JPH04277138A - Paper feeder - Google Patents

Abstract

PURPOSE:To stop a bottom plate so that the uppermost side of the record paper may be positioned at a certain constant level regardless of the change of load by turning off a stepping motor with specified timing after detection of the top of the record paper on the bottom plate with a paper level sensor and stopping and preserving the top end of the record paper at a predetermined level. CONSTITUTION:A bottom plate 6 is raised. At this time, a stepping motor 12 is driven, and a driving gear 15 is rotated, and a center gear 17 is rotated, which rotates the a bottom plate raising lever 10 clockwise, and pushes up a bottom plate 10. After a paper level sensor detects the top end of the record paper being raised with the bottom plate 10, the stepping motor 12 is stopped with specified timing. At this time, the record paper 5 rises to a predetermined level position, and is in contact with a pickup roller. By using the stepping motor as a motor for driving the bottom plate raising lever 10, it rotates at a certain revolution at all times, so it becomes possible to stop it so that the uppermost end of the record paper 5 may be positioned on a predetermined constant level.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper feeding device for image forming apparatuses such as laser printers and copying machines.

0002

2. Description of the Related Art Conventionally, a paper feeding device for an image forming apparatus, for example, a paper feeding device for a laser printer, has a pickup roller 1, a feed roller 2, and a reverse roller 3, as shown in FIGS. unit 4 and a bottom plate 6 on which the recording paper 5 is placed.
A paper feed cassette 7 that supports the paper feed cassette so as to be tiltable up and down and is removably attached to the main body of the image forming apparatus, and a bottom plate raising part 8 that raises the bottom plate 6 of the paper feed cassette 7 are provided.

The bottom plate lifting section 8 has a bottom plate lifting lever 10 fixed to a support shaft 9 and a drive device (not shown) that rotates the support shaft 9. pushes up the bottom plate 6.

Conventionally, a DC motor and a gear transmission have been used as the drive device, and the bottom plate lifting lever 10 is rotated by the drive of the DC motor to lift the bottom plate 6.
A method has been used in which the recording paper placed on the roller is raised until it comes into contact with the pickup roller 1.

In the conventional paper feeding device, the DC motor is turned on and the bottom plate lifting lever 10 is rotated to raise the bottom plate 6, and the paper height sensor 11 (FIG. 2) is turned on for a certain period of time, for example, about approx. After 40 ms, the DC motor was turned off and the bottom plate lifting lever 10 was stopped. However, since the load applied to the DC motor varies depending on the remaining amount of recording paper placed on the bottom plate 6, the size of the recording paper, etc., the rotation speed of the DC motor varies, and the rotation speed of the paper feed cassette 7 when the bottom plate 6 stops increases. The upper end stop position is different, and the height h from the upper end of the front wall of the paper feed cassette 7 to the uppermost end of the recording paper varies. The height h is normally set to about 5 cm, which corresponds to the height of about 50 sheets of recording paper. In particular, when the remaining amount of recording paper is small and the recording paper is small, the height h tends to increase. As the height h increases, the pressure applied by the pickup roller 1 increases, and if some of the recording paper has a low friction coefficient μ, slippage will occur in the part of the recording paper with a low friction coefficient, and from that part There was a problem in that several dozen sheets of recording paper on the paper entered between the feed roller 2 and the reverse roller 3 at once, resulting in poor separation and jamming.

Low-friction recording paper is usually stacked on a bottom plate, and when left for a long time, the topmost recording paper is exposed to air, causing its surface to deteriorate compared to other recording papers. The friction coefficient μ will change. When new recording paper is added onto recording paper that has been exposed to air for a long time and its friction coefficient μ has changed, the area near the boundary between the old and new recording paper groups will have a different coefficient of friction than the other recording paper. This results in a faulted portion where the recording paper comes into contact. The faulted portion makes it impossible to separate the recording paper, and even causes a jam.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above conventional problems and makes it possible to stop the bottom plate so that the top surface of the recording paper is at a constant height regardless of changes in load. Our goal is to provide a paper feeding device.

[0008]

[Means for Solving the Problems] The present invention solves the above problems by providing a removable paper feed cassette that supports a bottom plate on which recording paper is placed so as to be tiltable up and down, and a bottom plate lifting lever that raises the bottom plate. In a paper feeding device that includes a drive motor and a transmission device that move the bottom plate lifting lever up and down, and a feeding section that feeds recording paper, the drive motor is formed by a stepping motor, and a paper height sensor moves the bottom plate upward. This problem has been solved by a paper feeding device characterized in that the stepping motor is turned off at a predetermined timing after the upper end of the recording paper is detected to stop and hold the upper end of the recording paper at a constant height.

[0009]

[Operation] According to the present invention, the bottom plate lifting lever that raises the bottom plate is driven by a stepping motor, and the stepping motor is turned off at a predetermined timing after the paper height sensor detects the top end of the recording paper, so that it is simultaneously detected by the paper height sensor. Or the motor will be turned off after a certain period of time,
Since the stepping motor has a constant rotational speed regardless of changes in load, the height of the paper is always constant.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained based on the embodiments shown in the drawings.

The paper feeding device according to the present invention can utilize the conventional structure shown in FIGS. 1 and 2 for the feeding section 4 and the paper feeding cassette 7.

As shown in FIG. 3, the bottom plate lifting section 8 of the paper feeding device according to the present invention includes a stepping motor 12 and a rotating force of the stepping motor 12 that is transmitted to the rotation of a support shaft 9 to which a bottom plate lifting lever 10 is fixed. A transmission device 13 is provided.

The transmission device 13 includes, for example, a worm 14 provided on the output shaft of the stepping motor 12, a worm gear 15 meshing with the worm 14, and a drive gear 16.
, a suitable gear train 26 for transmission connection between the worm gear 15 and the drive gear 16, and a sector gear 17 as a gear meshing with the drive gear 16. The sector gear 17 is fixed to the support shaft 9.

One end of the support shaft 9 is supported in a fixed position by a bearing 18 (FIG. 4), and a bearing 19 that rotatably supports the support shaft 9 near the end where the sector gear 17 is fixed is movable to the side plate 20. The pressing spring 21 presses the sector gear 17 toward the position where it meshes with the drive gear 15.

The shaft 9 is connected to the shaft 9 through the bearing 19 or a suitable member.
A release lever 22 that presses one end of the lever against the force of a spring 21 is rotatably supported by a shaft 23. The release lever 22 has a first pawl 22a with a shaft 23 serving as the center of rotation in between.
and a base 2 pawl 22b, the first pawl 22a is formed to be able to abut or engage with and press a member that supports the bearing 19 or another support shaft 9, and the second pawl 22b is configured to press one of the paper feed cassettes 7. A cassette lever 24 provided on the section or paper feed cassette 7 is formed so as to be able to come into contact with it.

When the paper feed cassette 7 is installed, the release lever 22 at the position shown by the solid line in FIG. , the second pawl 22b is pressed by the cassette lever 24 or the like to the position shown by the two-dot chain line. At this time, the first pawl 22a releases the pressing force on the bearing 19, and the bearing 19 is conversely pressed by the pressing spring 21 and presses the sector gear 17 toward the drive gear 15.
Sector gear 17 meshes with drive gear 15 .

At the time of paper feeding, control is performed according to the control flow shown in FIG. 5, and first, the bottom plate 6 is raised. At this time, the stepping motor 12 is driven, the drive gear 15 is rotated, the sector gear 17 is rotated, the bottom plate lifting lever 10 is rotated counterclockwise in FIG. 1, and the bottom plate 10 is pushed up. Bottom plate 10
After the paper height sensor 11 detects the upper end of the recording paper that is being raised at the same time, the stepping motor 12 is stopped at a predetermined timing. At this time, the recording paper 5 rises to a certain height position and comes into contact with the pickup roller 1.

Paper feeding is started by the paper feeding signal, and as shown in FIG.
When the paper feed clutch 26 shown in FIG. Roller 1 is rotated clockwise.

Recording paper 5 pressed against pickup roller 1
is frictionally driven by the pickup roller 1 and sent.

When a certain period of time sufficient for the recording paper 5 to be fed to the nip position between the feed roller 2 and the reverse roller 3 has elapsed from the start of rotation of the pickup roller 1, the stepping motor 12 is driven in the reverse direction, and the bottom plate 6 is lowered. , the recording paper on the bottom plate 6 is released from contact with the pickup roller 1.

Since the reverse roller 3 is driven via a torque limiter, when one sheet of recording paper is fed, it is rotated along with the feed roller 2, and when two or more recording sheets are fed, it is sent back to the recording paper. Apply force to prevent double feeding.

By using a stepping motor as the motor that drives the bottom plate lifting lever 10 that raises the bottom plate 6, the rotation speed does not change due to load fluctuations unlike a DC motor, and the motor always rotates at a constant rotation speed. It has become possible to stop the recording paper 5 so that the top end thereof is always located at a constant height position. In other words, it has become possible to always keep the height h constant regardless of the size or remaining amount of recording paper. If the height h is set to a height that allows reliable separation even when a large number of recording sheets are fed to the feed roller, failure to separate them can be avoided.

When the paper feed cassette 7 is not installed, the sector gear 17 does not mesh with the drive gear 15, so even if the stepping motor 12 is driven for some reason, the support shaft 9 will not rotate, and therefore the bottom plate push-up lever 1 will not rotate.
0 can be maintained in the state before the paper feed cassette 7 is removed, and when the paper feed cassette 7 is installed, the bottom plate push-up lever is in the raised state, so the paper feed cassette cannot be installed or is damaged. This prevents the occurrence of

By applying a force to the sector gear 17 using a spring or the like to constantly lower the bottom plate push-up lever 10 until it hits the stopper 26, the sector gear 17 moves to the drive gear 1.
It is advantageous to configure such a structure that the bottom plate push-up lever 10 is lowered to the lower end position regardless of the position at which the paper feed cassette 7 is removed away from the paper feed cassette 5.

[0025]

[Effects of the Invention] According to the present invention, the uppermost edge of the recording paper on the bottom plate of the paper feed cassette after being raised can always be held in a fixed position, and is pressed against the pickup roller with a predetermined pressure, so that the uppermost edge of the recording paper Since low-friction paper was present in the feed roller, even if a large number of recording sheets were sent to the feed roller, they could be separated reliably and jams at the paper feed port could be prevented.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional paper feeding device.

FIG. 2 is a partial perspective view of FIG. 1;

FIG. 3 is a perspective view of a bottom plate rising portion according to the present invention.

FIG. 4 is a plan view of a portion of the bottom plate rising portion.

FIG. 5 is a control flowchart.

[Explanation of symbols]

4 Feeding section 5 Recording paper 6 Bottom plate 7 Paper cassette 8 Bottom plate rising part 9 Support shaft 10 Bottom plate lift lever 11 Paper height sensor 12 Stepping motor 13 Gear train 14 Gear (worm) 17 Gear (sector gear) 21 Pressure spring 22 Release lever 24 Cassette lever

Claims (2)

[Claims] 1. A removable paper feed cassette that supports a bottom plate on which recording paper is placed so that it can tilt up and down, a bottom plate lift lever that raises the bottom plate, a drive motor and a transmission device that move the bottom plate lift lever up and down. and a feeding unit that feeds recording paper, wherein the drive motor is formed by a stepping motor, and the stepping motor is activated at a predetermined timing after the upper end of the recording paper on the bottom plate is detected by a paper height sensor. A paper feeding device that is turned off to stop and hold the top end of the recording paper at a constant height. 2. The transmission device is formed by a gear train connecting a gear connected to the drive motor and a gear connected to the bottom plate lifting lever, and the gear connected to the bottom plate lifting lever is connected to the transmission device. 2. The paper feeding device according to claim 1, wherein the paper feeding device is formed so as to be movable toward and away from one gear of a gear train of the device, and the moving toward and away from the gear is linked to the movement of attaching and detaching the paper feeding cassette.