Sheet material detection device, sheet material transport device, and image forming device

Abstract

To detect a size of a sheet material being conveyed accurately and at low cost.SOLUTION: A sheet material detection device includes a tip flag 15, a protrusion 17Lc of a medium size flag 17L, a protrusion 17Rc of a medium size flag 17R, a protrusion 16Lb of a large size flag 16L, a protrusion 16Rb of a large size flag 16R, and a link 21, wherein the tip flag 15 is arranged in a width direction between the protrusion 17Lc and the protrusion 17Rc, the protrusion 17Lc is moved from a first standby position to a first operating position when the protrusion 16Lb moves from a third standby position to a third operating position, and the protrusion 17Rc is moved from a second standby position to a second operating position when the protrusion 16Rb moves from a fourth standby position to a fourth operating position, and a width of a sheet material is detected based on timing when the tip flag 15 moves and timing when the link 21 moves from the first position to the second position.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a sheet material detection device, a sheet material transport device, and an image forming apparatus, and more particularly to a sheet material detection device that is mounted in an image forming apparatus such as a copying machine or a printer and detects the size of a sheet material. [Background technology]

[0002] Image forming devices such as electrophotographic copiers and printers separate and transport stacked sheets, transfer images from an image carrier to the sheets in an image forming unit, and fix the images to the sheets by applying heat using a fixing unit. When fixing paper (hereinafter referred to as small-size paper) that is narrower than the maximum width (hereinafter referred to as the maximum paper-passing width) of the widths of sheets that can be transported by the image forming device (hereinafter referred to as the paper width), the following problem occurs: The portions of the fixing unit where the sheet does not pass (hereinafter referred to as the non-paper-passing portions) are not heat-absorbed by the sheet, and therefore become hotter than the portions of the fixing unit where the sheet passes (hereinafter referred to as the paper-passing portions). In particular, when small-size paper is continuously transported, the non-paper-passing portions of the fixing unit become excessively hot, which can cause the fixing unit to malfunction.

[0003] In addition, typical image forming apparatuses transport sheets with the center as the reference for transport in the width direction (hereinafter referred to as center-reference transport). Therefore, a width restriction member is provided in the sheet stacking section to restrict the movement of the sheet in the width direction, and the sheet is loaded in a centered state. However, users may mistakenly set the width restriction member to the maximum width of the sheet and then shift the sheet to one side. In this case, the non-paper passing area of the fixing unit becomes larger, making the fixing unit more susceptible to overheating. To prevent malfunctions due to excessive overheating of the fixing unit, image forming apparatuses have a width size detection unit in the transport path that detects the width of the sheet. For example, Patent Document 1 uses one photointerrupter and two recording material contact members to detect small-size paper, detecting both large and small-size paper. Patent Document 2 also uses the detection times of two photointerrupters and two recording material contact members to detect small-size paper, detecting both large and small-size paper. The number of sheets conveyed per unit time is called throughput. When a width detection unit detects that a sheet on the conveyance path is a small-size sheet, the interval between the sheets is made wider than that for a wide-size sheet (hereinafter referred to as a large-size sheet), reducing the throughput and thereby cooling the non-paper passing area of the fixing unit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-240831 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-116499 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method using one photointerrupter and two recording material contact members requires the following settings. Specifically, the throughput must be set to match the smallest sheet size that can be conveyed, so that the fixing unit does not become excessively hot even if the user conveys the sheet to one side of the image forming device. As a result, sheet materials other than those detected as large-size paper will have the throughput of small-size paper, resulting in reduced productivity. Furthermore, the method using two photointerrupters and two recording material contact members requires identical detection mechanisms on both sides to prevent false detection of large-size paper when the user conveys the sheet to one side of the image forming device. This increases costs. Given these factors, there is a demand for a low-cost, highly accurate method for detecting the size of the sheet being conveyed.

[0006] The present invention has been made under these circumstances, and an object of the present invention is to detect the size of a sheet material being conveyed at low cost and with high accuracy. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention has the following configuration. (1) An inner contact portion is provided in a conveying path through which a sheet material passes and is movable in contact with the sheet material; a first contact portion is arranged on one side of the center of the conveying path in a width direction perpendicular to the conveying direction of the sheet material and is movable between a first standby position and a first operating position; a second contact portion is arranged on the other side of the center in the width direction and is movable between a second standby position and a second operating position; a third contact portion is arranged upstream of the first contact portion and the second contact portion in the conveying direction and is arranged outside the first contact portion with respect to the center in the width direction and is movable between a third standby position and a third operating position; a fourth contact portion is arranged upstream of the first contact portion and the second contact portion in the conveying direction and is arranged outside the second contact portion with respect to the center in the width direction and is movable between a fourth standby position and a fourth operating position; a movable member that moves from the first position to a second position different from the first position when the first contact portion is positioned at the first standby position and / or the second contact portion is positioned at the second standby position, and that is restricted from moving from the first position to the second position when the first contact portion is positioned at the first standby position and / or the second contact portion is positioned at the second standby position, wherein in the width direction, the inner contact portion is disposed between the first contact portion and the second contact portion, the first contact portion is moved from the first standby position to the first operating position when the third contact portion moves from the third standby position to the third operating position, and the second contact portion is moved from the second standby position to the second operating position when the fourth contact portion moves from the fourth standby position to the fourth operating position, and the sheet material detection device is configured to detect the width of the sheet material based on the timing when the inner contact portion moves and the timing when the movable member moves from the first position to the second position. (2) A conveying member that conveys a sheet material; an inner contact portion that is provided in a conveying path through which the sheet material passes and is movable in contact with the sheet material; a first contact portion that is arranged on one side of the center of the conveying path in a width direction perpendicular to the conveying direction of the sheet material and is movable between a first standby position and a first operating position; a second contact portion that is arranged on the other side of the center in the width direction and is movable between a second standby position and a second operating position; a third contact portion that is arranged upstream of the first contact portion and the second contact portion in the conveying direction and is arranged outside the first contact portion with respect to the center in the width direction and is movable between a third standby position and a third operating position; a fourth contact portion that is arranged upstream of the first contact portion and the second contact portion in the conveying direction and is arranged outside the second contact portion with respect to the center in the width direction and is movable between a fourth standby position and a fourth operating position; and a movable member that is restricted from moving from the first position to the second position when the first contact portion is located at the first standby position and / or the second contact portion is located at the second standby position, wherein in the width direction, the inner contact portion is disposed between the first contact portion and the second contact portion, the first contact portion is moved from the first standby position to the first active position when the third contact portion moves from the third standby position to the third active position, and the second contact portion is moved from the second standby position to the second active position when the fourth contact portion moves from the fourth standby position to the fourth active position, and the sheet material conveying device is configured to change the number of sheets conveyed by the conveying member per unit time based on the timing at which the inner contact portion moves and the timing at which the movable member moves from the first position to the second position. (3) An image forming apparatus having an image forming unit that forms an image on a sheet material, characterized in that the image forming apparatus is equipped with the sheet material detection device described in (1), and the sheet material detection device is located upstream of the image forming unit in the conveying direction. (4) An image forming apparatus including an image forming section for forming an image on a sheet material, the image forming apparatus comprising the sheet material conveying device according to (2) above. [Effects of the Invention]

[0008] According to the present invention, the size of the sheet material being conveyed can be detected accurately at low cost. [Brief explanation of the drawings]

[0009] [Figure 1] Cross-sectional view of the image forming apparatus according to the first and second embodiments [Figure 2] Schematic diagram of a sheet material conveying path in Examples 1 and 2 [Figure 3] 1 is a perspective view of a sheet material detection mechanism according to a first embodiment; [Figure 4] Timing chart of the sheet size detection mechanism during central conveyance in the first embodiment [Figure 5] Timing chart of the sheet size detection mechanism during one-sided conveyance in the first embodiment [Figure 6] FIG. 10 is a perspective view of a sheet material detection mechanism according to a second embodiment of the present invention; [Figure 7] Timing chart of the sheet size detection mechanism during central conveyance in the second embodiment [Figure 8] Timing chart of the sheet size detection mechanism during one-sided conveyance in the second embodiment DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a detailed description of an embodiment of the present invention will be given with reference to the drawings. In the following description, the width of a sheet material is referred to as the paper width. The width is the length of the sheet material in a direction (width direction) perpendicular to the conveying direction of the sheet material.

[0011] The maximum paper width is the width of the paper that can be used to form an image in an image forming apparatus, in other words, the width that can be conveyed. Paper that is narrower than the maximum paper width is called small size paper.

[0012] The portion of the fixing unit through which small-sized paper does not pass is called a non-paper passing portion, and the portion of the fixing unit through which small-sized paper passes is called a paper passing portion.

[0013] When conveying a sheet material, the reference in the width direction is the center, which is called center-referenced conveyance. When conveying a sheet material, the reference is the edge of one end (e.g., the left side) or the other end (e.g., the right side) in the width direction, which is called side-biased conveyance.

[0014] A sheet material with a paper width wider than that of a small size paper is called a large size paper, and a sheet material with a paper width intermediate between the large size paper and the small size paper is called a medium size paper.

[0015] The interval between sheets refers to the length from the trailing edge of a sheet to the leading edge of the next sheet to be conveyed, and is also called the paper gap. The interval between sheets can also refer to the time (also called the time interval) depending on the sheet conveyance speed. Therefore, widening the interval between sheets (increasing the interval) means delaying the timing of conveying the next sheet. [Example]

[0016] [Image forming device] 1 is a cross-sectional view of an image forming apparatus according to a first embodiment. A sheet material S is regulated by a width regulating guide 1, which is a width regulating member, so that the sheet material S is conveyed toward the center in the width direction of the sheet material S, and is then stacked on a stacking unit 30. The sheet material S is separated one by one by a paper feeding unit 2, and conveyed to a conveying unit 4 along a conveying guide 3 that forms a conveying path through which the sheet material S passes. The sheet material S is conveyed by the conveying unit 4 to an image forming unit 5.

[0017] In this embodiment, the width regulation guides 1 are configured to move in conjunction with each other. One width regulation guide 1 and the other width regulation guide 1 are connected, and when one width regulation guide 1 is moved outward in the width direction, the other width regulation guide 1 also moves outward in the width direction. The pair of width regulation guides 1 (pair of width regulation members) causes the center of the sheet material to coincide with the center of the conveying path in the width direction. In other words, the center of the conveying path in the width direction coincides with the center of the pair of width regulation guides 1. The center in the width direction can be said to be the position that bisects the distance between the pair of width regulation guides 1.

[0018] A detection unit 6, which is a detection means, is disposed upstream of the image forming unit 5 in the conveying direction, and the timing of image formation is controlled based on the detection results of the detection unit 6. In addition, a detection unit 7, which is a first contact means and a second contact means, is disposed downstream of the detection unit 6 in the conveying direction, and the width of the sheet material S is detected by the detection unit 7, and control corresponding to the width of the sheet material S is performed based on the detection results of the detection unit 7.

[0019] In the image forming unit 5, which forms an image on the sheet material S, a charging roller 9 charges the photosensitive drum 8, and a laser unit 10 forms a latent image on the photosensitive drum 8. A developing roller 11 develops the latent image on the photosensitive drum 8 to form a toner image. The formed toner image is transferred to the sheet material S by a transfer roller 12. The sheet material S with the transferred toner image is subjected to heat and pressure by a fixing unit 13, and the unfixed toner image is fixed to the sheet material S. The sheet material S is then transported along a transport guide 3 to a discharge unit 14, and the sheet material S is discharged outside the image forming apparatus main body. The image forming apparatus feeds the next sheet material S at an interval corresponding to the length (length in the transport direction) of the sheet material S detected by the detection unit 6 and the width of the sheet material S detected by the detection unit 7, and performs continuous image formation. Note that the control for transporting the sheet material S at an interval corresponding to the width of the sheet material S is well known, and therefore a description thereof will be omitted.

[0020] The control unit 100 has a CPU 110, a ROM 111, a RAM 112, and a timer 113. The CPU 110 executes various programs stored in the ROM 111, and controls the image forming apparatus while using the RAM 112 as a temporary work area and referring to the timer 113. The control unit 100 detects the width of the sheet material S being conveyed based on the detection results of the detection units 6 and 7.

[0021] In this way, by detecting the width of the sheet material S, even when small-sized paper is conveyed, it is possible to provide an interval corresponding to the width of the sheet material S. This reduces the temperature of non-paper passing areas of the fixing unit 13, making it possible to continue image formation continuously without raising the temperature of the fixing unit 13 excessively high. Note that the image forming apparatus is not limited to the configuration shown in FIG. 1 and may be, for example, a color image forming apparatus.

[0022] In this embodiment, the paper feed unit 2, conveyance unit 4, photosensitive drum 8, fixing unit 13, and discharge unit 14 function as conveyance members that convey the sheet material S. The paper feed unit 2, conveyance unit 4, photosensitive drum 8, fixing unit 13, and discharge unit 14 are configured to be rotatable about their respective rotation axes. In this embodiment, the rotation axis direction of the paper feed unit 2, the rotation axis direction of the conveyance unit 4, the rotation axis direction of the photosensitive drum 8, the rotation axis direction of the fixing unit 13, the rotation axis direction of the discharge unit 14, and the width direction are parallel to one another. Throughput is the number of sheet materials S conveyed by the conveyance members per unit time. In this embodiment, reducing the throughput means widening the gap between the preceding sheet material S and the following sheet material S. Note that the throughput can also be reduced by reducing the conveyance speed of the conveyance members.

[0023] [Mechanism for detecting the width of the sheet material] A mechanism for detecting the width of sheet material S (hereinafter referred to as width detection mechanism), which is a sheet material detection device of embodiment 1, will be described with reference to Figs. 2 to 5. Fig. 2 is a schematic diagram of the conveyance path of sheet material S. Fig. 3 is a perspective view of the width detection mechanism. Fig. 4 is a timing chart of the width detection mechanism for sheet material S during center-based conveyance. Fig. 5 is a timing chart of the width detection mechanism for sheet material S during one-sided conveyance.

[0024] FIG. 2 shows a case where three sizes of sheet materials S—large size paper S1, medium size paper S2, and small size paper S3—are selectively transported at a reference position OO during center-reference transport, indicated by a dashed line. The arrangement of each sheet material S and the detectors 6 and 7 will be described using FIG. 2. Large size paper S1 has a first width W1. Medium size paper S2 has a second width W2 that is narrower than the first width. Small size paper S3 has a third width W3 that is narrower than the second width. Furthermore, the size relationship in the width direction, including L1, L2, and L3 (described later), is W1 > 2×L1 > W2 > 2×L2 > W3 > 2×L3. In this embodiment, the reference position OO coincides with the center of the transport path in the width direction.

[0025] Hereinafter, the detection unit 6 will be referred to as a leading edge flag (inner contact unit) 15. The leading edge flag 15 is provided on the conveying path along which the sheet material S is conveyed, and is included in a detection means for detecting the presence or absence of the sheet material S. The detection unit 7 also has a large size flag pair as the second contact means, and a medium size flag pair as the first contact means.

[0026] The large size flag pair includes a large size flag 16L and a large size flag 16R. The medium size flag pair includes a medium size flag 17L and a medium size flag 17R. The large size flag 16L is disposed symmetrically to the large size flag 16R with respect to the center in the width direction (the center of the conveying path), and the medium size flag 17L is disposed symmetrically to the medium size flag 17R with respect to the center in the width direction. In the width direction, the large size flag 16L and the medium size flag 17L are disposed on one side of the center of the conveying path, and the large size flag 16R and the medium size flag 17R are disposed on the other side of the center of the conveying path. The large size flag 16L is disposed outside the medium size flag 17L with respect to the center in the width direction, and the large size flag 16R is disposed outside the medium size flag 17R with respect to the center in the width direction.

[0027] 3, the medium-sized flag 17L has a protrusion 17Lc which is a first contact portion, and the medium-sized flag 17R has a protrusion 17Rc which is a second contact portion. The large-sized flag 16L has a protrusion 16Lb which is a third contact portion, and the large-sized flag 16R has a protrusion 16Rb which is a fourth contact portion. The protrusions 16Lb, 16Rb, 17Lc, and 17Rc are contact portions that can come into contact with the sheet material S.

[0028] As shown in FIG. 2, the protrusions 16Lb and 16Rb are disposed symmetrically with respect to the reference position OO, at a distance L1 (e.g., approximately 95 mm) from the reference position OO toward the outside in the width direction. The protrusions 16Lb and 16Rb are disposed upstream of the protrusions 17Lc and 17Rc in the conveying direction. The protrusion 16Rb is disposed symmetrically with respect to the center in the width direction to the protrusion 16Lb. The protrusion 17Rc is disposed symmetrically with respect to the center in the width direction to the protrusion 17Lc.

[0029] Protrusion 16Lb is located on one side of the center of the conveying path in the width direction, and is located further outward than protrusion 17Lc with respect to the center of the conveying path. Protrusion 16Rb is located on the other side of the center of the conveying path in the width direction, and is located further outward than protrusion 17Rc with respect to the center of the conveying path.

[0030] The protrusions 17Lc and 17Rc are arranged symmetrically with respect to the reference position OO, at a distance L2 (e.g., approximately 64 mm) from the reference position OO toward the outside in the width direction. This is intended to detect the sizes of sheet material S commonly available on the market, such as A4 (210 mm wide) and A5 (148 mm wide). Therefore, the specific numerical values may be changed depending on the paper width of the sheet material S used in the image forming device.

[0031] The protrusion 17Lc is positioned outward of the leading edge flag 15 in the width direction. The protrusion 17Rc is positioned symmetrically to the protrusion 17Lc with respect to the center in the width direction. The protrusion 17Lc is positioned on one side of the center of the conveying path in the width direction. The protrusion 17Rc is positioned on the other side of the center of the conveying path in the width direction. In the width direction, the leading edge flag 15 is positioned between the protrusion 17Lc and the protrusion 17Rc.

[0032] The medium size flag 17L changes to the first state when the large size flag 16L changes to the first state, and the medium size flag 17R changes to the first state when the large size flag 16R changes to the first state. On the other hand, the medium size flag 17L can change to the first state when the large size flag 16L is in the second state, and the medium size flag 17R can change to the first state when the large size flag 16R is in the second state.

[0033] Here, the first state is a state in which the flag is in contact with the sheet material S, and the second state is a state in which the flag is not in contact with the sheet material S. When each flag is in the second state, the flag protrudes into the conveying path, and when it comes into contact with the sheet material S, it transitions to the first state.

[0034] Specifically, in the second state of the medium size flag 17L, the protrusion 17Lc is located at the first standby position, and when the protrusion 17Lc comes into contact with the sheet material S and moves from the first standby position to the first actuated position, the medium size flag 17L transitions to the first state. In the second state of the medium size flag 17R, the protrusion 17Rc is located at the second standby position, and when the protrusion 17Rc comes into contact with the sheet material S and moves from the second standby position to the second actuated position, the medium size flag 17R transitions to the first state. In the second state of the large size flag 16L, the protrusion 16Lb is located at the third standby position, and when the protrusion 16Lb comes into contact with the sheet material S and moves from the third standby position to the third actuated position, the large size flag 16L transitions to the first state. In the second state of the large size flag 16R, the protrusion 16Rb is located at the fourth standby position, and when the protrusion 16Rb abuts against the sheet material S and moves from the fourth standby position to the fourth operating position, the large size flag 16R transitions to the first state.

[0035] In other words, the protrusion 17Lc is in the first standby position in the second state of the medium-size flag 17L, and is in the first actuated position in the first state of the medium-size flag 17L. That is, the protrusion 17Lc is movable between the first standby position and the first actuated position. Similarly, the protrusion 17Rc is in the second standby position in the second state of the medium-size flag 17R, and is in the second actuated position in the first state of the medium-size flag 17R. That is, the protrusion 17Rc is movable between the second standby position and the second actuated position.

[0036] The protrusion 16Lb is in a third standby position in the second state of the large-size flag 16L, and in a third actuated position in the first state of the large-size flag 16L. That is, the protrusion 16Lb is movable between the third standby position and the third actuated position. Similarly, the protrusion 16Rb is in a fourth standby position in the second state of the large-size flag 16R, and in a fourth actuated position in the first state of the large-size flag 16R. That is, the protrusion 16Rb is movable between the fourth standby position and the fourth actuated position.

[0037] As will be described later, when the protrusion 16Lb moves from the third standby position to the third actuation position, the large size flag 16L moves the medium size flag 17L so that the protrusion 17Lc moves from the first standby position to the first actuation position. When the protrusion 16Rb moves from the fourth standby position to the fourth actuation position, the large size flag 16R moves the medium size flag 17R so that the protrusion 17Rc moves from the second standby position to the second actuation position. In other words, when the protrusion 16Lb moves from the third standby position to the third actuation position, the protrusion 17Lc is moved from the first standby position to the first actuation position. When the protrusion 16Rb moves from the fourth standby position to the fourth actuation position, the protrusion 17Rc is moved from the second standby position to the second actuation position.

[0038] The medium-sized flags 17L and 17R are symmetrical in shape and have similar functions. The large-sized flags 16L and 16R are symmetrical in shape and have similar functions. In the following description, the suffixes L and R may be omitted unless the left and right are specified. For example, when describing protrusions 16Lb and 16Rb regardless of whether they are left or right, they may be written as protrusion 16b, omitting the L and R.

[0039] To detect the leading edge of the sheet S, a leading edge flag 15 is disposed at a distance L3 (e.g., approximately 30 mm) from the reference position OO toward the outside in the width direction, on one side of the reference position OO. For example, in the first embodiment, the leading edge flag 15 is disposed on the same side as the large size flag 16L and the medium size flag 17L. This is intended to detect the smallest size sheet S compatible with the image forming apparatus. In other words, the leading edge flag 15 is capable of detecting all sheet materials S that can be conveyed by the image forming apparatus. The leading edge flag 15 is disposed upstream in the conveying direction, the large size flag 16 is disposed downstream of the leading edge flag 15 in the conveying direction, and the medium size flag 17 is disposed downstream of the large size flag 16 in the conveying direction.

[0040] From the above, the width W1 of large-size paper S1 is greater than the distance (= 2 × L1) between the left and right protrusions 16Lb and 16Rb. The width W2 of medium-size paper S2 is equal to or less than the distance (= 2 × L1) between the protrusions 16Lb and 16Rb, and greater than the distance (= 2 × L2) between the protrusions 17Lc and 17Rc. The width W3 of small-size paper S3 is equal to or less than the distance (= 2 × L2) between the protrusions 17Lc and 17Rc, and greater than twice the distance (= 2 × L3) between the leading edge flag 15 and the reference position OO.

[0041] [Width detection mechanism operation] Next, the operation of the width detection mechanism will be described with reference to Figure 3. Leading edge flag 15 is held by spring 18 in a position shown in Figure 3(a) (hereinafter referred to as the standby position) where its leading edge protrudes from conveyance guide 3 (see Figure 1). Because its leading edge protrudes from conveyance guide 3, leading edge flag 15 interferes with the conveyed sheet material S. When sheet material S comes into contact with leading edge flag 15, leading edge flag 15 is pushed by sheet material S and swings to the position shown in Figure 3(b) (hereinafter referred to as the detection position).

[0042] The leading edge flag 15 has a detection unit 15a, which blocks light from the photointerrupter 23 when in the standby position (FIG. 3(a)), and transmits light when in the detection position (FIG. 3(b)). When the leading edge flag 15 swings, the detection unit 15a also swings in conjunction, switching the photointerrupter 23 between a light-blocking state and a light-transmitting state. When the photointerrupter 23 is light-blocking, no sheet material S is present in the conveying guide 3 (hereinafter referred to as "paper absent"), and this state is designated "Off." On the other hand, when the photointerrupter 23 is light-transmitting, a sheet material S is present in the conveying guide 3 (hereinafter referred to as "paper present"), and this state is designated "On." The leading edge flag 15 functions as a fifth contact unit (inner contact unit) that can be in a first state or a second state. The photointerrupter 23 functions as a first detection unit that detects the presence of a sheet when the fifth contact unit is in the first state, and detects the absence of a sheet when the fifth contact unit is in the second state. The leading edge flag 15 as the fifth contact portion and the photointerrupter 23 as the first detection portion are included in the detection means.

[0043] The large size flag 16 is held by a spring 19 in a standby position where its tip protrudes from the conveying guide 3 (FIG. 3(a)). That is, the large size flags 16R and 16L are in the second state. In this state, the protrusions 16Lb and 16Rb protrude into the conveying path. When the sheet material S contacts the protrusion 16b of the large size flag 16, the large size flag 16 swings to the detection position. That is, the large size flags 16 (16L, 16R) are in the first state. The large size flags 16R and 16L have contact portions 16La and 16Ra. The large size flag 16 is not in contact with the medium size flag 17 in the standby position. On the other hand, when the large size flag 16 swings to the detection position, the contact portion 16La of the large size flag 16L comes into contact with the contact portion 17La of the medium size flag 17L, causing the medium size flag 17 to swing to the detection position (FIG. 3(b)). When the contact portion 16Ra of the large-size flag 16R swings to the detection position, it comes into contact with the contact portion 17Ra of the medium-size flag 17R, causing the medium-size flag 17 to swing to the detection position (FIG. 3(b)). The contact portions 16La and 16Ra function as force applying portions that press the contact portions (force receiving portions) 17La and 17Ra.

[0044] On the other hand, when the medium size flag 17 moves from the standby position to the detection position, the contact portions 17a (17La, 17Ra) move in a direction away from the contact portions 16a (16La, 16Ra). This allows the medium size flag 17 to move to the detection position while the large size flag 16 is in the standby position (independently from the large size flag 16).

[0045] The medium size flag 17 is held by a spring 20 in a standby position where its tip protrudes from the conveying guide 3 (FIG. 3(a)). That is, the medium size flags 17R and 17L are in the second state. In this state, the protrusions 17Lc and 17Rc protrude into the conveying path. When the sheet material S comes into contact with the protrusion 17c of the medium size flag 17, the medium size flag 17 swings to the detection position. That is, the medium size flags 17R and 17L are in the first state. The medium size flag 17L has an abutment portion 17La that abuts against the large size flag 16L and an abutment portion 17Lb that abuts against the link 21. The medium size flag 17R has an abutment portion 17Ra that abuts against the large size flag 16R and an abutment portion 17Rb that abuts against the link 21. When the medium-sized flag 17L swings to the detection position, the contact portion 17Lb that comes into contact with the link 21 rotates in a direction away from the link 21 (FIG. 3(b)). When the medium-sized flag 17R swings to the detection position, the contact portion 17Rb that comes into contact with the link 21 rotates in a direction away from the link 21 (FIG. 3(b)).

[0046] The link 21 is loaded by a spring 22 in a direction that causes it to abut against the medium-size flag 17. The link 21 also has abutting portions 21a (21La, 21Ra) that abut against the abutting portions 17b (17Lb, 17Rb) of the medium-size flag 17. The rotational moment due to the weight of the link 21 is set to be less than half of the rotational moment due to the weight of the spring 20 and the medium-size flag 17. As a result, when one or both of the medium-size flags 17R and 17L are in the standby position, the link 21 is in the standby position and is restricted from moving to the detection position (FIG. 3(a)). When both the medium-size flags 17R and 17L swing to the detection position, the link 21 swings to the detection position (FIG. 3(b)). The link 21 has a detection portion 21b, which transmits light through the photointerrupter 24 when the detection portion 21b is in the standby position and blocks light when the detection portion 21b is in the detection position. This allows the photointerrupter 24 to detect that the link 21 has swung. When the photointerrupter 24 transmits light (no paper), it is off, and when it blocks light (paper present), it is on. The photointerrupter 24 functions as a second detector that detects the absence of a sheet when the link 21 is in the first position, and detects the presence of a sheet when the link 21 is in the second position.

[0047] The link 21 functions as a moving member that moves from a first position to a second position different from the first position depending on the states of the medium size flag 17L, the medium size flag 17R, the large size flag 16L, and the large size flag 16R. Here, the first position is the standby position described above, and the second position is the detection position. The link 21 moves from the first position to the second position when both the medium size flag 17L and the medium size flag 17R are in the first state. Furthermore, the medium size flags 17L and 17R are linked to the first state when the large size flags 16L and 16R are in the first state, so when the large size flags 16L and 16R are in the first state, the link 21 moves from the first position to the second position.

[0048] In other words, the movement of the link 21 is restricted by the abutment portions 17b (17Lb, 17Rb) of the medium-sized flag 17 coming into contact with the abutment portions 21a (21La, 21Ra). The abutment portions 17b (17Lb, 17Rb) of the medium-sized flag 17 come into contact with the abutment portions 21a (21La, 21Ra) as restricted portions, thereby functioning as restricting portions (movement restricting portions) that restrict the movement of the link 21. When the protrusion 17Lc moves to the first operating position and the protrusion 17Rc moves to the second operating position, the link 21 can move from the first position to a second position different from the first position. When the protrusion 17Lc is located in the first standby position and / or the protrusion 17Rc is located in the second standby position, the link 21 is restricted from moving from the first position to the second position.

[0049] [Central reference transport] Next, using Figure 4, we will explain the timing chart of each sensor flag and each photointerrupter when the sheet material S is transported with the center as the reference. In Figures 4(a) to (c), the top shows the state of the photointerrupter 23 (On (high level), Off (low level)), and the second shows the state of the photointerrupter 24 (On (high level), Off (low level)). The bottom shows the positional relationship between the sheet material S (S1 to S3) and each flag (15 to 17). The dashed line indicates the reference position OO, the dashed line indicates the path that the sheet material S passes through in the transport direction, and the broken lines indicate the timing when the outputs of the photointerrupters 23 and 24 switch. The left and right sides indicate the left and right sides as seen from the upstream side in the transport direction. In the following explanation, it is assumed that all sheet materials are transported at the same transport speed. In FIG. 4, the reference symbols 16L, 16R, 17L, and 17R indicate the positions of the protrusion 16Lb, the protrusion 16Rb, the protrusion 17Lc, and the protrusion 17Rc, respectively.

[0050] (large size paper) When large-size sheet S1 is transported center-based, it comes into contact with leading-edge flag 15, switching photointerrupter 23 from Off to On. As large-size sheet S1 moves downstream in the transport direction, it comes into contact with large-size flags 16L and 16R located on the left and right sides in the width direction. This causes left and right large-size flags 16L and 16R to swing, and in conjunction with this, left and right medium-size flags 17L and 17R also swing. As both left and right medium-size flags 17L and 17R swing, link 21 swings, and photointerrupter 24 switches from Off to On. The time from when photointerrupter 23 turns On to when photointerrupter 24 turns On is defined as T1 (FIG. 4(a)).

[0051] (medium size paper) When medium-sized paper S2 is transported center-referenced, it comes into contact with the leading edge flag 15, switching the photointerrupter 23 from Off to On. The medium-sized paper S2 moves downstream in the transport direction. Because the width of the medium-sized paper S2 is inside the positions of the two large-sized flags 16L and 16R, the medium-sized paper S2 does not come into contact with the large-sized flags 16L and 16R. As the medium-sized paper S2 further moves downstream in the transport direction, it comes into contact with the medium-sized flags 17L and 17R located on the left and right sides of the width. This causes the left and right medium-sized flags 17L and 17R to swing. The swinging of both the left and right medium-sized flags 17L and 17R causes the link 21 to swing, switching the photointerrupter 24 from Off to On. The time from when the photointerrupter 23 turns On to when the photointerrupter 24 turns On is defined as T2. Since the medium size flags 17L and 17R are located downstream in the transport direction from the large size flags 16L and 16R, the photointerrupter 24 for the medium size sheet S2 is switched on later than for the large size sheet S1. Therefore, the time T2 is longer than the time T1 (FIG. 4(b)) (T2>T1).

[0052] (small size paper) When small size sheet S3 is transported based on the center, it comes into contact with leading edge flag 15, and photointerrupter 23 switches from Off to On. Small size sheet S3 moves downstream in the transport direction, but because its width is inside the positions of large size flags 16L and 16R, small size sheet S3 does not come into contact with large size flags 16L and 16R. Small size sheet S3 also moves downstream in the transport direction, but because its width is inside the positions of medium size flags 17L and 17R, small size sheet S3 does not come into contact with medium size flags 17L and 17R. In other words, when small size sheet S3 is transported based on the center, photointerrupter 24 remains Off (does not turn On) (FIG. 4C). The trailing edge of small size sheet S3 passes (exits) leading edge flag 15, with photointerrupter 24 still Off. This switches the photointerrupter 23 from On to Off. As described above, the size of the sheet material S in the width direction can be detected from the detection times of the photointerrupters 23 and 24.

[0053] The control unit 100 determines that the sheet is a large-size sheet S1 based on the time T1 between when the leading edge flag 15 detects the presence of a sheet and when the link 21 moves to the second position as both the large-size flags 16L and 16R enter the first state. The control unit 100 determines that the sheet is a medium-size sheet S2 based on the time T2 between when the leading edge flag 15 detects the presence of a sheet and when the link 21 moves to the second position as both the medium-size flags 17L and 17R enter the first state. The control unit 100 determines that the sheet is a small-size sheet S3 based on the time between when the leading edge flag 15 detects the presence of a sheet and when the leading edge flag 15 detects the absence of a sheet without the link 21 moving to the second position. Here, the time when the leading edge flag 15 detects the presence of a sheet is when the leading edge of the sheet S reaches the leading edge flag 15. The time when the leading edge flag 15 detects the absence of a sheet is when the trailing edge of the sheet S passes (leaves) the leading edge flag 15. The control unit 100 functions as a determination unit that determines the width of the sheet material S based on the detection result by the leading edge flag 15 and the position of the link 21.

[0054] In this embodiment, the number of sheets S conveyed by the conveying member per unit time varies depending on the detected size of the sheet S. Specifically, when the control unit 100 determines that the sheet S is a large-size sheet S1, the control unit 100 controls the conveying member so that the interval between the sheets S is a first interval and the throughput is a first amount. When the control unit 100 determines that the sheet S is a medium-size sheet S2, the control unit 100 controls the conveying member so that the interval between the sheets S is a second interval and the throughput is a second amount. When the control unit 100 determines that the sheet S is a small-size sheet S3, the control unit 100 controls the conveying member so that the interval between the sheets S is a third interval and the throughput is a third amount. The second amount is smaller than the first amount, and the third amount is smaller than the second amount. The second interval is longer than the first interval, and the third interval is longer than the second interval.

[0055] [When transporting off to one side] Next, using FIG. 5, we will explain the timing chart of each flag and each photointerrupter when the sheet material S is conveyed with one side shifted while the width restriction guide 1 is maintained at the maximum width position. Note that FIGS. 5(a) and 5(b) are similar to FIGS. 4(a) to 4(c). Because the image forming apparatus is designed to convey the sheet with a center reference, this type of conveyance is not normally performed. However, due to a user's erroneous operation, the sheet material S may be conveyed with one side shifted to the left or right, based on the width of the large-size sheet S1, as shown in FIG. 5. While the first embodiment will be described with the left shifted position, the same applies to the right shifted position, with the left and right shifted positions reversed. In FIG. 5, reference numerals 16L, 16R, 17L, and 17R indicate the positions of the protrusions 16Lb, 16Rb, 17Lc, and 17Rc, respectively.

[0056] [When sheet material S4 is pushed to one side] For example, when the sheet S4 is conveyed with its left side shifted, it contacts the large size flag 16L but not the large size flag 16R, and it contacts both the medium size flags 17L and 17R. Note that when the sheet S4 is conveyed with its right side shifted, the left-right relationship is reversed. When the sheet S4 is shifted to the left, the sheet S4 contacts the leading edge flag 15, and the photointerrupter 23 switches from Off to On. The sheet S4 advances downstream in the conveyance direction, but is shifted to the left. Therefore, the sheet S4 contacts the left large size flag 16L but not the right large size flag 16R. In other words, the left large size flag 16L swings, and the left medium size flag 17L also swings in conjunction with this. However, since the right large size flag 16R does not swing, the right medium size flag 17R does not swing either. Therefore, only the medium size flag 17 on one side has swung to the detection position, and the link 21 does not move. That is, at this point, the photointerrupter 24 remains off.

[0057] As sheet S4 continues downstream in the transport direction, it comes into contact with the right-side medium-size flag 17R, causing the right-side medium-size flag 17R to swing. Because the left-side medium-size flag 17L has already swung to the detection position, the swing of the right-side medium-size flag 17R causes the link 21 to swing, switching the photointerrupter 24 from Off to On. The time from when the photointerrupter 23 turns On to when the photointerrupter 24 turns On is defined as T3. Time T3 is the same as time T2 in Figure 4(b), and the image forming device detects sheet S4 as medium-size paper. Because sheet S4 is shifted to the left when passing through the fixing unit 13, the non-paper-passing area on the right side is larger than when transporting with center reference. The non-paper-passing area on the right side of sheet S4 as it passes through the fixing unit 13 is the same as when transporting medium-size paper S2. Therefore, even if sheet material S4 is detected as medium-sized paper, there is no problem in terms of reducing the temperature rise in the non-paper passing areas if the interval between the transported sheets S is controlled in the same way as in the case of medium-sized paper S2.

[0058] [When sheet material S5 is pushed to one side] For example, when the sheet S5 is conveyed with its left side shifted, it contacts the large-size flag 16L and the medium-size flag 17L but does not contact the large-size flag 16R and the medium-size flag 17R. Note that when the sheet S5 is conveyed with its right side shifted, the left-right relationship is reversed. When the sheet S5 is shifted to the left, the sheet S5 contacts the leading edge flag 15, and the photointerrupter 23 switches from Off to On. The sheet S5 advances downstream in the conveyance direction, but is shifted to the left. Therefore, the sheet S5 contacts the large-size flag 16L on the left side but does not contact the large-size flag 16R on the right side. In other words, the left large-size flag 16L swings, and the left medium-size flag 17L swings accordingly. However, since the right large-size flag 16R does not swing, the right medium-size flag 17R does not swing either. Therefore, only one medium-size flag 17 swings to the detection position, and the link 21 does not move. That is, the photointerrupter 24 remains off.

[0059] Sheet S5 continues downstream in the conveyance direction, but because its right edge is shifted to the left of the medium-size flag 17R on the right side, it does not come into contact with the medium-size flag 17R. In other words, the photointerrupter 24 remains off (FIG. 5B). Therefore, only the photointerrupter 23 is turned on, allowing the image forming apparatus to detect sheet S5 as a small-size sheet. Because sheet S5 is shifted to the left when it passes through the fixing unit 13, the non-paper-passing area on the right side becomes larger than when conveyed using center-based conveyance. The non-paper-passing area on the right side of sheet S5 when it passes through the fixing unit 13 is the same as when small-size sheet S3 is conveyed. Therefore, even if sheet S5 is detected as a small-size sheet, there is no problem in terms of reducing the temperature rise in the non-paper-passing area by controlling the interval between conveyed sheets S in the same way as for small-size sheet S3.

[0060] In this way, the width and edge position of the sheet material S can be detected in stages using two photointerrupters, and the sheet conveying interval appropriate for the edge positions of multiple sheet materials S can be automatically selected at minimal cost. Furthermore, even in cases where a user accidentally conveys a sheet material S other than large size paper while setting the width restriction guide 1 to the width of large size paper, the image forming apparatus can automatically detect the width and right edge (or left edge) of the sheet material S. In other words, productivity can be improved without unnecessarily reducing the throughput of the image forming apparatus. The sheet material detection device of the first embodiment is configured to detect the width of the sheet material based on the timing when the inner contact portion moves and the timing when the movable member moves from the first position to the second position. Furthermore, the first embodiment may be a sheet material conveying device configured to change the number of sheets conveyed by the conveying member per unit time based on the timing when the inner contact portion moves and the timing when the movable member moves from the first position to the second position.

[0061] In the first embodiment, the leading edge flag 15 is disposed upstream of the size flags (16, 17) in the conveying direction, but it may also be disposed downstream in the conveying direction. That is, since times T1, T2 (= T3), etc. are the time difference between two timings, the leading edge flag 15 may be disposed upstream or downstream of the size flags (16, 17). In this way, the leading edge flag 15 (detection unit 6) may be disposed upstream of the detection unit 7 in the conveying direction, or may be disposed downstream of the detection unit 7 in the conveying direction.

[0062] Furthermore, although the size flags are arranged at widthwise positions to detect two sizes, A4 and A5, they may be arranged at any widthwise position. Furthermore, although two pairs of size flags are arranged to detect two sizes, three or more pairs may be arranged to detect three or more sizes. This makes it possible to provide an image forming apparatus that can automatically detect the width of a sheet material in multiple stages at low cost without relying on the user's setting of the width restriction guide 1, and that is highly productive. Note that, although detection of the width of a sheet material is applied to an image forming apparatus in the first embodiment, it may also be applied to an original reading apparatus or other apparatuses that have a sheet material transport apparatus.

[0063] As described above, according to the first embodiment, the size of the sheet material being conveyed can be detected accurately at low cost. [Example]

[0064] [Width detection mechanism operation] The second embodiment will be described with reference to FIGS. 6 to 8. Description of the same content as in the first embodiment will be omitted. The leading edge flag 26 is held in a standby position with its leading edge protruding from the conveying guide 3 by a spring 18 (FIG. 6(a)). When the sheet material S contacts the leading edge flag 26, the leading edge flag 26 swings to the detection position (FIG. 6(b)). The leading edge flag 26 has a detection unit 26a. When the leading edge flag 26 is in the standby position, the detection unit 26a blocks light from the photointerrupter 25, and when the leading edge flag 26 is in the detection position, the detection unit 26a transmits light through the photointerrupter 25, thereby detecting that the leading edge flag 26 has swung. When the photointerrupter 25 is shielded from light, it is set to Off (no paper), and when it is transmitted through, it is set to On (paper present). The photointerrupter 25 is a second detector that detects the absence of a sheet when the link 21 is in the first position and detects the presence of a sheet when the link 21 is in the second position.

[0065] The operations of the large size flag 16, the medium size flag 17, and the link 21 are the same as those in the first embodiment, and therefore will not be described here. The link 21 has a detection unit 21b, which transmits light to the photointerrupter 25 when the link 21 is in the standby position, and which blocks light from the photointerrupter 25 when the link 21 is in the detection position. The photointerrupter 25 is shared by the detection unit 26a of the leading end flag 26 and the detection unit 21b of the link 21.

[0066] [Central transport] Next, using FIG. 7, a timing chart of each sensor flag, detection unit, and photointerrupter when the sheet material S is conveyed with the center reference will be described. In FIGS. 7(a) to 7(c), the top line shows the state of the detection unit 26a (transmitting (high level), blocking (low level)), the second line shows the state of the detection unit 21b (transmitting (high level), blocking (low level)), and the third line shows the state of the photointerrupter 25 (On (high level), Off (low level)). Furthermore, the bottom line shows the positional relationship between the sheet material S (S1 to S3) and each flag (26, 16, 17). The dashed line indicates the reference position 00, the two-dot chain line indicates the path of the sheet material S in the conveying direction, and the broken line indicates the timing when the output of the photointerrupter 25 switches. The left and right sides indicate the left and right sides as viewed from the upstream side in the conveying direction. In the following description, it is assumed that all sheet materials are conveyed at the same conveying speed. In FIG. 7, the reference symbols 16L, 16R, 17L, and 17R indicate the positions of the protrusion 16Lb, the protrusion 16Rb, the protrusion 17Lc, and the protrusion 17Rc, respectively.

[0067] (large size paper) When large-size sheet S1 is transported center-referenced, it comes into contact with leading-edge flag 26, causing detector 26a to swing from the light-blocking position to the light-transmitting position. Because detector 21b is in the light-transmitting position, photointerrupter 25 switches from Off to On. As large-size sheet S1 moves downstream in the transport direction, it comes into contact with large-size flags 16L and 16R, causing large-size flags 16L and 16R to swing, which in turn causes medium-size flags 17L and 17R to swing. As both left and right medium-size flags 17L and 17R swing, link 21 swings, causing detector 21b to swing from the light-transmitting position to the light-blocking position. This causes photointerrupter 25 to switch from On to Off. The time from when photointerrupter 25 turns On to when it turns Off is defined as T4 (FIG. 7(a)).

[0068] (medium size paper) When medium-sized paper S2 is transported center-referenced, it comes into contact with the leading edge flag 26, causing the detection unit 26a to swing from the light-blocking position to the light-transmitting position. Because the detection unit 21b is in the light-transmitting position, the photointerrupter 25 switches from Off to On. The medium-sized paper S2 advances downstream in the transport direction, but because its width is inside the position where the large-sized flags 16L and 16R are located, it does not come into contact with the large-sized flags 16L and 16R. As the medium-sized paper S2 continues downstream in the transport direction, it comes into contact with the medium-sized flags 17L and 17R, causing the medium-sized flags 17L and 17R to swing. The swinging of both the left and right medium-sized flags 17L and 17R causes the link 21 to swing, causing the detection unit 21b to swing from the light-transmitting position to the light-blocking position. This causes the photointerrupter 25 to switch from On to Off. The time from when the photointerrupter 25 is turned on to when it is turned off is defined as T5. The photointerrupter 25 switches off with a delay corresponding to the position of the medium size flags 17L and 17R downstream of the large size flags 16L and 16R in the transport direction. Therefore, time T5 is longer than time T4 (FIG. 7(b)) (T5>T4).

[0069] (small size paper) When small-size sheet S3 is transported based on the center, it comes into contact with leading edge flag 26, and detection unit 26a swings from the light-blocking position to the light-transmitting position. Because detection unit 21b is in the light-transmitting position, photointerrupter 25 switches from Off to On. Small-size sheet S3 advances downstream in the transport direction, but because its width is inside the positions of large-size flags 16L and 16R, it does not come into contact with large-size flags 16L and 16R. Small-size sheet S3 further advances downstream in the transport direction, but because its width is inside the positions of medium-size flags 17L and 17R, it does not come into contact with medium-size flags 17L and 17R. In other words, photointerrupter 25 maintains the On state until the trailing edge of small-size sheet S3 passes leading edge flag 26 (FIG. 7(c)). As described above, the size of the sheet material S in the width direction can be detected from the detection time of the photointerrupter 25, that is, the time during which the photointerrupter 25 is turned on.

[0070] [When transporting off to one side] Next, using FIG. 8, we will explain the timing chart of each sensor flag, detection unit, and photointerrupter when the sheet material S is conveyed with one side shifted while the width restriction guide 1 is at the maximum width position. Since the image forming apparatus is designed to convey the sheet with a center reference, this type of conveyance is not normally performed. However, due to a user's erroneous operation, the sheet material S may be conveyed with the left or right shifted as shown in FIG. 8. While the description of the second embodiment focuses on the left shifted state, the same applies to the right shifted state, with the left and right shifted states simply reversed. Note that FIGS. 8(a) and 8(b) are similar to FIGS. 7(a) to 7(c). In FIG. 8, reference numerals 16L, 16R, 17L, and 17R indicate the positions of the protrusions 16Lb, 16Rb, 17Lc, and 17Rc, respectively.

[0071] [When sheet material S4 is pushed to one side] For example, when conveyed with the sheet material S4 shifted to the left, the sheet material has a width such that it contacts the large size flag 16L but not the large size flag 16R, and contacts both the medium size flags 17L and 17R. Note that when conveyed with the sheet material S4 shifted to the right, the left and right are reversed. When conveyed with the sheet material S4 shifted to the left, the sheet material S4 contacts the leading edge flag 26, and the detector 26a swings from the light-blocking position to the light-transmitting position. Because the detector 26b is in the light-transmitting position, the photointerrupter 25 switches from Off to On. As the sheet material S4 advances downstream in the conveyance direction, the width of the sheet material S4 is inside the position where the large size flag 16 is located, so the sheet material S4 contacts the left large size flag 16L but not the right large size flag 16R. In other words, the left large size flag 16L swings, and in conjunction with this, the left medium size flag 17L also swings, but because the right large size flag 16R does not swing, the right medium size flag 17R does not swing either. Therefore, since only one medium size flag 17 swings to the detection position, the link 21 does not move. In other words, at this point, the photointerrupter 25 remains on.

[0072] As the sheet S4 advances further downstream in the transport direction, it comes into contact with the right-side medium-size flag 17R, causing the right-side medium-size flag 17R to swing. Because the left-side medium-size flag 17L has already swung to the detection position, the swinging of the right-side medium-size flag 17R causes the link 21 to swing, and the detection unit 21b swings from the light-transmitting position to the light-blocking position. This switches the photointerrupter 25 from On to Off. The time from when the photointerrupter 25 turns On to when it turns Off is defined as T6. Time T6 is the same as time T5, and the image forming apparatus can detect the sheet S4 as a medium-size sheet (see FIG. 8A). Because the sheet S4 is shifted to the left when passing through the fixing unit 13, the non-paper-passing area on the right side becomes larger than when conveying with center-based conveyance. The non-paper-passing area on the right side when the sheet S4 passes through the fixing unit 13 is the same as when conveying medium-size sheet S2. Therefore, even if sheet material S4 is detected as medium-sized paper, there is no problem in terms of reducing the temperature rise in the non-paper passing areas if the interval between the transported sheets S is controlled in the same way as in the case of medium-sized paper S2.

[0073] [When sheet material S5 is pushed to one side] For example, when sheet material S5 is conveyed with its left side shifted, it comes into contact with the large size flag 16L and the medium size flag 17L but does not come into contact with the large size flag 16R and the medium size flag 17R. When sheet material S5 is conveyed with its right side shifted, the left and right are reversed. When sheet material S5 is shifted to the left, sheet material S5 comes into contact with the leading edge flag 26, and the detector 26a swings from the light-blocking position to the light-transmitting position. Because detector 21b is in the light-transmitting position, the photointerrupter 25 switches from Off to On. As sheet material S5 advances downstream in the conveyance direction, the width of sheet material S5 is inside the position where the large size flag 16 is located, so it comes into contact with the left large size flag 16L but does not come into contact with the right large size flag 16R. That is, the left large size flag 16L swings, and the left medium size flag 17L swings in conjunction with it, but because the right large size flag 16R does not swing, the right medium size flag 17R does not swing either. Therefore, because only one medium size flag 17 swings to the detection position, the link 21 does not move. That is, the photointerrupter 25 remains on.

[0074] Sheet S5 continues downstream in the conveyance direction, but because its right edge is inside the medium-size flag 17R on the right, it does not come into contact with the medium-size flag 17R. In other words, the photointerrupter 25 remains ON (FIG. 8B). Therefore, the photointerrupter 25 remains ON until the trailing edge of sheet S5 passes through, allowing the image forming apparatus to detect sheet S5 as a small-size sheet. Because sheet S5 is shifted to the left as it passes through the fixing unit 13, the non-paper-passing area on the right side becomes larger than in center-based conveyance. The non-paper-passing area on the right side of sheet S5 as it passes through the fixing unit 13 is similar to that when small-size sheet S3 is conveyed. Therefore, even if sheet S5 is detected as a small-size sheet, controlling the interval between conveyed sheets S in the same manner as for small-size sheet S3 does not pose a problem in terms of reducing the temperature rise in the non-paper-passing area.

[0075] In this way, in the second embodiment, the width and edge position of the sheet material S can be detected in stages using one photointerrupter 25, and the conveying interval of the sheet material S can be automatically selected at low cost to suit the edge positions of multiple sheet materials S. Furthermore, even in cases where a user accidentally conveys an arbitrary sheet material S while the width restriction guide 1 is set to the large size width, the image forming apparatus can automatically detect the width of the sheet material S. In other words, productivity can be increased without reducing the throughput of the image forming apparatus more than necessary.

[0076] Although the size flags are arranged at widthwise positions to detect two sizes, A4 and A5, they may be arranged at any widthwise position. Also, although two pairs of size flags are arranged to detect two sizes, three or more pairs may be arranged to detect three or more sizes. Furthermore, although the width detection mechanism is applied to an image forming apparatus in the second embodiment, it may also be applied to a document reading apparatus or other sheet conveying apparatus.

[0077] As described above, according to the second embodiment, the size of the sheet material being conveyed can be detected accurately at low cost. [Explanation of symbols]

[0078] 6. Detection unit 7. Detection unit 15 Tip Flag 16 (16L, 16R) Large size flag 17 (17L, 17R) Medium size flag 21 Links

Claims

1. an inner contact portion provided in a conveyance path through which the sheet material passes and movable in contact with the sheet material; a first contact portion disposed on one side of the center of the conveyance path in a width direction perpendicular to the conveyance direction of the sheet material, and movable between a first standby position and a first operating position; a second contact portion disposed on the other side of the center in the width direction and movable between a second standby position and a second operating position; a third contact portion that is disposed upstream of the first contact portion and the second contact portion in the conveying direction, that is disposed outward of the first contact portion with respect to the center in the width direction, and that is movable between a third standby position and a third operating position; a fourth contact portion that is disposed upstream of the first contact portion and the second contact portion in the conveying direction, that is disposed outward of the second contact portion with respect to the center in the width direction, and that is movable between a fourth standby position and a fourth operating position; a moving member that moves from a first position to a second position different from the first position when the first contact portion moves to the first operating position and the second contact portion moves to the second operating position, and that is restricted from moving from the first position to the second position when the first contact portion is located at the first standby position and / or the second contact portion is located at the second standby position; Equipped with the inner contact portion is disposed between the first contact portion and the second contact portion in the width direction, the first contact portion is moved from the first standby position to the first operating position when the third contact portion is moved from the third standby position to the third operating position, and the second contact portion is moved from the second standby position to the second operating position when the fourth contact portion is moved from the fourth standby position to the fourth operating position; A sheet material detection device characterized in that it is configured to detect the width of the sheet material based on the timing when the inner contact portion moves and the timing when the movable member moves from the first position to the second position.

2. The sheet detecting device according to claim 1 , wherein the inner contact portion is provided upstream of the third contact portion and the fourth contact portion in the conveying direction.

3. The sheet detecting device according to claim 1 , wherein the inner contact portion is provided downstream of the first contact portion and the second contact portion in the conveying direction.

4. a determining means for determining a width of the sheet material based on the movement of the inner contact portion and the position of the movable member; The determination means determining that the sheet material being conveyed is a sheet material having a first width based on the time between the timing when the movement of the inner contact portion is detected and the timing when the movable member moves from the first position to the second position as a result of the first state in which both the third contact portion and the fourth contact portion are in contact with the sheet material; determining that the sheet material being conveyed is a sheet material having a second width narrower than the first width based on the time between the timing when the movement of the inner contact portion is detected and the timing when the moving member moves from the first position to the second position as a result of both the first contact portion and the second contact portion being in the first state; A sheet material detection device as described in any one of claims 1 to 3, characterized in that when movement of the inner contact portion is detected but movement of the movable member to the second position is not detected, it is determined that the sheet material being transported is a sheet material having a third width narrower than the second width.

5. a first detection unit that detects that the inner contact portion has entered the first state; a second detection unit that detects that the moving member has moved from the first position to the second position; The sheet material detecting device according to claim 4, further comprising:

6. a detector that detects that the moving member has moved from the first position to the second position; 5. The sheet material detecting device according to claim 4, wherein the detecting section detects that the inner contact section has entered the first state.

7. the first contact portion is movable from the first standby position to the first operating position while the third contact portion is in the third standby position; 7. The sheet material detecting device according to claim 1, wherein the second contact portion is movable from the second standby position to the second operating position while the fourth contact portion is in the fourth standby position.

8. 8. A sheet material detection device according to claim 1, wherein the first contact portion and the second contact portion are arranged symmetrically with respect to the center in the width direction, and the third contact portion and the fourth contact portion are arranged symmetrically with respect to the center in the width direction.

9. a conveying member for conveying a sheet material; an inner contact portion provided in a conveyance path through which the sheet material passes and movable in contact with the sheet material; a first contact portion disposed on one side of the center of the conveyance path in a width direction perpendicular to the conveyance direction of the sheet material, and movable between a first standby position and a first operating position; a second contact portion disposed on the other side of the center in the width direction and movable between a second standby position and a second operating position; a third contact portion that is disposed upstream of the first contact portion and the second contact portion in the conveying direction, that is disposed outward of the first contact portion with respect to the center in the width direction, and that is movable between a third standby position and a third operating position; a fourth contact portion that is disposed upstream of the first contact portion and the second contact portion in the conveying direction, that is disposed outward of the second contact portion with respect to the center in the width direction, and that is movable between a fourth standby position and a fourth operating position; a moving member that moves from a first position to a second position different from the first position when the first contact portion moves to the first operating position and the second contact portion moves to the second operating position, and that is restricted from moving from the first position to the second position when the first contact portion is located at the first standby position and / or the second contact portion is located at the second standby position; Equipped with the inner contact portion is disposed between the first contact portion and the second contact portion in the width direction, the first contact portion is moved from the first standby position to the first operating position when the third contact portion is moved from the third standby position to the third operating position, and the second contact portion is moved from the second standby position to the second operating position when the fourth contact portion is moved from the fourth standby position to the fourth operating position; A sheet material conveying device characterized in that it is configured to change the number of sheet materials conveyed by the conveying member per unit time based on the timing when the inner contact portion moves and the timing when the moving member moves from the first position to the second position.

10. An image forming apparatus including an image forming unit that forms an image on a sheet material, A sheet material detecting device according to any one of claims 1 to 8 is provided, The image forming apparatus is characterized in that the sheet material detecting device is provided upstream of the image forming unit in the conveying direction.

11. An image forming apparatus including an image forming unit that forms an image on a sheet material, An image forming apparatus comprising the sheet material conveying device according to claim 9.

Images