Patent Publication Number: US-7903995-B2

Title: Cleaning device, image forming apparatus, and process cartridge

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cleaning device employing an electrostatic cleaning method; an image forming apparatus containing the cleaning device; and a process cartridge containing the cleaning device. 
     2. Description of the Related Art 
     In recent years, electrophotographic image forming apparatuses, which are employed, for example, in copiers, printers, plotters, facsimiles and complex machines having the functions thereof, have been increasingly being required to form an image of higher quality. In view of this, toner particles (i.e., coloring powder) used for image formation tend to have a smaller particle diameter. Also, in an attempt to reduce the production cost for toner and to increase the transfer rate thereof, some commercially available image forming apparatuses employ, rather than pulverized toner particles, spherical toner particles produced through, for example, the polymerization method. Meanwhile, in order to remove toner particles remaining after image formation on the surface of an image bearing member (e.g., a photoconductor), a blade cleaning method has conventionally been employed in many cases. The blade cleaning method removes toner particles by bringing a rubber blade into contact with the photoconductor surface. When the blade insufficiently comes into contact with the photoconductor surface, the spherical toner particles run through the contact portion therebetween, resulting in that the cleaning performance is prone to degrade. 
     When pressed against the photoconductor surface at a high contact pressure to avoid the above unfavorable phenomenon, the blade is undesirably warped to cause cleaning failures such as formation of streaky or belt-like scratches, making it difficult to stably attain desired cleaning performance. Such spherical toner particles can be cleaned when the linear pressure is considerably increased. But, in this case, the service life of an image forming apparatus using them becomes very short due to, for example, abrasion of a photoconductor drum and a cleaning blade. Further, as has been well known, spherical toner particles excellent in transferability are less cleaned with a blade than are pulverized (amorphous) toner particles. 
     Separately, there is known a brush cleaning method which reduces abrasion of the photoconductor surface and reliably removes spherical toner particles having a small particle diameter. The brush cleaning method is performed based, for example, on the following configuration: a brush roller is disposed so as to slidably contact with the photoconductor surface; a recovering roller is disposed so as to be in contact with the brush roller; and a rubber blade or another unit is disposed so as to remove toner particles from the recovering roller. In this configuration, cleaning is performed utilizing electrostatic force brought by applying a voltage to the recovering roller or both the recovering roller and the brush roller, which is advantageous in use of spherical toner particles, etc. 
     As has been well known, the voltage applied in a common transfer step has an opposite polarity to that of the toner after development and thus, the remaining toner particles on the photoconductor surface after transfer are a mixture of toner particles having the same polarity as those after development, toner particles having an opposite polarity to them, and toner particles having no polarity. 
     Various attempts have been made to clean such a mixture that contains positively-charged, negatively-charged, and non-charged toner particles. 
     For example, Japanese Patent Application Laid-Open (JP-A) No. 2002-202702 discloses an image forming device including a conductive cleaning blade positively (negatively) charged and a conductive cleaning roller negatively (positively) charged, the conductive cleaning blade being disposed upstream of the conductive cleaning roller in a direction in which a photoconductor is rotated, wherein the conductive cleaning roller charges the remaining toner particles, which have not been removed with the conductive cleaning blade, so as to have a single polarity, and then cleans them. 
     Japanese Patent (JP-B) No. 3994974 discloses an image forming apparatus including a conductive rotating member which is driven so as to rotate with being in contact with a surface of an image bearing member; a conductive member which is in contact with the image bearing member at a position upstream of the rotating member in a direction in which the image bearing member is moved; and a single DC constant current power source bound to one of the conductive rotating member and the conductive member, the other being connected to the ground. In this image forming apparatus, the single DC constant current power source generates a DC electric current flowing between the conductive rotating member and the conductive member via the image bearing member, forming a first electrical field, between the conductive rotating member and the image bearing member, which acts in a direction in which regularly charged toner particles are adsorbed on the conductive rotating member; and a second electrical field, between the conductive member and the image bearing member, which acts in a direction in which regularly charged toner particles are adsorbed on the image bearing member. 
     JP-B No. 3466825 discloses an image forming apparatus including a first image bearing member, a second image bearing member, a third image bearing member, a transfer unit, and a toner-recovering unit, wherein a toner image formed on the first image bearing member is primarily transferred onto the second image bearing member at a primary transfer portion between the first and second image bearing members; the transfer unit is configured to secondarily transfer the toner image from the second image bearing member onto the third image bearing member; and the toner-recovering unit is configured to contact-charging the toner particles remaining after secondary transfer on the second image bearing member. In this image forming apparatus, the remaining toner particles charged by the toner-recovering unit are recovered from the primary transfer portion to the image bearing member. Here, the toner-recovering unit includes a cleaning charging member and a charging bias power source for applying a voltage to the cleaning charging member, wherein the charging bias power source applies, to the cleaning charging member, a voltage obtained by superimposing an AC voltage on a DC voltage. Also, the DC voltage is constant-current controlled, and the AC voltage is constant-voltage controlled. 
     JP-A No. 2005-265907 discloses a cleaning method including controlling, through corotron charging which applies a voltage to a corona charger, the charge amount of toner to be cleaned; and cleaning positively and negatively charged toner particles using two brushes arranged in a row, one of the two brushes being positively charged for cleaning the negatively charged toner particles and the other being negatively charged for cleaning the positively charged toner particles. 
     The method disclosed in JP-A No. 2005-265907 can satisfactorily clean a mixture of positively-charged, negatively-charged, and non-charged toner particles. However, such a configuration that two brushes are arranged so as to face a photoconductor and toner-recovering devices for recovering toner particles adhering to the brushes are disposed cannot easily attain downsizing of image forming apparatuses. 
     BRIEF SUMMARY OF THE INVENTION 
     In recent years, photoconductor drums tend to be small in diameter in an attempt to downsize image forming apparatuses. In view of this, cleaning devices to be used are required to be small. In addition to the system described in JP-A No. 2005-265907 which has two brushes and corresponding recovering rollers thereto, some cleaning systems attempt to achieve more downsizing of image forming apparatuses as follows. Specifically, remaining toner particles are charged so as to have a single polarity by a toner polarity controlling blade to which a voltage is applied, and then the resultant toner particles are cleaned by an electrostatic cleaning device disposed downstream of the blade. One such electrostatic cleaning device uses a brush roller and a recovering roller which are given a predetermined voltage to form the difference in electrical potential therebetween. In this cleaning device, toner particles on a photoconductor are made to adhere to the brush roller, and then are recovered by the recovering roller. 
     Here, presumably, toner particles having undergone polarity control advantageously have a charge distribution covering a certain range of the horizontal axis. In an electrostatic cleaning part after polarity control, charge injection into toner particles occurs, in principle, to no small extent between the photoconductor drum and the brush roller and between the brush roller and the recovering roller, the degree of the charge injection depending on the intensity of voltage applied to each member (here, no detail description therefor is given). Thus, the toner particles having undergone polarity control may have a q/d distribution covering a certain range slightly distant from “0 fC/μm,” specifically may have a q/d distribution of “−0.2 fC/μm” or higher as an absolute value. The toner particles having such a q/d distribution remain negatively charged without inversion of their polarity even after charge injection slightly occurs as described above. Also, toner particles with a q/d distribution covering a higher range (i.e., more shifted to the left-hand side) have an increased charge amount. Such toner particles firmly adhere to a photoconductor drum and thus, are difficult to clean with the aid of electrostatic force brought by a brush roller. Therefore, the q/d distribution may have an upper limit, which is specifically “−0.8 fC/μm.” That is, when toner particles having undergone polarity control are controlled to have a q/d distribution of “−0.2 fC/μm to −0.8 fC/μm,” desired cleaning performance is attained. 
     Here, toner polarity controlling performance depends on the difference in electrical potential between the photoconductor surface and the toner polarity controlling blade. And, the greater the difference in electrical potential, the more toner particles are negatively charged. However, the photoconductor surface fluctuates in its electrical potential depending on the image area ratio and the presence or absence of a transfer current. As a result, there cannot be obtained such a difference in electrical potential that enables toner particles to have a q/d distribution falling within the above range, which problematically cause insufficient polarity control (problem 1). 
     Also, the cleaning performance of the electrostatic cleaning device depends on the difference in electrical potential between the brush roller and a portion of the photoconductor surface, the portion being a portion which has passed the toner polarity controlling blade. When the difference in electrical potential is too small, toner particles cannot be moved. Whereas when it is too great, the polarity of toner particles changes due to charge injection thereto. For this reason, there is an optimal difference in electrical potential. Meanwhile, the toner polarity controlling blade changes in resistance over time as a result of toner adhesion and application of voltage. The current value of the blade changes with a change in resistance, changing the surface potential of a portion of the photoconductor surface, the portion being a portion which has passed the toner polarity controlling blade. Thus, the difference in electrical potential also changes between the photoconductor surface and the brush roller, problematically leading to poor cleaning performance (problem 2). 
     Further, since the toner polarity controlling blade changes in resistance over time due to toner adhesion and application of voltage, and the current value of the blade changes with a change in resistance, the blade exhibits degraded toner polarity controlling performance, leading to poor cleaning performance (problem 3). 
     The present invention has been made in view of the foregoing. An object of the present invention is to provide a cleaning device having such a configuration that it exhibits a long-term, excellent cleaning performance by appropriately applying a voltage to a toner polarity controlling blade to solve the above problems; an image forming apparatus containing the cleaning device; and a process cartridge containing the cleaning device. 
     Means for solving the above-described problems are as follows. 
     &lt;1&gt; A cleaning device which removes and recovers powder remaining after image formation on a member to be cleaned, with being mounted to an image forming apparatus performing image formation using coloring powder, the cleaning device including: 
     a conductive member configured to charge the powder remaining on the member to be cleaned through application of a predetermined voltage so as to have a single polarity and configured to scrape off at least part of the powder remaining on the member to be cleaned, the conductive member being disposed so as to be in contact with the member to be cleaned; 
     a cleaning member configured to electrically adsorb the powder present on the member to be cleaned through application of a predetermined voltage, the cleaning member being disposed so as to be in contact with the member to be cleaned and located downstream of the conductive member in a direction in which the powder is conveyed on the member to be cleaned; 
     a first recovering member configured to electrically adsorb the powder present on the cleaning member through application of a predetermined voltage, the first recovering member being disposed so as to be in contact with the cleaning member; and 
     a second recovering member configured to scrape off the powder from the first recovering member through application of a predetermined voltage, the second recovering member being disposed so as to be in contact with the first recovering member, 
     wherein the conductive member is constant-current controlled. 
     &lt;2&gt; The cleaning device according to &lt;1&gt; above, wherein the member to be cleaned is any one of an image bearing member on which an image is formed with the coloring powder and which transfers the image onto an intermediate transfer member or a recording medium; an intermediate transfer member onto which the image on the image bearing member is transferred; and a transfer member which conveys a recording medium and transfers, onto the recording medium, the image on the image bearing member or the intermediate transfer member. 
     &lt;3&gt; The cleaning device according to any one of &lt;1&gt; and &lt;2&gt; above, wherein the coloring powder is a toner having a shape factor 1 (SF1) of 100 to 150. 
     &lt;4&gt; The cleaning device according to any one of &lt;1&gt; to &lt;3&gt; above, wherein the member to be cleaned is an image bearing member which is a photoconductor, and the cleaning device further includes a quenching member configured to quench the image bearing member, the quenching member being provided downstream of the conductive member but upstream of the cleaning member in a direction in which the image bearing member is rotated. 
     &lt;5&gt; An image forming apparatus including: 
     an image bearing member, 
     an image forming unit configured to form an image with coloring powder on the image bearing member, 
     a transfer unit configured to transfer the image formed on the image bearing member onto a recording medium, and 
     a cleaning unit configured to remove and recover powder remaining on a member to be cleaned, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;4&gt; above. 
     &lt;6&gt; An image forming apparatus including: 
     an image bearing member, 
     an image forming unit configured to form an image with coloring powder on the image bearing member, 
     a transfer unit configured to transfer the image formed on the image bearing member onto a recording medium directly or via an intermediate transfer member, and 
     a cleaning unit configured to remove and recover powder remaining on the image bearing member from which the image has been transferred onto the recording medium or the intermediate transfer member, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;4&gt; above. 
     &lt;7&gt; An image forming apparatus including: 
     an image bearing member, 
     an image forming unit configured to form an image with coloring powder on the image bearing member, 
     a transfer member configured to carry and convey a recording medium and to transfer the image formed on the image bearing member onto the recording medium, and 
     a cleaning unit configured to remove and recover powder remaining on the transfer member which has conveyed the recording medium, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;3&gt; above. 
     &lt;8&gt; An image forming apparatus including: 
     an image bearing member, 
     an image forming unit configured to form an image with coloring powder on the image bearing member, 
     a transfer unit configured to transfer the image formed on the image bearing member onto an intermediate transfer member, 
     a transfer unit configured to transfer the transferred image on the intermediate transfer member onto a recording medium, and 
     a cleaning unit configured to remove and recover powder remaining on the intermediate transfer member from which the transferred image has been transferred onto the recording medium, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;3&gt; above. 
     &lt;9&gt; An image forming apparatus including: 
     one image bearing member, 
     a plurality of developing units configured to form images with coloring powder on the image bearing member, 
     a transfer unit configured to transfer the images formed on the image bearing member onto a recording medium directly or via an intermediate transfer member, and 
     a cleaning unit configured to remove and recover powder remaining on the image bearing member from which the images have been transferred onto the recording medium or the intermediate transfer member, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;4&gt; above. 
     &lt;10&gt; An image forming apparatus including: 
     one image bearing member, 
     a plurality of developing units configured to form images with coloring powder on the image bearing member, 
     a transfer unit configured to transfer the images formed on the image bearing member onto an intermediate transfer member, 
     a transfer unit configured to transfer the transferred images on the intermediate transfer member onto a recording medium, and 
     a cleaning unit configured to remove and recover powder remaining on the intermediate transfer member from which the transferred images have been transferred onto the recording medium, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;3&gt; above. 
     &lt;11&gt; An image forming apparatus including: 
     a plurality of image forming sections each having at least one image bearing member and at least one developing unit configured to form at least one image with coloring powder on the at least one image bearing member, 
     a transfer unit configured to sequentially transfer images formed on the image bearing members of the image forming sections onto a recording medium or an intermediate transfer member in a superposed manner, and 
     a cleaning unit configured to remove and recover powder remaining on the image bearing members from which the images have been transferred onto the recording medium or the intermediate transfer member. 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;4&gt; above. 
     &lt;12&gt; An image forming apparatus including: 
     a plurality of image forming sections each having at least one image bearing member and at least one developing unit configured to form at least one image with coloring powder on the at least one image bearing member, 
     a transfer member configured to convey a recording medium sequentially to the image forming sections and sequentially transfers images formed on the image bearing members onto the recording medium in a superposed manner, and 
     a cleaning unit configured to remove and recover powder remaining on the transfer member which has conveyed the recording medium, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;3&gt; above. 
     &lt;13&gt; An image forming apparatus including: 
     a plurality of image forming sections each having at least one image bearing member and at least one developing unit configured to form at least one image with coloring powder on the at least one image bearing member, 
     a transfer unit configured to sequentially transfer images formed on the image bearing members of the image forming sections onto an intermediate transfer member in a superposed manner, a transfer unit configured to transfer the transferred image on the intermediate transfer member onto a recording medium at one time, and 
     a cleaning unit configured to remove and recover powder remaining on the intermediate member from which the transferred image has been transferred onto the recording medium, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;3&gt; above. 
     &lt;14&gt; The image forming apparatus according to any one of &lt;5&gt; to &lt;13&gt; above, wherein the image bearing member or the image bearing members are a photoconductor in which a filler is dispersed. 
     &lt;15&gt; The image forming apparatus according to any one of 5&lt;5&gt; to &lt;13&gt; above, wherein the image bearing member or the image bearing members are an organic photoconductor having a surface layer reinforced with a filling material, an organic photoconductor containing a cross-linkable charge transport material, or an organic photoconductor having a surface layer reinforced with a filling material and containing a cross-linkable charge transport material. 
     &lt;16&gt; The image forming apparatus according to any one of &lt;5&gt; to &lt;13&gt; above, wherein the image bearing member or the image bearing members are an amorphous silicon photoconductor. 
     &lt;17&gt; A process cartridge detachably mounted to an image forming apparatus main body, the process cartridge including: 
     an image bearing member, 
     a cleaning unit for the image bearing member, and 
     at least one unit selected from a charging unit and a developing unit, 
     the image bearing member, the cleaning unit, and the at least one unit being integrally supported, 
     wherein the cleaning unit is the cleaning device according to any one of &lt;1&gt; to &lt;4&gt; above. 
     &lt;18&gt; An image forming apparatus including: 
     the process cartridge according to &lt;17&gt; above. 
     A cleaning device of the present invention includes a conductive member (e.g., a toner polarity controlling blade) which is disposed so as to be in contact with a member to be cleaned, a cleaning member (e.g., a cleaning brush roller) which is disposed so as to be in contact with the member to be cleaned and which is located downstream of the conductive member in a direction in which powder is conveyed on the member to be cleaned, a first recovering member (e.g., a recovering roller) which is disposed so as to be in contact with the cleaning member, and a second recovering member (e.g., a recovering roller conductive cleaning blade) which is disposed so as to be in contact with the first recovering member. Here, the member to be cleaned is an image bearing member (e.g., a photoconductor) on which an image is formed with coloring powder (toner) and which transfers the image onto an intermediate transfer member or a recording medium, an intermediate transfer member (e.g., an intermediate transfer belt or an intermediate transfer drum) onto which an image on an image bearing member is transferred, or a transfer member (e.g., a transfer belt) which conveys a recording medium and transfers, onto the recording medium, an image on an image bearing member or an intermediate transfer member. The conductive member is configured to charge powder remaining on the member to be cleaned through application of a predetermined voltage so as to have a single polarity (i.e., so that the remaining powder is either positively or negatively charged) and configured to scrape off at least part of the remaining powder. The cleaning member is configured to electrically adsorb powder present on the member to be cleaned through application of a predetermined voltage. The first recovering member is configured to electrically adsorb powder present on the cleaning member through application of a predetermined voltage. The second recovering member is configured to scrape off powder from the first recovering member through application of a predetermined voltage. The cleaning device is characterized in that the conductive member (e.g., a toner polarity controlling blade) is constant-current controlled. When a voltage is applied to the conductive member (e.g., a toner polarity controlling blade) through constant current control, the difference in electrical potential is maintained almost constant between the surface of the member to be cleaned and the conductive member (toner polarity controlling blade). As a result, the conductive member stably exhibits its polarity controlling performance, achieving stable cleaning performance. 
     The present invention, therefore, realizes a cleaning device having such a configuration that it exhibits desired cleaning performance for a long period of time; an image forming apparatus containing the cleaning device; and a process cartridge containing the cleaning device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates essential parts of an exemplary image forming apparatus employing a cleaning device of the present invention. 
         FIG. 2  is a graph of a q/d distribution of remaining toner particles after transfer. 
         FIG. 3  is a graph of control voltages of a toner polarity controlling blade vs. q/d distributions of toner particles having undergone polarity control. 
         FIG. 4A  illustrates a photoconductor drum and a toner polarity controlling blade which are in contact with each other. 
         FIG. 4B  illustrates a photoconductor drum and a toner polarity controlling blade warped thereon. 
         FIG. 5  is a sketch in which a toner particle is in contact with a curled tip portion of a fiber of a brush roller. 
         FIG. 6  is a graph of a change in electrical surface potential of a portion of a photoconductor, the portion being a portion which has not passed a toner polarity controlling blade (before passing a polarity BL), wherein the graph is obtained when one A3 size image is printed out. 
         FIG. 7  is a graph of a change in electrical potential between a polarity BL and a photoconductor surface which has not passed a toner polarity controlling blade (before passing a polarity BL). 
         FIG. 8  is a graph of a change of a current value (polarity control I) of a toner polarity controlling blade, the graph being obtained when one A3 size image is printed out. 
         FIG. 9  is a graph of control currents of a toner polarity controlling blade vs. q/d distributions of toner particles having undergone polarity control. 
         FIG. 10  is a graph showing a change in electrical surface potential of a portion of a photoconductor, the portion being a portion which has not passed a toner polarity controlling blade (polarity BL) constant-current controlled (indicated by curve A) and a change in voltage of the polarity BL (indicated by curve B). 
         FIG. 11  is a graph of a change over time in surface potential of a portion of a photoconductor, the portion being a portion which has passed a toner polarity controlling blade (after passing a polarity BL). 
         FIG. 12  is a graph of a change over time in current (polarity control I) of a toner polarity controlling blade. 
         FIG. 13  is a graph of a change over time in electrical potential between a brush roller and a photoconductor surface which has passed a toner polarity controlling blade (polarity BL). 
         FIG. 14  is a graph of a change over time in surface potential of a portion of a photoconductor, the portion being a portion which has passed a toner polarity controlling blade (polarity BL) constant-current controlled. 
         FIG. 15  is a graph of a change in surface potential of a portion of a photoconductor, the portion being a portion which has passed a toner polarity controlling blade (polarity BL), wherein the graph is for comparing the case where a quenching lamp (QL) is operated with the case where a quenching lamp (QL) is not operated, the change in the former case being indicated by curve A and that in the latter case being indicated by curve B. 
         FIG. 16  illustrates an exemplary configuration of a quenching lamp. 
         FIG. 17A  is a cross-sectional view of a layer structure of an amorphous silicon photoconductor. 
         FIG. 17B  is a cross-sectional view of another layer structure of an amorphous silicon photoconductor. 
         FIG. 17C  is a cross-sectional view of still another layer structure of an amorphous silicon photoconductor. 
         FIG. 17D  is a cross-sectional view of yet another layer structure of an amorphous silicon photoconductor. 
         FIG. 18  is an explanatory illustration in relation to definition of shape factor (SF) 1. 
         FIG. 19  schematically illustrates essential parts of an exemplary multi-color image forming apparatus employing a cleaning device of the present invention. 
         FIG. 20  schematically illustrates essential parts of another exemplary multi-color image forming apparatus employing a cleaning device of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, next will be described in detail the configuration, operation and effect of a cleaning device (an image forming apparatus) of the present invention. 
       FIG. 1  schematically illustrates essential parts of an exemplary image forming apparatus employing a cleaning device of the present invention. In  FIG. 1 , reference numeral  1  denotes an image bearing member. Around the image bearing member  1  are disposed, for example, a charging unit  2 , an optical writing unit  3 , a developing unit  4 , a transfer unit  10  and a cleaning unit  14 . 
     The image bearing member  1  is a photoconductor drum and is rotated counterclockwise; i.e., in a direction indicated by an arrow in  FIG. 1 . 
     The charging unit  2  is, for example, a charging roller disposed in a non-contact manner, and uniformly charges the surface of the photoconductor drum  1 . 
     The optical writing unit  3  is, for example, an optical writing device employing laser light scanning which includes a laser light source, a coupling optical system, a light polarizer and a scanning imaging optical system. This applies laser light L, which is modulated correspondingly to image signals, to a charged photoconductor drum  1  to form a latent electrostatic image. 
     The developing unit  4  is a developing device containing, in a case, a coloring powder; i.e., a toner used as a one- or two-component developer. The case houses, for example, a developing roller  6  for carrying/conveying a developer to develop a latent image on the photoconductor drum with toner; a doctor blade  5  for controlling the amount of the developer carried on the developing roller; and developing screws  7  and  8  which stir the developer to convey it. 
     The transfer unit  10  is a transfer device  10  using a transfer belt  10 A. The transfer device carries/conveys a recording medium (e.g., a recording paper sheet) S which has been fed by an unillustrated paper feeding mechanism, and transfers, onto the recording medium S, an image (a toner image) on the photoconductor drum. The transfer belt  10 A is rotated in a direction indicated by an arrow in  FIG. 1 , with being supported by a driving roller  11 , a driven roller  12  and a transfer bias-applying roller  13 . 
     The cleaning unit  14  for the image bearing member is a cleaning device which includes a toner polarity controlling blade  16  disposed so as to be in contact with the photoconductor drum  1  to be cleaned; a cleaning brush roller  21  which is disposed so as to be in contact with the photoconductor drum  1  and which is located downstream of the toner polarity controlling blade  16  in a direction in which a toner is conveyed on the photoconductor drum; a recovering roller  23  disposed so as to be in contact with the cleaning brush roller  21 ; and a recovering roller conductive cleaning blade  24  disposed so as to be in contact with the recovering roller  23 . Here, the toner polarity controlling blade  16  is a conductive member configured to charge toner particles remaining on the photoconductor drum so as to have a single polarity when a predetermined voltage is applied from a power source (toner polarity controlling blade-power source)  27 , and configured to scrape off at least part of the remaining toner particles. The cleaning brush roller  21  is a cleaning member configured to electrically adsorb toner particles present on the photoconductor drum when a predetermined voltage is applied from a power source (cleaning brush shaft voltage applying power source  30  and brush tip voltage applying power source  31 ). The recovering roller  23  is a first recovering member configured to electrically adsorb toner particles present on the cleaning brush roller  21  when a predetermined voltage is applied from a power source (recovering roller shaft voltage applying power source)  28 . The recovering roller conductive cleaning blade  24  is a second recovering member configured to scrape off toner particles present on the recovering roller  23  when a predetermined voltage is applied from a power source (recovering roller conductive cleaning blade power source)  29 . 
     The cleaning device  14  has a cleaning case, and opening sections of the cleaning case are provided with a cleaning inlet seal  17 , a cleaning brush inlet seal  18  and a cleaning outlet seal  20 , so that toner particles recovered from the photoconductor drum  1  does not leak outside the case. Also, a toner discharging screw  19  is disposed in a lower portion of the cleaning case. The toner discharging screw discharges recovered toner particles to, for example, an unillustrated waste toner container or returns them to the developing device. 
     Furthermore, the cleaning unit (device)  14  for the photoconductor drum has a quenching member (e.g., a quenching lamp)  26  which quenches a photoconductor drum  1  and is located downstream of the toner polarity controlling blade  16  but upstream of the cleaning brush roller  21  in a direction in which the photoconductor drum  1  is rotated. 
     In  FIG. 1 , reference numerals  15  and  25  denote a blade holder and a recovering roller blade holder, respectively. 
     Next will be described the operation of the image forming apparatus having the configuration shown in  FIG. 1 . 
     A series of image forming processes in this image forming apparatus include non-contact charging employing a non-contact charging roller  2 , latent image formation, and N/P development (nega/posi development; i.e., toner particles adhere to a portion whose electrical potential is low). 
     In  FIG. 1 , when an unillustrated print button at an operation part is pressed, a predetermined voltage or current is sequentially applied at a predetermined timing to a non-contact charging roller  2 , a developing roller  6 , a transfer bias-applying roller  13  of the transfer device  10 , a toner polarity controlling blade  16 , a cleaning brush roller  21  and a recovering roller  23 . Almost simultaneously with this, a photoconductor drum  1 , the non-contact charging roller  2 , a transfer belt  10 A of the transfer device  10 , the developing roller  6 , a right developing screw  7 , a left developing screw  8 , a cleaning brush roller  21 , a recovering roller  23  and a toner discharging screw  19  each begin to rotate in predetermined directions. For example, the photoconductor drum is rotated at a rotation speed of 205 mm/s and also, the cleaning brush roller  21  and the recovering roller  23  each are rotated at a rotation speed of 205 mm/s. The photoconductor drum  1  is uniformly negatively charged (−690 V) by the non-contact charging roller  2  disposed in a non-contact manner, and then exposed to laser light L emitted from an optical writing device  3 , whereby a latent image is formed (electrical potential at a black solid portion: −120 V). The thus-formed latent image is developed with a magnetic brush formed on the developing roller  6  (developing bias: −550V) to form a toner image. In synchronization with formation of the toner image, a recording paper S is fed by an unillustrated paper feeding mechanism. A resist roller  9  temporarily holds the thus-fed recording paper so as to synchronize with the top end of the toner image, and then supplies it to between the photoconductor drum  1  and the transfer belt  10 A, whereby the toner image is transferred onto the recording paper S (transfer bias applied: 30 μA). The recording paper S is separated from the photoconductor drum  1  by an unillustrated separating mechanism, and then is discharged through an unillustrated fixing device as a print (or copy) image. 
     Meanwhile, after the toner image has been transferred onto the recording paper S by the transfer device  10 , toner particles remaining on the photoconductor drum  1  are a mixture of “positively charged” toner particles and “negatively charged” toner particles whose distribution is shown in  FIG. 2 . In accordance with rotation of the photoconductor drum  1 , the remaining toner particles are conveyed to a contact portion between the photoconductor drum and the toner polarity controlling blade  16 . The toner polarity controlling blade  16  mechanically scrapes off almost all the remaining toner particles. But, highly spherical toner particles, among them, tend to enter a nip portion between the toner polarity controlling blade  16  and the photoconductor drum  1  to run through the contact portion therebetween. Here, the toner polarity controlling blade  16  has the same polarity as the toner particles (negative polarity) by applying a voltage thereto using the toner polarity controlling blade power source  27  and thus, negatively charges the toner particles running through the contact portion between the toner polarity controlling blade  16  and the photoconductor drum  1 , whereby the toner particles are regularly charged. In accordance with rotation of the photoconductor drum  1 , the toner particles regularly charged by the toner polarity controlling blade  16  are conveyed to a position of the photoconductor drum  1  at which the cleaning brush roller  21  is disposed. The shaft of the cleaning brush roller  21  has positive polarity by applying a voltage thereto using the cleaning brush shaft voltage applying power source  30 , and the brush tips thereof have positive polarity by applying a voltage thereto using the brush tip voltage applying power source  31  via a brush tip voltage applying electrode rod  22 . Thus, the cleaning brush roller  21  electrostatically adsorbs the regularly charged toner particles. The adsorbed toner particles on the cleaning brush roller  21  are moved by an electric potential gradient to a recovering roller  23  which has higher positive polarity than the cleaning brush roller  21  by applying a higher voltage thereto using a recovering roller shaft voltage applying power source  28 . Subsequently, the toner particles moved on the recovering roller  23  are scraped off by a recovering roller conductive cleaning blade  24 , which is disposed so as to contact the recovering roller  23  and is given a predetermined voltage from a recovering roller conductive cleaning blade power source  29 . Thereafter, the scraped toner particles are discharged outside the apparatus by the toner discharge screw  19  or are returned to the developing device  4 . 
     Next will be described the polarity controlling function of the cleaning device  14 . 
     First will be described a mechanism in which toner particles change in polarity when they run through a contact portion between a photoconductor and a toner polarity controlling blade  16  which is charged to have the same polarity as the regularly charged toner particles.  FIG. 3  shows a relationship between the intensities of voltage applied to the toner polarity controlling blade (polarity BL)  16  and q/d distributions after controlling. As shown in  FIG. 3 , toner particles running through the contact portion between the photoconductor and the toner polarity controlling blade  16  change in polarity to have regular polarity with increasing of the difference in electrical potential between the photoconductor surface and the toner polarity controlling blade  16 . This electrical potential is caused by, for example, “friction charging,” “charge injection,” and “discharge” occurring between the photoconductor drum  1  and the toner polarity controlling blade  16 . As shown in  FIGS. 4A and 4B , the edge of the toner polarity controlling blade  16  is warped in a direction in which the photoconductor drum  1  is rotated; i.e., a stick slip phenomenon occurs. When the toner polarity controlling blade  16  is in a state shown in  FIG. 4B , toner particles are likely to run through the contact portion. And, when the toner particles are pressed between the toner polarity controlling blade  16  and the photoconductor drum  1 , an electric current is applied to them from the toner polarity controlling blade  16  to which a voltage has been applied. In this manner, before passing the toner polarity controlling blade  16 , the toner particles are charged to have the same polarity as the blade. Supposedly, change in polarity of the toner particles in this state is caused as a result of charge injection. Also, when the difference in electrical potential between the surface electrical potential of the photoconductor drum  1  and the voltage applied to the toner polarity controlling blade  16  is a value falling within a range in which discharge occurs, discharge occurs in micro gaps at wedge-shaped inlet and outlet portions each being defined by the photoconductor drum  1  and the toner polarity controlling blade  16 , whereby the toner particles are charged to have the same polarity as the blade. The wedge-shaped inlet portion is stained by toner particles since it mechanically scrapes off the tone particles. Thus, discharge in the micro gap occurs mainly at the wedge-shaped outlet portion. Also, the toner polarity controlling blade  16  is coated at its contact portion with a conductive acrylic resin. This resin coating decreases the friction coefficient between the photoconductor and the blade and thus, a stick slip phenomenon is difficult to occur, whereby the micro gaps are maintained. Furthermore, such a resin-coated blade becomes more resistant to ablation and can exhibit its functions for a long period of time. 
     Next will be described the cleaning function of the cleaning device  14 . 
     First will be described in detail the configuration of an electrostatic cleaning part. Since charges are prevented from injecting toner particles between the photoconductor drum  1  and the cleaning brush roller  21 , the cleaning brush roller  21  is composed of core-in-sheath fibers as shown in  FIG. 5 , each of the fibers being inclined downstream in a direction in which the brush roller  21  is rotated. When the cleaning brush roller  21  is disposed so that each fiber is curled as shown in  FIG. 5 , a cut surface of the fiber, where a conductive portion is exposed, is prevented from contacting with toner particles to the greatest extent possible, preventing charge injection into toner particles. Also, a recovering roller  23  is formed from a metal core, a PVDF tube wound around the core, and a surface insulating layer provided on the tube, in order that charges are prevented from injecting toner particles between the cleaning brush roller  21  and the recovering roller  23 . Furthermore, a brush roller metallic charging member (e.g., a brush tip voltage applying electrode rod)  22 , which has the same electrical potential as the shaft of the cleaning brush roller  21 , is disposed so as to contact the tip surface of the brush of the cleaning brush roller  21 . The reason why the brush tip voltage applying electrode rod is provided lies in that charges must be supplied to brush fibers since their insulating surfaces are decreased in electrical potential after toner particles have been moved from the cleaning brush roller  21  to the recovering roller  23 . Hitherto, the reason why the brush is decreased in surface electrical potential has not been unclear, but this has been thought to occur as a result of giving and receiving toner particles. At present, one possible reason is that the insulating brush surface is negatively charged through separating discharge occurring when charged toner particles adhering thereto are moved to the recovering roller  23 . Another possible reason is that toner particles negatively charge surface layers of fibers during adhering thereto, and negative charges remain after the toner particles have been moved therefrom. When decreased in electrical potential, the cleaning brush roller  21  exhibits a decreased property of removing toner particles from the photoconductor drum  1 . In view of this, the brush roller metallic charging member (e.g., a brush tip voltage applying electrode rod)  22 , which is given a voltage having the same intensity as that applied to the cleaning brush roller  21 , is provided as a member for compensating decrease in electrical potential on the fiber surfaces. 
     Similar to the case of the cleaning brush roller  21 , the recovering roller  23  is also decreased in surface electrical potential after toner particles thereon are scraped off with a recovering roller conductive cleaning blade  24 . The reason for this is still unclear, but one possible reason is that a high-resistance layer or an insulating layer is negatively charged through separating discharge occurring when charged toner particles adhering to a surface of the recovering roller  23  are scraped off with the recovering roller conductive cleaning blade  24 . Another possible reason is that toner particles negatively charge a surface layer of the recovering roller  23  during adhering thereto, and negative charges remain after the toner particles have been scraped off with the recovering roller conductive cleaning blade  24 . For this reason, similar to the case of the cleaning brush roller  21 , the recovering roller conductive cleaning blade  24 , which is in contact with the surface of the recovering roller  23 , is also given a voltage higher than that applied to the shaft of the recovering roller  23 . 
     Toner particles on the recovering roller  23  are mechanically scraped off with the recovering roller conductive cleaning blade  24 . Next will be described that even spherical toner particles can be removed from the recovering roller  23 . 
     First of all, unlike the case of the photoconductor drum  1 , the recovering roller  23  can be made of any materials, so long as it has the function of transferring toner particles adhering to the cleaning brush roller  21  to the recovering roller  23  by an electric potential gradient between the cleaning brush roller  21  and the recovering roller  23 . Thus, when a surface of the recovering roller  23  is coated with a material having low friction coefficient or the recovering roller  23  is formed by winding, around a metal roller, a tube having low friction coefficient, even spherical toner particles can be readily removed therefrom. Specifically, the recovering roller  23  is formed by subjecting a metal roller to fluorine coating, or by winding a PVDF or PFA tube around a metal roller. 
     Next will be given various information regarding constituent members of the cleaning device  14 . 
     [Toner Polarity Controlling Blade  16 ] 
     Material for toner polarity controlling blade: dispersion of ion-conducting agent and carbon conducting agent in polyurethane (conductive acrylic coat having a thickness of 5 μm is formed on surface) 
     Intrusion amount of toner polarity controlling blade with respect to photoconductor drum: 1 mm 
     Contact angle of toner polarity controlling blade with photoconductor drum: 20° 
     Thickness of toner polarity controlling blade: 2 mm 
     Free length of toner polarity controlling blade: 7 mm 
     Hardness of toner polarity controlling blade: 60 to 80 (JIS A hardness meter) 
     Rebound resilience of toner polarity controlling blade: 30% 
     Electrical resistance of toner polarity controlling blade: 106 g·cm to 10 8  Ω·cm 
     Control voltage for toner polarity controlling blade (constant voltage control): −1,200 V 
     [Cleaning Brush Roller  21 ] 
     Material of brush roller: conductive polyester 
     Diameter of brush roller: 14 mm 
     Fiber length of brush roller: 4 mm 
     Intrusion amount of brush roller with respect to photoconductor drum: 1 mm 
     Linear velocity of brush roller: 205 mm/s (equal to that of photoconductor drum) 
     Voltage applied to brush roller charge imparting member (electrode rod  22 ): 100 V 
     Voltage applied to shaft of brush roller: 100 V Electrical resistance of original yarn of brush roller: 10 8  Ω·cm 
     Fiber density of brush roller: 100,000/inch 2  (1 inch=0.0254 m) 
     Arrangement of fibers of brush roller: inclined downstream in a direction in which the brush roller is rotated 
     [Recovering Roller  23 ] 
     Material for recovering roller: SUS core metal, PVDF tube (100 μm) wound therearound, insulating acrylic surface layer (5 μm) 
     Diameter of recovering roller: 12 mm 
     Linear velocity of recovering roller: 205 mm/s 
     Voltage applied to shaft of recovering roller: 500 V 
     [Recovering Roller Conductive Cleaning Blade  24 ] 
     Material for recovering roller conductive cleaning blade: dispersion of ion-conducting agent and carbon conducting agent in polyurethane (conductive acrylic coat having a thickness of 5 μm is formed on surface) 
     Intrusion amount of recovering roller conductive cleaning blade with respect to recovering roller: 1 mm 
     Contact angle of recovering roller conductive cleaning blade with recovering roller: 200 
     Thickness of recovering roller conductive cleaning blade: 2 mm 
     Free length of recovering roller conductive cleaning blade: 7 mm 
     Hardness of recovering roller conductive cleaning blade: 60 to 80 (JIS A hardness meter) 
     Rebound resilience of recovering roller conductive cleaning blade: 30% 
     Electrical resistance of recovering roller conductive cleaning blade: 10 6  Ω·cm to 10 8  Ω·cm 
     Voltage applied to recovering roller conductive cleaning blade: 500 V 
     Similar to the above-described cleaning device  14  for the photoconductor drum, the transfer device  10  is also provided with a transfer belt cleaning device  32  which removes/recovers powder (e.g., toner particles and paper dust) adhering to the belt surface after conveyance of a recording medium. The transfer belt cleaning device  32  may have the same configuration as the cleaning device  14 . Also, in this case, no quenching member is required. 
     EXAMPLES 
     Next will be described an exemplary image forming apparatus to which the cleaning device  14  having the above-described configuration is mounted, together with its problems and measures against them. 
     Example 1 
     Problem 1 and Measure Against it 
     The cleaning device  14  having the above-described configuration was mounted as a photoconductor cleaning unit to an image forming apparatus shown in  FIG. 1 . The image forming apparatus was caused to print an A3 size image on one sheet.  FIG. 6  is a graph relating to the surface potential of a portion of the photoconductor after printing, the portion being a portion which has not passed the toner polarity controlling blade  16  (before passing a polarity BL). In  FIG. 6 , a charging roller power source  2  is on in areas A and D, the charging roller power source  2  and a bias-applying power source for a transfer device  10  are on in areas B and C, and an image is formed in area C. Here, a thick line corresponds to a change in surface potential of the photoconductor having undergone printing, on one sheet, an image with an image area ratio of 100%, while a thin line corresponds to a change in surface potential of the photoconductor having undergone printing, on one sheet, an image with an image area ratio of 10%. When the toner polarity controlling blade  16  is controlled at a constant voltage of −1,200 V, as shown in  FIG. 7 , the difference in electrical potential between the photoconductor surface and the toner polarity controlling blade  16  undesirably varies depending on the image area ratio of the image printed and on whether a transfer electric current is on or off. In addition, the electric current value of the toner polarity controlling blade  16  also changes with a change in photoconductor surface potential as shown in  FIG. 8 . In this configuration, when a transfer electric current is off, the sufficient difference in electrical potential (about −600 V) is not obtained, resulting in failure to control polarity so as to attain an optimal q/d distribution; i.e., resulting in insufficient polarity control as shown in  FIG. 3 . In this state, when toner particles or other materials remaining on the edge portion of the toner polarity controlling blade  16  run through the contact portion between the photoconductor and the blade, sufficient cleaning cannot be performed, leading to cleaning failure. 
     In the present invention, as a measure against the above problem, the toner polarity controlling blade  16  is constant-current controlled. Also in this case, similar to the case of constant voltage control, polarity controlling performance increases with increasing of the electric current value, so that the q/d distribution shifts toward a more negative range as shown in  FIG. 9 . For example, when the toner polarity controlling blade  16  is given a voltage through constant current control at −20 μA, the voltage of the toner polarity controlling blade  16  changes, as shown in  FIG. 10 , depending on a change in surface potential of the photoconductor. In this manner, in the above areas A to D, the difference in electrical potential is maintained constant between the photoconductor surface and the toner polarity controlling blade  16 . As a result, the cleaning device was able to stably exhibit desired polarity controlling performance and thus, to stably exhibit desired cleaning performance. 
     Problem 2 and Measure Against it 
     The image forming apparatus was caused to print an A4 size image having an image area ratio of 5% on 200 sheets with the toner polarity controlling blade  16  was being constant-voltage controlled at −1,200 V. As shown in  FIG. 11 , there was gradually increased the surface potential of a portion of the photoconductor after printing, the portion being a portion which has passed the toner polarity controlling blade  16  (after passing a polarity BL). Also, as shown in  FIG. 12 , the current value (polarity control I) of the toner polarity controlling blade  16  was gradually decreased. Meanwhile, the constant voltage is applied to the cleaning brush roller  21  disposed downstream in a direction in which the photoconductor is rotated. As a result, as shown in  FIG. 13 , the difference in electrical potential undesirably changes between the photoconductor surface and the brush roller  21 , leading to a drop in cleaning performance. The surface potential of the photoconductor increases over time due to a decrease in electric value of the toner polarity controlling blade  16 . The decrease of the electric value is caused by increase in electrical resistance of the toner polarity controlling blade  16 , which occurs as a result of toner adhesion to the toner polarity controlling blade  16  and/or change in physical properties of the conductive rubber member and the conductive tape. When the toner polarity controlling blade  16  was controlled at a constant voltage of −1,200 V, the current value was decreased from −30 μA to about −20 μA (as an absolute value). 
     In the present invention, as a measure against the above problem, for example, the toner polarity controlling blade  16  is given a voltage through constant current control at −20 μA. As is clear from a curve indicated by “b” in  FIG. 14 , there could be constantly stabilized the surface potential of a portion of the photoconductor, the portion being a portion which has passed the toner polarity controlling blade  16 . As a result, even when the constant voltage was applied to the cleaning brush roller  21 , the cleaning device was able to stably exhibit desired cleaning performance. In this case, since the resistance value increases and the current value is constant, the voltage value of the toner polarity controlling blade  16  increases over time. Although this affects the polarity controlling performance of the blade, such a problem does not arise that cleaning cannot be performed due to insufficient polarity control, even if the blade is somewhat excessively charged. This is because, in accordance with increasing of the voltage value of the toner polarity controlling blade  16 , the difference in electric potential becomes greater between the photoconductor surface and the toner polarity controlling blade  16 . 
     Problem 3 and Measure Against it 
     As described above in relation to problem 2, when the toner polarity controlling blade  16  is used for a certain period, its electrical resistance value increases and its current value decreases, as a result of toner adhesion thereto and/or change in physical properties of the conductive rubber member and the conductive tape. In this state, as compared with the initial state, charge injection into toner particles and discharge in micro gaps are difficult to occur, leading to decrease in polarity controlling performance thereof. 
     In the present invention, as a measure against this problem, for example, the toner polarity controlling blade  16  is given a voltage through constant current control at −20 μA. As a result, even when the resistant value of the toner polarity controlling blade  16  fluctuates, charge injection and discharge were able to be made to occur stably. Then, the blade was able to stably exhibit its cleaning performance, since its polarity controlling performance was desirably maintained over time. 
     Example 2 
     As described in Example 1, when the toner polarity controlling blade  16  is given a voltage through constant current control, the voltage of the toner polarity controlling blade  16  (polarity BL voltage) changes, as shown in  FIG. 10 , depending on a change in surface potential of the photoconductor (surface potential before passing a polarity BL). Thus, in areas A to D, the difference in electrical potential can be maintained constant between the photoconductor surface and the toner polarity controlling blade  16 , enabling its polarity controlling performance to be stable. Here, the toner polarity controlling blade  16  is constantly given a negative voltage. Thus, there is constantly negative the electrical potential of a portion of the photoconductor, the portion being a portion which has passed the toner polarity controlling blade  16 . As shown in  FIG. 1 , when a quenching member (e.g., a quenching lamp (QL))  26  is provided between the toner polarity controlling blade  16  and the cleaning brush roller  21 , there is constantly about 0 the electrical potential of a portion of the photoconductor, the portion being a portion which has passed the toner polarity controlling blade  16  (after passing a polarity BL) (see  FIG. 15 ). Thus, when the cleaning brush roller  21  is given a voltage at which the optimal difference in electrical potential is obtained between the photoconductor surface and the cleaning brush roller  21  (i.e., 600 V in this Example), the difference in electrical potential could be constantly maintained optimal therebetween, whereby the cleaning device could stably exhibit its cleaning performance. Notably, the quenching lamp (QL)  26  used had 16 light emitting diodes (LEDs) disposed at 22 mm intervals in a longitudinal direction of the shaft of the photoconductor (see  FIG. 16 ). 
     Example 3 
     Next will be described a photoconductor serving as an image bearing member of the image forming apparatus of the present invention. 
     An image bearing member used in the image forming apparatus of the present invention may be an amorphous silicon photoconductor. 
     Regarding Amorphous Silicon Photoconductor 
     The electrophotographic photoconductor used in the present invention may be an amorphous silicon photoconductor (hereinafter may be referred to as an “a-Si photoconductor”) having a conductive support and a photoconductive layer made of amorphous silicon (a-Si). The amorphous silicon photoconductor is produced by forming, on the conductive support heated at 50° C. to 400° C., the photoconductive layer through film formation such as vacuum vapor deposition, sputtering, ion plating, thermal CVD, photo-CVD or plasma CVD. Of these, preferably used is plasma CVD in which raw material gas is decomposed through DC, high-frequency or microwave glow discharge to form an a-Si deposition film on the support. 
     Regarding Layer Structure 
     The layer structure of the amorphous silicon photoconductor is, for example, that described below.  FIGS. 17A to 17D  are explanatory, schematic views of the layer structure. An electrophotographic photoconductor  500  shown in  FIG. 17A  has a support  501  and a photoconductive layer  502  made of a-Si:H,X (where H denotes a hydrogen atom and X denotes a halogen atom (F, Cl, Br or I)), the photoconductive layer being laid on the support. An electrophotographic photoconductor  500  shown in  FIG. 17B  has a support  501 , a photoconductive layer  502  made of a-Si:H,X, and an amorphous silicon-based surface layer  503 , these layers being laid on the support. An electrophotographic photoconductor  500  shown in  FIG. 17C  has a support  501 , a photoconductive layer  502  made of a-Si:H,X, an amorphous silicon-based surface layer  503 , and an amorphous silicon-based charge injection preventing layer  504 , these layers being laid on the support. An electrophotographic photoconductor  500  shown in  FIG. 17D  has a support  501 , a photoconductive layer  502  (a charge generation layer  505  made of a-Si:H,X+a charge transport layer  506  made of a-Si:H,X) and an amorphous silicon-based surface layer  503 , the photoconductive layer and the amorphous silicon-based surface layer being laid on the support in this order. 
     Regarding Support 
     The support  501  of the photoconductor  500  may be conductive or electrically insulative. The conductive support is made, for example, of a metal such as Al, Cr, Mo, Au, In, Nb, Te, V, Ti, Pt, Pd or Fe; and an alloy thereof (e.g., stainless steel). Also, there may be used an electrically insulating support (e.g., glass, ceramic and films or sheets of synthetic resin such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polystyrene or polyamide) in which at least a surface on which a conductive layer is to be laid has been subjected to a conductive treatment. The support may be a cylindrical, plate-like or endless belt support having a smooth or surface or irregular surface. The thickness of the support is appropriately determined so that an intended image forming apparatus photoconductor can be formed. When the image forming apparatus photoconductor is required to have flexibility, the support may be thin to the greatest extent possible so long as it can sufficiently exhibit its intrinsic functions. However, the thickness of the support is generally 10 μm or greater from the viewpoints of, for example, production suitability, handleability and mechanical strength. 
     Regarding Charge Injection Preventing Layer 
     In the amorphous silicon photoconductor used in the present invention, the charge injection preventing layer  504 , which prevents charges from being injected from the conductive support, is effectively provided between the conductive support  501  and the photoconductive layer  502  in accordance with needs (see  FIG. 17C ). The charge injection preventing layer  504  has a so-called polarity dependency; i.e., has the function of preventing injection of charges from a support to a photoconductive layer which has been positively (negatively) charged on its free surface, but does not have the function of preventing injection of charges from a support to a photoconductive layer which has been negatively (positively) charged on its free surface. In order for the charge injection preventing layer  504  to have such a function, an atom controlling conductivity is incorporated into it in a higher amount than into the photoconductive layer  502 . The thickness of the charge injection preventing layer  504  is preferably 0.1 μm to 5 μm, more preferably 0.3 μm to 4 μm, optimally 0.5 μm to 3 μm, from the viewpoints of, for example, attaining desired electrophotographic characteristics and being economically advantageous. 
     Regarding Photoconductive Layer 
     The photoconductive layer  502  is formed on an underlying layer in accordance with needs. The thickness of the photoconductive layer  502  is determined as desired in consideration of, for example, attaining desired electrophotographic characteristics and being economically advantageous. It is preferably 1 μm to 100 μm, more preferably 20 μm to 50 μm, optimally 23 μm to 45 μm. 
     Regarding Charge Transport Layer 
     The charge transport layer  506  is one layer of a functionally separated photoconductive layer  502  and mainly transports charges. The charge transport layer  506  contains, as a constituent component, at least a silicon atom, a carbon atom and a fluorine atom. If necessary, it is made of a-SiC(H, F, O) containing a hydrogen atom and an oxygen atom. The charge transport layer has desired photoconductive characteristics, among others, charge retaining characteristics, charge generating characteristics and charge transporting characteristics. In the present invention, it particularly preferably contains an oxygen atom. The thickness of the charge transport layer  506  is determined as desired in consideration of, for example, attaining desired electrophotographic characteristics and being economically advantageous. It is preferably 5 μm to 50 μm, more preferably 10 μm to 40 μm, optimally 20 μm to 30 μm. 
     Regarding Charge Generation Layer 
     The charge generation layer  505  is one layer of a functionally separated photoconductive layer  502  and mainly generates charges. The charge generation layer  505  contains, as a constituent component, at least a silicon atom but does not substantially contain a carbon atom. If necessary, it is made of a-Si:H containing a hydrogen atom. The charge generation layer has desired photoconductive characteristics, among others, charge generating characteristics and charge transporting characteristics. The thickness of the charge generation layer  505  is determined as desired in consideration of, for example, attaining desired electrophotographic characteristics and being economically advantageous. It is preferably 0.5 μm to 15 μm, more preferably 1 μm to 10 μm, optimally 1 μm to 5 μm. 
     Regarding Surface Layer 
     In the amorphous silicon photoconductor  500  of the present invention, if necessary, the surface layer  503  may be further provided on the photoconductive layer  502  formed on the support as described above. Preferably, an amorphous silicon-based surface layer is formed. The surface layer  503  has a free surface and is provided for the purpose of desirably attaining, among others, humidity resistance, durability to continuous, repetitive use, electric pressure resistance, resistance to environmental factors and durability, to such an extent that the objects of the present invention are achieved. In the present invention, the thickness of the surface layer  503  is generally 0.01 μm to 3 μm, preferably 0.05 μm to 2 μm, optimally 0.1 μm to 1 μm. When the thickness is smaller than 0.01 μm, the surface layer is lost due to, for example, ablation of the photoconductor during use. Whereas when the thickness is greater than 3 μm, electrophotographic characteristics degrade (e.g., increase in residual potential). 
     Also, the image bearing member used in the image forming apparatus of the present invention may be an organic photoconductor having a surface layer reinforced with a filling material, an organic photoconductor formed by using a cross-linkable charge transport material, or an organic photoconductor having a surface layer reinforced with a filling material and formed by using a cross-linkable charge transport material. 
     The outermost layer of such a photoconductor is made of polymer or copolymer of a compound(s) selected from vinyl fluoride, vinylidene fluoride, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene and perfluoroalkyl vinyl ether. The conductive support used is a cylinder or film made of metal (e.g., aluminum and stainless steel), paper or plastic. On the support may be provided an underlying layer (adhesion layer) having the barrier and adhesion functions. The underlying layer is formed for the purposes of, for example, improving adhesion between the photoconductive layer and the support, coating property and injection property of charges from the support; protecting the support and the photoconductive layer from electric coverage; and covering defects in the support. Examples of known materials for the underlying layer include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cellulose, ethylene-acrylic copolymers, casein, polyamides, nylon copolymers, glue and gelatin. Each of the materials is dissolved in a suitable solvent and applied onto the support. The thickness of the underlying layer is about 0.2 μm to about 2 μm. The photoconductive layer is classified into a laminated photoconductive layer consisting of a charge generation layer containing a charge generating compound and a charge transport layer containing a charge transport compound, and a single photoconductive layer containing a charge generating compound and a charge transport compound. Examples of the charge generating compound which can be used include pyrylium, thiopyrylium dyes, phthalocyanine pigments, anthoanthoron pigments, dibenzopyrene quinone pigments, pyranthoron pigments, trisazo pigments, disazo pigments, azo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanines and quinocyanines. Example of the charge transport compound which can be used include pyrene, N-ethylcarbazole, N-isopropylcarbazole, N-methyl-N-phenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine, N,N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine, p-diethylaminobenzaldehyde-N,N-diphenylhydrazone, triarylmethane compounds (e.g., p-diethylaminobenzaldehyde-2-methylphenyl)-phenylmethane), polyarylalkanes (e.g., 1,1-bis(4-N,N-diethylamino-2-methylphenyl)heptane and 1,1,2,2-tetrakis(4-N,N-dimethylamino-2-methylphenyl)ethane) and triarylamines. 
     Also, the image bearing member used in the image forming apparatus of the present invention may be a photoconductor having a protective layer into which a filler has been incorporated for the purpose of imparting enhanced ablation resistance thereto. Examples of the filler include organic fillers such as fluorine resin powder (e.g., polytetrafluoroethylene powder), silicone resin powder and α-carbon powder; inorganic fillers such as powders of metals (e.g., copper, tin, aluminum and indium), metal oxides (e.g., tin oxide, zinc oxide, titanium oxide, indium oxide, antimony oxide, bismuth oxide, tin oxide doped with antimony, and indium oxide doped with tin); and inorganic materials (e.g., potassium titanate). These fillers may be used individually or in combination, and may be dispersed in a protective layer coating liquid using an appropriate disperser. The filler preferably has an average particle diameter of 0.5 μm or lower, preferably 0.2 μm or lower, in consideration of transmittance of a protective layer formed. Furthermore, in the present invention, a plasticizer and/or a leveling agent may be incorporated into the protective layer. 
     Example 4 
     The image forming apparatus of the present invention has the cleaning device  14  configured such that desired cleaning performance can be maintained for a long time as described above. Thus, coloring powder used in a developer for image formation may be a toner having a shape factor (SF) 1 of 100 to 150. 
     Here, as shown in  FIG. 18 , the shape factor (SF) 1 refers to a value indicating sphericity of a spherical substance, which is obtained as follows. Specifically, the shadow of a spherical substance is cast on a two-dimensional plane to form an ellipsoidal projection image. Subsequently, the maximum length MXLNG of the image is multiplied by itself. The thus-obtained value is divided by an image area AREA, and then multiplied by 100π/4. That is, the shape factor (SF) 1 is defined as being a value calculated by the following equation.
 
SF1={(MXLNG) 2 /AREA}×(100π/4)
 
     In the image forming apparatus of the present invention, the cleaning device  14  having the above-described configuration can effectively remove/recover even a toner having such a shape factor (i.e., spherical toner). 
     The above embodiments and Examples describe a monochromatic image forming apparatus having the cleaning device of the present invention. In addition, the cleaning device of the present invention may be suitably used for cleaning a photoconductor, an intermediate transfer member, etc. in a multi-color image forming apparatus. Next will be given Examples using a multi-color image forming apparatus. 
     Example 5 
       FIG. 19  schematically illustrates essential parts of an exemplary multi-color image forming apparatus employing the cleaning device of the present invention. This multi-color image forming apparatus has one image bearing member  1 , a charging unit  2 , an optical writing unit  3 , a plurality of developing units  4 Y,  4 M,  4 C and  4 K which form an image on an image bearing member with coloring powder, a primary transfer device  40  which transfers the image from the image bearing member onto an intermediate transfer member  41 , a secondary transfer device  48  which transfers the image from the intermediate transfer member  41  onto a recording medium S, a fixing device  60  and an unillustrated paper feeding mechanism. 
     The image bearing member  1  is a photoconductor drum and is rotated counterclockwise; i.e., in a direction indicated by an arrow in  FIG. 19 . 
     The charging unit  2  is, for example, a charging roller disposed in a non-contact manner, and uniformly charges the surface of the photoconductor drum  1 . 
     The optical writing unit  3  is, for example, an optical writing device employing laser light scanning which includes a laser light source, a coupling optical system, a light polarizer and a scanning imaging optical system. This applies laser light L, which is modulated correspondingly to image signals, to a charged photoconductor drum  1  to form a latent electrostatic image. 
     The developing units are a yellow toner-developing device  4 Y which uses a yellow toner as a coloring powder of a developer, a magenta toner-developing device  4 M which uses a magenta toner as the coloring powder, a cyan toner-developing device  4 C which uses a cyan toner as the coloring powder, and a black toner-developing device  4 K which uses a black toner as the coloring powder. These four developing devices are housed in a rotary developing device  4 ′. The rotary developing device  4 ′ is rotated so that the developing device of a color selected is located so as to face the photoconductor drum  1 . The configurations of the developing devices are identical to one another. Each developing device has, in a case thereof, a developing roller for developing a latent image on the photoconductor drum with a toner carried/conveyed thereon, a doctor blade for controlling the amount of a developer on the developing roller, a developing screw for stirring/conveying the developer, and other members. 
     The primary transfer device  40  uses an intermediate transfer belt  41  as the intermediate transfer member. The intermediate transfer belt  41  is rotated in a direction indicated by an arrow in  FIG. 19  with being supported by a driving roller  42  and a plurality of driven rollers  43 ,  44  and  45 , and a transfer bias-applying roller, so that an image (toner image) on the photoconductor drum is transferred onto the intermediate transfer belt. 
     The secondary transfer device  48  uses a secondary transfer roller which conveys a recording medium (e.g., a recording paper sheet) S which has been fed by the unillustrated paper feeding mechanism and then transfers the image (toner image) from the intermediate transfer belt onto the recording medium S. The secondary transfer roller is disposed such that it can contact with or separate from the intermediate transfer belt  41 . When a toner image is primarily transferred from the photoconductor drum  1  onto the intermediate transfer belt  41 , the secondary transfer roller is spaced from the intermediate transfer belt  41 . Then, upon secondarily transferring the toner image from the intermediate transfer belt onto a recording medium S, the secondary transfer roller  48  contacts with the intermediate transfer belt  41  for secondary transfer. 
     Also, downstream of the secondary transfer device  48  in a direction in which a recording medium is fed, there are provided a conveyor belt  49  for conveying a recording medium S having undergone image transfer, a fixing device  60  for fixing the transferred image on the recording medium S through application of, for example, heat and pressure, and other members. 
     The cleaning unit  14  for the image bearing member has the same configuration as that shown in  FIG. 1 . It is a cleaning device which includes a toner polarity controlling blade  16  disposed so as to contact the photoconductor drum  1  to be cleaned; a cleaning brush roller  21  disposed so as to contact the photoconductor drum  1  downstream of the toner polarity controlling blade  16  in a direction in which a toner is conveyed; a recovering roller  23  disposed so as to contact the cleaning brush roller  21 ; and a recovering roller conductive cleaning blade  24  disposed so as to contact the recovering roller  23 . Here, the toner polarity controlling blade  16  is a conductive member configured to charge toner particles remaining on the photoconductor drum so as to have a single polarity when a predetermined voltage is applied from a power source (toner polarity controlling blade-power source)  27 , and configured to scrape off at least part of the remaining toner particles. The cleaning brush roller  21  is a cleaning member configured to electrically adsorb toner particles present on the photoconductor drum when a predetermined voltage is applied from a power source (cleaning brush shaft voltage applying power source  30  and brush tip voltage applying power source  31 ). The recovering roller  23  is a first recovering member configured to electrically adsorb toner particles present on the cleaning brush roller  21  when a predetermined voltage is applied from a power source (recovering roller shaft voltage applying power source)  28 . The recovering roller conductive cleaning blade  24  is a second recovering member configured to scrape off toner particles on the recovering roller  23  when a predetermined voltage is applied from a power source (recovering roller conductive cleaning blade power source)  29 . 
     The cleaning device  14  has a cleaning case, and opening sections of the cleaning case are provided with a cleaning inlet seal  17 , a cleaning brush inlet seal  18  and a cleaning outlet seal  20 , so that toner particles recovered from the photoconductor drum  1  does not leak outside the case. Also, a toner discharging screw  19  is disposed in a lower portion of the cleaning case. The toner discharging screw discharges recovered toner particles to, for example, an unillustrated waste toner container. 
     Furthermore, the cleaning unit (device)  14  has a quenching member (e.g., a quenching lamp)  26  which charge-quenches a photoconductor drum  1  and is located downstream of the toner polarity controlling blade  16  but upstream of the cleaning brush roller  21  in a direction in which the photoconductor drum  1  is rotated. 
     The primary transfer device  40  is provided with an intermediate transfer belt cleaning device  46  which removes/recovers toner particles remaining on the intermediate transfer belt  41  having undergone secondary transfer. The intermediate transfer belt cleaning device  46  may have a similar configuration to the photoconductor drum cleaning device  14 . But, in this case, no quenching member is required. Also, the intermediate transfer belt cleaning device  46  is disposed such that it can contact with or separate from the intermediate transfer belt  41  by a mechanism  47  such as a cam. When a toner image is primarily transferred from the photoconductor drum  1  onto the intermediate transfer belt  41 , the cleaning device is spaced from the intermediate transfer belt  41 . Then, upon secondarily transferring the toner image from the intermediate transfer belt onto a recording medium S, the intermediate transfer belt cleaning device  46  contacts with the intermediate transfer belt  41  and then removes/recovers toner particles remaining on the surface of the intermediate transfer belt having undergone secondary transfer. 
     Next will be described the operation of the multi-color image forming apparatus having the configuration shown in  FIG. 19 . 
     A series of image forming processes in this image forming apparatus include non-contact charging employing a non-contact charging roller  2 , latent image formation, and N/P development (nega/posi development; i.e., toner particles adhere to a portion whose electrical potential is low). 
     First of all, monochromatic image formation or color image formation is selected at an unillustrated operation part (here, color image formation is selected and a Y toner image, an M toner image, a C toner image and a K toner image are formed in this order). When a print button is pressed, a rotary developing device  4 ′ is rotated so that a yellow-toner developing device  4 Y is located so as to face a photoconductor drum  1 . Then, a predetermined voltage or current is sequentially applied at a predetermined timing to a non-contact charging roller  2 , a developing roller of the yellow-toner developing device  4 Y, a transfer bias-applying roller  13  for a primary transfer device  40 , a toner polarity controlling blade  16 , a cleaning brush roller  21  and a recovering roller  23 . Almost simultaneously with this, the photoconductor drum  1 , the non-contact charging roller  2 , an intermediate transfer belt  41  of the primary transfer device  40 , a developing roller and a developing screw of the yellow-toner developing device  4 Y, a cleaning brush roller  21 , a recovering roller  23  and a toner discharging screw  19  each begin to rotate in predetermined directions. The photoconductor drum  1  is uniformly negatively charged by the non-contact charging roller  2  disposed in a non-contact manner, and then is exposed to laser light L emitted from an optical writing device  3  to form a latent image to be developed with a yellow toner. The thus-formed latent image is developed with a yellow toner magnetic brush on the developing roller to form a yellow toner image. The yellow toner image is primarily transferred onto the intermediate transfer belt  41  with the aid of transfer bias brought by the transfer bias-applying roller  13 . Then, toner particles remaining on the photoconductor drum  1  having undergone primary transfer are removed/recovered by the photoconductor cleaning device  14 . Notably, the configuration and operation of the cleaning device  14  are the same as those as described above in  FIG. 1  and thus, no description about them is given. 
     After the above-described primary transfer, the rotary developing device  4 ′ is rotated so that the next magenta toner-developing device  4 M is located so as to face the photoconductor drum  1 . Then, similar to the above, the photoconductor drum  1  having undergone cleaning is subjected to charging, latent image formation and developing, to thereby form a magenta toner image on the photoconductor drum. Subsequently, the magenta toner image is primarily transferred onto the yellow toner image on the intermediate transfer belt  41  with the aid of transfer bias brought by the transfer bias-applying roller  13 , whereby a composite toner image is formed. Then, toner particles remaining on the photoconductor drum  1  having undergone primary transfer are removed/recovered by the photoconductor cleaning device  14 . 
     In addition, the above-described process (i.e., switching of a developing device, charging, latent image formation, developing, primary transfer and photoconductor cleaning) is repeated twice to form cyan and black toner images, whereby a composite toner image of four colors is formed on the intermediate transfer belt  41 . 
     In synchronization with primary transfer of a toner image of the fourth color onto the intermediate transfer belt  41 , the secondary transfer roller  48  comes into contact with the intermediate transfer belt. Then, the composite image of four color toner images is secondarily transferred at one time onto a recording paper S which has been fed by an unillustrated paper feeding mechanism to between the intermediate transfer belt  41  and the secondary transfer roller  48  so as to synchronize with the top end of the toner image by a resist roller  55 . The recording paper S is separated from the intermediate transfer belt  41  by an unillustrated separating mechanism, and then is discharged as a print (or copy) image through a transfer belt  49  and a fixing device  60 . 
     Also, in synchronization with secondary transfer, the intermediate transfer belt cleaning device  46  is moved so as to be in contact with the intermediate transfer belt  41 , and then removes/recovers toner particles remaining on the intermediate transfer belt having undergone secondary transfer. 
     After secondary transfer, the secondary transfer roller  48  is spaced from the intermediate transfer belt  41 , and the intermediate transfer belt cleaning device  46  after cleaning is also spaced from the intermediate transfer belt  41 , whereby the image forming apparatus is ready for the next image formation. 
     Example 6 
     Next will be described a multi-color image forming apparatus having another configuration. 
       FIG. 20  schematically illustrates essential parts of another exemplary multi-color image forming apparatus employing the cleaning device of the present invention. The multi-color image forming apparatus is a so-called tandem multi-color image forming apparatus having four image forming sections disposed in a row along an intermediate transfer belt  41  of a primary transfer device  40 . 
     The four image forming sections are identical in configuration to one another, except that colors used in developing units are different from one another (i.e., yellow (Y), magenta (M), cyan (C) or black (K)). Taking for example an image forming section using a yellow (Y) toner, this includes an image bearing member  1 Y, a charging unit  2 Y, an exposed area to laser light emitted from an optical writing unit  3 , a developing unit  4 Y, a primary transfer unit  13 Y and a cleaning unit  14 Y. Notably, among the constituent members of the image forming section, the image bearing member  1 Y, the charging unit  2 Y, the developing unit  4 Y and the cleaning unit  14 Y are housed in one cartridge to form a process cartridge. The process cartridge is detachably mounted to an image forming apparatus main body. 
     Each image forming section has the same configuration as shown in  FIG. 1 . The image bearing members  1 Y,  1 M,  1 C and  1 K are photoconductor drums and are rotated counterclockwise; i.e., in a direction indicated by an arrow in  FIG. 20 . 
     The charging units  2 Y,  2 M,  2 C and  2 K are, for example, charging rollers disposed in a non-contact manner, and uniformly charge the surface of the photoconductor drum. 
     The optical writing unit  3  is, for example, an optical writing device employing laser light scanning which includes four laser light sources and coupling optical systems, one light polarizer and four scanning imaging optical systems. This applies laser light, which is modulated correspondingly to image signals, to charged photoconductor drums  1 Y,  1 M,  1 C and  1 K to form latent electrostatic images. 
     The developing units  4 Y,  4 M,  4 C and  4 K are developing devices containing, in cases, respectively a yellow toner, a magenta toner, a cyan toner and a black toner as coloring powders; i.e., as toners used as one- or two-component developers. Each case houses, for example, a developing roller for carrying/conveying a developer to develop a latent image on the photoconductor drum with toner; a doctor blade for controlling the amount of the developer carried on the developing roller; and developing screws which stir the developer to convey it. 
     The image bearing member cleaning units  14 Y,  14 M,  14 C and  14 K each have the same configuration as shown in  FIG. 1 . Here, reference numerals are not given. Each cleaning unit is a cleaning device which includes a toner polarity controlling blade  16  disposed so as to contact the photoconductor drum  1 Y,  1 M,  1 C or  1 K to be cleaned; a cleaning brush roller  21  disposed so as to contact the photoconductor drum  1 Y,  1 M,  1 C or  1 K downstream of the toner polarity controlling blade  16  in a direction in which a toner is conveyed; a recovering roller  23  disposed so as to contact the cleaning brush roller  21 ; and a recovering roller conductive cleaning blade  24  disposed so as to contact the recovering roller  23 . Here, the toner polarity controlling blade  16  is a conductive member configured to charge toner particles remaining on the photoconductor drum so as to have a single polarity when a predetermined voltage is applied from a power source (toner polarity controlling blade-power source)  27 , and configured to scrape off at least part of the remaining toner particles. The cleaning brush roller  21  is a cleaning member configured to electrically adsorb toner particles present on the photoconductor drum when a predetermined voltage is applied from a power source (cleaning brush shaft voltage applying power source  30  and brush tip voltage applying power source  31 ). The recovering roller  23  is a first recovering member configured to electrically adsorb toner particles present on the cleaning brush roller  21  when a predetermined voltage is applied from a power source (recovering roller shaft voltage applying power source)  28 . The recovering roller conductive cleaning blade  24  is a second recovering member configured to scrape off toner particles on the recovering roller  23  when a predetermined voltage is applied from a power source (recovering roller conductive cleaning blade power source)  29 . 
     The primary transfer device  40  uses an intermediate transfer belt  41  as the intermediate transfer member. The intermediate transfer belt  41  is rotated in a direction indicated by an arrow in  FIG. 20  with being supported by a driving roller  42  and a plurality of driven rollers  43 ,  44  and  45 , and a transfer bias-applying roller, so that images (toner images) on photoconductor drums of image forming sections are sequentially transferred onto the intermediate transfer belt, to thereby form a composite toner image. 
     The secondary transfer device  56  uses a secondary transfer roller which conveys a recording medium S (e.g., a recording paper sheet), which has been fed through a paper feeding roller  52 , separating rollers  53 , conveying rollers  54 , resist rollers  55 , and other paper-feeding mechanisms from a selected paper-feeding part (e.g., a paper-feeding tray or a paper-feeding cassette)  50  or  51 , and which transfers an image from the intermediate transfer belt onto the recording medium S. 
     Also, downstream of the secondary transfer device  56  in a direction in which a recording medium is fed, there are provided a conveyor belt  48  for conveying a recording medium having undergone image transfer, a fixing device  60  for fixing the transferred image on the recording medium S through application of, for example, heat and pressure, a paper-discharging device  61  and other members. 
     The primary transfer device  40  is provided with an intermediate transfer belt cleaning device  46  which removes/recovers toner particles remaining on the intermediate transfer belt  41  having undergone secondary transfer. The intermediate transfer belt cleaning device  46  may have a similar configuration to the photoconductor drum cleaning device  14 . But, in this case, no quenching member is required. 
     Next will be described the operation of the multi-color image forming apparatus having the configuration shown in  FIG. 20 . 
     First of all, monochromatic image formation or color image formation is selected at an unillustrated operation part (here, color image formation is selected and a Y toner image, an M toner image, a C toner image and a K toner image are formed in this order). When a print button is pressed, each image forming section begins to operate. Then, a predetermined voltage or current is sequentially applied at a predetermined timing to non-contact charging rollers  2 Y,  2 M,  2 C and  2 K; developing rollers of developing devices  4 Y,  4 M,  4 C and  4 K; transfer bias-applying rollers  13 Y,  13 M,  13 C and  13 K of a primary transfer device  40 ; toner polarity controlling blades  16 , cleaning brush rollers  21  and recovering rollers  23  of cleaning devices  14 Y,  14 M,  14 C and  14 K (and an intermediate transfer belt cleaning device  46 ). Almost simultaneously with this, photoconductor drums  1 Y,  1 M,  1 C and  1 K; the non-contact charging rollers  2 Y,  2 M,  2 C and  2 K; an intermediate transfer belt  41  of the primary transfer device  40 ; the developing rollers and the developing screws of the developing devices  4 Y,  4 M,  4 C and  4 K; the cleaning brush rollers  21 ; the recovering rollers  23 ; and toner discharging screws  19  each begin to rotate in predetermined directions. The photoconductor drums  1 Y,  1 M,  1 C and  1 K each are uniformly negatively charged by the corresponding non-contact charging rollers  2 Y,  2 M,  2 C and  2 K disposed in a non-contact manner, and then are exposed to laser light L emitted from an optical writing device  3  to form latent images to be developed with color toners. The thus-formed latent images are developed with magnetic brushes each being formed of each color toner and formed on the developing roller of the developing device  4 Y,  4 M,  4 C or  4 K, to thereby form toner images corresponding to each color toner. The toner images are primarily transferred, in sequence, onto the intermediate transfer belt  41  so as to form a composite toner image with the aid of transfer bias brought by the transfer bias-applying roller  13 Y,  13 M,  13 C or  13 K. Then, toner particles remaining on the photoconductor drums  1 Y,  1 M,  1 C and  1 K having undergone primary transfer are removed/recovered by the photoconductor cleaning devices  14 Y,  14 M,  14 C and  14 K. Notably, the configuration and operation of the cleaning device  14 Y,  14 M,  14 C or  14 K are the same as those as described above in  FIG. 1  and thus, no description about them is given. 
     In synchronization with primary transfer of a toner image of the fourth color onto the intermediate transfer belt  41 , a recording paper S is fed to between the intermediate transfer belt  41  and the secondary transfer roller  48  so as to synchronize with the top end of the composite toner image by resist rollers  55  through a paper feeding roller  52 , separating rollers  53 , conveying rollers  54 , and other paper-feeding mechanisms from a selected paper-feeding part (e.g., a paper-feeding tray or a paper-feeding cassette)  50  or  51 . Then, the composite image of four color toner images is secondarily transferred at one time onto the recording paper S. The recording paper S is separated from the intermediate transfer belt  41  by an unillustrated separating mechanism, and then is discharged as a print (or copy) image through a conveyor belt  57 , a fixing device  60  and a paper-discharging device  61 . 
     After secondary transfer, toner particles remaining on the surface of the intermediate transfer belt are removed/recovered by the intermediate transfer belt cleaning device  46 . 
       FIG. 20  illustrates the configuration of an exemplary tandem multi-color image forming apparatus based on the intermediate transfer method using the intermediate transfer belt  41  serving as the primary transfer device  40 . Alternatively, there may be achieved a tandem multi-color image forming apparatus based on the direct transfer method in which toner images on photoconductor drums are transferred onto a recording medium to form a composite image, using, instead of the intermediate transfer belt, a transfer member (transfer belt) which carries/conveys a recording medium to each image forming section. In this case, no secondary transfer device is required. Also, a transfer belt cleaning device, which is provided in this image forming apparatus for cleaning the surface of a transfer belt after conveyance of a recording medium, may have the same configuration as the photoconductor cleaning device as shown in FIG.  1 .