Conveying device, image forming apparatus, and conveying method

Abstract

An advantage of some aspects of the invention is to prevent a failure due to a positional deviation of a recording medium after position correction.SOLUTION: A conveying device (30) for conveying a sheet (P) includes a first side 1CIS34 and a second side 2CIS35 for detecting a position of the sheet (P), and a holding roller (31) for correcting the position of the sheet (P) based on detection results of the first side 1CIS34 and the second side 2CIS35, wherein the position of the sheet (P) is detected by the first side 1CIS34 and the second side 2CIS35 after the position of the sheet (P) is corrected by the holding roller (31).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a conveying device, an image forming apparatus, and a conveying method. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been a conveying device provided with nipping rollers (correcting means) that corrects misalignment and inclination of a sheet of paper in the width direction while nipping and conveying the sheet of paper as a recording medium.

[0003] For example, in the conveying device of Patent Document 1 (Japanese Patent No. 6587060), multiple CISs (Contact Image Sensors) arranged in the paper conveying direction detect misalignment and tilt in the width direction of the paper, and clamping rollers correct the paper position. The corrected recording medium is sent to a transfer section downstream, where the image is transferred. Summary of the Invention [Problem to be solved by the invention]

[0004] Even if the position of the recording medium is corrected as in Patent Document 1, there is a problem that the recording medium may become misaligned for some reason after the correction. If the misaligned recording medium is transported as is, there is a problem that the misalignment causes abnormalities, such as causing abnormal images on the recording medium in a transport device installed in an image forming apparatus. This causes problems such as the operator not noticing the abnormality, or the misalignment also occurring on other recording media.

[0005] An object of the present invention is to prevent problems caused by misalignment of the recording medium after position correction. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a conveying device for conveying a recording medium, which comprises a position detection means for detecting the position of the recording medium and a correction means for correcting the position of the recording medium based on the detection result of the position detection means, and is characterized in that after the position of the recording medium is corrected by the correction means, the position of the recording medium is detected by the position detection means, and abnormality processing is performed when the amount of positional deviation of the recording medium calculated based on this detection result exceeds a predetermined threshold value. [Effects of the Invention]

[0007] In the present invention, it is possible to prevent problems caused by misalignment of the recording medium after position correction. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of an image forming apparatus. [Figure 2] FIG. 1 is a plan view of a transport device according to an embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram illustrating the amount of misalignment of a sheet. [Figure 4] 10 is a plan view showing detection of a sheet position after position correction by the conveying device. FIG. [Figure 5] FIG. 10 is a flowchart showing a series of procedures for determining an abnormality. [Figure 6] FIG. 10 is a plan view showing misalignment in the width direction of the paper. [Figure 7] FIG. 10 is a plan view showing the amount of skew of a sheet of paper. [Figure 8] FIG. 10 is a plan view showing sheet position detection using only the second CIS. [Figure 9] FIG. 6 is a flowchart showing a series of steps for determining abnormality processing according to an embodiment different from that shown in FIG. 5. [Figure 10] FIG. 2 is a functional block diagram showing a control configuration for controlling a paper transport operation. [Figure 11] 10 is a plan view showing a positional deviation of a sheet due to a deviation in nip pressure of a downstream roller; FIG. [Figure 12]10 is a flowchart showing a series of steps for determining abnormality processing according to an embodiment different from those shown in FIGS. 5 and 9. FIG. [Figure 13] 13 is a flowchart showing a series of steps for determining abnormality processing according to an embodiment different from those shown in FIGS. 5, 9, and 12. FIG. [Figure 14] FIG. 1 is a plan view showing a transport device having three CISs. [Figure 15] 15 is a plan view showing the pick-up operation of the pinch rollers in the conveying device of FIG. 14. FIG. [Figure 16] 15 is a plan view showing a state in which the leading edge of the paper reaches the nipping rollers in the conveying device of FIG. 14. FIG. [Figure 17] 15 is a plan view showing a correction operation by the pinch rollers in the conveying device of FIG. 14. FIG. [Figure 18] 15 is a plan view showing a state in which the leading edge of the paper reaches the second CIS in the conveying device of FIG. 14. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted.

[0010] FIG. 1 is a schematic explanatory diagram showing a state in which a sheet post-processing device is connected to an image forming apparatus according to one embodiment of the present invention (configuration of an image forming system).

[0011] As shown in FIG. 1, the image forming system 1 includes an image forming apparatus 10 and a paper post-processing device (hereinafter referred to as the post-processing device) 100. The post-processing device 100 can be attached to the discharge side of the image forming apparatus 10 where paper P is discharged. The image forming apparatus 10 includes an image forming unit 10A, a paper feed unit 10B, and a purge tray 60 as another discharge unit within its housing. The image forming unit 10A forms (prints) an image on paper P as a recording medium. The paper feed unit 10B has multiple paper feed trays T1, T2, ..., and supplies paper P from any of the paper feed trays to the image forming unit 10A. The purge tray 60 is a tray onto which paper determined to have an abnormality during the printing process is discharged. An operation display panel 70 as a display unit is installed above the exterior of the image forming apparatus 10. The post-processing device 100 includes a receiving port 102 for receiving printed matter, a post-processing unit, and a stacker 105 as a discharge unit for storing post-processed sheets.

[0012] As shown in FIG. 1, an intermediate transfer belt 8 is installed above the center of the image forming apparatus 10. Also, photoconductor drums 2Y, 2M, 2C, and 2K (imaging units) corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side facing the intermediate transfer belt 8. Furthermore, the intermediate transfer belt 8 presses against a secondary transfer roller 15 (secondary transfer belt 16) below it, forming a secondary transfer nip as an image forming unit. Around the photoconductor drum 2K corresponding to black, a charging unit 3, a developing unit 4, a cleaning unit 5, a charge removal unit, and the like are arranged. Then, an image creation process (charging process, exposure process, developing process, transfer process, cleaning process, and charge removal process) is performed on the photoconductor drum 2K, and a black image is formed on the surface of the photoconductor drum 2K. The peripheries of the other three photoconductor drums 2Y, 2M, and 2C are configured in a similar manner, and images corresponding to the respective toner colors are formed on the surfaces of the photoconductor drums 2Y, 2M, and 2C. Hereinafter, the description of the image forming process on the other three photosensitive drums 2Y, 2M, and 2C will be omitted as appropriate, and only the image forming process corresponding to black will be described.

[0013] The photosensitive drum 2K is rotated counterclockwise in FIG. 1 by a main motor. The surface of the photosensitive drum 2K is uniformly charged at the charging unit 3. The surface of the photosensitive drum 2K then reaches a position where it is irradiated with laser light emitted from the exposure unit 7. At this position, an electrostatic latent image corresponding to black is formed by exposure scanning in the width direction (the direction perpendicular to the plane of the paper in FIG. 1, the main scanning direction). The surface of the photosensitive drum 2K then reaches a position opposite the development unit 4. At this position, the electrostatic latent image is developed to form a yellow toner image. The surface of the photosensitive drum 2K then reaches a position opposite the intermediate transfer belt 8 and primary transfer roller 6. At this position, the toner image formed on the surface of the photosensitive drum 2K is primarily transferred to the surface of the intermediate transfer belt 8. The surface of the photosensitive drum 2K then reaches a position opposite the cleaning unit 5. At this position, any untransferred toner remaining on the photosensitive drum 2K is collected into the cleaning unit 5 by a cleaning blade.

[0014] Finally, the surface of the photosensitive drum 2K reaches a position facing a charge removal unit, where the residual potential on the photosensitive drum 2K is removed. This completes the series of image formation processes performed on the photosensitive drum 2K. The image formation process described above is also performed on the surfaces of the other photosensitive drums 2Y, 2M, and 2C in the same manner as the black photosensitive drum 2K. The toner images of each color formed on the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2K are then primarily transferred onto the intermediate transfer belt 8 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 8.

[0015] Thereafter, the intermediate transfer belt 8, onto which the toner images of each color have been superimposed and primarily transferred, reaches a position facing a secondary transfer roller 15 (secondary transfer belt 16). At this position, a secondary transfer nip is formed between the secondary transfer opposing roller 9 and the secondary transfer roller 15, sandwiching the intermediate transfer belt 8 and the secondary transfer belt 16. The four-color toner images formed on the intermediate transfer belt 8 are then secondarily transferred onto a sheet of paper P, such as paper, that has been transported to the position of this secondary transfer nip. Thereafter, the intermediate transfer belt 8 reaches the position of an intermediate transfer cleaning unit. At this position, untransferred toner and other deposits adhering to the surface of the intermediate transfer belt 8 are removed. This completes the series of transfer processes performed on the intermediate transfer belt 8.

[0016] The paper P transported to the secondary transfer nip (image forming unit) is transported from the paper feed unit 10B disposed below the image forming apparatus 10 via the paper feed conveyance unit K1, which includes the paper feed roller 11 and downstream roller 41. Specifically, multiple sheets of paper P are stacked and stored in each of the paper feed trays T1 and T2 of the paper feed unit 10B. When the paper feed roller 11 is driven to rotate counterclockwise in FIG. 1, the topmost sheet P is transported from the paper feed conveyance unit K1 to the conveyance device 30. The paper P is conveyed by the conveyance device 30, and after its positional deviation is corrected (described in detail below), it is fed between the rollers of the downstream roller 41. The downstream roller 41 conveys the paper P by rotating while sandwiching the paper P in the nip between the rollers. The downstream roller 41 controls the speed of the paper P to synchronize with the color image on the intermediate transfer belt 8. In this way, the desired color image is transferred onto the paper P. In this way, the downstream roller 41 is a transfer timing roller that adjusts the timing between the paper P being conveyed and the color image on the intermediate transfer belt 8.

[0017] Thereafter, the sheet P onto which the color image has been transferred at the secondary transfer nip position is conveyed by secondary transfer belt 16, separated from secondary transfer belt 16, and then conveyed by conveyor belt 18 to the position of fixing unit 19. At this position, the color image transferred to the surface of the sheet P is fixed onto the sheet P by heat and pressure from the fixing belt and pressure roller. The sheet P is then discharged to the outside of image forming apparatus 10 by sheet discharge rollers 25 via first discharge path K2-1. Furthermore, the sheet P discharged from image forming apparatus 10 is conveyed inside post-processing device 100, where it is subjected to post-processing such as bookbinding, punching, and binding. The post-processed sheet P (sheet stack) is then discharged to stacker (discharge tray) 105. In this way, a series of image formation processes (image forming operations) in image forming apparatus 10 is completed. In addition, when the post-processing device 100 is not attached to the image forming device 10, an output tray as an output section is provided downstream of the paper output outlet 26 of the image forming device 10 (for example, an output tray corresponding to the stacker 105 is provided immediately downstream of the paper output outlet 26).

[0018] Next, a case where a "double-sided print mode" for printing on both sides (front and back sides) of the paper P is selected will be described. In this case, the paper P, after the fixing process on the front side, is guided to the branched introduction path K3 by the operation of the first switching claw (paper discharge direction switching claw) 61 and the second switching claw 62. The paper P guided to the branched introduction path K3 is then guided to the second conveyance path (double-sided reversing branch path) K5 by the operation of the third switching claw 63 and the like. The paper P guided to the second conveyance path K5 then has its conveyance direction reversed by switching the drive of the double-sided reversing roller 64 from forward to reverse rotation, and is then guided to the double-sided reversing conveyance path K6 by the operation of the third switching claw 63 (double-sided switching claw) and the like. The paper P then passes through the paper feed conveyance section K1 and is conveyed again to the conveyance device 30, where its positional deviation is corrected, before reaching the secondary transfer nip (image forming section). Then, an image is formed on the back side of the paper P at the position of the secondary transfer nip by an image forming process (image forming operation) similar to that described above, and the paper P then undergoes a fixing process in the fixing section 19 and is discharged from the image forming device 10 via the first discharge path K2-1.

[0019] That is, when the "duplex print mode" is selected, the branch introduction path K3, the second conveyance path (duplex reversing branch path) K5, and the duplex reversing conveyance path K6 function as duplex conveyance paths. Furthermore, when the "reversing discharge mode" is selected in which the front and back sides of the sheet P are reversed and discharged, the sheet P, after the fixing process on the front side (or both sides) has been completed, is guided to the branch introduction path K3 by the operation of the first and second switching claws 61 and 62 without being discharged from the image forming apparatus 10. Then, the leading end side of the sheet P guided to the branch introduction path K3 is guided to the first conveyance path K4 by the operation of the third switching claw 63, etc. Then, the conveyance direction of the sheet P guided to the first conveyance path K4 is reversed by switching the drive of the discharge reversing roller 65 from forward rotation to reverse rotation, and then the sheet P is guided to the second discharge path K2-2 via the branch introduction path K3 by the operation of the second switching claw 62. Then, the inverted sheet P is discharged from the image forming apparatus 10 via the first discharge path K2-1.

[0020] That is, when the "reverse discharge mode" is selected, the branch introduction path K3, the first transport path K4, the second discharge path K2-2, and the first discharge path K2-1 function as the reverse discharge path. Note that the "single-sided print mode," "double-sided print mode," and "reverse discharge mode" are selected by the user operating the operation display panel 70.

[0021] Furthermore, any paper that is determined to have an abnormality during the printing process is discharged to the purge tray 60. Specifically, during abnormality processing, the paper P is guided to the branch introduction path K3 by the operation of the first switching claw 61 and the second switching claw 62. Furthermore, a control unit provided in the image forming apparatus 10 rotates the fourth switching claw 66 (switching means) so as to block the upstream portion of the second transport path K5. As a result, the paper P that has passed through the branch introduction path K3 is transported to the purge tray 60 via the first transport path K4.

[0022] The purge tray 60 is provided with a storage space for stacking and storing paper sheets P, and paper sheets P ejected onto the purge tray 60 fall into this space and are stored. This storage space can be opened to the outside by opening an opening / closing door that also functions as an exterior part of the image forming apparatus 10, allowing the stored paper sheets P to be removed. The purge tray 60 is large enough to store long sheets of paper. However, the storage space of the purge tray 60 may be shorter in the conveying direction than the longest sheet of paper P. In this case, the longest sheet of paper P will be curled up as it falls into the storage space of the purge tray 60 and stored. The purge tray 60 may be configured as a tray that can be opened to the outside of the image forming apparatus 10.

[0023] A jammed (jammed) state of paper P can be optically detected by jam detection sensors arranged at multiple locations along the transport path, such as jam detection sensor 24 arranged near discharge roller 25 and jam detection sensor 103 arranged near the entrance roller of post-processing device 100. A purge processing mode may be provided in which jammed paper P is transported to purge tray 60 based on the detection result.

[0024] A paper discharge reversal sensor 67 (third detection means), which is a photosensor that optically detects the paper P, and a photosensor 69 are provided on the branch introduction path K3 or the first transport path K4. The timing for switching the paper discharge reversal rollers 65 from forward rotation to reverse rotation is determined based on the detection results of the paper discharge reversal sensor 67 and the photosensor 69. Furthermore, a photosensor 68 (second detection means), which optically detects the paper P, is provided on the second transport path K5. The timing for switching the duplex reversal rollers 64 from forward rotation to reverse rotation is determined based on the detection results of the photosensor 68.

[0025] Next, the detailed configuration of the conveying device provided in the image forming apparatus will be described with reference to FIG.

[0026] As shown in FIG. 2, the conveying device 30 has a clamping roller 31 as a correction means, a first drive motor 32, a second drive motor 33, and a first CIS 34 and a second CIS 35 as position detection means. The direction of arrow A pointing from right to left in FIG. 2 is the paper conveyance direction (recording medium conveyance direction), and the direction along the surface of the paper P and perpendicular to the paper conveyance direction (the up-down direction in FIG. 2) is the width direction of the paper. The upstream and downstream sides of the paper conveyance direction are hereinafter simply referred to as the upstream and downstream sides. The first CIS 34 is an upstream detection means in this embodiment, located upstream of the second CIS 35, and the second CIS 35 is a downstream detection means.

[0027] The nip rollers 31 sandwich and transport the paper P in a nip formed by a pair of rollers. The nip rollers 31 are rotatable about the shafts 31a in both directions D along the surface of the paper P by the driving force of the first drive motor 32. The nip rollers 31 are also movable in both directions E across the width of the paper by the driving force of the second drive motor 33. The first drive motor 32 and the second drive motor 33 are connected to the nip rollers 31 via gears and cams, and transmit driving forces to the nip rollers 31. Encoders are provided on the drive shafts of the first drive motor 32 and the second drive motor 33, which indirectly detect the rotation direction D and amount of rotation of the nip rollers 31, or the movement direction and amount in the width direction E.

[0028] The first CIS 34 and the second CIS 35 are contact image sensors that use small LEDs (Light Emitting Diodes) as light sources and directly read images with a linear sensor via a lens.

[0029] On the downstream side of the second CIS 35, the aforementioned downstream roller 41 is provided.

[0030] The side edge position of the sheet P can be detected by the first CIS 34 or the second CIS 35. This makes it possible to calculate the amount of misalignment of the sheet P in the width direction. For example, as shown in FIG. 3, the second CIS 35 can detect the position of the side edge Pa of the sheet P. If a line passing through the ideal position of the sheet P in the width direction without misalignment is taken as a reference line B, the amount of misalignment of the sheet P in the width direction can be calculated as the distance B1 from the reference line B0 to the side edge Pa. The amount of misalignment in the width direction may also be calculated using the detection results of multiple CISs. Note that the clamping rollers 31 are not shown in FIG. 3.

[0031] Furthermore, the amount of skew of the paper P can be calculated by detecting the side edge positions of the paper P using the first CIS 34 and the second CIS 35. For example, when the leading edge Pb of the paper P reaches the second CIS 35, the distances B1 and B2 from the reference line B0 can be calculated from the detection results of each CIS. Then, since the distance C between the first CIS 34 and the second CIS 35 in the transport direction is predetermined, the skew angle α of the paper P with respect to the transport direction can be calculated using tan α = (B2 - B1) / C. The skew angle α (amount of skew α) of the paper P is the skew angle of the side edge Pa of the paper P with respect to the paper transport direction (the left-right direction in FIG. 3) in a plane parallel to the paper surface. Alternatively, it may be the skew angle of the leading edge Pb of the paper P with respect to the width direction.

[0032] At least one of the widthwise misalignment amount and the tilt amount, which are the misalignment amount of the sheet P calculated as described above, can be corrected by moving the clamping rollers 31 in the widthwise direction (moving in the direction of arrow E) or by rotating in direction D, as shown in Fig. 2. The clamping rollers 31 complete the correction of the misalignment of the sheet P by the time the leading edge of the sheet P reaches the downstream roller 41.

[0033] However, even when correction is performed using the nip rollers 31 as described above, if misalignment occurs on the paper P after the correction operation before it reaches the transfer position, the position of the image formed on the paper P will be misaligned, resulting in an abnormal image. In this case, the control unit of the image forming apparatus recognizes that the position correction has been completed successfully, and therefore fails to recognize that an abnormal image has been formed. Therefore, the operator may not notice the formation of an abnormal image until checking the paper P after printing, or the operator may continue to use the paper P without noticing the formation of an abnormal image. Note that an example of misalignment after position correction is misalignment that occurs while the downstream rollers 41 nip and transport the paper P due to a deviation in the width direction of the nip pressure on the paper P at the nip portion of the downstream rollers 41.

[0034] 4, after the position of the sheet P is corrected by the clamping roller 31, the first CIS 34 and the second CIS 35 continue to detect the side edge positions of the sheet P even after the leading edge of the sheet P reaches the downstream roller 41. If the amount of misalignment of the sheet P exceeds a set threshold, abnormality processing is performed. This threshold can be set, for example, based on the amount of misalignment that is acceptable for the quality of the image formed on the sheet P.

[0035] In this embodiment, "abnormal processing" refers to processing that is not performed during normal printing operations. As an abnormal processing, for example, printing is stopped. This prevents abnormal images from being formed on subsequent sheets of paper in the case of continuous printing, thereby preventing problems such as unnecessary printing operations and wasted paper. It also prevents problems such as an operator using a sheet of paper P on which an abnormal image has been formed without noticing that an abnormal image has been formed. The above-mentioned stopping of printing includes stopping the transport of the sheet of paper P by the transport device 30.

[0036] As another way to handle an abnormality, instead of stopping printing, the paper P can be discharged to a different discharge section, the purge tray 60 (see FIG. 1). This prevents paper P bearing an abnormal image due to misalignment from being discharged to the normal discharge section, the stacker 105 (see FIG. 1), preventing the paper P bearing the abnormal image from being mixed with paper P bearing a normal image. This prevents, for example, an operator from using paper P bearing an abnormal image without noticing the abnormal image. Furthermore, compared to stopping printing P as the abnormality handling method, this method does not halt subsequent printing operations. Therefore, it is suitable for handling abnormalities without reducing the productivity of the image forming apparatus when the amount of misalignment becomes large only on some of the sheets being printed continuously. In other words, for paper P bearing no abnormal image, images can be formed normally and the paper can be discharged to the stacker 105 (see FIG. 1) to complete the printing operation. Therefore, only the paper bearing the abnormal image can be printed later. An example of a case in which misalignment becomes large only on some sheets is when printing on different sized paper P during continuous printing. In this case, only the paper sheets of a size that will cause a large amount of misalignment can be discharged to the purge tray 60 (see FIG. 1), and the other paper sheets can be discharged to the stacker 105 (see FIG. 1).

[0037] Furthermore, as an abnormality processing method, the occurrence of an abnormality may be displayed on the operation display unit of the image forming device. This notifies the operator that an abnormality has occurred, preventing the operator from noticing the paper P on which an abnormal image has been formed or from continuing printing without noticing the abnormality. This prevents subsequent problems such as wasted printing or wasted paper. It also prevents the operator from using the paper P on which an abnormal image has been formed without noticing that an abnormal image has been formed. This processing may be performed in addition to the above-mentioned stopping of printing or discharging of the paper P to another discharge unit.

[0038] Next, the procedure for determining whether or not to transport a sheet by the transport device and perform abnormality processing will be described with reference to the flow chart of FIG.

[0039] 5, the paper P is conveyed by other rollers provided in the conveying device 30 or rollers on the upstream side of the conveying device 30, and the paper P reaches the nipping rollers 31. Then, the nipping rollers 31 rotate while nipping the paper P, and convey the paper P (step S1 in FIG. 5).

[0040] After that, detection of the paper position by each CIS is started at a predetermined timing (step S2), and the amount of misalignment is calculated. Based on the calculation result, the clamping rollers 31 start correcting the paper position (step S3). Then, correction of the paper position is completed by the time the leading edge of the paper P reaches the downstream roller 41 (step S4). The timing at which detection of the paper position starts is, for example, when the leading edge of the paper P reaches the second CIS 35. However, if only the amount of misalignment in the width direction of the paper P is calculated and corrected, detection of the paper position can be started earlier. Note that in step S4, only the amount of misalignment calculated initially may be corrected, or the position correction using the calculated amount of misalignment may be continued until the paper P reaches the downstream roller 41.

[0041] After correcting the paper position, each CIS continues detecting the position of the paper P. It is then determined whether the misalignment of the paper P exceeds a threshold (step S5), and if so, abnormality processing is performed (step S6). If the threshold is not exceeded, detection of the paper position continues, and it is determined whether the paper position detection end position has been reached (step S7). Paper position detection continues until the detection end position is reached, and steps S5 and S7 are repeated. If the detection end position has been reached, paper position detection ends and the series of operations ends (step S8). The paper position detection end position can be set, for example, to the most downstream position at which the CIS can detect the paper position and calculate the amount of misalignment, and can be set to a position downstream of the position at which the conveyance of the paper P by the clamping rollers 31 ends. The above operations are performed for the number of sheets of paper to be continuously printed. However, this does not apply when the conveyance of the paper and the printing operation are stopped due to abnormality processing. Furthermore, if the paper position misalignment amount is calculated to be 0 in step S2, the position of the paper P is not corrected by the clamping rollers 31 in step S3. Even in this case, the procedures from step S4 onwards are carried out in the same manner. In other words, in this embodiment, "after correcting the position of the paper (recording medium), continue detecting the position of the paper P by each CIS (position detection means)" also includes the case where it is determined in step S2 that there is no misalignment of the paper and no correction is made.

[0042] As the threshold for positional displacement judged in step S5, a threshold may be set according to the amount of misalignment of the paper P in the width direction, and whether or not abnormality processing should be performed may be judged based on whether or not the actual amount of misalignment B exceeds this threshold, as shown in Fig. 6, for example. Alternatively, the amount of skew of the paper P may be set as a threshold, and whether or not abnormality processing should be performed may be judged based on whether or not the actual amount of skew α exceeds this threshold, as shown in Fig. 7, for example. Furthermore, thresholds may be set for both the amount of misalignment and the amount of skew in the width direction, and abnormality processing may be performed if either one exceeds the threshold.

[0043] Furthermore, when calculating the amount of skew of the sheet P, in addition to using the detection results from two CISs as described above, it may also be calculated from the detection results from one CIS. That is, as shown in Fig. 8, when the trailing edge of the sheet P passes the first CIS 34 on the upstream side and the sheet P is detected only by the second CIS 35 on the downstream side, the amount of skew α of the sheet P can be obtained using the detection results from the second CIS 35 at multiple different times. That is, in tan α = (B2 - B1) / C, B2 and B1 are calculated from the detection results at different times, and C can be calculated by replacing C with the time difference between the two detection results multiplied by the transport speed of the sheet P.

[0044] FIG. 9 shows the procedure for error processing when the amount of skew of the sheet P is calculated using only the second CIS 35. Steps S1 to S4 are the same as in FIG. 5. In step S5, it is determined whether or not to perform error processing based on the amount of skew of the sheet P. If the calculated amount of skew does not exceed the set threshold, it is determined whether or not the trailing edge of the sheet P has passed the first CIS 34 (step S11). In step S11, the passage of the sheet P may be determined based on the sheet length and the time elapsed since the sheet P passed a predetermined point, or it may be determined when the first CIS 34 is no longer able to detect the sheet P. Then, the amount of skew of the sheet P is calculated based only on the detection result of the second CIS 35 (step S12). It is determined whether or not to perform error processing based on this amount of skew. This operation is continued until the position at which detection of the sheet position ends. Note that if it is initially determined in step S11 that the trailing edge of the sheet P has passed the first CIS 34, the detection operation by the first CIS 34 ends.

[0045] Next, a control configuration for controlling the paper transport operation will be described with reference to the functional block diagram of FIG.

[0046] 10, paper transport control unit 51 notifies CIS control unit 52 of the start of transport of paper P. Based on this notification, CIS control unit 52 starts detecting the paper position using first CIS 34 or second CIS 35. The detection results by first CIS 34 and second CIS 35 are transmitted to correction calculation unit 53. Correction calculation unit 53 calculates the amount of positional deviation of paper P based on this detection result, and controls the driving of first drive motor 32 and second drive motor 33 based on the calculated amount of positional deviation. In this way, the position of paper P is corrected by the clamping rollers.

[0047] A first encoder 54 is provided on the motor shaft of the first drive motor 32, and a second encoder 55 is provided on the motor shaft of the second drive motor 33. These encoders indirectly detect the amount of movement of the clamping rollers, i.e., the amount of position correction made by the clamping rollers, and this detection result is fed back to the correction calculation unit 53. The correction calculation unit 53 adjusts the drive amounts of the first drive motor 32 and the second drive motor 33 based on the transmitted detection result. This makes it possible to correct the position of the paper P with high precision.

[0048] Even after the position correction of the paper P is completed, the correction calculation unit 53 receives the detection results from the first CIS 34 and the second CIS 35. If the calculated positional misalignment amount exceeds a threshold, the correction calculation unit 53 notifies the abnormality detection unit 56. The abnormality detection unit 56 notifies the paper transport control unit 51 of the abnormality, and the paper transport control unit 51 performs abnormality processing.

[0049] Next, the relationship between the length of the paper in the transport direction (hereinafter also referred to as the paper length) and the amount of paper positional deviation due to the nip pressure deviation of the downstream roller will be described with reference to FIG.

[0050] 11, if there is a deviation in the nip pressure of the downstream roller 41 in the width direction, for example if the nip pressure on the lower side of the downstream roller 41 in FIG. 11 is greater than the nip pressure on the upper side of the downstream roller 41 in FIG. 11, the paper P will be transported to the upper side of FIG. 11, where the pressure is lower, causing the paper P to be misaligned (see arrow A1). With regard to misalignment caused by the deviation in the nip pressure of the downstream roller 41, the longer the time that the paper P is held between the downstream rollers 41, the greater the amount of misalignment. In other words, the longer the paper length, the greater the amount of misalignment, and the greater the amount of misalignment of the image formed on the paper P, increasing the possibility of an abnormal image.

[0051] For the above reasons, the detection of the paper position after position correction to determine whether or not to perform abnormality processing may be performed only when the paper length is long. Specifically, as shown in the flow diagram of FIG. 12, after the position of the paper P is corrected by the clamping roller 31, it is determined whether the paper length is greater than a predetermined value (step S21), and if the paper length is short, the detection of the paper position by the CIS is terminated (step S8). As a method for the image forming device to recognize the paper length, the operator may input the length of the paper to be used in advance, or another detection means may be provided. Note that explanations of parts common to FIG. 5 are omitted.

[0052] In the embodiment shown in FIG. 13, the position at which detection of the paper position ends is changed depending on the paper length. Specifically, as shown in FIG. 13, after paper transport by the transport device begins, the timing to end detection of the paper position is first determined based on the paper length (step S31). This timing may be, for example, until the trailing edge of the paper P passes the first CIS 34 (the most upstream position detection means), and this timing may be calculated based on the paper length and the transport speed of the paper P by the transport device 30. In other words, in this case, the longer the paper length, the longer the detection section after position correction. Also, when detecting the paper position using only one CIS as in the embodiment shown in FIG. 9, the end timing may be calculated based on the timing at which the trailing edge of the paper P passes the most downstream CIS, for example, the timing at which the most downstream CIS detects the leading edge of the paper P, and this timing may be used as the end timing. Furthermore, these may be set to a timing earlier than the timing at which the trailing edge of the paper P passes each CIS by an estimated error, taking into account errors in the transport speed, etc.

[0053] In the subsequent step S7, detection of the paper position is terminated based on the determined termination timing. Note that the other steps are the same as those in the embodiment shown in FIG.

[0054] Although the conveying device 30 of the above embodiment has been described as having a first CIS 34 and a second CIS 35 as position detection means, the configuration of the position detection means of the conveying device of the present invention is not limited to this. For example, the conveying device 30 shown in Fig. 14 has a first CIS 34 and a second CIS 35 provided upstream and downstream of the pinch roller 31, respectively, and also has a third CIS 36 as position detection means further upstream of the first CIS 34.

[0055] In this embodiment, first, as shown in FIG. 14, when the leading edge of the paper P reaches the first CIS 34, the third CIS 36 and the first CIS 34 detect the position of the paper and calculate the amount of misalignment.

[0056] 15, before the leading edge of the paper P reaches the pinch rollers 31, the pinch rollers 31 perform a pick-up operation in which they rotate and move in the width direction by the calculated amount of misalignment. Specifically, in FIG. 15, the pinch rollers 31 rotate counterclockwise and move downward. This allows the pinch rollers 31 to pick up the paper P in a state where they are facing the paper P directly.

[0057] 16, when the paper P reaches the pinch rollers 31 and is pinched by them, the pinch rollers 31 rotate and move in the width direction by the same amount as during the pick-up operation, but in the opposite direction. This corrects the positional deviation of the paper P, as shown in FIG. 17. By having the pinch rollers 31 perform the pick-up operation in advance, the pinch rollers 31 after the position correction are positioned directly facing the conveyance path.

[0058] Then, as shown in FIG. 18, when the leading edge of the paper P reaches the second CIS 35, the first CIS 34 and the second CIS 35 detect the paper position and calculate the amount of paper misalignment. Based on this amount of misalignment, the clamping roller 31 performs a paper re-correction operation. During the re-correction operation, the amount of misalignment is fed back based on the momentary detection results of each CIS, enabling highly accurate position correction. Note that if the length of the paper P in the transport direction is long and spans three CISs, the detection results of the third CIS 36 may be used during the re-correction operation. The re-correction operation is performed, for example, until the leading edge of the paper P reaches the downstream roller 41. Note that the period during which the re-correction operation is performed is not limited to this, and the re-correction operation may end earlier.

[0059] After the re-correction operation, the CIS (e.g., the first CIS 34 and the second CIS 35) continues to detect the position of the paper, as in the previous embodiment. If the calculated positional deviation exceeds a threshold, abnormality processing can be performed. The series of operations is similar to, for example, steps S5 to S8 in FIG. 5. However, this is not limiting, and the series of procedures for determining abnormality processing may be performed using the procedures in FIGS. 9, 12, and 13. Furthermore, if the paper length is long, the detection result of the third CIS 36 may be used.

[0060] As described above, in the conveying device of this embodiment, by continuing the operation of detecting the paper position using the CIS after the re-correction operation, the above-mentioned abnormality processing can be performed if the amount of positional misalignment of the paper P is large. Therefore, problems caused by misalignment of the recording medium after position correction can be prevented. Also, while the case where three CISs are provided as position detection means has been described, any appropriate position detection means other than line sensors such as CISs can be provided as long as it can detect the paper position and calculate the amount of misalignment or tilt in the width direction.

[0061] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0062] In the above description, an image forming apparatus capable of mounting a post-processing device has been exemplified, but the image forming apparatus may not be mounted with a post-processing device, or the image forming apparatus may include a post-processing device. Furthermore, the entire image forming apparatus may be a conveying device. Furthermore, the conveying device of the present invention is not necessarily limited to a conveying device provided in an image forming apparatus.

[0063] The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may also be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0064] Recording media include sheet-shaped paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic film, prepreg, copper foil, etc.

[0065] The aspects of the present invention are as follows, for example. <1> a position detection means for detecting the position of the recording medium; a correction unit that corrects the position of the recording medium based on the detection result of the position detection unit, This conveying device is characterized in that after correcting the position of the recording medium by the correction means, the position of the recording medium is detected by the position detection means, and when the amount of positional deviation of the recording medium calculated based on this detection result exceeds a predetermined threshold, abnormality processing is performed. <2> calculating a positional deviation amount in a width direction perpendicular to a conveying direction of the recording medium based on a detection result of the position detection means; When the displacement amount in the width direction of the recording medium exceeds a predetermined threshold, an abnormality process is performed. <1> The conveying device is as described above. <3> calculating the amount of tilt of the recording medium based on the detection result of the position detection means; When the tilt amount of the recording medium exceeds a predetermined threshold, abnormality processing is performed. <1> or <2> The conveying device is as described above. <4> The position detection means includes an upstream detection means and a downstream detection means disposed downstream of the upstream detection means in the recording medium conveyance direction, After the trailing edge of the recording medium in the transport direction passes the upstream detection means, the downstream detection means detects the position of the recording medium, and the amount of tilt is calculated based on a plurality of detection results obtained by the downstream detection means at different times. <3> The conveying device is as described above. <5> Only when the length of the recording medium in the transport direction is greater than a predetermined value, the position detecting means detects the recording medium and performs the abnormality processing. <1> from <4> The conveying device according to any one of the preceding claims. <6> The section to be detected by the position detecting means is changed for each length of the recording medium in the transport direction. <1> from <5> The conveying device according to any one of the preceding claims. <7> As the abnormality processing, the conveyance of the recording medium is stopped. <1> from <6> The conveying device is as described above. <8> <1> from <7> The conveying device according to any one of claims 1 to 4, and an image forming section that forms an image on the recording medium. <9> <1> from <6> The conveying device according to any one of claims 1 to 4, an image forming unit that forms an image on the recording medium; a discharge section for discharging the recording medium after image formation; and another discharge portion, The image forming apparatus discharges the recording medium to the other discharge unit as the abnormality processing. <10> a detecting step of detecting the position of the recording medium by a position detecting means; a correcting step in which a correcting means corrects the position of the recording medium based on the detection result of the position detecting means; This is a conveying method characterized by including an abnormality processing step in which, after correction by the correction means, the position of the recording medium is detected by the position detection means, and abnormality processing is performed when the positional deviation amount of the recording medium calculated based on this detection result exceeds a predetermined threshold. [Explanation of symbols]

[0066] 10 Image forming device 10A Image forming unit 30 Conveyor device 31 clamping roller (correction means) 34 First CIS (position detection means or upstream detection means) 35 Second CIS (position detection means or downstream detection means) 36 Third CIS (position detection means) 60 Purge tray (other discharge section) 105 Stacker (discharge section) A Paper transport direction (direction of transport of recording media) P Paper (recording medium) [Prior art documents] [Patent documents]

[0067] [Patent Document 1] Patent No. 6587060

Claims

1. a position detection means for detecting the position of the recording medium; a correction unit that corrects the position of the recording medium based on the detection result of the position detection unit, A conveying device characterized in that after correcting the position of the recording medium by the correction means, the position of the recording medium is detected by the position detection means, and abnormality processing is performed when the positional deviation amount of the recording medium calculated based on this detection result exceeds a predetermined threshold.

2. calculating a positional deviation amount in a width direction perpendicular to a conveying direction of the recording medium based on a detection result of the position detection means; 2. The conveying device according to claim 1, wherein an abnormality process is carried out when the amount of displacement in the width direction of the recording medium exceeds a predetermined threshold value.

3. calculating the amount of tilt of the recording medium based on the detection result of the position detection means; 2. The conveying device according to claim 1, wherein an abnormality process is carried out when the amount of tilt of the recording medium exceeds a predetermined threshold value.

4. The position detection means includes an upstream detection means and a downstream detection means disposed downstream of the upstream detection means in the recording medium conveyance direction, A conveying device according to claim 3, wherein after the trailing end of the recording medium in the conveying direction passes the upstream detection means, the downstream detection means detects the position of the recording medium, and the amount of tilt is calculated based on multiple detection results detected at different times by the downstream detection means.

5. 2. The conveying device according to claim 1, wherein the position detecting means detects the recording medium and performs the abnormality processing only when the length of the recording medium in the conveying direction is greater than a predetermined value.

6. 2. The conveying device according to claim 1, wherein the section detected by the position detecting means is changed for each length of the recording medium in the conveying direction.

7. 2. The conveying device according to claim 1, wherein the abnormality processing is performed by stopping the conveyance of the recording medium.

8. A conveying device according to any one of claims 1 to 7; an image forming apparatus including an image forming section for forming an image on the recording medium;

9. A conveying device according to any one of claims 1 to 6; an image forming unit that forms an image on the recording medium; a discharge section for discharging the recording medium after image formation; and another discharge portion, The image forming apparatus discharges the recording medium to the other discharge unit as the abnormality processing.

10. a detecting step of detecting the position of the recording medium by a position detecting means; a correcting step in which a correcting means corrects the position of the recording medium based on the detection result of the position detecting means; a conveying method characterized by including an abnormality processing step in which, after correction by the correction means, the position of the recording medium is detected by the position detection means, and abnormality processing is performed when the positional deviation amount of the recording medium calculated based on this detection result exceeds a predetermined threshold.

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