Patent Publication Number: US-8995898-B2

Title: Image forming apparatus and image erasing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-15601, filed on Jan. 30, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an image forming apparatus which forms an erasable image, and to an image erasing apparatus which erases an image. 
     BACKGROUND 
     An image erasing apparatus for erasing an image printed on a sheet is known. The image erasing apparatus includes an erasing unit that performs an erasing process, for example, heat process on a sheet on which an image is printed with an erasable color material to erase a color of an image on the sheet or to make a color of the color material forming the image transparent. 
     A user visually determines a level regarding whether to erase the image printed on the sheet before erasing the image using the erasing unit. The level regarding whether to erase the image refers to a level regarding whether erase of the image may be erased without restrictions. 
     The image erasing apparatus includes an image reading unit which reads the image of the sheet before erasing the image using the erasing unit, and a monitor which displays the read image before erasing the image using the erasing unit. The user views the image displayed on the monitor to determine the level regarding whether to erase the image. 
     If the user determines that a image to be erased is highly confidential in its contents and requires permission from a person who has predetermined authority in order to erase the image, the user may judge that the image to be erased is an image having a high level regarding whether to erase the image. If the user determines that an image to be erased is a brief note and is not required to check the contents of the image in order to erase the image, the user may judge that the image to be erased is an image at a low level regarding whether to erase the image. The user judges such a level regarding whether to erase an image for every sheet. 
     However, the level regarding whether to erase the image is visually judged by the user so that an erroneous judgment may be made. Since the user judges the level regarding whether to erase an image for every sheet, it is difficult to continuously erase images printed on a plurality of sheets so that it takes a long time to erase the images. Further, as the image reading unit is also required, the cost is increased for the image reading unit. It is burdensome to visually judge even an image of a low level regarding whether to erase an image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating an image forming apparatus according to a first embodiment. 
         FIGS. 2A to 2D  are views illustrating an erasing mode selection screen of a monitor which is used in the first embodiment. 
         FIG. 3  is a block diagram illustrating a control unit which controls the image forming apparatus according to the first embodiment. 
         FIG. 4  is a cross-sectional view illustrating an image erasing apparatus according to a second embodiment. 
         FIG. 5  is a block diagram illustrating a control unit which controls the image erasing apparatus according to the second embodiment. 
         FIGS. 6A to 6D  are views illustrating an erasing mode setting screen of a monitor which is used in the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, an image forming apparatus which forms an erasable image on a recording medium is provided. The image forming apparatus includes an image forming unit, an operation unit, and a control unit. The image forming unit accommodates a plurality of color materials which is erasable and has different erasing properties and forms an erasable image on a recording medium using at least one of the color materials. The operation unit receives selection of degrees of freedom regarding whether to erase the image formed by the image forming unit. The control unit allows the image forming unit to form the image using the at least one of color materials corresponding to the at least one of the degrees of freedom received by the operation unit. 
     According to another embodiment, an image erasing apparatus which erases an image formed on the recording medium is provided. The image erasing apparatus includes an erasing unit, an operation unit, and a control unit. The erasing unit erases the image on the recording medium using at least one of a plurality of erasing process conditions. The operation unit receives selection of at least one of degrees of freedom regarding whether to erase the image which is formed on the recording medium. The control unit allows the erasing unit to erase the image using the at least one of the erasing process conditions corresponding to the at least one of the degrees of freedom received by the operation unit. 
     Hereinafter, further embodiments will be described further with reference to the drawings. In the drawings, the same reference numeral denotes the same or similar part.  FIG. 1  is a cross-sectional view illustrating an image forming apparatus according to a first embodiment. As illustrated in  FIG. 1 , an image forming apparatus  10  prints an erasable image on a recording medium, for example, a sheet using, for example, a well-known electrophotographic method as an image forming method. The image forming apparatus  10  includes an image forming unit. The image forming unit includes a first developing unit  12 , a second developing unit  13 , a laser exposing unit  14 , a cleaning unit  15 , and a transfer unit  16  which are disposed around a photosensitive drum  11  which is an image carrier. 
     The photosensitive drum  11  is rotatably provided in the image forming apparatus  10 , and is charged with an electrostatic charge having a predetermined polarity by a charging unit (not illustrated), before being exposed by the laser exposing unit  14 . The laser exposing unit  14 , for example, has a light source which emits laser light, an exposure control unit which modulates the laser light based on information of an original image from a personal computer or a scanner, and an optical system which guides the laser light to the photosensitive drum  11 . The laser exposing unit  14  exposes the photosensitive drum  11  using the laser light to form an electrostatic latent image corresponding to an original image on the photosensitive drum  11 . 
     The first developing unit  12  includes an accommodating unit which accommodates a first toner which is a color material and a development roller which supplies a first toner charged with a predetermined polarity to the photosensitive drum  11 . The second developing unit  13  includes an accommodating unit which accommodates a second toner which is a color material and a development roller which supplies a second toner charged with a predetermined polarity to the photosensitive drum  11 . The first or second developing unit  12  or  13  supplies the first or second toner to the photosensitive drum  11  to develop the electrostatic latent image. After development, the first or second toner is electrostatically adhered to the electrostatic latent image to form a toner image on the photosensitive drum  11 . One of the first developing unit  12  and the second developing unit  13  which is selected to operate by the user using an operation unit  24 , which will be described below operates. 
     The first toner and the second toner according to the first embodiment are erasable color materials. The first toner and the second toner are color materials which have their own colors and color an image. When the first toner and the second toner are heated at a predetermined temperature or higher, the colors of the toners are erased or the colors of the toners become transparent. The predetermined temperatures (hereinafter, referred to as “erasing temperatures”), which are erasing properties, are different for the first toner and the second toner. The erasing temperature of the first toner (hereinafter, referred to as “a first erasing temperature”) is configured to be higher than the erasing temperature of the second toner (hereinafter, referred to as “a second erasing temperature”). The first toner and the second toner are configured such that the first erasing temperature and the second erasing temperature are higher than a fixing temperature for a fixing process which will be described below. Hereinafter, examples of the first toner and the second toner will be described. 
     Each of the first toner and the second toner includes a resin and a coloring agent. The coloring agent includes a coloration compound, a color developer, and a discoloration temperature regulator. The coloration compound is a color forming agent, and may use, for example, a leuco dye. The color developer may use, for example, phenols. If the discoloration temperature regulator is heated, the discoloration temperature regulator is compatible with the coloration compound and may use a material which does not have affinity for the color developer. The toner appears as a color when an interaction occurs between the coloration compound and the color developer and if the toner is heated at the erasing temperature or higher, the interaction between the coloration compound and the color developer is cut off so that the color of the toner disappears (a color of the toner becomes transparent). Further, the first toner and the second toner are appropriately combined with the discoloration temperature regulator so that the first erasing temperature becomes higher than the second erasing temperature. 
     The transfer unit  16  has, for example, a transfer roller which charges a sheet S so as to have a reverse polarity to that of the toner. The transfer unit  16  charges the sheet S which is conveyed to a transfer position  21  which is opposite to the photosensitive drum  11  to have a reverse polarity to that of the toner. The toner image of the photosensitive drum  11  is electrostatically adhered onto the sheet S to be transferred onto the sheet S. 
     The cleaning unit  15 , for example, includes a cleaning blade which is in contact with the photosensitive drum  11  to collect the toner from the photosensitive drum  11 . The cleaning unit  15  collects the toner which remains on the photosensitive drum  11  after being transferred from the photosensitive drum  11  to clean the photosensitive drum  11 . The photosensitive drum  11  is in a state where residual charges after cleaning are neutralized by a neutralizing unit, which is not illustrated, so as to form the toner image again. 
     The image forming unit of the image forming apparatus further includes sheet feeding units  17  and  18 , a conveying unit  19 , a fixing unit  22 , and a sheet discharging unit  23 . The sheet feeding units  17  and  18  include a plurality of sheet feeding cassettes which accommodates the sheet S onto which the toner image will be transferred and a sheet feeding roller which ejects the sheet S from the sheet feeding cassettes. The sheet feeding cassette may accommodate sheets S each having different sizes, for example. 
     The conveying unit  19  has a conveying mechanism, which conveys a sheet S, such as a registration roller  20  which is controlled to be rotated at a predetermined amount or stopped. The conveying unit  19  temporally abuts the sheet S ejected by the sheet feeding units  17  and  18  against the registration roller  20 , which is stopped, to adjust a gradient of the sheet S. Thereafter, the conveying unit  19  rotates the registration roller  20  to convey the sheet S to the transfer position  21  at a rotating timing of the photosensitive drum  11  on which the toner image is formed. 
     The fixing unit  22  includes a heating roller having a heat source and a pressure roller which is pressure-contacted with the heating roller and the heat source is controlled by the control unit which will be described below so that a surface of the heating roller is maintained at the fixing temperature. The fixing unit  22  applies a pressure to the toner image onto the sheet S while heating the toner image at the fixing temperature by conveying the transferred sheet S so as to be interposed between the heating roller and the pressure roller. As a result, the fixing unit  22  fixes the toner image onto the sheet S. 
     The sheet discharging unit  23  includes a rotating sheet discharging roller. The sheet discharging unit  23  discharges the fixed sheet S to a sheet discharging tray which is provided outside the image forming apparatus  10  using the sheet discharging roller. The image which is formed on the sheet S is formed by the first toner or the second toner. Accordingly, for example, in the image erasing apparatus, which will be described below, the image is heated at the erasing temperature or higher to erase the color of the toner and erase the image which is formed on the sheet S. 
     The image forming apparatus  10  further includes the operation unit  24  which is provided above a main body of the apparatus  10 . The operation unit  24  has a plurality of keys such as an image formation starting key and a touch panel type monitor  25  in order to receive the operation by the user. The operation unit  24  receives the operation by the user and outputs an operation signal in response to the operation of the user. The monitor  25  displays an erasing mode selection screen  30  for selecting a condition to form an image on the sheet S. The erasing mode selection screen has a mode display portion and a degree of freedom selecting portion. 
     In the first embodiment, it is possible to receive the selection of a degree of freedom regarding whether to erase the printed image which erases the printed image, as a condition to form an image. Specifically, the monitor  25  displays the erasing mode selection screen  30  in order to allow the user to select the degree of freedom regarding whether to erase the image. The monitor  25  receives the operation to select the degree of freedom by the user by using the mode display portion and the degree of freedom selecting portion of the erasing mode selection screen  30 . 
     A degree of freedom regarding whether to erase the image is varied in accordance with modes for determining whether to erase the image by the user. In the first embodiment, the monitor  25  displays a plurality of modes including such as an erasing level mode, an erasing temperature mode, a confidentiality mode, an erasing attention mode on the mode display portions in order to determine whether to erase the image. 
     The erasing level mode refers to a mode for determining whether to erase the image without restrictions. As the degree of freedom corresponding to the erasing level mode, the monitor  25  displays characters of “low erasing level” and “high erasing level” on the degree of freedom selection portion. The low erasing level means that the printed image may be erased without restrictions and the degree of freedom is high. The high erasing level means that it is hardly permitted to erase the printed image without restrictions and the degree of freedom is low. 
     The erasing temperature mode refers to a mode for determining whether to erase the image at a low erasing temperature. As the degree of freedom corresponding to the erasing temperature mode, the monitor  25  displays characters of “low temperature” and “high temperature” on the degree of freedom selection portions. The low temperature means that the image may be erased at a low temperature and the degree of freedom is high. The high temperature means that the image may be erased at a high temperature and the degree of freedom is low. 
     The confidentiality mode refers to a mode for determining whether to erase the image based on contents of characters contained in the image. As the degree of freedom corresponding to the confidentiality mode, the monitor  25  displays characters of “low confidential” and “high confidential” on the degree of freedom selection portion. The low confidential means that the contents of the characters contained in the image have low confidentiality and the degree of freedom is high. The high confidential means that the contents of the characters contained in the image have high confidentiality and the degree of freedom is low. 
     The erasing attention mode refers to a mode for determining whether to erase the image without attention for erasing the image. As the degree of freedom corresponding to the erasing attention mode, the monitor  25  displays characters of “attention required” and “no attention required” on the degree of freedom selection portion. The “no attention required” means that an attention to erase the image is not required and the degree of freedom is high. The “attention required” means that an attention to erase the image is required and the degree of freedom is low. 
       FIGS. 2A to 2D  illustrate examples of the erasing mode selection screen  30  according to the first embodiment. As illustrated in  FIGS. 2A to 2D , the erasing mode selection screen  30  includes an erasing level mode display portion  31 , an erasing temperature mode display portion  32 , a confidentiality mode display portion  33 , and an erasing attention mode display portion  34 , as mode display portions. The monitor  25  displays the mode display portions  31  to  34  on the erasing mode selection screen  30 , as a menu for allowing the user to select a mode for determining whether to erase the image. 
     The erasing level mode display portion  31  corresponds to the erasing level mode which is one of the modes for determining whether to erase the image. The erasing temperature mode display portion  32  corresponds to the erasing temperature mode which is one of the modes for determining whether to erase the image. The confidentiality mode display portion  33  corresponds to the confidentiality mode which is one of the modes for determining whether to erase the image. The erasing attention mode display portion  34  corresponds to the erasing attention mode which is one of the modes for determining whether to erase the image. In the mode display portions  31  to  34 , display colors which are displayed on the erasing mode selection screen  30  may be changed. 
     The erasing mode selection screen  30  further includes a first degree of freedom selecting portion  41  and a second degree of freedom selecting portion  42  as degree of freedom selecting portions. The monitor  25  displays the first degree of freedom selecting portion  41  and the second degree of freedom selecting portion  42  on the erasing mode selection screen  30  as a menu for allowing the user to select a level of a degree of freedom regarding whether to erase the image. The first degree of freedom selecting portion  41  has a degree of freedom display portion which displays characters indicating that the degree of freedom is low. The second degree of freedom selecting portion  42  has a degree of freedom display portion which displays characters indicating that the degree of freedom is high. 
     The monitor  25  changes display colors of the mode display portions  31  to  34  in response to receiving the operation (touch) of the user with respect to the mode display portions  31  to  34 . The monitor  25  changes the displayed characters (characters indicating that the degree of freedom is low) of the first degree of freedom selecting portion  41  and the displayed characters (characters indicating that the degree of freedom is high) of the second degree of freedom selecting portion  42  in response to receiving the operation of the user with respect to the mode display portions  31  to  34 . Specifically, the monitor  25  displays the characters indicating that the degree of freedom is low on the first degree of freedom selecting portion  41  in response to the mode for determining whether to erase the image. Further, the monitor  25  displays the characters indicating that the degree of freedom is high on the second degree of freedom selecting portion  42  in response to the mode for determining whether to erase the image. The character display indicating the mode in the mode display portions  31  to  34  or the character display indicating the degree of freedom in the degree of freedom selecting portions  41  and  42  are not limited to the above description but if the user may intuitively determine whether to erase the image, any display type is allowed. Further, not only the character display, but also a Figure or a symbol may be used. 
       FIG. 2A  illustrates the erasing mode selection screen  30  in a state where the erasing level mode display portion  31  receives the operation of the user (erasing level mode). As illustrated in  FIG. 2A , the monitor  25  changes the display color of the erasing level mode display portion  31  from gray to black in response that the erasing level mode display portion  31  receives the operation of the user. Further, in response that the erasing level mode display portion  31  receives the operation of the user, the monitor changes displayed contents of the first degree of freedom selecting portion  41  into characters of “high erasing level” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  42  into characters of “low erasing level” indicating that the degree of freedom is high. Therefore, in the erasing mode selection screen  30  illustrated in  FIG. 2A , the user determines the degree of freedom regarding whether to erase the image from the erasing level mode to select the “high erasing level” or the “low erasing level”. The monitor  25  displays a state where the erasing level mode display portion  31  is selected, as illustrated in  FIG. 2A , as an initial screen of the erasing mode selection screen  30 . 
       FIG. 2B  illustrates the erasing mode selection screen  30  in a state where the erasing temperature mode display portion  32  receives the operation of the user (erasing temperature mode). As illustrated in  FIG. 2B , in response that the erasing temperature mode display portion  32  receives the operation of the user, the monitor  25  changes the display color of the erasing temperature mode display portion  32  from gray to black. Further, in response that the erasing temperature mode display portion  32  receives the operation of the user, the monitor  25  changes displayed contents of the first degree of freedom selecting portion  41  into characters of “high temperature” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  42  into characters of “low temperature” indicating that the degree of freedom is high. Therefore, in the erasing mode selection screen  30  illustrated in  FIG. 2B , the user determines the degree of freedom regarding whether to erase the image from the erasing temperature mode to select the “high temperature” or the “low temperature”. 
       FIG. 2C  illustrates the erasing mode selection screen in a state where the confidentiality mode display portion  33  receives the operation of the user (confidentiality mode). As illustrated in  FIG. 2C , in response that the confidentiality mode display portion  33  receives the operation of the user, the monitor  25  changes the display color of the confidentiality mode display portion  33  from gray to black. Further, in response that the confidentiality mode display portion  33  receives the operation of the user, the monitor  25  changes displayed contents of the first degree of freedom selecting portion  41  into characters of “high confidential” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  42  into characters of “low confidential” indicating that the degree of freedom is high. Therefore, in the erasing mode selection screen  30  illustrated in  FIG. 2C , the user determines the degree of freedom regarding whether to erase the image from the confidentiality mode to select the “high confidential” or the “low confidential”. 
       FIG. 2D  illustrates the erasing mode selection screen in a state where the erasing attention mode display portion  34  receives the operation of the user (erasing attention mode). As illustrated in  FIG. 2D , in response that the erasing attention mode display portion  34  receives the operation of the user, the monitor  25  changes the display color of the erasing attention mode display portion from gray to black. Further, in response that the erasing attention mode display portion  34  receives the operation of the user, the monitor  25  changes displayed contents of the first degree of freedom selecting portion  41  into characters of “attention required” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  42  into characters of “no attention required” indicating that the degree of freedom is high. Therefore, in the erasing mode selection screen  30  illustrated in  FIG. 2D , the user determines the degree of freedom regarding whether to erase the image from the erasing attention mode to select the “attention required” or the “no attention required”. 
     When a degree of freedom of an image to be printed is low, it is desirable that the printed image is hardly erased. When a degree of freedom of an image to be printed is high, it is desirable that the printed image is easily erased. In the meantime, the printed image is formed by a toner which will be erased (the color of the toner becomes transparent) when being heated at a predetermined erasing temperature or higher. Therefore, when the erasing temperature is high, the printed image is hardly erased but when the erasing temperature is low, the printed image is easily erased. With that, in the first embodiment, the degree of freedom regarding whether to erase the image corresponds to the erasing temperature of the toner. The degree of freedom regarding whether to erase the image corresponds to the first toner and the second toner and also corresponds to the first developing unit  12  and the second developing unit  13  which accommodate the toner. Accordingly, if the monitor  25  receives the operation of selecting the degree of freedom by the user, the image forming apparatus  10  selects the first developing unit  12  or the second developing unit  13  corresponding to the operation of selecting the degree of freedom by the user to form an image. Specifically, the first degree of freedom selecting portion  41  (the degree of freedom is low) corresponds to the first developing unit  12  (the first toner which is hardly erased) and the second degree of freedom selecting portion  42  (the degree of freedom is high) corresponds to the second developing unit  13  (the second toner which is easily erased). 
     The image forming apparatus  10  further includes a control unit which controls each part.  FIG. 3  is a control block diagram illustrating a control unit which controls the image forming apparatus  10  according to the first embodiment. As illustrated in  FIG. 3 , a control unit  50  includes a processor  51 , for example, configured by a CPU (central processing unit) and a memory  52 . 
     The processor  51  acquires an operation signal from the operation unit  24  to read out display data of the erasing mode selection screen  30  (the erasing mode selection screen  30  illustrated in  FIGS. 2A to 2D ) corresponding to the mode display portions  31  to  34  which receive the operation of the user, from the memory  52  and allows the erasing mode selection screen  30  illustrated in  FIGS. 2A to 2D  to be displayed on the monitor  25 . The processor  51  further acquires the operation signal of the operation unit  24  to select the first developing unit  12  or the second developing unit  13  corresponding to the degree of freedom selecting portions  41  and  42  which receive the operation of the user. The processor  51  acquires the operation signal from the operation unit  24  to control the operation of each part of the image forming apparatus  10  described above. 
     The memory  52  is, for example, a semiconductor memory and includes a ROM (read only memory)  521  and a RAM (random access memory)  522 . The ROM  521  stores various control programs for performing display control of the monitor, selection control of the developing units  12  and  13 , and the operation control of each part of the image forming apparatus  10 . Further, the ROM  521  stores display data for displaying the erasing mode selection screen  30  illustrated in  FIGS. 2A to 2D . In addition, the RAM  522  has a storage area as a working area which is temporally provided to the processor  51  when the processor  51  performs the above-mentioned control operation. 
     Hereinafter, an operation of the image forming apparatus  10 , which selects the first developing unit  12  or the second developing unit  13  based on the control of the processor  51  to form an image on the sheet S, will be described. The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  reads out the display data of the erasing mode selection screen  30  illustrated in  FIG. 2A  from the ROM  521 . The monitor  25  displays the erasing mode selection screen  30  illustrated in  FIG. 2A  (the erasing mode selection screen  30  in the erasing level mode) based on the read out display data, as an initial screen. 
     In the initial screen, the erasing level mode display portion  31  is displayed in black and the erasing temperature mode display portion  32 , the confidentiality mode display portion  33 , and the erasing attention mode display portion  34  are displayed in gray. By the difference in the display colors of the mode display portions  31  to  34 , the user may visually recognize that the erasing mode selection screen  30  is in the erasing level mode. In the initial screen, characters of the high erasing level are displayed on the first degree of freedom selecting portion  41  and characters of the low erasing level are displayed on the second degree of freedom selecting portion  42 . The user may determine the degree of freedom regarding whether to erase the image from the erasing level mode to select the “high erasing level” or the “low erasing level”. 
     For example, when the image which may be erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is high), in the erasing mode selection screen  30  in the erasing level mode, the user touches the second degree of freedom selecting portion  42  to select the “low erasing level” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the second developing unit  13  corresponding to the second degree of freedom selecting portion  42  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . The photosensitive drum  11  rotates, the laser exposing unit  14  forms an electrostatic latent image on the photosensitive drum  11 , and the second developing unit  13  develops the electrostatic latent image. By the development, the toner image by the second toner is formed on the photosensitive drum  11 . Further, the transfer unit  16  transfers the toner image from the photosensitive drum  11  to the sheet S and the fixing unit  22  fixes the toner image onto the sheet S. By doing this, the image forming apparatus  10  uses the second developing unit  13  (second toner) to print the image on the sheet S. 
     For example, when the image which is hardly permitted to be erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is low), in the erasing mode selection screen  30  in the erasing level mode, the user touches the first degree of freedom selecting portion  41  to select the “high erasing level” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the first developing unit  12  corresponding to the first degree of freedom selecting portion  41  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . The photosensitive drum rotates, the laser exposing unit  14  forms an electrostatic latent image on the photosensitive drum  11 , and the first developing unit  12  develops the electrostatic latent image. By the development, the toner image by the first toner is formed on the photosensitive drum  11 . Further, the transfer unit  16  transfers the toner image from the photosensitive drum  11  to the sheet S and the fixing unit  22  fixes the toner image onto the sheet S. By doing this, the image forming apparatus  10  uses the first developing unit  12  (first toner) to print the image on the sheet S. 
     In the initial screen of the erasing mode selection screen  30  illustrated in  FIG. 2A , the user selects the erasing temperature mode display portion  32 . As a result, the operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  reads out the display data of the erasing mode selection screen  30  illustrated in  FIG. 2B  from the ROM  521 . The monitor  25  displays the erasing mode selection screen illustrated in  FIG. 2B  (the erasing mode selection screen  30  in the erasing temperature mode) based on the read out display data. In the erasing mode selection screen  30  illustrated in  FIG. 2B , the display color of the erasing temperature mode display portion  32  is changed from gray to black and the display color of the erasing level mode display portion  31  is changed from black to gray. By the difference in the display colors of the mode display portions  31  to  34 , the user may visually recognize that the erasing mode selection screen  30  is in the erasing temperature mode. The displayed characters of the first degree of freedom selecting portion  41  is changed to the “high temperature” and the displayed characters of the second degree of freedom selecting portion  42  is changed to the “low temperature”. Therefore, the user may determine the degree of freedom regarding whether to erase the image from the erasing temperature mode to select the “high temperature” or the “low temperature”. 
     For example, when the image which may be erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is high), in the erasing mode selection screen  30  in the erasing temperature mode, the user touches the second degree of freedom selecting portion  42  to select the “low temperature” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the second developing unit  13  corresponding to the second degree of freedom selecting portion  42  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . By starting the operation, the image forming apparatus  10  uses the second developing unit  13  (second toner) to print the image on the sheet S. 
     For example, when the image which is hardly permitted to be erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is low), in the erasing mode selection screen  30  in the erasing temperature mode, the user touches the first degree of freedom selecting portion  41  to select the “high temperature” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the first developing unit  13  corresponding to the first degree of freedom selecting portion  41  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . By doing this, the image forming apparatus  10  uses the first developing unit  12  (first toner) to print the image on the sheet S. 
     In the initial screen of the erasing mode selection screen  30  illustrated in  FIG. 2A , if the user selects the confidentiality mode display portion  33 , the operation unit receives the operation of the user to output the operation signal to the processor  51 . The processor  51  reads out the display data of the erasing mode selection screen  30  illustrated in  FIG. 2C  from the ROM  521 . The monitor  25  displays the erasing mode selection screen  30  illustrated in  FIG. 2C  (the erasing mode selection screen in the confidentiality mode) based on the read out display data. In the erasing mode selection screen  30  illustrated in  FIG. 2C , the display color of the confidentiality mode display portion  33  is changed from gray to black and the display color of the erasing level mode display portion  31  is changed from black to gray. By the difference in the display colors of the mode display portions  31  to  34 , the user may visually recognize that the erasing mode selection screen  30  is in the confidentiality mode. The displayed characters of the first degree of freedom selecting portion  41  is changed to “high confidential” and the displayed characters of the second degree of freedom selecting portion  42  is changed to “low confidential”. Therefore, the user may determine the degree of freedom regarding whether to erase the image from the confidentiality mode to select “high confidential” or “low confidential”. 
     For example, when the image which may be freely erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is high), in the erasing mode selection screen  30  in the confidentiality mode, the user touches the second degree of freedom selecting portion  42  to select “low confidential” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the second developing unit  13  corresponding to the second degree of freedom selecting portion  42  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . By starting the operation, the image forming apparatus  10  uses the second developing unit  13  (second toner) to print the image on the sheet S. 
     For example, when the image which is hardly permitted to be erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is low), in the erasing mode selection screen  30  in the confidentiality mode, the user touches the first degree of freedom selecting portion  41  to select “high confidential” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the first developing unit  13  corresponding to the first degree of freedom selecting portion  41  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . By starting the operation, the image forming apparatus  10  uses the first developing unit  13  (first toner) to print the image on the sheet S. 
     In the initial screen of the erasing mode selection screen  30  illustrated in  FIG. 2A , the user selects the erasing attention mode display portion  34 . As a result, the operation unit  24  receives the operation of the user to output the operation signal to the processor  51 . The processor  51  reads out the display data of the erasing mode selection screen  30  illustrated in  FIG. 2D  from the ROM  521 . The monitor  25  displays the erasing mode selection screen illustrated in  FIG. 2D  (the erasing mode selection screen  30  in the erasing attention mode) based on the read out display data. In the erasing mode selection screen  30  illustrated in  FIG. 2D , the display color of the erasing attention mode display portion  34  is changed from gray to black and the display color of the erasing level mode display portion  31  is changed from black to gray. By the difference in the display colors of the mode display portions  31  to  34 , the user visually recognize that the erasing mode selection screen  30  is in the erasing attention mode. The displayed characters of the first degree of freedom selecting portion  41  is changed to “attention required” and the displayed characters of the second degree of freedom selecting portion  42  is changed to “no attention required”. Therefore, the user may determine the degree of freedom regarding whether to erase the image from the erasing attention mode to select “attention required” or “no attention required”. 
     For example, when the image which may be freely erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is high), in the erasing mode selection screen  30  in the erasing attention mode, the user touches the second degree of freedom selecting portion  42  to select “no attention required” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the second developing unit  13  corresponding to the second degree of freedom selecting portion  42  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . By starting the operation, the image forming apparatus  10  uses the second developing unit  13  (second toner) to form the image on the sheet S. 
     For example, when the image which is hardly permitted to be erased without restrictions, by the image erasing apparatus which will be described below, is formed on the sheet S (in case that the degree of freedom of erasing the image is low), in the erasing mode selection screen  30  in the erasing attention mode, the user touches the first degree of freedom selecting portion  41  to select “attention required” and operates an image formation starting key of the operation unit  24 . The operation unit  24  receives the operation by the user to output the operation signal to the processor  51 . The processor  51  selects the first developing unit  13  corresponding to the first degree of freedom selecting portion  41  as a developing unit which forms a toner image and starts the operation of each part of the image forming apparatus  10 . By starting the operation, the image forming apparatus  10  uses the first developing unit  12  (first toner) to print the image on the sheet S. 
     As described above, according to the first embodiment, as a condition of printing the image, the user may select a degree of freedom regarding whether to erase the printed image. The degree of freedom corresponds to the erasing temperature. Accordingly, when the user selects the degree of freedom, the user may use the first developing unit  12  which uses the first toner having a high erasing temperature or the second developing unit  13  which uses the second toner having a low erasing temperature to print the image. 
     According to the first embodiment, the degree of freedom regarding whether to erase the printed image may be selected from different determination modes such as “erasing level”, “erasing temperature”, “confidentiality”, and “erasing attention”. Therefore, the user may instinctively determine and easily select the degree of freedom regarding whether to erase the printed image. Further, the user may select the first developing unit  12  or the second developing unit  13  in accordance with, for example, a degree of importance such as a security of a print image. 
     According to the first embodiment, when the image is erased from the sheet S on which the image is printed by the image erasing apparatus which will be described below, only by changing the heating temperature corresponding to the erasing temperature, the user may erase the image in accordance with a level regarding whether to erase the printed image without visually determining a level regarding whether to erase the printed image (a level indicating whether the print image may be erased without restrictions). 
     In the first embodiment, two types of toners having different erasing temperatures may be selected but three or more types of toners having different erasing temperature may be selected. In this case, the number of degree of freedom selecting portions in the erasing mode selection screen  30  illustrated in  FIGS. 2A to 2D  may be three or more in accordance with the types of toners. Further, the displayed contents of the degree of freedom selecting portion are not limited to the above description, and for example, in the erasing level mode, the displayed contents of the degree of freedom selecting portion may be a high erasing level, an intermediate erasing level, and a low erasing level. 
       FIG. 4  is a cross-sectional view illustrating an image erasing apparatus according to a second embodiment. An image erasing apparatus  100 , for example, erases the image printed on the sheet S by the image forming apparatus  10  according to the first embodiment. The image erasing apparatus  100 , as illustrated in  FIG. 4 , includes a conveyance mechanism which conveys the sheet S, an erasing unit which erases an image which is printed on the sheet S, an operation unit which receives the operation by the user, and a control unit which controls the erasing operation. 
     The conveyance mechanism includes a sheet feeding unit  101 , a sheet feeding roller  102 , an aligning roller  103 , a conveying unit  104 , and a sheet discharging roller  107 . The sheet feeding unit  101  includes a sheet feeding cassette which accommodates the sheets S. The sheet feeding roller  102  has one roller which rotates while being in contact with an uppermost sheet S which is accommodated in the sheet feeding unit  101  and ejects the sheet S from the sheet feeding unit  101  one by one. The aligning roller  103  has one pair of rollers which rotates while nipping the sheet S ejected from the sheet feeding unit  101  and conveys the sheet S to the conveying unit  104  at a predetermined timing. The conveying unit  104  has a belt which is bridged over two rollers to endlessly travel. The conveying unit  104  allows the belt to travel in order to convey the sheet S to the erasing unit  105 . The sheet discharging roller  107  has one pair of rollers which rotates while nipping the sheet S from which the image is erased and ejects the sheet S to the outside of the apparatus. 
     The erasing unit  105  includes a heating roller  105   a  and a pressure roller  105   b . The pressure roller  105   b  is provided so as to be pressure-contacted with the heating roller  105   a  and forms a nip portion  106  between the heating roller  105   a  and the pressure roller  105   b . The heating roller  105   a  has a first halogen lamp  106   a  therein as a heating source. The pressure roller  105   b  has a second halogen lamp  106   b  therein as a heating source. The first halogen lamp  106   a  and the second halogen lamp  106   b  heat the heating roller  105   a  and the pressure roller  105   b  so that the surface temperatures of the heating roller  105   a  and the pressure roller  105   b  become a predetermined temperature (hereinafter, referred to as a heating temperature) which is the erasing process condition. The heating temperature is controlled by the control unit  120  to be a first heating temperature or a second heating temperature which is lower than the first heating temperature in accordance with the degree of freedom selected by a monitor  109  of an operation unit  108 . The first heating temperature is, for example, a heating temperature for erasing the image formed by the first toner of the first embodiment so that if the first heating temperature is equal to or higher than the first erasing temperature, the first heating temperature may be arbitrarily set. The second heating temperature is a heating temperature for erasing the image formed by the second toner of the first embodiment so that if the second heating temperature is equal to or higher than the second erasing temperature, the second heating temperature may be arbitrarily set. The heating roller  105   a  and the pressure roller  105   b  conveys the sheet S while nipping the sheet in the nip portion  106  and pressurize and heat the sheet S at the first heating temperature or the second heating temperature to erase the image which is printed on one side or both sides of the sheet S. In the second embodiment, even though the heating source is provided in both the heating roller  105   a  and the pressure roller  105   b , the heating source may be provided in one of the heating roller  105   a  and the pressure roller  105   b , for example, only in the heating roller  105   a . The heating source is not limited to the lamp. 
     The operation unit  108  has a plurality of keys such as an image erase starting key and a touch panel type monitor  109  in order to receive operation by the user. The operation unit  108  receives operation by the user and outputs an operation signal to a processor  121  in response to the operation of the user. The monitor  109  displays an erasing mode setting screen  130  for setting the erasing process condition (heating temperature) of the image printed on the sheet S (the image formed by the first toner or the second toner). The erasing mode setting screen  130  includes a mode display portion and a degree of freedom selecting portion which receives the operation (touch) of the user. 
     In the second embodiment, the user may select a degree of freedom regarding whether to erase the image, in response to the heating temperature which is the erasing process condition of the image. Specifically, the monitor  109  displays the erasing mode setting screen  130  in order to allow the user to select the degree of freedom regarding whether to erase the image. The monitor  109  receives the operation to select the degree of freedom by the user by using the mode display portion and the degree of freedom selecting portion of the erasing mode setting screen  130 . 
     A degree of freedom regarding whether to erase the image varies depending on a mode for determining whether to erase the image by the user. In the second embodiment, similarly to the image forming apparatus  10  of the first embodiment, the monitor  109  displays a plurality of modes including, for example, an erasing level mode, an erasing temperature mode, a confidentiality mode, an erasing attention mode, as the mode for determining whether to erase the image, on the mode display portion. 
       FIGS. 6A to 6D  illustrate examples of the erasing mode setting screen according to the second embodiment. As illustrated in  FIGS. 6A to 6D , the erasing mode setting screen  130  includes an erasing level mode display portion  131 , an erasing temperature mode display portion  132 , a confidentiality mode display portion  133 , and an erasing attention mode display portion  134 , as mode display portions. The monitor  109  displays the mode display portions  131  to  134  on the erasing mode setting screen  130  as a menu for allowing the user to select a mode for determining whether to erase the image. 
     The erasing level mode display portion  131  corresponds to the erasing level mode which is one of the modes for determining whether to erase the image. The erasing temperature mode display portion  132  corresponds to the erasing temperature mode which is one of the modes for determining whether to erase the image. The confidentiality mode display portion  133  corresponds to the confidentiality mode which is one of the modes for determining whether to erase the image. The erasing attention mode display portion  134  corresponds to the erasing attention mode which is one of the modes for determining whether to erase the image. Further, in the mode display portions  131  to  134 , display colors which are displayed on the erasing mode setting screen  130  may be changed. 
     The erasing mode setting screen  130  further includes a first degree of freedom selecting portion  141  and a second degree of freedom selecting portion  142 , as degree of freedom selecting portions. The monitor  109  displays the first degree of freedom selecting portion  141  and the second degree of freedom selecting portion  142  on the erasing mode setting screen  130 , as a menu for allowing the user to select a level of a degree of freedom regarding whether to erase the image. The first degree of freedom selecting portion  141  has a degree of freedom display portion which displays characters indicating that the degree of freedom is low. The second degree of freedom selecting portion  142  has a degree of freedom display portion which displays characters indicating that the degree of freedom is high. 
     The monitor  109  changes display colors of the mode display portions  131  to  134  in response to receiving the operation (touch) of the user with respect to the mode display portions  131  to  134 . The monitor  109  changes displayed contents (characters indicating that the degree of freedom is low) of the first degree of freedom selecting portion  141  and displayed contents (characters indicating that the degree of freedom is high) of the second degree of freedom selecting portion  142 , in response to receiving the operation (touch) of the user with respect to the mode display portions  131  to  134 . Specifically, the monitor  109  displays characters indicating that the degree of freedom is low on the first degree of freedom selecting portion  141  in accordance with the mode for determining the degree of freedom selected by the user and characters indicating that the degree of freedom is high on the second degree of freedom selecting portion  142  in accordance with the mode for determining the degree of freedom selected by the user. The character display indicating the mode in the mode display portions  131  to  134  or the character display indicating the degree of freedom in the degree of freedom selecting portions  141  and  142  are not limited to the above description, but if the user may intuitively determine whether to erase the image, any display type is allowed. Further, not only the character display, but also a Figure or a symbol may be used. 
       FIG. 6A  illustrates the erasing mode setting screen  130  in a state where the erasing level mode display portion  131  receives the operation (touch) of the user (erasing level mode). As illustrated in  FIG. 6A , in response that the erasing level mode display portion  131  receives the operation of the user, the monitor  109  changes the display color of the erasing level mode display portion  131  from gray to black. Further, in response that the erasing level mode display portion  131  receives the operation of the user, the monitor  109  changes displayed contents of the first degree of freedom selecting portion  141  into characters of “high erasing level” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  142  into characters of “low erasing level” indicating that the degree of freedom is high. Therefore, in the erasing mode setting screen  130  illustrated in  FIG. 6A , the user determines the degree of freedom regarding whether to erase the image from the erasing level mode to select “high erasing level” or “low erasing level”. The monitor  109  displays a state where the erasing level mode display portion  131  is selected (erasing level mode), as illustrated in  FIG. 6A , as an initial screen of the erasing mode setting screen  130 . 
       FIG. 6B  illustrates the erasing mode setting screen  130  in a state where the erasing temperature mode display portion  132  receives the operation (touch) of the user (erasing temperature mode). As illustrated in  FIG. 6B , when the erasing temperature mode display portion  132  is selected by the user, the monitor  109  changes the display color of the erasing temperature mode display portion  132  from gray to black. Further, the monitor  109  changes displayed contents of the first degree of freedom selecting portion  141  into characters of “high temperature” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  142  into characters of “low temperature” indicating that the degree of freedom is high. Therefore, in the erasing mode setting screen  130  illustrated in  FIG. 6B , the user determines the degree of freedom regarding whether to erase the image from the erasing temperature mode to select “high temperature” or “low temperature”. 
       FIG. 6C  illustrates the erasing mode setting screen  130  in a state where the confidentiality mode display portion  133  receives the operation (touch) of the user (confidentiality mode). As illustrated in  FIG. 6C , when the confidentiality mode display portion  133  is selected by the user, the monitor  109  changes the display color of the confidentiality mode display portion  133  from gray to black. Further, the monitor  109  changes displayed contents of the first degree of freedom selecting portion  141  into characters of “high confidential” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  142  into characters of “low confidential” indicating that the degree of freedom is high. Therefore, in the erasing mode setting screen  130  illustrated in  FIG. 6C , the user determines the degree of freedom regarding whether to erase the image from the confidentiality mode to select “high confidential” or “low confidential”. 
     Further,  FIG. 6D  illustrates the erasing mode setting screen  130  in a state where the erasing attention mode display portion  134  receives the operation (touch) of the user (erasing attention mode). As illustrated in  FIG. 6D , when the erasing attention mode display portion  134  is selected by the user, the monitor  109  changes the display color of the erasing attention mode display portion  134  from gray to black. Further, the monitor  109  changes displayed contents of the first degree of freedom selecting portion  141  into characters of “attention required” indicating that the degree of freedom is low and displayed contents of the second degree of freedom selecting portion  142  into characters of “no attention required” indicating that the degree of freedom is high. Therefore, in the erasing mode setting screen  130  illustrated in  FIG. 6D , the user determines the degree of freedom regarding whether to erase the image from the erasing attention mode to select “attention required” or “no attention required”. 
     The image which is printed on the sheet S is formed by a toner which will be erased (the color of the toner becomes transparent) when being heated at a predetermined erasing temperature or higher. Therefore, as the erasing temperature of the toner which forms the image is high, the image is hardly erased, but as the erasing temperature of the toner which forms the image is low, the image is easily erased. As the heating temperature of the erasing unit  105  is high, the image is hardly erased, but as the heating temperature of the erasing unit  105  is low, the image is easily erased. In connection to this, when the degree of freedom regarding whether to erase the image which is printed on the sheet S is low, it is desirable that the image is hardly erased. Further, when a degree of freedom regarding whether to erase the image which is printed on the sheet S is high, it is desirable that the image is easily erased. Therefore, in the second embodiment, the degree of freedom regarding whether to erase the image corresponds to the first heating temperature and the second heating temperature of the erasing unit  105 . 
     Accordingly, if the monitor  109  receives the operation for selecting the degree of freedom by the user, the image erasing apparatus  100  heats the sheet S at the first heating temperature or the second heating temperature in accordance with the operation of the user to select the degree of freedom to erase the image. Specifically, the first degree of freedom selecting portion  141  (degree of freedom is low) corresponds to the first heating temperature and the second degree of freedom selecting portion  142  (degree of freedom is high) corresponds to the second heating temperature. 
       FIG. 5  is a control block diagram of a control unit  120  which performs the display control of the monitor  109  and the heating temperature control of the erasing unit  105 . The control unit  120  includes a processor  121 , for example, configured by a CPU (central processing unit) and a memory  122 . 
     The processor  121  acquires an operation signal from the operation unit  108  to read out display data of the erasing mode setting screen  130  (the erasing mode setting screen  130  illustrated in  FIGS. 6A to 6D ) corresponding to the mode display portions  131  to  134  which receive the operation of the user, from the memory  122  and allows the erasing mode setting screen  130  illustrated in  FIGS. 6A to 6D  to be displayed on the monitor  109 . The processor  121  acquires the operation signal from the operation unit  108  to read out heating temperature control data corresponding to the degree of freedom selecting portions  141  and  142  which receive the operation of the user, from the memory  122 , to output a heating temperature control signal for setting a heating temperature of the erasing unit  105  to the first heating temperature or the second heating temperature, to the erasing unit  105 . Further, the processor  121  measures, for example, surface temperatures of a heating roller  105 A and a pressure roller  105 B using a measurement result by a temperature sensor which is not illustrated and outputs the heating temperature control signal for maintaining the heating temperature at the first heating temperature or the second heating temperature to the erasing unit  105 . Further, in the second embodiment, the processor  121  acquires the operation signal from the operation unit  108  to control the operation of each part of the image erasing apparatus  100  described above. 
     The memory  122  is, for example, a semiconductor memory and includes a ROM (read only memory)  1221  and a RAM (random access memory)  1222 . The ROM  1221  stores various control programs for performing display control of the monitor  109 , heating temperature control of the erasing unit  105 , and the operation control of each part of the image erasing apparatus  100 . Further, the ROM  1221  stores display data for displaying the erasing mode setting screen  130  illustrated in  FIGS. 6A to 6D  and heating temperature control data regarding the first heating temperature and the second heating temperature. The RAM  1222  has a storage area as a working area which is temporally provided to the processor  121  when the processor  121  performs the above-mentioned control operation. 
     Hereinafter, an operation of the image erasing apparatus  100 , which controls the heating temperature of the erasing unit  105  based on the control of the control unit  120  to erase the image which is printed on the sheet S, will be described. The operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  51  reads out the display data of the erasing mode setting screen  130  illustrated in  FIG. 6A  from the ROM  1221 . The monitor  109  displays the erasing mode setting screen  130  illustrated in  FIG. 6A  (the erasing mode setting screen  130  in the erasing level mode) based on the read out display data, as an initial screen. 
     In the initial screen, the erasing level mode display portion  131  is displayed in black and the erasing temperature mode display portion  132 , the confidentiality mode display portion  133 , and the erasing attention mode display portion  134  are displayed in gray. By the difference in the display colors of the mode display portions  131  to  134 , the user may visually recognize that the erasing mode setting screen  130  is in the erasing level mode. Characters of the high erasing level are displayed on the first degree of freedom selecting portion  141  and characters of the low erasing level are displayed on the second degree of freedom selecting portion  142 . The user may determine the degree of freedom regarding whether to erase the image from the erasing level mode to select “high erasing level” or “low erasing level”. 
     In the erasing mode setting screen  130  in the erasing level mode, for example, the user touches the second degree of freedom selecting portion  142  to select “low erasing level” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism (a sheet feeding roller  102 , an aligning roller  103 , a conveying unit  104 , and a sheet discharging roller  107 ). The processor  121  reads out heating temperature data regarding the second heating temperature corresponding to the second degree of freedom selecting portion  142  from the ROM  1221  to output a heating temperature control signal for the second heating temperature to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed from the sheet feeding unit  101  by the conveyance mechanism, at the second heating temperature to erase the image. 
     In the erasing mode setting screen  130  in the erasing level mode, the user touches the first degree of freedom selecting portion  141  to select “high erasing level” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism. The processor  121  reads out heating temperature data regarding the first heating temperature corresponding to the first degree of freedom selecting portion  141  from the ROM  1221  to output a heating temperature control signal for the first heating temperature to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed by the conveyance mechanism, at the first heating temperature to erase the image. 
     In the initial screen of the erasing mode setting screen  130  illustrated in  FIG. 6A , the user selects the erasing temperature mode display portion  132 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  reads out the display data of the erasing mode setting screen  130  illustrated in  FIG. 6B  from the ROM  1221 . The monitor  109  displays the erasing mode setting screen  130  illustrated in  FIG. 6B  (the erasing mode setting screen  130  in the erasing temperature mode) based on the read out display data. 
     In the erasing mode setting screen  130  illustrated in  FIG. 6B , the erasing temperature mode display portion  132  is displayed in black and the erasing level mode display portion  131 , the confidentiality mode display portion  133 , and the erasing attention mode display portion  134  are displayed in gray. By the difference in the display colors of the mode display portions  131  to  134 , the user may visually recognize that the erasing mode setting screen  130  is in the erasing temperature mode. Further, characters of the high temperature are displayed on the first degree of freedom selecting portion  141  and characters of the low temperature are displayed on the second degree of freedom selecting portion  142 . The user may determine the degree of freedom regarding whether to erase the image from the erasing temperature mode to select “high temperature” or “low temperature”. 
     In the erasing mode setting screen  130  in the erasing temperature mode, for example, the user touches the second degree of freedom selecting portion  142  to select “low temperature” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism. The processor  121  outputs the heating temperature control signal for the second heating temperature corresponding to the second degree of freedom selecting portion  142  to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed from the sheet feeding unit  101  by the conveyance mechanism, at the second heating temperature to erase the image. 
     In the erasing mode setting screen  130  in the erasing temperature mode, for example, the user touches the first degree of freedom selecting portion  141  to select “high temperature” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism. Further, the processor  121  outputs the heating temperature control signal for the first heating temperature corresponding to the first degree of freedom selecting portion  141  to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed from the sheet feeding unit  101  by the conveyance mechanism, at the first heating temperature to erase the image. 
     In the initial screen of the erasing mode setting screen  130  illustrated in  FIG. 6A , the user selects the confidentiality mode display portion  133 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  reads out the display data of the erasing mode setting screen  130  illustrated in  FIG. 6C  from the ROM  1221 . The monitor  109  displays the erasing mode setting screen  130  illustrated in  FIG. 6C  (the erasing mode setting screen  130  in the confidentiality mode) based on the read out display data. 
     In the erasing mode setting screen  130  in the confidentiality mode illustrated in  FIG. 6C , the confidentiality mode display portion  133  is displayed in black and the erasing level mode display portion  131 , the erasing temperature mode display portion  132 , and the erasing attention mode display portion  134  are displayed in gray. By the difference in the display colors of the mode display portions  131  to  134 , the user may visually recognize that the erasing mode setting screen  130  is in the confidentiality mode. Further, characters of the high confidential are displayed on the first degree of freedom selecting portion  141  and characters of the low confidential are displayed on the second degree of freedom selecting portion  142 . The user may determine the degree of freedom regarding whether to erase the image from the confidentiality mode to select “high confidential” or “low confidential”. 
     In the erasing mode setting screen  130  in the confidentiality mode, for example, the user touches the second degree of freedom selecting portion  142  to select “low confidential” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism. Further, the processor  121  outputs the heating temperature control signal for the second heating temperature corresponding to the second degree of freedom selecting portion  142  to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed by the conveyance mechanism, at the second heating temperature to erase the image. 
     In the erasing mode setting screen  130  in the confidentiality mode, for example, the user touches the first degree of freedom selecting portion  141  to select “high confidential” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism. Further, the processor  121  outputs the heating temperature control signal for the first heating temperature corresponding to the first degree of freedom selecting portion  141  to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed by the conveyance mechanism, at the first heating temperature to erase the image. 
     In the initial screen of the erasing mode setting screen  130  illustrated in  FIG. 6A , the user selects the erasing attention mode display portion  134 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  reads out the display data of the erasing mode setting screen  130  illustrated in  FIG. 6D  from the ROM  1221 . The monitor  109  displays the erasing mode setting screen  130  illustrated in  FIG. 6D  (the erasing mode setting screen  130  in the erasing attention mode) based on the read out display data. 
     In the erasing mode setting screen  130  in the erasing attention mode illustrated in  FIG. 6D , the erasing attention mode display portion  134  is displayed in black and the erasing level mode display portion  131 , the erasing temperature mode display portion  132 , and the confidentiality mode display portion  133  are displayed in gray. By the difference in the display colors of the mode display portions  131  to  134 , the user may visually recognize that the erasing mode setting screen  130  is in the erasing attention mode. Further, characters of attention required are displayed on the first degree of freedom selecting portion  141  and characters of no attention required are displayed on the second degree of freedom selecting portion  142 . The user may determine the degree of freedom regarding whether to erase the image from the erasing attention mode to select “attention required” or “no attention required”. 
     In the erasing mode setting screen  130  in the erasing attention mode, for example, the user touches the second degree of freedom selecting portion  142  to select “no attention required” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism. Further, the processor  121  outputs the heating temperature control signal for the second heating temperature corresponding to the second degree of freedom selecting portion  142  to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed by the conveyance mechanism, at the second heating temperature to erase the image. 
     In the erasing mode setting screen  130  in the erasing attention mode, for example, the user touches the first degree of freedom selecting portion  141  to select “attention required” and operates the image erase starting key of the operation unit  108 . As a result, the operation unit  108  receives the operation by the user to output the operation signal to the processor  121 . The processor  121  drives the conveyance mechanism. Further, the processor  121  outputs the heating temperature control signal for the first heating temperature corresponding to the first degree of freedom selecting portion  141  to the erasing unit  105 . The erasing unit  105  heats an image printed on the sheet S, which is conveyed by the conveyance mechanism, at the first heating temperature to erase the image. 
     The user may select the mode for determining the degree of freedom from the plurality of mode display portions  131  to  134  which are menus selected by the user to exchange the erasing mode setting screen  130  of  FIGS. 6A to 6D . Therefore, the user may instinctively select the degree of freedom regarding whether to erase the image. 
     In the sheet feeding unit  101 , a sheet on which an image whose erasing temperature may be identified is printed (hereinafter, referred to as a sheet S 1 ), for example, a sheet on which the image is printed by the image forming apparatus  10  according to the first embodiment is accommodated. Specifically, a sheet on which the image is printed by the first toner having a high erasing temperature (hereinafter, referred to as a sheet S 11 ) and a sheet on which the image is printed by the second toner having a low erasing temperature (hereinafter, referred to as a sheet S 12 ) may be mixed to be accommodated in the sheet feeding unit  101 , or only the sheet S 11  may be accommodated in the sheet feeding unit  101 , or only the sheet S 12  may be accommodated in the sheet feeding unit  101 . In such a sheet accommodating state, in order to erase images on all sheets accommodated in the sheet feeding unit  101 , the heating temperature in the erasing unit  105  may be set to be high (first heating temperature). For example, in the erasing mode setting screen  130  in the erasing temperature mode, if the user touches the first degree of freedom selecting portion  141  to select the high temperature as the degree of freedom, the images on all sheets may be certainly erased at the first heating temperature. 
     In contrast, if only the sheet S 12  is accommodated in the sheet feeding unit  101 , in order to erase the images on all sheets accommodated in the sheet feeding unit  101 , the heating temperature in the erasing unit  105  may be high (first heating temperature) or may be low (second heating temperature). For example, in the erasing mode setting screen  130  in the erasing temperature mode, when the user touches the second degree of freedom selecting portion  142  to select the low temperature as the degree of freedom, the image may be erased with less power consumption. 
     The image printed on the sheet S 12  may be the image which may be erased without restrictions (for example, an image as a note) or an image having low confidentiality, or an image which does not require the attention to erase. Therefore, in the erasing mode setting screen  130  in the erasing level mode, even when the user touches the second degree of freedom selecting portion  142  to select the low erasing level as the degree of freedom, the image may be erased with less power consumption. In the erasing mode setting screen  130  in the confidentiality mode, even when the user touches the second degree of freedom selecting portion  142  to select the low confidential as the degree of freedom, the image may be erased with less power consumption. In the erasing mode setting screen  130  in the erasing attention mode, even when the user touches the second degree of freedom selecting portion  142  to select the no required attention as the degree of freedom, the image may be erased with less power consumption. As described above, the mode for determining the degree of freedom regarding whether to erase the image is changed to select the degree of freedom so that the user may erase the image with less power consumption. 
     In a case where the sheet S 11  and the sheet S 12  are mixed to be accommodated in the sheet feeding unit  101 , when the user wants to erase only the image on the sheet S 12  without erasing the image on the sheet S 11 , the heating temperature in the erasing unit  105  may be low. Therefore, for example, in the erasing mode setting screen  130  in the erasing temperature mode, when the user touches the second degree of freedom selecting portion  142  to select the low temperature as the degree of freedom, only the image on the sheet S 12  may be selectively erased without erasing the image on the sheet S 11 . Further, even when the user touches the second degree of freedom selecting portion  142  to select the low erasing level as the degree of freedom, only the image on the sheet S 12  may be selectively erased. In the erasing mode setting screen  130  in the confidentiality mode, even when the user touches the second degree of freedom selecting portion  142  to select the low confidential as the degree of freedom, only the image on the sheet S 12  may be selectively erased. In the erasing mode setting screen  130  in the erasing attention mode, even when the user touches the second degree of freedom selecting portion  142  to select the no attention required as the degree of freedom, only the image on the sheet S 12  may be selectively erased. As described above, before erasing the contents of the image on the sheet S, the user need not visually check the contents of the image whether the image printed on the sheet S is an image which is hardly permitted to be erased without restrictions or a high confidential image, or an image which requires an attention to erase the image, but the user may simply select the degree of freedom regarding whether to erase the image, so that it is possible to shorten the erasing time in the image erasing apparatus  100  and the high confidential image is not erroneously erased. Further, the image erasing apparatus  100  does not need a hardware configuration called as an image reading unit which checks the contents of the image on the sheet S 11  before being erased. 
     In the sheet feeding unit  101 , not only the sheet S 1 , but also a sheet on which the image is printed with an erasable toner whose erasing temperature is not identified (hereinafter, referred to as a sheet S 2 ) may be accommodated. Even in such a sheet accommodating state, in order to erase images on all sheets S 1  and S 2 , the heating temperature in the erasing unit  105  may be set to be high. For example, when the first heating temperature is set to a sufficiently high temperature, in the erasing mode setting screen  130  in the erasing temperature mode, the user touches the first degree of freedom selecting portion  141  to select the high temperature as the degree of freedom to erase the images, which are printed on all sheets S accommodated in the sheet feeding unit  101 , at the first heating temperature. 
     As described above, according to the image erasing apparatus  100  of the second embodiment, the user selects the degree of freedom regarding whether to erase the image so that the image may be erased at a heating temperature corresponding to the selected degree of freedom. The user may select the heating temperature which is the erasing process condition of the image. The user may select a mode that determines the degree of freedom regarding whether to erase the image and select the degree of freedom from the selected determination mode. 
     In the second embodiment, not only the sheet S whose image is erased, but also the sheet S whose image is not erased may be discharged by the sheet discharging roller  107 . Therefore, the discharged sheet S is scanned to inspect whether to erase the image and the discharging destination of the sheet S having an image and the sheet S having no image may be varied based on the inspecting result. 
     In the second embodiment, even though as the heating temperature, two types of temperatures, for example, high temperature and the low temperature are selected, the heating temperature may be selected from three or more types of different temperatures. In other words, three or more degree of freedom selecting portions illustrated in  FIG. 6  are provided and for example, in the case of the erasing level mode, the display of the degree of freedom selecting portion may be configured by a high erasing level, an intermediate erasing level, and a low erasing level. 
     Even though the first and second embodiments describe a case that both the image forming apparatus and the image erasing apparatus are single bodies, the image erasing apparatus of the second embodiment is provided in the image forming apparatus of the first embodiment and the fixing unit and the erasing unit may be shared. 
     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 fall within the scope and spirit of the inventions.