Patent Publication Number: US-7722036-B2

Title: Sheet conveying device and image forming system

Description:
This application is based on Japanese Patent Applications No. JP2006-007471 filed on Jan. 16, 2006, and No. JP2006-184398 filed on Jul. 4, 2006, the entire of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a sheet conveying device connected between an image forming device and a post-processing device, and relates to an image forming system. 
     BACKGROUND OF THE INVENTION 
     There has been used a post-processing device that conducts post-processing such as punching processing, stapling processing and sorting processing for sheets on which an image has been formed. For the purpose of making an option sorter connectable with outer equipment of plural types, as a post-processing device, there is proposed a technology to detect, by using an option sorter, the conveying speed for the sheet conveyed from the outer equipment, and thereby to control the conveying speed for the sheet in accordance with the detected conveying speed (for example, see Patent Document 1: Japanese Unexamined Patent Publication TOKKAI No. H03-227848). In many cases, the conveying speed for the sheet is usually adjusted at an entrance portion of a post-processing device as stated above. 
     However, when the conveying speed of the post-processing device is higher than the conveying speed of the image forming device, a sheet is stretched because of a speed difference when the sheet is conveyed to the post-processing device from the image forming device, and the image surface is rubbed by a conveying roller, which has been a problem. In the case of an image employing toner containing wax, in particular, the conveying roller rubs the sheet under the condition that wax is not solidified sufficiently, because the melting point of the wax is low, which has resulted in easy generation of uneven gloss. 
     When the conveying speed of the image forming device is different from that of the post-processing device, speed control of acceleration and deceleration is necessary on either one of the image forming device and the post-processing device, and for controlling speed acceleration and deceleration, it is necessary to secure a conveying path with a sufficient length, and it requires a load of providing an extra control mechanism on the image forming device or post-processing device, which has resulted in problems of large-sized apparatuses and complicated controls. 
     In a case where plural post-processing devices are connected to a single image forming device, neither acceleration nor deceleration is necessary between connected post-processing devices. Therefore, if a conveying path having a sufficient length for controlling acceleration and deceleration is provided on each post-processing device, conveying paths and control mechanism will be wasteful. 
     A subject of the invention is to prevent uneven gloss caused by acceleration of conveying speed in the case of conveying a sheet from an image forming device to a post-processing device whose conveying speed is higher than that of the image forming device. 
     SUMMARY OF THE INVENTION 
     In an aspect of the invention, there is provided a sheet conveying device connected between an image forming device for forming an image and a post-processing device of which sheet conveying speed is higher than a sheet conveying speed of the image forming device, the sheet conveying device including: 
     a feed-in roller for feeding in a sheet ejected from the image forming device; 
     a conveying roller for conveying the sheet; 
     an ejection roller for ejecting the sheet to the post-processing device; 
     a conveying path from the feed-in roller to the ejection roller; and 
     a controller for controlling sheet conveying speeds of the feed-in roller, conveying roller, and ejection roller, 
     wherein the controller performs control such that: 
     when the sheet conveying device feeds in the sheet ejected from the image forming device, the conveying speeds of the feed-in roller, conveying roller, and ejection roller are the same as a conveying speed at which the image forming device ejects the sheet; and 
     when the image forming device has completed ejection of a trailing edge of the sheet, the conveying speeds of the feed-in roller, conveying roller, and ejection roller are the same as a conveying speed at which the post-processing device feeds in the sheet. 
     In another aspect of the invention, there is provided an image forming system, including: 
     an image forming device for forming an image; 
     a post-processing device of which sheet conveying speed is higher than a sheet conveying speed of the image forming device; and 
     a sheet-conveying device, connected between the image forming device and post-processing device, for feeding in a sheet ejected from the image forming device and ejecting the sheet to the post-processing device, the sheet-conveying device including: 
     a feed-in roller for feeding in a sheet ejected from the image forming device; 
     a conveying roller for conveying the sheet; 
     an ejection roller for ejecting the sheet to the post-processing device; 
     a conveying path from the feed-in roller to the ejection roller; and 
     a controller for controlling sheet conveying speeds of the feed-in roller, conveying roller, and ejection roller, 
     wherein the controller performs control such that: 
     when the sheet conveying device feeds in the sheet ejected from the image forming device, the conveying speeds of the feed-in roller, conveying roller, and ejection roller are the same as a conveying speed at which the image forming device ejects the sheet; and 
     when the image forming device has completed ejection of a trailing edge of the sheet, the conveying speeds of the feed-in roller, conveying roller, and ejection roller are the same as a conveying speed at which the post-processing device feeds in the sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structural diagram of image forming system  1  in an embodiment of the invention; 
         FIG. 2  is a block diagram showing functional constitutions of image forming device  100 , sheet conveying device  200  and post-processing device  300  of the image forming system  1 ; 
         FIG. 3  is a flow chart showing processing at the time of power-on carried out by sheet conveying device  200 ; and 
         FIG. 4  is a flow chart showing processing carried out by sheet conveying device  200 , during image forming operation. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the invention will be described in detail as follows, referring to the drawings. 
       FIG. 1  shows a schematic structure of image forming system  1  in an embodiment of the invention. 
     As shown in  FIG. 1 , image forming system  1  includes image forming device  100 , sheet conveying device  200  and post-processing device  300 . 
     Image forming device  100  is provided with sheet feeding section  120  having plural sheet housing sections  121  and  122 , image forming section  130 , image reading section  140 , automatic document conveying section  141 , operation section  150 , sheet ejection roller  191 , sheet ejection sensor  192  and with sheet ejection outlet  193 . Further, in the image forming device  100 , there are provided sheet feeding path  101  through which the sheets are fed to image forming section  130  from sheet housing sections  121  and  122 , conveying path  102  covering from image forming section  130  to sheet ejection outlet  193  through sheet ejection roller  191  and conveying path for reverse side  103  that conducts reverse conveying. 
     Each of the sheet housing sections  121  and  122  houses sheets for image forming by collecting them in a respective group of the same paper sheet type and same sheet size, and feeds them to image forming section  130 . 
     The image forming section  130  forms a color image on a sheet. In the image forming section  130 , photoconductor  131  is charged by charging section  133 , then, the photoconductor  131  is subjected to exposure-scanning by a laser beam emitted from exposure section  134  based on image data of YMCK so that an electrostatic latent image is formed thereon, and the electrostatic latent image on the photoconductor  131  is developed by developing section  135  with toner in each color containing wax, thus, a toner image is transferred onto a sheet in transfer section  136 . Then, an image is formed by heat-fixing the toner image on the sheet in fixing section  132 . 
     Image reading section  140  reads a document sheet as image data. Specifically, a reflected beam resulting through reflection on the document sheet after being emitted from a light source is read by a CCD (Charge Coupled Device) image sensor. When using automatic document conveying section  141 , document sheets are conveyed to the image reading section  140  one by one from a bundle of documents set on the automatic document conveying section  141 , so that images are read. 
     Operation section  150  is equipped with various types of keys such as a numeral key and a start key. Further, the operation section  150  is equipped with a touch panel formed integrally with a display section such as LCD (Liquid Crystal Display), and it detects a position touched by a finger tip of a user or a touch pen, to receive operational instructions from the user. 
     Sheet ejection roller  191  ejects a sheet on which an image has been formed, from sheet ejection outlet  193 . Sheet ejection sensor  192  is a sensor to detect a sheet, and it detects a leading edge and a trailing edge of the sheet that is ejected from sheet ejection outlet  193 . 
     Sheet conveying device  200  is connected between image forming device  100  and post-processing device  300 , and it feeds in a sheet ejected from image forming device  100  and ejects the sheet to post-processing device  300 . As shown in  FIG. 1 , the sheet conveying device  200  has therein feed-in roller  241 , conveying rollers  242 ,  243 ,  244  and  245 , sheet ejection roller  246  and conveying path  201  covering from feed-in roller  241  to sheet ejection roller  246 . The aforesaid conveying path  201  is longer than a length in the conveying direction of the maximum sheet size processable by image forming device  100  and post-processing device  300 . Further, the conveying path  201  is a flex conveying path, and it is longer than a linear distance from feed-in roller  241  to an ejection roller. Owing to this, sheet conveying device  200  can be made small. 
     Post-processing device  300  is equipped with feed-in roller  341 , entrance sensor  342 , staple processing section  351 , stacker  352 , fixed sheet ejection tray  371  and up-and-down sheet ejection tray  372 . Further, on the post-processing device  300 , there are provided conveying path  301  for ejecting a sheet to fixed sheet ejection tray  371  and conveying path  302  for ejecting a sheet to up-and-down sheet ejection tray  372 . 
     Entrance sensor  342  is a sensor to detect a sheet, and it detects a leading edge and a trailing edge of the sheet that is fed in from feed-in roller  341 . 
     Staple processing section  351  conducts staple processing for a bundle of sheets stacked on stacker  352 . A bundle of sheets which has been subjected to staple processing is ejected to up-and-down sheet ejection tray  372 . 
     Sheets conveyed through conveying path  302  are stacked on stacker  352 . When conducting shift sheet ejection, shift processing is carried out for a bundle of sheets conveyed to stacker  352 . A bundle of sheets which has been subjected to shift processing is ejected to up-and-down sheet ejection tray  372 . 
     Even in the case of the mode where post-processing such as staple processing or shift processing is not carried out, sheets are ejected to up-and-down sheet ejection tray  372  through conveying path  302 , when forming a large amount of images. 
     Fixed sheet ejection tray  371  is a tray to which the sheets are ejected when a small amount of images are formed. Up-and-down sheet ejection tray  372  is a tray which can be ascended and descended depending on a thickness of a bundle of sheets to be ejected. 
       FIG. 2  is a block diagram showing a structure of control of image forming device  100 , sheet conveying device  200  and post-processing device  300  which construct image forming system  1 . Herein, description of the structure described in  FIG. 1  will be omitted. 
     AS shown in  FIG. 2 , image forming device  100  is equipped with controller  110 , sheet feeding section  120 , image forming section  130 , image reading section  140 , operation section  150 , reception section  160 , transmission section  170 , memory section  180 , sheet ejection roller  191 , and sheet ejection sensor  192 . 
     Controller  110  controls respective portions of image forming device  100  on an overall control basis, in accordance with an instruction inputted from operation section  150  or from reception section  160 . The controller  110  is equipped with CPU (Central Processing Unit), ROM (Read Only Memory) and RAM (Random Access Memory), while, CPU reads a program stored in ROM, then, loads the program into a work area in RAM, and carries out various types of processing in collaboration with the programs. 
     Sheet feeding section  120  feeds sheets housed in the sheet housing sections  121  and  122  to image forming section  130 . 
     Reception section  160  receives data from sheet conveying device  200 . For example, the reception section  160  receives, from sheet conveying device  200 , the information on types of post-processing showing a type of post-processing such as punch processing, folding processing or staple processing executable in post-processing device  300 , at the time of power-on. 
     Transmission section  170  transmits data to sheet conveying device  200 . For example, in the case of forming images, the transmission section  170  transmits to the sheet conveying device  200  the information on sheet ejection conveying speed showing conveying speed V 1  for ejecting sheets by image forming device  100 , the information on sheet type such as a sheet size and weight and the information of image forming such as color or black and white. 
     Memory section  180  stores data to be used for respective processing executed by image forming device  100  and data generated by various types of processing executed by image forming device  100 . 
     Sheet ejection roller  191  ejects, from the sheet ejection outlet  193 , the sheet on which images have been formed. 
     As shown in  FIG. 2 , sheet conveying device  200  is equipped with controller  210 , first transmission section  220 , first reception section  230 , second reception section  260 , second transmission section  270 , memory section  280 , feed-in roller  241 , conveying rollers  242 - 245  and sheet ejection roller  246 . 
     Controller  210  controls respective portions of sheet conveying device  200  on an overall control basis. The controller  210  is equipped with CPU, ROM and RAM, and CPU reads a program stored in ROM, then, load the program into a work area in RAM, and carries out various types of processing in collaboration with the programs. 
     First transmission section  220  transmits data to image forming device  100 . For example, second transmission section  220  transmits information on a type of post-processing to image forming device  100 , at the time of power-on. 
     First reception section  230  receives data from image forming device  100 . For example, first reception section  230  receives, from image forming device  100 , the information on conveying speed (V 1 ) for ejecting a sheet by image forming device  100 , the information on a type of sheet and information on image forming, during image forming operation. 
     Second reception section  260  receives data from post-processing device  300 . For example, the second reception section  260  receives, from post-processing device  300 , the information on conveying speed for feeding in showing conveying speed V 3  for feeding in a sheet in post-processing device  300  and the information on a type of post-processing, at the time of power-on. 
     Second transmission section  270  transmits data to post-processing device  300 . For example, the second transmission section  270  transmits information on a type of sheet and image forming information to post-processing device  300 , during image forming operation. 
     Controller  210  controls driving of feed-in roller  241 , conveying rollers  242 ,  243 ,  244  and  245  and sheet ejection roller  246 , and controls conveying speed for a sheet in sheet conveying device  200 . Specifically, the controller  210  makes the conveying speed in the case of feeding in the sheet ejected from image forming device  100  to be the same as conveying speed V 1  for ejecting the sheet by image forming device  100 , and when the ejection of the trailing edge of the sheet is detected by sheet ejection sensor  192  of image forming device  100 , the detected information is received by first receiving section  230  from image forming device  100 , and the controller  210  accelerates the conveying speed in sheet conveying device  200  to conveying speed V 3  that is the same as conveying speed V 3  for feeding in a sheet in post-processing device  300 . 
     Feed-in roller  241  feeds the sheet ejected from image forming device  100  into sheet conveying device  200 . 
     Memory section  280  stores data to be used for various types of processing conducted by sheet conveying device  200  and data generated by various types of processing conducted by sheet conveying device  200 . In the memory section  280 , there are stored information of conveying speed (V 1 ) for ejecting a sheet by image forming device  100  and information on conveying speed (V 3 ) for feeding in a sheet into post-processing device  300 . 
     Sheet ejection roller  246  ejects a sheet to post-processing device  300 . 
     AS shown in  FIG. 2 , post-processing device  300  is equipped with controller  310 , transmission section  320 , reception section  330 , feed-in roller  341 , post-processing section  350 , memory section  360  and sheet ejection section  370 . 
     Controller  310  controls respective portions of post-processing device  300  on an overall control basis. The controller  310  is equipped with CPU, ROM and RAM, and CPU reads out a program stored in ROM, then, loads the program into a work area in RAM, and carries out various types of processing in collaboration with the programs. 
     Transmission section  320  transmits data to sheet conveying device  200 . For example, the transmission section  320  transmits information on conveying speed (V 3 ) for feeding in a sheet in post-processing device  300  and information on a type of post-processing to sheet conveying device  200 , at the time of power-on. 
     Reception section  330  receives data from sheet conveying device  200 . For example, the reception section  330  receives, from sheet conveying device  200 , information on a sheet type and information on image forming, during image forming operation. 
     Feed-in roller  341  feeds in the sheet ejected from sheet conveying device  200  into post-processing device  300 . 
     Post-processing section  350  is equipped with a punch processing section (not shown), a folding processing section (not shown), staple processing section  351  and stacker  352 , and conducts post-processing such as punch processing, folding processing and staple processing for the sheet ejected from sheet conveying device  200  to be fed in. 
     Memory section  360  stores data to be used in respective types of processing conducted by post-processing device  300  and data generated by respective types of processing conducted by post-processing device  300 . 
     Sheet ejection section  370  has fixed sheet ejection tray  371  or up-and-down sheet ejection tray  372 , and ejects a sheet. 
     Next, operations in the present embodiment will be described. 
       FIG. 3  is a flow chart showing processing carried out by controller  240  of sheet conveying device  200  at the time of power-on. 
     First, when the power of image forming system  1  is turned on, information on conveying speed (V 3 ) for feeding in a sheet by post-processing device  300  is transmitted to sheet conveying device  200  from transmitting section  320  of post-processing device  300 . In the sheet conveying device  200 , information of conveying speed (V 3 ) for feeding in from the post-processing device  300  is received by second receiving section  260  (step S 1 ) to be stored in memory section  280  (step S 2 ). 
     Thus, the processing at the time of power-on is terminated. 
     Next,  FIG. 4  is a flow chart showing the processing carried out by controller  240  of the sheet conveying device  200  during image forming operation. 
     First, when image forming device  100  starts image forming operation, feed-in roller  241 , conveying rollers  242 ,  243 ,  244  and  245  and sheet ejection roller  246  are started to be driven by control of controller  240 , at conveying speed V 3  that is the same as conveying speed V 3  for feeding-in by post-processing device  300 , in the sheet conveying device  200  (step S 11 ). 
     When the leading edge of a sheet to be ejected is detected by sheet ejection sensor  192  of image forming device  100 , namely, immediately before the sheet is ejected from image forming device  100 , information on conveying speed (V 1 ) for ejecting a sheet by image forming device  100  is transmitted from transmitting section  170  of image forming device  100  to sheet conveying device  200 . In the sheet conveying device  200 , information on conveying speed (V 1 ) for sheet ejection is received from image forming device  100  by first receiving section  230  (step S 12 ) to be stored in memory section  280 . 
     Herein, when conveying speed V 3  for feeding-in by post-processing device  300  is higher than conveying speed V 1  by image forming device  100  (step S 13 ; Yes), controller  210  controls driving of feed-in roller  241 , conveying rollers  242 ,  243 ,  244  and  245  and sheet ejection roller  246  so that the conveying speed in sheet conveying device  200  is changed to the conveying speed that is the same as conveying speed V 1  for sheet ejection by image forming device  100 , wherein controller  210  decelerate the conveying speed from conveying speed V 3  to conveying speed V 1  (step S 14 ). 
     Then, the sheet ejected from image forming device  100  by conveying speed V 1  is fed in by feed-in roller  241  of sheet conveying device  200 . When the trailing edge of the sheet ejected is detected by sheet ejection sensor  192  of image forming device  100 , namely, when sheet ejection from image forming device  100  is completed (step S 15 ; Yes), controller  240  controls driving of feed-in roller  241 , conveying rollers  242 ,  243 ,  244  and  245  and sheet ejection roller  246  so that the conveying speed is changed to the conveying speed V 3  that is the same as the conveying speed V 3  by post-processing device  300 , wherein controller  240  accelerates the conveying speed from conveying speed V 1  to conveying speed V 3  (step S 16 ). Incidentally, since it is necessary to complete the change of conveying speed before the leading edge of the sheet is ejected from sheet conveying device  200 , the length of conveying path  201  of sheet conveying device  200  is set such that the condition by the following expression is satisfied. 
     (length of conveying path  201  of sheet conveying device  200 )≧(length, in the conveying direction, of maximum sheet size processable by image forming system  1 ) 
     After step S 16 , or when conveying speed V 3  of post-processing device  300  in step S 13  is not higher than conveying speed V 1  of image forming device  100  (step S 13 ; No), it is judged whether the sheet ejection is completed or not for post-processing device  300  in sheet conveying device  200  (step S 17 ). Completion of the sheet ejection by sheet conveying device  200  is judged based on detection of the trailing edge of the sheet by entrance sensor  342  of post-processing device  300 . 
     If the sheet ejection by sheet conveying device  200  to post-processing device  300  is completed (step S 17 ; Yes), it is judged whether a sheet to be ejected next is present or not (step S 18 ). When a subsequent sheet is present (step S 18 ; Yes), the flow goes back to step S 12 , then, information on conveying speed (V 1 ) for ejection of the subsequent sheet is received, and processing by steps S 12  to S 18  are repeated. 
     When a subsequent sheet is not present in step S 18  (step S 18 ; No), processing is terminated. 
     The sheet ejected from sheet conveying device  200  is fed in by post-processing device  300  at conveying speed V 3 , and is ejected after being subjected to post-processing. 
     As stated above, in the image forming system  1 , sheet conveying device  200  feeds in a sheet at conveying speed V 1  that is the same as conveying speed V 1  for sheet ejection by image forming device  100 , and when the trailing edge of the sheet is ejected from image forming device  100 , sheet conveying device  200  accelerates the conveying speed to conveying speed V 3  that is the same as conveying speed V 3  for feeding-in by post-processing device  300 . Therefore, it is possible to prevent uneven gloss caused by acceleration in the course of delivery in conveying of the sheet from image forming device  100  to post-processing device  300 . 
     Further, in sheet conveying device  200 , information on feed-in speed (v 3 ) for feeding-in by post-processing device  300  is received at the time of power-on, and information on sheet ejection speed (v 1 ) for sheet ejection by image forming device  100  is received during image forming operation. Therefore, even when information on sheet ejection speed (V 1 ) for sheet ejection at image forming device  100  and information of feed-in speed (V 3 ) for feeding-in by post-processing device  300  are not stored in sheet conveying device  200 , it is possible to cope with various combinations of image forming device  100  and post-processing device  300 , and thereby to enhance general versatility. 
     Further, since it is not necessary to provide a control mechanism for acceleration and deceleration for neither image forming device  100  nor post-processing device  300 , it is possible to relieve the load required for a control mechanism and the like for image forming device  100  and post-processing device  300 . 
     Further, in case of connecting various types of post-processing devices and image forming devices, the use of sheet conveying device  200  of a single type is sufficient, and it is possible to select a combination of an image forming device and a post-processing device freely. 
     Herein, the description of the aforesaid embodiment is an example of an image forming system relating to the invention to which the invention is not limited. Detailed structures and detailed operations of each device constituting the system may also be modified without departing from the spirit and scope of the invention. 
     In accordance with the invention, since a sheet conveying device accelerates the conveying speed of a sheet in the device, it is possible to prevent uneven glossiness which would be caused by a change in a conveying speed due to acceleration if a sheet be conveyed from an image forming device to a post-processing device without the above described conveying device between them. 
     Further, even without storing information on conveying speed for ejection of a sheet by an image forming device nor conveying speed for feeding in the sheet by a post-processing device, the sheet conveying device is applicable to various combinations of an image forming device and post-processing device, achieving a high versatility.