EP4660115A1

EP4660115A1 - Conveyance device and image forming apparatus

Info

Publication number: EP4660115A1
Application number: EP25171187.5A
Authority: EP
Inventors: Keisuke Takashima; Motoharu Takahashi
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2024-06-07
Filing date: 2025-04-17
Publication date: 2025-12-10
Also published as: JP2025184695A

Abstract

A conveyance device includes a conveyer (11, 19) to convey a recording medium in a conveyance direction; a shifter (11) to shift the recording medium, while conveying the recording medium, from a first conveyance line to a second conveyance line in a width direction; a detector (12a, 12b, 12c, 12d) facing a conveyance path to detect an edge of the recording medium to detect at least one of a skew and a shift of the recording medium, and a controller (511) that controls the shifter (11) to correct the at least one of the skew and the shift, shift the recording medium from the first conveyance line to the second conveyance line, and convey the recording medium along the second conveyance line while an edge of the recording medium is disposed outside an edge of the recording medium conveyed along the first conveyance line in the width direction.

Description

BACKGROUND

Technical Field

The present disclosure relates to a conveyance device and an image forming apparatus.

Related Art

To estimate a factor of the occurrence of an error of a recording medium, such as a sheet, in an image forming apparatus, for example, a technique is known in which an error related to a width, a center position, and a side position of the recording medium is detected according to an output signal of a reading unit such as a contact image sensor (CIS).
Further, to correct the skew and shift of the recording medium nonstop during the conveyance of the recording medium, a technique is known in which the amount of the skew and shift of the recording medium is detected at one side parallel to a conveyance direction and a correction of meandering is performed while the recording medium is conveyed by a conveyance roller.
To detect an accurate position of an edge of the sheet even when the reading unit has a partial abnormality, Japanese Unexamined Patent Application Publication No. 2009-137710 discloses a technique for detecting the accurate position of the sheet edge even when the partial abnormality occurs in the reading unit. In this technique, whether the reading unit, which is likely to be used to detect a position of the sheet edge, has an abnormality due to paper dust or other dust is detected in advance. When an abnormality is detected, the sheet is moved to an outer side of the paper dust in a direction orthogonal to the conveyance direction in advance before the position detection of the sheet edge to avoid the position detection of the sheet edge at this position.
However, in the above-described technique, paper dust is deposited on the contact image sensor, and thus the edge of the recording medium may be erroneously detected. As a result, the skew and shift of the recording medium may not be accurately corrected.

SUMMARY

The present disclosure has been made in view of the above, and an object of the present disclosure is to provide a conveyance device and an image forming apparatus that prevent erroneous detection of an edge of a recording medium and can continuously detect the edge accurately.
The present disclosure described herein provides an improved conveyance device including a conveyor, a shifter, a detector, and a controller. The conveyer conveys a recording medium on a conveyance path in a conveyance direction. The shifter shifts the recording medium on the conveyance path, while conveying the recording medium, from a first conveyance line to a second conveyance line shifted from the first conveyance line in a width direction orthogonal to the conveyance direction. The detector faces the conveyance path to detect an edge of the recording medium to detect at least one of a skew and a shift of the recording medium. The controller controls the shifter to correct the at least one of the skew and the shift of the recording medium, shift the recording medium from the first conveyance line to the second conveyance line when a certain amount of the recording medium has been conveyed, and convey the recording medium along the second conveyance line while an edge of the recording medium is disposed outside an edge of the recording medium conveyed along the first conveyance line in the width direction.
According to one aspect of the present disclosure, the conveyance device and the image forming apparatus prevent erroneous detection of the edge of the recording medium and can continuously detect the edge accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating a configuration of a line head printer;
FIGS. 2A and 2B are diagrams illustrating a configuration of a registration and image forming unit of a line head printer;
FIG. 3 is an enlarged view of a shift roller and the surroundings thereof in a line head printer;
FIG. 4 is an enlarged view of a shift roller and the surroundings thereof in a line head printer, illustrating an erroneous detection due to paper dust;
FIG. 5 is a block diagram illustrating a functional configuration of a line head printer;
FIG. 6 is a flowchart of a process for shifting a conveyance center position in a line head printer;
FIG. 7 is an enlarged view of a shift roller and the surroundings thereof in a line head printer, illustrating a process for correcting a main-scanning positional deviation and a skew amount and the process of FIG. 6; and
FIG. 8 is a block diagram of a controller and related components.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.
Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
A conveyance device and an image forming apparatus are described in detail below with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a configuration of a line head printer.
As illustrated in FIG. 1, a printer 100 includes a registration and image forming unit 1, a pre-coating unit 2, a sheet feeding unit 3, a drying and cooling unit 4, a reverse unit 5, and a sheet ejection unit 6. As illustrated in FIG. 1, the printer 100 conveys a recording medium, such as a sheet, in the direction indicated by arrow D and prints an image on the recording medium.
The sheet feeding unit 3 feeds and conveys sheets one by one. In other words, the sheet feeding unit 3 is a conveyor that conveys a sheet (i.e., a recording medium) to the registration and image forming unit 1 (which may be referred to simply as an image forming unit). The pre-coating unit 2 coats the sheet with an undercoat liquid in advance because ink may be difficult to fix depending on the properties of the sheet. The registration and image forming unit 1 detects and corrects registration and skew of the sheet. Then, the registration and image forming unit 1 delivers the sheet from a cylinder (upstream) to a drum by a gripper (sheet conveyance claw). The registration and image forming unit 1 is an image forming unit that prints an image on the sheet attracted onto the drum with ink discharged from a line head.
The drying and cooling unit 4 evaporates moisture in the ink to dry the ink. The sheet may become hot depending on the properties of the sheet. In such a case, the drying and cooling unit 4 cools the sheet. The reverse unit 5 reverses the sheet in switchback manner and conveys the sheet toward the registration and image forming unit 1 to print an image on the back surface of the sheet. The sheet ejection unit 6 stacks the printed sheets.
FIG. 2A is a diagram illustrating a configuration of a registration and image forming unit of a line head printer. The registration and image forming unit 1 includes edge sensors 12a and 12b (i.e., first detectors) that detect a main-scanning positional deviation, i.e., a positional deviation of a sheet 10 as a recording medium in a main scanning direction (i.e., an amount of shift or a shift amount of a medium center of the sheet 10 shifted from a first conveyance line) and an amount of skew (i.e., a skew amount of the sheet 10 skewed relative to the first conveyance line) of the sheet 10 before the sheet 10 enters a shift roller 11 (a pair of rollers). In other words, the edge sensors 12a and 12b serve as a detector disposed on a conveyance path of the sheet 10 conveyed from the sheet feeding unit 3 to detect the skew amount and the main-scanning positional deviation of the sheet 10 to be conveyed to the shift roller 11. A controller 511 of the registration and image forming unit 1 moves and swings the shift roller 11 to a position facing the sheet 10 in accordance with the detection result of the main-scanning positional deviation and the skew amount, and corrects the main-scanning positional deviation and the skew of the sheet 10 entering the shift roller 11 (i.e., a first correction).
In other words, the controller 511 functions as a control unit that shifts a conveyance center position (line) of the sheet 10 in a direction orthogonal to the conveyance direction of the sheet 10 based on the skew amount and the main-scanning positional deviation, or based on the presence or absence (i.e., a deposition) of foreign substances (e.g., the number of the conveyed sheets 10) to move an edge of the sheet 10 (edge of the conveyed sheet 10) outside the foreign substances such as paper dust. The conveyance direction may be referred to as a sub-scanning direction or a Y-axis direction. The direction orthogonal to the conveyance direction may be referred to as the main scanning direction or an X-axis direction. In addition, the controller 511 moves the edge of the conveyed sheet 10 outside the foreign substances other than the paper dust in the main scanning direction. Thus, even when there are the foreign substances other than paper dust on the detector or the conveyance path, the edge of the conveyed sheet 10 can be continuously detected. The controller 511 may repeatedly shift the conveyance center position. Such control can extend the operation time of a product (e.g., the conveyance device or the image forming apparatus). The controller 511 may prompt a user to perform cleaning (e.g., indicate a warning to clean the detector and the conveyance path) when the conveyance center position is shifted to a position at which the CIS of the edge sensors 12a and 12b does not detect the edge of the conveyed sheet 10 (out of the detection range of the CIS). One end of the detection range may be referred to as an edge sensor home position (HP) as illustrated in FIG. 3. Such control can avoid an error stop due to erroneous detection of an edge and enhance the operating rate of the product. The paper dust and dirt are examples of foreign substances.
Subsequently, in the registration and image forming unit 1, the edge sensor 12b (i.e., downstream end of the multiple first detectors in the conveyance direction) and an edge sensor 12c (i.e., a second detector) detect the main-scanning positional deviation and the skew amount of the sheet 10 being conveyed by the shift roller 11 again, and the controller 511 controls the shift roller 11 to correct the main-scanning positional deviation and the skew of the sheet 10 (i.e., a second correction). When the size of the conveyed sheet 10 is small, an edge sensor 12d is used instead of the edge sensor 12c to shorten the distance from the edge sensor 12b. Then, a gripper 13 grips the leading end of the corrected sheet 10. The gripper 13 is attached to an entrance cylinder 14 and mechanically opened and closed to grip the leading end of the sheet 10. The entrance cylinder 14, an image forming drum 15, and an exit cylinder 18 are coupled by gears to convey the sheet 10 sequentially gripped by grippers attached thereto.
Print heads 17 (17a, 17b, 17c, and 17d) of the registration and image forming unit 1 are line heads in which inkjet (IJ) heads are aligned in the X-axis direction (main scanning direction). The print heads 17 discharge ink onto the sheet 10 when the sheet 10 passes under the print heads 17. For example, the IJ heads discharge inks of colors of black (K), cyan (C), magenta (M), and yellow (Y). At this time, the controller 511 determines a print timing based on the timing at which the sheet 10 passes through a print timing sensor 16.
FIG. 3 is an enlarged view of the shift roller 11 and the surroundings thereof in the line head printer of FIGS. 2A and 2B. The shift roller 11 (shift and skew correction roller) is a roller which is swingable around a rotation center at one end of the shift roller 11 and movable in the X-axis direction. The printer has a function to correct the skew amount and the main scanning position deviation calculated based on the edges of the conveyed sheet 10 detected by the multiple edge sensors 12a to 12d.
In the printer, in a first sheet state illustrated in FIG. 3, the edge sensors 12a and 12b detect the main-scanning positional deviation and the skew amount before the sheet enters the shift roller 11.
In the printer, the controller 511 controls the shift roller 11 to move and swing to a position facing the sheet in accordance with the detection result of the main-scanning positional deviation and the skew amount. Then, the controller 511 controls the shift roller 11 to correct the main-scanning positional deviation and the skew amount of the sheet entering the shift roller 11 from the first sheet state to a second sheet state as illustrated in FIG. 3 (i.e., the first correction).
In the printer, the edge sensors 12b and 12c detect the main-scanning positional deviation and the skew amount of the sheet being conveyed by the shift roller 11 again, and the controller 511 controls the shift roller 11 to correct the main-scanning positional deviation and the skew amount from the second sheet state to a third sheet state as illustrated in FIG. 3 (i.e., the second correction). In the case of a small-size sheet, since the distance from the edge sensor 12b to the edge sensor 12c is too long to detect the main-scanning positional deviation and the skew amount of the sheet, the controller 511 switches the edge sensor 12b to the edge sensor 12d to correct the main-scanning positional deviation and the skew amount of the small-size sheet.
As described above, the shift roller 11 functions as a conveyor to convey the recording medium (sheet) on the conveyance path in the conveyance direction while aligning a center of the recording medium (i.e., the medium center) in the main scanning direction, orthogonal to the conveyance direction, with the conveyance center line (i.e., the first conveyance line) of the conveyance path. In other words, the edge of the recording medium is aligned with a sheet edge reference position illustrated in FIG. 3.
In addition, the shift roller 11 function as the shift and skew correction roller to swing around the rotation center at one end of the shift roller 11 in the main scanning direction to change a skew of the recording medium relative to the conveyance center line and move in the main scanning direction to shift the center of the recording medium from the conveyance center line (i.e., the first conveyance line) to a new conveyance center line (i.e., a second conveyance line shifted from the first conveyance line in the main scanning direction). In other words, the shift roller 11 also functions as a shifter to shift the recording medium on the conveyance path, while conveying the recording medium, from the first conveyance line to the second conveyance line in a direction orthogonal to the conveyance direction.
As described with reference to FIG. 2A, the shift roller 11 functions as the conveyor and the shifter. However, the conveyor and the shifter are not necessarily integrated in a single unit (i.e., the shift roller 11). For example, the shift roller 11 function as the shifter, and a conveyance roller pair 19 function as the conveyor as illustrated in FIG. 2B.
FIG. 4 is an enlarged view of a shift roller and the surroundings thereof in a line head printer, illustrating an erroneous detection due to paper dust. In the printer, the sheet is conveyed with high accuracy by the method described with reference to FIG. 3. However, as the number of sheets of paper passing through the conveyance path increases, paper dust is deposited on an outside 400 of the sheet edge reference position (e.g., on the detector or the conveyance path at another end opposite the one end) as illustrated in FIG. 4. When a certain amount of paper dust is deposited, the CIS does not distinguish between the edge of the sheet and the deposited paper dust. As a result, the edge sensors 12a to 12d may erroneously detect the edge position of the sheet, and thus the conveyance of the sheet may be stopped as an error due to deterioration in the correction accuracy of the main-scanning positional deviation and the skew amount of the sheet or a positional defect of the sheet.
FIG. 5 is a block diagram illustrating a functional configuration of a line head printer. As illustrated in FIG. 5, the printer 100 includes a sheet conveyor 506, the controller 511, and a cleaning notification unit 510. The controller 511 includes a conveyed sheet count storage unit 507, a count comparison unit 508, and a control determination unit 509.
The conveyed sheet count storage unit 507 receives a conveyance notification of the sheet from the sheet conveyor 506 including the shift roller 11, counts the number of conveyed sheets, and stores the count value of the conveyed sheets. After the conveyed sheet count storage unit 507 counts the number of the conveyed sheets, the count comparison unit 508 compares whether the count value (the number of the conveyed sheets) is equal to or more than a predetermined number of sheets. The control determination unit 509 notifies the sheet conveyor 506 whether to shift the conveyance center position of the sheet (i.e., motor control parameters) according to the comparison result between the number of the conveyed sheets and the predetermined number of sheets. The control determination unit 509 determines whether to notify the user of cleaning, and notifies the cleaning notification unit 510 of the determination result (cleaning notification). The cleaning notification unit 510 notifies the user of cleaning. Examples of the cleaning notification unit 510 include a display that displays a warning to clean the detector and the conveyance path and an alarm that gives a warning sign (e.g., a warning light and a warning sound) to clean the detector and the conveyance path.
The controller 511 controls the entire operation of the registration and image forming unit 1 including the operation of the shift roller 11. As illustrated in FIG. 8, the controller 511 includes a central processing unit (CPU) 512, a read-only memory (ROM) 513, a random-access memory (RAM) 514, an electrically erasable programmable read-only memory (EEPROM) 515, and a motor driver 516. The controller 511 is electrically connected to the edge sensors 12a to 12d, the print timing sensor 16, and a motor 517 via, for example, signal lines.
The ROM 513 stores programs executed by the CPU 512 and other data. The RAM 514 is used as a work area for the CPU 512. The EEPROM 1004 stores various kinds of data such as programs and retains various kinds of data even while the printer 100 is powered off. The motor driver 516 drives the motor 517 to move and swing the shift roller 11. The CPU 512 executes the programs to implement, for example, the conveyed sheet count storage unit 507, the count comparison unit 508, and the control determination unit 509 illustrated in FIG. 5.
FIG. 6 is a flowchart of a process for shifting a conveyance center position in a line head printer. In step S1, the conveyed sheet count storage unit 507 clears the count value of the number of the conveyed sheets. In step S2, the conveyed sheet count storage unit 507 receives a conveyance notification of the sheet from the sheet conveyor 506 that conveys the sheet. In step S3, the conveyed sheet count storage unit 507 counts up the number of the conveyed sheets.
In step S4, the count comparison unit 508 determines whether the number of the conveyed sheets counted by the conveyed sheet count storage unit 507 exceeds the predetermined number of sheets. When the number of the conveyed sheets is equal to or less than the predetermined number of sheets (No in step S4), the process returns to step S3, and the conveyed sheet count storage unit 507 continues counting the number of the conveyed sheets. On the other hand, when the number of the conveyed sheets exceeds the predetermined number of sheets (Yes in step S4), in step S5, the control determination unit 509 shifts the conveyance center position of the sheet of the conveyance path. In other words, the controller 511 shifts the medium center of the sheet based on the number of the conveyed sheets (recording media). Alternatively, the edge sensors 12a to 12d detects the presence or absence (i.e., the deposition) of the foreign substances on the edge sensors 12a to 12d (i.e., the detector) and the the conveyance path.
FIG. 7 is an enlarged view of the shift roller 11 and the surroundings thereof in the line head printer, illustrating a process for correcting the main-scanning positional deviation and the skew amount and the process of FIG. 6. The control determination unit 509 shifts the conveyance center position of the sheet so that the edge of the conveyed sheet is positioned on the outer side of paper dust each time the predetermined number of sheets are conveyed. Since the edge of the conveyed sheet is positioned on the outer side of the paper dust, the CIS can accurately detect the edge of the conveyed sheet to avoid erroneous detection due to the paper dust.
As described above, in the printer according to the present embodiment, the edge of the conveyed sheet can be positioned on the outer side of paper dust by shifting the conveyance center position of the sheet so that the edge of the conveyed sheet is outside the paper dust. As a result, the edge of the conveyed sheet can be prevented from being erroneously detected and can be continuously and accurately detected.
Although the image forming apparatus according to the above-described embodiment is a multifunction peripheral having at least two functions of copying, printing, scanning, and facsimile transmission, aspects of the present disclosure are applicable to any image forming apparatus such as a copier, a printer, a scanner, or a facsimile machine.
Aspects of the present disclosure are, for example, as follows.

Aspect 0

A conveyance device includes a conveyor, a shifter, a detector, and a controller. The conveyer conveys a recording medium on a conveyance path in a conveyance direction. The shifter shifts the recording medium on the conveyance path, while conveying the recording medium, from a first conveyance line to a second conveyance line shifted from the first conveyance line in a width direction orthogonal to the conveyance direction. The detector faces the conveyance path to detect an edge of the recording medium to detect at least one of a skew and a shift of the recording medium. The controller controls the shifter to correct the at least one of the skew and the shift of the recording medium, shift the recording medium from the first conveyance line to the second conveyance line when a certain amount of the recording medium has been conveyed, and convey the recording medium along the second conveyance line while an edge of the recording medium is disposed outside an edge of the recording medium conveyed along the first conveyance line in the width direction.

Aspect 1

A conveyance device includes a conveyor, a controller, and a detector. The conveyor conveys a recording medium to an image forming unit. The controller controls the conveyor. The detector is disposed on a conveyance path of the recording medium of the conveyor to detect a skew amount and a shift amount of the recording medium to be fed to the conveyor. The controller shifts a conveyance center position of the recording medium in a direction orthogonal to a conveyance direction of the recording medium and moves a conveyance sheet edge of the recording medium to an outer side of foreign substances based on the skew amount and the shift amount.
In other words, in the conveyance device according to Aspect 0, a shift roller functions as the conveyer and the shifter. The shift roller conveys the recording medium on the conveyance path in the conveyance direction while aligning a medium center of the recording medium in a main scanning direction, orthogonal to the conveyance direction, with the first conveyance line of the conveyance path, swing around a rotation center at one end of the shift roller in the main scanning direction to change the skew of the recording medium relative to the first conveyance line, and move in the main scanning direction to shift the medium center from the first conveyance line to the second conveyance line shifted from the first conveyance line in the main scanning direction. The detector faces the conveyance path at another end of the shift roller in the main scanning direction to detect a skew amount of the recording medium skewed relative to the first conveyance line and a shift amount of the medium center shifted from the first conveyance line. The controller controls the shift roller to correct the skew and the shift of the recording medium based on the skew amount and the shift amount detected by the detector, determines whether foreign substances are deposited at least on the detector or the conveyance path at said another end of the shift roller, and shifts the medium center from the first conveyance line to the second conveyance line in the main scanning direction in response to a determination of a deposition of the foreign substances.
Further, the controller counts a number of recording media including the recording medium conveyed on the conveyance path and determines the deposition of the foreign substances based on the number of recording media.
Alternatively, the detector further detects the deposition of the foreign substances on the detector and the conveyance path.
In addition, the detector includes multiple first detectors upstream from the shift roller in the conveyance direction and a second detector downstream from the shift roller in the conveyance direction. The multiple first detectors detect the skew amount and the shift amount of the recording medium to be conveyed to the shift roller. The second detector and downstream end of the multiple first detectors in the conveyance direction detect the skew amount and the shift amount of the recording medium passing through the shift roller. The controller controls the shift roller to perform a first correction of the skew and the shift of the recording medium based on the skew amount and the shift amount detected by the multiple first detectors and controls the shift roller to perform a second correction of the skew and the shift of the recording medium based on the skew amount and the shift amount detected by the second detector and the downstream end of the multiple first detectors.

Aspect 2

In the conveyance device according to Aspect 1, the foreign substances are paper dust, and the controller moves the conveyance sheet edge to the outer side of the foreign substances other than the paper dust in the direction orthogonal to the conveyance direction.
In other words, the foreign substances include paper dust, and the controller shifts the medium center from the first conveyance line to the second conveyance line in the main scanning direction to move an edge of the recording medium outside the paper dust in the main scanning direction.

Aspect 3

In the conveyance device according to Aspect 1 or 2, the controller repeats the movement of the conveyance center position to extend an operation time.
In other words, the controller repeatedly shifts the medium center to extend an operation time.

Aspect 4

In the conveyance device according to any one of Aspect 1 to 3, the detector includes a contact image sensor (CIS), and the controller prompts a user to perform cleaning when the conveyance center position is shifted to a position at which the CIS does not detect the edge of the conveyed sheet.
In other words, the conveyance device according to any one of Aspect 1 to 3, further includes a cleaning notification unit to indicate a warning to clean the detector and the conveyance path. The detector includes a contact image sensor. The controller causes the cleaning notification unit to indicate the warning when the medium center is shifted to a position at which an edge of the recording medium is out of a detection range of the contact image sensor.

Aspect 5

An image forming apparatus includes an image forming unit, a conveyor, a controller, and a detector. The conveyor conveys a recording medium to the image forming unit. The controller controls the conveyor. The detector is disposed on a conveyance path of the recording medium of the conveyor to detect a skew amount and a shift amount of the recording medium to be fed to the conveyor. The controller shifts a conveyance center position of the recording medium in a direction orthogonal to a conveyance direction of the recording medium and moves a conveyance sheet edge of the recording medium to an outer side of foreign substances based on the skew amount and the shift amount.
In other words, an image forming apparatus includes the conveyance device according to Aspect 1 and an image forming unit to form an image on the recording medium conveyed from the conveyance device.

Claims

A conveyance device comprising:
a conveyer (11, 19) to convey a recording medium on a conveyance path in a conveyance direction,

a shifter (11) to shift the recording medium on the conveyance path, while conveying the recording medium, from a first conveyance line to a second conveyance line shifted from the first conveyance line in a width direction orthogonal to the conveyance direction;

a detector (12a, 12b, 12c, 12d) facing the conveyance path to detect an edge of the recording medium to detect at least one of a skew and a shift of the recording medium:
a controller (511) configured to control the shifter (11) to:
correct the at least one of the skew and the shift of the recording medium;

shift the recording medium from the first conveyance line to the second conveyance line when a certain amount of the recording medium has been conveyed; and

convey the recording medium along the second conveyance line while an edge of the recording medium is disposed outside an edge of the recording medium conveyed along the first conveyance line in the width direction.
The conveyance device according to claim 1,
wherein a shift roller (11) functions as the conveyer (11, 19) and the shifter (11),

the shift roller (11):
conveys the recording medium on the conveyance path in the conveyance direction while aligning a medium center of the recording medium in a main scanning direction, orthogonal to the conveyance direction, with the first conveyance line of the conveyance path;

swings around a rotation center at one end of the shift roller (11) in the main scanning direction to change the skew of the recording medium relative to the first conveyance line; and

moves in the main scanning direction to shift the medium center from the first conveyance line to the second conveyance line in the main scanning direction.;

the detector (12a, 12b, 12c, 12d) faces the conveyance path at another end of the shift roller (11) in the main scanning direction to detect:
a skew amount of the recording medium skewed relative to the first conveyance line; and

a shift amount of the medium center shifted from the first conveyance line; and

the controller (511) is configured to:
control the shift roller (11) to correct the skew and the shift of the recording medium based on the skew amount and the shift amount detected by the detector (12a, 12b, 12c, 12d);

determine whether foreign substances are deposited at least on the detector (12a, 12b, 12c, 12d) or the conveyance path at said another end of the shift roller (11); and

shift the medium center from the first conveyance line to the second conveyance line in the main scanning direction in response to a determination of a deposition of the foreign substances.
The conveyance device according to claim 1 or 2,
wherein the controller (511) is further configured to:
count a number of recording media including the recording medium conveyed on the conveyance path; and

determine the deposition of the foreign substances based on the number of recording media.
The conveyance device according to claim 1 or 2,
wherein the detector (12a, 12b, 12c, 12d) further detects the deposition of the foreign substances on the detector (12a, 12b, 12c, 12d) and the conveyance path.
The conveyance device according to any one of claims 2 to 4,
wherein the detector (12a, 12b, 12c, 12d) includes:
multiple first detectors (12a, 12b) upstream from the shift roller (11) in the conveyance direction; and

a second detector (12c, 12d) downstream from the shift roller (11) in the conveyance direction,

the multiple first detectors (12a, 12b) detect the skew amount and the shift amount of the recording medium to be conveyed to the shift roller (11),

the second detector (12c, 12d) and downstream end of the multiple first detectors (12b) in the conveyance direction detect the skew amount and the shift amount of the recording medium passing through the shift roller (11), and

the controller (511) is further configured to:
control the shift roller (11) to perform a first correction of the skew and the shift of the recording medium based on the skew amount and the shift amount detected by the multiple first detectors (12a, 12b); and

control the shift roller (11) to perform a second correction of the skew and the shift of the recording medium based on the skew amount and the shift amount detected by the second detector (12c, 12d) and the downstream end of the multiple first detectors (12b).
The conveyance device according to any one of claims 1 to 5,
wherein the foreign substances include paper dust, and

the controller (511) is further configured to shift the medium center from the first conveyance line to the second conveyance line in the main scanning direction to move an edge of the recording medium outside the paper dust in the main scanning direction.
The conveyance device according to any one of claims 1 to 6,
wherein the controller (511) is further configured to repeatedly shift the medium center to extend an operation time.
The conveyance device according to any one of claims 1 to 7, further comprising a cleaning notification unit (510) to indicate a warning to clean the detector (12a, 12b, 12c, 12d) and the conveyance path,
wherein the detector (12a, 12b, 12c, 12d) includes a contact image sensor, and

the controller (511) is further configured to cause the cleaning notification unit (510) to indicate the warning when the medium center is shifted to a position at which an edge of the recording medium is out of a detection range of the contact image sensor.
An image forming apparatus (100) comprising:
the conveyance device according to claim 1 or 2; and

an image forming unit to form an image on the recording medium conveyed from the conveyance device.