressed against the waste toner collecting container  30 . The image forming apparatus is controlled to perform the image forming operation when this state is detected. With the control using the thus-configured installation sensor  65  serving as a detector, the image forming operation is reliably prevented from being performed in the separated state of the intermediate transfer belt  17 . 
     The present embodiment is configured such that, when the intermediate transfer belt  17  is separated from the photoconductor drum  11 K by the contact and separation mechanism, as illustrated in  FIGS. 4 and 5 , the waste toner collecting container  30  deliberately interferes with the contact and separation mechanism, and is prevented from being installed in the apparatus body  1 . 
     Alternatively, as illustrated in  FIGS. 9A and 9B , the contact and separation mechanism may be configured to raise the primary transfer bias roller  14 K and thereby bring the intermediate transfer belt  17  into contact with the photoconductor drum  11 K in accordance with the installation of the waste toner collecting container  30  into the apparatus body  1  of the image forming apparatus, and to lower the primary transfer bias roller  14 K and thereby separate the intermediate transfer belt  17  from the photoconductor drum  11 K in accordance with the removal of the waste toner collecting container  30  from the apparatus body  1  of the image forming apparatus. 
     Specifically, the image forming apparatus illustrated in  FIGS. 9A and 9B  includes a contact and separation mechanism including a shaft  59 , not-illustrated guide grooves, holders  58 , and a contact member  57 . The shaft  59  extends in the depth direction. The guide grooves guide vertical movement of the shaft  59 . The holders  58  are provided to opposed end portions of the shaft  59  in the depth direction to hold the shaft portion of the primary transfer bias roller  14 K. The contact member  57  is formed on the front side of the shaft  59  in the depth direction. As illustrated in  FIG. 9A , if the waste toner collecting container  30  is moved in the direction of arrow C to install the waste toner collecting container  30  in the apparatus body  1 , the projection  30   a  of the waste toner collecting container  30  having an inclined upper surface comes into contact with the contact member  57 . If the waste toner collecting container  30  is further moved in the direction of arrow C to install the waste toner collecting container  30  in the apparatus body  1 , the contact member  57  is moved upward by the projection  30   a , and the entire contact and separation mechanism is moved upward, as illustrated in  FIG. 9B . Thereby, the primary transfer bias roller  14 K also moves upward, bringing the intermediate transfer belt  17  into contact with the photoconductor drum  11 K. 
     Meanwhile, if the waste toner collecting container  30  is removed from the apparatus body  1 , the contact between the contact member  57  and the projection  30   a  is cancelled. Thereby, the primary transfer bias roller  14 K is moved downward by the weight thereof, and the intermediate transfer belt  17  separates from the photoconductor drum  11 K. In the thus-configured embodiment, therefore, the image forming apparatus is prevented from operating when the intermediate transfer belt  17  is separated from the photoconductor drum  11 K, similarly as in the foregoing embodiment. 
     As described above, the embodiments of the present invention are configured such that the removable waste toner collecting container  30  (i.e., a removable unit) is disposed proximal of the photoconductor drums  11 K,  11 Y,  11 M, and  11 C (i.e., image carriers) in the installation direction, and that the waste toner collecting container  30  is prevented from being correctly installed in the apparatus body  1  of the image forming apparatus unless the intermediate transfer belt  17  (i.e., a transfer member) is kept in correct contact with the photoconductor drum  11 K by the contact and separation mechanism. In the configuration, the intermediate transfer belt  17  is contactable with and separable from the photoconductor drum  11 K. Therefore, the image forming apparatus is reliably prevented from operating when the intermediate transfer belt  17  is separated from the photoconductor drum  11 K. 
     In the above-described embodiments, the photoconductor drum  11 , the charging roller  12 , the cleaning blade  15   a  (i.e., a cleaning device), and the lubricant supply device  16  in the image forming unit are integrated to form the process cartridge  15  so as to make the image forming unit compact and facilitate maintenance. Alternatively, the development device  13  may also be included in the process cartridge  15  as a component thereof. Further, the photoconductor drum  11  may be configured not as a component of the process cartridge  15  but as a separate member independently installable in and removable from the apparatus body  1 . In this case, it is preferable to configure the development roller  13   a  and the charging roller  12  to be separated from the photoconductor drum  11 . Also in this case, similar effects to those of the above-described embodiments are obtainable. 
     Further, in the above-described embodiments, the present invention is applied to the image forming apparatus including the development device  13  which employs the one-component development system using the one-component developer. The present invention, however, is also applicable to an image forming apparatus including the development device  13  which employs a two-component development system using a two-component developer. 
     Further, in the above-described embodiments, the present invention is applied to the tandem-type color image forming apparatus including the intermediate transfer belt  17 . The present invention, however, is also applicable to different types of image forming apparatuses, such as a tandem-type color image forming apparatus including a transfer feed belt, in which toner images on a plurality of photoconductor drums juxtaposed to face the transfer feed belt are superimposed and transferred onto a recording medium fed by the transfer feed belt, and a monochrome image forming apparatus including a transfer belt. In this case, the transfer feed belt or the transfer belt functions as a transfer member which transfers a toner image carried on an image carrier onto a recording medium fed to a position between the belt and the image carrier, and a contact and separation mechanism is provided which causes the transfer member to come into contact with or separate from the image carrier. Also in this case, similar effects to those of the above-described embodiments are obtainable. 
     Further, in the above-described embodiments, the waste toner collecting container  30  is used as a removable unit configured not to be correctly installed in the apparatus body  1  in the separated state of the intermediate transfer belt  17 . Alternatively, a unit other than the waste toner collecting container  30 , such as a large-capacity toner container, for example, may be used as the removable unit. Also in this case, similar effects to those of the above-described embodiments are obtainable. 
     Further, in the present application, the term “process cartridge” is defined as a unit which integrates an image carrier and at least one of a charging device that charges the image carrier, a development device that develops a latent image formed on the image carrier, and a cleaning device that cleans a surface of the image carrier, and which is removably installed in the body of an image forming apparatus. 
     The above-described embodiments and effects thereof are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements or features of different illustrative and embodiments herein may be combined with or substituted for each other within the scope of this disclosure and the appended claims. Further, features of components of the embodiments, such as number, position, and shape, are not limited to those of the disclosed embodiments and thus may be set as preferred. It is therefore to be understood that, within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein.