Patent Publication Number: US-7711291-B2

Title: Developing device with developer guide member and image forming apparatus

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
   The present invention relates to a developing device and an image forming apparatus. 
   In a conventional image forming apparatus such as a printer, a copier, and a facsimile, an image is formed through the following process. First, a charge roller charges a surface of a photosensitive drum. An exposure device such as an LED head exposes the surface of the photosensitive drum to form a static latent image or a latent image thereon. A developing roller attaches a thin layer of toner to the static latent image to form a toner image. A transfer roller transfers the toner image to a sheet or a recording medium, thereby forming an image or printing on the recording medium. A developing device is formed of the photosensitive drum, the charge roller, the developing roller, and so on. 
   After transferring the toner image, the sheet is transported to a fixing device, so that the fixing device fixes the toner image to the sheet. 
   In the conventional image forming apparatus described above, the developing device is provided with a developing device main body and a toner cartridge detachably attached to the developing device main body. The toner cartridge supplies toner to the developing device main body through a toner supply opening thereof. When the toner cartridge is removed from the developing device main body, toner sticking to a surrounding area of the toner supply opening may drop, thereby making inside the image forming apparatus dirty. To this end, the toner supply opening tends to have a small opening and be formed at a center portion of each of the toner cartridge and the developing device main body. 
   As described above, in the conventional developing device, the toner supply opening is formed at a center portion of each of the toner cartridge and the developing device main body. Accordingly, toner tends to drop only at a specific location inside the developing device. Especially, in the developing device before being used or after toner is detected to be a low level, when the toner cartridge is attached to the developing device main body and supplies toner, a large amount of toner is supplied at a center portion of the developing device main body, and a small amount of toner is supplied at both side portions thereof. Accordingly, it is difficult to uniformly supply toner along a longitudinal direction of the developing device, that is, a width direction of the image forming apparatus. As a result, a resultant image tends to have a difference in darkness in a width direction of a sheet, thereby deteriorating image quality. 
   In view of the problems described above, an object of the present invention is to provide a developing device and an image forming apparatus, in which it is possible to solve the problems in the conventional developing device. In particular, it is possible to prevent an image from having a difference in darkness in a width direction of a recording medium, and to improve image quality. 
   Further objects and advantages of the invention will be apparent from the following description of the invention. 
   SUMMARY OF THE INVENTION 
   In order to attain the objects described above, according to the present invention, a developing device includes a developer container having a developer supply opening and a developer storage section, so that developer is supplied from the developer container to the developer storage section through the developer supply opening. The developing device further includes a developer guide member disposed below the developer supply opening along a longitudinal direction of the developing device, and a developer delivery member disposed in the developer guide member for delivering developer supplied through the developer supply opening in a longitudinal direction of the developer guide member. The developer guide member has a wall portion having a shape so that developer flows out the developer guide member in a substantially uniform amount along the longitudinal direction of the developing device. 
   As described above, in the present invention, the developing device includes the developer container having the developer supply opening and the developer storage section, so that developer is supplied from the developer container to the developer storage section through the developer supply opening. The developing device further includes the developer guide member disposed below the developer supply opening along the longitudinal direction of the developing device, and the developer delivery member disposed in the developer guide member for delivering developer supplied through the developer supply opening in the longitudinal direction of the developer guide member. The developer guide member has the wall portion having a shape so that developer flows out the developer guide member in a substantially uniform amount along the longitudinal direction of the developing device. 
   With the configuration described above, it is possible to prevent an image from having a difference in darkness in a width direction of a recording medium, and to improve image quality. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic sectional view showing a main portion of developing device according to a first embodiment of the present invention; 
       FIG. 2  is a schematic view showing a printer according to the first embodiment of the present invention; 
       FIG. 3  is a schematic sectional view of the developing device according to the first embodiment of the present invention; 
       FIG. 4  is a schematic perspective view showing a main portion of the developing device according to the first embodiment of the present invention; 
       FIG. 5  is a schematic perspective view showing the developing device according to the first embodiment of the present invention; 
       FIG. 6  is a schematic view (No. 1) showing an operation of a toner amount detection sensor according to the first embodiment of the present invention; 
       FIG. 7  is a schematic view (No. 2) showing an operation of a toner amount detection sensor according to the first embodiment of the present invention; 
       FIG. 8  is a schematic view showing a developer container without a toner guide in a state that a level of toner is low according to the first embodiment of the present invention; 
       FIG. 9  is a schematic view showing the developer container without the toner guide in a state that toner is supplied therein according to the first embodiment of the present invention; 
       FIG. 10  is a schematic view showing the developer container without the toner guide in a state that a level of toner is full at a side portion of the developer container according to the second embodiment of the present invention; 
       FIG. 11  is a schematic view showing the developer container without the toner guide in a state that a level of toner is full at a center portion of the developer container according to the second embodiment of the present invention; 
       FIG. 12  is a schematic view showing the developer container with the toner guide in a state that a level of toner is low according to the first embodiment of the present invention; 
       FIG. 13  is a schematic view showing the developer container with the toner guide in a state that toner is supplied therein according to the first embodiment of the present invention; 
       FIG. 14  is a schematic view showing the developer container with the toner guide in a state that a level of toner is full at the side portion of the developer container according to the first embodiment of the present invention; 
       FIG. 15  is a schematic view showing the developer container with the toner guide in a state that a level of toner is full at the center portion of the developer container according to the first embodiment of the present invention; 
       FIG. 16  is a schematic perspective view showing a main portion of the developing device according to the first embodiment of the present invention; 
       FIG. 17  is a schematic perspective view showing a main portion of the developing device according to a second embodiment of the present invention; 
       FIG. 18  is a schematic perspective view showing a main portion of the developing device according to a third embodiment of the present invention; 
       FIG. 19  is a schematic perspective view showing a toner guide according to a fourth embodiment of the present invention; 
       FIG. 20  is a schematic perspective view showing a toner guide according to a fifth embodiment of the present invention; 
       FIG. 21  is a schematic perspective view showing a toner guide according to a sixth embodiment of the present invention; and 
       FIG. 22  is a schematic plan view showing the toner guide according to the sixth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Hereunder, embodiments of the present invention will be explained with reference to the accompanying drawings. In the embodiments, a color printer will be explained as an image forming apparatus for forming an image. 
   First Embodiment 
     FIG. 2  is a schematic view showing a printer  40  according to a first embodiment of the present invention. As shown in  FIG. 2 , the printer  40  includes a lower cover or lower housing  41 , and an upper cover or upper housing  43  disposed to be rotatable around a supporting shaft  42  relative to the lower cover  41  for freely opening and closing the printer  40 . A stacker  44  is disposed in the upper cover  43  for receiving a sheet or recording medium after printing. In  FIG. 2 , a line Sd represents a boundary between the lower cover  41  and the upper cover  43 . 
   A sheet supply cassette  50  is disposed at a lower portion inside the lower cover  41  as a medium storage unit for storing a sheet. A supply roller or medium supply member  51  is disposed at a front end of the sheet supply cassette  50  for supplying a sheet to a sheet transport path  49 . The sheet transport path  49  has an S character shape, and is provided with sheet supply rollers  45  to  47  and a belt unit or sheet transport member  53 . The belt unit  53  includes a drive roller or first roller R 1 ; a follower roller or second roller R 2 ; and a transport belt or transport member  52  placed between the drive roller R 1  and the follower roller R 2 . 
   In the belt unit  53 , the transport belt  52  moves to transport a sheet, so that the sheet passes through between transfer rollers or transfer devices  57  and a plurality of developing devices or image forming units (image drum units)  55 Bk,  55 Y,  55 M, and  55 C for forming images in colors such as black, yellow, magenta, and cyan. 
   Each of the developing devices  55 Bk,  55 Y,  55 M, and  55 C includes a photosensitive drum or image supporting member  12 ; a charge roller or charge device  13  disposed around the photosensitive drum  12 ; and a developing roller or developer supporting member  16  for holding developer or toner. Recording heads or exposure devices  56  are disposed adjacent to the developing devices  55 Bk,  55 Y,  55 M, and  55 C, respectively. The transfer rollers  57  are disposed to face the developing devices  55 Bk,  55 Y,  55 M, and  55 C with the transport belt  52  in between. 
   In the developing devices  55 Bk,  55 Y,  55 M, and  55 C, the photosensitive drums  12  are driven with drum motors or drive devices (not shown) to rotate in a specific direction for forming an image. While the photosensitive drums  12  rotate, the charge rollers  13  uniformly charge surfaces of the photosensitive drums  12 . The recording heads  56  expose the surfaces of the photosensitive drums  12  to form latent images thereon. Toner on the developing rollers  16  is electrostatically attached to the latent images to form toner images or developer images. 
   After a sheet is supplied to the sheet transport path  49  and transported with the sheet supply rollers  45  and  46 , the sheet passes through between the transfer rollers  57  and the developing devices  55 Bk,  55 Y,  55 M, and  55 C. Each of the transfer rollers  57  sequentially transfers the toner image or the developer image in each color formed at each of the developing devices  55 Bk,  55 Y,  55 M, and  55 C to the sheet, thereby forming the toner image in colors. 
   Afterward, the sheet is transported to a fixing unit or fixing device  54  for fixing the toner image in colors to the sheet, thereby forming a color image. After discharged from the fixing unit  54 , the sheet is transported with the sheet supply roller  47  and discharged with a discharge roller  48  to the stacker  44 . 
   A configuration of the developing devices  55 Bk,  55 Y,  55 M, and  55 C will be explained next. Since the developing devices  55 Bk,  55 Y,  55 M, and  55 C have an identical configuration, only the developing device  55 Bk will be explained in detail. 
     FIG. 1  is a schematic sectional view showing a main portion of the developing device according to the first embodiment of the present invention.  FIG. 3  is a schematic sectional view of the developing device according to the first embodiment of the present invention.  FIG. 4  is a schematic perspective view showing a main portion of the developing device according to the first embodiment of the present invention.  FIG. 5  is a schematic perspective view showing the developing device according to the first embodiment of the present invention. 
   As shown in FIGS.  1  and  3 - 5 , the developing device  55 Bk includes the charge roller  13  for charging the photosensitive drum  12  while rotating in a state that the charge roller  13  contacts with the photosensitive drum  12 ; the developing roller or developer supporting member  16  for supplying toner to the photosensitive drum  12 ; a developer blade  17  for controlling an amount of toner on the developing roller  16 ; a supply roller or developer supply member  18  for supplying toner to the developing roller  16 ; a developer storage section  19  for storing toner or developer therein; and a cleaning member  21  for removing toner remaining on the photosensitive drum  12 . 
   In the developing device  55 Bk, the photosensitive drum  12 , the charge roller  13 , the developing roller  16 , and the supply roller  18  rotate in arrow directions shown in  FIG. 3 . 
   A toner cartridge  22  is detachably attached to a main body of the developing device  55 Bk, i.e., a developing device main body. In the embodiment, the toner cartridge  22  constitutes a developer container having a toner supply opening  22   a  formed in a bottom portion thereof, so that toner is supplied to the developer storage section  19  through a toner supply opening  14  formed in the developing device  55 Bk. The toner supply opening  14  is formed at a center portion of an upper portion  28  of the developing device  55 Bk in a longitudinal direction thereof. A stirring bar or first stirring device  29  is disposed inside the toner cartridge  22  for stirring toner to be supplied to the developer storage section  19 . 
   Further, stirring members or second and third stirring devices  23  and  24  are disposed inside the developer storage section  19  for stirring toner inside the developer storage section  19 . The stirring members  23  and  24  are arranged adjacent to the supply roller  18  and in parallel with each other. A toner amount detection sensor or developer amount detection unit  15  is disposed inside the developer storage section  19  for detecting an amount of toner inside the developer storage section  19 . 
   Further, a spiral or developer delivery member  26  and a toner guide or developer guide member  27  having a U character shape are provided inside the developer storage section  19  for delivering toner supplied from the toner supply opening  22   a  of the toner cartridge  22  through the toner supply opening  14  of the developing device  55 Bk in a width direction of the printer  40 , i.e., a longitudinal direction of the developer storage section  19 . In the embodiment, the stirring member  23 , the stirring member  24 , the toner amount detection sensor  15 , the spiral  26 , and the toner guide  27  are arranged along a longitudinal direction of the developing device  55 Bk. 
   A space B is formed between a wall portion  27   a  of the toner guide  27  and the upper portion  28  of the developing device  55 Bk covering the developer storage section  19 . As shown in  FIG. 1 , an upper edge of the wall portion  27   a  is curved. Accordingly, the wall portion  27   a  has a height largest at a center portion of the toner guide  27  close to the toner supply opening  14 , and the height is gradually decreasing toward both end sides and becomes about zero at the both ends. As a result, the space B becomes small at the center portion of the toner guide  27 , and increases toward the both end sides of the toner guide  27 . That is, B 1  is smaller than B 2 , in which B 1  is the space B at the center portion and B 2  is the space at the both end sides. Seal sponge members or seal members  35  are disposed at the both end sides of the toner guide  27 . 
   As shown in  FIG. 3 , in the sectional view of the developing device  55 Bk, the toner guide  27  is situated at a right side of the developer storage section  19 , that is, above a downstream side of the supply roller  18  in a rotational direction thereof (side contacting with the developing roller  16 ). The space B is situated at an approximately upper center portion of the developer storage section  19 . 
   With the configuration described above, toner dropping from the toner guide  27  accumulates on the left side of the developer storage section  19  from the center portion thereof in  FIG. 3 , that is, the upstream side of the supply roller  18  in the rotational direction thereof. In other words, toner does not accumulate on the downstream side of the supply roller  18  in a rotational direction thereof. Accordingly, toner newly supplied from the toner cartridge  22  is not supplied toward the downstream side of the supply roller  18  (close to a contact point between the supply roller  18  and the developing roller  16 ), thereby not being consumed predominantly. Old toner (toner existing in the developer storage section  19  before) does not tend to remain in the developer storage section  19  for a long time, and is sequentially consumed. Accordingly, it is possible to prevent toner from staying in the developing device  55 Bk for a long time without being consumed. 
   In  FIG. 3 , a position T represents a position of an upper surface of toner inside the developer storage section  19 , i.e., a toner position or developer position, when a level of toner is detected to be low just before the toner cartridge  22  is replaced. When toner is located at the toner position T, it is necessary to supply toner. When the toner amount detection sensor  15  detects a state that toner does not exist in the developer storage section  19 , or a toner low (toner end) or developer low, the toner cartridge  22  is replaced. 
   When the toner cartridge  22  is replaced and the developing device  55 Bk is used, toner is supplied to the developer storage section  19  from the toner supply opening  22   a  of the toner cartridge  22  through the toner supply opening  14  of the developing device  55 Bk with the stirring bar  29  disposed inside the toner cartridge  22  as the rotatable stirring member, so that toner is accommodated in the toner guide  27 . 
   As shown in  FIG. 4 , the spiral  26  has a thread on one side from a center to one end opposite to that on the other side from the center to the other end. Accordingly, when the spiral  26  rotates in an arrow direction D, toner is divided inside the toner guide  27  in opposite arrow directions E and F. 
   As described above, the wall portion  27   a  of the toner guide  27  has a height largest at the center portion of the toner guide  27  close to the toner supply opening  14 , and the height is decreasing gradually toward the both end sides. As a result, the space B becomes small at the center portion of the toner guide  27 , and increases toward the both end sides of the toner guide  27 . Accordingly, tone accumulated in the toner guide  27  is divided and delivered in the opposite arrow directions E and F, and flows outside the toner guide  27  through the space B. 
   When the developer storage section  19  is filled with toner, toner inside the toner cartridge  22  is no longer supplied. When the developing device  55 Bk performs a series of image forming processes, the stirring bar  29  and the spiral  26  continue to rotate. As a result, toner reaching at the both end sides of the toner guide  27  is circulated in arrow directions G and H through the rotation of the spiral  26  at an upper layer of toner inside the developer storage section  19 . 
   An operation of the toner amount detection sensor  15  will be explained next.  FIG. 6  is a schematic view (No. 1) showing the operation of the toner amount detection sensor according to the first embodiment of the present invention.  FIG. 7  is a schematic view (No. 2) showing the operation of the toner amount detection sensor according to the first embodiment of the present invention. 
   As shown in  FIGS. 6 and 7 , the toner amount detection sensor  15  is provided with a stirring member  31  and a sensor  32 . The stirring member  31  is rotated at a cycle τ for stirring toner, thereby preventing toner inside the developer storage section  19  from being agglomerated. The stirring member  31  is rotated inside the developer storage section  19  from a lowermost point to an uppermost point with a regulating member (not shown) pushing the stirring member  31 , and rotates with own weight from the uppermost point to the lowermost point. According to an amount of toner inside the developer storage section  19 , it is controlled to change a period of an off time during which the stirring member  31  reaches the lowermost point from the uppermost point, that is, the sensor  32  detects the stirring member  31  to turn on. 
   As shown in  FIG. 6 , when an amount of toner at a low level, the period of the off time becomes short. On the other hand, as shown in  FIG. 7 , when an amount of toner at a full level, i.e., toner full or developer full, the period of the off time becomes long. 
   A sensor signal of the sensor  32  is sent to a control unit (not shown), so that a developer amount detection processing unit of the control unit performs a developer amount detection process. In the developer amount detection process, first, the developer amount detection processing unit detects the toner low according to the sensor signal. Upon detecting the toner low, the developer amount detection processing unit performs a display process, so that a message prompting replacement of the toner cartridge  22  is displayed on a display unit (not shown). Further, an image forming operation processing unit of the control unit performs an image forming operation process, thereby completing an image forming process or printing process. 
   As shown in  FIG. 6 , when an amount of toner at a low level, the toner position T is situated below the toner guide  27  and the spiral  26 . 
   When the developing device  55 Bk is used for the first time or the toner low is detected just before the toner cartridge  22  is replaced, toner is supplied to the developer storage section  19  and accumulated inside the developer storage section  19  in a state explained below. 
     FIG. 8  is a schematic view showing the developer container without the toner guide in a state that a level of toner is low.  FIG. 9  is a schematic view showing the developer container without the toner guide in a state that toner is supplied therein.  FIG. 10  is a schematic view showing the developer container without the toner guide in a state that a level of toner is full at a side portion of the developer container.  FIG. 11  is a schematic view showing the developer container without the toner guide in a state that a level of toner is full at a center portion of the developer container.  FIG. 12  is a schematic view showing the developer container with the toner guide in a state that a level of toner is low according to the first embodiment of the present invention.  FIG. 13  is a schematic view showing the developer container with the toner guide in a state that toner is supplied therein according to the first embodiment of the present invention.  FIG. 14  is a schematic view showing the developer container without the toner guide in a state that a level of toner is full at the side portion of the developer container according to the first embodiment of the present invention.  FIG. 15  is a schematic view showing the developer container with the toner guide in a state that a level of toner is full at the center portion of the developer container according to the first embodiment of the present invention.  FIG. 16  is a schematic perspective view showing a main portion of the developing device according to the first embodiment of the present invention. 
   In  FIGS. 8-16 , ta represents toner contained in the developer storage section  19  at a low level (toner low); tb represents toner supplied from the toner cartridge  22 ; and  30  represents a boundary between ta and tb. 
   In a case that the toner guide  27  is not provided, when the toner tb is supplied into the developer storage section  19  through the toner supply opening  14  disposed at the center portion in the longitudinal direction, the toner tb is accumulated locally on the toner tb right below the toner supply opening  14  as shown in  FIG. 9 . As a result, a toner accumulated surface T′ becomes high at a position just below the toner supply opening  14  to form a top of a mountain shape, and is declining away from the top of the mountain shape. Accordingly, the toner tb locally accumulated pushes the toner ta toward the both side portions, so that the toner ta forms a valley shape with a bottom situated just below the toner supply opening  14  and ascending away from the bottom. 
   In the state described above, when toner is supplied continuously and filled within the developer storage section  19 , toner is accumulated at the both side portions of the developer storage section  19  in a state shown in  FIG. 10 , and at the center portion of the developer storage section  19  in a state shown in  FIG. 11 . That is, the boundary  30  is situated above the toner position T at the both side portions, and is situated below the toner position T at the center portion. 
   In this case, a weight of the toner tb is applied to a center portion of the toner ta, and is not applied to both side portions of the toner ta. As a result, the center portion of the toner ta is compressed as opposed to the both side portions thereof, thereby making it difficult to deliver the center portion of the toner ta to the developing roller  16  with the supply roller  18 . When the toner ta is used for printing, a resultant image tends to have a difference in darkness along a width direction of a sheet, thereby deteriorating image quality. 
   On the other hand, in a case that the toner guide  27  is provided, when toner is supplied through the toner supply opening  14 , toner is temporarily accumulated in the toner guide  27 . Then, toner is delivered toward the both end sides of the toner guide  27  with the spiral  26 . As described above, the space B is small at the center portion of the toner guide  27 , and enlarges toward the both end sides of the toner guide  27 . Accordingly, a part of toner moves over the wall portion  27   a , and flows out of the toner guide  27  through the space B. A remaining part of toner is delivered toward the both end sides with the spiral  26 . 
   While being delivered, toner flows out of the toner guide  27  through the space B. Accordingly, an amount of toner decreases as toner is delivered closer to the both end sides of the toner guide  27 . As described above, the space B enlarges toward the both end sides of the toner guide  27 , thereby making it easy for toner to flow out of the toner guide  27 . As a result, as shown in  FIG. 13 , an amount of toner flowing out of the toner guide  27  through the space B in an arrow direction G becomes uniform along the longitudinal direction of the developer storage section  19 . That is, the toner accumulated surface T′ becomes flat along the longitudinal direction of the developer storage section  19 . 
   When toner is supplied continuously and filled within the developer storage section  19 , toner is accumulated at the both side portions of the developer storage section  19  in a state shown in  FIG. 14 , and at the center portion of the developer storage section  19  in a state shown in  FIG. 15 . That is, the boundary  30  is situated at a level same as that of the toner position T at the both side portions and the center portion. 
   In this case, the weight of the toner tb is uniformly applied to both the center portion and the both side portions of the toner ta. As a result, it is possible to stably deliver both the center portion and the both side portions of the toner ta. When the toner ta is used for printing, it is possible to prevent a resultant image from having a difference in darkness along a width direction of a sheet, thereby improving image quality. 
   After the developer storage section  19  is filled with toner, toner is consumed for printing. Until all of toner inside the toner cartridge  22  is consumed and the toner amount detection sensor  15  detects the toner low, an amount of toner flowing out of the toner guide  27  is maintained at a constant level along the longitudinal direction of the developer storage section  19 . Further, as shown in  FIG. 5 , toner is circulated in the arrow directions G and H, thereby maintaining image quality. 
   In the embodiment, an amount of toner inside the toner cartridge  22  is, for example, 60 g. When the developing device  55 Bk is filled with toner, an amount of toner inside the developing device  55 Bk is, for example, 50 g. An amount of toner inside the developer storage section  19  just before the toner cartridge  22  is replaced is, for example, 30 g. A length of the developer storage section  19  in the longitudinal direction thereof is, for example, about 230 mm. 
   When toner is supplied from the toner cartridge  22  and an amount of toner inside the developer storage section  19  reaches 50 g, the stirring bar  29  inside the toner cartridge  22  no longer delivers toner. Accordingly, unless toner is consumed for printing, toner is not supplied to the developer storage section  19 . Just after the toner cartridge  22  is replaced, toner is supplied in an amount of 20 g. An amount of toner per unit length along the longitudinal direction is 0.09 g/mm until the developer storage section  19  is filled with toner. The supplied amount of toner per unit length along the longitudinal direction 0.09 g/mm is determined by an amount of toner delivered with the spiral  26  and a size of the space B associated with the shape of the toner guide  27 . 
   In the embodiment, through adjusting a size of the space B, it is possible to uniformly accumulate toner inside the developer storage section  19  along the longitudinal direction thereof with the spiral  26  rotating at a constant rotational speed without controlling an amount of toner supplied from the toner cartridge  22  or the rotational speed of the spiral  26 , or rotating and stopping the spiral  26 . Accordingly, it is possible to prevent an image from having a difference in darkness along a width direction of a sheet, thereby improving image quality. 
   Further, it is not necessary to control an amount of toner supplied from the toner cartridge  22 , or an amount of toner delivered with the spiral  26 , thereby reducing cost of the printer  40 . In the embodiment, the upper edge of the wall portion is curved, and may have a step shape connected with straight lines as shown in  FIG. 16 . 
   Second Embodiment 
   A second embodiment of the present invention will be explained next. Components similar to those in the first embodiment are designated with the same reference numerals, and explanations thereof are omitted. The components similar to those in the first embodiment provide the similar effects. 
     FIG. 17  is a schematic perspective view showing a main portion of the developing device according to the second embodiment of the present invention. As shown in  FIG. 17 , the toner supply opening  14  is formed at one end side of the developer storage section  19  in the longitudinal direction thereof. Accordingly, an upper edge of the wall portion  27   a  of the toner guide  27  has a height largest at one end side of the toner guide  27  adjacent to the toner supply opening  14 , and is decreasing toward the other end side. 
   Further, the spiral  26  has a thread circling in a same direction over a whole axial direction. Accordingly, when the spiral  26  rotates in an arrow direction R, toner is delivered inside the toner guide  27  from the one end side to the other end side in an arrow direction P. 
   Third Embodiment 
   A third embodiment of the present invention will be explained next.  FIG. 18  is a schematic perspective view showing a main portion of the developing device according to the third embodiment of the present invention. 
   As shown in  FIG. 18 , the toner supply openings  14  are formed at both end sides of the developer storage section  19  in the longitudinal direction thereof. Accordingly, an upper edge of the wall portion  27   a  of the toner guide  27  has a height smallest at the center portion of the toner guide  27 , and is decreasing toward the both end sides thereof. 
   The spiral  26  has a thread on one side from a center to one end opposite to that on the other side from the center to the other end, and the thread circles in a direction opposite to that in the first embodiment. Accordingly, when the spiral  26  rotates in an arrow direction D, toner is delivered inside the toner guide  27  in opposite arrow directions U and T. 
   Fourth Embodiment 
   A fourth embodiment of the present invention will be explained next.  FIG. 19  is schematic perspective view showing a toner guide  101  according to the fourth embodiment of the present invention. 
   As shown in  FIG. 19 , the toner guide  101  includes a bottom portion  101   b  having a depth largest adjacent to the toner supply opening  14  (center portion) and decreasing away from the toner supply opening  14  (toward both end sides), and a wall portion  101   a  having a length in a vertical direction largest adjacent to the toner supply opening  14  and decreasing toward the both end sides. 
   In the embodiment, a part of toner (not shown) supplied through the toner supply opening  14  moves over the wall portion  101   a  and flows out the toner guide  101 , and a remaining portion of toner is delivered with the spiral  26  ( FIG. 4 ) toward the both end sides. Toner is discharged outside the toner guide  101  while being transported, so that an amount of toner delivered decreases toward the both end sides. As described above, the wall portion  101   a  has a length in a vertical direction decreasing toward the both end sides. Accordingly, toner is discharged outside the toner guide  101  more easily toward the both end sides. As a result, an amount of toner becomes uniform along the longitudinal direction of the developer storage section  19  ( FIG. 13 ). 
   Fifth Embodiment 
   A fifth embodiment of the present invention will be explained next.  FIG. 20  is a schematic perspective view showing a toner guide  201  according to the fifth embodiment of the present invention. 
   As shown in  FIG. 20 , the toner guide  201  includes a wall portion  201   a  with a slit  201   c  having a width smallest adjacent to the toner supply opening  14  and increasing away from the toner supply opening  14 . That is, the slit  201   c  is formed to become narrow at a center portion of the wall portion  201   a  and wide at both end sides thereof. 
   In the embodiment, a part of toner (not shown) supplied through the toner supply opening  14  flows out the toner guide  201  through the slit  201   c , and a remaining portion of toner is delivered with the spiral  26  ( FIG. 4 ) toward the both end sides. Toner is discharged outside the toner guide  201  while being transported, so that an amount of toner delivered decreases toward the both end sides. As described above, the slit  201   c  has a width increasing toward the both end sides. Accordingly, toner is discharged outside the toner guide  201  more easily toward the both end sides. As a result, an amount of toner becomes uniform along the longitudinal direction of the developer storage section  19  ( FIG. 13 ). 
   Sixth Embodiment 
   A sixth embodiment of the present invention will be explained next.  FIG. 21  is a schematic perspective view showing a toner guide  301  according to the sixth embodiment of the present invention.  FIG. 22  is a schematic plan view showing the toner guide  301  according to the sixth embodiment of the present invention. 
   As shown in  FIGS. 21 and 22 , the toner guide  301  includes a wall portion  301   a  having a curved shape and a wall portion  301   b  having a flat shape. Accordingly, the toner guide  301  has a width largest adjacent to the toner supply opening  14  and decreasing away from the toner supply opening  14 . That is, the toner guide  301  is formed to have a wide width J 1  at a center portion of the wall portion  301   a  for easily holding toner and a narrow width J 2  at both end sides thereof where it is difficult to hold a large amount of toner. 
   In the embodiment, a part of toner (not shown) supplied through the toner supply opening  14  moves over the wall portion  301   a  and flows out the toner guide  301 , and a remaining portion of toner is delivered with the spiral  26  ( FIG. 4 ) toward the both end sides. Toner is discharged outside the toner guide  301  while being transported, so that an amount of toner delivered decreases toward the both end sides. As described above, the toner guide  301  has the narrow width J 2  at the both end sides. Accordingly, toner is discharged outside the toner guide  301  more easily toward the both end sides. As a result, an amount of toner becomes uniform along the longitudinal direction of the developer storage section  19  ( FIG. 13 ). 
   In the embodiments described above, the image forming apparatus is the printer as an example. The present invention is applicable to a copier, a facsimile, and a multi-function device. 
   The disclosure of Japanese Patent Application No. 2005-289080, filed on Sep. 30, 2005, is incorporated in the application. 
   While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.