JPH10213769A - Lens holding device and optical beam scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the plane tilt error of a polygon mirror in an optical beam scanning optical device and to adjust the diameter of a beam waist on a photosensitive body by simple mechanism and work. SOLUTION: When the optical device is provided with a convex cylindrical lens 5 and a concave cylindrical end 6 between an optical beam light source and the polygon mirror, these lenses 5, 6 converge an optical beam to the vicinity of the deflection face of the polygon mirror only in a sub-scanning direction. The two lenses 5, 6 are unitedly held by a lens barrel 25, which is fixed on a V groove 22 formed on a mount 21. The positions of the lenses 5, 6 in the optical axis A direction and their rotational angles around the optical axis A can be unitedly adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens holding device and a light beam scanning optical device, and more particularly to a lens holding device and a light beam scanning optical device used as an image writing means of a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, various light beam scanning optical devices have been known as means for writing an image on an electrophotographic photosensitive member.
They basically deflect a light beam emitted from a light source unit by a polygon mirror, and form and scan an image on a photosensitive member via an optical member such as a scanning lens. Then, in order to correct the surface tilt error of each deflecting surface of the polygon mirror, a condensing lens (normally, a condensing lens) that condenses the light beam only in the sub scanning direction near the deflecting surface between the light source unit and the deflector
In addition to the provision of a cylindrical lens, a lens member for condensing the light beam on the photoconductor in the sub-scanning direction is also provided between the deflector and the photoconductor. In addition, adverse effects on the image due to surface tilt error (pitch variation in the sub-scanning direction)
In order to reduce the magnification, the magnification of the scanning lens in the sub-scanning direction is set to an absolute value of 2 or less.

[0003] However, when the magnification in the sub-scanning direction is reduced, the beam waist diameter on the photosensitive member, which is the image plane of the scanning optical system, becomes smaller, and the depth of focus becomes shorter. In this case, when defocus occurs in the scanning optical system due to a change in the environment, the change in the size of the beam waist diameter on the photoreceptor becomes large, so that there is a problem that image quality is likely to deteriorate due to the change in the environment. there were.

Therefore, in a conventional light beam scanning optical device, in order to correct a light beam on a photoreceptor to a desired shape, a flat aperture is used at the expense of light use efficiency, or the size of the device is increased. Inevitably, a cylindrical lens having a long focal length was used.

In view of such circumstances, the present applicant can adjust the beam waist diameter on the photoreceptor to be small with a short optical path length, and automatically compensates for the beam waist diameter even when the environmental temperature changes. A possible light beam scanning optical device has been proposed (see Japanese Patent Application Laid-Open No. 9-97065). In this optical beam scanning optical device, the cylindrical lens is composed of a first lens which is a convex lens and a second lens which is a concave lens, so that a lens principal point corresponding to an image on the deflection surface of the polygon mirror is a light source. Side to shorten the combined focal length of the first and second lenses.

[0006]

However, in the light beam scanning optical device described in the above publication, the photosensitive member is adjusted by adjusting the rotation angles of the two cylindrical lenses individually about the optical axis and the optical axis. In order to adjust the beam waist diameter, there is a problem that the adjusting mechanism is complicated and the adjusting operation is complicated.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a configuration for correcting a surface tilt error of a polygon mirror by combining two cylindrical lenses having various advantages, and to simplify a beam waist diameter on a photosensitive member. An object of the present invention is to provide a lens holding device and a light beam scanning optical system which can be adjusted by various mechanisms and operations.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above objects, the present invention provides a lens holding device for holding one cylindrical lens for each of concave and convex located between a light source unit and a deflector. The cylindrical lens has a function of condensing the light beam emitted from the light source unit near the deflection surface of the deflector only in the sub-scanning direction, and a lens holder that integrally holds the two cylindrical lenses is moved in the optical axis direction. And the angle of rotation about the optical axis can be adjusted.

The light beam scanning optical device according to the present invention further comprises, in addition to the light source unit, the deflector, one cylindrical lens for each of the concave and convex portions, and the lens holder, a light beam deflected by the deflector on a light receiving surface. A scanning lens for focusing and scanning, the magnification of the scanning lens in the sub-scanning direction is set to an absolute value of 2 or less, and the lens holder holds two cylindrical lenses so as to satisfy the following conditional expression. I did it.

0.1 <{L (L-f ₁ ) / f ₁ f ₂ } <1 f ₁ : focal length of convex cylindrical lens f ₂ : focal length of concave cylindrical lens L: rear side main of convex cylindrical lens Distance between point and front principal point of concave cylindrical lens

In the present invention, one cylindrical lens for each of the concave and convex portions is integrally held by a single holder, and by moving this holder in the optical axis direction, focus adjustment on the light receiving surface is performed. Is rotated about the optical axis to adjust the shape of the beam waist diameter on the light receiving surface. The configuration and arrangement of the two cylindrical lenses satisfy the above-mentioned conditional expression.
A combined focal length shorter than that of one cylindrical lens can be obtained, and the focus and waist diameter can be easily adjusted by the same procedure as that of one cylindrical lens. As for the correction of the tilt error,
By setting the magnification of the scanning lens in the sub-scanning direction to an absolute value as low as 2 or less, the adverse effect of the surface tilt error can be minimized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a lens holding device and a light beam scanning optical device according to the present invention will be described with reference to the accompanying drawings.

In FIG. 1, the light beam scanning optical device comprises:
Generally, a light source unit 1 composed of a laser diode 2 and a collimator lens 3, a pair of concave and convex cylindrical lenses 5, 6, a polygon mirror 9, three fθ lenses 11, 12, 13 and a cylindrical lens 14 are combined. It comprises a scanning lens 10 and a plane mirror 15. FIG. 2 shows an optical path of a light beam by this optical system.

The modulation of the laser diode 2 is performed based on the image signal, and the laser diode 2 emits a light beam as diffused light. This light beam is converted into parallel light (or convergent light) by the collimator lens 3 and reaches the polygon mirror 9 via the cylindrical lenses 5 and 6. Cylindrical lens 5,
Reference numeral 6 condenses the light beam linearly in the main scanning direction near the deflection surface of the polygon mirror 9.

The polygon mirror 9 is driven to rotate at a constant speed in the direction of arrow a. The light beam is deflected at an equal angular velocity on each deflecting surface based on the rotation of the polygon mirror 9, passes through the scanning lens 10, is reflected by the plane mirror 15, forms an image on the photoconductor drum 30, and moves in the direction of arrow b. Scan. f
The .theta. lenses 11, 12, and 13 receive the light beam deflected by the polygon mirror 9 at a constant angular velocity on the light receiving surface (photosensitive drum 30).
It has a function of correcting the above main scanning speed to a constant speed, that is, a function of correcting distortion. The cylindrical lens 14 has power only in the sub-scanning direction, and corrects the tilt error of the polygon mirror 9 in cooperation with the cylindrical lenses 5 and 6.

The photosensitive drum 30 is driven to rotate at a constant speed in the direction of arrow c, and the polygon mirror 9 and the scanning lens 10 are rotated.
An image (electrostatic latent image) is written on the photoconductor drum 30 by the main scanning in the direction of arrow b by the above and the sub-scanning of the photoconductor drum 30 in the direction of arrow c.

Next, the cylindrical lenses 5 and 6 will be described. The cylindrical lens 5 has a positive refractive power only in the sub-scanning direction, and has a convex surface facing the light source unit 1 side. The cylindrical lens 6 has a negative refractive power only in the sub-scanning direction, and is a concave lens whose plane faces the light source unit 1 side. Incidentally, another cylindrical lens 14 is a convex lens having a positive refractive power only in the sub-scanning direction and having a convex surface facing the light source unit 1 side.

In this embodiment, in order to form a parallel light beam emitted from the light source unit 1 in the sub-scanning direction in the vicinity of the deflecting surface of the polygon mirror 9, each of the concave and convex cylindrical lenses 5 and 6 is used. The refractive power is divided. As a result, the lens principal point corresponding to the image on the deflection surface moves to the light source unit 1 side, and the cylindrical lenses 5, 6
Becomes shorter.

The cylindrical lenses 5 and 6 are held by a holding device 20 shown in FIGS. 3 and 4A. The holding device 20 includes a pedestal 21, a lens barrel 25, and a plate belt 29. The lens barrel 25 has a cylindrical shape having a circular cross section, and the lens 5 is provided in the recess 26, and the lens 6 is provided in the recess 27.
Are fixed by an adhesive or a spring plate (not shown). The lens barrel 25 is placed in the V-groove 22 of the pedestal 21, and both ends of the plate belt 29 are screwed onto the pedestal 21, so as to be pressed / fixed to the V-groove 22. Pedestal 2
1 is fixed by screwing through a mounting hole 23 on a substrate portion of a housing (not shown).

This holding device 20, as shown in FIG.
The cylindrical lenses 5 and 6 are connected to the pedestal 2 via the lens barrel 25.
1 and the pedestal 21 is mounted on the substrate portion of the housing so that the centers of the lenses 5 and 6 coincide with the optical axis A. Therefore, regarding the positions of the lenses 5 and 6 in the direction of the optical axis A, the lens barrel 25 by the plate belt 29 is used.
Is adjusted by moving the fixing position along the V-groove 22. Further, by moving the pedestal 21 itself by the clearance between the mounting hole 23 and a screw (not shown), fine adjustment in the direction of the optical axis A is possible. Such movement in the direction of the optical axis A adjusts the focus on the photosensitive drum 30 in the sub-scanning direction. On the other hand, the adjustment of the beam waist shape on the photosensitive drum 30 is performed by slightly loosening the plate belt 29.
This is performed by rotating the lens barrel 25 by a small angle in the V-groove 22. At this time, the rotation angles of the lenses 5 and 6 are changed integrally about the optical axis A. FIG. 4 (b)
Shows a lens barrel 25 'as another example.

Here, the change of the beam waist diameter when the lenses 5 and 6 are integrally rotated about the optical axis A will be described with reference to FIGS. First, as a premise, Tables 1 and 2 show first and second examples of the contraction data of the optical system.

[0022]

[Table 1]

[0023]

[Table 2]

In Tables 1 and 2, the conditional expression indicates the positional relationship between the cylindrical lenses 5 and 6 held in the lens barrel 25, and is shown below. 0.1 <{L (L-f ₁ ) / f ₁ f ₂ } <1 f ₁ : focal length of convex cylindrical lens f ₂ : focal length of concave cylindrical lens L: rear principal point and concave of convex cylindrical lens Distance of the front principal point of the cylindrical lens

FIG. 5 shows a change in beam waist diameter when the cylindrical lenses 5 and 6 are integrally rotated about the optical axis A using the holding device 20, and FIG. 0 ° and (B) show the case where the deflection angle is 30 °. As is clear from FIG. 5, the beam waist diameter can be adjusted relatively slowly. FIG. 6 shows that when the concave lens 6 is held by the lens barrel 25 with a rotation error of 1 ° with respect to the convex lens 5, the lenses 5 and 6 are integrated around the optical axis A using the holding device 20. Shows the change in beam waist diameter when rotated. As is clear from FIG. 6, although the center value of the rotation angle at which the beam waist diameter becomes the minimum is shifted from 0 ° to 2.8 °, the degree of change is the same as that in FIG.

On the other hand, FIG. 7 shows a change in the beam waist diameter when only one convex cylindrical lens 5 is rotated (the concave cylindrical lens 6 is fixed) for comparison. In this case, a slight rotation of the convex cylindrical lens 5 greatly changes the beam waist diameter. As is clear from the comparison between FIGS. 5, 6 and 7, if the two lenses 5 and 6 are integrally rotated, fine adjustment of the beam waist diameter is easy.

As described above, when the two cylindrical lenses can be integrally adjusted, the number of parts required for the rotation adjustment and the optical axis adjustment is reduced to about half as compared with the case where they are individually held. The configuration of the scanning optical device can be simplified, and the number of components requiring precision is reduced, which contributes to cost reduction. Further, even when the positions of the entire two cylindrical lens units change due to environmental changes or the like, this error is caused by a change in the beam waist diameter on the image plane rather than a change in the relative mounting position between the cylindrical lenses. Is small, the optical system in which the waist diameter hardly changes even when the environmental conditions change can be obtained.

In the present embodiment, the correction of the surface tilt error of the polygon mirror 9 is performed by the cylindrical lens 5,
6 and the cylindrical lens 14. Regarding the correction of the surface tilt error, the absolute value of the magnification of the scanning lens in the sub-scanning direction becomes a problem, and the value is preferably 2 or less. Incidentally, in the configuration of the optical system shown in Table 1 and Table 2, the magnification (absolute value) of the scanning lens in the sub-scanning direction is the first.
In the example, it was set to 1.5, and in the second example it was set to 0.74.

Further, in the above conditional expression, the upper limit is set to 1 when the two cylindrical lenses 5 and 6 are used, and the combined focal length is longer than the focal length when one conventional cylindrical lens is used. Also means shorter. Therefore, the optical path length at the previous stage of the polygon mirror 9 can be shortened to make the optical system compact. Further, the reason why the lower limit value of the conditional expression is set to 0.1 is that if it is less than that, it becomes difficult to correct aberration.

In this embodiment, the cylindrical lenses 6 and 14 are made of resin, and so-called temperature compensation can be performed so that the beam waist diameter on the photosensitive drum 30 does not change even if the environmental temperature changes. It is preferable to configure as follows. The other lenses are made of glass. A resin lens has a large change in refractive index and a change in shape with respect to a change in environmental temperature as compared with a glass lens. However, if this characteristic is positively used, in the sub-scanning direction, the fluctuation of the positive refractive power of the cylindrical lens 14 and the fluctuation of the negative refractive power of the cylindrical lens 6 due to the fluctuation of the environmental temperature cause the deviation of the imaging position. Cancels out the photosensitive drum 3
The beam waist diameter above 0 can be properly maintained.

It should be noted that the lens holding device and the light beam scanning optical device according to the present invention are not limited to the above embodiment, but can be variously modified within the scope of the invention. In particular, the cylindrical lens 14 downstream of the polygon mirror 9 is omitted, and any one of the fθ lenses 11, 12, and 13 is configured with a toroidal surface or an aspheric surface to provide a function of correcting a surface tilt error. Is also good. The configuration in which the lens barrel 25 is attached to the pedestal 21 and the configuration in which the pedestal 21 is attached to the substrate are arbitrary.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a light beam scanning optical device according to an embodiment of the present invention.

FIG. 2 is an optical path diagram of the optical beam scanning optical device, (A) showing a cross section in the main scanning direction, and (B) showing a cross section in the sub scanning direction.

FIG. 3 is a perspective view showing a lens holding device according to an embodiment of the present invention.

4A and 4B are cross-sectional views of a lens barrel of the lens holding device. FIG. 4A shows the lens barrel shown in FIG. 3, and FIG. 4B shows another example of the lens barrel.

FIG. 5 is a graph showing a change (design value) of a beam waist diameter in the light beam scanning optical device.

FIG. 6 is a graph showing a change in a beam waist diameter in the optical beam scanning optical device (when a concave lens has a rotation error of 1 ° with respect to a convex lens).

FIG. 7 is a graph showing a change in a beam waist diameter in the light beam scanning optical device (a comparative example in a case where a concave lens is fixed and only a convex lens is rotated).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source unit 5 ... Convex cylindrical lens 6 ... Concave cylindrical lens 9 ... Polygon mirror 10 ... Scanning lens 20 ... Lens holding device 21 ... Base 25, 25 '... Lens barrel A ... Optical axis

Claims (2)

[Claims] 1. A lens holding device for holding one cylindrical lens for each of concave and convex located between a light source unit and a deflector, wherein the two cylindrical lenses deflect a light beam emitted from the light source unit. A lens holder having a function of condensing light only in the sub-scanning direction in the vicinity of the deflection surface of the device, and a lens holder integrally holding the two cylindrical lenses, the position in the optical axis direction and the rotation angle about the optical axis. A lens holding device provided so as to be adjustable. 2. A light source unit that emits a parallel or converged light beam, a deflector that deflects the light beam, and a light beam that is emitted from the light source unit is sub-scanned near a deflection surface of the deflector. One cylindrical lens for each of concave and convex that condenses light only in the direction, and a lens that integrally holds the two cylindrical lenses and that can adjust the position in the optical axis direction and the rotation angle about the optical axis. A holder, and a scanning lens that condenses and scans the light beam deflected by the deflector on a light receiving surface and has a magnification in the sub-scanning direction of 2 or less in absolute value, and the lens holder has the following conditional expression: keeping the two cylindrical lenses so as to satisfy, 0.1 <{L (L- f 1) / f 1 f 2} <1 f 1: focal length of the convex cylindrical lens f _2: concave cylindrical lens Focal length L: projection light beam scanning optical apparatus according to claim distance of the front principal point of the rear principal point and the concave cylindrical lens after the cylindrical lens.