JPH1152263A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanner capable of facilitating the adjustment of scanning pitch and converting the density of printing dots into a specified value with respect to a laser beam printer, etc., using plural-beam scanning. SOLUTION: This scanner is provided with a focal distance variable lens 2 arranged between a light beam generating element 1 and a rotary polygon mirror, and a detector 8 detecting the distances of plural beams, which are deflected to perform scanning, in a scanning perpendicular direction. The focal distance of the lens 2 is varied based on a signal from the detector 8 so that a distance between scanning beam spots may be a specified value. By varying the focal distance of the lens 2 in accordance with a signal from the outside and also varying the revolving speed of the mirror 4 and the modulation frequency of plural beams, the density of the printing dots is changed to the specified one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning apparatus used for a laser beam printer, a copying apparatus, and the like, and more particularly, to a plural beam scanning optical system. Hereinafter, a laser beam printer will be described as an example.

[0002]

2. Description of the Related Art In order to realize high-speed printing and high dot density printing with a laser beam printer, it is necessary to increase the number of scans per unit time. Also, due to the diversification of output patterns in recent years, it has become increasingly necessary to change the print dot density with the same printer device. In order to increase the number of repetitive scanning lines, it is necessary to increase the number of rotations of the rotating polygon mirror or to increase the number of mirrors.
It is possible to some extent by increasing the number of surfaces, but there is a limit. Therefore, it is well known that a multi-beam scanning method for scanning a large number of laser beams at once is effective. For example, a single laser light source is separated into a plurality of laser beams, each of which has an output pattern.
Scanning on a scanning surface simultaneously through a single rotating polygonal mirror and an Fθ lens by modulating with a scanning signal (Japanese Patent Laid-Open No. 62-239 / 1987).
119) Alternatively, a plurality of individually modulatable semiconductor laser elements are arranged in an array, and each emitted light is collimated by a single collimator lens, and scanned via a rotating polygon mirror and an Fθ lens. There is a method of simultaneously scanning the surface with a plurality of laser beams (Japanese Patent Publication No. 60-33019). However, these multi-beam scanning optical systems do not consider changing the print dot density. On the other hand, a two-beam scanning optical system having a function of changing the interval between two beams according to a predetermined dot density has been proposed (US Pat. No. 5,006,705). However, in this case, since the beam spot diameter is constant, the appropriate change range of the dot density is limited, and it is not suitable for a wide range of changes in the print dot density.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical system for a plurality of beams that can be adjusted with high precision when adjusting the printing pitch. Conventionally, the printing pitch adjustment method is performed by rotating around the optical axis of a plurality of beam generating elements. In this case, it is necessary to adjust the rotation angle of the plurality of beam generating elements in small increments in order to adjust the printing pitch. To do this faithfully requires very expensive equipment, which has been a problem.
In addition, a mechanism that is inexpensive but does not cut the adjustment angle finely,
In order to properly adjust this pitch, it took a long time to adjust the pitch, which was a problem.

Another object of the present invention is to realize a simple and highly reliable printing dot density changing system which can cope with various printing patterns with an optical system for a plurality of beams. It is. For this purpose, it is necessary that the spot diameters of a plurality of beams on the scanning surface and the intervals between the beams can be converted into appropriate values in accordance with the print dot density.

[0005]

According to the present invention, a plurality of optical beams capable of independently modulating light intensity are provided.
And a plurality of light beams emitted from the generating means.
An optical beam generating means and a rotary polygonal mirror in an optical scanning device having a rotary polygonal mirror for deflecting and scanning a beam collectively and an Fθ lens for converging each beam on a scanning surface to a predetermined spot diameter. A variable focal length lens disposed between them, and a detector for detecting the distance in the scanning perpendicular direction of the plurality of beam beams deflected and scanned, so that the distance between the scanning beam spots becomes a predetermined value. Thus, the present invention is characterized in that the focal length of the focal length variable lens is changed based on the signal from the detector. By doing so, the pitch of the plurality of beams can be easily and accurately adjusted.

In the above-described optical scanning apparatus, the focal length of the variable focal length lens is changed in accordance with an external signal, and the number of rotations of the rotary polygon mirror and the modulation frequency of the plurality of beams are changed. It is characterized in that it can be changed to the print dot density.

According to the multi-beam scanning optical system of the present invention,
By changing the focal length of the variable focal length lens, both the interval between a plurality of beams on the scanning surface and the convergent spot diameter can be changed simultaneously, including the rotational speed of the rotating polygon mirror and the modulation frequency of the plurality of beams. The print dot density can be converted by changing the print dot density in accordance with the target print dot density.

[0008]

FIG. 1 shows an embodiment of the present invention. The plurality of lights from the plurality of beam generating elements 1 pass through the variable focal length lens 2 and are expanded into parallel light beams of a predetermined size. The multi-beam generating element 1 has a configuration as shown in FIG.
14 are arranged at equal intervals, from which the beam lights 15, 1
6, 17, and 18 occur. This figure 2
In this example, the case where the number of a plurality of beams is four is shown, but the same applies to any number of beams. After this, the cylindrical lens 3 inserted for correcting the tilt of the rotary polygon mirror 4
And is deflected and scanned by the rotating polygon mirror 4. The rotary polygon mirror 4 is rotated by a motor 5 at a predetermined rotation speed. A plurality of beams deflected and scanned by the rotary polygon mirror 4 are imaged on the photosensitive member 7 by the Fθ lens 6, respectively.
The number of the beams on the photoreceptor 7 is the same as the number of the beams of the multiple beam generating element 1. When this number is 4, beam 1 in FIG.
Arrows 2, 9, 20, 21, 22
Scanned as 3, 24, 25, 26. Since the beam intervals are equal, the scanning pitch distances 27, 28,
29 are equal. Here, intervals 27, 28, 2
So that 9 is equal to the scan pitch to be printed
The tilt angle θ of the plurality of beams is roughly adjusted. For the adjustment, the beam generating element 1 may be rotated, or a beam light rotating element may be inserted between the rotary polygon mirror 4 and the beam generating element 1.
This may be performed by rotating.

A first feature of the present invention is that the printing pitch can be adjusted with high accuracy in an optical system for a plurality of beams. If the focal length of the variable focal length lens 2 can be changed by a small distance, the distance of the beam spot to be scanned can be changed by a small distance.

Here, a specific example of the variable focal length lens 2 will be described. FIG. 6 is an arrangement diagram when the focal length is 394.125 mm. 6, reference numeral 41 denotes a lens having a focal length of 198.94 mm, reference numeral 42 denotes a lens having a focal length of -198.94 mm, and reference numeral 43 denotes a lens.
Is a lens having a focal length of 472.95 mm. FIG. 7 shows a lens configuration when the focal length is 413.831 mm. The lenses are the same as in FIG. 6, but the overall focal length can be changed by changing only the lens arrangement.

For example, the focal length of the variable focal length lens 2 is 1%, that is, from 394.125 mm to 398.06.
It is easy to change it to 6 mm. In this case, the printing pitch on the photoconductor 7, that is, the distances 27, 28, 2 in FIG.
9 can be made 100 ÷ 101 times the distance, that is, 1% smaller. Here, the focal length variable lens 2 changes the focal length from 394.125 mm in FIG.
The state where the focal length is long, that is, the focal length is 398.06
FIG. 8 shows a specific lens arrangement of 6 mm. That is, by changing the state of FIG. 6 to the state of FIG. 8, the overall focal length can be increased by 1%.

In the conventional method, the scanning pitch is similarly set to 1%
To change the angle, θ in FIG.
It was necessary to change to 101 degrees, which required very high precision.

Although the description has been made so far mainly on the focal length of the variable focal length lens 2, the detector 8 is arranged, the scanning pitch is actually measured, and the size of the variable focal length lens is determined based on the size thereof. If the focal length is controlled by feedback, an optical scanning device which is more accurate and highly reliable automatically can be obtained.

As the detector 8, for example, a detector as shown in FIG. 4 may be used. It is assumed that the beam lights 30, 31, 32, and 33 are always scanned as indicated by arrows. There, a detector 35 consisting of a slit 34 and a photodetector therein is pointed by an arrow 36.
Is scanned as follows. The output from this detector at this time is as shown in FIG. 5, and peaks 37, 38, 39, and 40 can be obtained. If the distance T between the peaks is obtained and the scanning speed of the detector 35 is obtained, the scanning interval of the beam light can be obtained by calculation.

The second feature of the present invention is that the diameter of the light spot to be scanned and its pitch can be changed by changing the focal length of the variable focal length lens 2 from a state where the spot diameter and the scanning pitch are appropriate. It is.

Specifically, the focal length of the variable focal length lens 2 is 394.125 mm at first, and then 413.125 mm.
Consider the case of changing to 831 mm. When the focal length is 394.125 mm, the spot diameter on the photoreceptor 7 is 90 μm and the pitch is 63.5 μm, and the number of rotations of the rotary polygon mirror 4 and the modulation frequency of a plurality of beams are set to 40.
0 dpi, the latent image on the photoreceptor 7 is 400 dpi
i. In this state, upon receiving a 420 dpi signal from the host computer 10, the control unit 9 sets the focal length of the variable focal length lens 2 to 413.831 mm, modulates the number of rotations of the rotary polygon mirror 4, and modulates a plurality of beams. 420d frequency
pi, the spot diameter on the photoconductor 7 is 86 μm.
m, the scanning pitch becomes 60.5 μm, and the latent image formed on the photoconductor 7 becomes 420 dpi.

That is, according to the present invention, according to the signal from the host computer 10, the focal length of the variable focal length lens 2, the number of rotations of the rotary polygon mirror 4, and the modulation frequency of a plurality of beams are provided. By changing the above, it is possible to provide an optical scanning device having a predetermined print dot density.

[0018]

As described above, according to the present invention, the scanning pitch can be adjusted with high accuracy, and good printing without pitch unevenness can be performed. Also, the scanning spot diameter and the scanning beam according to the print dot density in multiple beam scanning.
By changing the rotation interval of the rotating polygon mirror and the light intensity modulation frequency together, the printing dot density can be easily converted.
A variety of printing can be supported.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a perspective view showing an example of a multiple beam generating element used in the present invention.

FIG. 3 is an explanatory diagram showing a state of a beam spot on a photoconductor.

FIG. 4 is a side view showing an example of a detector used in the present invention.

FIG. 5 is a characteristic diagram showing a measurement state of a scanning interval.

FIG. 6 is a layout diagram of a variable focal length lens used in the present invention.

FIG. 7 is an arrangement diagram showing a changed state of a variable focal length lens used in the present invention.

FIG. 8 is an arrangement diagram showing a changed state of a variable focal length lens used in the present invention.

[Explanation of symbols]

1 is a multiple beam generating element, 2 is a variable focal length lens, 3
Is a cylindrical lens, 4 is a rotating polygon mirror, 5 is a lens
, 6 is an Fθ lens, 7 is a photoreceptor, 8 is a detector, 9 is a control unit, 10 is a host computer, 11, 12, 13,
14 is a light source, 15, 16, 17, and 18 are beam light states, 19, 20, 21, and 22 are spots, 23, 24,
Reference numerals 25 and 26 denote the direction of advance of the spot, reference numerals 27, 28 and 29 denote scanning pitches, reference numerals 30, 31, 32 and 33 denote spots, reference numeral 34 denotes slits, reference numeral 35 denotes a detector, and reference numeral 36 denotes an arrow indicating movement.
7, 38, 39, and 40 are peaks of a signal from the detector, 41 is a lens having a focal length of 198.94 mm, and 42 is a focal length−
198.94 mm lens, 43 is focal length 472.9
This is a 5 mm lens.

Claims (2)

[Claims] 1. A plurality of light beams capable of independently modulating light intensity.
And a plurality of light beams emitted from the generating means.
An optical beam generating means and a rotary polygonal mirror in an optical scanning device having a rotary polygonal mirror for deflecting and scanning a beam collectively and an Fθ lens for converging each beam on a scanning surface to a predetermined spot diameter. A variable focal length lens disposed between them, and a detector for detecting the distance in the scanning perpendicular direction of the plurality of beam beams deflected and scanned, so that the distance between the scanning beam spots becomes a predetermined value. As described above, the optical scanning device changes the focal length of the variable focal length lens based on a signal from the detector. 2. The optical scanning device according to claim 1, wherein the focal length of the variable focal length lens is changed according to an external signal, and the number of rotations of the rotary polygon mirror and the modulation frequency of the plurality of beams are adjusted. An optical scanning device wherein the density is changed to a predetermined print dot density.