JPH0787280A - Optical scanner - Google Patents

Abstract

PURPOSE:To provide an optical scanner by which a scanning area of a synchronizing signal generating light beam is not superposed on a scanning area of an image forming light beam. CONSTITUTION:An image forming light beam B and a synchronizing signal generating light beam B' are made incident on the rotary shaft direction of a rotary polygon mirror 3 at the same angle, and also, are made incident on the rotational direction of the rotary polygon mirror 3 so as to satisfy the following relational expression. theta2-theta1>=4pi/n, in the case the image forming light beam and the synchronizing signal generating light beam are made incident on a normal of the reflecting surface of the rotary polygon mirror from the same side, and theta2-theta1>=2pi/n, in the case the image forming light beam and the synchronizing signal generating light beam are made incident on the normal of the reflecting surface of the rotary polygon mirror from a mutually opposite side. In this regard, (n) denotes the number of reflecting surfaces for constituting the rotary polygon mirror.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming light beam that is modulated in accordance with an image signal to form an image, and a synchronization signal generating light beam for detecting the modulation start timing of the image forming light beam. The present invention relates to an optical scanning device that reflects and on the same reflecting surface of a rotary polygon mirror.

2. Description of the Related Art In a laser beam printer or the like which uses a rotary polygon mirror for scanning a laser beam as a light beam, there is a slight manufacturing error in the angular division accuracy of the reflecting surface of the rotary polygon mirror, and the rotary polygon mirror. Due to the uneven rotation and the vibration associated with the rotation, the scanning area of the light beam is not necessarily aligned in the scanning direction. Therefore, a light receiving unit that detects the light beam is provided on the upper side of the image forming area on the scanning line, and the light beam starts modulation based on the image signal after a predetermined time has elapsed since the light beam was detected by the light receiving unit. As described above, by synchronizing the timing of starting the modulation, the image writing positions of the scanning lines are aligned in the scanning direction. However, the light receiving unit for detecting the light beam and controlling the synchronization of the modulation described above,
Since it needs to be provided on the scanning line of the light beam, it has a drawback that the scanning area that can be used for image formation becomes narrow. Therefore, there is one in which a different light beam is used for image formation and for generating a synchronization signal so that the entire scanning region of the light beam for image formation can be used for image formation (for example, Japanese Patent Laid-Open Publication No. Sho. 53-3833).

In this system, when the image forming light beam scans near the starting point of the scanning area, the synchronizing signal generating light beam is made incident on the light receiving portion. Since the scanning area of the light beam for generation overlaps the scanning area of the light beam for image formation, be sure to check the beam for synchronization signal generation before the beam for synchronization signal generation reaches the scanning area of the light beam for image formation. Had to be turned off, and it was necessary to accurately control the turning on / off of the synchronization signal generating beam. An object of the present invention is to solve such a problem.

In order to solve the above problems, the present invention provides an image forming light beam which is modulated according to an image signal to form an image and a modulation start timing of the image forming light beam. An optical scanning device for reflecting a synchronizing signal generating light beam for detection on the same reflecting surface of a rotating polygon mirror, wherein the image forming light beam and the synchronizing signal generating light beam are a rotating polygon mirror. It is characterized in that the light is incident at the same angle with respect to the rotation axis direction of, and is incident so as to satisfy the following relational expression with respect to the rotation direction of the rotating polygon mirror. When the image forming light beam and the synchronizing signal generating light beam are incident from the same side with respect to the normal of the reflecting surface of the rotary polygon mirror, θ2-θ1 ≧ 4π / n The image forming light beam and the synchronizing signal generating When the light beam is incident from the side opposite to the normal of the reflecting surface of the rotating polygon mirror, θ2-θ1 ≧ 2π / n where θ1 is the normal of the reflecting surface of the image forming light beam incident on the reflecting surface. And θ2 is the angle between the synchronizing signal generating light beam incident on the reflecting surface and the normal to the reflecting surface, and n is the number of reflecting surfaces that make up the rotating polygon mirror.

That is, since the image forming light beam and the synchronizing signal generating light beam are made incident so as to satisfy the above relational expression with respect to the rotating direction of the rotary polygon mirror, the synchronizing signal generating light beam is generated. Scans an area other than the scanning area of the image forming light beam, and even if the synchronizing signal generating light beam is held in the lighting state without being turned off, the image forming area (the image forming light beam There is no danger of scanning the scanning area) and the synchronization signal generating light beam is turned on / off.
Light-off control can be roughly performed.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a scanning device of a laser beam printer which is an example of the optical scanning device of the present invention. An image forming semiconductor laser 1 oscillates an image forming laser beam B, which is an example of an image forming light beam, and is modulated based on an input image signal. The image forming laser beam B oscillated from the image forming semiconductor laser 1
Is collimated by the collimator lens 2 and reflected by the reflecting surface 3a having the polygon mirror 3 rotating at high speed. The rotation of the polygon mirror 3, which is an example of a rotary polygon mirror, changes the inclination of the reflecting surface of the image forming laser beam B with respect to the image forming laser beam B, and accordingly, the reflected image forming laser beam B of the photosensitive drum 4 is reflected. Scanning is performed in the longitudinal direction (this direction is the main scanning direction). The image forming laser beam B is converged by the fθ lens 5 to form an image on the uniformly charged photosensitive drum 4, and the charging potential at that position is reduced. Then, the photosensitive drum 4
By repeating this scanning with the constant speed rotation of
An electrostatic latent image is formed on the photosensitive drum 4. After that, although not shown in the figure, toner, which is a color pigment, is selectively adhered to the electrostatic latent image portion and developed, and the output paper is brought into contact with the toner image surface to transfer the toner image onto the paper surface. By heating, the toner is melted and fixed on the paper, and an output image is obtained. Further, in addition to the image forming semiconductor laser 1, a synchronizing signal generating semiconductor laser 6 is provided. This semiconductor laser 6 for generating a synchronization signal
The synchronizing signal generating laser beam B ′ oscillated from the laser beam is collimated by the collimator lens 7 different from that for the image forming laser beam B, and is simultaneously reflected by the reflecting surface 3 a where the image forming laser beam B is reflected. Is reflected. Then, the reflected sync signal generating laser beam B ′ is configured to be scanned in an area including the sync control light receiving unit 8 as the polygon mirror 3 rotates. The synchronization control light receiving unit 8 is for aligning the latent image formation start position for each scanning line with respect to the rotation direction of the photosensitive drum 4 (this direction is the sub-scanning direction). That is, since there is a slight manufacturing error in the angle division accuracy of each reflecting surface of the polygon mirror 3, and because there is uneven rotation of the polygon mirror 3 and vibration associated with rotation, the scanning area of the image forming laser beam B is the main scan. It is not always aligned in the direction. Therefore, the synchronization signal generating laser beam B ′ simultaneously reflected by the reflecting surface 3a of the polygon mirror 3 on which the image forming laser beam B is reflected is based on the time when the synchronization control light receiving unit 8 receives the laser beam B ′. The modulation for the image forming laser beam B scanned on the photosensitive drum 4 is controlled. Further, as the polygon mirror 3 rotates, the synchronization signal generating laser beam B ′ is also scanned in the same direction as the image forming laser beam B, but the image forming laser beam B is scanned and the photosensitive member is scanned. A semiconductor laser for generating a synchronization signal is generated so that the laser beam B ′ for generating a synchronization signal, which is similarly scanned, reaches the light receiving portion 8 for synchronization control when the starting end portion of the latent image forming area on the drum 4 is reached. 6 is positioned with respect to the image forming semiconductor laser 1. The output from the synchronization control light receiving unit 8 is input to the modulation control device 9. Then, the modulation control device 9 receives the synchronization signal generating laser beam B ′ from the modulation control light receiving unit 8 and, when the output exceeds the set value, the laser driving unit 10 for the image forming semiconductor laser 1. In addition, the synchronizing signal SOS is output. Laser drive 10
Receives this signal SOS, takes in data based on the input image signal from the memory 11, and starts direct modulation for the image forming semiconductor laser 1. As a result, formation of an electrostatic latent image using the modulated laser beam B for image formation is started. With the above-described configuration, the electrostatic latent image formed on the photosensitive drum 4 by repeating the scanning a plurality of times has the writing start positions of the image in the main scanning direction aligned between the scanning lines. Further, since the synchronizing signal SOS is generated by using the synchronizing signal generating laser beam B ′ different from the image forming laser beam B, the image forming laser beam B is the minimum necessary for the image forming. That is, the image forming speed can be increased as compared with the configuration in which the image forming laser beam B is scanned up to the synchronous control light receiving unit 8. FIG. 2 is a diagram showing a state of the image forming light beam B and the synchronizing signal generating light beam B ′ which are incident on the polygon mirror 3. The image forming light beam B and the synchronizing signal generating light beam B ′ are incident at the same angle with respect to the rotation axis direction of the polygon mirror 3, and scan within the same plane. By appropriately setting the incident angles of these two light beams B and B ′ to the reflecting surface 3a of the polygon mirror 3 with respect to the rotation direction of the polygon mirror 3, the synchronization signal generating light beam B ′ is directed to the photosensitive drum 4. It is possible to prevent the latent image forming area S from being scanned. FIG. 2 shows a case where the image forming light beam B and the synchronizing signal generating light beam B ′ are incident from the same side with respect to the normal line N of the reflecting surface 3a. Reflective surface 3a
The incident angle of the image forming light beam B is [θ
1], the incident angle of the synchronizing signal generating light beam B ′ is [θ2]
Then, both light beams B after being reflected by the reflecting surface 3a,
B ′ is deflected while maintaining the angle of [θ2−θ1]. This reflecting surface 3a has an inclination with respect to any light beam (B or B ') as the polygon mirror 3 rotates.
2π / n (n is the reflecting surface 3a that constitutes the polygon mirror 3)
The number of) changes. Therefore, both the light beams B and B'after being reflected by the reflecting surface 3a are deflected within the range of [± 2π / n] from the illustrated position. That is, the synchronization signal generating light beam B ′ is applied to the latent image forming area S of the photosensitive drum 4.
In order to prevent the scanning, the scanning area of the synchronizing signal generating light beam B ′ and the scanning area of the image forming light beam B after being reflected by the reflecting surface 3a must not overlap. Is. That is, the condition is θ2-θ1 ≧ 4π / n. FIG. 3 shows a case where the image forming light beam B and the synchronizing signal generating light beam B ′ are incident from the reflection side with respect to the normal line N of the reflection surface 3a. In this case, since the image forming light beam B and the synchronizing signal generating light beam B ′ are incident on the normal line N from the reflection side,
The scanning area of the synchronizing signal generating light beam B ′ and the scanning area of the image forming light beam B after being reflected by the reflecting surface 3a do not overlap. However, the reflective surface 3
The image forming light beam B incident on a and the synchronizing signal generating light beam B ′ reflected on the reflecting surface 3a do not intersect, and the synchronizing signal generating light beam B ′ incident on the reflecting surface 3a is reflected. It is necessary to set the incident angles θ1 and θ2 so as not to intersect with the image forming optical beam reflected by the surface 3a. That is, the condition is θ2-θ1 ≧ 2π / n. As a result, even if the synchronization signal generating laser beam B ′ is always kept in the on state without being turned off, a latent image that becomes noise for the image information is not formed on the photosensitive drum 4. Therefore, it is possible to avoid causing image deterioration. In the embodiment, the image forming laser beam B and the synchronizing signal generating laser beam B ′ are obtained separately from the two semiconductor lasers 1 and 6, respectively. Alternatively, either one or both may be obtained by a gas laser or a solid-state laser. Further, the laser beam B for image formation may be obtained by separating the laser beam B for image formation by the same gas laser or fixed laser with an appropriate optical element. Further, instead of the various laser beams described above, a light beam from the LED may be used for generating a synchronizing signal, and these are collectively referred to as a synchronizing signal generating light beam B '. The optical scanning device according to the present invention, in addition to the laser beam printer described in the previous embodiment,
It can be applied to a laser facsimile, a laser COM system and the like. For example, when high-density recording is performed as in a laser COM system, the image forming light beam B is configured to be narrowed down to an extremely small diameter by a scanning lens such as the fθ lens 5, so that a synchronization signal is generated. In order to prevent the light beam B ′ from being excessively narrowed down and becoming difficult to be detected by the light receiving unit 8 for synchronization control, the light beam B ′ for generating synchronization signal is the fθ lens 5 or the like as shown in the previous embodiment. It is preferable not to pass the scanning lens of. In this case, since the scanning lens such as the fθ lens 5 needs to cover only the scanning range of the image forming light beam B, it can be made compact.

As described above, according to the present invention, an image forming light beam that is modulated according to an image signal to form an image and a synchronization for detecting the modulation start timing of the image forming light beam. An optical scanning device for reflecting a signal generating light beam on the same reflecting surface of a rotating polygon mirror, wherein the image forming light beam and the synchronizing signal generating light beam are arranged in a rotation axis direction of the rotating polygon mirror. Since the light beams are incident at the same angle with respect to each other and so as to satisfy the above relational expression with respect to the rotation direction of the rotary polygon mirror, the synchronization signal generating light beam is not included in the scanning region of the image forming light beam. Therefore, even if the synchronization signal generating light beam is held in the ON state without being turned off, there is no risk of scanning the image forming area (scanning area of the image forming light beam) signal The ON / OFF control of the raw light beam can be carried out roughly.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an optical scanning device according to the present invention.

FIG. 2 is a diagram showing how a laser beam for image formation and a laser beam for generating a synchronization signal are incident on a polygon mirror.

FIG. 3 is a diagram showing how a laser beam for image formation and a laser beam for generating a synchronization signal are incident on a polygon mirror.

[Explanation of symbols]

3: rotating polygonal mirror, 3a: reflecting surface, 4: photoconductor, B: image forming laser beam, B ': synchronizing signal generating laser beam, S: latent image forming area.

Claims (1)

[Claims] 1. A rotary polygon mirror comprising an image forming light beam that is modulated according to an image signal to form an image, and a synchronizing signal generating light beam that detects the modulation start timing of the image forming light beam. An optical scanning device that reflects the light on the same reflecting surface, wherein the image forming light beam and the synchronization signal generating light beam are incident at the same angle with respect to the rotation axis direction of the rotating polygon mirror. An optical scanning device characterized in that light is incident so as to satisfy the following relational expression with respect to a rotation direction of a mirror. When the image forming light beam and the synchronizing signal generating light beam are incident from the same side with respect to the normal of the reflecting surface of the rotary polygon mirror, θ2-θ1 ≧ 4π / n The image forming light beam and the synchronizing signal generating When the light beam is incident from the side opposite to the normal of the reflecting surface of the rotating polygon mirror, θ2-θ1 ≧ 2π / n where θ1 is the normal of the reflecting surface of the image forming light beam incident on the reflecting surface. And θ2 is the angle between the synchronizing signal generating light beam incident on the reflecting surface and the normal to the reflecting surface, and n is the number of reflecting surfaces that make up the rotating polygon mirror.