Patent Application
20170355186
The present invention relates to an image forming apparatus which performs image formation while continuously conveying sheets such as a copying machine and a printer.
Conventionally, in an image forming apparatus such as a copying machine and a laser beam printer, the recording position of an image with respect to a recording sheet sometimes deviates due to variations in sheet conveying accuracy, positional accuracy of a toner image to be recorded and so on. Therefore, various techniques have been proposed regarding the registration of the toner image with respect to the sheet.
For example, the technique is proposed by Japanese Patent Laid-Open No. S60-120369 in which the registration is carried out in the configuration in which a sheet detection sensor is disposed in the sheet conveying path, and once a sheet reaches the detection sensor, the pair of registration rollers is temporarily stopped, and the pair of registration rollers is driven for conveying again taking into consideration the arrival timing of the formed toner image.
In addition, the technique has been proposed by Japanese Patent Application Laid-open No. H03-36559 in which an image is formed with the timing based on a detection signal from a sheet detection sensor, and the formed toner image is transferred to a sheet.
In these techniques, it is common to design the apparatus such that the feeding control of sheets from a sheet stacking portion at the timing as early as possible and a large margin of delay for sheet conveying from the sheet stacking section to the pair of registration rollers is allowed. This is because the sheet jam is suppressed by presuming a reduction in conveying efficiency caused by roller slip due to abrasion or paper dust adhesion of rollers up to the registration roller pair and separation failure due to the sheets on the sheet stacking portion sticking to each other.
However, when the control for starting the sheet feeding at the timing as early as possible is performed, if the image formation interval becomes large by for example adjustment control for stabilizing the color tone, the sheet conveyed to the pair of registration roller has to wait there for a time longer than usual. In such a case, special paper such as coated paper has a possibility that the surface of the sheet is deformed due to long-time roller gripping and image defects occurs due to transfer failure of the deformed portion. Similarly, when a standby state continues for a long time with a sheet being in contact with the registration roller, there is a possibility that a loop shape is made and remains at a tip portion of the sheet thereby causing a transfer failure.
An object of the present invention is to provide an image forming apparatus capable of suppressing image defects even when an image formation interval becomes large in a case where special paper such as coated paper is used.
An image forming apparatus according to the present invention, comprising:
a feeding portion configured to feed a sheet;
an image forming portion configured to form an image on the sheet fed by the feeding portion;
a conveying portion configured to stop the sheet fed by the feeding portion at a predetermined position and to convey the sheet to the image forming portion in accordance with timing of an image formation by the image forming portion;
a type discriminating portion configured to discriminate a type of the sheet to be fed; and
a controlling portion configured to change a sheet feeding start timing of the feeding portion in accordance with the type of the sheet discriminated by the type discriminating portion such that a time period in which the sheet is being stopped by the conveying portion is changed.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Next, embodiments of an image forming apparatus according to the present invention will be explained with reference to the drawings.
<Overall Configuration of the Image Forming Apparatus>
First of all, an overall configuration of an image forming apparatus as well as the operation thereof will be briefly explained.
The image forming portion 3 of the present embodiment employs an electro-photographic system in which toner images of respective colors of yellow, magenta, cyan, and black are sequentially formed on four photosensitive drums 3a arranged side by side, and the toner images are transferred and superposed on the intermediate transfer belt 3b so as to form a color image, and the color image is transferred to the conveyed sheet. The sheet on which the toner image has been transferred is conveyed upward, heated and pressed by the fixing portion 4 thereby fixing the toner image thereon, and then discharged to the discharge portion 5.
The image reading portion 6 is arranged on the upper part of the apparatus. The image reading portion 6 sequentially feeds an original document sheet set in the original document tray 6a, optically reads the original document sheet with the scanner portion 6b, converts the read information into a digital signal, and sends the digital signal to the image forming portion 3.
(Sheet Feeding Apparatus)
Next, a sheet feeding configuration for feeding a sheet to the image forming portion 3 will be explained.
The registration roller 14 is a registration member and constitutes a conveying portion. The fed sheet is temporarily stopped at a predetermined position (the nip portion of the roller in the present embodiment) to stand by and the registration roller 14 is driven and rotated in synchronization with the timing of imaging of the toner image by the image forming portion 3 thereby conveying the sheet S again. As a result, the sheet is fed to the secondary transfer portion 15 in synchronization with the toner image formed by the image forming portion 3 and the toner image is transferred to a proper position of the sheet.
In the above explanation, as the configuration of the sheet feeding apparatus, the sheet feeding configuration from the feeding tray 2 is explained, however, the sheet feeding configuration from the sheet cassettes 1a and 1b is the same as that explained above.
(Controlling Portion)
The CPU 301 performs the original document feeding control of the image reading portion 6 via the original document feeding control portion 480. Further, the CPU 301 reads the image of the fed original document with the image sensor via the image reader control portion 280.
In the copy operation, the image signal control portion 281 processes a signal from the image sensor or the external computer 283 and outputs the processed signal to the printer control portion 285 via the external interface 282. The printer control portion 285 instructs the image forming portion 3 to form an image based on an instruction from the CPU 301. The image forming portion 3 drives the photosensitive drums 3a and so on based on the input video signal.
Also, based on an instruction from the CPU 301, the sheet feeding and the conveying control are performed for the sheet conveying portion 270 which controls driving of the pickup roller 12, the registration roller 14 and so on, which constitute the sheet feeding apparatus.
The operation portion 330 is used for selecting a color mode of forming an image, for displaying the state of the image forming apparatus, and for instructing a start of a copy and so on. Further, when the CPU 301 detects the sheet set on the feeding tray 2, a sheet size selection screen is displayed. The mode setting selected here is stored in the RAM 303.
<Operation Portion>
Next, the operation portion 330 will be explained.
After the sheet size has been determined, when the CPU 301 detects no sheet based on the state of the sheet presence/absence sensor 9, the sheet size information is made uncertain and this information is also stored in the RAM 303. Thereafter, when the sheet S is set, the sheet size selection screen is displayed again. The printing operation cannot be started until the sheet size is determined.
On the sheet type selection screen, the thin paper button 331, the plain paper button 332, the thick paper button 333, the coated paper button 334, the recycled paper button 335, the carbon paper button 336, the carbonless paper button 337, the OHP button 338 and the type OK button 339 are arranged. By selecting one of the buttons 331 to 338 and then pressing the type OK button 339, the preselected feeding stage and sheet type are determined and this information is stored in the RAM 303. In the present embodiment, the type of sheet of each feeding stage is previously selected. However, the apparatus may be configured such that after the size OK button 325 is pressed, for example, the sheet type selection screen is displayed and the sheet type may be chosen on the sheet type selection screen. Further, the default sheet type of the present embodiment is set as plain paper.
In the present embodiment, the type of the sheet to be fed is determined, and the feeding timing is changed according to the type of the sheet. Further, in the present embodiment, the type determining portion determines the type of sheet based on the designation from the operation portion 330.
In the present embodiment, two sheet type groups for which the feeding start timing is changed are provided. The two sheet type groups consist of a first sheet type group including at least plain paper and a second sheet type group including at least coated paper. On the surface of a sheet whose type belongs to the first sheet type group including plain paper, deformation or the like hardly occurs on even when the sheet waits for a predetermined time at the position of the registration roller 14. Further, on the surface of a sheet whose type belongs to the second sheet type group including coated paper, deformation or the like easily occurs when the sheet waits for a predetermined time at the position of the registration roller 14.
In the present embodiment, as shown in
<Feeding Timing of a Sheet Whose Type Belongs to the First Sheet Type Group>
As explained above, in the present embodiment, the feeding timing performed in feeding type A when a sheet whose type belongs to the first sheet type group is different from the feeding timing performed in feeding type B when a sheet whose type belongs to the second sheet type group. Next, the feeding type A and the feeding type B will be explained in detail.
First, the feeding type A for feeding a sheet which belongs to the first sheet type group will be explained.
First, the image forming timing in the image forming portion 3 will be explained. At timing T11, the image formation of the page (n−1) is started, and image formation of the page (n) is started at timing T 14 while maintaining a predetermined image formation interval. Similarly, the image formation of the page (n+1) is performed at the timing T18.
In the secondary transfer portion 15, the toner images formed by the image forming portion 3 are matched with the conveyed sheets and secondarily transformed on the conveyed sheets at the timing T15 (page (n−1)), the timing T20 (page (n)) and the timing T22 (page (n+1)), respectively.
The feeding control is performed for the page (n−1) from the timing T00. Specifically, the timing TOO is determined by calculation from the timing T11 and the timing T13 so as to be the same as the timing of the following page.
In the sheet feeding control, a sheet from the feeding tray 2 is fed and the sheet is conveyed to the registration roller 14. In the present embodiment, when the sheet is conveyed to the registration roller 14, the sheet temporarily stops (waits) there with the leading edge of the sheet being in contact with the nip portion of the registration roller 14 thereby forming a loop. Then, the time t_r is determined based on the image formation start timing T11 of the current page so as to match the timing T15 at which the toner image of the page (n−1) reaches the secondary transfer portion 15. At the timing T13 at which the time t-r has elapsed from the image formation start timing T11, the sheet conveying control is restarted and at the timing T15, the sheet and the image are matched at the secondary transfer portion 15. As a result, the page (n−1) waits for the time t_w1 from the end of the feeding control to the restart of the conveying control. In the conveying control according to the present embodiment, a control is made for the conveying of the sheet from the registration roller 14 to the secondary transfer portion 15.
The page (n) waits for the time t_s from the image formation start timing T11 of the previous page (n−1) and the feeding control is started at the timing T12. This means that the feeding control of the target page starts from the image formation start timing of the previous page of the target page. Similarly to the previous page (n−1), the conveying control is restarted at the timing T17 at which the time t_r has elapsed from the image formation start timing T14 of the current sheet and at the timing T20, the toner image and the image are matched at the secondary transfer portion 15. As a result, the page (n) also waits for the time t_w1 from the end of the feeding control to the restart of the conveying control.
The feeding control for the page (n+1) is started at the timing T16 at which the page (n+1) has waited for the time t_s from the image formation start timing T14 of the previous page (n). Similarly to the other pages, the conveying control is restarted at the timing T21 at which the time t_r has elapsed from the image formation start timing T18 of the current sheet and at the timing T22, the toner image and the image are matched at the secondary transfer portion 15. As a result, the page (n+1) also waits for the time t_w1 from the end of the feeding control to the restart of the conveying control.
As explained above, in the case of the feeding type A which feeds a sheet whose type belongs to the first sheet type group, the sheet is fed from the feeding tray 2 prior to the image formation start timing. In this manner, by performing the sheet feeding control from the feeding tray 2 at an earlier timing, it is possible to perform retrying a plurality of times for a feeding error from the feeding tray 2, so that the apparatus is stopped less frequently due to feeding errors.
Next, the sheet feeding timing in the case where the image adjustment is performed while the images of a plurality of pages are continuously formed will be explained. In the image adjustment, for example, adjustment control for stabilizing the color taste is performed and the image formation is stopped during that time. Therefore, when image adjustment is not performed, the image formation is continuously performed at a predetermined interval, whereas when image adjustment is performed, the image formation interval becomes longer than the predetermined interval.
Similarly to
At timing T31, the image forming portion 3 starts the image formation of the page (n−1), and starts the image formation of the page (n) at the timing T34 while maintaining a predetermined image formation interval. Then, the image adjustment is performed from the timing T38 at which image formation of the page (n) has ended. Thereafter, the image formation on the page (n+1) is performed from the timing T41 at which the image adjustment is completed.
In the secondary transfer portion 15, the toner images formed by the image forming portion 3 are matched with the conveyed sheets and secondarily transformed on the conveyed sheets at the timing T35 (page (n−1)), the timing T40 (page (n)) and the timing T43 (page (n+1)), respectively.
The feeding for the sheet of page (n−1) is performed at the timing T30. Specifically, the timing T30 is determined by calculation based at the timing T31 or the timing T33 so as to be the same as the timing of the following page. The time t_r is determined based the image formation start timing T31 of the current page so as to match the timing T35 at which the toner image of the page (n−1) reaches the secondary transfer portion 15. At the timing T33 at which the time t-r has elapsed from the image formation start timing T31, the sheet conveying control is restarted and at the timing T35, the sheet and the image are matched at the secondary transfer portion 15. As a result, the page (n−1) waits for the time t_w1 from the end of the feeding control to the restart of the conveying control.
The sheet of the page (n) waits for the time t_s from the image formation start timing T31 of the previous page (n−1) and the feeding control is started at the timing T32. This means that the feeding control of the target page starts from the image formation start timing of the previous page of the target page. Similarly to the previous page (n−1), the conveying control is restarted at the timing T37 at which the time t_r has elapsed from the image formation start timing T31 of the current sheet and at the timing T40 the toner image and the image are matched at the secondary transfer portion 15. As a result, the page (n) also waits for the time t_w1 from the end of the feeding control to the restart of the conveying control.
The feeding control for the sheet of the page (n+1) is started at the timing T36 at which the page (n+1) has waited for the time t_s from the image formation start timing T34 of the previous page (n). The feeding control is completed at the timing T39. However, because the image adjustment is performed before the image formation of the page (n+1), the image formation of the page (n+1) is not immediately started. When the image formation of the page (n+1) is started at the timing T41 at which the image adjustment has ended, the conveying control is restarted at the timing T42 at which the time t_r has elapsed and at the timing T43, the toner image and the image are matched at the secondary transfer portion 15.
The feeding control for the sheet of the page (n+1) after the image adjustment is performed as explained above is started at the image formation start timing of the page (n). However, the restart of the conveying control is performed at the timing T42 and, as a result, the sheet of the page (n+1) waits for the time t_w2. Since the inequality T_w1<t_w2 holds, the sheet waits for a toner image for a longer time period at the registration roller 14. However, in the case of a sheet whose type belongs to the first sheet type group such as plain paper, the surface shape is not deformed even if it is pressed against the registration roller 14 for a little longer period, so that a transfer failure or the like does not occur at the secondary transfer portion 15.
<Feeding Timing of a Sheet Whose Type Belongs to the Second Sheet Type Group>
When the type of a sheet to be fed belongs to the second sheet type group including coated paper and carbonless paper, there is a possibility that deformation or bending of the surface and so on may occur due to the sheet being pressed against the registration roller 14 for a long time. As a result, as shown in
In the present embodiment, it is exemplified that the sheet is stopped with the leading edge of the sheet being pressed to the nip portion of the registration roller 14. However, the leading edge of the sheet may not be pressed to the nip portion roller and the sheet may stand by while being nipped between a pair of rollers including the registration roller 14. That is, if the sheet is stopped for a long time with the sheet being nipped by the registration roller, there is a possibility that an image defect may occur due to a change in the surface property of the nipped portion of the sheet by the pressure of the roller pair.
Therefore, in the present embodiment, the sheet feeding start timing of the feeding type B for feeding a sheet whose type belongs to the second sheet type group is different from that of the feeding type A.
Similarly to
First, at timing T50, the image forming portion 3 starts the image formation of the page (n−1), and starts the image formation of the page (n) at the timing T53 while maintaining a predetermined image formation interval. Subsequently, the image adjustment is performed from the timing T57 and the image formation of the page (n+1) is performed from the timing T59.
In the secondary transfer portion 15, the toner images formed by the image forming portion 3 are matched with the conveyed sheets and secondarily transformed on the conveyed sheets at the timing T54 (page (n−1)), the timing T58 (page (n)) and the timing T62 (page (n+1)), respectively.
In the feeding type B, the sheet feeding control for the page (n−1) is performed from the image formation start timing T50 of the page (n−1). In the feeding type B, unlike the feeding type A, the feeding control is performed with the image formation start timing of the current sheet as a trigger. Specifically, the feeding operation is started immediately after the image formation start timing of the current sheet.
Then, the time t_r is determined based on the image formation start timing T50 of the current page so as to match the timing T54 at which the toner image of the page (n−1) reaches the secondary transfer portion 15. At the timing T62 at which the time t-r has elapsed from the image formation start timing T50, the conveying control is restarted and at the timing T54, the sheet and the image are matched at the secondary transfer portion 15. As a result, the page (n−1) waits for the time t_w3 from the end of the feeding control to the restart of the conveying control.
In this case, it is exemplified that the feeding operation is started immediately after the image formation start timing of the current sheet. However, it suffices if the feeding operation is performed accompanying the start of the image formation of the current sheet. For example, the feeding operation may be started after a predetermined time period elapsed from the image formation start timing of the current sheet. Also, the feeding operation may be started simultaneously with the image formation start timing of the current sheet, or the feeding operation may be started immediately before the image formation start timing of the current sheet.
Similarly, the feeding control for the page (n) is started from the image formation start timing T53 of the page (n). Next, the conveying control is restarted at the timing T56 at which the time t_r has elapsed from the image formation start timing T53 of the current sheet and at the timing T58 the toner image and the image are matched at the secondary transfer portion 15. As a result, the page (n) also waits for the time t_w3 from the end of the feeding control to the restart of the conveying control.
Similarly, the feeding control for the page (n+1) is started on the image formation start timing T59 of the current page. In this case, unlike the feeding type A, the feeding control is performed with the image formation start timing of the current sheet after the adjustment as a trigger. When the image formation for the page (n+1) is started at the timing T59, the conveying control is restarted at the timing T61 at which the time t_r has elapsed and the toner image and at the timing T62, the image are matched at the secondary transfer portion 15. As a result, the page (n+1) also waits for the time t_w3 from the end of the feeding control to the restart of the conveying control.
As explained above, in the feeding type A for feeding a sheet whose type belongs to the first sheet type group, the sheet feeding start timing of the sheet is set with the image formation start of the previous page as a trigger and the sheet is fed from the feeding tray 2 at a first timing prior to the image formation start timing of the current sheet. On the other hand, in the feeding type B for feeding a sheet whose type belongs to the second sheet type group, the image formation timing of the current sheet is used as a trigger and feeding is started at a second timing which is later than the first timing.
As explained above, by changing the sheet feeding timing between the case where the type of a sheet belongs to the first sheet type group and the case where the type of a sheet belongs to the second sheet type group, the inequality t_w3<t_w1<t_w2 holds for the waiting time periods at the registration roller 14. As a result, in the feeding type B which feeds a sheet whose type belongs to the second sheet type group, it is possible to reduce the waiting time as compared with the control of the feeding type A, and it is possible to prevent the image defect as shown in
<Flowchart Showing Sheet Feeding>
Here, with reference to
As explained above, it is possible to decide whether the feeding control is started at the image formation start timing of the previous sheet or the feeding control is started at the image formation start timing of the current sheet depending on the feeding type.
As explained above, according to the present embodiment, it is possible to perform a stable sheet conveying while preventing image defects by switching waiting time at the registration roller depending on whether the sheet is of a type in which it is highly possible that image defects such as transfer failure at the secondary transfer portion occur or not.
Next, a second embodiment of the present invention will be explained with reference to
In the first embodiment, in feeding a sheet whose type belongs to the second sheet type group, the sheet feeding timing is set with the image formation timing of the current sheet as a trigger irrespective of whether the image adjustment has occurred or not. However, in the present embodiment, when the image formation interval is equal to or less than the predetermined interval, the feeding is performed with the image formation timing of the previous sheet as a trigger, and when the image formation interval becomes longer than the predetermined interval due to image adjustment or the like, the feeding is performed with the image formation timing of the current sheet as a trigger. Whether image adjustment is to be performed or not is determined at the stage of image formation at least several pages before the image adjustment is performed.
Similarly to the other timing charts which are explained above, the vertical axis in
First, the timing of image formation in the image forming portion 3 will be explained. At timing T71, the image formation of the page (n−1) is started and the image formation of the page (n) is started at the timing T74 while maintaining a predetermined image formation interval. Then, the image adjustment is performed from the timing T77. The image formation of the page (n+1) is performed from the timing T79.
(Feeding Timing without Image Adjustment)
In the secondary transfer portion 15, the toner images formed by the image forming portion 3 are matched with the conveyed sheets and secondarily transformed on the conveyed sheets at the timing T75 (page (n−1)), the timing T78 (page (n)) and the timing T81 (page (n+1)), respectively.
The feeding for the sheet of the page (n−1) is performed at the timing T70. Specifically, the timing T70 is determined by calculation based at the timing T71 or the timing T73 so as to be the same as the timing of the following page (not shown). The time t_r is determined based the image formation start timing T71 of the current page so as to match the timing T75 at which the toner image of the page (n−1) reaches the secondary transfer portion 15. At the timing T73 at which the time t-r has elapsed from the image formation start timing T71, the sheet conveying control is restarted and at the timing T75, the sheet and the image are matched at the secondary transfer portion 15. As a result, the page (n−1) waits for the time t_w4 from the end of the feeding control to the restart of the conveying control.
The page (n) waits for the time t_s from the image formation start timing T71 of the previous page (n−1) and the feeding control is started at the timing T72. This means that the feeding control of the target page is started from the image formation start timing of the previous page of the target page. Similarly to the previous page (n−1), the conveying control is restarted at the timing T76 at which the time t_r has elapsed from the image formation start timing T71 of the current sheet and at the timing T78, the toner image and the image are matched at the secondary transfer portion 15. As a result, the page (n) also waits for the time t_w4 from the end of the feeding control to the restart of the conveying control.
(Feeding Timing with Image Adjustment)
The image adjustment is performed between the page (n) and the page (n+1). When it is determined that the image adjustment is to be performed, the control portion performs the feeding control not at the timing at which the time t_s has elapsed from the image formation start timing T74 of the previous page (n) as explained above, but at the image formation timing T79 of the current sheet.
When the image formation of the page (n+1) is started at the timing T79, the conveying control is restarted at the timing T80 at which the time t_r has elapsed, and at the timing T81, the toner image and the image are matched at the secondary transfer portion 15. As a result, the page (n+1) waits for the time t_w5 from the end of the feeding control to the restart of the conveying control.
As explained above, the feeding control is performed for the page (n+1) with the image formation timing of the current sheet as a trigger, the inequality t_w5<t_w4 holds. Thus, even if the image adjustment is performed between the pages, it is possible to prevent image defects as shown in
At the step S1303, it is determined whether the image formation or the image adjustment is to be performed next. When the image adjustment is to be performed next, the feeding control for the page (n) is ended, when the image formation is to be performed next, the process proceeds to the step S1304 where the process waits for the time t_s and determines whether there is a next sheet at the step S1305. When a next sheet exists, the process advances to the step S1306 where the feeding control of the next page (n+1) is started.
As explained above, when the image adjustment is to be performed next, the process proceeds to the next step without performing the feeding control.
As explained above, according to the present embodiment, when the image forming interval is equal to or less than a predetermined time even in the feeding type B, the image formation timing of the previous page is used as a trigger and a sheet is fed from the feeding tray 2 at an early timing. As a result, it is possible to perform retrying a plurality of times for a feeding error, so that the apparatus is stopped less frequently due to feeding errors. Further, when the image formation interval is longer than a predetermined interval, it is possible to prevent image defects by shortening the conveying stop time.
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 modifications, equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2016-116132, filed Jun. 10, 2016, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-116132 | Jun 2016 | JP | national |
