Patent Publication Number: US-8532558-B2

Title: Printing machine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application Nos. 2010-002026, filed on Jan. 7, 2010, and 2010-261293, filed on Nov. 24, 2010, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printing machine which can reduce a time period required to complete printing. 
     2. Description of the Related Art 
     Recently, a printing machine has widely spread which is connected to a computer through a network, receives image data generated by the computer through the network, and performs printing based on the received data. 
     As a device for appropriately controlling a printing process of such printing machine, Japanese Patent No. 3989208 proposes a print control device which terminates a control operation either upon completion of all procedures in a printing process or upon detection of an error while the printing process is in progress. 
     Meanwhile, Japanese Unexamined Patent Application Publication No. 08-63306 discloses a printing machine configured as follows. The printing machine calculates reception time required for receiving print data of multiple pages to be received in a current session, on the bases of average reception time of print data of one page. In addition, the printing machine calculates the minimum print time required to print the multiple pages to be received in the current session on the basis of the minimum print time of one page. When the print data corresponding to the number of pages that can be received in a time by which the printing data take longer to receive than to print is stored, the printing machine starts printing the stored print data. 
     SUMMARY OF THE INVENTION 
     However, the print control device disclosed in Japanese Patent No. 3989208 and the printing machine disclosed in Japanese Unexamined Patent Application Publication No. 08-63306 start printing after reception of the print data for a first page is completed. For this reason, quite a lot of time is required before starting printing, and therefore, time for completing printing is made longer as a consequence. 
     An object of the present invention is to provide a printing machine which is capable of reducing a time period before starting printing and thereby reducing a time period to complete printing. 
     An aspect of the present invention is a printing machine comprising: a reception unit configured to receive image data; a printing unit configured to print on a print medium based on the image data received by the reception unit; a first paper feeding unit configured to take out and convey a print medium on a paper feed tray one by one; a second paper feeding unit configured to convey a print medium conveyed by the first paper feeding unit to the printing unit; and a print control unit configured to drive the first paper feeding unit to start conveyance of a print medium upon start of reception of the image data by the reception unit. 
     According to this aspect, the first paper feeding unit is caused to start the conveyance of the print medium when the reception unit starts receiving the image data. Hence, there is no need to wait for completion of reception of the image data by the reception unit, and a time period until starting printing is reduced. In this way, it is possible to obtain a first printed material earlier than the related art. 
     The printing machine may further comprise a transfer unit configured to transfer the image data received by the reception unit to the printing unit, wherein the print control unit is configured to drive the second paper feeding unit to start conveyance of a print medium upon completion of transfer of the image data corresponding to a prescribed number of lines by the transfer unit. 
     According to this configuration, the second paper feeding unit is caused to start conveyance of the print medium when the transfer unit completes transfer of the image data corresponding to the prescribed number of lines. Hence, there is no need to wait for completion of transfer of the image data by the transfer unit, and a time period until starting printing is reduced. 
     The printing machine may further comprise a reception condition monitoring unit configured to monitor a condition of reception of the image data by the reception unit, wherein the print control unit is configured to drive the printing unit to abort printing and to deliver a print medium out of the printing unit upon judgment of failure of reception of the image data by the reception condition monitoring unit after start of reception of the image data and before completion of the reception. 
     According to this configuration, when the reception condition monitoring unit judges, after start of reception of the image data, that reception of the image data has failed before completion of reception of the image data corresponding to one sheet, the printing unit is caused to abort printing and the print medium is delivered out from the printing unit. Hence the paper sheet will not remain inside the device, and a user is not bothered by removing of a jammed sheet. 
     The printing machine may further comprise: a detecting unit configured to detect a leading edge of a print medium to be conveyed from the second paper feeding unit to the printing unit; a paper discharge unit configured to discharge a print medium delivered from the printing unit out of the printing machine; a reversing unit configured to turn over a print medium delivered from the printing unit and to convey the print medium as turned over to the second paper feeding unit; a switching unit configured to guide a print medium delivered from the printing unit to any one of the paper discharge unit and the reversing unit; and a discharge control unit, upon judgment of failure of reception of the image data by the reception condition monitoring unit after start of reception of the image data and before completion of the reception, configured to switch the switching unit to guide a print medium to the paper discharge unit when the leading edge of the print medium is detected by the detecting unit, and to switch the switching unit to guide a print medium to the reversing unit when the leading edge of the print medium is not detected by the detecting unit. 
     According to this configuration, when the reception condition monitoring unit judges, after start of reception of the image data, that reception of the image data has failed before completion of reception of the data corresponding to one sheet, the switching unit is switched so as to guide the print medium to the paper discharge unit in a case where the leading edge of the print medium is detected by the detection unit, while the switching unit is switched so as to guide the print medium to the reversing unit in a case where the leading edge of the print medium is not detected by the detection unit. Hence it is possible to reuse the print medium if the print medium is reusable. It is also possible to cause the switching unit to perform the switching process depending on detection of the leading edge of the paper sheet by the detection unit and on a lapse of a time period required for the leading edge of the paper sheet to reach the printing unit after detection by the detection unit (a time period calculated by dividing a distance between the detection unit and the printing unit by a conveyance speed). In this case, it is possible to judge whether or not the print medium is reusable more precisely, and thereby to reduce wasting of the print medium. 
     The printing machine may further comprise: a detecting unit configured to detect a leading edge of a print medium to be conveyed from the second paper feeding unit to the printing unit; a paper discharge unit configured to discharge a print medium delivered from the printing unit out of the printing machine; a reversing unit configured to turn over a print medium delivered from the printing unit and to convey the print medium as turned over to the second paper feeding unit; a switching unit configured to guide a print medium delivered from the printing unit to any one of the paper discharge unit and the reversing unit; and a discharge control unit, upon judgment of failure of reception of the image data by the reception condition monitoring unit after start of reception of the image data and before completion of the reception, configured to switch the switching unit to guide a print medium to the paper discharge unit when the leading edge of the print medium is detected by the detecting unit, and to switch the switching unit to guide a print medium to one of the paper discharge unit and the reversing unit in accordance with a type of the print medium set based on external input when the leading edge of the print medium is not detected by the detecting unit. 
     According to this configuration, when the reception condition monitoring unit judges, after start of reception of the image data, that reception of the image data has failed before completion of reception of the data corresponding to one sheet, the switching unit is switched so as to guide the print medium to the paper discharge unit in a case where the leading edge of the print medium is detected by the detection unit, while the switching unit is switched so as to guide the print medium to any one of the paper discharge unit and the reversing unit depending on the type of the print medium set up based on the external input in a case where the leading edge of the print medium is not detected by the detection unit. Hence it is possible to reuse the print medium if the print medium is reusable. 
     The print control unit may be configured to drive the first paper feeding unit to convey only a single print medium upon start of reception of the image data by the reception unit, and control the first paper feeding unit to enable the second paper feeding unit to convey a print medium at a prescribed sheet interval after completion of printing on the conveyed single print medium by the printing unit. 
     According to this configuration, when the reception unit starts reception of the image data, the first paper feeding unit is caused to convey only a single sheet of the print medium. In addition, the first paper feeding unit is controlled in a way that the second paper feeding unit can convey the print media at a prescribed sheet interval after the printing unit completes printing on the conveyed single printed medium. Hence it is possible to perform printing more stably. 
     The print control unit may be configured to drive the first paper feeding unit to convey only a single print medium upon start of reception of the image data by the reception unit, and control the first paper feeding unit to enable the second paper feeding unit to convey a print medium at a prescribed sheet interval after completion of transfer of the image data for the single print medium by the transfer unit. 
     According to this configuration, when the reception unit starts reception of the image data, the first paper feeding unit is caused to convey only a single sheet of the print medium. In addition, the first paper feeding unit is controlled in a way that the second paper feeding unit can convey the print media at a prescribed sheet interval after the transfer unit completes transfer of the image data for the single printed medium. Hence it is possible to perform printing more stably. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall configuration diagram showing an overall configuration of a printing machine according to a first embodiment of the present invention. 
         FIG. 2  is a functional configuration diagram showing a functional configuration of the printing machine according to the first embodiment of the present invention. 
         FIG. 3  is a flowchart showing a print starting process in the printing machine according to the first embodiment of the present invention. 
         FIG. 4A  is a timing chart showing processes from reception of image data to paper discharge in a related art, and  FIG. 4B  is a timing chart showing processes from reception of image data to paper discharge by the printing machine in the first embodiment of the present invention. 
         FIGS. 5A and 5B  are timing charts showing processes from reception of image data to paper discharge by the printing machine in the first embodiment of the present invention. 
         FIG. 6  is a flowchart showing a copy starting process in the printing machine according to the first embodiment of the present invention. 
         FIG. 7A  is a timing chart showing processes from reading of image data to paper discharge in the related art, and  FIG. 7B  is a timing chart showing processes from reading of image data to paper discharge in the printing machine according to the first embodiment of the present invention. 
         FIG. 8  is a flowchart showing a print monitoring process in the printing machine according to the first embodiment of the present invention. 
         FIG. 9A  is a timing chart showing processes from reception of image data to paper discharge in two-side printing in the related art, and  FIG. 9B  is a timing chart showing processes from reception of image data to paper discharge in two-side printing by the printing machine according to the first embodiment of the present invention. 
         FIG. 10A  is a timing chart showing processes from reading of image data to paper discharge in two-side printing in the related art, and  FIG. 10B  is a timing chart showing processes from reading of image data to paper discharge in two-side printing by the printing machine according to the first embodiment of the present invention. 
         FIG. 11  is a timing chart showing processes from reception of image data to paper discharge in a printing machine according to a second embodiment of the present invention. 
         FIG. 12  is a timing chart showing processes from reception of image data to paper discharge in a printing machine according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Embodiments of the present invention will be described with reference to the accompanying drawings. 
     (First Embodiment) 
     A first embodiment of the present invention will describe an inkjet printing machine as an example. The inkjet printing machine is configured to execute a printing process in which printing is performed in response to a request from a terminal connected via a network and a copying process in which printing is performed based on an operation of an operating unit by a user. 
     (Overall Configuration of Printing Machine) 
       FIG. 1  is an overall configuration diagram showing an overall configuration of a printing machine  1  according to the first embodiment of the present invention. Arrows illustrated in  FIG. 1  explain flow of a print medium. 
     As shown in  FIG. 1 , a printing machine  1  includes an image reader  2  and an image forming part  3 . 
     The image reader  2  is provided on the image forming part  3 . Although not illustrated, the image reader  2  includes a contact glass used for placing a manuscript thereon, a cover provided attachably to and detachably from this contact glass, a scanning unit configured to scan the manuscript placed on the contact glass, a lens configured to focus a scanned image, and an image processor configured to process a focused image. 
     The image reader  2  causes the scanning unit to scan the manuscript placed on the contact glass one line at a time, and causes the image processor to process the scanned image, thereby reading the image data to be printed by the image forming part  3 . 
     The image forming part  3  includes a side paper feeder  10 , an internal paper feeder  20 , a printing unit  30 , a paper discharge unit  40 , and a reversing unit  50 . 
     The side paper feeder  10  includes a paper feed tray  11  on which print paper sheets W are stacked, a primary paper feeder  12  configured to convey only the topmost print paper sheet W on the paper feed tray  11  onto a paper feed system conveyance path FR, and a secondary paper feeder  14  configured to convey the print paper sheet W conveyed by the primary paper feeder  12  to the printing unit  30 . The print paper sheet W conveyed on the paper feed system conveyance path FR by the primary paper feeder  12  comes into contact with the secondary paper feeder  14 , whereby a leading edge of the print paper sheet W is aligned and an inclination thereof is corrected. Then, the print paper sheet W is conveyed on a circulation system conveyance path CR to the printing unit  30  at prescribed timing. 
     The internal paper feeder  20  includes a paper feed tray  21   a  on which print paper sheets W are stacked, a primary paper feeder  22   a  configured to convey only the topmost print paper sheet W on the paper feed tray  21   a  onto the paper feed system conveyance path FR, a paper feed tray  21   b  on which print paper sheets W are stacked, a primary paper feeder  22   b  configured to convey only the topmost print paper sheet W on the paper feed tray  21   b  onto the paper feed system conveyance path FR, a paper feed tray  21   c  on which print paper sheets W are stacked, a primary paper feeder  22   c  configured to convey only the topmost print paper sheet W on the paper feed tray  21   c  onto the paper feed system conveyance path FR, a paper feed tray  21   d  on which print paper sheets W are stacked, and a primary paper feeder  22   d  configured to convey only the topmost print paper sheet W on the paper feed tray  21   d  onto the paper feed system conveyance path FR. 
     Each of the print paper sheets W conveyed onto the paper feed system conveyance path FR by the primary paper feeders  22   a ,  22   b ,  22   c , and  22   d  is conveyed on the paper feed system conveyance path FR by multiple conveyance rollers  23  and the like which are disposed on the paper feed system conveyance path FR. Thereafter, the print paper sheet W comes into contact with the secondary paper feeder  14 , whereby the leading edge of the print paper sheet W is aligned and an inclination thereof is corrected. Then, the paper sheet W is conveyed on the circulation system conveyance path CR to the printing unit  30  at prescribed timing. 
     The printing unit  30  includes a head unit  31  incorporating multiple print heads, and an annular conveyance belt  32  provided so as to face the head unit  31 . The print paper sheet W fed by the secondary paper feeder  14  is suctioned on the conveyance belt  32  by unillustrated suctioning means disposed inside the annular conveyance belt  32 , then conveyed at a speed determined in accordance with a printing condition. Thereafter, printing is performed on the print paper sheet W one line at a time with inks ejected from the head unit  31 . Then, the print paper sheet W is discharged. The printing unit  30  includes a top edge sensor  33  configured to detect the leading edge of the print paper sheet W to be conveyed to the head unit  31 . The timing for starting printing is adjusted based on detection of the leading edge of the print paper sheet W by the top edge sensor  33 . 
     The print paper sheet W printed by and discharged from the printing unit  30  is conveyed on the circulation system conveyance path CR by use of conveyance rollers and the like disposed on the circulation system conveyance path CR. A switching mechanism  43  is provided on the circulation system conveyance path CR and is configured to switch whether to guide the print paper sheet W conveyed on the circulation system conveyance path CR to the paper discharge unit  40  or to recirculate the print paper sheet W on the circulation system conveyance path CR (to guide the print paper sheet W to the reversing unit  50 ). 
     The paper discharge unit  40  includes a paper receiving tray  41  having a tray-like shape protruding from an enclosure of the printing machine  1 , and a pair of discharge rollers  42  configured to guide the print paper sheet W to the paper receiving tray  41 . Moreover, the print paper sheet W printed by the printing unit  30  is conveyed to the paper receiving tray  41  by the discharge rollers  42  and is stacked on the paper receiving tray  41  with the printed surface facing downward. 
     The reversing unit  50  includes a reversing tray  51  for reversing the print paper sheet W, and reversing rollers  52  configured to convey the print paper sheet W from the circulation system conveyance path CR to the reversing tray  51  and from the reversing tray  51  to the circulation system conveyance path CR. 
     The print paper sheet W guided to the reversing unit  50  by the switching mechanism  43  is conveyed from the circulation system conveyance path CR to the reversing tray  51  by the reversing rollers  52 , and is conveyed from the reversing tray  51  to the circulation system conveyance path CR after a lapse of a prescribed time period. Hence the print paper sheet W is turned over relative to the circulation system conveyance path CR. Thereafter, the print paper sheet W thus turned over is conveyed on the circulation system conveyance path CR by multiple rollers such as conveyance rollers  53  provided on the circulation system conveyance path CR, and comes into contact the secondary paper feeder  14 , whereby the leading edge of the print paper sheet W is aligned and the inclination thereof is corrected. Then, the print paper sheet W is conveyed on the circulation system conveyance path CR to the printing unit  30  at prescribed timing. 
     (Functional Configuration of Printing Machine) 
       FIG. 2  is a functional configuration diagram showing a functional configuration of the printing machine  1  according to the first embodiment of the present invention. 
     As shown in  FIG. 2 , the printing machine  1  according to the first embodiment of the present invention is connected to a terminal  100  via a network  9 . 
     The terminal  100  generates image data and transmits the generated image data to the printing machine  1  via the network  9  by executing software. 
     The printing machine  1  includes the image reader  2  and the image forming part  3 . 
     The image forming part  3  includes the side paper feeder  10 , the internal paper feeder  20 , the printing unit  30 , the paper discharge unit  40 , the reversing unit  50 , an operating unit  60 , a controller  70 , a network interface  81 , and an external interface  82 . Among these constituents, the side paper feeder  10 , the internal paper feeder  20 , the printing unit  30 , the paper discharge unit  40 , and the reversing unit  50  have already been described, and description thereof will be omitted. 
     The operating unit  60  is provided in an upper portion of the printing machine  1 , and is provided with a display/input panel  61  and various operating keys such as a start key to start reading, printing, and so forth, a stop key to stop reading, printing, and so forth, a numerical keypad to input the number of prints and the like (none of them are shown). The operating unit  60  supplies operating signals based on operations by a user to the controller  70 . 
     The display/input panel  61  of the operating unit  60  includes a transparent touch panel either of a pressure sensitive type or of an electrostatic type disposed on a front surface, and a liquid crystal display panel disposed on a back surface of this touch panel (none of them are shown). The user directly touches the surface of the touch panel with the finger while viewing the display screen of the liquid crystal display panel to perform various setting input operations such as a setting of a one-side printing mode or a two-side printing mode, and setting of types of print paper sheets for the paper feed tray  11  and the paper feed trays  21   a  to  21   d.    
     The network interface  81  is a communication interface such as a network card. By connecting the printing machine  1  to the network  9  using this network interface  81 , the image data are received from the terminal  100  connected to the network  9 , and various signals are transmitted and received. 
     The external interface  82  is a connection interface with the image reader  2 , and supplies the image data read by the image reader  2  to the controller  70 . 
     The controller  70  performs central control of the printing machine  1 . From the viewpoints of functions thereof, the controller  70  includes a reception unit  70   a , a transfer unit  70   b , a print control unit  70   c , a reception condition monitoring unit  70   d , and a discharge control unit  70   e.    
     The reception unit  70   a  receives the image data transmitted from the terminal  100  via the network interface  81 . The reception unit  70   a  also receives the image data transmitted from the image reader  2  via the external interface  82 . 
     The transfer unit  70   b  transfers the image data received by the reception unit  70   a  to the printing unit  30 . 
     When the reception unit  70   a  starts reception of the image data, the print control unit  70   c  causes the primary paper feeder  12  to start conveyance of the print paper sheet W. When the transfer of the image data corresponding to a prescribed number of lines is completed by the transfer unit  70   b , the print control unit  70   c  causes the secondary paper feeder  14  to start conveyance of the print paper sheet W. Further, when the reception condition monitoring unit  70   d  judges that the reception of the image data has failed, the print control unit  70   c  aborts printing by the printing unit  30  and causes the printing unit  30  to discharge the print paper sheet W. 
     The reception condition monitoring unit  70   d  monitors a condition of reception of the image data by the reception unit  70   a.    
     In a case where the leading edge of the print paper sheet W is detected by the top edge sensor  33  when the reception condition monitoring unit  70   d  judges that the reception of the image data has failed, the discharge control unit  70   e  switches the switching mechanism  43  so as to guide the print paper sheet W to the paper discharge unit  40 . In a case where the tip of the printed sheet W is not detected by the top edge sensor  33  when the reception condition monitoring unit  70   d  judges that the reception of the image data has failed, the discharge control unit  70   e  switches the switching mechanism  43  so as to guide the print paper sheet W to any one of the paper discharge unit  40  and the reversing unit  50  depending on the type of the print paper sheet W set up based on the external input. 
     (Actions of Printing Machine) 
     Next, actions of the printing machine  1  according to the first embodiment of the present invention will be described. 
     The printing machine  1  according to the first embodiment of the present invention mainly performs a print starting process, a copy starting process, and a print monitoring process. The processes will be described below in detail. 
     (Print Starting Process) 
     Details of the print starting process in the printing machine  1  according to the first embodiment of the present invention will be described. 
       FIG. 3  is a flowchart showing the print starting process in the printing machine  1  according to the first embodiment of the present invention. Here, a case of printing an image on the print paper sheet W stacked on the paper feed tray  11  of the side paper feeder  10  will be described as an example. 
     As shown in  FIG. 3 , the reception unit  70   a  of the controller  70  judges whether or not the image data transmitted from the terminal  100  via the network  9  are received (step S 101 ). When a judgment is made in step S 101  that the image data are received (YES), the controller  70  calculates prescribed numbers of lines L A  and L B  as described below (step S 102 ). 
     The controller  70  calculates the prescribed number of lines L A  for performing transmission of the image data so that the transfer of the image data from the transfer unit  70   b  to the printing unit  30  does not proceed ahead of the reception of the image data by the reception unit  70   a . For example, if a reception speed Vr of the image data by the reception unit  70   a  is equal to or faster than a transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30 , the controller  70  sets the prescribed number of lines L A  to “1”. If the reception speed Vr of the image data by the reception unit  70   a  is slower than the transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30 , the controller  70  calculates the prescribed number of lines L A  by use of the following (formula 1). Here, the number of total lines in the image data is defined as N. As for the number N, if such value is included in header information or the like sent together with the image data, this value may be used. Alternatively, a value estimated from the size of the manuscript included in the header information or the like may be used. In the following (formula 1), ROUNDUP indicates a function to round a numerical value in parenthesis up to the nearest integer. The same applies to (formula 2) to (formula 5) to be described later.
 
 L   A =ROUNDUP[ N× (1 −Vr/Vt )]+1  (formula 1)
 
     The controller  70  calculates the prescribed number of lines L B  for performing printing so that the printing by the printing unit  30  do not proceed ahead of the transfer of the image data from the transfer unit  70   b  to the printing unit  30  and so that the printing by the printing unit  30  is performed after the printing preparation and the (primary) paper feeding is completed. Firstly, the controller  70  calculates a candidate B 1  for the prescribed number of lines. Specifically, if the transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30  is equal to or faster than a printing speed Vp by the printing unit  30 , the controller  70  sets the candidate B 1  for the prescribed number of lines to “L A +1”. If the transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30  is slower than the printing speed Vp by the printing unit  30 , the controller  70  calculates the candidate B 1  for the prescribed number of lines by use of the following (formula 2). Here, the number of total lines in the image data is defined as N.
 
 B 1=ROUNDUP{[ N× (1 −Vt/Vp )+1 ]×Vr/Vt}+L   A   (formula 2)
 
     Next, the controller  70  calculates a candidate B 2  for the prescribed number of lines. Specifically, the controller  70  defines a “number obtained by converting a total time period of a time period for the printing preparation and a time period for the (primary) paper feeding into the number of lines in the reception” as the candidate B 2  for the prescribed number of lines. 
     Then, the controller  70  determines a larger one of the calculated candidate B 1  for the prescribed number of lines and candidate B 2  for the prescribed number of lines as the prescribed number of lines L B . 
     After step S 102 , the processing goes to steps S 103 , S 104 , or S 106 . 
     In step S 103 , the controller  70  firstly performs the printing preparation. Specifically, the controller  70  causes the paper feed tray  11  on which the print paper sheets W appropriate for the received image data are stacked to be in a state capable of feeding the topmost print paper sheet W, and also performs a process to warm inks, for example. In the case of a printing machine having a structure in which a bottom plate disposed at the bottom inside the paper feed tray is moved vertically in response to a remaining amount of the print paper sheets, the process for causing the paper feed tray  11  to be in a state capable of feeding the topmost print paper sheet W includes a process to lift the tray bottom plate up to a prescribed height so that the print paper sheet can be supplied onto the conveyance path. 
     After completing the printing preparation, the print control unit  70   c  of the controller  70  causes the primary paper feeder  12  to start paper feeding. Specifically, the print control unit  70   c  causes the primary paper feeder  12  to convey only the topmost print paper sheet W from the paper feed tray  11  onto the paper feed system conveyance path FR. In this way, the print paper sheet W thus conveyed is in contact with the secondary paper feeder  14  after reception of the image data corresponding to the candidate B 2  for the prescribed number of lines. 
     In step S 104 , the print control unit  70   c  of the controller  70  judges whether or not the image data corresponding to the prescribed number of lines L A  have been received already. 
     When a judgment is made in step S 104  that the image data corresponding to the prescribed number of lines L A  have been received already (YES), the transfer unit  70   b  of the controller  70  starts data transfer of the image data received by the reception unit  70   a  to the printing unit  30  (step S 105 ). 
     In step S 106 , the print control unit  70   c  of the controller  70  judges whether or not the image data corresponding to the calculated prescribed number of lines L B  have been received already. 
     When a judgment is made in step S 106  that the image data corresponding to the prescribed number of lines L B  have been received already (YES), the print control unit  70   c  of the controller  70  causes the secondary paper feeder  14  and the printing unit  30  to start the printing process (secondary paper feeding and printing) (step S 107 ). Specifically, in accordance with an instruction given by the print control unit  70   c , the secondary paper feeder  14  conveys the print paper sheet W in contact therewith onto the circulation system conveyance path CR to the printing unit  30 . Thereafter, the print paper sheet W conveyed to the printing unit  30  by the secondary paper feeder  14  is suctioned on the conveyance belt  32 , and then subjected to printing one line at a time with the inks ejected from the head unit  31  of the printing unit  30  while being conveyed at the printing speed Vp. Then, the print paper sheet W is delivered. Subsequently, the paper discharge unit  40  discharges the print paper sheet thus delivered (step S 108 ). 
       FIG. 4A  is a timing chart showing processes from the reception of the image data to the paper discharge in the related art.  FIGS. 4B ,  5 A, and  5 B are timing charts showing processes from the reception of the image data to the paper discharge in the printing machine  1  according to the first embodiment of the present invention.  FIG. 4B  represents a case where the candidate B 1  for the prescribed number of lines is greater than the candidate B 2  for the prescribed number of lines, while  FIG. 5A  represents a case where the candidate B 1  for the prescribed number of lines is equal to or smaller than the candidate B 2  for the prescribed number of lines. A distance from the secondary paper feeder  14  to the printing unit  30  is relatively short, and a time period from a point when the secondary paper feeder  14  starts conveying the print paper sheet W on the circulation system conveyance path CR to the printing unit  30  to a point when the printing unit  30  starts ejecting the inks is relatively short. For this reason, in  FIGS. 4A ,  4 B, and  5 A, the secondary paper feeder  14  and the printing unit  30  are illustrated as a single unit for the purpose of simplification. The same applies to  FIGS. 5B ,  7 A,  7 B,  9 A,  9 B,  10 A,  10 B,  11 , and  12  to be described later. 
     As shown in  FIG. 4A , according to the related art, a reception unit starts receiving the image data corresponding to a first page at a time point t 1 . Then, after completing the reception at a time point t 4 , a transfer unit of a controller starts the transfer of the image data corresponding to the first page to a printing unit. Then, the printing preparation and the paper feeding are performed after the transfer to the printing unit is completed at a time point t 10 . Then the printing is started at a time point t 11 , and the paper discharge is started at a time point t 12 . Accordingly, a period from the time point t 1  to a time point t 13  when the paper discharge is completed, i.e., a period until completion of the printing of the first page requires about 8 (seconds), for example. 
     On the other hand, as shown in  FIGS. 4B and 5A , according to the printing machine  1  of first embodiment of the present invention, when the reception unit  70   a  starts receiving the image data corresponding to the first page at a time point t 1 , the controller  70  causes the primary paper feeder  12  to start the paper feeding after the printing preparation. 
     Then, after the image data corresponding to the prescribed number of lines L A  are received at a time point t 2 , the transfer unit  70   b  of the controller  70  starts the transfer of the image data. Thereafter, the printing process is started at a time point t 3  after the image data corresponding to the prescribed number of lines L B  are received. Then the paper discharge is started at a time point t 5 . Accordingly, a period from the time point t 1  to a time point t 6  when the paper discharge is completed, i.e., a period until completion of the printing of the first page can be reduced to about 6 (seconds), for example. As described above, while the related art requires the time period from the time point t 1  to the time point t 11  to start the printing, the first embodiment of the present invention only requires the time period from the time point t 1  to the time point t 3  to start the printing process. 
     As described above, according to the printing machine  1  of the first embodiment of the present invention, by executing the print starting process, the primary paper feeder  12  is caused to start the conveyance of the print paper sheet W when the reception unit  70   a  starts reception of the image data. Hence it is possible to reduce a time period required until the start of the printing of the first print paper sheet W. 
     The above-described embodiment is configured to start the printing preparation and the paper feeding immediately after the calculation of the prescribed numbers of lines L A  and L B  (almost right after starting the data reception). However, the present invention is not limited only to this configuration. For example, if the candidate B 1  for the prescribed number of lines is greater than the candidate B 2  for the prescribed number of lines, as shown in  FIG. 5B , the printing preparation and the paper feeding may not be started immediately after the calculation of the prescribed numbers of lines L A  and L B . Instead, the printing preparation and the paper feeding may be started upon receipt of the image data corresponding to the number of lines which is equal to the number obtained by subtracting the candidate B 2  for the prescribed number of lines from the candidate B 1  for the prescribed number of lines. Then the printing process may be performed subsequent to the completion of the paper feeding. In addition, the calculation methods and the calculation formulae used for the determination of the timing to start the printing process are not limited only to the foregoing. 
     (Copy Starting Process) 
     Details of the copy starting process in the printing machine  1  according to the first embodiment of the present invention will be described. 
       FIG. 6  is a flowchart showing the copy starting process in the printing machine  1  according to the first embodiment of the present invention. Here, a case of printing an image on the print paper sheet W stacked on the paper feed tray  11  of the side paper feeder  10  will be described as an example. 
     As shown in  FIG. 6 , the controller  70  judges whether or not the image reader  2  has started reading the image data (step S 201 ). Specifically, the controller  70  judges that the reading has been started, when the user presses down the start key in the operating unit  60  to start the reading. 
     In the image reader  2 , the scanning unit scans the manuscript placed on the contact glass one line at a time, and the image processor processes the scanned image. Thus, the image reader  2  reads the image data to be printed by the image forming part  3 . Then a judgment is made whether or not the image data thus read out are supplied to the controller  70  via the external interface  82 . 
     When a judgment is made in step S 201  that the reading of the image data is started (YES), the controller  70  calculates prescribed numbers of lines L C , L D , and L E  as described below (step S 202 ). 
     The controller  70  calculates the prescribed number of lines L C  for reception so that the reception of the image data by the reception unit  70   a  does not proceed ahead of the reading by the image reader  2 . For example, if a reading speed Vs of the image reader  2  is equal to or faster than a receiving speed Vr of the image data by the reception unit  70   a , the controller  70  sets the prescribed number of lines L C  to “1”. If the reading speed Vs of the image reader  2  is slower than the receiving speed Vr of the image data by the reception unit  70   a , the controller  70  calculates the prescribed number of lines L C  by use of the following (formula 3). Here, the number of total lines in the image data is defined as N. The number N may be a value estimated from the size of the manuscript placed on the image reader  2 , or may be a value calculated from the size of the paper sheet to be used if the size of the manuscript is undefined and unreadable.
 
 L   c =ROUNDUP[ N× (1− Vs/Vr )]+1  (formula 3)
 
     The controller  70  calculates the prescribed number of lines L D  for performing transfer so that the transfer of the image data from the transfer unit  70   b  to the printing unit  30  do not proceed ahead of the reception of the image data by the reception unit  70   a  to the printing unit  30 . For example, if the reception speed Vr of the image data by the reception unit  70   a  is equal to or faster than the transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30 , the controller  70  sets the prescribed number of lines L D  to “L C +1”. If the reception speed Vr of the image data by the reception unit  70   a  is slower than the transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30 , the controller  70  calculates the prescribed number of lines L D  by use of the following (formula 4). Here, the number of total lines in the image data is defined as N.
 
 L   D =ROUNDUP{[ N× (1− Vr/Vt )+1]× Vs/Vr}+L   C   (formula 4)
 
     The controller  70  calculates the prescribed number of lines L E  for performing printing so that the printing by the printing unit  30  do not proceed ahead of the transfer of the image data from the transfer unit  70   b  to the printing unit  30 , and so that the printing by the printing unit  30  is performed after the printing preparation and the (primary) paper feeding is completed. 
     Firstly, the controller  70  calculates a candidate E 1  for the prescribed number of lines. Specifically, if the transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30  is equal to or faster than the printing speed Vp by the printing unit  30 , the controller  70  sets the candidate E 1  for the prescribed number of lines to “L C +LD+1”. If the transfer speed Vt of the image data from the transfer unit  70   b  to the printing unit  30  is slower than the printing speed Vp by the printing unit  30 , the controller  70  calculates the candidate E 1  for the prescribed number of lines by use of the following (formula 5). Here, the number of total lines in the image data is defined as N.
 
 E 1=ROUNDUP{[ N× (1− Vt/Vp )+1]× Vr/Vt}+L   C   +L   D   (formula 5)
 
     Next, the controller  70  calculates a candidate E 2  for the prescribed number of lines. Specifically, the controller  70  defines a “number obtained by converting a total time period of a time period for the printing preparation and a time period for the (primary) paper feeding into the number of lines in the reception” as the candidate E 2  for the prescribed number of lines. 
     Then, the controller  70  determines a larger one of the calculated candidate E 1  for the prescribed number of lines and candidate E 2  for the prescribed number of lines as the prescribed number of lines L E . 
     After step S 202 , the processing goes to steps S 203 , S 204 , S 206 , or S 208 . 
     In step S 203 , the controller  70  firstly performs the printing preparation. Specifically, the controller  70  causes the paper feed tray  11  on which the print paper sheets appropriate for the read image data are stacked to be in a state capable of feeding the topmost print paper sheet W, and also performs a process to warm inks, for example. In the case of a printing machine having a structure in which a bottom plate disposed at the bottom inside the paper feed tray is moved vertically in response to a remaining amount of the print paper sheets, the process for causing the paper feed tray  11  to be in a state capable of feeding the topmost print paper sheet W includes a process to lift the tray bottom plate up to a prescribed height so that the print paper sheet can be supplied onto the conveyance path. 
     After completing the printing preparation, the print control unit  70   c  of the controller  70  causes the primary paper feeder  12  to start paper feeding. Specifically, the print control unit  70   c  causes the primary paper feeder  12  to convey only the topmost print paper sheet W from the paper feed tray  11  onto the paper feed system conveyance path FR. In this way, the print paper sheet W thus conveyed is in contact with the secondary paper feeder  14  after reception of the image data corresponding to the candidate B 2  for the prescribed number of lines. 
     In step S 204 , the print control unit  70   c  of the controller  70  judges whether or not the image data corresponding to the prescribed number of lines L C  have been read already. 
     When a judgment is made in step S 204  that the image data corresponding to the prescribed number of lines L C  have been read already (YES), the reception unit  70   a  of the controller  70  starts data reception of the image data from the image reader  82  via the external interface  82  (step S 205 ). 
     In step S 206 , the print control unit  70   c  of the controller  70  judges whether or not the image data corresponding to the prescribed number of lines L D  have been read already. 
     When a judgment is made in step S 206  that the image data corresponding to the prescribed number of lines L D  have been read already (YES), the transfer unit  70   b  of the controller  70  starts data transfer of the image data received by the reception unit  70   a  to the printing unit  30  (step S 207 ). 
     In step S 208 , the print control unit  70   c  of the controller  70  judges whether or not the image data corresponding to the prescribed number of lines L E  have been read already. 
     When a judgment is made in step S 208  that the image data corresponding to the prescribed number of lines L E  have been read already (YES), the print control unit  70   c  of the controller  70  causes the secondary paper feeder  14  and the printing unit  30  to start the printing process (secondary paper feeding and printing) (step S 209 ). Specifically, in accordance with an instruction given by the print control unit  70   c , the secondary paper feeder  14  conveys the print paper sheet W in contact therewith onto the circulation system conveyance path CR to the printing unit  30 . Thereafter, the print paper sheet W conveyed to the printing unit  30  by the secondary paper feeder  14  is suctioned on the conveyance belt  32 , and then subjected to printing one line at a time with the inks ejected from the head unit  31  of the printing unit  30  while being conveyed at the printing speed Vp. Then, the print paper sheet W is delivered. Subsequently, the paper discharge unit  40  discharges the print paper sheet thus delivered (step S 210 ). 
       FIG. 7A  is a timing chart showing processes from the reading of the image data to the paper discharge in the related art.  FIG. 7B  is a timing chart showing processes from the reading of the image data to the paper discharge in the printing machine  1  according to the first embodiment of the present invention, and is a case where the candidate E 1  for the prescribed number of lines is greater than the candidate E 2  for the prescribed number of lines. The timing chart of a case where the candidate E 1  for the prescribed number of lines is equal to or smaller than the candidate E 2  for the prescribed number of lines is conceivably be similar to  FIG. 5A  that has been described already, and description thereof will be omitted. 
     As shown in  FIG. 7A , according to the related art, the image reader starts reading the image data at a time point t 1 . Then, after completing the reading at a time point t 5 , the reception unit starts receiving the image data corresponding to the first page. Then, the transfer unit of the controller starts the transfer of the image data corresponding to the first page to the printing unit at a time point t 10 . Thereafter, printing preparation and the paper feeding are performed after the transfer to the printing unit is completed at a time point t 11 . Then the printing process is started at a time point t 12 , and the paper discharge is started at a time point t 13 . Here, a period from the time point t 1  to a time point t 14  when the paper discharge is completed, i.e., a period until completion of the printing of the first page requires about 10 (seconds), for example. 
     Meanwhile, as shown in  FIG. 7B , according to the printing machine  1  of the first embodiment of the present invention, when the reading is started at a time point t 1  and the image data corresponding to the prescribed number of lines L C  are read at a time point t 2 , the reception unit  70   a  starts receiving the image data corresponding to the first page. Moreover, when the reading of the image data is started, the controller  70  causes the primary paper feeder  12  to start the paper feeding after the printing preparation. 
     Then, after the image data corresponding to the prescribed number of lines L D  are received at a time point t 3 , the transfer unit  70   b  of the controller  70  starts the transfer of the image data. Thereafter, the printing process is started at a time point t 4  after the image data corresponding to the prescribed number of lines L E  are received. Then, the paper discharge is started at a time point t 6 . Here, a period from the time point t 1  to a time point t 7  when the paper discharge is completed, i.e., a period until completion of the printing of the first page can be reduced to about 8 (seconds), for example. As described above, while the related art requires the time period from the time point t 1  to the time point t 12  to start the printing, the first embodiment of the present invention only requires the time period from the time point t 1  to the time point t 4  to start the printing process. 
     As described above, according to the printing machine  1  of the first embodiment of the present invention, by executing the copy starting process, the controller  70  performs the printing preparation, and causes the primary paper feeder  12  to start the conveyance of the print paper sheet W when the image reader  2  starts reading of the image data. Hence it is possible to reduce a time period required until the start of the printing of the first print paper sheet W. 
     The above-described embodiment is configured to start the printing preparation and the paper feeding immediately after the reading the image data. However, the present invention is not limited only to this configuration. For example, if a candidate D 1  for the prescribed number of lines is greater than a candidate D 2  for the prescribed number of lines, the printing preparation and the paper feeding may not be started immediately after the reading of the image data. Instead, the printing preparation and the paper feeding may be started upon the reading of the image data corresponding to the number of lines which is equal to the number obtained by subtracting the candidate D 1  for the prescribed number of lines from the candidate D 2  for the prescribed number of lines. Then the printing process may be performed subsequent to the completion of the paper feeding. In addition, the calculation methods and the calculation formulae used for the determination of the timing to start the printing process are not limited only to the foregoing. 
     (Print Monitoring Process) 
     Details of the print monitoring process in the printing machine  1  according to the first embodiment of the present invention will be described. 
       FIG. 8  is a flowchart showing the print monitoring process in the printing machine  1  according to the first embodiment of the present invention. Here, a case of printing an image on the print paper sheet W stacked on the paper feed tray  11  of the side paper feeder  10  will be described as an example. 
     As shown in  FIG. 8 , the reception condition monitoring unit  70   d  of the controller  70  judges whether or not an error occurs in the reception unit  70   a  (step S 301 ). Specifically, the reception condition monitoring unit  70   d  monitors a reception condition of the image data by the reception unit  70   a  and judges whether or not an error code is sent from the reception unit  70   a.    
     When a judgment is made in step S 301  that an error has occurred in the reception unit  70   a  (YES), the print control unit  70   c  judges whether or not the printing preparation is in progress (step S 303 ). 
     When a judgment is made in step S 303  that the printing preparation is in progress (YES), the print control unit  70   c  aborts the printing preparation (step S 305 ). 
     On the other hand, when a judgment is made in step S 303  that the printing preparation is not in progress (NO), the print control unit  70   c  judges whether or not the paper feeding is in progress (step S 307 ). 
     When a judgment is made in step S 307  that the paper feeding is in progress (YES), the print control unit  70   c  aborts the paper feeding (step S 309 ). 
     On the other hand, when a judgment is made in step S 307  that the paper feeding is not in progress (NO), the print control unit  70   c  judges whether or not the printing is in progress (step S 311 ). Specifically, the print control unit  70   c  judges whether or not the secondary paper feeder  14  has started driving, i.e., whether or not the secondary paper feeder  14  has conveyed the print paper sheet W in contact therewith onto the circulation system conveyance path CR to the printing unit  30 . 
     If a judgment is made in step S 311  that the printing is in progress (YES), the print control unit  70   c  aborts the printing and delivers the print paper sheet W from the printing unit  30  (step S 313 ). 
     Next, the discharge control unit  70   e  of the controller  70  judges whether or not the top edge sensor  33  detects the leading edge of the print paper sheet W conveyed to the head unit  31  (step S 315 ). 
     When a judgment is made in step S 315  that the print paper sheet W is detected (YES), the print paper sheet W is already printed and the paper discharge unit  40  discharges the print paper sheet W delivered from the printing unit  30  out of the printing machine  1  (step S 317 ). Specifically, the switching mechanism  43  guides the print paper sheet W conveyed on the circulation system conveyance path CR to the paper discharge unit  40  based on an instruction by the discharge control unit  70   e . In this way, the guided print paper sheet W is conveyed to the paper receiving tray  41  by the discharge rollers  42  and is stacked on the paper receiving tray  41  with the printed surface facing downward. 
     On the other hand, if a judgment is made in step S 315  that the print paper sheet W is not detected (NO), the print paper sheet W is yet to be printed and may therefore be reusable. 
     Accordingly, the discharge control unit  70   e  judges whether or not the print paper sheet W is a print paper sheet applicable to two-side printing (step S 319 ). Specifically, the discharge control unit  70   e  makes the following judgment on the basis of the setting on the type of the print paper sheets, the setting being set up by the user using the display/input panel  61  of the operating unit  60 . For example, the discharge control unit  70   e  judges that the print paper sheet W is a print paper sheet applicable to one-side printing in a case of a print paper sheet provided with a special coating only on one surface, such as mat paper, and judges that the print paper sheet W is a print paper sheet applicable to two-side printing in a case of paper processed to have the same quality on both of surfaces, such as ordinary paper. 
     When a judgment is made in step S 319  that the print paper sheet W is a print paper sheet applicable to two-side printing (YES), the print paper sheet W turns out to be reusable. 
     Accordingly, the reversing unit  50  turns over the print paper sheet W and conveys the print paper sheet W thus turned over to the secondary paper feeder  14  (step S 321 ). Specifically, the switching mechanism  43  guides the print paper sheet W not to the paper discharge unit  40  but to the reversing unit  50  instead on the basis of an instruction by the discharge control unit  70   e . In this way, the guided print paper sheet W is conveyed from the circulation system conveyance path CR to the reversing tray  51  by way of the reversing rollers  52 , and is then conveyed from the reversing tray  51  to the circulation system conveyance path CR after a lapse of a prescribed time period. Hence the print paper sheet W is turned over relative to the circulation system conveyance path CR. Thereafter, the print paper sheet W thus turned over is conveyed on the circulation system conveyance path CR by means of the multiple rollers such as the conveyance rollers  53  provided on the circulation system conveyance path CR, comes into contact with the secondary paper feeder  14 , and stands by until the next printing instruction is issued. Then, when the next printing instruction is issued, the print paper sheet W standing by at the secondary paper feeder  14  is fed, and the printing is executed. In this way, when the print paper sheet W is prone to get jammed before reaching the secondary paper feeder  14 , it is possible to prevent occurrence of such jam. In addition, the first printed matter can be obtained earlier. 
     As described above, according to the printing machine  1  of the first embodiment of the present invention, in a case where the print paper sheet W is detected by the top edge sensor  33  when the reception condition monitor unit  70   d  judges that reception of the image data has failed, the switching mechanism  43  is switched so as to guide the print paper sheet W to the paper discharge unit  40 . On the other hand, in a case where the print paper sheet W is not detected by the top edge sensor  33 , the switching mechanism  43  is switched so as to guide the print paper sheet W to any one of the paper discharge unit  40  and the reversing unit  50  depending on the type of the print paper sheet W set up based on the external input. As a consequence it is possible to reuse the print paper sheet W designed to be reusable. 
     In the first embodiment of the present invention, in a case where the leading edge the print paper sheet W is not detected by the top edge sensor  33  when the reception condition monitoring unit  70   d  judges that the reception of the image data has failed, the switching mechanism  43  is switched so as to guide the print paper sheet W to any one of the paper discharge unit  40  and the reversing unit  50  depending on the type of the print paper sheet set up based on the external input. However, the present invention is not limited only to this configuration. For example, when the reception condition monitoring unit  70   d  judges that the reception of the image data has failed, the switching mechanism  43  may be switched so as to guide the print paper sheet W to the reversing unit  50  irrespective of the result of detection by the top edge sensor  33 . 
     (Print Starting Process when Two-Side Printing is Set) 
     When the image data transmitted from the terminal  100  is set to a two-side printing mode, the printing machine  1  according to the first embodiment of the present invention starts printing in the two-side printing mode. 
       FIG. 9A  is a timing chart showing processes from the reception of the image data to the paper discharge in the two-side printing in the related art, and  FIG. 9B  is a timing chart showing processes from the reception of the image data to the paper discharge in the two-side printing by the printing machine  1  according to the first embodiment of the present invention. 
     As shown in  FIG. 9A , according to the related art, when the reception unit starts receiving front surface image data of a first page at a time point t 1  and completes reception of the front surface image data at a time point t 3 , the reception unit starts reception of back surface image data of the first page. 
     Then, when the reception unit completes reception of the back surface image data at a time point t 6 , the transfer unit of the controller starts transfer of the front surface image data of the first page to the printing unit. When the transfer of the front surface image data is completed at a time point t 9 , the transfer unit of the controller starts transfer of the back surface image data of the first page to the printing unit. 
     Subsequently, after the transfer of the back surface image data to the printing unit is completed at a time point t 10 , the printing preparation and the paper feeding are performed, and then the printing process of the front surface image data is started at a time point t 11 . Thereafter, the print paper sheet is turned over at a time point t 12 . Subsequently, when the turning-over is completed at a time point t 13 , the printing process of the back surface image data is started. Then, the paper discharge is started when the printing process of the back surface image data is completed at a time point t 14 . Accordingly, the printing of the first page until completion requires a time period from the time point t 1  to a time point t 15  when the paper discharge is completed. 
     On the other hand, as shown in  FIG. 9B , according to the printing machine  1  of the first embodiment of the present invention, in the case where the two-side printing mode is set, the controller  70  firstly performs the printing preparation and then causes the primary paper feeder  12  to start the paper feeding when the reception unit  70   a  starts reception of the front surface image data for the first page at a time point t 1 . 
     Then, upon receipt of the front surface image data corresponding to the prescribed number of lines L A  at a time point t 2 , the transfer unit  70   b  of the controller  70  starts the transfer of the image data. Thereafter, when the reception unit  70   a  completes the reception of the front surface image data of the first page at a time point t 3 , the reception unit  70   a  starts reception of the back surface image data of the first page. 
     Thereafter, upon receipt of the front surface image data corresponding to the prescribed number of lines L B  at a time point t 4 , the printing process of the front surface image data is started. Then the print paper sheet is turned over at a time point t 5 . Subsequently, when the turning-over is completed at a time point t 6 , the printing process of the back surface image data is started. Next, paper discharge is started as the printing of the back surface image data is completed at a time point t 7 . Accordingly, it is possible to reduce the time period for completing the printing of the first page to a period from the time point t 1  to a time point t 8  when the paper discharge is completed. 
     As described above, while the related art requires the time period from the time point t 1  to the time point t 11  to start the printing, the first embodiment of the present invention only requires the period from the time point t 1  to the time point t 4  even in the case where the two-side printing mode is set. 
     As described above, according to the printing machine  1  of the first embodiment of the present invention, the following effect can be obtained by executing the print starting process even in the case where the two-side printing mode is set. Since the printing preparation is performed and the primary paper feeder  12  is caused to start the conveyance of the print paper sheet W when the reception unit  70   a  starts the reception of the image data, the time period required until the start the printing of the first page of the print paper sheet W can be reduced. 
     (Copy Starting Process when Two-Side Printing is Set) 
     As described above, the printing machine  1  according to the first embodiment of the present invention starts copying in the two-side printing mode when the two-side printing mode is set up by the operation of the user using the display/input panel  61 . 
       FIG. 10A  is a timing chart showing processes from the reading of the image data to the paper discharge in the two-side printing in the related art.  FIG. 10B  is a timing chart showing processes from the reading of the image data to the paper discharge in the two-side printing by the printing machine according to the first embodiment of the present invention, and shows a case where the candidate E 1  for the prescribed number of lines is greater than the candidate E 2  for the prescribed number of lines. 
     As shown in  FIG. 10A , according to the related art, when the reader starts reading front surface image data of a first page at a time point t 1  and completes the reading of the front surface image data at a time point t 4 , the reader starts reading back surface image data of the first page. Then, when the reading of the back surface image data is completed at a time point t 6 , the reception unit starts receiving the front surface image data of the first page. When the reception of the front surface image data is completed at a time point t 10 , reception of the back surface image data of the first page is started. 
     Subsequently, after the reception of the back surface image data is completed at a time point t 11 , the transfer unit of the controller starts transfer of the front surface image data of the first page to the printing unit. When the transfer of the front surface image data is completed at a time point t 12 , the transfer unit of the controller starts transfer of the back surface image data of the first page to the printing unit. 
     Subsequently, after the transfer of the back surface image data to the printing unit is completed at a time point t 13 , the printing preparation and the paper feeding are performed, and then the printing process of the front surface image data is started at a time point t 14 . Thereafter, the print paper sheet is turned over at a time point t 15 . Subsequently, when the turn-over is completed at a time point t 16 , the printing process of the back surface image data is started. Then, the paper discharge is started when the printing of the back surface image data is completed at a time point t 17 . Accordingly, the printing of the first page until completion requires a time period from the time point t 1  to a time point t 18  when the paper discharge is completed. 
     Meanwhile, as shown in  FIG. 10B , according to the printing machine  1  of the first embodiment of the present invention, in a case where the two-side printing mode is set, the reading is started at a time point t 1  and the reception unit  70   a  starts receiving front surface image data of a first page at a time point t 2 . Moreover, when the reading of the image data is started, the controller  70  causes the primary paper feeder  12  to start the paper feeding after the printing preparation. 
     Then, after the front surface image data corresponding to the prescribed number of lines L D  are read at a time point t 3 , the transfer unit  70   b  of the controller  70  starts transfer of the image data. 
     Thereafter, when the front surface image data corresponding to the prescribed number of lines L B  are read at a time point t 5 , the printing process of the front surface image data is started. Then the print paper sheet is turned over at a time point t 6 . Subsequently, when the turning-over of the print paper sheet is completed at a time point t 7 , the printing process of the back surface image data is started. Next, the paper discharge is started when the printing of the back surface image data is completed at a time point t 8 . Accordingly, it is possible to reduce the time period for completing printing of the first page to a period from the time point t 1  to a time point t 9  when the paper discharge is completed. 
     As described above, while the related art requires the time period from the time point t 1  to the time point t 14  to start the printing, the first embodiment of the present invention only requires the time period from the time point t 1  to the time point t 5  to start the printing process even in the case where the two-side printing mode is set. 
     As described above, according to the printing machine  1  of the first embodiment of the present invention, the following effect can be obtained by executing the copy starting process even in the case where the two-side printing mode is set. Since the controller  70  performs the printing preparation and cause the primary paper feeder  12  to start the conveyance of the print paper sheet W when the image reader  2  starts the reading of the image data, the time period required until the start the printing of the first page of the print paper sheet W can be reduced. 
     Moreover, the inkjet line color printing machine which performs printing one line at a time has been described as an example of the printing machine  1  according to the first embodiment of the present invention. However, the present invention is not limited only to this example and may be applicable to printing machines of modes such as serial inkjet, laser, and stencil printing. 
     (Second Embodiment) 
     In the first embodiment of the present invention, the primary paper feeder  12  is caused to start the conveyance of the print paper sheet W when the reception unit  70   a  starts receiving the image data. However, the present invention is not limited only to this configuration. 
     A second embodiment of the present invention will describe an example of the printing machine  1  which is configured to cause the primary paper feeder  12  to convey only a single print paper sheet W when the reception unit  70   a  starts receiving the image data, and to control the primary paper feeder  12  in a way that the secondary paper feeder  14  can convey the print paper sheets W at a prescribed sheet interval after the printing unit  30  completes printing on the conveyed single print paper sheet W. 
       FIG. 11  is a timing chart showing processes from reception of image data to paper discharge in a printing machine  1 A according to the second embodiment of the present invention. 
     As shown in  FIG. 11 , according to the printing machine  1 A of the second embodiment of the present invention, when the reception unit  70   a  starts receiving the image data of a first page at a time point t 1 , the controller  70  performs the printing preparation, and then causes the primary paper feeder  12  to start the paper feeding of a first print paper sheet. 
     Then, upon receipt of the image data equivalent to the prescribed number of lines L A  at a time point t 2 , the transfer unit  70   b  of the controller  70  starts transfer of the image data. Meanwhile, the printing process is started at a time point t 3  upon receipt of the image data corresponding to the prescribed number of lines L B , and the paper discharge is started at a time point t 6 . Subsequently, the paper feeding of a second print paper sheet is started after the paper discharge of the first print paper sheet is completed at a time point t 7 . 
     Thereafter, concerning a third print paper sheet and so on, the primary paper feeder  12  is caused to start the conveyance of the print paper sheet W in a way that the print paper sheet W can be conveyed at a prescribed sheet interval, i.e., in a way that the secondary paper feeder  14  can convey the print paper sheets W at the prescribed sheet interval when the reception unit  70   a  starts receiving the image data. 
     As described above, according to the printing machine  1 A of the second embodiment of the present invention, the primary paper feeder  12  is caused to convey only a single print paper sheet W, and is controlled in a way that the secondary paper feeder  14  can convey the print paper sheets W at the prescribed sheet interval after the printing unit  30  completes the printing of the conveyed single print paper sheet W. Therefore, the printing process of the second print paper sheet and so on will not be started until the printing process of the first print paper sheet is completed. In this way, it is possible to perform printing more stably. 
     In the second embodiment of the present invention, the primary paper feeder  12  is caused to convey only a single print paper sheet W when the reception unit  70   a  starts receiving the image data, and is controlled in a way that the secondary paper feeder  14  can convey the print paper sheets W at the prescribed sheet interval after the printing unit  30  completes the printing of the conveyed single print paper sheet W. However, the present invention is not limited only to this configuration. For example, the primary paper feeder  12  may be caused to convey only a single print paper sheet W when the reception unit  70   a  starts receiving the image data, and may be controlled in a way that the secondary paper feeder  14  can convey the print paper sheets W at the prescribed sheet interval after the transfer unit  70   b  completes the transfer of the image data for the single print paper sheet W. 
     (Third Embodiment) 
       FIG. 12  is a timing chart showing processes from reception of image data to paper discharge in a printing machine  1 B according to a third embodiment of the present invention. 
     As shown in  FIG. 12 , the print control unit  70   c  causes paper feeding of a second print paper sheet to be started at a time point t 5  after completion of the transfer of the image data for a first print paper sheet W. Then, the paper discharge of the first print paper sheet is started at a time point t 6  upon completion of the printing process of the first print paper sheet. 
     As described above, according to the printing machine  1 B of the third embodiment of the present invention, the primary paper feeder  12  is caused to convey only a single print paper sheet W, and is controlled in a way that the secondary paper feeder  14  can convey the print paper sheets W at the prescribed sheet interval after the transfer unit  70   b  completes transfer of the image data for the single print paper sheet W. Therefore, the printing process of the second print paper sheet and so on will not be started until the transfer of the image data for the first print paper sheet is completed. In this way, it is possible to perform printing more stably. 
     A printing machine according to the embodiments of the present invention has been described above. However, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
     Moreover, the effects described in the embodiments of the present invention are only a list of optimum effects achieved by the present invention. Hence, the effects of the present invention are not limited to those described in the embodiment of the present invention.