JP4392456B2 - Paper conveying apparatus and image forming apparatus - Google Patents

Description

The present invention relates to a paper conveying device in an image forming apparatus such as a laser printer, PPC, or facsimile.

In a paper conveying apparatus equipped in an image forming apparatus that forms an image by an electrophotographic method or the like, a paper feeding roller for feeding paper from a paper stacking unit, a separating means for separating paper into one sheet, and a paper feeding roller It has been conventionally known to provide a sheet conveying means for conveying a sheet provided further downstream (see, for example, Patent Documents 1 to 3).
Patent Document 1 describes that when the fed paper is drawn downstream from the separation unit and the on-timing of the paper leading edge detection sensor is earlier than the theoretical value, the paper feeding unit is temporarily stopped or conveyed at a low speed. The paper spacing is adjusted. However, this is only a paper gap adjusting means and does not prevent continuous feeding.
In Patent Document 2, the sheet feeding motor is driven at a low speed when there is a double feed during sheet separation (when the intermediate sheet leading edge detection sensor is on earlier than the theoretical value). The purpose of this is to accurately determine the registration position of the paper even when there is a double feed, and is not intended to prevent double feed and continuous feed.
In Patent Document 3, the follow-up detection means detects whether or not a cut sheet exists at a predetermined time with a reflection type sensor upstream of the separation roller. This does not prevent continuous transmission.
FIG. 15 is a schematic view showing a cross section of a sheet feeding / conveying section (using the FRR separation method) of a conventional image forming apparatus. The sheet 2 stacked on the sheet stacking table 1 has a leading end position A. The pickup roller 3 descends and rotates with a paper feed signal that tells the paper transport device to start feeding as a trigger, and sends the uppermost paper to the separating section B.
The feed roller 4 and the reverse roller 5 are driven simultaneously with the driving of the pickup roller 3 to separate the paper 2 into one sheet. In this embodiment, the pickup roller 3, the feed roller 4, and the reverse roller 5 are driven by one motor.
When the leading edge of the sheet 2 separated into one sheet reaches the first sensor C, the pickup roller 3 rises, the drive is cut off, and the sheet 2 is not conveyed by the pickup roller 3. Thereafter, the sheet 2 is conveyed by the conveying force of the feed roller 4 and reaches the conveying roller 6.
The feed roller 4 is driven after the second sensor 7 detects that the leading edge of the paper has reached. Since the second sensor 7 is located downstream of the first conveying roller 6, the driving of the feed roller 4 is turned off after the leading edge of the sheet reaches the first conveying roller 6.
After the drive of the feed roller 4 is cut, the paper 2 is fed by the first transport roller 6. Thereafter, the leading edge of the sheet passes through the second conveyance roller 8. Image writing to the photoconductor 12 is started with a trigger that the leading edge of the sheet has passed the third sensor 9 (= the third sensor 9 has detected the leading edge of the sheet).

The first and second transport rollers 6 and 8 are driven by separate motors (first and second transport roller motors (not shown)). After the time t2 has elapsed since the leading edge of the sheet reached the fourth sensor 10 (at this time, t2 is set so that the leading edge of the sheet reaches the registration roller 11), the registration roller 11 is stopped.
By setting the time t2, the leading edge of the sheet is slackened in front of the registration roller 11 to perform skew correction. In this embodiment, at t2 = 37.5 msec, the conveyance roller motor is turned off, and the first and second conveyance rollers 6 and 8 are driven off.
After that, the conveyance roller motor is turned on simultaneously with the driving of the registration roller 11, the first and second conveyance rollers 6, 8 start to rotate, and the sheet 2 is sent to the transfer unit composed of the photoconductor 12 and the transfer roller 13. The image is transferred.
The timing at which the registration roller 11 is turned on is set to be turned on after a lapse of time t3 after the third sensor 9 is turned on. As a result, the image written on the photosensitive member is aligned with the leading edge of the paper. In an image forming apparatus such as a copy or a printer, the sheet 2 is separated and conveyed by the sheet feeding unit as described above, and an image is printed.
In recent years, with the widespread use of color printers and color copiers, there is an increasing need to print on paper with high surface smoothness such as art paper or paper coated with resin or the like on the surface.

Japanese Patent Laid-Open No. 9-249333 JP 2001-026337 A Japanese Patent Laid-Open No. 9-067037

In the case of such a sheet with high surface smoothness or a sheet coated with a resin or the like on the surface, it is difficult for air to enter between the sheets, and the adhesion between the sheets increases. In addition, the adhesion between the sheets may be increased due to electrostatic adsorption, and it becomes difficult to separate and convey the sheets as compared with normal plain paper.
As a result, a state where the paper is transported in an insufficiently separated state, that is, a double feeding in which the papers are overlapped can occur. In order to reduce such paper separation failure, conventionally, in addition to a normal separation mechanism, there is a mechanism in which air is blown to a paper separation portion to reduce the adhesion of the paper. However, when a mechanism for blowing air to the separation unit is provided, the apparatus increases in cost and size.
In view of the above problems, the object of the present invention is to carry out double feeding, particularly where a part of the preceding paper and the following paper are overlapped without adding a large mechanism such as air blowing to the conventional paper feeding device. An object of the present invention is to provide a sheet conveying apparatus having means effective for preventing feeding.

In order to achieve the above object, an invention according to claim 1 is a paper transport device in an image forming apparatus such as an electrophotographic system, wherein a paper feed roller for feeding paper from a paper stacking unit, and one sheet of paper In the paper transporting apparatus provided with the separating means for separating the paper into the paper, the paper transporting means for transporting the paper provided downstream of the paper feed roller, and the registration means provided downstream of the paper transporting means, A carry detection sensor for determining the presence or absence of the paper provided in the paper conveyance path after the separating means and before the registration means, and a trailing edge of the preceding paper when the paper is conveyed continuously is the carry detection. The output signal of the following detection sensor is confirmed at a timing when it is predicted that the sensor will pass through the sensor. A control unit that slows down the paper conveyance speed of the paper conveyance means provided upstream of the paper, and a paper position sensor that determines the presence or absence of paper provided in the paper conveyance path downstream of the follow-up detection sensor. The timing is a timing obtained from information on an elapsed time and a paper length after the leading edge of the preceding paper is detected by the paper position sensor.
According to a second aspect of the present invention, there is provided a sheet conveying device in an electrophotographic image forming apparatus, a sheet feeding roller for feeding sheets from a sheet stacking unit, and a separating unit for separating sheets into one sheet. In the paper transport device provided with the paper transport means for transporting the paper provided downstream from the paper feed roller and the registration means provided downstream from the paper transport means, after the separation means and before the registration means And a feed detection sensor for determining the presence or absence of the paper provided in the paper transport path, and a timing at which the trailing edge of the preceding paper when the paper is continuously transported is predicted to pass through the feed detection sensor The output signal of the follow-up detection sensor is confirmed at, and when the follow-up detection sensor detects the presence of paper at this time, the above-mentioned use provided upstream from the follow-up detection sensor A controller that slows down the paper conveyance speed of the conveyance means; and a paper position sensor that determines the presence or absence of paper provided in a paper conveyance path downstream from the follow-up detection sensor. After the leading edge of the preceding sheet is detected by the sensor, the timing is obtained from information on the rotation amount and the sheet length of the sheet conveying means provided downstream from the carry detection sensor.
請 Motomeko 3 the described invention, in an image forming apparatus having a sheet conveying apparatus according to claim 1 or 2.

According to the present invention, a sensor for determining the presence or absence of paper is provided as a feed detection sensor 7 in the paper transport path downstream from the separation unit, and the trailing edge of the paper being transported passes through the transport detection sensor 7. Observe the signal of the feed detection sensor at the expected timing.
At this time, if the signal of the carry detection sensor detects that there is a sheet, it is determined that the sheet currently detected by the carry detection sensor is longer than a predetermined length, that is, the carry detection sensor, and upstream of the carry detection sensor. The sheet conveying speed of the sheet conveying means provided in the is reduced.
As a result, the transport speed of the succeeding paper that is fed over the preceding paper becomes slower than that of the preceding paper, so that the paper overlap decreases with the passage of time, the overlap is eliminated, and the carry-over is eliminated. it can.

FIG. 1 is a schematic view of a sheet feeding / conveying section (using an FRR separation method) of a sheet conveying apparatus of an image forming apparatus according to the present invention. FIG. 2 is a schematic diagram showing a first embodiment of a conveyance path to a second conveyance roller of the paper conveyance device of FIG. 3 is the same schematic diagram as FIG. 2 showing the configuration up to the second transport roller of the paper transport apparatus of FIG. 4 is the same schematic view as FIG. 2 showing up to the second transport roller of the paper transport apparatus of FIG.
1 to 4 are almost the same as the configuration of the prior art in FIG. 15, and the same reference numerals are given to the same parts as in FIG. 15, but a fifth sensor 14 is added to the paper transport path 17. However, it is different.
The second sensor 7 is a paper presence / absence detection sensor that detects the presence / absence of paper. In the prior art, the second sensor 7 is used as a trigger for turning off the feed roller 4. That is, after it is detected that the leading edge of the paper has reached the second sensor 7, the drive connection of the feed roller 4 is disconnected by the control means.
In the present embodiment, in addition to the function of the conventional apparatus shown in FIG. 15, the second sensor 7 is also used for detection of paper that has been sent as a continuous feed of paper 2 (= feed detection sensor). is doing. The position of the second sensor 7 is provided at a position downstream from the first conveying roller 6 by a distance LE-G.
The fifth sensor 14 (paper position sensor 14) is a sensor that detects the presence or absence of the paper 2 in the same manner as the second sensor 7, and is provided at a position downstream from the second sensor 7 by a distance LG-G ′.
Both sensors 7 and 14 are arranged on the conveyance path between the first conveyance roller 6 and the second conveyance roller 8.

FIG. 5 is a flowchart for explaining the flow of the operation of the sheet conveying apparatus according to the present invention. The operation flow of the sheet conveying apparatus will be described with reference to this flowchart and FIGS.
When paper feeding is started (S1), when the trailing edge of the currently transported paper 2 (P1) leaves the position of the second sensor 7 (= timing at which the second sensor 7 is turned on → off). Predicted (S2).
When the paper P1 is transported in a state where there is no carry, it is predicted that the timing at which the trailing edge of the paper P1 passes through the second sensor 7 is not significantly different from the predicted timing.
Therefore, if the second sensor 7 detects that the trailing edge of the preceding paper P1 has passed through the second sensor 7 and the sensor is turned off, the leading edge of the succeeding paper has overlapped. Since there is a high probability of being in the state, the second sensor 7 is used as a follow-up detection sensor.
If the second sensor 7 detects the absence of paper at the timing when the rear end of the predicted preceding paper P1 passes through the second sensor 7 (= the second sensor 7 is off), the paper is fed normally without being accompanied. (S3), and the paper is fed in the same manner as the conventional paper transport.
However, if the second sensor 7 detects that there is a sheet (= the second sensor 7 is on) at the timing when the rear end of the predicted sheet P1 passes through the second sensor 7, a feed occurs. Therefore, the conveyance speed of the succeeding paper P2 by the first conveyance roller 6 is switched to a low speed (FIG. 3) (S4).

The first conveying roller 6 and the second conveying roller 8 provided downstream thereof are driven by separate motors, and the sheet feeding speeds of the first conveying roller 6 and the second conveying roller 8 are switched independently. It is like that.
Thereafter, after detecting that the trailing edge of the preceding paper P1 has passed through the position of the paper position sensor (fifth sensor 14) (= the paper position sensor 14 is turned off), the first time after a certain time T1 (including 0) has elapsed. The paper transport speed of the transport roller 6 is restored (S5, S6).
That is, as shown in FIG. 4, the conveyance speed of the first conveyance roller 6 that nips the subsequent sheet P2 is shifted from low speed to normal speed. Thereafter, the normal operation is performed. According to this, it is possible to detect the carry with a high probability by looking at the state of the second sensor 7 at the predicted timing of the paper removal using the second sensor 7 as the carry detection sensor.
As described above, when it is determined to be accompanied by the signal from the second sensor 7, the overlap of the sheets can be eliminated by switching the sheet conveying speed of the upstream sheet conveying unit to the low speed. Accordingly, it is possible to eliminate the carry-in.
After it is determined by this signal that the carry is carried out, the paper carrying speed of the paper carrying means provided upstream from the carry detection sensor (second sensor 7) is switched from low to normal after canceling the carry.
Thus, after the overlap between the preceding sheet and the succeeding sheet is eliminated, the succeeding sheet can be conveyed so that an image is normally formed. In this way, it is possible to send subsequent sheets without any problem after canceling the carry-in.
After it is determined by the signal of the second sensor 7 that feeding is to be carried out, the trailing edge position detection sensor (fifth sensor 14) provided downstream from the second sensor 7 (feeding detection sensor) detects the trailing edge of the preceding sheet. Detected (rear end position detection sensor 14 is off).
Thereafter, the sheet conveying speed of the sheet conveying means provided upstream from the carry detection sensor 7 is switched from low speed to normal speed. Thus, if it is not reliably detected that the overlap of the sheets is eliminated, the succeeding sheet is not conveyed, and it is possible to more reliably eliminate the carry-in.

FIG. 6 is a schematic view showing a second embodiment up to the second transport roller of the paper transport apparatus of FIG. 7 is the same schematic view as FIG. 6 showing up to the second transport roller of the paper transport apparatus of FIG. 8 is the same schematic view as FIG. 6 showing up to the second transport roller of the paper transport apparatus of FIG.
The second sensor 7 is a sensor that detects the presence or absence of the paper 2 and is used as a trigger for cutting off the driving of the feed roller 4 in the prior art (after it is detected that the front end of the paper has reached the second sensor 7, The feed roller 4 is turned off by the control means).
In this embodiment, in addition to its function, it is also used for detection of paper that has been sent as a continuous feed of paper (= feed detection sensor). The position of the second sensor 7 is provided at a position downstream of the first conveying roller 6 by the distance LE-G.
FIG. 9 is a flowchart for explaining an operation flow in the second embodiment of the sheet conveying apparatus according to the present invention. The operation flow of the sheet conveying apparatus will be described with reference to this flowchart and FIGS.
When the paper feeding is started (S11), it is predicted when the trailing edge of the currently transported paper sheet P1 leaves the position of the second sensor 7 (= the timing when = changes from on to off) (S12).
When the paper is transported in a state where there is no carry, it is predicted that the timing at which the trailing edge of the paper P1 passes through the second sensor 7 is not significantly different from the predicted timing. Accordingly, when the second sensor 7 detects that there is a sheet at the timing when the rear end of the predicted sheet passes through the second sensor 7 (S13), the second sensor 7 has a high probability of being accompanied. Is used as a feed detection sensor.

If the second sensor 7 detects that there is no paper at the timing when the predicted trailing edge of the paper leaves the second sensor 7 (= second sensor off), it is determined that the paper is being fed normally without being accompanied. Then, the sheet is fed in the same manner as the conventional sheet conveyance.
However, if the second sensor 7 detects that there is a sheet (= second sensor ON) at the timing when the rear end of the predicted sheet P1 passes through the second sensor 7, it is determined that a carry has occurred (FIG. 6). Then, the sheet conveying speed of the first conveying roller 6 is switched to a low speed (S14) (FIG. 7).
The first conveying roller 6 and the second conveying roller 8 provided downstream thereof are driven by separate motors, and the sheet feeding speeds of the first conveying roller 6 and the second conveying roller 8 are switched independently. It is like that.
Thereafter, the paper transport speed of the first transport roller 6 is restored to the original (low speed → normal speed) after a lapse of a fixed time T1 (including 0) from the timing when the trailing edge of the preceding paper P1 is removed from the second sensor 7. S15) (S16) (FIG. 8). Thereafter, the normal operation is performed (S17).
This eliminates the need for a new sensor (fifth sensor 14) for detecting the trailing edge of the paper, and can prevent the occurrence of follow-up with a simple mechanism. Of course, it is more certain that a new sensor is provided in terms of certainty, but in the case of an apparatus that is not required so far, for example, it is effective in a low-cost machine.
Further, there is a case where the overlap between the preceding sheet and the succeeding sheet is eliminated without reducing the conveying speed of the succeeding sheet until the trailing end of the preceding sheet passes through the trailing end position detection sensor.
For example, if the overlap amount (distance) of paper is Ld, the distance LG-G ′ between the second sensor 7 and the fifth sensor 14, and the first transport roller 6 after the second sensor 7 determines that the accompanying feed has occurred. Lf is the amount of paper that is fed before the low speed is switched to low speed, the normal paper feed speed is V0, and the paper feed speed at low speed is V1 (V1 <V0). -(Ld + Lf)) × (1−V1 / V0) is opened.
At this time, if the overlap amount Ld is small, the paper is made to wait for that much, and the paper conveyance interval may become larger than necessary. On the other hand, if a certain time T has elapsed after the conveyance speed of the first conveyance roller is slowed, the paper conveyance interval is not increased more than necessary, and the succeeding paper is made to wait to increase the print productivity. It is possible to prevent the decrease.

FIG. 10 is a flowchart for explaining another operation flow in the first embodiment of the sheet conveying apparatus according to the present invention. The operation flow of the sheet conveying apparatus will be described with reference to this flowchart and FIGS.
When paper feeding is started (S21), it is predicted when the trailing edge of the currently transported paper sheet P1 leaves the position of the second sensor 7 (= timing at which the second sensor 7 is turned on → off). (S22).
If the second sensor 7 detects the absence of paper at the timing when the rear end of the predicted paper 2 passes through the second sensor 7 (= the second sensor 7 is off), the paper is sent normally without being accompanied. (S23), and the paper is fed in the same manner as the conventional paper conveyance.
However, when the second sensor 7 detects that there is a sheet (= second sensor 7 is on) at the timing when the rear end of the predicted sheet 2 passes through the second sensor 7, there is an accompanying feed (FIG. 2). The sheet conveyance speed of the first conveyance roller 6 is switched to a low speed (FIG. 3) (S24).
Thereafter, after detecting that the preceding sheet has been removed from the position of the sheet position sensor (fifth sensor 14) (= the sheet position sensor 14 is turned off) (S25), a certain period of time has passed since the transport roller has rotated slowly. It is determined whether T1 (including 0) has elapsed (S26). Next, the sheet conveying speed of the first conveying roller 6 is restored (S27).
That is, the shift from low speed to normal speed in FIG. Thereafter, the normal operation is performed (S28). According to this, it is possible to detect the carry with a high probability by looking at the state of the second sensor 7 at the predicted timing of the paper removal using the second sensor 7 as the carry detection sensor.

After a subsequent sheet conveyance speed is switched to a low speed, when a predetermined time T has elapsed, the sheet conveyance speed of the first conveyance roller 6 is returned to the original regardless of the signal from the second sensor 14 (low speed → normal speed). ).
In other words, the sheet transport speed of the first transport roller 6 is restored to “the rear end position detection sensor 14 detects the rear end of the preceding paper P1, and after a certain time T1 has elapsed (including 0), the rear After the conveyance of the sheet P2 to be carried out is stopped, after a certain time T has elapsed, whichever is earlier ".
Thus, until the fixed time T elapses, the fifth sensor 14 detects that the overlap of the sheets has been eliminated, and then the driving of the first conveying roller 6 is resumed. Regardless of the signal, the driving of the first conveying roller 6 is resumed.
Until the fixed time T elapses, the fifth sensor 14 detects that the overlap of the sheets is eliminated, and then the sheet conveyance speed of the first conveyance roller 6 is returned to the original, so that the carry-out can be surely eliminated. It becomes possible.
Further, when the predetermined time T is reached after switching the sheet conveying speed of the first conveying roller 6 to the low speed, the sheet conveying speed of the first conveying roller 6 is restored to the original regardless of the signal of the fifth sensor 14. As described above, it is possible to prevent the productivity of printing from being lowered by waiting the succeeding paper without increasing the paper conveyance interval.

FIG. 11 is a flowchart for explaining the flow of still another operation in the first embodiment of the sheet conveying apparatus according to the present invention. The operation flow of the sheet conveying apparatus will be described with reference to this flowchart and FIGS.
Since FIG. 11 is almost the same as the operation flow related to FIG. 10, only the differences will be described here. The fifth sensor 14 does not detect the trailing edge of the preceding paper (the fifth sensor 14 continues to detect the presence of paper) until the fixed time T2 elapses (S36) after switching the paper conveyance speed of the following paper to low speed. If it is, the paper feeding operation is determined to be abnormal (S36). A signal indicating that the conveyance of the sheet is abnormal is output to the control unit of the apparatus. As a result, the subsequent operation of the apparatus enters the abnormal processing mode. In the case of normal carry-forward, it is considered that the overlap is eliminated within a certain time T2, and it is determined that there is an abnormality.
Specifically, for example, when the paper is jammed and stopped at the position of the fifth sensor 14, or when the paper is overlapped so as not to be eliminated (= the amount of overlap of the paper is the second sensor 7). And the fifth sensor 14 distance LG-G ′).
Until the fixed time T2 elapses after the sheet conveyance speed of the succeeding sheet is switched to the low speed, the sheet conveyance of the first conveyance roller 6 is performed after the fifth sensor 14 detects that the sheet overlap is eliminated as described above. By returning the speed to the original value (switching from low speed to normal speed), it becomes possible to reliably eliminate the carry-forward.
When the signal from the fifth sensor 14 detects the presence of paper when the time from the low speed switching of the first transport roller 6 is equal to or longer than the predetermined time T2 while the first transport roller 6 is switched to the low speed. Then, it is determined that there is an abnormality in the conveyance of the sheet, and a signal indicating that the conveyance of the sheet is abnormal is output to the control unit of the apparatus.
Thereby, for example, when the paper is jammed and stopped at the position of the fifth sensor 14 or when the paper is overlapped so as not to be resolved (the amount of overlap of the paper is the second sensor 7 and the fifth sensor. It is possible to detect an abnormality in conveyance such as when the distance 14 is greater than the distance LG-G ′. In this case, it is also possible to automatically shift the operation of the apparatus thereafter to the abnormality processing mode. It becomes.

FIG. 12 is a flowchart for explaining another operation flow in the first embodiment of the sheet conveying apparatus according to the present invention. The operation flow of the sheet conveying apparatus will be described with reference to this flowchart and FIGS.
Since FIG. 12 is almost the same as the operation flow related to FIG. 11, only the differences will be described here. After the paper transport speed of the succeeding paper is switched to a low speed, the fifth sensor 14 returns to the original paper speed (switches from the low speed to the normal speed) (S58), and the fifth sensor 14 passes until a predetermined time T3 elapses. It is assumed that the trailing edge of the preceding paper is not detected.
The fifth sensor 14 (in this embodiment (here, the rear end of the preceding paper is detected by the fifth sensor 14, but a sensor provided further downstream, for example, the third sensor 9 is also possible)) Then, it is determined that the sheet feeding operation is abnormal.
A signal indicating that the conveyance of the sheet is abnormal is output to the control unit of the apparatus (S60).
As a result, the subsequent operation of the apparatus enters the abnormal processing mode. In the case of normal carry-forward, it is considered that the overlap is eliminated within a certain time T3, and it is determined to be abnormal.
For example, when the paper is jammed and stopped at the position of the fifth sensor 14 or when the paper is overlapped so as not to be resolved (= the amount of paper overlap is between the second sensor 7 and the fifth sensor 14) The distance LG-G ′).
Even if a certain time T3 elapses after it is determined that there is an overlap of sheets and the sheet conveyance speed is switched to a low speed after switching to a low sheet conveyance speed (switching from a low speed to a normal speed). If the rear end of the preceding sheet cannot be detected by the fifth sensor 14, it is determined that an abnormality has occurred in the conveyance of the sheet, and a signal indicating that the conveyance of the sheet is abnormal is output to the control unit of the apparatus.
Thereby, for example, when the paper is jammed and stopped at the position of the fifth sensor 14, or when the paper is overlapped so as not to be resolved (the amount of overlap of the paper is the second sensor 7 and the fifth sensor). It is possible to detect a conveyance abnormality such as a case where the distance between the sensors 14 is larger than the distance LG-G ′). In this case, the operation of the apparatus thereafter is automatically shifted to the abnormality processing mode. It is also possible.

Next, FIG. 1 will be further described. Prediction of the timing at which the sheet 2 passes through the carry detection sensor (second sensor 7) is predicted after the leading edge of the sheet is detected by the sheet position sensor (fifth sensor 14) provided downstream from the carry detection sensor 7. It is obtained from information on time Tb and paper length.
Specifically, when the time Tb after the leading edge of the preceding sheet P1 passes through the sheet position sensor 14 becomes the predicted time Ta until the trailing edge of the sheet passes the carry detection sensor 7 (Tb = Ta). The sheet conveyance speed of the first conveyance roller 6 is restored (switched from low speed to normal speed).
The predicted time Ta is obtained as follows,
Ta = (paper length−LG−G ′) / paper feeding speed−Tr ± α
LG−G ′ = Distance between second sensor 7 and fifth sensor 14 Tr = Standby time of paper at registration roller 11 α = Error due to roller slip, variation in outer diameter, and the like.
The timing at which the paper P1 exits the take-up detection sensor (second sensor) 7 can be accurately predicted, and as a result, the carry-detection sensor 7 can accurately detect the take-up. It is possible to prevent feeding.

Prediction of the timing at which the paper P1 exits the carry detection sensor 7 is determined based on the second transport roller 8 after the leading edge of the paper is detected by the paper position sensor (fifth sensor) 14 provided downstream of the carry detection sensor 7. It is obtained from the information on the rotation amount Rb and the length of the paper P1.
Specifically, when the rotation amount Rb after the leading edge of the sheet passes through the sheet position sensor 14 becomes the predicted rotation amount Ra until the trailing edge of the sheet passes through the carry detection sensor 7 (Rb = Ra). ) Is controlled so that the sheet conveying speed of the first conveying roller 6 is restored (switched from low speed to normal speed).
Ra is calculated as follows,
Ra = (paper length−LG−G ′) ± α
LG-G ′ = distance between the second sensor 7 and the fifth sensor 14 is estimated to be an error due to roller slip, variation in outer diameter, and the like.
The amount of rotation of the second transport roller 8 is determined by the amount of rotation of the stepping motor (not shown) used for driving the second transport roller 8 (total step amount). As another method, a rotary encoder may be provided on the roller shaft, and a value obtained by directly measuring the rotation amount may be used.
It is possible to accurately predict the timing at which the paper P1 exits the carry detection sensor 7, and as a result, to accurately detect the carry by the carry detection sensor 7 and prevent the carry accurately. Is possible.

In FIG. 1, after the paper 2 reaches the registration roller 11 and stops, the prediction of the timing at which the paper 2 passes through the carry detection sensor 7 is stopped and the time Tr from the resumption of the paper 2 feeding by the registration roller 11 and the paper. We are seeking from length information.
Specifically, when the time Tr becomes the predicted time Tr0 until the trailing edge of the paper passes through the carry detection sensor 7 (when Tr = Tr0), based on the paper conveyance speed of the first conveyance roller 6. It is controlled to return (switch from low speed to normal speed).
Tr0 is obtained as follows,
Tr0 = (paper length−LG−R) / paper feed speed ± α
LG-R = Distance between second sensor 7 and registration roller 11 α = Error due to roller slip, outer diameter variation, and the like.
It is possible to accurately predict the timing at which the sheet 2 exits the carry detection sensor 7 and, as a result, accurately detect the carry by the carry detection sensor 7 and prevent the carry with high accuracy. Is possible. Since the registration roller 11 is a paper leading edge position regulating roller, a paper leading edge position regulating roller is not required separately, and it is possible to prevent feeding with high accuracy with a simple configuration.
With respect to FIG. 1, the prediction of the timing at which the sheet 2 exits the carry detection sensor 7 is made as follows: the rotation amount Rr and the sheet length after the sheet 2 reaches the registration roller 11 and stops after the registration roller 11 resumes feeding. I'm looking for it from the information.
Specifically, when the rotation amount Rr reaches an estimated time Rr0 until the trailing edge of the sheet passes through the carry detection sensor 7 (when Rr = Rr0), the rotation amount Rr is based on the sheet conveying speed of the first conveying roller 6. It is controlled to return (switch from low speed to normal speed).
Rr0 is obtained as follows,
Rr0 = (paper length−LG−R) ± α
LG-R = Distance between second sensor 7 and registration roller 11 α = Error due to roller slip, outer diameter variation, and the like.
It is possible to accurately predict the timing at which the sheet 2 exits the carry detection sensor 7 and, as a result, accurately detect the carry by the carry detection sensor 7 and prevent the carry with high accuracy. Is possible. Since the registration roller 11 is a paper leading edge position regulating roller, a paper leading edge position regulating roller is not required separately, and it is possible to prevent feeding with high accuracy with a simple configuration.

FIG. 13 is the same schematic diagram as FIG. 2 except for the presence of a bellows-like sheet located up to the second conveying roller of the sheet conveying apparatus of FIG.
When it is determined that the sheet is abnormally conveyed (when the fifth sensor 14 provided downstream from the follow-up detection sensor 7 does not detect the absence of paper), if the paper feeding operation is abnormally conveyed, the control unit of the apparatus receives the paper. Outputs a signal that the conveyance is abnormal. In response to this signal, the device stops operating.
As shown in FIG. 13, when the paper is jammed on the conveyance path in a bellows shape, it is determined that the conveyance is abnormal. In this case, if the conveyance is forcibly continued, the apparatus may be damaged such as abnormal wear of the rollers and deformation of the guide plate. For this reason, it is desirable to stop the apparatus immediately when it is determined that the conveyance state is abnormal.
In the present invention, when it is determined that the conveyance is abnormal, the operation of the apparatus is stopped, so that such damage to the apparatus can be prevented.

FIG. 14 is a schematic view showing a cross section of a paper feed / conveying section (using the FRR separation method) of the image forming apparatus according to the present invention. When it is determined that the sheet is abnormally conveyed (when the fifth sensor 14 provided downstream from the carry detection sensor 7 does not detect the absence of the sheet), the control unit of the apparatus determines that the sheet feeding operation is abnormally conveyed. A signal is output indicating that the transport is abnormal.
In response to this signal, the sheet 2 is guided to a misprint evacuation conveyance path 15 provided downstream from the registration rollers 11 and is evacuated to a misprint evacuation tray 16.
Switching between the misprint evacuation conveyance path 15 and the normal conveyance path is performed by a branch claw (not shown).
The sheets stacked on the misprint evacuation tray 16 are provided so that they can be removed by pulling out the misprint evacuation tray 16.
Some devices are configured so that the above-mentioned clogging of the bellows-like paper is very unlikely to occur, and some devices do not stop the device when abnormal conveyance occurs, but must output the abnormal conveyance as a print output. Some are not a problem.
In such a case, it may be more problematic that productivity is lowered by stopping the apparatus. In the present invention, when the abnormal conveyance state is determined, the apparatus is not stopped and the abnormally conveyed paper is guided to the misprint evacuation tray 16 so that the print on the abnormally conveyed paper is not output. It is possible to continue without problems.

As described above, in the present invention, the sensor for determining the presence or absence of the sheet 2 is provided in the sheet conveyance path downstream from the separation unit as the conveyance detection sensor 7, and the trailing edge of the sheet being conveyed is the conveyance detection sensor 7. The signal of the carry detection sensor 7 is observed at a timing that is predicted to exit.
At this time, when the signal of the carry detection sensor 7 detects the presence of a sheet, it is determined that the sheet currently detected by the carry detection sensor 7 is longer than a predetermined length, that is, the carry detection sensor. 7, the sheet conveying speed of the sheet conveying means provided upstream is decreased (= the conveying speed of the succeeding sheet sent overlapping the preceding sheet is slower than that of the preceding sheet).
Since the conveyance speed of the succeeding paper that is sent over the preceding paper is slower than that of the preceding paper, the overlap of the paper is reduced with time and the overlap is eliminated. In this way, the carry-in can be eliminated.
Further, in the paper transport device, when a signal indicating that the paper transport is abnormal (feed double feed) is output to the control unit of this device, this paper is placed in parallel with the normal paper transport path as an abnormal processing mode. Is guided to the misprint evacuation conveyance path 15 provided in the printer, and discharged to the misprint evacuation tray 16.
This prevents the device from being damaged by the paper transport, and by feeding the paper again and reprinting the misprinted image, normal printing can be performed without outputting the misprint to the user. The convenience of the user can be improved by outputting.
The paper conveying apparatus shown in each of the above embodiments can be applied to electrophotographic image forming apparatuses such as copying machines, facsimiles, and printers, and other image forming apparatuses.

FIG. 3 is a schematic diagram showing a cross section of a sheet feeding / conveying section (using the FRR separation method) of the sheet conveying apparatus of the image forming apparatus according to the present invention. Schematic which shows 1st Embodiment to the 2nd conveyance roller of the paper conveying apparatus of FIG. FIG. 3 is a schematic view similar to FIG. 2 showing up to a second transport roller of the paper transport device of FIG. 1. FIG. 3 is a schematic view similar to FIG. 2 showing up to a second transport roller of the paper transport device of FIG. 1. 6 is a flowchart for explaining the flow of operations of the sheet conveying apparatus according to the present invention. Schematic which shows 2nd Embodiment to the 2nd conveyance roller of the paper conveying apparatus of FIG. FIG. 7 is a schematic view similar to FIG. 6 showing up to a second transport roller of the paper transport apparatus of FIG. 1. FIG. 7 is a schematic view similar to FIG. 6 showing up to a second transport roller of the paper transport apparatus of FIG. 1. 9 is a flowchart for explaining an operation flow in the second embodiment of the sheet conveying apparatus according to the present invention. 6 is a flowchart for explaining another operation flow in the first embodiment of the sheet conveying apparatus according to the present invention; 12 is a flowchart for explaining a flow of still another operation in the first embodiment of the sheet conveying apparatus according to the present invention. 6 is a flowchart for explaining another operation flow in the first embodiment of the sheet conveying apparatus according to the present invention; FIG. 3 is a schematic view identical to FIG. 2 except for an accordion-shaped sheet up to a second conveying roller of the sheet conveying apparatus of FIG. 1. FIG. 3 is a schematic diagram illustrating a cross section of a paper feed conveyance unit (using an FRR separation method) of the image forming apparatus according to the present invention. FIG. 6 is a schematic diagram showing a cross section of a sheet feeding / conveying section (using an FRR separation method) of a conventional image forming apparatus.

Explanation of symbols

1 Paper loading table (paper loading section)
2 Paper 3 Pickup roller (feed roller)
4 Feed roller (paper transport means)
5 Reverse roller (separation means)
6 1st conveyance roller 7 2nd sensor (accompaniment detection sensor)
8 Second transport roller 9 Third sensor (paper position sensor)
11 Registration roller (paper tip position regulating roller)
12 Photoconductor 14 Fifth sensor (paper position sensor, paper presence / absence detection sensor)
15 Misprint evacuation conveyance path 16 Misprint evacuation tray 17 Paper conveyance path

Claims (3)

A sheet conveying device in an image forming apparatus such as an electrophotographic method, provided with a sheet feeding roller for feeding sheets from a sheet stacking unit, a separating unit for separating sheets into one sheet, and a downstream of the sheet feeding roller In a paper transport device provided with a paper transport means for transporting the received paper, and a registration means provided downstream from the paper transport means,
A follow-up detection sensor for determining the presence or absence of the paper provided in the paper conveyance path after the separating means and before the registration means, and a trailing edge of the preceding paper when the paper is continuously conveyed is The output signal of the carry detection sensor is confirmed at a timing predicted to pass through the detection sensor, and when the carry detection sensor detects the presence of paper at this time, the output provided upstream from the carry detection sensor A controller that slows down the paper transport speed of the paper transport means, and a paper position sensor that determines the presence or absence of paper provided in the paper transport path downstream from the feed detection sensor,
The paper transport apparatus according to claim 1, wherein the timing is a timing obtained from information on an elapsed time and a paper length after the leading edge of the preceding paper is detected by the paper position sensor. A sheet conveying device in an image forming apparatus such as an electrophotographic method, provided with a sheet feeding roller for feeding sheets from a sheet stacking unit, a separating unit for separating sheets into one sheet, and a downstream of the sheet feeding roller In a paper transport device provided with a paper transport means for transporting the received paper, and a registration means provided downstream from the paper transport means,
A follow-up detection sensor for determining the presence or absence of the paper provided in the paper conveyance path after the separating means and before the registration means, and a trailing edge of the preceding paper when the paper is continuously conveyed is The output signal of the carry detection sensor is confirmed at a timing predicted to pass through the detection sensor, and when the carry detection sensor detects the presence of paper at this time, the output provided upstream from the carry detection sensor A controller that slows down the paper transport speed of the paper transport means, and a paper position sensor that determines the presence or absence of paper provided in the paper transport path downstream from the feed detection sensor,
The timing is a timing obtained from information on a rotation amount and a sheet length of a sheet conveying unit provided downstream of the carry detection sensor after the leading edge of the preceding sheet is detected by the sheet position sensor. A paper conveying device characterized by the above. An image forming apparatus comprising the sheet conveying device according to claim 1 .

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