JPH05132212A - Paper discharging device for image former - Google Patents

Abstract

PURPOSE:To make a tip of paper being discharged out of an image forming part easily insertable into a paper discharge roller pair, preventing a paper rear end to be discharged out of the paper discharge pair rides on the paper discharge roller from occurring without entailing any projection marks on the paper, and make the paper so as to be stacked on a paper discharge tray. CONSTITUTION:This paper discharger is provided with a means (solenoid) 10 which makes a pressure-contact position of a driven roller 5b caning into pressure-contact with a paper discharge roller 5a to this roller 5b, variable, and when it receives a tip of a sheet of paper 3 being discharged out of an image forming part, it is situated in a position of a nip part where the paper tip is easily receivable, and when the paper rear end is discharged, a tangent of the nip part of the paper discharge pair is situated in such a position as being crossed with a small angle to the surface of a paper discharge tray 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper discharge device for an image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system such as an electrophotographic copying machine, a printer or a facsimile, a toner image formed on the photoconductor 1 by the electrophotographic system is transferred to a transfer charger 2 as shown in FIG. It is transferred onto the transfer paper 3 under the action of, for example, the fixing roller 4a and the pressure roller 4b.
The sheet is fixed by a fixing device 4 having a sheet feeding roller 5a which is rotatably driven and a driven roller 5b which sandwiches a sheet path and is driven in pressure contact with the sheet discharging roller 5a. The sheet is discharged onto the sheet discharge tray 6, rises along the surface of the sheet discharge tray, then slides down, and the lower end is aligned with the abutting surface at the lower end of the tray and stacked.

In this case, depending on the relationship between the inclination of the paper discharge tray 6 and the inertia force of the transfer paper when the transfer paper is discharged by the paper discharge roller pair 5, the rear end of the transfer paper is not reliably separated from the paper discharge roller 5a. In some cases, the trailing edge of the transfer sheet may ride on the sheet ejection roller 5a, the trailing edge of the transfer sheet may not hit the lower edge of the sheet ejection tray, and the sheet may not be properly stacked.

As a preventive measure, as shown in FIGS. 7 and 8, projections 7 are provided in the radial direction at both ends of the peripheral surface of the paper discharge roller 5a, and the rear end of the transfer paper 3 serves as the paper discharge roller 5a. After leaving the nip portion with the driven roller 5b, there is known a method in which the rear end of the transfer sheet is kicked off by the projection 7 so that the rear end of the transfer sheet is separated from the discharge roller 5a and aligned with the lower end abutting portion of the discharge tray. Has been.

However, when this method is adopted, the protrusions 7 are pressed against the sheet conveyed by the pair of discharge rollers, and the marks of the protrusions are formed on the sheet. Especially, the image surface comes into contact with the sheet discharge roller 5a side and the sheet is discharged. When printed, there is a drawback that the traces of protrusions impair the image quality on the image surface.

Further, in recent years, the image forming apparatus has become smaller and lighter, and the distance between the fixing device 4 and the paper discharge roller 5 has become very narrow. Therefore, depending on the angle at which the paper enters the paper discharge roller 5. The curl and wrinkles of the paper are greatly affected, and the distance between the paper discharge roller 5 and the paper discharge tray 6 is narrowed. Therefore, the stacking property is greatly affected depending on the paper discharge direction from the paper discharge roller 5. However, it is becoming very difficult to satisfy both of them.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the paper discharge device having the above-described structure of the conventional image forming apparatus, the present invention has the rear end of the paper discharged from the paper discharge roller pair on the paper discharge rollers. When you get on the
A paper discharge device of an image forming apparatus capable of preventing the image quality from deteriorating and improving the insertability of the paper into the paper discharge roller pair and the stacking property of the paper discharged from the paper discharge rollers. The challenge is to provide.

[0008]

In order to solve the above-mentioned problems, the present invention has means for switching the pressure contact position of the driven roller with respect to the paper discharge roller, and the leading end of the paper is inserted into the nip portion of the paper discharge roller pair. In this case, the driven roller is pressed against the paper discharge roller at a position where it is easy to receive the leading edge of the paper discharged from the image forming unit. It is characterized in that the pressure contact position of the driven roller with respect to the paper discharge roller is controlled so that the tangential direction and the paper discharge direction along the paper discharge tray form a small angle.

[0009]

Since the paper discharge device of the present invention is constructed as described above, the pressure contact position of the driven roller with respect to the paper discharge roller is determined when the front end of the paper discharged from the image forming portion is received and when the rear end of the paper is discharged. When the leading edge of the sheet is received, the leading edge of the sheet ejected from the image forming unit is easily inserted into the nip portion of the pair of ejection rollers and smoothly nipped and conveyed. The trailing edge of the paper ejected from the section is ejected in the tangential direction of the nip, and is then bent along a small angle with a small radius of curvature and ejected along the surface of the paper ejection tray. It is easy to deform in the direction along and the rear end of the paper is prevented from riding on the paper discharge roller and stopping.

[0010]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment in which the present invention is applied to the paper discharge device described with reference to FIG. Therefore, members having the same function will be described with the same reference numerals.

In this embodiment, the driven roller 5b of the discharge roller pair 5 is movable in the longitudinal direction of the lever 9 at the tip of the lever 9 which swings around the fulcrum 8 and is moved toward the discharge roller 5a by a spring (not shown). Is supported by a biased bearing,
The solenoid 10 and the spring 11 can displace between the position shown by the solid line and the position shown by the broken line in the state of being pressed against the paper discharge roller 5a. A paper discharge sensor 12 is provided at the outlet of the fixing device 4.

As shown in the circuit diagram of FIG. 4, the solenoid 10 is turned on / off by a driver 14 which is operated by a signal from the CPU to which the detection signal of the paper discharge sensor 12 is input. FIG. 5 shows the relationship between the on / off timing of the paper discharge sensor 12 and the on / off timing of the solenoid 10.

When the paper is not passed, the paper discharge sensor 12 is off, the solenoid 10 is also off, and the lever 9 and the driven roller 5b are held by the spring 11 at the position shown by the solid line in FIG. There is. At the time of image formation, the sheet is ejected from the fixing device, the sheet ejection sensor 12 is turned on by the sheet 3, the passage of the trailing edge of the sheet is detected, and the trailing edge of the sheet is sandwiched by the ejection roller pair 5 After a lapse of ΔT time The solenoid 10 is turned on for a predetermined time, during which the lever 9 and the driven roller 5b are displaced to the position shown by the broken line in FIG. 1 against the force of the spring 11.

As a result, the leading edge of the sheet 3 discharged from the fixing device 4 is smoothly inserted into the sheet discharging roller pair 5 as shown in FIG. 2, and the leading edge of the sheet 3 discharged from the sheet discharging roller pair 5 is shown in FIG. In the tangential direction of the nip portion between the driven roller 5b and the paper discharge roller 5a shown by the solid line in FIG.
It smoothly bends along the discharge tray 6 intersecting at ₁ and advances. The trailing edge of the paper is detected by the paper ejection sensor 12,
After the time T, the driven roller 5b is displaced to the position indicated by the broken line in FIG. 1, and when the trailing edge of the sheet 3 is ejected, the direction of ejection by the pair of ejection rollers 5 is as shown in FIG. When the trailing edge of the paper is separated from the discharge roller pair 5 by bending at a small angle θ ₂ with the surface of the sheet and the trailing edge of the paper is separated from the discharge roller pair 5, the paper stretches by itself and follows the surface of the discharge tray. Riding on the discharge roller 5a is prevented, and the stack is favorably stacked on the discharge tray.

[0016]

In the paper discharge device of the present invention, since the protrusion of the paper is not used to prevent the trailing edge of the paper from climbing onto the paper discharge roller, the strain of the paper itself is used. It is possible to smoothly receive the paper in the pair of paper discharge rollers and discharge the paper without any protrusion marks on the paper, and to stack the paper satisfactorily on the paper discharge tray.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a paper discharge device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state when a leading edge of a sheet is inserted between a pair of sheet discharging rollers.

FIG. 3 is a cross-sectional view showing a state in which a trailing edge of a sheet is discharged from the pair of discharge rollers.

FIG. 4 is a block diagram showing the control circuit thereof.

FIG. 5 is a timing chart of the paper discharge sensor and a solenoid.

FIG. 6 is a cross-sectional view showing an example of a configuration in the vicinity of a paper discharge device of a conventional image forming apparatus.

FIG. 7 is a cross-sectional view showing an example of an apparatus for preventing a trailing edge of a sheet from climbing onto a sheet discharge roller.

FIG. 8 is a perspective view of the paper discharge roller.

[Explanation of symbols]

 3 Paper 4 Fixing Device 5 Paper Ejection Roller Pair 5a Paper Ejection Roller 5b Driven Roller 6 Paper Ejection Tray 9 Lever 10 Solenoid 11 Spring 12 Paper Ejection Sensor 13 CPU

Claims (1)

[Claims] 1. A paper discharge roller which is rotatably driven and a driven roller which sandwiches a paper path and presses against the paper path. The paper after image formation is nipped and conveyed at a nip portion of these roller pairs to a paper discharge tray. A sheet discharging device of an image forming apparatus that discharges and stacks has means for switching the press contact position of the driven roller with respect to the sheet discharging roller, and when the leading edge of the sheet is inserted into the nip portion of the roller pair, the discharging roller is discharged. The pressure contact position with respect to the paper roller is at a position where it is easy to receive the front end of the paper discharged from the image forming unit, and when discharging from the roller pair nip portion at the rear end of the paper, the tangential direction of the nip portion and the paper discharge tray A paper discharge device, wherein the pressure contact position of the driven roller with respect to the paper discharge roller is changed so that the paper discharge direction along the paper sheet becomes a small angle.