JPH11149037A - Cylinder lens unit and scanning optical device using the unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain a high definition image free from uneven density by inclining the optical axis of a plastic optical element (cylinder lens) with reference to a luminous flux made incident on the optical element by a prescribed angle. SOLUTION: The optical axis M of a glass cylinder lens 4a is nearly parallel to the luminous flux made incident on the cylinder lens 4a, the optical axis L of the plastic cylinder lens 4b is inclined with reference to the luminous flux made incident on the cylinder lens 4b by a prescribed angle in a main scanning plane. Besides, a reflection preventing film is not formed on the lens face (surface) of the plastic cylinder lens 4b. By appropriately setting the inclined angle of the optical axis L of the plastic cylinder lens 4b with reference to the incident luminous flux in the main scanning plane in such a way, the light quantity fluctuation of a semiconductor laser 1 caused by return light 21 from the cylinder lens 4b not coated with the reflection preventing film is prevented, then, the high definition image free from the uneven density is easily obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder lens unit and a scanning optical apparatus using the same, and more particularly to deflecting and reflecting a light beam modulated and emitted from a light source means by an optical deflector (deflection element) comprising a rotary polygon mirror or the like. Then, a laser beam printer (LB having an electrophotographic process, for example) is configured to optically scan the surface to be scanned through an imaging optical system (imaging element) having fθ characteristics to record image information.
P) or a device such as a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, in a scanning optical apparatus such as a laser beam printer, a light beam (light beam) which is light-modulated and emitted from a light source means in accordance with an image signal is converted into an optical deflector comprising, for example, a rotating polygon mirror (polygon mirror). , Periodically focused by a focusing optical system having an fθ characteristic, and focused on a photosensitive recording medium (photosensitive drum) surface in the form of a spot, and the surface is optically scanned to record an image.

FIG. 6 is a schematic view of a main part of a conventional scanning optical device.

In FIG. 1, a divergent light beam emitted from a semiconductor laser 61 as a light source means is collimated by a collimator lens 6.
The light beam is converted into a substantially parallel light beam by 2 and is incident on a cylinder lens (cylindrical lens) 64 having a predetermined refractive power only in the sub-scanning direction with the light beam (light amount) restricted by a stop 63. Of the substantially parallel light beams incident on the cylinder lens 64, they are emitted as they are in the state of substantially parallel light beams in the main scanning plane. In the sub-scanning plane, the light is converged and formed as a substantially linear image on a deflecting surface (reflection surface) 65a of an optical deflector 65 composed of a rotating polygon mirror.

The light beam deflected and reflected by the deflecting surface 65a of the optical deflector 65 is passed through an imaging optical system (fθ lens) 66 having fθ characteristics to a photosensitive drum surface 68 as a surface to be scanned.
By guiding the light upward, and rotating the light deflector 5 in the direction of arrow A, the surface of the photosensitive drum 68 is optically scanned in the direction of arrow B in the figure to record image information.

[0006]

The cylinder lens used in such a scanning optical device is capable of reducing the weight of the device,
From the viewpoint of cost reduction and productivity, there is a shift from conventional glass lenses to plastic lenses.

Further, by combining a glass cylinder lens having a positive refractive power and a plastic cylinder lens having a negative refractive power, for example, an imaging optical system (fθ lens) is constituted by a plastic scanning lens. In some cases, the effects of environmental changes are compensated for.

Although such a plastic cylinder lens has the advantages of light weight, low cost, and high productivity, it is difficult to form an antireflection film on the lens surface, so that there is a large amount of surface reflected light. There is.

Further, since the lens surface of the plastic cylinder lens in the main scanning plane has a planar shape, the light beam reflected on the lens surface, so-called return light, is condensed and returned near the light emitting point of the semiconductor laser. There are points. This return light is the near field (emission point) of the semiconductor laser,
Since it acts on the stem and the pin photo for APC (automatic light intensity control) to cause light intensity fluctuations, such a scanning optical device causes unevenness in density due to return light, and a high quality image cannot be obtained. There is a point.

According to the present invention, the optical axis of a plastic optical element (cylinder lens) is tilted by a predetermined amount with respect to a light beam incident on the optical element, so that the amount of light of the semiconductor laser due to the return light from the plastic optical element It is an object of the present invention to provide a cylinder lens unit capable of preventing fluctuations and easily obtaining a high-quality image without density unevenness, and a scanning optical apparatus using the same.

[0011]

According to the present invention, there is provided a cylinder lens unit comprising: (1) a cylinder lens unit having a plastic cylinder lens and a glass cylinder lens; Is characterized by being inclined with respect to the long axis in the generatrix direction of the glass cylinder lens.

(2) In a cylinder lens unit having a plastic cylinder lens, an optical axis of the plastic cylinder lens is inclined with respect to a light beam incident on the cylinder lens.

(3) The scanning optical device of the present invention converts (3) the light beam emitted from the light source means into a substantially parallel light beam in the main scanning plane via the first optical element, and converts the converted substantially parallel light beam into the second parallel light beam. An image is formed linearly in the main scanning direction on the deflecting surface of the deflecting element via the optical element, and the light beam deflected and reflected by the deflecting element is spot-shaped on the surface to be scanned via the third optical element. In the scanning optical device which scans the surface to be scanned by focusing on the optical element, the second optical element has at least one plastic optical element, and the optical axis of the optical element is directed to the optical element. Is inclined in the main scanning plane with respect to the incident light beam.

In particular, (3-1) Assuming that the focal length of the first optical element is f and the inclination angle of the optical axis of the plastic optical element with respect to the incident light beam is θ, fxtan2θ> 0.1. Or (3-2) the second optical element is a glass cylinder lens having a positive refractive power,
(3-3) The optical axis of the glass cylinder lens and the optical axis of the plastic cylinder lens are within the main scanning plane. , And
(3-4) that the second optical element has one plastic cylinder lens having a positive refractive power, and (3-5) that the second optical element is arranged in the optical axis direction. It is characterized by being movable.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of the present invention, FIG. 2 is a perspective view of a main part of a second optical element shown in FIG. 1, and FIG. FIG. 3 is a cross-sectional view (main scanning cross-sectional view) of a main part in the main scanning direction up to an optical deflector.

In FIG. 1, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. Reference numeral 2 denotes a collimator lens as a first optical element, which converts a light beam (light beam) emitted from the light source means 1 into a substantially parallel light beam in the main scanning plane. Reference numeral 3 denotes an aperture stop for adjusting the diameter of a passing light beam.

Reference numeral 4 denotes a cylinder lens unit as a second optical element, which includes a glass cylinder lens 4a having a positive refractive power and a plastic cylinder lens 4b having a negative refractive power. The light beam passing through the aperture stop 3 is formed as a substantially linear image on a deflecting surface of an optical deflector to be described later in the sub-scanning section.

The optical axis M of the glass cylinder lens 4a in this embodiment is substantially parallel to the incident light beam incident on the cylinder lens 4a, and the optical axis L of the plastic cylinder lens 4b is
Is inclined by a predetermined amount in the main scanning plane with respect to the incident light beam incident on the main scanning plane. In addition, plastic cylinder lens 4
No antireflection film is formed on the lens surface (surface) b.

Reference numeral 5 denotes an optical deflector as a deflecting element, for example, a polygon mirror (rotating polygon mirror), which is rotated at a constant speed in a direction indicated by an arrow A in FIG.

Reference numeral 6 denotes an fθ lens (imaging optical system) composed of a single lens having fθ characteristics as a third optical element, and is formed of, for example, a plastic lens. A light beam based on the reflected image information is formed into a spot image on the photosensitive drum surface 8 as a surface to be scanned, and the deflection of the deflecting surface of the optical deflector 5 is corrected.

In the present embodiment, a divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam in the main scanning plane by a collimator lens 2, and the light beam (light amount) is restricted by an aperture stop 3 to a cylinder lens unit 4. Incident on The light beam incident on the cylinder lens unit 4 is emitted as it is in the main scanning section. In the sub-scan section, the light converges and is substantially a line image on the deflection surface 5a of the optical deflector 5 (a line image elongated in the main scanning direction).
As an image. The light beam deflected and reflected by the deflecting surface 5a of the light deflector 5 passes through the fθ lens 6 having different refractive powers in the main scanning direction and the sub-scanning direction, and the photosensitive drum surface 8
The light is guided upward, and the light deflector 5 is rotated in the direction of arrow A, whereby the photosensitive drum surface 8 is optically scanned in the direction of arrow B. Thus, an image is recorded on the photosensitive drum surface 8 as a recording medium.

As shown in FIG. 2, the cylinder lens unit 4 in this embodiment has a glass cylinder lens 4a having a positive refractive power and a plastic cylinder lens having a negative (concave) refractive power in the sub-scanning direction. 4b and the glass cylinder lens 4a as described above.
Is substantially parallel to the incident light beam incident on the cylinder lens 4a, and the optical axis L of the plastic cylinder lens 4b is within the main scanning plane with respect to the incident light beam incident on the cylinder lens 4b. At a predetermined angle. That is, the major axis of the plastic cylinder lens 4b in the main scanning direction (general line direction) is attached at an angle θ with respect to the major axis of the glass cylinder lens 4a in the main scanning direction (general line direction).

Since the plastic cylinder lens 4b in this embodiment does not have an anti-reflection film formed on the lens surface as described above, a part of the light beam is reflected by the lens surface as shown in FIG. Return light 21 is generated as shown by the broken line. After a part of the return light 21 is restricted by the aperture stop 3, the return light 21 passes through the collimator lens 2 again and returns to the direction of the semiconductor laser 1.

However, in the present embodiment, as described above, the plastic cylinder lens 4 is disposed within the main scanning plane.
Since the optical axis L of b is inclined by the angle θ with respect to the incident light beam, the return light 21 reflected by the lens surface (surface) of the cylinder lens 4 b is shifted from the light emitting point E of the semiconductor laser 1 by a certain amount. Return to When the focal length of the collimator lens 2 is f and the inclination angle of the optical axis L of the plastic cylinder lens 4b with respect to the incident light beam is θ, the displacement amount dy can be expressed as dy = f × tan2θ.

Generally, in consideration of the shape of the light emitting point of the semiconductor laser, it is desirable to set the shift amount dy of the return light to 0.1 (mm) or more. Therefore, in this embodiment, the optical axis L of the plastic cylinder lens 4b with respect to the incident light beam
Is set so as to satisfy the following condition: f × tan2θ> 0.1 ‥‥‥‥ (1)

Conditional expression (1) is for defining the inclination angle θ of the optical axis L of the plastic cylinder lens 4b in the main scanning plane with respect to the incident light beam. Return light reflected by the lens surface of the lens 4b is condensed in the vicinity of the light emitting point E of the semiconductor laser 1, causing a fluctuation in the amount of light, and a high-quality image cannot be obtained.

In this embodiment, the focal length of the collimator lens 2 is set to f = 16.0 (mm), and the inclination angle θ of the optical axis L of the plastic cylinder lens 4b to the incident light beam is set to 20 '. The semiconductor laser 1
The displacement amount dy of the return light 21 at the light emitting point E of
6 (mm), so that the return light 21 from the cylinder lens 4 b is emitted from the light emitting point E of the semiconductor laser 1.
The light quantity fluctuation is prevented by not returning to the vicinity.

In the present embodiment, the spot diameter of the return light 21 can be adjusted by moving the cylinder lens unit 4 by a predetermined amount in the optical axis direction.

In this embodiment, the case where surface reflection occurs on the incident surface of the plastic cylinder lens 4b and the light flux returns to the direction of the semiconductor laser 1 is shown. It can be considered almost the same as the above, and the effect of the present embodiment can be sufficiently exhibited.

As described above, in this embodiment, the inclination angle of the optical axis L of the plastic cylinder lens 4b with respect to the incident light beam in the main scanning plane with respect to the incident light beam is set so as to satisfy the conditional expression (1) as described above. Return light 2 from the cylinder lens 4b on which the anti-reflection film is not formed
1 can prevent a change in the amount of light of the semiconductor laser 1, thereby easily obtaining a high-quality image without shading.

FIG. 4 is a sectional view (main scanning sectional view) of a main part in the main scanning direction from the light source means to the optical deflector according to the second embodiment of the present invention. In the figure, the same elements as those shown in FIG. 3 are denoted by the same reference numerals.

This embodiment differs from the first embodiment in that the optical axis of the glass cylinder lens constituting the cylinder lens unit and the optical axis of the plastic cylinder lens coincide with each other. That is, the incident light beam incident on the cylinder lens unit is inclined by a predetermined amount in the main scanning plane. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numeral 14 denotes a cylinder lens unit, which includes a glass cylinder lens 14a having a positive refractive power and a plastic cylinder lens 14b having a negative (concave) refractive power in the sub-scanning direction. have. In the present embodiment, the optical axis of the plastic cylinder lens 14b and the optical axis of the glass cylinder lens 14a are made to coincide with each other, and the coincident optical axis L is main-scanned with respect to the incident light beam incident on the cylinder lens unit 14. It is inclined by an angle θ in the plane.

Since the plastic cylinder lens 14b in this embodiment does not have an anti-reflection film formed on the lens surface as in the first embodiment, a part of the light beam is not reflected as shown by the broken line in FIG. The light is reflected by the lens surface (surface), passes through the collimator lens 2 again, and returns to the direction of the semiconductor laser 1.

Therefore, in this embodiment, the optical axis L of the cylinder lens unit 14 is tilted by an angle θ with respect to the incident light beam in the main scanning plane with respect to the incident light beam, so that the plastic cylinder lens is formed. 14
The return light 21 reflected by the lens surface b is prevented from returning to the vicinity of the light emitting point E of the semiconductor laser 1.

That is, in this embodiment, the focal length of the collimator lens 2 is set to f = 16.0 (mm), and the inclination angle θ of the optical axis L of the cylinder lens unit 14 with respect to the incident light beam is set to 15 '. Thereby, the shift amount dy of the return light 21 at the light emitting point E of the semiconductor laser 1 is set to 0.140.
(mm), whereby the return light 21 from the plastic cylinder lens 14b is prevented from returning to the vicinity of the light emitting point E of the semiconductor laser 1, thereby preventing light amount fluctuation.

As described above, in the present embodiment, by appropriately setting the inclination angle of the optical axis L of the cylinder lens unit 14 with respect to the incident light beam in the main scanning plane so as to satisfy the conditional expression (1) as described above. Fluctuations in the amount of light of the semiconductor laser 1 due to the return light 21 from the plastic cylinder lens 14b on which the anti-reflection film is not formed can be prevented, thereby easily obtaining a high-quality image without density unevenness. .

Further, in this embodiment, the structure of the cylinder lens unit 14 can be simplified by matching the optical axis of the glass cylinder lens 14a with the optical axis of the plastic cylinder lens 14b.

FIG. 5 is a sectional view (main scanning sectional view) of a main part in the main scanning direction from the semiconductor laser to the optical deflector according to the third embodiment of the present invention. In the figure, the same elements as those shown in FIG. 3 are denoted by the same reference numerals.

The present embodiment differs from the first embodiment in that the cylinder lens unit is constituted by one plastic cylinder lens having a positive refractive power.
That is, the optical axis of the cylinder lens is inclined by a predetermined amount in the main scanning plane with respect to the incident light beam incident on the cylinder lens. Other configurations and optical functions are the same as those of the first embodiment.
This is substantially the same as described above, and thus, a similar effect is obtained.

That is, in the figure, reference numeral 24 denotes a cylinder lens unit having a single plastic cylinder lens 24b having a positive refractive power, and the optical axis L of the cylinder lens 24b is set to the cylinder lens 24.
b is inclined by an angle θ in the main scanning plane with respect to the incident light beam incident on b.

Also in this embodiment, as in the first embodiment, since the plastic cylinder lens 24b does not have an anti-reflection film formed on the lens surface, a part of the light flux as shown by the broken line in FIG. The light is reflected by the lens surface, passes through the collimator lens 2 again, and returns to the direction of the semiconductor laser 1.

Therefore, in this embodiment, the optical axis L of the plastic cylinder lens 24b is inclined by an angle θ with respect to the incident light beam in the main scanning plane while satisfying the conditional expression (1). The return light 21 reflected by the lens surface 24b is prevented from returning to the vicinity of the light emitting point E of the semiconductor laser 1.

That is, in this embodiment, the focal length of the collimator 2 is set to f = 16.00 (mm), and the inclination angle θ of the optical axis L of the plastic cylinder lens 24b with respect to the incident light beam is set to 15 ′. By the semiconductor laser 1
The displacement amount dy of the return light 21 at the light emitting point E is 0.14.
0 (mm), so that the return light 21 from the cylinder lens 24 b does not return to the vicinity of the light emitting point E of the semiconductor laser 1, thereby preventing light amount fluctuation.

As described above, in this embodiment, the inclination angle of the optical axis L of the plastic cylinder lens 24b with respect to the incident light beam in the main scanning plane with respect to the incident light beam is set so as to satisfy the conditional expression (1) as described above. As a result, it is possible to prevent a change in the amount of light of the semiconductor laser 1 due to the return light 21 from the cylinder lens 24b on which the anti-reflection film is not formed, thereby easily obtaining a high-quality image without density unevenness. .

[0046]

According to the present invention, as described above, the optical axis of the plastic optical element (cylinder lens) is tilted by a predetermined amount with respect to the light beam incident on the optical element, whereby the light from the plastic optical element can be reduced. It is possible to prevent a change in the amount of light of the semiconductor laser due to the return light, thereby achieving a cylinder lens unit capable of easily obtaining a high-quality image without density unevenness and a scanning optical device using the same.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a perspective view of a main part of the cylinder lens unit shown in FIG. 1;

FIG. 3 is a cross-sectional view of a main part in a main scanning direction from a light source unit to an optical deflector according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a main part in a main scanning direction from a light source unit to an optical deflector according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a main part in a main scanning direction from a light source unit to an optical deflector according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a main part of a conventional scanning optical device in a main scanning direction.

[Explanation of symbols]

Reference Signs List 1 light source means (semiconductor laser) 2 first optical element (collimator lens) 3 stop 4, 14, 24 second optical element (cylinder lens unit) 4a, 14a glass cylinder lens 4b, 14b plastic cylinder Lens 24b Plastic cylinder lens 5 Deflection element (optical deflector) 6 Third optical element (fθ lens) 8 Scanned surface (photosensitive drum surface) 21 Return light

Claims (8)

[Claims] 1. A cylinder lens unit having a plastic cylinder lens and a glass cylinder lens, wherein the major axis of the plastic cylinder lens in the generatrix direction is the major axis of the glass cylinder lens in the generatrix direction. A cylinder lens unit that is tilted toward. 2. A cylinder lens unit having a plastic cylinder lens, wherein an optical axis of the plastic cylinder lens is inclined with respect to a light beam incident on the cylinder lens. 3. A light beam emitted from a light source means is converted into a substantially parallel light beam in a main scanning plane via a first optical element, and the converted substantially parallel light beam is deflected via a second optical element. The light beam deflected and reflected by the deflecting element is imaged into a spot on the surface to be scanned via a third optical element, and the image is formed on the deflecting surface. In a scanning optical apparatus that scans a scanning surface, the second optical element has at least one plastic optical element, and an optical axis of the optical element is a main scanning light beam incident on the optical element. A scanning optical device which is inclined in a plane. 4. Assuming that a focal length of the first optical element is f and an inclination angle of an optical axis of the plastic optical element with respect to an incident light beam is θ, a condition of f × tan2θ> 0.1 is satisfied. 4. The scanning optical device according to claim 3, wherein: 5. The apparatus according to claim 3, wherein the second optical element includes a glass cylinder lens having a positive refractive power and a plastic cylinder lens having a negative refractive power. Or the scanning optical device according to 4. 6. The scanning optical device according to claim 5, wherein an optical axis of said glass cylinder lens and an optical axis of said plastic cylinder lens coincide with each other in a main scanning plane. 7. The scanning optical apparatus according to claim 3, wherein the second optical element has one plastic cylinder lens having a positive refractive power. 8. The scanning optical device according to claim 5, wherein the second optical element is movable in an optical axis direction.