JPH11180594A - Sheet conveyor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an abnormality in sheet conveying with accuracy even if sheets have a distortion, corner fold, break or the like on their either side. SOLUTION: A sensor 1 and a sensor 2 are arranged on the same line that is perpendicular to the sheet feed direction to detect both leading and trailing ends of sheets. If any sheet has a distortion, corner fold, break or the like on either leading or trailing end, the sensors 1 and 2 produce mutually different detection times, the difference between which is then counted by a skew count means 16. Such a counted value as is larger than a preset abnormality-detection reference value convinces a main control part 10 that the sheet has a distortion, corner fold, break or the like on either leading or trailing end as an accurate detection of an abnormality in the sheet conveying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper transport apparatus, and more particularly, to a paper transport apparatus, which is built in an image forming apparatus such as a copying machine or a printer, and transfers a fixed-size sheet to a predetermined position along a predetermined transport path. The present invention relates to a sheet conveying device for conveying.

[0002]

2. Description of the Related Art For example, Japanese Patent Publication No. 7-108740 discloses a technique for detecting a distortion (skew) of a sheet when a sheet of a fixed size is conveyed in a conventional image forming apparatus or the like. According to the technique described in this publication, a plurality of sensors are arranged near a conveyance path of the fixed form paper to detect the leading end of the fixed form paper. Further, in general, a skew detection apparatus for a standard paper detects only one of the leading end and the rear end of the standard paper. For this reason, in the case where the undetected one end is distorted, bent at the corner, damaged in the paper, or the like, such a defect cannot be detected, and the image may be transferred to the paper in this state.

[0003] A skew detection method for fixed-form paper in various conventional paper transport systems will be outlined below.

FIG. 1 shows a paper transport system in which a paper 4 is pushed out by a paper transport belt 5. This paper transport system
When a standard paper 4 on a paper conveyance path is conveyed to a recording transfer position by a printer, a copying machine, or the like, a standard paper is provided by a paper conveyance belt 5 and a paper conveyance guide 6 provided on the conveyance path and driven and controlled by a main control unit. 4 is a method of transporting the sheet. A first skew sensor 1 is provided at a first reference position in a conveyance path near a position where a sheet is to be conveyed, and a first skew sensor 1 is disposed on a line 52 extending along a line 52 perpendicular to the conveyance direction from the first reference position. The second skew sensors 2 are arranged at reference positions 2 respectively.

In the conventional skew detection method applied to this paper transport system, it is assumed that skew cannot occur at the trailing edge of the paper, that is, the end surface on the paper transport guide 6 side, and only the leading edge of the paper is detected by the skew sensors 1 and 2. ing. However, when the paper transport belt 5 is worn or the paper transport guide 6 is damaged, it cannot be said that skew cannot occur at the rear end of the paper.

FIG. 2 shows a paper transport system in which the paper 4 is pulled in by the paper transport roller 7. This paper transport system
When the fixed form paper 4 on the paper transport path is transported to the recording transfer position by a printer, a copying machine, or the like, a paper transport belt 8 provided on the transport path and driven and controlled by a main control unit is used.
In this method, the sheet 4 is temporarily conveyed obliquely to the sheet conveying direction, that is, in the direction of the sheet conveying path guard 3, and the sheet 4 is drawn in by the sheet conveying rollers 7 that are driven and controlled by the main controller.

In the conventional skew detection method applied to the paper transport system, the skew sensor 1 and the
2, and the leading end of the sheet, that is, the sheet transport roller 7
It is assumed that skew cannot occur on the side end surface, and only the trailing edge of the sheet is detected by the skew sensors 1 and 2. However, when the paper 4 is transported by the paper transport belt 8, it cannot be said that skew cannot occur at the leading edge of the paper due to an impact on the paper transport path guard 3 or wear of the paper transport roller 7. Absent.

In addition, as a method of detecting skew of standard paper, the falling / rising of sensor signals from skew sensors 1 and 2 arranged in the same manner as above is detected.
There is a method of detecting the skew of a sheet based on the time (count value) between the fall and the rise. FIG. 3 shows various timing patterns of the sensor signal according to the state of the standard paper in this method. This method is configured by hardware, and can obtain a small skew amount equal to or smaller than a predetermined value (for example, 1 cm). However, in this method, if the paper end surface that arrives at a sensor provided at a position that is orthogonal to the paper transport path is the paper front end and the paper end surface that is late is the paper rear end, conventionally, the paper front end or the paper rear end Only one of them was detected.

In this case, as shown in FIG. 3A, there is no abnormality in the sheet conveyance, or as shown in FIG. 3B, although the sheet is skewed, there is no corner break at the leading and trailing ends of the sheet. In some cases,
It is possible to detect only one of the leading edge and the trailing edge of the sheet.

However, when a corner break occurs at the leading end of the sheet as shown in FIG. 3C, an abnormality due to the corner break cannot be detected by monitoring only the trailing end of the sheet, that is, the rising edge of the sensor signal. Similarly, when a corner break occurs at the trailing end of the sheet as shown in FIG. 3D, an abnormality due to the corner break cannot be detected by monitoring only the leading end of the sheet, that is, the falling edge of the sensor signal.

By the way, it has been frequently practiced in offices and the like to form a plurality of binding holes near the end of a sheet and bind the sheet to a file using the binding holes. When the paper edge detection technology as described above is applied to transport a sheet having a binding hole near the end as described above, the binding hole may be erroneously detected as the sheet end. .

[0012]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems. Even if the paper is distorted at one end, the corner is broken, the paper is broken, etc. A first object of the present invention is to provide a paper transport device capable of accurately detecting a transport abnormality, and to provide a paper transport device capable of preventing erroneous detection when a paper is provided with a binding hole or the like. As a second object.

[0013]

According to a first aspect of the present invention, there is provided a sheet conveying apparatus for conveying a sheet of a fixed size to a predetermined position along a predetermined conveying path. Detecting whether or not the sheet is present at a first reference position in a transport path near the predetermined position, and based on the detection result, each of the leading end and the trailing end of the sheet is the first position. Detecting means for detecting that the sheet has passed the reference position, and the sheet exists at a second reference position in a conveyance path on a line extending from the first reference position in a direction perpendicular to the conveyance direction. Second detection means for detecting whether or not each of the leading end and the trailing end of the sheet has passed the second reference position based on the detection result; and The time when the sheet has passed through the first reference position and the leading edge of the sheet have passed through the second reference position. Based on the difference between the time when the rear end of the sheet has passed the first reference position and the time when the rear end of the sheet has passed the second reference position. Abnormality detecting means for detecting that an abnormality has occurred in conveyance.

Further, in order to achieve the second object,
In the paper transport device according to claim 2, in the paper transport device according to claim 1, the first detection unit and the second detection unit change from a state where the sheet is present at the reference position to a state where the sheet is not present. Switching, and by detecting that the trailing edge of the sheet has passed the reference position by not returning to the state where the sheet does not exist at the reference position within a predetermined time after the switching. I do.

The paper transport device according to the first aspect of the present invention is a paper transport device for transporting a sheet of a fixed size to a predetermined position along a predetermined transport path, for example, an image forming apparatus such as a copying machine or a printer. The present invention is applied to a paper transport device that transports recording paper to a predetermined image recording position, a paper transport device that transports a document to be copied by a copying machine to a predetermined image reading position, and the like.

In such a paper transport apparatus, the first detecting means determines whether or not the paper is at the first reference position in the transport path near the predetermined position (ie, the target position of the paper transport). Is detected, and based on the detection result, it is detected that each of the leading edge and the trailing edge of the sheet has passed the first reference position.

On the other hand, the second detecting means detects whether or not the sheet exists at a second reference position in a conveyance path on a line extending in a direction perpendicular to the conveyance direction from the first reference position, Based on the detection result, it is detected that each of the leading edge and the trailing edge of the sheet has passed the second reference position.

Here, for example, the first detecting means and the second detecting means
Detecting means that the sheet is at the reference position (the first reference position, the second reference position,
(The reference position), it is possible to detect that the leading edge of the sheet has passed the reference position by switching from the state where the sheet does not exist to the state where the sheet exists.

According to a second aspect of the present invention, the first detecting means and the second detecting means switch between a state in which the sheet is at the reference position and a state in which the sheet is not present, and within a predetermined time after the switching. Is not returned from the state where it does not exist at the reference position to the state where it exists, it is possible to detect that the trailing edge of the sheet has passed the reference position.

As described above, the first detecting means and the second detecting means detect that the trailing edge of the sheet has passed the reference position simply by switching from the state where the sheet is present at the reference position to the state where the sheet is not present. Rather than switching to the above and detecting that the trailing edge of the sheet has passed the reference position by not returning to the state where the sheet does not exist at the reference position within a predetermined time after the switching and switching, ,
It is possible to prevent a binding hole or the like provided in the sheet from being erroneously detected as the rear end of the sheet.

By the way, since the second reference position is on a line extending from the first reference position in a direction perpendicular to the conveying direction, if there is no paper distortion, corner breakage, paper breakage, etc. at the leading end of the paper, Is the same as the time when the tip of the. Has passed through the first reference position and the time when it has passed through the second reference position. That is, only when the leading end of the sheet has distortion, corner breakage, breakage, or the like of the sheet, there is a difference between the time when the leading end of the sheet passes through the first reference position and the time when the leading end of the sheet passes through the second reference position.

Similarly, if there is no distortion, corner breakage, or breakage of the sheet at the trailing edge of the sheet, the time at which the trailing edge of the sheet passes the first reference position and the time at which the trailing edge passes the second reference position are determined. Will be the same. That is, the difference between the time when the trailing edge of the sheet passes through the first reference position and the time when the trailing edge of the sheet passes through the second reference position is determined only when the trailing edge of the sheet is distorted, bent, or damaged. Occurs.

Therefore, the abnormality detecting means, if the difference between the time when the leading end of the sheet has passed through the first reference position and the time when it has passed through the second reference position is larger than a predetermined abnormality determination reference value, It detects that a paper sheet has been distorted, bent at the leading edge, broken, or the like, and that an abnormality has occurred in the paper conveyance. If the difference between the time when the trailing edge of the sheet has passed the first reference position and the time when the trailing edge of the sheet has passed the second reference position is larger than a predetermined abnormality determination reference value, In this case, it is detected that an abnormality has occurred in the conveyance of the sheet due to the distortion of the sheet, the bent corner, the breakage of the sheet, and the like.

As described above, it is possible to detect the occurrence of paper distortion, corner breakage, paper breakage, and the like, that is, abnormal paper conveyance at both the leading and trailing ends of the paper. In the event that paper breakage or the like has occurred, it is possible to accurately detect paper transport abnormalities.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a paper transport device according to the present invention will be described below. The paper transport device according to the present invention,
The present invention is applied to a paper transport device that transports recording paper to a predetermined image recording position in an image forming apparatus such as a copying machine or a printer, and a paper transport device that transports a document to be copied by the copying machine to a predetermined image reading position. The present invention can be applied to any of the above-described paper transport systems shown in FIGS.

[Apparatus Configuration for Detecting Paper Transport Abnormality] An apparatus configuration for detecting an abnormal paper transport will be described below with reference to FIG. As shown in FIGS. 1 and 2, the paper transport device 50 according to the present embodiment is installed at a first reference position in a transport path near a position where the paper is to be transported, and
A first skew sensor 1 that outputs a high signal when the paper 4 does not exist at the reference position and a low signal when the paper 4 exists, and a first skew sensor 1 that outputs a high signal in a direction perpendicular to the transport direction from the first reference position. A high signal is provided when the sheet 4 does not exist at the second reference position in the transport path on the extended line 52 and the sheet 4 does not exist on the second reference position, and a low signal is provided when the sheet 4 exists. A second skew sensor 2 for outputting is provided.

Further, based on the signals from the first skew sensor 1 and the second skew sensor 2, the paper conveying device 50 determines the time when the leading end of the paper 4 has passed the first reference position and the second time. A skew detection circuit 9 for counting the difference between the time when the sheet 4 has passed the reference position and the time between the time when the trailing edge of the sheet 4 has passed the first reference position and the time when the rear end has passed the second reference position; A main control unit 10 is provided which fetches information relating to the time difference between the leading end and the trailing end of the sheet from the circuit 9 and detects the occurrence of an abnormality in sheet transport based on the information. In addition, the main control unit 10
It may be a main control unit that controls the overall processing of the image forming apparatus including the paper transport device 50.

The skew detecting circuit 9 includes a leading edge detecting circuit 11 for detecting the leading edge of the sheet based on the rise and fall of the signal from each of the first skew sensor 1 and the second skew sensor 2. And a leading edge detecting circuit 13 for detecting the trailing edge of the sheet based on the rising and falling edges of the signal from the CPU.
1 and a detection timing generating means 14 to be supplied to the trailing edge detecting circuit 13, an erroneous detection preventing circuit 15 for performing a control operation (described later) for preventing erroneous detection of the trailing edge of the sheet due to a binding hole of the sheet, and a leading edge of the sheet. Skew counting means 16 for counting the difference between the time when each of the trailing edges has passed the first reference position and the time when it has passed the second reference position, and main control when the leading or trailing edge of the sheet is detected A main controller interrupt means 12 for outputting an interrupt signal to the unit 10 is provided.

The skew counting means 16 includes a leading edge counter 17 when the first skew sensor 1 detects the leading edge of the sheet first, and a leading edge counter when the second skew sensor 2 detects the leading edge of the sheet first. 18, a rear end counter 19 when the first skew sensor 1 detects first at the rear end of the paper, and a rear end counter 20 when the second skew sensor 2 detects first at the rear end of the paper. ing.

In the paper transporting apparatus 50 having such a configuration, signals from the first skew sensor 1 and the second skew sensor 2 are transmitted to the leading edge detecting circuit 11 and the trailing edge detecting circuit 1.
3 is entered. Front end detection circuit 11 and rear end detection circuit 1
Reference numeral 3 detects the rising or falling of the input sensor signal. In the present embodiment, the sensor signal is low active, that is, when the sensor signal is 0, the sheet is present, and when the sensor signal is 1, it indicates that the sheet is not present.

The detection timing generating means 14
A detection timing signal of one clock is generated every 4 microseconds, and the front end detection circuit 11 and the rear end detection circuit 13 are operated. This corresponds to a transport distance of about 0.05 mm in an image forming apparatus having a transport speed of 100 ppm or more.

The leading edge detecting circuit 11 transmits the detection of the leading edge of the sheet to the main controller interrupting means 12, and the main controller interrupting means 12 detects that the leading edge of the sheet has been detected.
To communicate. The trailing edge detection circuit 13 transmits the detection of the trailing edge of the sheet to the erroneous detection prevention circuit 15.

The erroneous detection prevention circuit 15 is provided with a counter 34 for preventing minute chattering of sensor signals from the first skew sensor 1 and the second skew sensor 2 and erroneous detection due to paper binding holes. Edge detection circuit 1
3, the counter 34 is started each time a rising edge of the sensor signal is detected, and the counter 34 is stopped each time a falling edge of the sensor signal is detected, thereby preventing erroneous detection (details will be described later).

The erroneous detection prevention circuit 15 transmits the detection of the trailing edge of the sheet to the main controller interrupting means 12, and the main controller interrupting means 12 detects that the trailing edge of the sheet has been detected.
Transmit to 0.

The skew counting means 16 starts the leading edge counter 17 when the first skew sensor 1 detects the leading edge of the sheet first, and starts counting the leading edge counter 17 when the second skew sensor 2 detects the leading edge of the sheet. Stop. On the other hand, when the second skew sensor 2 detects the leading edge of the sheet first, the skew counting means 16 starts the leading edge counter 18 and stops the leading edge counter 18 when the first skew sensor 1 detects the leading edge of the sheet. Let it.

When the first skew sensor 1 detects the trailing edge of the sheet first,
The trailing end counter 19 is started, and stopped when the second skew sensor 2 detects the trailing end of the sheet. On the other hand, when the second skew sensor 2 detects the trailing edge of the sheet first, the skew counting means 16 starts the trailing edge counter 20, and the trailing edge is detected when the first skew sensor 1 detects the trailing edge of the sheet. The counter 20 is stopped.

Further, the skew counting means 16 includes a first
When the skew sensor 1 and the second skew sensor 2 detect the leading edge or the trailing edge of the sheet at the same time, the counter is not started.

[Skew detection circuit 9 in various paper states]
Here, the operation of the skew detection circuit 9 in various paper states will be specifically described. First, an operation in the case where there is no skew or chatter (fluttering) on the sheet and no binding hole is provided on the sheet will be described. FIG.
Indicates output states of various signals in this case.

The timing at which the leading edge and the trailing edge of the sheet arrive at the first skew sensor 1 and the second skew sensor 2 is calculated in advance in the main control unit 10, and the main control unit 10 determines that the timing is close to the timing. The front end detection circuit enable signal 23 and the rear end detection circuit enable signal 24 are activated. In the present embodiment, the circuits (the front end detection circuit 11 and the rear end detection circuit 13) operate when the enable signal is high. The same applies to the following examples.

The leading edge detection circuit 11 detects the falling of the first skew sensor signal 21 and the second skew sensor signal 22 at the N2th detection timing signal 25, and the rear edge detection circuit 13 detects the falling edge of the detection timing signal 25. 25 N
The first skew sensor signal 21 and the second
Of the skew sensor signal 22 is detected.
In the case of FIG. 5, since there is no skew or chattering on the paper and no binding hole is provided on the paper, only the interrupt signal detected at the same time is transmitted to the main control unit 10. None of the skew counters operate.

Next, the operation in the case where there is no chattering in the sheet and there is no binding hole in the sheet but there is skew in the sheet will be described. FIG. 6 shows output states of various signals in this case.

When the leading end detection circuit 11 detects the falling edge of the first skew sensor signal 21 at the N2th detection timing signal 25, it starts the leading end counter 17, and at the N3th detection timing signal 25, the second leading end counter 17 starts counting. When the fall of the skew sensor signal 22 is detected, the tip counter 17 is stopped.

When detecting the rising edge of the first skew sensor signal 21 at the N10th detection timing signal 25, the rear end detection circuit 13 starts the rear end counter 19 via the erroneous detection prevention circuit 15, and the detection timing signal 25
When the rising edge of the second skew sensor signal 22 is detected at the N11th time, the rear end counter 19 is stopped via the false detection prevention circuit 15. The erroneous detection prevention circuit 15
The operation of will be described later.

Next, the operation in the case where the binding holes are not provided in the sheet but the sheet has skew and chatter will be described. FIG. 7 shows output states of various signals in this case.

When the leading edge detection circuit 11 detects the falling edge of the first skew sensor signal 21 at the N2th detection timing signal 25, it starts the leading edge counter 17, and the second at the N4th detection timing signal 25. When the fall of the skew sensor signal 22 is detected, the tip counter 17 is stopped. Thus, even if the leading edge of the sheet has chattering, the leading edge detection interrupt signal is transmitted to the main control unit 10 upon detecting the first falling of the signal,
Start and stop the tip counter.

When the trailing edge detection circuit 13 detects the rise of the first skew sensor signal 21 at the N17th detection timing signal 25, it starts the counter of the erroneous detection prevention circuit 15. When the fall of the skew sensor signal 21 is detected, the counter of the false detection prevention circuit 15 is stopped. When the rising edge of the first skew sensor signal 21 is detected again at the N19th detection timing signal 25, the rear end counter 19 is started via the false detection prevention circuit 15.

When the trailing edge detection circuit 13 detects the rise of the second skew sensor signal 22 at the N19th detection timing signal 25, the counter of the false detection prevention circuit 15 is started. When the fall of the skew sensor signal 22 of No. 2 is detected, the counter of the erroneous detection prevention circuit 15 is stopped. When the rising edge of the second skew sensor signal 22 is detected again at the N21th detection timing signal 25, the false detection prevention circuit 1
After 5, the rear end counter 19 is stopped. As described above, when chattering occurs at the trailing edge of the sheet, the counter of the false detection prevention circuit 15 is started each time a rising edge of the sensor signal is detected, and the false detection prevention circuit 15 is triggered every time a falling edge of the sensor signal is detected. Stop the counter. That is, the last rising edge of the sensor signal is detected, a rear-end detection interrupt signal is transmitted to the main controller 10 via the false detection prevention circuit 15, and the rear-end counter is started and stopped.

Next, the operation in the case where the paper has skew and chatter and the paper has a binding hole will be described. FIG. 8 shows output states of various signals in this case.

When the leading edge detection circuit 11 detects the falling edge of the first skew sensor signal 21 at the N2th detection timing signal 25, it starts the leading edge counter 17, and at the N4th detection timing signal 25, the second edge detection circuit 11 starts the second timing. When the fall of the skew sensor signal 22 is detected, the tip counter 17 is stopped. Even if the front end of the sheet has chattering and a sheet binding hole, it detects the first fall of the signal, transmits a front end detection interrupt signal to the main control unit 10, and starts and stops the front end counter.

When the trailing edge detection circuit 13 detects the rise of the first skew sensor signal 21 at the N16th detection timing signal 25, it starts the counter of the erroneous detection prevention circuit 15. When the fall of the skew sensor signal 21 is detected, the counter of the false detection prevention circuit 15 is stopped. When the rising edge of the first skew sensor signal 21 is detected again at the N19th detection timing signal 25, the rear end counter 19 is started via the false detection prevention circuit 15.

When the trailing edge detection circuit 13 detects the rise of the second skew sensor signal 22 at the N18th detection timing signal 25, the counter of the erroneous detection prevention circuit 15 is started. When the falling edge of the second skew sensor signal 22 is detected, the counter of the false detection prevention circuit 15 is stopped. When the rising edge of the second skew sensor signal 22 is detected again at the N21th detection timing signal 25, the rear end counter 19 is stopped via the false detection prevention circuit 15. As described above, if there is a paper binding hole at the rear end of the paper, the last rising of the sensor signal is detected to prevent erroneous detection due to the paper binding hole, and the rear end is passed through an erroneous detection prevention circuit 15. The detection interrupt signal is transmitted to the main controller 10, and the rear end counter is started and stopped.

[One Example of Operation of False Detection Prevention Circuit 15] Next, an example of the false detection prevention circuit 15 will be described with reference to FIG.

The erroneous detection prevention circuit 15 receives the rear end sensor rising pulse signal 26 from the rear end detection circuit 13 and
By this reception, the output of the D flip-flop with enable 31 becomes high. The output of the D flip-flop 31 with the enable and the detection timing signal 28 are output to the enable of the counter 34 through the AND circuit 33.

The counter 34 operates in synchronization with the clock 30. After the trailing edge sensor-rising pulse signal 26 makes the output of the D flip-flop 31 with enable high, the pulse signal of the detection timing signal 28 becomes high. Count each time. Then, the counter 34 sets the output of the counter 34 to high at the point in time when the counter 34 counts for a preset false detection prevention time. The high signal output from the counter 34 is output to the main control unit interrupt unit 12 and the skew count unit 16 as an interrupt pulse signal 37 via the AND circuit 33, the inverter 32, and the D flip-flop 36. Also, the interrupt pulse signal 37
Is a D flip-flop 31 with an enable and a counter 3 via an inverter 38, a negative OR circuit (BNOR) 35
4 to clear the D flip-flop 31 with enable and the counter 34.

By the way, if the rear end sensor falling pulse signal 27 is input from the rear end detection circuit 13 while the counter 34 is counting the false detection prevention time, the rear end sensor falling pulse signal 27 Clears the D flip-flop 31 with enable and the counter 34 via the inverter 39 and the BNOR 35.

Thereafter, the erroneous detection prevention circuit 15 outputs the rear end sensor rising pulse signal 26 from the rear end detection circuit 13.
Is received, the counter 34 again counts the erroneous detection prevention time as described above, and when the erroneous detection prevention time is counted, the high signal output from the counter 34 is used as the interrupt pulse signal 37, and the main control unit interrupt is output. Output to the means 12 and the skew counting means 16.

By the above operation, even if there is a binding hole or the like at the rear end of the paper, the trailing edge of the paper can be accurately detected by detecting the rising edge of the last sensor signal.

[Regarding the Control by the Main Control Unit 10] When the main control unit 10 receives an interrupt signal for detecting the leading end from the main control unit interrupt unit 12, the main control unit 10 executes the interrupt processing of FIG.
When the interrupt signal for the rear end detection is received, the execution of the interrupt process of FIG. 11 is started. Hereinafter, these will be described.

The main control unit 10 includes a main control unit interrupt unit 1
When an interrupt signal for detecting the leading end is received from the leading end counter 17 or the leading end counter 1 in step 102 of FIG.
Wait for the end of counting of 8. When the counting by the counter is completed, the count value is fetched in step 104, and it is determined in next step 106 whether the count value is larger than a preset abnormality detection reference value. Here, if the count value is not larger than the abnormality detection reference value, the interrupt routine of FIG. 10 ends.

On the other hand, if the count value is larger than the abnormality detection reference value, the routine proceeds to step 108, where the sheet conveyance is immediately stopped, and a warning message indicating that a problem has occurred in the sheet conveyance and the sheet is removed from the inside of the apparatus. A message prompting the operator is displayed on a display (not shown) of the image forming apparatus.

By the interruption process at the time of detecting the leading edge of FIG. 10, the difference between the time when the leading edge of the sheet has passed through the first skew sensor 1 and the time when the leading edge of the sheet has passed through the second skew sensor 2 is a predetermined value (abnormality detection). If it is larger than the reference value, it is assumed that the leading edge of the paper is distorted, bent, broken, etc., or that the paper is skewed. Can be. Then, it is possible to quickly respond to an abnormality.

When the main control unit 10 receives the interrupt signal for the detection of the rear end from the main control unit interrupt means 12, it waits for the rear end counter 19 or the rear end counter 20 to finish counting at step 122 in FIG. When the counting by the counter is completed, the count value is fetched in step 124, and it is determined in next step 126 whether the count value is larger than a preset abnormality detection reference value. Here, if the count value is not larger than the abnormality detection reference value, the interrupt routine of FIG. 11 ends.

On the other hand, if the count value is larger than the abnormality detection reference value, the flow advances to step 128 to immediately stop the sheet conveyance, and to remove a sheet from the inside of the apparatus and a warning message indicating that a problem has occurred in the sheet conveyance. A message prompting the operator is displayed on a display (not shown) of the image forming apparatus.

By the interrupt processing at the time of detecting the trailing edge of FIG. 11, the difference between the time when the trailing edge of the sheet has passed through the first skew sensor 1 and the time when the trailing edge has passed through the second skew sensor 2 is a predetermined value ( (Abnormality detection reference value), it is possible to accurately detect that an abnormality has occurred in the paper transport due to paper distortion, corner breakage, paper breakage, etc. at the rear end of the paper, and to quickly respond to abnormalities be able to.

According to the present embodiment described above, occurrence of paper distortion, corner breakage, paper breakage, etc., that is, abnormal paper conveyance can be detected at both the leading and trailing ends of the paper. When paper distortion, corner breakage, paper breakage, or the like occurs, it is possible to accurately detect a paper transport abnormality. Further, it is possible to prevent a binding hole or the like provided in the sheet from being erroneously detected as the rear end of the sheet.

In the above description, when the main control unit 10 detects a sheet conveyance error when detecting the front end of the sheet, the main control unit 10 immediately stops the sheet conveyance and prompts the operator to cope with the abnormality. After detecting both of these, control may be performed so as to stop the sheet conveyance and prompt the operator to cope with the abnormality.

[0067]

As described above, according to the first aspect of the present invention, occurrence of paper distortion, corner breakage, paper breakage, and the like, that is, abnormal paper conveyance, at both the leading and trailing ends of the paper. Since the sheet can be detected, when the sheet is distorted, the corner is broken, the sheet is damaged, or the like at one end of the sheet, the sheet conveyance abnormality can be accurately detected.

According to the second aspect of the present invention, the first
The second detecting means switches from a state where the sheet is present at the reference position to a state where the sheet is not present, and does not return to a state where the sheet does not exist at the reference position within a predetermined time after the switching. Accordingly, since it is detected that the rear end of the sheet has passed the reference position, it is possible to prevent a binding hole or the like provided in the sheet from being erroneously detected as the rear end of the sheet.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a paper transport system in which a paper is pushed out by a paper transport belt.

FIG. 2 is a diagram illustrating a paper transport system in which paper is drawn by a paper transport roller.

3A and 3B are diagrams showing sensor signals output in various paper transport states, where FIG. 3A shows sensor signals when the paper transport state is normal, and FIG. 3B shows the case where the paper is skewed; (C) is a diagram showing a sensor signal when a corner break occurs at the leading end of a sheet, and (D) is a diagram showing a sensor signal when a square break occurs at a trailing end of the sheet.

FIG. 4 is a block diagram illustrating an apparatus configuration related to detection of a sheet conveyance abnormality in the embodiment.

FIG. 5 is a timing chart showing an output state of various signals when there is no skew or chatter on a sheet and no binding hole is provided on the sheet.

FIG. 6 is a timing chart showing an output state of various signals in a case where there is no chattering on the sheet and no binding hole is provided, but there is skew on the sheet.

FIG. 7 is a timing chart showing output states of various signals when a binding hole is not provided in a sheet but the sheet has skew and chatter.

FIG. 8 is a timing chart showing output states of various signals when a sheet has skew and chatter and a sheet has a binding hole.

FIG. 9 is a circuit diagram illustrating a configuration example of a false detection prevention circuit;

FIG. 10 is a flowchart showing an interrupt processing routine at the time of detecting a leading end;

FIG. 11 is a flowchart showing an interrupt processing routine at the time of rear end detection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st skew sensor 2 2nd skew sensor 4 Fixed form paper 9 Skew detection circuit 10 Main control part 11 Front-end detection means 13 Rear-end detection means 15 False detection prevention circuit 16 Skew count means

Claims (2)

[Claims] 1. A sheet conveying device for conveying a sheet of a fixed size to a predetermined position along a predetermined conveying path, wherein the sheet exists at a first reference position in the conveying path near the predetermined position. A first detecting unit for detecting whether or not each of the leading end and the trailing end of the sheet has passed the first reference position based on the detection result; and It is detected whether or not the sheet is present at a second reference position in a conveyance path on a line extending in a direction perpendicular to the conveyance direction from the position. Second detecting means for detecting that the sheet has passed the second reference position, and a time when the leading edge of the sheet has passed the first reference position and a time when the leading edge of the sheet has passed the second reference position. And the time when the trailing edge of the sheet has passed the first reference position and the A sheet conveyance device, comprising: an abnormality detection unit configured to detect that an abnormality has occurred in the conveyance of the sheet based on a difference from a time when a rear end of the sheet has passed the second reference position. 2. The method according to claim 1, wherein the first detection unit and the second detection unit switch from a state where the sheet is present at the reference position to a state where the sheet is not present, and within a predetermined time after the switch, the sheet is set at the reference position. 2. The sheet conveying device according to claim 1, wherein a state that the rear end of the sheet has passed the reference position is detected by not returning to a state where the sheet does not exist.