Patent Publication Number: US-2013235411-A1

Title: Printing apparatus, printing apparatus control method, and storage medium storing a program

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printing apparatus that performs processing for printing on printing paper based on a print job, a method for controlling a printing apparatus, and a storage medium storing a program. 
     2. Description of the Related Art 
     Conventionally, in order to shorten the time (downtime) during which a printing apparatus stops printing, the printing apparatus has a function such that if a paper jam occurs during printing, the printing is automatically resumed after the jammed paper is removed. 
     Meanwhile, in recent years, there are printing apparatuses that produce a printed matter using predetermined paper with sequentiality, such as tabbed paper having tabs on which headers or titles can be written or paper that is provided with page numbers in advance. 
     Japanese Patent Laid-Open No. 2002-318509 discloses a printing apparatus that produces printed matter including tabbed paper. The printing apparatus disclosed in Japanese Patent Laid-Open No. 2002-318509 stops printing if a paper jam occurs, and if the print job is not one using tabbed paper, the printing apparatus automatically resumes the printing after the jammed paper is removed. On the other hand, if the print job is one using the tabbed paper, the printing apparatus prompts the user to check the order of tabbed paper in a paper feed tray rather than automatically resuming the printing after the jammed paper is removed. Thereafter, the printing apparatus resumes printing upon accepting a user instruction. It is disclosed that a change in the order of the tabbed paper to be inserted in the printed matter can be thus prevented. 
     However, in the case of a print job using the predetermined paper with sequentiality, the conventional printing apparatus stops printing and waits to resume the printing after the jammed paper is removed until the user instruction is given, regardless of whether or not the predetermined paper is remaining on a conveying path. For example, if the print job is one for printing using plain paper and tabbed paper, there are times when only plain paper exists on the conveying path. In this case, the order of the tabbed paper is maintained when printing is automatically resumed after the jammed paper is removed, but the conventional printing apparatus waits for resuming of the printing after the jammed paper is removed, resulting in occurrence of downtime. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to eliminate the above-mentioned problems with the conventional technology. The present invention provides a printing apparatus that prevents downtime from occurring at the time of occurrence of a paper jam, a printing apparatus control method, and a storage medium storing a program. 
     The present invention in its first aspect provides a printing apparatus that conveys printing paper via a conveying path and performs printing, comprising: a detection unit configured to detect a paper jam on the conveying path; a stop unit configured to stop the printing if the paper jam is detected by the detection unit; a determination unit configured to determine whether or not predetermined paper with sequentiality exists on the conveying path; and a control unit configured to wait for an instruction from a user and resume the printing after the paper jam is resolved, if the printing is stopped by the stop unit and it is determined by the determination unit that the predetermined paper with sequentiality exists on the conveying path, and to resume the printing without waiting for the instruction from the user after the paper jam is resolved, if the printing is stopped by the stop unit and it is determined by the determination unit that the predetermined paper with sequentiality does not exist on the conveying path. 
     The present invention in its second aspect provides a method for controlling a printing apparatus that conveys printing paper via a conveying path and performs printing, comprising: a detection step of detecting a paper jam on the conveying path; a stop step of stopping the printing if the paper jam is detected in the detection step; a determination step of determining whether or not predetermined paper with sequentiality exists on the conveying path; and a control step of waiting for an instruction from a user and resuming the printing after the paper jam is resolved, if the printing is stopped in the stop step and it is determined in the determination step that the predetermined paper with sequentiality exists on the conveying path, and resuming the printing without waiting for the instruction from the user after the paper jam is resolved, if the printing is stopped in the stop step and it is determined in the determination step that the predetermined paper with sequentiality does not exist on the conveying path. 
     The present invention in its third aspect provides a computer-readable storage medium storing a program for causing a computer to execute: a detection step of detecting a paper jam on a conveying path; a stop step of stopping printing if the paper jam is detected in the detection step; a determination step of determining whether or not predetermined paper with sequentiality exists on the conveying path; and a control step of waiting for an instruction from a user and resuming the printing after the paper jam is resolved, if the printing is stopped in the stop step and it is determined in the determination step that the predetermined paper with sequentiality exists on the conveying path, and resuming the printing without waiting for the instruction from the user after the paper jam is resolved, if the printing is stopped in the stop step and it is determined in the determination step that the predetermined paper with sequentiality does not exist on the conveying path. 
     According to the present invention, downtime when a paper jam occurs can be suppressed. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an overall configuration of a printing system; 
         FIG. 2  is a block diagram showing a configuration of an image forming apparatus; 
         FIG. 3  is a block diagram showing a module configuration of a paper monitoring program; 
         FIG. 4  is a diagram showing a configuration of the vicinity of a printing paper conveying path within the image forming apparatus; 
         FIGS. 5A to 5D  are diagrams showing exemplary screens for registering printing paper with respect to paper feed trays; 
         FIG. 6  is a diagram showing an exemplary screen for setting printing paper information; 
         FIG. 7  is a diagram showing an exemplary content of printing paper registration with respect to the paper feed trays; 
         FIG. 8  is a diagram for illustrating processing for acquiring remaining printing paper information; 
         FIG. 9  is a diagram showing exemplary information about printing paper remaining on the convey path; 
         FIG. 10  is a flowchart showing a procedure of print control processing at the time of occurrence of a paper jam in a first embodiment; 
         FIG. 11  is a flowchart showing a procedure for acquiring information about paper remaining on the conveying path; and 
         FIG. 12  is a diagram showing an exemplary screen for prompting a user to check the paper feed trays. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will now be described hereinafter in detail, with reference to the accompanying drawings. It is to be understood that the following embodiments are not intended to limit the claims of the present invention, and that not all of the combinations of the aspects that are described according to the following embodiments are necessarily required with respect to the means to solve the problems according to the present invention. Note that the same reference numerals will be given to the same components, and the description thereof will be omitted. 
     First Embodiment 
       FIG. 1  is a diagram showing an overall configuration of a printing system according to an embodiment of the present invention. The printing system includes client PCs  101  and  102 , and an image forming apparatus  121 , which is an example of a printing apparatus. The client PCs  101  and  102  and the image forming apparatus  121  are connected via a network  110  so as to be able to communicate with one another. In the present embodiment, the image forming apparatus  121  is a so-called MFP (Multifunction Peripheral) that includes a printing unit, as well as a scanning unit for optically scanning originals, and so on. On the client PC  101  or  102 , the user can create image data of an original to be printed, and give a print instruction by transmitting the created image data and print settings to the image forming apparatus  121 . In this case, the client PCs  101  and  102  can display a print output state of the image forming apparatus  121  to the user, and the user can perform editing or the like on the original data on the client PCs  101  and  102 , based on a print preview display. Although  FIG. 1  shows the two client PCs  101  and  102 , a configuration may be adopted in which only one client PC is connected to the network  110 , or three or more client PCs may be connected to the network  110 . Hereinafter, the client PCs  101  and  102  will be referred to simply as “the client PC” when at least one or the other is being described, unless stated otherwise. 
     The image forming apparatus  121  can receive image data of an original from the client PC, and also read an image on the original by a scanning operation of an original scanning unit  200 , which is provided within the image forming apparatus  121 , to acquire the original image data. The image forming apparatus  121  performs printing on a printing medium (hereinafter referred to as “printing paper”) according to the settings of a print job, based on the original image data received from the client PC, or the original image data acquired by the original scanning unit  200 . In the present embodiment, printing paper includes plain paper, as well as tabbed paper, OHP film, and glossy paper, for example. During printing processing based on the print job, the image forming apparatus  121  performs various types of image processing, such as image correction, file merging, page insertion/deletion, page layout editing, and imposition, on the original image data as needed. After performing image processing on the original image data, the image forming apparatus  121  performs finishing, such as paper folding, saddle-stitch binding, case binding, cutting, enclosing, and collating, on the printed printing paper in accordance with the set content of the print job. 
       FIG. 2  is a block diagram showing a configuration of the image forming apparatus  121 . The image forming apparatus  121  includes the original scanning unit  200 , a main body control unit  210 , a PDL processing unit  220 , an image output unit  230 , an operation unit  240 , and a data storage unit  250 . The original scanning unit  200  includes an original paper feed unit  201  and an original scanning unit  202 . The main body control unit  210  includes a CPU  211 , a ROM  212 , and a RAM  213 . The image output unit  230  includes an image forming unit  231 , a paper discharge unit  232 , and a paper feed unit  233 . 
     The original scanning unit  200  reads out an original that the user placed in a paper feed tray in the original paper feed unit  201  in accordance with a duplicate (copying)/image forming (printing) instruction accepted via the operation unit  240 , under the control of the CPU  211 . The main body control unit  210  includes the CPU  211  that controls the overall image forming apparatus  121 , the ROM  212  that stores a control program for implementing each operation in the present embodiment, and the RAM  213  used as a work memory of the CPU  211 . Based on the control program stored in the ROM  212 , the CPU  211  controls the original scanning unit  200 , the PDL processing unit  220 , the image output unit  230 , the operation unit  240 , the data storage unit  250 , and so on, to implement each operation in the present embodiment. 
     In the present embodiment, the image forming apparatus  121  receives the original in the form of PDL (Page Description Language) data from the client PC. Upon the image forming apparatus  121  receiving the PDL data, the PDL processing unit  220  generates image data to be printed on a printing paper from the PDL data, under the control of the CPU  211 . 
     In the printing processing for printing an image in accordance with the image data received from the original scanning unit  200  or the PDL processing unit  220 , the image output unit  230  performs various types of image processing, such as image correction, file merging, page insertion/deletion, and imposition, on the image data under the control of the CPU  211 . After performing the image processing, the CPU  211  controls the paper discharge unit  232  and the paper feed unit  233  to convey the printing paper to the image forming unit  231 , and controls the image forming unit  231  to perform printing on the printing paper. In addition, the CPU  211  performs finishing, such as paper folding, saddle-stitch binding, case binding, cutting, enclosing, and collating, on the printed printing medium. 
     The operation unit  240  accepts an instruction from the user via a display unit such as a display. Upon the operation unit  240  accepting the instruction from the user, the CPU  211  stores key information corresponding to the instruction in the RAM  213 . The key information is, for example, a selected item on a selection screen displayed on the display unit. The CPU  211  controls the overall image forming apparatus  121  based on the key information stored in the RAM  213 . The data storage unit  250  holds system software, the original image data, and so on. The data storage unit  250  also holds information indicating types of printing paper designated as special paper (predetermined paper). In the present embodiment, an instruction from the user is a trigger for resuming of printing that has been stopped due to jamming of a specific kind of printing paper, and this specific kind of printing paper can be specified in advance. 
       FIG. 3  is a block diagram showing a module configuration of a paper monitoring program stored in the ROM  212 . In the present embodiment, each module function shown in  FIG. 3  is implemented by the CPU  211  executing the paper monitoring program  300 . The paper monitoring program  300  includes a paper state specifying portion  301 , a fed paper number monitoring portion  302 , and a discharged paper number monitoring portion  303 . The fed paper number monitoring portion  302  and the discharged paper number monitoring portion  303  acquire and manage the number of sheets of discharged printing paper that have been discharged from the paper discharge unit  232  and the number of sheets of fed printing paper that have been fed by the paper feed unit  233 , based on detection signals from paper feed tray sensors and paper discharge tray sensors, which will be described later. The paper state specifying portion  301  specifies the type of printing paper remaining on the conveying path within the image forming apparatus  121 , based on the fed paper number and the discharged paper number provided from the fed paper number monitoring portion  302  and the discharged paper number monitoring portion  303 . 
       FIG. 4  is a diagram showing a configuration of a printing paper conveying path and therearound within the image forming apparatus  121 . A conveying path  401  in the image forming apparatus  121  spans from paper feed trays  402   a  to  402   c  provided in the paper feed unit  233  to paper discharge trays  403   a  to  403   c  provided in the paper discharge unit  232 . The conveying path  401  is provided with the paper feed tray sensors  404   a  to  404   c , paper jam detection sensors  405   a  to  405   d , and the paper discharge tray sensors  406   a  to  406   c . The paper feed tray sensors  404   a  to  404   c  detect, respectively, that a printing paper has been fed from the paper feed trays  402   a  to  402   c  to the conveying path  401  within the image forming apparatus  121 . The paper jam detection sensors  405   a  to  405   d  detect a paper jam on the conveying path  401  within the image forming apparatus  121 . The paper discharge tray sensors  406   a  to  406   c  detect that printing paper has been discharged from the conveying path  401  within the image forming apparatus  121  to the paper discharge trays  403 . 
     Upon the image forming apparatus  121  receiving the print job from the client PC, the CPU  211  controls the paper feed unit  233  so as to feed printing paper from the paper feed trays  402  to the conveying path  401 . The paper feed unit  233  feeds printing paper from the paper feed trays  402   a  to  402   c  to the conveying path  401 . If the CPU  211  receives a detection signal indicating that the paper feed tray sensors  404   a  to  404   c  have detected passage of printing paper, the CPU  211  determines that printing paper has been fed correctly from the paper feed tray  402 . 
     The printing paper fed to the conveying path  401  within the image forming apparatus  121  is conveyed to the image forming unit  231 . The image forming unit  231  then performs image formation processing on the printing paper under the control of the CPU  211 . During this image formation processing, the paper jam detection sensors  405   a  to  405   d  monitor the occurrence of jamming of the printing paper that is being conveyed on the conveying path  401 . If a predetermined time period has elapsed without printing paper that has passed through one paper jam detection sensor passing through the next paper jam detection sensor, the CPU  211  determines that a paper jam has occurred. Note that the predetermined time period may be decided in accordance with the distance between adjoining paper jam detection sensors. The predetermined time may be set approximately to a value obtained by dividing the distance between the paper jam detection sensors by the conveying speed. If jamming of printing paper has occurred on the conveying path  401 , the CPU  211  receives a detection signal indicating that the paper jam detection sensors  405   a  to  405   d  have detected a paper jam, and controls the components to stop the printing paper conveying operation. Note that the number and positions of the paper jam detection sensors  405   a  to  405   d  are only an example, and is not limited to this example as long as a configuration is employed in which a paper jam occurring on the conveying path can be detected. 
     Printing paper on which the image formation processing has been performed by the image forming unit  231  is conveyed to the paper discharge unit  232 . The CPU  211  controls the paper discharge unit  232  to discharge the printing paper to a predetermined paper discharge tray  403   a  to  403   c  in the paper discharge unit  232 . If the CPU  211  receives a detection signal indicating that the paper discharge tray sensors  406   a  to  406   c  have detected passage of the printing paper, the CPU  211  determines that the printing paper has been discharged correctly from the paper discharge tray  403 . 
     The CPU  211  determines that paper discharge has been completed if it receives a detection signal indicating that printing paper has passed through one of the paper discharge tray sensors  406   a  to  406   c  within a predetermined time period. After the printing paper passed through the paper jam detection sensor  405   c , if a predetermined time period has elapsed without the printing paper passing through any one of the paper discharge tray sensors  406   a  to  406   c , the CPU  211  determines that a paper jam has occurred, and controls each component to stop the printing paper conveying operation. The predetermined time period may be decided in accordance with the distance from the paper jam detection sensor  405   c  to each of the paper discharge tray sensors  406   a  to  406   c.    
     Next, registration of printing paper for the respective paper feed trays in the image forming apparatus  121  by the user will be described with reference to  FIGS. 5A to 5D  and  FIG. 6 .  FIG. 5A  is a diagram showing a printing paper registration screen  500  displayed on the display unit in the operation unit  240 . On the registration screen  500 , various setting items are organized by group, and a paper setting registration key  501  is displayed that can be selected by the user on the registration screen  500 . Upon the paper setting registration key  501  being pressed by the user, the CPU  211  displays a printing paper feed tray selection screen  510  on the display unit in the operation unit  240 . 
       FIG. 5B  is a diagram showing the printing paper feed tray selection screen  510 . In the paper feed tray selection screen  510 , paper feed tray keys  511  indicating the paper feed unit  233 , paper feed tray numbers  512 , remaining paper amount indications  513  indicating a remaining paper amount in the paper feed trays, paper type indications  514  indicating the types of paper in the paper feed trays, and paper sizes  515  indicating the sizes of paper in the paper feed trays are displayed. The remaining paper amount indications  513  indicating the remaining paper amount in the corresponding paper feed trays and the paper sizes  515  indicating the sizes of paper in the paper feed trays are displayed based on a count value obtained by a placed paper amount sensor, which is provided within each paper feed tray, counting the number of sheets of printing paper when the printing paper is fed into the paper feed trays. Upon one of the paper feed tray key  511  and a setting key  516  being pressed by the user, the CPU  211  starts processing for allocating the paper type to the corresponding paper feed tray. The CPU  211  also displays a paper type registration screen  520  on the display unit in the operation unit  240 . 
       FIG. 5C  is a diagram showing the paper type registration screen  520 . On the paper type registration screen  520 , paper types  521  are displayed. On the paper type registration screen  520 , a plurality of paper types that can be registered are displayed. Upon a desired paper type  521  being pressed by the user, the CPU  211  allocates the paper type selected in  FIG. 5C  to the paper feed tray selected in  FIG. 5B . In this example, it is assumed that the user pressed and thus selected “Tabbed paper”. In this case, the CPU  211  displays a screen  530  for setting the tab count on tabbed paper on the display unit in the operation unit  240 . 
       FIG. 5D  is a diagram showing the screen  530  for setting a tab count on a tabbed paper. On the screen  530  for setting the a tab count on a tabbed paper, tab count information  531  indicating a user input value, input keys  532 , and a setting confirmation key  533  are displayed. The screen  530  for setting a tab count on tabbed paper is a screen for the user to input the tab count on tabbed paper. When the CPU  211  detects the tab count on tabbed paper input by the user using the input keys  532 , the CPU  211  stores the tab number as tab count information  531  about the tabbed paper in the RAM  213 . Then, upon the setting confirmation key  533  being pressed by the user, the CPU  211  displays a paper information registration setting screen  600  on the display unit in the operation unit  240 . 
       FIG. 6  is a diagram showing the paper information registration setting screen  600 . The details of  FIG. 6  will be described in a second embodiment. 
       FIG. 7  is a diagram showing an exemplary content set through the registration screens shown in  FIGS. 5A to 5D  and  FIG. 6 . As shown in  FIG. 7 , information about the type of printing medium placed in each paper feed tray and the paper feed trays for which the printing order is designated is registered. The information shown in  FIG. 7  is stored in the RAM  213 , and read out as needed by the CPU  211 , for example. 
     Next, acquisition of information about printing paper remaining within the image forming apparatus  121  when a paper jam has occurred will be described.  FIGS. 8 and 9  are diagrams for illustrating processing for acquiring information about printing paper remaining within the image forming apparatus  121  when a paper jam has occurred. Here, as shown in  FIG. 8 , it is assumed that a print job  800  that is currently targeted for printing is a print job consisting of 11 pages. The paper types of the respective pages of the print job  800  are a cover page  801  that is fed from an inserter in the paper feed unit  233 , plain paper  802   a , plain paper  802   b , tabbed paper  803   a , tabbed paper  803   b , and colored paper  804 . 
     If a paper jam occurs during printing processing according to the print job  800 , the discharged paper number monitoring portion  303  and the fed paper number monitoring portion  302  specify the types of printing paper remaining on the conveying path  401  based on detection signals from the paper feed tray sensors and the paper discharge tray sensors, under the control of the CPU  211 . In the present embodiment, the paper state specifying portion  301  determines that no printing paper remains on the conveying path  401  if the number of sheets of printing paper that have already been fed and the number of sheets of printing paper that have already been discharged satisfy expression (1). 
       Fed paper number−discharged paper number=0  (1)
 
     On the other hand, the paper state specifying portion  301  determines that there is printing paper remaining on the conveying path  401  if expression (2) is satisfied. 
       Fed paper number−discharged paper number&gt;0  (2)
 
     If it is determined that printing paper remains on the conveying path  401 , the CPU  211  specifies a leading page and a trailing page of the printing paper remaining on the conveying path  401 , based on the fed paper number and the discharged paper number. A value obtained by subtracting the discharged paper number from the total page number in the current print job is specified as the leading page. A value obtained by subtracting the fed paper number from the total page number in the current print job is specified as the trailing page. The CPU  211  specifies the types of printing paper remaining on the conveying path  401  by comparing the leading page and the trailing page to the types of printing paper of the respective pages set in the print job  800  by the user. 
       FIG. 9  is a diagram showing exemplary information in which the types of printing paper remaining on the conveying path  401  at the time of occurrence of a paper jam are specified. As shown in  FIG. 9 , it is clear that the number of sheets of printing paper that have already been fed from the paper feed trays and the inserter is nine. It is also clear that the number of sheets of discharged paper that have been printed and output is three. In other words, based on those two values, the number of sheets of printing paper remaining on the conveying path  401  at the time of occurrence of the paper jam is calculated to be six from page  4  to page  9  in the print job  800 . The CPU  211  compares the remaining printing paper to the types of printing paper on the respective pages set in the print job  800  (e.g.,  FIG. 8 ), and determines that five sheets of plain paper and one sheet of colored paper remain on the conveying path  401 . 
     A procedure of print control processing at the time of occurrence of a paper jam will be described with reference to  FIG. 10 .  FIG. 10  is a flowchart showing the procedure of the print control processing at the time of occurrence of a paper jam in the present embodiment. The processing shown in  FIG. 10  is implemented by the CPU  211  executing the control program stored in the ROM  212 , for example. The CPU  211  waits for receipt of a print job from the client PC  101  or  102  (S 1001 , S 1002 ). Here, upon the image forming apparatus  121  receiving the print job, the CPU  211  controls the PDL processing unit  220  and the image output unit  230  to perform the printing processing on each page with respect to the received print job (S 1003 ). The CPU  211  determines whether or not a paper jam has occurred on the conveying path  401  during the printing processing, based on detection signals from the paper feed tray sensors  404 , the paper jam detection sensors  405 , and the paper discharge tray sensors  406  (S 1004 ). If it is determined in step S 1004  that a paper jam has not occurred, the CPU  211  determines whether or not the printing processing has finished on all pages. Here, if it is determined that the printing processing has finished on all pages, the processing shown in  FIG. 10  is ended. On the other hand, if is determined that the printing processing has not finished on all pages, the processing from step S 1003  onward is repeated. 
     If it is determined in step S 1004  that a paper jam has occurred, the CPU  211  stops the printing paper conveying operation, and displays a paper jam handling procedure on the display unit in the operation unit  240  (S 1006 ). The paper jam handling procedure is, for example, an illustration of the location where the paper jam has occurred and a procedure for resolving the paper jam. The user can resolve the paper jam by removing the paper remaining on the conveying path  401  in accordance with the paper jam handling procedure. The data for displaying the paper jam handling procedure is stored in advance in the data storage unit  250 . Subsequently, the CPU  211  continues to cause the screen of the paper jam handling procedure to be displayed on the operation unit  240  until the user finishes the paper jam handling procedure (S 1007 ). After the paper jam is resolved, the CPU  211  advances the processing to step S 1008 . 
     Next, the CPU  211  determines whether or not the print job received in step S 1002  is a print job for which the user needs to open and close the paper feed unit  233  to check the printing paper placed in the paper feed trays  402  (S 1008 ). At this time, if the print job is not a print job in which the printing processing is performed using special paper such as tabbed paper set on the screens shown in  FIGS. 5A to 5D , the CPU  211  determines that the print job is not a print job for which checking of the printing paper placed on the paper feed unit  233  is necessary. Then, the CPU  211  returns to the printing processing in step S 1003 , and automatically resumes the stopped printing processing. On the other hand, if the print job is a print job in which the printing processing is performed using special paper such as tabbed paper set on the screens shown in  FIGS. 5A to 5D , the CPU  111  determines that the print job is a print job for which checking of the printing paper placed in the paper feed trays is necessary, and advances the processing to step S 1009 . This is because, in the case of a print job in which the printing processing is performed using the tabbed paper set on the screens of  FIGS. 5A to 5D , there is a possibility that the consistency between the tabbed paper that has already been discharged and the tabbed paper that is fed after the printing is resumed cannot be maintained, if the printing is simply resumed after removing the paper on the conveying path  401 . 
     The CPU  211  acquires information about the printing paper that currently remains on the conveying path  401  to facilitate the task of the user checking the paper feed unit  233  (S 1009 ). In the present embodiment, the CPU  211  determines whether or not tabbed paper is included in the paper information acquired in step S 1009  (S 1301 ). In other words, the CPU  211  determines whether or not special paper exists on the conveying path  401 . Here, if it is determined that tabbed paper is not contained, the CPU  211  returns to the printing processing in step S 1003 , and resumes the stopped printing processing. On the other hand, if it is determined that tabbed paper is contained, the CPU  211  displays a pop-up screen shown in  FIG. 12  on the display unit in the operation unit  240  (S 1010 ). The screen shown in  FIG. 12  is a screen for prompting the user to open and close the paper feed tray in which the tabbed paper is placed to check the paper set therein. The user views the screen and arranges the order of the tabbed paper set in the paper feed tray. Specifically, the tabbed paper can be arranged so that the tabbed paper that should come after the tabbed paper that has already been discharged is at the top in the paper feed tray. On the display unit, a button (not shown) for accepting an instruction to resume (continue output) or stop the printing is also displayed. Here, if a resuming instruction from the user is accepted, the CPU  211  returns to the printing processing in step S 1003  and resume printing. On the other hand, if a stop instruction is accepted from the user, the CPU  211  stops the printing and ends the processing (S 1011 ). 
       FIG. 11  is a flowchart showing the procedure in S 1009  for acquiring information about paper remaining on the conveying path  401 , and the procedure in step S 1301  for determining whether or not special paper exists. The processing shown in  FIG. 11  is implemented by the CPU  211  executing the control program stored in the ROM  212 , for example. The CPU  211  controls the fed paper number monitoring portion  302  and the discharged paper number monitoring portion  303  to acquires the number of sheets of fed and discharged paper in the paper feed unit  233  and the paper discharge unit  232  (S 1101 ). The CPU  211  controls the paper state specifying portion  301 , compares the acquires number of sheets of fed and discharged paper to the types of the printing paper corresponding to the respective pages designated in the print job, and specifies the types of the printing paper remaining on the conveying path  401  (S 1102 ). 
     As described above, in the present embodiment, it is determined, at the time of occurrence of a paper jam, whether or not to automatically resume the printing after the paper jam is resolved, based on whether or not tabbed paper is included among the paper remaining on the conveying path  401 . Therefore, if tabbed paper is not included among the paper remaining on the conveying path  401 , unnecessary downtime can be prevented from occurring. 
     Second Embodiment 
     The first embodiment has been described, taking an example in which it is determined, at the time of occurrence of a paper jam, whether or not to automatically resume printing after the paper jam is resolved, based on whether or not tabbed paper is included among the paper remaining on the conveying path  401 . 
     The special paper with sequentiality is not limited to tabbed paper. For example, paper to which page numbers are provided in advance (paper including plain paper and thick paper) are also categorized as special paper with sequentiality. 
     In the present embodiment, an example will be described in which, in the case of printing an image on such paper, it is also determined, at the time of occurrence of a paper jam, whether or not to automatically resume printing after the paper jam is resolved, based on whether or not special paper is included among the paper remaining on the conveying path. 
     In the present embodiment, the user selects one paper type  521  to be registered for the paper feed tray from among the plurality of paper types on the paper type registration screen  520  shown in  FIG. 5C . Upon the user selecting one of the paper types  521 , the CPU  211  allocates the paper type selected in  FIG. 5C  to the paper feed tray selected in  FIG. 5B . Furthermore, the CPU  211  displays the paper information registration setting screen  600  shown in  FIG. 6  on the display unit in the operation unit  240 . On the paper information registration setting screen  600 , paper printing order designation information selection keys  601  and a setting confirmation key  602  are displayed. The paper information registration setting screen  600  is a screen for the user to set that the type of printing paper set in the paper feed tray is a type with respect to which the printing order has to be considered. If the CPU  211  detects that the user has selected “Designated” with the paper printing order designation information selection key  601 , it stores, in the RAM  213 , information indicating that the type of the printing paper set in the paper feed tray is a paper type with respect to which the printing order has to be considered. On the other hand, if the CPU  211  detects that the user has selected “Not designated” with the paper printing order designation information selection key  601 , it stores, in the RAM  213 , information indicating that the type of printing paper that is currently set is a paper type with respect to which the printing order need not be considered. Upon the setting confirmation key  603  being pressed, the CPU  211  ends this screen. Using the screen shown in  FIG. 6 , the user selects “Designated” when configuring settings for the paper feed tray in which paper that is provided in advance with page numbers is set. 
     Next, a procedure of print control processing at the time of occurrence of a paper jam will be described with reference to  FIGS. 10 and 11 .  FIG. 10  is a flowchart showing the procedure of the print control processing at the time of occurrence of a paper jam. The processing shown in  FIG. 10  is implemented by the CPU  211  executing processing based on the control program stored in the ROM  212 , for example. 
     The processing in the steps other than steps S 1008 , S 1301  and S 1302  is the same as that in the first embodiment, and will not be described here in detail. 
     In step S 1008 , the CPU  211  determines whether or not the print job received in step S 1002  is a print job for which the user needs to open and close the paper feed unit  233  to check the printing paper placed on the paper feed unit  233  (S 1008 ). At this time, if the print job is not a print job for performing the printing processing using the paper that has been designated as printing order designated paper on the screen shown in  FIG. 6 , the CPU  211  determines that the print job is not a print job for which the printing paper placed in the paper feed trays in the paper feed unit  233  needs to be checked. Then, the CPU  211  returns to the printing processing in step S 1003  and automatically resumes the stopped printing processing. On the other hand, if the print job is a print job for performing the printing processing using paper that has been designated as the printing order designated paper, the CPU  211  determines that the print job is a print job for which the printing paper placed in the paper feed trays needs to be checked, and advances the processing to step S 1009 . This is because, in the case of a print job for performing the printing processing using paper that has been designated as the printing order designated paper, there is a possibility that the consistency between the page numbers on the paper that has already been discharged and on the paper that is fed after the printing is resumed cannot be maintained if, the printing is resumed after only removing the paper on the conveying path  401 . 
     Then, the CPU  211  acquires information about paper that currently remains on the conveying path  401  to facilitate the user operation to check the paper feed unit  233  (S 1009 ). In the present embodiment, the CPU  211  determines whether or not the paper information acquired in step S 1009  contains special paper with sequentiality (S 1301 ). In other words, the CPU  211  determines whether or not special paper exists on the conveying path  401 . Here, if it is determined special paper is not contained, the CPU  211  returns to the printing processing in step S 1003  and resumes the stopped printing processing. On the other hand, if it is determined the special paper is contained, the CPU  211  displays a pop-up screen shown in  FIG. 12  on the display unit in the operation unit  240  (S 1010 ). The screen shown in  FIG. 12  is a screen for prompting the user to open and close the paper feed tray in which the special paper is placed to check the special paper set therein. The user views this screen and arranges the order of the special paper set in the paper feed tray. Specifically, the paper can be arranged so that the paper with a page number that should come after the paper that has already been discharged is at the top in the paper feed tray. 
     Other Embodiments 
     Note that in the above embodiments, an example has been described in which, in step S 1010 , the CPU  211  displays the screen shown in  FIG. 12 , thereby displaying the screen for prompting the user to open and close the paper feed tray in which the special paper is placed to check the special paper that is set therein. However, the present invention is not limited thereto. The paper feed trays may be provided with a structure for opening the paper feed trays under the control of the CPU  211 , and in step S 1010 , the CPU  211  may perform control for automatically opening the paper feed tray from which the special paper existing on the conveying path  401  was fed. Thus, the user can more easily adjust the state of special paper set in the paper feed trays. Furthermore, the CPU  211  may perform control so as not to accept a printing resuming instruction until it is detected that the paper feed trays have been opened, or closed after being opened to check the special paper. Thus, the special paper can be prevented from shifting after the printing is resumed. Note that each of the above-described embodiments may be implemented independently, or may be arbitrarily combined for implementation. 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable storage medium). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2012-053678, filed Mar. 9, 2012, which is hereby incorporated by reference herein in its entirety.