JP6391351B2 - Sheet detecting apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet detection apparatus that detects a sheet in an image forming apparatus such as a copying machine, a printer, and a facsimile machine, and an image forming apparatus including the same.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines, printers, facsimiles, and the like detect a conveyed sheet in order to detect, for example, the timing at which the sheet is conveyed or whether the sheet remains in the apparatus when a jam occurs. A sheet detection device is provided. As this type of sheet detection apparatus, for example, as shown in FIGS. 14 and 15, the rotation arm 256 that rotates around the rotation shaft 254 when the sheet S comes in contact with the light from the optical sensor 253. There is a sheet detection device 250 provided with a shieldable flag 255. The sheet detection device 250 is provided between the fixing device 230 that fixes the toner image on the sheet S and the discharge device 240 that discharges the sheet S to the outside in the sheet conveyance direction. The flag 255 rotates around the rotation shaft 254 as the rotation arm 256 rotates, and the rotation arm 256 rotates a predetermined amount or more to shield the light from the optical sensor 253, thereby enabling the seat Detect the presence of S.

  By the way, the conventional sheet detection apparatus 250 is formed such that the rotation arm 256 extends from the rotation shaft 254 in a crank shape, and the angle formed between the rotation arm 256 and the sheet S at the standby position shown in FIG. θ50. At this time, the force applied to the sheet S by the rotating arm 256 is a component force of Fθ50 and Fθ50, and the force applied in the direction opposite to the conveyance direction of the sheet S (hereinafter referred to as the folding force) is Fθ50a and the conveyance direction of the sheet S. The force applied in the vertical direction is defined as Fθ50b. Further, as shown in FIG. 15, the angle between the leading edge of the sheet S and the rotating arm 256 when the leading edge of the sheet S comes into contact with the rotating arm 256 and the sheet S is conveyed by an arbitrary amount is θ51. . At this time, the force applied to the sheet S by the rotating arm 256 is the component force of Fθ51 and Fθ51, and the force (folding force) applied in the direction opposite to the conveyance direction of the sheet S is Fθ51a and the direction perpendicular to the conveyance direction of the sheet S. This force is defined as Fθ51b. When the folding forces Fθ50a and Fθ51a are large, the leading edge of the sheet S is likely to be folded.

Here, if θ50 = 90 °, for example, the rotation amount x = x90 ° of the rotation arm 256 is large, but the bending force Fθ50a is
Fθ50a = Fθ50 × sin90 ° = Fθ50
And the maximum. For this reason, the leading edge of the sheet S is likely to be bent.

On the other hand, when the angle between the rotating arm 256 and the sheet S is set small, for example, θ50 = 20 °, the folding force Fθ50a is
Fθ50a = Fθ50 × sin20 °
Becomes smaller. However, since the rotation amount x = x20 ° of the rotation arm 256 becomes small, the leading edge of the sheet S is not easily broken, but the necessary rotation amount of the rotation arm 256 for reliably detecting the sheet S is small. There is a possibility that the accuracy in detecting the sheet S may be deteriorated.

In the conventional sheet detection apparatus 250, since the contact surface of the rotating arm 256 with the sheet is formed linearly, when the sheet S is conveyed by an arbitrary amount after contacting the rotating arm 256, the sheet S And the rotation arm 256 are gradually reduced in angle. Therefore, θ50> θ51. If the biasing force of a biasing spring (not shown) that holds the rotating arm 256 at the standby position is very small, Fθ50 = Fθ51. As a result, the relational expression of the folding force when the sheet S contacts the rotating arm 256 and when the sheet S is conveyed by an arbitrary amount after contacting the rotating arm 256 is as follows.
Fθ51a = Fθ51 × sin θ51 = Fθ50 × sin θ51 <Fθ50a

  That is, the folding force Fθ51a when the sheet S is conveyed by an arbitrary amount after coming into contact with the rotating arm 256 decreases with the peak folding force Fθ50a at the moment when the sheet S comes into contact with the rotating arm 256 (FIG. 16). reference).

  Further, conventionally, a sheet detection apparatus having an arm that rotates in contact with a conveyed sheet and a blocking unit that blocks light from the light emitting unit to the light receiving unit of the photo interrupter by rotating the arm. It has been proposed (see Patent Document 1).

  The arm of the sheet detecting device has a contact surface with the conveyed sheet formed in an arc shape, and the conveyed sheet is configured to pass smoothly while contacting the arc-shaped contact surface. . The sheet detection device detects the sheet by rotating the arm when the sheet contacts the arm, and the blocking unit blocking light from the light emitting unit to the light receiving unit as the arm rotates.

JP 11-165909 A

  In the conventional sheet detection apparatus 250, folding is most likely to occur at the leading edge of the sheet S at the moment when the sheet S comes into contact with the rotating arm 256. Further, there is a problem that if the angle formed between the rotating arm 256 and the sheet S in the standby state is increased, the sheet S is likely to be bent, and if the angle formed is decreased, there is a possibility of erroneous detection.

  Further, in the sheet detection apparatus described in Patent Document 1, the angle formed between the contact surface of the arm and the leading end of the sheet is greatly changed due to the movement of the sheet conveyance position guided by the conveyance guide. For this reason, damage to the front end of the sheet when the sheet comes into contact with the contact surface of the arm is not sufficiently reduced, and the front end of the sheet may be broken particularly in a sheet with a low waist.

  Accordingly, the present invention provides a sheet detecting apparatus in which a curved portion that comes into contact with a sheet is formed in a shape recessed at an upstream side in the sheet conveying direction so that an angle formed with the sheet is an acute angle, thereby solving the above-described problem. An object of the present invention is to provide an image forming apparatus.

The present invention comprises a conveying means for conveying the sheet over preparative, in contact with the sheet conveyed by said conveying means in the standby position, and a rotation unit that rotates around a pivot point, wherein the pivot In the sheet detection device that detects the presence of a sheet based on the rotation of the unit, the rotation unit conveys the sheet so that an angle that contacts the sheet conveyed by the conveyance unit at the standby position is an acute angle. in the direction, have a curved portion curved in a concave shape on the upstream side, the curved portion, the angle of contact with the sheet conveyed by said conveying means, said conveying means is constant in the course of conveying the sheet It is formed as follows.

  In the present invention, the curved portion of the rotating portion that comes into contact with the sheet is formed in a shape that is recessed upstream in the sheet conveying direction so that the angle formed with the sheet is an acute angle. As a result, the force that affects the folding of the leading edge of the sheet can be reduced, and the rotation stroke of the rotation unit can be increased so that the sheet is not erroneously detected. In addition, even if the sheet conveyance position is slightly deviated, the angle between the curved portion and the leading edge of the sheet is not greatly affected, and thus the folding of the leading edge of the sheet can be reliably prevented.

1 is an overall cross-sectional view of a printer according to a first embodiment of the present invention. The right perspective view which shows the sheet | seat detection apparatus which concerns on the 1st Embodiment of this invention. 1 is a left perspective view showing a sheet detection apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view illustrating a sheet detection apparatus according to a first embodiment of the present invention. It is sectional drawing which shows the sheet | seat detection apparatus which concerns on the 1st Embodiment of this invention, Comprising: The figure which shows the moment when a sheet | seat contacts a curved part. It is sectional drawing which shows the sheet | seat detection apparatus which concerns on the 1st Embodiment of this invention, Comprising: The figure which the curved part rotated predetermined amount with the sheet | seat. FIG. 3 is a cross-sectional view illustrating the sheet detection apparatus according to the first embodiment of the present invention, and illustrates a moment when a rear end of the sheet comes out of a curved portion. FIG. 3 is a cross-sectional view illustrating the sheet detection apparatus according to the first embodiment of the present invention, and illustrates a force applied to the sheet at a standby position. FIG. 3 is a cross-sectional view illustrating the sheet detection apparatus according to the first exemplary embodiment of the present invention, and illustrates a force applied to the sheet in a state where the sheet is conveyed by a predetermined amount. The figure which shows the relationship between the folding force which concerns on the 1st Embodiment of this invention, and a sheet conveyance amount. It is sectional drawing which shows the sheet | seat detection apparatus which concerns on the 2nd Embodiment of this invention, Comprising: The figure which shows the force concerning the sheet | seat in a standby position. FIG. 10 is a cross-sectional view illustrating a sheet detection apparatus according to a second embodiment of the present invention, and illustrates a force applied to the sheet in a state where the sheet is conveyed by a predetermined amount. The figure which shows the relationship between the folding force which concerns on the 2nd Embodiment of this invention, and a sheet conveyance amount. It is sectional drawing which shows the conventional sheet | seat detection apparatus, Comprising: The figure which shows the force concerning the sheet | seat in a standby position. It is sectional drawing which shows the conventional sheet | seat detection apparatus, Comprising: The figure which shows the force concerning a sheet | seat in the state in which the sheet | seat was conveyed by predetermined amount. The figure which shows the relationship between the folding force which concerns on the conventional sheet detection apparatus, and a sheet conveyance amount.

(First embodiment)
First, a first embodiment of the present invention will be described. The image forming apparatus according to the embodiment of the present invention may be any apparatus provided with a sheet feeding apparatus capable of feeding sheets, such as a copying machine, a printer, a facsimile machine, and a multifunction machine thereof. The following embodiments will be described using an electrophotographic laser beam printer 1 (hereinafter referred to as a printer) that forms toner images of four colors.

  As shown in FIG. 1, the printer 1 includes a sheet feeding unit 10 that feeds a stored sheet, an image forming unit 20 that forms an image on the sheet, and a discharge unit 40 that discharges the sheet to the outside. I have. The sheet feeding unit 10 feeds the cassette 11 that can be pulled out from the apparatus main body, the sheet stacking plate 12 on which the sheet S is stacked in the cassette 11, and the sheet S stacked on the sheet stacking plate 12. And a roller 13. Further, the sheet feeding unit 10 includes a separation roller 14 and a conveyance roller 15 that separate and convey the sheets S fed by the feeding roller 13 one by one. The feeding timing of the sheet S fed by the feeding roller 13 is adjusted by a registration roller 17 on the conveyance path 16. In this embodiment, only one cassette for storing sheets is provided, but a plurality of cassettes may be provided to store sheets of different sizes.

  The image forming unit 20 includes an exposure device 21 and four process cartridges 22Y, 22M, 22C, and 22Bk that form images of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). It is equipped with. Since the four process cartridges 22Y, 22M, 22C, and 22Bk have the same configuration except that the color of the image to be formed is different, the configuration of the process cartridge 22Y will be described, and the process cartridges 22M, 22C, and 22Bk will be described. Omitted. The process cartridge 22Y includes a photosensitive drum 23Y, a charging roller 24Y that charges the photosensitive drum 23Y, and a developing roller 25Y that develops an electrostatic latent image formed on the photosensitive drum 23Y. Further, the process cartridge 22Y includes a cleaning device 26Y that collects the toner remaining on the photosensitive drum 23Y.

  The image forming unit 20 includes an intermediate transfer belt 27 on which a toner image on a photosensitive drum (for example, 23Y) of each process cartridge is primarily transferred, and primary transfer rollers 28Y, 28M, and 28C that primarily transfer the toner image to the intermediate transfer belt 27. , 28Bk. Further, the image forming unit 20 includes a secondary transfer roller 29 that secondarily transfers the primary-transferred toner image onto the sheet P, and a fixing device 30 (conveying means) that heat-fixes the secondary-transferred toner image. I have. The intermediate transfer belt 27 is wound around a driving roller 31 that drives the intermediate transfer belt 27, a tension roller 32, and a secondary transfer counter roller 33 that faces the secondary transfer roller 29.

  The fixing device 30 includes a heating unit 34 and a pressure roller 35. The discharge unit 40 includes a discharge roller 42 that discharges the sheet S to the discharge tray 41, and a discharge roller 43 that rotates following the discharge roller 42.

  When an image formation command is output to the printer 1, the exposure device 21 irradiates laser light toward the photosensitive drums (for example, 23Y) of the process cartridges 22Y, 22M, 22C, and 22Bk based on the input image information. At this time, the photosensitive drum is charged in advance by a charging roller (for example, 24Y), and an electrostatic latent image is formed on the photosensitive drum by irradiation with laser light. Thereafter, the electrostatic latent image is developed by a developing roller (for example, 25Y), and yellow (Y), magenta (M), cyan (C), and black (Bk) toner images are formed on each photosensitive drum. The toner images of the respective colors formed on the respective photosensitive drums are transferred to the intermediate transfer belt 27 by the primary transfer rollers 28Y, 28M, 28C, and 28Bk, and are conveyed to the secondary transfer roller 29 by the intermediate transfer belt 27. The toner remaining on each photosensitive drum after transfer to the intermediate transfer belt 27 is collected by a cleaning device (for example, 26Y).

  In parallel with the image forming operation described above, the sheets S stored in the sheet feeding unit 10 are fed one by one toward the registration roller 17. Then, the toner image on the intermediate transfer belt 27 is collectively transferred by the secondary transfer roller 29 to the sheet S conveyed at a predetermined conveyance timing by the registration roller 17. The sheet S to which the toner image has been transferred is heated and pressed at a nip portion N formed by the heating unit 34 and the pressure roller 35 in the fixing device 30 to fix the toner image. The sheet S passes through the fixing device 30, passes through the discharge conveyance path 44, and is discharged to the discharge tray 41 by the discharge roller 42 and the discharge roller 43.

  Next, the sheet detection device 50 that detects the sheet S on the upstream side in the sheet conveyance direction with respect to the fixing device 30 will be described. 2 and 3, the sheet detection device 50 includes a holder 51 supported by the frame of the printer 1, a sheet detection flag 52 (rotation unit) supported by the holder 51, and an optical sensor 53 ( And a flag spring 54a. The optical sensor 53 includes a light emitting member 53a that emits light, and a light receiving member 53b that receives light from the light emitting member 53a. The sheet detection flag 52 includes a rotation shaft 54, a flag 55 (shielding portion) that is fixed to the rotation shaft 54 and protrudes opposite to the rotation shaft 54 (rotation fulcrum), and a sheet contact. Arm 56.

  As shown in FIG. 4, the sheet contact arm 56 includes a curved portion 56a that contacts the sheet S that has passed through the fixing device 30, and a connecting portion 56b that connects the rotating shaft 54 and the curved portion 56a. ing. The connecting portion 56b is formed to be curved along the outer peripheral surface of the pressure roller 35 that is one rotating body constituting the fixing device 30, and the curvature of the connecting portion 56b is equal to the curvature of the bending portion 56a. Different. That is, the sheet contact arm 56 has an inflection point between the curved portion 56a and the connecting portion 56b. Further, in the present embodiment, the rotation shaft 54 is arranged on the upstream side in the sheet conveyance direction with respect to the bending portion 56a. Therefore, in combination with the curved shape of the connection portion 56b, the space near the sheet detection device 50 can be widely used. Further, by freely changing the arrangement of the rotation shaft 54 and the shape of the connection portion 56b, the degree of freedom in design can be improved without changing the arrangement and curvature of the bending portion 56a described later.

  In FIG. 4, the sheet detection flag 52 is at the standby position. At the standby position, the flag 55 does not block the light of the optical sensor 53 and detects a state in which the sheet S is not in the sheet detection area A. Yes. The sheet detection flag 52 is held in the standby state by the biasing force of the flag spring 54a.

  Next, the sheet detection operation of the sheet detection apparatus 50 will be described. FIG. 5 shows a state at the moment when the sheet S conveyed by the fixing device 30 contacts the curved portion 56a of the sheet contact arm 56 in the standby position. When the leading end of the sheet S comes into contact with the curved portion 56 a, the sheet contact arm 56 rotates in the B direction shown in the drawing around the rotation shaft 54. As the sheet contact arm 56 rotates in the B direction, the flag 55 also rotates. As shown in FIG. 6, when the sheet contact arm 56 rotates more than a predetermined amount, the flag 55 emits light from the optical sensor 53. Shield from light. Accordingly, the sheet detection device 50 detects a state where the sheet S is in the sheet detection area A.

  FIG. 7 shows a state at the moment when the rear end of the sheet S comes out of the curved portion 56a of the sheet contact arm 56 (from the contact state to the non-contact state). When the rear end of the sheet S comes out of the curved portion 56a, the sheet contact arm 56 rotates in the C direction shown in the drawing by the urging force of the flag spring 54a. As the sheet contact arm 56 rotates in the C direction, the flag 55 also rotates, and the optical sensor 53 transmits light again. As a result, the sheet detection device 50 detects that the sheet S has passed the sheet detection area A, and the sheet contact arm 56 returns to the standby position shown in FIG.

  Next, the relationship between the shape of the curved portion 56a of the sheet contact arm 56 and the force applied to the leading edge of the sheet S will be described in detail. FIG. 8 shows a moment when the sheet S contacts the curved portion 56a of the sheet contact arm 56 in a state where the sheet contact arm 56 is in the standby position. The curved portion 56a is formed to be curved in a shape recessed in the upstream side in the sheet conveyance direction, and an angle (angle) formed with the leading edge of the sheet S is θ10. At this time, the force applied to the sheet S by the bending portion 56a is a component force of Fθ10 and Fθ10, and the force applied to the direction opposite to the conveyance direction of the sheet S (hereinafter referred to as a bending force) is Fθ10a and the conveyance direction of the sheet S. The force applied in the vertical direction is Fθ10b. The curved portion 56a is formed to be curved so that θ10 becomes an acute angle regardless of variations in the transport position of the sheet S by a transport guide (not shown). Therefore, even if the sheet conveyance position is slightly deviated, the angle between the curved portion 56a and the leading edge of the sheet S is not greatly affected, and the folding of the leading edge of the sheet S can be reliably prevented.

  Also, as shown in FIG. 9, the angle between the leading edge of the sheet S and the curved portion 56a when the leading edge of the sheet S contacts the curved portion 56a and the sheet S is conveyed by an arbitrary amount is defined as θ11. At this time, the force applied to the sheet S by the bending portion 56a is a component force of Fθ11 and Fθ11, and the force (folding force) applied in the direction opposite to the conveyance direction of the sheet S is applied in the direction perpendicular to the conveyance direction of Fθ11a and the sheet S. The force is Fθ11b. The forces that affect the folding of the leading edge of the sheet are mainly the folding forces Fθ10a and Fθ11a. By reducing these folding forces Fθ10a and Fθ11a, the folding at the leading edge of the sheet can be prevented.

In the present embodiment, the bending portion 56a is configured such that the angle θ11 formed by the sheet S and the bending portion 56a gradually decreases in the process in which the fixing device 30 conveys the sheet after the sheet S comes into contact with the bending portion 56a. Is formed. Therefore, θ10> θ11 is always satisfied. If the biasing force of the flag spring 54a that holds the sheet contact arm 56 at the standby position is very small, Fθ10 = Fθ11. Thereby, the relational expression of the folding force when the sheet S contacts the bending portion 56a and when the sheet S is conveyed by an arbitrary amount after contacting the bending portion 56a is as follows.
Fθ11a = Fθ11 × sin θ11 = Fθ10 × sin θ11 <Fθ10a

  That is, the folding force Fθ11a when the sheet S is conveyed by an arbitrary amount after coming into contact with the bending portion 56a decreases with the peak folding force Fθ10a at the moment when the sheet S comes into contact with the bending portion 56a.

  FIG. 10 shows the relationship between the folding forces Fθ50a and F51a in the above-described conventional sheet detection apparatus 250, the folding forces F10a and F11a in the present embodiment, and the conveyance amount y of the sheet S. For example, the conveyance amount of the sheet S at the folding force Fθ11a is y11. Here, for example, Fa is a force that actually causes the leading edge of the sheet S to be bent. The folding force Fθ50a in the conventional sheet detection apparatus 250 may exceed the force Fa that causes folding at the leading edge of the sheet S, for example, when the angle θ50 formed by the sheet S and the rotating arm 256 is large. In the present embodiment, the angle formed between the sheet S and the bending portion 56a so that the bending force Fθ10a at the moment when the sheet S and the bending portion 56a abuts is lower than the force Fa that causes the sheet S to be bent. θ10 is set small. Further, the bending portion 56a of the present embodiment is formed so that θ10> θ11 is always established, and therefore the folding force Fθ11a decreases as the fixing device 30 conveys the sheet S. Therefore, since the folding forces Fθ10a and Fθ11a do not exceed the force Fa that causes folding at the leading edge of the sheet S, it is possible to prevent folding from occurring at the leading edge of the sheet S.

  Further, the bending portion 56a is formed to be curved in a shape recessed toward the upstream side in the sheet conveyance direction so as to approach the direction perpendicular to the sheet conveyance direction toward the tip of the bending portion 56a. . Accordingly, the rotation stroke of the sheet contact arm 56 can be made larger than that of the conventional rotation arm 256 of the sheet detection apparatus 250 in which the contact surface with the sheet is linearly formed. In addition, erroneous detection of the sheet can be prevented.

  Note that the curvature of the bending portion 56a may be freely set in consideration of the relationship between the angle θ10 formed by the leading edge of the sheet S and the bending portion 56a and the rotation stroke of the sheet contact arm 56. Accordingly, it is possible to obtain an appropriate curved portion 56a according to the strength of the seat and the sheet detection accuracy.

  In this embodiment, the optical sensor is used to detect the sheet. However, the present invention is not limited to this, and the sheet may be detected using another sensor such as a potentiometer or a pressure sensor.

  In the present embodiment, the connection portion 56b of the sheet contact arm 56 is formed to be curved along the outer peripheral surface of the pressure roller 35. However, the shape of the connection portion 56b is not limited and is, for example, a crank shape. You may form in. In addition, the pressure roller 35 is arranged on the side close to the connecting portion 56b in the rotating body constituting the fixing device 30, but the arrangement of the pressure roller 35 and the heating unit 34 may be changed.

  In the present exemplary embodiment, the sheet detection device 50 is provided in the vicinity of the fixing device 30. However, the present invention is not limited to this, and the sheet detection device 50 may be disposed on any conveyance unit.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. Since the second embodiment is different from the first embodiment only in the configuration of the bending portion, the same configuration as the first embodiment is provided. Is omitted, or the same reference numerals are attached to the drawings and description thereof is omitted. The sheet detection device 150 includes a sheet contact arm 156, and the sheet contact arm 156 includes a bending portion 156a and a connection portion 56b. The curved portion 156a is formed to be curved in a shape recessed to the upstream side in the sheet conveyance direction.

  In FIG. 11, the sheet contact arm 156 is in the standby position, and the angle formed with the leading edge of the sheet S is θ70. At this time, the force applied to the sheet S by the bending portion 156a is a component force of Fθ70 and Fθ70, and the force applied to the direction opposite to the conveyance direction of the sheet S (hereinafter referred to as a folding force) is defined as Fθ70a and the conveyance direction of the sheet S. The force applied in the vertical direction is Fθ70b. The curved portion 156a is formed to be curved so that θ70 becomes an acute angle regardless of variations in the transport position of the sheet S by a transport guide (not shown). Therefore, the folding force that affects the folding of the leading edge of the sheet S can be reduced regardless of variations in the transport position of the sheet S.

  As shown in FIG. 12, the angle between the leading edge of the sheet S and the curved portion 156a when the leading edge of the sheet S contacts the curved portion 156a and the sheet S is conveyed by an arbitrary amount is defined as θ71. At this time, the force applied to the sheet S by the bending portion 156a is the component force of Fθ71 and Fθ71, and the force (folding force) applied in the direction opposite to the conveyance direction of the sheet S is applied in the direction perpendicular to the conveyance direction of Fθ71a and the sheet S. The force is Fθ71b.

  In the present embodiment, the bending portion 156a is configured such that the angle θ71 formed by the sheet S and the bending portion 156a is constant in the process in which the fixing device 30 conveys the sheet after the sheet S contacts the bending portion 156a. Is formed. Therefore, θ70 = θ71 is always established. As a result, if the biasing force of the flag spring 54a that holds the sheet contact arm 156 in the standby position is very small, the folding force Fθ70a = Fθ71a.

  Therefore, as shown in FIG. 13, the folding force Fθ70a = Fθ71a is constant regardless of the transport amount y of the sheet S. In the present embodiment, the angle θ70 = θ71 formed by the sheet S and the bending portion 56a is set to be small so that the folding force Fθ70a = Fθ71a is lower than the force Fa that causes folding at the leading edge of the sheet S. As a result, the folding force Fθ70a = Fθ71a does not exceed the force Fa that causes folding at the leading edge of the sheet S, so that folding at the leading edge of the sheet S can be prevented.

  Further, since the curvature of the bending portion 156a is set so that θ70 = θ71 is always obtained, the folding force Fθ70a = Fθ71a, and more stable sheet conveyance can be performed.

1: printer (image forming apparatus), 30: fixing device (conveying means), 35: pressure roller (one rotary member), 50, 150: sheet detection device, 52: sheet detection flag (rotation unit), 53 : Optical sensor (detection unit), 53a: light emitting member, 53b: light receiving member, 54: rotating shaft (rotating fulcrum), 55: flag (shielding unit), 56a, 156a: curved portion, 56b: connecting portion, S: Sheet

Claims (6)

Conveying means for conveying the sheets, in contact with the sheet conveyed by said conveying means in the standby position, and a rotation unit that rotates around the rotating fulcrum, the rotation of the rotator In a sheet detection device for detecting the presence of a sheet based on
The rotating unit, the angle of contact with the sheet conveyed by said conveying means at said standby position so that an acute angle, in the conveying direction of the sheet, have a curved portion curved in a concave shape on the upstream side,
The curved portion is formed such that an angle of contact with the sheet conveyed by the conveying unit is constant in the process of conveying the sheet by the conveying unit.
A sheet detection apparatus characterized by the above. A detection unit for detecting rotation of the rotation unit ;
The sheet detection apparatus according to claim 1. The rotating part has at least one inflection point;
Sheet detection apparatus according to claim 1 or 2. The rotation fulcrum is arranged on the upstream side of the curved portion in the sheet conveyance direction,
The rotating part is formed to be curved along the outer peripheral surface of one of the rotating bodies constituting the conveying means, and has a connecting part for connecting the rotating fulcrum and the bending part.
The sheet detection apparatus according to claim 3 . The detection unit includes a light emitting member that emits light, and a light receiving member that receives light emitted from the light emitting member,
The rotating portion rotates together with the curved portion rotating in contact with the sheet conveyed by the conveying means, and has a shielding portion that can shield between the light emitting member and the light receiving member.
The sheet detection apparatus according to claim 2 . An image forming unit for forming an image on a sheet;
A sheet detection device according to any one of claims 1 to 5 ,
An image forming apparatus.

Images