JPH08146321A - Optical scanner - Google Patents

Abstract

PURPOSE: To eliminate the influence of ghost light and to execute good optical scanning by providing a part of a holding frame holding a long-sized lens with a regular reflection preventive means. CONSTITUTION: Parallel beams A from a light source device 1 are condensed by a cylindrical lens 2, are transmitted through transparent parallel plates 3 and are imaged near the deflective reflection surface 4 of a rotary polygonal mirror 5. The reflected luminous fluxes B by this deflective reflection surface 4 are transmitted through the parallel flat plates 3 and are made incident toward an imaging optical system. This imaging optical system is composed of a lens system part 6 having an fθ function and the long-sized lens 8. A part of the holding frame of the long-sized lens 8 is provided with a black light absorbing member 10 as the regular reflection preventive means. The reflected luminous fluxes B are absorbed by the light absorbing material 10 and the influence of the ghost light generated by reflection of the holding frame 9 is eliminated. Then, the incidence of the ghost light on the surface 7 to be planned does not arise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device.

[0002]

2. Description of the Related Art An optical scanning device deflects a light beam from a light source by a light deflecting means, and converges the deflected light beam as a light spot on a surface to be scanned by an imaging optical system to perform optical scanning. Is a device for writing data, and is widely known in connection with printers, digital copying machines, and the like.

The "rotating polygon mirror" which is widely used as the "light deflecting means" produces a so-called "wind noise" with high speed rotation. Therefore, in order to prevent noise, the rotating polygon mirror is generally sealed with a housing. Is being done.

A "window" is formed in the housing, and the incidence of light on the rotary polygon mirror and the emission of a deflected light beam are performed through a "transparent parallel plate" that closes the window. In this case, a part of the light flux or the deflected light flux that enters the parallel plate from the light source side,
There is a problem that "ghost light" is reflected by the parallel flat plate and is incident on the surface to be scanned to deteriorate the quality of a recorded image by optical scanning.

Ghost light includes static light and dynamic light. The "static ghost light" is a light beam that is incident on the parallel plate from the light source side and is partly reflected by the parallel plate, and its direction does not change with time. "Dynamic ghost light"
Means that when the deflected light beam reflected by the deflective reflection surface exits from the window, a part of it is reflected by the parallel plate and returns to the deflective reflective surface, is reflected again by the deflective reflective surface, and exits from the window. Yes, the direction changes with the rotation of the deflecting / reflecting surface.

As a method for effectively removing the influence of the above-mentioned "static ghost light", a method disclosed in Japanese Patent Laid-Open No. 63-316821 is known. Also, as a method for effectively removing the influence of "dynamic ghost light", Japanese Patent Laid-Open No. 52-7
The one disclosed in Japanese Patent No. 6939 is known.

By the way, among the lenses forming the image forming optical system in the optical scanning device, the lens closest to the surface to be scanned is often a "long lens". When such a long lens is used, the above-mentioned JP-A-63-316821 is used.
It has been found by the inventor that the effect of ghost light may not be completely removed only by the method disclosed in Japanese Patent Laid-Open No. 52-76939.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an imaging optical system for converging a deflected light beam as a light spot on a surface to be scanned includes a long lens. In this case, it is an object of the present invention to provide a novel optical scanning device capable of effectively removing the influence of ghost light and performing excellent optical scanning.

[0009]

[Means for Solving the Problems] In the following description,
The "main scanning corresponding direction" is a virtual optical path (virtual optical path) obtained by linearly developing the optical path from the light source to the surface to be scanned in the state where the deflected light beam is orthogonally incident on the surface to be scanned. Assuming that, on this virtual optical path, the direction corresponding to the main scanning direction in parallel is said, and the "sub-scanning corresponding direction" is the direction orthogonal to the virtual optical path and the main scanning corresponding direction on the virtual optical path. Say

In the "optical scanning device" of the present invention, "a light beam from a light source is imaged as a long line image in the main scanning corresponding direction by the first imaging optical system, and the line image is formed in the vicinity of the image forming position. Deflection at a constant angular velocity by a rotating polygon mirror with a deflecting reflection surface,
An optical scanning device that converges the deflected light flux as a light spot on the surface to be scanned by the second imaging optical system and optically scans the surface to be scanned at a constant speed "and is characterized by the following points.

That is, the rotary polygon mirror is sealed by the "housing". The housing has a single "window"
It is closed by a transparent “parallel plate”.

The single "window" accepts the light beam from the first imaging element side toward the deflective reflection surface of the rotary polygon mirror, and at the same time, deflects the light beam deflected by the deflective reflection surface to the second imaging element. Eject toward the child side. Therefore, the parallel plate that closes the window is the first
And "commonly" (to the first and second imaging optical systems) between the second imaging optical system and the deflective reflection surface of the rotary polygon mirror.

The "parallel plate" is arranged at a "small angle" with respect to the rotation axis of the rotary polygon mirror. "Small corner" is 2
It is preferably about 4 degrees. In this way, by tilting the parallel plate at a small angle with respect to the rotation axis of the rotary polygon mirror, the influence of the above-mentioned "dynamic ghost light" can be eliminated.

The "second imaging optical system" has a conjugate imaging lateral magnification: β _{s in the} sub-scanning corresponding direction satisfying 0> β _s > -1. Furthermore, the second imaging optical system includes a "long lens held by the holding frame".

The angle formed by the optical axis of the light beam incident on the deflecting and reflecting surface from the side of the first image-forming optical system and the optical axis of the second image-forming optical system is "α", and the angle is set to the second image-forming optical system. When the effective maximum angle of view of the incident deflected light flux is “θ _max ” and the angle formed by the parallel plate and the optical axis of the second imaging optical system in the deflection plane is “γ”, these α, θ _max , γ However, the condition: θ _max <α ≦ π / 2, (π +
The arrangement of parallel flat plates is determined so as to satisfy θ _max −α) / 2 <γ ≦ π / 2.

The "effective maximum angle of view" is the angle of view corresponding to the end of the effective scanning area where the optical scanning is effectively performed.

The "deflection surface" is a surface formed by sweeping a deflected light beam that is ideally deflected by the rotary polygon mirror, and is a plane orthogonal to the ideal rotation axis of the rotary polygon mirror.

The "holding frame" holds the long lens in the longitudinal direction, and a part thereof has a regular reflection preventing means.

The long lens and the holding frame body may be separated from each other, but "the long lens and the holding frame body may be integrally formed of resin" (claim 2).

Whether the long lens and the holding frame are integrated or separate, the regular reflection preventing means may be "a light absorbing member integrated with the holding frame" (Claim 3), or It may also be a "diffusion surface member integrated with the holding frame" (claim 4).

The light absorbing member may be an "antireflection film" or a "black paint", and the diffusing surface member may be a tape having a diffusive surface, for example, attached to a holding frame, or holding. The holding frame body surface portion itself may be used as a diffusion surface member by forming a “diffusion surface structure” directly on the surface of the holding frame body by roughening the surface of the frame body.

Further, the regular reflection preventing means may be provided, for example, on the entire inner peripheral portion of the holding frame body, or may be provided only on "a predetermined end portion of the holding frame body in the longitudinal direction". 5).

As described above, the regular reflection preventing means can be provided separately from the holding frame body as an antireflection film or a tape having a diffusive surface, or can be directly formed on the holding frame body. Like the diffusion surface, a part of the holding frame body may be formed as the regular reflection preventing means, but it is also possible to "constitute the regular reflection preventing means by the shape of the holding frame body".

That is, "it can be used as a regular reflection preventing means by reducing the width of at least one end portion in the longitudinal direction of a portion of the holding frame body where the long lens is sandwiched in the sub-scanning corresponding direction" ( In a sixth aspect of the present invention, or in the case where the long lens and the holding frame have an integral structure, "a rib is not formed on at least one end of the holding frame in the longitudinal direction, thereby providing a regular reflection preventing means. It can be done (Claim 7).

[0025]

With respect to the ghost light generated when the long lens is provided, the light flux reflected by the parallel flat plate provided in the window of the housing that seals the rotary polygon mirror is reflected by the inner peripheral surface of the holding frame that holds the long lens. It has been found by the inventor that this occurs.

In the present invention, the "inner peripheral surface of the holding frame" and the form of the holding frame itself have the regular reflection preventing means,
The ghost light does not enter the surface to be scanned.

[0027]

EXAMPLES Specific examples will be given below. FIG. 1 is a diagram for explaining one embodiment of the present invention.

In FIG. 1A, a parallel light beam is emitted from the light source device 1, and only in the sub-scanning corresponding direction (direction orthogonal to the drawing) by the cylindrical lens 2 which is the "first imaging optical system". Collected.

The condensed light beam passes through a transparent parallel flat plate 3 provided in a window of a "housing" (not shown) that seals the rotary polygon mirror 5, and is transmitted in the vicinity of the deflective reflection surface 4 in the "main scanning corresponding direction". Image as a long line image.

The light beam reflected by the deflecting / reflecting surface 4 passes through the parallel plate 3 and enters the second imaging optical system. The second image forming optical system is a lens system portion 6 that performs the “fθ function”.
(Consists of lenses 6'and 6 '') and a long lens 8.

Reference numeral 9 indicates a holding frame. The long lens 8 is made of the same material (resin such as plastic) as the holding frame 9, and the holding frame 9 and the long lens 8 are formed "integrally with each other" (claim 2).

The light beam incident on the second image forming optical system is condensed on the surface 7 to be scanned "in the direction corresponding to the main scanning" by the lens system portion 6. That is, the elongated lens 8 has no substantial image forming action in the main scanning corresponding direction.

In the sub-scanning corresponding direction, the incident light beam is condensed on the surface 7 to be scanned by the action of the lens system portion 6 and the elongated lens 8. Therefore, a "light spot" is obtained on the surface 7 to be scanned.

In the "imaging relationship in the sub-scanning corresponding direction" of the second imaging optical system, the position of the deflective reflecting surface 4 (the position of the line image) and the position of the scanned surface 7 are "conjugate relationship". So
Even if the deflecting and reflecting surface 4 has a “face tilt” and the direction of the deflected light beam changes in the sub-scanning corresponding direction, the light spot position does not change in the sub-scanning direction. That is, this optical scanning device has a "face tilt correction function".

In the second imaging optical system, the conjugate imaging lateral magnification: β _s in the sub-scanning corresponding direction is in the range of 0> β _s > -1, which is the reduction magnification in the sub-scanning corresponding direction. The long lens 8 becomes closer to the surface 7 to be scanned, and the length of the long lens 8 becomes longer.

When the rotary polygon mirror 5 rotates at a constant speed, the light flux reflected by the deflecting / reflecting surface 4 is deflected at a constant angular velocity, and the light spot moves on the scan surface 7 in the main scanning direction to optically scan the scan surface. To do.

Since the lens system portion 6 of the second imaging optical system fulfills the "fθ function" as described above, the movement of the light spot in the main scanning direction is made uniform. That is, the moving speed of the light spot in the main scanning direction is made uniform according to the “fθ characteristic” of the second imaging optical system.

FIG. 2 shows the positional relationship between the parallel flat plate 3 and the deflection reflection surface 4 "in the deflection surface". In the figure, the angle α is formed by the optical axis (principal ray) of the light beam A that enters the deflective reflection surface 4 from the first imaging optical system side and the optical axis D of the second imaging optical system. It is a horn.

Light flux A incident from the first imaging optical system side
Is reflected on the surface of the parallel plate 3 to be reflected light B, and is reflected on the back surface of the parallel plate 3 (the surface on the side of the deflection reflection surface) to be reflected light C.

In the deflection plane, the angle formed by the optical axis D of the second image-forming optical system and the parallel plate 3 is "γ" as shown in the figure, and the deflection plane of the outward normal of the surface of the parallel plate 2 is shown. Is 3N, the incident angle of the light flux A on the parallel plate is “α + γ− (π /
2) ”.

The angle formed by the projection 3N and the optical axis D is "(π
/ 2) -γ ", the angle formed by the reflected lights B and C and the optical axis D is" ω "as shown in the figure, and using the fact that the incident angle and the reflection angle are equal to each other, it is clearly" α + γ " -(Π / 2) =
“ω + (π / 2) −γ” is established, and when this relation is solved for “ω”, “ω = α + 2γ−π” is obtained.

Of the deflected light beams incident on the second image forming optical system, the angle of view of the light beam which forms an image at the outermost end of the effective scanning area of the optical scanning, that is, the effective maximum angle of view is represented by "θ _max ". , Ω> θ
If it is _max , the reflected lights B and C will not enter the effective scanning area as "static ghost light" even if they enter the second imaging optical system.

When "ω = α + 2γ-π" is solved for γ, "γ = (π + ω-α) / 2" is obtained. However, the above-mentioned "ω> θ _max " is a condition under which the static ghost light is not affected. Therefore, for γ, “γ ≧ (π + θ _max −α) / 2” should be satisfied, and in general, when α> θ _max , α ≦ π /
Since it is set to 2, the above α, θ _max and γ satisfy the condition: θ
_max <α ≦ π / 2, (π + θ _max −α) / 2 <γ ≦ π / 2
The arrangement state (angle: γ) of the parallel plate 3 is determined so as to satisfy

Further, in order to eliminate the influence of "dynamic ghost light", the parallel plate 3 has a rotary axis of the rotary polygon mirror 5 (see FIG. 1).
In (a), a "small angle", that is, about 2 to 4 degrees, is inclined. By doing so, it is possible to prevent the "dynamic ghost light" from entering the scanned area, as in the invention disclosed in Japanese Patent Laid-Open No. 52-76939.

Returning to FIG. 1A, the light beam B reflected by the parallel plate 3 passes through the lens system portion 6 and then passes just outside the outermost end of the elongated lens 8 as shown in the figure. This is because the angle “γ” is equal to the condition “(π + θ _max −
This is because the disposition state of the parallel flat plate 3 is determined so as to satisfy α) / 2 <γ ≦ π / 2.

As described above, the reflected light beam B does not directly enter the elongated lens 8, but since the elongated lens 8 is held by the holding frame body 9, the end portion of the holding frame body (reference numeral 9). (Indicated by ').

FIG. 3 (a) is an explanatory view showing a state in the vicinity of a portion indicated by reference numeral 9'in FIG. 1 (a) at an end portion of the long lens 8 in the longitudinal direction.

FIG. 3A shows a state in which the long lens 8 (shown by a broken line) and the holding frame 9 are viewed from the sub-scanning corresponding direction, and FIG. 3B is a view seen from the main-scanning corresponding direction. Shows.

The holding frame 9 is integral with the elongated lens 8,
As shown in FIG. 3A, the reflected light beam B from the parallel plate 3 is reflected when it enters the position 9 ′ of the inner wall of the “rib portion” of the holding frame 9 at the longitudinal end of the elongated lens 8. It passes through the long lens 8.

Since the parallel plate 3 is tilted by a "small angle" with respect to the rotation axis of the rotary polygon mirror, the reflected light beam B is angled (4 to 4) upward or downward (upward in the example in the figure) in the sub-scanning corresponding direction. Therefore, the light beam B that has passed through the long lens 8 has a wavelength of 8 degrees). Therefore, as shown in FIG. Of these, it is incident on and reflected by the position 9 ″ of the “upper part in the figure”.

As described above, since the light flux reflected by the holding frame 9 is directed to the scanning area side of the surface to be scanned, it is affected as "ghost light". This is a kind of "static ghost light". The ghost light is not so strong in light intensity because it is reflected twice by the holding frame 9, but the ghost light irradiates a fixed position in the main scanning direction, so that a “streak parallel to the sub scanning direction” or the like appears on the recorded image. Appears as dirt.

In order to eliminate the influence of the ghost light generated by the reflection of the holding frame body 9 in this embodiment, a part of the holding frame body 9 (in this example, as shown in FIG. 1B) is used in this embodiment. , The portion where the reflected light beam B is reflected at the position 9 ', passes through the elongated lens 8 and then enters, that is, the portion indicated by reference numeral 9 "in FIG. Was set up.

By absorbing the reflected light beam B by the light absorbing member 10, the influence of ghost light can be eliminated. The regular reflection preventing means may be provided on the inner peripheral surface of the holding frame including the position 9 ′ in FIG. 1 (b).

FIG. 4 shows another embodiment. (A) is the figure which looked at the holding frame 9 from the longitudinal direction of the elongate lens 8,
(B) is the state of (a) viewed from the right side of the figure.

In this embodiment, a diffusing surface structure 11 is formed as a "regular reflection preventing member" at the same position where the light absorbing member 10 is provided in the embodiment of FIG. 1 to diffuse the light flux which becomes ghost light. This prevented the light from condensing on the surface to be scanned. Of course, the diffusion surface structure may be formed on the inner peripheral surface side of the rib portion at the longitudinal end of the holding frame body 9 (the portion including the position 9 ′ in FIG. 1B).

In the embodiment shown in FIG. 5, at the end portion in the longitudinal direction of the holding frame body 12 (the end portion on the side on which the reflected light flux B from the parallel plate is incident), the "long lens 8 is moved in the sub-scanning corresponding direction (FIG. End part 1 in the longitudinal direction in the part that is sandwiched between
By making the width of 2 '"small, it is used as a regular reflection preventing means.

That is, the light beam B is reflected at the position 9'and passes through the long lens 8, but the width of the holding frame 12 is small at the portion emitted from the long lens 8, so the light beam B
Will go straight on without being further reflected by the holding frame, and will not go toward the optical scanning region.

In the embodiment shown in FIG. 5, the width of the holding frame is reduced only at the longitudinal end 12 'of the holding frame 12, but as in the embodiment shown in FIG. Of the portion sandwiching the long lens 8 in the sub-scanning corresponding direction, the shape of the portion 120 'on the side where the scanning light beam is emitted is formed into a bow according to the lens shape ", and the width of the end portion in the longitudinal direction is reduced. By doing so, the light flux reflection at this portion may be avoided.

In the embodiment shown in FIG. 7, by not forming a rib portion on at least one end portion (on the side where the light beam B is incident) in the longitudinal direction of the elongated lens 8 in the holding frame 90, regular reflection is achieved. It is used as a preventive measure (claim 7).

Since the rib portion is not formed in the longitudinal direction of the holding frame 90, the reflected light flux B from the parallel plate goes straight without being reflected by the rib portion, as shown in FIG. 7B. It does not affect the optical scanning area as static ghost light.

[0061]

As described above, according to the present invention, a novel optical scanning device can be provided (claim 1).
~ 7).

Since the optical scanning device according to the present invention is constructed as described above, it is not affected by the static / dynamic ghost light known in the related art, and the ghost light generated by the frame of the elongated lens is not affected. It is possible to effectively remove the influence and perform good optical scanning.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram for explaining removal of an influence of static ghost light.

FIG. 3 is a diagram for explaining ghost light from a holding frame.

FIG. 4 is a diagram illustrating another embodiment.

FIG. 5 is a diagram for explaining another embodiment.

FIG. 6 is a diagram for explaining another embodiment.

FIG. 7 is a diagram for explaining another embodiment.

[Explanation of symbols]

 1 Light Source 2 First Imaging Optical System 3 Transparent Parallel Plate 4 Deflection / Reflecting Surface 5 Rotating Polygonal Mirror 6,8 Second Imaging Optical System 7 Scanned Surface 8 Long Lens 9 Holding Frame

Claims (7)

[Claims] 1. A rotary polygonal mirror having a light-reflecting surface in the vicinity of an image forming position of the line image formed by forming a light beam from a light source as a long line image in a main scanning corresponding direction by a first image forming optical system. In the optical scanning device, the deflected light beam is deflected at a constant angular velocity by the second imaging optical system to form a light spot on the surface to be scanned as a light spot, and the surface to be scanned is optically scanned at a constant speed. The window of the housing that seals the mirror is closed, and a transparent parallel plate is provided in common between the first and second imaging optical systems and the deflecting / reflecting surface of the rotating polygon mirror, The flat plate is arranged at a small angle with respect to the rotation axis of the rotary polygonal mirror, and the second imaging optical system has a conjugate imaging lateral magnification in the sub-scanning corresponding direction: β _s 0> β _s > -1. And including a long lens held by a holding frame, the first imaging optical system side The angle formed by the optical axis of the light beam incident on the deflecting / reflecting surface from the optical axis of the second imaging optical system is α,
When the effective maximum angle of view of the deflected light beam incident on the second imaging optical system is θ _max and the angle formed by the parallel plate and the optical axis of the second imaging optical system in the deflection plane is γ, the above α , Θ _max ,
γ is a condition: θ _max <α ≦ π / 2, (π + θ _max −α) /
An optical scanning device characterized in that the arrangement of the parallel plates is determined so as to satisfy 2 <γ ≦ π / 2, and a part of the holding frame has regular reflection preventing means. 2. The optical scanning device according to claim 1, wherein the elongated lens and the holding frame are integrally formed of resin. 3. The optical scanning device according to claim 1, wherein the regular reflection preventing means is a light absorbing member integrated with the holding frame. 4. The optical scanning device according to claim 1, wherein the regular reflection preventing means is a diffusion surface member integrated with the holding frame. 5. The optical scanning device according to claim 3 or 4, wherein the specular reflection preventing means is provided at a predetermined end portion in the longitudinal direction of the holding frame. 6. The optical scanning device according to claim 1, wherein the width of at least one end portion in the longitudinal direction of a portion of the holding frame body in which the long lens is sandwiched in the sub-scanning corresponding direction is reduced. An optical scanning device using specular reflection preventing means. 7. The optical scanning apparatus according to claim 2, wherein a rib portion is not formed on at least one end portion of the holding frame body in the longitudinal direction to form a regular reflection preventing means. apparatus.