Patent Publication Number: US-7899369-B2

Title: Powder conveying device and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 2007-0086370, filed on Aug. 28, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a powder conveying device, and more particularly to a powder conveying device and an image forming apparatus having the same. 
     2. Description of the Related Art 
     A powder conveying device is used to convey powder composed of fine particles such as, for example, toner particles. Generally, a powder conveying device may be used in manufacturing equipments for various products to convey powder type row material, or in a device that uses powder material in operation to convey a predetermined amount of powder. 
     An example of a powder conveying device is described in U.S. Pat. No. 7,076,192 to Tsuda et al. (“Tsuda”), which discloses a powder conveying device employed in an electrophotographic image forming apparatus to convey toner. The powder conveying device disclosed by Tsuda includes a coil spring (a rotary type feeding member) placed inside a conveying pipe and a driving device to rotate the coil spring. Toner in the conveying pipe is conveyed toward an outlet by the rotation of the coil spring. 
     The coil spring type powder conveying device, e.g., disclosed by Tsuda, may, unfortunately, cause unpleasant noise from the coil spring contacting against the inner surface of the curved conveying pipe while rotating inside, and being elastically deformed by the curved shape of, the conveying pipe. Further, a significantly large space may be required for forming the curved conveying path of the toner, which increases the overall size of the image forming apparatus. 
     Another type of powder conveying device may utilize an auger having a helical-shaped blade, by the rotation of which the toner particles may be conveyed in a conveying path. Examples of the auger type powder conveying devices are described in, e.g., Japanese Patent Laid-open Publication No. 2007-57790 to Yoshinori (“Yoshinori”) and Japanese Patent Laid-open Publication No. 2007-17464 to Tomoyuki (“Tomoyuki”). 
     These auger type powder conveying devices, e.g., of Yoshinori or Tomoyuki, because they require a motor to rotate the auger and a gear train to transmit the driving force, unfortunately, also tends to be expensive and to increase the overall size of the image forming apparatus. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an aspect of the invention to provide a powder conveying device and an image forming apparatus having the same that contributes to smaller size and lower cost of the image forming apparatus. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In accordance with an aspect of the invention, there is provided a powder conveying device to convey powder, comprising: a conveying plate having a surface on which the powder to be conveyed is supported; a vibration generating device configured to cause the conveying plate to vibrate; and a plurality of conveying protrusions provided on the surface of the conveying plate to promote a movement of the powder from an upstream end of the conveying plate to a downstream end of the conveying plate, each of the plurality of conveying protrusions having a first inclined surface facing the upstream end of the conveying plate and a second inclined surface facing the downstream end of the conveying plate, each first inclined surface of an associated one of the plurality of conveying protrusions having a smaller incline angle than the second inclined surface of the associated one of the plurality of conveying protrusions. 
     Each of the conveying protrusions may have a height that is less than or equal to ten times of a volume average diameter of particles of the powder. 
     Each of the conveying protrusions may have a height that is less than or equal to five times of the volume average diameter of particles of the powder. 
     Each of the conveying protrusions can be formed integrally with the conveying plate. 
     The vibration generating device may be mounted at the upstream end of the conveying plate. 
     The vibration generating device comprises a flat vibration brushless motor. 
     The first inclined surface of a conveying protrusion may form a first angle with respect to the surface of the conveying plate, the second inclined surface forming a second angle with respect to the surface of the conveying plate, the first angle being between 1° to 20°, and the second angle being between 20° to 150°. 
     The first angle may be between angle of 1° to 15°. 
     The powder conveying device may further comprise: a collision member disposed at a location within a range of motion of the conveying plate such that, when the conveying plate vibrates, the conveying plate collides with the collision member. 
     The collision member may be disposed near the downstream end of the conveying plate. 
     The conveying plate and the plurality of conveying protrusions may be coated with a coating layer to prevent the powder from adhering to surfaces of at least one of the conveying plate and the plurality of conveying protrusions. 
     The vibration generating device has a vibration intensity between 1 G to 11 and a number of revolution between 1,000 to 100,000 revolution per minute, where G is a unit of measuring the acceleration due to gravity at the Earth&#39;s surface, also known to those of ordinary skill in the art as “G-force”. 
     In accordance with another aspect of the invention, there is provided an image forming apparatus comprising: a main body defining an exterior appearance of the image forming apparatus; and a toner conveying device disposed in the main body, the toner conveying device comprising: a conveying plate having a surface on which toner to be conveyed is supported; a vibration generating device configured to cause the conveying plate to vibrate; and a plurality of conveying protrusions provided on the surface of the conveying plate to promote a movement of the toner from an upstream end of the conveying plate to a downstream end of the conveying plate, each of the plurality of conveying protrusions having a first inclined surface facing the upstream end of the conveying plate and a second inclined surface facing the downstream end of the conveying plate, each first inclined surface of an associated one of the plurality of conveying protrusions having a smaller incline angle than the second inclined surface of the associated one of the plurality of conveying protrusions. 
     The image forming apparatus may further comprise: a developing unit disposed in the main body, the developing unit may include: a supply roller disposed adjacent to the downstream end of the conveying plate so as to receive toner from the toner conveying device; and a developing member disposed adjacent to the supply roller to receive the toner from the supply roller, the developing member being configured to apply the toner received from the supply roller to an electrostatic latent image formed on a photosensitive body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the embodiments of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, of which: 
         FIG. 1  is a side-sectional view schematically illustrating an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  is a side-sectional view schematically illustrating a developing unit of the image forming apparatus shown in  FIG. 1 ; 
         FIG. 3  is a side view schematically illustrating a powder conveying device of the developing unit shown in  FIG. 2 ; 
         FIGS. 4 to 6  are side views illustrating a portion of the powder conveying device shown in  FIG. 3 ; 
         FIGS. 7   a  and  7   b  are side views illustrating several embodiments of the conveying protrusions of the powder conveying device; and 
         FIGS. 8 and 9  are side views schematically illustrating a powder conveying device according to yet another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     As shown in  FIG. 1 , an image forming apparatus according to this embodiment may be, e.g., an electrophotographic type color image forming apparatus, which includes a main body  11  that defines the exterior appearance of the image forming apparatus, developing units  30  of four colors (e.g., yellow, magenta, cyan and black) mounted in the main body  11 , and powder conveying devices  40  mounted in the respective developing units  30  to convey toner. 
     According to this embodiment, inside the main body  11  are mounted four exposure units  20  to irradiate light to the respective developing units  30 , a transfer unit  60  to transfer visible toner images formed on the respective developing units  30  onto a printing medium, and a fusing unit  70  to fuse the transferred visible images to the printing medium. In addition, inside the main body  11  are mounted a printing medium feeding device  12  to supply a printing medium, a pickup device  13  to pick up the printing medium loaded in the printing medium feeding device  12 , a feeding roller  14  to feed the picked-up printing medium toward the developing units  30 , and a discharge roller  15  to discharge the printing medium that has passed through the fusing unit  70  to the outside of the main body  11 . 
     The transfer unit  60  may include a feeding belt  61  to feed the printing medium, plural belt driving rollers  62  to run the feeding belt  61 , and plural transfer rollers  63  to transfer visible images formed on photosensitive bodies  33  provided in the developing units  30  onto the printing medium fed by the feeding belt  61 . The fusing unit  70  may include a heating roller  71  to generate heat, and a press roller  72  provided to rotate while being in pressing contact with the heating roller  71 . 
     As shown in  FIG. 2 , each of the developing units  30  includes a housing  31 , a photosensitive body  33  mounted at an end portion of the housing  31  in such a way that a portion of the photosensitive body  33  is exposed to the outside, on which an electrostatic latent image is formed by receiving light from the exposure unit  20 , a charge device  34  to charge the surface of the photosensitive body  33  to a predetermined electric potential, a developing member  35  to form a visible image by attaching toner to the photosensitive body  33  on which the electrostatic latent image has been formed, a supply roller  36  to supply toner to the developing member  35 , and a powder conveying device  40  to convey toner to the supply roller  36 . 
     The housing  31  is provided with a supply port  32  at an upper portion thereof, and a toner container  50  for supplying toner into the housing  31  is coupled to the upper portion of the housing  31 . The toner in the toner container  50  is supplied into the housing  31  through the supply port  32 . The powder conveying device  40  conveys the toner supplied through the supply port  32  near one end of the housing  31  towards the supply roller  36  mounted at the other end of the housing  31 . 
     The powder conveying device  40  includes a conveying plate  41  on which toner particles are carried, a plurality of conveying protrusions  42  provided on the surface of the conveying plate  41 , a vibration generating device  43  to vibrate the conveying plate  41 , and a collision member  45  mounted spaced apart from the conveying plate  41  so as to collide with the conveying plate  41 . As shown in  FIG. 3 , if the vibration generating device  43  operates to vibrate the conveying plate  41 , the toner on the surface of the conveying plate  41  is applied with a propulsive force in horizontal and vertical directions, and is conveyed toward the supply roller  36  by the interaction with the conveying protrusions  42 . 
     The conveying plate  41  and the conveying protrusions  42  may be made of the same material, or may be made of different materials from each other. The conveying plate  41  and the conveying protrusions  42  can be made of various materials, for example, a metallic material such as aluminum, stainless steel (SUS), brass or the like, or a resin material such as acrylic resin, silicone resin, polycarbonate resin or the like. The surfaces of the conveying plate  41  and the conveying protrusions  42  may be coated with a coating layer  44 , which may be, e.g., silicone or Teflon, so as to prevent the toner from being adhered to the conveying plate  41  and/or the conveying protrusions  42 . 
     Although the conveying plate  41  and the conveying protrusions  42  are not depicted in detail because the drawings show the shapes of the conveying plate  41  and the conveying protrusions  42  viewed from the side, the conveying plate  41  may be formed as a flat rectangular plate shape having a regular width. Each of the conveying protrusions  42  may have a length equal to the width of the conveying plate  41 , and may have a triangular or a ramp cross-sectional shape. Preferably, the plurality of conveying protrusions  42  are arranged on the surface of the conveying plate  41  with a regular gap therebetween, the size of which gap may vary. 
     As shown in  FIG. 4 , if the vibration generating device  43  operates to vibrate the conveying plate  41 , particles P of the powder on the surface of the conveying plate  41  are applied with a propulsive force that is substantially isotropic in the horizontal and vertical directions. The particles P, to which such a propulsive force is applied, are conveyed to the right as shown in the drawing by the interaction with the plurality of conveying protrusions  42 . 
     As shown in  FIG. 5 , it is preferred that each of the conveying protrusions  42  has a height H, which may be up to ten times the volume average diameter of the powder particles P. More preferably, the height H of each of the conveying protrusions  42  may be less than or equal to five times the volume average diameter of the powder particles P. The slope of the upstream ramp (with respect to the conveying direction of toner) of each of the conveying protrusions  42  is smaller than the slope of the downstream ramp. In other words, the upstream incline angle α formed between the upstream ramp surface  42   a  of the conveying protrusion  42  and the surface of the conveying plate  41  is smaller than the downstream angle β formed between the downstream ramp surface  42   b  of the conveying protrusion  42  and the surface of the conveying plate  41 . Since the conveying protrusion  42  is shaped such that the upstream angle α is smaller than the downstream angle β, a force Fup required for the powder particle P on the upstream surface  42   a  to climb up the upstream ramp surface  42   a  against the gravity Fg is smaller than the force Fdown required for the powder particle P on the downstream surface  42   b  to climb up the downstream ramp surface  42   b  against the gravity Fg. Accordingly, when the propulsive force is applied to the powder by the vibration generating device  43 , the amount of powder moving in the downstream direction is larger than the amount of powder moving in the upstream direction. As a result, the powder is conveyed in the downstream direction. 
     The upstream angle α of the conveying protrusion  42  is preferably in the range of 1° to 20°, more preferably 1° to 15°. When the upstream angle α is larger than 15°, the performance of conveying the powder in the downstream direction may deteriorate. The downstream angle β is preferably in the range of 20° to 150°. If the downstream angle β is set beyond this range, the conveyance of the powder may become difficult. 
     The vibration generating device  43  is mounted under the conveying plate  41  to vibrate the conveying plate  41 . Various devices capable of vibrating the conveying plate  41 , for example, a piezoelectric element, a vibration motor having an eccentric rotating body, a flat vibration brushless motor, etc., can be used as the vibration generating device  43 . A vibration intensity of the vibration generating device  43  varies depending on the type of the powder. For example, when the powder of polyester resin with a volume average diameter of 8.0 μm is intended to be conveyed, it is preferable to use the vibration generating device  43  having a vibration intensity of between 1 G to 11 G. 
     Taking the size and cost into consideration, it is preferable to use a flat vibration brushless motor (for example, a flat vibration brushless motor disclosed in Japanese Patent Laid-open Publication No. Hei 5-38093 (published on Feb. 12, 1993 to Makoto), the disclosure of which is incorporated herein by reference) as the vibration generating device  43 . While the scope of the present invention is not so limited, it may be preferred that the motor has a number of revolutions of between 1,000 to 100,000 revolutions per minute (rpm). A number of revolutions smaller than 1,000 rpm may not provide a sufficient conveyance of the toner particles. If the number of revolutions is larger than 100,000 rpm, the cost of the motor may be high. 
     The collision member  45  is provided to enhance the conveyance of toner. As shown in  FIG. 6 , the collision member  45  is disposed in the downstream side from the conveying plate  41  on the toner conveying path, at a predetermined distance D from the end of the conveying plate  41 . The distance D between the conveying plate  41  and the collision member  45  can vary depending on the vibration intensity of the vibration generating device  43 , the distance between the vibration generating device  43  and the collision member  45  and the material of the conveying plate  41 , however, the distance D may be preferably in the range of 0.1 mm to 1 mm. When the conveying plate  41  vibrates by the vibration generating device  43 , the end of the conveying plate  41  collides with the collision member  45 , reducing the velocity of the conveying plate  41 . However the toner on the surface of the conveying plate  41  continue to move in the downstream direction by the inertial force. Accordingly, the toner conveying performance may be enhanced. The collision member  45  may be made of various materials which are not deformed by the collision, such as a metallic material, a ceramic material, a resin material or the like. 
       FIGS. 7   a  and  7   b  show examples of other embodiments of the conveying protrusions  42 ′ and  42 ″. Many other variations may be possible, including, as shown in  FIG. 7A , curved ramp surfaces. 
       FIGS. 8 and 9  show schematically a powder conveying device according to another embodiment. Similarly to the powder conveying device  40  of the previous embodiment, a powder conveying device  80  shown in  FIGS. 8 and 9  includes a conveying plate  81  and a plurality of conveying protrusions  83  arranged on the surface of the conveying plate  81 . A vibration generating device  84  is mounted to the end in the upstream side of the conveying plate  41 , and a collision member  85  is mounted below the conveying plate  81 . The conveying plate  81  is provided with a collision portion  82  on the lower surface thereof. The collision portion  82  of the conveying plate  81  is disposed at a predetermined distance from the collision member  85 , and collides with the collision member  85  when the conveying plate  81  vibrates. Since the collision member  85  is mounted below the conveying plate  81 , the conveyed powder can be prevented from being attached to the end of the conveying plate  81  and the collision surface of the collision member  85 . 
     As shown in  FIG. 9 , when the vibration generating device  84  is mounted at the upstream end of the conveying plate  81 , the powder particles P on the surface of the conveying plate  81  can be applied with a larger propulsive force in the downstream direction, and thereby the powder conveyance may be enhanced. 
     Hereinafter, results of the experimental measurements of the conveyance performance of several proto-type powder conveying devices will be explained. 
     Embodiment 1-1 
     The conveying plate  41  of this embodiment is manufactured by the use of the photo-shaping method disclosed in Japanese Patent Laid-open Publication No. 2006-348214 (published on Dec. 28, 2006 to Katsuyuki et al.), the disclosure of which is incorporated herein by reference. The manufacturing steps are as follows. 
     First, dipentaerythritol hexaacrylate of 80 g, ethoxy trimethylolpropane triacrylate of 20 g, CGI403 of 3 g, 4-diethyl thioxanthone of 2 g, 4-dimethylaminobenzoate ethylester of 0.5 g, Yellow6G Gran of 2 g, SH28PA (manufactured by Ciba Specialty Chemicals Corporation of Basel, Switzerland) of 0.06 g, FM0411-TH (manufactured by Chiba Specialty Chemicals Corporation) of 0.18 g, and allyl ether copolymer (Mariarim AAB-0851: manufactured by Nippon Oils and Fats Co., Ltd. of Tokyo, Japan) of 6.5 g are added into a container having a mixing device, and are mixed at a temperature of 60° C. for 1 hour. Subsequently, alumina particles (TM-DAR: manufactured by Daimei Chemical Industry Co., Ltd. of Japan) of 209 g is added, and then is evenly dispersed by the use of a homogenizer (trade name “T. K. HOMODISPER™”, manufactured by Tokushu Kika Kogyo Co., Ltd or Special Machine Industry Co., Ltd. both of Japan), thereby manufacturing a photo-curable liquid composition. 
     Thereafter, so manufactured photo-curable liquid composition is positioned on a stage which is moves up and down in the container, forming a thin layer of the liquid composition. The mask and the stage are selectively exposed to light to thereby forming the conveying plate  41 . The plurality of conveying protrusions  42  are arranged with a predetermined gap therebetween on the surface of the conveying plate  41 . 
     In this embodiment, the conveying plate  41  has a length of 100 mm, a width of 20 mm, and a thickness of 2 mm. Each of the conveying protrusions  42  has a height H of 0.03 mm, an upstream angle α of 5°, and a downstream angle β of 90°. The conveying protrusions  42  are arranged with a gap of 0.5 mm therebetween. 
     A flat motor (FM88E: manufactured by Tokyo Part Industry Co., Ltd. of Japan) is used as the vibration generating device  43 , and is adhered to the upstream end of the conveying plate  41  by use of a double-sided adhesive tape with a thickness of 0.1 mm. 
     Embodiment 1-2 
     The powder conveying device of this embodiment has the same structure as the powder conveying device of the embodiment 1-1, except that the upstream angle α of the conveying protrusion  42  is 10°. 
     Embodiment 1-3 
     The powder conveying device of this embodiment has the same structure as the powder conveying device of the embodiment 1-1, except that the upstream angle α of the conveying protrusion  42  is 15°. 
     Embodiment 1-4 
     The powder conveying device of this embodiment has the same structure as the powder conveying device of the embodiment 1-1, except that the upstream angle α of the conveying protrusion  42  is 30°. 
     After placing 0.1 g of the powder on the upstream end of the conveying plate  41  of each of the powder conveying devices of the four aforementioned embodiments, a time required for the powder to be conveyed to the downstream of the conveying plate  41  was measured. The measured results are shown in the below table 1. 
     The powder used in the test was formed in such a way that the particles made of polyester resin, a staining agent and wax was externally treated with silica and titanium dioxide. The powder has a volume average diameter of 8.3 μm, a density of 0.44 g/cm 3 , and an average sphericity of 0.912. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Embodiment 
                 Embodiment 
                 Embodiment 
                 Embodiment 
               
               
                   
                 1-1 
                 1-2 
                 1-3 
                 1-4 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Conveying 
                 10 
                 15 
                 30 
                 Not Conveyed 
               
               
                 Time (Sec) 
               
               
                   
               
            
           
         
       
     
     As can be seen from the above table 1, when the upstream angle α is smaller, the conveyance performance may be better. 
     Embodiment 2 
     The powder conveying device  40  of this embodiment has the same structure as the powder conveying device of the embodiment 1-1, except that the height H of the conveying protrusion  42  is 0.1 mm and the gap between the adjacent conveying protrusions is 1.5 mm. The powder conveying test was performed with respect to the powder conveying device of this embodiment under the same conditions as the aforementioned test. However, the powder could not be conveyed from the upstream end to the downstream end. 
     Embodiment 3 
     The powder conveying device  40  of this embodiment has the same structure as the powder conveying device of the embodiment 1-1, except that the vibration generating device  43  is mounted under the middle portion of the conveying plate  41 . The powder conveying test was performed with respect to the powder conveying device of this embodiment under the same conditions as the aforementioned test. It took 25 seconds for the powder to be conveyed from the upstream end of the conveying plate to the downstream. 
     While in the above description various embodiments of powder conveying devices are described mainly in connection with their utility in supplying toner in developing units of image forming apparatuses, it should be readily apparent however that the powder conveying devices described herein have wider utilities. For example, powder conveying devices described herein can also be used to convey waste toner in an image forming apparatus, or can be used in any apparatuses, including manufacturing equipment, that requires conveyance of powder type material. 
     To that end, the powder conveying devices described herein may provide the advantages of taking up less space and/or of lower cost when compared with the conventional auger type, coil spring type or belt conveyor type powder conveying device. 
     Although embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.