Sheet transport device and image forming apparatus

Abstract

To reduce the frequency of sheet removal at a discharge unit.SOLUTION: A sheet carrier, for carrying a sheet along a sheet transport path, comprises detection means 90a that detects at least one of position information and posture information of a sheet P on the sheet transport path based on a detection result of one or more detecting sections 4, 21 and 22, and compares the detected information with a reference value to detect an error from the reference value, classification means 90b that classifies the sheet P into at least three types of a normal sheet that can be carried, a transportable abnormal sheet that can be carried and a transport-concerned abnormal sheet that has a concern in transport, based on a magnitude of an error detected by the detection means, and change-over means 90c that changes over one or more branch units 6 and 9 so as to carry a normal sheet to a first transport path 101 connected to a first discharge unit, a transportable abnormal sheet to a second transport path 102 connected to a second discharge unit and a transport-concerned abnormal sheet to a third transport path 103 connected to a third discharge unit (purge tray 50), based on a classification result of the classification means.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a sheet conveyance device and an image forming apparatus configured to detect types of conveyance failures of a sheet such as paper and switch a sheet discharge destination for each type of the conveyance failure.

Background Art

[0002] In an image forming apparatus such as a copying machine or a printer, if there are conveyance failures such as conveyance delays or skews of sheets sent to an image forming unit, normal image formation cannot be performed. Therefore, a technique of automatically conveying and storing sheets that have become defective images due to conveyance failures as invalid sheets to a discharge unit (a purge tray) is known. This technique is disclosed, for example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2020-144251) as a printing recovery technique by automatic purge control.

[0003] By this printing recovery technique, it is possible to reduce the machine downtime and maintain the productivity of the machine. When the discharge unit approaches being full, this is detected by a sensor, and the user is prompted to remove the sheets in the discharge unit.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, many of the conventional image forming apparatuses have a discharge unit provided inside the main body of the image forming apparatus, and there are limitations in the capacity of the discharge unit, the corresponding sizes, etc. For this reason, the frequency of removing sheets from the discharge unit is high, and there is a limit to reducing the downtime.

[0005] Therefore, an object of the present invention is to reduce the frequency of removing sheets from the discharge unit.

Means for Solving the Problems

[0006] To solve the above problems, the present invention provides a sheet conveying device for conveying sheets along a sheet conveying path, comprising: detection means for detecting at least one of position information and orientation information of a sheet in the sheet conveying path based on the detection results of one or more detection units, and for detecting an error from the detected detection information by comparing it with a reference value; classification means for classifying the sheets into at least three types based on the magnitude of the error detected by the detection means: normal sheets that can be conveyed, abnormal sheets that can be conveyed, and abnormal sheets with transport concerns that pose a transport risk; and switching means for switching one or more branching units to convey the normal sheets to a first conveying path connected to a first discharge unit, the abnormal sheets that can be conveyed to a second conveying path connected to a second discharge unit, and the abnormal sheets with transport concerns to a third conveying path connected to a third discharge unit, respectively, based on the classification results of the classification means. [Effects of the Invention]

[0007] According to the present invention, the frequency of sheet removal in the discharge section can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1A] This is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. [Figure 1B] This is a schematic diagram showing the path for discharging the sheet to the second discharge section of the image forming apparatus. [Figure 1C] This is a schematic diagram showing the state in which a sheet is discharged and loaded into the second discharge section of the image forming apparatus. [Figure 2A] This is a schematic diagram showing the path for discharging the sheet to the third discharge section of the image forming apparatus. [Figure 2B] This is a schematic diagram showing the state in which a sheet is discharged and loaded into the third discharge section of the image forming apparatus. [Figure 2C] This is a schematic diagram showing the state when the third discharge section of the image forming apparatus is nearing full capacity. [Figure 3A] This is a block diagram of the control unit. [Figure 3B]It is a block diagram showing the connection relationship between the control unit, the detection unit, and the branching unit. [Figure 4] It is a schematic configuration diagram of an image forming apparatus provided with a plurality of detection means. [Figure 5] It is a diagram showing a state in which a single sheet and a double-fed sheet are detected by a double-feed detection device. [Figure 6A] It is a plan view of a sheet posture correction device. [Figure 6B] It is a plan view of a sheet posture correction device. [Figure 6C] It is a plan view of a sheet posture correction device. [Figure 6D] It is a plan view of a sheet posture correction device. [Figure 6E] It is a plan view of a sheet posture correction device. [Figure 6F] It is a plan view of a sheet posture correction device. [Figure 7] It is a schematic configuration diagram of an image forming apparatus provided with a plurality of detection means also in the reverse conveyance path of FIG. 4. [Figure 7A] It is a schematic side view of a device for detecting conveyance concern abnormalities. [Figure 7B] It is a schematic side view of a device for detecting conveyance concern abnormalities. [Figure 8] It is a schematic configuration diagram of an image forming apparatus according to another embodiment of the present invention. [Figure 9A] It is a plan view of a sheet posture correction device. <​​​​​​​​​​​​​​​​​​​​ [Figure 12A] It is a flowchart for determining conveyance abnormalities of the same sheet multiple times and updating the determination result. [Figure 12B] It is a flowchart for determining conveyance abnormalities of the same sheet multiple times and updating the determination result. [Figure 12C] It is a flowchart for determining conveyance abnormalities of the same sheet multiple times and updating the determination result. [Figure 12D] It is a flowchart for determining conveyance abnormalities of the same sheet multiple times and updating the determination result. [Figure 13] It is a flowchart after the sheet passes through the branch section.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. In each drawing, components such as members and components having the same function or shape are given the same reference numerals as much as possible, and the description thereof will be omitted after being described once.

[0010] (●Image forming apparatus)

[0011] FIG. 1A is a schematic configuration diagram showing an example when the sheet conveyance device of the present invention is applied to a printer 110 as an image forming apparatus. This printer 110 has a paper feed tray 111 arranged in a plurality of stages in the vertical direction, an image forming unit 12, and a post-processing unit 11. The paper feed tray 111 stacks sheets P such as paper in a bundle, separates the sheets P of a predetermined size one by one in response to a printing command, and supplies them to the downstream image forming unit 12.

[0012] The image forming unit 12 has an image forming section 5 at the upper part and a reverse conveyance path 104 at the lower part. Below the reverse conveyance path 104, a purge tray 50 as a third discharge section for discharging conveyance-suspicious abnormal sheets is arranged.

[0013] The image forming unit 5 has four image forming units, each corresponding to a different color (yellow, magenta, cyan, and black), arranged horizontally above the intermediate transfer belt, facing the intermediate transfer belt.

[0014] The reversal transport path 104 forms a loop that reverses direction from the branching section 9 and returns to the upstream side. As will be described later, the transport concern abnormality sheet is transported and stored in the purge tray 50 from the branching section 9.

[0015] The post-processing unit 11 has two transport paths that branch off from the branching section 6. The lower transport path is the first transport path 101, and the upper transport path is the second transport path 102. The first discharge section 8 and the second discharge section 7 are connected to the downstream ends of the transport paths 101 and 102, respectively. The branching sections 6 and 9 are switched by a switching means 90c, which will be described later.

[0016] The image forming unit 12 includes an image forming section 5 that forms an image on a sheet P, and a detection section 4 that detects the transport state of the sheet P. The detection section 4 detects at least one of the position information and orientation information of the sheet P in the sheet transport path. The detection means 90a of the control unit 90 shown in Figure 3B, which will be described later, compares the detected information with a reference value and detects the error from the reference value.

[0017] Furthermore, the transport path of the image forming unit 12 includes a reversal transport path 104 for reversing the printed surface of the sheet P, a branching section 9 for switching to a double-sided transport path for double-sided printing, and a purge tray 50 for releasing abnormally transported paper outside the transport path inside the machine.

[0018] The post-processing unit 11 has multiple discharge trays (first discharge section 8, second discharge section 7) for accumulating printed materials after image formation is complete. Switching between the first discharge section 8 and the second discharge section 7 is performed by switching the path of a branching section 6 located inside the post-processing unit 11.

[0019] The printer 110 has a loop-shaped return transport path and a branching section 9 that serves as a return transport switching section, which inverts the image-forming surface of the sheet P in order to form an image on both sides of the sheet and transports it back to the image-forming section 5.

[0020] Figure 1A shows the transport flow during normal printing. The sheet P passes through the transport concern detection devices 21 and 22 and the transportable abnormality detection device 4, then passes through the image forming unit 5 and enters the post-processing unit 11, and is discharged to the first discharge unit 8.

[0021] The post-processing unit 11 performs post-processing on the sheet on which the image has been formed. This post-processing includes transporting the sheet P to the first discharge unit 8 and the second discharge unit 7. In addition, post-processing units for punching, stapling, etc., on the sheet P on which the image has been formed may be provided in the transport paths 101 and 102.

[0022] Figure 1B shows the sheet transport path when the detection unit 4 detects a transportable abnormality. The detection unit 4 detects abnormalities that impair print quality, such as skew, double feeding, lateral displacement, and false detection by the attitude detection sensor of the sheet P. Sheets P for which an abnormality has been detected by the detection unit 4 and the detection means 90a of the control unit 90 in Figure 3B are classified as "transportable abnormal sheets" by the classification means 90b in Figure 3B.

[0023] When a "transportable abnormal sheet" is detected and classified, the branching section 9 is temporarily switched to the reverse transport path 104. This causes the transportable abnormal sheet to be transported towards the purge tray 50 below. This is to buy time to avoid interference with the preceding sheet.

[0024] Subsequently, the transportable abnormal sheet is switched back upwards before reaching the purge tray 50 and sent back along the reverse transport path 104 to the branching section 6. The branching section 6 has been pre-switched to the second transport path 102 based on the detection result of the detection unit 4 mentioned above. Therefore, the transportable abnormal sheet that has been switched back is discharged to the second discharge section 7 through the second transport path 102.

[0025] The detection result from the detection unit 4 is sent to the control unit 90 shown in Figure 1A, and the branching unit 6 is controlled by the control unit 90. Details of the control unit 90 will be described later in Figures 3A and 3B.

[0026] After an abnormal sheet that cannot be transported is ejected, the machine becomes empty. Therefore, reprinting (starting paper feeding from the paper tray) can be performed as shown in Figure 1C. The specific configuration of the detection unit 4 is explained in Figures 6A to 6F and 7A to 9B.

[0027] Figure 2A shows the sheet transport path when a sheet transport malfunction is detected by the detection unit 21 or 22 and the detection means 90a of the control unit 90. The detection unit 21 or 22 measures the timing of the passage of the sheet P during transport as it passes through the detection unit 21 or 22.

[0028] If the passage timing is abnormally earlier or later than the expected standard passage timing, it is classified as a "transport concern abnormality sheet" by the classification means 90b described later. If the passage timing of sheet P is abnormally later than the expected standard timing, it is presumed that, for example, a "stagnant jam" has occurred. In that case, a warning message prompting the user to remove the stagnant jam can be displayed on the operation panel or the like.

[0029] The specific configurations of the detection units 21 and 22 are explained in Figure 5. The placement of the detection units 21 and 22 is not limited to the positions shown in Figure 2A. The detection units 21 and 22 can be placed at any position and in any number along the sheet transport path from the paper feed tray 111 to the discharge units 7 and 8.

[0030] Based on the detection results from the detection units 21 and 22, the branching unit 9 is switched to the reversal transport path 104 leading to the purge tray 50, thereby allowing any abnormal sheets of transport concern to be discharged into the purge tray 50. Multiple detection units 21 and 22 can be arranged at regular intervals along the sheet transport path, and similar detection units can be arranged at locations other than those shown in Figures 1A to 2C, which will be described later.

[0031] The purge tray 50, acting as the third discharge section, can continue to contain the transport-related abnormal sheets until its capacity limit is reached. Reprinting can then be performed as shown in Figure 2B until the capacity limit of the purge tray 50 is reached.

[0032] When the purge tray 50 reaches its capacity limit, the machine stops as shown in Figure 2C. The user is then prompted to remove the sheets from the purge tray 50.

[0033] To prompt the user to remove the sheet, a warning message is displayed on the operation panel of the printer 110. Alternatively, a warning is issued by illuminating a lamp on the printer 110. The color of the lamp can be associated with the action the user needs to take (sheet removal). Alternatively, the warning can be displayed on a communication terminal owned by the user or a dedicated terminal for operating the printer 110.

[0034] (●Control Unit) The control unit 90 will be described in more detail with reference to Figures 3A and 3B. As shown in Figure 3A, the control unit 90 includes a CPU (Central Processing Unit) 241, a ROM (Read Only Memory) 242, a RAM (Random Access Memory), and an I / O port 244.

[0035] The CPU 241 is an arithmetic unit that performs sequential, branching, and iterative processing by executing programs stored in the ROM 242. The ROM 242 is a non-volatile memory device that stores programs and other data executed by the CPU 241. The RAM 243 is memory that functions as the work area (workspace) for the operation of the CPU 241.

[0036] As shown in Figure 3B, the control unit 90 functionally includes a detection means 90a, a classification means 90b, and a switching means 90c. The detection means 90a is connected to three detection units 4, 21, and 22 via the I / O port 244 described below. The detection means 90a compares the detection results obtained from these three detection units 4, 21, and 22 with a reference value and detects the error with the reference value.

[0037] The classification means 90b classifies the sheets being transported along the transport path into "transportable normal sheets," "transportable abnormal sheets," or "transportable abnormal sheets with transport concerns" based on the detection results obtained by the detection means 90a. The switching means 90c is connected to two branching sections 6 and 9 to switch the discharge destination of the three classified sheets.

[0038] The bus line 245 in Figure 3A is an address bus, data bus, etc., for electrically connecting each component such as the CPU 241. The I / O port 244 is an interface that receives output signals from the three detection units 4, 21, and 22 and outputs control signals for controlling the motors that operate the branching units 6 and 9. The operation of the branching units 6 and 9 may be performed by solenoids or the like instead of motors.

[0039] The control unit 90 does not necessarily have to be configured as described above. For example, each function of the control unit 90 can be realized by one or more processing circuits. Here, "processing circuit" in this specification includes processors programmed to execute each function by software, such as CPUs implemented by electronic circuits, and devices such as ASICs (Application Specific Integrated Circuits), DSPs (digital signal processors), FPGAs (field programmable gate arrays), and conventional circuit modules designed to execute the functions described above.

[0040] (● Embodiment 1) Figure 4 shows a schematic configuration diagram of Embodiment 1 of the printer 110. In this Embodiment 1, upstream of the image forming unit 5, there is a detection unit 4 which includes a double-feed detection device 31 and line sensors 33-35 that act as sheet posture detection devices. As explained in Figures 5-6F, the double-feed detection device 31 and line sensors 33-35 can also detect abnormal sheets that may be causing transport problems.

[0041] The double feed detection device 31 detects whether a double feed has occurred at the double feed detection point 32 after the double feed detection device 31 has passed. As the double feed detection device 31, for example, an ultrasonic method can be considered that detects a double feed abnormality by relatively determining whether the sheet is being fed together or individually using ultrasound. Alternatively, as shown in Figure 5, an optical method can be considered for the double feed detection device 31, using a light-emitting element 39 and a light-receiving element 38 on the opposite side.

[0042] In this optical system, the output of the photodetector 38 changes depending on the difference in the amount of light shielding by the sheet P between single feed and double feed. By utilizing this change in output, it is possible to determine whether or not double feed is occurring and to detect a double feed abnormality.

[0043] As shown in Figure 5, ultrasonic waves or light are irradiated from the light-emitting element 39, and the output is checked by the light-receiving element 38. Since the output differs between single feed and double feed, it is possible to determine whether or not a double feed is occurring. If a double feed is detected, the sheet is discharged to the second discharge section 7 outside the machine as an abnormal sheet that can be transported.

[0044] Line sensors 33-35, acting as a sheet posture detection device, detect the sheet posture at detection point 36 when the sheet P passes the furthest downstream line sensor 35. Each of the line sensors 33-35 detects the position of the sheet P in the sheet transport direction and in the direction perpendicular to it (upward or depth direction in Figure 6A).

[0045] The depth direction of the seat P can also be the vertical direction in Figure 6A or the longitudinal direction of the line sensors 33-35. Alternatively, the depth direction of the seat P can also be the axial direction of the seat posture correction device 37.

[0046] The sheet posture correction device 37 has a pair of upper and lower transport rollers. The sheet P can be held between the pair of transport rollers and transported downstream.

[0047] The seat posture correction device 37 is capable of shifting vertically as shown in Figure 6A, and is also capable of rotating horizontally as shown in Figure 6B. Therefore, by shifting and rotating while the seat P is being held and transported, the positional displacement of the seat P can be corrected (skew correction, shift correction).

[0048] The line sensors 33 and 34 are positioned parallel to each other and offset from each other on the upstream side of the seat posture correction device 37. As shown in Figure 6A, the line sensors 33 and 34 simultaneously detect the side edges of the seat P.

[0049] As shown in Figure 6A, if there is a vertical deviation in the detection results of line sensors 33 and 34, it means that the sheet P is being transported bent (inclined) (skewed). To correct the skew, the detected deviation amount is input to the sheet posture correction device 37, and the acceptance angle of the sheet posture correction device 37 is changed as shown in Figure 6B.

[0050] After the seat posture correction device 37 grips (holds) the front end of the seat P as shown in Figure 6C, the seat posture correction device 37 is returned to its initial state as shown in Figure 6D. This corrects the posture of the seat P, making it skew-free.

[0051] Furthermore, the seat posture correction device 37 is shifted by an amount of deviation perpendicular to the transport direction, derived from the detection results of the line sensors 33 and 34 (from top to bottom in Figure 6E). This corrects the position of the seat P perpendicular to the transport direction (Figure 6E ⇒ Figure 6F).

[0052] As shown in Figure 6F, after the seat posture correction device 37 has completed the correction of the seat P, the line sensors 34 and 35 upstream and downstream of the seat posture correction device 37 detect the position of the side edges of the seat P. The final posture and position of the seat P are determined from these corrected detection results.

[0053] If the information regarding the posture and position does not exceed a certain threshold (reference value) A when compared with the reference value, the corrected sheet P is classified as a transportable normal sheet. After that, the sheet P is transported to the image forming unit 5, where an image is formed on the sheet P, and then discharged to the normal first discharge unit 8.

[0054] Next, if the orientation and position information of sheet P exceeds a certain threshold A when compared to a reference value, a printing defect (quality defect) such as image misregistration will occur. Image misregistration refers to the discrepancy between the image position on the back of sheet P and the image position on the front of sheet P.

[0055] Therefore, the sheet P that results in printing defects is classified as a transportable abnormal sheet. Transportable abnormal sheets are discharged to the second discharge section 7 outside the machine, as shown in Figures 1B and 1C above.

[0056] If the error in the orientation and position information of sheet P compared to the reference value exceeds threshold B, which is greater than threshold A, then sheet P is classified as a sheet with transport concerns. An error exceeding threshold B occurs when there is excessive positional deviation or excessive skew.

[0057] In such cases, side effects can occur, such as the sheet P interfering with the side plate of the downstream sheet guide, the excess space at the leading edge of the sheet P becoming smaller, or the sheet P becoming entangled with the fixing roller. Therefore, such sheets P are classified as sheets with transport concerns.

[0058] Then, as shown in Figures 2A-2C, the branching section 9 is switched to the third transport path 103, and the abnormal transport sheet P is discharged through the third transport path 103 to the purge tray 50, which serves as the third discharge section. The purge tray 50 is located inside the machine, so it is situated upstream of the first discharge section 8 and the second discharge section 7, which are located outside the machine. As mentioned above, the abnormal transport sheet has significant side effects, such as getting tangled in the fixing roller, so in order to maintain the productivity of the machine, it is desirable to discharge it to the purge tray 50 as far upstream as possible as early as possible.

[0059] Figure 7 is a specific layout diagram showing the application of the transport concern anomaly detection device to the printer 110 of Embodiment 1 in Figure 4. In Figure 7, the aforementioned detection unit 21 is arranged as detection units 51a to 51af of the transport concern anomaly detection device.

[0060] The detection units 51a to 51af can be configured, for example, as reflective sensors having a light-emitting element and a light-receiving element. The presence or absence of the sheet P can be detected by detecting the reflected light from the sheet P on the detection units 51a to 51af as the output of the light-receiving element.

[0061] The detection units 51a to 51af can measure the arrival time and passage time of the sheet P for each detection unit 51a to 51af by measuring the passage time of the edges of the sheet P (leading edge in the transport direction, trailing edge in the transport direction) at each detection unit 51a to 51af. The times measured by the detection units 51a to 51af are all measured based on the same standard.

[0062] The travel time between detection units 51a and 51af can be measured from the arrival and passing times of detection units 51a to 51af. In addition, the transport speed of sheet P and the distance between detection units 51a and 51af are managed by the controller in the printer 110. Therefore, the controller can determine the ideal time when sheet P is transported between detection units 51a and 51af without delay.

[0063] Figure 7A shows a detection mechanism for transport concern anomalies related to the sheet arrival time, focusing on the leading edge of the sheet P. In this detection mechanism, the system waits for an ideal time t[s] + delay allowance margin α[s] from the time the leading edge of the sheet P reaches the upstream transport concern anomaly detection device, detection unit 51c, until it reaches the next downstream detection unit 51d.

[0064] If sheet P can be transported without delay, the leading edge of sheet P can reach the downstream detection unit 51d within t+α[s], and it will be determined to be a normal sheet. In this case, the normal sheet will be discharged to the first discharge unit 8.

[0065] If the sheet does not reach the detection unit 51d after waiting t+α[s], the sheet P is classified as a sheet with transport concerns or abnormalities. Then, the normal discharge of the sheet with transport concerns or abnormalities is interrupted, and the discharge destination is switched to the purge tray 50, which is the third discharge unit inside the machine body.

[0066] Figure 7B shows a detection mechanism for transport concerns regarding the arrival time of sheet P, focusing on the rear end of sheet P. In this detection mechanism, after the leading edge of the sheet reaches the upstream detection unit 51c and the rear end of sheet P passes through, the system waits for an ideal time t[s] + delay allowable margin α[s] until the rear end reaches the next downstream detection unit 51d.

[0067] If sheet P can be transported without delay, the rear end of sheet P will pass through the downstream detection unit 51d within t+α[s], and the sheet will be judged as normal. In this case, the normal sheet will be discharged to the first discharge unit 8.

[0068] If the rear end of sheet P does not detach from the detection unit 51d after waiting t+α[s], it is classified as a sheet with transport concerns or abnormalities. Then, the normal discharge of the sheet with transport concerns or abnormalities is interrupted, and the discharge destination is switched to the purge tray 50, which is the third discharge unit inside the machine body.

[0069] (● Embodiment 2) Next, Figure 8 shows a schematic configuration diagram of the printer 110 according to Embodiment 2. In this Embodiment 2, upstream of the image forming unit 5, there is a double-feed detection device 41 and a sheet posture detection device 43 as transportability abnormality detection devices.

[0070] The double-feed detection device 41 and the sheet posture detection device 43 also function as transport concern abnormality detection devices, as explained in Figures 5 to 6F. Furthermore, similar to Embodiment 1, there are multiple detection units 51a to 51x within the sheet transport path from paper feeding to discharge.

[0071] In this embodiment, the double-feed detection device 41 and the sheet posture detection device 43, which differ from those in Embodiment 1, will be described below. The double-feed detection device 41 performs double-feed detection at the double-feed detection point 42 after the sheet P has passed the double-feed detection device 41, to detect whether or not a double-feed has occurred.

[0072] The double-feed detection device 41 is a sensor that detects the vertical position of the upper part of the roller in the sheet transport path. The vertical position is the position in the thickness direction of the sheet P being transported. Since the amount the roller rises when a sheet passes through differs depending on the thickness of the sheet P, it is possible to determine whether the sheet is being fed together or individually from the difference in the output of the double-feed detection device 41.

[0073] The sheet posture detection device 43 detects the position of the sheet P in the depth direction (perpendicular to the transport direction) at detection point 44 and detects the sheet's posture (skew) at the downstream detection point 45. The sheet posture detection device 43 detects the position of the sheet in the depth direction relative to the transport direction using a line sensor.

[0074] In Embodiment 2, the skew is corrected by bringing the leading edge of the sheet P in the transport direction against the sheet posture correction mechanism 46 shown in Figures 9A and 9B. The sheet posture correction mechanism 46 has a pair of cylindrical first rollers 46b at both ends of the rotating shaft 46a. It also has a pair of cylindrical second rollers 46c between the first rollers 46b.

[0075] The second roller 46c has a projection 46c1 on a part of its outer circumference. The leading edge of the sheet P in the conveying direction abuts against this projection 46c1.

[0076] The second roller 46c also has arcuate surfaces 46c2 and 46c3 that are the same diameter as the outer surface of the first roller 46b, centered on the rotation axis 46a. One arcuate surface 46c2 is located in front of the projection 46c1, and the other arcuate surface 46c3 is located behind the projection 46c1.

[0077] A feed roller 47 is positioned above the first roller 46b so as to be able to move up and down. This feed roller 47 is connected to a motor, which serves as a drive source, via gears. The rotating shaft 46a of the seat posture correction mechanism 46 is also connected to the motor via gears.

[0078] The feed roller 47 moves downward and comes into contact with the first roller 46b, receiving the sheet P being transported from the upstream side. The rotating shaft 46a is basically set to rotate continuously in one direction.

[0079] However, during the rotation process of the rotating shaft 46a, when the projection 46c1 of the second roller 46c reaches the initial position where it abuts the leading edge of the sheet P, the rotating shaft 46a stops temporarily. Then, when the leading edge of the sheet P abuts the projection 46c1, rotation control is executed to restart the rotation of the rotating shaft 46a.

[0080] After the seat P's posture is corrected by the seat posture correction mechanism 46, the downstream seat posture detection device 43 detects the vertical (depth or shift) misalignment, as shown in Figure 9C. Based on this detection result, the depth-direction misalignment of the seat P is detected, and the seat posture correction mechanism 46, which is gripping and transporting the seat P, is shifted in the depth direction to correct the misalignment.

[0081] After correcting the positional misalignment of the seat P in the depth direction, the seat posture detection device 43 detects the vertical positional misalignment again and detects the amount of misalignment relative to the target position (positional misalignment in the longitudinal direction of the seat posture detection device 43). If this amount of misalignment does not exceed the threshold (reference value) A', it is classified as a normal seat and discharged to the first discharge unit 8 outside the machine.

[0082] Next, if the amount of misalignment exceeds the threshold A', it results in a quality defect called image registration misalignment, and the sheet is classified as a transportable abnormal sheet. Such transportable abnormal sheets are discharged to the first discharge unit 8 outside the machine, as described above in Figures 1B and 1C.

[0083] Furthermore, if the amount of deviation becomes threshold B', which is even greater than threshold A', it is classified as a transport concern abnormality sheet. In this case, the transport concern abnormality sheet is discharged to the purge tray 50, which is the third discharge section, as described above in Figures 2A to 2C.

[0084] If the amount of displacement does not exceed threshold A', transport is continued, and the sheet posture detection device 43 detects the positional displacement of the sheet P in the depth direction again, as shown in Figures 9E and 9F. Based on the position detection results of the two points in the depth direction after position correction, it is determined whether the posture of the sheet P is correct or not.

[0085] If the amount of deviation in the orientation of sheet P does not exceed the threshold C, sheet P is classified as a normal sheet. If the detection result in Figure 9D is also a normal sheet, the image forming unit 5 forms an image on the sheet and discharges the sheet to the normal first discharge unit 8 outside the machine.

[0086] If the detection result in Figure 9D indicates a transportable abnormal sheet, it is classified as a transportable abnormal sheet and discharged to the first discharge section 8 outside the machine. If the detection result in Figure 9D indicates a transportable concern abnormal sheet, it is classified as a transportable concern abnormal sheet and discharged to the purge tray 50, which is the third discharge section inside the machine.

[0087] Next, if the deviation in the orientation of sheet P exceeds the threshold C, it results in a quality defect called image registration misalignment. For this reason, sheet P is classified as a transportable abnormal sheet. In this case, if the detection result in Figure 9D is a normal sheet or a transportable abnormal sheet, the sheet is classified as a transportable abnormal sheet as described above in Figures 1B and 1C, for example, and is discharged to the second discharge unit 7 outside the machine.

[0088] If the detection result in Figure 9D indicates a transport concern abnormality sheet, it is classified as a transport concern abnormality sheet and discharged into the purge tray 50, which is the third discharge section inside the machine. Furthermore, if the amount of deviation in the orientation of sheet P exceeds threshold D, which is greater than threshold C, it is classified as a transport concern abnormality sheet. In this case, regardless of the detection result in Figure 9D, it is discharged into the purge tray 50 as a transport concern abnormality sheet.

[0089] (●Flowchart) Figure 10 shows the decision flow for detecting abnormal sheet transport conditions. Sheet detection (S1) includes detection by the transportable abnormality detection device and the transport concern abnormality detection device described above. Based on the results of the above detection, the detected sheet is determined by the classification means 90b to be one of the following: "normal sheet" (S4), "transportable abnormal sheet" (S5), or "transport concern abnormal sheet" (S6).

[0090] In Figure 10, the presence or absence of an abnormality is determined (S2, S3), but the configuration is not limited to this. For example, instead of determining the presence or absence of an abnormality, the classification means 90b may determine from the sheet detection result (S1) whether it is a "normal sheet," a "transportable abnormal sheet," or a "transportable abnormal sheet."

[0091] Figure 11 is a flowchart that determines the destination of the sheet after the state of the sheet in Figure 10 is detected. In other words, Figure 11 shows the control flow of the branching sections 6 and 9 by the switching means 90c.

[0092] The order of judgment by the classification means 90b does not have to start with the normal sheet; the judgments may be made in the order of "transportable abnormal sheet," "transportable abnormal sheet," and "normal sheet." Alternatively, the judgments may be made in the order of "transportable abnormal sheet," "transportable abnormal sheet," and "normal sheet."

[0093] The printer 110 in each of the embodiments described above (Figures 1A to 9F) is equipped with a transportability abnormality detection device and a transport risk abnormality detection device. Furthermore, as shown in Figure 7, it has multiple transport risk abnormality detection devices (detection units 51a to 51af). Therefore, in Figures 12A to 12D, when multiple detections are performed on the same sheet, the detection results of the sheet are updated to the latest state.

[0094] For example, this applies when sheet P is detected in Figure 5 and then again in Figure 6A, when it is detected from Figure 7A to Figure 7B, when it is detected from Figure 9D to Figure 9F, when it is detected by a transport concern abnormality detection device (Figure 2A, Figures 7-7B) installed in the transport path from paper feeding to discharge, and when these detection devices are combined.

[0095] As shown in the flowcharts in Figures 12A to 12D, (1) to (3) are the key points. (1) Even if a sheet is determined to be "normal" or "transportable but abnormal" upstream in the transport direction, the detection result may be overwritten depending on the downstream detection result (S16, S17 in Figure 12B, S22 in Figure 12C). (2) If a "conveying concern abnormality sheet" is detected upstream in the conveying direction, the "conveying concern abnormality sheet" will be issued regardless of the detection results downstream (S24, S26, S27 in Figure 12D). (3) If the detection result downstream is better than the judgment result upstream in the transport direction, the information is not updated (S19 in Figure 12C, S24 and S26 in Figure 12D).

[0096] Thus, the priority order (high to low) for updating the judgment results is "Transportation Concern Abnormal Sheet," "Transportable Abnormal Sheet," and "Normal Sheet." In terms of the destination of the sheets, this can also be expressed as "Purge Tray 50," "Second Discharge Unit 7," and "First Discharge Unit 8."

[0097] Although the flow in Figure 10 shows two detections, it is possible to perform three or more detections before the sheet is ejected. In this case, the state of sheet A is repeatedly determined according to points (1) to (3) above.

[0098] Figure 13 is a flowchart showing what happens after sheet A passes through branching point 9. If no abnormality is detected in sheet A downstream of branching point 9, sheet A is discharged to the destination corresponding to the previous detection result (S34).

[0099] For example, if the latest judgment result is a normal sheet, it is discharged to the designated discharge tray (first discharge unit 8 in this example). If the latest judgment result is a transportable abnormal sheet, it is discharged to the designated discharge tray (second discharge unit 7 in this example). If an abnormality is detected in sheet A downstream of branching unit 9, and the judgment result is a transportable abnormal sheet, it is discharged to the designated discharge tray (second discharge unit 7 in this example) (S32).

[0100] On the other hand, if the determination result is that the sheet is a transport-prone abnormal sheet, sheet A is discharged to the second discharge section 7 outside the machine, and the sheets upstream of the branching section 9 are discharged to the purge tray 50 (S33). If sheet A is a jammed sheet, it will take longer to discharge to the second discharge section 7 than a transportable abnormal sheet. Therefore, by discharging the sheets upstream of the branching section 9 to the purge tray 50, interference with sheet A can be prevented.

[0101] The present invention is not limited to the embodiments described above. For example, the following is also possible. (1) The detection units 4, 21, and 22 that detect the sheet being transported only need to be able to detect and classify the sheet into one of three categories based on the detection result: "sheet with transport concern abnormality", "sheet with transportable abnormality", or "normal sheet", and there only needs to be at least one of each. (2) The sheet posture correction mechanism is not limited to being located upstream of the image forming unit 5, which is the transfer position, but may also be provided in the reversal transport path 104 after passing through the fixing device. (3) If a sheet is determined to be a "conveying problem abnormal sheet" or a "conveyable abnormal sheet" upstream of the branching section 9, all sheets in the machine from that sheet to the upstream paper feed tray 111 may be discharged into the purge tray 50. (4) Image formation is not limited to electrophotography, but may also be done by inkjet. (5) The detection means 90a may detect one or more types of abnormal sheets that are different from the "abnormal sheet of transport concern" or the "abnormal sheet that can be transported," and the abnormal sheets may be discharged to separate discharge units. (6) Branching sections 6 and 9 do not necessarily need to be provided in pairs; it is also possible to switch between three transport routes with a single branching section. (7) The sheet transport device of the present invention is also applicable to sheet transport devices other than the printer 110 in Figure 1A, such as sheet inspection devices.

[0102] <Note> Preferred embodiments of the present invention are described below. <First aspect> The first embodiment is a sheet conveying device that conveys sheets along a sheet conveying path, comprising: detection means for detecting at least one of position information and orientation information of a sheet in the sheet conveying path based on the detection results of one or more detection units, and for detecting an error from the detected detection information compared with a reference value; classification means for classifying the sheets into at least three types based on the magnitude of the error detected by the detection means: normal sheets that can be conveyed, abnormal sheets that can be conveyed, and abnormal sheets with transport concerns that pose a transport risk; and switching means for switching one or more branching units to convey the normal sheets to a first conveying path connected to a first discharge unit, the abnormal sheets that can be conveyed to a second conveying path connected to a second discharge unit, and the abnormal sheets with transport concerns to a third conveying path connected to a third discharge unit, respectively, based on the classification results of the classification means. <Second aspect> The second embodiment is a sheet conveying device of the first embodiment, characterized in that a plurality of detection units are arranged from the upstream side to the downstream side of the sheet conveying path, the classification means sequentially updates the classification of the sheets conveyed along the sheet conveying path based on the error of the sheets from the reference value corresponding to the conveying position of the sheets, and the switching means operates the one or more branching units based on the updated classification. <Third aspect> A third aspect is a sheet conveying device according to the first or second aspect, characterized in that the classification means classifies the sheet as a sheet with transport concerns, regardless of the updated error. <Fourth aspect> A fourth aspect is a sheet conveying device according to the first or second aspect, characterized in that the classification means classifies the sheet as a conveyable abnormal sheet even if, based on the updated error, the sheet would be classified as a conveyable normal sheet. <Fifth aspect> The fifth embodiment is a sheet conveying device according to any one of the first to fourth embodiments, comprising a plurality of branching sections, wherein at least one detection section is disposed downstream of the upstream branching section among the plurality of branching sections, and when the classification section classifies the sheet as a sheet of transport concern abnormality based on the error detected by the detection means from the detection result of the at least one detection section, the switching means switches the plurality of branching sections so that the sheet is discharged to the first discharge section or the second discharge section, and the sheets upstream of the upstream branching section are discharged to the third discharge section. <Sixth aspect> The sixth embodiment is a sheet conveying device according to any one of the first to fifth embodiments, characterized in that the sheet conveying path is arranged inside the image forming apparatus, the first discharge unit and the second discharge unit are arranged outside the image forming apparatus, and the third discharge unit is arranged inside the image forming apparatus. <Seventh aspect> The seventh embodiment is an image forming apparatus characterized by having a sheet transport device according to any one embodiment of the first to fifth embodiments. [Explanation of symbols]

[0103] 4: Detection unit (detection means) 5: Image forming unit 6: Branching section 7: Second discharge section 8: First discharge section 9: Branch section 11: Post-processing unit 12: Image forming unit 21, 22: Detection unit; 31: Double feed detection device 32: Double feed detection point 33-35: Line sensor 36: Detection point 37: Seat posture correction device 38: Light-receiving element 39: Light-emitting element 41: Double feed detection device 42: Double feed detection point 43: Seat posture detection device 44, 45: Detection points 46: Seat posture correction mechanism 46a: Rotation axis 46c1: projection; 46c2, 46c3: arcuate surface 47: Feed roller 50: Purge tray (third discharge section) 51a~51af~51x: Detection unit 90: Control unit 90a: Detection means 90b: Classification means 90c: Switching mechanism 101: First transport path 102: Second transport path 104: Reversal transport path 110: Printer (image forming machine) 111: Paper feed tray P: Sheet [Prior art documents] [Patent Documents]

[0104] [Patent Document 1] Japanese Patent Publication No. 2020-144251

Claims

1. In a sheet conveying device that conveys sheets along a sheet conveying path, A detection means that detects at least one of the position information and orientation information of a sheet in the sheet transport path based on the detection results of one or more detection units, and compares the detected information with a reference value to detect the error from the reference value, A classification means that classifies the sheet into at least three types based on the magnitude of the error detected by the detection means: a normal sheet that can be transported, a transportable abnormal sheet that can be transported, and a transportable abnormal sheet that raises concerns about transport. A switching means that switches one or more branching points to transport the normal sheets to the first transport path connected to the first discharge section, the transportable abnormal sheets to the second transport path connected to the second discharge section, and the transportable abnormal sheets to the third transport path connected to the third discharge section, based on the classification results of the classification means, Equipped with, Multiple detection units are arranged from the upstream side to the downstream side of the sheet transport path. The classification means sequentially updates the classification of the sheets based on the error of the sheets being transported along the sheet transport path from the reference value corresponding to the transport position of the sheets. The sheet conveying device is characterized in that the switching means operates one or more branching sections based on the updated classification.

2. The sheet conveying device according to claim 1, characterized in that the classification means classifies the sheet as a sheet of transport concern abnormality, regardless of the updated error.

3. The sheet conveying device according to claim 1, characterized in that the classification means classifies the sheet as a conveyable abnormal sheet even if, based on the updated error, the sheet would be classified as a conveyable normal sheet.

4. The branch section comprises multiple such sections, Of the aforementioned multiple branching sections, at least one of the detection units is located downstream of the upstream branching section. The sheet conveying device according to claim 1, characterized in that, if the classification means classifies the sheet as a sheet of transport concern abnormality based on the error detected by the detection means from the detection result of at least one detection unit, the switching means switches the plurality of branching units so that the sheet is discharged to the first discharge unit or the second discharge unit, and sheets upstream of the upstream branching unit are discharged to the third discharge unit.

5. A sheet transport device according to any one of claims 1 to 4, characterized in that the sheet transport path is disposed inside the image forming apparatus, the first discharge unit and the second discharge unit are disposed outside the image forming apparatus, and the third discharge unit is disposed inside the image forming apparatus.

6. An image forming apparatus characterized by having a sheet transport device according to any one of claims 1 to 4.

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