Patent Publication Number: US-8538283-B2

Title: Image forming apparatus having control unit

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to an image forming apparatus. In particular, the present invention relates to an image forming apparatus for forming an image on a continuous print medium having a long sheet shape. 
     In a conventional image forming apparatus for forming an image on a continuous print medium, when a print job is complete, the continuous print medium is cut. After the continuous print medium is cut, a printing operation is resumed (refer to Patent Reference).
     Patent Reference: Japan Patent Publication No. 2000-327189   

     As described above, in the conventional image forming apparatus, the continuous print medium is cut per every print job. Accordingly, it is necessary to reset the continuous print medium every time when the printing operation is resumed, thereby causing inconvenience. Further, when the continuous print medium is cut, a space is created in the continuous print medium. Accordingly, it is difficult to efficiently utilize the continuous print medium. 
     In view of the problems described above, an object of the present invention is to provide an image forming apparatus capable of solving the problems of the conventional image forming apparatus. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     In order to attain the objects described above, according to an aspect of the present invention, an image forming apparatus for printing an image on a continuous print medium includes an image processing unit for converting print data received to image data printable; a developer image forming unit for forming a developer image using specific developer according to the image data; a transfer unit for transporting the continuous print medium and transferring the developer image to the continuous print medium; and a control unit for instructing timings of the developer image forming unit to form the developer image and the transfer unit to transport the continuous print medium when the control unit receives a conversion process completion notice from the image processing unit. Further, it is arranged so that an initialization operation of the developer image forming unit is performed before the developer image forming unit forms the developer image. 
     In the present invention, it is possible to perform a print job without cutting the continuous print medium every time when the print job is completed. Accordingly, it is possible to efficiently use a space of the continuous print medium and reduce a printing time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view showing a main configuration of an image forming apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a block diagram showing a control system of the image forming apparatus according to the first embodiment of the present invention; 
         FIG. 3(   a ) is a time chart showing an operation control timing of the image forming apparatus according to the first embodiment of the present invention; 
         FIG. 3(   b ) is a time chart showing an operation timing of an initialization operation of the image forming apparatus according to the first embodiment of the present invention; 
         FIG. 4  is a block diagram showing a control system of an image forming apparatus according to a second embodiment of the present invention; and 
         FIG. 5  is a time chart showing an operation control timing of the image forming apparatus according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereunder, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     First Embodiment 
     A first embodiment of the present invention will be explained.  FIG. 1  is a schematic side view showing a main configuration of a color printer as an image forming apparatus  1  according to the first embodiment of the present invention. 
     As shown in  FIG. 1 , the image forming apparatus  1  includes a medium sheet supply mechanism  131 ; a printing unit  101 ; and a winding device  124 . The medium sheet supply mechanism  131  supplies a continuous print medium  102 . After the printing unit  101  prints on the continuous print medium  102 , the winding device  124  winds the continuous print medium  102 . 
     In the embodiment, the medium sheet supply mechanism  131  includes a medium stacker  132  for retaining the continuous print medium  102  wound in a roll shape; a medium detection unit  133  for detecting the continuous print medium  102  passing therethrough; and a second medium transportation unit  134 . The second medium transportation unit  134  pulls out the continuous print medium  102  from the medium stacker  132 , and transports the continuous print medium  102  thus pulled out to the printing unit  101 . 
     In the embodiment, the printing unit  101  has a configuration of a tandem type color electric photography printer capable of printing in four colors, i.e., black (K), yellow (Y), magenta (M), and cyan (C). Further, the printing unit  101  includes a sheet supply detection unit  103 ; a first medium transportation unit  104 ; a medium leading edge detection unit  105 ; an image forming unit (described later); a loosened medium detection unit  106 ; a fixing unit  121 ; a first discharge detection unit  122 ; and a second discharge detection unit  123  disposed in this order from an upstream side in a transportation direction that the continuous print medium  102  is transported. 
     In the embodiment, the image forming unit includes developing devices  151 K,  151 Y,  151 M, and  151 C (collectively referred to as a developing device  151 ) for black (K), yellow (Y), magenta (M), and cyan (C); and a transfer unit  152  having transfer belt drive units  108  and  109 ; a transfer belt  107 ; and transfer rollers  115 K,  115 Y,  115 M, and  115 C (collectively referred to as a transfer roller  115 ). The developing devices  151 K,  151 Y,  151 M, and  151 C as developer image forming units are arranged in this order from the upstream side in the transportation direction that the continuous print medium  102  is transported. 
     In the embodiment, the developing devices  151 K,  151 Y,  151 M, and  151 C arranged linearly have an identical configuration, and use toner as developer in difference colors, i.e., black (K), yellow (Y), magenta (M), and cyan (C). In the following description, the configuration of the developing device  151 K of black (K) will be explained as an example, and explanations of the configuration of the developing devices  151 Y,  151 M, and  151 C are omitted. 
     In the embodiment, the developing device  151 K of black (K) includes a photosensitive drum  110 K rotating in an arrow direction for supporting a toner developer image; a charge roller  111 K for charging a surface of the photosensitive drum  110 K; an exposure device  112 K formed of an LED (Light Emitting Diode) head for forming a static latent image on the surface of the photosensitive drum  110 K; a developing roller  113 K for developing the static latent image using toner to form the toner developer image; a toner supply roller  114 K for supplying toner from a toner tank (not shown) to the developing roller  113 K; a cleaning blade  116 K for removing toner remaining on the photosensitive drum  110 K after the toner developer image on the photosensitive drum  110 K is transferred to the continuous print medium  102 ; and a waste toner collection unit  117 K for collecting toner remaining on the photosensitive drum  110 K (waste toner) thus removed. 
     Similarly, the developing devices  151 Y,  151 M, and  151 C include photosensitive drums  110 Y,  110 M, and  110 C (collectively referred to as a photosensitive drum  110  including the photosensitive drum  110 K); charge rollers  111 Y,  111 M, and  111 C (collectively referred to as a charge roller  111  including the charge roller  111 K); exposure devices  1121 ,  112 M, and  112 C (collectively referred to as an exposure device  112  including the exposure device  112 K); developing rollers  113 Y,  113 M, and  113 C (collectively referred to as a developing roller  113  including the developing roller  113 K); toner supply rollers  114 Y,  114 M, and  114 C (collectively referred to as a toner supply roller  114  including the toner supply roller  114 K); cleaning blades  116 Y,  116 M, and  116 C (collectively referred to as a cleaning blade  116  including the cleaning blade  116 K); and waste toner collection units  117 Y,  117 M, and  117 C (collectively referred to as a waste toner collection unit  117  including the waste toner collection unit  117 K), respectively. 
     In the embodiment, the transfer roller  115 K of the transfer unit  152  is pressed against the photosensitive drum  110 K through the transfer belt  107  to rotate in an arrow direction. The transfer belt drive units  108  and  109  drive the transfer belt  107  to rotate in an arrow direction for transporting the continuous print medium  102 , so that the transfer roller  115 K transfers the toner image on the photosensitive drum  110 K to the continuous print medium  102 . 
     Accordingly, when the transfer belt  107  transports the continuous print medium  102  to pass through the developing device  151 K, the toner image in black is transferred to the continuous print medium  102 . Similarly, when the transfer belt  107  transports the continuous print medium  102  to pass through the developing devices  151 Y,  151 M, and  151 C, the toner image in yellow, the toner image in magenta, and the toner image in cyan are sequentially overlapped and transferred to the continuous print medium  102 . 
     In the embodiment, the fixing unit  121  includes a heating roller  121   a  and a pressing roller  121   b . After the developing device  151  and the transfer roller  115  sequentially overlap and transfer the toner images in colors to the continuous print medium  102 , the heating roller  121   a  and the pressing roller  121   b  presses and heats the toner images, so that the toner images are fixed to the continuous print medium  102 . After the toner images are fixed to the continuous print medium  102 , the winding device  124  disposed at a last stage winds the continuous print medium  102 . 
       FIG. 2  is a block diagram showing a control system of the image forming apparatus  1  according to the first embodiment of the present invention. The control system of the image forming apparatus  1  will be explained next with reference to  FIGS. 1 and 2 . 
     As shown in  FIG. 2 , the control system includes an image processing unit  201  for receiving print data from a host device such as a personal computer connected to the image forming apparatus  1 , and for converting the print data thus received to image data printable. The control system further includes a central control unit  202  connected to the medium leading edge detection unit  105 , the first discharge detection unit  122 , and the second discharge detection unit  123 . The medium leading edge detection unit  105 , the first discharge detection unit  122 , and the second discharge detection unit  123  are arranged in the image forming apparatus  1  as shown in  FIG. 1 . 
     In the embodiment, the control system further includes a fixing motor drive unit  203  for driving a fixing motor (not shown) to rotate the heating roller  121   a  and the pressing roller  121   b  of the fixing unit  121  (refer to  FIG. 1 ). The control system further includes a drum motor drive unit  204  for driving a drum motor (not shown) to rotate the photosensitive drum  110  (refer to  FIG. 1 ). The control system further includes a belt motor drive unit  205  for driving a belt motor (not shown) to drive the transfer belt drive units  108  and  109  (refer to  FIG. 1 ), thereby rotating the transfer belt  107 . 
     In the embodiment, the control system further includes a first medium transport motor drive unit  206  for driving a first sheet supply motor (not shown) to drive the first medium transportation unit  104  (refer to  FIG. 1 ). The control system further includes a second medium transport motor drive unit  207  for driving a second sheet supply motor (not shown) to drive the second medium transportation unit  134  (refer to  FIG. 1 ). The control system further includes a process control unit  208  formed of a high voltage power source  210  and the exposure device  112  (refer to  FIG. 1 ). 
     In the embodiment, the high voltage power source  210  is connected to the charge roller  111 , the developing roller  113 , the toner supply roller  114 , and the transfer roller  115  of the image forming unit for supplying a high voltage necessary for each component. The central control unit  202  is connected to the fixing motor drive unit  203 , the drum motor drive unit  204 , the belt motor drive unit  205 , the first medium transport motor drive unit  206 , the second medium transport motor drive unit  207 , and the high voltage power source  210  for instructing an operation of each component and controlling an entire operation of the image forming apparatus  1 . 
     An operation of the image forming apparatus  1  will be explained next with reference to time charts shown in  FIGS. 3(   a ) and  3 ( b ).  FIG. 3(   a ) is a time chart showing an operation control timing of the image forming apparatus  1  according to the first embodiment of the present invention. 
     When the image processing unit  201  receives the print data as a first print job from the host device, the image processing unit  201  deploys the print data to image information and converts the print data to the image data. After the image processing unit  201  converts the print data to the image data, the image processing unit  201  notifies the central control unit  202  that the conversion process is complete. 
     As shown in  FIG. 3(   a ), when the central control unit  202  receives the notice from the image processing unit  201  at a timing t 1 , the central control unit  202  sends signals to the drum motor drive unit  204 , the belt motor drive unit  205 , and the fixing motor drive unit  203  to drive the drum motor of the photosensitive drum  110 , the belt motor of the transfer belt  107 , and the fixing motor of the fixing unit  121 , respectively. At the same time, the central control unit  202  sends a signal to the process control unit  208  to instruct the high voltage power source  210 , so that an initialization operation of a process starts at the same time when the photosensitive drum  110  starts rotating. 
       FIG. 3(   b ) is a time chart showing an operation timing of the initialization operation of the image forming apparatus  1  according to the first embodiment of the present invention. 
     As shown in  FIG. 3(   b ), the high voltage power source  210  applies a voltage to the high voltage power source  210  at the same time when the photosensitive drum  110  starts rotating. When a position of the photosensitive drum  110  contacting with the charge roller  111  moves to a position contacting with the developing roller  113  upon rotating, the high voltage power source  210  applies a high voltage to the developing roller  113  and the toner supply roller  114 . Afterward, the high voltage thus applied is maintained for a period of time that the photosensitive drum  110  rotates at least one rotation since the photosensitive drum  110  starts rotating, thereby completing the initialization operation of the image forming apparatus  1 . 
     When the image forming apparatus  1  as the electro-photography printer starts a printing operation, it is necessary to establish a static state of a component dealing with static electricity such as the charge roller  111 , the developing roller  113 , the toner supply roller  114 , and the photosensitive drum  110  within a specific allowable range in a balanced state. With the initialization operation of the image forming apparatus  1  described above, it is possible to establish the balanced state. 
     After the initialization operation of the image forming apparatus  1 , the central control unit  202  sends a signal to the first medium transport motor drive unit  206  and the second medium transport motor drive unit  207  at a timing t 2 . Accordingly, the first sheet supply motor and the second sheet supply motor are driven, so that the first medium transportation unit  104  and the second medium transportation unit  134  start supplying the continuous print medium  102 . Note that the high voltage power source  210  applies a high voltage different from that in the initialization operation to the charge roller  111 , the developing roller  113 , and the toner supply roller  114  at the timing t 2  when the first sheet supply motor and the second sheet supply motor are driven (not shown). 
     When the continuous print medium  102  passes through the medium leading edge detection unit  105  at a timing t 3 , a sensor signal of the medium leading edge detection unit  105  changes. Accordingly, the central control unit  202  confirms that a leading edge of the continuous print medium  102  reaches the medium leading edge detection unit  105 . Afterward, the central control unit  202  sends the image data converted as printable data to the exposure device  112  at a timing t 4  after a specific period of time from when the leading edge of the continuous print medium  102  is detected. Accordingly, the exposure device  112  starts an exposure process to form the static latent image on the photosensitive drum  110 . 
     Afterward, the developing roller  113  develops the static latent image to form the toner image on the photosensitive drum  110 , and the transfer roller  115  transfers the toner image to the continuous print medium  102 . Then, the fixing unit  121  fixes the toner image to the continuous print medium  102 , thereby completing the printing operation. 
     In the description above, the transfer process of the developing device  151  and the transfer roller  115  with respect to the continuous print medium  102  is explained collectively. In an actual case, the developing devices  151 K,  151 Y,  151 M, and  151 C and the transfer rollers  115 K,  115 Y,  115 M, and  115 C operate at operation timings shifted by a time difference in timings when the continuous print medium  102  passes through different transfer positions corresponding to each color. 
     When the printing operation is complete at a timing t 5 , the central control unit  202  sends signals to the drum motor drive unit  204 , the belt motor drive unit  205 , the fixing motor drive unit  203 , the first medium transport motor drive unit  206 , and the second medium transport motor drive unit  207  to stop the belt motor, the fixing motor, the first sheet supply motor, and the second sheet supply motor, respectively. Further, the high voltage power source  210  stops applying the voltages to the charge roller  111 , the developing roller  113 , and the toner supply roller  114 . At this moment, the continuous print medium  102  stays in a stationary state on a transportation path. 
     In order to prevent the fixing unit  121  from excessively heating the continuous print medium  102 , it may be arranged to move at least one of the heating roller  121   a  and the pressing roller  121   b  of the fixing unit  121 , so that the heating roller  121   a  is situated away from the pressing roller  121   b . Further, when it is specified that the printing operation is performed on the continuous print medium  102 , a fixing temperature may be set to a lower level, so that it is controlled such that the continuous print medium  102  is transported at a slower transportation speed. 
     In the next step, when the image processing unit  201  receives the print data as a second print job from the host device, similar to the first print job, the image processing unit  201  deploys the print data to image information and converts the print data to the image data. After the image processing unit  201  converts the print data to the image data, the image processing unit  201  notifies the central control unit  202  that the conversion process is complete. 
     At this moment, a signal of the medium leading edge detection unit  105  or the first discharge detection unit  122  is turned on. Accordingly, when the central control unit  202  receives the notice from the image processing unit  201  at a timing t 6 , the central control unit  202  confirms that the central control unit  202  stays in the stationary state on the transportation path, and starts controlling the process. 
     More specifically, the central control unit  202  sends signals to the drum motor drive unit  204 , the belt motor drive unit  205 , the fixing motor drive unit  203 , the first medium transport motor drive unit  206 , and the second medium transport motor drive unit  207  to drive the drum motor, the belt motor, the fixing motor, the first sheet supply motor, and the second sheet supply motor, respectively. At the same time, the central control unit  202  sends a signal to the process control unit  208  to instruct the high voltage power source  210 , so that the initialization operation of the process starts at the same time when the photosensitive drum  110  starts rotating. The initialization operation is the same as that starting at the timing t 1  shown in  FIG. 3(   b ), and an explanation thereof is omitted. 
     In the initialization operation, it may be arranged to move at least one of the photosensitive drum  110  of the developing device  151  and the transfer belt  107 , so that the photosensitive drum  110  of the developing device  151  is situated and rotates away from the transfer belt  107 . In this case, it is not necessary to rotate the transfer belt  107 . 
     After the initialization operation, when the transfer belt  107  contacts with the photosensitive drum  110 , the heating roller  121   a  and the pressing roller  121   b  of the fixing unit  121  rotate to pull the continuous print medium  102 , thereby removing a slack of the continuous print medium  102 . Afterward, the transfer belt  107 , the first medium transportation unit  104 , and the second medium transportation unit  134  are driven. 
     When the initialization operation is complete, different from when the print data are printed for the first time, the continuous print medium  102  is situated on the transportation path already. Accordingly, the high voltage power source  210  applies a high voltage different from that in the initialization operation to the charge roller  111 , the developing roller  113 , and the toner supply roller  114  at a timing t 7  when the initialization operation is complete (not shown). Afterward, the central control unit  202  sends the image data converted as printable data to the exposure device  112  at a timing t 8  after a specific period of time. Accordingly, the exposure device  112  starts the exposure process to form the static latent image on the photosensitive drum  110 . 
     Afterward, similar to the printing operation of the print data for the first time after the timing t 4 , the developing roller  113  develops the static latent image to form the toner image on the photosensitive drum  110 , and the transfer roller  115  transfers the toner image to the continuous print medium  102 . Then, the fixing unit  121  fixes the toner image to the continuous print medium  102 , thereby completing the printing operation. 
     When the printing operation is complete at a timing t 9 , the central control unit  202  sends signals to the drum motor drive unit  204 , the belt motor drive unit  205 , the fixing motor drive unit  203 , the first medium transport motor drive unit  206 , and the second medium transport motor drive unit  207  to stop the belt motor, the fixing motor, the first sheet supply motor, and the second sheet supply motor, respectively. Further, the high voltage power source  210  stops applying the voltages to the charge roller  111 , the developing roller  113 , and the toner supply roller  114 . 
     As described above, in the embodiment, the image forming apparatus  1  resumes the printing operation without cutting the continuous print medium  102 . Accordingly, it is not necessary to set the continuous print medium  102  one more time every time when the print job is received and the printing operation is resumed. 
     Second Embodiment 
     A second embodiment of the present invention will be explained next.  FIG. 4  is a block diagram showing a control system of an image forming apparatus according to the second embodiment of the present invention. 
     In the image forming apparatus in the second embodiment shown in  FIG. 4 , different from the image forming apparatus  1  in the first embodiment shown in  FIG. 2 , a central control unit  302  includes a calculation unit  311  and a count unit  312 . According to the different configuration, the central control unit  302  operates in a different operation. 
     Components of the image forming apparatus in the second embodiment similar to those of the image forming apparatus  1  in the first embodiment are designated with the same reference numerals, and explanations thereof are omitted. Note that the image forming apparatus in the second embodiment includes the components similar to those of the image forming apparatus  1  in the first embodiment shown in  FIG. 1 , and the following description refers to  FIG. 1  as necessary. 
     As shown in  FIG. 4 , the central control unit  302  includes the count unit  312  for counting a period of time (described later) from when the first print job is complete to when the image processing unit  201  performs the conversion process on the next print job. The central control unit  302  further includes the calculation unit  311  for determining whether a measured value of the count unit  312  is within a specific period of time (described later). 
     An operation of the image forming apparatus will be explained next with reference to a time chart shown in FIG.  5 .  FIG. 5  is the time chart showing an operation control timing of the image forming apparatus according to the second embodiment of the present invention. 
     When the image processing unit  201  receives the print data as the first print job from the host device, the image processing unit  201  deploys the print data to the image information and converts the print data to the image data. After the image processing unit  201  converts the print data to the image data, the image processing unit  201  notifies the central control unit  202  that the conversion process is complete. 
     As shown in  FIG. 5 , when the central control unit  302  receives the notice from the image processing unit  201  at a timing t 11 , the central control unit  302  sends signals to the drum motor drive unit  204 , the belt motor drive unit  205 , and the fixing motor drive unit  203  to drive the drum motor, the belt motor, and the fixing motor, respectively. At the same time, the central control unit  302  sends a signal to the process control unit  208  to instruct the high voltage power source  210 , so that the initialization operation of the process starts at the same time when the photosensitive drum  110  starts rotating. The initialization operation is the same as that starting at the timing t 1  shown in  FIG. 3(   b ), and an explanation thereof is omitted. 
     After the initialization operation, the central control unit  302  sends a signal to the first medium transport motor drive unit  206  and the second medium transport motor drive unit  207  at a timing t 12 . Accordingly, the first sheet supply motor and the second sheet supply motor are driven, so that the first medium transportation unit  104  and the second medium transportation unit  134  start supplying the continuous print medium  102 . Note that the high voltage power source  210  applies a high voltage different from that in the initialization operation to the charge roller  111 , the developing roller  113 , and the toner supply roller  114  at the timing t 12  when the first sheet supply motor and the second sheet supply motor are driven (not shown). 
     When the continuous print medium  102  passes through the medium leading edge detection unit  105  at a timing t 13 , a sensor signal of the medium leading edge detection unit  105  changes. Accordingly, the central control unit  302  confirms that the leading edge of the continuous print medium  102  reaches the medium leading edge detection unit  105 . The operation up to this step is the same as that of the image forming apparatus  1  in the first embodiment. 
     Afterward, the central control unit  302  sends the image data converted as printable data to the exposure device  112  at a timing t 14  after a specific period of time from when the leading edge of the continuous print medium  102  is detected. Accordingly, the exposure device  112  starts the exposure process to form the static latent image on the photosensitive drum  110 . 
     While the static latent image is formed during the exposure process, when the image processing unit  201  receives the print data as the second print job from the host device at a timing t 15 , the image processing unit  201  deploys the print data to the image information and converts the print data to the image data. After the developing roller  113  develops the static latent image formed on the photosensitive drum  110  to form the toner image in the first print job, and the transfer roller  115  transfers the toner image to the continuous print medium  102 , the fixing unit  121  fixes the toner image to the continuous print medium  102 , thereby completing the printing operation. 
     When the printing operation is complete at a timing t 16 , the central control unit  302  sends signals to the drum motor drive unit  204 , the belt motor drive unit  205 , the fixing motor drive unit  203 , the first medium transport motor drive unit  206 , and the second medium transport motor drive unit  207  to stop the belt motor, the fixing motor, the first sheet supply motor, and the second sheet supply motor, respectively. Further, the high voltage power source  210  stops applying the voltages to the charge roller  111 , the developing roller  113 , and the toner supply roller  114 . At this moment, the continuous print medium  102  stays in the stationary state on the transportation path. 
     At this moment, the image processing unit  201  has not completed the transfer process. Accordingly, the central control unit  302  controls the count unit  312  to start counting at the timing t 16  when the printing operation of the first print job is complete, thereby measuring a wait time T until a timing t 17  when the image processing unit  201  completes the conversion process of the second print job. More specifically, when the image processing unit  201  notifies the central control unit  302  that the conversion process is complete, the count unit  312  stops counting. Then, the calculation unit  311  determines whether a measured value of the count unit  312  at this moment is within the specific period of time. 
     In the embodiment, the specific period of time is determined according to a dark decay time of the photosensitive drum  110  of the printing unit  101 , and does not affect on the printing operation. More specifically, the specific period of time may be set to two seconds within which the photosensitive drum  110  does not decay to an extent that the initialization operation is necessary. A dark decay is a phenomenon in which a surface potential of the photosensitive drum  110  decays even in a dark place due to charged carriers or thermally excited carriers after the charge roller  111  charges the surface of the photosensitive drum  110 . 
     In the next step, when the image processing unit  201  notifies the central control unit  302  that the conversion process is complete or the printing operation is ready to start at a timing t 17 , the central control unit  302  determines whether the wait time T is within the specific period of time (two seconds in the embodiment). When the central control unit  302  determines that the wait time T is within the specific period of time, the central control unit  302  determines that the initialization operation is not necessary. 
     Accordingly, without performing the initialization operation shown in  FIG. 3(   b ), the central control unit  302  sends the signals to the drum motor drive unit  204 , the belt motor drive unit  205 , the fixing motor drive unit  203 , the first medium transport motor drive unit  206 , and the second medium transport motor drive unit  207  to drive the drum motor, the belt motor, the fixing motor, the first sheet supply motor, and the second sheet supply motor, respectively. Afterward, the central control unit  302  sends the image data converted as printable data to the exposure device  112  at a timing t 18  after a specific period of time. Accordingly, the exposure device  112  starts the exposure process to form the static latent image on the photosensitive drum  110 . 
     Note that the high voltage power source  210  applies a high voltage different from that in the initialization operation to the charge roller  111 , the developing roller  113 , and the toner supply roller  114  at the timing t 17  when the first sheet supply motor and the second sheet supply motor are driven (not shown). 
     Afterward, the developing roller  113  develops the static latent image to form the toner image on the photosensitive drum  110 , and the transfer roller  115  transfers the toner image to the continuous print medium  102 . Then, the fixing unit  121  fixes the toner image to the continuous print medium  102 , thereby completing the printing operation. 
     When the printing operation is complete at a timing t 19 , the central control unit  302  sends signals to the drum motor drive unit  204 , the belt motor drive unit  205 , the fixing motor drive unit  203 , the first medium transport motor drive unit  206 , and the second medium transport motor drive unit  207  to stop the belt motor, the fixing motor, the first sheet supply motor, and the second sheet supply motor, respectively. Further, the high voltage power source  210  stops applying the voltages to the charge roller  111 , the developing roller  113 , and the toner supply roller  114 . 
     When the central control unit  302  determines that the wait time T is not within the specific period of time, the central control unit  302  determines that the initialization operation is necessary. Accordingly, similar to the process after the timing t 6  shown in  FIG. 3(   a ), the initialization operation of the process starts at the same time when the photosensitive drum  110  starts rotating. Afterward, the central control unit  302  sends the image data to the exposure device  112 , so that the exposure device  112  starts the exposure process to form the static latent image on the photosensitive drum  110 . The process after this step is similar to that described above. 
     As described above, in the embodiment, the central control unit  302  includes the calculation unit  311  and the count unit  312 . Accordingly, even when the second print data are processed after a relatively long period of time after the first print data are processed, it is possible to continue the printing operation without performing the initialization operation when it is within the specific period of time. Accordingly, it is possible to efficiently print on the continuous print medium. 
     In the embodiments described above, the tandem type color electric photography printer capable of printing in four colors, i.e., black (K), yellow (Y), magenta (M), and cyan (C) is explained as the image forming apparatus. The present invention is not limited thereto, and is applicable to a monochrome printer as far as the image forming apparatus is an electro-photography apparatus for printing on a continuous medium. 
     The disclosure of Japanese Patent Application No. 2008-268183, filed on Oct. 17, 2008, is incorporated in the application by reference. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.