Patent Publication Number: US-7715745-B2

Title: Image forming apparatus having remaining toner removing part and method of removing remaining toner therefrom

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of Korean Application No. 2006-131204, filed Dec. 20, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Aspects of the present invention relate to an image forming apparatus having a remaining toner removing part and a method of removing remaining toner, and more particularly, to an image forming apparatus having a remaining toner removing part and a method to remove remaining toner which efficiently remove toner remaining on a belt. 
   2. Description of the Related Art 
   Generally, an image forming apparatus of an electrophotographic type forms an image on a printing medium through a series of processes. These processes include charging the printing medium and other components, exposing an electrostatic latent image on a photosensitive medium, developing the image on the photosensitive medium, transferring the image to the printing medium, and fixing the image to the printing medium. Furthermore, a variety of electrophotographic type image forming apparatuses are currently on the market including, for example, a laser printer, a scanner, a copier, a multi function device, etc. 
   As shown in  FIG. 1 , a conventional image forming apparatus  1  of an electrophotographic type includes a plurality of development cartridges  40 Y,  40 M,  40 C, and  40 K to respectively store yellow (Y) toner, magenta (M) toner, cyan (C) toner and black (K) toner, and a plurality of transfer rollers  50 Y,  50 M,  50 C, and  50 K disposed adjacent to a corresponding plurality of photosensitive media  45 Y,  45 M,  45 C, and  45 K. A printing medium transfer belt  31  is interposed between the plurality of development cartridges  40 Y,  40 M,  40 C, and  40 K and the corresponding plurality of transfer rollers  50 Y,  50 M,  50 C, and  50 K. A belt unit  30  includes the printing medium transfer belt  31  and a plurality of support rollers  32 ,  33 ,  35  and  36  which rotatably support the printing medium transfer belt  31 . 
   Printing media P, such as sheets of paper, transparency sheets, etc., are stacked in a knock up plate  13 . An individual printing medium P is picked up from the stack by a pick up roller  15  and transferred to the printing medium transfer belt  31  by a transport roller  21  to pass between the photosensitive media  45 Y,  45 M,  45 C and  45 K and the corresponding transfer rollers  50 Y,  50 M,  50 C and  50 K. When the printing medium P passes between the photosensitive media  45 Y,  45 M,  45 C and  45 K and the corresponding transfer rollers  50 Y,  50 M,  50 C, and  50 K, a yellow toner image, a magenta toner image, a cyan toner image and a black toner image are respectively transferred from the photosensitive media  45 Y,  45 M,  45 C and  45 K and overlapped onto the printing medium P by an electric attraction of each transfer roller  50 Y,  50 M,  50 C and  50 K. 
   When the toner is transferred to the printing medium P, some of the toner may be attached to the printing medium transfer belt  31  and remain on the printing medium transfer belt  31 . To remove the remaining toner and clear the printing medium transfer belt  31 , a blade  37   a  protrudes from a blade unit  37  which is connected to a frame of the image forming apparatus  1 . The blade  37   a  is disposed in a position to contact the printing medium transfer belt  31  and scrape off the remaining toner. 
   However, in the above mechanical removing method, since the printing medium transfer belt  31  and the blade  37   a  constantly contact each other to enable the blade  37   a  to remove the remaining toner, the blade  37   a  wears down over time, deteriorating the quality of the belt cleaning. 
   Also, there is a conventional method of removing remaining toner from the printing medium transfer belt  31  using electricity, in which a separate toner charging device (not shown) is used to charge the toner remaining on the printing medium transfer belt  31  to have a polarity opposite to an original polarity, and thereby collect the remaining toner. However, in the conventional electric cleaning method, a separate charging device (not shown) and a control device (not shown) to control the charging device are used. Employing the separate charging device (not shown) and the control device (not shown) increases the cost of cleaning the printing medium transfer belt  31  and prevents an efficient use of space. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide an image forming apparatus and a remaining toner removing method thereof to clean toner remaining on a belt efficiently and at a low cost. 
   According to an aspect of the present invention, an image forming apparatus includes a belt, a plurality of support rollers which rotatably supports the belt, a photosensitive medium which has a surface on which a visible toner image is formed by a charged toner, a transfer roller which is disposed adjacent to the photosensitive medium with the belt interposed therebetween, a power supplying part which supplies power to the transfer roller so that a surface of the transfer roller has an electrical potential, and a control part which controls the power supplying part to supply a pulse power which has a middle power having a same polarity as a polarity of the charged toner to the transfer roller so that the charged toner remaining on the belt is transferred back to the photosensitive medium. 
   According to an aspect of the invention, the charged toner is negatively charged, and the pulse power includes a pulse voltage having a maximum voltage which is equal to or less than +500V and a minimum voltage which is equal to or more than −3,000V. 
   According to an aspect of the invention, the image forming apparatus further includes a development cartridge which includes a cleaning blade which contacts the surface of the photosensitive medium to separate the remaining toner from the surface of the photosensitive medium, a casing which rotatably supports the photosensitive medium, and a storage part disposed inside the casing and extending from the cleaning blade, which stores the toner separated from the surface of the photosensitive medium by the cleaning blade. 
   According to an aspect of the invention, the transfer roller and the photosensitive medium are plural in number. 
   According to an aspect of the invention, the control part controls the power supplying part to supply one of the plurality of transfer rollers with a pulse power having a different amplitude from an amplitude of a pulse power supplied to another of the plurality of transfer rollers. 
   According to an aspect of the invention, the belt is provided to transfer a printing medium past the photosensitive media and the control part controls the power supplying part to supply the pulse power having increasing amplitudes to the respective transfer rollers along a direction in which the printing medium is transferred past the photosensitive media by the belt. 
   According to an aspect of the invention, at least two of the plurality of transfer rollers have electrical resistances which increase along a direction in which a printing medium is transferred past the photosensitive media by the belt, and the power supplying part supplies a pulse current to the at least two transfer rollers. 
   According to an aspect of the invention, the control part controls the power supplying part to supply the pulse power to at least one but less than all of the plurality of transfer rollers. 
   According to an aspect of the invention, the power supplying part includes a pulse power generating circuit which generates the pulse power, and a direct current power generating circuit which generates power having a polarity opposite to the polarity of the charged toner. 
   According to an aspect of the invention, the control part connects the pulse power generating circuit to one of the plurality of transfer rollers, and connects the direct current power generating circuit to another of the plurality of transfer rollers. 
   According to an aspect of the invention, the image forming apparatus further includes a power switching part which is interposed between the power supplying part and the transfer rollers to switch between the power supplied from the pulse power generating circuit and the direct current power generating circuit of the power supplying part, wherein the control part controls the power switching part to connect the direct current power generating circuit to each of the plurality of transfer rollers during printing, and to connect the pulse power generating circuit to at least one of the transfer rollers during cleaning of the remaining toner. 
   According to an aspect of the invention, the control part connects the pulse power generating circuit to one or more of the transfer rollers and connects the direct current power generating circuit to one or more of the transfer rollers during the cleaning of the remaining toner. 
   According to an aspect of the invention, the toner is positively charged, and the pulse power includes a pulse voltage having a maximum voltage which is equal to or less than +3,000V, and a minimum voltage which is equal to or greater than −500V. 
   According to another aspect of the present invention, there is a method of removing remaining toner from a belt which is driven by a plurality of support rollers in an image forming apparatus, the image forming apparatus including a photosensitive medium having a surface on which a visible toner image is formed by charged toner, and a transfer roller which is disposed adjacent to the photosensitive medium with the belt interposed therebetween, the method including determining whether to remove toner remaining on the belt, and if the determining indicates that the toner remaining on the belt should be removed, generating a pulse power having an average value which has a same polarity as a polarity of the toner, and supplying the pulse power to the transfer roller. 
   According to another aspect of the invention, the pulse power includes a pulse voltage having a maximum voltage which is equal to or less than +500V, and a minimum voltage which is equal to or greater than −3,000V. 
   According to another aspect of the invention, the image forming apparatus includes a plural number of the transfer roller and the photosensitive medium, and the supplying of the pulse power includes supplying the pulse power to at least one of the plurality of transfer rollers. 
   According to another aspect of the invention, the belt is provided to transfer a printing medium past the photosensitive media and the supplying of the pulse power further includes respectively supplying pulse powers having increasing amplitudes to each the plurality of transfer rollers in a direction in which the printing medium is transferred past the photosensitive medium by the belt. 
   According to another aspect of the invention, the supplying of the pulse power further includes supplying the pulse power to at least one but less than all of the plurality of transfer rollers. 
   According to another aspect of the invention, the p supplying of the pulse power further includes supplying power which has a polarity opposite to the polarity of the charged toner to one of the plurality of transfer rollers. 
   According to another aspect of the present invention, an image forming apparatus includes a belt, a photosensitive medium which has a surface on which a visible toner image is formed by charged toner, a transfer roller which is disposed adjacent to the photosensitive medium with the belt interposed therebetween, and a power supplying part which supplies electric power to the transfer roller to repel the charged toner off the belt, wherein the electric power comprises a pulse voltage with positive and negative components which are supplied according to negative and positive amounts of the charged toner remaining on the belt. 
   According to another aspect of the present invention, there is another method of removing toner from a belt which is driven by a plurality of support rollers and transfers a printing medium in an image forming apparatus, the image forming apparatus including a photosensitive medium having a surface on which a visible toner image is formed by charged toner and a transfer roller which is disposed adjacent to the photosensitive medium with the belt interposed therebetween, the method including supplying power to the transfer roller to repel the charged toner off the belt, wherein the power includes a pulse power with positive and negative components which are supplied according to negative and positive amounts of the charged toner remaining on the belt. 
   According to another aspect of the invention, the method further includes storing a determination condition which indicates whether to initiate the supplying of the power. 
   According to another aspect of the invention, the determination condition is based on a number of the printing media which have been printed or a length of printing time. 
   According to another aspect of the invention, the method further includes performing the supplying of the power when the determination condition is satisfied. 
   According to another aspect of the invention, the method further includes determining whether the image forming apparatus includes a plural number of the transfer roller. 
   According to another aspect of the invention, the method further includes if the determining of whether the image forming apparatus includes the plural number of the transfer roller indicates that the image forming apparatus does not include the plural number of the transfer roller, supplying the pulse power to the transfer roller; and if otherwise, determining whether the power supplying part is set to a general mode. 
   According to another aspect of the invention, the method further includes if the determining of whether the image forming apparatus is set to the general mode indicates that the power supply part is set to the general mode, supplying the pulse power to each of the plurality of transfer rollers; and if otherwise, modulating an amplitude of the pulse power. 
   According to another aspect of the invention, the method further includes determining whether the power supplying part is set to a power saver mode. 
   According to another aspect of the invention, the method further includes if the determining of whether the power supply part is set to the power saver mode indicates that the power supply part is set to the power saver mode, supplying the modulated pulse power having gradually increasing amplitudes to at least one but less than all of the transfer rollers in a direction in which the printing medium is transferred; and if otherwise, determining whether a large amount of toner having an opposite polarity of the charged toner remains on the belt. 
   Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a sectional view of a conventional image forming apparatus; 
       FIG. 2  is a sectional view of an image forming apparatus according to a first embodiment of the present invention; 
       FIG. 3  is a partially enlarged sectional view of the image forming apparatus shown in  FIG. 2 ; 
       FIG. 4  is an enlarged sectional view schematically illustrating a belt unit of the image forming apparatus shown in  FIG. 2  during a printing process; 
       FIG. 5  is a partially enlarged sectional view illustrating the belt unit of the image forming apparatus shown in  FIG. 2  during a process of removing remaining toner; 
       FIG. 6  illustrates a pulse voltage supplied to a transfer roller during the process of removing the remaining toner shown in  FIG. 5 ; 
       FIG. 7  illustrates a first transfer roller of the belt unit shown in  FIG. 2  during the process of removing the remaining toner; 
       FIG. 8  illustrates pulse voltages respectively supplied to a plurality of transfer rollers of an image forming apparatus according to a second embodiment of the present invention; 
       FIG. 9  illustrates pulse voltages respectively supplied to a plurality of transfer rollers of an image forming apparatus according to a third embodiment of the present invention; 
       FIG. 10  illustrates a process of removing toner remaining on a belt of the image forming apparatus shown in  FIG. 9 ; 
       FIG. 11  illustrates pulse voltages respectively supplied to a plurality of transfer rollers of an image forming apparatus according to a fourth embodiment of the present invention; and 
       FIG. 12  is a flowchart of a method of removing toner remaining on a belt according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
   Hereinafter, an image forming apparatus according to aspects of the present invention will be described using an electrophotographic image forming apparatus of a single path type including a plurality of photosensitive media as an example. As shown in  FIG. 2 , an image forming apparatus  100  according to a first embodiment of the present invention includes a feeding part  110 , a belt unit  130 , a plurality of development cartridges  140 Y,  140 M,  140 C and  140 K, a transfer roller unit  150  having a plurality of transfer rollers  151 ,  153 ,  155  and  157 , and a fixing unit  160 . 
   The feeding part  110  includes a knock up plate  113  and a pick up roller  115  to pick up a printing medium P, such as a sheet of paper, a transparency sheet, a sheet of recycled paper, letterhead, stationary, etc., on the knock up plate  113 . The printing medium P picked up by the pick up roller  115  is transported toward the belt unit  130  by a pair of transport rollers  121 . 
   The belt unit  130  includes a belt  131  and support rollers  133  and  135  rotatably supporting the belt  131 . The belt  131  is formed out of a conductive material so that the printing medium P attaches to a surface of the belt  131  by static electricity after the printing medium P is transported to the belt  131  by the transport rollers  121 . It is understood that various types of conductive materials may be used to form the belt  131 , such as metallic materials. 
   The development cartridges  140 Y,  140 M,  140 C and  140 K respectively store yellow (Y) toner, magenta (M) toner, cyan (C) toner and black (K) toner. Each of the development cartridges  140 M,  140 C and  140 K have the same configurations as the configuration of the yellow development cartridge  140 Y except for the color of toner stored therein. Hereinafter, a configuration of the yellow development cartridge  140 Y will be representatively described in order to describe the configuration of each of the four development cartridges  140 Y,  140 M,  140 C, and  140 K. It is understood, however, that aspects of the present invention are not limited to being applied to an image forming apparatus having four development cartridges, and may instead be applied to other types of image forming apparatuses, such as, for example, an image forming apparatus with three development cartridges corresponding to red, green, and blue toner. 
   The yellow development cartridge  140 Y includes a charge roller  141 Y, a supply roller  142 Y, a developing roller  143 Y and a photosensitive medium  145 Y. The charge roller  141 Y charges a surface of the photosensitive medium  145 Y to a uniform electric potential (approximately −1,200V) before a light emitting unit  125  emits light to the photosensitive medium  145 Y. It is understood that the charge roller  141 Y may charge the surface of the photosensitive medium  145 Y to more or less than approximately −1,200 V. 
   The supply roller  142 Y supplies yellow toner stored in the development cartridge  140 Y to the photosensitive medium  145 Y, and friction-charges the toner so that the toner has a negative electric charge. Then, the developing roller  143 Y rotates to attach the negatively charged toner to a surface of the developing roller  143 Y, and develops an electrostatic latent image formed on a surface of the photosensitive medium  145 Y with the toner to form a visible toner image. The electrostatic latent image is formed by a potential difference between an area exposed to light and an area which is not exposed to light when the light emitting unit  125  emits light corresponding to yellow image information to a surface of the photosensitive medium  145 Y charged with a uniform electric potential. The yellow image information may be transmitted to the light emitting unit  125  from a variety of sources, such as a host computer (not shown). 
   The yellow development cartridge  140 Y further includes a cleaning blade  147 Y shown in  FIG. 3  which contacts a surface of the photosensitive medium  145 Y to remove toner remaining on the surface of the photosensitive medium  145 Y after the photosensitive medium  145 Y has applied the yellow toner to the printing medium P. The toner removed by the cleaning blade  147 Y is collected in a remaining toner storage part  146 Y shown in  FIG. 3 . The yellow development cartridge  140 Y also includes a casing  144 Y ( FIG. 7 ) which rotatably supports the photosensitive medium  145 Y. 
   Transfer rollers  151 ,  153 ,  155  and  157  are respectively disposed next to the photosensitive media  145 Y,  145 M,  145 C and  145 K of the yellow, magenta, cyan and black development cartridges  140 Y,  140 M,  140 C and  140 K, with the belt  131  interposed therebetween. The respective photosensitive media  145 Y,  145 M,  145 C and  145 K and the corresponding transfer rollers  51 ,  153 ,  155  and  157  press against each other through the belt  131  interposed therebetween. 
   The fixing unit  160  includes a heating roller  161  and a pressing roller  163 . The heating roller  161  applies heat to the printing medium P and the pressing roller  163  presses the toner image to the printing medium P to fix the toner image to the printing medium P. 
   As shown in  FIG. 3 , the image forming apparatus  100  according to an embodiment of the present embodiment further includes a power supplying part  170 , a power switching part  180  and a control part  190 . The power supplying part  170  supplies a current power or a voltage power to the transfer roller  150  to charge a surface of the transfer roller  150 . Hereinafter, the power supplying part  170  will be described as supplying voltage power as an example. According to an aspect, the power supplying part  170  is integrally configured with a high voltage power supply (HVPS) which supplies a high voltage to the photosensitive media  145 Y,  145 M,  145 C, and  145 K, the charging rollers  141 Y,  141 M,  141 C, and  141 K, the developing rollers  143 Y,  143 M,  143 C, and  143 K and the supply rollers  142 Y,  142 M,  142 C, and  142 K of the development cartridges  140 Y,  140 M,  140 C and  140 K. However, it is understood that the power supplying part  170  may be connected to voltage sources other than an HVPS. 
   As shown in  FIG. 3 , the power supplying part  170  includes a direct current power generating circuit  173  to generate a direct current transfer voltage having the opposite polarity of the polarity of an electric charge of the toner, and a pulse power generating circuit  175  to generate a pulse power having a middle power of the same polarity as the polarity of the electric charge of the toner. The direct current transfer voltage should generally be set to be within approximately +1,200V to +1,800V based on resistance of the printing medium P and environmental conditions, such as temperature, humidity, etc. However, it is understood that the direct current transfer voltage is not limited to being generated within the range of +1,200 V to +1,800 V, and may instead be generated within other ranges. 
   The pulse power generating circuit  175  overlaps a direct current power and an alternating current power to generate pulse power having a pulse shape. The pulse power has a middle power of the same polarity as the polarity of an electric charge of the toner to transfer toner remaining on the belt  131  back toward the photosensitive media  145 Y,  145 M,  145 C and  145 K by an electric repulsion. 
   According to the embodiment shown in  FIG. 6 , since the toner is charged with a negative charge, the pulse generating circuit  175  generates a middle, or average, voltage value which has a negative value. Also, if current instead of the voltage shown in  FIG. 6  is supplied to the transfer roller unit  150 , a middle current has a negative value. Furthermore, the maximum voltage of the pulse power is equal to or less than +500V, and the minimum voltage thereof is equal to or greater than −3,000V. It is understood that this range may differ according to other aspects of the present invention. 
   The pulse power generating circuit  175  further includes a pulse amplitude modulating circuit (not shown) to modulate the amplitude of the pulse power. The pulse amplitude modulating circuit (not shown) generates a pulse voltage, a middle voltage value of which has a negative value. Alternatively, the pulse amplitude modulating circuit (not shown) generates a pulse voltage having a uniform amplitude. 
   The power switching part  180  controls the direct current power generating circuit  173  to supply a direct voltage to the transfer roller  150  when a visible toner image formed on the photosensitive media  145 Y,  145 M,  145 C and  145 K is transferred to the printing medium P, in other words, when the image forming apparatus  100  is operating in a print mode. On the other hand, the power switching part  180  controls the pulse power generating circuit  175  to supply pulse power to the transfer roller  150  when toner remaining on the belt  131  is removed, in other words, when the image forming apparatus  100  is operating in a belt cleaning mode. 
   According to another aspect of the invention, the control part  190  performs the functions of the power switching part  180 . Thus, the control part  190  controls the direct current power generating circuit  173  and the pulse power generating circuit  175  to be turned on and off according to whether the image forming apparatus  100  is operating in the print mode or the belt cleaning mode. Consequently, the power switching part  180  may be omitted. Also, according to yet another aspect of the invention, the power switching part  180  may be integrally provided with the power supplying part  170 . 
   Hereinafter, a color image forming process of the image forming apparatus  100  will be described by referring to  FIG. 4 . The power supplying part  170  shown in  FIG. 3  is described as power supplying part which supplies a voltage power. 
   If a user is printing color images on the printing medium P, the control part  190  drives the pick up roller  115  to transport the printing medium P stacked in the knock up plate  113  to the transport roller  121 , as shown in  FIG. 2 . The transported printing medium P contacts a printing medium charge roller  123  to which the high voltage power supply (HVPS) supplies a voltage of +500V to +1,000V. An electric resistance of the printing medium P is then measured based on the supplied voltage. The control part  190  controls the direct power generating circuit  173  of the power supplying part  170  to generate a direct current transfer voltage having a value within a range corresponding to the measured electric resistance of the printing medium P. Also, the printing medium P is attached to the transport roller  121  to pass between the photosensitive media  145 Y,  145 M,  145 C and  145 K and the belt  131 . The control part  190  controls the power switching part  180  shown in  FIG. 3  to supply the direct current transfer voltage generated by the direct current power generating circuit  173  to the transfer roller  150 . 
   A surface of the photosensitive medium  145 Y of the yellow development cartridge  140 Y is uniformly charged to have an electric potential of −1,200V by the charge roller  141 Y, and is exposed to a light emitted from the light emitting unit  125  corresponding to yellow image information so that an electrostatic latent image can be formed on the surface of the photosensitive medium  145 Y. Negatively charged yellow toner is applied to the electrostatic latent image on the surface of the photosensitive medium  145 Y by an electric force with the developing roller  143 Y. Accordingly, a yellow visible toner image is formed on the surface of the photosensitive body  145 Y. 
   The negatively charged visible yellow toner image is transferred to the printing medium P passing between the belt  131  and the photosensitive medium  145 Y by an electric attraction between the negatively charged yellow toner and the positively charged first transfer roller  151 . 
   Next, when the printing medium P passes through the development cartridges  140 M,  140 C, and  140 K which respectively store magenta, cyan and black toner, magenta, cyan and black visible toner images are formed on the printing medium P in an overlapping fashion through the same process described above with reference to the development cartridge  140 Y. Accordingly, a complete color image is formed on the printing medium P. Then, the printing medium P having the color image applied thereon passes through the fixing unit  160  which fixes the color image to the printing medium P using heat and pressure respectively supplied from the heating roller  161  and the pressing roller  163 . Then, the printing medium P is discharged to the outside of the image forming apparatus  100 . 
   Hereinafter, a process of removing toner remaining on the belt  131  of the image forming apparatus  100  according to an embodiment will be described by referring to  FIGS. 5 and 7 . 
   To remove toner remaining on the belt  131 , the control part  190  controls the power switching part  180  to supply a pulse voltage generated by the pulse power generating circuit  175  to all of the transfer rollers  511 ,  153 ,  155  and  157 . Electric charges of the photosensitive media  145 Y,  145 M,  145 C and  145 K are removed so that a surface potential of each of the photosensitive media  145 Y,  145 M,  145 C and  145 K is approximately −50V to 0V. 
   As shown in  FIG. 6 , the control part  190  controls the pulse power generating circuit  175  to generate a pulse voltage B, a middle voltage value of which is smaller than a surface potential A of each of the photosensitive media  145 Y,  145 M,  145 C and  145 K. Also, the control part  190  rotates the support rollers  133  and  135  to circulate the belt  131  while the pulse voltage B is supplied. 
     FIG. 7  is an enlarged view illustrating the first transfer roller  151  of the belt unit  130  shown in  FIG. 2  during the process of removing remaining toners R 1  and R 2  on the belt  131 . As shown in  FIG. 7 , the remaining toners R 1  and R 2  are transferred back to the photosensitive media  145 Y by the pulse voltage supplied to the first transfer roller  151  shown in  FIG. 5 . Generally, negatively charged toner R 1  remains on the belt  131  after the image forming process. Additionally, positively charged toner R 2  may on occasion remain on the belt  131 . 
   When the pulse voltage is supplied to the first transfer roller  151 , the negatively charged toner R 1  on the belt  131  reciprocates between the belt  131  and the photosensitive medium  145 Y according to a frequency and an electric force of the pulse voltage. Part of the toner moves to the photosensitive medium  145 Y, and another part of the toner remains on the belt  131 . 
   Specifically, when component C of the pulse voltage shown in  FIG. 6  is supplied to the first transfer roller  151 , the negatively charged toner R 1  becomes electrically attracted towards the belt  131 . When component D of the pulse voltage is supplied to the first transfer roller  151 , the negatively charged toner R 1  becomes electrically repulsed toward the photosensitive medium  145 Y. Since the absolute value of the component D is greater than the absolute value of the component C, the electric repulsion is greater than the electric attraction so that the amount of toner transferred back toward the photosensitive medium  145 Y is relatively large compared to the amount of toner attracted to the belt  131 . In other words, the pulse power has positive and negative components which are supplied according to negative and positive amounts of the charged toner remaining on the belt  131 . Here, since a surface potential of the photosensitive medium  145 Y is greater than the component D of the pulse voltage which is supplied to the transfer roller  151 , an electric repulsion between the photosensitive medium  145 Y and the negatively charged toner R 1  is negligible. 
   Although the negatively charged toner R 1  is electrically attracted to the belt  131  to be attached thereto, the attaching force becomes significantly weakened over time. Therefore, the negatively charged toner R 1  is easily transferred back to the photosensitive medium  145 M of the magenta development cartridge  140 M by a second transfer roller  153 . The negatively charged toner R 1  transferred back to the photosensitive medium  145 Y is scraped off by the cleaning blade  147 Y and collected into the remaining toner storage part  146 Y. 
   Meanwhile, the positively charged toner R 2  receives an electric repulsion by the component C of the pulse voltage shown in  FIG. 6  which repels the positively charged toner R 2  back towards the photosensitive medium  145 Y. However, since the absolute value of the component D is greater than the absolute value of the component C, an amount of the positively charged toner R 2  repelled towards the photosensitive medium  145 Y by the component C is less than an amount of the negatively charged toner R 1  repelled towards the photosensitive medium  145 Y by the component D. 
   The following Table 1 discloses an experimental result indicating the number of belt rotations to completely remove toner remaining on the belt  131  in the case that a direct current reverse transfer voltage having the same polarity as the charged toner is applied to the transfer roller unit  150 , and in the case that the pulse voltage is supplied to the transfer unit  150 , to transfer the toner remaining on the belt  131  back to the photosensitive media  145 Y,  145 M,  145 C, and  145 K. In the experiment, the types of voltages were changed, while all the other conditions except the applied voltage remained constant. 
   
     
       
         
             
             
             
             
           
             
               TABLE 1 
             
             
                 
             
             
               direct current 
               belt 
                 
               belt 
             
             
               reverse transfer 
               rotation 
                 
               rotation 
             
             
               voltage (V) 
               number 
               pulse voltage (V) 
               number 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
          
             
               −500 
               9 
               Middle voltage −500, amplitude 
               6 
             
             
                 
                 
               500 
             
             
               −1,000 
               7 
               Middle voltage −1,000, amplitude 
               5 
             
             
                 
                 
               1,000 
             
             
               −1,500 
               5 
               Middle voltage −1,500, amplitude 
               4 
             
             
                 
                 
               1,500 
             
             
               −2,000 
               4 
               Middle voltage −2,000, amplitude 
               2 
             
             
                 
                 
               2,000 
             
             
               −2,500 
               3 
               Middle voltage −2,500, amplitude 
               2 
             
             
                 
                 
               2,500 
             
             
               −3,000 
               2 
               Middle voltage −3,000, amplitude 
               1 
             
             
                 
                 
               3,000 
             
             
                 
             
          
         
       
     
   
   The belt rotation number, which represents the number of cycles the belt  131  rotates, and an amount of time in which the remaining toner is cleaned from the belt  131 , are in proportion to each other. Accordingly, as shown in Table 1, an amount of time needed to remove toner remaining on the belt  131  is smaller when the pulse voltage is supplied to the transfer roller unit  150  compared to when the direct current reverse transfer voltage is supplied to the transfer roller unit  150 . For example, when a direct current reverse transfer voltage of −500V is supplied to the transfer roller unit  150 , the belt  131  rotates nine times before the toner remaining on the belt  131  is fully cleaned off. In contrast, when the power supplying part  170  supplies a pulse voltage having a middle voltage of −500V and an amplitude of 500V, in other words, supplies a pulse voltage having a maximum voltage of 0V and a minimum voltage of −1,000V, the power supplying part  170  reduces the number of times that the belt  131  rotates to 6 rotations, thereby reducing the cleaning time by approximately 33%. 
   Also, as voltage supplied to the transfer roller unit  150  is increased, the cleaning time accordingly decreases. However, as the supplied voltage becomes higher, more power is consumed by the transfer roller unit  150 . Accordingly, users should consider power consumption limits when determining how much voltage to supply to the transfer roller unit  150 . 
   An image forming apparatus (not shown) according to a second embodiment of the present invention supplies a pulse voltage shown in  FIG. 8  to the transfer roller unit  150  shown in  FIG. 2  similar to the manner in which the image forming apparatus  100  of the first embodiment supplies the pulse voltage shown in  FIG. 6  to the transfer roller unit  150  to remove toner remaining on the belt  131 . However, in contrast to the image forming apparatus  100  of the first embodiment, the image forming apparatus (not shown) according to a second embodiment further includes a pulse amplitude modulating control part (not shown) to modulate and transmit pulses with different pulse amplitudes to each transfer roller  151 ,  153 ,  155 , and  157 . 
   The pulse amplitude modulating control part (not shown) controls the pulse power generating circuit  175  to generate four pulse powers having different amplitudes from each other according to the equation W 1 &lt;W 2 &lt;W 3 &lt;W 4 . The pulse amplitude modulating control part (not shown) supplies a pulse power having the smallest amplitude W 1  to the first transfer roller  151  shown in  FIG. 2 , and respectively supplies pulse powers having increasing amplitudes W 2 , W 3 , and W 4  to a second transfer roller  153 , a third transfer roller  155 , and a fourth transfer roller. Thus, the plurality of transfer rollers  151 ,  153 ,  155 , and  157  within the transfer roller unit  150  shown in  FIG. 2  are respectively supplied with the pulse powers W 1 , W 2 , W 3 , and W 4  having amplitudes which increase along a direction in which the printing medium P moves past the plurality of photosensitive media  145 Y,  145 M,  145 C, and  145 K while being transferred by the belt  131 . 
   Accordingly, the pulse power having the smallest amplitude W 1  is supplied to the first transfer roller  151  to transfer the toner remaining on the belt  131  back to the photosensitive medium  145 Y at a point when the most toner is attached to the belt  131 . Also, the pulse power W 4  having the largest amplitude is supplied to the fourth transfer roller  157  to transfer back toner which remains on the belt  131  due to a relatively strong attractive force after the majority of the toner remaining on the belt  131  has been removed. Accordingly, by gradually increasing the amplitudes W 1 , W 2 , W 3 , and W 4 , the efficiency of the belt cleaning operation is improved. 
   Also, since the amount of the toner remaining on the belt  131  which is transferred back to each photosensitive medium  145 Y,  145 M,  145 C and  145 K by the gradually increasing amplitudes W 1 , W 2 , W 3 , and W 4  is substantially similar, the remaining toner storage parts  146 Y,  146 M,  146 C and  146 K may be designed to be relatively small and to have the same shapes. If a pulse voltage of a uniform amplitude is supplied to each of the transfer rollers  150 Y  150 M,  150 C, and  150 K of the transfer roller unit  150 , the amount of toner remaining on the belt  131  which is transferred back to each photosensitive medium  145 Y,  145 M,  145 C and  145 K is largest in the photosensitive medium  145 Y of a yellow development cartridge  140 Y, and the amount of toner transferred back to the photosensitive media  145 M,  145 C, and  145 K gradually decreases. Accordingly, the sizes of the remaining toner storage parts  146 Y,  146 M,  146 C, and  146 K of the respective development cartridges  140 Y,  140 M,  140 C, and  140 K should be gradually reduced. However, by applying the gradually increasing amplitudes W 1 , W 2 , W 3 , and W 4 , the other remaining toner storage parts  146 M,  146 C and  146 K may be designed to be substantially similar in size and shape, thereby making a more efficient use of space. 
   That is, since the toner remaining on the belt  131  which is not transferred back while passing through the first, second, and third transfer rollers  151 ,  153 , and  155 , respectively, has a relatively large attaching force compared to the toner which is transferred back to one of the first, second, and third transfer rollers  151 ,  153  and  155 , a reverse transfer efficiency is improved by enlarging the amplitude of the pulse power W 4  supplied to the fourth transfer roller  157  in comparison to supplying the pulse power of a uniform amplitude to all of the first, second, third, and fourth transfer rollers  151 ,  153 ,  155 , and  157 . Accordingly, it is unnecessary to supply excess power, thereby reducing power consumption and maintenance costs. 
   The first, second, third, and fourth transfer rollers  151 ,  153 ,  155 , and  157  used in the image forming apparatuses of the first and the second embodiments are formed of the same materials, and have the same electric resistances. However, according to another aspect of the present invention, if a pulse current power having a uniform amplitude is supplied to the transfer rollers  151 ,  153 ,  155 , and  157 , the four transfer rollers  151 ,  153 ,  155 , and  157  may be designed to have different electrical resistances. Specifically, the electrical resistance of the transfer rollers  151 ,  153 ,  155 , and  157  may be increased from a small electrical resistance to a large electrical resistance in the first, second, third, and fourth transfer rollers  151 ,  153 ,  155 , and  157  in sequence, thereby obtaining the same effect as supplying the pulse voltage shown in  FIG. 8 . 
   An image forming apparatus (not shown) according to a third embodiment of the present invention supplies voltage as shown in  FIG. 9  to the first, second, third, and fourth transfer rollers  151 ,  153 ,  155  and  157 , respectively. In an image forming apparatus (not shown) according to a third embodiment of the present invention, the control part  190  shown in  FIG. 3  supplies the direct current transfer voltage described in the first embodiment to one of the first, second, third and fourth transfer rollers  151 ,  153 ,  155  and  157 , and supplies pulse voltage to the remaining number. In  FIG. 9 , the direct current transfer voltage is supplied to the second transfer roller  153 . Alternatively, the control part  190  can supply the direct current transfer voltage to one of the first, third, or fourth transfer rollers  151 ,  155  or  157 . 
   As shown in  FIG. 10 , positively charged toner R 2  remaining on a belt  131  with a strong attractive force is transferred back to the photosensitive medium  145 M of the magenta development cartridge  140 M by the second transfer roller  153 . The positively charged toner R 2  is then scraped off the photosensitive medium  145 M by a cleaning blade  147 M and collected in a remaining toner storage part  146 M. Accordingly, the positively charged toner R 2  which is attached to the belt  131  with a strong attractive force is easily removed from the belt  131   
   According to another aspect, a positive pulse power having polarity opposite to the polarity of the toner, in other words, a pulse having a middle voltage or a middle current with a positive polarity, may be used instead of the direct current transfer voltage applied to the second transfer roller, as shown in  FIG. 9 . Also, if a positive pulse voltage is supplied to the second transfer roller  153 , the positive pulse voltage may be symmetrical with respect to a time axis, such as, for example, the pulse voltage shown in  FIG. 6 . 
   An image forming apparatus (not shown) according to a fourth embodiment of the present invention supplies voltage as shown in  FIG. 11  to at least one but less than all of the first, second, third, and fourth transfer rollers  151 ,  153 ,  155  and  157  to remove toner remaining toner on the belt  131  shown in  FIG. 2 . In the image forming apparatus according to the second embodiment, the respective transfer rollers  151 ,  153 ,  155  and  157  shown in  FIG. 2  are each supplied with a pulse voltage having different amplitudes from each other. However, in the fourth embodiment of the present invention, only the first transfer roller  151  and the third transfer roller  155  are supplied with pulse voltages having different amplitudes. 
   Accordingly, during the operation to remove the toner remaining on the belt  131 , only two of the transfer rollers  151  and  155  are supplied with the pulse voltage, thereby reducing power consumption and maintenance costs. It is understood that the pulse voltages are not limited to being applied to the first and third transfer rollers  151  and  155 , and may instead be applied to any two rollers, such as the second and fourth transfer rollers  153  and  157 . 
   Hereinafter, a remaining toner removing method of an image forming apparatus  100  according to an embodiment of the present invention will be described by referring to  FIG. 12 . 
   At operation S 10 , a determination condition is stored in a storage medium in communication with the image forming apparatus  100 . The determination condition determines when to remove the toner remaining on the belt  131  based on any number of factors, including, for example, when a predetermined number of printing media have been printed or when a predetermined length of printing time has elapsed. The determination condition may further determine a period of time in which the toner remaining on the belt  131  is removed. In operation S 20 , it is determined whether the remaining toner should be removed based on the stored determination condition. For example, when the determination condition is based on whether a predetermined number of printing media have been printed or whether a predetermined length of printing time has elapsed, by detecting that the number of printing media have been printed, or that the predetermined length of time has elapsed, it can be determined whether the remaining toner should be removed. 
   Also, the determination condition may be set so that the toner remaining on the belt  131  is removed directly after a printing operation is finished. Furthermore, according to another aspect, a user may manually enter a command to remove the toner remaining on the belt  131 , in which case no determination condition is necessary, and operation S 10  may be omitted. 
   Then, at operation S 30 , the power supplying part  170  generates a pulse power having a middle power with the same polarity as the polarity of the charged toner. Then, in operation S 40 , it is determined whether the transfer roller unit  150  includes a plurality of transfer rollers. If it is determined in operation S 40  that the transfer roller unit  150  does not include a plurality of transfer rollers, the power supplying part  170  supplies pulse power to the single transfer roller in operation S 50 . If it is determined in operation S 40  that the transfer roller unit  150  includes a plurality of transfer rollers, such as, for example, the first, second, third, and fourth transfer rollers  151 ,  153 ,  155 , and  157  ( FIG. 2 ), it is determined in operation S 60  whether the power supplying part  170  is set to a normal mode. If it is determined in operation S 60  that the power supplying part  170  is set to the normal mode, the power supplying part  170  supplies the pulse power to each of the plurality of transfer rollers in the transfer roller unit  150  at operation S 70 . 
   If it determined in operation S 60  that the power supplying part  170  is not set to the normal mode, in other words, if it is determined that the power supplying part  170  is set to a reverse transfer high efficiency mode, the pulse amplitude modulating circuit (not shown) modulates the amplitude of the pulse power at operation S 80 . Then, it is determined whether the power supplying part  170  is set to a power saving mode at operation S 90 . 
   If it is determined in operation S 90  that the power supplying part  170  is set to the power saving mode, the power supplying part  170  transmits pulse powers having gradually increasing amplitudes to at least one but less than all of the transfer rollers in the transfer roller unit  150 , such as, for example, the first and third transfer rollers  151  and  155 , in a transferring direction at operation S 100 . The transferring direction of the belt  131  refers to a direction in which the printing medium P moves past the photosensitive media  145 Y,  145 M,  145 C and  145 K while being transferred by the belt  131 . For example, voltage as shown in  FIG. 11  may be respectively supplied to the first, second, third, and fourth transfer rollers  151 ,  153 ,  155  and  157 . 
   If it is determined in operation S 90  that the power supplying part  170  is not set to the power saving mode, it is then determined in operation S 110  whether a large amount of toner having a polarity opposite to the original polarity of the charged toner remains on the belt  131 . This determination may be automatically performed using a toner polarity sensor (not shown). Alternatively, a user may manually enter a command indicating that the belt  131  contains a large amount of toner having an opposite polarity. Furthermore, a user may set a default mode permanently indicating that a large amount of toner has opposite polarity. 
   As shown in  FIG. 2 , since toner stored in the development cartridge  140 Y is friction-charged to a negative charge by the supply roller  142 Y, the toner with opposite polarity refers to toner remaining on the belt  131  which is positively charged. It is understood, however, that if the toner is friction-charged to a positive charge, the toner with opposite polarity refers to toner remaining on the belt  131  having a negative charge. 
   If it is determined in operation S 110  that a large amount of toner having an opposite polarity remains on the belt  131 , the power supplying part  170  supplies at least one but less than all of the transfer rollers in the transfer roller unit  150 , such as, for example, the second transfer roller  153 , with direct current power in operation S 120 . Here, direct current power refers to a direct current voltage power or a direct current power having a polarity opposite to the original polarity of the charged toner. Also, at operation S 130 , the power supplying part  170  supplies a remaining number of the transfer rollers, such as, for example, the first, third, and fourth transfer rollers  151 ,  155 , and  157 , respectively, with pulse powers having amplitudes which respectively increase in magnitude along a proceeding direction of the belt. For example, voltages including a direct current transfer voltage and pulse power, such as the voltages shown in  FIG. 9 , are supplied to the first, second, third, and fourth transfer rollers  151 ,  153 ,  155  and  157 , respectively. As shown in  FIG. 9 , the amplitude of the transfer voltages supplied to the first, third, and fourth transfer rollers  151 ,  155  and  157  increase in magnitude from the first transfer roller  151  to the fourth transfer roller  157 . 
   If it is determined in operation S 110  that there is not a large amount of toner having an opposite polarity remaining on the belt  131 , the power supplying part  170  supplies each of the transfer rollers  151 ,  153 ,  155 , and  157  with pulse powers having amplitudes which respectively increase along a direction in which the printing medium P is transferred by the belt  131  at operation S 140 . 
   Accordingly, aspects of the present invention enable the remaining toner on the belt  131  to be removed without adding many additional devices, thereby saving space and reducing manufacturing costs. 
   Also, aspects of the present invention improve durability in comparison with the mechanical method of removing toner remaining on the belt  131  with the blade  37   a  shown in  FIG. 1 . 
   Furthermore, by supplying pulse power to the transfer roller to intensify movement of the remaining toner on the belt  131 , an attaching force of the remaining toner is weakened in a short period of time. Accordingly, the remaining toner is easily removed from the belt  131 . 
   The belt  131  is exemplarily described above as a printing medium transfer belt to statically attach and transport a printing medium P through the image forming apparatus  100 , but aspects of the present invention are not limited thereto. Alternatively, aspects of the present invention may be applied to a transfer belt type in which a visible toner image formed on a photosensitive medium is transferred to the surface of the transfer belt, and the visible toner image on the transfer belt is then transferred to the printing medium P. Additionally, it is understood that aspects of the present invention may be used with other types of belts and apparatuses as well. 
   As described above, an image forming apparatus having a remaining toner removing part and a method of removing remaining toner according to aspects of the present invention remove toner remaining on a belt  131  without adding many separate devices. 
   Furthermore, an image forming apparatus having a remaining toner removing part and a method of removing remaining toner according to aspects of the present invention save space and reduce manufacturing costs. 
   Also, an image forming apparatus having a remaining toner removing part and a method of removing remaining toner according to aspects of the present invention have improved durability in comparison with a mechanical remaining toner removing part and method of mechanically removing remaining toner, and continuously maintain efficient removal of the remaining toner despite being used for a long period of time. Accordingly, cleaning deterioration due to a long period of use is prevented. 
   Also, an image forming apparatus having a remaining toner removing part and a method of removing remaining toner according to aspects of the present invention weaken an attaching force of toner attached to the belt  131  by supplying a pulse power to a transfer roller unit  150  in a short period of time. Accordingly, the toner remaining on the belt  131  is removed more rapidly. 
   Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.