JPH11165909A - Sheet detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exactly detect the tip part and the rear end part of a sheet, regardless of various kinds of differences in sheets, by having a curved surface part into which a sheet is inserted in mid-way of a sheet carrier path and having a sheet detecting member which rotates according to the insertion of a sheet and detects the passing of the sheet. SOLUTION: When a sheet S is carried within a carrier path 48, a sheet detecting arm 41 rotates till the arm 41 hits against an upper limit stopper 47 by carrier force of the sheet S, a shielding arm 43 interrupts light from a light source of a photointerrupter and the attainment of the tip part of the sheet S to the sheet detecting arm 41 is detected. Also the shielding arm 43 revolves together with revolution of the sheet detecting arm 41, the arm 43 is pulled out from the light source 45 and thereby the passing of the rear end part of the sheet S through the sheet detecting arm 41 is detected. The time when the sheet tip part is inserted into the sheet detecting arm 41 and the time when the sheet rear end part passes the sheet detecting arm 41 can be made constant and high accurate detection of both end parts of the sheet S can be performed without errors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by conveying a sheet such as paper, for example, a sheet detecting apparatus in a printer, a facsimile, a copying machine, and the like.

[0002]

2. Description of the Related Art A laser beam printer will be described as an example of a conventional image forming apparatus. FIG. 6 is a sectional view showing a schematic configuration thereof.

The laser beam printer 1 is capable of forming an image on both sides of a sheet such as paper and the like, and an image forming section 2 for forming an image and a sheet reversing section for reversing the sheet. 3 is provided.

[0004] Reference numeral 4 denotes a controller board for controlling the laser beam printer main body. The controller board 4 also has a function of performing image forming processing on an image signal transmitted from an external information device such as another computer. .

Reference numeral 5 denotes a laser scanner, which irradiates a laser beam L corresponding to an image signal generated by the controller board 4 onto the rotating photosensitive drum 6A to sequentially form an electrostatic latent image. is there.

Reference numeral 6 denotes a process unit including a developing unit, which sequentially visualizes an electrostatic latent image formed on the photosensitive drum 6A with toner supplied from the developing unit and transfers the latent image to a transfer roller 7. Transport to the site.

Reference numeral 8 denotes a stacking cassette on which sheets are stacked. The sheets S stacked and stored in the stacking cassette are sequentially sent out one by one from a top to a feeding path 10 one by one by a half-moon-shaped feeding roller 9. The pair 11 is transported to the stopped registration roller 12.

The sheet S that has reached the registration roller pair 12
After the leading end abuts the nip of the registration roller pair 12, the conveyance is continued until a predetermined loop is formed, and the skew state is corrected.

The sheet S whose skew has been corrected is fed between the photosensitive drum 6A and the transfer roller 7 by the registration roller pair 12, where the toner image on the photosensitive drum 6A is transferred. Sheet S after transfer of toner image
Is transported to the fixing roller pair 14 over the transport guide 13, and the transferred toner image is fixed.

Here, when the laser beam printer main body 1 performs only one-sided image formation, that is, when the one-sided image formation mode is selected, the deflector 15 is switched to the position 15A, and the sheet S is transported by the conveying roller pair 18. , Passes through the tray discharge path 16 and passes through the discharge roller pair 1
9, the paper is discharged onto a paper discharge tray 17 at the top of the main body 1.

However, when double-sided image formation is performed, that is, when the double-sided image formation mode is selected, the deflector 15 is switched to the position 15B, and the reverse connection path 20 is set.
, The sheet S is fed to the sheet reversing unit 3 side.

The sheet S fed to the sheet reversing unit 3 is
The sheet is conveyed to the switchback roller pair 27 from the conveying roller pairs 22 and 24 through the conveying path 25 while being corrected by the curl removing roller pairs 21 and 23 for correcting curl and crimp of the sheet.

The conveyance path 25 includes a detection arm 26A which is rotated by the conveyance force of the sheet S as means for detecting the leading end and the rear end of the sheet S. The sheet detecting device 26 provided with the blocking arm 26B for blocking the light source is provided.

When the leading end of the sheet S does not pass through, the sheet detecting device 26 has a detecting arm 26A at a position indicated by a solid line, and the sheet S is sent out by the conveying roller pair 24, and the sheet S is fed by the conveying force. Detection arm 26A
Is moved in the direction of arrow P to a position indicated by the broken line, the blocking arm 26B blocks the light source of the photointerrupter 28, and it is detected that the leading end of the sheet S has reached the transport path 29. Things.

Thereafter, the sheet S is conveyed by the switchback roller pair 27 to the right switchback path 30 in the figure.

When the rear end of the sheet S has passed through the detection arm 26A, the detection arm 26A returns to the position indicated by the solid line, so that the light source of the photointerrupter 28 is not shut off. The part is the transport path 29
Is reached.

As a result of this detection, the switchback roller pair 27 rotates in the reverse direction, and is conveyed to the conveying roller pair 32 through the conveying path 31 with the rear end of the sheet S leading.

Thereafter, the sheet S is conveyed by a pair of conveying rollers 32 and is conveyed through a reference plate 35 by a pair of skew feeding rollers 33 and 34 pressed by rollers having an arbitrary inclination with respect to the rollers. As a result, the position of the sheet S is corrected, passes through the transport path 37, and further passes through the transport roller 38, the re-feed path 39, and the re-feed roller 40, from the re-feed path 8A in the stacking cassette 8 to the image forming unit 2. Conveyed.

In the image forming section 2, the image forming process for the back surface of the sheet S is performed in the same manner as the image forming process for the front surface of the sheet S, and then the sheet S is discharged onto a discharge tray 17.

[0020]

In the above-described image forming apparatus, when the leading end of the sheet comes into contact with the detecting arm 26A, the leading end of the sheet abuts on the detecting arm 26A. May be scratched, and in the case of a sheet having a weak stiffness, there may be a case where the sheet is bent or broken in the conveyance path, and the timing of blocking the light source of the photo interrupter 28 by the blocking arm 26B is shifted. An error sometimes occurred in sheet detection.

In the case of a sheet having a hole for filing, a contact portion between the detection arm 26A and the sheet falls into the hole, and a sheet detection error may occur.

Further, when a curled or crimped sheet is conveyed, the rear end of the sheet is conveyed along one of the walls of the conveying path. , The detection positions of the leading end and the trailing end of the sheet by the detection arm 26A are not fixed, and a detection error is likely to occur.

The object of the present invention is to control the leading and trailing edges of a sheet without being affected by differences between various sheets, such as a curled or crimped sheet, a sheet without stiffness, a sheet with a hole for filing, and the like. Is to provide a sheet detecting device capable of accurately detecting a sheet.

[0024]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and includes a sheet conveying means for conveying a sheet, and a sheet provided in the middle of a sheet conveying path and conveyed by the sheet conveying means. It has a curved surface part to be inserted,
A sheet detection device that rotates as the sheet is inserted into the curved surface portion and has a sheet detection member that detects passage of the sheet; and thereby, is affected by differences between various sheets. Instead, the leading end and the trailing end of the sheet can be accurately detected.

The present invention has been made in view of the above circumstances, and has a conveying means for conveying a sheet, a photosensor comprising a light emitting section and a light receiving section, In the sheet detecting device having a sheet detecting member freely supported by a shaft, the sheet detecting member has a curved surface portion with which the sheet contacts and a shielding portion for shielding the light emitting portion and the light receiving portion, The sheet is rotated by pressing the curved surface portion by the conveying force, and the shielding unit detects the passage of the sheet by shielding the light emitting unit and the light receiving unit. The front end and the rear end of the sheet can be accurately detected without being affected by the difference.

[0026]

(Embodiment 1) Hereinafter, an embodiment of a sheet detecting apparatus according to the present invention will be described with reference to the drawings.

FIGS. 1 and 2 are diagrams for explaining the configuration and operation of the sheet detecting apparatus according to the present invention.

In FIG. 1, reference numeral 41 denotes a sheet detection arm provided in the middle of the transport path, which is provided rotatably about a support shaft 42. Also, this sheet detection arm 41
Is provided with a shielding arm 43.

Reference numeral 44 denotes a photo-interrupter. When a shielding arm 43 provided on the sheet detection arm 41 rotates in the direction of arrow D when the sheet passes, a light source 45 is provided.
Is configured to be shielded.

Reference numeral 46 denotes a lower limit stopper of the sheet detection arm 41, and 47 denotes an upper limit stopper.

The transport path 48 has a left wall of curvature R near the contact point 49 between the sheet S and the sheet detection arm 41, and has a width B between the left wall before the start of the left wall of curvature R and the contact point 49.
Is set to be larger than the path width A.
1 is arranged.

The sheet detecting arm 41 is connected to the contact 4
9 forms an arc-shaped portion 50 having a curvature r, and forms an acute angle C with the left wall 48a. This radius of curvature is set to be larger than the width of the sheet conveying path.

At the portion adjacent to the arc-shaped portion 50 having the curvature r,
A straight portion 51 is formed.

The arc-shaped portion 50 having the curvature r is not particularly limited to an arc shape, but may have any shape (for example, an elliptical shape or a multidimensional shape) as long as the sheet S can be inserted smoothly. Curves, etc.).

When the sheet S is conveyed in the conveyance path 48, the sheet S starts to rotate the sheet detection arm 41 at the contact point 49, and the sheet S is inserted according to the arc shape of the curvature r. Then, the sheet detection arm 41 rotates about the support shaft 42 in the direction of arrow D.

As shown in FIG. 2, the sheet detecting arm 41 is rotated by the conveying force of the sheet S until the sheet detecting arm 41 hits the upper limit stopper 47. At this time, the shielding arm 43 blocks the light from the light source of the photo interrupter, It is detected that the section has reached the sheet detection arm 41. At this time, the linear portion 51 of the sheet detection arm 41 is substantially parallel to the lower wall of the transport path 48.

Then, immediately after the sheet S is conveyed to the switchback roller pair 52 and the rear end of the sheet S has finished passing through the linear portion 51 of the sheet detection arm 41, the sheet detection arm 41 moves the support shaft 42. As the center of rotation, it is lowered by its own weight until it hits the lower limit stopper 46 in the clockwise direction. Here, the protruding portion 41 a of the sheet detection arm 41 traversing the transport path 48 has, for example, an arc shape having a radius T connecting the rear end of the linear portion 51 about the rotation center 42 (this portion is
In particular, the shape is not limited to the arc shape, and may be, for example, an elliptical shape or a multidimensional curved shape.
The rear end portion of the sheet S does not catch on the protruding portion 41a.

With the rotation of the sheet detection arm 41, the shielding arm 43 also rotates, and comes out of the light source 45, whereby it is detected that the rear end of the sheet S has passed through the sheet detection arm 41, and the switchback roller pair 52 Accurate timing at the time of reverse rotation can be obtained.

With the above configuration, the timing when the leading end of the sheet is inserted into the sheet detecting arm 41 and the timing when the trailing end of the sheet passes through the sheet detecting arm 41 are always kept constant. As a result, it is possible to detect the leading edge and the trailing edge of the sheet with less error and high accuracy.

(Embodiment 2) FIG. 3 is a view showing another embodiment in which the conveying path on the upstream side of the sheet detecting apparatus in FIG. 1 is straight.

The sheet S conveyed by the pair of conveying rollers 53 is guided and pressed by a sheet-like elastic body 55 as a guiding member against a lower wall 54a of the conveying path 54, and the curvature of the sheet detecting arm 56. The contact is made at a contact portion 58 with the arc-shaped portion 57 of r ′.

Thereafter, the sheet detecting arm 56 is pushed up while rotating about the support shaft 59 by the conveying force of the sheet S, and at the same time, the shielding arm 61 is also moved by the light source of the photo interrupter 62 against the pulling force of the spring 60. It turns in the direction (arrow E direction) that blocks 63.

FIG. 4 is a view showing a state in which the conveyance of the sheet S has progressed. The linear portion 66 of the sheet detection arm 56 is substantially parallel to the lower wall 54 a of the conveyance path 54 and abuts against the upper limit stopper 65. State.

Further, when the sheet S is further conveyed and its rear end passes through the sheet detection arm 56, the sheet detection arm 56 rotates in the direction of arrow F due to the pulling force of the spring 60, and hits the lower limit stopper 64. This is in a state of waiting for conveyance of the next sheet.

(Embodiment 3) FIG. 5 relates to Embodiment 3 of the present invention. The length u of the linear portion 69 of the sheet detection arm 68 is larger than the diameter of the filing hole 67 formed in the sheet S. Is set long so that a detection error caused by the sheet detection arm 68 dropping into the sheet S can be avoided.

[0046]

As described above, according to the sheet detecting apparatus of the present invention, various sheets such as a curled or crimped sheet and a waistless sheet are not affected by the influence of the sheet. It is possible to provide a sheet detecting device that can accurately detect the leading end and the trailing end of a sheet without causing a problem such as bending of the leading end.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the configuration and operation of a sheet detection device according to the present invention.

FIG. 2 is a diagram for explaining the configuration and operation of a sheet detection device according to the present invention.

FIG. 3 is a diagram for explaining the configuration and operation of a sheet detection apparatus according to another embodiment when the transport path on the upstream side of the sheet detection apparatus is linear.

FIG. 4 is a diagram for explaining the configuration and operation of a sheet detection apparatus according to another embodiment when the transport path on the upstream side of the sheet detection apparatus is linear.

FIG. 5 is a diagram illustrating a case where the length of a linear portion of a sheet detection arm is set to be longer than the diameter of a filing hole formed in a sheet.

FIG. 6 is a cross-sectional view showing a schematic configuration of a conventional laser beam printer and a sheet detecting device thereof.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser beam printer 2 image forming unit 3 sheet reversing unit 4 controller board 5 laser scanner 6 process unit 7 transfer roller 8 stacking cassette 9 feed roller 10 feed path 11 transport roller pair 12 registration roller 13 transport roller 14 fixing guide pair 15 Deflector 16 Tray discharge path 17 Discharge tray 18 Conveying roller pair 19 Discharge roller pair 20 Reverse connection path 21, 23 Curling roller pair 22, 24 Conveying roller pair 25 Conveying path 26 Sheet detecting device 27 Switchback roller 28 Photo interrupter 29 transport path 30 switchback path 31 transport path 32, 33 transport roller pair 34 skew roller pair 35 skew roller pair 36 reference plate 37 transport path 38 transport roller 39 re-feed path 40 re-feed roller 41 sheet Outgoing arm 42 Support shaft 43 Shielding arm 44 Photo interrupter 45 Light source 46 Lower limit stopper 47 Upper limit stopper 48 Transport path 49 Contact section 50 Arc shape 51 Linear section 52 Switchback roller pair 53 Transport roller pair 54 Transport path 55 Sheet elastic body 56 Sheet Detection arm 57 Arc shape 58 Contact part 59 Support shaft 60 Spring 61 Shielding arm 62 Photointerrupter 63 Light source 64 Lower limit stopper 65 Upper limit stopper 66 Linear part

Claims (11)

[Claims] 1. A sheet conveying means for conveying a sheet, a shielding member for shielding between a light emitting member and a light receiving member, and a curved surface provided in the middle of a sheet conveying path and into which a sheet conveyed by the sheet conveying means is inserted. A sheet detection member having a portion, the sheet is rotated as the sheet is inserted into the curved surface portion, the shielding member moves between the light emitting member and the light receiving member, A sheet detecting device for detecting passage. 2. The curved surface portion of the sheet detecting member is provided with a straight portion following the curved portion, and when the sheet is placed on the straight portion from the curved surface portion, the straight line portion is provided between the light receiving member and the light emitting member. The sheet detecting device according to claim 1, wherein the shielding member moves. 3. A curved surface portion of the sheet detecting member has a curvature on an upstream side in a sheet conveying direction, and a tangent between a wall on one side of a conveying path and the curved surface portion forms an acute angle. 2. The sheet detecting device according to claim 1. 4. The sheet detecting apparatus according to claim 1, further comprising an elastic member for urging the sheet detecting member in a direction opposite to a sheet conveying direction. 5. The sheet detecting apparatus according to claim 1, wherein a radius of curvature of a curved surface portion of the sheet detecting member is set to be larger than a width of a sheet conveying path. 6. A sheet conveying device for conveying a sheet, a photosensor comprising a light emitting unit and a light receiving unit, and a sheet detecting member provided in the middle of the sheet conveying path and rotatably supported by a shaft. In the sheet detection device, the sheet detection member has a curved surface portion that contacts the sheet and a shielding portion that shields the light emitting unit and the light receiving unit, and the sheet presses the curved surface portion by a sheet conveying force of the conveying unit. A sheet detecting device for detecting the passage of the sheet by rotating the light emitting device and shielding the light emitting unit and the light receiving unit by the shielding unit. 7. The sheet detecting device according to claim 6, wherein a straight portion continues to the curved surface of the sheet detecting member. 8. The sheet detecting member according to claim 6, wherein the curved surface portion has a curvature on the upstream side in the sheet conveying direction, and a tangent to a wall on one side of the conveying path forms an acute angle. Sheet detection device. 9. The sheet detecting apparatus according to claim 6, further comprising an elastic member for urging the sheet detecting member in a direction opposite to a sheet conveying direction. 10. The sheet detecting device according to claim 6, further comprising an upper limit regulating member and a lower limit regulating member for regulating the rotation of the sheet detecting member. 11. The sheet detecting apparatus according to claim 6, wherein a radius of curvature of a curved portion of the sheet detecting member is set to be larger than a width of a sheet conveying path.