Abstract:
An image forming apparatus for discharging a sheet from a discharge port to a sheet tray, includes a main unit provided with a discharge port and movably provided with a sheet tray to hold the sheet discharged from the discharge port, a drive unit to start movement of the sheet tray toward a position of the discharge port on the basis of an instruction of image forming start, and an image forming unit to compare sheet tray movement time which is time required for the sheet tray to reach the discharge port by the drive unit with image formation processing time which is time of an image forming process performed before discharging the sheet from the discharge port and when the sheet tray movement time does not exceed the image formation processing time, to start the image forming process.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-98526 filed on Mar. 31, 2006, the entire contents of which are incorporated herein by reference. 
   BACKGROUND 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus aiming at speed-up of a process and a control method for the image forming apparatus. 
   2. Description of the Related Art 
   The operation of an image forming process of an MFP (Multi Function Peripheral) which is a conventional image forming apparatus will be explained. 
     FIG. 1  is a flow chart showing an example of the operation of the image forming process of a conventional MFP. Here, the image forming process when performing double-side print will be explained. The control unit of the MFP, upon receipt of an instruction (the start button is pressed) of image forming process setting and image forming process start from a user, executes this flow. Firstly, the control unit supplies a sheet from a cassette to an image forming unit, conveys the sheet with an image formed one side thereof by the image forming unit to an ADU (Auto Duplex Unit) (S 112 ), and furthermore, after conveying the sheet, stops the sheet by an aligning roller (S 113 ). 
   Next, the control unit judges whether the sheet tray selected as a discharge destination of the image forming process is the same as the sheet tray in use now as a discharge destination of the just prior image forming process or not (S 121 ). When the selected sheet tray is the same as the sheet tray in use now (YES at S 121 ), the control unit goes to Step S 131 . On the other hand, when the selected sheet tray is different from the sheet tray in use now (NO at S 121 ), the control unit moves the selected sheet tray (S 122 ). 
   Next, the control unit judges whether the movement of the selected sheet tray is completed or not (S 131 ). When the movement is not completed (NO at S 131 ), the control unit repeats Step S 131 . On the other hand, when the movement is completed (YES at S 131 ), the control unit starts conveying of the sheet from the aligning roller to the image forming unit (S 132 ). The sheet, after image forming by the image forming unit, is discharged to the selected sheet tray. 
   Further, as a prior art relating to the present invention, as indicated in Japanese Patent Application Publication No. 2001-282074, there is an image forming apparatus for controlling the timing of starting the operation of the image forming means according to the time required for the operation other than the image forming means and the time required for starting the image forming means. 
   However, as mentioned above, the control unit of the conventional MFP stops the sheet at the position of the aligning roller immediately before conveying it from the ADU to the image forming unit, moves the selected sheet tray, and at the point of time when the movement is completed, conveys the sheet to the image forming unit. 
   Namely, the sheet is stopped during movement of the sheet tray, so that the processing time of the MFP is increased. 
   SUMMARY 
   An object of the present invention is to provide an image forming apparatus for suppressing an increase in the processing time due to movement of a sheet tray and a control method for the image forming apparatus. 
   According to the embodiments of the present invention, there is provided an image forming apparatus for discharging a sheet from a discharge port to a sheet tray, comprising a main unit provided with a discharge port and movably provided with a sheet tray to hold the sheet discharged from the discharge port; a drive unit to start movement of the sheet tray toward a position of the discharge port on the basis of an instruction of image forming start; and an image forming unit to compare sheet tray movement time which is time required for the sheet tray to reach the discharge port by the drive unit with image formation processing time which is time of an image forming process performed before discharging the sheet from the discharge port and when the sheet tray movement time does not exceed the image formation processing time, to start the image forming process. 
   Furthermore, according to the embodiments of the present invention, there is provide an image forming apparatus for discharging a sheet from a discharge port to a sheet tray, comprising holding means provided movably on a main unit for holding the sheet discharged from the discharge port; drive means for starting movement of the holding means toward a position of the discharge port on the basis of an instruction of image forming start; and image forming means for comparing holding means movement time which is time required for the holding means to reach the discharge port by the drive means with image formation processing time which is time of an image forming process performed before discharging the sheet from the discharge port and when the holding means movement time does not exceed the image formation processing time, for starting the image forming process. 
   According to the embodiments of the present invention, there is provided a control method for an image forming apparatus for discharging a sheet from a discharge port to a sheet tray, comprising driving the sheet tray so as to start movement toward a position of the discharge port on the basis of an instruction of image forming start; and comparing sheet tray movement time which is time required for the driven sheet tray to reach the discharge port with image formation processing time which is time of an image forming process performed before discharging the sheet from the discharge port and when the sheet tray movement time does not exceed the image formation processing time, starting the image forming process. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a flow chart showing an example of the operation of the image forming process of the conventional MFP; 
       FIG. 2  is a schematic cross sectional view showing an example of the constitution of the MFP relating to the embodiments of the present invention; 
       FIG. 3  is a flow chart showing an example of the operation of the image forming process of the MFP relating to a first embodiment of the present invention; 
       FIG. 4A  is a table showing the sheet tray movement time; 
       FIG. 4B  is a table showing the image formation processing time; 
       FIG. 5  is a flow chart showing an example of the operation of the image forming process of the MFP relating to a second embodiment of the present invention; and 
       FIGS. 6A to 6C  are respectively schematic views showing the relationship between the stapler position of the finisher and sheets different in size. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Hereinafter, the embodiments of the present invention will be explained with reference to the accompanying drawings. 
   Firstly, the constitution of an MFP (Multi Function Peripheral)  10  relating to this embodiment will be explained. 
     FIG. 2  is a schematic cross sectional view showing an example of the constitution of the MFP  10  relating to this embodiment. The MFP  10  includes a control unit  11 , a sheet supply cassette  21 , a sheet supply roller  22 , an aligning roller  23 , an image forming unit  31 , an ADU  32 , a finisher  40 , a discharge unit  41 , a stapler  42 , a discharge port  43 , sheet trays  44   a  and  44   b  which are holding means for holding discharged sheets, and a sheet tray moving drive unit  51 . The control unit  11  controls each unit of the MFP  10 . The sheet tray moving drive unit  51  installed inside the finisher  40  moves the sheet tray selected by the control unit  11  among the sheet trays  44   a  and  44   b  to the discharge port  43 . 
   Next, the route of sheets in the MFP  10  will be explained. 
   For example, when double-side print is set in the MFP  10 , a sheet to be imaged is supplied from the sheet supply cassette  21  to the sheet supply roller  22  and is conveyed to the image forming unit  31  by the aligning roller  23 . The sheet is imaged on the front surface by the image forming unit  31 , is turned upside down by the ADU  32 , and is conveyed again from the aligning roller  23  to the image forming unit  31 . The sheet is imaged on the rear surface by the image forming unit  31 , is discharged from the discharge port  43  by the discharge unit  41 , and is held by the sheet tray  44   a . Further, for example, when the stapling process is set in the MFP  10 , the sheet imaged and conveyed to the discharge unit  41  is subject to the stapling process by the stapler  42 . After the stapling process, the sheet is discharged from the discharge port  43  and is held by the sheet tray  44   a . Further, the aligning roller  23  can keep the sheet stopped and the sheet conveyed from the aligning roller  23  to the image forming unit  31  cannot be stopped, thereby is discharged from the discharge port  43 . 
   Next, the operation of the image forming process of the MFP will be explained. 
     FIG. 3  is a flow chart showing an example of the operation of the image forming process of the MFP  10  relating to the first embodiment. The control unit  11 , upon receipt of an instruction of setting of the image forming process and start of the image forming process (the start button is pressed), executes this flow. The control unit  11 , on the basis of setting of the image forming process, selects the sheet tray ( 44   a  or  44   b ) to be used (S 11 ). Here, the setting of the image forming process includes, for example, setting of single-side print or double-side print, sheet size, sheet thickness, setting of the image data process such as image quality correction or forming a plurality of images on one sheet, and setting of the stapling process. In this example, the setting of the image forming process is setting of double-side print. 
   Next, the control unit  11  calculates the time required for movement of the selected sheet tray from the current stop position to the discharge port  43  and assumes the calculated result as sheet tray movement time. Furthermore, the control unit  11  calculates the time required from the start of the image forming process to discharging of the sheet from the discharge port  43  on the basis of the setting of the image forming process and assumes the calculated result as image formation processing time (S 12 ). 
   The control unit  11  includes a sheet tray movement time table ( FIG. 4A ) and an image formation processing time table ( FIG. 4B ). 
   In the sheet tray movement time table, the identification (ID) of the sheet tray (data indicating the discharge destination) and the sheet tray movement time corresponding to the current position are recorded beforehand. As shown in  FIG. 4A , when the sheet tray is at the position A and the sheet tray A is selected, the time required for the sheet tray A to move to the discharge port  43  is zero second. When the sheet tray is at the position A and the sheet tray B is selected, the time required for the sheet tray B to move to the discharge port  43  is x seconds. When the sheet tray is at the position B and the sheet tray A is selected, the time required for the sheet tray B to move to the discharge port  43  is y seconds. When the sheet tray is at the position B and the sheet tray B is selected, the time required for, the sheet tray B to move to the discharge port  43  is zero second. 
   In the image formation processing time table, in correspondence to the setting of the image forming process, the image formation processing time is recorded beforehand. As shown in  FIG. 4B , when the sheet size is A 3 , the time required for processing is AS seconds. When the sheet size is A 4 , the time required for processing is BS seconds. When the sheet size is B 5 , the time required for processing is CS seconds. When the process is required for the image data, the processing time is P seconds. When no process is required, the processing time is Q seconds. When executing stapling at two places, the processing time is a seconds. When executing stapling at one place, the processing time is .beta. seconds. When executing no stapling, the processing time is .gamma. seconds. 
   At Step S 12 , the control  11  obtains the ID of the sheet tray and the sheet tray movement time corresponding to the current position from the sheet tray movement time table. Further, the control  11  obtains the time of the image forming process corresponding to the setting of the image forming process from the image formation processing time table. Further, the sheet tray movement time may be calculated by the ID of the sheet tray, the current position, and a predetermined calculation formula. Further, the image formation processing time may be calculated using the calculation formula for totaling the processing time included in the image forming process on the basis of the setting of the image forming process. 
   Next, the control unit  11  judges whether the sheet tray ( 44   a  or  44   b ) selected at Step S 11  is the same as the sheet tray  44   a  in use now as a discharge destination of the just prior image forming process or not (S 21 ). When the selected sheet tray is the same as the sheet tray  44   a  in use now (YES at S 21 ), the control unit  11  goes to Step S 31 . On the other hand, when the selected sheet tray is the sheet tray  44   b  different from the sheet tray  44   a  in use now (NO at S 21 ), the control unit  11  makes the sheet tray moving drive unit  51  start movement of the selected sheet tray  44   b  (S 22 ). 
   Next, the control unit  11 , according to the route aforementioned, supplies the sheet to the image forming unit  31  from the sheet supply cassette  21  by the sheet supply roller  22  and conveys the sheet one side of which is printed by the image forming unit  31  to the ADU  32  (S 31 ). 
   Next, the control unit  11  judges whether the sheet tray movement time calculated at Step S 12  exceeds the image formation processing time calculated or not (S 41 ). When the sheet tray movement time does not exceed the image formation processing time (YES at S 41 ), the control unit  11  goes to Step S 51 . On the other hand, when the sheet tray movement time exceeds the image formation processing time (NO at S 41 ), the control unit  11  stops the sheet arriving at the aligning roller  23  (S 42 ). 
   Next, the control unit  11  judges whether the movement of the selected sheet tray  44   b  is completed or not (S 51 ). When the movement is not completed (NO at S 51 ), the control unit  11  repeats Step S 51 . On the other hand, when the movement is completed (YES at S 51 ), the control unit  11  starts conveying of the sheet from the aligning roller  23  to the image forming unit  31  (S 52 ). The sheet is conveyed to the selected sheet tray ( 44   a  or  44   b ) from the discharge port  43  via the image forming unit  31  and discharge unit  41  and the flow is finished. 
   Further, at Step S 12 , the control unit  11  further calculates the “sheet tray movement time—image formation processing time” as sheet stop time and instead of Step S 51 , may perform a process of calculating the time after arrival of the sheet at the aligning roller  23  and keeping the sheet stopped until this time reaches the sheet stop time. 
   Further, at Step S 12 , the control unit  11  may take the time required for the sheet to be conveyed from a place where the aligning roller  23  can stop to the discharge port  43  as image formation processing time and execute Step S 41  at the point of time when the sheet arrives at the place. 
   In this embodiment, the case that setting of the image forming process is setting of double-side print is described. When setting of the image forming process is setting of single-side print, the necessary time of single-side print recorded beforehand in the image formation processing time table results in the image formation processing time. At this time, instead of Step S 31 , the control unit  11  performs a process of only supplying the sheet from the sheet supply cassette  21  by the sheet supply roller  22 . Namely, the image formation processing time is less than that of double-side print by the processing time from the ADU  32  to the image forming unit  31 . 
   Further, when adding another process to the image forming process, the necessary time of the process is included in the image formation processing time. For example, when setting of the image data process is included in setting of the image forming process, the necessary time of the image data process recorded beforehand in the image formation processing time table is included in the image formation processing time. Further, for example, when setting of the stapling process is included in setting of the image forming process, the necessary time of stapling recorded beforehand in the image formation processing time table is included in the image formation processing time. 
   According to this embodiment, the control unit  11 , upon receipt of an instruction of start of the image forming process, starts immediately movement of the sheet tray and when the sheet tray movement time exceeds the image formation processing time, adjusts the conveying time of the sheet by the aligning roller, thereby can shorten the image formation processing time accompanied by the movement of the sheet tray. 
     FIG. 5  is a flow chart showing an example of the operation of the image forming process of the MFP relating to the second embodiment. 
   Steps S 201  to S 206  shown in  FIG. 5  are the same as Steps S 11  to S 41  shown in  FIG. 3 , so that the explanation thereof will be omitted. At Step S 206 , when it is judged that the sheet tray movement time exceeds the image formation processing time (NO at S 206 ), the image formation is kept stopped (S 207 ). Next, the control unit  11  judges whether the movement of the sheet tray is completed or not (S 208 ). The control unit  11 , when judging that the movement is not completed (NO at S 208 ), repeats Step S 208 . The control unit  11 , when judging that the movement of the sheet tray is completed (YES at S 208 ), starts image formation (S 209 ). Further, at Step S 206 , the control unit  11 , when judging that the sheet tray movement time does not exceed the image formation processing time (YES at S 206 ), starts image formation (S 209 ). 
   Further, for calculation of the image formation processing time aforementioned, it is possible to obtain information of a mounting condition of an option, thereby change the calculation table. 
     FIG. 6A  shows a case that short sheets are used, which is a case that the finisher  40  is mounted optionally. 
   As shown in  FIG. 6A , the distance from the stapler  42  to the discharge port  43  is slightly shorter than the length of the short sheets in the sheet conveying direction. Therefore, on the sheet tray  44 , a plurality of sheets are all stacked and may be moved to the discharge port  43  before stapling them. However, as shown in  FIG. 6B  in which long sheets are used, when the distance from the stapler  42  to the discharge port  43  is considerably shorter than the length of the long sheets in the sheet conveying direction, unless the sheet tray  44  moves to the discharge port  43  before one sheet is stapled, it falls down. As mentioned above, the calculation of the image formation processing time is varied with the sheet length. 
   However, an option can be changed and it is assumed that as shown in  FIG. 6C , the finisher  40  when the distance from the stapler  42  to the discharge port  43  is slightly shorter than the length of the long sheets in the sheet conveying direction is switched to the finisher  40  shown in  FIGS. 6A and 6B . If this occurs, on the sheet tray  44 , a plurality of sheets are all stacked and may be moved to the discharge port  43  before stapling them, and even if similarly long sheets are used, by use of the finisher  40 , conveyance of the sheets arriving at the aligning roller can be started early, thus the throughput is improved. 
   Further, by use of the current position of the sheet tray to be used and the sheet tray movement time table, the sheet tray movement time can be calculated easily. Further, by use of the image formation processing time table, appropriate image formation processing time according to the process included in the setting of the image forming process can be calculated. 
   This embodiment is explained using the case that the functions for executing the invention are recorded beforehand in the apparatus. However, the present invention is not limited to it, and similar functions may be loaded down into the apparatus from the network, and a recording medium storing similar functions may be installed in the apparatus. As a recording medium, a recording medium which can store a program and can be read by the apparatus such as CD-ROM is acceptable regardless of its form. Further, the functions obtained beforehand by installation or down load like this may be realized in partnership with the operating system (OS) inside the apparatus. 
   Further, the sheet tray corresponds to the sheet trays  44   a  and  44   b  in the embodiments. Further, the sheet tray moving drive unit corresponds to the sheet tray moving drive unit  51  in the embodiments. Further, the image forming unit corresponds to the sheet supply cassette  21 , sheet supply roller  22 , aligning roller  23 , image forming unit  31 , ADU  32 , discharge unit  41  and stapler  42  in the embodiments. 
   Further, the sheet tray moving drive step corresponds to Steps S 21  and S 22  in the embodiments. Further, the image forming step corresponds to Steps S 41 , S 42 , S 51  and S 52  in the embodiments. 
   According to the present invention, an increase in the processing time due to movement of the sheet tray can be suppressed.