JPH05319630A - Sheet feeding method for image forming device - Google Patents

Abstract

PURPOSE:To surely feed sheets to an image forming section at timings in synchronization with image forming movement and at the required minimum sheet intervals. CONSTITUTION:The first sheet stop position where a sheet P is temporarily stopped with the end hitting a timing roller 12 to be fed thereto in synchronization with sheet feeding movement by an image forming section, and the second sheet stop position, at least the length of the sheet P in the carrying direction stop from the first sheet stop position onto the upsteam side of a sheet carrying passage 8, where the sheet P held by a gripping roller 7 is temporarily stopped are provided. During not only the time when the preceding sheet P1 is stopped at the first sheet stop position but also the time when the following sheet P2 is carried to the second sheet stop position, great sheet interval irregularity, if occurring at a sheet separation section, is corrected and reduced at the second sheet stop position as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a sheet feeding method for an image forming apparatus such as a laser beam printer, a digital copying machine, and a plain paper facsimile that sequentially feeds the sheets separated and fed out to an image forming unit.

[0002]

2. Description of the Related Art As a conventional sheet feeding method for an image forming apparatus, for example, there is a method described in JP-A-59-227639. That is, the stacked sheets are sent out to the sheet separating section by the pickup roller, and the sheet is conveyed by the sheet separating section and a pair of conveying rollers provided on the downstream side of the conveying, and the trailing end of the sheet is the sheet separating section. The next sheet is again fed by the pickup roller after passing through the sensor provided on the downstream side of the sheet conveyance, and when the sensor detects the leading edge of the sheet to be conveyed thereafter, the sheet conveyance is temporarily stopped and the sheet is separated. Uniformly corrects the sheet variation in position. This operation is always performed by the same operation regardless of the sheet length of the fed sheet.

[0003]

However, in the case of such a sheet feeding method, the sheet fed by the pickup roller is, for example, 1 sheet by a sheet separating section made of a pair of rollers pressed against each other in the vertical direction. When the sheets are separated, the sheets are fed while slipping at different slip amounts for each sheet, so even if the pickup roller always sends the sheets accurately at a fixed time interval, it will pass the sheet separation section. In this case, a large variation occurs in the sheet interval between the preceding sheet and the following sheet.

Therefore, in the conventional sheet feeding method, as shown in FIG.
As shown in FIG. 3, in consideration of the maximum variation width Bmax, the succeeding sheet P2 is fed at the timing when the sheet interval La is opened between the preceding sheet P1 and the succeeding sheet P2. .. By the way, in the conventional analog type copying machine, since the scanning time of the manuscript is intervened every time an image is formed on the sheet, it is necessary to make the sheet interval large. Further, in a page printer or plain paper facsimile, it takes a long time for image processing to perform printing, so that feeding with a short sheet interval has not been taken up.

However, due to the advent of digital copying machines in recent years, speeding up of image processing apparatuses installed in printers and facsimiles, and further improvement in efficiency, sheet intervals are reduced as much as possible (for example, about 5 mm). There has been a growing demand for high-speed processing that maximizes the number of prints that can be processed per hour.

Therefore, for example, as shown in FIG. 13, the grip roller 23 is arranged on the downstream side of the sheet separating section 24 in the conveyance, and the timing roller 22 is arranged on the downstream side thereof, and the sheet separating section 24 separates the sheet into one sheet. Grip roller 2
The sheet conveyed to the timing roller 22 in the stopped state by 3 is conveyed at a predetermined timing at a higher speed than the conveying speed up to that point (a portion), and the preceding sheet P1 and the succeeding sheet P2 are conveyed. If the sheet interval La is reduced on the conveyance path to the image forming unit 20 so that the small sheet interval Ls can be obtained, high-speed processing that can obtain a large number of prints per unit time becomes possible.

However, in the case of the conventional sheet feeding method, as shown in FIG. 13, the variation width Bmax of the succeeding sheet P2 at the time when the sheet separating section 24 is passed.
Is very large, so when the slippage at the sheet separating section 24 is minimal, the fastest feeding (line b),
When the leading edge of the sheet P2 is fed to the point c and reaches the timing roller 22, the sheet P2 has to be abutted against the timing roller 22 which is originally in a stopped state and registration adjustment is required. Then, as shown in the figure, the timing roller 22 moves the preceding sheet P1.
Since it is the timing when the trailing edge of the trailing edge has just been conveyed, the trailing edge of the trailing edge of the sheet P2 has not been completely stopped yet, and there is not enough time for the trailing edge of the sheet P2 to abut. Therefore, in such a case, accurate registration adjustment of the subsequent sheet P2 cannot be performed.

The present invention has been made in view of the above-mentioned problems, and ensures accuracy of sheets at the minimum sheet interval necessary for the image forming section and at the timing synchronized with the image forming operation by the image forming section. The purpose is to enable good continuous feeding. It is also an object to be able to feed a sheet at a timing synchronized with the image forming operation regardless of the sheet size.

[0009]

In order to achieve the above object of the present invention, in the sheet feeding method of the image forming apparatus as described above, the image forming operation by the image forming section and the sheet feeding to the image forming section are performed. A first sheet stop position at which the sheet is temporarily stopped to synchronize the sheet feeding timing, and a position separated from the first sheet stop position on the upstream side of the sheet conveyance path by a distance equal to or more than the length in the sheet conveyance direction. An image in which a second sheet stop position for temporarily stopping the sheet is provided, and a subsequent sheet is conveyed to the second sheet stop position, including a period in which the preceding sheet is stopped at the first sheet stop position. A sheet feeding method for a forming apparatus is provided.

In the sheet feeding method of the image forming apparatus, the second sheet stop position may be changed according to the length of the sheet to be fed in the conveying direction, or the leading edge of the sheet to be fed may be changed. The sheet conveyance speed during the period from the second sheet stop position to the first sheet stop position may be changed according to the length of the sheet in the conveyance direction. Further, the length of the sheet conveyance path between the first sheet stop position and the second sheet stop position may be changed according to the length of the sheet to be fed in the conveyance direction, or the second sheet stop position may be changed. It is preferable that the timing of restarting the transportation of the sheet stopped at the position is after a certain period of time including 0 after the restart of the transportation of the sheet stopped at the first sheet stop position.

Further, the arrival of the sheet at the second sheet stop position has passed since the point at which the means for detecting the sheet on the upstream side of the second sheet stop position detects the leading edge of the sheet. You should figure out by time. Further, when a sheet having a long length in the conveying direction is fed such that the trailing edge of the sheet reaches the upstream side of the second sheet stopping position in the conveying state while the sheet is stopped at the first sheet stopping position, There is also provided a sheet feeding method of an image forming apparatus, which does not start the feeding operation of a succeeding sheet until the re-conveying of the preceding sheet stopped at the first sheet stop position is started.

[0012]

According to the sheet feeding method of the image forming apparatus,
Stop the trailing sheet because the trailing sheet is conveyed to the second sheet stop position including the period in which the preceding sheet is stopped at the first sheet stop position for timing adjustment. As a result, even if there is a large variation in the sheet spacing in the sheet separating section, it can be corrected and reduced. Further, if the second sheet stop position is changed according to the length of the sheet to be fed in the transport direction, the second sheet stop position corresponding to each length of the sheet to be fed can be changed.
The seat can be stopped at the seat stop position.

Further, the sheet conveying speed during the period in which the leading edge of the sheet to be fed from the second sheet stop position to the first sheet stop position is changed according to the length of the sheet in the conveying direction. , Even if the following sheet is stopped too much at the second sheet stop position as in the case of a small size sheet and the preceding sheet is too wide to absorb the variation between them, By increasing the conveying speed, the variation can be absorbed, and the sheet interval can be set to the preset minimum interval.

Further, if the length of the sheet conveying path between the first and second sheet stop positions is changed according to the length of the sheet to be fed in the conveying direction, the sheet is conveyed according to the sheet size. Since the length of the path can be changed, even if a large size sheet is fed through the long transport path, the trailing edge of the sheet at the first sheet stop position is moved to the second sheet stop position. Since it is possible to prevent the sheet from reaching the second sheet, it is possible to surely correct the sheet variation generated when the succeeding sheet is stopped at the second sheet stop position and the sheet is separated into one sheet.

Further, if the timing of resuming the conveyance of the sheet stopped at the second sheet stop position is a certain period of time including 0 after the resumption of the conveyance of the sheet stopped at the first sheet stop position, Since the sheet that has already passed through the sheet separating portion that is likely to cause variations in the sheet interval and has stopped at the second sheet stop position is fed at the above timing, the sheet can be controlled in a very simple manner. It is possible to reliably correct variations in feeding.

Further, the arrival of the sheet at the second sheet stop position has passed since the time when the means for detecting the sheet on the upstream side of the second sheet stop position detects the leading edge of the sheet. If the indexing is performed based on time, the position of the sheet to be stopped at the second stop position can be adjusted corresponding to each size of sheet with a simple configuration.

Then, in the state where the sheet is stopped at the first sheet stop position, a sheet having a long length in the conveying direction is reached such that the trailing end of the sheet reaches the upstream side of the second sheet stop position in the conveying direction. When the sheet is fed, the feeding operation of the succeeding sheet is not started until the re-conveying of the preceding sheet stopped at the first sheet stop position is started. If the trailing edge reaches the second sheet stop position and the trailing sheet cannot be stopped at the second stop position, the feeding of the subsequent sheet is Since the paper operation is stopped and the preceding sheet is re-fed and then fed,
Even a large size sheet will not cause any problems.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic diagram showing a conveying system of a sheet feeding apparatus for carrying out a sheet feeding method of an image forming apparatus according to an embodiment of the present invention.

In this sheet feeding apparatus, the pickup roller 2 of the sheet feeding apparatus 1 is rotated in the direction of arrow A, and the sheets P stacked on the sheet stacking portion 3 are sequentially fed in the direction of arrow B from the upper side, and the sheets are fed. When a rotational force is applied to the feed roller 5 rotatable in the arrow direction and a torque limiter (not shown) in the arrow direction counter to the rotation, and the torque becomes equal to or less than a predetermined torque as in the case of double feeding, the direction indicated by the arrow. The sheet is separated by the known FRR type sheet separating section 4 including a reverse roller 6 that rotates together with the feed roller 5 only when there is only one sheet P that has a load exceeding a predetermined torque. The sheet is fed on the sheet conveying path 8.

On the downstream side of the sheet separating section 4 in the conveying direction, a grip roller 7 in which the rollers are brought into pressure contact with each other in the vertical direction is arranged, and on the upstream side thereof, means for detecting the sheet conveyed in the sheet conveying path 8 is detected. And a grip sensor 9 which is, for example, a reflection type photo sensor is provided. Further, a pair of abutting rollers 11 are provided on the downstream side of the grip roller 7 in the sheet transport path 8 from which the grip rollers 7 are transported, a pair of timing rollers 12 is disposed downstream thereof, and a pair of transport rollers 14 is disposed further downstream thereof. Provided, timing roller 12
A timing sensor 13, which is, for example, a reflection type photo sensor, is provided on the upstream side of the conveyance of.

The sheet feeding device includes a photosensitive drum 1
The sheet P is temporarily stopped in order to synchronize the image forming operation by the image forming section in which the sheet No. 5 is arranged with the sheet feeding timing to the image forming section.
The first sheet stop position where is located, and the sheet is temporarily stopped on the upstream side of the sheet transport path 8 from the first sheet stop position at a position more than the length of the standard size sheet in the transport direction. There is provided a second sheet stop position where the sheet P2 is located.

Then, the succeeding sheet P2 is conveyed to the second sheet stop position, including the period in which the preceding sheet P1 is stopped at the first sheet stop position. That is, the sheets P sent out from the sheet stacking unit 3 by the pickup roller 2 and separated one by one by the sheet separating unit 4 to the timing roller 12 in the stopped state by the grip roller 7 and the abutting roller 11 on the sheet conveying path 8. When the sheet P1 is conveyed, the leading end thereof is abutted against the sheet P1 as shown by the sheet P1, and when the sheet P1 is skewed, it is corrected.

Then, including the period in which the preceding sheet P1 is stopped at the first sheet stop position, the succeeding sheet P2 is similarly fed by the pickup roller 2 at a predetermined feeding timing, and the leading end thereof is After a lapse of a predetermined time from the time when the grip sensor 9 detects the sheet, the sheet P2 is stopped at the second sheet stop position shown in FIG.

Next, the timing roller 12 is rotated at a timing at which the sheet P1 preceding the image formed on the surface 15a of the photosensitive drum 15 of the image forming section is synchronized.
By conveying the sheet P1, the image is transferred to the predetermined position without displacement, and the succeeding sheet P2 is also fed by the same feeding method, and the image is transferred thereto.

By the way, in general, when a sheet is fed, the slip amount is different for each sheet at the stage of the sheet separating section for separating the sheet into one sheet, so that the sheet interval is likely to vary. Therefore, when the sheets are separated one by one and continuously fed as described above, a normal sheet interval is maintained between the preceding sheet P1 and the subsequent succeeding sheet P2. A sheet P that follows at a timing with an interval corresponding to the sheet variation
2 need to start feeding.

However, this sheet variation does not pose a problem when the conveying speed of the image forming unit is a normal speed, but the image forming unit is made faster by increasing the speed and efficiency of image processing in recent years. There was a problem when the sheets were packed and conveyed so that the sheet interval was minimized.

That is, as described with reference to FIG. 13, the succeeding sheet P2 has the smallest amount of slippage in the sheet separating portion, and its leading end is fed to the point c in the shortest time within the variation range. When the timing roller 22 reaches the timing roller 22, it is the timing immediately after the conveyance of the trailing edge of the preceding sheet P1 at that point in time, so the leading edge of the sheet P2 is abutted with the timing roller 22 stopped. Even if I try to do it, I have no time to spare.

Therefore, if the leading edge of the trailing sheet P2 hits the timing roller 22 when it has not stopped completely yet, the leading edge of the sheet P2 will be located at a position beyond the nip of the timing roller 22. Since the sheet P2 is stopped, the stop position of the sheet P2 deviates from the original position by that amount, and the sheet cannot be accurately positioned. Therefore, the position of the image transferred on the sheet P2 is displaced by that amount.

However, in this embodiment, as described with reference to FIG. 1, the preceding sheet P1 is the timing roller 1
The following sheet P2 is conveyed including the period in which the sheet P2 is abutted against the sheet 2 and stopped at the first sheet stop position, and after a certain time has elapsed since the grip sensor 9 detected the leading edge of the sheet P2, the grip roller 7 And by stopping the driving of the feed roller 5 and the like on the upstream side, the sheet P2 is conveyed to the second sheet stop position and stopped to perform positioning, and between the trailing edge of the sheet P1 and the leading edge of the sheet P2. Since the variation width of the sheet spacing is corrected in advance at the stage of the second sheet stop position before reaching the first sheet stop position, the variation width is corrected in advance at the stage of the first sheet stop position. A large time margin is provided for adjusting the registration of the succeeding sheet P2 by the roller 12, and the image can be formed with the minimum sheet interval even in a high-speed image forming apparatus. ..

The manner in which the resist adjustment of the succeeding sheet P2 can be performed with a margin by correcting the variation width of the sheet to be small will be described in detail with reference to the diagram of FIG. The sheet P2 following the sheet separating section 4 has a large amount of variation Bmax in position in the conveying direction as shown in the figure (for example, about 50 mm) because the slip amount at the time of separation is different for each sheet.

Now, assuming that the slip amount is the smallest and the trailing sheet P2 within the variation is the fastest and is fed as shown by the line b, after the front end of the sheet P2 is detected by the grip sensor 9. After a lapse of a certain time, the sheet is conveyed to the second sheet stop position, temporarily stopped until the time of point d, and then fed again to the abutting roller 11. Therefore, due to the position alignment correction of the sheet P2 at the second sheet stop position, the variation amount of the sheet P2 after the grip roller 7 and the variation amount Bma before that are Bma.
The variation amount Bas is small with respect to x (for example, 30 mm).

Therefore, when the leading edge of the following sheet P2 is conveyed to the point c and reaches the timing roller 12, the trailing edge Pb of the preceding sheet P1 has already passed through the timing roller 12 with a margin. Therefore, the timing roller 12 can be stopped completely and the leading edge of the sheet P2 to be subsequently moved can be abutted against it with a margin while the registration adjustment is possible.

Therefore, even in the case of the high-speed image forming apparatus in which the sheet interval is shortened as much as possible by increasing the number of prints per unit time by performing the high-speed conveyance in the portion a as described above, the fed sheet is conveyed. Can be reliably and continuously fed at a timing synchronized with the image forming operation by the image forming unit.

In this embodiment, as described with reference to FIG. 1, the second sheet stop position is located upstream of the first sheet stop position in the sheet conveying path 8 and is the length of the standard size sheet in the conveying direction. Since the sheet is provided at a position where the sheet is temporarily stopped at the above position, the following sheet P2 is stopped at the second sheet stop position as shown in FIG. 1 when the standard size sheet is being fed. The leading edge of the sheet P1 does not interfere with the trailing edge of the preceding sheet P1 while the sheet P1 is moving.

FIG. 3 is a schematic diagram for explaining a sheet feeding method of the image forming apparatus in which the second sheet stop position is changed according to the length of the sheet to be fed in the feeding direction. In the sheet feeding method of the image forming apparatus according to this embodiment, the second sheet stop position is changed in the direction of arrow E in FIG. 3 according to the length of the sheet P to be fed in the transport direction.

When the sheet P is smaller than the standard size sheet and remains in the second sheet stop position described in FIG. 1, the preceding sheet P1 has a length in the conveying direction as shown in FIG. Since the length is short, the rear end Pb has a dimensional difference L with respect to the standard size sheet Pm indicated by an imaginary line.
It comes to stop at a position closer to the abutting roller 11 side by 1.

The leading edge Pa of the following sheet P2 is
As in the case of the standard size sheet at the second sheet stop position, the standard size sheet P
Dimensional difference L1 compared to the sheet spacing La when m is fed
Only the distance is widened. So, in this example,
The second sheet stop position is changed in the direction of arrow E in FIG. 3 in accordance with the length of the sheet P in the conveying direction (size of the sheet P) to prevent the sheet interval from expanding.

That is, in the case of a sheet having a short length in the conveying direction as shown in FIG. 3, the second sheet stop position is changed to the abutting roller 11 side as shown in FIG. The sheet distance La between the rows P1 and P2 is adjusted to an optimum value. The second when feeding the small size sheet
A case in which the seat stop position is not changed and a case in which the seat stop position is changed will be described with reference to FIG.

When the second sheet stop position is not changed as it is for the standard size sheet, the transport roller 14 becomes as shown by the alternate long and short dash line in FIG.
The sheet interval La in the vicinity becomes extremely wide, and high-speed processing that increases the number of prints per unit time cannot be performed.

However, if the second sheet stop position is moved to the abutting roller 11 side as shown by the solid line,
Sheet distance Ld near the transport roller 14
Narrows down and enables high-speed processing. Even in this case, the period in which the preceding sheet P1 and the succeeding sheet P2 catch up with each other due to the difference in the linear velocity becomes a short period as the length in the sheet conveying direction becomes short. Compared with, the sheet spacing is slightly enlarged.

FIG. 6 is a diagram for explaining the sheet feeding method of the image forming apparatus in which the sheet conveying speed is changed during the period in which the leading edge of the sheet to be fed is from the second sheet stop position to the first sheet stop position. It is a diagram showing. In this embodiment, the sheet conveyance speed during the period from the second sheet stop position to the first sheet stop position at which the leading edge of the sheet to be fed on the sheet conveyance path 8 (see FIG. 1) is set to be the length in the sheet conveyance direction. Change accordingly.

That is, at the time of feeding the sheet, high speed conveyance can be performed by simply moving the second sheet stop position as shown by the phantom line in FIG.
The sheet interval Ls does not reach the ideal minimum sheet interval Ls described above, and the sheet interval Ld is wider than that (when the transport speed from the first sheet stop position is the same).

Therefore, in order to compensate for this in this embodiment, the sheet conveying speed of either the grip roller 7 or the abutting roller 11 or both of them is set so that the leading edge of the sheet P2 following the second sheet stop position. The problem is solved by changing the speed at a high speed in accordance with the length of the sheet in the sheet conveying direction in the period from the first sheet stop position to the first sheet stop position. If it is possible to further increase the sheet conveying speed in the above period, the second
It is also possible to set the minimum sheet interval Ls only by increasing the sheet conveying speed without moving the sheet stop position of.

FIG. 7 is a view for explaining the sheet feeding method of the image forming apparatus in which the length of the sheet conveying path between the first and second sheet stop positions is changed according to the length in the sheet conveying direction. Similarly, FIG. 8 is a diagram showing a diagram of the same embodiment.

When the sheet size is longer than the standard sheet, the length of the sheet in the conveying direction becomes long. Therefore, in each of the above-described embodiments, the trailing edge of the preceding sheet at the first sheet stop position is Since it reaches the second sheet stop position, it becomes difficult to set the second sheet stop position. Therefore, in this embodiment, in the case of such a sheet that is long in the conveying direction, the first sheet stop position and the second sheet stop position are set.
The length of the sheet conveying path between the sheet stopping position and the sheet stopping position is changed according to the length of the sheet to be fed in the conveying direction.

That is, the bypass conveyance path 10 is provided between the first sheet stop position and the second sheet stop position of the linear sheet conveyance path 8, and the switching claws 16 and 17 are provided at the respective branch portions. When the length of the sheet to be provided and fed in the conveying direction is longer than that of the standard size sheet, the switching claws 16 and 17 are switched to the positions shown by the solid lines in FIG. Is set to a position indicated by an imaginary line and the seat is advanced straight.

In this way, when the length of the sheet in the sheet conveying direction is longer than that of the standard size sheet, the sheet is passed through the bypass sheet conveying path 10 so that it is not shown by the broken line in FIG. Since the sheet P2 shown in FIG.
It can be stopped at the seat stop position.

In this embodiment, the sheet P2 following the preceding sheet P1 catches up with the sheet P2 due to the difference in linear velocity for a longer period as the sheet length becomes longer. Therefore, the sheet interval is set to the minimum interval during that period. It will be easier to fill up, and the stop time can be extended by that amount, and the margin for sheet variations will be further expanded.

FIG. 9 shows the image formation in which the timing for restarting the conveyance of the sheet stopped at the second sheet stop position is after a certain time including 0 after the restart of the conveyance of the sheet stopped at the first sheet stop position. FIG. 6 is a timing chart for explaining a sheet feeding method of the apparatus. In this embodiment, the conveyance restart timing of the succeeding sheet P2 stopped at the second sheet stop position is constant including 0 after the conveyance restart of the preceding sheet P1 stopped at the first sheet stop position. After the time T has elapsed.

As described above, the timing for restarting the conveyance of the sheet P2 stopped at the second sheet stop position is set by appropriately maintaining the distance between the leading edge of the sheet and the trailing edge of the preceding sheet P1. This is because it is necessary.

Therefore, in this embodiment, after the second sheet stop position, the variation of the sheet conveyance caused by the slip of the sheet has already been corrected to be small in the sheet separating portion, and the second sheet on the downstream side of the sheet conveyance is corrected. In consideration of the fact that the sheet feeding timing can be corrected again at the sheet stop position of No. 1, the conveyance of the sheet P1 preceded by the fixed time T determined by the size of the sheet to be fed or the length of the selected conveyance path is restarted. After a lapse of time, a very simple control operation of uniformly restarting the feeding of the succeeding sheet P2 stopped at the second sheet stop position is performed.

For example, in an apparatus using a one-chip microcomputer, a value corresponding to the sheet size and the length of the selected sheet conveyance path is selected from a constant table prepared in advance for the selection of the constant time T. It is realized by a simple method such as referencing.

FIG. 10 illustrates a sheet feeding method of the image forming apparatus for determining that the sheet has arrived at the second sheet stop position according to the time elapsed from the time when the sheet detecting means detects the leading edge of the sheet. FIG. In this embodiment, the grip sensor 9, which is a means for detecting the arrival of the sheet at the second sheet stop position in the sheet conveying path upstream of the second sheet stop position, detects the leading edge of the sheet. Time elapsed from the time when
Figure out by.

That is, as shown in FIG.
After the time t (indicated by different times t1 and t2 for each sheet size) seconds from the time when the grip sensor 9 detects the leading edge Pa of the sheet P conveyed on the sheet conveying path 8, the grip roller 7 and the feed roller 5 ( The grip motor 18 driving both (see FIG. 1) is stopped, and the sheet P is controlled to be stopped at the second sheet stop position while being held by the grip roller 7.

The time t is set to be relatively short in the case of the standard size sheet Pm as shown in FIG. 10B, so that the sheet stop position is changed from the grip roller 7 to the leading edge Pa of the sheet. Is a position that protrudes a small amount by distance L2. Further, in the case of a small-sized sheet Ps having a short length in the transport direction, the leading end Pa projects a large distance from the grip roller 7 at the stop position of the sheet Ps by setting a relatively long time t2. To the position. The method of selecting the time t according to the sheet size can be easily realized by a device using a one-chip microcomputer as in the case of the embodiment of FIG.

In FIG. 11, when a sheet having a long length in the conveying direction is fed, the start of the feeding operation of the succeeding sheet is stopped at the first sheet stop position, and the re-conveying of the preceding sheet is started. FIG. 6 is a schematic diagram for explaining a sheet feeding method of the image forming apparatus that is not performed until now.

In this embodiment, when the sheet P1 is stopped at the first sheet stop position, the trailing edge P of the sheet P1 is
b is upstream of conveyance from the second sheet stop position (right side in the figure)
When a sheet having a long length in the conveyance direction is fed, the re-conveyance of the preceding sheet P1 which has stopped the feeding operation of the succeeding sheet P2 at the first sheet stop position is started. Not done until

In this way, the length of the preceding sheet P1 in the conveying direction is longer than that of the standard size sheet, and the trailing edge Pb of the grip roller 7 is at the second sheet stop position.
The leading edge P of the sheet P2 which has reached to
When a cannot be held by the grip roller 7 and stopped at the second sheet stop position, the sheet feeding operation of the subsequent sheet P2 from the sheet stacking unit 3 is started at the first sheet stop position. It is not performed until the re-conveyance of the preceding sheet P1 which has been stopped is started.

As described above, depending on the sheet that is long in the transport direction, the sheet may be fed by the conventional feeding method without providing the second sheet stop position. FIG. 12 shows a diagram relating to sheet feeding in this case. In the case of a sheet that is long in the transport direction, the preceding sheet P1 is transported at the image forming speed for a long period of time, so that the succeeding sheet P2 can easily catch up, so that the sheet P2 is stopped at the second stop position as shown in the figure. You can reduce the sheet spacing without doing so.

[0060]

As described above, according to the present invention, the succeeding sheet is positioned at the second sheet stop position even during the period in which the leading sheet is positioned with high accuracy at the first stop position. Therefore, even if there is a large variation in the sheet position in the sheet separation unit, the subsequent sheet is stopped at the second sheet stop position to correct the large variation in the sheet interval generated in the sheet separation unit. Since it is possible to reduce the size, it becomes possible to have a time margin for the sheet positioning for the registration adjustment performed at the next first stop position. Therefore, the sheets can be continuously and reliably fed to the image forming unit with a minimum required sheet interval at a timing synchronized with the image forming operation by the image forming unit.

If the second sheet stop position is changed in accordance with the length of the sheet to be fed in the conveying direction,
The sheet can be stopped at the optimum second sheet stop position for each length of the sheet to be fed, whereby the sheet interval to be fed can be minimized.

Further, the sheet conveying speed during the period in which the leading edge of the sheet to be fed from the second sheet stopping position to the first sheet stopping position is changed according to the length of the sheet in the conveying direction. , Even when the following sheet is opened too much just by stopping the following sheet at the second sheet stop position as in the case of a small size sheet, and the variation cannot be absorbed, By increasing the sheet feeding speed, the variation can be absorbed and the sheet interval can be set to the preset minimum interval.

If the length of the sheet conveying path between the first and second sheet stop positions is changed according to the length of the sheet to be fed in the conveying direction, the sheet is conveyed according to the sheet size. Since the length of the path can be changed, even if a large size sheet is fed through the long transport path, the trailing edge of the sheet at the first sheet stop position is moved to the second sheet stop position. Since it can be prevented from reaching the sheet, the succeeding sheet is stopped at the second sheet stop position, the sheet variation generated when the sheet is separated into one sheet is surely corrected, and the sheet is fed. Sheet spacing can be minimized.

Further, if the timing for resuming the conveyance of the sheet stopped at the second sheet stop position is a certain time period including 0 after the resumption of the conveyance of the sheet stopped at the first sheet stop position, Sheets that have already passed through the sheet separation unit where the sheet spacing is likely to vary and are stopped at the second sheet stop position are fed at that timing, so the sheet feeding is very simple, even though the control is simple. It is possible to reliably correct the variation in feeding and minimize the sheet interval to be fed.

Further, the arrival of the sheet at the second sheet stop position has passed since the point at which the means for detecting the sheet on the upstream side of the second sheet stop position detects the sheet. If the indexing is performed based on time, the position of the sheet to be stopped at the second stop position can be adjusted corresponding to each size of sheet with a simple configuration.

Then, in a state where the sheet is stopped at the first sheet stop position, a sheet having a long length in the conveying direction is fed such that the trailing edge of the sheet reaches the upstream side of the second sheet stop position. When the sheet is fed, the feeding operation of the following sheet is not started until the re-conveying of the preceding sheet stopped at the first sheet stop position is started. Even long and large sheets can be fed without any hindrance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a conveyance system of a sheet feeding device for carrying out a sheet feeding method of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a diagram when a sheet is fed by the sheet feeding method.

FIG. 3 shows the second sheet according to the length of the sheet to be fed in the transport direction.
6 is a schematic diagram for explaining a sheet feeding method of the image forming apparatus for changing the sheet stop position of FIG.

FIG. 4 is a schematic view showing a second sheet stop position when a sheet having a short length in the transport direction is fed in the same embodiment.

FIG. 5 is a diagram showing a diagram of the same embodiment.

FIG. 6 is a diagram illustrating an example of a sheet feeding method of an image forming apparatus that changes a sheet conveying speed during a period in which a leading edge of a sheet to be fed is from a second sheet stop position to a first sheet stop position. FIG.

FIG. 7 illustrates an example of a sheet feeding method of an image forming apparatus in which a length of a sheet conveyance path between first and second sheet stop positions is changed according to a length in a sheet conveyance direction. FIG.

FIG. 8 is a diagram showing a diagram of the same embodiment.

FIG. 9 is a diagram illustrating an image forming apparatus in which a timing of restarting conveyance of a sheet stopped at the second sheet stop position is set to a certain time period including 0 after restart of conveyance of a sheet stopped at the first sheet stop position. It is a timing chart for explaining an example of a sheet feeding method.

FIG. 10 illustrates an example of the sheet feeding method of the image forming apparatus that determines that the sheet arrives at the second sheet stop position based on the time elapsed from the time when the sheet detecting unit detects the leading edge of the sheet. FIG.

FIG. 11: When feeding a sheet having a long length in the feeding direction, start the sheet feeding operation of the succeeding sheet until the re-feeding of the preceding sheet stopped at the first sheet stop position is started. FIG. 6 is a schematic diagram for explaining an example of a sheet feeding method of the image forming apparatus that is not provided.

12 is a diagram showing a diagram in the embodiment of FIG.

FIG. 13 shows a time margin even when the leading edge of the succeeding sheet is abutted against the timing roller when the following sheet has a large variation width after passing through the separating / conveying means by the conventional sheet feeding method. It is a diagram which shows the diagram for demonstrating the state which cannot be served.

[Explanation of symbols]

1 Paper Feeding Device 4 Sheet Separation Part 7 Grip Roller 8 Sheet Conveying Path 8 Grip Sensor 10 Bypass Conveying Path 11 Abutting Roller 12 Timing Roller 14 Transport Roller 15 Photoreceptor Drum P Sheet

Claims (7)

[Claims] 1. A sheet feeding method for an image forming apparatus, wherein sheets fed separately by a sheet feeding device are fed one by one to an image forming section, the image forming operation by the image forming section and the image forming section. A first sheet stop position at which the sheet is temporarily stopped in order to synchronize the sheet feeding timing to the sheet, and a length in the sheet conveying direction from the first sheet stop position to an upstream side of the sheet conveying path. A second sheet stop position for temporarily stopping the sheet is provided at a distant position, and a subsequent sheet is included in the second sheet including a period in which the preceding sheet is stopped at the first sheet stop position. A sheet feeding method for an image forming apparatus, characterized in that the sheet is conveyed to a stop position. 2. The sheet feeding method for an image forming apparatus according to claim 1, wherein the second sheet stop position is changed according to a length of a sheet to be fed in a conveying direction. Sheet feeding method for forming apparatus. 3. The sheet feeding method of the image forming apparatus according to claim 1, wherein the leading edge of the sheet to be fed is a sheet conveyance speed during a period from the second sheet stop position to the first sheet stop position. Is changed in accordance with the length of the sheet in the conveying direction. 4. The sheet feeding method for an image forming apparatus according to claim 1, wherein the length of a sheet conveying path between the first sheet stop position and the second sheet stop position is the sheet to be fed. A sheet feeding method for an image forming apparatus, wherein the sheet feeding method is changed according to the length of the sheet in the conveying direction. 5. The sheet feeding method for an image forming apparatus according to claim 1, wherein the conveyance restart timing of the sheet stopped at the second sheet stop position is set to the first sheet The sheet feeding method of the image forming apparatus, wherein the sheet is stopped at the sheet stop position after a predetermined time period including 0 is resumed after the sheet is resumed. 6. The sheet feeding method for an image forming apparatus according to claim 1, wherein the arrival of the sheet at the second sheet stop position is indicated by the second sheet stop position. A sheet feeding method for an image forming apparatus, wherein the sheet detecting means in the sheet conveying path on the upstream side determines the time based on the time elapsed from the time when the leading edge of the sheet is detected. 7. The sheet feeding method for an image forming apparatus according to claim 1, wherein the trailing edge of the sheet is located at the first sheet stop position from the second sheet stop position while the sheet is stopped at the first sheet stop position. Also, when feeding a sheet having a long length in the feeding direction such that it reaches the upstream side of the feeding, it is possible to re-feed the preceding sheet that has stopped the feeding operation of the succeeding sheet at the first sheet stop position. A sheet feeding method for an image forming apparatus, which is not performed until the start.