JP2006232475A - Sheet feeder and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet feeder capable of enhancing productivity by shortening a feeding interval as much as possible while ensuring a gap necessary as a sheet gap when the sheets are continuously fed. <P>SOLUTION: When two sheets of sheets are continuously fed with a constant interval, the preceding paper is conveyed by a pair of conveying rollers, a rear end of the preceding paper and a leading end of the succeeding paper are detected (step S14) during the succeeding paper is paid out from a paying out roller. A gap of the rear end of the preceding paper and the leading end of the succeeding paper is determined from the detection result and when it is determined that the determined gap is shorter than a predetermined value Ls ("YES" in step S15), a paying out speed of the succeeding paper by the paying out roller is decelerated (step S18) to spread the paper gap. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sheet feeding apparatus and an image forming apparatus that feed and convey sheets one by one from a sheet storage unit.

A sheet feeding apparatus provided in an image forming apparatus such as a printer is configured to feed sheets one by one from a sheet bundle accommodated in a sheet feeding cassette. Specifically, a sheet feeding cassette, a feeding roller that feeds out the sheet from the sheet feeding cassette, a winding roller that is arranged at a position downstream of the feeding roller in the sheet conveyance direction, In general, the apparatus includes a conveyance roller that receives and conveys the sheet separated into two sheets. In such a configuration, even if a plurality of sheets are overlapped and fed from the sheet feeding cassette by the feeding roller, only one of them is sent to the transport roller by the rolling roller, and so-called double feeding can be prevented.
JP 2004-43158 A

  However, in the case of the above-described configuration, when the sheet that has been left behind (not sent to the conveyance roller) is viewed, the leading end of the sheet protrudes from the sheet feeding cassette toward the separation roller. On the other hand, when only one sheet is fed by the feeding roller, the leading edge of the sheet to be fed next is positioned at the original position in the sheet feeding cassette without protruding from the sheet feeding cassette. It will be. That is, the position of the leading edge of the next sheet varies between the original position and the winding roller depending on the sheet feeding state by the feeding roller.

  The fact that the position of the leading edge of the sheet to be fed next varies means that the feeding start position at the leading edge of the sheet when the sheet is fed is different every time the paper is fed. In the case of continuous feeding, the variation causes a variation in the interval (sheet interval) between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet. Such a variation is not limited to the case of carrying out the rolling, but also occurs, for example, when the sliding amount between the feeding roller and the surface of the sheet changes from time to time depending on the type of the sheet, the wear of the feeding roller, and the like.

  By the way, in an image forming apparatus such as a printer, when the sheet interval is as short as possible, the number of sheets supplied to the image forming unit per unit time can be increased, and productivity can be improved accordingly. However, in practice, the sheet interval cannot be made zero, and the shortest interval is required. The shortest interval is, for example, an interval necessary for the detection sensor for detecting jam to detect the leading edge and trailing edge of the sheet being conveyed, and the timing roller pair in which the leading edge of the sheet being conveyed is stopped. This is the interval necessary for forming the loop when a loop is formed at the leading end of the sheet by slightly conveying the sheet in a state where it is in contact with the nip portion of the sheet, and the skew (diagonal) of the sheet is corrected by the loop. .

  Accordingly, it is most productive to feed the sheets one by one at the shortest interval. However, if the sheet is fed at the shortest interval, the sheet interval is the shortest due to the above variation. The case where it becomes still shorter than a space | interval will arise. For this reason, in actuality, there is a problem in that it is necessary to design the sheet interval to be somewhat longer than the shortest interval in consideration of the variation, and it is impossible to further improve productivity.

  The present invention has been made in view of the above problems, and in the case of continuously feeding sheets, it is possible to improve the productivity by shortening the feeding interval as much as possible while securing a necessary interval as a sheet interval. An object of the present invention is to provide a sheet feeding apparatus and an image forming apparatus that can be used.

  In order to achieve the above object, the present invention provides a sheet feeding device that feeds and conveys a sheet from a sheet bundle stacked in a sheet storage unit, and feeds the sheet from the sheet bundle at a first speed; When the feeding unit that receives the fed sheet and conveys it at the second speed and when the two sheets are successively fed sequentially, the preceding sheet is being conveyed by the conveying unit, and the succeeding sheet is The distance between the preceding sheet and the succeeding sheet on the conveying path between the sheet feeding position by the feeding means and the sheet conveying position by the conveying means is shorter than a predetermined value while being fed by the feeding means. And detecting the first speed relative to the second speed when the detecting means detects that the interval is shorter than the predetermined value. To decrease, characterized in that it comprises, a speed control means for controlling the feeding means and / or the transport means.

Here, the sheet feeding position means a feeding member provided in the feeding means for feeding the sheet in contact with the sheet, for example, a contact position of the feeding roller with the sheet, and the sheet conveying position is the conveying position. Meaning means means a contact position of a conveyance roller, for example, a conveyance roller, which contacts the sheet and conveys the sheet.
Further, the speed control means controls the feeding means to decelerate the first speed. Here, the deceleration is used in the meaning including stopping the seat with the first speed set to zero.

Further, the speed control means returns the first speed to the original speed after a predetermined time has elapsed.
The detection means includes a sensor provided on the conveyance path and configured to detect a leading edge and a trailing edge of a passing sheet, and a trailing edge of the preceding sheet and a leading edge of the succeeding sheet reach a predetermined time. Is not detected by the sensor, or when the time from when the trailing edge of the preceding sheet is detected by the sensor until the leading edge of the succeeding sheet is detected is equal to or shorter than a predetermined detection time, the interval is It is detected that it is shorter than a predetermined value.

Further, the speed control means determines a speed change amount based on the size of the interval.
Further, the image forming apparatus further includes another conveyance unit that receives the sheet conveyed by the conveyance unit and conveys the sheet at a third speed, and the detection unit detects that the preceding sheet is being conveyed by the another conveyance unit and the subsequent sheet While the sheet is being conveyed by the conveying unit, the interval between the preceding sheet and the succeeding sheet between the sheet conveying position by the other conveying unit and the sheet conveying position by the conveying unit is shorter than another predetermined value. The speed control unit detects that the sheet interval between the sheet conveying position by the another conveying unit and the sheet conveying position by the conveying unit is shorter than the another predetermined value by the detecting unit. Then, the conveying means is controlled to reduce the second speed.

Here, the sheet conveyance position by the other conveyance means means a contact position of a conveyance member, for example, a timing roller, which is provided in the other conveyance means and conveys the sheet in contact with the sheet.
The present invention is an image forming apparatus that forms an image on a sheet fed from a sheet feeding apparatus, and includes the above sheet feeding apparatus.

  In this way, when it is detected that the distance between the preceding sheet and the succeeding sheet is shorter than the predetermined value, the first speed with respect to the second speed is reduced. Even if the distance from the preceding sheet is shorter than the predetermined value, it can be returned to the predetermined value, and the sheet feeding interval can be made shorter than before while ensuring the necessary distance, thereby improving productivity. can do.

Hereinafter, an embodiment of a sheet feeding apparatus according to the present invention will be described using a tandem color digital printer (hereinafter simply referred to as “printer”) as an example.
(First embodiment)
FIG. 1 is a diagram illustrating the overall configuration of the printer 1.
As shown in FIG. 1, the printer 1 includes a feeding unit 10, an image forming unit 20, a fixing unit 30, and a control unit 40. Is received, printing is executed based on the instruction.

  The feeding unit 10 is disposed at a position on the downstream side of the feeding roller 102 in the sheet conveyance direction, the sheet feeding cassette 101 that stores the sheet S as a recording sheet, the feeding roller 102 that feeds the sheet in the sheet feeding cassette 101, and A pair of sheeting rollers 103 that conveys the fed sheets one by one and conveys one sheet that has been fed, a pair of conveyance rollers 104 and 105 that convey the sheet along the conveyance path 100, and a secondary transfer position 261. Via a drive system 113 including a timing roller pair 106 that takes the timing of feeding the paper, detection sensors 107, 108, 109, and 112 for detecting the leading and trailing edges of the fed paper in the conveyance direction, a gear transmission mechanism, and the like. A pair of conveying rollers 104 via a paper feed motor 110 and another drive system 114 that rotationally drive the feeding roller 102 and the separating roller pair 103; And a like conveying motor 111 for rotationally driving the 05.

The detection sensors 108, 109, and 112 are mainly for detecting a paper jam (jam), and the detection sensor 107 sequentially feeds a plurality of sheets in a feed control described later. In this case, it is used as a sensor for detecting the sheet interval between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet.
The image forming unit 20 rotates in the direction of arrow a with image forming units 2Y, 2M, 2C, and 2K corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). An intermediate transfer unit 21 including the intermediate transfer belt 22 is provided.

  The image forming units 2Y to 2K are arranged in series along the intermediate transfer belt 22 at a predetermined interval, and each of the image forming units 2Y to 2K is a photosensitive drum 3Y to 3K as an image carrier and a charger 4Y to 4K arranged around the photosensitive drum 3Y to 3K. The image forming apparatus includes print heads 5Y to 5K, developing units 6Y to 6K, primary transfer rollers 7Y to 7K facing the photosensitive drums 3Y to 3K with the intermediate transfer belt 22 interposed therebetween, and a cleaner (not shown).

The intermediate transfer unit 21 is pressed against the drive roller 23 with the intermediate transfer belt 22 sandwiched between the intermediate transfer belt 22, the drive roller 23, the driven rollers 24 and 25 on which the belt is stretched, and the secondary transfer position 261. A secondary transfer roller 26 is provided.
Members necessary for image formation such as the photosensitive drums 3Y to 3K and the driving roller 22 are rotationally driven by a main motor 27 via a driving system 28. The driving force of the main motor 27 is also transmitted to the timing roller pair 106 via the clutch 29.

  In such a configuration, when receiving a print instruction from the external terminal, the control unit 40 receives an image signal from the external terminal, converts it to a digital image signal of Y, M, C, K colors, and prints it. A drive signal for driving the heads 5Y to 5K is generated. Further, the main motor 27 is driven. As a result, members such as the photosensitive drums 3Y to 3K and the driving roller 23 are rotationally driven. Note that the clutch 29 is kept disconnected and the timing roller pair 106 is stopped.

The print heads 5Y to 5K emit a laser beam in response to a drive signal from the control unit 40, and expose and scan the photosensitive drums 3Y to 3K in the main scanning direction.
The photosensitive drums 3Y to 3K are subjected to the removal of residual toner on the surface with a cleaner before being subjected to the exposure, and are discharged by irradiating an unillustrated eraser lamp, and then uniformly charged by the chargers 4Y to 4K. When exposed to the laser beam in such a charged state, electrostatic latent images are formed on the surfaces of the photosensitive drums 3Y to 3K.

  Each electrostatic latent image is developed by developing units 6Y to 6K, whereby Y, M, C, and K color toner images are formed on the surfaces of the photosensitive drums 3Y to 3K, and the primary transfer roller 7Y is formed at the primary transfer position. The images are sequentially transferred onto the rotating intermediate transfer belt 22 by an electrostatic action of ˜7K. At this time, the image forming operation for each color is executed while shifting the timing in the order of Y, M, C, and K colors so that the toner images are superimposed on the same position on the intermediate transfer belt 22.

On the other hand, the paper is fed from the feeding unit 10 in parallel with the image forming operation so as to match the image forming timing of each color toner image on the intermediate transfer belt 22.
Specifically, the paper feed motor 110 is driven by the control unit 40, and the feeding roller 102 and the roller pair 103 are driven to rotate. As a result, the paper in the cassette 101 is fed out toward the conveyance path 100 by the feeding roller 102. At that time, even if a plurality of sheets are fed out together, the sheets are separated one by one by the separation by the pair of separation rollers 103.

  The sheet fed by the feed roller 102 is transported to the transport roller pair 104 along the transport path 100. The drive of the transport motor 111 is started between the time when the paper is fed out and the time when the leading edge arrives at the transport roller pair 104, whereby the paper is received by the transport roller pair 104, and the transport roller pair 104 The sheet is conveyed to the timing roller pair 106 via 105. In addition, when the sheet feeding speed by the feeding roller 102 and the separating roller pair 103 is Vf (first speed) and the sheet conveying speed by the conveying roller pairs 104 and 105 is Vc (second speed), basically The rotational speed of each roller is set so as to be approximately Vf = Vc.

  When the leading edge of the sheet is detected by the detection sensor 108 during the conveyance of the sheet, the sheet feeding motor 110 is stopped, and the rotation of the feeding roller 102 and the separating roller pair 103 is stopped. At this time, although the trailing edge of the sheet may still be on the pair of whirling rollers 103, the feeding roller 102 and the pair of whirling rollers 103 are rotated by following the conveyed sheet. This transmits only the driving force in one rotation direction (the rotation direction for feeding the paper) to the rotation shafts of the feeding roller 102 and the separating roller pair 103, and idles against the driving force in the opposite rotation direction. This is because a known one-way clutch (not shown) that does not transmit power is provided. A clutch having the same function as that of the one-way clutch is also provided on the rotation shafts of the conveying roller pairs 104 and 105.

The sheet being conveyed on the conveying path 100 stops at the pressure contact portion (nip portion) of the timing roller pair 106 whose leading end is stopped, but the middle portion continues to be conveyed by the conveying roller pair 105. As a result, a loop 121 is formed at the leading end of the sheet.
When the loop 121 is formed, the transport motor 111 is stopped, and the rotation of the transport roller pair 104 and 105 is stopped. The conveyance motor 111 is stopped when a predetermined time elapses after the leading edge of the sheet passes through the detection sensor 109 and is required to hit the nip portion of the timing roller pair 106 to form the loop 121.

  The clutch 29 is moved in accordance with the movement timing of the toner image to the secondary transfer position 261 so that the leading edge of the toner image primarily transferred onto the intermediate transfer belt 22 and the leading edge of the sheet coincide at the secondary transfer position 261. The timing roller pair 106 is rotationally driven. As a result, the paper that has been temporarily stopped at the timing roller pair 106 is transported again to the secondary transfer position 261.

  At the secondary transfer position 261, the toner image on the intermediate transfer belt 22 is secondarily transferred onto the paper by an electrostatic action generated between the secondary transfer roller 26 and the driving roller 23. The paper that has passed the secondary transfer position 261 is conveyed to the fixing unit 30 where the toner image is pressed and heated to be fixed on the paper, and then discharged onto the discharge tray 31. Note that the timing roller pair 106, the secondary transfer roller 26, the intermediate transfer belt 22, and the like are stopped after the secondary transfer to the paper is completed.

  In the above description, the printing operation on one sheet has been described. However, when a plurality of sheets, for example, two sheets are printed continuously, the succeeding sheet is fixed after the start of feeding the preceding sheet. The paper is fed out after a certain time (the drive of the paper feed motor 110 is started), conveyed toward the timing roller pair 106 so as to follow the preceding paper, and is subjected to secondary transfer through a loop formation at the timing roller pair 106. Sent to position 261. At this time, for example, the preceding sheet is being conveyed by the conveying roller pairs 104 and 105, and while the succeeding sheet is being fed by the feeding roller 102 and the separating roller 103, the preceding sheet and the succeeding sheet in the conveying direction. When it is detected that the distance (paper interval) is shorter than the predetermined value Ls, the feeding speed Vf of the succeeding sheet is decelerated from the current speed (substantially Vc) while the transport speed Vc of the preceding sheet is kept constant, and then The sheet feeding control is performed to return to the original speed, and the sheet interval is returned to the predetermined value Ls.

Such feeding control is performed for the following reason.
In other words, when a plurality of sheets are sequentially fed at a certain time, the subsequent sheets are placed in their original positions in the sheet feeding cassette 101 as described in the section “Problems to be solved by the invention” above. In the case (see the position of the paper indicated by the broken line in FIG. 5A), or in a case where the paper is stopped while projecting toward the pair of roller rollers 103 (solid line in FIG. 5A). There is also a variation in the position of the paper at the time of feeding. There is also a variation in the amount of paper feed due to variations in the amount of sliding of the feed roller 102 with the paper surface, the roller diameter, and the like. Hereinafter, such variations are collectively referred to as “feed variation”.

  For example, when the succeeding sheet is protruding toward the pair of roller rollers 103 due to such a variation in feeding, the leading end of the succeeding sheet is closer to the preceding sheet at the start of feeding than when it is at the original position. The sheet interval is shortened by (d in FIG. 5A). If the paper interval is shortened, paper detection by the detection sensor cannot be performed well, or the paper interval is almost eliminated after the loop is formed, and the leading edge of the preceding paper and the leading edge of the succeeding paper overlap to cause double feeding at the timing roller pair 106 and jamming occurs. This will lead to deterioration of transportability.

  Therefore, in the actual design, as the paper feed condition, the paper interval becomes the shortest due to the paper feed variation (the condition that the subsequent paper is transported the fastest. Specifically, the paper pops out fully in the transport direction. When it is assumed that the slip on the paper surface is the least, etc. (hereinafter referred to as “shortest condition”), the shortest paper interval (corresponding to the above Ls) can be secured even when the paper is fed out. The paper feeding interval (the above-mentioned fixed time) is set according to the conditions.

  For this reason, the sheet interval Ls can be secured when the subsequent sheet is fed out under the shortest condition, but on the other hand, the condition in which the sheet interval is the longest (the condition in which the subsequent sheet is conveyed latest is the latest. For example, when it is assumed that the sheet is in its original position and the slip on the sheet surface is the largest, the sheet interval is considerably longer than Ls when the sheet is fed out in the following “longest condition”. become.

  On the other hand, the operation interval for each sheet at the time of image formation is determined based on the longest case when the paper interval varies (when the image formation operation interval is determined based on the shortest case, it is caused by paper feed variation. If the paper interval becomes longer than that, the subsequent paper will not be transported to the secondary transfer position 261 in time). As a result, the paper interval must be increased to a certain extent within a range in which variations in paper feed can be absorbed. It was not possible to improve productivity by shortening.

Therefore, in the present embodiment, the paper feeding interval is determined so that the paper interval is as short as possible without being bound by the shortest condition, and it is detected that the paper interval is shorter than Ls during feeding of the subsequent paper. The subsequent sheet feeding speed Vf is decelerated to ensure the necessary interval Ls as the sheet interval.
Hereinafter, the contents of the feeding control will be specifically described with reference to FIGS.

  FIG. 2 is a flowchart illustrating the content of the feed control by the control unit 40, FIGS. 3 and 4 are timing charts of the feed control, and FIG. It is the figure which showed typically a mode that was conveyed. 3 and 4, ON of the detection sensor indicates that a sheet is detected, and OFF indicates that no sheet is detected.

As shown in FIG. 2, the control unit 40 starts feeding the subsequent sheet S (step S <b> 11) (time T <b> 1 in FIG. 3A). Specifically, the drive of the paper feed motor 110 is started when the predetermined time has elapsed since the start of feeding of the preceding paper. At this time, the rotational speed of the paper feed motor 110 is adjusted so that the feeding speed Vf is substantially the same as the transport speed Vc.
Time counting by an internal timer is started from the start of feeding of subsequent sheets (step S12), and it is determined whether or not a predetermined time t has elapsed (step S13).

  The predetermined time t is longer than a time t01 that is assumed to be required for the leading edge of the subsequent sheet S to pass through the detection sensor 107, for example, when the subsequent sheet S is fed out under the shortest condition. When the subsequent sheet S is decelerated when the predetermined time has elapsed, it is assumed that the decelerated sheet S is conveyed toward the conveying roller pair 104 at the same timing as when the sheet S is decelerated most slowly under the longest condition. Is set in advance to be shorter than the time t02, that is, a relationship of t01 <t <t02, for example, an intermediate value between t01 and t02. Stored in ROM or the like.

  When the elapse of the predetermined time t is determined (“YES” in step S13), it is determined whether the preceding sensor trailing edge and the succeeding sheet leading edge have been detected by the detection sensor 107 (step S14). Here, FIG. 3A shows an example in the case where it is detected (at time T2 and T3), and FIG. 3B shows an example in the case where it is not detected (see section 91). As an example of the case where no detection is made, as shown in FIG. 5B, the leading edge of the preceding sheet and the leading edge of the succeeding sheet are substantially connected, or the rolling by the pair of rolling rollers 103 does not work normally. A case where the preceding and succeeding sheets are fed out in a state where they overlap each other can be considered.

  If it is determined that the detection is detected by the detection sensor 107 (“YES” in step S14), the interval between the preceding sheet and the succeeding sheet is obtained, and it is determined whether or not the obtained sheet interval is shorter than Ls (step S15). ). Here, FIG. 3A shows an example when the paper interval is Ls or more (between T2 and T3), and FIG. 4 shows an example when the paper interval is shorter than Ls (between T11 and T12). ing. As a method for obtaining the sheet interval, for example, at the feeding speed Vf, the detection time from when the trailing edge of the preceding sheet is detected by the detection sensor 107 until the leading edge of the succeeding sheet is detected (OFF time of the detection sensor 107) The method of multiplying can be taken. Here, an example in which the sheet interval is captured by distance has been described, but it can also be captured by time. In this case, the detection time may be compared with a predetermined time (a time corresponding to the time from when the preceding sheet trailing edge is detected by the detection sensor 107 when the sheet interval is Ls to when the following sheet leading edge is detected).

  If it is determined that the sheet interval is not shorter than Ls, that is, not less than Ls (“NO” in step S15), it is determined whether or not the leading edge of the subsequent sheet is detected by the detection sensor 108 (step S16). If it is determined that the leading edge of the succeeding sheet is not detected (“NO” in step S16), the sheet feeding motor 110 is driven to rotate on the assumption that it is necessary to continue feeding the succeeding sheet by the feeding roller 102 and the separating roller pair 103. continue.

When it is determined that the leading edge of the succeeding sheet is detected (“YES” in step S16) (at time T4 in FIG. 3A), the succeeding sheet is transported by the pair of transport rollers 104 and 105, and is fed out. Assuming that it is no longer necessary to feed the subsequent sheet by the roller 102 or the like, the sheet feed motor 110 is stopped (step S17), and the process is terminated.
On the other hand, if it is determined in step S14 that it has not been detected, the feed speed Vf is decelerated while keeping the transport speed Vc constant (step S18), and then returned to the original speed (step S19) (section 92 in FIG. 3B). ), And proceeds to step S16. This deceleration is performed here by reducing the rotational speed of the paper feed motor 110, and as a deceleration amount (time, speed, etc.) at that time, a predetermined value is used as a value when not detected. . Specifically, this is an amount necessary to widen the sheet interval to Ls when the preceding and succeeding sheets overlap with the maximum amount assumed, and is obtained in advance from experiments and stored in a ROM or the like. As a result, even if double feeding occurs, the necessary sheet interval Ls can be obtained as shown in FIG.

  If it is determined that the sheet interval is shorter than Ls (“YES” in step S15), the same deceleration control of the feeding speed Vf is performed in steps S18 and S19. The deceleration amount here is smaller than the section 92 shown in FIG. 3B as shown in the section 93 of FIG. This is because it is possible to reduce the amount by which the progress of the succeeding paper is delayed as compared with the case of double feeding.

  The deceleration amount of Vf is determined according to the detected amount of paper interval. For example, the amount of deceleration required to increase the sheet interval to Ls when the sheet interval is 0 (zero) mm, the amount of deceleration required for 1 mm, the amount of deceleration required for 2 mm, etc. are tested in advance. It is possible to take a method of determining the amount of deceleration by reading the deceleration amount corresponding to the detected sheet interval from the ROM or the like, storing information in which the sheet interval and the amount of deceleration are associated with each other, stored in a ROM, etc. . Further, a formula for obtaining an optimum deceleration amount from the detected sheet interval may be derived in advance from an experiment or the like, and a method for determining the deceleration amount using the formula may be used. In this sense, the detection sensor 107 and the control unit 40 function as a detection unit that detects that the sheet interval is shorter than a predetermined value, and the control unit 40 controls the speed of the subsequent sheet feeding speed Vf by decelerating. Also works. Further, the feed roller 102, the drive system 113, the paper feed motor 110, and the like function as a feed means for feeding out the paper, and the transport roller 104, the drive system 114, the transport motor 111, and the like function as a transport means for transporting the paper. I can say that.

  FIG. 6 is an operation diagram showing how the preceding and succeeding sheets (shaded portions) during sheet feeding move from the position of the roller pair 103 to the position of the detection sensor 108 over time. (A) shows an example in the case where the feeding control of the present embodiment is performed, and (b) shows an example in which the feeding control is not performed. Here, the horizontal axis is the time axis, and the vertical axis indicates the distance in the transport direction. Further, the leading edge line is a line indicating the movement locus of the leading edge of the sheet, and the trailing edge line is a line indicating the movement locus of the trailing edge of the sheet. For example, looking at the leading edge line of the preceding sheet, it can be seen that the leading edge is located at the pair of roller rollers 103 at t0 and has moved to the detection sensor 108 at t1.

  Subsequent sheets are shown for both the case of feeding under the shortest condition (one-dot chain line) and the case of feeding out under the longest condition (two-dot chain line). As described above, when a plurality of sheets are continuously fed, the sheets are fed out at regular intervals. However, the sheet spacing varies due to the presence of sheet feeding variations. Therefore, the movement trajectory changes for each sheet according to the sheet feeding condition when the subsequent sheet is fed. That is, in the case of feeding under the shortest condition, the movement locus shows a one-dot chain line, and in the case of feeding out under the longest condition, it shows a two-dot chain line. For example, a line (broken line) located between the one-dot chain line and the two-dot chain line is shown.

From FIG. 6A, it can be seen that the leading edge of the succeeding sheet is located at the pair of roller rollers 103 at t2 in the shortest condition, and is located at t4 in the longest condition, and the period from t2 to t4 corresponds to the paper feed variation. Is. Accordingly, any time point between t2 and t4 is set as the start time of the subsequent sheet feeding.
In FIG. 6A, when the movement locus (one-dot chain line) when the succeeding sheet is fed out under the shortest condition is seen, the leading line of the succeeding sheet is the leading end line of the preceding sheet between t2 and t3. It can be seen that it is located at the top. This indicates that the preceding sheet and the succeeding sheet are being double-fed (the state shown in FIG. 5B).

In this case, since the sheet interval is zero, “NO” is determined in step S14, and deceleration control is performed in steps S18 and S19 to decelerate the subsequent sheet feeding speed Vf (from time t3 to time t5). Until). The slope of the tip line represents the speed, and therefore the slope becomes smaller in the deceleration zone.
After the deceleration is finished and the feeding speed of the succeeding sheet returns to the original speed (after t5), the time difference between the trailing end of the preceding sheet and the leading end of the succeeding sheet is ts. This time difference ts is a time corresponding to the time difference when the sheet interval is Ls, and it can be seen that Ls can be secured as the sheet interval after deceleration.

  On the other hand, when the movement trajectory (two-dot chain line) when the subsequent sheet is fed out under the longest condition, the deceleration as in the shortest condition is not performed. This is because the sheet interval is a value greater than or equal to Ls, and “NO” is determined in step S15. In this case, the time difference between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet is tm. This tm is a time corresponding to the time difference when the paper interval is Lm (the longest allowable paper interval). That is, the sheet interval (time difference) varies in a range of Ls ≦ sheet interval ≦ Lm (ts ≦ time difference ≦ tm) due to paper feed variation, and the interval between image forming operations on each sheet is as described above. Based on the interval Lm (longest), it is determined based on the interval that image formation on each sheet is performed properly. Note that if the subsequent sheet becomes slower than the longest condition due to deceleration, the sheet interval Lm cannot be used as a reference, and the value of the predetermined time t in step S13 is determined so that this does not occur.

On the other hand, in the case where the feeding control in FIG. 6B is not performed, in order to secure the sheet interval Ls (time difference ts) in the case of the shortest condition, the feeding timing of the subsequent sheet is delayed. The subsequent sheet is stopped between t2 and t11, and any time point between t11 and t12 is set as the subsequent sheet feeding time.
Since the sheet feeding variation itself is the same as that in FIG. 6A, the trailing edge of the preceding sheet and the leading edge of the succeeding sheet when the succeeding sheet is fed out under the longest condition by the amount that the start of feeding is delayed. The time difference tm ′ is longer than tm in FIG. Accordingly, the longest paper interval is also longer than Lm, and accordingly, the image forming operation interval is longer than that of the configuration in which the feeding control of FIG. 6A is performed, and productivity is lowered. In the above description, an example in which two sheets are sequentially fed sequentially has been described, but the same control is performed even when there are three or more sheets, for example, the second sheet is the preceding sheet, the third sheet. Is fed as a succeeding sheet.

  As described above, in this embodiment, when a plurality of sheets are continuously fed, if it is detected that the interval between the preceding sheet and the following sheet is shorter than the predetermined value Ls, the following sheet is detected. The feeding speed Vf is decelerated to increase the sheet interval. Therefore, even if there is a paper feed variation, the feeding interval of each sheet can be made shorter than in the prior art, so that productivity can be improved and the image forming operation interval can be shortened to improve the efficiency of image formation. .

(Second Embodiment)
In the first embodiment, the feeding speed Vf is decelerated. However, in the present embodiment, the transport speed Vc is also decelerated as necessary, which is different. In other words, the necessary sheet interval can be secured while the subsequent sheet is being fed by the deceleration of the feeding speed Vf. However, if there is a variation such as the amount of slip between the conveyance roller pairs 104 and 105 and the timing roller pair 106 and the paper, even if the rotation speed of each roller is set so that the paper conveyance speed is the same, In some cases, the interval between the trailing edge of the preceding sheet and the leading edge of the preceding sheet gradually decreases until the leading edge of the succeeding sheet reaches the timing roller pair 106 via the pair of conveying rollers 104 and 105.

  Therefore, when the preceding paper is being conveyed by the timing roller pair 106 and the subsequent paper is being conveyed by the conveying roller pair 104, 105, if the paper interval becomes shorter than a predetermined value, the conveying speed of the subsequent paper Vc is decelerated to widen the sheet interval. Hereinafter, the description of the same contents as those of the first embodiment will be omitted, and different parts will be mainly described.

FIG. 7 is a flowchart showing the contents of the deceleration control of the conveyance speed Vc. The deceleration control process is executed by the control unit 40 while the preceding paper is being conveyed by the timing roller pair 106 and the subsequent paper is being conveyed by the conveying roller pair 104 and 105.
As shown in the figure, the control unit 40 first detects the sheet interval during conveyance (step S21). In the present embodiment, the detection sensor 112 is used as a sensor for detecting the interval between sheets being conveyed, and the control unit 40 detects the leading edge of the succeeding sheet after the detecting sensor 112 detects the trailing edge of the preceding sheet. The time until printing is measured, and the sheet interval near the position of the detection sensor 112 is determined as the sheet interval during conveyance from the measured time and the conveyance speed Vc.

It is determined whether or not the obtained sheet interval is shorter than a predetermined value Lp (step S22). Here, the predetermined value Lp is a “minimum” paper interval required for loop formation, and can be set to a value larger than, for example, Ls. Since the Lp value itself is determined according to the device configuration, it may actually be a value smaller than or equal to Ls.
If it is determined that the sheet interval is not shorter than Lp, that is, not less than Lp (“NO” in step S22), the process ends. On the other hand, if it is determined that it is shorter than Lp (“YES” in step S22), the transport speed of the subsequent paper is decelerated (the transport speed of the preceding paper is constant) (step S23), and then returned to the original speed. (Step S24), the process ends. This deceleration is performed by lowering the rotation speed of the transport motor 111, and the deceleration amount at that time depends on the detected amount of the sheet interval as in the case of the feeding speed Vf of the first embodiment. Can be decided. In this sense, the control unit 40 and the detection sensor 112 function as a detection unit that detects that the sheet interval during the conveyance is shorter than a predetermined value, and the control unit 40 controls the conveyance speed of the subsequent sheet by decelerating. It also functions as a speed control means.

FIG. 8 is an operation diagram showing how the preceding and succeeding sheets move when the deceleration control is performed, and shows the operation from the pair of whirling rollers 103 to the pair of timing rollers 106.
As shown in the figure, when the movement locus (one-dot chain line) of the subsequent sheet under the shortest condition is seen, the subsequent sheet feeding speed is decelerated between t21 and t22. This point is the first embodiment. It is the same as the form.

  Between t22 and t23 is a section in which the subsequent sheet is conveyed by the conveyance roller pair 104, and the one-dot chain line has a larger gradient than the solid line, and this is because the subsequent sheet is more than the preceding sheet. Also shows an example when the moving speed is fast. The difference in speed between the preceding and succeeding sheets is due to the existence of variations such as the amount of slip with the sheet for each roller as described above.

Between t23 and t24, the gradient of the alternate long and short dash line is gentle, indicating that the conveyance speed of the subsequent sheet is decelerated (corresponding to the processing of steps S21 to S23 in FIG. 7). As a result, the interval between the sheets being conveyed is increased.
After t24, the gradient is substantially the same for the preceding and succeeding sheets, indicating that the transport speed has returned to the substantially original speed. Here, the time difference between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet is tp. This time difference tp is a time corresponding to the time difference when the paper interval becomes Lp, and it can be seen that Lp can be secured as the paper interval during conveyance after deceleration. In the figure, tn is a time corresponding to the time difference when the sheet interval during conveyance under the longest condition is Ln (longest), and at t25, the time when the subsequent sheet is conveyed under the shortest condition. This is the loop formation end point, and t26 indicates the loop formation end point when the sheet is conveyed under the longest condition. Further, at t27, the end point of loop formation of the preceding paper is shown, and te shows the interval of the image forming operation.

  Since the interval of the image forming operation is indicated by te, the conveyance timing of the preceding sheet to the secondary transfer position 261 is t27, and the conveyance timing of the subsequent sheet to the secondary transfer position 261 is At t26. Therefore, when the succeeding sheet is conveyed under the shortest condition, it waits for t25 to t26 with the loop formed, and is conveyed to the secondary transfer position 261 at t26. In this sense, it can be said that the figure shows an example in which the interval of the image forming operation is determined based on the sheet interval under the longest condition.

  The present invention is not limited to the sheet feeding device, and may be the above-described sheet feeding control method. Furthermore, the method may be a program executed by a computer. The program according to the present invention includes, for example, a magnetic disk such as a magnetic tape and a flexible disk, an optical recording medium such as a DVD-ROM, DVD-RAM, CD-ROM, CD-R, MO, and PD, and a flash memory recording medium. It can be recorded on various computer-readable recording media, and may be produced, transferred, etc. in the form of the recording medium, wired and wireless various networks including the Internet in the form of programs, In some cases, the data is transmitted and supplied via broadcasting, telecommunication lines, satellite communications, or the like. In some cases, some or all of the predetermined processing can be executed using dedicated hardware.

(Modification)
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.
(1) In the first embodiment, the feeding speed Vf is reduced only when the set speeds of the feeding speed Vf and the sheet conveying speed Vc are substantially equal and the sheet interval is shorter than a predetermined value. For example, after the feeding speed Vf is temporarily reduced to zero (after the subsequent sheet is temporarily stopped), the original speed can be returned to the original speed. In this sense, deceleration can be regarded as a concept including stopping.

  Further, in terms of increasing the sheet interval, the method is not limited to the method of decelerating only the subsequent sheet, and for example, a method of temporarily accelerating the preceding sheet can be used. Furthermore, they may be combined. Further, the feeding speed Vf and the transport speed Vc are not limited to be substantially equal. In short, it is only necessary to widen the sheet interval. In this sense, control is performed to lower the feeding speed Vf with respect to the transport speed Vc (the value of Vc−Vf is larger than the current value) regardless of the set speeds of Vf and Vc. Any configuration can be used.

In the second embodiment, basically, the sheet conveyance speed (third speed) by the timing roller pair 106 is fixedly determined in accordance with the image forming operation speed. The method of decelerating the transport speed is taken.
(2) In the above-described embodiment, the apparatus including the roller pair 103 at the position downstream of the sheet feeding cassette 101 in the transport direction is taken as an example. However, the present invention can also be applied to a configuration that does not include the roller pair 103. In this case, the variation in the sheet interval is mainly caused by the variation in the feed amount when the sheet is fed.

  In the above, when feeding each sheet continuously, the feeding of the succeeding sheet is started after a lapse of a certain time from the start of feeding the preceding sheet. It is not limited to. For example, a method may be employed in which the feeding of the succeeding sheet is started when a predetermined time has elapsed after the leading edge of the preceding sheet has passed the detection sensor 108.

(3) In the above, a roller (feeding roller 102) is used as a feeding member for feeding out the paper. However, the roller is not limited as long as the paper can be fed out from a set of paper, and for example, a belt or the like is used. Also good. The same applies to the conveyance members such as the conveyance roller pair 104.
(4) In the above-described embodiment, an example in which the sheet feeding apparatus according to the present invention is applied to a printer has been described. However, apparatuses that receive and process continuously fed sheets, such as copiers, fax machines, and MFPs. (Multiple Function Peripheral) and other sheet feeding apparatuses can be applied in general.

  Further, the above embodiment and the above modification examples may be combined.

  The sheet feeding apparatus according to the present invention is useful in a technique for improving productivity by shortening a feeding interval as much as possible while securing a necessary interval as a sheet interval when continuously feeding sheets.

1 is a diagram illustrating an overall configuration of a printer 1 including a sheet feeding device according to the present invention in a first embodiment. FIG. FIG. 6 is a flowchart illustrating the contents of feeding control by the control unit 40 of the printer 1. It is a figure which shows the timing chart of feed control. It is a figure which shows another timing chart of feeding control. FIG. 10 is a diagram schematically illustrating a state in which a sheet is conveyed by feeding control. FIG. 10 is an operation diagram showing how the preceding and succeeding sheets during sheet feeding move from the position of the roller pair 103 to the position of the detection sensor as time elapses. It is a figure which shows the flowchart which shows the content of the feeding control in 2nd Embodiment. FIG. 10 is an operation diagram showing how the preceding and succeeding sheets during sheet feeding move from the position of the roller pair 103 to the position of the timing roller pair 106 over time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 10 Feed part 40 Control part 100 Conveyance path 103 Feeding roller 104,105 Conveyance roller pair 107,108,109,112 Detection sensor

Claims (7)

A sheet feeding device that feeds and conveys sheets from a bundle of sheets stacked in a sheet storage unit,
A feeding means for feeding the sheets from the sheet bundle at a first speed;
A conveying means for receiving the fed sheet and conveying it at a second speed;
When two sheets are successively fed sequentially, the sheet feeding position by the feeding unit while the preceding sheet is being conveyed by the conveying unit and the subsequent sheet is being fed by the feeding unit. Detecting means for detecting that an interval between the preceding sheet and the succeeding sheet on a conveying path between sheet conveying positions by the conveying means is shorter than a predetermined value;
When the detecting means detects that the interval is shorter than the predetermined value, the speed for controlling the feeding means and / or the conveying means so that the first speed with respect to the second speed decreases. Control means;
A sheet feeding apparatus comprising: The speed control means is
The sheet feeding apparatus according to claim 1, wherein the feeding unit is controlled to reduce the first speed. The speed control means is
The sheet feeding apparatus according to claim 2, wherein the first speed is returned to the original speed after a predetermined time has elapsed. The detection means includes
A sensor that is provided on the conveyance path and that detects a leading edge and a trailing edge of a passing sheet;
When the trailing edge of the preceding sheet and the leading edge of the succeeding sheet have not been detected by the sensor even when a predetermined timing is reached, or after the trailing edge of the preceding sheet is detected by the sensor, The sheet feeding according to any one of claims 1 to 3, wherein when the time until the leading edge is detected is equal to or shorter than a predetermined detection time, the interval is detected to be shorter than a predetermined value. apparatus. The speed control means is
5. The sheet feeding apparatus according to claim 1, wherein an amount of change in speed is determined based on the size of the interval. Another transport means for receiving and transporting the sheet transported by the transport means at a third speed;
The detection means includes
While the preceding sheet is being conveyed by the other conveying unit and the subsequent sheet is being conveyed by the conveying unit, the sheet between the sheet conveying position by the other conveying unit and the sheet conveying position by the conveying unit is Detecting that the distance between the preceding sheet and the succeeding sheet is shorter than another predetermined value;
The speed control means is
When the detection unit detects that the sheet interval between the sheet conveyance position by the another conveyance unit and the sheet conveyance position by the conveyance unit is shorter than the another predetermined value, the conveyance unit is controlled to The sheet feeding apparatus according to claim 1, wherein the second speed is reduced. An image forming apparatus for forming an image on a sheet fed from a sheet feeding apparatus,
An image forming apparatus comprising the sheet feeding device according to claim 1 as the sheet feeding device.

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