Patent Publication Number: US-8983341-B2

Title: Developing device and electrophotographic image forming apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 from Korean Patent Application No. 10-2011-0120319, filed on Nov. 17, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to a developing device and an electrophotographic image forming apparatus including the same, and more particularly, to a developing device for increasing the amounts of contained toners and an electrophotographic image forming apparatus including the same. 
     2. Description of the Related Art 
     An image forming apparatus using an electrophotographic method, such as a laser printer, a general paper facsimile, a copier, or the like, prints an image on a medium by using an electrophotographic image forming system. An electrophotographic image forming system forms an electrostatic latent image by irradiating light corresponding to image information to a photosensitive body and forms a toner image by supplying a toner to the electrostatic latent image. Then, the toner image is transferred onto a recording medium and heat and pressure are applied thereto, thereby printing an image onto the recording medium. 
     An electrophotographic color image forming apparatus may include four developing devices that respectively contain toners of, for example, cyan (C), magenta (M), yellow (Y), and black (K). When a toner contained in a developing device is exhausted, the developing device is replaced with a new developing device. When a color image forming apparatus is used, since a text document is frequently printed, black toner is rapidly consumed. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides a developing device for increasing the amounts of contained toners while minimizing the size of an image forming apparatus, and an electrophotographic image forming apparatus including the same. 
     Additional features and utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     The present general inventive concept also provides a developing device for increasing the amount of a contained toner that is highly frequently used while minimizing the size of an image forming apparatus, and an electrophotographic image forming apparatus including the same. 
     Exemplary embodiments of the present general inventive concept can also provide an electrophotographic image forming apparatus including a plurality of photosensitive bodies, an exposer to irradiate light to each of the plurality of photosensitive bodies to form an electrostatic latent image, and a plurality of developing devices each including a developing unit to supply a toner to the electrostatic latent image on a corresponding photosensitive body from among the plurality of photosensitive bodies to form a toner image and a first toner containing unit to contain a toner to be supplied to the developing unit, where at least one developing device from among the plurality of developing devices includes a second toner containing unit in aside opposite to the first toner containing unit with respect to an optical path of light that is irradiated to the corresponding photosensitive body of the at least one developing device and a connecting unit to connect the first and second toner containing units. 
     The electrophotographic image forming apparatus may further include an intermediate transfer belt that is disposed to face the plurality of photosensitive bodies and to which the toner image is transferred, where the at least one developing device may be disposed on a most downstream region with respect to a proceeding direction of the intermediate transfer belt. 
     Pitches of the plurality of photosensitive bodies may be equal to each other in the proceeding direction of the intermediate transfer belt. 
     In the electrophotographic image forming apparatus, the second toner containing unit is disposed on a downstream region with respect to the proceeding direction, compared to the first toner containing unit of the developing unit. Each of the plurality of developing devices may include a waste toner containing unit to contain waste toner removed from the photosensitive bodies, and the waste toner containing unit of the at least one developing device may be disposed below the second toner containing unit. 
     The plurality of developing devices may have the same length in the proceeding direction. 
     The plurality of developing devices may have the same height. 
     A length of the at least one developing device in the proceeding direction may be greater than a length of the remaining developing devices in the proceeding direction. The first toner containing units of the plurality of developing devices may have the same length in the proceeding direction. The plurality of developing devices may have the same height. 
     The connecting unit may be disposed outside an effective width of the optical path. An agitating member to supply toner to the first toner containing unit through the connecting unit may be disposed in the second toner containing unit. The agitating member may include a rotation axis that extends in a width direction and an agitating wing that extends from the rotation axis in a radial direction. A bottom portion of the second toner containing unit may be inclined downward in the width direction toward the connecting unit. The agitating wing may include a first wing portion and a second wing portion adjacent to the connecting unit, and a length of the second wing portion in the radial direction may be greater than a length of the first wing portion in the radial direction. 
     In the electrophotographic image forming apparatus, the at least one developing device is a black developing device for developing a black toner image. 
     Exemplary embodiments of the present general inventive concept can also provide an electrophotographic image forming apparatus including a first and second photosensitive bodies, and first and second developing devices to develop electrostatic latent images formed on the first and second photosensitive bodies, each of the first and second developing devices including a first toner containing unit to contain a toner, the second developing device further including a second toner containing unit connected to the first toner containing unit by a connection unit. 
     The electrophotographic image forming apparatus may further include a transfer medium to which toner images formed on the first and second photosensitive bodies are transferred, where the first and second toner containing units may be disposed on upstream and downstream regions in a proceeding direction of the transfer medium, respectively. 
     The first and second developing devices may include respective optical paths on which light for exposing the first and second photosensitive bodies is incident, where the optical path of the second developing device may be disposed between the first and second toner containing units of the second developing device. 
     A length of the second developing device in the proceeding direction may be greater than a length of the first developing device in the proceeding direction, and heights of the first and second developing devices may be equal to each other. 
     A bottom portion of the second toner containing unit may be inclined downward in a width direction toward the connecting unit, where an agitating member may be installed in the second toner containing unit to supply a toner to the first toner containing unit through the connecting unit, the agitating member includes a rotation axis that extends in the width direction and an agitating ring that extends from the rotation axis in a radial direction, and the agitating wing may include a first wing portion and a second wing portion adjacent to the connecting unit, where a length of the second wing portion in the radial direction is greater than a length of the first wing portion in the radial direction. 
     The at least one developing device may be a black developing device for developing a black toner image. 
     Exemplary embodiments can also provide a developing device including a developing unit to supply a toner to an electrostatic latent image formed on an photosensitive body and developing the electrostatic latent image, a first toner containing unit that is disposed in one side with respect to an optical path of light irradiated to the photosensitive body and contains a toner to be supplied to the developing unit, a second toner containing unit that is disposed in another side with respect to the optical path and contains a toner, and a connecting unit to connect the first and second toner containing units. 
     The developing unit may be disposed on a downstream region from the first toner containing unit with respect to a proceeding direction of the light. 
     A waste toner containing unit to contain waste toner removed from the photosensitive body may be disposed in the other side, and the waste toner containing unit may be disposed on a downstream region from the second toner containing unit with respect to the proceeding direction of the light. The connecting unit may be disposed outside an effective width of the optical path. 
     A bottom portion of the second toner containing unit may be inclined downwardly toward the connection unit. 
     The second toner containing unit may include an agitating member for agitating a toner toward a supplying path of the toner. 
     The agitating member may include a rotation axis that extends in a width direction of the second toner containing unit and an agitating wing disposed on the rotation axis, where the agitating wing may include a first wing portion and a second wing portion adjacent to the connecting unit, and a length of the second wing portion in a radial direction may be greater than a length of the first wing portion in the radial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other features and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic structural view illustrating an electrophotographic image forming apparatus according to exemplary embodiments of the present general inventive concept; 
         FIG. 2  is a cross-sectional view illustrating a detailed structure of a developing device, according to exemplary embodiments of the present general inventive concept; 
         FIG. 3  is a diagram illustrating intervals between a plurality of photosensitive drums, according to exemplary embodiments of the present general inventive concept; 
         FIGS. 4A-4B  are cross-sectional views illustrating a detailed structure of a second developing device, according to exemplary embodiments of the present general inventive concept; 
         FIG. 5A  is a partial perspective view illustrating the shape of a connecting unit of a second toner containing unit and  FIG. 5B  is a partial perspective view illustrating a first toner containing unit without the second toner containing unit attached thereto, according to exemplary embodiments of the present general inventive concept; 
         FIG. 6  is a cross-sectional view illustrating a bottom portion of a second toner containing unit, according to exemplary embodiments of the present general inventive concept; 
         FIG. 7  is a perspective view illustrating a second agitating member according to exemplary embodiments of the present general inventive concept; 
         FIG. 8  is a cross-sectional view illustrating a bottom portion of a second toner containing unit according to exemplary embodiments of the present general inventive concept; and 
         FIG. 9  is a perspective view illustrating a second agitating member according to exemplary embodiments of the present general inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a developing device and an electrophotographic image forming apparatus including the developing device will be described with regard to exemplary embodiments of the invention with reference to the attached drawings. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, where like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept while referring to the figures. 
       FIG. 1  is a schematic structural view illustrating an electrophotographic image forming apparatus according to exemplary embodiments of the present general inventive concept. The electrophotographic image forming apparatus can be an electrophotographic color image forming apparatus to print a color image by using an electrophotographic method. 
       FIG. 1  illustrates a plurality of photosensitive drums  1 Y,  1 M,  1 C, and  1 K, a plurality of developing devices  10 Y,  10 M,  10 C, and  10 K, and an intermediate transfer belt  30 . Each photosensitive drum  1  is, for example, a photosensitive body having a surface on which an electrostatic latent image is formed and may include a conductive metal pipe and a photosensitive layer formed on an outer circumferential surface thereof. Hereinafter, the photosensitive drums  1 Y,  1 M,  1 C, and  1 K may be collectively referred to as the photosensitive drums  1  and the developing devices  10 Y,  10 M,  10 C, and  10 K may be collectively referred to as the developing devices  10 . 
     The developing devices  10  may respectively correspond to the photosensitive drums  1 . Each developing device  10  may form a toner image on a surface of the photosensitive drum  1  by supplying and developing toner to an electrostatic latent image formed on the photosensitive drum  1 . Each of the developing devices  10  may be replaced with a new developing device, without replacing the photosensitive drums  1 . In addition, the developing devices  10  may be cartridges respectively including the photosensitive drums  1 . 
     In order to print a color image, the developing devices  10  may include the developing device  10 Y to contain a toner of yellow (Y), the developing device  10 M to contain a toner of magenta (M), the developing device  10 C to contain a toner of cyan (C), and the developing device  10 K to contain a toner of black (K). However, the exemplary embodiments of the present general inventive concept are not limited to this case and thus the developing devices  10  may include developing devices to contain various colors such as light magenta, white, or the like in addition to the above-described colors. Further, according other exemplary embodiments of the present general inventive concept, the developing devices  10  may include developing devices to contain various colors such as light magenta, white, or the like instead of one or more of the above-described colors. For example, the developing devices  10  may include a developing device to contain a toner for yellow, a developing device to contain a toner for magenta, a developing device to contain a toner for white, and a developing device to contain a toner for black. Hereinafter, a case where the electrophotographic image forming apparatus includes the developing devices  10 Y,  10 M,  10 C, and  10 K will be described. Unless otherwise indicated herein, elements marked together with Y, M, C, and K refer to elements for printing images by using toners of Y, M, C, and K colors, respectively. 
     An exposer  20  may respectively form electrostatic latent images corresponding to images of Y, M, C, and K on the photosensitive drums  1 Y,  1 M,  1 C, and  1 K by irradiating light that is modulated to correspond to image information to the photosensitive drums  1 Y,  1 M,  1 C, and  1 K, which will be described later. Examples of the exposer  20  may include a laser scanning unit (LSU) using a laser diode as a light source, a light emitting diode (LED) exposer using an LED as a light source, and the like. 
     The intermediate transfer belt  30  is an example of a transfer medium. Toner images of Y, M, C, and K respectively developed on the photosensitive drums  1 Y,  1 M,  1 C, and  1 K are temporally accommodated on the intermediate transfer belt  30  prior to being transferred to a recording medium P. The intermediate transfer belt  30  may be supported by, for example, supporting rollers  31  and  32  and may rotate around the supporting rollers  31  and  32 . 
     A plurality of first transfer rollers  40 Y,  40 M,  40 C, and  40 K are arranged to respectively face the photosensitive drums  1 Y,  1 M,  1 C, and  1 K, where the intermediate transfer belt  30  is interposed between the photosensitive drums  1 Y,  1  M,  1 C, and  1 K and the first transfer rollers  40 . The first transfer rollers  40  are, for example, first transferring devices to transfer the toner images to the intermediate transfer belt  30  from the photosensitive drums  1 Y,  1 M,  1 C, and  1 K, respectively. An intermediate transfer bias voltage is applied to the first transfer rollers  40  by a power supply (not illustrated) so as to transfer the toner images developed on the photosensitive drums  1  to the intermediate transfer belt  30 . The first transfer rollers  40 Y,  40 M,  40 C, and  40 K and the photosensitive drums  1 Y,  1 M,  1 C, and  1 K may be in pressing contact to each other, respectively, with the intermediate transfer belt  30  disposed therebetween. Instead of the first transfer rollers  40 , a corona transferring device or a pin scorotron transferring device may be used. 
     A second transfer roller  50  is an example of a second transferring device to transfer the toner images from the intermediate transfer belt  30  to the recording medium P. The second transfer roller  50  may be disposed to face the supporting roller  31 , where the intermediate transfer belt  30  is disposed between the second transfer roller  50  and the supporting roller  31 . A transfer bias voltage is applied to the second transfer roller  50  by the power supply so as to transfer the toner images transferred to the intermediate transfer belt  30  to the recording medium P. The second transfer roller  50  and the supporting roller  31  may be in pressing contact to each other, with the intermediate transfer belt  30  disposed therebetween. Instead of the second transfer roller  50 , a corona transferring device or a pin scorotron transferring device may be used. 
     A pickup roller  71  may pick up the recording medium P on a sheet-by-sheet basis from a loading board  70 . A set of feed rollers  72  may feed the recording medium P to a transfer region where the second transfer roller  50  and the intermediate transfer belt  30  face each other. 
     The electrophotographic image forming apparatus of  FIG. 1  transfers the toner images developed on the photosensitive drums  1 Y,  1 M,  1 C, and  1 K to the intermediate transfer belt  30  and then transfers the toner images to the recording medium P passing between the intermediate transfer belt  30  and the second transfer roller  50 . However, the present general inventive concept is not limited to this case. Alternatively, the toner images may be directly transferred from the photosensitive drums  1 Y,  1 M,  1 C, and  1 K, respectively, to the recording medium P, without using the intermediate transfer belt  30 . In this case, the second transfer roller  50  may not be equipped, a paper moving belt (not illustrated) to move the recording medium P while maintaining the recording medium P on a surface thereof by an electrostatic force may be used instead of the intermediate transfer belt  30 , and the recording medium P may be a transfer medium. 
     A fuser  60  fuses an image transferred to the recording medium P by applying heat and/or pressure to the image. A shape of the fuser  60  is not limited to  FIG. 1 . The recording medium P passing through the fuser  60  is discharged by a discharge roller  73 . 
       FIG. 2  is a cross-sectional view illustrating a detailed structure of a developing device  10 , according to exemplary embodiments of the present general inventive concept. Referring to  FIG. 2 , the developing device  10  may include a first toner containing unit  100 , a developing unit  200 , and a waste toner containing unit  300 . 
     The first toner containing unit  100  may contain toner to provide to the developing unit  200 . The developing unit  200  forms a toner image by supplying toner provided by the first toner containing unit  100  to an electrostatic latent image formed on a photosensitive drum  1 . The waste toner containing unit  300  contains waste toner, impurities, or the like that is removed from a surface of the photosensitive drum  1 . 
     A developing roller  5  may be installed in the developing unit  200 . The developing roller  5  supplies toner contained in the developing device  10  to the photosensitive drum  1 . A developing bias voltage may be applied to the developing roller  5  by the power supply. A regulating member  6  regulates the amount of toner supplied to a developing region where the photosensitive drum  1  and the developing roller  5  face each other by the developing roller  5 . 
     When a dual-component developing method is used, a magnetic carrier and a toner are contained in the developing device  10 , and the developing roller  5  is spaced apart from the photosensitive drum  1  by, for example, several tens to several hundreds of microns. Although not illustrated in  FIG. 2 , the developing roller  5  may be a magnetic roller. Also, the developing roller  5  may include a developing sleeve and a magnetic roller disposed in the developing sleeve. The toner in the developing device  10  is attached to a surface of the magnetic carrier. The magnetic carrier with the toner attached thereto is attached to a surface of the developing roller  5  and is moved to the developing region where the photosensitive drum  1  and the developing roller  5  face each other. Only the toner is supplied from the developing roller  5  to the photosensitive drum  1  without the magnetic carrier by the developing bias voltage applied between the developing roller  5  and the photosensitive drum  1  by the power supply, and thus the electrostatic latent image formed on the surface of the photosensitive drum  1  is developed to a visible toner image. When a mono-component developing method is used, the developing roller  5  may contact the photosensitive drum  1  and rotate. Alternatively, while the developing roller  5  rotates, the developing roller  5  may be spaced apart from the photosensitive drum  1  by, for example, several tens to several hundreds of microns. 
     A supplying roller  7  to attach toner to the surface of the developing roller  5  may be installed in the developing unit  200 . A supplying bias voltage may be applied to the supplying roller  7  by the power supply. An agitator  8  may be installed in the developing unit  200 . The agitator  8  may agitate the toner to charge the toner with triboelectricity and may move the toner toward the supplying roller  7 . An example of the agitator  8  may include a paddle. 
     When a dual-component developing method is used, the agitator  8  may mix and agitate the toner contained in the developing unit  200  with the magnetic carrier, and may move the mixture of the toner and the magnetic carrier to the developing roller  5 . In this case, the agitator  8  may be an auger to move the toner and the carrier in a widthwise direction W (see  FIG. 5B ) of the developing device  10  and the developing unit  200  may include a plurality of agitators  8 . 
     A charging roller  2  charges the photosensitive drum  1  to have a uniform surface potential. Instead of the charging roller  2 , a charging brush, a corona charger, or the like may be used. A charging roller cleaner  3  removes impurities such as toner, dust, or the like attached to a surface of the photosensitive drum  1 , the charging roller  2 , and the like. 
     A cleaning blade  4  removes waste toner and impurities that remain on the surface of the photosensitive drum  1  after an intermediate transfer process is performed. Instead of the cleaning blade  4 , a different type of cleaning device such as a rotatable brush or the like may be used. Waste toner and impurities removed from the surface of the photosensitive drum  1  are contained in the waste toner containing unit  300 . 
     With respect to light  12  irradiated from the exposer  20  to the photosensitive drum  1 , the developing unit  200  and the first toner containing unit  100  are disposed at one side (e.g., a left side), and the waste toner containing unit  300  is disposed at another side (e.g., a right side). Thus, an optical path  11  through which the light  12  passes is formed between a set of the developing unit  200  and the first toner containing unit  100 , and the waste toner containing unit  300 . The optical path  11  extends in a vertical direction. The light  12  is irradiated from above the photosensitive drum  1 . The first toner containing unit  100  may be disposed above the developing unit  200  with respect to the direction of gravity so that toner may be smoothly supplied from the first toner containing unit  100  to the developing unit  200  by gravity. With respect to a proceeding direction of the light  12 , the developing unit  200  is disposed on a region downstream from the first toner containing unit  100 . By disposing the first toner containing unit  100  above the developing unit  200 , the amount of toner contained in the first toner containing unit  100  may be increased without increasing a length L of the electrophotographic image forming apparatus, as such arrangement of the first toner containing unit  100  does not increase a length L 1  of the developing device  10 . A first agitating member  510  may be installed in the first toner containing unit  100  so as to agitate toner and to supply the toner to the developing unit  200 . 
     Thus far, an example of a developing method of an image forming apparatus according to an embodiment of the present general inventive concept has been described. However, the present general inventive concept is not limited to this case. The developing method may be modified and changed in various ways. 
     By the above-described structure, the exposer  20  may respectively scan a plurality of light beams modulated to correspond to image information of colors to the photosensitive drums  1 Y,  1 M,  1 C, and  1 K to form electrostatic latent images. The developing devices  10 Y,  10 M,  10 C, and  10 K may respectively supply toners of Y, M, C, and K to the electrostatic latent images formed on the photosensitive drums  1 Y,  1 M,  1 C, and  1 K to respectively form visible toner images of Y, M, C, and K on the photosensitive drums  1 Y,  1 M,  1 C, and  1 K. The toner images of Y, M, C, and K are sequentially transferred to the intermediate transfer belt  30  by the intermediate transfer bias voltage applied to the first transfer rollers  40  by the power supply. The recording medium P loaded on the loading board  70  is moved between the second transfer roller  50  and the intermediate transfer belt  30  by the pickup roller  71  and the moving roller  72 . The toner images of Y, M, C, and K transferred to the intermediate transfer belt  30  are transferred to the recording medium P by a transfer bias voltage applied to the second transfer roller  50  by the power supply. When the recording medium P passes through the fuser  60 , the toner images are fused onto the recording medium P by heat and pressure. The recording medium P on which the toner images are completely fused is discharged to a tray  74  by the discharge roller  73  from the fuser  60 . When duplex printing is performed, the recording medium P, after having passed through the fuser  60  to print an image on one surface of the recoding medium P, is guided to a duplex printing path  80 . Thus, the recording medium P is supplied between the intermediate transfer belt  30  and the second transfer roller  50  again. Another image is transferred to a rear surface of the recording medium P as the recording medium P passes between the intermediate transfer belt  30  and the second transfer roller  50  again. The recording medium P is discharged to the tray  74  by the discharge roller  73  after having been passed through the fuser  60  again to fuse the toner images on the rear surface of the recording medium P. 
     Different colors of toners are contained in the first toner containing units  100  of the developing devices  10 Y,  10 M,  10 C, and  10 K, respectively. When the toners are exhausted, the toners need to be refilled. The toner of each developing device  10  may be refilled by supplying the toner to the first toner containing unit  100 , or changing only the first toner containing unit  100 , or changing the developing device  10  itself, or the like. 
     With regard to a color image forming apparatus, one color may be more frequently used than other colors. For example, a text document of a single color (e.g., a black color) may be more frequently printed. That is, if a toner of the black color is used most frequently in printing, the toner of the developing device  10 K is refilled most frequently, and thus a replacement cycle of the developing device  10 K is the shortest from among the developing devices  10 Y,  10 M,  10 C, and  10 K. In order to increase the replacement cycle of the developing device K, the size of the developing device  10 K needs to be increased so as to contain as large an amount of black toner as possible. For example, the amount of black toner contained in the first toner containing unit  100  may be increased by extending the first toner containing unit  100  of the developing device  10 K upward or in a longitudinal direction. However, in this case, a height H or the length L of the image forming apparatus may be increased due to the increased size of the first toner containing unit  100  of the developing device  10 . With regard to a single-path type color image forming apparatus illustrated in  FIG. 1 , toners of Y, M, C, and K are sequentially developed and transferred. When an interval P 1  between the photosensitive drums  1 Y and  1 M, an interval P 2  between the photosensitive drums  1 M and  1 C, and an interval P 3  between the photosensitive drums  1 C, and  1 K are equal to one another, as illustrated in  FIG. 3 , a point of time to begin development and transfer of the toners to the intermediate transfer belt  30  can be controlled. However, when the first toner containing unit  100  of the developing device  10 K is extended in a longitudinal direction, the interval P 3  between the photosensitive drums  1 C and  1 K may be greater than each of the interval P 1  between the photosensitive drums  1 M and  1 C and the interval P 2  between the photosensitive drums  1 M, and  1 C, and thus it may be complicated to control a point of time to begin development and transfer of the toner to the intermediate transfer belt  30 . Thus, there is a need for increasing a capacity to contain the toner in the developing device  10 K while minimizing the size of the image forming apparatus. In addition, there is a need for increasing a capacity to contain the toner in the developing device  10 K while maintaining the intervals P 1 , P 2 , and P 3  between the photosensitive drums  1 Y,  1 M,  1 C, and  1 K to be equal to one another. 
     Hereinafter, the developing devices  10 Y,  10 M, and  10 C will be referred to as first developing devices  101  and the developing device  10 K will be referred to as a second developing device  102  in order to differentiate the developing devices  10 Y,  10 M, and  10 C, and the developing device  10 K. Similarly, the photosensitive drums  1 Y,  1 M, and  1 C may be referred to as first photosensitive drums, and the photosensitive drum  1 K may be referred to as a second photosensitive drum. 
     The first developing device  101  has the same structure as that illustrated in  FIG. 2 . The second developing device  102  may be disposed on a region downstream from the first developing device  101  with respect to a proceeding direction A of the intermediate transfer belt  30 . That is, as illustrated in  FIG. 1 , the second developing device  102  is disposed on a most downstream region with respect to the proceeding direction A. 
     An example of a structure of the second developing device  102  is illustrated in  FIGS. 4A and 4B . The structure of the second developing device  102  of  FIG. 4A  may be the same as the structure of the first developing device  101  of  FIG. 2 , except that the second developing device  102  of  FIG. 4A  further includes a second toner containing unit  400  and a connecting unit  410  to connect the second toner containing unit  400  and the first toner containing unit  100 . As illustrated in  FIG. 4A , with respect to the optical path  11 , the second toner containing unit  400  is disposed at the other side, that is, a side opposite to the first toner containing unit  100 . Toner is contained in the second toner containing unit  400 . The second toner containing unit  400  is disposed above the waste toner containing unit  300 . That is, with respect to the proceeding direction of the light  12 , the waste toner containing unit  300  is disposed on a region downstream from the second toner containing unit  400 . By this structure, the second toner containing unit  400  may be disposed in a space above the waste toner containing unit  300 , thereby increasing the amount of toner contained in the second developing device  102  without increasing the length (which corresponds to ‘L’ of  FIG. 1 ) of the image forming apparatus. The second toner containing unit  400  is disposed such that the height of the second toner containing unit  400  is substantially equal to the height of the first toner containing unit  100 , and thus the height H 2  is not increased by the second toner containing unit  400 . 
     Toner contained in the second toner containing unit  400  is supplied to the first toner containing unit  100  through the connecting unit  410 .  FIG. 5A  is a partial perspective view to illustrate the shape of the connecting unit  410 , according to an embodiment of the present general inventive concept. As illustrated in  FIG. 5A , the connecting unit  410  is disposed in a region outside an effective width W 1  of the optical path  11 . For example, connecting units  410  may be disposed in two regions outside the effective width W 1  of the optical path  11  (as illustrated in  FIG. 6 ). Alternatively, the connecting unit  410  may be disposed on only one region outside the effective width W 1  of the optical path  11  (as illustrated in  FIG. 8 ). A second agitating member  520  may be installed in the second toner containing unit  400 . The second agitating member  520  may include a rotation axis member  521  with a rotation axis  521 a and an agitating wing  522  that extends in a radial direction of the rotation axis member  521 . The agitating wing  522  may be made of a flexible material, so has, for example, a flexible film type of material. A length of the agitating wing  522  in the radial direction is determined such that the agitating wing  522  may flexibly contact an inner wall of the second toner containing unit  400  so as to move the toner in the second toner containing unit. The rotation axis member  521  extends in a width direction of the second toner containing unit  400 . When the second agitating member  520  rotates, toner contained in the second toner containing unit  400  may be moved to the first toner containing unit  100  through the connecting unit  410  by the agitating wing  522 . In order to easily supply the toner from the second toner containing unit  400  to the first toner containing unit  100 , at least a bottom portion  411  of the connecting unit  410  may be inclined downwards in a direction from the second toner containing unit  400  toward the first toner containing unit  100 . 
     The second agitating member  520  including the agitating wing  522 , which extends from the rotation axis  521  in the radial direction, moves the toners contained in the second toner containing unit  400  in a longitudinal direction of the second toner containing unit  400 , but does not move the toner in a width direction of the second toner containing unit  400 . Thus, there is a need for moving toner in the width direction in the second toner containing unit  400  so that the toner in the second toner containing unit  400  is in a location that corresponds to the connecting unit  410  (e.g., a location of the second toner containing unit  400  adjacent to the connecting unit  410 ). To achieve this, a separate mover may be disposed in the second toner containing unit  400  to move the toner in the width direction of the second toner containing unit  400 . However, according to the exemplary embodiments of the present general inventive concept, the toner may be moved in the width direction by the shape of the second toner containing unit  400  without using any separate mover, as described below. 
       FIG. 4B  illustrates an exemplary embodiment of the second developing device  102 , where the second toner containing unit  400  is detachable from the first toner containing unit  100 . In this embodiment, one end of the connecting unit  410  facing with an opening may be detachably connected to the first toner containing unit  100 . When the second toner containing unit  400  is detached from the first toner containing unit  100 , the second developing device  102  may have the same structure as the first developing device  101 , having only the first toner containing unit  100 . Thus, the image forming apparatus may be provided with developing devices with only the first toner containing units  100 , where each of the first toner containing units  100  can receive the second toner containing unit  400  via a receiving portion  110  to attach the second toner containing unit  400 . The second toner containing unit  400  may be attached or detached to the first toner containing unit  100 , depending on whether the color of the toner for the developing device is frequently used. For example, if it is determined that yellow color is used frequently, then a user can attach a second toner containing unit  400  for the yellow color to the first toner containing unit  100  in the developing device  10 Y for the yellow color. This provides flexibility by enabling a user to vary toner container capacities for different colors, depending on which color is more used. The receiving portion  110  of the first toner containing unit  100  and the connecting portion  410  of the second toner containing unit  400  may be provided with an engaging mechanism (e.g., a notch and a groove) to firmly engage the second toner containing unit  400  with the first toner containing unit  100 . 
       FIG. 5B  is a partial perspective view illustrating a first toner containing unit without the second toner containing unit attached thereto.  FIG. 5B  may be an exemplary embodiment of the second developing device  102  with the second toner containing unit  400  detached from the first toner containing unit  100 . Also,  FIG. 5B  may be an exemplary embodiment of the first developing device  101  having only the first toner containing unit  100 . As described above, the first toner containing unit  100  and the developing unit  200  disposed under the first toner containing unit  100  are disposed in one side, and the waste toner containing unit  300  is disposed in the other side, and the photosensitive drum  1  is disposed between the developing unit  200  and the waste toner containing unit  300 . The first toner containing unit  100  has the first agitating member  510  to agitate toner and to supply the toner to the developing unit  200 . The first toner containing unit  100  may have the receiving portion  110  to receive a connecting portion  410  of the second toner containing unit  400  to attach the second toner containing unit  400  to the first toner containing unit  100 . When the second toner containing unit  400  is not used, a cap  120  may be placed to cover the receiving portion  110 . The developing unit  200  has the agitator  8  that may be an auger to move the toner and the carrier in a widthwise direction W of the developing device. 
       FIG. 6  illustrates a cross-sectional view of the second toner containing unit  400  taken along a line Y-Y′ of  FIG. 4A , according to an embodiment of the present general inventive concept. Referring to  FIG. 6 , connecting units  410  are disposed in two regions R 1  and R 1  outside the effective width W 1  of the optical path  11 . In this case, the bottom portion  401  of the second toner containing unit  400  is inclined downward from a central portion thereof toward two lateral portions corresponding to the two regions R 1  and R 1 , that is, toward the connecting units  410 . When the second agitating member  520  rotates in the second toner containing unit  400 , the toner may flow via the second toner containing unit  400 . Toner is a very small particle and may have high liquidity. Thus, the toner that flows due to the second agitating member  520  may flow toward the two lateral portions where the connection units  410  are positioned, according to the inclination of the bottom portion  401  and a force of gravity. Since toner has high fluidity, the toner may easily flow toward the two lateral portions by using only a small inclination, such as an inclination of about 2 to about 3 mm from the central portion. The inclination of the bottom portion  401  may be shaped like a straight line shape or a curve line shape. By this structure, when the connecting units  410  are disposed in the two lateral portions of the second toner containing unit  400 , toner contained in the second toner containing unit  400  may be easily moved to the first toner containing unit  100  through the connecting units  410  by using the second agitating member  520  including the agitating wing  522  extending from the rotation axis member  521  in the radial direction. Referring to  FIG. 7 , the agitating wing  522  may include a first wing portion  523  and a second wing portion  524  next to the connecting units  410  to correspond with the connecting units  410 , respectively. The length of the second wing portion  524  in the radial direction is greater than the length of the first wing portion  523  in the radial direction. Thus, toner may be easily supplied to the connecting unit  410  while maintaining a low rotation load of the second agitating member  520 . 
     In exemplary embodiments of the present general inventive concept illustrated in  FIG. 8 , when the connecting unit  410  is disposed in one lateral portion R 1  only, the bottom portion  401  may be inclined downward from the other lateral portion toward the connecting unit  410 . In addition, as illustrated in  FIG. 9 , the second agitating member  520  may be configured such that the second wing portion  524  may be formed in one region only. 
     The volume of the waste toner containing unit  300  may be smaller than the volume of the first toner containing unit  100 . With respect to the optical path  11 , when the first toner containing unit  100  and the developing unit  200  disposed under the first toner containing unit  100  are disposed in one side, and the waste toner containing unit  300  is disposed in the other side, the waste toner containing unit  300  may occupy a space at almost the same level as the developing unit  200  in a vertical direction. Thus, a space above the waste toner containing unit  300 , that is, a space next to the first toner containing unit  100 , may correspond to a spare space. According to the exemplary embodiments of the present general inventive concept, the second toner containing unit  400  is disposed in the spare space and is connected to the first toner containing unit  100  by the connecting unit  410 , thereby increasing the amount of toner contained in the second developing device  102  without increasing the size of the image forming apparatus. For example, when the second toner containing unit  400  is formed such that a length L 1  (refer to  FIG. 2 ) of the first developing device  101  may be equal to a length L 2  of the second developing device  102 , the total length L (refer to  FIG. 1 ) of the image forming apparatus is not changed by the second toner containing unit  400 . In addition, when a height H 1  (refer to  FIG. 1 ) of the first developing device  101  is equal to a height H 2  (refer to  FIG. 4A ) of the second developing device  102  including the second toner containing unit  400 , the total height H (refer to  FIG. 1 ) of the image forming apparatus is not changed by the second toner containing unit  400 . 
     In exemplary embodiments of the present general inventive concept, in order to further increase the amount of toner contained in the second toner containing unit  400 , the second toner containing unit  400  may further extend in a longitudinal direction, as indicated by dotted lines of  FIG. 4A . That is, a length L 2 ′ of the second developing device  102  may be greater than the length L 1  (refer to  FIG. 2 ) of the first developing device  101 . In this case, a position of the photosensitive drum  1 K is not changed and only the second toner containing unit  400  extends in the longitudinal direction. That is, since the second developing device  102  is disposed on a region downstream from the first developing device  101  with respect to the proceeding direction A of the intermediate transfer belt  30 , although the position of the second toner containing unit  400  extends in the longitudinal direction, the position of the photosensitive drum  1 K may not be changed. Thus, as illustrated in  FIG. 3 , the intervals P 1 , P 2 , and P 3  between the photosensitive drums  1 Y,  1 M,  1 C, and  1 K may be maintained to be equal to each other. In this example, the waste toner containing unit  300  may be extended in a longitudinal direction, as indicated by dotted lines of  FIG. 4A , to an extent that the second toner containing unit  400  is extended. 
     While the present general inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made in these embodiments without departing from the spirit and scope of the present general inventive concept as defined by the following claims and their equivalents.