JPH04125230A - Paper feed device - Google Patents

Abstract

PURPOSE:To make the pressing force against a paper feed roller constant, irrespective of an increase or a decrease in loading, by providing a pressing spring for pushing up a bottom plate, and a compensating spring for urging the bottom plate in the opposite direction with an urging force smaller than that of the pressing spring. CONSTITUTION:A bottom plate 53 on which sheets are loaded is journalled rotatably in the vertical direction to pins 34 on both sides thereof. A push-up arm 37 for pushing up the bottom plate 33 is secured to the center part of a coupling shaft 36 which are journalled between side plates on both sides of a lower frame, and a lever 38 is secured to one end of the coupling shaft 36. A pressing spring 40 is stretched from a top plate to the front end of the lever 38 so that the bottom plate 33 is urged by the push-up arm 37 in the direction in which the bottom plate 33 is pushed up. Further, a compressing spring 42 is stretched between the intermediate part of the lever 38 and the side plate on the side remote from the pressing spring. The tension force of the compressing spring 42 is smaller than that of the pressing spring 40 so that the compensating spring 42 cancels an increase in the push-up force of the pressing force 40, thereby it is possible to make the push-up force constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a paper feeding device for feeding sheets stacked in a paper feeding cassette, paper feeding tray, etc. one by one in a printer, a copying machine, or the like.

Long rice devil ■! In a paper feeding device where the bottom plate on which paper is loaded is urged by the biasing force of a pressure spring to press the paper against the paper feed roller, the more paper is loaded, the more weight is applied to the bottom plate.
Since the biasing force of the pressure spring on the bottom plate is weakened,
The pressing force of the paper against the paper feed roller decreases, and conversely, when the loading amount is small, the pressing force increases.For example, when 250 sheets of B4 size plain paper are set, the
00 gf is applied, but when a single sheet is pressed, the pressing force increases significantly to approximately 700 gf, making it easier to double feed when a small number of sheets are being fed.

Conventionally, some paper feed cassettes or paper feed trays are set diagonally to reduce the influence of changes in the amount of paper loaded on the pressing force.

However, this is not enough, and in order to make the pressing force more constant, it is necessary to increase the angle of inclination. Not applicable to type.

An object of the present invention is to feed paper that can maintain the force of pressing the paper against the paper feed roller below a certain level with a very simple structure using a spring, without having to set the paper feed cassette or paper feed tray diagonally. The purpose is to provide equipment.

The present invention provides a paper feed device in which the bottom plate on which paper is loaded is urged by the urging force of a pressure spring to press the paper against the paper feed roller. It is characterized by the provision of a correction spring that biases in the opposite direction with biasing force.

The base end of the correction spring can be made movable within a predetermined range so that after the bottom plate is raised above a predetermined position by the pressure spring, it is urged against the pressure spring.

As the amount of paper on the bottom plate decreases and its loaded weight decreases, the biasing force exerted by the pressure spring on the bottom plate increases, and as a result, the opposing force of the correction spring against the pressure spring increases. Since the force applied to the bottom plate by the pressure spring is reduced accordingly, the force pressing the paper against the paper feed roller is not significantly affected by changes in the paper loading amount and is kept below a certain level.

By making the base end of the correction spring movable within a predetermined range, when there is a large amount of paper loaded, the biasing force of the pressure spring is fully applied to the bottom plate, reducing the number of sheets loaded and making double feeding more likely to occur. By starting the correction spring, the biasing force exerted on the bottom plate by the pressure spring can be reduced.

Example Next, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows a paper feeding device 10 according to the present invention in a printer main body 1.
1 is a schematic configuration diagram of a laser printer provided in a lower frame lla of FIG. This paper feeder! ! Reference numeral 10 designates a paper feed cassette 12 that is horizontally housed in a lower frame lla in a removable manner, and the sheets 13 in the paper feed cassette 12 are transferred one by one to the upper frame llb of the printer main body 11 by a paper feed roller 14.
feed paper inside. The fed paper 13 is timed by a pair of registration rollers 15 and conveyed to a belt-shaped photoreceptor 16 . The photoreceptor 16 is moved clockwise, and its surface is charged by a charger 17 at this time. Then, the photoreceptor 16 is irradiated with laser light from the laser unit 18, and an electrostatic latent image is formed on the photoreceptor 16. This latent image is made visible by toner when passing through the developing device 119, and a toner image is formed. This toner image is transferred onto the paper 13 conveyed to the photoreceptor 16 by the action of the transfer charger 20 . The paper 13 after transfer is transferred to the photoreceptor 16'
separated by the curvature of After that, the paper 13 is
After the toner image is fixed by the fixing device 21, it is sent by the first paper discharge rollers 22 and 23.

The paper 13 that has passed through the first paper ejection rollers 22 and 23 is either ejected in the direction of arrow A with the image side facing up according to the direction switching by the switching claw 24, or it is formed by the paper conveyance guides 25 and 26. The sheet is further conveyed in the direction of arrow B by the second sheet discharge rollers 28 and 29 through the reversing conveyance path 27, and is discharged with the image side facing down to the sheet discharge section 30 on the printer main body 11.

On the other hand, the photoreceptor 16 after the transfer is cleaned of residual toner by a cleaning device 31, and is further discharged from residual charge by a discharge lamp 32, and is ready for the next printing.

The paper feeding device 110 is specifically shown in FIGS. 1 and 2. FIG.

Inside the paper feed cassette 12, there is a bottom plate 33 on which paper 13 is loaded.
are pivotably mounted on pins 34 on both sides so as to be movable up and down. On the other hand, a bottom plate push-up arm 37 for pushing up the bottom plate 33 from below the paper feed cassette 12 is fixed to the center of a connecting shaft 36 supported between the side plates 35 on both sides of the lower frame 11a. A lever 38 is fixed to one end of the shaft 36. A pressure spring 40 is stretched between the tip (free end) of the lever 38 and a spring fixing portion 39a provided on the top plate 39 of the lower frame lla. Further, a pressure spring 4o is provided between the intermediate portion of the lever 38 and a fixed pin 41 protruding from the side plate 35.
A correction spring 42 is stretched on the opposite side. The pressure spring 40 urges the lever 38 clockwise in FIG. 1 in order to push up the bottom plate 33 by the bottom plate push-up arm 37. On the other hand, the correction spring 42
Push the lever 38 counterclockwise.

The tension force of the correction spring 42 is weaker than the tension force of the pressure spring 40, and the paper 13 on the bottom plate 33 is pressed against the paper feed roller 14 by the action of the pressure spring 40, separated by the friction pad 43, and fed. roller 1
4, the sheets are fed one by one.

Note that when the paper feed cassette 12 is pulled out a little, the connecting shaft 36 is rotated via an appropriate member by a cam portion (not shown) provided on the paper feed cassette 12, and the bottom plate push-up arm 37 is rotated.
is rotated counterclockwise to the retracted position where it is removed from the paper feed cassette 12 as shown by the chain line in FIG. 1, and the paper feed cassette 12
can be extracted. On the other hand, when the paper feed cassette 12 is inserted into the lower frame lla, the bottom plate push-up arm 37 moves into the paper feed cassette 12 and pushes up the bottom plate 33.

Since the bottom plate 33 is pushed down by the thickness of the stacked paper 13 on it, the pressure spring 40 expands by that amount, increasing the tensile force. The pushing up force 33 is weakened by the amount of paper mold. Therefore, the force with which the paper 13 is pressed against the paper feed roller 14 is determined by these balances.

However, compared to the degree of decrease in the paper weight due to a decrease in the paper loading amount, the degree of decrease in the pushing force exerted by the pressure spring 40 on the bottom plate 33 is generally small. As the amount decreases, the pressing force against the paper feed roller 14 increases, and when the amount of paper loaded becomes small, there is a risk of double feeding.

However, in this paper feeding device 10, the pressure spring 40
Since a correction spring 42 is provided to oppose the paper, the correction spring 42 expands as the bottom plate 33 rises and compensates by reducing the increase in the pressing force caused by the pressure spring 40. It is not greatly affected by the size of the load and is kept below a certain level.

In the above embodiment (first example), the base end of the correction spring 42 is fixed, but it may be made movable within a predetermined range as in the second example shown in FIGS. , an oval ring portion 42a is provided at the base end of the correction spring 42.
@: is provided, and this ring portion 42a is movable relative to the fixing pin 41 within its length range. In this way,
When the bottom plate 33 falls below a predetermined height due to a large amount of paper loaded, the correction spring 42 does not act on the lever 38 as shown in (A), that is, it does not oppose the pressure spring 40, but it When the load capacity decreases and the bottom plate 33 rises above a predetermined height, the ring part 4 is raised as shown in (B).
2a is locked to the fixed pin 41, the tensile force of the correction spring 42 acts on the lever 38, and the pressure spring 4
Compete with 0.

Then, as the paper load decreases and the bottom plate 33 rises from this point on, the correction spring 42 expands in response to the decrease in paper weight and the increase in the pushing force of the bottom plate 33 by the pressure spring 40. In order to increase the tensile force, an increase in the force pressing the paper against the paper feed roller 14 is prevented.

FIG. 5 shows the relationship between changes in paper weight, spring urging force, and paper pressing force against paper feed roller 14 with respect to changes in paper loading amount. ■ is a change in paper weight including the weight of the bottom plate 33, ■ is a change in the biasing force of the pressure spring 40, ■ is a change in the force pressing the paper against the paper feed roller 14 when there is no correction spring 42, and ■ is a book Changes in the biasing force of the correction spring 42 in the case of the second example of the invention, and ■ change in the force pressing the paper against the paper feed roller 14 in the case of the second example of the invention.

(2) is a change in the biasing force of the correction spring 42 in the case of the first example of the present invention; (2) is the change in the biasing force of the correction spring 42 in the case of the first example of the present invention;
Each represents the change in paper pressing force.

According to the present invention, by simply providing a correction spring that opposes the pressure spring, the pressing force of the paper against the paper feed roller can be kept below a certain level without being affected by changes in the amount of paper loaded. Therefore, double feeding when the amount of paper on the bottom plate decreases can be accurately prevented with a simple and inexpensive configuration.

[Brief explanation of drawings]

FIG. 1 is a side view showing the mechanism of a first example of a paper feeding device according to the present invention, FIG. 2 is a front view thereof, FIG. 3 is a schematic configuration diagram of a laser printer equipped with the paper feeding device, and FIG. 4 (A) ・(
B) is a side view of the main part of the second example of the present invention, and FIG. 5 is a graph showing the relationship between changes in paper weight, spring biasing force, and paper pressing force against the paper feed roller with respect to changes in paper loading amount. It is. 10... Paper feed device, 14... Paper feed roller, 33... Bottom plate, 40... Pressure spring, 42... Correction spring.

Claims (1)

[Scope of Claims] 1. In a paper feeding device in which a bottom plate on which paper is loaded is urged by a biasing force of a pressure spring to press the paper against a paper feed roller, a biasing force weaker than the pressure spring and its biasing force. A paper feeding device characterized by being provided with a correction spring that biases in the opposite direction. 2. The base end of the correction spring is movable within a predetermined range so that the base plate is urged by the pressure spring after the base plate is raised beyond a predetermined position by the pressure spring. Features: Paper feeding device.