Abstract:
A developer includes a toner container divided by a partition into first and second chambers. The first and the second chambers communicate with each other via first and second openings. A third opening is also formed in the partition for passing excessive toner from the second to the first chamber. The first chamber is provided with a first screw for transferring the toner from the first to the second opening, while the second chamber with a second screw for transferring the toner in the opposite direction. A toner scraping blade is arranged above the second screw. The toner scraped in the second chamber is led into the first chamber through the third opening. Adjusting means is provided for controlling the passage of the toner through the third opening, thereby achieving uniform toner distribution in the second chamber.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a developer used for an electrophotographic image forming apparatus.  
           [0003]    2. Description of the Related Art  
           [0004]    An example of a conventional developer is shown in FIG. 9 of the accompanying drawings. The illustrated developer includes a toner container  1 , a partition  2 , first and second screws  3 A- 3 B, a conveyor roller  4 , a first toner blade  40 , a second toner blade  50 , and two developer rollers  5 A- 5 B.  
           [0005]    The space within the container  1  is divided into a first portion  10 A and a second portion  10 B by the partition  2 . The first screw  3 A is provided in the first portion  10 A, while the second screw  3 B is provided in the second portion  10 B. The first toner blade  40  is arranged adjacent to the conveyor roller  4 , while the second toner blade  50  is arranged adjacent to the first developer roller  5 A. The toner contains magnetic particles or carriers.  
           [0006]    Additional toner is supplied from a toner hopper  60  into the first portion  10 A of the container  1 . The supplied toner is mingled with the magnetic carriers by a rotary mixer  61 . Then, as shown in FIG. 10, the toner is sent in an Na-direction by the first screw  3 A toward a first opening  20 A (see arrow Q 1 ) formed at one lower corner of the partition  2 . Through this opening, the toner is supplied from the first portion  10 A to the second portion  10 B (see arrow Q 2 ) . Then, the toner is sent in an Nb-direction, opposite to the Na-direction, by the second screw  3 B toward a second opening  20 B (see arrow Q 3 ) formed at the other lower corner of the partition  2 . Through the second opening  20 B, the toner returns to the first portion  10 A of the container  1  (see arrow Q 4 ).  
           [0007]    Referring back to FIG. 9, the conveyor roller  4  and the two developer rollers  5 A- 5 B are elongated generally in parallel to the second screw  3 B. In operation, the conveyor roller  4  picks up the toner in the second portion  10 B of the container  1 , to pass it to the first developer roller  5 A. At this time, an excessive amount of toner is scraped off the conveyor roller  4  by the first toner blade  40 . Likewise, an excessive amount of toner passed onto the first developer roller  5 A is scraped off by the second toner blade  50 .  
           [0008]    With the above arrangement, the toner in the second portion  10 B of the container  1  is expected to be uniformly distributed along the entire length of the second screw  3 B. Consequently, the toner maybe supplied to the first developer roller  5 A uniformly over its entire length (and to the second developer roller  5 B) via the conveyor roller  4 . The excessive toner scraped off by the toner blade  40  or  50  will fall into the second portion  10 B of the container  1 , to be picked up again by the conveyor roller  4 .  
           [0009]    The conventional developer has been found disadvantageous in the following points.  
           [0010]    For proper circulation of the toner within the container  1 , the four toner transfer rates Q 1 -Q 4  need to be well balanced. Unfortunately, however, the transferability of the toner tends to worsen with time (as the print count increases), which makes the toner circulation irregular In such an instance, the toner transfer rate Q 4  through the second opening  20 B may unduly be smaller than the toner transfer rate Q 3  by the second screw  3 B. As a result, an excessive amount of toner will accumulate around the second opening  20 B in the second portion  10 B of the container  1 . Such an imbalance in toner distribution makes it impossible to supply toner uniformly over the entire length of the developer rollers  5 A- 5 B, which gives rise to the deterioration of the print quality. In addition, the accumulated toner may leak out of the container  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a developer in which toner is uniformly distributed over the entire length of a developer roller even if the transferability of the toner deteriorates with time.  
           [0012]    According to the present invention, there is provided a developer including: a container for holding developing material; a partition dividing the container into a first chamber and a second chamber, the partition being formed with first and second openings for causing the first and the second chambers to communicate with each other, the partition being also formed with a third opening above the second opening for introducing an excessive amount of developing material from the second chamber into the first chamber; a first screw arranged in the first chamber for transferring the developing material from the second opening to the first opening; a second screw arranged in the second chamber for transferring the developing material from the first opening to the second opening; a developer roller arranged generally in parallel to the second screw and including a cylindrical surface onto which the developing material in the second chamber is supplied; a blade arranged above the second screw for scraping off an excessive amount of developing material; and adjusting means for controlling a quantity of the developing material passing through the third opening.  
           [0013]    According to a preferred embodiment, the adjusting means may include a movable shutter for at least partially closing the third opening. In this case, preferably, the developer may further include a memory for storing data for controlling the shutter. The data to be stored in the memory may be obtained experimentally.  
           [0014]    Preferably, the stored data may relate to the relation between the current print condition and the operation of the shutter. An example of the current print condition is the number of the performed printing operations (which may be deduced by monitoring how many times the photosensitive drum of a printer has been rotated).  
           [0015]    Preferably, the developer may further include a sensor for detecting the developing material adjacent to the second opening in the second chamber for output of a detection signal. In this case, the shutter may be operated based on the detection signal.  
           [0016]    According to a preferred embodiment, the developer may further include a conveyor roller for supplying the developing material to the developer roller. In this case, the adjusting means may include an additional developing material scraping blade which is arranged adjacent to the conveyor roller and movable relative to the conveyor roller.  
           [0017]    Preferably, the additional blade may be pivotable about a predetermined axis. As the blade is caused to pivot about the axis, the clearance between the tip of the blade and the conveyor roller can be adjusted.  
           [0018]    Preferably, the developer may further include a memory for storing data relating to a relation between a print condition and an operation of the additional blade. In operation, the posture of the additional blade is controlled in accordance with the data. 
       
    
    
       [0019]    Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a sectional side view showing a developer according to a first embodiment of the present invention;  
         [0021]    [0021]FIG. 2 is a sectional view taken along lines II-II in FIG. 1;  
         [0022]    [0022]FIG. 3 is a sectional view taken along lines III-III in FIG. 2;  
         [0023]    [0023]FIG. 4 is a sectional view showing a developer according to a second embodiment of the present invention;  
         [0024]    [0024]FIG. 5 is a sectional view showing a developer according to a third embodiment of the present invention;  
         [0025]    [0025]FIG. 6 is a sectional view taken along lines VI-VI in FIG. 5;  
         [0026]    [0026]FIG. 7 is a sectional view showing a developer according to a fourth embodiment of the present invention;  
         [0027]    [0027]FIG. 8 is a sectional view showing a developer according to a fifth embodiment of the present invention;  
         [0028]    [0028]FIG. 9 is a sectional view showing a conventional developer; and  
         [0029]    [0029]FIG. 10 is a sectional view taken along lines X-X in FIG. 9. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    The preferred embodiments of the present invention will be described below with reference to the accompanying drawings.  
         [0031]    Reference is first made to FIGS.  1 - 3  showing a developer according to a first embodiment of the present invention. As seen from the comparison between FIG. 1 and FIG. 9, the developer A 1  of the present invention and the conventional developer have many things in common. Hereinbelow, the components of the developer A 1  which are identical or similar to those of the conventional developer are indicated by the same reference numerals or signs.  
         [0032]    Though the developer A 1  of the present invention and the conventional developer are similar in many respects, there are some significant differences between them. Specifically, as best shown in FIG. 2, the partition  2  of the present invention is formed with a rectangular cutout or third opening  20 C (which is not found in the conventional device), in addition to the first and the second openings  20 A,  20 B formed at the lower corners of the partition  2 . Further, a shutter  29  is provided in the developer A 1 , to adjustably close the cutout  20 C. The cutout  20 C is formed at one of the upper corners of the partition  2  that is located above the second opening  20 B. As shown in FIG. 1, the cutout  20 C is disposed under the second toner blade  50 , so that the excessive toner scraped off the first developer roller  5 A is led into the first portion  10 A of the container  1 .  
         [0033]    Of course, the cutout  20 C may be disposed at a different location, as long as the excessive toner can be properly led into the first portion  10 A. In this case, the second blade  50  may also be arranged at a different location than the illustrated one in FIG. 1. For instance, the second blade  50  may be located below the first developer roller  5 A, whereby an excessive amount of scraped toner is led into the first portion  10 A before the toner is passed onto the first developer roller  5 A from the conveyor roller  4 .  
         [0034]    The shutter  29 , which is large enough to entirely close the cutout  20 C, is horizontally movable, as indicated by a two-headed arrow Ne in FIG. 2. To this end, the shutter  29  is supported by a horizontal, threaded shaft  28  which is rotatably connected to the opposing side walls  11   a,    11   b  of the container  1 . The shutter  29  is provided with an internally threaded through-hole into which the shaft  28  is screwed. One end of the shaft  28  is connected to a reversible motor M via a pair of pulleys  63   a - 63   b  and a connecting belt  63   c.  Upon actuating the motor M, the shaft  28  is rotated about its axis, while the shutter  29  remains unrotated due to the sliding contact with the partition  2  (see FIG. 3). As a result, the shutter  29  is moved to the right or left in FIG. 2, depending on the rotating direction of the motor M. By controlling the actuation of the motor M, the horizontal displacement of the shutter  29  is adjusted, thereby closing or opening the cutout  20 C in a desired manner. To this end, a driver  72 , a controller  70  and a memory  71  are provided. The driver  72  is connected to the motor M and operates under the control of the controller  70 . The memory  71  stores data on the number of performed print operations, and also data on the relation between the number of print operations and the suitable opening width of the cutout  20 C. For instance, the opening width of the cutout  20 C may be set to 100 mm when the number of performed print operations is 0-49,999, or 80 mm when the number is 50,000-99,999, or 60 mm when the number is 100,000-199,999, or 40 mm when the number is 200,000-299,999, or 20 mm when the number is 300,000-399,999, or 0 mm when the number is 400,000 or more.  
         [0035]    The controller  70  is provided with a CPU (central processing unit). Under the control of the CPU, which operates based on the data stored in the memory  71  and the current number of print operations, the driver  72  actuates the motor M so that a desired opening width is achieved at the cutout  20 C. The number of print operations may be determined by monitoring the number of rotation of the photosensitive drum  62  or the developer rollers  5 A,  5 B. The current number of rotation of the drum  62  or the rollers  5 A,  5 B may be constantly monitored, and the data regarding the rotation number is sent to the controller  70 .  
         [0036]    The function of the developer A 1  will be described below.  
         [0037]    In operation, the toner present in the first portion  10 A of the container  1  is transferred in the N 1 -direction (FIG. 2) by the first screw  3 A. After being brought to the right end of the screw  3 A, the toner is supplied to the second portion  10 B of the container  1  via the first opening  20 A. Then, the toner is transferred in the opposite N 2 -direction by the second screw  3 B. After being brought to the left end of the second screw  3 B, the toner is brought back to the first portion  10 A via the second opening  20 B (the end of one cycle of the toner circulation).  
         [0038]    As in the conventional developer, the toner present in the second portion  10 B is picked up by the conveyor roller  4  to be supplied to the developer rollers  5 A and  5 B, as shown in FIG. 1. With two developer rollers, the toner transfer onto the drum  62  can be reliably performed, thereby coping with high-speed printing. Of course, the present invention is applicable to a developer including only one developer roller.  
         [0039]    An excessive amount of toner clinging to the conveyor roller  4  or first developer roller  5   a  is scraped off by the first toner blade  40  or second toner blade  50 . The toner scraped from the conveyor roller  4  falls in the second portion  10 B. However, the toner scraped from the first developer roller  5 A will partly fall in the second portion  10 B, but partly fall into the first portion  10 A of the container  1  through the cutout  20 C, unless the shutter  29  completely closes the cutout  20 C. In this manner, the scraped toner is prevented from falling only into the second portion  10 B. As a result, the unfavorable toner accumulation near the second opening  20 B can be prevented.  
         [0040]    According to the present invention, the opening width of the cutout  20 C may be adjusted in accordance with the data on how many times the photosensitive drum  62  has been rotated. This is advantageous in the following points.  
         [0041]    As stated above, the transferability of the toner along the first or second screw  3 A or  3 B is initially good, but will deteriorate with time. Thus, at the initial stage, the toner is transferred along the second screw  3 B (and the first screw  3 A as well) very smoothly, which may cause a toner accumulation at the second opening  20 B. To avoid this, the cutout  20 C is widely opened, so that a large part of the excessive toner scraped off the first developer roller  5 A will fall into the first portion  10 A of the container  1 . Thus, the amount of the toner present in the second portion  10 B is reduced, thereby preventing the unfavorable toner accumulation at the second opening  20 B.  
         [0042]    Conversely, after the developer A 1  is used for a relatively long period of time, the toner transferability becomes worse. Consequently, the toner will not be smoothly transferred along the second screw  3 B, thereby producing a toner-scarce region near the second opening  20 B in the second portion  10 B of the container  1 . To address this problem, the cutout  20 C may be partly or completely closed by the shutter  29 , so that a larger part of the toner scraped off the first developer roller  5 A will fall into the second portion  10 B of the container  1 . In this manner, the nonuniform toner distribution in the second portion  10 B is avoided.  
         [0043]    It should be noted that such a nonuniform toner distribution may be found in the first portion  10 A of the container  1 . However, the nonuniformity in the first portion  10 A is not a problem since the conveyor roller  4  does not pick up toner from the first portion  10 A. Thus, even if the toner distribution happens to be nonuniform in the first portion  10 A, it is possible to maintain the high print quality when the toner distribution in the second portion  10 B is uniform.  
         [0044]    [0044]FIG. 4 shows a developer A 2  according to a second embodiment of the present invention. The developer A 2  of this embodiment is basically similar to the previous developer A 1 , except that a toner level sensor  73  is provided in the first side wall  11   a  of the container  1 . The sensor  73  outputs a detection signal when the height of the toner accumulation near the second opening  20 B in the second portion  10 B is over a predetermined value H. The sensor  73  may be a magnetic or optical device. A magnetic sensor may be designed to respond to the carriers of the developing material.  
         [0045]    The detection signal outputted from the sensor  73  is supplied to a controller  70 A via an A/D converter  74 . Based on this detection signal, the controller  70 A actuates the motor M for adjusting the position of the shutter  29 . Specifically, when no detection signal is supplied to the controller  70 A from the sensor  73  (i.e., when the toner accumulation is low), the shutter  29  may be brought to the left extremity position (as viewed in FIG. 4) to completely close the cutout  20 C. On the other hand, when a detection signal is supplied to the controller  70 A (i.e., when the toner accumulation is high), the shutter  29  may be brought to the right extremity position shown in FIG. 4, to completely open the cutout  20 C.  
         [0046]    In the illustrated embodiment, only one toner level sensor is used, though the present invention is not limited to this. Two or more sensors may be provided at different heights in the first side wall  11   a,  so that the positional adjustment of the shutter  29  can be performed more finely.  
         [0047]    [0047]FIGS. 5 and 6 show a developer A 3  according to a third embodiment of the present invention. In this embodiment, no shutter is provided at the cutout  20 C, as best shown in FIG. 6. Instead, the first blade  40  is made pivotable about a horizontal shaft  41 , so that the clearance S between the blade  40  and the conveyor roller  4  is variable. For actuating the blade  40 , a reversible motor M is connected to the blade  40  via a pair of pulleys  64   a - 64   b  and a belt  64   c.  The operation of the motor M is controlled by a driver  72 , a controller  70 B and a memory  71 B. The memory  71 B stores data on the relation between the number of printing operations and the inclination angle of the first blade  40  (or the clearance S). Based on this data and the information about the current number of the printing operations, the controller  70 B adjusts the inclination angle of the first blade  40  via the driver  72  and the motor M, so that the clearance S is set to a required value.  
         [0048]    According to the third embodiment described above, the adjustment of the clearance S indirectly contributes to the control of the amount of the toner that is scraped off the first developer roller  5 A and led into the first portion  10 A via the cutout  20 C. Specifically, when the clearance S is relatively small, a larger amount of toner is scraped off the conveyor roller  4 , whereby a smaller amount of toner is supplied to the first developer roller  5 A. Accordingly, a smaller amount of toner is scraped off the developer roller  5 A by the second blade  50 , which reduces the amount of toner to fall into the first portion  10 A via the cutout  20 C. On the contrary, when the clearance S is relatively large, a smaller amount of toner is scraped off the conveyor roller  4 , whereby a larger amount of toner is supplied to the first developer roller  5 A. Accordingly, a larger amount of toner is scraped off the developer roller  5 A by the second blade  50 , which increases the amount of toner to fall into the first portion  10 A via the cutout  20 C.  
         [0049]    In the third embodiment, the clearance S is made relatively large when the number of performed printing operations is relatively small (i.e., when the toner accumulation at the second opening  20 B in the second portion  10 B is more likely to occur). Conversely, the clearance S is made relatively small when the number of performed printing operations is relatively large (i.e., when the toner accumulation at the second opening  20 B in the second portion  10 B is less likely to occur) . In this manner, it is possible to equalize the toner distribution along the second screw  3 B, no matter how many times the printing operations have been performed.  
         [0050]    [0050]FIG. 7 shows a developer A 4  according to a fourth embodiment of the present invention. In this embodiment, the first blade  40  is caused to pivot by the same mechanism as in the third embodiment (FIG. 5). In addition, the developer A 4  is provided with a toner level sensor  73  for determining whether or not the toner accumulation near the second opening  20 B in the second portion  10 B is over a predetermined level. A detection signal from the sensor  73  is supplied to a controller  70 C via an A/D converter  74 . When no detection signal is supplied to the controller  70 C, the clearance S is made relatively small, so that a larger amount of toner scraped off the conveyor roller  4  or first developer roller  5 A will remain in the second portion  10 B of the container  1 . Conversely, when a detection signal is supplied to the controller  70 C, the clearance S is made relatively large, so that a larger amount of toner scraped off the developer roller  5 A will fall into the first portion  10 A via the cutout  20 C.  
         [0051]    [0051]FIG. 8 shows a developer A 5  according to a fifth embodiment of the present invention. In this embodiment, use is made of both a pivotable first blade  40  and a horizontally movable shutter  29  for adjustably closing the cutout  20 C of the partition  2 . In this manner, synergistic effects by a combination of the blade  40  and the shutter  29  are expected. Thus, the amount of toner scraped off the second blade  50  and led into the first portion  10 A can be adjusted more finely.  
         [0052]    The present invention being thus described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to those skilled in the art are intended to be included within the scope of the following claims.