SHEET CONVEYANCE APPARATUS

A sheet conveyance apparatus includes a conveyance roller, an abutment member including an abutment surface against which a side edge, in a width direction, of the sheet abuts, and configured to correct a skew of the sheet, an obliquely conveying roller configured to convey the sheet such as the side edge of the sheet is conveyed toward the abutment surface, a sheet side edge detection portion configured to detect a position of the side edge of the sheet, and a control unit configured to control that a conveyance force, in the width direction, by the obliquely conveying roller in response to a detection result of the sheet side edge detection portion becomes smaller than that in an abutment movement.

BACKGROUND OF THE INVENTION

Field of the Invention

This disclosure relates to a sheet conveyance apparatus conveying a sheet.

Description of the Related Art

Japanese Patent Laid-Open No. H11-189355 suggests an image forming apparatus including a sheet feeding unit feeding a sheet, an alignment unit correcting a posture of a fed sheet, and a registration unit conveying the sheet with the posture corrected at the alignment unit to an image forming unit in a predetermined timing.

The alignment unit includes a reference guide extending along a sheet conveyance direction, an obliquely conveying roller conveying the sheet to the reference guide, a conveyance roller moving the sheet in a width direction orthogonal to a sheet conveyance direction, a sheet passage detection sensor detecting a position of a leading edge of the sheet, and a side edge detection sensor detecting a position of a side edge of the sheet.

To be noted, the obliquely conveying roller corrects a skew of the sheet by conveying the sheet along the reference guide. The conveyance roller moves the sheet in the width direction based on a detection signal of the side edge detection senser.

However, the alignment unit described in Japanese Patent Laid-Open No. H11-189355 does not take into consideration a timing of the completion of the skew correction performed by the obliquely conveying roller and the reference guide, and releases a nip of the obliquely conveying roller based on a detection timing of the sheet passage detection sensor.

Therefore, the obliquely conveying roller has conveyed the sheet while slipping over the sheet after the skew of the sheet has been corrected by being conveyed along the reference guide, during the time until the nip of the obliquely conveying roller is released. For example, in a case where a low stiffness sheet such as a thin paper is conveyed, there is a risk of buckling the sheet and causing conveyance failure. Further, in a case where a sheet with a surface coated, such as a coated paper is conveyed, there is a risk of peeling off a part of a coated layer on the sheet and causing image defects.

SUMMARY OF THE INVENTION

The purpose of the present invention is to reduce conveyance failure of the sheet and image defects while properly correcting a skew of the sheet.

According to one aspect of the present invention, a sheet conveyance apparatus includes a conveyance roller configured to convey a sheet, an abutment member disposed downstream of the conveyance roller and extending along a sheet conveyance direction, the abutment member including an abutment surface against which a side edge, in a width direction orthogonal to the sheet conveyance direction, of the sheet abuts, and configured to correct a skew of the sheet, an obliquely conveying roller disposed downstream of the conveyance roller in the sheet conveyance direction, and configured to convey the sheet such as the side edge of the sheet is conveyed toward the abutment surface, a sheet side edge detection portion configured to detect a position of the side edge of the sheet in the width direction and change an output value in response to the position of the side edge of the sheet conveyed by the obliquely conveying roller, and a control unit configured to control that a conveyance force, in the width direction, by the obliquely conveying roller in response to a detection result of the sheet side edge detection portion becomes smaller than that in an abutment movement, the abutment movement being a movement in which the side edge of the sheet is brought to abut against the abutment surface by the obliquely conveying roller conveying the sheet.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

General Arrangement

At first, a first embodiment of this disclosure will be described. A printer1, serving as an image forming apparatus, is a full color laser beam printer of an electrophotographic system. As shown inFIG. 1, the printer1includes a sheet feed unit51, a conveyance unit54, a registration unit800, an image forming unit513, a fixing unit58, and a branch conveyance unit59. Further, the printer1includes an inversion conveyance unit501, a duplex conveyance unit502, a sheet discharge tray500, and an escape tray601.

The image forming unit513includes four process cartridges99Y,99M,99C, and99Bk forming toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), and exposing units111,112,113, and114. To be noted, configurations of four process cartridges99Y,99M,99C, and99Bk are the same except for colors in which the images are formed. Therefore, only the configuration and an image forming process of the process cartridge99Y will be described, and descriptions of the process cartridges99M,99C, and99Bk will be omitted herein.

The process cartridge99Y includes a photosensitive drum508, a charge roller, a developing unit510, and a cleaner509. The photosensitive drum508is constructed by coating an organic photoconductive layer on an outer circumferential surface of an aluminum cylinder, and rotatably driven by a driving motor. Further, an intermediate transfer belt506rotatably driven in an arrow B direction by a driving roller504is disposed in the image forming unit513, and is wound around a tension roller505, the driving roller504, and a secondary transfer inner roller503. Inside the intermediate transfer belt506, primary transfer rollers507Y,507M,507C, and507Bk are disposed, and, outside the intermediate transfer belt506, a secondary transfer outer roller56is disposed opposite the secondary transfer inner roller503.

The fixing unit58includes a fixing roller pair58aand a pre-fixing conveyance unit57conveying the sheet to a nip of the fixing roller pair58a. The sheet feed unit51includes a lift plate52ascending and descending while stacking a sheet S, and a pneumatic sheet feed unit53feeding the sheet S stacked on the lift plate52. The pneumatic sheet feed unit53sorts the sheet stacked on the lift plate52pneumatically, and conveys an uppermost sheet on the lift plate52while sucking with air. To be noted, in place of the pneumatic sheet feed unit53, it is acceptable to apply the other sheet feed units such as a roller and a belt.

Next, an image forming operation of the printer1configured as described above will be described. When an image signal is input to the exposing unit111from a personal computer and the like, a laser beam is irradiated onto the photosensitive drum508from the exposing unit111corresponding to the image signal.

At this time, a surface of the photosensitive drum508has been uniformly charged in a predetermined polarity and electric potential beforehand by the charge roller, and an electrostatic latent image is formed on the surface with the laser beam irradiated by the exposing unit111via a mirror512. The electrostatic latent image formed on the photosensitive drum508is developed by the developing unit510, and the toner image of yellow (Y) is formed on the photosensitive drum508.

Similarly, the photosensitive drums of the process cartridges99M,99C, and99Bk are respectively irradiated with the laser beam by the exposing units112,113, and114, and the toner images of magenta (M), cyan (C), and black (K) are formed on each of the photosensitive drums. Each color of the toner images formed on each of the photosensitive drums is transferred to the intermediate transfer belt506by the primary transfer rollers507Y,507M,507C, and507Bk. Then, a full color toner image is conveyed by the intermediate transfer belt506rotatably driven by the driving roller504to a secondary transfer nip T2formed by the secondary transfer inner roller503and the secondary transfer outer roller56. A residual toner remained on the photosensitive drum508is collected by the cleaner509. To be noted, the image forming process of each color is performed in a timing superimposing the toner image on an upstream toner image primarily transferred onto the intermediate transfer belt506.

In parallel with this image forming process, the sheet S is fed from the sheet feed unit51, and conveyed to the registration unit800by the conveyance unit54. After a skew has been corrected by registration unit800, the sheet S is conveyed to the secondary nip T2, serving as an image forming portion, in a predetermined conveyance timing. The full color toner image on the intermediate transfer belt506is transferred onto a first sheet surface (front surface) of the sheet S by applying a secondary transfer bias to the secondary transfer outer roller56. A residual toner remained on the intermediate transfer belt506is collected by a belt cleaner46.

The sheet S onto which the toner image has been transferred is conveyed to the fixing roller pair58aby the pre-fixing conveyance unit57. Then, the sheet S is provided with predetermined heat and pressure by the fixing roller pair58a, so that a toner is melted and bonded (fixed). The branch conveyance unit59performs path selection selecting a conveyance path for the sheet S passed through the fixing unit58between a first discharge path59aand a second discharge path59b.

In a case where the image is formed on only one of the surfaces of the sheet S, the sheet S is conveyed from the branch conveyance unit59to the first discharge path59a, and discharged to the sheet discharge tray500, serving as a first tray.

In a case where the image is formed on both surfaces of the sheet S, the sheet S is conveyed to the second discharge path59bby the branch conveyance unit59. Then, a guide member600performs a path selection selecting a conveyance path for the sheet S conveyed to the second discharge path59bbetween an escape path600aand an inversion path600b. The sheet S guided to the escape path600aby the guide member600is discharged to the escape tray601. For example, the sheet S which is not usable as deliverables due to image defects and the like is discharged to the escape tray601.

The conveyance of the sheet S conveyed to the inversion path600bis switchbacked in the inversion conveyance unit501. The switchbacked sheet S is conveyed from the inversion conveyance unit501to the duplex conveyance unit502, and guided to the conveyance unit54. Thereafter, the image is formed on a second sheet surface (back surface) of the sheet S at the secondary transfer nip T2, and the sheet S is discharged to the sheet discharge tray500.

Registration Unit

Next, usingFIG. 2, the registration unit800inFIG. 1will be described. The registration unit800includes a conveyance roller portion300, an obliquely conveying roller portion700, a registration roller pair7, a reference member750serving as a abutment member, a CIS400, a first pre-registration sensor801, and a second pre-registration sensor802. The CIS400is constructed by a contact image sensor.

The conveyance roller portion300includes a plurality (4pairs in this embodiment) of conveyance roller pairs301,302,303, and304. These conveyance roller pairs301to304are disposed parallel to each other in a sheet conveyance direction D1, and similar in a configuration to each other. For example, the conveyance roller pair301includes a rotation shaft301a, serving as a first rotation shaft extending in a width direction W, and roller portions301band301b, serving as first rotary members rotatably supported by the rotation shaft301a. The width direction W, as an axial direction, orthogonally intersects with the sheet conveyance direction D1.

The obliquely conveying roller portion700includes a plurality (3 pairs in this embodiment) of obliquely conveying roller pairs701,702, and703. These obliquely conveying roller pairs701to703are disposed parallel to each other in the sheet conveyance direction D1, and similar in a configuration to each other. For example, the obliquely conveying roller pair701includes a rotation shaft701a, serving as a second rotation shaft extending in a direction intersecting with the sheet conveyance direction D1and the width direction W, and a roller portion701b, serving as a second rotary member rotatably supported by the rotation shaft701a. The obliquely conveying roller pair701is disposed downstream of the conveyance roller pair301in the sheet conveyance direction D1.

A radial direction of the roller portion701binclines to an abutment surface750aof the reference member750by an angle Θ, and the roller portion701bis configured to convey the sheet S toward the abutment surface750a. The skew of the sheet S is corrected by abutting an edge in the width direction W on the abutment surface750a.

The CIS400, serving as a sheet side edge detection portion, is disposed between the conveyance roller pairs303and304in the sheet conveyance direction D1. Further, the CIS400is disposed on one side with respect to the center line CCP of a conveyance path CP through which the sheet S passes. The CIS400changes an output value depending on a position of the edge of the sheet S in the width direction W, so that it is possible to detect the position of the edge of the sheet S in the width direction W. To be noted, a disposition of the CIS400is not limited to this. Further, the CIS400is not limited to the contact image sensor, and it is acceptable to apply a variety of sensors of a contact type and a non-contact type. For example, in place of the CIS400, it is acceptable to apply a flag sensor and a photo sensor of a transmitting type or a reflection type.

The first and second pre-registration sensors801and802are disposed on the center line CCP. The first pre-registration sensor801is disposed between the conveyance roller pair304and the obliquely conveying roller pair701in the sheet conveyance direction D1, and the second pre-registration sensor802is disposed downstream of the obliquely conveying roller pairs701,702and703in the sheet conveyance direction D1. These first and second pre-registration sensors801and802each are photo sensors having a light emitting component and a photosensing portion, and detect a timing of the passage of the sheet S by receiving the light emitted by the light emitting component and reflected by the sheet S by the photosensing portion.

The registration roller pair7is capable of aligning a position of the toner image formed on the intermediate transfer belt506with a position of the sheet S in the width direction W by moving in the width direction W with the sheet S nipped.

Control Block

Next, usingFIG. 3, a control block of the printer1will be described. As shown inFIG. 3, the printer1includes a controller100, and the controller100, serving as a control unit, includes a CPU (central processing unit)101, a ROM (read-only memory)102, a RAM (random-access memory)103, and an obliquely conveying timer104. The CPU101controls each unit of the printer1by reading various programs stored in the ROM102. The RAM103is used as a work area of the CPU101. The obliquely conveying timer104is capable of counting time.

The CIS400, the first and second pre-registration sensors801and802, obliquely conveying driving motors710,720, and730, and obliquely conveying detachment units711,721, and731are coupled to the controller100. Further, conveyance driving motors310,320,330, and340and conveyance detachment units311,321,331, and341, a switching motor610, and a display part900are coupled to the controller100.

The obliquely conveying driving motors710,720, and730respectively drives the obliquely conveyance roller pairs701,702, and703. The obliquely conveying detachment units711,721, and731respectively move one or both of a pair of rollers constituting the obliquely conveying roller pairs701,702, and703in a direction coming into contact with or being separated from each other. To be noted, in this embodiment, driven rollers of the obliquely conveying roller pairs701,702, and703are configured to come into contact with or to be separated from driving rollers.

The conveyance driving motors310,320,330, and340respectively drive the conveyance roller pairs301,302,303, and304. The conveyance detachment units311,321,331, and341move one or both of a pair of rollers constituting the conveyance roller pairs301,302,303, and304in a direction coming into contact with or being separated from each other. To be noted, in this embodiment, driven rollers of the conveyance roller pairs301,302,303, and304are configured to come into contact with or to be separated from driving rollers.

The switching motor610is capable of swinging the guide member600, and capable of switching the conveyance path of the sheet S between the escape path600aand the inversion path600b. The display part900is capable of displaying a screen.

Abutment Movement of Sheet

Next, using a flowchart inFIG. 4, an abutment movement of the sheet S on the abutment surface750awill be described. The abutment movement is a movement in which the side edge Sa of the sheet S is brought to abut against the abutment surface750aby the obliquely conveying roller pairs701,702, and703conveying the sheet S. As shown inFIG. 4, at first, the controller100holds the obliquely conveying roller pairs701,702, and703in a non-nipping state by the obliquely conveying detachment units711,721, and731(STEP51). Further, the controller100holds the conveyance roller pairs301,302,303, and304in the nipping state by the conveyance detachment units311,321,331, and341(STEP S2). To be noted, the non-nipping state is a state in which a pair of rollers are separated from each other so as to release a nip, and a nipping state is a state in which the pair of rollers come into contact with each other so as to form the nip.

Then, the conveyance roller portion300conveys the sheet S by the conveyance roller pairs301,302,303, and304, which are in the nipping state, by being driven by the conveyance driving motors310,320,330, and340(STEP S3). Next, the controller100judges based on a detection result of the first pre-registration sensor801whether or not the sheet S has entered the obliquely conveying roller portion700by a predetermined amount (STEP S4).

In a case where it is judged that the sheet S has not entered the obliquely conveying roller portion700by the predetermined amount (STEP S4: No), the controller100returns to STEP S3. As shown inFIG. 5B, in a case where it is judged that the sheet S has entered the obliquely conveying roller portion700by the predetermined amount (STEP S4: Yes), the controller100switches the obliquely conveying roller pairs701,702, and703to the nipping state (STEP S5). Further, the controller100switches the conveyance roller pairs301,302,303, and304to the non-nipping state by the conveyance detachment units311,321,331, and341(SPEP S6). To be noted, it is acceptable to stop the conveyance roller pairs301,302,303, and304at this time by stopping driving the conveyance driving motors310,320,330, and340.

Then, the obliquely conveying roller portion700conveys the sheet S by the obliquely conveying roller pairs701,702, and703by being driven by the obliquely conveying driving motors710,720, and730(STEP S7). At this time, by starting counting a time with the obliquely conveying timer104, the controller100starts counting a conveyance time of the sheet S by the obliquely conveying roller portion700(hereinafter referred to as an obliquely conveying time) (STEP S8).

Then, as shown inFIGS. 6A and 6B, the sheet S is conveyed toward the abutment surface750aof the reference member750. When a side edge Sa of the sheet S in the width direction W is conveyed after the abutment surface750a, the skew of the sheet S is corrected. With the side edge Sa of the sheet S being after the abutment surface750a, the side edge Sa is positioned inside a predetermined range R1at a position of the CIS400. The predetermined range R1is, for example, an area which is within 0.3 mm with respect to a position of the abutment surface750ain the width direction W.

As shown inFIG. 4, next, the controller100judges whether or not a position of the side edge Sa of the sheet S detected by the CIS400is inside the predetermined range R1(STEP S9). In a case where the side edge Sa is inside the predetermined range R1(STEP S9: Yes), the controller100waits the passing of a predetermined time t1(STEP S10). In this embodiment, the predetermined time t1is about 50 msec (millisecond). Then, when the predetermined time t1has passed (STEP S10: Yes), the controller100judges whether or not the position of the side edge Sa of the sheet S detected by the CIS400has been continuingly inside the predetermined range R1during the predetermined time t1(STEP S11).

In a case where the position of the side edge Sa has been continuingly inside the predetermined range R1(STEP S11: Yes), the controller100judges that the abutment movement of the sheet S on the abutment surface750ahas been completed (STEP S12). In other words, in a case where an output value of the CIS400has continued to be inside the predetermined range R1during the predetermined time t1, the controller100judges that the abutment movement of the sheet S on the abutment surface750ahas been completed.

At this point, usingFIG. 7, STEPS S7to S12will be described in detail.FIG. 7is a graph with time on the horizontal axis and the output value of the CIS400on the vertical axis. The time on the horizontal axis is counted by the obliquely conveying timer104. Having been conveyed by the conveyance roller pairs301to304at first (refer to STEP S3), the sheet S is conveyed by the obliquely conveying roller pairs701to703(obliquely conveying section; refer to STEP S7). When the sheet S is conveyed by the obliquely conveying roller pairs701to703, the position of the side edge Sa detected by the CIS400(hereinafter referred to as a detection position) gradually approaches the position of the abutment surface750aof the reference member750in the width direction W (hereinafter referred to as a reference position750R).

Then, the predetermined time t1is counted from the time P1when the detection position described above has entered the predetermined range R1(refer to STEPS S9and S10). When the detection position further approaches the reference position750R and the side edge Sa comes into slide contact with the abutment surface750a, the detection position is maintained at the reference position750R (reference member slide contact conveyance section).

In a case where the detection position is inside the predetermined range R1at the time P2when the predetermined time t1has passed from the time P1, the controller100judges that the abutment movement of the sheet S on the abutment surface750ahas been completed (refer to STEPS S11and S12). While, in this embodiment, the time P2is the time when the predetermined time t1has passed from the time P1, it is not limited to this. For example, it is acceptable that the time P2is the time when the sheet S has been conveyed by as much as a predetermined distance. Further, it is acceptable that, depending on expected printing precision and a sheet size, the predetermined range R1and the predetermined time t1are suitably set at default values beforehand or provided to be settable by a user.

To be noted, because of following reasons, the detection positions from the time t1to the time P2when the predetermined time t1has passed from the time P1are used for the judgement of the completion of the abutment movement as described above. For example, a case where the sheet S is conveyed by the conveyance roller portion300in a posture as shown inFIG. 8Aand delivered to the obliquely conveying roller portion700is considered.

InFIG. 8A, while the side edge Sa of the sheet S is positioned inside the predetermined range R1, at this time, the side edge Sa of the sheet S does not come into slide contact with the abutment surface750aof the reference member750, and the skew of the sheet S is not corrected. Therefore, if, based on a detection result that the side edge Sa of the sheet S is inside the predetermined range R1at a time ofFIG. 8A, it is judged that the abutment movement has been completed, it leads to an erroneous judgement.

Further, for example, when the predetermined time t1has passed from the time ofFIG. 8A, the posture of the sheet S becomes a posture as shown inFIG. 8Bby being conveyed by the obliquely conveying roller portion700. At a time ofFIG. 8B, the sheet S is still in the middle of the abutment movement, and the side edge Sa of the sheet S is outside the predetermined range R1. As described above, by detecting the positions of the side edge Sa of the sheet S not only at the time ofFIG. 8Abut also at the time ofFIG. 8B, it is possible to reduce the erroneous judgement on the completion of the abutment movement.

As shown inFIG. 4, in a case where the position of the side edge Sa detected by the CIS400is outside the predetermined range R1in STEP S9(STEP S9: No), the controller100judges whether or not the time counted by the obliquely conveying timer104is within the predetermined time (STEP S13). In a case where the time counted by the obliquely conveying timer104is within the predetermined time (STEP S13: Yes), the controller100returns to SPEP S9.

In a case where the time counted by the obliquely conveying timer104is not within the predetermined time (STEP S13: No), the controller100judges that the abutment movement has not been completed (STEP S14). That is, in a case where the side edge Sa has not come inside the predetermined range R1within the predetermined time after the obliquely conveying timer104started counting the time, the controller100judges that the abutment movement has not been completed.

Here, usingFIGS. 12A to 13C, reference examples of the image defects caused by the skew of the sheet S will be described. For example, a case in which a deliverable (printed matter) as shown inFIG. 13Chas been anticipated is considered. If, as shown inFIG. 12A, the sheet S has reached the registration roller pair7before abutting on the reference member750, the image printed on the sheet S inclines as shown inFIG. 13A.

Further, if, as shown inFIG. 12B, the side edge Sa is continued to be pressed to the abutment surface750aby the obliquely conveying roller pairs701,702, and703even after the skew of the sheet S has been corrected by abutting on the abutment surface750aof the reference member750, the sheet S is bent in some cases. This often occurs especially in a case of a low stiffness sheet such as a thin sheet. Then, the sheet S reaches the registration roller pair7in a bent state, and, as shown inFIG. 13B, the image is printed on the sheet S with the image shifted to one side in the width direction W. As described above, in a case where it is not judged that the abutment movement has been completed, there is a risk of the occurrence of the image defects.

On the other hand, in this embodiment, it is possible to infallibly judge the completion and non-completion of the abutment movement of the sheet S by the use of the CIS400. In a case where it is judged at STEP S12that the abutment movement has been completed, the following operations are performed. That is, as shown inFIG. 9A, the controller100switches a part or all of the conveyance roller pairs301,302,303, and304to the nipping state by the conveyance detachment units311,321,331, and341(STEP S15).

Further, the controller100switches the obliquely conveying roller pairs701,702, and703to the non-nipping state by the obliquely conveying detachment units711,721, and731(SPEP S16). For example, the controller100performs a separating action of moving the roller portion701bof the obliquely conveying roller pair701in a separation direction from the sheet S. As shown inFIG. 1, the obliquely conveying roller pair701includes a roller portion701c, serving as a third rotary member, which forms a nip with the roller portion701band conveys the sheet while nipping at the nip. The separating action above is an action of separating the roller portion701bfrom the roller portion701cand release the nip. That is, a conveyance force, in the width direction W, by the obliquely conveying roller pairs701,702, and703becomes smaller than that in the abutment movement.

Herewith, it is possible to convey the sheet S in the sheet conveyance direction D1by the conveyance roller portion300again, and possible to prevent the sheet S from excessively abutting on the reference member750. Therefore, since it is possible to reduce a force which the sheet S receives from the abutment surface750aof the reference member750, it is possible to suppress the damage to and the bent of the sheet S and suppress the image defects.

Further, in a case where it is judged at S IEP S14that the abutment movement has not been completed, as shown inFIG. 9B, the controller100interrupts the conveyance of the sheet S by the printer1(STEP S17). Thereafter, as shown inFIG. 10, the controller100displays on the display part900, serving as an informing portion, a message informing the non-completion of the abutment movement (STEP S18). Further, such message transmits a possibility of the occurrence of the image defects (print misalignment) due to the non-completion of the abutment movement and a stop of the sheet conveyance to the user, and urges the user to remove the sheet remained inside the printer1.

To be noted, this kind of message is not limited to the message as shown inFIG. 10, and any message will be used. Further, it is acceptable to transmit the non-completion of the abutment movement to the user by flickering of a lamp, a warning sound, or the like instead of displaying the message on the display part900. That is, in a case where it is judged that the abutment movement has not been completed within the predetermined time after the obliquely conveying roller pairs701to703started the conveyance of the sheet, the informing portion such as the display part900, the lamp, and a buzzer is activated.

As described above, in this embodiment, it is possible to infallibly judge the completion and non-completion of the abutment movement of the sheet S in response to the detection result of the CIS400, and possible to reduce conveyance failure and the image defects by properly correcting the skew of the sheet S.

Second Embodiment

While a second embodiment will be described next, the second embodiment is different from the first embodiment only in the control performed at the time of the completion of the abutment movement. Therefore, configurations similar to the first embodiment will be described by omitting illustrations or by putting the same reference characters on drawings.

In a case where it is judged at STEP S12that the abutment movement has been completed, as shown inFIG. 11A, the controller100switches a part of the obliquely conveying roller pairs701to703to the non-nipping state by the obliquely conveying detachment units711,721, and731(STEP S21). Then, the controller100conveys the sheet S to the registration roller pair7by the obliquely conveying roller pairs which are kept in the nipping state. That is, a conveyance force, in the width direction W, by the obliquely conveying roller pairs701,702, and703becomes smaller than that in the abutment movement.

Herewith, it is possible to reduce an abutment force of the sheet S on the abutment surface750a, and prevent the sheet S from excessively abutting on the reference member750. Therefore, it is possible to reduce a force that the sheet S receives from the abutment surface750aof the reference member750, and suppress the image defects by reducing a damage to and the bent of the sheet S.

Third Embodiment

While a third embodiment will be described next, the third embodiment is different from the first embodiment only in the control performed at the time of the completion of the abutment movement. Therefore, configurations similar to the first embodiment will be described by omitting illustrations or by putting the same reference characters on drawings.

In a case where it is judged at STEP S12that the abutment movement has been completed, as shown inFIG. 11B, the controller100performs a control so that a part or all of the obliquely conveying roller pairs701,702, and703reduce nip pressure (STEP S31). For example, the controller100performs a separating action of moving the roller portion701bof the obliquely conveying roller pair701in a separating direction from the roller portion701c(refer toFIG. 1). Such separating action is an action of reducing the nip pressure at the nip between the roller portion701band the roller portion701cfrom the first pressure at the time of the abutment movement to the second pressure, that is lower than the first pressure, without releasing the nip. That is, a conveyance force, in the width direction W, by the obliquely conveying roller pairs701,702, and703becomes smaller than that in the abutment movement.

Herewith, the sheet S becomes easy to slip on the obliquely conveying roller pairs701,702, and703, and it is possible to prevent the sheet S from excessively abutting on the reference member750. Therefore, it is possible to reduce a force that the sheet S receives from the abutment surface750aof the reference member750, and suppress the image defects by reducing the damage to and the bent of the sheet S.

Fourth Embodiment

While a fourth embodiment will be described next, the fourth embodiment is different from the first embodiment only in the control performed at the time of the completion of the abutment movement. Therefore, configurations similar to the first embodiment will be described by omitting illustrations or by putting the same reference characters on drawings.

In a case where it is judged at STEP S14that the abutment movement has not been completed, as shown inFIG. 11C, the controller100drives the guide member600by the switching motor610. Then, the controller100switches the conveyance path so as to convey the sheet S toward the escape path600a(STEP S41).

The sheet S guided to the escape path600aby the guide member600is discharged to the escape tray601, serving as a second sheet discharge tray different from the sheet discharge tray500(STEP S42). Herewith, it is possible to distinguish a defectively printed sheet caused by the non-completion of the abutment movement from the sheet discharged to the sheet discharge tray500, and possible to easily remove the sheet discharged to the escape tray601. Therefore, it is possible to improve usability.

To be noted, while, in this embodiment, the escape tray601is disposed inside the printer1, it is not limited to this. For example, it is acceptable to discharge the defectively printed sheet to the other trays disposed above or below the sheet discharge tray500. Further, it is acceptable to discharge the defectively printed sheet to the other apparatus coupled to downstream of the printer1.

Other Embodiments

To be noted, while in any of the embodiments described above, the obliquely conveying roller portion700is disposed in front of the secondary transfer nip T2, it is not limited to this. For example, it is acceptable to apply this disclosure by disposing the obliquely conveying roller portion700in the other apparatus coupled to downstream of the duplex conveyance unit502or the printer1.

While in any of the embodiments described above, 4 pairs of conveyance roller pairs are disposed in the conveyance roller portion300and 3 pairs of obliquely conveying roller pairs are disposed in the obliquely conveying roller portion, a number of roller pairs are not limited to this. Further, while the obliquely conveying roller pairs701to703each are inclined with respect to the sheet conveyance direction D1by a similar angle, it is not limited to this, and acceptable that inclination angles with respect to the sheet conveyance direction D1are different from each other.

Further, it is acceptable to combine the first to fourth embodiments arbitrarily. For example, when the abutment movement has not been completed, it is acceptable to perform both of displaying the message on the display part900(the first embodiment) and discharging the sheet to the escape tray601(the fourth embodiment).

While, in any of the embodiments described above, this disclosure is described taking the registration unit800, serving as a sheet conveyance apparatus including the controller100, as an example, it is acceptable to regard the printer1as the sheet conveyance apparatus.

While, in any of the embodiments described above, the descriptions are provided using the printer1of the electrophotographic system, the present disclosure is not limited to this. For example, it is possible to apply the present disclosure to an image forming apparatus of an ink jet system which forms the image on the sheet by ejecting a liquid ink through a nozzle.

This application claims the benefit of Japanese Patent Application No. 2020-186739, filed Nov. 9, 2020, which is hereby incorporated by reference herein in its entirety.