JP7333006B2 - Conveying device and image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conveying device for conveying a sheet, and an image forming apparatus equipped with the same, such as a copier, printer, facsimile machine, or a multifunction machine or printing machine.

Conventionally, in an image forming apparatus such as a copier or a printer, a sheet is conveyed toward a pair of registration rollers that are not rotating, and the sheet is bent while being brought into contact with the pair of registration rollers. A technique for correcting skew is known (see, for example, Patent Document 1).

Specifically, a transport roller pair (second transport roller pair) is installed upstream of the registration roller pair (first transport roller pair). Then, the conveying roller pair conveys the sheet toward the registration roller pair that is in a state where rotation is stopped. By continuing to convey the sheet by the conveying roller pair for a while while the leading edge of the sheet is in contact with the nip of the pair of registration rollers, skew correction is performed in a state in which the sheet is warped. Rotation is stopped. Thereafter, the pair of registration rollers and the pair of conveying rollers are rotated to convey the sheet toward the transfer position (image forming section) where the image formed on the photosensitive drum is transferred.

On the other hand, Japanese Patent Application Laid-Open No. 2002-200001 discloses a technique for preventing the problem that skew correction accuracy varies depending on the type of sheet.
Specifically, when the leading edge of the sheet is detected by a registration sensor (sheet detection sensor) installed between the pair of conveying rollers (second pair of conveying rollers) and the pair of resist rollers (first pair of conveying rollers), the conveying rollers Temporarily stop rotating the pair. Thereafter, the rotation of the conveying roller pair is resumed, and after the leading edge of the sheet is brought into contact with the registration roller pair and the sheet is flexed as desired, the rotation of the registration roller pair is started, and the sheet is moved to the transfer position ( image forming section).
Here, in Patent Document 1, the "target deflection" of the sheet is adjusted for each type of sheet by adjusting the time from the restart of the rotation of the conveying roller pair in the rotation stopped state to the start of rotation of the registration roller pair. It is formed by

In the conventional image forming apparatus, even if the flexure is formed at the position of the first conveying roller pair (registration roller pair), the sheet is pushed back to the downstream side by the stiffness of the sheet, and the flexure disappears. In some cases, the accuracy of the skew correction is lowered because the desired deflection is not formed.
On the other hand, in Japanese Patent Application Laid-Open No. 2002-200010, the time from restarting the rotation of the conveying roller pair in the rotation stopped state to starting the rotation of the registration roller pair is adjusted for each sheet type. It can be expected that the problem will be reduced to some extent. However, when the rotation of the conveying roller pair is stopped at the timing when the leading edge of the sheet is detected by the registration sensor, the stopping position of the sheet fluctuates in the conveying direction. There is a possibility that the accuracy of the skew correction cannot be sufficiently improved because the deflection is not formed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a conveying apparatus and an image forming apparatus capable of correcting skew of a sheet with high accuracy.

A conveying device according to the present invention includes a first conveying roller pair that is rotationally driven by a first driving mechanism to convey a sheet, and a second driving mechanism that is rotationally driven to convey a sheet toward the first conveying roller pair. and a second conveying roller pair arranged at a position on the upstream side in the conveying direction with respect to the first conveying roller pair and at a position on the downstream side in the conveying direction with respect to the second conveying roller pair. A sheet detection sensor that detects the leading edge of a passing sheet and a detection unit that detects the type or stiffness of the conveyed sheet are provided, and the second conveying roller pair is rotationally driven by the second driving mechanism. By continuing, the sheet is brought into contact with the first conveying roller pair in a state in which the sheet continues to be conveyed toward the first conveying roller pair whose rotational driving by the first driving mechanism is stopped, thereby bending the sheet. After a predetermined time has passed since the leading edge of the sheet was detected by the sheet detection sensor without stopping the rotational driving of the second conveying roller pair, the first conveying roller is driven by the first drive mechanism. When the detection unit detects that a sheet having stiffness exceeding a predetermined range is conveyed, the sheet whose stiffness is within the predetermined range is detected. The predetermined time is adjusted to be longer than when it is detected that the sheet is conveyed, and the detection unit detects that the sheet whose stiffness does not reach the predetermined range is conveyed. Also in this case, the predetermined time is adjusted to be longer than when it is detected that the sheet whose stiffness is within the predetermined range is conveyed.

According to the present invention, it is possible to provide a conveying device and an image forming apparatus with high skew correction accuracy for a sheet.

1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; FIG. It is a block diagram which shows a conveying apparatus. 4A and 4B are diagrams showing the operation of the sheet in the conveying device; FIG. 4 is a timing chart showing control of the conveying device; FIG. 10 is a diagram showing the operation of a sheet in a conventional conveying device; FIG. 10 is a diagram showing the operation of a sheet during double-sided conveyance in the conveying device; 4 is a timing chart showing control during double-sided transport in the transport device;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant description thereof will be appropriately simplified or omitted.

First, the overall configuration and operation of the image forming apparatus 100 will be described with reference to FIG.
In FIG. 1, reference numeral 100 denotes a printer as an image forming apparatus; 1, a photosensitive drum on which a toner image is formed; 7, exposure light L based on image information input from an input device such as a personal computer; 1 shows an exposed portion (writing portion), which is illuminated on the top.
Further, 9 is a transfer roller for transferring the toner image carried on the surface of the photosensitive drum 1 to the sheet P conveyed to the transfer position N (image forming section), and 10 is the photosensitive drum 1, the charging roller 4 and the developing device. 5 and a cleaning device 2 are integrated into a process cartridge, 12 is a feeding device (paper feed cassette) containing sheets P such as paper, and 13 is a manual feeder for feeding manually set sheets P. A feeding device (manual feed tray) is shown.
Reference numeral 16 denotes a registration roller pair as a first conveying roller pair for conveying the sheet P toward a transfer position N (see FIG. 2) where a nip is formed by contact between the photosensitive drum 1 and the transfer roller 9; denotes an upstream side transport roller pair (second transport roller pair) arranged upstream of the registration roller pair 16, and 18 denotes a double-sided exit roller (second transport roller pair) arranged near the exit of the double-sided transport path K4 show.
A fixing device 20 fixes an unfixed image on the sheet P, and an operation display panel 90 displays various information in the image forming apparatus 100 and inputs various commands.

Here, around the photosensitive drum 1, a charging roller 4, a developing device 5, a cleaning device 2, and the like are arranged. These members (the photosensitive drum 1, the charging roller 4, the developing device 5, and the cleaning device 2) are integrated as a process cartridge 10, which is detachable from the image forming apparatus main body 100 ( replaceable). The process cartridge 10 is replaced with a new one in a fixed replacement cycle.

A normal image forming operation in image forming apparatus 100 will be described with reference to FIG.
First, when image information is transmitted from an input device such as a personal computer to the exposure unit 7 of the image forming apparatus 100 , the exposure light L (laser light) based on the image information is emitted from the exposure unit 7 onto the surface of the photosensitive drum 1 . emitted towards.
On the other hand, the photosensitive drum 1 is rotating in the direction of the arrow (clockwise). First, the surface of the photosensitive drum 1 is uniformly charged at the portion facing the charging roller 4 (charging step). Thus, a charging potential (approximately -900 V) is formed on the photosensitive drum 1 . After that, the charged surface of the photosensitive drum 1 reaches the position where the exposure light L is irradiated. Then, the potential of the portion irradiated with the exposure light L becomes the latent image potential (approximately 0 to -100 V), and an electrostatic latent image is formed on the surface of the photosensitive drum 1 (in the exposure step). .).

After that, the surface of the photosensitive drum 1 on which the electrostatic latent image is formed reaches a position facing the developing device 5 . Then, toner is supplied from the developing device 5 onto the photosensitive drum 1, and the latent image on the photosensitive drum 1 is developed to form a toner image (developing process).
After that, the surface of the photosensitive drum 1 after the development process reaches the transfer position N (image forming portion) with the transfer roller 9 . At the transfer position N, a transfer bias (a bias having a polarity different from the polarity of the toner) is applied from the power source to the transfer roller 9, so that the sheet P conveyed by the registration roller pair 16 has a , the toner image formed on the photosensitive drum 1 is transferred (transfer step).

After the transfer process, the surface of the photosensitive drum 1 reaches a position facing the cleaning device 2 . At this position, the cleaning blade mechanically removes the untransferred toner remaining on the photosensitive drum 1 and collects it in the cleaning device 2 (cleaning process).
Thus, a series of image forming processes on the photosensitive drum 1 are completed.

On the other hand, the sheet P conveyed to the transfer nip portion (transfer position) between the photosensitive drum 1 and the transfer roller 9 operates as follows.
First, the uppermost one of the sheets P stored in the feeding device 12 is fed by the feeding roller 15 toward the curved conveying path K1 (conveying path). When the manual feeding device 13 is selected, the sheet P placed on the manual feeding device 13 is conveyed toward the conveying path by the feeding rollers 19 .
After that, the sheet P reaches the position of the registration roller pair 16 (first conveying roller pair). Then, the sheet P, which has reached the position of the registration roller pair 16, is aligned with the image formed on the photoreceptor drum 1 at the transfer position N (the transfer roller 9 and the photoreceptor drum 1). , which is the image forming portion).

After the transfer process, the sheet P passes through the transfer position N (image forming section) and then reaches the fixing device 20 via the transport path K3. After reaching the fixing device 20, the sheet P is fed between the fixing roller 21 and the pressure roller 22, and the image is fixed by the heat received from the fixing roller 21 and the pressure received from both members 21 and 22. . The sheet P on which the image is fixed is delivered from between the fixing roller 21 and the pressure roller 22 (fixing nip portion), and is then discharged from the image forming apparatus main body 100 by the discharge roller pair 25 through the conveying path. and placed on the discharge tray.
Thus, a series of image forming processes are completed.

Note that when the "double-sided print mode" for printing on both sides of the sheet P (the front side and the back side) is selected (during double-sided conveyance), the fixing process on the front side is performed. After the sheet P is conveyed to the position of the discharge roller pair 25, the conveying direction of the sheet P is reversed (switched back) by the reverse rotation of the discharge roller pair 25. FIG. Then, the reversed sheet P is guided to the double-sided conveying path K4 by the switching claw and conveyed along the double-sided conveying path K4 in the direction of the arrow. Then, the sheet P is conveyed by the double-sided outlet roller pair 18, and passes through a junction X (a position where the conveying path K1 from the feeding device 12 to the position of the registration roller pair 16 merges, see FIG. 2). Then, it reaches the transfer position N (image forming section) again. Then, at the transfer position N, an image is formed on the back surface of the sheet P by the same image forming process (image forming operation) as described above. It is ejected from the image forming apparatus main body 100 by the pair 25 and placed on the ejection tray.

The configuration and operation of the conveying device 50, which are characteristic of this embodiment, will be described in detail below.
As shown in FIG. 2, the image forming apparatus 100 according to the present embodiment is provided with a conveying device 50 that conveys the sheet P from the feeding device 12 or the double-sided conveying path K4 (K5) toward the transfer position N. there is
The conveying device 50 includes a registration roller pair 16 as a first conveying roller pair, an upstream conveying roller pair 17, a double-sided outlet roller pair 18, a registration sensor 41 as a sheet detection sensor, a double-sided outlet sensor 42, first to first 3 motors 61 to 63 are provided.

The conveying device 50 in the present embodiment is configured such that the two-sided conveying route K4 (curved conveying route K5) merges at a junction X provided in the middle of the conveying route from the feeding device 12 to the registration roller pair 16. It is
A first curved conveying path K1 (not a straight conveying path but a curved conveying path) is provided in the conveying path from the feeding device 12 to the pair of registration rollers 16. , an upstream conveying roller pair 17 is installed.
In addition, a second curved transport path K5 is provided at a portion of the double-sided transport path K4 that reaches the junction X. As shown in FIG. The curvature of the second curved conveying path K5 is larger than the curvature of the first curved conveying path K1. The double-sided outlet roller pair 18 is arranged in the double-sided conveying paths K4 and K5 at a position closest to the position (junction X) where the conveying path from the feeding device 12 to the registration roller pair 16 merges. In other words, although several transport roller pairs are installed in the double-sided transport paths K4 and K5, the double-sided exit roller pair 18 is the transport roller pair located furthest downstream in the double-sided transport paths K4 and K5. A double-sided outlet sensor 42 (photosensor) for detecting the sheet P is installed near the downstream side of the double-sided outlet roller pair 18 .
The conveying paths in the conveying device 50 (image forming apparatus 100) are formed by conveying guide plates facing each other with a gap (a gap through which the sheet P is conveyed). Therefore, the sheet P is conveyed along the conveying path indicated by the arrows in FIGS. 1 and 2 while being guided by the guide plate. Note that the guide plate installed above the upstream side of the registration roller pair 16 has a space so as not to hinder the formation of the bending of the sheet P (the portion surrounded by the dashed line in FIG. 3B), which will be described later. formed.

Here, the registration roller pair 16 as the first conveying roller pair is a conveying roller pair that is rotationally driven by a first motor 61 as a first driving mechanism (first driving means) and conveys the sheet P while nipping it. be. In the registration roller pair 16, a driving roller and a driven roller are in contact with each other to form a nip, and when the driving roller is rotationally driven by the first motor 61, the driven roller is driven to rotate along with the rotation. It will be. Then, as described above, the registration roller pair 16 conveys the sheet P toward the transfer position N serving as the image forming section in time.

The first motor 61 (first drive mechanism) transmits drive to the registration roller pair 16 via a gear train and an electromagnetic clutch, and transmits drive to the registration roller pair 16 by turning on the electromagnetic clutch. The rotation of the registration roller pair 16 can be driven by turning off the electromagnetic clutch, and the rotation of the registration roller pair 16 can be stopped by interrupting the drive transmission to the registration roller pair 16 by turning off the electromagnetic clutch. In the present embodiment, such rotation/stopping of the registration roller pair 16 is expressed by turning on/off the first motor 61 for the sake of simplicity.
The configuration of the first drive mechanism is not limited to that of the present embodiment, and various configurations may be used as long as it can switch between rotation and non-rotation of the first conveying roller pair. can be done.

The upstream conveying roller pair 17 is rotationally driven by a second motor 62 as a second driving mechanism (second driving means) to convey the sheet P toward the registration roller pair 16 (first conveying roller pair). It functions as two transport roller pairs. In the upstream side conveying roller pair 17, a driving roller and a driven roller are in contact with each other to form a nip, and when the driving roller is rotationally driven by the second motor 62, the driven roller is driven along with the rotation. will rotate.
The double-sided exit roller pair 18 is also rotationally driven by a third motor 63 as a second drive mechanism during double-sided conveyance, and is a second roller pair that conveys the sheet P toward the registration roller pair 16 (first conveying roller pair). It functions as a conveying roller pair, and the operation during double-sided conveying will be described in detail later with reference to FIGS. 6 and 7. FIG.

A second motor 62 (or a third motor 63) as a second drive mechanism transmits drive to the upstream conveying roller pair 17 (or the double-sided outlet roller pair 18) via a gear train or an electromagnetic clutch. By turning on the electromagnetic clutch, the drive is transmitted to the upstream transport roller pair 17 (or the double-side exit roller pair 18) to rotationally drive the upstream transport roller pair 17 (or the double-side exit roller pair 18). Alternatively, by turning off the electromagnetic clutch, the drive transmission to the upstream side conveying roller pair 17 (or the double-side exit roller pair 18) can be interrupted to stop the registration roller pair 16 from rotating. In this embodiment, for the sake of simplicity, such rotation/stopping of the upstream conveying roller pair 17 (or double-side exit roller pair 18) is expressed as turning on/off the second motor 62. FIG.

The registration sensor 41 as a sheet detection sensor is positioned upstream in the transport direction with respect to the registration roller pair 16 (first transport roller pair), and the upstream transport roller pair 17 as a second transport roller pair (or It is arranged at a position on the downstream side in the conveying direction with respect to the duplex exit roller pair 18) and detects the leading edge of the sheet P passing through that position.
Specifically, the registration sensor 41 (sheet detection sensor) is a photosensor composed of a light-emitting element and a light-receiving element. It detects. In particular, in the present embodiment, the registration sensor 41 is arranged downstream of the junction X and close to the registration roller pair 16 .

In the present embodiment, referring to FIGS. 3A to 3C and 4, the upstream side transport roller pair 17 (second transport roller pair) is driven by the second motor 62 (second drive mechanism). By continuing to rotate, the registration rollers continue to convey the sheet P toward the registration roller pair 16 (first conveying roller pair) whose rotational driving by the first motor 61 (first driving mechanism) is stopped. 16, the sheet P is bent, and the leading edge of the sheet P is detected by the registration sensor 41 (sheet detection sensor) without stopping the rotational driving of the upstream conveying roller pair 17. After a lapse of a predetermined time T, the rotation of the registration roller pair 16 by the first motor 61 is started.
That is, until the sheet P reaches the transfer position N from the position of the upstream transport roller pair 17, the upstream transport roller pair 17 always rotates without stopping. 3(B), thereby performing skew correction (skew correction) and aligning the image with the image on the photosensitive drum 1. The sheet P is conveyed toward the transfer position N at the correct timing.

Specifically, as shown in FIG. 3A, the sheet P fed from the feeding device 12 is passed through the pair of registration rollers 16 (which are in a state where rotation is stopped) by the pair of upstream conveying rollers 17 . transported to a position. Then, the leading edge of the sheet P is detected at the position of the registration sensor 41 . At this time, as shown in FIG. 4, the second motor 62 remains on, the signal from the registration sensor 41 changes from off to on, and the time from that point is counted.
After that, as shown in FIG. 3B, as the sheet P is conveyed and the leading edge of the sheet P collides with the registration roller pair 16, the sheet P bends (the portion surrounded by the dashed line). It is formed. As a result, even if the sheet P is conveyed in a skewed state, the leading edge of the sheet P is displaced along the nip of the registration roller pair 16 due to the force that attempts to restore the deflection. It will be. As a result, the skew of the sheet P is corrected. At this time, the upstream transport roller pair 17 continues to rotate without being stopped.
Then, as shown in FIG. 3(C), after the sheet P is bent as desired and the skew is corrected, the registration roller pair 16 is started to be driven toward the transfer position N in time. A sheet P is being conveyed. At this time, as shown in FIG. 4, the timing for starting rotation of the registration roller pair 16 (the timing for switching the first motor 61 from the OFF state to the ON state) is the same as that described with reference to FIGS. This is the timing when the predetermined time T has elapsed since the signal from the registration sensor 41 changed from off to on. Therefore, during this "predetermined time T", the target deflection is formed in the sheet P without stopping the rotational driving of the upstream conveying roller pair 17, and furthermore, the image on the photosensitive drum 1 and the transfer position N are positioned at the transfer position N. It will be adjusted according to the timing for matching.
After that, when the sheet P passes the position of the registration roller pair 16, the registration roller pair 16 stops rotating again in preparation for the sheet P to be conveyed next.

As described above, in the present embodiment, the skew correction of the sheet P is performed at the position of the registration roller pair 16 that has stopped rotating, and the sheet P is conveyed by the registration roller pair 16 that has started rotating after that. Since the side conveying roller pair 17 continues to rotate without stopping, the deflection of the sheet P during skew correction is less likely to disappear, and the skew correction accuracy of the sheet P can be improved.
Specifically, as in the conveying device 150 shown in FIG. 5, if the rotation of the upstream conveying roller pair 17 is stopped immediately after the sheet P is bent at the position of the registration roller pair 16, the sheet The sheet P may be pushed back downstream (in the direction of the white arrow) due to the stiffness of the sheet P, and the bending may disappear. Further, the sheet P may not be sufficiently flexed because the sheet P is too weak. In such cases, the sheet P is not bent as intended, and the accuracy of the skew correction is lowered. In particular, when the curved conveying path K1 is formed as in the conveying apparatus of the present embodiment, the sheet P is more likely to be pushed back as described above than when the position is on the straight conveying path. Become. Also, in a device (high-speed machine) in which the sheet P is conveyed at a high speed, the sheet P is more likely to be pushed back than in a low-speed machine.
Further, if the rotation of the upstream-side transport roller pair 17 is stopped at the timing when the leading edge of the sheet P is detected by the registration sensor 41, the stop position of the sheet P varies in the transport direction. Even if the conveying roller pair 17 and the registration roller pair 16 are started to rotate with a target time difference, the target deflection is not formed in the sheet P, and the skew correction accuracy cannot be sufficiently improved. In particular, in a device (high-speed machine) in which the sheet P is conveyed at a high speed, the stop position of the sheet P tends to vary.
In contrast, in the present embodiment, skew correction and conveyance to the transfer position N are performed while the upstream conveying roller pair 17 is always rotated, so the above-described problems are less likely to occur. Therefore, the accuracy of skew correction of the sheet P can be improved.

Here, in the present embodiment, the operation display panel 90 also functions as a detection unit that indirectly detects the type (or stiffness) of the sheet P to be conveyed. Specifically, when the user inputs information about the sheet P (for example, brand name, product number, etc.) using the operation display panel 90, the controller 60 controls the type of the sheet P based on the information. Or strength of stiffness) is grasped.
Then, the “predetermined time T” described above with reference to FIG. 4 and the like is adjusted according to the detection result of the operation display panel 90 (detection section). More specifically, when the operation display panel 90 (detection unit) detects that the sheet P whose stiffness is outside the predetermined range W is conveyed, the sheet P whose stiffness is outside the predetermined range W is detected. The “predetermined time T” is adjusted to be longer than when it is detected that the inner sheet P is conveyed. Specifically, when the control unit 60 grasps the type (or stiffness) of the sheet P, it compares it with a pre-stored control table to obtain the optimal "predetermined time T". The timing of starting rotation of the registration roller pair 16 is adjusted by the "predetermined time T".
Such control is performed for a sheet P whose stiffness exceeds a predetermined range W (for example, a cardboard or the like). is likely to occur, and the deflection is formed in anticipation of the loss. In addition, the sheet P whose stiffness does not reach the predetermined range W (for example, thin paper) does not have enough stiffness to cause the skew correction even if the bending is formed. A large amount of deflection is formed to compensate for the weakness of the stiffness.
Instead of the operation display panel 90, a sensor that directly detects the type or stiffness of the conveyed sheet P can be used as the detection unit. Also, an input device such as a personal computer can be used as the detection unit instead of the operation display panel 90 .

Here, as shown in FIGS. 6 and 7, in this embodiment, when the sheet P is conveyed from the two-sided conveying paths K4 and K5 toward the transfer position N during double-sided conveying, the second conveying roller After the double-sided outlet roller pair 18 that functions as a pair starts to convey, the double-sided outlet roller pair 18 is controlled to continue rotating without stopping.
That is, the rotational driving by the first motor 61 (first driving mechanism) is stopped by continuing to rotationally drive the duplex exit roller pair 18 (second conveying roller pair) by the third motor 63 (second driving mechanism). While the sheet P continues to be conveyed toward the registration roller pair 16 (first conveying roller pair), the sheet P is brought into contact with the registration roller pair 16, and the sheet P is flexed. After a predetermined time T2 has elapsed since the leading edge of the sheet P was detected by the registration sensor 41 (sheet detection sensor) without stopping the rotational driving of the (second conveying roller pair), the registration roller pair is detected by the first motor 61. 16 rotation drive is started.

Specifically, first, as shown in FIG. 6A, the sheet P conveyed along the double-sided conveying path K4 is nipped by the pair of double-sided exit rollers 18, and the tip of the sheet P is detected by the double-sided exit sensor 42. It will be in a standby state (transportation stopped state). That is, as shown in FIG. 7, when the output signal of the double-sided exit sensor 42 changes from off to on, the third motor 63 is switched from on to off. This is because the sheets P may be simultaneously fed (continuously fed) from the feeding device 12 during double-sided transport, so the optimum interval ( This is because it is necessary to time the start of the transport from the double-sided outlet roller pair 18 so that the sheet is transported within the space between sheets. Then, as shown in FIG. 7, the third motor 63 is switched from the OFF state to the ON state after a predetermined time T1 has passed with such timing, and the registration roller pair 16 by the duplex exit roller pair 18 is turned on. Transportation to the is started.
Then, as shown in FIG. 6B, the double-sided exit roller pair 18 advances the sheet P toward the position of the registration roller pair 16 (in which rotation is stopped). Then, the leading edge of the sheet P is detected at the position of the registration sensor 41 . At this time, as shown in FIG. 7, the third motor 63 remains on, the signal from the registration sensor 41 changes from off to on, and the time from that point is counted.
Thereafter, as shown in FIG. 6C, as the sheet P is conveyed and the leading edge of the sheet P collides with the registration roller pair 16, the sheet P bends (the portion surrounded by the dashed line). It is formed. As a result, even if the sheet P is conveyed in a skewed state, the leading edge of the sheet P is displaced along the nip of the registration roller pair 16 due to the force that attempts to restore the deflection. It will be. As a result, the skew of the sheet P is corrected. At this time, the double-side exit roller pair 18 continues to rotate without being stopped.
Then, as shown in FIG. 6(D), after the sheet P is bent as desired and the skew is corrected, the registration roller pair 16 is started to be driven toward the transfer position N, and the timing is adjusted. A sheet P is being conveyed. At this time, as shown in FIG. 7, the timing for starting rotation of the registration roller pair 16 (the timing for switching the first motor 61 from the OFF state to the ON state) is the timing described with reference to FIGS. This is the timing when the predetermined time T2 has elapsed since the signal from the registration sensor 41 changed from off to on. Therefore, during this "predetermined time T2", the target deflection is formed in the sheet P without stopping the rotational driving of the duplex exit roller pair 18, and the image on the photosensitive drum 1 and the transfer position N are aligned. will be adjusted according to the timing for
After that, when the sheet P passes the position of the registration roller pair 16, the registration roller pair 16 stops rotating again in preparation for the sheet P to be conveyed next.
Note that the "predetermined time T2" described above is also adjusted according to the type and stiffness of the sheet P detected by the detection unit.

As described above, even during double-sided conveyance, the skew correction of the sheet P is performed at the position of the registration roller pair 16 that has stopped rotating, and then the sheet P is conveyed by the registration roller pair 16 that has started rotating. Since the roller pair 18 continues to rotate without stopping, the bending of the sheet P during skew correction is less likely to disappear, and the skew correction accuracy of the sheet P can be improved.
In particular, during double-sided conveyance, the sheet P passes through the second curved conveying path K5 having a larger curvature than the first curved conveying path K1. , the application of the present invention becomes useful.

As described above, the conveying device 50 in the present embodiment has the upstream conveying roller pair 17 (or , double-sided conveying roller pair 18) to convey the sheet P toward the registration roller pair 16 (first conveying roller pair) whose rotational driving by the first motor 61 (first drive mechanism) is stopped. In this state, the sheet P is brought into contact with the registration roller pair 16 to bend the sheet P, and the sheet P is kept without stopping the rotational driving of the upstream side conveying roller pair 17 (or the duplex conveying roller pair 18). After a predetermined time T (or a predetermined time T3) has elapsed since the leading edge of the sheet was detected by the registration sensor 41 (sheet detection sensor), the rotation of the registration roller pair 16 by the first motor 61 is started.
As a result, the accuracy of skew correction of the sheet P can be improved.

In this embodiment, the present invention is applied to the conveying apparatus 50 in which the curved conveying paths K1 and K5 are provided in part of the conveying path from the second conveying roller pairs 17 and 18 to the first conveying roller pair 16. Although applied, the present invention can of course also be applied to a conveying apparatus in which a curved conveying path is provided along the entire conveying path from the second conveying roller pair to the first conveying roller pair.
Further, in the present embodiment, a first driving mechanism that rotationally drives the registration roller pair 16 (first conveying roller pair) as the first conveying roller pair, and an upstream conveying roller pair 17 (the second conveying roller pair). Alternatively, a second drive mechanism for rotationally driving the double-side exit roller pair 18) is separately provided. Alternatively, the first drive mechanism and the second drive mechanism may be provided integrally. As such an integral drive mechanism, for example, a gear train leading from one motor to the first conveying roller pair and a gear train leading to the second conveying roller pair are provided, and the former gear train is provided with an electromagnetic drive mechanism. It is possible to use one provided with a drive cut-off means such as a clutch.
Further, in the present embodiment, the present invention can also be applied to a conveying device that conveys the sheet P from the manual feeding device 13 toward the transfer position N.
Also, in the present embodiment, the present invention is applied to the monochrome image forming apparatus 100, but the present invention can of course be applied to a color image forming apparatus.
In addition, in the present embodiment, the present invention is applied to the electrophotographic image forming apparatus 100, but the application of the present invention is not limited to this, and other types of image forming apparatuses (for example, inkjet system image forming apparatus, offset printing press, etc.), as long as the conveying device is installed, the present invention can of course be applied.
Even in these cases, the same effects as those of the present embodiment can be obtained.

It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be appropriately modified within the scope of the technical idea of the present invention other than suggested in the present embodiment. be. Moreover, the number, position, shape, etc. of the constituent members are not limited to those of the present embodiment, and the number, position, shape, etc. can be set to be suitable for carrying out the present invention.

In this specification and the like, "sheet" is not limited to paper (paper), but includes all sheet-like recording media, such as coated paper, label paper, OHP sheet, metal sheet, color sheet, etc. is also included.

12 feeding device,
15 feeding rollers,
16 registration roller pair (first conveying roller pair),
17 upstream transport roller pair (second transport roller pair),
18 double-sided exit roller pair (second conveying roller pair),
41 registration sensor (sheet detection sensor),
42 double-sided exit sensor,
61 first motor (first drive mechanism),
62 second motor (second drive mechanism),
63 third motor (second drive mechanism),
50 transport device,
90 operation display panel (detection unit),
100 image forming apparatus (image forming apparatus main body),
P sheet (recording medium),
K1, K5 curved conveying path, K4 double-sided conveying path,
N transfer position (image forming portion), X confluence portion.

Japanese Patent No. 2760648

Claims (5)

a first conveying roller pair that is rotationally driven by a first drive mechanism to convey the sheet;
a second conveying roller pair that is rotationally driven by a second drive mechanism to convey the sheet toward the first conveying roller pair;
It is arranged at a position on the upstream side in the conveying direction with respect to the first conveying roller pair and at a position on the downstream side in the conveying direction with respect to the second conveying roller pair, and detects the leading edge of the sheet passing through that position. a sheet detection sensor;
a detection unit that detects the type or stiffness of the conveyed sheet;
with
By continuing to rotationally drive the second conveying roller pair by the second driving mechanism, the sheet continues to be conveyed toward the first conveying roller pair whose rotational driving by the first driving mechanism is stopped. The sheet is brought into contact with the first conveying roller pair to bend the sheet, and the leading edge of the sheet is detected by the sheet detection sensor without stopping the rotational driving of the second conveying roller pair. After a lapse of time, the first drive mechanism starts rotating the first conveying roller pair,
When the detecting unit detects that a sheet whose stiffness exceeds the predetermined range is conveyed, it is detected that a sheet whose stiffness is within the predetermined range is conveyed. is adjusted so that the predetermined time is longer than in the case of
Even when the detection unit detects that a sheet whose stiffness does not reach the predetermined range is conveyed, it is detected that a sheet whose stiffness is within the predetermined range is conveyed. The conveying device is adjusted so that the predetermined time is longer than when the conveying device is set . 2. The conveying apparatus according to claim 1, wherein a curved conveying path is provided in part or all of the conveying path from the second conveying roller pair to the first conveying roller pair. The second conveying roller pair is a pair of double-sided outlet rollers arranged at a position closest to a position where the second conveying roller pair joins the conveying route from the feeding device to the first conveying roller pair in the double-sided conveying route. The conveying device according to claim 1 or 2. The first conveying roller pair is a registration roller pair that conveys the sheet toward the image forming unit with matching timing,
4. The conveying apparatus according to any one of claims 1 to 3, wherein said predetermined time is adjusted according to said timing. An image forming apparatus comprising the conveying device according to any one of claims 1 to 4.

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