JPS5828733A - Image recorder - Google Patents

Abstract

PURPOSE:To compensate the fall angle of a polyhedral mirror and to avoid the deterioration of the image quality, by changing the diameter of the light beam which irradiates a photoreceptor with the scan deflection in accordance with the fall angle of the polyhedral mirror. CONSTITUTION:The image signal is converted into a light beam by a laser light source 3, and a rotary polyhedral mirror 4 gives the deflecting scan to the surface of a photoreceptor 1. A rotary position detector 7 is connected to the shaft of a motor 6 which drives the mirror 4, and a rotary sensor 8 detects the surface of the mirror 4 which is being scanned. The sensor 8 is connected to a mirror surface detecting circuit 14 that detects each surface number of the mirror 4, a switching means 15 of light beam diameters and a laser driving circuit 16 respectively to change the diameter of the light beam in accordance with the fall angle of the mirror 4. In such a way, an error of the fall angle can be easily compensated for the mirror 4, and accordingly the deterioration can be effectively prevented for the quality of a recorded image.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a rotating polygon mirror as a light deflector to irradiate a light beam such as a laser beam onto a photoreceptor while scanning and deflecting it, thereby detecting characters and numbers.

The present invention relates to an electrophotographic image recording device that records entire images such as symbols.

In laser printers, rotating polygon mirrors are widely used as optical deflectors. The inclination angle precision (inclination angle precision) of each surface of the rotating polygon mirror with respect to the optical scanning surface greatly affects the recorded image. Figure 1 (a) shows the arrangement of the light beam spots when there is no inversion angle error of the rotating polygon mirror.
b) fl: Indicates the arrangement of light beam spots when the inclination angle error of the rotating polygon mirror is large. In the case of (b), an unirradiated area as shown by twigs occurs between the scanning beams. In positive recording, where the light irradiated area is developed white,
Black streaks appear in the non-irradiated area 3 page 1, resulting in an image with many background stains V. In negative recording in which the light-irradiated areas are developed black, white spots occur in the non-irradiated areas, resulting in white spots in the image.

If the inclination angle error of the rotating polygon mirror is large in this way, image deterioration occurs. Assuming that the scanning pitch error Δp is the focal length of the imaging lens (Hf), the inclination angle error β of the polygon mirror is expressed by the following equation.

ρ≦±Δp/f2 (1) In normal laser printers, this inclination angle error is ±6 seconds to ±
It takes less than 10 seconds and requires very strict processing precision. Therefore, the cost of the rotating polygon mirror has been extremely high.

The present invention corrects inclination angle errors of polygon mirrors to prevent image deterioration and enables the use of low-cost rotating polygon mirrors. The present invention will be explained below based on the illustrated embodiments. FIG. 1 is a schematic diagram of the main parts of an embodiment of the present invention. In the figure, a photoreceptor 1 is charged by a corona charger 2 f'
After that, an image is irradiated by a light beam or a person, creating an electrostatic latent image.

This electrostatic latent image is visualized by a developer 69 and transferred onto the recording paper 1o by a transfer charger 11.

The image signal is converted into a light beam by a laser light source 3.
, irradiated 1. The light beam is transmitted to the photoreceptor 1 by a rotating polygon mirror 4.
Deflection scans n on the 0 plane. Reference numeral 5 denotes an imaging lens for forming an image of a light beam on the same surface of the photoreceptor 1. This is a motor that drives the six-sided rotating polygon mirror 4. A rotational position detector 7 is connected to the shaft of the motor 6, and the rotational position sensor 8 is capable of detecting the polygonal mirror surface currently being used for scanning.

Note that the rotation sensor 8 does not include a pole element or a photodetector. Reference numeral 14 denotes a mirror surface detection circuit for detecting each mirror surface number sound of the rotating polygon mirror 4. The scanning start position on each mirror surface can be easily determined by a synchronization detector (not shown) provided at the laser scanning start position. Reference numeral 15 denotes a light beam diameter switching means corresponding to each mirror surface number, which selects all light beam diameters in accordance with the n-angle of inclination of the rotating polygon mirror 4. Here, the inclination angle of each mirror surface of the polygon mirror is measured in advance from 1 to 1. 16 is a laser drive circuit, and when 3 is used as a semiconductor laser light source, the method of changing the drive current shown in page 6 is used as a method for switching the light beam diameter. In addition, the first
In the figure, 12 is a cleaning device for the photoreceptor 1, and 13 is a photostatic discharge device.

FIG. 3(a) is a diagram showing the relationship between the driving current of the semiconductor laser and the optical power. When the current is completely decreased (A1) or increased (A3) with respect to the standard drive current (person 2), the optical power becomes (B1) or (B3).3 Laser light has a Gaussian energy density distribution. Therefore, as shown in Fig. 3(b), the optical power density distribution when the drive current is completely decreased or increased is t'LG1 with respect to the optical power density distribution G2 of the standard output. ．． It becomes G3.

Assuming that the exposure amount required for recording on the photoreceptor is ET from FIG. 3(b), the diameter of the recording spot on the photoreceptor will change depending on the drive current.

Here, if the recording spot diameter is d and the laser light output is Po, then d = a 1n(P, /bE,)...-=(2)
becomes. Here, a and b are constants that change depending on the distribution condition.

FIG. 4 shows a correction state when the light beam diameter is changed by 6'·- in response to the inclination f angle error of the rotating polygon mirror 4 (in the figure, the beam spot diameter is increased). From FIG. 4, it can be seen that the background stains in positive recording or the white smudges in negative recording have disappeared.

FIG. 6 shows a case of positive recording in which the portion irradiated with the light beam develops in white. In the figure, the area not irradiated with the light beam is recorded as a black line r5. If the diameter of the light beam is increased to accommodate the inversion angle error of the rotating polygon mirror, the horizontal lines parallel to the main scanning direction will become slightly smaller at adjacent points of the enlarged light beam, and the horizontal lines perpendicular to the main scanning direction will become smaller. The vertical line becomes thinner at the point where the light beam becomes larger. When horizontal lines become thinner, it is hardly noticeable in the image, but when vertical lines become larger or smaller, it may be noticeable. As a countermeasure against this problem, an effective method is to use all of the vertically elongated light beam spots. In the case of semiconductor lasers, the divergence angle of the light beam is different in the direction perpendicular to the bonding surface and in the horizontal direction, so by utilizing this property, it is possible to easily create a long light beam spot in the direction perpendicular to the main scanning direction. .

Page 7] Another countermeasure is shown in Figure 6. As shown in the figure, when the adjacent spots in the main scanning direction are black in repository recording and the point to be recorded is white, the light beam diameter should be returned to the standard state. In this case, a small black beard corresponding to one spot is generated in order to return the light beam diameter to the standard state, but this n- is hardly noticeable when the spot diameter is about 10011111. Determining whether or not adjacent spots in the main scanning direction are black can be easily realized using a 3-bit shift register and a P1'' or "O" determination circuit.

As described above, according to the present invention, the tilting angle error of the rotating polygon mirror can be easily corrected by changing the entire beam diameter.
Deterioration of recorded images can be effectively prevented. moreover,
According to the present invention, there are many advantages such as the possibility of using a low-cost rotating polygon mirror because the angle accuracy of the rotating polygon mirror can be made loose.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are arrangement diagrams of light beam spots for explaining image deterioration caused by tilt angle error of a rotating polygon mirror, and FIG. 2 is an image recording apparatus according to an embodiment of the present invention. Figure 3 (+1) is a diagram showing the relationship between semiconductor laser drive current and optical power, Figure 3 (b) is a diagram of optical power density distribution, and Figure 4 is a diagram of changing the optical beam diameter. Figures 5 and 6 are array diagrams of light beam spots showing the state of image correction based on the light beam diameter in the case of positive recording. . 1...Photoreceptor, 2...Corona charger,
3... Laser light source, 4... Rotating polygon mirror, 6... Motor, 7... Rotating position detector,
8...Rotation sensor, 9...Developer, 1
o...Recording paper, 11...Transfer charger,
14... Mirror surface detection circuit, 15... Light beam diameter switching means, 16... Laser drive circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person
6 ′- WR chain Fig. 3 is also uuα positive - Fig. 5 Fig. 6 @

Claims (1)

[Scope of Claims] (1) An electrophotographic image recording apparatus that records the entire image by irradiating a light beam onto a photoreceptor while scanning and deflecting it using a rotating polygon mirror, wherein when the rotating polygon mirror scans, The mirror surface detection means for detecting each mirror surface and the light beam diameter variable means for changing the diameter of the light beam are provided, and the diameter of the light beam is changed from the normal size according to the angle of inclination of each mirror surface of the polygon mirror. An image recording device characterized by: (2. In claim (1), when performing positive recording in which a portion irradiated with light and sound is developed to become white, the spot to be recorded is white, and at least An image recording device characterized in that when one spot is black, the diameter of the light beam is not changed and the diameter of the light beam is set to the normal size. An image recording device characterized in that a semiconductor laser is used as a 2'/2' light source, and the diameter of the light beam is changed by changing the current that drives the entire semiconductor laser.