JPS61194419A - Optical scanning device - Google Patents

Abstract

PURPOSE:To adjust a convergence point on a surface to be scanned by providing a beam shaping optical system with a cylindrical lens and supporting the cylindrical lens by a supporting means which is movable in optical-axis direction. CONSTITUTION:The cylindrical lens 42 in the beam shaping optical system 40 is moved in an optical-axis direction to correct subscanning-directionl defocusing on the surface 30 to be scanned. The beam shaping optical system 40 which includes the cylindrical lens 42 is moved in the optical-axis direction together with a light source 10 in one body to obtain the same effect. When the cylindrical lens 42 is adjusted, a U-sectioned guide member 61 is fixed along the optical axis and a lens support frame 62 on which the lens 42 is stuck is made slidable in optical-axis directions. Consequently, even hen a semiconductor laser as the light source has variance in angle of radiation, the arrangement of an optical element is only altered to adjust the convergence position on the surface to be scanned.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical scanning device such as a laser printer optical system using a semiconductor laser as a light source. The present invention relates to an optical scanning device having an adjusting means to achieve good light condensation.

[Prior Art 1] FIG. 5 shows a cross-sectional view of an optical scanning device of a conventionally used laser printer optical system taken along a plane perpendicular to the scanning plane along the optical axis. 10 is a light source using a semiconductor laser; 20
Reference numeral 30 indicates an optical deflection device that deflects and scans a light beam, such as a rotating polygon mirror, and 30 indicates a surface to be scanned, such as a drum on which a photosensitive material or the like is placed. Between the light source 10 and the optical deflection device 20, there is a beam shaping device consisting of a frimeter lens 41 that converts the light beam from the light source 10 into parallel light, and a cylindrical lens 42 that has refracting power for the parallel light in the sub-scanning direction. Optical system 4
0, and the beam is focused near the rotating polygon mirror of the optical deflector 20. This cylindrical lens 42 is a light deflector 71
When a rotating polygon mirror is used as 20, this is for correcting the inclination angle of the rotating polygon mirror.

Further, between the optical deflection device 20 and the surface to be scanned 30, there is an fθ lens 51 for forming an image of the light beam on the surface to be scanned and a uniform scanning speed, and an fθ lens 51 that is connected to the cylindrical lens 42 in the sub-scanning direction. An optical imaging element 50 including a cylindrical lens 52 having refractive power is disposed, and the optical deflection device 20 and the surface to be scanned 30 are in a conjugate relationship to form an image of the light beam on the surface to be scanned 30. .

In such a laser printer optical system, the wave amplitude distribution in the cross section perpendicular to the optical axis is expressed by a Gaussian function. The imaging position will be different. Therefore, if the radiation angle of the semiconductor laser that is the light source 10 differs from the radiation angle assumed at the time of design, the output diameter of the collimator lens in the sub-scanning direction will differ and the light will not be focused on the scanned surface 30- exactly as designed. .

Conventionally, the radiation angle of the semiconductor laser, which is the light source 10, has no stability in mass production and varies over a wide range.In contrast, in the laser printer optical system, a collimator lens of 7:4
1 with a different focal length or replacing the focal length of the cylindrical lens χ42 disposed between the collimator lens 41 and the optical deflection device 20 with an appropriate one to absorb the variation in the radiation angle. This was done by constructing a large number of cylindrical lenses and moving the elements to change the focusing distance. However, the above adjustment work was extremely time-consuming.

[Problems to be Solved by the Invention] The present invention can solve the problem by simply changing the arrangement of the optical elements without replacing the optical elements even when the radiation angle of the semiconductor laser that is the light source varies. It is an object of the present invention to provide an optical scanning device that makes it possible to adjust the focusing position 1n.

Means for Solving 1 Problem 1 The present invention aims to achieve the object 1. The present invention provides an optical deflection device that deflects and scans a light beam, and a beam that makes the light beam incident on the light deflection device. An optical scanning device comprising a shaping optical system and an imaging optical system disposed between the light deflection device and the surface to be scanned, wherein the beam shaping optical system has a cylindrical lens with a fixed focal length; The present invention provides an optical scanning device characterized in that a cylindrical lens is supported by support means movable in the optical axis direction.

1 Effect] If the radiation angle of the semiconductor laser that is the light source varies, an image will not necessarily be formed on the scanned surface. This is a result of the characteristic behavior of the U-shaped beam, which violates the laws of geometric optics, and has an imaging position that depends on the incident beam diameter.

FIG. 3 shows the optical axis perpendicular to the scanning surface along the optical axis of the scanning optical system when an optical imaging element consisting of an fθ lens 51 and a cylindrical lens 52 is disposed between the optical deflection device 20 and the surface to be scanned 30. This figure shows the off-axis optical path on the plane.

It is known that the beam diameter of the beam spot on the scanned surface 30'2 takes a fixed value in the vicinity of the beam waist with respect to minute changes in the optical axis direction.

On the other hand, when the beam waist shifts from the surface to be scanned, a slight change in the position of the surface to be scanned causes a change in the beam diameter on the surface to be scanned, and the requirements for field curvature become stricter.

Furthermore, if the fθ lens or the like is made of a material whose refractive index changes depending on the environment, if the beam waist is not on the scanned surface, the optical system will be designed with extremely small tolerances, which is undesirable in terms of device design.

The positional fluctuation of the beam waist near the scanned surface is caused by the positional fluctuation of the beam waist at a position conjugate with this beam waist, that is, near the optical deflection device 20 formed by the cylindrical lens 42. depends on the incident beam diameter.

The smaller the incident beam diameter is, the more the cylindrical lens 42
A beam waist is formed near the.

For the optical imaging element consisting of the rθ lens 51 and the cylindrical lens 52, when the diameter of the beam incident on the cylindrical lens 42 is smaller, if there is a beam waist on the fθ lens side, images can be formed on the same scanned surface. . Therefore, the cylindrical lens 4 of the beam shaping optical system
By shortening the distance between the cylindrical lens 42 and the f.theta.

The present invention provides a cylindrical lens 4 in a beam shaping optical system.
The beam shaping optical system including the cylindrical lens 42 may be moved integrally with the light source ]O in the tapering direction. The effect of

It goes without saying that the movable cylindrical lens may have a toric or modified cylindrical surface as described below.

[Example 1 1.2 of the cylindrical lens 42 from the light source side, f
3rd and 4th surfaces of the θ lens 51, cylindrical lens 52
The following example will be shown for the fifth and sixth sides of .

However, the fifth surface of the cylindrical lens 52 was a modified cylindrical surface. The modified cylindrical surface corrects field curvature by employing this modified cylindrical surface. As shown in Figure 4, the modified cylindrical surface is a rotationally symmetrical surface with the straight line Q as the axis, and the sub-scanning section at the center of the optical axis is the straight RQ. It has a circular shape with a radius equal to the interval R, and the cross section has a radius of curvature of I in the main scanning section.

FIG. 1 shows a main scanning section of the next embodiment.

,,,:',,' RD N (sub-scanning direction) Wavelength 780 old n1
200.000 5.00 1.510722
φ 410.00 3 -78.055 7.00 1.738144
-53.642 170.00 5 18.300 4.00 1.485956
1400.000 To the drum surface 43, 5 mm 6th surface Aspheric coefficient = 0.0 81 = -1,290471) -07P] = 4.
000082= 1.42943D-11P2=
6.000083=-1,57648D-15r
'3 = 8.000084 = 8.24341D
-20P4= 10.000085=-1,733
50D-24P5= 12.0000 1st surface: Cylindrical ν Cal 5th surface: Deformed cylindrical surface with main scanning direction curvature radius R
=-920,0 =8- 6th surface 2 rotation inscribed aspherical surface It is expressed by the following formula.

C=1/R The polygon surface is positioned 30mm in front of the third surface.The incident beam diameter is 4.0+0+n in the sub-scanning direction in front of the first surface.
If the beam diameter is 766+nτ0, there will be 60μ on the scanned surface.
An image is formed with a beam diameter of rn.

In this example, the radiation angle of the semiconductor laser that is the light source varies, and it is 40 + nm in front of the first surface by 1.10 nm in the sub-scanning direction.
Assuming that the beam waist has a diameter of +n+n, the imaging position on the sub-scanning surface is shifted 3.7+n+n toward the lens side from the scanned surface. Further, if the radiation angle varies toward the larger side and a beam waist with a diameter of 2.8+nm in the sub-scanning direction is brought to 40 l in front of the first surface, the imaging position will shift by 0.65 mm in the direction away from the lens on the scanned surface.

Generally, the smaller the beam diameter, the greater the amount of defocus.

Therefore 1.1. The out-of-focus is large when the radiation angle creates an O++on beam waist. In this case, the distance between the cylindrical lens and the rotating polygon mirror is 38 according to the design value.
0 +n m, but by moving this to 31.0 tnm, the focus position can be suppressed to shift by only 0.22 m + n to the opposite side, which is convenient for focusing.

Therefore, when the radiation angle of the semiconductor laser, which is the light source, varies, the out-of-focus in the sub-scanning direction can be corrected by moving the cylindrical lens in the beam shaping optical system in the optical axis direction.

Fig. 2 shows an example of a lens support part that allows the movement and adjustment of the cylindrical lens 42 in the shaping optical system in the optical axis direction.
1 is fixed along the optical axis, and a lens support frame 62 to which a cylindrical lens 42 is attached on the inside is slidable in the optical axis direction.
It is fixed to the side member 61 from the upper surface side of the movement adjustment member 61 by means of set screws 63 through elongated holes 611 provided on both sides of the member.

In this embodiment, only the cylindrical lens 42 is fixed to the lens support frame 62, but the semiconductor laser, the collimator lens, and the cylindrical lens 42 are fixed to the lens support frame 62 at designed intervals, and these are integrated into one body. It may be moved in the optical axis direction.

[Effects of the Invention] According to the present invention, an optical system such as a laser printer using a semiconductor laser as a light source can be assembled and adjusted so that the semiconductor lasers are selected and the semiconductor laser having the radiation angle of the design value is installed. The extra steps were omitted.

In addition, when replacing a semiconductor laser, it took a lot of time and effort to absorb variations in the radiation angle, but this has the effect of greatly simplifying the process.

[Brief explanation of drawings]

FIG. 1 is a lens arrangement diagram showing one embodiment of the present invention. FIG. 2 shows a cylindrical lens position adjustment section showing an embodiment of the present invention. FIG. 3 is an explanatory diagram of the optical path of the optical imaging element section. FIG. 4 is a shape explanatory diagram of a modified cylindrical lens. Figure 5 is a diagram of the lens arrangement of the laser printer optical system. 10...Light source 20...Light deflection device 30...Scanned surface 40...Beam shaping optical system 41...Collimator lens 42... ...Cylindrical lens 50...
・Optical imaging element 51... fθ lens 52... Cylindrical lens 61...
・Guide member 62...Lens support frame

Claims (1)

[Claims] An optical system consisting of an optical deflection device that deflects and scans a light beam, a beam shaping optical system that makes the light beam incident on the optical deflection device, and an imaging optical system that is disposed between the optical deflection device and the surface to be scanned. An optical scanning device, wherein the beam shaping optical system has a cylindrical lens, and the cylindrical lens is supported by support means movable in the optical axis direction.