Abstract:
An image forming apparatus includes a detachably mountable developing device including a developer container, a developer carrying member, a feeding member, provided in contact with the carrying member, for supplying the developer to the carrying member, and a developer regulator; and a voltage device capable of applying to the carrying member and the regulator respective voltages different from each other. The apparatus carries outs, when a fresh developing device is mounted, an initial operation in which the carrying member is rotated. In the initial operation, the voltage device applies, to at least one of the carrying member and the regulator, a voltage for the initial operation which is different from the voltage for normal image forming operation, so as to urge a material applied to the carrying member in the fresh developing device toward the regulator from the carrying member.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile machine, and the like, which uses an electrophotographic or electrostatic recording method. 
         [0002]    Conventionally, an electrophotographic image forming apparatus such as an electrophotographic copying machine, a laser beam printer, a facsimile machine, etc., is equipped with a developing device. The developing device is provided with a developer container, a developer bearing member (development roller), and a developer regulating member (regulation blade). The developer bearing member is in the form of a roller. It is disposed in such a manner that it blocks the opening of the developer container while being partially exposed from the developer container through the opening. The developer regulating member is placed in contact with the peripheral surface of the developer bearing member to keep constant at a preset value, the amount by which the developer is conveyed by the developer bearing member, per unit area of the peripheral surface of the developer bearing member. 
         [0003]    As the toner adhered to the peripheral surface of the development roller is conveyed through the area of contact between the development roller and regulation blade by the rotation of the development roller, the excessive amount of developer on the peripheral surface of the development roller is removed, and is returned to the developer container. Consequently, a thin and uniform layer of toner is formed on the development roller. At the same time, the toner is given triboelectric charge by the friction which occurs between the toner and regulation blade. Consequently, the toner on the development roller transfers from the development roller onto the electrostatic latent image formed on the peripheral surface of the photosensitive drum, in the area in which the development roller is exposed, from the developer container, while the photosensitive drum rotates, with its peripheral surface being virtually in contact with the peripheral surface of the development roller. Moreover, the developing device is provided with a developer supply roller (supply roller), a developer recovering member, etc. The developer supply roller is placed in contact with the development roller, and is rotated at a preset speed which is different from the speed at which the development roller is rotated. The developer recovering member is for recovering the toner on the peripheral surface of the development roller. 
         [0004]    Usually, a developing device delivered from a factory to a user is in the form of a cartridge (development cartridge). Thus, as a developing device becomes too short of toner to allows an image forming apparatus to continue an image forming operation, a user is to purchase a fresh developing device (development cartridge), which is removably installable in an image forming apparatus, and insert the cartridge into the apparatus to continue the image forming operation. 
         [0005]    A fresh developing device is provided with a sealing member for preventing the toner in the developer container from leaking out of the developer container during the shipment of the developing device. This sealing member is not removed before the developing device is shipped out by a factory. 
         [0006]    In the case of a fresh developing device, it sometimes takes a substantial length of time for the peripheral surface of the development roller to be sufficiently supplied with the toner in the developer container. If the development roller in a developing device is rotationally driven before the development roller is supplied with a sufficient amount of toner, the friction which occurs between the development roller and regulation blade as the developing device is driven, and the friction which occurs between the development roller and supply roller as the developing device is driven, become very large, making it possible for various components related to the driving of the developing device to be damaged, and/or the torque necessary to drive the developing device to become large enough to damage the mechanism for driving the developing device. 
         [0007]    In Japanese Laid-open Patent Applications H08-227212 and 2002-229333, technologies for reducing a developing device in the amount of torque necessary to drive a developing device are proposed. According to these patent applications, before a fresh developing device is shipped out of a factory, powdery substance such as toner is applied as coating agent to the peripheral surface of its development roller in order to cause the powdery substance to function as lubricant. 
         [0008]    However, in the cases of Japanese Laid-open Patent Applications H08-227212 and 2002-229333, the amount by which the development roller is coated with the coating agent is rather small. Thus, if a fresh developing device which requires a substantial length of time for the peripheral surface of its development roller to be sufficiently supplied with toner after it begins to be driven for the first time is used for the first time by an image forming apparatus, the image forming apparatus sometimes outputs images which suffer from “vertical streaks” right after it began to be used. 
         [0009]    In a case where an image forming apparatus outputs images which suffer from vertical streaks, there are usually found foreign substances such as dust, paper burrs, and the like, sandwiched between the portions of the regulating edge of the regulation blade, which correspond in position to the locations of the vertical streaks of the images, and the peripheral surface of the development roller. These foreign substances disturb the thin toner layer on the peripheral surface of the development roller. Consequently, the image forming apparatus outputs images which suffer from vertical streaks. 
         [0010]    In a case where the amount by which a development roller is coated with coating agent is small, the amount by which the coating agent is adhered to the portion (toner capturing portion) of the regulation blade, which is in the area of contact between the regulation blade and development roller, is very small immediately after a fresh developing device began to be driven. Thus, there occur gaps (portions which are not filled with coating agent) between the regulating edge of the regulation blade and the peripheral surface of the development roller, in terms of the lengthwise direction of the regulation blade. 
         [0011]    In a case of a developing device which requires a substantial length of time for the peripheral surface of its development roller to be sufficiently supplied with toner after it begins to be driven, it takes a substantial length of time for the adjacencies of the capturing portion of the its regulation blade to be sufficiently filled with toner. Thus, the developing device is driven for a relatively long time while the gaps are remaining in parts of the adjacencies of the capturing portion of the regulation blade and development roller. It is this period of time that the foreign substances such as dust, paper burs, and the like, which were remaining adhered to the adjacencies of the regulation blade enter the gaps, and remain sandwiched between the regulation blade and development roller. 
         [0012]    In order to prevent foreign substances such as dust, paper burrs, and the like from entering a developing device, the developing device production line has to be kept extremely clean. In order to keep the production extremely clean, it takes a large amount of labor and related cost. This in turn increases production cost, which is undesirable. 
         [0013]    It is possible to increase the amount by which the peripheral surface of the development roller is coated with the powdery coating agent before the developing device  4  is shipped out of a factory, in order to insure that there will be no gaps (area which are not filled with coating agent) between the regulation blade and development roller. In such a case, however, the amount by which the peripheral surface of the development roller is coated with the coating agent has to be strictly controlled. That is, if it is not strictly controlled, the coating agent may scatter during the process in which the development roller is coated with the coating agent on the production line and/or while a developing device is transported after it is shipped out of the factory. Therefore, increasing the amount by which the peripheral surface of the development roller is coated with the coating agent is not desirable. 
         [0014]    In order to minimize the length of time it takes for the peripheral surface of the development roller to be supplied with a sufficient amount of toner, some developing devices are not provided with a toner seal. In the case of these developing devices, it is possible for toner to leak from the toner container as described above. Therefore, providing a developing device with no toner seal is not desirable. 
         [0015]    The present invention is made to solve the above-described problems. Thus, the primary object of the present invention is to provide an image forming apparatus which is capable of preventing the occurrence of image defects such as “vertical streaks” even if a fresh developing device which is relatively small in the amount of the coating agent on its development roller is installed in the main assembly of the apparatus. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention is made in consideration of the above-described problems, and is a result of further development of conventional technologies. 
         [0017]    According to an aspect of the present invention, there is provided an image forming apparatus comprising a developing device detachably mountable to a main assembly of said image forming apparatus, said developing device including a developer accommodating container for accommodating a developer, a developer carrying member for carrying the developer, a developer feeding member, provided in contact with said developer carrying member, for supplying the developer to said developer carrying member, a developer regulating member for regulating the developer carried on said developer carrying member; and a voltage applying device capable of applying to said developer carrying member and said developer regulating member respective voltages different from each other, wherein said image forming apparatus carries outs, when a fresh developing device is mounted to said main assembly, an initial installing operation in which the developer carrying member is rotated, and wherein in the initial installing operation, said voltage applying device applies, to at least one of said developer carrying member and said developer regulating member, a voltage for the initial installing operation which is different from the voltage for normal image forming operation, so as to urge a material applied to said developer carrying member in the fresh developing device toward said developer regulating member from said developer carrying member. 
         [0018]    Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a sectional view of a typical image forming apparatus to which the present invention is applicable. It is for describing the structure of the apparatus. 
           [0020]      FIG. 2  is a combination of a sectional view of a process cartridge and a system for controlling the process cartridge. It is for describing the structure of the cartridge and control system. 
           [0021]      FIG. 3  is a sectional view of the coating device for coating the developer bearing member with the coating agent, and is for describing the structure of the device. 
           [0022]      FIG. 4  is a flowchart of an initializing operation. 
           [0023]      FIG. 5  is a timing chart which shows the bias application timing, and the timing with which the developer bearing member is rotationally driven, in the first and second embodiments of the present invention. 
           [0024]      FIG. 6  is a timing chart which shows the bias voltage application timing, and the timing with which the developer bearing member of the developing device in the third embodiment, and the developer bearing member of a comparative developing device are rotationally driven. 
           [0025]      FIG. 7  is a table which shows the relationship between the amount by which the coating agent is applied, and the severity of the vertical streaks, in each embodiment of the present invention, and also, in the case of the comparative developing device. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Hereinafter, preferred embodiments of the present invention are concretely described with reference to appended drawings. By the way, the dimensions, materials, and shapes of the structural components of the developing devices in the following embodiments of the present invention, and the positional relationship among the components, are not intended to limit the present invention in scope, unless specifically noted. 
       &lt;Image Forming Apparatus&gt; 
       [0027]    To begin with, referring to  FIG. 1 , a typical image forming apparatus to which the present invention is applicable is described about its structure. An image forming apparatus  100  shown in  FIG. 1  is an example of a full-color laser beam printer of the so-called inline type, and also, of the so-called intermediary transfer type. The image forming apparatus  100  can form a full-color image on a sheet of recording medium (recording paper, plastic, fabric, etc.) according to image formation information. The image formation information is inputted into the main assembly of the image forming apparatus  100  from an image reading device which is in connection to the main assembly of the image forming apparatus  100 , or a host device such as a personal computer which is in connection to the main assembly of the image forming apparatus  100  in such a manner that communication is possible between the host device and the main assembly of the image forming apparatus  100 . 
         [0028]    The main assembly of the image forming apparatus  100  internally holds process cartridges  7 Y,  7 M,  7 C and  7 K which are removably installable in the main assembly. The process cartridges  7  have image forming sections  14 Y,  14 M,  14 C and  14 K which are image forming means for forming yellow Y, magenta M, cyan C and black K images, respectively. The image forming sections  14 Y,  14 M,  14 C and  14 K in this embodiment are aligned in parallel and tandem in the direction (left-right direction) which is intersectional to the direction which is perpendicular to  FIG. 1 . By the way, for the sake of convenience, the image forming sections  14 Y,  14 M,  14 C and  14 K may be described as an image forming section  14 . This will apply to the description of the other image processing means of the image forming apparatus  100  as well. 
         [0029]    The process cartridge  7  is structured so that it can be removably installable in the main assembly of the image forming apparatus  100  through unshown cartridge installing means such as installation guides, positioning members, etc., with which the main assembly of the image forming apparatus  100  is provided. In this embodiment, the four process cartridges  7  for forming monochromatic images, different in color, one for one, are the same in shape. The developer container  9  stores (contains) toner  10  (yellow Y, magenta M, cyan C and black K toners, as developer) one for one. The process cartridges  7  in this embodiment are described as a process cartridge which has: a developing device  3  as a development unit; and a photosensitive unit  13  having a photosensitive drum  1  as an image bearing member, which are integrally disposed in the shell of the process cartridge. However, the process cartridges  7  may be structured so that the developing device  3  is removably installable in the main assembly of the image forming apparatus  100 , independently from the photosensitive unit  13 . 
         [0030]    Referring to  FIG. 2 , the photosensitive drum  1  is rotationally driven by a motor  15  which is a mechanical force source which is controlled by a control section  25  which is a controlling means. There is disposed a scanner unit  30 , which is an image exposing means, in the adjacencies of the peripheral surface of the photosensitive drum  1 . The scanner unit  30  forms an electrostatic latent image by scanning the uniformly charged peripheral surface of the photosensitive drum  1  with a beam  11  of laser light which it emits while modulating the beam  11  according to the image information. As the toner  10  is supplied to the electrostatic latent image formed on the peripheral surface of the photosensitive drum  1  by the developing device  3  which is a developing means, a toner image is formed on the peripheral surface of the photosensitive drum  1 . 
         [0031]    There is provided an intermediary transfer belt  31 , which is disposed so that it opposes the photosensitive drums  1 Y,  1 M,  1 C and  1 K which correspond to yellow Y, magenta M, cyan C and black K colors, respectively. The intermediary transfer belt  31  is structured so that it functions as an intermediary member for transferring the toner image on the photosensitive drum  1  onto a sheet  12  of recording medium. The intermediary transfer belt  31  is suspended by a driver roller  31   a  and an idler roller  31   b . It is an endless belt, and it circularly moves (rotates) in the counterclockwise direction indicated by an arrow mark B in  FIG. 1 , while remaining in contact with the peripheral surface of all the photosensitive drums  1 . 
         [0032]    There are disposed four primary transfer rollers  32 Y,  32 M,  32 C and  32 K, which are primary transferring means, on the inward side of the loop which the intermediary transfer belt  31  forms. The primary transfer rollers  32 Y,  32 M,  32 C and  32 K oppose the peripheral surface of the corresponding photosensitive drums  1 Y,  1 M,  1 C and  1 K, respectively. To each of the primary transfer rollers  32 , primary transfer bias voltage, the polarity of which is opposite to the polarity to which the toner  10  is normally chargeable, is applied from an unshown primary transfer bias power source. Therefore, the toner image on the peripheral surface of the photosensitive drum  1  is transferred (primary transfer) onto the outward surface of the intermediary transfer belt  31 . 
         [0033]    There is also disposed a secondary transfer roller  33  which is the secondary transferring means, on the outward side of the loop which the intermediary transfer belt  31  forms. It is positioned so that it opposes the driver roller  31   a . To the secondary transfer roller  33 , the secondary transfer bias voltage is applied from an unshown secondary transfer bias power source. The polarity of the secondary transfer bias voltage is opposite from the polarity to which the toner  10  is normally chargeable. As a result, the toner image on the outward surface of the intermediary transfer belt  31  is transferred (secondary transfer) onto the sheet  12  of recording medium. 
         [0034]    In an image forming operation for forming a full-color image, for example, the above-described image formation process is sequentially carried out in the image formation sections  14 Y,  14 M,  14 C and  14 K. Thus, yellow Y, magenta M, cyan C and black K toner images are sequentially transferred in layers (primary transfer) onto the outward surface of the intermediary transfer belt  31 . Thereafter, the sheet  12  of recording medium is fed into the main assembly of the image forming apparatus  100  by a combination of a sheet feeder roller and a separating means, is conveyed to a pair of registration rollers  24 , is corrected in attitude by the registration rollers  24 , and then, is conveyed to the secondary transferring section, which is the nip between the secondary transfer roller  33  and intermediary transfer belt  31 , in synchronism with the movement of the intermediary transfer belt  31 . Then, the four monochromatic toner images, different in color, on the outward surface of the intermediary transfer belt  31  are transferred together (secondary transfer) onto the sheet  12 , by the function of the secondary transfer roller  33  which is kept pressed against the intermediary transfer belt  31  with the presence of the sheet  12  between itself and intermediary transfer belt  31 . 
         [0035]    After the transfer of the toner images onto the sheet  12  of recording medium, the sheet  12  is conveyed to a fixing device  34  as a fixing means. In the fixing device  34 , the toner  10  on the sheet  12  is subjected to heat and pressure. Consequently, the toner images become fixed to the sheet  12 . 
       &lt;Process Cartridge&gt; 
       [0036]    Next, referring to  FIG. 2 , the process cartridge  7  which is installable in the main assembly of the image forming apparatus  100  is described about its structure.  FIG. 2  is a sectional view of the process cartridge  7  in this embodiment of the present invention. It is for describing the structure of the process cartridge  7 . By the way, in this embodiment, the four process cartridges  7  are the same in structure and operation, although they are different in the type (color) of the toner  10  which they store in their developer container  9 . The process cartridge  7  has: the photosensitive unit  13  which has the photosensitive drum  1 , etc., and developing device  3  which is a development unit having the development roller  4 , etc. 
       &lt;Photosensitive Unit&gt; 
       [0037]    To the photosensitive unit  13 , the photosensitive drum  1  is rotatably attached with the placement of unshown bearings between the unit  13  and photosensitive drum  1 . As the photosensitive drum  1  receives driving force from the motor  15 , which is a power source for driving the photosensitive drum  1 , it is rotationally driven in the direction indicated by an arrow mark A in  FIG. 2 , by the driving force received from the motor  15 . 
         [0038]    The photosensitive unit  13  has a charge roller  2  as a charging means, and a cleaning member  6  as a cleaning means, which are disposed in contact with the peripheral surface of the photosensitive drum  1 . To the charge roller  2 , charge bias voltage which is sufficient to charge the peripheral surface of the photosensitive drum  1  to a given potential level, is applied from an unshown charge bias power source. In this embodiment, the charge bias voltage is applied to the charge roller  2  so that the peripheral surface of the photosensitive drum  1  is given −550 V of potential. 
         [0039]    As the peripheral surface of the photosensitive drum  1 , which has just been uniformly charged by the charge roller  2 , is scanned by the beam  11  of laser light emitted from the scanner unit  30  while being modulated according to the image information, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum  1 . In this embodiment, the intensity of beam  11  of laser light is set to 0.2 μJ/cm 2 , so that as the charged peripheral surface of the photosensitive drum  1  is scanned by the beam  11  of laser light, an electrostatic latent image which is 150 V in potential level is formed on the peripheral surface of the photosensitive drum  1 . 
       &lt;Developing Device&gt; 
       [0040]    Referring to  FIG. 2 , the developing device  3  has: the developer container  9  in which the toner  10  is stored; and the development roller  4 , as a developer bearing member, which bears the toner  10 . It has also a toner supply roller  5 , as a developer supplying member, which is disposed in contact with the development roller  4  to supply the development roller  4  with the toner  10 . Further, it has the regulation blade  8 , as a developer regulating member, which is for forming a thin layer of the toner  10  by regulating in thickness the layer of toner  10  on the peripheral surface of the development roller  4  (developer bearing member), etc. 
         [0041]    The developing device  3  has a development chamber  18   a  and a toner storage chamber  18   b . In this embodiment, the toner storage chamber  18   b  is on the underside of the development chamber  18   a . In other words, in this embodiment, the developing device  3  is structured so that it takes a substantial length of time to convey the toner  10  in the toner storage chamber  18   b  to the development chamber  18   a , and supply the peripheral surface of the development roller  4  with the toner  10 . In this embodiment, the normal polarity to which the toner  10  is charged is negative. However, it is not mandatory that the normal polarity to which the toner  10  is charged is negative. 
         [0042]    When the developing device  3  is fresh, there is stored a preset amount of toner  10 , as developer, in the toner storage chamber  18   b , and there is no toner  10  in the development chamber  18   b . In this embodiment, when the developing device  3  is fresh, it has a toner seal  19  in the developer container  9 . The toner seal  19  is fixed to the developer container  9  with the use of an unshown adhering means to keep the developer container  9  partitioned from the development chamber  18   b . The toner seal  19  is not removed when the developing device  3  is shipped out of a factory. 
         [0043]    The toner seal  19  prevents the toner  10  leaking out of the developing device  3  through the gap between the edge of the opening of the development chamber  18   a  and the development roller  4  during the distribution of the developing device  3 , that is, during the period in which the fresh developing device  3  is shipped out of a factory, and is delivered to a user. In this embodiment, as the fresh process cartridge  7  is installed into the image forming apparatus  100 , the toner seal  19  is peeled away by an unshown toner seal pealing means. The unshown toner seal peeling means is driven by the same driving force as that which rotationally drives the development roller  4 , toner supply roller  4 , toner conveying member  20 , etc., of the developing device  3 . However, the process cartridge  7  may be structured so that the toner seal  19  is to be peeled away by a user. 
         [0044]    There is provided the toner conveying member  20  for conveying the toner  10  to the development chamber  18   a , in the toner storage chamber  18   b . The toner conveying member  20  is rotationally driven in the direction indicated by an arrow mark G by a motor  16 , as driving force source, which is controlled by the control section  25 . Thus, the toner conveying member  20  scoops up the toner  10  in the toner storage chamber  18   b , which is on the bottom side in  FIG. 2 , and delivers the scooped toner  10  upward into the development chamber  18   a.    
         [0045]    Compared to the amount by which the toner  10  is delivered to the development chamber  18   a  of a developing device structured so that the development chamber  18   a  is disposed under or horizontally next to the toner storage chamber  18   b , the amount by which the toner  10  is delivered to the development chamber  18   a  of the developing device  3  in this embodiment is rather small. In the case of the developing device  3  in this embodiment, therefore, the development roller  4 , toner supply roller  5 , toner conveying member  20 , etc., of the developing device  3  have to be driving a substantial length of time to peel the toner seal  19  and fill the development chamber  18   a  with the toner  10  to make it possible for the image forming apparatus  100  to form images. 
         [0046]    In the development chamber  18   a , the development roller  4 , as the developer bearing member, which is in contact with the peripheral surface of the photosensitive drum  1 , and is rotated in the direction indicated by an arrow mark D in  FIG. 2 , by the driving force it receives from the motor  16 , as a driving force source, which is under the control of the control section  25 , is disposed. In this embodiment, the development roller  4  and photosensitive drum  1  are rotated in such directions that their peripheral surface moves in the same direction, in the area of contact between the development roller  4  and photosensitive drum  1 . 
         [0047]    Further, in the development chamber  18   a , there is disposed the toner supply roller  5  which supplies the development roller  4  with the toner  10  conveyed to the development chamber  18   a  from the toner storage chamber  18   b . Moreover, in the development chamber  18   a , there is disposed the regulation blade  8 , as a developer regulating member, which regulates in the amount per unit area, the toner  10  on the peripheral surface of the development roller  4 , to which the toner  10  was delivered by the toner supply roller  5 , and also, gives electrical charge to the toner  10 . 
         [0048]    The development roller  4  and toner supply roller  5  rotate in the directions E and F, respectively, by receiving rotational driving force from the motor  16 , as a driving force source, which is under the control of the control section  25 . In this embodiment, the toner supply roller  5  is disposed so that its peripheral surface remains in contact with the peripheral surface of the development roller  4 . The amount of hypothetical intrusion of the toner supply roller  5  into the peripheral surface of the development roller  4  is 1.0 mm. The speeds with which the development roller  4  and toner supply roller  5  are rotationally driven are 100 rpm (revolutions per minute) and 200 rpm, respectively. Further, the development roller  4  and toner supply roller  5  are rotated in such directions that the peripheral surface of the development roller  4  and that of the toner supply roller  5  move in the same direction, in the area of contact between the two rollers  4  and  5 . 
         [0049]    After the development roller  4  is supplied with the toner  10  by the toner supply roller  5 , the toner  10  on the development roller  4  is made to enter the area of contact between the regulation blade  8  and development roller  4  by the rotation of the development roller  4  in the direction indicated by the arrow mark D. Then, in the area of contact between the regulation blade  8  and development roller  4 , the toner  10  is given triboelectrical charge by the friction between the peripheral surface of the development roller  4  and the regulation blade  8 , while the layer of the toner  10  on the peripheral surface of the development roller  4  is regulated in thickness. After being regulated in thickness, the layer of the toner  10  on the peripheral surface of the development roller  4  is conveyed by the rotation of the development roller  4  to the area of contact between the peripheral surface of the development roller  4  and that of the photosensitive drum  1 , in which the electrostatic latent image on the peripheral surface of the development roller  4  is developed into a visible image, that is, an image formed of the toner  10  (which hereafter will be referred to simply as toner image). 
         [0050]    Referring to  FIG. 2 , to the electrically conductive supporting members of the development roller  4 , toner supply roller  5 , and regulation blade  8 , preset voltages, which are different in properties, are applied by voltage applying sections  21 - 23 , as voltage applying means (voltage applying devices), with which the image forming apparatus  100  is provided, through unshown electrically conductive contacts. The voltage applying section  21  which is in connection to the development roller  4 , and the voltage applying section  23  which is in connection to the regulation blade  8 , are structured so that they can be varied in the voltage they apply to the development roller  4  and regulation blade  8 , respectively. Further, the voltage applying section  22  which is in connection to the toner supply roller  5  is structured so that the voltage it applies to the toner supply roller  5  can be made different from the voltage applied to the development roller  4  from the voltage applying section  21 . 
         [0051]    Next, referring to  FIG. 2 , the development roller  4 , toner supply roller  5 , and regulation blade  8  are described about their structure. The development roller  4  is 15 mm in external diameter. It is made up of an electrically conductive metallic core which is 6 mm in external diameter, a silicone rubber layer, as substrative layer, which covers the peripheral surface of the metallic core, and a urethane rubber layer, as the surface layer, which covers the outward surface of the silicone rubber layer. The volume resistivity of the development roller  4  is in a range of 1×10 4 Ω-1×10 12 Ω. 
         [0052]    As for the toner supply roller  5 , it is 15 mm in external diameter. It is an electrically conductive and elastic sponge roller. It is made up of an electrically conductive metallic core which is 6 mm in external diameter, and a foamed layer formed on the peripheral surface of the metallic core. Its volume resistivity is in a range of 1×10 4 Ω-1×10 8 Ω. 
         [0053]    The regulation blade  8  is a piece of metallic plate made of stainless steel (SUS), which is 0.1 mm in thickness. It is disposed in contact with the development roller  4  in such a manner that its free edge (regulating edge) is on the upstream side of its base portion, in terms of the rotational direction of the development roller  4  indicated by the arrow mark D in  FIG. 2 . As the regulation blade  8 , it is possible to use a blade made of an electrically conductive supporting member, such as a piece of metallic plate made of stainless steel (SUS), and a layer of polyamide resin, which was made electrically conductive and is laminated to the supporting member. Further, the regulating end of the regulation blade  8  may be given curvature. 
       &lt;Bias Voltages Applied During Normal Image Forming Operation&gt; 
       [0054]    Next, the bias voltages to be applied to the development roller  4 , toner supply roller  5 , and regulation blade  8  during the normal image forming operation are described. The bias voltage to be applied to the toner supply roller  5  is −400 V. The bias voltage to be applied to the development roller  4  is also −400 V. Thus, the amount of difference in terms of potential level between the toner supply roller  5  and development roller  4  is 0 V. 
         [0055]    The bias voltage to be applied to the regulation blade  8  is −500 V. Thus, the difference between the regulation blade  8  and development roller  4  in terms of potential level is −100 V. This difference in potential level works in the direction to move the toner  10  from the regulation blade  8  to the development roller  4 . In comparison, the potential level (pre-exposure level Vd) of the peripheral surface of the photosensitive drum  1  is −550 V as described above. Thus, the amount of difference in terms of potential level between the development roller  4  and the peripheral surface of the photosensitive drum  1  is −150 V. 
       &lt;Coating Agent&gt; 
       [0056]    Next, referring to  FIG. 3 , the coating agent  50  on the peripheral surface of the development roller  4  is described. It is applied to the peripheral surface of the development roller  4  with the use of a coating agent applying method (which is described later), when the process cartridge  7  is shipped out of a factory. In this embodiment, silicone resin particles (Tospearl 120 (commercial name): product of GE-Toshiba Silicone Co., Ltd.) which are 2 μm in average diameter are used as the coating agent  50 . Tospearl 120 (commercial name) is the same in characteristic as the toner  10  in that it becomes negatively charged like the toner  10 . As the coating agent  50 , it is possible to use other particled substance than silicone resin particles. That is, this embodiment is not intended to limit the present invention in terms of the coating agent for the development roller  4 . That is, any particled substance can be used as the coating agent  50 , as long as it becomes negatively charged like the coating agent  50 . For example, the toner  10  itself can be used as the coating agent  50 . 
         [0057]    That is, in a process cartridge manufacturing process, the development roller  4  is to be coated in advance with toner which is to be used as the coating agent  50 , that is, toner which is different from the toner  10  stored in the toner storage chamber  18   b . By the way, in a case where toner is used as the coating agent  50 , toner which is different in color from the toner  10  in the toner storage chamber  18   b , may be used. That is, in this embodiment, there are contained the yellow Y, magenta M, cyan C and black K toners in the process cartridges  7 Y,  7 M,  7 C and  7 K, respectively. However, the toners to be applied to the development rollers  4  of the process cartridges  7  may be the same in color. 
         [0058]    For example, yellow Y toner can be used as the coating agent  50  for all the process cartridges  7 Y,  7 M,  7 C and  7 K. In such a case, the toner to be applied to the development roller  4  is different from the toners  10  to be stored in the toner storage chamber  18   b  of process cartridges  7 M,  7 C and  7 K. On the other hand, in the case of the process cartridge  7 Y, the toner to be coated on the development roller  4  is the same as the toner  10  to be stored in the toner storage chamber  18   b.    
         [0059]    The following are examples of particled substance, which can be used as the coating agent  50 , in addition to the toner  10 . 
         [0060]    As for particled resinous substance, silicone resin, polyalkylene resin such as polyethylene, polypropylene, etc., and fluorine resin such as polyfluorovinylidene, polytetrafluoroethylene, can be used. Further, polyethylene resin such as polyethyleneterephthalate, polybutyleneterephthalate, etc., styrene resin such as polystyrene, etc., acrylic resin such as polymethyl-methacrylate, etc., styrene-acrylic resin such as copolymer of styrene-methyl acrylate, etc., can be used. Moreover, phenol resin, urea resin, melamine resin, epoxy resin, urethane resin, polyamide resin, etc., can be also be used. 
         [0061]    Further, as for particled fatty acid, such long chain fatty acid as undecyl acid, myristic acid, lauric acid, undecanoic acid, palmitic acid, pentadecanoic acid, stearic acid, heptadecanoic acid, arachidic acid, montanic acid, olein acid, linoleic acid, arachidonic acid, etc., can be used. In addition, as for metallic salts, salts of such metals as zinc, iron, magnesium, aluminum, calcium, sodium, lithium, etc., can be used. 
         [0062]    Moreover, as materials for particled inorganic substance, such inorganic substances as inorganic metallic oxides, inorganic nitride, inorganic carbonate, sulfate, or metallic salt carbonate, etc., can be used. More concretely, such oxides as silicon oxide, titanium oxide, strontium titanate, aluminum oxide (alumina), etc., such nitride as boron nitride, silicon nitride, etc., such carbonate as silicon carbonate, titanium carbonate, boron carbonate, etc., such boride as tungsten boride, etc., can be listed. 
         [0063]    These particled substances are treated on their surface with silane coupler, titanium coupler, silicone oil, high polymer of fatty acid, or their metallic salts, to make them hydrophobic, or to control them in property in terms of triboelectric charge. 
         [0064]    The information regarding the property of the particled substances in terms of triboelectric charge, can be obtained by finding out whether they become positively charged relative to a substance against which they rub, or negatively. 
         [0065]    Generally speaking, however, silicone resin, fluorine resin, and polyester resin can be listed as a substance which is likely to become negatively charged. On the other hand, phenol resin, melamine resin, epoxy resin, urethane resin, and polyamide resin can be listed as a substance which is likely to become positively charged. 
       &lt;Method for Applying Coating Agent&gt; 
       [0066]    Next, referring to  FIG. 3 , the method for applying coating agent  50  is described. In this embodiment, a method for coating the peripheral surface of the development roller  4  with the coating agent  50  is used as the method for placing the coating agent  50  between the development roller  4  and a component which is in contact with the development roller  4 . Here, this method is described with reference to  FIG. 3 . However, this embodiment is not intended to limit the present invention in scope in terms of the coating agent applying method, that is, the method for directly applying the coating agent  50  to the peripheral surface of the development roller  4 . For example, the coating agent applying method may be such that the coating agent  50  is applied to the toner supply roller  5  to transfer the coating agent  50  to the development roller  4  from the toner supply roller  5  which is in contact with the development roller  4 . 
         [0067]      FIG. 3  is a sectional view of the coating agent applying device for applying the coating agent  50  to the peripheral surface of the development roller  4 . It shows the structure of the device. The coating agent applying device is provided with an application roller  5  for applying the coating agent  50  to the development roller  4 , a supply roller  52  for supplying the application roller  53  with the coating agent  50 , and a regulation member  54  for regulating the coating agent  50  on the application roller in the amount per unit area. There is the coating agent  50  in the coating agent applying device  51 . The coating agent applying device  51  is structured so that the development roller  4  can be rotatably attached to the coating agent applying device  51  with the placement of unshown development roller mounting members between the development roller  4  and the frame of the coating agent applying device  51 . The development roller  4 , application roller  53 , and supply roller  52  rotate in the directions F, H and I, respectively, by receiving rotational force from a motor  17  as a driving force source. 
         [0068]    The supply roller  52  for supplying the application roller  53  with the coating agent  50  in the coating agent applying device  51  is an elastic sponge roller, which is similar to the toner supply roller  5  shown in  FIG. 2 . That is, it is made of an electrically conductive metallic core, and a layer of foamed substance which covers the peripheral surface of the metallic core. It is disposed in such a manner that its peripheral surface contacts the peripheral surface of the application roller  53 , and forms a nip having a preset size. As the supply roller  52  is rotated in the direction indicated by an arrow mark I in  FIG. 3 , it supplies the application roller  53  with the coating agent  50  in the coating agent applying device  51 . 
         [0069]    After the coating agent  50  is supplied to the application roller  53  by the supply roller  52 , the coating agent  50  on the application roller  53  is made to enter the area of contact between the application roller  53  and regulation member  54  by the rotation of the application roller  53  in the direction indicated by the arrow mark H in  FIG. 3 . Then, the coating agent  50  is charged, that is, given triboelectric charge, by the friction between itself and the peripheral surface of the application roller  53 , and the friction between itself and the regulation member  54 , while the layer of the coating agent  50  is regulated in thickness. Then, the layer of the coating agent  50  which has a preset thickness, is conveyed to the area of contact between the application roller  53  and development roller  4 , by the rotation of the application roller  53  in the direction indicated by the arrow mark H in  FIG. 3 . 
         [0070]    To the application roller  53 , an application bias voltage which is sufficient to transfer the coating agent  50  onto the development roller  4  is applied from an unshown application bias power source. Thus, the coating agent  50  on the peripheral surface of the application roller  53  transfers onto the development roller  4  in a manner to uniformly cover the peripheral surface of the development roller  4  in terms of the lengthwise direction of the development roller  4 . 
         [0071]    The coating agent  50  on the development roller  4  functions to lubricate between the development roller  4  and toner supply roller  5  of the developing device  3 . Thus, it is possible to reduce the friction which occurs between the development roller  4  and toner supply roller  5 , and the friction which occurs between the development roller  4  and regulation blade  8 , as the two rollers  4  and  5  are rotationally driven. Therefore, it is possible to reduce the amount of rotational torque necessary to rotationally drive the developing device  3 . 
       &lt;Vertical Streaks&gt; 
       [0072]    It sometimes occurred immediately after the fresh developing device  3  began to be used for the first time by an image forming apparatus such as the image forming apparatus  100  that the image forming apparatus outputted an image having vertical streaks. In a case where the amount of the coating agent  50  on the development roller  4  is small, the amount by which the coating agent  50  enters the area of contact between the development roller  4  and regulation blade  8  immediately after the fresh developing device  3  begins to be driven is also small. Therefore, there occurs a substantial number of small gaps, that is, areas which are not filled with the coating agent  50 , between the peripheral surface of the development roller  4  and regulation blade  8 , in terms of the lengthwise direction of the development roller  4  (regulation blade  8 ). Further, it takes a substantial length of time for the peripheral surface of the development roller  4  to be supplied with the toner  10  after the development roller  4 , toner supply roller  5 , and toner conveying member  20  of the fresh developing device  3  begin to be rotationally driven. 
         [0073]    Therefore, it takes a substantial length of time for the toner capturing area, which is between the regulating edge of the regulation blade  8  and development roller  4 , to be sufficiently filled with the toner  10 . Therefore, the development roller  4 , toner supply roller  5 , and toner conveying member  20  of the developing device  3  end up rotating for a relatively long period of time with the presence of the substantial number of gaps between the regulating area. During this period, foreign substances such as dust, paper burrs, etc., in the developing device  3 , which had adhered to the adjacencies of the regulation blade  8 , enter the above-described gaps in the toner capturing area, and get stuck in the gaps, causing thereby the image forming apparatus  100  to output images having vertical streaks. 
         [0074]    As the means for minimizing the frequency with which the image forming apparatus  100  outputs images having vertical streaks, it is effective to carry out the following method from when the development roller  4 , toner supply roller  5 , and toner conveying member  20  of the fresh developing device  3  begin to be rotated to when the peripheral surface of the development roller  4  is provided with a preset amount of the toner  10 . That is, it is effective to keep the coating agent  50  collected in the toner capturing area, that is, the immediate adjacencies of the regulating edge portion of the regulation blade  8 . With the presence of a relatively large amount of coating agent  50  along the regulating edge of the regulation blade  8 , it is possible to prevent the foreign substances such as dust, paper burrs, etc., from entering, and getting stuck, in the abovementioned gaps in the toner capturing area. 
         [0075]    Here, to supply the peripheral surface of the development roller  4  with a preset amount of toner  10  means to supply the development chamber  18   a  with the toner  10  by such an amount that is sufficient to fill the interface between the regulating edge of the regulation blade  8  and development roller  4  with the toner  10  as the development roller  4 , toner supply roller  5 , and toner conveying member  20  of the developing device  3  are rotationally driven, even when the aforementioned various biases to be applied for image formation are the normal ones. 
         [0076]    As long as the toner capturing area, which is in the adjacencies of the regulating edge of the regulation blade  8 , is supplied with the toner  10  by an amount which is enough to fill up the toner capturing area, it is possible to prevent foreign substances such as dust, paper burrs, etc., from entering the adjacencies. Therefore, the settings for the various bias voltages may be the same as those for the normal image formation. 
         [0077]    In this embodiment, the control sequence for collecting and keeping the coating agent  50  in the toner capturing area, which is in the immediate adjacencies of the regulating edge of the regulation blade  8  is as follows. This control sequence is carried out as the initialization control (initialization sequence) which is to be carried out during the period between when the fresh developing device  3  is installed in the main assembly of the image forming apparatus  100  and when the image forming apparatus  100  becomes ready for image formation, that is, it is put on standby. 
       &lt;Control of Initializing Operation&gt; 
       [0078]    Next, referring to  FIGS. 4-6 , the control of the initializing operation is described. In the case of the image forming apparatus  100  in this embodiment, the first operation to be carried out after the installation of the fresh developing device  3  into the main assembly of the image forming apparatus  100  is the initializing operation in which the development roller  4 , toner supply roller  5 , and toner conveying member  20  of the development roller  4  are rotationally driven. 
         [0079]    In Step S 1  in  FIG. 4 , the control section  25  which is the controlling means with which the main assembly of the image forming apparatus  100  is provided decides whether the developing device  3  has ever been used (is fresh) or not. Whether or not the developing device  3  has ever been used (is fresh) is detected by one of known detecting means. If the developing device  3  has never been used, the control section  25  proceeds to Step S 2 . If the developing device  3  has been used, the control section  25  proceeds to Step S 7 , in which it readies the image forming apparatus  100  for image formation, and then, keeps the apparatus  100  on standby. In Step S 2 , the control section  25  decides whether or not the initializing operation has been carried out. If the developing device  3  has been initialized, the control section  25  proceeds to Step S 7 , in which it readies the image forming apparatus  100  for image formation and keeps the apparatus on standby. If the initializing operation has not been carried out, the control section  25  proceeds to Step S 3 . 
         [0080]    In Step S 3 , the control section  25  sets the voltage application sections  21 - 25 , for the application of the initialization bias voltages. Then, in Step S 4 , the control section  25  drives the motor  16  to rotationally drive the toner conveying member  20 , toner supply roller  5 , and development roller  4  of the developing device  3  until the development chamber  18   a  is provided with a preset amount of toner  10 . 
         [0081]    Next, in Step S 5 , the control section  25  switches the voltage application sections  21 - 23  in bias voltage from the initialization bias voltage to the image formation bias voltage. Next, in Step S 6 , the control section  25  drives the motor  16  to rotationally drive the toner conveying member  20 , toner supply roller  5 , and development roller  4  of the developing device  3  until the development chamber  18   a  is provided with the preset amount of toner  10 . Thereafter, it proceeds to Step S 7 , in which its readies the image forming apparatus  100  for image formation, and keeps the apparatus  100  on standby. 
         [0082]    In this embodiment, in Step S 3 , the bias voltages are set so that it is possible to collect and keep the coating agent  50  in the toner capturing area, which is in the immediate adjacencies of the regulating edge of the regulation blade  8 . Then, in Step S 4 , the developer conveying member  20 , toner supply roller  5 , and development roller  4  of the developing device  3  begin to be rotationally driven, and are continuously driven until the toner  10  in the toner storage chamber  18   b  is delivered to the development chamber  18   a  by the preset amount. 
         [0083]    The length of time the developing device  3  needs to be rotationally driven is affected by the structure of the developing device  3 . Thus, it is desired to be set to a proper value. In this embodiment, the length of time necessary for the development chamber  18   a  to be supplied with the preset amount of toner  10  was long enough for the development roller  4  to be rotated 100 times, even in consideration of how the developing device  3  was stored, and the like factors. 
         [0084]    In the above-described Step S 5 , the control section  25  changes the voltage application sections  21 - 23  in bias voltage from those for initialization to those for the normal image formation. Then, in Step S 6 , it rotationally drives the developing device  3  until the development chamber  18   a  is supplied with a sufficient amount of toner  10 . The sufficient amount by which the development chamber  18   a  is to be supplied with toner  10  is such an amount that makes it possible for the image forming apparatus  100  to output high density images such as solid images which do not suffer from defects. 
         [0085]    In the above-described Step S 5 , the control section  25  changes the voltage application sections  21 - 23  in bias voltage from those for the initialization to those for the normal image formation, for the following reason. That is, if the developing device  3  is rotationally driven for a long time while the bias voltages to be applied by the voltage application sections  21 - 23  are left the same as those for the initialization set in Step S 6 , the toner  10  solidly adheres to the regulating edge of the regulation blade  8 . Further, the length of time the developing device  3  is to be rotationally driven in Step S 6  is affected by the structure of the developing device  3 . Thus, it is desired to be appropriately set. In this embodiment, the total length of time the developing device  3  is to be rotationally driven for the initialization is equivalent to the length of time necessary to rotate the development roller  4  roughly 500 times. 
         [0086]      FIGS. 5 and 6  show how the control section  25  controls the bias voltages to be applied to the development roller  4 , regulation blade  8 , and toner supply roller  5  with the use of the voltage application sections  21 - 23 , respectively, in Steps S 3  and S 5  in  FIG. 4 . More concretely,  FIGS. 5 and 6  are timing charts which show the timings with which the voltage application sections  21 - 23  are changed in bias voltage in the first to third embodiments, and in the case of the comparative developing device  3 . They show the rotational speed (rpm) of the developing device  3  along with the timings. 
         [0087]    Further, in order to verify the effects of this embodiment, six development rollers  4  which were different in the amount (5 mg, 10 mg, 30 mg, 50 mg, 70 mg and 90 mg, as shown in  FIG. 7 ) by which they were coated with the coating agent  50  before they are shipped out of a factory were prepared. Then, these rollers  4  were subjected to experiments for comparing them in terms of their effects upon the severity of the vertical streaks. 
         [0088]    The reason why the six development rollers  4  which were different in the amount by which their peripheral surface was coated with the coating agent  50  were tested in the experiments is as follows. If it is possible to reduce the amount by which the development roller  4  is to be coated with the coating agent  50  when the developing device  3  is shipped out of a factory, it becomes unnecessary to strictly control the amount by which the development roller  4  is to be coated. Therefore, it has an excellent effect that it reduces the cost for manufacturing the developing device  3 . In addition, if it is possible to reduce the amount by which the development roller  4  is to be coated with the coating agent  50 , it is possible to reduce the risk that the coating agent  50  scatters during the process of applying the coating agent  50 , on the developing device manufacture line, and also, while the developing device  3  is transported after its shipment out of a factory. 
         [0089]    Then, the images formed with the use of the six development rollers  4  which were different in the amount by which their peripheral surface was coated with the coating agent  50  before they were shipped out of a factory were examined regarding the presence or absence of the vertical streaks, as shown in  FIG. 7 . With these experiments, it was possible to clearly verify the effects of this embodiment. More concretely, in the case of the development roller  4 , which was 0 mg in the amount of the coating agent  50  on its peripheral surface, the developing device  3  was higher in the amount of torque that was required to rotate the development roller  4 . Thus, there occurred such a problem that the regulation blade  8  breaks. In comparison, in the case of the development roller  4 , which was 100 mm in the amount of the coating agent  50  on its peripheral surface, there occurred such problems that the coating agent  50  scatters while the coating agent  50  was applied on the manufacture line, and while the developing device  3  was transported after it was shipped out of a factory. 
         [0090]    By the way, in order to make the developing devices in the first to third embodiment, and the comparative developing device, the same in the amount of their internal dust, paper burrs, etc., they were made the same in the condition under which they were assembled. The experiments were carried out in an environment which was 23° C. in temperature, and 50% in humidity. In the case of each of the development rollers  4  which are different in the amount of the coating agent  50 , the fresh process cartridge  7  was installed in the main assembly of the image forming apparatus  100 , and the initializing operation was carried out. Then, immediately after the initializing operation was completed, such a solid black image that is capable of covering a sheet of recording paper from one end of the sheet to the other (area across which image is formable) in terms of the lengthwise direction of the photosensitive drum  1 ), that is, such a solid image that is highest in print ratio, was printed. 
         [0091]    Referring to  FIG. 7 , the severity of the vertical streaks was evaluated in three levels of severity. “G” stands for a case where there was no visible vertical streak, and “F” stands for a case where vertical streaks were faintly visible. “NG” stands for a case where vertical streaks were unacceptably severe. 
         [0092]    Next, referring to  FIGS. 5 to 7 , the results of the experiments in which the developing device  3  in the first to third embodiments of the present invention, and the comparative developing device  3 , were tested are described. 
       &lt;Comparative Developing Device&gt; 
       [0093]    In the case of the comparative developing device  3 , which corresponds to the bottom half of  FIG. 6 , and  FIG. 7 , such a bias voltage that works in the direction to cause the coating agent  50  to move from the regulation blade  8  to the development roller  4  was applied between the development roller  4  and regulation blade  8  during the initializing operation. In the case of the comparative developing device  3  which corresponds to the bottom half of  FIG. 6 , −400 V was applied to the development roller  4 , and −500 V was applied to the regulation blade  8 . These bias voltages were the same in properties as those applied for the normal image formation. Referring to  FIG. 7 , in the case of the comparative developing device  3 , vertical streaks occurred regardless of the amount by which the peripheral surface of the development roller  4  was coated with the coating agent  50  (whether amount was 5 mg, 10 mg, 30 mg, 70 mg or 90 mg). 
         [0094]    In the case of the developing device  3  in the first embodiment, which corresponds to the top half of  FIG. 5 , and  FIG. 7 , such a bias voltage that works in the direction to cause the coating agent  50  to move from the development roller  4  to the regulation blade  8  is applied between the development roller  4  and regulation blade  8  during the initializing operation. In the case of the developing device  3  in the first embodiment, which corresponds to the top half of  FIG. 5 , −400 V was applied to the development roller  4 , and −300 V was applied to the regulation blade  8 . 
         [0095]    In the initializing operation, such bias voltages (voltages for initializing operation) that are different from those applied to the development roller  4  and regulation blade  8  by the voltage application sections  21  and  23  during a normal image forming operation are applied to the development roller  4  and regulation blade  8  during the period from when the development roller  4  begins to be rotationally driven until the peripheral surface of the development roller  4  is supplied with the preset amount of toner  10 . These bias voltages (voltages for initializing operation) which are different from those applied during a normal image forming operation were the same as those to be applied to cause the coating agent  50  which was applied to the peripheral surface of the development roller  4  before the developing device  3  was shipped out of a factory, to move toward the regulation blade  8 . 
         [0096]    To describe in greater detail, during a normal image forming operation, it is necessary to cause the negatively charged toner  10  to move from the regulation blade  8  to the development roller  4 . During a normal image forming operation, therefore, such bias voltage that puts the potential level of the regulation blade  8  on the negative side (toner potential side) of that of the development roller  4  is applied to the regulation blade  8 . That is, during a normal image forming operation, −500 V is applied to the regulation blade  8 , and −400 V is applied to the development roller  4 . Thus, the toner  10  which is negative in polarity is pressured to move from the regulation blade  8  to the development roller  4 . 
         [0097]    On the other hand, during an initializing operation, in order to keep the coating agent  50  (silicone resin particles) which became negatively charged, attracted to the regulation blade  8 , such bias (voltage) that is on the positive side of the potential level of the development roller  4  is applied to the regulation blade  8 . That is, during an initializing operation, −300 V is applied to the regulation blade  8 , and −400 V (the same as voltage applied during image forming operation) is applied to the development roller  4 . Therefore, the negative charged coating agent  50  is pressured to move from the development roller  4  to the regulation blade  8 . 
         [0098]    That is, the voltage applied to the development roller  4  during a normal image forming operation is the same as the voltage applied to the development roller  4  during an operation in which no image is formed. In comparison, the voltage applied to the regulation blade  8  changes in the polarity relative to the voltage applied to the development roller  4 . That is, during an image forming operation, the voltage (−500 V) applied to the regulation blade  8  is on the negative side (the same side as toner  10  and coating agent  50 ) of the voltage (−400 V) applied to the development roller  4 . During an initializing operation, the voltage (−300 V) applied to the regulation blade  8  is on the plus side (opposite side from those of toner  10  and coating agent  50 ) of the voltage (−400 V) applied to the development roller  4 . 
         [0099]    In other words, the voltage (−300 V) to be applied to the development roller  4  during an initialization operation is on the plus side (opposite side of polarity of toner  10  and coating agent) of the voltage (−500 V) to be applied to the regulation blade  8  during an image forming operation. 
         [0100]    By controlling the bias voltages as described above, it is possible to attract the negatively charged coating agent  50  on the peripheral surface of the development roller  4 , to the toner catching portion of the regulation blade  8 . Therefore, it is possible to collect the coating agent  50  by the catching portion of the regulation blade  8  and keep the collected coating agent  50  attached to the catching portion to prevent gaps from forming between the catching portion of the regulation blade  8  and the peripheral surface of the development roller  4 . Therefore, it is possible to prevent foreign substances such as dust, paper burrs, etc., from entering between the catching portion (regulating edge) of the regulation blade  8 , and the peripheral surface of the development roller  4  in order to prevent the occurrence of the vertical streaks. Referring to  FIG. 7 , according to the results of these experiments, unlike in the case of the comparative developing device  3 , in the case of the developing device  3  in this embodiment, as the amount by which the coating agent  50  was applied to the development roller  4  was increased to roughly 30 mg, the occurrences of the vertical streaks began to reduce. Then, as the amount was set in a range of 50 mg-90 mg, the vertical streaks did not occur. 
       Embodiment 2 
       [0101]    In the case of the developing device  3  in the second embodiment of the present invention, shown in the bottom half of  FIG. 5 , and  FIG. 7 , in addition to the bias voltage applied during an initializing operation in the first embodiment, such a bias voltage that works in the direction to move the coating agent  50  from the toner supply roller  5  to the development roller  4  is applied between the toner supply roller  5  and development roller  4 . In the case of the developing device  3  shown in the bottom half of  FIG. 5 , during the initializing operation, −400 V was applied to the development roller  4 , and −300 V was applied to the regulation blade  8 . Further, −600 V was applied to the toner supply roller  5 . 
         [0102]    The initializing operation applies to the development roller  4  and toner supply roller  5 , such bias voltages that are different from those applied to them during a normal image forming operation, with the use of the voltage application sections  21  and  22 , during the period between when the development roller  4  begins to be rotationally driven, to when the peripheral surface of the development roller  4  is supplied with the preset amount of toner  10 . These bias voltages which are different from those applied during a normal image forming operation are such voltages that work in the direction to cause the coating agent  50  coated on the peripheral surface of the development roller  4  before the fresh developing device  3  was shipped out of the factory, to move from the toner supply roller  5  to the development roller  4 . 
         [0103]    To describe in greater detail, the voltage to be applied to the toner supply roller  5  has a value (−600 V) which is on the minus side (the same side as toner  10  and coating agent  50 ) of the voltage (−400) which is to be applied to the development roller  4  during an initializing operation. 
         [0104]    By the way, in this embodiment, the voltage to be applied to the toner supply roller  5  during a normal image forming operation has the same value (−600 V) as the voltage to be applied to the toner supply roller  5  during an initializing operation. However, the value of the voltage to be applied to the toner supply roller  5  during an image forming operation may be switched to the same value (−400 V:  FIG. 5(   a )) as the one in the first embodiment, while keeping the voltage to be applied to the toner supply roller  5  during an initializing operation at −600 V. 
         [0105]    By controlling the bias voltages as described above, it is possible to reduce the amount by which the coating agent  50  on the peripheral surface of the development roller  4  is stripped away from the development roller  4  by the toner supply roller  5 . Therefore, it becomes possible to increase the amount by which the coating agent  50  collects on the catching portion of the regulation blade  8 . Referring to  FIG. 7 , according to the above-described experiments, as the amount by which the coating agent  50  was applied to the peripheral surface of the development roller  4  was increased to roughly 10 mg, the occurrence of the vertical streaks began to reduce, and the vertical streaks did not occur when the amount of the coating agent  50  on the development roller  4  was in a range of 30 mg-90 mg, which was wider than that in the above-described first embodiment. That is, the second embodiment was better in terms of the effect of blocking foreign substances such as dust, paper burrs, etc., to prevent the occurrence of vertical streaks, even though the amount by which the coating agent  50  was applied to the peripheral surface of the development roller  4  of the developing device  3  before the developing device  3  was shipped out of a factory was smaller. 
       Embodiment 3 
       [0106]    In the case of the developing device  3  in the third embodiment shown in the top half of  FIG. 6 , and  FIG. 7 , in addition to the bias voltage control carried out during an initializing operation in the above-described second embodiment, the speed with which the development roller  4  of the developing device  3  is rotated in Step S 4  in  FIG. 4  was made slower than the speed with which the development roller  4  is rotated during an image forming operation. In the above-described second embodiment, −400 V was applied to the development roller  4 , and −300 V was applied to the regulation blade  8 . Further, −600 V was applied to the toner supply roller  5 . In this embodiment, in addition to the above-described bias voltage control, the speed with which the development roller  4  is rotated during an initializing operation was reduced to 33 rpm, whereas in the first and second embodiments, it was 100 rpm which is the same as the rotational speed of the development roller  4  for an image forming operation. By the way, to the toner supply roller  5 , −400 V was applied. 
         [0107]    An initializing operation is such an operation that is carried out from when the development roller  4  begins to be rotationally driven to when the peripheral surface of the development roller  4  is supplied with a preset amount of toner  10 . During the initializing operation in this embodiment, the development roller  4  is rotated at 30 rpm, which is substantially slower than 100 rpm which is the fastest of the speeds with which the development roller  4  of the developing device  3  is rotatable while the image forming apparatus  100  is actually forming images. 
         [0108]    That is, the development roller  4  is sometimes changed in rotational speed according to the image formation condition. For example, when an image is printed on a sheet of cardstock, it sometimes takes a longer time than when an image is printed on a sheet of ordinary printing paper. Thus, it is possible to structure that image forming apparatus  100  (developing device  3 ) so that when an image is printed on a sheet of ordinary printing paper, the speed for the development roller  4  is set to 100 rpm, or the fastest one, whereas when an image is printed on a sheet of cardstock, the speed of the development roller  4  is set (reduced) to 33 rpm. 
         [0109]    If the image forming apparatus  100  (developing device  3 ) is structured as described above, the speed with which the development roller  4  is rotated during an initializing operation has only to be set to 33 rpm which is the same as the development roller  4  is rotated when an image is printed on a sheet of cardstock. It is also possible to structure the image forming apparatus  100  (developing device  3 ) so that the speed with which the development roller  4  is rotated during an image forming operation is fixed to 100 rpm. In such a case, the image forming apparatus  100  (developing device  3 ) may be structured so that the development roller  4  can be rotated at a slower speed which is exclusively for an initializing operation. 
         [0110]    By reducing the speed with which the development roller  4  is rotated during an initializing operation (relative to fast speed for image formation) as described above, it is possible to reduce the amount by which the coating agent  50  slips by the development bias as the development roller  4  is rotated. In other words, it is possible to increase the amount by which the coating agent  50  is regulated by the regulation blade  8 . Thus, it is possible to collect and keep the coating agent  50  in the immediate adjacencies of the toner capturing portion of the regulation blade  8  by a greater amount. 
         [0111]    Referring to  FIG. 7 , according to the experiments in which the developing device  3  in this embodiment was tested, the vertical streaks did not occur when the amount of the coating agent  50  on the development roller  4  was in a range of 5 mg-90 mg, which is wider than the range in which the vertical streaks did not occur when the developing devices  3  in the first and second embodiments were tested. That is, even though the amount by which the peripheral surface of the development roller  4  is coated with the coating agent  50  before the developing device  3  is shipped out of its factory is reduced compared to the first and second embodiment, excellent results were obtained. That is, the foreign substances such as dust, paper burrs etc., were blocked, and therefore, vertical streaks did not occur. 
         [0112]    By the way, if such bias voltage that works in such direction that the toner  10  is moved from the development roller  4  to the regulation blade  8  is applied between the development roller  4  and regulation blade  8 , there occurs a problem that the peripheral surface of the development roller  4  is too thinly coated with the toner  10 , and therefore, solid images outputted by the image forming apparatus  100  will be insufficient in density. Further, if the printing operation by the image forming apparatus  100  is continued with the bias voltage similarly set, there occurs a problem that as print count reaches roughly 1,000, the toner  10  solidly adheres to the regulating edge of the regulation blade  8 . In this embodiment, during an initializing operation, which is not a part of an image forming operation, the control section  25  sets the voltage application sections  21 - 23  to apply the bias voltages for an initializing operation. This setting can be done in a relatively short length of time, while the image forming apparatus  100  is prepared for an image forming operation. 
         [0113]    By the way, in this embodiment, when the peripheral surface of the development roller  4  of the fresh developing device  3  was not coated with the coating agent  50 , the amount of torque necessary to drive the developing device  3  was substantial, which results in the occurrence of such a problem that the regulation blade  8  is damaged. This is why an example in which the peripheral surface of the development roller  4  was coated with the coating agent  50  before the developing device  3  was shipped out of its factory was described. 
         [0114]    On the other hand, even in a case where the peripheral surface of the development roller  4  of the fresh developing device  3  is not coated with the coating agent  50 , the occurrence of the vertical streaks can be reduced by carrying out such a bias voltage control as those in the preceding embodiment that collects and keeps developer along the regulating edge of the regulation blade  8 . 
         [0115]    This is possible because the above-described bias voltage control is effective to keep virtually the entirety of the minuscule amount of the toner  10  supplied from the toner storage chamber  18   b  to the development chamber  18   a , along the regulating edge of the regulation blade  8 . Therefore, it is possible to prevent the foreign substances from entering the interface between the regulation blade  8  and development roller  4  until the amount by which the toner is supplied to the interface becomes large enough to fill up the toner capturing area, which is in the immediately adjacencies of the regulating edge (toner catching portion) of the regulation blade  8 . Therefore, it is possible to reduce the occurrence of the vertical streaks. 
         [0116]    According to this embodiment, the following control is carried out from when the fresh developing device  3  begins to be driven to when the peripheral surface of the developing device  3  is supplied with a preset amount of toner  10 . That is, the control section  25  appropriately controls the bias voltages to be applied to the development roller  4 , regulation blade  8 , and toner supply roller  5 , with the use of the voltage application sections  21 - 23 , one for one. 
         [0117]    Therefore, it is possible to collect and keep the coating agent  50  or toner  10  along the toner capturing portion of the regulation blade  8 . Therefore, it is possible to prevent foreign substances entering the toner (coating agent) catching area, which extends along the regulating edge of the regulation blade  8 . Therefore, it is possible to prevent the occurrence of the vertical streaks. 
       Effects of Present Invention 
       [0118]    Lastly, the effects provided by the above-described embodiments of the present invention can be summarized as follows. According to each of the above-described embodiments of the present invention, with the use of the bias voltage control carried out during an initializing operation, it is possible to keep a sufficient amount of coating agent in the toner capturing area which extends along the regulating edge of the developer regulating member. Therefore, it is possible to prevent foreign substances from entering between the developer bearing member (development roller) and regulating member (regulation blade). Therefore, it is possible to control the occurrence of the vertical streaks. 
         [0119]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
         [0120]    This application claims the benefit of Japanese Patent Application No. 2014-044519 filed on Mar. 7, 2014, which is hereby incorporated by reference herein in its entirety.