JPH05289014A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus in which throughput does not decrease even if the pixel density is switched. [Structure] On a DC motor 1, a polygon mirror 3 having eight reflecting surfaces and a polygon mirror 4 having four reflecting surfaces are attached. The current flowing through the semiconductor lasers 5 and 6 is O
By turning on / off, one of the semiconductor lasers 5 and 6 is selected to emit light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic process such as a copying machine or a laser printer for visualizing a latent image formed on an image carrier (photosensitive drum) which is scanned by a light beam. The present invention relates to an image forming apparatus used.

[0002]

2. Description of the Related Art A conventional image forming apparatus has a pair of light sources and a rotating polygonal mirror, and when changing the pixel density, the rotating polygonal mirror is used to change the number of times of light scanning on a photosensitive drum per unit time. The number of rotations of the rotating means (motor) for rotating was changed.

[0003]

However, in the above-mentioned conventional example, the number of rotations of the rotary polygon mirror must be changed when switching the pixel density, and the rotation of the rotating means for rotating the polygon mirror is decelerated / accelerated. It takes time to get
When the pixel density is switched during continuous printing, there is a drawback that throughput decreases and different rotation speeds must be accurately maintained by one motor.

It is an object of the present invention to provide an image forming apparatus in which throughput does not decrease even when the pixel density is switched and it is not necessary to accurately maintain different rotation speeds.

[0005]

An image forming apparatus of the present invention is an image forming apparatus for visualizing a latent image formed on an image carrier on which a light beam is scanned to form an image. And a plurality of rotating polygon mirrors having different numbers of surfaces for respectively deflecting the light beams from the plurality of light emitting sources,
It is characterized in that it has a rotating means for rotating the plurality of rotary polygon mirrors on a concentric axis, and a switching means for selecting any one of the plurality of light emitting sources to emit light.

The image forming apparatus of the present invention includes one in which a plurality of rotary polygon mirrors having different numbers of surfaces are integrated in layers, and one in which the reflecting surfaces of the plurality of rotary polygon mirrors have different angles. .

[0007]

The pixel density can be switched simply by changing the light source, and the throughput is not sacrificed even in continuous printing. Further, since the rotation speed of the rotating means can be made constant regardless of the pixel density, it is possible to provide a highly accurate rotation speed.

[0008]

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

1A and 1B show the appearance of a first embodiment of the present invention. FIG. 1A is a plan view of an essential part and FIG. 1B is a side view of the essential part.

A first rotating polygon mirror (hereinafter referred to as a polygon mirror) 3 which is a deflector having eight reflecting surfaces and a second polygon having four reflecting surfaces are provided on a DC motor 1 which is a rotating means. The mirrors 4 are mounted on the same shaft. Around the polygon mirrors 3 and 4, two semiconductor lasers 5 and 6 which are light sources, a photosensitive drum 7 necessary for a known electrophotographic process, and a laser beam for forming an image on the photosensitive drum 7 are formed. A group of lenses 8 ₁ and 8 ₂ are arranged respectively.

Now, if the number of rotations of the DC motor 1 that rotates the two polygon mirrors 3 and 4 is constant, the luminous flux of the laser beam scans the photosensitive drum 7 per unit time (direction of arrow b). The number of times of doing is proportional to the number of surfaces of the polygon mirrors 3 and 4 which are the deflectors of the laser light. Therefore, the pixel density in the sub-scanning direction (the direction of arrow a) is doubled when the 8-sided polygon mirror 3 is used as compared with the 4-sided polygon mirror 4. The pixel density in the main scanning direction (direction of arrow b) is changed according to the density of image signals described later.

FIG. 2 is a block diagram of this embodiment.

One-chip microcomputer (hereinafter C
PU) 9 controls the operation of the recording apparatus. The photodiodes 21 and 22 are those whose current amount changes according to the light amount of each semiconductor laser.
Reference numeral 6 is for converting the current from the photodiodes 21 and 22 into a voltage. The constant current circuits 11 and 12 change the light intensity of the semiconductor lasers 5 and 6, respectively.
6 controls the current, and changes the current according to the signal levels LP1 and LP2 from the CPU 9. CPU
Numeral 9 detects the laser light amount by the photodiodes 21 and 22, and sets the signal level LP so that each light amount becomes a predetermined light amount.
By changing the values of 1 and LP2, the currents to the lasers 5 and 6 are controlled via the constant current circuits 11 and 12. Switching circuit 1
3 and 14 turn on / off the current flowing through the semiconductor lasers 5 and 6.
By turning off the semiconductor lasers 5, 6
It is a switching means for performing N / OFF, and the input signal is "High.
It is turned on at the "h" level and turned off at the "Low" level.

When the signal MON from the CPU 9 becomes "High", the motor drive circuit 20 controls the rotation speed of the DC motor 1 to be constant based on the tack signal from the DC motor 1.

Next, the operation of this embodiment will be described.

In order to switch the lasers 5 and 6 to be used, one switching circuit 13 receives a signal VD1 obtained by ANDing the laser switching signal LCHNG from the CPU 9 and the image signal VD0, and the other switching circuit 1
By inputting a signal VD2 obtained by ANDing the inversion signal of the laser switching signal LCHNG and the image signal VD0 to 4, when the laser switching signal LCHNG is set to "High", the laser 5 lights up in accordance with the image signal VD0,
When set to "Low", the laser 6 lights up in accordance with the image signal VD0.

FIG. 3 is a time chart showing the sequence of the above operation. Using an 8-sided polygon mirror 3,
When the pixel density is doubled compared to when the four-sided polygon mirror 4 is used, the density of the image signal VD0 is also doubled. This is to double the pixel density in the direction of arrow b (main scanning direction) in FIG. 1 described above.

4 (a) and 4 (b) are external views of the second embodiment of the present invention. The four-sided polygon mirror 24 and the eight-sided polygon mirror 23 are integrated, and the four-sided polygon mirror 4 and the eight-sided polygon mirror 3 shown in FIG.
It is possible to reduce the size more than using two polygon mirrors consisting of

5A and 5B are external views of the third embodiment of the present invention. An eight-sided polygon mirror 25 having a laser reflecting surface at an angle with respect to the axis of rotation causes the reflected light 23 to
When the polygon mirror 4 of the surface is used, the reflected light 24 and the lenses 8 ₁ and 8 ₂ come close to each other at the light incident positions,
It is possible to reduce the thickness of the lenses 8 ₁ and 8 ₂ and reduce the difference in image forming position on the photosensitive drum 7 for each polygon mirror used.

[0020]

As described above, according to the present invention, a plurality of light sources and a plurality of polygon mirrors are used to switch the light source and the polygon mirror to be used according to the pixel density. Since it is not necessary to change the rotation speed of the rotating motor, it is possible to eliminate a decrease in throughput due to acceleration / deceleration of the motor when pixel density switching is performed during continuous printing. Further, since the motor is rotated at a constant number of rotations regardless of the pixel density, it is possible to suppress uneven rotation such as jitter.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, (a) is a plan view of a main part, and (b) is a side view of the main part.

FIG. 2 is a block diagram of a first embodiment.

FIG. 3 is a time chart of the first embodiment.

4A and 4B show a second embodiment of the present invention, in which FIG. 4A is a plan view of a main part, and FIG. 4B is a side view of the main part.

5A and 5B show a third embodiment of the present invention, in which FIG. 5A is a plan view of an essential part and FIG. 5B is a side view of the essential part.

[Explanation of symbols]

1 DC motor 3,4 polygon mirror 5, 6 semiconductor laser 7 photosensitive drum 8 _1, 8 ₂ lens

Front page continuation (72) Inventor Hitoshi Machino 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Soya Endo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Within

Claims (3)

[Claims] 1. An image forming apparatus for forming an image by visualizing a latent image formed on an image carrier, which is scanned by a light beam, comprising: a plurality of light sources emitting the light beam; and light beams from the light emitting sources. A plurality of rotary polygon mirrors having different numbers of surfaces for respectively deflecting, a rotating means for rotating the plurality of rotary polygon mirrors on a concentric axis, and a switching means for selecting any one of the plurality of light emitting sources to emit light. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein a plurality of rotary polygon mirrors having different numbers of surfaces are integrated in a layered manner. 3. The reflecting surfaces of the plurality of rotating polygon mirrors have different angles with respect to the rotation axis.
Alternatively, the image forming apparatus described in 2.