JP2011042447A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve skew correction efficiency, by effectively using moving operation of register roller pairs for moving a sheet in the width direction. <P>SOLUTION: This image forming device 60 includes a register device 65 having this side-innermost side movable units 82A and 82B respectively arranged on both sides of a carrying passage 84 and correcting a skew of the sheet by registering the side end of the sheet and the register roller pairs 7 for making the center of the sheet coincide with the center CT of the carrying passage by moving the sheet of registering the side end by this side-innermost side movable units in the width direction of the carrying passage 84. Since register roller pairs 7 stop by holding and moving the sheet of correcting the skew by one movable unit among this side-innermost side movable units to the center CT of the carrying passage and moves the sheet to the center of the carrying passage by holding the sheet continuously carried by correcting the skew by the other movable unit from its stopped state, reciprocating operation in the sheet width direction is effectively used. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet whose skew has been corrected by a sheet skew correcting device.

  In the image forming apparatus, the skew of the sheet and the positional deviation in the width direction of the sheet that occur during the conveyance of the sheet include sheet jamming, poor delivery between the image forming apparatus and the optional apparatus, and the positional deviation of the image forming position with respect to the sheet. It was the cause of the outbreak. For this reason, some conventional image forming apparatuses include a registration device as a sheet skew correction device that corrects the skew of a sheet, as described in Japanese Patent Application Laid-Open No. H10-228707. A plan view of the resist device is shown in FIG. FIG. 8 is a diagram for explaining the operation of the registration apparatus. In FIG. 8, hatched portions indicate main parts related to the operation of each process.

  The registration device 400 corrects the skew of the sheet that is conveyed (so-called center reference conveyance) by making the center in the width direction coincide with the center CT in the width direction of the conveyance path 84 that conveys the sheet. The registration device 400 is provided, for example, instead of the registration device 65 of the image forming apparatus shown in FIG. In the following description, FIG. 6 may be used. In that case, the registration device 65 in FIG. 6 is replaced with the registration device 400, and the registration roller pair 7 is replaced with the registration roller pair 75, and FIG. .

  The sheet is transferred from the upstream conveying unit to the pre-slope feeding roller pair 1a and 1b and conveyed in the direction of arrow F (sheet conveying direction). At this time, since the sheet has been transported through a long transport path from the sheet feeding unit, errors in the transport timing are accumulated. For this reason, after the passage timing is detected by the pre-registration sensor 4, the sheet is temporarily stopped at the position sandwiched between the pre-slope feeding roller pair 1 b and the accumulated error is reset. The sheet is conveyed to the skew feeding unit 401 (FIG. 8A).

  The skew feeding unit 401 includes a fixed guide 70 and a movable guide 71 that can reciprocate in the direction of arrow J (the width direction of the sheet) in the drawing depending on the size of the sheet. The movable guide 71 is configured as a unit including an abutting reference guide 73 and a pair of inclined feeding rollers 72a to 72c that are inclined by a predetermined angle so as to generate a conveying component in a direction in which the sheet is abutted against the abutting reference guide 73.

  The movable guide 71 can be adjusted to an optimum position in a direction orthogonal to the sheet conveyance direction of the abutting reference guide 73 according to the size of the sheet. The optimum position in the main scanning direction means a position obtained by adding a margin G to the end position K of the nominal image in the main scanning direction of the image (or sheet) defined by the center reference. That is, some sheets have variations in position in a direction orthogonal to the sheet conveyance direction of the sheet conveyed on the center reference. The optimum position of the direction position orthogonal to the sheet conveyance direction is to ensure that the sheet follows the abutting reference guide 73 without interfering with the entrance of the abutting reference guide 73 even if the sheet varies in this way. Offset position.

  Accordingly, the sheet whose skew has been corrected by the skew feeding roller pairs 72a to 72c and the abutting reference guide 73 is displaced from the nominal image position by an amount corresponding to the abutting G. For this reason, the registration roller pair 75 as the moving means downstream of the skew feeding unit 401 abuts in the direction of the arrow R1 in the figure orthogonal to the sheet G while conveying the sheet in the direction of arrow F (sheet conveyance direction) in the figure. Only the sliding movement is made (FIG. 8B).

  When the conveyance of the sheet by the skew feeding roller pairs 72a to 72c is started, the upstream pre-slip feeding roller pair 1a, 1b releases the nip. When the registration roller pair 75 starts sliding, the skew feeding roller pairs 72a to 72c release the nip.

  The sheet having both the skew and the reference position in the direction orthogonal to the sheet conveying direction corrected in the above manner is further conveyed between the downstream secondary transfer outer roller 66 (FIG. 6) and the intermediate transfer belt 606. Then, the toner image is transferred. When conveyance by the secondary transfer outer roller 66 is started, at the same time, as shown in FIG. 8C, the registration roller pair 75 releases the nip and abuts in preparation for the next job. Returning to the direction of arrow R2 in FIG. 7 by G (home position operation is performed). In this way, when the registration roller pair 75 returns to the home position and the trailing edge of the sheet (Nth) of the previous job passes through the registration roller pair 75, as shown in FIG. The sheet ((N + 1) th) enters the skew feeding unit 401. N is a positive integer.

(Reciprocating (reciprocating) timing)
FIG. 9 shows a time chart regarding the reciprocating operation of the registration roller pair 75 described in FIG. In addition, the numerical value taken up is a reference numerical value and is not a limited numerical value. FIG. 9 is a timing chart showing operation timing of a reciprocating motor (pulse motor) which is a driving source of reciprocating operation, timing of nip attaching / detaching operation of a registration roller pair, and sheet passing timing of the registration roller pair in the same time axis from the top. It is.

  Assuming that the timing at which the Nth sheet enters the registration roller pair 75 is t = 0 ms, the registration roller pair 75 is in a nip-attached state in which the rollers are in contact with each other to convey the sheet, and the designated image is displayed. The reciprocating operation starts to return the sheet to the position. Therefore, the drive pulse of the reciprocating motor is started from 0 pps to the self-starting frequency PLs and accelerated to the steady frequency PLt. When a general 42 mm square pulse motor that generates an appropriate driving torque is used as the reciprocating motor, the self-starting frequency PLs = 600 pps and the steady frequency PLt = 690 pps, and the acceleration time t 1 from PLs to PLt is about 10 ms. Cost. Similarly, when the reciprocating motor is stopped, deceleration time t2 = about 10 ms is required.

  Further, assuming that the driving specification of the reciprocating operation is a driving accuracy of about 0.1 mm per pulse, a total input of 100 pulses is required when the contact G = 10 mm. Of these, the number of pulses required between the acceleration time t1 = 10 ms and the deceleration time t2 = 10 ms is about 6.5 pulses from the self-starting frequency PLs = 600 pps and the steady frequency PLt = 690 pps, that is, a total of about 13 pulses is required. It will be.

  Therefore, the time required for the reciprocating operation at the steady frequency PLt = 690 pps is (103−10) / (690 × 1000) ≈126 ms. From the above, when the reciprocating operation is started at t = 0 ms, it takes 10 + 126 + 10 = 146 ms to complete the operation of the predetermined movement amount (butting G = 10 mm), and it takes about 150 ms. This state is a position A in FIG. 9, that is, a state where the sheet has been moved in accordance with the nominal image position.

  Here, the distance from the registration roller pair 75 to the secondary transfer outer roller 66 in FIG. 7 is 130 mm, the conveyance speed of the registration roller pair 75 is 600 mm / s, and the image forming speed is 300 mm / s. The sheet coincides with the image at the secondary transfer outer roller 66 from the passage timing of the post-registration sensor 12 and the passage timing of the image on the intermediate transfer belt 606 detected by the image detection sensor 2 (FIG. 6). Thus, the speed is reduced from 600 mm / s to 300 mm / s.

  Considering this deceleration, the time for the leading edge of the sheet to reach the secondary transfer outer roller 66 from the registration roller pair 75 is approximately 370 ms. Since this state is the position B in FIG. 9 and A <B, it can be seen that the movement of the registration roller pair 75 is completed sufficiently before the sheet reaches the secondary transfer outer roller 66. 9B is also a position where the secondary transfer outer roller 66 (FIG. 6) and the intermediate transfer belt 606 start conveying the sheet.

  When the sheet is conveyed to the secondary transfer outer roller 66, as shown in FIG. 9, the registration roller pair 75 is in a nip-removed state, and the reciprocating motor is reversely rotated to start returning to the home position. At this time, the self-starting frequency PLs = 600 pps, the steady frequency PLt = 690 pps, the acceleration time t1 = 10 ms, and the deceleration time t2 = 10 ms are similarly required, so that it takes about 150 ms for the registration roller pair 75 to return to the home position. .

  Accordingly, in terms of the accumulated time, it can be seen that a series of reciprocating operations are completed at the time of 370 + 150 = 520 ms, that is, the position C in FIG. 9, and the time required for the registration roller pair 57 to make one round trip is 520 ms. Become.

  On the other hand, the time required for the trailing edge of the sheet reaching the secondary transfer outer roller 66 to pass through the registration roller pair 75 is (L-130) / (300 × 1000), where L is the sheet length in the transport direction. (Ms). In other words, the smaller the size, the faster it will come out. For example, in the B5 size (L = 182 mm), it will come out in about 173 ms.

  Accordingly, it can be seen from the accumulated time that the sheet completely leaves the registration roller pair 75 at the time of 370 + 173 = 543 ms, that is, at the position D in FIG. Since C <D, it can be seen that the reciprocating operation of the registration roller pair 75 is completed immediately before the sheet exits the registration roller pair 75.

  After the sheet passes through the registration roller pair 75, the next (N + 1) th sheet is obliquely fed at a time point of an accumulation time of 600 ms (position E in FIG. 9) that takes a margin of conveyance timing (about 50 ms). Part 401 is entered. At this time, again, the registration roller pair 75 is in the nip state and the reciprocating motor starts to start.

JP 2005-314045 A

  In the time chart shown in FIG. 9, the criterion for making the (N + 1) th sheet enter the skew feeding unit 401 is whether or not the Nth sheet has passed the registration roller pair 75 because C <D. . Within the range in which this relationship is maintained, if the interval between the Nth sheet and the (N + 1) th sheet is reduced, that is, the interval between D and E in FIG. 9 is reduced, the image forming speed of the image forming apparatus is changed. Thus, the productivity of the image forming apparatus can be improved. Productivity is the number of sheets on which an image is formed per unit time.

  However, there is a limit to reducing the sheet interval. This will be described below.

  In order to greatly improve the productivity of the image forming apparatus, it is generally performed to increase the image forming speed. When the image forming speed of the image forming apparatus is increased with respect to the registration apparatus 400 that operates according to the time chart shown in FIG. 9, the relationship of the time chart changes as shown in FIG. Since the drive specifications of the reciprocating motor are the same, the position of A does not change in about 150 ms, but the position of B where the leading edge of the sheet reaches the secondary transfer outer roller 66 and the trailing edge of the sheet are the registration roller pair. The position of D, which is the time through 75, is shortened.

  However, the section from B to C, which is the time required for the return operation of the registration roller pair 75, remains unchanged. For this reason, when the image forming speed exceeds a certain value, the relationship of C> D in FIG. 9 is reversed as in the time chart shown in FIG. That is, in FIG. 10, a relationship of C <D is established. For example, when the calculation is performed under the condition of the image forming speed of 300 mm / s in FIG. 9, the reversal of the relationship of C> D occurs when the image forming speed is about 347 mm / s. Thus, when the relationship C> D is reversed, even if the Nth sheet passes through the registration roller pair 75, the registration roller pair 75 has not yet returned to the home position. For this reason, the next criterion for making the (N + 1) th sheet enter the skew feeding unit 401 is determined by whether or not the reciprocating operation is completed.

  In addition, when switching the reciprocating motor from rotating in the direction to return to the home position to reverse rotation again, the reciprocating motor is reduced by the amount of damping time so that the pulse does not step out due to vibration due to inertia of the driven object or gear backlash. Need to be stopped. Although this decay time depends on the configuration of the drive system, it needs to be at least about 50 ms, and the timing E at which the (N + 1) th sheet reaches the registration roller pair 75 is about 50 ms after C at the earliest. N is a positive integer.

  As described above, since the determination criterion for causing the (N + 1) th sheet to enter the skew feeding unit 401 is waiting for completion of the reciprocating operation, even if an attempt is made to increase the image forming speed of the image forming apparatus, the operation restriction of the reciprocating motor eventually results. This makes it difficult to improve productivity.

  In order to eliminate such a state, for example, it is necessary to change the reciprocating motor as the driving means to a higher-spec one. However, the cost increases significantly, and the reciprocating motor increases in size, which may increase the size of the apparatus.

  The present invention provides an image forming apparatus including a sheet skew correction device that corrects skew of a sheet that is conveyed with the center in the width direction aligned with the center in the width direction of a conveyance path that conveys the sheet. The purpose is to improve.

  The present invention includes a sheet skew correction device that corrects the skew of a sheet that is conveyed by making the center in the width direction coincide with the center of the width direction of the conveyance path for conveying the sheet. In an image forming apparatus that forms an image on a sheet whose line has been corrected by an image forming unit, a pair of skews that are arranged on both sides of the conveyance path and that correct the skew of the sheet by aligning the side edges of the sheet. Line correction means, and moving means for moving a sheet whose side edges are aligned by the pair of skew correction means in the width direction of the conveyance path so that the center of the sheet coincides with the center of the conveyance path. The pair of skew correction means alternately correct the skew of the sheets continuously conveyed on the conveyance path, and the moving means is one of the pair of skew correction means. Holding the sheet whose skew has been corrected by the line correcting means, The sheet is moved to the center of the sheet and stopped, and then, from the stopped state, the sheet is continuously skew-corrected by the other skew-correcting unit and held and moved to the center of the transport path. It is characterized by.

  In the image forming apparatus according to the present invention, the moving unit moves the sheet, which has been skew-corrected by one skew correcting unit, to the center of the conveyance path and stops, and from the stopped state, the other skew correcting unit The skew-corrected sheet is moved to the center of the conveyance path. For this reason, the sheet skew feeding correction device of the present invention returns the individual skew-corrected sheets to the center of the conveyance path during the forward and backward movements of the reciprocating movement of the moving means in the sheet width direction. Thus, the skew correction efficiency of the sheet can be increased.

  Since the image forming apparatus of the present invention includes the sheet skew correcting device that increases the sheet skew correcting efficiency, the image forming efficiency can be increased.

FIG. 2 is a plan view of a registration device as a sheet skew correction device and a transport unit before and after the registration device in the embodiment of the present invention. It is a figure for operation | movement description of the registration apparatus of FIG. 2 is a time chart for explaining the operation of the registration apparatus of FIG. 1. It is a perspective view of a registration roller unit. It is a perspective view of the drive part of a registration roller unit. FIG. 2 is a schematic cross-sectional view along the sheet conveying direction of the image forming apparatus in the embodiment of the present invention. FIG. 6 is a plan view of a registration device as a conventional sheet skew correction device and a conveyance unit before and after the registration device. It is a figure for operation | movement description of the registration apparatus of FIG. 8 is a time chart for explaining the operation of the registration apparatus of FIG. 8 is a time chart for explaining operations when the sheet conveyance speed is increased in the registration apparatus of FIG.

  Hereinafter, a registration apparatus as a sheet skew correction apparatus according to an embodiment of the present invention and an image forming apparatus including the registration apparatus in an apparatus main body will be described with reference to the drawings. FIG. 6 is a schematic cross-sectional view along the sheet conveyance direction of the image forming apparatus according to the embodiment of the present invention.

  The image forming apparatus 60 is a color image forming apparatus that employs a so-called intermediate transfer tandem system in which four color photosensitive drums 608 are arranged along an intermediate transfer belt 606.

(Sheet feeding process)
The sheets S are stacked and stored on the lift-up device 62 in the sheet storage 61. The sheet S is fed by the paper feeding unit 63 in accordance with the image formation timing. The sheet feeding unit 63 separates and feeds the sheets one by one by air separation and adsorption. The sheet S sent out by the paper supply unit 63 passes through a transport path 64 a included in the transport unit 64 and is transported to the registration device 65. The sheet S is subjected to skew correction and timing correction by the registration device 65 and then sent to the secondary transfer unit 74. The secondary transfer portion 74 is formed by the opposing secondary transfer inner roller 603 and secondary transfer outer roller 66, and forms a toner image transfer nip portion to the sheet S. The secondary transfer unit 74 transfers a toner image onto the sheet S by applying a predetermined pressure and an electrostatic load bias to the sheet.

(Image formation process of image)
An image forming process of the toner image sent to the secondary transfer unit 74 in accordance with the timing at which the sheet S is fed to the secondary transfer unit 74 will be described. The image forming unit 613 mainly includes a photosensitive drum 608, an exposure unit 611, a developing unit 610, a primary transfer unit 607, a photosensitive drum cleaner 609, and the like. An exposure unit 611 is driven on the photosensitive drum 608 whose surface is uniformly charged in advance by a charger (not shown) and rotated in the direction of the arrow m in FIG. An electrostatic latent image is formed through the mirror 612 and the like as appropriate. This electrostatic latent image is visualized as a toner image on the photosensitive drum 608 through toner development by the developing device 610. Thereafter, the toner image is transferred to the intermediate transfer belt 606 by applying a predetermined pressure and an electrostatic load bias to the intermediate transfer belt 606 by the primary transfer unit 607. The transfer residual toner slightly remaining on the photosensitive drum 608 is collected by the photosensitive drum cleaner 609 and used again for the next image formation.

  In FIG. 6, the image forming unit 613 includes four sets of yellow (Y), magenta (M), cyan (C), and black (Bk).

  Next, the intermediate transfer belt 606 will be described. The intermediate transfer belt 606 is stretched around a driving roller 604, a tension roller 605, and a secondary transfer inner roller 603, and circulates in the direction of arrow n in the figure. The image forming process of each color processed in parallel by the image drums 608 of Y, M, C, and Bk described above is performed by applying the downstream color toner image onto the upstream color toner image primarily transferred onto the intermediate transfer belt 606. This is done at the timing of overlapping. As a result, a full-color toner image is finally formed on the intermediate transfer belt 606. The full-color toner image is conveyed to the secondary transfer unit 74 by the intermediate transfer belt 606.

(Process after secondary transfer)
As described above, the full-color toner image is secondarily transferred onto the sheet S in the secondary transfer unit 74 by the sheet feeding process and the image forming process described above. Thereafter, the sheet S is conveyed to the fixing device 68 by the pre-fixing conveyance unit 67. The fixing device 68 fixes the toner image on the sheet S by a predetermined pressure applied by a pair of opposing rollers (or a belt pair) and a heat source such as a heater. The sheet S on which the toner image is fixed is directly discharged onto the discharge tray 600 by the branch conveyance device 69.

  When a toner image is formed on both sides of a sheet, the sheet is conveyed to a reverse conveying device 601 and conveyed in a switchback, the front and back ends are reversed, the front and back are reversed, and the double-sided conveying device 602 is transferred. Be transported. Thereafter, the sheet S joins the refeed path 64 b of the transport unit 64 and is sent to the secondary transfer unit 74 at a timing that does not interfere with subsequent sheets transported from the sheet storage 61. Since the image forming process on the back surface (second surface) is the same as the image forming process on the front surface (first surface) described above, description thereof is omitted.

  Note that the image forming apparatus 60 employs a switchback method to reverse the sheet S upside down. At the time of switchback, the front and rear edges of the sheet are interchanged, so the common reference side on the front and back can be the edge along the sheet conveyance direction, not the sheet conveyance direction edge (sheet leading edge). (Side end) is preferable.

  Therefore, the registration device 65 in the image forming apparatus 60 employs a skew feeding registration system that is non-stop skew correction in which the side edge of the sheet is obliquely butted against the butting guide portions 16 and 18. Further, in order to reverse the sheet, the image forming apparatus 60 is configured to convey the sheet on the basis of the center by aligning the center in the width direction of the sheet with the center in the width direction of the conveyance path for conveying the sheet. .

(Configuration of resist device 65)
FIG. 1 is a plan view of the resist device 65 and the transport unit before and after the resist device 65. The conveying direction of the sheet is an arrow F direction in the figure. The portion shown in FIG. 1 is mainly divided into a pre-registration conveyance unit 81, a skew feeding unit 82, a slide unit 83, and a secondary transfer unit 74 from upstream. The skew feeding portion 82 and the slide portion 83 constitute a registration device 65. These units are arranged along a conveyance path 84 through which the sheet is conveyed.

  The pre-registration conveyance unit 81 includes a pair of pre-slipping rollers 1a and 1b, a pre-registration sensor 4, and a conveyance guide 3. The pre-registration conveyance unit 81 temporarily stops the sheet S at the position of the pre-slipping roller pair 1b based on the detection signal from the pre-registration sensor 4 in order to reset the accumulated error of the conveyance timing that occurs during the long conveyance path. It is supposed to let you.

  Next, the skew feeding part 82 is composed of a front side movable unit 82A and a back side movable unit 82B. The front side movable unit 82A is formed by the movable guide 13, the skew feeding roller pairs 5a to 5c, and the front side reference guide 8, and is unitized. The back side movable unit 82B is formed by the movable guide 14, the skew feeding roller pairs 6a to 6c, and the back side reference guide 9, and is unitized.

  The image forming apparatus 60 according to the present embodiment aligns the center of the sheet in the width direction with the center (CT) in the width direction of the conveyance path that conveys the sheet, and forms the image on the sheet and conveys the sheet. This is done based on the center.

  For this reason, both the movable units 82A and 82B can reciprocate by an equal amount in the directions opposite to each other in the directions of the arrows J1 and J2 to the optimum standby positions according to the size of the sheet S, respectively. Here, the optimum standby position means a position obtained by adding a margin G to the end position K of the nominal direction in the direction orthogonal to the sheet conveyance direction of the image (or sheet) defined by the center reference. This is because, when the variation in the position of the side edge of the sheet conveyed on the basis of the center is eliminated along the one of the front side reference guide 8 and the back side reference guide 9, the reference guides 8 and 9 to be moved along. This is to prevent the sheet from interfering with the entrance of the sheet. Therefore, the sheet S, whose skew has been corrected by the front side reference guide 8 or the back side reference guide 9, is the sheet width direction (in the direction of the arrow J1 or the arrow J2) by the amount of G against the nominal image position. ) Is misaligned.

  Next, the slide portion 83 includes the conveyance guide 10, the registration roller unit 40 (FIGS. 4 and 5), the pre-registration sensor 11, and the post-registration sensor 12. The registration roller pair 7 is supported by a support mechanism so as to be movable in the directions of arrows R1 and R2 in FIG. The registration roller pair 7 sandwiches the sheet S in the directions of the arrows R1 and R2 in order to adjust the position in the width direction of the sheet S that has been offset by the amount of contact G to the image position on the intermediate transfer belt 606 (FIG. 6). It can be moved. The registration roller pair 7 is moved in the directions of arrows R1 and R2 by a reciprocating motor 57 (FIG. 5) described later.

  When the registration roller pair 7 sandwiches the sheet and moves in the directions of arrows R1 and R2 in FIG. 1, it is necessary to release at least the nips of the upstream feeding roller pairs 5a to 5c and 6a to 6c. . The timing for releasing the nip is based on the detection operation of the pre-registration sensor 4.

  Next, the secondary transfer unit 74 includes the secondary transfer outer roller 66 and the secondary transfer inner roller 603 shown in FIG. In the secondary transfer unit 74, the timing at which the sheet S is fed between the secondary transfer outer roller 66 and the intermediate transfer belt 606, and the timing at which the toner image on the intermediate transfer belt 606 is sent to the secondary transfer outer roller 66. And come to fit. This sheet feeding timing is performed based on the detection of the passage of the toner image on the intermediate transfer belt 606 by the image detection sensor 2 in FIG. 6 and the detection of the passage of the sheet S by the post-registration sensor 12. The sheet feeding timing is achieved by changing the deceleration timing of the conveyance speed by the registration roller pair 7. The above-described plan view of FIG. 1 is a diagram in which necessary driven rollers and guide plates are omitted for convenience of explanation, but these are actually provided.

(Description of skew correction operation of registration device 65)
The skew correction operation by the registration device 65 having the above configuration will be described with reference to FIG. FIG. 2A is a diagram illustrating a state in which a certain Nth sheet is conveyed to the skew feeding unit 82. When the N-th sheet is conveyed to the skew feeding section 82, the skew feeding roller pairs 5a to 5c are in a state where a nip is formed, and the opposite skew feeding roller pairs 6a to 6c are in a state where the nip is released. It has become. Therefore, only the skew feeding roller pairs 5a to 5c contribute to the conveyance of the sheet. As a result, the sheet is conveyed obliquely toward the near-side reference guide 8 and is skewed along the abutting surface 16. The registration roller pair 7 is prepared for conveyance with the nip released and kept at the near side standby position Pf.

  At this time, when the size of the Nth sheet is a large size exceeding, for example, the A3 size, the rear end portion (upstream end portion) of the sheet that has been conveyed obliquely (tilted) and changed its posture is the opposite. It may be damaged by interfering with the vicinity of the entrance of the rear reference guide 9 on the side. Therefore, as shown in FIG. 1, an abutting guide portion 17 that is opened outward by a certain angle with respect to the conveying direction F with respect to the abutting surface 18 is formed at the upstream end portion of the back side reference guide 9. is there. Similarly, an abutting guide portion 15 is also formed on the near side reference guide 8.

  In FIG. 2A, the front-side reference guide 8 and the back-side reference guide 9 are respectively referred to from the end position K of the designation in which the selected sheet size width is equally distributed with respect to the image formation and conveyance center CT. , Is at an offset position separated by G. Therefore, the side edge of the Nth sheet whose skew has been corrected is shifted in position by G when it abuts against the near side. Further, the registration roller pair 7 disposed downstream of the oblique feeding portion 82 is brought to the near side standby position Pf by a reciprocating motor 57 (FIG. 5) described later.

  The sheet that has been skew-feeded to the skew-feed roller pairs 5a to 5c and has been skewed and corrected by abutting G toward the near side is fed to the registration roller pair 7 with the nip released. The registration roller pair 7 forms a nip, holds the sheet, conveys it in the direction of arrow F, and plays a role of returning the deviation of G by abutting the sheet.

  That is, as shown in FIG. 2B, the registration roller pair 7 moves in the direction of the arrow R1 from the near side standby position Pf while nipping and conveying the sheet, and stops at the back side standby position Pr. At this time, the sheet is slid in the direction of the arrow R1 by the registration roller pair 7, but the nips of the skew feeding roller pairs 5a to 5c are all released so as not to inhibit this sliding movement. The registration roller pair 7 moves the sheet in the direction of the arrow R1 while conveying the sheet in the direction of the arrow F. However, in order to ensure the operation, the registration roller pair 7 moves the sheet in the direction of the arrow R1 and then conveys the sheet in the direction of the arrow F. May be.

  In this way, the reference position of the sheet in the direction orthogonal to the skew and the sheet conveyance direction is corrected, and the relative positional relationship with the image on the intermediate transfer belt 606 (FIG. 6) is matched. At this time, the next (N + 1) th sheet is temporarily stopped at the position of the pre-slip feed roller pair 1b described with reference to FIG.

  As shown in FIG. 2C, when the trailing edge of the Nth sheet passes through the registration roller pair 7 and the waiting (N + 1) th sheet is conveyed to the skew feeding unit 82, The pair of skew feeding rollers 6a to 6c forms a nip, and the pair of skew feeding rollers 5a to 5c on the near side releases the nip. Therefore, only the back-side oblique feed roller pairs 6a to 6c contribute to the conveyance of the sheet. As a result, the (N + 1) th sheet is conveyed obliquely toward the back side reference guide 9 and along the abutting surface 18, and the skew correction is completed. The side edge of the (N + 1) th sheet whose skew has been corrected is displaced from the center (CT) by the distance G against the back reference guide 9 side. At this time, the registration roller pair 7 releases the nip and is ready for conveyance while being moved to the back side standby position Pr.

  As shown in FIG. 2C, the sheet whose skew has been corrected along the abutting guide surface 18 of the back side reference guide 9 is sandwiched between the registration roller pair 7. As shown in FIG. 2D, the registration roller pair 7 moves in the direction of arrow R2 while nipping and conveying the sheet in the direction of arrow F, and moves from the registration roller back side standby position Pr to the front side standby position Pf. Moving. At this time, all the nips of the skew feeding roller pairs 6a to 6c are released so that the sliding movement of the sheet is not hindered. In this way, the reference position of the (N + 1) th sheet in the direction orthogonal to the skew and the sheet conveying direction is corrected similarly to the Nth sheet, and the relative positional relationship with the image on the intermediate transfer belt 606 is corrected. Combined. At this time, the (N + 2) th sheet waiting at the position of the upstream skew feeding roller pair 1b is then subjected to skew correction again in the same manner as the operation shown in FIG. .

(Configuration in which the registration roller pair 7 is reciprocated (reciprocated))
FIG. 4 shows a registration roller unit in which the registration roller pair 7 and a drive device that causes the registration roller pair 7 to perform a reciprocating operation (reciprocating operation) between the front standby position Pf (FIG. 2) and the back standby position Pr are shown in FIG. This will be described with reference to FIG.

  FIG. 4 is an overall perspective view of the registration roller unit 40. The registration roller pair 7 includes a driving roller 7b and a driven roller 7a. A reciprocating drive ring 41 is fixed to a reciprocating shaft 44 which is a shaft of the driving roller 7b. A reciprocating driven ring 42 is fixed to the shaft 45 of the driven roller 7a. The reciprocating driven ring 42 is fitted so as to be sandwiched between the flanges 46 at both ends of the reciprocating drive ring 41.

  Thus, when the driving roller 7b performs a reciprocating operation in the longitudinal direction, the driven roller 7a also performs a reciprocating operation in conjunction with the contact of the flange 46. The driven roller 7a is brought into contact with and separated from the driving roller 7b by a device (not shown). This contact and separation can also be performed because the reciprocating driven ring 42 is fitted to the flanges 46 at both ends of the reciprocating drive ring 41. A reciprocating drive 43 is connected to the reciprocating shaft 44.

  FIG. 5 is a detailed view of the reciprocating drive unit 43. The reciprocating shaft 44 is provided with a registration roller driving gear 50 so as to rotate integrally, and further, a holder 52 is provided so as to support the reciprocating shaft 44 rotatably. The registration roller driving gear 50 meshes with the idler gear 51. A registration conveyance motor (not shown) that rotates the drive roller 7 b is connected to the upstream of the idler gear 51.

  The holder 52 is coupled by an idler belt 501 and a reciprocating connecting plate 53. The idler belt 501 is stretched around idler pulleys 54 and 55. The idler pulley 55 and the reciprocating drive pulley 59 are fixed on the same shaft 55a supported by the idler shaft holder 502 and rotate integrally.

  The reciprocating drive pulley 59 is rotated by a reciprocating motor 57 via a driving belt 500 and a motor pulley 58. The reciprocating motor 57 is attached to the motor support plate 56. The idler shaft holder 502 that supports the shafts 54 a and 55 a of the idler pulleys 54 and 55 is supported by a support member (not shown) that is different from the motor support plate 56.

  In the above configuration, when the reciprocating motor 57 rotates in the CW direction (forward direction) and the CCW direction (reverse direction), the reciprocating operation of the driving roller 7 b is performed by the connection between the idler belt 501 and the holder 52. Further, the idler gear 51 has a tooth width in consideration of the reciprocating range so as to be compatible with the reciprocating operation.

  In FIG. 2, the two near side standby positions Pf and back side standby position Pr to which the registration roller pair 7 moves are obtained by attaching a sensor flag to the holder 52, for example, and separately detecting the sensor flag by an optical sensor. Can be detected.

(Reciprocating operation time chart)
The registration device 65 uses two reference guides 8 for consecutive sheets such as the Nth and (N + 1) th, that is, the odd-numbered and even-numbered continuous jobs, or the first and second sides of the double-sided image forming job. , 9 can alternately perform skew correction. As a result, the registration device 65 can increase productivity without being restricted by the conventional operation constraints of electric parts such as the reciprocating motor 57.

  These points will be described based on a time chart of the operation of the resist device shown in FIG. In order to clarify the effect of the present invention, the specification of the reciprocating motor 57 is the same as that of the conventional reciprocating motor, and the configuration of the image forming apparatus is different from that of the registration apparatus except for the conventional image. The configuration is the same as that of the forming apparatus, but is not limited thereto. Further, the same parts as those in the prior art are denoted by the same reference numerals.

  FIG. 3 is a time chart assuming that t = 0 ms when the Nth sheet reaches the registration roller pair 7. Moreover, FIG. 3 shows a case where skew correction of a small size sheet (for example, B5) is performed for a short time from when the leading edge of the sheet enters the secondary transfer outer roller 66 until the trailing edge passes through the registration roller pair 7. Is assumed.

  Since the drive specifications of the reciprocating motor are the same as those in FIGS. 9 and 10, the self-starting frequency PLs = 600 pps and the steady frequency PLt = 690 pps, and the operation shown in FIG. The timing for completing A is about 150 ms. In addition, the timing of B when the leading edge of the sheet reaches between the outer side of the secondary transfer outer roller 66 and the intermediate transfer belt 606 and the timing of D when the trailing edge of the sheet passes through the registration roller pair 7 increased the image forming speed. The same as the conventional case of FIG. Furthermore, t1 is the acceleration time of the reciprocating motor and t2 is the deceleration time of the reciprocating motor, both of which are 10 ms.

  In the registration device 65 of the present invention, the pair of registration rollers does not reciprocate once for one sheet, but the pair of registration rollers reciprocates once for two sheets. Therefore, the operation of the reciprocating motor 57 is completed sufficiently before the position D where the trailing edge of the sheet passes through the registration roller pair 7. Therefore, the criterion for making the next (N + 1) th sheet enter the skew feeding section 82 is determined whether or not the trailing edge of the Nth sheet has passed through the registration roller pair 7, that is, at time D in FIG. . If the timing of D can be defined, E, that is, the (N + 1) th sheet feeding portion 82 entry timing can be created so that the margin of the conveyance timing (for example, about 50 ms) is between D and E.

  As described above, the resist device 65 is not affected by the operation of the reciprocating motor 57 even if the image forming speed of the image forming apparatus is increased, and thus the productivity can be improved.

  Incidentally, if the image forming speed is increased without changing the structure of the image forming apparatus, there is no physical relationship of B ≧ D. If the image forming speed is further improved from the state of FIG. Eventually, it will be reversed as A> B. However, since the relationship of A> B means that the reference position alignment in the direction orthogonal to the sheet conveying direction cannot be performed before the leading edge of the sheet reaches the secondary transfer outer roller 66, this is the production. The upper limit of sex. However, in other words, productivity can be improved by increasing the image forming speed of the image forming apparatus without being affected by the operation restriction of the reciprocating motor 57 until the relationship is reversed to the relationship of A> B.

  In the embodiment described above, three skew feeding roller pairs are arranged in the conveying direction, but the number of arrangement is not limited to this.

  As described above, the registration device 65 serving as the sheet skew correction device is a pair of skew corrections that are arranged on both sides of the conveyance path 84 and correct the skew of the sheet by aligning the side edges of the sheet. A front side movable unit 82A and a back side movable unit 82B are provided as means. Further, the registration device 65 moves the sheet whose side ends are aligned by the front side movable unit 82A and the back side movable unit 82B in the width direction of the conveyance path 84 so that the center of the sheet coincides with the center of the conveyance path 84. A registration roller pair 7 is provided as means. Then, the front side movable unit 82A and the back side movable unit 82B are configured to alternately correct the skew of the sheets continuously conveyed on the conveyance path 84.

  In such a configuration, the registration roller pair 7 holds the sheet whose skew has been corrected by one of the front and back movable units 82A and 82B and moves it to the center CT of the conveyance path 84. It comes to stop. Subsequently, the registration roller pair 7 is moved from the stopped state to the center CT of the conveyance path 84 while holding the sheet that has been skew-corrected by the other movable unit and continuously conveyed. .

  For this reason, the registration device 65 of the present invention uses different sheets, which are skew-corrected, at the center CT of the conveyance path during the forward and backward movements of the registration roller pair 7 in the sheet width direction. It can be returned and productivity can be increased.

  Further, the registration device 65 of the present invention is configured such that the front and back movable units 82A and 82B as the skew feeding correcting means move the sheet in the width direction of the conveyance path 84, and the registration roller pair 7 conveys the sheet. The distance moved to the center of the path 84 is set to be the same.

  For this reason, the registration apparatus 65 of the present invention can make the center in the width direction of the sheet coincide with the center in the width direction of the conveyance path 84, regardless of which movable unit is used to correct the skew of the sheet.

  Further, the front and back movable units 82A and 82B in the registration device 65 of the present invention include reference guides 8 and 9 provided along the sheet conveyance direction. Further, the near side and back side movable units 82A and 82B are a pair of skew feeding rollers 5a to 5c as a skew feeding means that obliquely conveys the sheet from the center CT of the conveyance path 84 toward the reference guides 8 and 9. And 6a to 6c.

  For this reason, the registration device 65 of the present invention can correct the skew of the sheet while conveying the sheet, and can improve productivity.

  Further, the registration roller pair 7 in the registration device 65 of the present invention has a driving roller 7 b and a driven roller 7 a as a pair of rotating bodies that can move toward and away from each other and can move in the width direction of the conveyance path 84. . The driving roller 7b and the driven roller 7a receive the sheet that is skew-corrected while being separated from each other, and then convey the sheet to the downstream side in the sheet conveying direction while holding the sheet and moving it to the center CT of the conveying path 84. It is supposed to be.

  Thus, in the registration device 65 of the present invention, the driving roller 7b and the driven roller 7a hold the sheet and move it to the center CT of the conveyance path 84 and convey it downstream in the sheet conveying direction. , Can increase productivity.

  S: sheet, G: butting, J: arrow (sheet width direction), F: arrow (sheet conveyance direction), Pf: front standby position of registration roller pair, Pr: back standby position of registration roller pair, CT: image (conveyance) center, K: nominal image (conveyance) end position, 5a to 5c: skew feeding roller pair (slope feeding means), 6a to 6c: skew feeding roller pair (slope feeding means), 7: Registration roller pair (moving means), 7a: driven roller (rotating body pair), 7b: driving roller (rotating body pair), 8: front side reference guide, 9: back side reference guide, 57: reciprocating motor, 60: image Forming device, 65: registration device (sheet skew correction device), 82A: front side movable unit (skew correction unit), 82B: back side movable unit (skew correction unit), 613: image forming unit

Claims (4)

A sheet skew correction device that corrects the skew of the conveyed sheet by making the center in the width direction coincide with the center of the width direction of the conveyance path for conveying the sheet, and the skew correction is performed by the sheet skew correction device. In an image forming apparatus for forming an image on a sheet with an image forming unit,
A pair of skew correction means disposed on both sides of the conveyance path, for correcting the skew of the sheet by aligning the side edges of the sheet;
Moving means for moving a sheet whose side edges are aligned by the pair of skew feeding correcting means in the width direction of the conveyance path so that the center of the sheet coincides with the center of the conveyance path;
The pair of skew correction means alternately correct skew of the sheets continuously conveyed on the conveyance path;
The moving means holds the sheet that has been skew-corrected by one of the pair of skew correcting means, moves it to the center of the conveyance path, stops, and then stops. From the above, the sheet that has been subjected to skew correction by the other skew correction unit and is continuously conveyed is held and moved to the center of the conveyance path.
An image forming apparatus. The distance by which each skew correction unit of the pair of skew correction units moves the sheet in the width direction of the conveyance path and the distance by which the movement unit moves the sheet to the center of the conveyance path are set to be the same. Being
The image forming apparatus according to claim 1. Each skew correction unit of the pair of skew correction units conveys a sheet obliquely from the center of the conveyance path to the side toward a reference guide provided along the sheet conveyance direction. A skew feeding means for
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The moving means has a pair of rotating bodies that are movable toward and away from each other and movable in the width direction of the transport path,
The pair of rotating bodies receives the sheet to be skew-corrected while being separated from each other, and then conveys the sheet to the downstream side in the sheet conveying direction while holding the sheet and moving it to the center of the conveying path.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images