Patent Publication Number: US-8977181-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-1325, filed on Jan. 8, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an image forming apparatus having a function of erasing an image formed on a recording medium. 
     BACKGROUND 
     An image forming apparatus such as a multi function peripheral (MFP) that forms an image on a recording medium, for example, a sheet is proposed. The image forming apparatus includes a development unit that develops an electrostatic latent image formed on a photoreceptor using a two-component developer formed of, for example, a toner and a carrier, as a color material. The development unit stirs the two-component developer to charge the toner. The development unit supplies the charged toner to the photoreceptor to develop the electrostatic latent image of the photoreceptor, thereby forming a toner image. The image forming apparatus transfers the toner image onto the sheet and further fixes the toner image, thereby forming an image on the sheet. Since the toner is consumed for each image forming process, a new toner is supplied to the development unit when an internal toner concentration is a predetermined value or less. 
     A remaining toner which is not used for each image forming process is accumulated in the development unit. The accumulated toner is stirred whenever an image is formed, and charging performance thereof gradually deteriorates. The deteriorated, toner causes deterioration of the formed image, such as attachment to a non-image area of the sheet. In the image forming apparatus, for example, when the image forming process of a low printing rate with low toner consumption is continued, the deteriorated toner is easily accumulated in the development unit, and a trouble such as deterioration of the formed image easily occurs. 
     Accordingly, in order to solve the problem of the deteriorated toner, the image forming apparatus periodically performs a toner refresh process between the image forming processes. The toner refresh process is a process of forcibly forming an image on a photoreceptor by the development unit to consume the deteriorated toner in the development unit. 
     In addition, an image forming apparatus which can perform an image forming process of forming an image on a sheet using a color-erasable toner, and an erasing process of erasing the image formed on the sheet using an erasable toner has been developed. Even in the image forming apparatus, in order to solve the accumulation of the deteriorated toner, it is conceivable to periodically Perform the refresh process between the image forming processes. However, during the period of performing the refresh process, another process cannot be performed, and thus it is preferable that the period of performing the refresh process be short as possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating main units of an image forming apparatus according to a first embodiment. 
         FIG. 2  is a flowchart illustrating an image forming process and a refresh process of the image forming apparatus according to the first embodiment. 
       FIG,  3  is a flowchart illustrating the refresh process of the image forming apparatus according to the first embodiment. 
         FIG. 4  is a flowchart illustrating an erasing process and the refresh process of the image forming apparatus according to the first embodiment. 
         FIG. 5  is a cross-sectional view illustrating main units of an image forming apparatus according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, an image forming apparatus which has an erasing function of erasing an image formed on a recording medium using an erasable toner is provided. The image forming apparatus includes an image forming unit, an erasing unit, and a control unit. The image forming unit performs an image forming process of forming an image on an image bearing body by a toner and transferring the toner image from the image bearing body onto a recording medium, and a refresh process of forming an image on the image bearing body by the toner and removing the toner image from the image bearing body. The erasing unit erases the image formed on the recording medium using an erasable toner. The control unit controls the image forming unit such that the image forming unit performs the refresh process together with the erasing process performed by the erasing unit. 
     Hereinafter, the embodiment will be further described with reference to the drawings. In the drawings, the same sign represents the same or similar portion. A first embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a cross-sectional view illustrating main units of an image forming apparatus  1  of the first embodiment. The image forming apparatus  1  can perform an image forming process of forming an image on a recording medium, for example, a sheet using a color-erasable toner, and an erasing process of erasing the image formed on the sheet using the erasable toner. The erasable toner is a toner, color of which is erased, for example, by heating. The image forming apparatus  1  may be configured as an MFP which can perform a scanner process, a FAX process or the like in addition to the processes described above. The image forming apparatus  1  includes an image forming unit. As illustrated in  FIG. 1 , the image forming unit includes a laser unit  11 , a photoreceptor drum  12  and a transfer belt as an image bearing body, a development unit  13 , cleaning blades  14  and  17 , a driving roller  18 , and a secondary transfer opposed roller  19 . The image forming apparatus  1  includes a transfer unit. The transfer unit includes a primary transfer roller  16  and a secondary transfer roller  20 . The image forming apparatus  1  includes an erasing unit. The erasing unit includes a heating unit  21  also serving as a fixing unit. The image forming apparatus  1  includes a control unit  22 . The image forming apparatus  1  further includes first and second sheet feeding cassettes (not illustrated) that accommodate sheets. 
     The first cassette accommodates a sheet P 1  on which an image is not formed. The second sheet feeding cassette accommodates a sheet P 2  on which an image is formed by the erasable toner. The laser unit  11  performs exposure scanning on the photoreceptor drum  12  to form an electrostatic latent image on the photoreceptor drum  12 . The photoreceptor drum  12  has a photosensitive surface, an outer peripheral surface of which is formed of an organic photo conductor (OPO) or the like. The photoreceptor drum  12  bears a toner image formed on the photosensitive surface by a development unit  13  to be described later, and rotates clockwise in  FIG. 1 . 
     The development unit  13  supplies the erasable toner to the photoreceptor drum  12  to develop the electrostatic latent image of the photoreceptor drum  12 , thereby forming a toner image on the photoreceptor drum  12 . The development unit  13  includes a development chamber  131 , a stirring member  132 , and a development roller  133 . The development chamber  131  accommodates a two-component developer formed of an erasable toner and a carrier. The erasable toner includes, for example, a coloring compound, a developer, and a decolorant. The coloring compound may be, for example, a Leuco dye which develops color in blue. The developer may be, for example, phenols. The decolorant may be, for example, a substance that is compatible with the coloring compound by heating and has no affinity to the developer. The erasable toner is colored by interaction between the coloring compound and the developer, and is decolored by disconnection of the interaction between the coloring compound and the developer by heating at equal to or higher than an erasing temperature. 
     The stirring member  132  stirs the developer in the development chamber  131  to charge the erasable toner by friction, for example, to a negative polarity. The development roller  133  includes a magnet roller therein. The development roller  133  absorbs the toner by magnetic force of the magnet roller, and forms a magnetic brush bristled along magnetic field lines of the magnet roller on an outer peripheral surface. The development roller  133  allows the magnetic brush to be rubbed against the photoreceptor drum  12  while rotating, to supply the toner to the electrostatic latent image of the photoreceptor drum  12 . The development unit  13  supplies the toner to the photoreceptor drum  12  to develop the electrostatic latent image, thereby forming an image using the toner on the photoreceptor drum  12 . 
     The cleaning blade  14  is provided in a state of being pressed to the photoreceptor drum  12  by a constant pressure, by a biasing member such as a spring. The cleaning blade removes the toner which is not transferred onto the transfer belt  15  and remains on the photoreceptor drum  12 , from the photoreceptor drum  12 . The transfer belt  15  is supported in an endless-ring shape by the driving roller  18  and the secondary transfer opposed roller  19 . The transfer belt  15  is driven by the driving roller  18 , and rotates counterclockwise in  FIG. 1 . The transfer belt  15  bears the toner image transferred from the photoreceptor drum  12 , and transfers the toner image onto the sheet P 1  in cooperation with the secondary transfer roller  20 . 
     The primary transfer roller  16  is formed of a metal roller having conductivity. The primary transfer roller  16  is opposed to the photoreceptor drum  12  with the transfer belt  15  interposed therebetween. For example, a positive transfer bias voltage is applied to the primary transfer roller  16 . When the transfer bias voltage is applied to the primary transfer roller  16 , a transfer electric field directed from the primary transfer roller  16  to the photoreceptor drum  12  is formed. The primary transfer roller  16  transfers the negatively charged toner image of the photoreceptor drum  12  to the transfer belt  15 . 
     The cleaning blade  17  is provided in a state of being pressed to the transfer belt  15  at a constant pressure by a biasing member such as a spring. The cleaning blade  17  removes the toner which is riot transferred onto the sheet P 1  and remains on the transfer belt  15 , from the transfer belt  15 . The driving roller  18  drives the transfer belt  15  to rotate. The secondary transfer opposed roller  19  is formed of a metal roller having conductivity. The secondary transfer opposed roller  19  interposes the sheet with the secondary transfer roller  20 , with the transfer belt  15  interposed therebetween. 
     The secondary transfer roller  20  is formed of a metal roller having conductivity. The secondary transfer roller  20  is supported to be contactable and separable with respect to the transfer belt  15  by a contact and separation mechanism (not illustrated). The secondary transfer roller  20  is moved to a position coming in contact with the transfer belt  15  by the contact and separation mechanism when the image forming process is performed. The position where the secondary transfer roller  20  comes in contact with the transfer belt  15  is referred to as a secondary transfer position U. When the image forming process is performed, the sheet P 1  is transported from the first cassette to the secondary transfer position U. A positive transfer bias is applied to the secondary transfer roller  20  when the sheet P 1  is transported to the secondary transfer position U. When the positive transfer bias is applied to the secondary transfer roller  20 , a transfer electric field directed from the secondary transfer roller  20  to the transfer belt  15  side (the secondary transfer opposed roller  19 ) is formed, and the negatively charged toner image of the transfer belt  15  is transferred onto the sheet P 1 . 
     The heating unit  21  includes a heating roller  211  and a pressure roller  212 . The heating roller  211  has a heater therein, and is configured to control a heating temperature. The pressure roller  212  forms a nip portion with the heating roller  211 . The heating unit  21  interposes the sheet in the nip portion such that heat conduction from the heating roller  211  to the sheet is fine. 
     When the image forming process is performed, the heating unit  21  serves as the fixing unit, and the heating temperature is controlled to be a fixing temperature. The heating unit  21  heats and presses the sheet P 1  onto which the image formed by the erasable toner is transferred, at the fixing temperature, for example, 80° C., to dissolve the erasable toner of the sheet P 1 , and fixes the image formed by the erasable toner to the sheet P 1 . When the erasing process is performed, the heating unit  21  serves as the erasing unit, and the heating temperature is controlled to be an erasing temperature. The heating unit  21  heats and presses the sheet P 2  at the erasing temperature higher than the fixing temperature, for example, 90° C., to erase the image formed by the erasable toner. 
     The control unit  22  controls the whole of the image forming apparatus  1 . The control unit  22  includes a processor, an application specific integrated circuit (ASIC), a memory, and a hard disk drive (HOD). The processor executes a program stored in the memory or the HDD to realize various functions. The ASIC is a circuit only for realizing a specific function. The ASIC may play a role of a proper function which the processor realizes. 
     The image forming process and a toner refresh process performed by the image forming apparatus  1  will be described with reference to  FIG. 2 .  FIG. 2  is a flowchart illustrating the image forming process and the toner refresh process of the image forming apparatus  1 . As illustrated in  FIG. 2 , in Act  1 , the control unit  22  determines whether an instruction of the image forming process is received or an instruction of the erasing process is received from a user by an operation panel (not illustrated). When the control unit  22  determines that the instruction of the image forming process is received (Yes in Act  1 ), the operation of the image forming apparatus  1  proceeds to Act  2 . In Act  2 , the control unit  22  drives constituent elements related to the image forming process of the image forming apparatus  1 . The image forming apparatus  1  takes the sheet P 1  out of a first cassette (not illustrated), and forms an image on the sheet P 1  by the erasable toner. Specifically, the control unit  22  rotates the photoreceptor drum  12 , and controls the operations of the laser unit  11  and the development unit  13 . The laser unit  11  forms an electrostatic latent image on the photoreceptor drum  12 . The development unit  13  develops the electrostatic latent image to form an image on the photoreceptor drum  12  by, for example, a negatively charged erasable toner. In addition, the control unit  22  rotates the transfer belt  15 , and applies a positive transfer bias voltage to the primary transfer roller  16 . The primary transfer roller  16  transfers the image formed by the erasable toner from the photoreceptor drum  12  to the transfer belt  15 . In addition, the control unit  22  moves the secondary transfer roller  20  to a position coming in contact with the transfer belt  15 . 
     After the image formed by the erasable toner is transferred onto the transfer belt  15 , the control unit  22  controls a transport unit (not illustrated) to transport the sheet P 1  to the secondary transfer position U. The control unit  22  applies a positive transfer bias voltage to the secondary transfer roller  20  to form a transfer electric field directed from the secondary transfer roller  20  to the transfer belt  15  side (the secondary transfer opposed roller  19 ). The secondary transfer roller  20  transfers the image formed by the negative erasable toner of the transfer belt  15 , onto the sheet P 1  by the transfer electric filed. The control unit  22  controls the heating temperature of the heating unit  21  at the fixing temperature, for example, 80° C. The heating unit  21  heats and presses the sheet P 1  to fix the image formed by the erasable toner to the sheet P 1 . 
     After the image forming process, in Act  3 , the control unit  22  updates a count value of the number of accumulated image-formed sheets P 1  from an initial state by increasing by “1” as the number of image formation times. The image forming apparatus  1  performs the toner refresh process periodically, for example, whenever images are formed on 500 sheets P 1 . Specifically, in Act  4 , the control unit  22  determines whether the count value of the number of accumulated image-formed sheets reaches a predetermined performance value, for example, 500 sheets. When the control unit  22  determines that the count value of the number of accumulated image-formed sheets does not reach the predetermined performance value (NO in Act  4 ), the operation of the image forming apparatus  1  returns to Act  1 . When the control unit  22  determines that the count value of the number of accumulated image-formed sheets reaches the predetermined performance value (YES in Act  4 ), the operation of the image forming apparatus  1  proceeds to Act  5 . In Act  5 , the image forming apparatus performs the toner refresh process. Hereinafter, the periodically performed toner refresh process may be merely referred to as a refresh process  1 . 
     The refresh process  1  will be described with reference to  FIG. 3 .  FIG. 3  is a flowchart illustrating the refresh process  1  of the image forming apparatus  1 . As illustrated in  FIG. 3 , in Act  51 , the control unit  22  moves the secondary transfer roller  20  to a position separated from the transfer belt  15  by a contact and separation mechanism not illustrated). In Act  52 , the control unit  22  rotates the photoreceptor drum  12  and the transfer belt  15  to operate the development unit  13  for the refresh process  1 . The development unit  13  forms an image formed by the toner, for example, a solid image in which an A4-size area is filled by the erasable toner, on the photoreceptor drum  12 . In Act  53 , the control unit  22  applies a transfer bias to the primary transfer roller  16 . The primary transfer roller  16  transfers the solid image from the photoreceptor drum  12  onto the transfer belt  15 . In Act  54 , the transfer belt  15  rotates to transport the solid image to a position of the cleaning blade  17 . The cleaning blade  17  removes the solid image from the transfer belt  15 . The image forming apparatus  1  forms the solid image as described above to discharge the deteriorated erasable toner from the inside of the development unit  13 , thereby forcibly consuming the erasable toner. 
     In the refresh process  1 , since the secondary transfer roller  20  is moved to the position separated from the transfer belt  15 , the solid image is prevented from being attached from the transfer belt  15  to the secondary transfer roller  20 . In Act  52  to Act  54 , the control unit  22  continuously forms the solid images with the number to sufficiently consume the deteriorated toner of the development unit  13 , and further removes the solid image from the upper face of the transfer belt  15 , thereby performing the refresh process  1 . 
     After performing the refresh process  1 , the operation of the image forming apparatus  1  proceeds to Act  6 . In Act  6 , the control unit  22  initializes the count value of the number of accumulated image-formed sheets to 0. After initializing the count value, the operation of the image forming apparatus  1  returns to Act  1 . Meanwhile, in Act  1 , when the control unit  22  determines that the instruction of the erasing process from the user is received (NO in Act  1 ), the operation of the image forming apparatus  1  proceeds to Act  7 . In Act  7 , the image forming apparatus  1  performs the toner refresh process with the erasing process. Hereinafter, the toner refresh process performed with the erasing process may be merely referred to as a refresh process  2 . 
     The decoloring process and the refresh process  2  will be described with reference to  FIG. 4 .  FIG. 4  is a flowchart illustrating the erasing process and the refresh process  2  of the image forming apparatus  1 . As illustrated in  FIG. 4 , in Act  71 , the control unit  22  moves the secondary transfer roller  20  to a position coming in contact with the transfer belt  15  by the contact and separation mechanism, to transport the sheet P 2  to the heating unit  21 . In Act  72 , the control unit  22  rotates the photoreceptor drum  12  and the transfer belt  15  to operate the development unit  13  for the refresh process  2 . Similarly to Act  52 , the development unit  13  forms an A4-size solid image formed by the erasable toner, on the photoreceptor drum  12 . In Act  73 , the control unit  22  applies a transfer bias to the primary transfer roller  16 . Similarly to Act  53 , the primary transfer roller  16  transfers the solid image from the photoreceptor drum  12  to the transfer belt  15 . 
     In Act  74 , the control unit  22  controls the bias voltage applied to the secondary transfer roller so as not to transfer the solid image to the sheet P 2 . For example, the control unit  22  controls the bias voltage such that the bias voltage is the negative bias voltage with the polarity reverse to the polarity at the time of transferring. By applying the negative bias voltage to the secondary transfer roller  20 , a non-transfer electric field directed from the transfer belt  15  side (the secondary transfer opposed roller  19 ) to the secondary transfer roller  20  is formed. Instead of the negative bias voltage, the bias voltage may not be applied to the secondary transfer roller. In Act  75 , the control unit  22  controls a sheet transport unit (not illustrated) to take the sheet P 2  out of the second cassette and to cause the sheet P 2  to pass through the secondary transfer position U. When the sheet P 2  passes through the secondary transfer position U, the secondary transfer roller  20  suppresses that the negative solid image of the transfer belt  15  is transferred onto the sheet P 2  by the non-transfer electric field directed from the transfer belt  15  side to the secondary transfer roller  20 . Even when the solid image comes in contact with the sheet P 2  at the secondary transfer position U, the solid image is not transferred onto the sheet P 2  and remains on the transfer belt  15 . 
     In Act  76 , the control unit  22  controls the heating temperature of the heating unit  21  to the erasing temperature, for example, 90° C. The sheet P 2  passes through the secondary transfer position U, and is transported to the heating unit  21 . The heating unit  21  heats and presses the sheet P 2  to erase the image formed on the sheet P 2  by the erasable toner. Even when the whole or a part of the solid image is transferred from the transfer belt  15  onto the sheet P 2  as the sheet P 2  passes through the secondary transfer position U, the solid image is formed by the erasable toner and thus the heating unit  21  erases the solid image. 
     In Act  77 , the transfer belt  15  rotates to transport the solid image to the position of the cleaning blade  17 . The cleaning blade  17  removes the solid image from the transfer belt  15 . As described from Act  71  to Act  77 , the control unit  22  controls the refresh process  2  to form, for example, the solid image once during the decoloring process of one sheet, to remove the solid image. When the decoloring process of a plurality of sheets is continuously performed, a larger number of solid images than the number of sheets P 2  to be erase-processed may be formed depending on the number of sheets P 2  to be erase-processed. 
     After performing the decoloring process and the refresh process  2  from Act  71  to Act  77 , the operation of the image forming apparatus  1  proceeds to Act  8 . In Act  8 , the control unit  22  corrects the predetermined performance value of the number of accumulated printed sheets according to the number of formed solid images. For example, the control unit  22  increases the predetermined, performance value, for example, by from 500 to 700 according to the number of formed solid images. In other words, the control unit  22  increases the predetermined performance value by from 500 to 700 according to the number of solid images formed in the refresh process  2 , thereby extending the period of the next refresh process  1 . 
     When the erasing process is performed, the image forming apparatus  1  rotates the transfer belt  15  to transport the sheet P 2  to the heating unit  21  although the image forming process is not performed. As described above, the transfer belt  15  comes in contact with the cleaning blade  17 . Accordingly, when the toner refresh process is not performed and the erasing process is frequently performed, the period of rotating the transfer belt  15  in a state where the toner is not transferred from the photoreceptor drum  12  lengthens, and thus the cleaning blade  17  easily deteriorates by friction against the transfer belt  15 . 
     When the erasing process is performed, the image forming apparatus  1  according to the first embodiment forms a solid image on the transfer belt  15  for the refresh process  2 . Accordingly, the transfer belt  15  is in a state where a toner film is coated by the solid image. The toner film serves as a lubricant, and it is suppressed that the cleaning blade  17  deteriorates by friction against the transfer belt  15 . In addition, since the image forming apparatus  1  according to the first embodiment performs the refresh process  2  with the erasing process, it is possible to extend the period of the refresh process  1  performed according to the number of accumulated printed sheets, and thus it is possible to shorten the period of performing only the refresh process  1  overall. 
     When the refresh process  2  is performed with the decoloring process, in Act.  8 , the predetermined performance value of the number of accumulated printed sheets is increased, for example, by from 500 to 700, to extend the period of the next toner refresh process  1 , but the embodiment is not limited to the extending method. For example, when the refresh process  2  is performed at least once before the period of the next toner refresh process  1 , the count value of the number of accumulated printed sheets is initialized to 0, and the next refresh process  1  may not be performed. In addition, in the period to the next toner refresh process  1 , when the refresh process  2  is performed, the number of solid images formed in the refresh process  1  may be decreased according to the number of solid images formed in the refresh process  2 . 
     The refresh process  2  with the decoloring process may be performed at a timing overlapped with the decoloring process. The electric field forming unit that forms the transfer electric field is not limited to the transfer roller, may be a member coming in contact with the transfer belt  15  with conductivity, and may be, for example, a conductive rubber blade, a conductive brush, and a conductive sheet. 
     When the image forming process is performed, the positive transfer bias voltage is applied to the secondary transfer roller  20  to transfer the image formed by the erasable toner of the transfer belt  15  onto the sheet P 1 , but the toner image of the transfer belt  15  may be transferred onto the sheet P 1  by applying the negative transfer bias voltage to the secondary transfer opposed roller  19 . When the negative transfer bias voltage is applied to the secondary transfer opposed roller  19 , the secondary transfer opposed roller  19  is the electric field forming unit. 
     In the image forming apparatus  1 , the heating unit  21  serves as both of the fixing unit and the erasing unit, but the erasing unit and the fixing unit are configured as separate units. In addition, in the image forming apparatus  1 , the two-component developer formed of the erasable toner and the carrier is used, but one-component developer formed of only the erasable toner may be used. 
     In the first embodiment, the erasing unit has a configuration of heating the toner image of the sheet to erase the toner image using the toner decolored by heat as the erasable toner. However, the erasing unit may have a configuration of degrading the toner image by irradiating the sheet with light such as near-infrared light using a photodegradable toner degraded by irradiation of light such as near-infrared light, as the erasable toner. In addition, the erasing unit may have a configuration of immersing the sheet in a treatment liquid to peel off the toner image from the sheet using a toner peeled off from the sheet by immersion in the treatment liquid, as the erasable toner. 
     An image forming apparatus according to a second embodiment will be described with reference to  FIG. 5 .  FIG. 5  is a cross-sectional view illustrating main units of an image forming apparatus  100  according to the second embodiment. The image forming apparatus  100  according to the second embodiment can form a color image, and can form an image using an erasable toner and a non-erasable toner. As illustrated in  FIG. 5 , the image forming apparatus  100  includes photoreceptor drums  120 Y to  120 K and development units  130 Y to  130 K. The photoreceptor drums  120 Y to  120 K and the development units  130 Y to  130 K are photoreceptor drums and development units for the non-erasable toner, respectively. The image forming apparatus  100  includes photoreceptor drums  12 Y to  12 K and development units  13 Y to  13 K. The photoreceptor drums  12 Y to  12 K and the development units  13 Y to  13 K are photoreceptor drums and development units for the erasable toner, respectively. The photoreceptor drums  12 Y to  12 K and the development units  13 Y to  13 K are provided along the transfer belt  15 . The photoreceptor drums  120 Y to  120 K and the development units  130 Y to  130 K are provided along the transfer belt  15  and at a position further to the secondary transfer position U side than the photoreceptor drums  12 Y to  12 K and the development units  13 Y to  13 K. Although not illustrated in  FIG. 5 , as described in the first embodiment, the image forming apparatus  100  further includes a laser unit  11 , a primary transfer roller  16 , and a cleaning blade  14  for each of the photoreceptor drums  12 Y to  12 K and  120 Y to  120 K. The positions of the photoreceptor drums  120 Y to  120 K and the development units  130 Y to  130 K may be reverse to the positions of the photoreceptor drums  12 Y to  12 K and the development units  13 Y to  13 K. 
     Each of the development units  13 Y to  13 K and  130 Y to  130 K accommodates corresponding toner of yellow (Y), magenta (M), cyan (C), or black (K) different in color. As described in the first embodiment, the image forming apparatus  100  performs the image forming process, the toner refresh process, and the erasing process illustrated in  FIG. 2  to  FIG. 4 . When the erasing process is performed, a solid image formed by the non-erasable toner may be formed on the transfer belt  15  by the photoreceptor drums  120 Y to  120 K and the development units  130 Y to  130 K, and may perform the refresh process  2  of the development units  130 Y to  130 K. In addition, when the erasing process is performed, both of a solid image formed by the erasable toner and a solid image formed by the non-erasable toner may be formed, and the refresh process  2  of the development units  13 Y to  13 K and  130 Y to  130 K may be performed. A proper number of development units may be provided in the image forming apparatus  100  according to kinds of colors to be used. For example, when one black color is to be used, the image forming apparatus  100  may be provided with only combination of the development unit  13 K accommodating the black erasable toner and the development unit  130 K accommodating the black non-erasable toner. 
     In the embodiment, the transfer belt may not be provided, and a configuration in which the toner image is directly transferred from the photoreceptor drum onto the sheet may be used. In the case of the direct transferring, for example, the photoreceptor drum is the image bearing body, the primary transfer roller  16  is the transfer unit that directly transfers the toner image from the photoreceptor drum onto the sheet, and the cleaning blade  14  is the cleaning blade that removes the toner image of the image bearing body. The process sequence in each of the embodiments may be different from the sequence exemplified in the embodiments. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fail within the scope and spirit of the inventions.