JP2013043716A - Sheet detecting apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce such failures that a reflection sensor is irradiated with disturbance light, and dust and dirt adhere to the reflection sensor, thereby, reduce erroneous detection.SOLUTION: The sheet detecting apparatus 20 includes: the reflection sensor 11 configured to detect a sheet by receiving a light reflected from the conveyed sheet which has been irradiated with the light; a flag 12 configured to be actuated by the conveyed sheet; and a shielding plate 13 configured to be positioned opposed to the reflection sensor to shield the disturbance light with which the reflection sensor is irradiated. The shielding plate is provided on the flag, and the opposed state of the plate with respect to the reflection sensor is maintained till the sheet is conveyed. Accordingly, the reflection sensor is prevented from being irradiated with the disturbance light, and the dust and dirt are prevented from adhering to the reflection sensor. When the sheet is conveyed, the flag is rotated with pressure of the sheet, then, the shielding plate is moved to release the opposed state thereof. Accordingly, the sheet can be detected by the reflection sensor.

Description

  The present invention relates to a sheet detection device that detects a sheet, and an image forming apparatus including the sheet detection device.

  In general, in order to form a high-quality image on a sheet, the image forming apparatus often includes a sheet detection device that detects the position and state of the sheet being conveyed. The sheet detection apparatus detects a jam, skew, position, etc. of a sheet by a sensor provided on the sheet conveyance path, and transmits the sheet conveyance state to the control unit of the image forming apparatus.

  As described in Patent Document 1, the sensor includes a light emitting element that emits light to a sheet and a light receiving element that receives reflected light from the sheet, receives reflected light from the sheet, There is a reflection sensor for detecting the state.

  FIG. 11 shows a conventional use example of a reflection sensor other than Patent Document 1.

  The reflection sensor 107 is provided upstream of the image forming unit 105 including a plurality of line heads 101Y, 101M, 101C, and 101K of an ink jet printing apparatus 150 as an image forming apparatus. The reflection sensor 107 is disposed below the light passage hole 108a formed in the conveyance plate 108 that guides and supports the conveyance belt 102 that circulates under the line head, and detects the entrance of the sheet P through the light passage hole 108a. It is like that.

JP 2007-57892 A

  However, in both Patent Document 1 and FIG. 11, since the reflection sensor is disposed at a position facing the sheet, there is nothing to block the light receiving element when the sheet is not conveyed, and it is exposed and exposed. It is in the state. For this reason, when the reflection sensor is irradiated with disturbance light, it may erroneously detect that the sheet is passing. In FIG. 11, disturbance light may enter from the light passage hole 108a and irradiate the reflection sensor 107 in some cases.

  Examples of ambient light include sunlight and incandescent lamps. Incandescent lamps contain a lot of light in the infrared emission region. The light in the infrared light emitting region is common with the light emitting region of the LED, and the reflection sensor may detect the light of the incandescent lamp as reflected light of the light emitted by itself.

  The sheet detection device is often provided in the housing of the image forming apparatus, and disturbance light enters through a gap in the housing, an insertion port for manually inserting the sheet into the housing, a sheet discharge port, or the like. The disturbance light may be erroneously detected as reflected light from the sheet.

  In addition, when the reflection sensor is used for a long time, dust may adhere to it, and the dust may be mistakenly detected as a sheet.

  The present invention relates to a sheet detection apparatus in which occurrence of false detection is reduced by reducing the reflection sensor from being exposed to ambient light or from attaching dust to the reflection sensor, and image formation including the sheet detection apparatus. Providing a device.

  The sheet detection apparatus of the present invention irradiates the reflection sensor that receives the light reflected on the conveyed sheet and detects the sheet, the actuating member operated by the conveyed sheet, and the reflection sensor. A shielding member that shields ambient light against the reflection sensor, and one of the reflection sensor and the shielding member is provided on the operating member, and the shielding member until the sheet is conveyed. The facing state with respect to the reflection sensor is maintained, and the operating member is actuated by the conveyed sheet so that the one moves to release the facing state so that the reflection sensor can detect the sheet. It is characterized by that.

  An image forming apparatus of the present invention includes the above sheet detection device, and an image forming unit that starts image formation on the sheet and forms an image on the sheet based on the timing at which the sheet detection device detects the sheet. It is characterized by that.

  In the sheet detection apparatus of the present invention, the shielding member and the reflection sensor are kept facing each other until the sheet is conveyed so that the reflection sensor is not irradiated with disturbance light, so that erroneous detection due to disturbance light is reduced. be able to.

  In addition, since the sheet detection apparatus of the present invention is configured to maintain the opposing state of the shielding member and the reflection sensor, the shielding member prevents the dust from adhering to the reflection sensor, thereby preventing erroneous detection due to dust. Can be reduced.

1 is a schematic front view of an ink jet printing apparatus as an image forming apparatus according to an embodiment of the present invention, and includes a sheet detection apparatus according to an embodiment of the present invention. 1 is a perspective view of a sheet detection apparatus according to a first embodiment of the present invention. It is a perspective view of the shielding board, flag, and weight in the sheet | seat detection apparatus of FIG. It is the perspective view which looked at the shielding board, flag, and weight of FIG. 3 from the downward direction. It is a figure for operation | movement description of the sheet | seat detection apparatus of FIG. (A) is the figure by which the sheet | seat has been conveyed. (B) is the figure which the reflection sensor detected the sheet | seat. (C) is the figure which the sheet | seat passed the reflection sensor. It is a perspective view of the sheet | seat detection apparatus which concerns on 2nd Embodiment of this invention. It is a perspective view of the shielding board, flag, and weight in the sheet | seat detection apparatus of FIG. It is the perspective view which looked at the shielding board of FIG. 7, a flag, and the weight from the downward direction. It is a figure for operation | movement description of the sheet | seat detection apparatus of FIG. (A) is the figure by which the sheet | seat has been conveyed. (B) is the figure which the reflection sensor detected the sheet | seat. (C) is the figure which the sheet | seat passed the reflection sensor. It is the figure which showed the reflector of another form. It is the figure which showed the example of conventional use of a reflection sensor.

  Hereinafter, a sheet detection apparatus according to an embodiment of the present invention and an inkjet printing apparatus as an image forming apparatus including the sheet detection apparatus will be described with reference to the drawings.

(Inkjet printer)
FIG. 1 is a schematic front view of an ink jet printing apparatus as an image forming apparatus according to an embodiment of the present invention, and is a view provided with a sheet detection apparatus according to an embodiment of the present invention.

  The ink jet printing apparatus 10 includes an image forming unit 7. The image forming unit 7 includes a plurality of line heads 1Y, 1M, 1C, and 1K, a conveyance belt 2, a conveyance motor 4, a conveyance plate 8, and the like.

  The line heads 1Y, 1M, 1C, and 1K are provided side by side in the sheet conveyance direction, and discharge inks of yellow, magenta, cyan, and black in a direction orthogonal to the sheet conveyance direction (sheet width direction). Thus, an image is formed on the sheet. The conveying belt 2 is stretched between a pair of conveying pulleys 3A and 3B, and circulates below the line heads 1Y, 1M, 1C, and 1K in order to convey the sheet P and form an image on the sheet P. It has become. The transport motor 4 is a circulation drive source of the transport belt 2 and is also a tensioner that applies tension to the transport belt 2 to put the transport belt 2 in a tensioned state. The conveyor belt 2 is a toothed belt having teeth formed on the inner periphery, and the drive pulley 4a of the conveyor motor 4 is a toothed pulley. The conveying belt 2 and the driving pulley 4a are configured to transmit the rotational force of the conveying motor 4 to the conveying belt 2 without slipping due to the meshing of the teeth.

  The conveyance plate 8 is a member that supports the portion of the conveyance belt 2 that faces the line head and serves as a reference for the conveyance surface of the sheet conveyance. The transport plate 8 in FIG. 1 is separated from the transport belt 2 so that the structure of the ink jet printing apparatus 10 can be easily understood, but actually, the transport plate 2 is in contact with the transport belt 2 to support the transport belt 2. It has become.

  A conveyance entrance roller 5 is provided upstream of the image forming unit 7 in the sheet conveyance direction. The transport inlet roller 5 is driven to rotate by pressing the transport belt 2 against the upstream transport pulley 3A by a spring (not shown). When the sheet is conveyed, the conveyance inlet roller 5 escapes in a direction away from the conveyance belt 2 according to the thickness of the sheet, and nipping and conveying the sheet with the conveyance belt 2.

  Between the conveyance entrance roller 5 and the yellow line head 1Y, a sheet detecting device 20 for detecting the leading edge of the sheet is provided.

  A conveyance exit roller 6 is provided downstream of the image forming unit 7 in the sheet conveyance direction. The transport outlet roller 6 is also driven to rotate by pressing the transport belt 2 against the downstream transport pulley 3B by a spring (not shown). When the sheet is conveyed, the conveyance outlet roller 6 escapes in a direction away from the conveyance belt 2 in accordance with the thickness of the sheet, and conveys the sheet while sandwiching the sheet with the conveyance belt 2.

The frictional force of the conveyance belt 2 and the conveyance inlet roller 5 and the conveyance outlet roller 6 against the sheet P is as follows:
Conveying belt 2> Sheet P> Conveying entrance roller 5
Conveying belt 2> Sheet P> Conveying exit roller 6
It is designed to be.

  The sheet P is conveyed by the circulation and frictional force of the conveyance belt 2. The conveyance inlet roller 5 and the conveyance outlet roller 6 press the sheet P against the conveyance belt 2, help the adhesion between the conveyance belt 2 and the sheet P, and prevent the sheet P from being lifted, thereby conveying the sheet P in a stable state. I can do it.

  The inkjet printing apparatus 10 conveys the sheet P fed from a cassette (not shown) between the conveyance inlet roller 5 and the conveyance belt 2, and further passes under the line head by circulation of the conveyance belt 2, The paper is discharged by the transport exit roller 6 and the transport belt 2. During this time, the sheet detection device 20 detects the leading edge Pa of the sheet P so that the timing at which the line head ejects ink can be measured. For this reason, the inkjet printing apparatus 10 can form an image at a desired position from the leading edge of the sheet by the sheet detection apparatus 20.

(Sheet detection device of the first embodiment)
FIG. 1 is a view in which a sheet detection device according to a first embodiment of the present invention is provided in an ink jet printing apparatus, and is a front view of the sheet detection device. FIG. 2 is a perspective view of the sheet detection apparatus according to the first embodiment of the present invention. FIG. 3 is a perspective view of a shielding plate, a flag, and a weight in the sheet detection apparatus of FIG. 4 is a perspective view of the shielding plate, flag, and weight of FIG. 3 as viewed from below. FIG. 5 is a diagram for explaining the operation of the sheet detection apparatus of FIG. FIG. 5A is a diagram in which a sheet has been conveyed. FIG. 5B is a diagram in which the sensor detects the sheet. FIG. 5C is a diagram in which the sheet passes through the sensor.

  The configuration of the sheet detection apparatus will be described.

  The sheet detection device 20 is provided between the conveyance entrance roller 5 and the image forming unit 7 and detects the leading edge Pa of the sheet P.

  The sheet detection device 20 includes a reflection sensor 11 that detects light by receiving light reflected on the conveyed sheet, and a flag 12 as an operation member that operates (rotates) by the conveyed sheet. I have. Further, the sheet detection apparatus 20 includes a shielding plate 13 as a shielding member that shields disturbance light that irradiates the reflection sensor 11 so as to face the reflection sensor 11. The reflection sensor 11 is fixed, and the shielding plate 13 is provided on the flag 12. The sheet detection device 20 detects (acts) the sheet by releasing (or rotating) the shielding plate 13 and releasing the opposed state to the reflection sensor 11 when the flag 12 is activated (rotated) by the conveyed sheet. It has become.

  The reflection sensor 11 is fixed to a fixing member (not shown) (for example, the transport plate 8) below the transport plate 8 between the transport inlet roller 5 and the yellow line head 1Y. The reflection sensor 11 (FIG. 2) includes a light emitting unit 11 a that irradiates light to the sheet and a light receiving unit 11 b that receives reflected light from the sheet. The reflection sensor 11 is provided to detect the leading edge Pa of the sheet P and determine the timing for forming an image on the sheet P by ejecting ink from the image forming unit 7 after a predetermined time has elapsed. A light passage hole 8 a is formed in the transport plate 8 so as to face the reflection sensor 11. The light passage hole 8a allows light from the reflection sensor 11 that irradiates the sheet and reflected light from the sheet to pass therethrough. Further, a bundle wire (not shown) for transmitting a signal is connected to the reflection sensor 11, and the signal is transmitted to a substrate unit that controls the device.

  The flag 12 is a plate-like member having a bent shape, and rotates in the sheet conveying direction around a support shaft 14 provided on a fixing member (not shown). The detection piece 12a that is the upper end portion of the flag 12 passes through the long hole 8b of the conveyance plate 8 and protrudes from the upper surface of the conveyance plate 8 so that the leading edge Pa of the sheet abuts. The long hole 8b is formed along the sheet conveying direction so as to allow the flag 12 to rotate. A weight 15 is provided at the lower end 12b of the flag 12 so that the flag 12 can maintain the standing state. The weight 15 is set such that when the flag 12 is pushed by the sheet, the weight 15 falls down downstream without causing the leading end of the sheet to bend. Usually, the flag 12 is held upright by the detection piece 12a protruding from the long hole 8b by the weight 15 and received by the upstream end 8ba (FIG. 2) of the long hole 8b.

  A spring (not shown) may be provided between the flag 12 and the fixing member instead of the weight. Even in this case, the elasticity of the spring needs to be set to such an extent that when the flag 12 is pushed by the sheet, the spring 12 falls down without causing the leading end of the sheet to bend.

  The shielding plate 13 is integrated with the flag 12. A plate-like reflection plate 16 is provided on the surface of the shielding plate 13 (FIG. 4) facing the reflection sensor 11.

  A member having a light reflectivity smaller than that of the sheet (sheet P> reflector 16) is used for the reflector 16.

  The operation of the sheet detection apparatus 20 will be described.

  The flag 12 is held upright until the sheet is conveyed, and the detection piece 12a protrudes upward from the conveyance plate 8. At this time, the shielding plate 13 integrated with the flag 12 is located between the light passage hole 8 a of the transport plate 8 and the reflection sensor 11 and faces the reflection sensor 11. For this reason, the shielding plate 13 is kept facing the reflection sensor 11 until the sheet is conveyed. Thereby, the shielding board 13 shields the disturbance light which approachs from the light passage hole 8a. As a result, when the shielding plate 13 is located at a facing position facing the reflection sensor 11, the reflection sensor 11 is not irradiated with disturbance light. The reflection sensor 11 is attached to the shielding plate 13 to detect the reflection plate 16 whose light reflectance is known, detects the shielding plate 13 from the light reflectance of the reflection plate 16, and detects the sheet. You can judge that it is not.

  In the above state, the conveyance belt 2 and the conveyance inlet roller 5 pinch the conveyed sheet P. The conveyance belt 2 is circulated by a conveyance motor 4 and conveys the sheet P together with the conveyance inlet roller 5 under the line head. During this time, the detection piece 12a of the flag 12 is pushed downstream by the leading edge Pa of the conveyed sheet, and the flag 12 rotates around the support shaft 14 and falls in the downstream direction. The frictional force of the conveyance belt 2 is larger than that of the sheet P and is larger than that of the conveyance inlet roller 5. For this reason, even if a sheet pushes down the flag 12 downstream and receives a reaction force, the conveyance belt 2 can convey the sheet without slipping.

  As the flag 12 is pushed by the leading edge of the sheet and rotates about the support shaft 14, the opposing state of the shielding plate 13 and the reflection sensor 11 is released, and the shielding plate 13 is separated from the reflection sensor 11. . As a result, the shielding plate 13 retracts from between the light passage hole 8a of the transport plate 8 and the reflection sensor 11, and the reflection sensor 11 faces the sheet P through the light passage hole 8a and detects the sheet. Since the light reflectance of the sheet P is higher than the light reflectance of the reflecting plate 16 attached to the shielding plate 13, the reflection sensor 11 can detect that the sheet P has entered. The inkjet printing apparatus 10 starts forming an image at a predetermined position on the sheet based on the timing when the reflection sensor 11 detects the sheet.

  In FIG. 5B, when the reflection sensor 11 detects the sheet, the leading edge Pa of the sheet moves downstream by a distance L on the reflection sensor 11. For this reason, when the reflection sensor 11 detects the leading edge of the sheet, the inkjet printing apparatus 10 considers that the sheet has moved by the distance L, and measures the timing to start forming an image on the sheet. Yes.

  Thereafter, when the sheet P passes through the detection piece 12a, the flag 12 returns to the original standing state by the weight 15, and the detection piece 12a protrudes on the conveyance plate 8 and is in a state orthogonal to the conveyance plate 8. . During this time, the shielding plate 13 faces the reflection sensor 11.

  As described above, the sheet detection device 20 keeps the shielding plate 13 and the reflection sensor 11 facing each other when the sheet is not conveyed so that the reflection sensor is not irradiated with ambient light. Therefore, it is possible to reduce false detection due to disturbance light.

  In addition, the sheet detection device 20 maintains the opposing state of the shielding plate 13 and the reflection sensor 11, thereby preventing the dust from adhering to the reflection sensor by the shielding plate, and reducing detection errors due to dust. it can.

  Since the inkjet printing apparatus 10 includes the sheet detection apparatus 20 that reduces detection errors due to ambient light and dust, a high-quality image can be formed on the sheet.

(Sheet detection device of the second embodiment)
FIG. 6 is a perspective view of a sheet detection apparatus according to the second embodiment of the present invention. FIG. 7 is a perspective view of a shielding plate, a flag, and a weight in the sheet detection apparatus of FIG. FIG. 8 is a perspective view of the shielding plate, flag, and weight of FIG. 7 as viewed from below. FIG. 9 is a diagram for explaining the operation of the sheet detection apparatus of FIG. FIG. 9A is a diagram in which a sheet has been conveyed. FIG. 9B is a diagram in which the sensor detects the sheet. FIG. 9C is a diagram in which the sheet passes through the sensor.

  The configuration of the sheet detection device 120 will be described.

  Similarly to the sheet detection device 20 of the first embodiment, the sheet detection device 120 of the second embodiment is also provided between the conveyance entrance roller 5 (FIG. 1) and the image forming unit 7, and the leading edge Pa of the sheet P. Is to be detected.

  The sheet detection apparatus 120 of the second embodiment also receives a reflection sensor 111 that receives light reflected and reflected on the conveyed sheet and detects the sheet, and a flag 112 as an operating member that operates according to the conveyed sheet. And. Further, the sheet detection device 120 includes a shielding plate 113 as a shielding member that shields the disturbance light that irradiates the reflection sensor 111 against the reflection sensor 111.

  The shielding plate 113 has a reflection plate 116 and is fixed to the lower surface of the transport plate 8, and the reflection sensor 111 is provided on a flag 112 as an operating member. For this reason, the sheet detecting device 120 operates (rotates) the flag 112 by the conveyed sheet, the reflection sensor 111 moves together with the flag 112, and releases the facing state with the shielding plate 113 as the shielding member. The sheet is moved to a position for detecting the sheet. Since other parts are the same as those of the sheet detection apparatus 20 of the first embodiment, the same parts are denoted by the same reference numerals, and the description of the same parts is partially omitted.

  The operation of the sheet detection device 120 will be described.

  The flag 112 is held upright until the sheet is conveyed, and the detection piece 112a protrudes upward from the conveying plate 8. At this time, the reflection sensor 111 integrated with the flag 112 faces the shielding plate 113. For this reason, until the sheet is conveyed, the reflection sensor 111 is kept facing the shielding plate 113 and is not irradiated with ambient light. Particularly, since the reflection sensor 111 faces the shielding plate 113 without facing the light passage hole 8a, the reflection sensor 111 is not irradiated with disturbance light entering from the light passage hole 8a. In addition, the reflection sensor 111 is attached to the shielding plate 113 and detects the reflection plate 116 whose light reflectance is known in advance, detects the shielding plate 113 from the light reflectance of the reflection plate 116, and the sheet. Can be determined not to be detected.

  In the above state, the detection piece 112a of the flag 112 is pushed downstream by the leading edge Pa of the sheet being conveyed by the conveyance belt 2 and the conveyance inlet roller 5, and the flag 112 rotates around the support shaft 14. It falls down in the downstream direction. The frictional force of the conveyance belt 2 is larger than that of the sheet P and is larger than that of the conveyance inlet roller 5. For this reason, even if a sheet pushes down the flag 112 downstream and receives a reaction force, the conveyance belt 2 can convey the sheet without slipping.

  As the flag 112 is pushed by the leading edge of the sheet and rotates about the support shaft 14, the opposing state of the reflection sensor 111 and the shielding plate 113 is released, and the reflection sensor 111 is separated from the shielding plate 113. . Accordingly, the reflection sensor 111 faces the light passage hole 8a, faces the sheet P through the light passage hole 8a, and detects the sheet. Since the light reflectance of the sheet P is higher than the light reflectance of the reflecting plate 116 attached to the shielding plate 113, the reflection sensor 111 can detect that the sheet P has entered.

  The inkjet printing apparatus 10 starts forming an image at a predetermined position on the sheet based on the timing when the reflection sensor 111 detects the sheet.

  In FIG. 9B, when the reflection sensor 111 detects the sheet, the leading edge Pa of the sheet moves downstream by a distance L on the reflection sensor 111. For this reason, when the reflection sensor 111 detects the leading edge of the sheet, the inkjet printing apparatus 10 takes into account that the sheet has moved by the distance L, and measures the timing at which an image starts to be formed on the sheet. Yes.

  Thereafter, when the sheet P passes through the detection piece 112a, the flag 112 returns to the original standing state by the weight 15, and the detection piece 112a protrudes on the conveyance plate 8 and is in a state orthogonal to the conveyance plate 8. . During this time, the reflection sensor 111 faces the shielding plate 113.

  6 to 9, reference numeral 112b indicates the lower end of the flag. Reference numeral 111a indicates a light emitting portion of the reflection sensor 111, and 111b indicates a light receiving portion.

  As described above, the sheet detection device 120 maintains the opposed state of the shielding plate 113 and the reflection sensor 111 when the sheet has not been conveyed so that the reflection sensor is not irradiated with ambient light. , False detection due to ambient light can be reduced.

  In addition, the sheet detection device 120 maintains the opposing state of the shielding plate 113 and the reflection sensor 111, thereby preventing the dust from adhering to the reflection sensor by the shielding plate and reducing erroneous detection due to dust. it can.

  Since the inkjet printing apparatus 10 includes the sheet detection device 120 that reduces detection errors due to ambient light and dust, a high-quality image can be formed on the sheet.

  In the above-described sheet detection devices 20 and 120, the reflection sensors 11 and 111 detect the sheet through the light passage hole 8a so that the type and size of the sheet material can be detected based on the light reflectance when the sheet is irradiated. It comes to irradiate.

  Further, the sheet detection devices 20 and 120 detect the leading edge of the sheet in order to measure the timing at which an image starts to be formed on the sheet. The skew of the sheet may be detected. Accordingly, the sheet detection devices 20 and 120 are not used only for measuring the timing for starting image formation on a sheet.

  Further, the sheet detection devices 20 and 120 utilize the fact that the light reflectivity of the reflection plates 16 and 116 is known in advance, so that the light reception caused by the decrease in the light emission amount of the LED accompanying the aging deterioration of the reflection sensors 11 and 111. You may enable it to adjust the fall of an electric current. Specifically, by increasing the light emission current to the LED or changing the resistance value on the light reception current side, the light emission amount can be adjusted to make the light reception amount constant.

  Further, the sheet detection devices 20 and 120 have been described in the case where it is known in advance that the light reflectance of the sheet P is higher than the firing rate of the reflectors 16 and 116. However, as shown in FIG. 10, reflecting plates 16 a, 16 b, 116 a, and 116 b having different light reflectivities that are known in advance may be provided on the shielding plates 13 and 113. If it does in this way, the reflection sensors 11 and 111 can detect a sheet | seat by detecting that the light reflectance of the reflecting plate changed. In this case, it is assumed that either the reflection sensor or the shielding plate moves in the arrow direction. It should be noted that the reflection plates having different light reflectivities are not limited to two types, and a plurality of types may be provided.

  P: sheet, Pa: sheet leading edge, line head: 1Y, 1M, 1C, 1K, 2: transport belt, 3A, 3B: transport pulley, 4: transport motor, 4a: drive roller, 7: image forming unit, 8 : Transport plate, 8a: light passage hole, 10: ink jet printing apparatus (image forming apparatus), 11: reflection sensor, 12: flag (operation member), 12a: detection piece, 13: shielding plate (shielding member), 14: Support shaft, 15: weight, 16: reflector, 16a: reflector, 16b: reflector, 20: sheet detection device of the first embodiment, 111: reflection sensor, 112: flag (operation member), 112a: detection piece , 111: reflection sensor, 113: shielding plate (shielding member), 116: reflection plate, 120: sheet detection apparatus of the second embodiment.

Claims (6)

A reflection sensor that detects the sheet by receiving light reflected from the conveyed sheet; and
An actuating member actuated by the conveyed sheet;
A shielding member that shields ambient light that irradiates the reflection sensor against the reflection sensor, and
Either one of the reflection sensor and the shielding member is provided on the operating member,
The opposing state of the shielding member and the reflection sensor is maintained until the sheet is conveyed. When the operating member is actuated by the conveyed sheet, the one moves and the opposing state is released. Allowing the reflection sensor to detect the sheet;
A sheet detection apparatus characterized by that. The shielding member is provided on the operating member, and moves when the operating member is operated by the conveyed sheet to release the opposed state to the reflection sensor.
The sheet detection apparatus according to claim 1. The reflection sensor is provided in the operating member, and the operating member is moved by the sheet that has been conveyed to move, so that the opposed state to the shielding member is released.
The sheet detection apparatus according to claim 1. The light reflectance of the shielding member is set smaller than the light reflectance for the sheet,
The sheet detection apparatus according to any one of claims 1 to 3, wherein the sheet detection apparatus includes: The reflection sensor can detect the type of sheet by the light reflectance of the sheet,
The sheet detection apparatus according to claim 1, wherein the sheet detection apparatus is a sheet detection apparatus. The sheet detection apparatus according to any one of claims 1 to 5,
An image forming unit that starts image formation on the sheet and forms an image on the sheet based on the timing at which the sheet detection device detects the sheet;
An image forming apparatus.

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