JPH04371431A - Sheet transport mechanism - Google Patents

Abstract

PURPOSE:To make sheet conveyance reliable in the sheet conveyance mechanism. CONSTITUTION:The conveyance mechanism comprises a conveyance roller pair 20 consisting of a drive roller 20a and a driven roller 20b opposed to each other, a paper passage sensor 34 provided near the conveyance roller, and a sensing lever 36 having a fore end portion 36a capable of abutting against a sheet 32 carried toward the conveyance roller pair 20. The sheet conveyance mechanism arranged to cause the paper sheet sensor 34 to produce a signal permitting start of the drive roller 20a rotation when the fore end portion 36 of the sensing lever 36 abuts against the sheet 32 and is pressed and moved up to a sheet sensor position L, is so constructed that the sheet sensing position L may be set between the first imaginary plane P1 including a rotary shaft Sh1 of the drive roller 20a and a rotary shaft Sh2 of the driven roller 20b and the second imaginary plane P2 constituting a common surface of contact with the drive roller 20a and the driven roller 20b from the upstream side in the sheet conveyance direction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveyance mechanism for an image forming apparatus.

0002

2. Description of the Related Art Generally, in a sheet conveyance mechanism such as a laser printer, a pair of conveyance rollers consisting of a driving roller and a driven roller facing each other, and a pair of conveyance rollers are provided near the pair of conveyance rollers to detect the presence or passage of a sheet. A sheet conveyance mechanism equipped with a sheet passage sensor is known, and examples of this type of sheet conveyance mechanism include those shown in FIGS. 7 and 8.

In FIGS. 7 and 8, 1 is a pair of conveying rollers; 2 is a pair of conveying rollers;
3 is a driving roller, 3 is a driven roller, 4 is a paper passing sensor, 5 is a detection lever, and 6 is recording paper. The detection lever 5 is rotatably connected to the paper passing sensor 4, and after the leading end 5a abuts the recording paper 6 and is pressed and moved to the sheet detection position L0, the paper passing sensor 4 is connected to the drive roller 2. A signal allowing the start of rotation is output to a control unit (not shown). For example, if the conveyance roller pair 1 is a registration roller that sends the recording paper 6 to a transfer position between a photoconductor and a transfer charger at a predetermined timing, after the sheet is detected by the paper passing sensor 4, the recording paper 6 is moved to the image position on the photoconductor. The conveying roller pair 1 starts rotating at the same timing. Note that the paper passing sensor 7 is similar to the paper passing sensor 4, and uses the detection lever 8 to detect the passage of recording paper.

0004

However, such a conventional sheet conveyance mechanism has a problem in that the sheet cannot be conveyed reliably for the following reasons. Because the sheet detection position L0 of the tip 5a of the detection lever 5 was not set to a position sufficiently close to the transport roller pair 1, that is, the sheet detection position L0 was set at a common position where the sheet detection position L0 was in contact with the driving roller 2 and the driven roller 3 from the upstream side. Since it is located upstream of the virtual plane P0 which is the contact surface, for example, when this sheet conveyance mechanism is used in a manual paper feed unit, the pressure when the recording paper 6 is inserted toward the pair of conveyance rollers 1, etc. There is a possibility that the recording paper 6 is detected even though the recording paper 6 has not reached the transport roller pair 1, and the drive roller 2 is rotated idly.

[0005]Furthermore, even when the transport roller pair 1 of such a sheet transport mechanism is used, for example, as a registration roller, a similar problem may occur, and the recording paper 6 cannot be transported in a timely manner. This became a problem. Therefore, an object of the present invention is to ensure sheet conveyance.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a transport roller pair consisting of a driving roller and a driven roller facing each other, a paper passing sensor provided near the transport roller pair, a detection lever connected to the sheet passing sensor and having a tip that can come into contact with a sheet being conveyed toward a pair of conveying rollers, the tip of the detection lever coming into contact with the sheet until it reaches a sheet detection position. In a sheet conveying mechanism in which a sheet passing sensor outputs a signal that allows the drive roller to start rotating when pressed and moved, the sheet detection position is located at a point where the rotation axis of the drive roller and the rotation axis of the driven roller are aligned. and a second virtual plane that is a common contact surface that contacts the drive roller and the driven roller from the upstream side in the sheet conveyance direction.

Further, assuming that a driving-side virtual cylinder and a driven-side virtual cylinder are coaxial with the driving roller and the driven roller, and each has a radius of 1/2 of the driving roller and the driven roller, the sheet detection position is The third virtual plane may be set between the first virtual plane and a third virtual plane that is a common contact surface that contacts the driving-side virtual cylinder and the driven-side virtual cylinder from upstream in the sheet conveyance direction.

Further, a cylindrical elastic member is partially provided on the surface of at least one roller of the pair of conveying rollers, and the diameter of the cylindrical elastic member is equal to the diameter of the roller, or the cylindrical elastic member is The diameter of the member may be larger than the diameter of the roller. Furthermore, a notch is formed by cutting out the roller surface facing the cylindrical elastic member,
The width of the notch may be larger than the width of the cylindrical elastic member.

[0009]

[Operation] In the present invention, since sheet detection is performed when the sheet is sufficiently close to the pair of conveying rollers, the pair of conveying rollers does not start rotating when the sheet is separated from the pair of conveying rollers. Idling is less likely to occur. Further, by detecting the sheet when the sheet comes sufficiently close to the pair of conveying rollers or when the sheet comes into contact with the pair of conveying rollers, idle rotation of the pair of conveying rollers becomes more difficult to occur.

Further, by providing a cylindrical elastic member on the surface of the pair of conveying rollers, the sheet can be easily gripped by the pair of conveying rollers, and idle rotation of the pair of conveying rollers can be reliably prevented. Furthermore, by forming the notch facing the cylindrical elastic member, deformation of the cylindrical elastic member becomes less likely to occur.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. 1 to 4 are diagrams showing a first embodiment of a sheet conveyance mechanism according to the present invention, and show an example in which the present invention is applied to a laser printer and images are formed on recording paper by manual feeding. .

First, the configuration will be explained. In Figure 1, 1
1 is a laser printer main body;
1 includes a paper feeding device 12, a photosensitive drum 13, a laser optical system 14, a developing device 15, and a fixing device 16. The paper feeding device 12 transports the recording paper 19 along a paper feeding guide 17 and a first sheet transport path 18 to a pair of transport rollers 20 (details will be described later). Conveying roller pair 20
After passing through, the recording paper 19 is conveyed to the photosensitive drum 13. The surface of the photosensitive drum 13 is charged by the charging charger 21 as it rotates counterclockwise in the figure. Next, the laser optical system 14 irradiates the surface of the photoreceptor drum 13 with laser light to form an electrostatic latent image, and the developing device 15 visualizes the electrostatic latent image with toner. After the visible image is transferred to the recording paper 19 by the transfer charger 22, the recording paper 19 is conveyed to the fixing device 16. After the fixing device 16 heat-fixes the visible image on the recording paper 19, the recording paper 19 is discharged to the discharge section 23. Photosensitive drum 1 after transfer of visible image
3, the surface is neutralized by the static elimination lamp 24, and the residual toner on the surface is removed by the cleaning device 25. Note that 26 is an operation panel, 27 is a main motor, and 28 is a paper discharge roller.

On the other hand, 31 is a manual feed stand, and the manual feed stand 3
1 constitutes a part of a second sheet conveyance path 33 that joins the first sheet conveyance path 18 and opens at the right end of the laser printer main body 11 in the figure. That is, the manual feed stand 31 is provided so as to protrude from the laser printer main body 11, and the manual feed tray 31 is provided so as to protrude from the laser printer main body 11. When a user inserts recording paper of a possible size into the laser printer main body 11 one by one, this manual feeding recording paper 32 functions as a guide stand.

[0014] When using the manual feed stand 31 in this way,
The manual feed recording paper 32 is passed from the manual feed table 31 to the second sheet conveyance path 33 and the first sheet conveyance path 18 to the conveyance roller pair 2.
You will be guided to 0. As shown in FIGS. 2 and 3, this conveyance roller pair 20 consists of a drive roller 20a and a driven roller 20b that face each other. The drive roller 20a is rotated by the power of a drive unit (not shown), and the driven roller 20b rotates as the drive roller 20a rotates. Paper passing sensors 34 and 35 are provided near the upstream side of the conveyance roller pair 20 and near the downstream side of the conveyance roller pair 20 . The paper passing sensor 34 includes a pair of conveying rollers 2.
A detection lever 36 is rotatably connected to the detection lever 36, which has a tip 36a that can come into contact with the manually fed recording paper 32 (or ordinary recording paper) that is conveyed toward zero.
The distal end portion 36a is capable of reciprocating in the left-right direction in the figure. That is, when the tip end 36a of the detection lever 36 comes into contact with the manual recording paper 32 and is pressed and moved to the sheet detection position L (left side in the figure), the paper passing sensor 34 allows the drive roller 20a to start rotating. It is configured to output a signal to a control unit (not shown). Note that a detection lever 37 is similarly connected to the paper passing sensor 35.

The sheet detection position L of this tip portion 36a is as follows:
It is positioned very close to the contact point C of the driving roller 20a and the driven roller 20b, and the manual feed recording paper 3
2 reaches the conveying roller pair 20 and comes into contact with it, and then it is detected. That is, as shown in FIG. 4, the sheet detection position L is located between the first virtual plane P1 including the rotation axis Sh1 of the drive roller 20a and the rotation axis Sh2 of the driven roller 20b, and the position between the drive roller 20a and the driven roller 20b from the upstream side. The sheet detection position L is set between the second imaginary plane P2, which is a common contact surface, and in particular, in this embodiment, the sheet detection position L is set between the driving roller 20a and the driven roller 20b.
Assuming a driving-side virtual cylinder Sy1 and a driven-side virtual cylinder Sy2, which are coaxial with each of and have a radius of 1/2 of the driving roller 20a and the driven roller 20b, respectively,
It is set between the first imaginary plane P1 and a third imaginary plane P3, which is a common tangent surface that contacts the driving-side virtual cylinder Sy1 and the driven-side virtual cylinder Sy2 from upstream.

In this embodiment having such a configuration, when manually feeding paper, the sheet of the manually feeding recording paper 32 is not detected when it comes into contact with (sufficiently close to) the transport roller pair 20. Since this is done, manually feed recording paper 3
2 is separated from the transport roller pair 20, the transport roller pair 20 does not start rotating, and the transport roller pair 20
Idling is less likely to occur. Therefore, the pair of conveyor rollers 2
It is possible to prevent zero idle rotation, and the manual feeding recording paper 32 can be transported reliably.

FIG. 5 shows a second sheet conveying mechanism according to the present invention.
It is a figure showing an example of. In this embodiment, the same members and the like as those in the first embodiment described above are denoted by the same reference numerals, and redundant explanation thereof will be omitted. In FIG. 5, 41 is a cylindrical elastic member, and the cylindrical elastic member 41 is partially provided at a predetermined location on the surface of the drive roller 20a of the transport roller pair 20. It is fixed to the rotating shaft Sh1 so as to be gripped by the drive roller 20a. The diameter of this cylindrical elastic member 41 is approximately equal to the diameter of the drive roller 20a.

According to such a configuration, not only can the same effects as in the first embodiment be obtained, but also the manual feed recording paper 32 is easily gripped by the pair of conveying rollers 20, and the idle rotation of the pair of conveying rollers 20 is further reduced. Since this is less likely to occur, the sheet can be conveyed more reliably. Note that the cylindrical elastic member 41 may be provided on the driven roller 20b, or may be provided on both the drive roller 20a and the driven roller 20b. Further, the diameter of the cylindrical elastic member 41 may be larger than the diameter of the drive roller 20a (driven roller 20b).

FIG. 6 shows the third sheet conveying mechanism according to the present invention.
It is a figure showing an example of. In this embodiment, the same members and the like as those in the first and second embodiments described above are denoted by the same reference numerals, and their redundant explanation will be omitted. In FIG. 6, 51 is a notch, and the notch 51 is a circumferential groove formed by cutting out the roller surface facing the cylindrical elastic member 41, and the width is the width of the cylindrical elastic member 41. It's bigger.

According to such a configuration, not only can the same effects as those of the first and second embodiments be obtained, but also the manual feed recording paper 32 is the only thing that comes into contact with the cylindrical elastic member 41. Deformation of the elastic member 41 can be prevented.

[0021]

According to the present invention, it is possible to prevent the pair of conveyance rollers from idling when manually feeding sheets, etc., and it is possible to reliably convey the sheet. In addition, by providing a cylindrical elastic member on the surface of the pair of conveyance rollers,
It is possible to more reliably prevent the conveyance roller pair from idling, and furthermore, by forming the notch facing the cylindrical elastic member, deformation of the cylindrical elastic member can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram of a laser printer to which a sheet conveyance mechanism according to the present invention is applied.

FIG. 2 is a side view of a first embodiment of the sheet conveyance mechanism according to the present invention.

FIG. 3 is a perspective view in FIG. 2;

4 is a diagram showing the positional relationship between a sheet detection position L and a pair of conveyance rollers in FIG. 2. FIG.

FIG. 5 is a front view of a second embodiment of the sheet conveyance mechanism according to the present invention.

FIG. 6 is a front view of a third embodiment of the sheet conveyance mechanism according to the present invention.

FIG. 7 is a side view of a conventional example of a sheet conveyance mechanism.

FIG. 8 is a perspective view of FIG. 7;

[Explanation of symbols]

20 Conveyance roller pair 20a Drive roller 20b Followed roller 32 Manual feed recording paper (sheet) 34
Sheet passing sensor 36 Detection lever 36a Tip 41 Tubular elastic member 51 Notch L Sheet detection position Sh1 Rotating shaft Sh2 Rotating shaft P1 First virtual plane P2 Second virtual plane P3 Third virtual plane Sy1 Drive-side virtual column Sy2 Driven side virtual cylinder

Claims (4)

[Claims] 1. A conveying roller pair consisting of a driving roller and a driven roller facing each other, a sheet passing sensor provided near the conveying roller pair, and connected to the sheet passing sensor,
a detection lever having a tip that can come into contact with a sheet being conveyed toward a pair of conveyance rollers, and when the tip of the detection lever comes into contact with the sheet and is pressed and moved to a sheet detection position, In a sheet conveyance mechanism in which a sheet passing sensor outputs a signal for allowing a drive roller to start rotating, the sheet detection position is located between a first virtual plane including a rotation axis of the drive roller and a rotation axis of a driven roller, and a sheet A sheet conveyance mechanism, characterized in that the sheet conveyance mechanism is set between a second imaginary plane that is a common contact surface that contacts the drive roller and the driven roller from the upstream side in the conveyance direction. 2. Assuming that a driving-side virtual cylinder and a driven-side virtual cylinder are coaxial with the driving roller and the driven roller, and each has a radius of 1/2 of the driving roller and the driven roller, the sheet detection position is 2. The sheet according to claim 1, wherein the sheet is set between the first virtual plane and a third virtual plane that is a common contact surface that contacts the driving side virtual cylinder and the driven side virtual cylinder from upstream in the sheet conveyance direction. Conveyance mechanism. 3. A cylindrical elastic member is partially provided on the surface of at least one roller of the pair of transport rollers, and the diameter of the cylindrical elastic member is equal to the diameter of the roller, or the cylindrical elastic member is 3. A sheet conveyance mechanism according to claim 1, wherein the diameter of the member is larger than the diameter of the roller. 4. The roller according to claim 3, wherein a notch is formed by cutting out the surface of the roller facing the cylindrical elastic member, and the width of the notch is larger than the width of the cylindrical elastic member. Sheet transport mechanism.