JP3385766B2 - Light beam 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 a light beam scanning apparatus, and more particularly to an electrophotographic apparatus such as a laser printer, a laser copying machine, a laser facsimile machine or the like, in which a light beam is deflected by a reflection type optical deflector to be recorded on a recording medium. The present invention relates to a light beam scanning device for scanning.

[0002]

2. Description of the Related Art In recent years, laser beam printers (hereinafter referred to as "LBP") have attracted attention due to their advantages such as good image quality and high-speed printout. This LB
The light beam scanning device can be said to be the heart of P, and the performance of this light beam scanning device largely determines the quality of the image quality of the LBP. For high-speed printout, it is necessary to rotate a polygon mirror (rotary polygon mirror) applied as a reflection type optical deflector at high speed. At this time, if the surrounding air is not clean, the mirror surface that reflects the light beam becomes dirty and the image quality is adversely affected. Further, the vibration due to the rotation of the polygon mirror may cause noise. Therefore, it is necessary to cover the polygon mirror with a shielding cover for soundproof and dustproof. In addition, the shielding cover is provided with an opening for passing a light beam, and a plate glass is so-called fitted to the opening so as to prevent the soundproof and dustproof effect from being deteriorated due to the opening.

However, with the above configuration, the reflectance R _s of the S-polarized component of the light beam tends to increase as the incident angle θ of the light beam incident on the mirror surface of the polygon mirror increases, and the light amount distribution becomes inconsistent. There is a problem in that the image quality becomes uniform and the recording image quality deteriorates.

Conventionally, as a measure for solving such a problem, the technique disclosed in Japanese Patent Laid-Open No. 1-131516 is known. The contents of the technique according to Japanese Patent Laid-Open No. 1-131516 will be described below with reference to FIG.

In FIG. 1, a light beam L emitted from a laser light source 2 passes through a plate glass 42 and is deflected by a polygon mirror 36 as a reflection type light deflector to be a deflected light beam (hereinafter referred to as "deflected beam") L. It again passes through the plate glass 42 and is focused by the scanning lens 6 onto a recording medium (not shown). Since the polygon mirror 36 is rotating in the direction of the arrow in the figure, the deflected beam L is reflected by the laser light source 2.
The direction is changed so as to sweep over a plane (meridional plane) including the light beam incident from the and the optical axis of the scanning lens 6, and the recording medium is scanned in the main scanning direction. Image recording and the like is performed by moving the recording medium and scanning in the sub-scanning direction.

Further, as shown in FIG. 1, the plate glass 4
2 is inclined such that the line where the surface of the plate glass 42 irradiated with the light beam (hereinafter referred to as “incident surface”) intersects the meridional plane has a predetermined angle with respect to the optical axis LL of the scanning lens 6. It is arranged. Therefore, when the plate glass 42 is not tilted, the change in the optical path length in the plate glass 42 is small and the transmittance T _s of the plate glass of the S deflection component of the light beam is kept substantially constant. ,
The change of the optical path length in the plate glass 42 becomes large, and the transmittance T _s increases.
The fluctuation range of can be increased. Moreover, as the incident angle θ of the light beam on the mirror surface is larger and the reflectance R _s is larger, the incident angle of the deflected beam on the plate glass is larger and the transmittance T _s is larger.
Also tends to be smaller. Therefore, by appropriately setting the inclination angle of the plate glass 42, the change in the reflectance R _s of the polygon mirror can be canceled by the change in the transmittance T _s of the plate glass.

As described above, according to the conventional method, the plate glass is tilted so that the line where the incident surface of the plate glass and the meridional plane intersect with each other forms a predetermined angle with respect to the optical axis of the scanning lens. The change in the reflectance and the change in the transmittance of the plate glass are canceled out to make the light quantity distribution of the deflected beam uniform and prevent the deterioration of the image quality.

[0008]

However, in the above-mentioned conventional technique, the reflectance of the polygon mirror is offset by simply utilizing the difference in the incident angle of the deflected beam in the scanning direction of the plate glass and the angular dependence of the transmittance. However, there is a problem that the shield cover and the plate glass that cover the periphery of the polygon mirror become large due to the necessity of widening the incident angle range. Further, if the shielding cover and the plate glass become large and the angle of inclination of the plate glass becomes large, the polygon mirror and the scanning lens for converging the deflected beam on the recording medium cannot necessarily be arranged close to each other, which makes the device large. However, there was a problem in that the cost would be too high due to the cost reduction.

Further, since the incident angle range is large, when the inexpensive single coating is applied to the glass plate, the transmittance of the beam passing through the glass plate offsets the reflectance as the image end area in the main scanning direction is scanned. There is also a problem that the image quality in the vicinity of the image end area in the main scanning direction deteriorates because it becomes excessively low.

In consideration of the above facts, the present invention provides a light beam scanning device capable of suppressing the light amount distribution of a light beam, reducing the incident angle range of a deflected beam on a plate glass, and arranging a polygon mirror and a plate glass close to each other. The first purpose is to provide.

A second object of the present invention is to provide a light beam scanning device in which the shield cover and the plate glass are made as small as possible under given conditions.

[0012]

In order to achieve the first object, the invention described in claim 1 is a reflection type optical deflector for reflecting and deflecting a light beam, and a light beam after the reflection and deflection is transmitted. A plate-shaped body, in a light beam scanning device for scanning a light beam transmitted through the plate-shaped body on a meridional plane through a scanning lens by reflection deflection, the plate-shaped body,
The angle formed by the line formed by the plane of incidence of the plate and the meridional plane and the optical axis of the scanning lens is a predetermined value other than 90 degrees, and the plane of incidence of the plate is The angle with the meridional plane is 45 degrees or more 80
The feature is that it is arranged so as to be less than or equal to the degree.

In order to achieve the second object, the invention according to claim 2 is a reflection type optical deflector for reflecting and deflecting a light beam, and the reflection type optical deflector having an opening. A shield cover disposed so as to cover the plate, and a plate-like member fitted in the opening so that the incident light beam and the deflected beam that is the deflected and deflected light beam can be transmitted. In the light beam scanning device that scans on a meridional plane via a scanning lens, the plate-shaped body is
The plane of incidence of the plate and the meridional plane intersect
Angle formed by the line formed by
It becomes a predetermined value other than 90 degrees, and the incident surface of the plate-like body
And the angle between the meridional plane is 45 degrees or more 80
The plate-like body is arranged so that
An incident beam incident on the reflection-type optical deflector is transmitted through one of the boundary portions of the plate-like body, which is closest to the shielding cover and located in the meridional plane, and
The outermost light beam of the deflected beam passes through the other boundary portion and is fitted into the shielding cover so as to have a predetermined clearance with the reflection surface of the reflection type light deflector.

[0014]

According to the first aspect of the invention, the light-transmissive plate-like member, for example, the plate glass, fitted in the opening of the shield cover for covering the reflection type light deflector is arranged as follows. .

That is, the angle between the optical axis of the scanning lens and the line formed when the plane of incidence of the plate-shaped body intersects the meridional plane containing the optical axis of the scanning lens and the incident light beam is other than 90 degrees. It is tilted to a predetermined value of
The plate-shaped body is arranged so as to be inclined such that the angle of incidence with the meridional plane is 45 degrees or more and 80 degrees or less. That is, the plate-shaped body is tilted in two directions, the scanning direction and the non-scanning direction.

Therefore, the optical path length in the plate-like body changes by an amount obtained by combining the optical path length change due to the inclination in the scanning direction and the optical path length change due to the inclination in the non-scanning direction. Therefore, when the incident surface of the plate-shaped body is orthogonal to the optical axis of the scanning lens,
The change width of the optical path length is small and the transmittance T _s is kept substantially constant. On the other hand, when tilted in two directions, the change width of the optical path length in the plate-like body becomes large, and therefore the transmittance T _s of The range of change becomes large. For example, when the incident beam is incident on the mirror surface at a large incident angle, and thus the reflectance R _s is large, the incident angle of the deflected beam on the plate is larger, and the transmittance T _s is the tilt of the plate. It tends to be smaller than when it is not present.

As described above, in the present invention, since the change in the optical path length is combined by inclining the plate member in two directions, the optical path length can be increased even if the inclination in each direction is reduced. You can Therefore, even in a smaller incident angle range, the fluctuation range of the transmittance that cancels the fluctuation of the reflectance R _s can be achieved. That is, it is possible to keep the incident angle range small while maintaining the effect that the light amount of the deflected beam is kept substantially constant. Therefore, there is no need to increase the angle of incidence on the plate-like member and to apply the expensive multi-coating to the plate-like member, and there is an advantage that an inexpensive single coating is sufficient.

When the inclination in the non-scanning direction in the present invention exceeds 80 degrees, the change in the optical path length does not increase so much. On the contrary, when it is less than 45 degrees, a problem such as a large shield cover occurs. Therefore, as described above, it is preferably 45 degrees or more and 80 degrees or less.

According to the second aspect of the present invention, there is provided a shielding cover having an opening for covering the polygon mirror, and a light-transmissive plate member is fitted in the opening.

That is, the light beam incident on the polygon mirror is transmitted through one boundary portion which is closest to the shield cover in the plate-like body and is in the meridional plane, and the outermost light beam of the deflected beam is , The plate-like body is fitted in the opening of the shielding cover so as to pass through the other boundary portion and to have a predetermined clearance with the reflecting surface of the polygon mirror.

Therefore, the size of the minimum required plate-like body and the shielding cover is determined under given conditions, and the clearance is set to 1 to 2 mm, especially about 2 mm, so that in addition to soundproofing and dustproofing. The effects of preventing heat generation due to windage and facilitating the work of attaching the shield cover can be obtained.

Further , as described above, the opening portion of the shielding cover
The plate-shaped body that is fitted into the
Intersect the meridional plane containing the axis and the incident light beam.
The angle formed by the line formed when crossing and the optical axis of the scanning lens
Tilt the plate to a specified value other than 90 degrees, and
The angle between the plane of incidence of the object and the meridional plane is 45 degrees or less.
By arranging it so that it is up to 80 degrees or less, it is a plate shape.
Since the shield cover and the plate-shaped body can be made as small as possible while sufficiently obtaining the variation width of the optical path length in the body, it is possible to provide the light beam scanning device in which the polygon mirror and the scanning lens can be arranged close to each other.

[0023]

【Example】

(First Embodiment) FIG. 2 is a view showing the outline of the arrangement of a light beam scanning apparatus according to the first embodiment used in an electrophotographic apparatus.

In FIG. 2, the laser diode 10 emits laser light, and the emitted laser light is collimated by a collimator lens to be parallel light, and then passes through a slit and a cylinder lens (not shown so far), as shown in the figure. The light beam L is applied to the polygon mirror 14 as a reflection type light deflector.

The polygon mirror 14 is formed in a polygonal column shape whose side surface is composed of a plurality of rectangular mirror surfaces.
As shown in the drawing, it rotates clockwise around the point O at a predetermined constant angular velocity. The polygon mirror 14 is arranged at a position where the irradiated light beam L is reflected by one of the mirror surfaces of the polygon mirror 14.
The reflected light beam L is deflected as a deflected beam L at a constant angular velocity. Further, the polygon mirror 14 is covered with a light-shielding cover 16 for dustproof and soundproof, so that deterioration of image quality due to dirt of the mirror is prevented.

The shield cover 16 has the same central axis as the polygon mirror 14 as shown in FIGS.
The casing has a circular trapezoidal shape with an open bottom, and covers the polygon mirror 14 by covering it. Further, the shielding cover 16 is the polygon mirror 1.
4 has an opening on its side surface for passing the light beam L and the deflected beam L incident on the light source 4.
The rectangular plate glass 12 is so-called fitted and killed, and the soundproof and dustproof effect is maintained. The shield cover 16 is fixed to the casing of the electrophotographic apparatus, and is arranged so that the light beam L emitted toward the polygon mirror 14 always enters the plate glass 12 at the same angle.

As shown in FIG. 2, the plate glass 12 has a scanning lens 18 in which a line at which the incident surface and the meridional plane (the plane including the optical axis of the scanning lens 18 and the incident light beam L) intersect. Has a predetermined angle (tilt angle α) with respect to a line that intersects the plane orthogonal to the optical axis of and the meridional plane, and as shown in FIG. And the sagittal plane M orthogonal to each other is inclined at a predetermined angle β. In other words, the plate glass 12 has a predetermined angle other than 90 ° with respect to the optical axis of the scanning lens 18 at which a line whose incident surface intersects with the meridional plane, and the incident surface has a predetermined angle with respect to the meridional plane. 90 ° -β
Tilted to meet in.

The inclination angle β from the sagittal plane M is about 10 ° to 45 ° (45 ° in terms of the angle formed by the plane of incidence of the plate glass 12 and the meridional plane).
It is -80 °. ). The reason why the above range is adopted as the range of the inclination angle β is that if the setting is less than 10 °, the change of the optical path length in the plate glass 12 is not sufficient, while if it is set larger than 45 °, the shielding cover 16 becomes large. This is because a problem such as a problem occurs.

A scanning lens 18 is arranged near the plate glass 12 and the shielding cover 16. The scanning lens 18 is composed of an Fθ lens so that the deflected beam L scans the recording medium at a constant speed. The scanning lens 18 is arranged so that the deflected beam L deflected by the polygon mirror 14 always passes through the scanning lens 18 and is condensed on the recording medium.

Further, a cylindrical lens of a tilt correction optical system (not shown) is arranged between the polygon mirror 12 and the laser diode 10 and between the scanning lens 18 and a recording medium (not shown) to generate a light beam and a deflected beam. By refracting light only in one direction (vertical direction), the uneven pitch of the scanning lines is prevented and the scanning lines are equally spaced.

Next, the operation of the first embodiment will be mainly described with reference to FIG.
Follow along. First, laser light is emitted from the laser diode 10. The emitted laser light passes through a collimator lens (not shown) to become parallel light, then passes through a slit and a cylinder lens (not shown), and passes through a light beam L.
Is irradiated toward the polygon mirror 14 so that a slender line image is formed in the main scanning direction for reflection.

The radiated light beam L first enters the plate glass 12 fitted in the shield cover 16 covering the periphery of the polygon mirror 14 at a constant angle θ ₁ , and the plate glass 1
After passing through 2, the light beam is incident on one of the mirror surfaces of the polygon mirror, that is, the mirror surface 20 in FIG. 2, at an incident angle θ determined by the rotation position of the polygon mirror 14. Then, the light is reflected by the mirror surface 20 at the same reflection angle θ as the incident angle θ,
It again enters the plate glass 12, passes through the plate glass 12, and enters the scanning lens 18 as a deflected beam L. In this case, as the polygon mirror 14 rotating at a constant angular velocity rotates, the incident angle θ on the mirror surface 20 changes, and the incident angle of the deflected beam L on the plate glass 12 also changes. Then, the deflected beam is converged on the recording medium through the scanning lens 18 including the Fθ lens,
Scanning is performed at a constant speed in the main scanning direction.

Specifically, first, the deflected beam when the incident angle on the plate glass 12 (hereinafter, simply referred to as “incident angle”) is θ ₂ is transmitted through the scanning lens 18 and then S (not shown).
The deflected beam L ₂ (SOS) reaches the OS sensor, and a scan start signal is generated for each scan. As a result, it is possible to prevent the deviation of the recording position due to the accumulation of scanning fluctuations.

When the incident angle becomes θ ₃ , the deflected beam becomes S
The deflection beam L ₃ (SOL) that scans the image end on the OS side is generated, and image recording is started. And the incident angle is θ ₄
Then, the deflection beam becomes a deflection beam L ₄ (COS) that scans the center (COS) of the image area, and when it is further scanned and the incident angle becomes θ ₅ , the deflection beam goes to the end (EOS) of the image in the main scanning direction. Beam L ₅ (EOL),
After that, the main scanning in the relevant row ends.

Since the polygon mirror 14 continues to rotate even after the scanning in the row is completed, the reflecting surface is changed from the mirror surface 20 to the mirror surface 22, and the light beam scanning by the mirror surface 22 is similarly performed. . The deflected beam is also scanned in the sub-scanning direction, the recording position is changed in a direction different from the main scanning direction, and image recording or the like is performed.

When the light beam L incident on the polygon mirror 14 is reflected by the mirror surface 20, the light beam L is reflected by the reflectance determined by the angle of incidence on the mirror surface 20.
The energy of the S-wave polarization component is attenuated. In this case, the angle of incidence on the mirror surface 20 (range 0 ° to 90 °)
Is larger, the reflectance R _s is larger, and conversely, the smaller the incident angle is, the smaller the reflectance R _s is. That is, the deflected beams L _{1 to} L ₅ before re-incident on the plate glass 12 have different intensities.

The light beam L incident on the mirror surface 20 at a large incident angle becomes a deflected beam which is re-incident on the plate glass 12 at a large incident angle (range of 0 ° to 90 °). In this case, the transmittance T _{s of the} plate glass 12 (represented by the energy intensity ratio of the S-wave polarization component of the light beam before and after passing through the plate glass 12) is determined as the incident angle to the plate glass 12 increases. Since the optical path length to pass becomes large,
It tends to become smaller. That is, the transmittance T _s shows an increasing / decreasing trend opposite to the reflectance R _{s in} relation to the incident angle.
Therefore, if the plate glass 12 is preferably tilted so that the transmittance T _s and the reflectance R _s cancel each other out, the light quantity distribution of the polarized beam can be made uniform.

By the way, according to the first embodiment, in the plate glass 12, the line where the incident surface and the meridional plane intersect is 90 ° -α with respect to the optical axis of the scanning lens 18 (hereinafter, referred to as "scanning direction"). Angle α ”), and its incident surface is 90 ° − with the meridional plane.
It is arranged so as to be inclined so as to form an angle β (hereinafter, referred to as “angle β in the non-scanning direction”).

Therefore, as compared with the prior art in which only the scanning direction angle α is added and β = 0, the optical path length in the plate glass 12 is increased, and the fluctuation range of the transmittance T _s is reduced even when α is decreased. Can be increased.

When the inclination angles α and β are in two directions,
The increase in optical path length can be explained by considering the following case. That is, the plate glass 12 having the thickness d
Letting δ be the refraction angle in the meridional plane and ε be the refraction angle in the sagittal plane, the optical path length l ₁ of the deflection beam in the plate glass 12 is expressed by the following equation.

L ₁ = d / (cos δ · cos ε) where 0 ° <δ <90 °, 0 <ε <9
It is 0 °.

From the expressions, the refraction angle δ and the refraction angle ε are 90 °.
It can be seen that the larger the range below, the larger the optical path length l ₁ . By the way, the deflected beam incident on the plate glass 12 at a constant angle φ has a larger refraction angle δ within the plate glass 12 as the inclination angle α increases, and has a larger refraction angle ε as the inclination angle β increases.

When the tilt angle β = 0 in the non-scanning direction as in the conventional case, ε = 0 and cos ε = _1. Therefore, in order to secure the optical path length l ₁ above a certain value, the tilt angle α Was required to be increased to increase the refraction angle δ. However, in the case of the first embodiment, since the inclination angle β is also present in the non-scanning direction, the effect of cos ε is obtained from the equation, and even if the inclination angle α is made small, the optical path length l ₁ above a certain level can be secured. it can.
In other words, by adding the tilt angle β, the tilt angle α
Even if the plate glass 12 is arranged with a smaller value than in the conventional case, it is possible to obtain a variation range of the transmittance T _S sufficient to cancel the variation range of the reflectance R _S.

Here, the effect of having the inclination angles α and β in the two directions is represented by the effect of one combined angle γ.
That is, the larger the composite angle γ, the larger the optical path length in the plate glass 12, and therefore the smaller the transmittance T _s , and if the composite angle γ is the same, the optical path lengths are equal, and therefore,
The transmittances T _s are also equal. The relationship between the synthetic angle γ and the tilt angles α and β is as follows. That is, the origin is O
The vector A in the XYZ coordinate system is projected onto the XY plane, and the angle formed by the vector with the Y axis is α, Y
When the angle formed by the vector projected on the Z plane and the Y axis is β, the combined angle γ is the angle formed by the vector A and the Y axis in the plane including the origin O, the vector A, and the Y axis.

FIG. 4 shows a change curve of the combined angle γ when the angle α in the scanning direction and the angle β in the non-scanning direction are variously changed. In FIG. 4, the horizontal axis represents the tilt angle β (5 ° in the non-scanning direction).
Up to 45 °), the vertical axis represents the change in the combined angle γ with respect to the change in the tilt angle β, and the tilt angle α in the scanning direction is 3
Five kinds of 0 °, 40 °, 50 °, 60 ° and 70 ° were selected and shown in the graph.

From FIG. 4, when the tilt angle α in the scanning direction is large, the combined angle γ does not change much even if the tilt angle β in the non-scanning direction is increased, but when α is small, the combined angle γ does not change. You can see that there are many. By utilizing this property, the tilt angle α can be reduced, and as a result, the incident angle range can be reduced.

Next, how the light amount distribution after passing through the plate glass 12, which is the most problematic, changes depending on the inclination angle β will be described. The plate glass 12 is β = 0 in the non-scanning direction.
The light quantity distribution after passing through the plate glass 12 when tilted at 5 °, 10 °, 20 °, and 30 ° are as shown in FIGS. 5 to 9. The conditions in this case were set as follows.

Focal length of scanning lens 266 mm Incident beam angle to polygon mirror 14 58 ° Image area 297 mm SOS position 165 mm from center of image area θ ₁ Incident beam −36 ° θ ₂ SOS −14 ° θ ₃ SOL −11 ° θ ₄ COS 22 ° θ ₅ EOL 54 ° FIG. 5 is a diagram showing changes in transmittance from SOS to EOL when β = 0 °, that is, when the plate glass 12 is not tilted at all in the non-scanning direction. Here, the horizontal axis is the incident angle of the reflected deflected beam with respect to the plate glass 12, and the vertical axis is the energy ratio between the incident beam before reflection and the deflected beam after passing through the plate glass 12 with SOS as 100 (%). Represents the ratio (hereinafter, FIG. 6, FIG. 7, FIG. 8,
The same in FIG. 9). That is, the reflectance of the mirror and the plate glass 1
It represents the light amount distribution including the offset with the transmittance of 2, and the smaller the distribution difference, the better. For comparison, the change curve when the single coating is applied to the plate glass 12 is shown by a broken line (the same applies to FIGS. 6, 7, 8, and 9 below), and the case where the multi-coating is applied is shown by a solid line. expressed.

According to FIG. 5, when an inexpensive single coating is applied, the transmittance of the deflected beam passing through the plate glass 12 becomes lower as it goes from COS to EOL, exceeding the offset of the reflectance, so that the vicinity of EOL is reduced. The image quality deteriorates. This means that under the above conditions, the incident angle (SO
This is a phenomenon that occurs when the reflection of the plate glass 12 cannot be ignored because the range of (S to EOL) is large. On the other hand, when multi-coating is applied, the difference in light amount distribution becomes small. Therefore, when β = 0, it can be seen that an expensive multi-coating process is required.

FIG. 6 is a diagram showing the light amount distribution when the single coated plate glass 12 is tilted 5 ° in the non-scanning direction (β = 5 °). According to FIG. 6, SOL-EO
The difference in the light amount distribution of L is about 13%, and β as shown in FIG.
It can be seen that it is improved compared to the case of = 0 °.

FIG. 7 shows a case where the single coated plate glass 12 is tilted by 10 ° in the non-scanning direction (β = 10).
It is a figure showing the light amount distribution of (degree). According to FIG. 7, SOL
It can be seen that the difference in the light quantity distribution between EOL and EOL is about 9%, which is even better than in the case of β = 5 ° as shown in FIG.

FIGS. 8 and 9 show single-coated glass sheet 12 at 20 ° and 3 in the non-scanning direction, respectively.
It is a figure showing the light amount distribution when inclining by 0 ° (β = 20 °, 30 °). The difference in light amount distribution between SOL and EOL is about 5% according to FIG. 8 and about 2% according to FIG. 9, and the difference in light amount distribution becomes smaller as the tilt angle β in the non-scanning direction increases. It can be seen that the image quality deterioration can be prevented more effectively.

When the above results are summarized and evaluated, the following Table 1
become that way.

[0054]

[Table 1]

In Table 1, the inclination angle β in the non-scanning direction is 0 °, 5
Correspondence diagrams in each case of °, 10 °, 20 °, and 30 °, SOS to EOL light amount distribution immediately after passing through a single-coated plate glass, and incidence indicating a range of incident angles of the deflected beam with respect to the plate glass 12. The evaluation based on the angle difference and the light amount distribution is described. By the way, since the influence on the actual light amount distribution on the recording medium includes the influence of the scanning lens 18, the folding mirror (not shown), etc. (5% to 10%), it is necessary to consider that amount. In actual use, the light amount distribution on the recording medium is 20% P
Therefore, it is necessary to control the light intensity distribution of the deflected beam when it passes through the plate glass to 10% or less.

According to Table 1, when β = 0 °, the difference in the incident angle of the deflected beam with respect to the plate glass 12 is set to a wide range of 54 ° in order to cancel the difference in reflectance depending on the incident angle under the above conditions. I have to take it. However, in the case where a single coating covers a wide range, the decrease in the transmittance of the plate glass becomes too large when the incident angle is large, and the light amount distribution becomes a large value of 17% PP. Therefore,
The target of 10% P-P cannot be achieved, and the evaluation result is bad.

On the other hand, the incident angle difference is 49 when β = 5 °.
However, the target cannot be achieved although the light intensity distribution is still large and the light amount distribution is as small as 13% PP.

However, from β = 10 °, the light amount distribution becomes 9%, and the target can be cleared. β = 20
In the case of ° and 30 °, the light quantity distributions are 5% and 2%, respectively. Moreover, the incident angle differences are 44 °, 34 °, 24, respectively.
It can be extremely small as °.

Therefore, while maintaining the effect of making the light quantity distribution substantially constant, the incident angle range can be made small, the shield cover 16 and the plate glass 12 can be made small, and the cost can be kept low by the inexpensive single coating. Becomes Further, the tilt angle α of the plate glass 12 in the scanning direction
Since the size can be reduced, the polygon mirror 14 and the scanning lens 18 can be arranged close to each other, and the entire apparatus can be downsized, which is also advantageous in terms of cost.

The inclination angle β in the non-scanning direction is 10 ° to 3
It has been shown that the case of 0 ° is preferable, but if β becomes too large, there arises a problem that the transmittance of the plate glass is extremely lowered and the shielding cover becomes large, so an upper limit of about 45 ° is appropriate. . Therefore, the range of the tilt angle β is 10 ° or more and 45 ° or less (a preferable range is 45 ° or more and 80 ° or less when the angle between the incident surface and the meridional plane is taken).

The light beam scanning device according to the first embodiment has been described above, but the invention is not limited to the above example. For example, the plate glass fitted in the shielding cover does not necessarily have to be a glass material, and may be a light-transmissive plate-like body such as a transparent plate made of plastic or the like. Further, although the case where the polygon mirror is used as the reflection type optical deflector is described, the present invention can be applied to other reflection type optical deflectors such as a galvanometer mirror and a resonant scanner, and the scanning lens is not limited to the Fθ lens. (Second Embodiment) FIG. 10 is a view showing the arrangement of a light beam scanning apparatus according to the second embodiment. The same constituents as those in the first embodiment are designated by the same reference numerals as those shown in FIG. 2 and their explanations are omitted.

According to FIG. 10, the light beam scanning device according to the second embodiment is characterized by the following points. That is, in the plate glass 12, the incident light beam L is closest to the shield cover 16 in the plate glass 12 and is transmitted through one boundary portion (point A) in the meridional plane, and is the outermost part of the deflected beam. A light beam (a deflected beam EOL that goes to the image end on the EOS side) passes through the other boundary portion (point B) and is fitted into the shielding cover 16 so as to have a predetermined clearance with the circumscribed circle 24 of the polygon mirror 14. The feature is that As the value of this Δ, for example, 1 to 2
mm is adopted.

The points A and B may be determined as follows. That is, the luminous flux 2 of the incident light beam L
Of the points formed when 6 intersects with the outside of the shielding cover 16, the point closest to the SOS sensor is point A, and EOS is
Beam 30 of the deflected beam L5 (EOL) going to the image end on the side
Among the points that can be made when intersecting with the outside of the shielding cover 16,
The point closest to the EOS side is point B. Then, of the two boundaries in the meridional plane between the plate glass 12 and the shielding cover 16, the shielding cover is arranged so that the point A becomes one SOS side boundary and the point B becomes the other EOS side boundary. The plate glass 12 is fitted into the opening of 16.

Next, the operation of the second embodiment will be described. The points A and B are the SOS of the plate glass 12, respectively.
By setting the side boundary and the EOS side boundary, it is possible to make the plate glass 12 as small as possible under given conditions while maintaining the effect of making the light amount distribution uniform. Also, this allows the scanning lens and the polygon mirror 14
And can be placed close to each other.

On the other hand, the plate glass 12 and the polygon mirror 14
By providing an appropriate clearance Δ with the circumscribed circle 24, the polygon mirror 14 can be protected from heat generation due to wind loss, and the effect of facilitating the work of attaching the cover can be obtained in addition to the soundproof and dustproof effect. Especially Δ is 1-2 mm
By adjusting the amount to such an extent, it is possible to reduce the cost by reducing the size of the shielding cover and the like as much as possible while maintaining the above effect.

The above is the contents of the second embodiment, but the present invention is not limited to this. For example, the points A and B
In addition to the points, the point A or its vicinity and the point B or its vicinity may be the boundary points of the plate glass 12. In order to reduce the range of the incident angle, the plate glass 12 is formed so that the incident surface of the plate glass 12 forms an angle of 45 ° to 80 ° with the main scanning surface as shown in the first embodiment.
May be tilted. Thereby, the plate glass 12 and the shield cover 16 can be further reduced in size.

The clearance Δ may have a value other than 1 to 2 mm, as long as the effect of the invention according to the second embodiment is exhibited.
Of course, other values may be used. Then, as one criterion for determining this clearance, instead of the circumscribing circle 24, a circle formed by a locus formed when the polygon mirror 14 rotates or a point where the reflecting surface is closest to the plate glass 12 may be selected. Therefore, the present invention can be applied to the case where the polygon mirror 14 is not a regular polygonal figure or a reflection type optical deflector which does not use the polygon mirror 14.

[0068]

According to the first aspect of the present invention, in a plate-like member such as a plate glass fitted in the shielding cover, the line where the incident surface intersects with the meridional plane and the optical axis of the scanning lens have a predetermined angle. Since the incident surface is inclined at an angle of 45 ° to 80 ° with respect to the meridional plane, the incident angle range can be made extremely small while maintaining a uniform light amount distribution. Therefore, the scanning lens and the polygon mirror can be arranged close to each other, and the device can be downsized.

According to the second aspect of the present invention, the incident beam and the outermost deflected beam are transmitted through the boundary portion of the plate glass with the shielding cover in the meridional plane, and the reflection surface of the polygon mirror is formed. Since the plate glass was fitted into the opening of the shielding cover with a proper clearance, under the given conditions, the plate glass and the shielding cover can be made as small as possible, and at the same time soundproof and dustproof, and prevention of heat generation due to windage loss. Effects such as ease of cover installation work can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a light beam scanning device according to a conventional technique.

FIG. 2 is a configuration diagram of a light beam scanning device according to a first embodiment.

FIG. 3 is a side view showing arrangement of plate glasses on a shielding cover according to the first embodiment.

FIG. 4 is a diagram showing a relationship between a non-scanning direction angle and a combined angle of the plate glass according to the first example.

FIG. 5 is a relationship diagram between a scanning direction angle and a light amount distribution when the plate glass according to the first example is not tilted in the non-scanning direction.

FIG. 6 is a plan view of the plate glass according to the first embodiment, which is 5 ° in a non-scanning direction.
FIG. 9 is a relationship diagram between a scanning direction angle and a light amount distribution when tilted.

FIG. 7 is a plan view of the flat glass according to the first embodiment in the non-scanning direction.
FIG. 6 is a relationship diagram between a scanning direction angle and a light amount distribution when tilted at an angle of °.

FIG. 8 is a plan view of the flat glass according to the first embodiment in a non-scanning direction.
FIG. 6 is a relationship diagram between a scanning direction angle and a light amount distribution when tilted at an angle of °.

FIG. 9 is a plan view of the flat glass according to the first embodiment, which is provided with 30 in the non-scanning direction.
FIG. 6 is a relationship diagram between a scanning direction angle and a light amount distribution when tilted at an angle of °.

FIG. 10 is a configuration diagram of a polygon mirror according to a second embodiment.

[Explanation of symbols]

10 Laser diode 12 Flat glass 14 polygon mirror 16 Shielding cover 18 scanning lens

Claims (2)

(57) [Claims] 1. A reflection type optical deflector for reflecting and deflecting a light beam, and a plate-shaped body through which the light beam after the reflection and deflection is transmitted,
In a light beam scanning device that scans a light beam that has passed through the plate-shaped body on a meridional plane through a scanning lens by reflection and deflection, the plate-shaped body has an incident surface of the plate-shaped body and the meridional plane intersect. The angle formed by the line formed by the scanning lens and the optical axis of the scanning lens is a predetermined value other than 90 degrees, and the angle formed by the plane of incidence of the plate and the meridional plane is 45 degrees or more and 80 degrees or less. A light beam scanning device, which is characterized in that 2. A reflection type light deflector for reflecting and deflecting a light beam, a shield cover having an opening and arranged to cover the reflection type light deflector, an incident light beam and after reflection and deflection. comprising of a plate-like body fitted in the opening so as to deflect the beam is a light beam passes through, and in the light beam scanning device for scanning on a meridional plane through the scanning lens the deflected beam, wherein the plate The plate-like body is composed of the plane of incidence of the plate-like body and the meridional.
A line formed by intersecting a plane and the optical axis of the scanning lens
The angle formed by and becomes a predetermined value other than 90 degrees, and
The angle between the plane of incidence of the plate and the meridional plane is
The plate-shaped body is arranged so as to be 45 degrees or more and 80 degrees or less, and the incident beam incident on the reflection type optical deflector is closest to the shield cover of the plate-shaped body and the meridional plane. So as to allow the outermost light beam of the deflected beam to pass through the other boundary portion and to have a predetermined clearance with the reflecting surface of the reflective optical deflector. A light beam scanning device, wherein the light beam scanning device is fitted in the shielding cover.