JPS62206569A - Electrophotographic device using laser - Google Patents

Abstract

PURPOSE:To prolong the life of a photosensitive body and to prevent an unfavorable influence upon the image quality by providing a means which changes the laser power of a laser beam and making the laser power for a non-image area of the photosensitive body lower than that for an image area of the photosensitive area when the laser beam is projecting to these areas. CONSTITUTION:The laser power of a laser diode LD is raised to a required level F1 in an image effective range part from a print start position S to a print end position E on a photosensitive body 3, namely, but the image area is held in a lower level F3 in the non-image are other than this area. Generally, the life of the LD or the other laser light generating means is determined in accordance with the quantity of the conducted current. If the LD or the like is allowed to emit light with a large quantity of light only when a required quantity is reduced, the life is prolonged by the reduction of the quantity of light.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field C) The present invention relates to an electrophotographic apparatus using a laser, such as a laser printer.

(Prior Art) Generally, in a laser printer, an electrostatic latent image is formed on the photoreceptor by exposing a uniformly charged photoreceptor with a light-modulated laser beam, and the electrostatic latent image is transferred to a toner or the like. A desired printed product is created by developing with a developer to obtain a developed image, transferring the developed image onto a transfer paper, and further fixing the developed image onto the transfer paper using a fixing device.

Generally, a photoreceptor has an image area where an electrostatic latent image is formed and a non-image area where an electrostatic latent image is not formed.

In conventional laser printers, the laser power is always set to a predetermined amount (N light emission amount) required for forming a latent image, regardless of the image area or non-image area of the photoreceptor. Light irradiation was performed with a laser beam at all times.

In conventional electrophotographic devices that constantly irradiate a photoreceptor with a laser beam at the same amount of light emitted during exposure, a large current always flows through the laser beam generating means, such as a laser diode, so the life of the beam generating means is short. There are drawbacks. Furthermore, if the amount of light of the laser beam irradiated corresponding to the non-image area of the photoconductor is set to the above-mentioned relatively large amount of light emitted during exposure, the laser beam will be reflected within the laser exposure means, causing this The diffusely reflected light also impinges on the image area of the photoreceptor, adversely affecting the electrostatic latent image formed within the image area. For example, white streaks appear on printed products.

(Objective) In view of the above-mentioned points, an object of the present invention is to provide a laser electrophotographic device that can prolong the life of a laser beam generating means such as a laser diode, and can prevent the adverse effects on image quality. .

This purpose is achieved by providing means for changing the laser power of the laser beam, and when the laser beam irradiation position corresponds to a non-image area of the photoreceptor, the laser power is made weaker than when irradiating the image area of the photoreceptor. .

Hereinafter, the present invention will be explained based on Examples.

FIG. 1 is an example of an electrophotographic device using a laser,
1 is an overall view of a laser printer that is one line of the present invention; FIG. In the figure, a belt-shaped photoreceptor 3, which is passed between two rollers 1 and 2, rotates in the direction indicated by the arrow. This photoreceptor 3
has an image area and a non-image uI area, and these areas are uniformly banded by the charger 4. The charged image area is image exposed by a loser exposure device 5,
As a result, a static iIm image is formed within the area. This electrostatic latent image is developed into a developed image by the developing device 6 and then conveyed to the transfer charger 7.

A sheet of transfer paper is fed between the transfer charger 7 and the photoreceptor 3 from either of two paper feed trays 8, 8, and the transfer T paper and the above-mentioned image are fed into the transfer charger. They are overlapped at 7. At this time, transfer charger 7
The developed image is transferred onto the transfer paper by the charging action of the . Thereafter, the transfer paper undergoes a fixing operation by a heat roller fixing device 10 having two rollers 9aw9b, and is then discharged as a print product into a paper discharge stacker 12 via a conveyance path 11.

In the figure, numeral 13 is a static eliminator for the photoconductor 3, and 14 is a static eliminator for the photoconductor 3.
15 is a power supply, 16 is a cooling fan, and 17 is a control system circuit board.

As shown in FIG. 2 (a diagram taken along the arrow in FIG. 1), the laser exposure device 5 includes a laser diode unit (LD unit) (LD secondary) 18, L which has a built-in laser diode (LD).
A rotating polygon mirror (polygon mirror) 19 that reflects the laser beam from the D unit 18 and rotates at an appropriate speed, and the reflected laser beam is reflected again by the polygon mirror 19 and guided to the photoreceptor 3 (FIG. 1). Mirror 2D5 and f arranged between polygon mirror 19 and mirror 20
The device is equipped with a θ lens 21.

When the polygon mirror 19 rotates counterclockwise in FIG. 2, the laser beam moves from the left side to the right side of the mirror 20. If you look at this in FIG. 1, it moves from the front to the back in the direction perpendicular to the page. and move on.

As a result, the photoreceptor 3 receives an image exposure operation in a direction perpendicular to the direction of movement of the photoreceptor 3 (the direction of entry in FIG. 1).

Generally, this direction is called the main scanning direction. Incidentally, as the photoreceptor 3 rotates in the incoming direction, the photoreceptor 3 also receives image exposure work in that direction. Generally, this direction is called the sub-scanning direction. Eventually, the photoreceptor 3 receives main scanning exposure due to the rotation of the polygon mirror 19 and sub-scanning exposure due to the rotation of the photoreceptor itself, thereby carrying an electrostatic latent image within the image area.

FIG. 3 is a control block diagram. host computer 2
2 transfers signals such as characters and graphics to the image controller 23. The image controller 23 converts the transferred character signal etc. into a (Dra)N turn and sends it to the print sequence controller (PSC) 24, and also sends a print start signal which is a signal to start printing work.
Send to SC24. PSC that received the print start signal
24 starts driving the main motor 25 which drives the photoreceptor 3 (FIG. 1) and other devices. Main motor 25
The pulse 273f generated from the rotating main motor 25 is counted by a counter built in the PSC 24.

As shown in FIG. 4, a photoreceptor mark detection m sensor (mark sensor) 26 is provided near the charger 4, and a mark sensor 26 is provided at a predetermined position on the force photoreceptor 3. It is marked with a mark M. Therefore, each time the photoreceptor 3 driven by the main motor 25 makes one revolution, a detection pulse P1 is generated as shown in FIG.

Predetermined printing operations such as charging, exposure, development, etc. are performed at predetermined timings based on timing pulses from the main motor 25 with the detection pulse P1 as a reference. In the embodiment, after a predetermined time has elapsed since the detection pulse pt, the charger 4 is turned on at time t1 in FIG. 5, and charging work is performed. FIG. 4 shows the state just at this point, and therefore, in this state, the portion S of the photoreceptor facing the charger 4 becomes the printing start position on the photoreceptor. When 11 hours have passed after the start of charging, the print start position S reaches the exposure position EX by the laser exposure device 5 (Fig. 1), and at this time (12) the laser power of the LD reaches the amount F1 required for exposure. The image is uploaded and image exposure work begins.

The charger 4 is turned off when the photoreceptor 3 is charged by the length of the effective image range. In the embodiment, the effective image range is set between the print start position S and the print end position E, which is a position downstream from the print start position S by a distance @t from the print start position S in FIG. After charging has started in this state, when the print end position E passes the charger 4 (at tsl in FIG. 5, the charger 4 is turned off. After that, time t1 has passed and the print end position E has passed the exposure position EX). When passing through, the laser power is lowered to the minimum value F3, and at the same time, the image exposure operation ends.

In addition to the above-mentioned charging and exposure operations, the various printing processes explained in connection with FIG. That is, it is cleared every time the photoreceptor 3 makes one revolution.

As is clear from the above explanation, the effective image range from the print start position S to the print end position E of the laser power generating means 3 of the LD, that is, the image area, requires f.
The amount increases to lF1, and is maintained at a smaller amount F3 in other parts (non-image areas). Generally, the lifespan of an LD or other laser light generating means is determined depending on the amount of current flowing therethrough. Therefore, if the LD or the like is made to emit a large amount of light only when necessary as described above, the life span can be extended by the amount of light that is kept low.

Note that the configuration for changing the laser power is not limited to any special means. For example, as shown in FIG.
/A converter 28 and LD driver 29
There is a method to drive the LD power and to adjust the power by the LD power detection circuit 27. According to this method, D/
When the input bit of the A frequency converter 2'8 is incremented from 001, the power of the LD gradually increases as shown by the straight line Q in the graph of FIG. This power is LD
2) When a reference value ψ preset in the power detection circuit 27 is exceeded, the output of the circuit 27 changes from "L" to "H", and this H signal increases the laser power to a predetermined amount, for example for image exposure. It is possible to know that the required amount F1 has been reached.

Therefore, when a large amount of light is required corresponding to the image area, the power of the D/A converter 28 is increased until the output of the LD power detection circuit 27 becomes "L", and the power of the D/A converter 28 is increased to the minimum level corresponding to the one-way valve image area. When maintaining the light intensity, keep the manual power of the D/A converter 28 within a range where the output of the LD power detection circuit 27 does not become "H". When it becomes “H”, that is, the laser power is the reference value ψ
When exceeding ・The manual bit value of the D/A converter 28 is stored in the memory in advance, and the LD is driven with this stored bit value corresponding to the image area, and a lower power value is used in the non-image area. It is also possible to drive L.n with an input bit value corresponding to .

The above description relates to the case where the I and D powers are weakened in the circumferential direction of the photoreceptor 3, that is, in the sub-scanning direction, corresponding to the non-image area of the photoreceptor.

The advantage of weakening the LD power is not limited to the sub-scanning direction but is also brought about in the main scanning direction. below,
Let me explain about it.

As mentioned above, image exposure in the main scanning direction is brought about by the rotation of the polygon mirror 19 in FIG. In this case, image exposure within the image area of the photoreceptor 3 is performed while the laser beam reflected by the polygon mirror 19 moves within the predetermined width W of the mirror 20. Therefore, when the laser light travels toward a portion other than the width W, the light is not applied to the image area of the photoreceptor 3, but corresponds to one non-image area. As described above, it is not preferable from the viewpoint of the life of the LD to maintain the LD power at a large amount of light even when dealing with the non-image area of the photoreceptor. Therefore, it is desirable to maintain the required laser power FIK only when the laser beam is within the image area width W, and to lower the laser power or turn it off when the laser beam is within the non-image area. The timing of changing the laser power in this case can be easily determined by the PSC 24, which controls the print process based on timing pulses.In addition, when trying to turn off the LD/power in a non-image area in the main scanning direction, may require special attention. As in the laser exposure device 5 shown in FIG.
When using a laser exposure apparatus of the type in which the laser beam reflected at 0 is received by the synchronized m sensor 31, the output of the mouth opening sensor 31 is sent to the phase synchronized circuit 32 as shown in FIG. The phase synchronization circuit 32 issues a start command to the LD driver 4 so that the image area of the photoreceptor 3 (FIG. 1) whose rotation is controlled by the PSC 24 and the laser beam are synchronized. In the laser exposure apparatus of the above type. , if the laser beam is QFFed when corresponding to a non-image area, the above-mentioned synchronization work will essentially become impossible. Therefore, as shown in FIG. During the width W, the laser is emitted with a required light emission amount F1, and prior to the emission, the laser is emitted within a predetermined range T with a light emission amount F2 that is smaller than the above-mentioned necessary light emission amount F1. This predetermined range T is a range in which it is assumed that the laser beam will collide with the synchronization mirror 30 if the laser is emitted within this range, and is a range set in advance by the phase synchronization circuit 32. When this synchronization laser beam is detected by the synchronization sensor 31, the synchronization detection signal P
2 is generated, and the LD is turned off using this signal as a signal.

In this embodiment, the light intensity F2 of the laser beam for 1 synchronization is set lower than the light intensity F of the laser beam for image exposure due to the following reason.
If the laser beam is to be irradiated with the required light amount F1, the laser beam hits other parts other than the mirror 20 in the non-image area and is diffusely reflected. Since the diffusely reflected light is guided to the photoreceptor 3 (FIG. 1) via the mirror 20, the light hits an image area that should not be hit by the light at this time. As a result, inconveniences such as white smear appear on printed products. On the other hand, if the light amount F2 is kept low, the above-mentioned diffused reflection will be weakened and its influence on the image will be reduced. For this purpose, it is desirable to set the light amount F2 to the minimum amount within the range in which the synchronization sensor 31 can detect the laser beam.

(Effects) As described above, according to the present invention, since the LD is made to emit light within the minimum necessary range, the life of the LD can be extended. Also, it is possible to extend the life of the LD. By keeping the amount of laser light low, it is possible to prevent image quality from deteriorating due to diffuse reflection.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a laser printer that is an embodiment of the present invention, FIG. 2 is a plan view taken along arrow n in FIG. 1, FIG. 3 is a control block diagram, and FIG. Enlarged view - 5th
6 is a diagram showing a timing chart, FIG. 6 is a diagram showing a timing chart of another column, and FIG. 7 is a graph showing an operation mode of an example of means for changing the laser power. 3... Photoreceptor, 4... Charging device, 5... Laser exposure device, 24.28, 29.27... Means for changing laser power Fig. 2

Claims (4)

[Claims] (1) A photoconductor having an image area and a non-image area, a charging device that uniformly charges the image area of the photoconductor, and a main scanning and In an electrophotographic apparatus equipped with a laser exposure device that forms an electrostatic latent image within the image area by sub-scanning, a means for changing the laser power of the laser beam is provided, and the laser beam irradiation position is adjusted so that the laser beam irradiation position is on the photoreceptor. An electrophotographic apparatus characterized in that when irradiating a non-image area, the laser power is made weaker than when irradiating an image area of a photoreceptor. (2) The electrophotographic apparatus according to claim 1, wherein the laser power is weakened for a non-image area of the photoreceptor in the sub-scanning direction. (3) The electrophotographic apparatus according to claim 1, wherein the laser power is weakened for a non-image area of the photoreceptor in the main scanning direction. (4) In order to synchronize the laser beam and the photoconductor, a synchronizing laser beam is generated within the non-image area of the photoconductor in the main scanning direction, and the light intensity of this laser beam corresponds to the image area of the photoconductor. 4. The electrophotographic apparatus according to claim 3, wherein the amount of light is smaller than the amount of laser light generated by the electrophotographic apparatus.