JP2013018583A - Sheet conveyance device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveyance device that can properly correct a sheet skew even if a sheet is not rectangular like a tab sheet without complicating software control.SOLUTION: The sheet conveyance device includes: end detection sensors 6, 7 that detect the skews of the sheets S at its end; a line sensor 8 that detects the skew of the sheet S at its side; and skew correction rollers 2, 3 that are disposed to be perpendicular to a conveyance direction of the sheet S at a constant interval so that peripheral velocity differences enable the skew of the sheet S to be corrected. The skew of the sheet S is corrected by controlling peripheral velocities of the skew correction rollers 2, 3 based on detection results by the end detection sensors 6, 7 when the end detection sensors 6, 7 do not detect tabs of the sheets S, and a detection result by the line sensor 8 when the end detection sensors 6, 7 detect the tabs of the sheets S.

Description

  The present invention relates to a sheet conveying apparatus, and more particularly to a technique for correcting skew of a sheet such as a recording sheet being conveyed.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines, printers, and facsimiles are provided with a sheet conveying apparatus that conveys a sheet such as recording paper (paper) to the image forming unit. Some sheet conveying apparatuses include a skew correction unit that corrects the skew of the sheet in order to adjust the posture and position of the sheet before the sheet is conveyed to the image forming unit.

  As a method of correcting the skew of the sheet in the skew correction unit, the skew correction is performed by rotating the sheet while transporting it using two sensors and two sets of the skew correction rollers that rotate independently. There is a method (active resist system) to do (see Patent Document 1).

  In the active registration method, first, based on the sheet detection signals from the two sensors when the leading edge of the sheet crosses two sensors provided on the coaxial line orthogonal to the sheet conveying direction in the sheet conveying path. Detects skew at the tip. Subsequently, the skew amount of the sheet is detected based on detection signals from these two sensors. Thereafter, by controlling the rotational speeds of the two drive motors that drive the two sets of left and right skew correction rollers according to the detected skew amount, the sheet conveyance speed of the two sets of skew correction rollers is set to the sheet skew. Change according to the amount of lines to correct the skew of the sheet. More specifically, the sheet conveyance speed of the skew correction roller on one side is made slower (skew deceleration control) or faster than the conveyance speed of the skew correction roller on the opposite side according to the sheet skew amount. The skew of the sheet is corrected by (skew acceleration control).

  On the other hand, in recent years, the demand for image formation for various types of sheets has increased, and it is desired to pass sheets that are not necessarily rectangular, for example, sheets with tabs, to the image forming apparatus. The tabbed sheet is a sheet provided with a tab portion at the end for entering a headline or the like for classification. The position of the tab portion of the tabbed sheet is not constant. Specifically, the tab portion is provided so as to be shifted stepwise so that it is easy to confirm a headline or the like written in the tab portion.

  As such a skew correction method of the tabbed sheet, the tab position information is transmitted to the skew correction control unit, and the skew detection unit corresponding to the tab width is determined depending on whether or not the skew detection unit detects the tab part. There has been proposed a method of correcting skew information by correcting information from (see Patent Document 2).

Japanese Patent Application Laid-Open No. 10-032682. JP2003-146485A.

  In the technique proposed in Patent Document 2 above, when the tab portion of the tabbed sheet is at a position detected by the skew detection sensor, the tab width along the transport direction is set to the offset amount to be subtracted from the detected skew amount. It needs to be reflected. That is, the actual accurate offset amount is a value obtained by dividing the offset amount by COSθ when the skew angle is θ, and is slightly longer than the tab width along the transport direction.

  Therefore, in the method in which the tab width of the tabbed sheet is detected by the sensor and the tab width along the conveyance direction is used as the offset amount, the detected skew amount includes an error. Therefore, if skew correction is performed based on the detected skew amount, an image is not formed at a desired position with respect to the sheet. In addition, management of information such as the position and width of the tab portion for each conveyed sheet, and notification of such information to the skew correction control unit, make the control by software complicated. There's a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying apparatus capable of accurately correcting skew feeding even for a non-rectangular sheet such as a tabbed sheet without complicating control by software.

  The sheet conveying apparatus according to the present invention includes a leading edge detection sensor that detects a leading edge of a sheet to be conveyed, and a detection amount of a skew and a skew of the sheet based on detection signals of a plurality of leading edges of the sheet by the leading edge detection sensor. Based on a leading edge skew correction amount detection unit that calculates a row direction, a side edge detection sensor that detects a side edge position of the sheet, and detection signals of side edge positions at a plurality of positions of the sheet by the side edge detection sensor. The side edge skew correction amount detection unit for calculating the skew amount and skew direction of the sheet is disposed at different positions in the direction orthogonal to the sheet conveyance direction, and is driven independently to convey the sheet. While, the skew correction amount is calculated by each of the pair of skew correction rollers for correcting the skew of the sheet, and the leading edge skew correction amount detection unit and the side edge skew correction amount detection unit. Based on one side A roller drive control unit that independently controls the peripheral speeds of the pair of skew correction rollers and corrects the skew of the sheet, and the roller drive control unit detects the leading skew correction amount. When the difference between the skew amount calculated by the section and the skew amount calculated by the side edge skew correction amount detection unit exceeds a predetermined comparison value, the skew calculated by the side edge skew correction amount detection unit is calculated. The skew correction of the sheet is performed based on the line amount and the skew direction, and when the difference is equal to or smaller than the predetermined comparison value, the sheet is corrected based on the skew amount and the skew direction by the leading skew correction amount detection unit. The skew correction of the sheet is performed.

  According to the present invention, since it is not necessary to manage various pieces of information about the tabs by software, it is possible to avoid complication of control by software, and even if a non-rectangular sheet such as a tabbed sheet is accurately skewed. It can be corrected.

1 is a schematic configuration diagram of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention. FIG. 2 is a block diagram of a skew feeding correction device included in the sheet conveying device shown in FIG. 1. FIG. 3 is a peripheral speed chart of a decelerating roller during skew correction control by the roller drive control unit shown in FIG. 2. FIG. 3 is a diagram schematically illustrating the behavior of a sheet during sheet skew correction control in the sheet conveying apparatus illustrated in FIG. 1. FIG. 6 is another diagram (continuing from FIG. 4) schematically showing the behavior of the sheet during the sheet skew correction control in the sheet conveying apparatus shown in FIG. 1. FIG. 6 is a diagram illustrating a sheet skew correction control operation in the sheet conveying apparatus illustrated in FIG. 1.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Schematic configuration of image forming apparatus>
FIG. 1 is a schematic configuration diagram of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention. The image forming apparatus includes a photosensitive drum 100 and a laser scanner 101. The image forming apparatus irradiates a photosensitive drum 100, which is an image carrier, with laser light from the laser scanner 101 based on image information, and an electrostatic latent image is formed on the photosensitive drum 100. Form. The photosensitive drum 100 is driven in the rotation direction indicated by an arrow B by a motor (not shown).

  A charger 102 for uniformly charging the photosensitive drum 100 is disposed on the upstream side in the rotation direction of the photosensitive drum 100 with respect to the laser beam irradiation position by the laser scanner 101. Further, on the downstream side of the laser beam irradiation position by the laser scanner 101 with respect to the photosensitive drum 100, a developing device 103 that develops the electrostatic latent image formed on the photosensitive drum 100 with toner and forms a toner image. Is provided.

  An endless transfer belt 106 is wound around a roller 105, and is a primary transfer charge for transferring a toner image from the photosensitive drum 100 to the transfer belt 106 at a position facing the photosensitive drum 100 via the transfer belt 106. A container 108 is arranged. A secondary transfer roller 107 for transferring the toner image from the transfer belt 106 to the sheet S is disposed at a position facing one roller 105 via the transfer belt 106. The transfer belt 106 rotates in the direction of arrow A in accordance with the rotation driving of the roller 105.

  The toner image is transferred and formed on the transfer belt 106 from the photosensitive drum 100 by the primary transfer charger 108, and then transferred from the transfer belt 106 to the sheet S by the secondary transfer roller 107. A cleaner 104 that scrapes off excess toner on the photosensitive drum 100 is disposed downstream of the position where the primary transfer charger 108 is disposed with respect to the photosensitive drum 100.

  The image forming apparatus includes a cassette 109 that stores sheets such as recording paper and an OHP sheet, and the sheet S is supplied from the cassette 109 to the secondary transfer roller 107 by a paper feed roller 110. The sheet S taken out from the cassette 109 by the paper feed roller 110 is transferred by the vertical path roller 113 to the transport rollers 114 and 115 disposed downstream of the image forming reference sensor 1.

  The sheet S is transferred from the conveyance roller 115 to the skew correction rollers 2 and 3. Details of the configuration of the skew correction rollers 2 and 3 will be described later with reference to FIG. A pair of leading edge detection sensors 6 and 7 are arranged on the upstream side of the skew feeding correction rollers 2 and 3 in the sheet conveying direction and are arranged perpendicular to the conveying direction of the sheet S and detect the leading edge of the conveyed sheet S. ing. Further, a line sensor 8 as a side edge detection sensor that detects a side edge position (hereinafter referred to as “side position”) of the sheet S at a timing described later between the skew correction rollers 2 and 3 and the leading edge detection sensors 6 and 7. Is arranged. The sheet S is transferred from the skew feeding correction rollers 2 and 3 to the secondary transfer roller 107 (and the roller 105 facing the secondary transfer roller 107).

  In the image forming apparatus, the skew correction control unit 116 controls the speed of the skew correction rollers 2 and 3, and the image control unit 111 receives a laser beam detection signal from the laser scanner 101, and synchronizes with the laser light detection signal. An image pulse corresponding to the image data is transmitted to the scanner 101. The laser beam detection signal is generated when a laser beam reflected by a polygon mirror (not shown) that deflects the laser beam built in the laser scanner 101 is detected by a laser beam detection sensor.

  In the image forming apparatus, the controller 112 temporarily stores image data transmitted from a PC or a reader, and based on the image request signal and the horizontal synchronization signal from the image control unit 111, the image data is transferred to the image control unit 111. Send to. The horizontal synchronization signal is generated based on a laser light detection signal output from a photosensor (not shown) built in the laser scanner 101. After a predetermined number of horizontal synchronization signals are counted based on the image request signal, the controller 112 transmits image data to the image control unit 111 every predetermined number of lines in synchronization with the horizontal synchronization signal. The image data is converted by the image control unit 111 into image pulses having a pulse width corresponding to the data level.

<Image Forming Operation in Image Forming Apparatus>
When the sheet S is fed from the cassette 109 and the leading edge of the sheet S is detected by the image formation reference sensor 1, the image formation reference sensor 1 outputs a detection signal to the image control unit 111. Upon receiving this detection signal, the image control unit 111 outputs an image request signal to the controller 112. The controller 112 transmits the image data to the image control unit 111 in synchronization with the horizontal synchronization signal according to the received image request signal, and the image control unit 111 transmits an image pulse corresponding to the image data to the laser scanner 101.

  The laser scanner 101 rotates laser light corresponding to the received image pulse (or laser light modulated based on image data corresponding to data from an image memory (not shown)) in the direction indicated by the arrow B. Irradiate onto the photosensitive drum 100. The photosensitive drum 100 is charged in advance by a charger 102, and an electrostatic latent image is formed on the photosensitive drum 100 by irradiation with laser light.

  The electrostatic latent image formed on the photosensitive drum 100 is developed by the developing unit 103, thereby forming a toner image. The toner image thus formed on the photosensitive drum 100 is transferred onto the transfer belt 106 by the action of the primary transfer bias voltage applied by the primary transfer charger 108. On the other hand, the sheet S is skew-corrected by the skew correction rollers 2 and 3 via the conveying rollers 114 and 115. The toner image transferred onto the transfer belt 106 is transferred by the secondary transfer roller 107 to the sheet S thus corrected for skew.

<Sheet skew correction>
In the sheet conveying apparatus according to the present embodiment, the portion (skew correction apparatus) related to the skew correction of the sheet in the mechanism that conveys the sheet S as described above in the image forming apparatus is the center (characteristic configuration). Yes. Therefore, next, a skew correction apparatus related to the skew correction control unit 116 will be described.

  FIG. 2 is a block diagram showing a configuration of the skew feeding correction apparatus. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG. When the image forming reference sensor 1 detects the leading edge of the sheet S conveyed from the upstream side of the sheet conveying path, it outputs a detection signal to the side edge skew correction amount detection unit 10. The skew correction rollers 2 and 3 arranged at different positions in the width direction of the sheet S (the direction parallel to the sheet surface and perpendicular to the sheet conveying direction) are independently driven by motors (stepping motors) 4 and 5, respectively. Is done. Each of the skew feeding correction rollers 2 and 3 has a pair of structures that sandwich the sheet S therebetween.

  The skew correction of the sheet S can be performed by making the conveyance speeds of the skew correction rollers 2 and 3 different. In the present embodiment, skew correction is performed in such a manner that one of the skew correction rollers 2 and 3 decelerates from a low speed.

  The leading edge detection sensors 6 and 7 are also sensors that are arranged at different positions in the width direction of the sheet S and take the start timing of the skew correction rollers 2 and 3. That is, when the leading edge detection sensor 6 detects the leading edge of the sheet S, the skew feeding correction roller 2 starts to rotate after a lapse of a predetermined time. When the leading edge detection sensor 7 detects the leading edge of the sheet S, the skew is detected after the lapse of a predetermined time. The rotation of the row correction roller 3 is started. Control related to the start of rotation of the skew correction rollers 2 and 3 is performed by the roller drive control unit 18.

  The line sensor 8 is arranged such that its longitudinal direction is perpendicular to the sheet conveying direction and parallel to the sheet surface. The line sensor 8 is configured such that when the first detection position of the sheet S conveyed in the “conveying direction” indicated by an arrow in FIG. 2 reaches just below the line sensor 8 and the second detection position of the sheet S is the line sensor 8. The position of the side edge of the sheet S is detected at each time when it reaches directly below. Note that the side edge position refers to the position of a side of the sheet S that is substantially parallel to the sheet conveyance direction. The first detection position is the position of the sheet S that has reached the position immediately below the line sensor 8 after the first time has elapsed since the image forming reference sensor 1 detected the leading edge of the sheet S. The second detection position is the position of the sheet S that has reached the position immediately below the line sensor 8 after a lapse of a second time longer than the first time since the image forming reference sensor 1 detected the leading edge of the sheet S. .

  Although details will be described later, the first detection position and the second detection position are separated from each other by a certain distance in the conveyance direction of the sheet S, and are detected at two positions of the first detection position and the second detection position, respectively. The difference between them indicates the skew amount of the sheet S. The detection signal of the line sensor 8 is sent to the side edge skew correction amount detection unit 10.

  The side edge skew correction amount detection unit 10 obtains the side edge position of the sheet S based on the detection signal from the line sensor 8, and calculates the skew direction and the amount of skew of the sheet S. The side edge skew correction amount detection unit 10 controls the light emission of a light source (LED) built in the line sensor 8 with respect to the line sensor 8. In addition, the side edge skew correction amount detection unit 10 transmits to the line sensor 8 a horizontal synchronization signal and a control clock for outputting charge information charged in the photoelectric element built in by the reflected light by the light emission of the LED. .

  The base area facing the line sensor 8 in the sheet conveyance path is black (painted), and absorbs the light of the LED of the line sensor 8. The surface of the sheet S is different from the base area. Therefore, the side edge skew correction amount detection unit 10 can detect the side edge position of the sheet S from the output level difference of the photoelectric elements that receive the reflected light. The management of the detection timing of the side edge position of the sheet S by the line sensor 8, that is, the setting management of the first detection position and the second detection position is performed based on the leading edge detection signal of the sheet S by the image forming reference sensor 1 ( Details will be described later with reference to FIGS. 4C and 5A). The setting management of the first detection position and the second detection position may be based on the leading edge detection signal of the sheet S by the leading edge detection sensor 6 or the leading edge detection sensor 7.

  The side edge skew correction amount detection unit 10 determines a “side edge detection skew direction” indicating the skew direction of the sheet S. The side edge skew correction amount detection unit 10 detects the distance from the predetermined reference position to the side edge position of the sheet S detected at the first detection position of the sheet S at the second detection position of the sheet S. When the distance to the side edge position of the sheet S is longer than “1”, the side edge detection skew direction is set to “1”. In this case, the skew is preceded by the left side of the sheet S toward the downstream side in the conveyance direction of the sheet S.

  As shown in FIG. 2, the “reference position” is set at one end of the line sensor 8 outside the sheet conveyance path. The distance from the reference position to the side edge position of the sheet S detected at the first detection position of the sheet S is “dot1” shown in FIG. Further, the distance from the reference position to the side edge position of the sheet S detected at the second detection position of the sheet S is “dot2” shown in FIG. 'Dot1' and 'dot2' are each indicated by the number of dots based on the configuration of the photoelectric elements included in the line sensor 8.

  The side edge skew correction amount detection unit 10 detects the side edge detection skew amount by the line sensor 8 at the second detection position of the sheet S from the number of dots detected by the line sensor 8 at the first detection position of the sheet S. A value obtained by subtracting the number of dots is obtained and output to the conversion unit 19 described later.

  On the other hand, the side edge skew correction amount detection unit 10 detects the distance from the reference position to the side edge position of the sheet S detected at the first detection position of the sheet S at the second detection position of the sheet S. When the distance to the side edge position of S is the same or shorter, the side edge detection skew direction is set to “0”. Then, the side edge skew correction amount detection unit 10 uses the line sensor 8 at the first detection position of the sheet S from the number of dots detected by the line sensor 8 at the second detection position of the sheet S as the side edge detection skew amount. A value obtained by subtracting the detected number of dots is obtained and output to the conversion unit 19 described later.

  The skew correction control unit 116 includes a leading skew correction amount detection unit 11 that detects a time difference when the leading edge of the sheet S passes the leading edge detection sensors 6 and 7 based on detection signals of the leading edge detection sensors 6 and 7. ing. When the detection signal input time of the tip detection sensor 6 is earlier than the tip detection sensor 7, the tip skew correction amount detection unit 11 sets the tip detection skew direction to “1” and the detected time difference is a system clock (not shown). The count value counted in is output as the tip detection skew amount. Further, when the detection signal input time of the tip detection sensor 6 is later than or at the same time as the tip detection sensor 7, the tip skew correction amount detection unit 11 sets the tip detection skew direction to “0” and detects the time difference of detection. Is output as the tip detection skew amount.

  The skew correction control unit 116 converts the side edge detection skew amount expressed by the number of dots of the line sensor 8 detected by the side edge skew correction amount detection unit 10 into the leading edge detection skew amount expressed by the system clock. A conversion unit 19 for converting into a corresponding amount is provided.

  The conversion formula used in the conversion unit 19 is as follows. As shown in FIG. 2, the distance between the leading edge detection sensors 6 and 7 is ‘L1’, and the distance between the first detection position and the second detection position of the sheet S is ‘L2’. Further, the distance of one dot of the line sensor 8 is “dotD”, the skew amount (number of dots) of the sheet S output by the side edge skew correction amount detection unit 10 is “dotNUM”, and one cycle of the system clock. The distance that the sheet S is conveyed is defined as “clkD”. Then, the side edge detection skew amount is converted into (L1 × dotD × dotNUM) / (L2 × clkD), which is an amount corresponding to the tip detection skew amount represented by the system clock.

  The skew correction control unit 116 outputs the leading edge detected skew amount output from the leading edge skew correction amount detection unit 11 and the converted side edge detected skew amount output from the conversion unit 19 (a tip detection skew amount equivalent amount). Has an addition unit 13 for calculating the amount of addition. The skew correction control unit 116 also outputs the tip detection skew amount output from the tip skew correction amount detection unit 11 and the converted side edge detection skew amount output from the conversion unit 19 (a tip detection skew amount equivalent amount). ) Has a subtracting unit 14 for calculating a difference amount.

  The skew correction control unit 116 includes an XOR 12 and a first selector 15. The first selector 15 uses the exclusive OR output from the XOR 12 having the side edge detection skew direction and the tip detection skew direction as inputs as a selection signal. When the value is “1”, the first selector 15 outputs the output from the adder 13. In the case of “0”, the output from the subtracting unit 14 is selected. Therefore, the first selector 15 outputs a difference between the side edge detection skew amount (amount corresponding to the tip detection skew amount) and the tip detection skew amount.

  The skew correction control unit 116 includes a comparison unit 16 that compares the output of the first selector 15 with a predetermined comparison value, and the comparison unit 16 determines that the output of the first selector 15 is equal to or less than the comparison value. 1 is output, and when the output of the first selector 15 exceeds the comparison value, “0” is output. The skew correction control unit 116 includes a second selector 17 that uses the output of the comparison unit 16 as a selection signal. When the output value from the comparison unit 16 is “1”, the skew correction control unit 116 has a tip skew. The tip detection skew amount and the tip detection skew direction from the row correction amount detection unit 11 are selected. On the other hand, when the output value from the comparison unit 16 is “0”, the second selector 17 performs the side edge detection skew direction from the side edge skew correction amount detection unit 10 and the converted value from the conversion unit 19. Select the side edge detection skew amount (equivalent to the tip detection skew amount). The second selector 17 outputs the selected skew direction and skew amount to the roller drive controller 18.

  The roller drive control unit 18 transmits a pulse signal to the motors 4 and 5 to drive the motors 4 and 5 to rotate the skew correction rollers 2 and 3. The roller drive control unit 18 starts the rotation of the skew feeding correction roller 2 at the timing when the leading edge detection sensor 6 detects the leading edge of the sheet S, and increases the rotational speed (circumferential speed) to a steady speed. Further, the roller drive control unit 18 starts the rotation of the skew feeding correction roller 3 at the timing when the leading edge detection sensor 7 detects the leading edge of the sheet S, and increases the rotational speed (circumferential speed) to a steady speed.

  Thereafter, the roller drive control unit 18 starts skew correction after a predetermined time has elapsed with reference to the tip detection sensor 6 or 7 with the later detection timing. Specifically, in this skew correction, first, a skew correction roller that decelerates is selected based on the skew direction and skew amount selected from the second selector 17, and the target speed at the time of deceleration is Calculated. When the skew direction from the second selector 17 is ‘1’, the skew correction roller 2 is a deceleration target, and when it is ‘0’, the skew correction roller 3 is a deceleration target. Hereinafter, the skew correction roller to be decelerated is appropriately referred to as a “deceleration side roller”.

  When the skew amount is zero (0), the roller drive control unit 18 does not perform skew correction regardless of the signal indicating the skew direction, and rotates both the skew correction rollers 2 and 3 at a steady speed. Let When the skew amount occurs, the roller drive control unit 18 calculates the deceleration target speed so that the skew amount = correction time × (steady speed−deceleration target speed). Then, the roller drive control unit 18 controls the rotation of the deceleration side roller so that the deceleration target speed is maintained until the correction time elapses from the start of deceleration. Next, such control will be described in detail with reference to FIG.

  FIG. 3 is a peripheral speed chart of the decelerating side roller during the skew correction control by the roller drive control unit 18. When the skew correction sensor corresponding to the deceleration side roller detects the leading edge of the sheet S at time t1, the peripheral speed of the deceleration side roller is accelerated from the self-starting speed VS to the steady speed V0. After the peripheral speed of the speed reducing roller reaches the steady speed V0 at time t2, the speed reducing roller pinches the conveyed sheet. The control up to this point is similarly performed for the skew correction roller that does not perform the deceleration control.

  At time t3, the deceleration side roller starts to decelerate, and the peripheral speed changes from the steady speed V0 to the deceleration target speed V1. The correction time at the time of skew correction is set to a predetermined time in advance for the convenience of the configuration of the apparatus. The target speed V1 during deceleration is set so that the area of the shaded portion: [(V0−V1) × correction time] is equal to the skew amount. At time t4, the speed transition from the deceleration target speed V1 to the steady speed V0 is started, and the skew correction is completed when the peripheral speed of the roller returns to the steady speed V0. Note that 'correction time = t4-t3'. Thereafter, at the time t5 when the trailing edge of the sheet S passes through the skew detection sensor and the sheet S is released from the holding state of the deceleration side roller, the steady speed V0 of the peripheral speed of the deceleration side roller is changed to the self-starting speed VS. The deceleration starts and stops.

<Flow of Sheet S and Flow of Skew Correction Control>
Next, the conveyance mode (behavior during conveyance) of the sheet S and the flow of the skew correction control of the sheet S will be described with reference to FIGS. 4 and 5. 4 and 5 are diagrams schematically illustrating the behavior of the sheet S during the sheet skew correction control in the sheet conveyance path. In FIGS. 4 and 5, notations other than the skew feeding correction rollers 2 and 3, the tip detection sensors 6 and 7, and the line sensor 8 are omitted.

  FIG. 4A shows a state where the leading edge detection sensor 7 has detected the tab portion of the sheet S. As a result, the skew feeding correction roller 3 starts rotating, and the leading edge skew correction amount detection unit 11 outputs “0” as the leading edge skewing direction and starts counting the skew amount by the system clock. FIG. 4B shows a state where the leading edge detection sensor 6 has detected the sheet S. As a result, the skew correction roller 2 starts rotating, the leading skew correction amount detection unit 11 stops counting the skew amount, and outputs the leading edge detected skew amount.

  FIG. 4C shows a state where the first detection position of the sheet S has reached directly below the line sensor 8. The internal counter of the side edge skew correction amount detection unit 10 starts counting after receiving the output signal from the image forming reference sensor 1. The first detection position is set as a position where the count value by the internal counter becomes a predetermined count value set in advance.

  At this time, the side edge skew correction amount detection unit 10 outputs a control signal to the line sensor 8, and the line sensor 8 outputs due to the reflected light from the sheet S and the reflected light from the ground area. The level of the analog signal corresponding to each dot is determined. Then, the side edge skew correction amount detection unit 10 determines the dot position (that is, the number of dots indicating the distance from the reference position to the side edge position of the sheet S) that matches the signal whose level exceeds a predetermined threshold value. Stack as dot1 '.

  FIG. 5A shows a state in which the second detection position of the sheet S has reached directly below the line sensor 8. The second detection position is also set as a position where the internal counter of the side edge skew correction amount detection unit 10 has a predetermined count value. At this time, the side edge skew correction amount detection unit 10 stacks “dot2” as in the case of the first detection position described above. In this embodiment, since “dot1” is larger than “dot2”, the side edge skew correction amount detection unit 10 outputs “1” as the side edge detection skew direction. On the other hand, since the leading edge detection skew direction from the leading skew correction amount detector 11 is ‘0’, the output from the XOR 12 is ‘1’.

  Therefore, the first selector 15 outputs a value obtained by adding the leading edge detection skew amount and the side edge detection skew amount by the adding unit 13. The output value from the first selector 15 is compared with a predetermined comparison value by the comparison unit 16. The output value from the first selector 15 is the difference between the skew amount at the leading edge of the sheet S and the skew amount at the side edge position, and both the leading edge detection sensors 6 and 7 must detect the tab portion of the sheet S. For example, the output value from the first selector 15 is a value close to zero (0).

  That is, the comparison value used in the comparison unit 16 is an index for determining whether one of the leading edge detection sensors 6 and 7 is detecting the tab portion of the sheet S. The comparison value is set within an allowable error range of the skew amount, such as a difference between the skew amounts of the two sides resulting from an allowable right-angle error of the sheet S, for example. In this embodiment, the leading edge detection sensor 7 detects a tab, and the difference in skew amount between the leading edge and the side edge of the sheet S is significant. Therefore, the output value from the first selector 15 is larger than the comparison value, and in this case, the comparison unit 16 outputs “0”.

  When receiving the output “0” from the comparison unit 16, the second selector 17 selects the side edge detection skew amount and the side edge detection skew direction from the side edge skew correction amount detection unit 10, and performs roller drive control. To the unit 18. The roller drive control unit 18 receives '1' in the side edge detection skew direction as the skew direction, and the skew correction roller 2 on the side where the leading edge of the sheet S precedes changes the peripheral speed at the timing shown in FIG. Thus, the drive of the motor 4 is controlled. Thereby, the skew correction of the sheet S is completed as shown in FIG.

  4 and 5 show the case where the tab portion of the sheet S is detected by the leading edge detection sensor 7, but when the tab portion of the sheet S is not detected by any of the leading edge detection sensors 6 and 7, There is almost no difference between the tip detection skew amount and the side edge detection skew amount. In this case, the input to the XOR 12 is the same, and the output is '0'. Thereby, in the first selector 15, the output from the subtracting unit 14 is selected as the difference between the leading edge detection skew amount and the side edge detection skew amount. Since the selected value is a difference value, the comparison unit 16 determines that the selected difference is equal to or less than the comparison value, and outputs “1”. The second selector 17 selects the tip detection skew amount and the tip detection skew direction based on the output “1”, and transmits it to the roller drive controller 18. Therefore, the roller drive control unit 18 controls the skew feeding correction roller based on the information of the tip detection sensor.

  As described above, when the tab portion of the sheet S is not detected by the leading edge detection sensors 6 and 7, the skew correction control unit 116 corrects the skew of the sheet S based on the detection information, and the tab of the sheet S is corrected. When the leading edge is detected by the leading edge detection sensors 6 and 7, the skew correction of the sheet S is performed based on the detection information by the line sensor 8.

  The reason for performing such control is that the leading edge skew detection by the leading edge detection sensors 6 and 7 has higher detection accuracy than the side edge skew detection by the line sensor 8. Therefore, the difference in detection accuracy between the leading edge skew detection and the side edge skew detection will be described. In the configuration of FIG. 2, it is assumed that the system clock for counting the difference in detection timing in the skew detection of the leading edge is 20 MHz and the sheet conveyance speed is 500 mm / s. Further, it is assumed that the distance L1 between the tip detection sensors 6 and 7 is 150 mm.

  In this case, the distance that the sheet S is conveyed during one period 50 ns of the system clock is 0.025 μm. Therefore, according to the tip detection sensors 6 and 7, a resolution of 0.025 μm can be obtained per 150 mm which is the distance L1 between the tip detection sensors 6 and 7.

  On the other hand, assuming that the distance L2 (see FIG. 2) between the first detection position and the second detection position when detecting side edge skew is 100 mm, even if a line sensor 8 of 4800 dpi is used, Has a resolution of 7.9375 μm. From these detection accuracy values, the tip skew detection by the tip detection sensors 6 and 7 has much higher resolution per unit length than the side edge skew detection by the line sensor 8, that is, the detection accuracy is higher. I understand that it is expensive.

  Therefore, when the leading edge detection sensors 6 and 7 do not detect the tab portion of the sheet S as in the present embodiment, the skew detection information by the leading edge detection sensors 6 and 7 is used, so that the accuracy is high. Skew correction can be performed.

<Skewing Correction Control Operation of Sheet S by Skew Correction Control Unit 116>
FIG. 6 is a diagram illustrating a skew correction control operation for one sheet S performed in the skew correction control unit 116. First, when the sheet S is conveyed from the upstream side of the sheet conveyance path and both the leading edge detection sensors 6 and 7 detect the leading edge of the sheet S (step S1), the leading edge skew correction amount detection unit 11 detects the leading edge skew amount. Is calculated (step S2).

  When the sheet S is conveyed by the skew correction rollers 2 and 3 and the first detection position of the sheet S reaches just below the line sensor 8, the side edge position 1 of the sheet S by the side edge skew correction amount detection unit 10 is detected. A second detection is performed (step S3). When the sheet S is further conveyed and the second detection position of the sheet S reaches just below the line sensor 8, the second detection of the side edge position of the sheet S is performed by the side edge skew correction amount detection unit 10 (Step S1). S4).

  The side edge skew correction amount detection unit 10 calculates the side edge detection skew amount from the side edge position information detected in steps S3 and S4 (step S5). Next, the XOR 12 determines the difference in skew direction between the leading edge skew detection and the side edge skew detection (step S6). The first selector 15 outputs the output from the subtraction unit 14 as a difference between the two skew amounts when the skew direction is the same, and outputs the output from the addition unit 13 when both the skew directions are different. The difference is output as the skew amount difference (step S7).

  Subsequently, the comparison unit 16 compares whether or not the difference between the tip detection skew amount and the side edge detection skew amount is larger than a predetermined comparison value (step S8). When the difference is larger than the comparison value (“YES” in S8), the second selector 17 selects the side edge skew detection amount and the side edge skew direction, and the roller drive control unit 18 determines the sheet S based on the information. Skew correction is executed (step S9). On the other hand, when the difference is equal to or smaller than the comparison value (“NO” in S8), the leading skew detection amount and the leading skew direction are selected by the second selector 17, and based on the information, the roller drive control unit 18 determines the sheet S. Skew correction is performed (step S10). By executing step S9 or step S10, the skew correction of one sheet S is completed.

  As described above, in this embodiment, the leading edge detected skew amount based on the leading edge of the sheet S is compared with the side edge detected skew amount based on the side edge position of the sheet S, and a tab is formed on the leading edge of the sheet S. It is determined whether or not the tip detection sensors 6 and 7 detect whether or not there is a portion. If the leading edge detection sensors 6 and 7 do not detect the tab portion, the skew correction of the sheet S is performed based on the leading edge detection skew amount, and if the leading edge detection sensors 6 and 7 detect the tab portion. The skew correction of the sheet S is performed based on the side edge detection skew amount.

  As a result, it is not necessary to perform correction such as subtracting the offset amount using the leading skew information when detecting the tab portion of the sheet S as in the prior art. Further, since the sheet conveying apparatus itself determines whether or not the leading edge detection sensors 6 and 7 have detected the tab portion, it is not necessary to manage various information regarding the tab portion by software. Thereby, complication of control by software can be avoided, and a sheet having a tab portion can be accurately skew-corrected.

  The skew correction control unit 116 may be configured by a CPU, and the CPU may execute the skew correction control operation described above with software.

<Other embodiments>
Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of this invention, and it is also possible to combine each embodiment suitably.

  For example, in the above embodiment, the first detection position and the second detection position of the sheet S are set by a predetermined count value by the internal counter of the side edge skew correction amount detection unit 10, and at this time, the count start by this internal counter is started. A signal from the image formation reference sensor 1 was used as a trigger for the above. However, the present invention is not limited to this, and a signal received from one or both of the tip detection sensors 6 and 7 may be used as a trigger for starting counting by the internal counter.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program code. It is a process to be executed. In this case, the program and the storage medium storing the program constitute the present invention.

DESCRIPTION OF SYMBOLS 1 Image formation reference sensor 2,3 Skew correction roller 6,7 Tip detection sensor 8 Line sensor 10 Side edge skew correction amount detection part 11 Tip skew correction amount detection part 18 Roller drive control part 116 Skew correction control part

Claims (3)

A leading edge detection sensor for detecting the leading edge of the conveyed sheet;
A leading edge skew correction amount detection unit that calculates a skew amount and a skew direction of the sheet based on detection signals of a plurality of leading edge sides of the sheet by the leading edge detection sensor;
A side edge detection sensor for detecting a side edge position of the sheet;
A side edge skew correction amount detector that calculates a skew amount and a skew direction of the sheet based on detection signals of a plurality of side edge positions of the sheet by the side edge detection sensor;
A pair of skew correction rollers that are arranged at different positions in a direction perpendicular to the sheet transport direction and that are driven independently to correct the skew of the sheet while transporting the sheet;
The peripheral speed of each of the pair of skew correction rollers is determined based on one of the skew amount and the skew direction calculated by each of the leading skew correction amount detection unit and the side edge skew correction amount detection unit. A roller drive control unit that independently controls and corrects the skew of the sheet,
When the difference between the skew amount calculated by the leading skew correction amount detection unit and the skew amount calculated by the side edge skew correction amount detection unit exceeds a predetermined comparison value, the roller drive control unit The skew correction of the sheet is performed based on the skew amount and the skew direction calculated by the side edge skew correction amount detection unit, and when the difference is equal to or smaller than the predetermined comparison value, the leading edge skew is performed. A sheet conveying apparatus that performs skew correction of the sheet based on a skew amount and a skew direction by a correction amount detection unit.   The sheet conveying apparatus according to claim 1, wherein a resolution per unit length by the leading edge detection sensor is higher than a resolution per unit length of the side edge detection sensor. The leading edge detection sensors are a pair of sensors that are arranged at different positions in the direction orthogonal to the sheet conveying direction and detect the leading edge of the conveyed sheet,
The leading edge skew correction amount detection unit calculates the skew amount and skew direction of the sheet based on a time difference at which each of the leading edge detection sensors detects the leading edge of the sheet,
The side edge detection sensor is a line sensor whose longitudinal direction is a direction orthogonal to the sheet conveyance direction,
The side edge skew correction amount detection unit is configured to skew the sheet based on the side edge position of the sheet detected by the side edge detection sensor at two positions apart from the sheet by a certain distance in the sheet conveyance direction. 3. The sheet conveying apparatus according to claim 1, wherein the amount and the skew direction are calculated.

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