JP3206996B2 - Optical scanning device - Google Patents

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 using a laser beam used for a laser printer, a laser fax, a digital copier, and the like.

[0002]

2. Description of the Related Art Generally, in a laser printer, recording information is placed on a laser beam from a semiconductor laser, and the laser beam is deflected and scanned by an optical system to converge on a charged photoreceptor surface as an image forming surface. The body is exposed to light and recorded information is recorded as an electrostatic latent image on the photoreceptor. The electrostatic latent image is then developed with toner, and further transferred to paper at a transfer unit.

[0003] As an optical scanning device used in such an apparatus, for example, a polygon mirror is rotated so as to deflect and scan a laser beam. As a device for deflecting and scanning laser light using such a polygon mirror,
For example, a pre-object type using an fθ lens is known.

As shown in FIG. 13, a semiconductor laser 1 is used as a light source, a laser beam from the semiconductor laser 1 is converted into a parallel light through a collimator lens 2, and the parallel light is polygonally controlled. The mirror 3 irradiates the mirror 3 with scanning light, and the scanning light is reflected by the reflection mirror 5 via the fθ lens 4 and then irradiated on the photosensitive drum 7 via the cylindrical lens 6.

[0005] Further, as one not using a polygon mirror, for example, one disclosed in JP-A-1-131513 is known. This is as shown in FIG.
1, a pyramidal mirror 12 is rotatably provided, and the pyramidal mirror 12 is surrounded by a cylindrical slit member 13. A circular slit 14 at the bottom of the slit member 13
And a rectangular slit 15 is provided in a portion of the peripheral surface facing the reflection surface of the pyramidal mirror 12. And
As shown in FIG. 14 , the laser light L from the semiconductor laser unit 16 is made incident on the circular slit 14 of the deflector 11 and reflected on the reflecting surface of the pyramidal mirror 12, and the reflected light is emitted from the rectangular slit 15 as scanning light. . Then, the scanning light is reflected by the reflection mirror 1 through the fθ lens 17.
The light is reflected on the photosensitive drum 20 via the toroidal lens 19. Reference numerals 21 and 22 denote an optical fiber and a photosensor for taking out synchronous light for determining a writing position.

[0006]

The polygon mirror was manufactured by a method of applying an aluminum reflective film to a glass polished product, so that it was considerably expensive. The cost can be greatly reduced by the method of drawing. However, even if the cost can be reduced, the cutting of the polygon mirror requires a special processing machine and the required accuracy is extremely high, so it accounts for more than 10% of the total cost of the optical scanning device and the fundamental cost It was difficult to achieve the decline. In addition, since the polygon mirror has a plurality of reflecting surfaces, surface tilt due to a processing error of each reflecting surface occurs. Therefore, an optical system for correcting surface tilt is required, and the fθ lens 4 and the cylindrical lens 6 are used.

As described above, in the case of using the former polygon mirror 3, a special processing machine is required for cutting the polygon mirror 3, and the required accuracy becomes extremely high.
In addition, since a surface tilt due to a processing error of each reflecting surface occurs, the fθ lens 4 and the cylindrical lens 6 must be disposed for correcting the surface tilt, and the reflection mirror 5 and the cylindrical lens 6 There is a problem that the cost increases and the configuration becomes complicated and large due to the close arrangement.

[0008] The latter type, which does not use a polygon mirror, has only one reflecting surface, so that there is no problem such as a demand for processing accuracy or surface inclination. However, the fθ lens 17 and the toroidal lens 19 are arranged, and the reflecting mirror is provided. Since the lens 18 and the toroidal lens 19 are arranged near the photosensitive drum 20, there is a problem that the configuration becomes complicated and the size becomes large similarly to the former.

Accordingly, the present invention can reduce the size with a simple structure and can provide a highly accurate deflection with respect to the image plane.
It is intended to provide an optical scanning device that can scan.

[0010]

[0011]

The invention corresponding to claim 1 is:
A laser light emitting means for emitting laser light, and a motor rotated by the motor, and the laser light from the laser light emitting means is incident parallel to the rotation axis of the motor and with the central axis away from the rotation axis, and the incident laser light is A reflector having a plurality of reflecting surfaces that reflects in a direction perpendicular to the rotation axis of the motor and deflects and scans a plane in the direction perpendicular to the axis by rotation, and provided near this reflector, and deflects light from the reflector. It comprises a meniscus lens that is convex with respect to the image forming surface that converges on the image forming surface. The meniscus lens sets the radius of curvature of the exit surface smaller than the incident surface and sets the deflected light at a scan angle of 0 °.
Deflected light is on the image plane with respect to the center of this lens
The convex direction of the curve of the scanning locus drawn to those arranged such that the position separated a predetermined distance in the opposite direction.

[0012]

[0013]

In the present invention having such a configuration, the laser beam from the laser beam emitting means is converted into a slightly divergent light beam, and is then deflected and scanned by the reflector. The deflected light passes through a meniscus lens that is convex with respect to the image forming surface whose exit surface has a smaller radius of curvature than the incident surface, and is condensed on the image forming surface. This reduces the variation in the beam diameter of the deflecting light on the image plane.

In the present invention, the laser beam from the laser beam emitting means is incident on the reflector parallel to the rotation axis of the motor and with the central axis away from the rotation axis. The reflector reflects the incident laser light in a direction perpendicular to the rotation axis of the motor, and deflects and scans the plane by rotation in a direction perpendicular to the rotation axis of the motor. The deflected light from the reflector enters the meniscus lens at a predetermined distance away from the center of the lens in the direction opposite to the convex direction of the curve drawn by the scanning trajectory of the deflected light from the reflector, and passes through the meniscus lens. The deflected light condenses on the image plane. As a result, the scanning bending amount of the deflecting light on the image plane is reduced.

[0015]

An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 to 3, a laser beam from a semiconductor laser oscillator 31 is converted into a slightly divergent light beam by a converging lens 32, and then formed into a circular beam by a slit 33. After changing the optical path at right angles by reflecting the light, the rotor 35a of the scanner motor 35
The two 45-degree reflecting surfaces of the right-angle prism 36 as a reflector disposed on the rotation axis 35b are illuminated. That is, the right-angle prism 36 has two surfaces orthogonal to each other as reflection surfaces, and the center of the remaining surfaces is arranged in accordance with the rotation axis 35b of the scanner motor 35. The rotating shaft 3 is separated from the rotating shaft 35b of the scanner motor 35 by about several mm.
5b.

The scanner motor 35 has a magnet 35c integrally attached to a rotor 35a. The rotating shaft 3
5b is rotatably attached to the stator member 35d via a ball bearing 35e. The stator member 35
d, a circuit board 35g is fixed via a spacer 35f,
A coil 35h is mounted on the back surface of a portion of the circuit board 35g facing the magnet 35c.

The right-angle prism 36 is connected to the scanner motor 3.
5, the light reflected from the reflection mirror 34 is reflected by a reflection surface, and the rotation axis 35b of the scanner motor 35 is rotated.
Is deflected and scanned in a plane direction perpendicular to. The deflected light from the right-angle prism 36 is incident on a meniscus lens 37 having a smaller radius of curvature on the exit surface than the incident surface disposed in the vicinity, and convex toward the image forming surface.

The polarized light passing through the meniscus lens 37 forms an image on an image forming surface, for example, a photosensitive surface of a photosensitive drum.

The semiconductor laser oscillator 31, the converging lens 32 and the slit 33 are integrated as a light emitting unit 38, and the meniscus lens 37 is incorporated in a case 39.

Then, the light emitting unit 38 is fitted into the upper rear of a casing 40 surrounding the entire device made of, for example, synthetic resin, and the reflecting mirror 34 is embedded in an upper front inclined portion of the casing 40. The case 39 is connected to the housing 4
No. 0 is screwed together with the front opening. The housing 40 has a flange portion connected to the scanner motor 35.
Is fixed to the peripheral portion of the stator member 35d by screws.

In the embodiment having such a configuration, the laser beam from the semiconductor laser oscillator 31 is converted into a slightly divergent light beam by the converging lens 32, and then a circular beam is formed by the slit 33. This beam is reflected by the reflection mirror 34, changes the optical path at right angles, and irradiates the reflection surface of the right-angle prism 36 disposed on the rotation axis 35b of the scanner motor 35.

The right-angle prism 36 is rotated by a scanner motor 35, and deflects and scans an incident laser beam by a reflection surface. The deflected light passes through the meniscus lens 37 and forms an image on the photosensitive surface of the photosensitive drum.

As shown in FIG. 4, the radius of curvature of the entrance surface of the meniscus lens 37 is rin (mm), the radius of curvature of the exit surface is rout (mm), and the meniscus is shifted from the deflection point (the reflection point of the right-angle prism 36). The distance from the plane of incidence to the lens 37 is a (mm), the thickness of the meniscus lens 37 is t (mm), and the distance from the deflection point to the image plane (photosensitive surface of the photosensitive drum) is L.
(Mm), and the deflection angle of the right-angle prism 36 is θ (deg).

Since the laser beam from the semiconductor laser oscillator 31 is converted into a slightly divergent light beam by the converging lens 32 and then enters the meniscus lens 37, as shown in FIG. Let Lcnv (mm) be the distance between the apparent light emitting point P and the deflection point.

As a result, the results shown in Table 1 were obtained. In this table, NO. 1 to NO. 16 is a meniscus lens 37
To glass (BK7; n, λ = 780 nm, 1.5114
This is an example in the case of the configuration of FIG. 17 to NO. 2
Reference numeral 5 indicates that the meniscus lens 37 is made of an acrylic resin (n, λ = 7).
80 nm, 1.48601).

[0027]

[Table 1] As can be seen from this table, the deflection angle θ is 70 (deg) to 1
In 00 (deg), as θ increases, a, r
Both in and rout become smaller.

The meniscus lens 37 is made of glass, the deflection angle is set to 70 degrees, and the lens thickness t is set to 5-1.
NO. When changed to 0 mm. 1 to NO. 7 results were obtained. That is, a = 15 to 17 mm, rin = −77 to −
83 mm, rout = -31 to -34 mm, L = 211 to 22
When 3 mm and Lcnv = -189 to -218 mm, it was found that the entire apparatus can be made substantially the same size as the diameter of the scanner motor 35, and the entire apparatus can be sufficiently miniaturized.

Furthermore, if this apparatus is used, there is no need to interpose various lenses between the meniscus lens 37 and the image plane, and the beam diameter variation on the image plane can be reduced.

As described above, it is possible to reduce the size of the apparatus and stabilize the beam on the image plane.

For example, NO. 2 is 2mm x 2
When simulating a beam with a diameter of mm,
The spot diameter at a deflection angle of 0 deg is 12.0265 μm (diameter in the main scanning direction) × 12.0265 μm (diameter in the sub-scanning direction)
The spot diameter at a deflection angle of 5deg is 9.98563 μm × 10.581
9 μm, and the spot diameter at a deflection angle of 10deg is 6.06.
588 μm × 6.6858 μm, the spot diameter at a deflection angle of 15 deg is 9.32646 μm × 5.69855 μm, and the spot diameter at a deflection angle of 20 deg is 18.9335 μm × 15.0884
μm, and the spot diameter at a deflection angle of 25deg is 28.850.
1 μm × 25.7444 μm, the spot diameter at a deflection angle of 30 deg is 33.4721 μm × 35.5764 μm, and the spot diameter at a deflection angle of 35 deg is 27.6386 μm × 42.6738 μ
m.

Note that the simulation value here indicates a geometrical convergence state, and cannot be narrowed down to the wave optics.

FIG. 2 shows a simulation state for the second embodiment.

Further, in this apparatus, since the variation in the beam diameter is reduced with emphasis on the field curvature correction, the fθ characteristic is slightly deteriorated. Therefore, it is necessary to perform the fθ correction. However, the fθ correction can be performed electrically. it can.

Further, NO. 1 to NO. 25, a =
12 to 23 mm, rin = -63 to -86 mm, rout = -2
3 to -34 mm, θ = 70 to 100 deg, L = 150 to 2
It was found that the whole device could be sufficiently miniaturized when 23 mm and Lcnv = -129 to -218 mm.

Only a structure in which a right-angle prism 36 is fixed on a rotating shaft 35b of a scanner motor 35, and a case 39 containing a light emitting unit 38, a reflecting mirror 34 and a meniscus lens 37 is mounted at a predetermined position of a housing 40 In addition, since no lens or reflecting mirror is used, the configuration is simple.

[0037]

Next, another embodiment of the present invention will be described with reference to the drawings. The same parts as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 7 shows a semiconductor laser oscillator 3.
1. A light emitting unit 41 in which a converging lens 32 and a slit 33 are integrally housed is attached to the center of the top of a housing 42, and the laser light from the semiconductor laser oscillator 31 is converted into a divergent light beam by the converging lens 32. After, slit 3
The beam is formed into a circular beam by 3 and the beam is directly applied to the reflecting surface of the right-angle prism 36 disposed on the rotation axis 35b of the rotor 35a of the scanner motor 35. The deflected light from the reflection surface of the right-angle prism 36 is used for the meniscus lens 3 incorporated in the case 39.
7, an image is formed on an image forming surface, for example, a photosensitive surface of a photosensitive drum. The case 39 is the case 4
2 and is supported and fixed by a support table 43 fixed to the support table 2.

In this embodiment, there is no need for a reflecting mirror for reflecting a circular beam obtained through the slit 33, so that the structure can be simplified and the device can be made more compact.

Thus, also in this embodiment, it is possible to reduce the size of the apparatus and stabilize the beam on the image plane, and to obtain the same effects as in the above embodiment.

FIG. 8 shows a meniscus lens 37.
The positioning of the case 39 containing the
When the scanning angle of the deflection light from the right-angle prism 36 is 0 °, the incident position is such that the deflection light from the right-angle prism 36 is drawn on the photosensitive surface with respect to the center O of the meniscus lens 37.
Deflection from the right-angle prism 36 at a position separated by a predetermined distance in the direction opposite to the convex direction of the scanning trajectory curve , in other words,
Scanning trajectory that light draws on the entrance surface of the meniscus lens 37
It is performed so as to be located at a predetermined distance in the same direction as the convex direction of the trace curve . That is, the case 39 is arranged so that the incident position of the deflecting light on the meniscus lens 37 is located below the center of the meniscus lens 37.

In this embodiment, as shown in FIG. 9A, when the right-angle prism 36 is at the position indicated by the solid line in the figure, that is, when the deflected light from the right-angle prism 36 enters the center of the meniscus lens 37. Indicates that the incident laser light I is emitted in the direction of the reflected light R, and when the right-angle prism 36 is at the position shown by the dotted line in the figure, the incident laser light I is emitted in the direction of the reflected light R '. At the position indicated by the two-dot chain line, the incident laser light I is emitted in the direction of the reflected light R ". At this time, the position of the laser light I incident on the reflecting surface of the right-angle prism 36, that is, the position of the deflection point is shown in FIG.
As shown in FIG. 9B, when the scanning angle of the deflected light is 0 ° (FIG. 9).
(In the case of the solid line in FIG. 9A), the position of the point a is obtained. However, when the reflection surface is rotated and the scanning angle is increased (in the case of the dotted line and the two-dot chain line in FIG. Position, the deflection point position becomes higher.

As a result, the scanning trajectory of the deflected light incident on the meniscus lens 37 is as shown in FIG. 9C, and it is convex downward with respect to the position of the scanning angle 0 °, that is, as it goes to the scanning end. It becomes a quadratic curve that curves upward.

The direction of the deflected light is reversed by the meniscus lens 37. That is, the scanning trajectory of the deflecting light reaching the photosensitive surface is a quadratic curve convex upward.

The incident position of the deflecting light on the meniscus lens 37 is set at a scanning angle of 0 ° as shown in FIG.
In this case, the deflection light at the scanning angle of 0 ° (when the position of the deflecting point with respect to the reflecting surface of the right-angle prism 36 is the position indicated by the solid line in the figure) is deflected by the meniscus lens. When the scanning angle is large (when the position of the deflection scanning point with respect to the reflection surface of the right-angle prism 36 is the position indicated by the dotted line in the figure), the deflected light is bent downward by the passage of the meniscus lens 37. However, the amount of bending is small. As a result, even if the scanning trajectory of the deflecting light reaching the photosensitive surface becomes a quadratic curve convex upward, the amount of bending is considerably small. Therefore, laser beam scanning can be performed in a form close to a straight line with respect to the photosensitive surface (imaging surface), and highly accurate deflection scanning can be performed.

On the other hand, when the incident position of the deflected light on the meniscus lens 37 is made to coincide with the lens center O when the scanning angle is 0 ° as shown in FIG. The deflection light at 0 ° passes through the meniscus lens 37 as it is, and the deflection light at a large scanning angle is greatly bent downward by passing through the meniscus lens 37, so that the scanning of the deflection light reaching the photosensitive surface is performed. The trajectory is a quadratic curve that is largely convex upward. That is, the amount of curvature of the scanning line increases.

In the drawing, δ1 indicates the off-axis amount which is the distance between the rotation center of the scanner motor 35 and the deflection point, δ2 indicates the off-axis amount of the meniscus lens 37, and δ3 and δ4 indicate the scanning line bending amounts. Is shown.

For example, the off-axis amount δ1 is 2 mm, the thickness of the meniscus lens 37 is 7 mm, the radius of curvature of the entrance surface is -7.77.5374 mm, and the radius of curvature of the exit surface is -2.
Use a meniscus lens 37
As a result of an experiment in which the lens incident surface coordinate with respect to is 16.5547 and the maximum scanning angle is 90 °, when the off-axis amount δ2 is approximately 2 mm, the scanning line curvature δ3 is 166.974.
When the off-axis amount .delta.2 was set to 0 mm, the scanning line bending amount .delta.4 was 547.432 .mu.m.

As described above, by setting the off-axis amount of the meniscus lens 37 to approximately 2 mm, the amount of scanning line bending can be suppressed to 1/3 or less as compared with the case where the off-axis amount is 0 mm.

Here, the radius of curvature of the entrance surface of the meniscus lens 37 is rin (mm) and the radius of curvature of the exit surface is rout (m).
m), the distance from the deflection point (the reflection point of the right-angle prism 36) to the entrance surface to the meniscus lens 37 is a (mm), the thickness of the meniscus lens 37 is t (mm), L (mm), the deflection angle of the right-angle prism 36 is θ (deg), and the distance between the apparent light emitting point P and the deflection point when the converging lens 32 is not provided is Lcnv (mm). Table 2 shows the relationship between the off-axis amount δ1 and the off-axis amount δ2 of the meniscus lens 37.
The result shown in FIG.

[0052]

[Table 2] For example, in the case of Sample 1 in Table 2, the radius of curvature of the entrance surface of the meniscus lens 37 is rin = -77.537 mm, the radius of curvature of the exit surface is rout = -28.419 mm, and the distance from the deflection point to the entrance surface to the meniscus lens 37 Is a = 16.5547 mm,
The thickness t of the meniscus lens 37 is 7 mm, the distance L from the deflecting point to the image plane is 171.392 mm, the deflection angle θ by the right-angle prism 36 is 90 deg, and the apparent distance between the light emitting point P and the deflecting point is Lcnv = -166.248mm, Off-axis amount δ1 = 2.0m
m, the beam diameter on the image plane and the meniscus lens 37
When the relationship with the off-axis amount δ2 was examined, the beam diameter in the main scanning direction was as shown by a solid line graph g1 in FIG.
The beam diameter in the sub-scanning direction is indicated by a dotted line graph g2 in FIG.
When, for example, the target values of the beam diameter in the main scanning direction and the beam diameter in the sub-scanning direction are set to 60 μm or less,
The effective area is the area range shown in the figure.

The relationship between the amount of scan line curvature δ3 on the image forming surface and the off-axis amount δ2 of the meniscus lens 37 was examined. The result is shown in a graph g3 of FIG. 12, and for example, the target value of the amount of scan line curvature δ3 Is 200 μm or less, the effective area is the area range shown in the figure.

When the effective area shown in FIG. 11 is superimposed on the effective area shown in FIG. 12, the common effective area becomes an area indicated by oblique lines in the figure. That is, if the off-axis amount δ2 of the meniscus lens 37 is set within this common effective area, the beam diameter in the main scanning direction and the beam diameter in the sub-scanning direction on the image forming surface will be 60 μm or less, and the scanning line curvature amount δ3 will be 200 μm. It is as follows. Then, the optimal off-axis amount Δ2 was determined from the relationship between the beam diameter and the scanning line curvature amount Δ3. As a result, Δ2 = 1.980 mm. Thus, the off-axis amount δ2 of the sample 1 is determined.

Samples 2 to 4 in Table 2 can be similarly determined.

By setting the off-axis amount δ2 of the meniscus lens 37 in this way, the amount of scan line curvature δ3 on the image plane can be made sufficiently small, and the beam diameter can be made small. High deflection scanning can be performed.

In this embodiment, the size of the apparatus can be reduced and the beam can be stabilized on the image plane, and the same effects as in the above embodiment can be obtained.

In each of the above embodiments, the use of a right-angle prism as a reflector has been described. However, the present invention is not limited to this, and may be an isosceles reflection prism, a deflection mirror, or the like.

As described above, according to the present invention, downsizing can be achieved with a simple configuration , and moreover, high precision can be achieved with respect to the image plane.
There deflection scanning Ru can.

[0060]

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the present invention with a housing omitted.

FIG. 2 is a sectional view taken along the line AA in FIG. 1;

FIG. 3 is a front view of the embodiment.

FIG. 4 is a diagram showing a relationship between a radius of curvature, a deflection point, and an image forming surface of the meniscus lens of the embodiment.

FIG. 5 is a diagram showing a relationship among a meniscus lens, a deflection point, and an apparent light emitting point in the embodiment.

FIG. 6 is a view showing an example of a simulation state in the embodiment.

FIG. 7 is a sectional view showing another embodiment of the present invention.

FIG. 8 is a sectional view showing another embodiment of the present invention.

FIG. 9 is a view for explaining scanning bending of the deflection light in the embodiment.

FIG. 10 is a view for explaining the relationship between the scanning angle of the deflecting light, the center position of the meniscus lens, and the amount of scanning curvature in the embodiment.

FIG. 11 is a graph showing the relationship between the beam diameter on the image plane and the off-axis amount δ2 of the meniscus lens in the case of Sample 1 in the same embodiment.

FIG. 12 shows a scanning line curvature amount δ3 and an off-axis amount δ of the meniscus lens on the image plane in the case of Sample 1 in the same embodiment.
Graph showing the relationship with 2.

FIG. 13 is a perspective view showing a conventional example.

FIG. 14 is a configuration diagram showing another conventional example.

FIG. 15 is a diagram showing a configuration of a conventional deflector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 31 ... Semiconductor laser oscillator 32 ... Convergent lens 35 ... Scanner motor 36 ... Right angle prism 37 ... Meniscus lens

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 1-211718 (JP, A) JP-A 64-111222 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 26/10

Claims (1)

(57) [Claims] 1. A laser light emitting means for emitting laser light, which is rotated by a motor, and receives laser light from the laser light emitting means in parallel with a rotation axis of the motor and with a central axis separated from the rotation axis. A reflector having a plurality of reflecting surfaces that reflects the incident laser light in a direction perpendicular to the rotation axis of the motor and deflects and scans a plane in the perpendicular direction by rotation, and is provided near the reflector, It comprises a meniscus lens that is convex with respect to the image plane that converges the deflected light from the reflector on the image plane, and the meniscus lens sets the radius of curvature of the exit surface smaller than the entrance surface and sets the scanning angle. 0 position incident position of the deflected light is that a predetermined distance in a direction opposite to the convex direction of the curve of the scanning locus which the deflected light is drawn on the image plane with respect to the lens <br/>'s center in °
Optical scanning apparatus characterized by the arranged such that.