JPH03251813A - Scanning optical device - Google Patents

Abstract

PURPOSE:To correct the inclination of an end surface at an end part without deteriorating the quantity of curvature of an image plane due to the manufacture error of a lens system by making a lens which is at least a part of an image formation optical system eccentric with the optical axis with a specific quantity. CONSTITUTION:A means which adjusts the eccentricity of a toric lens 1 consists of respective elements, i.e. a pressure spring 2, an adjusting screw 3, and a leaf spring 4. Thus, the toric lens 1 as a lens constituting part of an f-theta lens system 10 is made eccentric to adjust the inclination error of curvature of field on a scan surface. Namely, while the length direction of the lens 1 is set along an abutting surface 11a, the lens is made eccentric in parallel by the leaf spring 4, the quantity of eccentricity of the lens 1 itself with the abutting surface 11a is adjusted, and the deviation in the optical axis from other lenses constituting the lens system 10 is eliminated to make corrections so that the inclination of the image plane on the image formation plane reaches the specific quantity of curvature of field. Thus, the quantity of eccentricity is adjusted only by the lens as a part of the f-theta lens system 10 without adjusting the inclination due to the rotation of the whole scanning optical system to easily improve the optical performance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a scanning optical device that scans a scanning surface such as a photosensitive drum surface using a beam of light from a laser, and particularly relates to a scanning optical device that scans a scanning surface such as a photosensitive drum surface using a beam of light from a laser. This invention relates to a scanning optical device suitable for, for example, a laser beam printer, which has an adjustment means to satisfactorily correct field curvature that occurs when scanning a scanning plane due to manufacturing errors in an imaging optical system such as a θ lens. be.

(Prior Art) Conventionally, in a scanning optical device such as a laser beam printer, a laser beam from a laser light source is optically modulated according to an image signal. The optically modulated laser beam is then periodically deflected by an optical deflector such as a rotating polygon mirror, and f-
An image J8 is recorded by focusing the light into a spot on the surface of a photosensitive recording medium and scanning it with exposure using an imaging optical system such as a θ lens.

In recent years, the features of this popular scanning optical device are the miniaturization of the scanning optical system and the high resolution of the laser beam spot (miniaturization of the laser beam spot diameter).

In particular, increasing resolution is extremely important because it has a great influence on increasing the quality of output images, and recently various techniques related to increasing resolution have been proposed. The high resolution of this laser beam spot is mainly due to the high NA of the scanning optical system (
This can be achieved by reducing the spot diameter of the laser beam by increasing the numerical aperture.

However, while miniaturizing the spot diameter of the laser beam can improve image quality and resolution, it also reduces the depth of the scanning optical system. For this reason, in order to obtain various optical characteristics in a well-balanced manner, it is necessary to make the processing and mounting of the f-theta lens constituting the scanning optical system extremely strict.

In general, when the depth of the scanning optical system becomes shallow, for example, an error in the tilt of the imaging plane (field curvature) occurs due to eccentricity of the lens system that makes up the scanning optical system, and it becomes very difficult to obtain the desired optical characteristics. come.

Therefore, in the conventional scanning optical device, in order to correct the tilt error (field curvature) of the imaging plane due to eccentricity of the lens system, etc., an adjustment means for adjusting the tilt is provided in the scanning optical device.

FIG. 4 is a schematic diagram of a main part of a conventional scanning optical device equipped with such a field curvature adjustment mechanism.

In the figure, a laser beam emitted from a laser unit 41 having a semiconductor laser, a collimator lens, etc. is reflected by a reflecting surface of an optical deflector 48 consisting of a rotating polygon mirror. Then, the reflected laser beam is used for scanning f
An image is formed by a -θ lens system (imaging optical system) 43 on an imaging plane 44 which is a scanning plane. At this time, the f-θ lens system 4
An image plane adjustment mechanism provided within the scanning optical device corrects the tilt error of the image plane caused by the eccentricity of the image forming apparatus 3.

Next, an adjustment method for correcting the tilt error of the image plane using the image plane adjustment mechanism at this time will be described.

In the figure, a dowel 45 is installed on the bottom surface of the scanning optical system 40 to serve as a center of rotation when adjusting the inclination of the imaging plane.

The don 45 is inserted into a predetermined hole drilled on the optical base of the printer main body (not shown), and an eccentric bottle or the like inserted into the rotation slot 46 is rotated with the bin 45 as the rotation center. As a result, the inclination of the imaging plane is corrected by rotating the scanning optical system in the direction indicated by the arrow shown in the figure, that is, by rotating the entire scanning optical system.

After adjusting the range where a good spot diameter can be obtained (best image plane) and the scanned surface (for example, the photosensitive drum surface) to match, the fixing hole 47 provided in the scanning optical system 40 It is fixedly mounted on the optical base of the illustrated printer body.

By adjusting the inclination of the image plane in this way, the designed image formation position on the printer body (actually, the position corresponding to the scanned surface of the photosensitive drum, for example) and the image formation plane by the scanning optical system (the best image formation position) can be adjusted. The inclination with the surface (surface) is adjusted to within the permissible depth.

(Problems to be Solved by the Invention) On the other hand, the scanning shape of the imaging plane, which is the scanning plane by the scanning optical system, generally does not lie on a straight line perpendicular to the optical axis within the scanned plane due to various errors.

This generally results in an M-shaped distribution shape that is bilaterally symmetrical with respect to the optical axis, as shown in FIG. 5, due to various aberrations occurring within the f-theta lens constituting the scanning optical system, for example.

FIG. 5 is an explanatory diagram showing the scanning distribution of the imaging plane by the scanning optical system within the scanned plane. In the figure, 51 is the optical axis of a scanning optical system (not shown), and 52 is the best image plane, which is a surface that is good on average (a surface that can obtain a good spot diameter) over the entire surface to be scanned. It shows.

In general, a scanning optical system is arranged such that, for example, a photosensitive drum surface (scanned surface) is located at the position of this best image plane.

For example, if the lens system constituting the scanning optical system has no tilt error of the imaging plane due to eccentricity, etc., the practical effective image area will be range A shown in the figure, which is The image forming surface has a well-balanced M-shaped distribution shape.

In general, it is desirable to obtain such a distribution of the image forming plane within the scanned surface because the amount of field curvature can be kept small and desired optical characteristics can be obtained.

On the other hand, if an error in the inclination of the imaging plane occurs in the lens system constituting the scanning optical system due to eccentricity, for example, the practical effective image area moves from range A to range B shown in the same figure, and this is due to the light This results in an image forming surface with an asymmetrical distribution shape with respect to the axis 51, making it impossible to obtain good optical performance.

Now, looking at the amount of curvature of field on the image plane, if there is no eccentricity in the lens system, the amount of curvature of field is C as shown in FIG. 6(A).

On the other hand, if the lens system has eccentricity or the like, the amount of curvature of field becomes D as shown in FIG.

In this way, if the lens system that constitutes the scanning optical system has an error in the tilt of the image plane due to eccentricity, etc., the image plane at the end of the scanned surface will be tilted, as shown in Figure (B). There is a problem.

For example, if the scanning optical device equipped with the conventional image plane adjustment mechanism described above is used to correct the tilt of the image plane, the distribution of the image plane after adjustment will be as shown in Figure 6 (C). become.

As can be seen from the same figure (C), the tilt of the image plane at the right end of the scanned surface is relatively corrected, but the amount of curvature of field on the other hand is E, which is due to the lens system. The disadvantage is that the curvature of field tc becomes larger than that without eccentricity.

In this way, in a scanning optical device using a conventional image plane adjustment mechanism, the tilt of the image plane at the end of the scanned surface is relatively corrected, but on the other hand, the amount of curvature of the image plane tends to increase. Therefore, it was not possible to obtain the good image forming surface shown in FIG. 6(A), and as a result, it was very difficult to improve the optical performance.

The present invention provides an adjusting means for decentering at least some of the lenses constituting the imaging optical system (f-theta lens system), so that the image plane when scanning on the scanning plane is provided in a part of the imaging optical system. An object of the present invention is to provide a scanning optical device that can suppress the amount of curvature of an image forming surface to a small value and can satisfactorily correct the inclination of the image surface at the end of the surface to be scanned.

(Means for Solving the Problems) The scanning optical device of the present invention deflects a light beam from a light source with an optical deflector, and then guides the light onto a scanning surface via an imaging optical system.
In the scanning optical device that scans the scanning surface, at least one lens constituting the imaging optical system is decentered with respect to the optical axis by an adjustment means, so that the image surface when scanning the scanning surface with the light beam is decentered. It is characterized by corrected curvature.

(Embodiment) FIG. 1 is a schematic diagram of an f-theta lens system as an imaging optical system constituting a part of a scanning optical device according to a first embodiment of the present invention.

In the figure, reference numeral 10 denotes an f-theta lens system, which is arranged in the same position as the f-theta lens system 43 in FIG. 4, for example, in the scanning optical device. 1 is a toric lens,
It constitutes a part of the f-θ lens system 1o. Reference numeral 2 denotes a presser spring, which presses the longitudinal direction of the toric lens 1 against an adjustment screw 3 provided on a lower mirror 811 of the toric lens 1 in the drawing. Reference numeral 4 denotes a leaf spring, which is provided on a part of the base material 11 such as a lens barrel, and fixes the toric lens 1 by pressing the lateral direction of the toric lens 1 against the abutting surface 11a of the base material 11.

In this embodiment, the presser spring 2, the adjusting screw 3, and the plate spring 4 constitute an adjusting means for adjusting the eccentricity of the toric lens 1.

Next, by decentering the toric lens 1, which is a lens constituting the f-θ lens system 10 of this embodiment,
A method of adjusting the tilt error of field curvature on the scanning plane will be described.

In this embodiment, with the configuration shown above, the toric lens 1 is made orthogonal to the optical axis A by rotating the adjusting screw 3 by a predetermined amount to correct the tilt error (field curvature) of the image plane caused by the above-mentioned causes. This is corrected by moving it in the direction and making it eccentric.

That is, the toric lens 1 is moved in the direction perpendicular to the optical axis A with the short side of the toric lens 1 pressed by the leaf spring 4 along the abutment surface 11a, that is, parallel decentered.

By adjusting the eccentricity of the toric lens 1 itself with respect to the abutment surface 11a by such an adjustment method and eliminating optical axis misalignment with other lenses constituting the f-theta lens system 10, the image plane on the image forming plane can be adjusted. For example, the slope of is shown in Figure 6 (
The amount of curvature shown in A) is well corrected.

In particular, in this embodiment, it is possible to satisfactorily correct the inclination of the image plane at the end of the scanned surface without deteriorating the amount of field curvature on the imaging plane.

Furthermore, unlike the above-mentioned conventional method of adjusting the image plane inclination by rotating the entire scanning optical system, the method of adjusting the inclination of the image plane in this embodiment involves adjusting the eccentricity of some of the lenses themselves constituting the f-θ lens system 10. In order to do this, the amount of field curvature after the tilt adjustment as shown in FIG. 6(C) does not become larger than the initial state (when there is no eccentricity in the lens system constituting the scanning optical system). It has the following characteristics.

Therefore, in this example, the distribution shape of the imaging plane when the lens system shown in FIG. 6(B) has eccentricity can be obtained by implementing this example. It is possible to obtain a good distribution shape of field curvature similar to that in the case where there is no eccentricity.

FIG. 2 is a schematic diagram of an f-0 lens system as an imaging optical system forming a part of a scanning optical device according to a second embodiment of the present invention. In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals.

In the figure, 21 is a spacer for adjustment, and as shown in the figure, it is interposed between the abutment surface 22a of the toric lens 1 in the short direction and the base material 22 such as a lens barrel that supports the toric lens 1. I'm letting you do it.

Next, a method of adjusting the tilt error of the image plane due to eccentricity of the lens of this embodiment will be explained.

In this example, a toric lens 1 is used as shown in the figure.
In the drawing, the lower abutment surface 22a is set in advance by subtracting the thickness of the spacer 21 from the design reference position. On the other hand, the amount of inclination of the image plane on the imaging plane is measured, and the amount of movement of the toric lens 1 in the direction perpendicular to the optical axis is converted to the amount of inclination of the image plane.

Based on this conversion result, the adjustment amount of the spacer is calculated, and a spacer of an appropriate thickness is inserted between the abutment surface 22a of the toric lens 1 in the transverse direction and the base material 22. Alternatively, if the thickness is thinner than the standard spacer, replace it with another spacer as appropriate and use an appropriate spacer.

And presser bar: 2 d, Jl:')l'-rick lens 1
The longitudinal direction of the toric lens 1 is pressed against the spacer 21 side, and the toric lens 1 is fixed by being pressed against the abutment surface 22a of the lens barrel 22 in the short direction by the leaf spring 4.

As described above, in this embodiment, in order to correct the inclination of the image plane, a spacer of an appropriate thickness, which constitutes an element of the adjustment means, is used, and the toric lens 1 is moved perpendicularly to the optical axis A by the adjustment means. By moving the toric lens 1 by a predetermined amount, that is, by decentering the toric lens 1, the inclination error of the image plane on the image forming plane is favorably corrected. By using such an adjustment method, the same effects as those of the previous embodiment can be obtained.

FIG. 3 is a schematic diagram of an f-theta lens system as an imaging optical system that constitutes a part of a scanning optical device according to a third embodiment of the present invention. In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals.

Next, a method of adjusting the tilt error of the image plane due to eccentricity of the lens of this embodiment will be explained.

In this example, the amount of inclination of the image plane on the image forming plane was measured in advance, and the adjustment in the longitudinal direction of the toric lens 1 was measured using a cage while sliding it on the abutment surface 31a of the toric lens 1 in the lateral direction. After that, the toric lens 1 is fixed to a base material 31 such as a lens barrel using an adhesive or the like, and the short direction of the toric lens 1 is fixed to the abutment surface 31 using a plate spring 4.
It is fixed by pressing it against a.

In this way, in this embodiment, adjustment in the longitudinal direction of the toric lens 1 can be performed by abutting the toric lens 1 in the lateral direction without using the adjustment screws, presser springs, etc. used in the first embodiment as adjustment means. This is done while sliding on the surface 31a, thereby adjusting the inclination of the image plane. Even with such an adjustment method, it is possible to obtain the same effects as in the above-mentioned embodiment.

In each of the embodiments, a configuration has been described in which a part of one lens constituting the f-θ lens system is provided with an adjusting means for adjusting eccentricity in a direction perpendicular to the optical axis of the lens. The configuration may be such that all the lenses constituting the -θ lens system are provided with adjustment means similar to the adjustment means described above.

Furthermore, the object of the present invention can be similarly achieved by using, as an adjusting means, a parallel eccentricity in which the lens is moved in a direction perpendicular to the optical axis, a tilt eccentricity in which the lens is tilted with respect to the optical axis, or used independently. can do.

(Effects of the Invention) According to the present invention, the imaging optical system (f
By providing a part of the imaging optical system with an adjusting means for decentering at least a part of the lenses (-θ lens system) by a predetermined amount with respect to the optical axis, the image on the scanning plane that occurs due to manufacturing errors in the lens system, etc. A scanning optical device that can easily and favorably correct the amount of curvature of the surface (imaging surface) without deteriorating it can be achieved.

[Brief explanation of drawings]

1st. Second. FIG. 3 shows the first, second, and third embodiments of the present invention in order. A schematic diagram of an f-θ lens system as an imaging optical system constituting a part of the scanning optical device of the third embodiment, and FIG. 4 shows the main part of the conventional scanning optical device equipped with a field curvature adjustment mechanism. Schematic diagram, 5th
The figure is an explanatory diagram showing the distribution state of the imaging plane within the scanned surface.
FIG. 6 is an explanatory diagram showing the distribution state of the imaging plane due to tilt adjustment. In the figure, 1 is a toric lens, 2 is a presser spring, 3 is an adjustment screw, 4 is a leaf spring, 10 is an f-θ lens system, 21 is a spacer, 11, 21.31 are base materials, lla, 22a,
31a is an abutting surface, and 31a is an optical axis.

Claims (3)

[Claims] (1) In a scanning optical device that deflects a light beam from a light source with an optical deflector, guides the light onto a scanning surface via an imaging optical system, and scans the scanning surface. 1. A scanning optical device, characterized in that at least a part of the lenses constituting the device is decentered with respect to an optical axis by an adjustment means, thereby correcting field curvature when scanning a scanning surface with the light beam. (2) The scanning optical device according to claim 1, wherein at least some of the lenses are decentered in a direction perpendicular to the optical axis and/or tilted and decentered with respect to the optical axis. (3) The scanning optical device according to claim 1, wherein the imaging optical system is comprised of an f-theta lens.