Patent Publication Number: US-9885975-B2

Title: Electrophotographic image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/677,308, filed on Apr. 2, 2015, which claims priority benefit from Korean Patent Application No. 10-2014-0067794, filed on Jun. 3, 2014 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. 
    
    
     BACKGROUND 
     1. Field 
     One or more embodiments relate to an electrophotographic image forming apparatus that forms an image on a recording medium by using electrophotography. 
     2. Description of the Related Art 
     An image forming apparatus using electrophotography prints an image on a recording medium by supplying toner to an electrostatic latent image formed on a photoreceptor to form a visible toner image on the photoreceptor, transferring the visible toner image onto the recording medium, and fusing the transferred visible toner image on the recording medium. 
     A process cartridge is an assembly of components for forming a visible toner image. The process cartridge is a consumable product that is detachable from a main body of an image forming apparatus and replaceable after lifespan thereof has ended. A process cartridge may have various structures such as a structure in which a photoreceptor, a development roller that supplies toner to the photoreceptor, and a container portion containing toner are integrally formed, a structure divided into an image cartridge including a photoreceptor and a development roller and a toner cartridge containing toner, or a structure divided into a photoreceptor cartridge including a photoreceptor, a development cartridge including a development roller, and a toner cartridge containing toner. 
     In a process cartridge having a structure including an imaging cartridge and a toner cartridge, the imaging cartridge has a structure in which a photoreceptor unit including a photoreceptor and a development unit including a development roller are connected to each other. 
     SUMMARY 
     In an aspect of one or more embodiments, there is provided an electrophotographic image forming apparatus whereby a stable image quality may be obtained during the lifetime of a process cartridge by reducing toner stress in a development unit. 
     In an aspect of one or more embodiments, there is provided an electrophotographic image forming apparatus which includes: a toner supply unit that includes a toner containing unit and a toner discharging unit in which a toner outlet is provided; a photoreceptor unit including a photoreceptor on which an electrostatic latent image is formed; a development unit including a development roller that supplies toner to the electrostatic latent image to develop the electrostatic latent image and a supply roller that supplies toner received from the toner containing unit via the toner outlet to the development roller; a first toner supply member that supplies toner of the toner containing unit to the toner discharging unit; and a second toner supply member that transports toner of the toner discharging unit to the toner outlet, wherein the first toner supply member is located in a second quadrant from among first through fourth quadrants which are determined based on a vertical line and a horizontal line which intersect at the second toner supply member as the origin, and wherein the photoreceptor and the supply roller and the development roller are located in the fourth quadrant. 
     The photoreceptor may be exposed by light that passes through the first quadrant. 
     The toner supply unit may include a waste toner containing unit in which waste toner removed from the photoreceptor is accommodated and a waste toner dispersing member that is disposed in the waste toner containing unit and disperses waste toner, and the waste toner dispersing member may be located in the third quadrant. 
     The development unit may further include: a toner inlet facing the toner outlet and a first toner transporting member that transports toner supplied through the toner inlet in an axial direction of the supply roller and a toner supply guide that is disposed between the first toner transporting member and the supply roller and includes a slit which has a length in the axial direction and through which toner is dropped onto the supply roller, wherein the first toner transporting member is located in the fourth quadrant. 
     The development unit may further include a second toner transporting member that stirs toner in the development unit to supply the toner in the development unit to the supply roller, and the second toner transporting member may be located in the third quadrant. 
     The slit may be disposed upstream of a contact area between the supply roller and the development roller with respect to a rotational direction of the supply roller. 
     At least a portion of a projection area of the slit may overlap with a projection area of the supply roller in a gravitational direction. 
     The slit may be inclined with respect to the axial direction. 
     The slit may include a plurality of slits arranged in the axial direction. 
     Among the plurality of slits, an opening area of a slit located further away from the toner inlet may be greater than an opening area of a slit located closer to the toner inlet. 
     Respective opening areas of the plurality of slits may increase with distance from the toner inlet. 
     The toner supply guide may be downwardly inclined from a first end portion close to the toner inlet to a second end portion that is opposite to the first end portion. 
     The first toner transporting member may include a rotational shaft and a spiral wing, the spiral wing may include a first spiral wing that is close to the toner inlet and a second spiral wing that is disposed downstream of the first spiral wing with respect to a toner transportation direction, and a pitch of the first spiral wing may be smaller than a pitch of the second spiral wing. 
     A spiral direction of the first spiral wing may be the same as a spiral direction of the second spiral wing. 
     The spiral wing may further include a third spiral wing that is disposed downstream of the second spiral wing with respect to the toner transportation direction, and a spiral direction of the third spiral wing may be opposite to the spiral direction of the first spiral wing. 
     The electrophotographic image forming apparatus may further include a toner level detecting unit that detects a toner level of the development unit. 
     The toner level detecting unit may include: a light emitting unit; a first light guide member that includes a light exit surface through which light that is emitted from the light emitting unit is transmitted; a second light guide member that includes a light incident surface that is spaced apart from and faces the light exit surface, wherein the light transmitted through the light exit surface is incident to the light incident surface; and a light receiving unit that detects the incident light. 
     The light emitting unit and the light receiving unit may be disposed outside the development unit, and the light exit surface and the light incident surface may be disposed inside the development unit. 
     The electrophotographic image forming apparatus may further include: a second toner transporting member that rotates to supply toner of the development unit to the supply roller; and a wiper that is mounted in the second toner transporting member and periodically wipes the light exit surface and the light incident surface. 
     When a radius of the supply roller is r 1 , a radius of the development roller is r 2 , an axial distance between the supply roller and the development roller is D, r 1 =8.5 mm to 9.5 mm, and r 2 =9.5 mm to 10.5 mm, r 1 +r 2 −D may be 0.8 mm or smaller. 
     r 1 +r 2 −D may be 0.2 mm or greater. 
     The toner supply unit may be in the form of a replaceable toner cartridge. 
     The development unit and the photoreceptor unit may be in the form of a replaceable imaging cartridge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic structural diagram of an electrophotographic image forming apparatus according to an embodiment; 
         FIG. 2  illustrates replacement of a toner cartridge; 
         FIG. 3A  is a diagram of an arrangement of a photoconductive drum and a development roller according to a contact development method; 
         FIG. 3B  is a diagram of an arrangement of a photoconductive drum and a development roller according to a non-contact development method; 
         FIG. 4  is a cross-sectional view of a process cartridge according to an embodiment; 
         FIG. 5  is a plan view of a toner supply guide according to an embodiment; 
         FIG. 6  is a cross-sectional view illustrating a position relationship between a supply roller and a slit; 
         FIG. 7  is a cross-sectional view of the process cartridge cut along a line A-A′, wherein toner is supplied from a toner inlet portion to a development unit; 
         FIG. 8  is a plan view of a toner supply guide illustrated in  FIG. 7  according to an embodiment; 
         FIG. 9  is a cross-sectional view of a toner supply guide illustrated in  FIG. 7  according to an embodiment; 
         FIG. 10  is a plan view of a first toner transporting member according to an embodiment; 
         FIG. 11  is a partial cross-sectional perspective view of a development unit in which a toner level detecting unit is disposed; 
         FIG. 12  is a schematic structural diagram of a toner level detecting unit; and 
         FIG. 13  illustrates a position relationship between a supply roller and a development roller. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In the specification and drawings, elements having substantially the same functions and structures will be labeled with the same reference numerals. In this regard, embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, embodiments are merely described below, by referring to the figures, to explain aspects of the present description. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
       FIG. 1  is a schematic structural diagram of an electrophotographic image forming apparatus according to an embodiment. 
     Referring to  FIG. 1 , a main body  1  of the image forming apparatus and a process cartridge  2  are shown. The main body  1  includes an opening  11  providing a passage for the process cartridge  2  to be mounted in or removed from the main body  1 . A cover  12  closes or opens the opening  11 . The main body  1  includes an exposure unit  13 , a transfer roller  14 , and a fusing unit  15 . Also, the main body  1  includes a recording medium transfer structure for loading and transferring a recording medium P where an image is to be formed. 
     The process cartridge  2  may include a toner containing unit  101 , a photoconductive drum  21  having a surface on which an electrostatic latent image is formed, and a development roller  22  that receives toner from the toner containing unit  101  to supply the toner to the electrostatic latent image so as to develop the electrostatic latent image into a visible toner image. 
     The process cartridge  2  may have a first structure divided into an imaging cartridge  400  including the photoconductive drum  21  and the development roller  22  and a toner cartridge  100  including the toner containing unit  101 , a second structure divided into a photoreceptor cartridge  200  including the photoconductive drum  21 , a development cartridge  300  including the development roller  22 , and a toner cartridge  100  including the toner containing unit  101 , a third structure divided into a photoreceptor cartridge  200  and a development cartridge  300  including the toner containing unit  101 , or a fourth structure in which a photoreceptor cartridge  200 , a development cartridge  300 , and a toner cartridge  100  are integrally formed with one another. 
     In the process cartridge  2  having the first structure (or the second structure), when the toner cartridge  100  is mounted in the main body  1 , the toner cartridge  100  is connected to the imaging cartridge  400  (or the development cartridge  300 ). For example, when the toner cartridge  100  is mounted in the main body  1 , a toner discharging unit  102  of the toner cartridge  100  and a toner inlet portion  301  of the imaging cartridge  400  (or the development cartridge  300 ) are connected to each other. 
     For example, the process cartridge  2  according to the present embodiment has the first structure. The imaging cartridge  400  and the toner cartridge  100  may be individually attached to or detached from the main body  1 . The process cartridge  2  is a consumable product that is replaced after its lifespan expires. In general, the lifespan of the imaging cartridge  400  is longer than the lifespan of the toner cartridge  100 . When toner contained in the toner cartridge  100  is completely consumed, just the toner cartridge  100  may be individually replaced as illustrated in  FIG. 2 , and thus, costs for replacement of consumables may be reduced. Referring to  FIG. 2 , for example, a guide protrusion  100   a  is formed on a side portion of the toner cartridge  100 , and a guide rail  30  that guides the guide protrusion  100   a  may be provided in the main body  1 . The toner cartridge  100  may be guided via the guide rail  30  to be attached to or detached from the main body  1 . While not shown in the drawing, a guide unit that guides the imaging cartridge  400  is provided in the main body  1 . 
     The photoreceptor cartridge  200  includes the photoreceptor drum  21 . The photoconductive drum  21  is an example of a photoreceptor, an electrostatic latent image being formed on a surface thereof, and may include a conductive metal pipe and a photosensitive layer around the conductive metal pipe. A charging roller  23  is an example of a charger for charging the photoconductive drum  21  to have a uniform surface potential. A charging brush or a corona charger may be used instead of the charging roller  23 . A reference numeral  24  denotes a cleaning roller for removing foreign materials from a surface of the charging roller  23 . A cleaning blade  25  is an example of a cleaning unit for removing toner and foreign materials from a surface of the photoconductive drum  21  after a transfer process which will be described later. A cleaning unit having another shape, such as a rotating brush, may be used instead of the cleaning blade  25 . 
     The development cartridge  300  receives toner from the toner cartridge  100  and supplies the toner to the electrostatic latent image formed on the photoconductive drum  21  so that the electrostatic latent image formed on the photoconductive drum  21  is developed into the visible toner image. 
     Examples of a development method include a one-component development method in which toner is used and a two-component development method in which toner and a carrier are used. The process cartridge  2  according to the current embodiment uses a one-component development method. The development roller  22  is used to supply toner to the photosensitive drum  21 . A development bias voltage to supply toner to the photosensitive drum  21  may be applied to the development roller  22 . The one-component development method may be classified into a contact development method, wherein the development roller  22  and the photoconductive drum  21  are rotated while contacting each other, and a non-contact development method, wherein the development roller  22  and the photoconductive drum  21  are rotated by being spaced apart from each other by dozens to hundreds of microns.  FIG. 3A  is a diagram of an arrangement of the photoconductive drum  21  and the development roller  22  in the contact development method, and  FIG. 3B  is a diagram of an arrangement of the photoconductive drum  21  and the development roller  22  in the non-contact development method. Referring to  FIG. 3A , in the contact development method, a gap maintaining member  22 - 2   a  having a smaller diameter than the development roller  22  may be provided on each of both ends of a rotation shaft  22 - 1  of the development roller  22 . A contact amount of the development roller  22  to the photoconductive drum  21  is constrained by the gap maintaining member  22 - 2   a  which contacts the surface of the photoconductive drum  21 . A development nip N is formed as the development roller  22  contacts the photoconductive drum  21 . Referring to  FIG. 3B , in the non-contact development method, a gap maintaining member  22 - 2   b  having a larger diameter than the development roller  22  may be provided on each of the both ends of the rotation shaft  22 - 1  of the development roller  22 . A development gap g between the development roller  22  and the photoconductive drum  21  is constrained by the gap maintaining member  22 - 2   b  which contacts the surface of the photoconductive drum  21 . To maintain the development gap g and the development nip N, it is sufficient that the gap maintaining members  22 - 2   a  and  22 - 2   b  contact an object, and the gap maintaining members  22 - 2   a  and  22 - 2   b  do not necessarily have to contact the surface of the photoconductive drum  21 . 
     A regulator  26  regulates an amount of toner supplied from the development roller  22  to a development region where the photoconductive drum  21  and the development roller  22  face each other. The regulator  26  may be a doctor blade elastically contacting a surface of the development roller  22 . A supply roller  27  supplies toner in the process cartridge  2  to a surface of the development roller  22 . To this end, a supply bias voltage may be applied to the supply roller  27 . 
     When a two-component development method is used, the development roller  22  is spaced apart from the photoconductive drum  21  by dozens to hundreds of microns. Although not illustrated in the drawings, the development roller  22  may have a structure in which a magnetic roller is disposed in a hollow cylindrical sleeve. The toner is adhered to a surface of a magnetic carrier. The magnetic carrier is adhered to the surface of the development roller  22  to be transferred to the development region where the photoconductive drum  21  and the development roller  22  face each other. Only the toner is supplied to the photoconductive drum  21  according to the development bias voltage applied between the development roller  22  and the photoconductive drum  21 , and thus the electrostatic latent image formed on the surface of the photoconductive drum  21  is developed into the visible toner image. The process cartridge  2  may include an agitator (not shown) for mixing and stirring the toner and a carrier and transporting the mixture to the development roller  22 . The agitator may be, for example, an auger, and a plurality of agitators may be provided in the process cartridge  2 . 
     The exposure unit  13  forms the electrostatic latent image on the photoconductive drum  21  by irradiating light modulated according to image information to the photoconductive drum  21 . The exposure unit  13  may be a laser scanning unit (LSU) using a laser diode as a light source, or a light-emitting diode (LED) exposure unit using an LED as a light source. 
     The transfer roller  14  is an example of a transfer unit for transferring a toner image from the photoconductive drum  21  to the recording medium P. A transfer bias voltage for transferring the toner image to the recording medium P is applied to the transfer roller  14 . A corona transfer unit or a transfer unit using a pin scorotron method may be used instead of the transfer roller  14 . 
     The recording media P are picked up one by one from a loading table  17  by a pickup roller  16 , and are transferred by feed rollers  18 - 1  and  18 - 2  to a region where the photoconductive drum  21  and the transfer roller  14  face each other. 
     The fusing unit  15  applies heat and pressure to an image transferred to the recording medium P so as to fuse and fix the image on the recording medium P. The recording medium P that passed through the fusing unit  15  is discharged outside the main body  1  by a discharge roller  19 . 
     According to the above-described structure, the exposure unit  13  irradiates the light modulated according to the image information to the photoconductive drum  21  to develop the electrostatic latent image. The development roller  22  supplies the toner to the electrostatic latent image to form the visible toner image on the surface of the photoconductive drum  21 . The recording medium P loaded in the loading table  17  is transferred to the region where the photoconductive drum  21  and the transfer roller  14  face each other by the pickup roller  16  and the feed rollers  18 - 1  and  18 - 2 , and the toner image is transferred on the recording medium P from the photoconductive drum  21  according to the transfer bias voltage applied to the transfer roller  14 . After the recording medium P passes through the fusing unit  15 , the toner image is fused and fixed on the recording medium P according to heat and pressure. After the fusing, the recording medium P is discharged by the discharge roller  19 . 
     Hereinafter, the imaging cartridge  400 , the photoreceptor cartridge  200 , the development cartridge  300 , and the toner cartridge  100  will be respectively referred to as an imaging unit ( 400 ), the photoreceptor unit  200 , the development unit  300 , and a toner supply unit. The photoreceptor unit  200  and the development unit  300  may be connected to each other such that the development nip N or the development gap g is maintained. 
       FIG. 4  is a cross-sectional view of the process cartridge  2  according to an embodiment. Referring to  FIG. 4 , the development unit  300  is disposed below the toner containing unit  101  in a gravitational direction. According to this structure, toner contained in the toner containing unit  101  may be easily supplied to the development unit  300  due to gravity. 
     The toner contained in the toner containing unit  101  is discharged from the toner cartridge  100  through a toner outlet  107  provided at the toner discharging unit  102  and is supplied to the development unit  300  through a toner inlet  302  that is provided at the toner inlet portion  301  to face the toner outlet  107 . The toner outlet  107  is disposed at an end portion of the toner discharging unit  102  in a length direction thereof. The length direction of the toner discharging unit  102  and the toner inlet portion  301  refers to an axial direction of the photoconductive drum  21  and the development roller  22 . Hereinafter, the ‘length direction’ refers to the axial direction of the photoconductive drum  21 , the development roller  22 , and the supply roller  27 . 
     A first toner supply member  103  that supplies toner to the toner discharging unit  102  is disposed in the toner containing unit  101 . A second toner supply member  104  that transports toner to the toner outlet  107  disposed at the end portion of the toner discharging unit  102  is disposed in the toner discharging unit  102 . The first toner supply member  103  radially transports the toner to supply the same to the toner discharging unit  102 . For example, a rotating paddle may be used as the first toner supply member  103 . The second toner supply member  104  transports the toner supplied by using the first toner supply member  103  in the length direction. For example, an auger may be used as the second toner supply member  104 . 
     A first toner transporting member  41  that transports toner in the length direction may be disposed in the toner inlet portion  301 . For example, an auger may be used as the first toner transporting member  41 . A toner supply guide  50  that extends in the length direction is disposed under the first toner transporting member  41 . The toner supply guide  50  is disposed above the supply roller  27  in a gravitational direction. For example, the toner supply guide  50  may have a shape surrounding a lower portion of the first toner transporting member  41  disposed thereinside. A slit  51  is formed in the toner supply guide  50 . Toner that is transported by using the first transporting member  41  in the length direction drops into the inner space of the development unit  300  through the slit  51 . The toner may immediately drop on a surface of the supply roller  27  and part of the toner may drop into the inner space of the development unit  300 . 
     A second toner transporting member  42  may be further disposed in the development unit  300 . The second toner transporting member  42  supplies to the supply roller  27  again the toner that is not immediately supplied from the toner inlet  302  to the surface of the supply roller  27  and is supplied to the development chamber  45  and toner that is separated from the surface of the supply roller  27 . For example, a paddle that radially transports toner may be used as the second toner transporting member  42 . 
     A waste toner discharging member  43  is included, which transports in an axial direction waste toner that is removed from a surface of the photoconductive drum  21  by using the cleaning blade  25  after transferring, to an end portion of the waste toner accommodation space  44 . The waste toner is carried to a waste toner containing unit  120  that is provided in the toner containing unit  101  via a waste toner transporting unit  45  that connects the waste toner accommodation space  44  and the waste toner containing unit  120 . The waste toner containing unit  120  is provided below the toner containing unit  101  in a gravitational direction. Accordingly, a difference in heights of the waste toner transporting member  42  and the waste toner containing unit  120  may be kept small so as to stably and effectively transporting waste toner to the waste toner containing unit  120 . A waste toner dispersing member  121  that disperses the waste toner inside the waste toner containing unit  120  may be disposed in the waste toner containing unit  120 . 
     As illustrated in  FIG. 4 , the process cartridge  2  may be divided into four quadrants Q 1 , Q 2 , Q 3 , and Q 4  by a vertical line Lv and a horizontal line Lh which intersect at the second toner supply member  104  as the origin. When the toner containing unit  101  and the first toner supply member  103  are located in the second quadrant Q 2 , the supply roller  27 , the development roller  22 , and the photoconductive drum  21  are located in the fourth quadrant Q 4  that is in a diagonal direction to the second quadrant Q 2 . According to this structure, toner may be spontaneously supplied from the toner containing unit  101  to the development unit  300  due to gravity. The waste toner containing unit  120  and the waste toner dispersing member  121  are located in the third quadrant Q 3  below the second quadrant Q 2 . According to this structure, a step between the waste toner discharging member  43  and the waste toner containing unit  120  in a gravitational direction may be reduced, and thus, the waste toner removed from the photoconductive drum  21  may be easily transported to the waste toner containing unit  120 . The first toner transporting member  41  is located in the fourth quadrant Q 4 . A capacity of the waste toner containing unit  120  is relatively small compared to that of the toner containing unit  101 . Accordingly, the inner space of the development unit  300  extends from the fourth quadrant Q 4  to the third quadrant Q 3 , and the second toner transporting member  42  is disposed in the extended portion. That is, the second toner transporting member  42  is located in the third quadrant Q 3 . Accordingly, the development unit  300  and the photoreceptor unit  200  may be efficiently arranged in the third quadrant Q 3  and the fourth quadrant Q 3  so as to reduce a length of the process cartridge  2  or the imaging unit (imaging cartridge)  400 . Light B that exposes the photoconductive drum  21  passes through the first quadrant Q 1  and is incident on the photoconductive drum  21 . 
       FIG. 5  is a plan view of the toner supply guide  50  according to an embodiment. Referring to  FIG. 5 , a slit  51  is inclined with respect to the length of the toner supply guide  50 , that is, with respect to the length direction of the supply roller  27 . An amount of toner supplied to the supply roller  27  through the slit  51  is proportional to an area of an opening of the slit  51 . According to the structure of  FIG. 5 , by using the toner supply guide  50  including the slit  51  that is inclined, a length of the slit  51  may be longer than a length of the toner supply guide  50 , and thus, an opening area of the slit  51  may be increased. Accordingly, toner may be easily and stably supplied to the supply roller  27 . 
       FIG. 6  is a cross-sectional view illustrating a position relationship between the supply roller  27  and the slit  51 . Referring to  FIG. 6 , the slit  51  is disposed above the supply roller  27  in a gravitational direction. At least a portion of a projection area B 1  of the slit  51  in the gravitational direction overlaps with a projection area B 2  of the supply roller  27  in the gravitational direction. The slit  51  is disposed upstream of a contact area B 3  located between the development roller  22  and the supply roller  27  with respect to a rotational direction of the supply roller  27 . According to the above-described structure, toner drops from the slit  51  onto the supply roller  27 , and thus, fresh toner supplied from the toner cartridge  100  may be immediately supplied to the development roller  22  through the supply roller  27 . Toner supplied from the toner cartridge  100  has a low degree of stress and thus an image may be stably formed by using the toner. Thus, degradation of toner properties due to stress and degradation in an image quality resulting therefrom may be prevented. 
     Also, the first toner transporting member  41  rotates in a direction  41   c  in which toner is supplied towards the contact area B 3  located between the supply roller  27  and the development roller  22 . Accordingly, toner that is transported along the toner supply guide  50  in the length direction by the first toner transporting member  41  drops into the development unit  300 , and a dropping direction thereof is spontaneously deviated toward the supply roller  27  according to the rotational direction  41   c  of the first toner transporting member  41 . Accordingly, fresh toner may be easily supplied to the supply roller  27 . 
       FIG. 7  is a cross-sectional view of the process cartridge  2  cut along a line A-A′, wherein toner is supplied via the toner inlet  302  to the development unit  300 .  FIG. 8  is a plan view of the toner supply guide  50  illustrated in  FIG. 7  according to an embodiment.  FIG. 9  is a cross-sectional view of the toner supply guide  50  illustrated in  FIG. 7  according to an embodiment. 
     Referring to  FIGS. 4, 7, and 8 , the slit  51  includes a plurality of slits  51 - 1  through  51 - n  that are arranged in the length direction. The plurality of slits  51 - 1  through  51 - n  are inclined with respect to the length direction, that is, with respect to an axial direction  27   a  of the supply roller  27 . An amount of toner that is supplied to the supply roller  27  through the slit  51  is proportional to an opening area of the slit  51 . According to the structure illustrated in  FIG. 8 , by using the toner supply guide  50  including the plurality of slits  51 - 1  through  51 - n  that are inclined with respect to the axial direction  27   a  of the supply roller  27 , the opening area of the plurality of slits  51 - 1  through  51 - n  may be increased, thereby easily and stably supplying toner to the supply roller  27 . 
     The plurality of slits  51 - 1  through  51 - n  each include an overlapping portion  52  where adjacent slits  51 - 1  through  51 - n  overlap. As the overlapping portion  52  is provided, toner may be supplied without leaking to any area in the length direction of the supply roller  27 . 
     At least a portion of a projection area of the plurality of slits  51 - 1  through  51 - n  overlaps with a projection area of the supply roller  27  in a gravitational direction. The plurality of slits  51 - 1  through  51 - n  are located upstream of the contact area B 3  (see  FIG. 6 ) located between the supply roller  27  and the development roller  22  with respect to a rotational direction of the supply roller  27 . According to the above-described structure, fresh toner supplied from the toner cartridge  100  may be immediately supplied to the development roller  22  through the supply roller  27 , and thus, degradation in properties of toner due to stress and degradation in an image quality resulting therefrom may be prevented. 
     In order to obtain uniform image quality, an amount of toner that is supplied to the supply roller  27  has to be uniform in a length direction, that is, in the axial direction  27   a . Toner is supplied to the toner supply guide  50  through the toner inlet  302 , and is transported in the length direction of the toner supply guide  50  by using the first toner transporting member  41 . Thus, an amount of toner in the toner supply guide  50  may be larger towards the toner inlet  302 , and may be smaller away from the toner inlet  302 . Considering that the amount of toner in the toner supply guide  50  depends on the location of toner with respect to the toner inlet  302 , an opening area of the slit  51 - n  that is relatively far from the toner inlet  302  may be greater than an opening area of the slit  51 - 1  that is relatively close to the toner inlet  302 . Opening areas of the plurality of slits  51 - 1  through  51 - n  may be increased with distance from the toner inlet  302 . The plurality of slits  51 - 1  through  51 - n  may be divided into a plurality of groups, and opening areas of slits of the plurality of groups may be increased with distance from the toner inlet  302 . For example, a width W-n of the slit  51 - n  may be greater than a width W- 1  of the slit  51 - 1 . Widths W- 1  through W-n of the plurality of slits  51 - 1  through  51 - n  may be increased away from the toner inlet  302 . In addition, the plurality of slits  51 - 1  through  51 - n  may be divided into a plurality of groups, and, among the plurality of groups, a width of slits of a group that is relatively far from the toner inlet  302  may be increased to be greater than a width of slits of a group that is relatively close to the toner inlet  302 . 
     In order to provide toner to the supply roller  27  such that the toner amount is uniform in the length direction, a method in which toner is supplied to the toner supply guide  50  through the toner inlet  302  and transported easily in the length direction through the toner supply guide  50  may be considered. Referring to  FIG. 9 , the toner supply guide  50  may be downwardly inclined from first end portion  50 - 1  adjacent to the toner inlet  302  toward the second end portion  50 - 2  that is opposite thereto. That is, the toner supply guide  50  may be inclined downward at an angle θ. According to the above-described structure, toner may be easily transported from the first end portion  50 - 1  to the second end portion  50 - 2  of the toner supply guide  50  due to the influence of a gravitational force, and uniformity of an amount of toner supplied to the supply roller  27  in the length direction may be further increased. 
       FIG. 10  is a plan view of the first toner transporting member  41  according to an embodiment. Referring to  FIG. 10 , the first toner transporting member  41  includes a rotational shaft  41   a  and a spiral wing  41   b . When the first toner transporting member  41  rotates, toner is transported in the length direction along the spiral wing  41   b . The amount of transported toner increases as the pitch of the spiral wing  41   b  decreases. The first end portion  50 - 1  of the toner supply guide  50  is adjacent to the toner inlet  302 , and thus, a relatively large amount of toner may accumulate around the first end portion  50 - 1 . Thus, the toner around the first end portion  50 - 1  of the toner supply guide  50  needs to be quickly transported in the length direction. In order to increase an amount of toner transported near the first end portion  50 - 1  of the toner supply guide  50 , that is, around the toner inlet  302 , the pitch of the spiral wing  41   b  around the toner inlet  302  may be small. The spiral wing  41   b  may include a first spiral wing  41 - 1  and a second spiral wing  41 - 2  that are arranged in the length direction. A spiral direction of the first spiral wing  41 - 1  is the same as a spiral direction of the second spiral wing  41 - 2 . Accordingly, the first spiral wing  41 - 1  and the second spiral wing  41 - 2  transport toner in the same direction. The first spiral wing  41 - 1  is disposed adjacent to the toner inlet  302 , and the second spiral wing  41 - 2  is disposed downstream of the first spiral wing  41 - 1  with respect to a toner transportation direction. A pitch P 1  of the first spiral wing  41 - 2  is smaller than a pitch P 2  of the second spiral wing  41 - 2 . According to the above-described structure, toner supplied through the toner inlet  302  is quickly transported in the length direction, thereby limiting the amount of toner that accumulates around the toner inlet  302  and preventing a toner supply failure due to the accumulation of toner and degradation in an image quality due to the toner supply failure. 
     Referring to  FIG. 10  again, toner that is supplied through the toner inlet  302  is transported from the first end portion  50 - 1  to the second end portion  50 - 2  of the toner supply guide  50  via the first and second spiral wings  41 - 1  and  41 - 2 . When the toner reaches the second end portion  50 - 2  of the toner supply guide  50 , toner is not able to be transported further, and thus, toner may accumulate around the second end portion  50 - 2 . According to the present embodiment, the spiral wing  41   b  may further include a third spiral wing  41 - 3  that is disposed at the second end portion  50 - 2  of the toner supply guide  50 . A spiral direction of the third spiral wing  41 - 3  is opposite to those of the first and second spiral wings  41 - 1  and  41 - 2 . Accordingly, toner is transported in a reverse direction via the third spiral wing  41 - 3 , and toner accumulation at the second end portion  50 - 2  of the toner supply guide  50  may thereby be prevented. 
     To achieve a uniform image quality during the lifetime of the process cartridge  2 , a degree of toner stress which is the cause of degradation in the properties of toner is to be reduced. If toner stays for a long time in the inner space of the development unit  300 , the toner is stirred by the second toner transporting member  42  and receives stress. If too much toner exists in the development unit  300 , a toner pressure increases. The excessive toner pressure is the cause of an increase in toner stress and an increase in a driving load of the process cartridge  2 . Thus, by maintaining a toner level of the development unit  300  at a predetermined level such that new toner is supplied from the toner containing unit  101  to the development unit  300  only when the toner level drops below the predetermined level, stress applied to the toner may be reduced. 
     A toner level detecting unit  310  that detects a level of toner therein is disposed in the development unit  300 .  FIG. 11  is a partial cross-sectional perspective view of the development unit  300  in which the toner level detecting unit  310  is disposed.  FIG. 12  is a schematic structural diagram of the toner level detecting unit  310 . 
     Referring to  FIGS. 11 and 12 , the toner level detecting unit  310  includes a light emitting unit  313  and a light receiving unit  314 . Light  315  emitted from the light emitting unit  313  passes through the development unit  300  to be incident to the light receiving unit  314 . The light emitting unit  313  and the light receiving unit  314  are disposed outside the development unit  300  in order to prevent pollution thereof by toner. First and second light guide members  311  and  312  that guide the light  315  emitted from the light emitting unit  313  to pass through the development unit  300  up to the light receiving unit  314  are provided. The first and second light guide members  311  and  312  are spaced apart from each other in the development unit  300 . The first light guide member  311  guides the light  315  emitted from the light emitting unit  313  to the inner space of the development unit  300 . The second light guide member  312  guides the light  315  that has passed through the development unit  300  to the light receiving unit  314 . The first and second light guide members  311  and  312  respectively include first and second light path converting units  311   a  and  312   a . The first light path converting unit  311   a  reflects the light  315  emitted from the light emitting unit  313 , toward the second light path converting unit  312   a , and the second light path converting unit  312   a  reflects the incident light  315  toward the light receiving unit  314 . The first and second light guide members  311  and  312  may be formed of a light-transmissive material such that the light  315  may pass therethrough. The first and second light path converting units  311   a  and  312   a  may be, for example, inclined surfaces having a predetermined inclination angle. An inclination angle of the inclined surfaces may be, for example, an angle that satisfies a total internal reflection condition. 
     According to the above-described structure, an amount of light detected by the light receiving unit  314  is varied according to the toner level of the development unit  300 , and thus, the toner level in the development unit  300  may be detected based on the amount of light received by the light receiving unit  314 . When the toner level in the development unit  300  is lower than a predetermined reference level, the first toner supply member  103  and the second toner supply member  104  may be driven to supply toner from the toner cartridge  100  to the development unit  300 . Accordingly, excessive supply of toner to the development unit  300  and an increase in the toner pressure may be prevented to thereby reduce a stress applied to the toner. 
     The light exit surface  311   b  and the light incident surface  312   b  which face each other, of the first and second light guide members  311  and  312 , contact toner in the developing unit  300 . If the light exit surface  311   b  and the light incident surface  312   b  are polluted by the toner, it is difficult to reliably detect the toner level. Referring to  FIG. 11 , a wiper  316  that wipes the light exit surface  311   b  and the light incident surface  312   b  is provided in the development unit  300 . The wiper  316  periodically wipes the light exit surface  311   b  and the light incident surface  312   b  to remove toner attached on the light exit surface  311   b  and the light incident surface  312   b . According to an embodiment, the wiper  316  may be mounted at a rotational shaft  42 - 1  of the second toner transporting member  42  to rotate therewith and wipe the light exit surface  311   b  and the light incident surface  312   b . This structure may improve reliability of detection of the toner level. 
       FIG. 13  illustrates a position relationship between the supply roller  27  and the development roller  22 . Referring to  FIG. 13 , the supply roller  27  and the development roller  22  rotate in contact with each other. A contact nip N 2  is formed in the contact area B 3  located between the supply roller  27  and the development roller  22 . The greater the size of contact nip N 2 , the greater a frictional force between toner, the supply roller  27  and the development roller  22  at the contact nip N 2 , and thus, toner stress is increased. On the contrary, if the size of the contact nip N 2  is too small, a force for supplying toner to the development roller  22  is degraded. According to experiments, a force appropriate for supplying toner may be secured when the contact nip N 2  is 0.2 mm or greater. In addition, when a radius of the supply roller  27  is r 1 , a radius of the development roller  22  is r 2 , an axial distance between the supply roller  27  and the development roller  22  is D, r 1  is 9.5 mm to 10.5 mm, r 2  is 8.5 mm to 18.6 mm, and the contact nip N 2 , r 1 +r 2 −D is 0.8 mm or smaller, no excessive toner stress results and a stable image quality may be obtained during the lifetime of the process cartridge  2 . That is, by setting the contact nip N 2  to be from about 0.2 mm to about 0.8 mm, a force for supplying toner applied from the supply roller  27  to the development roller  22  may be secured, and at the same time, a toner stress may be kept at an appropriate level or lower. 
     While the process cartridge  2  having the first structure is described with reference to the above-described embodiments, embodiments are not limited thereto. The process cartridge  2  according to embodiments may also have a second, third, or fourth structure. In this case, a ‘cartridge’ may refer to the imaging cartridge  400  having the first structure, the developing cartridge  300  having the second structure, the developing cartridge  300  having the third structure including the toner containing unit  101 , or the process cartridge  2  having the fourth structure. 
     It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. 
     While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims and their equivalents.