Abstract:
A developing apparatus for supplying toner includes a toner hopper configured to hold unused toner, a developing tub, and a toner hopper mounting part provided between the developing tub and the toner hopper. The toner hopper is adapted to be mounted to and removed from the toner hopper mounting part. The toner hopper mounting part includes a vibration apparatus for vibrating the toner hopper mounting part to loosen the unused toner stored in the toner hopper.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a developing apparatus for converting an electrostatic latent image to a visible image and to an image forming apparatus using the inventive developing apparatus. The present invention also relates to a method of supplying toner in an image forming apparatus. 
     2. Discussion of the Background 
     In the image forming apparatus to which the electrophotographic copying method is applicable such as copying machine, facsimile device, or printer, a developing process of supplying toner employed as developer (i.e., a developing agent) (hereinafter, “toner”) to an electrostatic latent image formed on the image carrier, such as a photosensitive body is performed. The electrostatic latent image is converted to a visible image. 
     The developing apparatus employed in the developing process is constructed with a developing sleeve opposing the image carrier in the developing tub and supplying the toner carried on the surface thereof to the image carrier. A toner replenishing part is mounted on the developing tub and contains unused toner in the interior of the developing tub. 
     In the developing apparatus, visible image treatment for the electrostatic latent image (i.e., the developing process) is performed by electrostatically absorbing toner carried on the developing sleeve by the action of the electrostatic attraction force of the electrostatic latent image formed on the image carrier. When the amount of the toner contained in the developing tub becomes insufficient, the toner is replenished from the toner replenishing part. 
     The toner replenishing part is provided with, for instance, a container (such as a bottle, a hopper, etc.) containing unused toner in the interior thereof and disposed such that the opening thereof is directed downward. By driving the toner replenishing member installed on the opening part, the necessary (or required) amount of the toner is replenished to the developing tub. 
     Here, the toner contained in the toner replenishing part has a comparatively strong attraction force between the toner particles, and the toner is apt to be solidified in the container. When the toner is solidified therein, only a part of the solidified toner is peeled off in the container, and the other part thereof remains solidified in the container, and thus, all toner cannot be replenished on some occasions. 
     Furthermore, even though the toner slips down in the container, the solidified toner may set into the developing tub and/or cause the exhaust opening to become clogged with the solidified toner. 
     In order to solve such troublesome matters, a vibration is applied to the toner discharged from the container, and the toner is broken into pieces and/or pulverized. As a result, the toner is dispersed uniformly and supplied into the developing tub. Such structure is disclosed, for instance, in the published specification of the Japanese Laid-Open Patent Publication No. 6-222672/1994. Or otherwise, the bottle is rotated and pulsed so that the toner contained in the developing tub is demolished by an agitating member disposed therein. 
     Such structure is disclosed, for instance, in the published specification of the Japanese Laid-open Utility Model Publication No. 6-69961/1994. 
     However, according to the former structure, the solidification of the toner contained in the bottle or the hopper cannot be eliminated, while, according to the latter structure, there arises a new problem that it is necessary to further prepare a special structure for equipping the bottle with the agitating member and/or controlling the rotation of the bottle. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to solve the problems discussed above. 
     It is another object of the present invention to provide a developing apparatus and an image forming apparatus using the developing apparatus that avoid the problems discussed above. 
     It is still another object of the present invention to provide a developing apparatus and an image forming apparatus using the developing apparatus capable of preventing the problem that the contained toner remains in the container, in particular, in consideration of the structure of replenishing the toner. 
     It is still another object of the present invention to provide a developing apparatus and an image forming apparatus using the developing apparatus, having a simple structure and a low maintenance cost. 
     These and other objects are achieved according to the invention by providing a developing apparatus that supplies toner to a latent image on a latent image carrier. The developing apparatus includes a toner hopper configured to hold unused toner, a developing tub, and a toner hopper mounting part provided between the developing tub and the toner hopper. The toner hopper is adapted to be mounted to and removed from the toner hopper mounting part. The toner hopper mounting part includes a vibration apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a schematic perspective view illustrating the developing apparatus of the present invention; 
     FIG. 2 is a cross-sectional view of the developing apparatus of FIG. 1 showing how toner is discharged when the vibration apparatus  5  of the developing apparatus is not operating; 
     FIG. 3 is a cross-sectional view of the developing apparatus of FIG. 1 when the vibration apparatus is operating; 
     FIG. 4A is a schematic view illustrating a motor used as the vibration apparatus  5  of the developing apparatus of FIG. 1; 
     FIGS. 4B through 4G are plan views showing examples of eccentric members attached to the shaft of the motor in FIG. 4A; 
     FIG. 5 is an explanatory diagram showing the state of the vibrating toner when the motor shown in FIG. 4A is used; 
     FIG. 6A is a schematic view illustrating the use of a piezoelectric element  5 B as the vibration apparatus; 
     FIG. 6B is a diagram illustrating the vibration of the piezoelectric element  5 B when a voltage is applied thereto; 
     FIG. 7 is an enlarged schematic perspective view illustrating the structure of the piezoelectric element  5 B shown in FIG. 6; 
     FIG. 8 is a schematic perspective view illustrating how a plurality of vibration apparatuses may be implemented with a single developing apparatus; 
     FIG. 9 is a graph explaining the vibration transmission rate on the basis of the relationship between the applied vibration frequency of the vibration apparatus and the inherent vibrations of the toner hopper; 
     FIG. 10 is a block diagram showing how the applied vibration frequency of the vibration apparatus is changed; 
     FIG. 11 is a cross-sectional view of the image forming apparatus of the present invention; 
     FIG. 12 is a perspective external view of image forming apparatus in FIG. 11 with the upper cover removed; 
     FIG. 13 is a perspective external view of the image forming apparatus in FIG. 11; 
     FIG. 14 is a partial perspective view of the toner replenishing parts of the image forming apparatus in FIG. 11; 
     FIG. 15 is a perspective view of a toner replenishing part; 
     FIG. 16 is a cross-sectional view of the toner hopper serving as the toner supplying device in the toner replenishing part in FIG. 15; and 
     FIG. 17A is a cross-sectional view of a modified toner hopper; and 
     FIG. 17B is a perspective view of a shutter member  210  of the toner hopper. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, there is illustrated a developing apparatus  1  for supplying toner to a latent image carried on a latent image carrier and for converting the latent image to a visible image with the toner. The developing apparatus  1  includes a toner hopper  3  containing unused toner and a toner hopper mounting part  4  provided with a vibration apparatus  5 . FIG. 11 shows an image forming apparatus using the above-mentioned developing apparatus  1 . 
     In order to attain the aforementioned objects of the present invention, in the developing apparatus there is provided a toner hopper containing therein unused toner and a toner hopper mounting part communicating with a developing tub in the developing apparatus with the toner hopper and capable of setting up the toner hopper therein. The toner hopper mounting part includes a vibration apparatus mounted thereon. 
     The vibration apparatus includes a motor and an eccentric part formed on the rotative shaft of the motor. The motor is fixed on the wall (or surface) portion of the toner hopper mounting part, and the size of the above-mentioned eccentric part is smaller than the outer size of the motor. The vibration apparatus is constructed with a piezoelectric element mounted on the wall portion of the toner hopper mounting part. The toner hopper mounting part has plurality of vibration apparatuses. 
     In such developing apparatus, given that the frequency of the vibration, fm, and the inherent frequency of the toner hopper mounting part, fs, the respective factors are set so as to satisfy the following inequalities 
     
       
         ( fm/ {square root over (2)})&lt; fs&lt; ({square root over (2)} ·fm ). 
       
     
     On the other hand, given the frequency of the applied vibration, fm, and the inherent frequency of the toner hopper, fh, the respective factors are set so as to satisfy the following inequalities 
     
       
         ( fm/ {square root over (2)})&lt; fh&lt; ({square root over (2)} ·fm ). 
       
     
     In this latter case, the vibration applying frequency fm can be changed. 
     In the image forming apparatus using the developing apparatus as mentioned heretofore, when the density of a standard density pattern image reaches a value equal to or smaller than a predetermined density, the vibration apparatus provided in the toner hopper mounting part, on which the toner hopper is detachably supported, is driven such that the toner hopper resonates, and toner is caused to flow in the toner hopper and supplies the latent image carrier. 
     A plurality of developing apparatuses may be provided corresponding to the electrostatic latent images for each of the respective colors formed on the latent image carrier. The developing apparatus is disposed in an opening portion capable of opening and closing by use of a cover provided on the upper part of the main body of the image forming apparatus. 
     A toner supplying unit for supplying toner may be attached to, and detached from, the developing apparatus at the opening. The vibration apparatus can initiate lengthwise (i.e., vertical) vibration. The vibration apparatus can be controlled to initiate the vibration at times other than the image forming time. The developing apparatus is constructed such that the vibration of the vibration apparatus does not propagate between the respective colors. The developing apparatus can change the vibration applying intensity of the vibration apparatus for each of the respective colors. The hoppers are square-shaped in the respective developing apparatuses. One end of the hopper is made in a conical shape. An opening portion is formed at the tip end portion of the hopper. A toner supply controlling device for controlling the supply of toner is provided in the opening portion. The toner supply controlling device is formed of a mesh material having mesh size of 50 to 500 μm. The hopper is constructed such that the toner contained therein can be seen from outside the hopper. The hopper may be provided with a cap having an opening portion capable of being opened and closed, and the hopper is replenished with toner by removing the cap. 
     FIG. 1 is a schematic diagram for explaining the principle and the structure of a developing apparatus according to the present invention. 
     In FIG. 1, the developing apparatus  1  is provided with a developing tub  2  containing therein a developing sleeve and an agitating wing and a toner hopper  3 . The developing sleeve is constructed with a rotative sleeve capable of forming a magnetic brush, and the agitating wing agitates the toner contained in the developing tub. Thus, the toner is frictionally charged. 
     The toner hopper  3  is mounted on a toner hopper mounting part  4  provided on a suitable portion of the developing tub  2  so as to be attached to, or detached from, the toner hopper mounting part  4 . The hopper  3  can be exchanged. The toner hopper mounting part  4  is provided on the communicating portion between the developing tub  2  and the toner hopper  3 . The toner hopper  3  can be mounted so as to be attached to, or detached from, the toner hopper mounting part  4 . 
     A vibration apparatus  5  is mounted on an outer surface of the toner hopper mounting part  4 . The vibration apparatus  5  controls the vibration starting time and the vibration duration time in accordance with a signal received from the density sensor. When the outer wall of the toner hopper mounting part  4  is vibrated by the vibration apparatus  5 , the vibration is transmitted to the toner hopper  3 . In the present invention, when the density sensor detects that the density of a standard density pattern formed on the photosensitive body reaches a value equal to or smaller than a predetermined density value, the vibration apparatus operates until the density thereof exceeds the predetermined value. 
     In the structure of the present embodiment, the toner hopper  3  containing the unused toner is inserted into the toner hopper mounting part  4 . When the density sensor detects that the density of a standard density pattern formed on the photosensitive body is low, the vibration apparatus  5  starts its operation, and in this manner, the outer wall of the toner hopper mounting part  4  is vibrated. 
     When the outer wall thereof is vibrated, the vibration of the outer wall is transmitted to the toner hopper  3 . When the vibration is transmitted to the toner hopper  3 , the toner hopper  3  is also vibrated. The vibration is applied to the toner contained in the toner hopper  3  and the toner is broken into small pieces and/or pulverized. The distance between the toner particles increases to the extent that the attraction (or attracting) force between the toner particles does not cause the toner particles to clump together. Thus, the toner can flow toward the discharging opening of the toner hopper  3 . 
     As shown in FIG. 2, when the vibration from the vibration apparatus  5  is not transmitted to the toner hopper mounting part  4 , the toner T contained in the interior of the toner hopper solidifies due to the influence of the attraction force between the toner particles. Thus, the toner is not apt to slide down toward the toner discharging opening. 
     However, as shown in FIG. 3, when the vibration apparatus  5  operates, the toner particles T themselves are mutually vibrated due to the vibration of the toner hopper through the toner hopper mounting part  4  (for convenience, represented by vibration waves), and the distance between the toner particles is widened, and thereby the mutual positions of the toner particles are changed. Consequently, the toner particles become in a fluid-like state and are able to slip down to the toner discharging portion. 
     Furthermore, since the toner particles are caused to settle downward by the action of the vibration, the toner can flow out from the toner discharging opening without clogging the toner discharging opening. 
     Since the toner particles contained in the toner hopper  3  are vibrated by applying the vibration to the entire toner hopper  3  instead of the toner discharging opening, the fluidity of the toner can be obtained over the entire area of the interior of the toner hopper  3 . Consequently, the toner solidified on positions other than the toner discharging opening in the toner hopper  3  can be prevented from remaining solidified within the hopper. 
     In order to vibrate the entire area of the toner hopper  3 , the vibration apparatus, such as a motor, may be placed in the toner hopper  3 . However, the motor may clog the toner and/or fail to vibrate. 
     On the other hand, if a vibration apparatus is mounted on the outer wall surface of the toner hopper mounting part  4 , the motor cannot clog the toner and is less likely to malfunction. Furthermore, since the vibration apparatus  5  is provided on the toner hopper mounting part  4  instead of the toner hopper  3 , the toner hopper can be easily exchanged with other toner hoppers. Furthermore, it is not necessary to perform the troublesome task of installing the vibration apparatus in the new toner hopper when the toner hopper  3  is exchanged. 
     Furthermore, when the vibration apparatus  5  is driven based on the density of a standard density pattern formed on the photosensitive body. When the density is lower than (or equal to or lower than) the density of the standard density pattern, the attraction of the toner particles to one another can be greatly reduced. Also, situations in which the toner is blocked or clumps of toner is replenished can be avoided. Consequently, it is possible to supply the new toner uniformly to the photosensitive body. Thus, the unevenness of the density on the photosensitive body can be eliminated. Alternatively or in addition to being formed on the photosensitive body, the same standard density pattern or a different standard density pattern may be formed on an intermediate transfer body (e.g., drum, belt, etc.), if the image forming apparatus is provided with an intermediate transfer body. 
     FIG. 4A shows a motor  5 A employed as the vibration apparatus  5 . FIG. 4A is a perspective view showing the overall structure of the vibration apparatus. FIGS. 4B through 4G are plan views showing some examples of eccentric members attached to the shaft of the motor  5 A. In FIG. 4A, the motor  5 A is a small-sized motor such as the type used to vibrate a portable telephone set. A weight  5 A 2  is fixed on the area corresponding to one side of the circular circumferential direction of the rotation shaft  5 A 1 . 
     The size of the outer diameter of the weight  5 A 2  is smaller than that of the motor  5 A. When the motor rotates, the weight  5 A 2  is not brought into contact with the outer surface (wall) of the toner hopper mounting part  4 . Several possible shapes of the weights  5 A 2  attached to the motor shaft are as shown in FIGS. 4B through 4G. Those weights can be fixed on the shaft by a screw, adhesive agent, by tight (fixed) insertion, etc. The eccentric member (i.e., weight  5 A 2 ) vibrates, and its vibration is transmitted to the toner hopper  3  through the toner hopper mounting part  4 . 
     In such structure of the present embodiment as mentioned above, the motor  5 A is fixed on the outer surface of the toner hopper mounting part  4 . As in the case of the embodiment shown in FIG. 1, the motor  5 A is rotated by the signal from the density sensor. When the rotation shaft  5 A 1  is rotated by the motor  5 A, the motor  5 A itself is vibrated by the action of the centrifugal force due to the shift of the center of gravity of the weight  5 A 2  around the center of the rotation shaft  5 A 1 . 
     As shown in FIG. 5, since the weight  5 A 2  does not directly hit the outer surface of the toner hopper mounting part  4  and the vibration of the motor  5  occurs due to the centrifugal force, the vibration applying frequency can be made comparatively low. Thus, it is possible to prevent the toner from being consolidated due to the small impact force exerted on the toner. Consequently, the toner can be kept fluid. 
     FIG. 6A shows a piezoelectric element  5 B used as the vibration apparatus  5 . FIG. 6A is a perspective view showing the overall structure thereof. FIG. 6B is a diagram showing the state of the vibration of the piezoelectric element at the time of applying the AC or pulse voltage thereto. In FIG. 6A, the piezoelectric element  5 B has a laminer structure and is fixed to the outer surface of the toner hopper. The laminating direction of the laminar structure is perpendicular to the outer surface of the toner hopper mounting part  4 . The piezoelectric element vibrates as shown in FIG. 6B, and its vibration is transmitted to the toner hopper  3  through the toner hopper mounting part  4 . 
     As shown in FIG. 7, the piezoelectric element  5 B is constructed by laminating a plurality of the piezoelectric plates  5 B 1 . The directions of the polarization of the adjacent piezoelectric plates  5 B 1  differ by 180° from each other. The respective piezoelectric plates  5 B 1  are electrically driven in parallel by an electric power source. The displacement of the piezoelectric plates may occur in the laminating direction. Assuming that the number of the laminations of the piezoelectric plates  5 B 1  is N, the applied voltage is V, and the multiplier (multiplying number) is d 33 . The displacement x occurring on the piezoelectric element  5 B having such shape can be represented by the following equation 
     
       
         
           x=N d 
           33 
           ·V. 
         
       
     
     Since the present embodiment adopts the structure as mentioned heretofore, the laminating direction of the piezoelectric element  5 B is set to a direction perpendicular to the outer surface of the toner hopper mounting part  4 . The piezoelectric element  5 B is mounted on the outer wall surface thereof so as to be fixed thereon. 
     By applying the voltage to the piezoelectric plate  5 B 1 , the displacement on the respective piezoelectric plates  5 B 1  occurs. Although the displacement amount of the piezoelectric plate  5 B 1  per one layer is very small, the displacement amount thereof can be increased in proportion to the number N of the laminations by adjusting the number N. 
     In particular, by inputting a pulse voltage to the laminated piezoelectric plates  5 B 1 , the vibration can be altered by altering the frequency of the pulse. 
     According to the present invention, the fluidity of the toner can be optimized by changing the vibration frequency. In addition, the space for installing the vibration apparatus  5  required for that purpose can be reduced. 
     FIG. 8 illustrates how a plurality of vibration apparatuses  5  may be used with a developing apparatus. In FIG. 8, the vibration apparatuses  5  are installed to uniformly generate vibrations over the entire area of the outer surface of the toner hopper mounting part  4 . By installing the vibration apparatuses  5  on plural positions of the outer surface of the toner hopper mounting part  4 , the entire area of the outer wall surface thereof can be uniformly vibrated. 
     Since the present embodiment adopts the structure as mentioned heretofore, it is possible to apply the external force caused by the uniform vibration to the toner particles which may be in aggregate or solid form. Consequently, the state of the toner particles remain in a static state until the stress between the toner particles reaches a value greater than the adhesion force between the toner particles. In this manner, the toner particles are made to flow fluidly. 
     Furthermore, since the distance between the toner articles is widened by the vibrations, the positions of the toner particles can change, and the distance therebetween is widened to a distance in which the adhesion (or attraction) force between the toner particles is reduced. Thus, the toner particles can flow as mentioned above. 
     In particular, since a plurality of vibration apparatus  5  are installed on the overall area of the toner hopper mounting part  4  so as to enable vibrations to be transmitted to the entire area of the toner hopper  3  in which the toner is contained, the aforementioned fluidity property of the toner can be obtained throughout the entire toner containing part in the toner hopper  3 . 
     Here, the vibration apparatuses  5 ,  5 A,  5 B are adjusted such that the relationship between the vibration applying frequency, fm, of the vibration apparatus itself and the inherent vibration frequency, fs, of the toner hopper mounting part  4  satisfies the following inequality 
     
       
         ( fm/ {square root over (2)})&lt; fs&lt; ({square root over (2)} ·fm ). 
       
     
     By setting such a relationship, even though a slight (very small) vibration applying force is generated in the vibration apparatuses  5 ,  5 A,  5 B in order to resonate the toner hopper mounting part  4 , since the vibration can be effectively transmitted to the toner hopper  3 , energy savings can be realized. In addition the fluidity of the toner in the toner hopper  3  can be secured. 
     FIG. 9 is a graph showing the vibration transmitting rate. FIG. 9 explains the vibration transmitting rate on the basis of the relationship between the vibration frequency of the vibration apparatus  5 ,  5 A,  5 B and the inherent vibration frequency of the toner hopper. In FIG. 9, when the ratio between the vibration applying frequency, fm, and the inherent vibration frequency of the toner hopper is equal to 1 (i.e., when both of the above values coincide with each other), the amplitude of the vibration reaches a maximum. Thereby, several hundred times the amplitude of the vibration applying can be obtained according to some attenuation ratio. 
     Furthermore, the relationship between the vibration applying frequency fm of the above-mentioned vibration apparatus and the inherent vibrations number, fh, of the toner hopper  3  satisfies the following inequality 
     
       
         ( fm/ {square root over (2)})&lt; fh&lt; ({square root over (2)} ·fm ). 
       
     
     Even by setting such a relationship in the developing apparatus, the toner hopper is resonated via the toner hopper mounting part  4 . Thus, even though a slight (faint) vibration force exists, the toner hopper  3  can be effectively vibrated. Therefore, the toner in the toner hopper  3  can be prevented from remaining therein. In addition, to prevent clogging at the opening for exhausting the toner, the fluidity of the toner can be maintained using less energy. The relationship between the vibration frequency, fm, of the vibration apparatuses  5 ,  5 A,  5 B and the inherent vibration frequency, fs, of the toner hopper mounting part  4 , and/or the inherent vibration frequency, fh, of the toner hopper  3  can be set by the control circuit of the structure shown in FIG.  10 . 
     FIG. 10 is a block diagram explaining the structure for setting the vibration frequency of the abovementioned vibration apparatus. In FIG. 10, the vibration apparatus (for convenience, the one represented by the reference numeral  5  is used) sets the vibration applying frequency in accordance with the signal received from the vibration applying frequency controlling apparatus  6 . The vibration applying frequency controlling apparatus  6  sets the vibration applying frequency on the basis of the signal received from the toner amount detecting sensor  7 . The toner amount detecting sensor detects the amount of toner contained in the toner hopper  3 . 
     The vibration frequency controlling apparatus  6  changes the vibration frequency for resonating the toner hopper  3  at a maximum amplitude on the basis of the mass variation of the toner hopper  3 , corresponding to the amount of the toner contained in the toner hopper  3 . As the mass in the toner hopper changes, the newly set vibration applying frequency is output to the vibration apparatus  5 . 
     Furthermore, it may be also possible to use an acceleration pickup capable of detecting the acceleration of the toner hopper  3  at the time of the vibration thereof instead of using the above-mentioned toner amount detection. 
     The image forming apparatus having the developing apparatus provided with the above-mentioned vibration apparatus is described hereinafter in detail. The image forming apparatus may be a color printer, for example, capable of forming a multiple-color image including a full-color image. Moreover, it is possible, as a matter of course, to use the image forming apparatus according to the present invention for electrophotographic copying devices such as a copying machine, facsimile device, etc. 
     FIG. 11 is a cross-sectional view showing the entire internal structure of an exemplary image forming apparatus. In FIG. 11, the color printer  100  is provided with an intermediate transfer belt  101  therein. The visible image for each of the respective colors formed on the photosensitive drum equipped in the image station is superposedly transferred onto the intermediate transfer belt  101 . The image thus transferred onto the belt  101  is further transferred onto a sheet of the transfer paper P. The intermediate transfer belt  101  has a belt length which is longer than the movement direction length of the transfer paper P maximum size by the non-image area length including the detour (roundabout way) length of the respective rollers (discussed below). 
     The intermediate transfer belt  101  is suspended respectively on a driving roller  102  and a driven roller  103 , both situated at both ends in the suspending direction and moved in the direction shown by an arrow in FIG.  11 . In FIG. 11, the reference numeral  104  represents a tension roller of the intermediate transfer belt  101 , and the reference numeral  101 A represents a cleaning apparatus. 
     A density sensor detects the toner density on the upper suspending surface of the intermediate belt  101  and on the upper part of the driving roller  102 . The density sensor detects the variation between the density of a standard density pattern and the density pattern formed on the intermediate transfer belt  101 . 
     In FIG. 11 a first image station  105  and a second image station  106  are respectively arranged on the lower suspending surface of the intermediate transfer belt  101  at a predetermined interval along the suspending direction. 
     The first and second image stations  105  and  106  are respectively provided with photosensitive drums  107  and  107 ′. Developers (developing agents) for the dissolved colors and other developers for the complementary colors thereof are respectively supplied to the photosensitive drum. The development medium for supplying the developers is divided for each of the respective image stations, and the respective development media thus divided are installed in one lot (by the gross) per two colors which are half of the color dissolving number. 
     The first and second image stations  105  and  106  supply different developer colors to the photosensitive drum, but the structures of the image stations  105  and  106  are the same. Thus, only the structure of the first image forming station  105  is described. 
     The first image station  105  includes the elements for performing the electrophotographic process along the rotating direction of the photosensitive drum  107 . These elements include a charging apparatus  108 , a writing-in apparatus  109 , a developing apparatus  110 , a cleaning apparatus  111 , and a transferring apparatus  112  opposite the photosensitive drum  107  through the intermediate transfer belt  101 . The photosensitive drum  107  rotates in the direction shown by the arrow in FIG.  11 . 
     The developing apparatuses  110  and  110 ′ are provided for each of the respective colors in order to supply the developers of the colors corresponding to the complementary color of the color-dissolved colors. In the structure shown in FIG. 11, two-components-system developer is used for causing the carrier to carry the toner. 
     The developing apparatus  110  is constructed with a developing part provided with a developing sleeve  110 A installed in the casing and opposing to the photosensitive drum  107  and an agitating paddle  110 B; and a toner replenishing part having a conveying screw  110 C situated in the neighborhood of the agitating paddle  110 B and a toner replenishing part installed in the casing on the upper part of the conveying screw and capable of mounting thereon the toner hopper  3  shown in FIG.  1 . The toner replenishing part is described below. 
     The agitating paddle  110 B is provided with a spiral wing and a plurality of plates. The plates are arranged in a radial state in order to agitate the developer and convey the developer. 
     The conveying screw  110 C is shaped as a spirally wound wing and rotates in the direction reverse of the agitating paddle  110 B. Thus, the developer is conveyed in the reverse direction and the developer can be uniformly distributed in the axis direction of the developing sleeve  110 A. 
     A roller-state transferring apparatus  113  opposing the driven roller  103  is disposed on a position passing through the second image station  106  in the movement direction of the intermediate transfer belt  101 . The superposed image on the intermediate transfer belt  101  is transferred in gross onto the transfer paper P conveyed from the paper feeding apparatus. The timing of the paper feeding is set by the registration roller  114 . 
     After the transfer paper P having the superposed image passes through the transfer position, the image is thermally fixed by a fixing apparatus  115  provided with a heating roller. Thereafter, the transfer paper P is discharged onto the paper discharging tray  117  through a paper discharging apparatus  116 . An air exhausting fan  117 A is provided in the image forming apparatus  100  shown in FIG.  11 . The electric parts disposed under the paper exhausting tray  117  is not heated under the influence of the heat emitted from the fixing apparatus  115  by the action of the above air exhausting fan  117 A. In FIG. 11 the reference numeral  115 A represents the roller brought into direct contact with the roller at the heating side and applying the off-set preventing liquid thereto. 
     FIGS. 12 through 14 respectively show the external appearance of the image forming apparatus including the toner replenishing parts of the developing apparatus with the covers in various states. The developing apparatus is disposed in a first space of a first opening portion of the image forming apparatus capable of being opened and closed by use of a first cover provided on the upper part of the main body of the image forming apparatus, each of the toner supplying media (or toner replenishing parts) for respectively supplying toner to the developing apparatus is disposed in a second space of a second opening portion capable of being opened and closed by use of a second cover also provided on the upper part of the main body of the image forming apparatus. Each of the toner supplying devices can be inserted into and taken away from the second opening portion of the image forming apparatus. 
     A toner hopper mounting part communicating with the space of the conveying screw  110  contained therein is provided in the toner replenishing part of the above-mentioned developing apparatus. The toner hopper mounting part is contained in a part of the casing of the apparatus main body as shown in FIG.  12 . 
     FIG. 12 shows a main body with the cover  100 A removed from the upper part of the housing of the image forming apparatus. An image forming unit  105 P forming the first and second image stations  105  and  106  is detachably provided on the position adjacent to the toner hopper  3 . For the convenience, only the unit in connection with the first image station is shown in FIG.  12 . 
     As shown in FIG. 12, the toner hoppers  3  serves as the toner replenishing medium containing the toners of the colors consumed in the respective developing apparatuses. The toner hoppers  3  are arranged so as to be aligned in the housing portion of the image forming apparatus  100  corresponding to the toner hopper mounting part. 
     As shown in FIG.  12  and FIG. 14, an opening  100 B for inserting and removing the toner hopper  3  is formed on the portion corresponding to the toner hopper mounting part in the housing of the image forming apparatus shown in FIG. 13. A cover member  118  capable of being opened and closed is provided at the opening  100 B, as shown in FIG.  14 . 
     The toner hopper  3  may be inserted into, and removed from, the opening  100 B, and is provided in the toner replenishing part. The toner hopper  3  is supported by the structure shown in FIG.  15 . 
     FIG. 15 is an explanatory perspective view for explaining the operation and the structure of the toner replenishing part shown in FIG.  14 . In FIG. 15, the toner hopper  3  is supported by a supporting member  201  provided in the toner hopper mounting part and by detachably inserting and removing the tip end of the supporting member  201  having a toner exhausting opening in the bored portion  201 A thereof. 
     The supporting member  201  is constructed with a housing formed so as to open the upper surface thereof supported on the base plate  202  provided in the floating state in the toner hopper mounting parts. The toner hopper mounting parts are mounted corresponding to the respective developing apparatuses through the coil spring  203  serving as an attenuating member. 
     The vibration apparatus  5  provided with the motor  5 A shown in FIG. 4 is mounted on a part of the side wall of the supporting member  201 . The vibration apparatus  3  can change the vibration applying intensity for each of the respective developing apparatuses. In such structure, in the case of increasing the toner replenishing speed and employing the toners of the plural colors at the same time, the replenishment of the insufficient toner can be promptly performed, and thereby the quality of the image can be prevented from lowering. 
     The vibration apparatus  5  is mounted to induce lengthwise (vertical) vibration in the direction shown by the arrow in FIG. 15, i.e., such that the weight  5 A 1  can rotate in the vertical plane. In such structure, the vertical vibration of the supporting member  201  is induced and thereby the toner hopper  3  can be vibrated in the vertical direction. 
     When the vibration is induced in the toner hopper  3 , since the vibration of the supporting member  201  is buffered (absorbed) by the coil spring  203 , the vibration is not transmitted to the supporting member  201 . 
     As shown in FIG.  15  and FIG. 16, the toner hoppers  3  are formed in the same almost rectangular shape. The toner hopper  3  has a male tip end portion to be inserted into the female bored portion  201 A of the supporting member  201 . A toner exhausting opening  3 A (FIG. 16) is formed on the tip end portion of the toner hopper  3 . Furthermore, the toner hopper  3  is constructed with a semitransparent or transparent container. Therefore, it is possible to view the amount of the toner contained in the container. In addition, since the tip end portion of the toner hopper  3  is shaped as a right pyramid or circular cone, the falling toner can be funneled into the toner exhausting opening  3 A. 
     As shown in FIG. 16, a mesh-member  204  having a mesh size of 50 to 500 μm is provided as the toner-supply controlling member on the toner exhausting opening  3 A of the toner hopper  3 . 
     A replenishment opening  3 B is formed on the bottom portion at the opposite side of the tip end portion of the toner hopper  3 . A cap  3 C is detachably mounted on the replenishment opening  3 B. When a grasping portion  3 C 1  unitarily provided on the cap  3 C is grasped and the cap  3 C is removed from the replenishment opening  3 B, the toner hopper  3  can be replenished with new toner. 
     When the vibration does not occur, the toner contained in the toner hopper  3  is solidified under the force of gravity and becomes a static toner mass. However, by inducing the lengthwise (vertical) vibration, the vibration is applied to the toner mass at the same time when the vibration apparatus  5  initiates vibration. In such state, the distance between the toner particles is widened to the extent (distance) that the adhesive force is not exerted on each other between the toner particles. As the result, the toner particles can move freely. 
     In particular, since the vibration apparatus  5  vibrates lengthwise (vertically), the separated toner may fall freely under its own weight. In addition, the fallen toner is collected on the toner exhausting opening  3 A owing to the right pyramidal or conical shape of the tip end of the toner hopper  3 . Only separated toner particles can be easily exhausted from the toner exhausting opening  3 A through the mesh member  204 . 
     The mesh member  204  does not permit the solidified toner in the mass state to pass therethrough. The member  204  permits only the separated toner particles to pass therethrough. With the mesh structure  204 , the toner mass and the toner particles can be separated, and thereby the supply of the toner can be controlled. 
     In the case of forming a full-color image, electrostatic latent images are formed for each of the respective color-dissolved colors on the photosensitive drums  107  and  107 ′ by use of the writing apparatus  109 . The electrostatic latent images are converted to the visible images by the respective developing apparatuses. 
     In the image forming apparatus  100  in FIG. 11, until the processed visible image on the intermediate transfer belt  101  arrives at the transfer positions respectively provided in the first image station  105  and the second image station  106 , the image of the color different from that of the image formed in the first image station  105  is formed in the second image station  106 . Thereafter, the image thus formed is superposedly transferred onto the intermediate transfer belt  101 . 
     Regarding the method of transferring the image to the intermediate belt  101 , the following two methods may be implemented: 
     (1) The visible images of the first color and the second color respectively formed in the first and second image stations  105  and  106  are superposedly transferred in order onto the intermediate transfer belt  101  at the time of the first rotation of the belt  101 . 
      The visible images of the third color and the fourth color respectively formed in the first and second image stations  105  and  106  are superposedly transferred in order onto the previously transferred image of the above-mentioned first and second colors formed on the intermediate transfer belt  101  at the time of the second rotation of the belt  101 . Thereafter, those four superposedly transferred images are transferred in gross onto the transfer paper P. 
     (2) The image of the same color as that of the first color previously transferred, namely, the image of the color corresponding to the first color is transferred once again, in the first image station  105 , on the new surface of the moving intermediate transfer belt  101 , on which the visible image of the second color formed in the second image station  106  is superposedly transferred onto the visible image of the first color formed in the first image station  105 . Next, when the previously transferred image of the first color arrives at the second image station  106 , the image of the second color is superposedly transferred thereon. Following this step, when the image of the first color transferred once again arrives at the second image station  106 , the visible image of the second color is superposedly transferred onto the image of the first color. Then, when the image previously superposedly transferred in the first and second image stations  105  and  106  arrives once again at the first image station  105  after one rotation of the intermediate transfer belt  101 , the visible image of the third color is transferred onto the superposedly transferred image in the first image station  105 . Thereafter, successively, the visible image of the fourth color is transferred onto the superposedly transferred image in the second image station  106 . 
      The above-mentioned superposedly transferred image is further transferred in gross onto the transfer paper P. 
      Furthermore, following the step of transferring the image in gross onto the transfer paper, when the superposedly transferred image of the first and second colors arrives at the first image station  105  in accordance with the movement of the intermediate transfer belt  101 , the image of the third color is superposedly transferred thereto in the first image station  105 , and the image of the fourth color is superposedly transferred thereto in the second image station  106 . The image thus transferred is further transferred in gross onto the transfer paper P. 
     In the case of method (1), the images of the different colors are superposedly transferred once for each rotation of the intermediate transfer belt  101 , while, in the case of method (2), the image of the color previously transferred is transferred once again in the first and second image stations  105 ,  106  during the time period when the intermediate transfer belt  101  rotates by half rotation (180°), and the images of the same color are successively transferred. According to method (1), the visible image which is superposedly transferred when the intermediate transfer belt  101  rotates twice is further transferred in gross onto the transfer paper P. 
     On the other hand, according to method (2), the visible image which is superposedly transferred when the intermediate transfer belt  101  rotates one-and-a-half times (540°) is transferred in gross onto the first transfer paper P, and the visible image is transferred onto the second transfer paper P in the delayed state in the intermediate transfer belt  101  until the image forming area to be treated with one-time transferring in the gross. Therefore, the transferred image is further transferred in the gross onto the transfer paper when the intermediate transfer belt  101  rotates two-and-a-half times, corresponding to the shift of the transfer position between the first and second image stations  105  and  106 . The method of the item (2) is effective in shortening the image forming time when a plurality of transferred objects (e.g., copied sheets) have to be obtained. 
     When the density of the toner images of the respective colors on the intermediate transfer belt  101  is low or the amount of the toner in the respective developing apparatuses is low, the toner is replenished from the toner replenishing part. When this occurs, the vibration apparatus begins to vibrate and thereby the lengthwise (vertical) vibration is induced in the toner hopper mounting part. The vibration applying time is set to occur at a time other than the time of forming the image onto the photosensitive drum  107  such that the vibration is not unexpectedly transmitted to the developing apparatus side when the image is formed. 
     The transmission of such vibration can be prevented by the buffering action of the coil spring  203  disposed between the supporting member  201  and the base plate  202 . Thus, the vibration is not transmitted to any one of the toner hoppers  3  (except for the one for replenishing the toner), all of which are installed in the toner replenishing part. 
     When the lengthwise (vertical) vibration from the vibration apparatus  5  is induced on the supporting member  201  of the toner hopper mounting part, the toner hopper  3  vibrates in the lengthwise (vertical) direction and the toner contained in the toner hopper  3  also vibrates. Thus, the toner particles solidified in a mass are separated into pieces by the vibration between the respective toner particles and enabled to easily slip down in the toner hopper. The toner particles arrive at the toner discharging opening  3 A of the toner hopper  3 . At the opening  3 A, only the toner particles of the size corresponding to the mesh size of the mesh member  204  pass through the mesh member  204  and are discharged therefrom. 
     When the vibration of the toner hopper  3  stops, the toner in the toner hopper  3  is accumulated by the empty weight thereof in the circumferential portion of the toner exhausting opening  3 A and solidified in a mass. At this time, since the size of the solidified toner becomes larger than that of the individual toner particles and the mesh size of the mesh member  204 , the toner mass cannot pass through the mesh member  204 . As a result, the toner accumulates in the toner hopper  3 . Since the toner hopper  3  is a transparent or semitransparent container, the state of the toner in the toner hopper  3  can be confirmed by observing the toner from outside the toner hopper  3 . When the toner is not in a predetermined state, the toner hopper can be easily exchanged, or the toner can be easily replenished. 
     Since the shape of the toner hopper  3  is the same as the shape applicable to the toner replenishing part of the respective developing apparatuses, the toner hopper can be used for recycling. The toner hopper is formed in the shape of a square column. Therefore, the amount of toner contained can be maximized. As a result, the replenishment cycle of the toner can be made long. Thus, the troublesome work of maintenance, etc. can be reduced or eliminated. Furthermore, since the toner hopper  3  has a tip end portion of the toner exhausting opening  3 A formed in the shape of a pyramid, the toner separated into particles out of the toner mass can easily slip down in the toner hopper  3 . Thus, the toner can be successively exhausted from the toner exhausting opening  3 A. Consequently, the toner can be promptly replenished. 
     The toner exhausting opening  3 A of the toner hopper  3  permits only toner particles to pass therethrough and controls the toner supply by providing the mesh member  204  at the opening  3 A. However, according to the present invention, it is also possible to control the toner exhaust by optionally opening and closing the toner exhausting opening. 
     As shown in FIG. 17, at the toner exhausting opening there is provided a shutter member  210  capable of opening and closing the toner exhausting opening. At the toner exhausting opening  3 A′ of the toner hopper (for convenience, represented by the reference numeral  3 ′), there is provided a mesh member (for convenience, represented by the reference numeral  204 ′) having a plurality of slits or narrow openings instead of the mesh member  204 . Furthermore, in the vicinity of the mesh member  204 ′, there is provided a shutter member  210  capable of sliding in across the mesh member  204 ′. Sliding the shutter member  210  narrows the slits to a size that permits only toner particles to pass therethrough as in the case of the mesh member  204  described in the above embodiment. 
     The shutter member  210  is constructed with a plate member having an opening  210 A formed thereon capable of exposing the entire area of the opening of the mesh member  204 ′. The shutter member  210  is tightly (or fixedly) inserted into and slidably supported by a supporting piece  204 A′ constructed with a bent piece formed on the mesh member  204 ′. 
     A stop hole  210 B constructed with an opening is formed on one end of the shutter member  210  in the sliding direction. A stop piece  211   a  of the driving member  211  for sliding the shutter member  210  is tightly inserted into the stop hole  210 B. The driving member  211  is slidably provided at the base plate  202  side of the toner hopper mounting part. An operating piece capable of being operated from the outside is formed on a portion of the driving member  211 . The operating piece is connected to a driving medium, such as a solenoid, and the operating piece can slide thereon. 
     The solenoid is energized when the vibration starts due to the operation of the apparatus  5 . At this time, the stop piece  211 A is pulled or pushed, and thereby the opening  210 A of the shutter member  210  and the slit in the mesh member  204 ′ communicate with each other. On this occasion, the solenoid serving as the driving member sets the position of the driving member  211  such that the opening  210 A of the shutter member  210  does not communicate with the slits of the mesh member  204 ′ when the solenoid is not energized. The opening of the mesh member  204 ′ communicates with the opening  210 A of the shutter member  210  when the solenoid is energized, as mentioned above. 
     Even though the vibration by the vibration apparatus  5  stops, when the toner hopper  3  vibrates by the action of the inertia force, the careless exhaust of the toner particle can be prevented. Thus, the excessive replenishment of the toner can be also prevented. Consequently, the proper amount of toner is replenished, and thereby the image density can be prevented from varying greatly. 
     As is apparent from the foregoing description of the embodiments according to the present invention, many advantageous functional effects as mentioned below can be attained. The vibration apparatus is provided in the toner hopper mounting part. The vibration is not applied to the toner exhausting opening. Instead, the vibration is applied to the entire portion of the toner hopper supported by the toner exhausting opening. In such structure, since the toner particles contained in the toner hopper can be mutually vibrated, it is possible to obtain the preferred fluidity of the toner over the entire area in the toner hopper. Thus, the toner can be prevented from solidifying and remaining in the exhausting opening. Furthermore, since a vibration apparatus is provided for the toner hopper mounting part, the toner hopper can be easily exchanged. In addition, it is not necessary to perform the troublesome work of individually installing the vibration apparatus for the exchanged toner hopper on all such occasions. Consequently, the exhausting property of the toner can be improved with the simple structure, and the clogging can be surely prevented. 
     According to the present invention, further advantageous effects as mentioned below can be attained. By applying the vibration of low noise and comparatively low frequency, the toner can be prevented from being consolidated by ramming and the preferable fluidity of the toner can be secured. The vibration applying force can be controlled by controlling the applied voltage, and therefore, the degree of fluidity (i.e., fineness) of the toner can easily be set. A uniform vibration can be caused over the entire area of the toner hopper, and therefore, almost all of the toner in the toner hopper is vibrated and the fluidity of the toner can be improved. Thus, the occurrence of unused toner can be reduced or eliminated. Even though the output of the vibration apparatus is reduced, the fluidity of the toner can be effectively maintained, and therefore, energy savings can be realized. Furthermore, even though the output of the apparatus is reduced, the toner hopper can be effectively resonated, and thus, the fluidity of the toner can be effectively secured. The density unevenness of the image developed on the photosensitive body and the occurrence of the density unevenness can be prevented with little energy. In addition, the low noise can be attained, resulting in the reduction of noise pollution. 
     When plural developing apparatuses are employed to form the image, the toner can be replenished for each of the respective developing apparatuses. Furthermore, the toner hopper employed for the toner replenishment can be commonly used for the respective developing apparatuses. In addition, both of the confirmation of the toner level and the replenishment of the toner are possible. Therefore, the recycling property of the member employed for the toner replenishing part is enhanced, and thus, the maintenance cost can be reduced in the case of employing plural developing apparatuses. Furthermore, by setting the vibration mode of the vibration apparatus to generate vertical vibration, when the solid toner mass is separated into the toner particles, the toner can easily slip down in the hopper. Thus, the toner can be successfully exhausted. Consequently, the toner can be promptly replenished. 
     The vibration is caused by the vibration apparatus does not occur during image formation, and the vibrations are not mutually transmitted to each other between the plural developing apparatuses. Consequently, the adverse effects of vibration on the image formation can be avoided. In particular, at the time of forming the color image, the superposing transfer to the intermediate transfer body from the photosensitive body is performed. Therefore, the quality of the image can be prevented from being lowered, without causing the shift of the transferring position due to the vibration. The vibration applying intensity of the vibration apparatus can be changed for each of the respective colors. The replenishing time is shortened for the toner of the color to be replenished by large volume, and thus the toner can be promptly replenished. 
     The toner supply controlling medium having a mesh prevents the solid toner mass from passing through the exhausting opening and permits only small, separated toner particles to pass through the mesh member and be exhausted therefrom. Consequently, the exhausted and replenished toner can be easily and uniformly dispersed. Thus, the dispersion density of the toner to be supplied to the photosensitive body from the developing apparatus can be made uniform. Consequently, the image quality can be prevented from deteriorating. 
     A control unit (e.g., the vibration applying frequency controlling apparatus  6  in FIG. 10) may be used to receive inputs from a user and/or any of the sensors described above to control the various functions of the developing apparatus and/or the image forming apparatus of the present invention. The control unit preferably includes an appropriately programmed microprocessor and a memory for storing information, such as the predetermined toner density values discussed above. Thus, the control unit can be implemented to control the operation of the vibrating apparatus, as well as perform processing for any the various functions of the developing unit and image forming apparatus described above. 
     In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the present invention is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents which operate in a similar manner. 
     Obviously, other numerous embodiments or numerous modifications of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 
     This application is based on Japanese Patent Application No. JPAP10-125,505, filed on May 8, 1998, and another Japanese Patent Application No. JPAP10-349,526, filed on Dec. 9, 1998. JPAP10-125,505 and JPAP10-349,526, and all references cited therein, are incorporated herein by reference.