JPS63214712A - Scanning optical device - Google Patents

Abstract

PURPOSE:To eliminate astigmatism on an image carrier without exerting any influence upon the relation between a light source and a collimator lens by enabling the distance between a scanning means and the collimator lens to be adjusted. CONSTITUTION:A beam from a semiconductor laser array 1 is emitted from light emission points 11a and 11b and projected on the collimator lens 12. While the interval between the lens 12 and laser 11 is held constant, they are moved forth and back on the optical axis to absorb the deviation of the intersection of main light beams 12a and 12b from a polygonal mirror 13 due to common differences in the angle between the points 11a and 11b and the interval. The main light beams 12a and 12b are passed through a cylindrical lens 21 and reflected and scanned on the reflecting surface 13 of a mirror 13 as the scanning means to form two spots on a photosensitive body drum 1 through an ftheta lens 14. Two scanning lines 20a and 20b are therefore formed by one scan through the rotation of the mirror 13.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a scanning optical device used in a laser beam printer, etc., and in particular, it sequentially scans a plurality of beams emitted from a light source into images via a collimator lens and a scanning means. The present invention relates to a scanning optical device for scanning onto a carrier.

(Prior Art) Generally, in a laser beam printer in which a light beam is scanned on a scanned medium (image carrier) by a polygon mirror, the number of rotations of the polygon mirror is inevitably increased in order to improve the scanning speed. Or, the number of surfaces of the polygon mirror had to be increased. However, increasing the rotation speed of the polygon mirror as described above has a limit to the rotation speed of the scanner motor for rotating the polygon mirror, and increasing the number of surfaces of the polygon mirror increases the diameter of the polygon mirror. As a result, the load on the scanner motor has increased.

Therefore, conventionally, as shown in Japanese Patent Publication No. 60-33019, it has been considered to provide a plurality of light sources and scan the scanned medium with a plurality of spots.
In FIG. 4(a) shown in FIG. 4(b), 100 is a semiconductor laser array that emits two beams, 101a, 10
1b is a light emitting point of the semiconductor laser array 100. The light flux emitted from the semiconductor laser array 100 is
The polygon mirror 103, which is made into parallel light by the collimator lens 102 and directed toward the reflective surface 103a of the polygon mirror 103, is rotated in the direction of arrow a by the scanner motor 104. As a result, the beam is directed to the reflecting surface 10
3a, and then two scanning tees y108a, 1 are reflected onto the photoreceptor drum 107 by the fθ lens 106
It is scanned and imaged as shown in 08b.

Here, as shown in FIG. 4(b), the semiconductor laser array 100 is arranged at an angle θ with respect to the main scanning direction X, where X is the main scanning direction. This is because the scanning optical system as a whole is an enlarging system.
When trying to
When ta, 1o1b are arranged perpendicular to the scanning direction Luminous point Iota, 1
Since the spacing between o1b is limited to approximately 50 l, the angle θ must be approximately 4.8° in order to have an apparent value of 21L.

(Problem to be Solved by the Invention) However, in such a conventional example, when the light source is tilted at an angle θ with respect to the main scanning direction, the chief ray of each light beam that passes through the collimator lens comes out from the collimator lens. later diverges,
Therefore, the light will be irradiated to distant positions on the polygon mirror. Therefore, there is a problem in that the polygon mirror must be made larger in order to utilize all the chief rays irradiated to distant positions. Further, since the reflection points are far apart on the polygon mirror, stigmatism (astigmatism) occurs on the imaging surface, resulting in the problem that a good spot cannot be imaged.

In particular, in a configuration in which a cylindrical lens is provided between a polygon mirror and a collimator lens for tilt correction and an image is formed on the polygon mirror, the above-mentioned problem becomes conspicuous.

As a means to solve this problem,
No. 58-211735 is disclosed,
If the pitch or emission angle of the laser varies due to these factors, as shown in 4th [ff1(c), the reflection point on the polygon mirror will be separated, resulting in 7 stigmatism (astigmatism) on the imaging plane as described above. This results in the problem that a good spot cannot be imaged.

Therefore, the present invention has been made to solve the above-mentioned problems of the conventional example, and its purpose is to eliminate non-uniformity on the image carrier without affecting the relationship between the light source and the collimator lens. An object of the present invention is to provide a scanning optical device that can eliminate point aberration.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a plurality of beams emitted from a light source are sequentially connected to a collimator lens,
In a scanning optical device that scans onto an image carrier through a scanning means, the distance between the light source and the collimator lens is maintained constant, and the distance between the scanning means and the collimator lens is adjustable. has been done.

(4J11: 田) In the present invention having the above configuration, by making it possible to adjust the distance between the scanning means and the collimator lens while keeping the distance between the light source and the collimator lens constant,
without affecting the relationship between the light source, stiffness, and meter.
This eliminates astigmatism on the image carrier.

(Example) The present invention will be explained below based on the illustrated example. Third
The figure is a configuration diagram of a laser beam printer to which the present invention is applied. In the figure, l is CdS, amorphous silicon (A-3t
) or a photosensitive drum as an image carrier coated with a photosensitive layer such as OPc, 2 a laser scanning device for image exposure, 3 a primary charger, 4 a developer containing toner,
5 is a transfer charger, 6 is a cleaner, 7 is a pre-exposure lamp, 8
9 is a fixing device, and 9 is a cassette for storing transfer paper.

In the above configuration, the image forming process is performed as follows. First, the primary charger 3 charges the photoreceptor drum 1 rotating in the direction of the arrow to give a uniform potential, and then the laser beam emitted from the laser scanning device 2 is applied to the photoreceptor drum 1. Exposure is performed according to the image information, and an electrostatic latent image is formed. Toner is attached to the latent image on the photosensitive drum 1 due to the potential difference between the latent image and the developing device 4, and a 1 m image is formed. In this way, a toner image is formed on the photoreceptor drum 1. This toner image is transferred from the back side of the transfer material (not shown) to a transfer charger 5.
By applying a corona charge of opposite polarity to the toner,
The image is transferred onto the transfer material. The transfer material carrying the toner image is passed through a fixing device 8, whereby the toner is fixed onto the transfer material. On the other hand, toner and paper dust remaining on the photosensitive drum l without being transferred are removed by a cleaner 6. Furthermore, the charge remaining on the photoreceptor drum l is removed by exposure from the pre-exposure lamp 7. Thereafter, the same image process is repeatedly performed on the photosensitive drum 1 again.

On the other hand, FIG. 2(a) is a principle diagram showing an embodiment of the scanning optical device according to the present invention. It becomes possible to connect the intersection of the chief rays 12a and 12b on the reflective surface 10 of the polygon mirror 13.
For example, the angle between the two light emitting points 11a and llb is 1.
29°, interval 0.1mm, 1. Each error is 0.1
°, 5 pm, due to this error, the intersection of the two principal rays 12a and 12b after passing through the collimator lens 12 is 2.38 degrees off the reflective surface lO of the polygon mirror 13. , two light emitting points 11a.

By increasing the distance from the collimator lens 12 to the polygon mirror 13 by 2.38 m while keeping the distance between the collimator lens 11b and the collimator lens 12 constant, the intersection of the two principal rays 12a and 12b is placed on the surface of the polygon mirror 13. can be tied to

That is, in order to adjust the distance between the collimator lens 12 and the polygon mirror 13, for example, as shown in FIG. Attach gear 24 to one end of. Further, by attaching a gear 26 to the shaft of the servo motor 25, meshing the gear 26 and the gear 24, and driving the servo motor 25, the gears 24, 26 . Feed screw 23
The collimator lens 12 is moved through the . Furthermore, a rack 22a is carved in the lower part of the frame 22, and the amount of movement of the collimator lens 12 is detected by meshing this rack 22a with a pinion 28 attached to a detector 27. 29 is an amplifier. With such a configuration, a desired position of the collimator lens 12 is set in advance, and when the collimator lens 12 reaches that position, it is detected and stopped.

Further, FIG. 1 shows a specific embodiment of the scanning optical device according to the present invention, and in the same figure, the beams emitted from the semiconductor laser array 11 as a light source are emitted from light emitting points 11a, ll.
The luminous fluxes emitted from the zero light emitting points 11a and llb emitted from the point b are each made into parallel beams by the collimator lens 12.

In the figure, the dashed line indicates the optical axis of the lens, 12a,
Reference numeral 12b indicates the chief ray of the beam, and by moving the collimator lens 12 and the semiconductor laser 11 back and forth on the optical axis using the above method while keeping the distance between them constant, the angle formed by the light emitting point 11a and llb of the semiconductor laser 11 is determined. It is possible to absorb the deviation of the intersection of the chief rays 12a and 12b from the polygon mirror 13 due to the respective tolerances of the distance and the distance. chief ray 1
After exiting the collimator lens 12, the two light beams 2a and 12b pass through the cylindrical lens 21, strike the reflective surface 13a of a polygon mirror 13 as a scanning means rotated in the direction of the arrow by the scanner motor 15, and are reflected and scanned. Further, the light flux reflected by the reflecting surface 13a is fθ
The lens 14 forms images on the photosensitive drum 1 as two spots. Therefore, by rotating the polygon mirror 13, two scan lines 20a and 2 are generated in one scan.
0b will be formed.

In the above embodiment, a servo motor was used as a driving means for adjusting the distance between the collimator lens 12 and the polygon mirror 13, but a step motor may also be used.

(Effects of the Invention) The scanning optical device according to the present invention has the above-described configuration and operation, and by adjusting the distance between the collimator lens and the scanning means while keeping the distance between the light source and the collimator lens constant, The intersection point of the principal ray of each of the plurality of beams with the optical axis can be located on the scanning means surface, and as a result, there is an effect that a good spot can be imaged without producing astigmatism.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing an embodiment of a scanning optical device according to the present invention, FIG. 2(a) is a principle diagram of the same embodiment, and FIG.
b) is an explanatory diagram showing means for adjusting the distance between the collimator and the scanning means in the same embodiment, FIG. 3 is a configuration diagram of a laser beam printer to which the same embodiment is applied, and FIG.
a) is a perspective view showing a conventional scanning optical device; FIG. 4(b)
4 is a diagram showing the scanning direction and scanning line of the semiconductor laser in the conventional example, and FIG. 4C is a diagram showing the optical path of the chief ray from the collimator lens to the scanning means in the conventional example. Explanation of symbols l...Photosensitive drum (image carrier) 11...Semiconductor laser array (light source) 12...Collimator lens 13...Polygon mirror (scanning means) 25...Servo motor FIG. 1b Fig. 2 C6) Fig. 2 (b)

Claims (1)

[Claims] In a scanning optical device that sequentially scans a plurality of beams emitted from a light source onto an image carrier via a collimator lens and a scanning device, the distance between the light source and the collimator lens is maintained constant, and the distance between the scanning device and the scanning device is maintained constant. A scanning optical device characterized in that the distance to a collimator lens can be adjusted.