JP2971005B2 - 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 device used in a writing optical system of an image forming apparatus such as a laser printer, a digital copying machine, a laser facsimile and the like.

[0002]

2. Description of the Related Art As a writing optical system of an image forming apparatus such as a laser printer, a digital copying machine, and a laser facsimile, a laser beam, intensity-modulated according to an image signal, is deflected and scanned by a deflector to scan a photosensitive member or the like. 2. Related Art An optical scanning device that scans a surface and writes an image is known. FIG. 11 shows an example of an optical system of a conventional optical scanning device. In FIG. 11, a divergent light beam emitted from a light source 21 composed of a semiconductor laser or the like is coupled by a coupling lens 22 and is sub-scanning direction (perpendicular to the deflection surface) near a deflector 24 composed of a rotary polygon mirror or the like by a cylinder lens 23. Direction)
Is condensed once, and then enters the deflecting reflection surface of the deflector 24. The light beam deflected by the deflector 24 is condensed by an image forming optical element 25 such as an fθ lens, and is reflected on a scanning surface 28 such as a photosensitive member via a reflection mirror 30 and a cylinder lens 27 for correcting surface tilt. An image is formed as a minute spot light, and the image forming point moves on the surface to be scanned at a constant speed as the deflector 24 rotates. In a light beam whose deflection angle by the deflector 24 exceeds the effective writing range, the detection unit 2
A folding mirror 31 and a cylindrical lens 32 for guiding a light beam to the light source 9 are arranged so that the light is condensed in the detection unit 29. The detection unit 29 receives the light beam from the deflector 24 via the return mirror 31 and the cylindrical lens 32, detects the scanning position of the light beam, and generates a synchronization signal such as a start of writing.

[0003]

In the optical scanning device having the configuration shown in FIG. 11, a light beam for guiding a light beam to a detection unit 29 is provided in addition to the imaging optical element 25 for scanning, the reflection mirror 30, and the cylinder lens 27. Since the folding mirror 31 and the cylindrical lens 32 are provided, the number of components constituting the optical system is large, the device becomes large, and the cost is disadvantageous. In addition, it is necessary to position and fix each optical component, and there is a problem that it takes time to assemble and adjust. In addition, since the detection unit detects a light beam at a position where the deflection angle of the deflector exceeds the effective writing range,
The light incident on the deflector may be vignetted due to the end of the deflecting reflection surface, and the beam shape at the detection unit is asymmetric, causing an error when performing synchronous position detection. There is.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a low-cost and compact optical scanning device which can reduce the number of parts as compared with the conventional device and which can be easily adjusted. Another object of the present invention is to provide an optical scanning device capable of accurately detecting a synchronous position even if vignetting due to a deflector occurs.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, an optical scanning device includes a light source (1) for emitting a laser beam and a light beam from the light source (1). A deflector (4) for deflecting at an angular velocity, and the deflector (4)
An imaging mirror (5) having a function of converging the light beam deflected by the laser beam on the surface to be scanned (8) and making the optical scanning on the surface to be scanned uniform.
A detecting unit (9) for receiving a light beam deflected and scanned by the deflector (4) and detecting a position where the light beam is scanned; and a detection optical element for guiding the light beam to the detecting unit (9) ( 6), wherein the imaging optical element for detection (6) and the imaging mirror (5) are integrally formed of a plastic material,
It consists of a member whose surface is mirror-coated (FIG. 1).

Here, as an example, the image forming mirror (5) and the image forming optical element for detection (6) have a concave shape at least in the main scanning direction. The power in the main scanning direction is set to be larger than the power of the imaging mirror (5) in the main scanning direction. The detection optical element (6) has an anamorphic shape in which the power in the main scanning direction and the power in the sub-scanning direction are different, or the detection optical element (6) has a coaxial spherical surface. The light flux forms an image at least in the main scanning direction in the vicinity of the detection surface of the detection unit.

Further, in the invention according to the first aspect, the effective diameter (R) of the imaging optical element for detection (6) is made smaller than the diameter of the incident light beam, and after passing through the imaging optical element for detection (6). Is characterized in that the light intensity distribution of the light beam is substantially line-symmetric with respect to the principal ray (FIG. 10).

Further, in the invention according to claim 2, the light source (1) for emitting a laser beam, the deflector (4) for deflecting the light beam from the light source (1) at a constant angular velocity, and the deflector (4). 4)
Imaging optical element (5) having the function of converging the deflected light beam on the surface to be scanned (8) and making the optical scanning on the surface to be scanned uniform.
And an optical scanning device having a detector (9) for receiving a light beam deflected and scanned by the deflector (4) and detecting a position scanned by the light beam, wherein the detector (9) is provided by the deflector (4).
A part of the light beam guided to the device causes vignetting by the deflector (4), and a light shielding plate that shields a part of the light beam that has vignetted between the deflector (4) and the detection unit (9). (13) is provided (FIG. 7). According to the third aspect of the invention, in addition to the configuration of the second aspect, the light shielding plate (13)
The light intensity distribution of the luminous flux after passing through is substantially line-symmetric about the principal ray (FIG. 9).

[0009]

In the optical scanning device according to the first aspect, the imaging mirror for optical scanning and the imaging optical element for guiding the light beam to the detection unit for synchronization detection are integrally formed of a plastic material, and the mirror is formed on the surface. By using a coated member, the number of components can be reduced, and a mirror can be used for the imaging optical element for detection, so that the degree of freedom of layout is increased and a light with a low-cost and compact optical system is provided. A scanning device can be provided. In the optical scanning device according to claim 1, the effective diameter of the imaging optical element for detection is smaller than the diameter of the incident light beam, and the light intensity distribution of the light beam after passing through the imaging optical element for detection is a chief ray. , The detection unit can obtain a substantially symmetric beam shape even if vignetting occurs due to the deflector, making it possible to accurately detect the synchronous position. .

Further, in the optical scanning device according to the second and third aspects, when a part of the light beam guided to the detection unit by the deflector causes vignetting by the deflector, the light scanning device is disposed between the deflector and the detection unit. Since a light-shielding plate that blocks a part of the vignetting light beam is placed, the light intensity distribution of the light beam after passing through the light-shielding plate can be made almost linearly symmetric about the principal ray. Even if vignetting occurs due to the detector, a substantially symmetrical beam shape can be obtained in the detection unit, and it becomes possible to accurately detect a synchronous position.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an example of the optical system of the optical scanning device according to the present invention. In FIG. 1, a divergent light beam emitted from a light source 1 composed of a semiconductor laser or the like is coupled to a coupling lens 2.
After being condensed by the cylinder lens 3 once in the sub-scanning direction (direction perpendicular to the deflecting surface) in the vicinity of the deflector 4 composed of a rotating polygon mirror or the like, and then incident on the deflecting and reflecting surface of the deflector 24. I do. And the deflector 24
The light beam deflected by the deflecting reflecting surface condenses the deflecting light beam on the surface 8 to be scanned and equalizes the speed of light scanning on the surface 8 to be scanned. )
The light is reflected by the lens 5, and further formed as an image on a surface 8 to be scanned such as a photoconductor as a minute spot light via a barrel-shaped toroidal lens 7 as an optical element for correcting surface tilt. It moves on the scanned surface 8 at a constant speed with the rotation.
Further, a detection imaging optical element 6 is integrally formed with a part of the coaxial aspherical reflection mirror 5 on which a light beam at a position where the deflection angle of the deflector 4 exceeds the effective writing range is integrally formed. The light beam from the deflector 4 is guided to the detection unit 9 by the image optical element 6. The imaging optical element 6 for detection and the imaging mirror 5 can be integrally formed by molding using a plastic material or the like, and can be formed by mirror coating the surface.

The detecting section 9 is composed of a light detecting element using a photodiode or the like, and detects a light beam that scans over the detecting element.
This is for generating a synchronizing signal such as the start of image writing. Therefore, since the detecting unit 9 must accurately detect the position of the light beam that scans over it, the detecting unit 9 collects at least the main scanning direction (deflection scanning direction). It must be lit. The synchronization signal generated by the detection unit 9 is for keeping the image writing position on the scanned surface 8 in the main scanning direction constant in each scan, and a control unit (not shown) controls the light source after a predetermined timing from the synchronization signal. 1 emits light in accordance with an image signal, and performs image exposure for each scan. Here, the predetermined timing means that after the generation of the synchronizing signal, the deflected light beam from the deflector 4 passes through the imaging optical element 6 for detection and reaches the desired writing start position on the surface 8 to be scanned. It is time to be done.

In this embodiment, the imaging optical element 6 for detection is used.
Is set to be larger than the power of the coaxial aspherical reflecting mirror 5 in the main scanning direction, so that the detecting unit 9 is located at a position higher than the position where the light beam is imaged by the scanning optical elements (5, 7). The distance can be reduced, and the number of parts is prevented from increasing.

As described above, the optical scanning device having the configuration shown in FIG. 1 has a function of condensing the deflecting light beam by the deflector 4 on the surface 8 to be scanned and making the optical scanning on the surface to be scanned uniform. An imaging mirror 5 is used as an imaging optical element, and a detection imaging optical element 6 that guides a light beam to the imaging mirror 5 and a detection unit 9 for synchronization detection.
The number of components can be reduced as compared with the conventional optical scanning device having the configuration shown in FIG. 11, and an optical scanning device having a low-cost and compact optical system can be realized. .

Another advantage of the present invention is that since a mirror can be used for the imaging optical element 6 for detection, the degree of freedom in the layout of the detection unit is higher than in the conventional configuration in which the folding mirror 31 and the lens 32 are combined. Is to increase. That is, since the detection imaging optical element 6 is of a reflection type, the degree of freedom of the arrangement position of the detection unit 9 is large. As shown in FIG. 2, the detection units are denoted by reference numerals 9, 9 ', 9 "in the figure. can be arranged in the position shown. for example, to direct the light beam at a position a certain detector 9 of FIG. 2, as shown in FIG. 3, the optical axis L ₁ of the detection imaging optical element 6 it may be the angle theta ₁ which sandwich the optical path extending from the light path and the detection imaging optical element 6 in the detecting unit 9 toward the detection imaging optical element 6 from the deflector 4 to bisect. Similarly detection when the parts are in the position of 9 'in FIG. 2, as shown in FIG. 4, the optical axis L ₂ of the detection imaging optical element 6, the optical path toward the detection imaging optical element 6 from the deflector 4 And the angle θ ₂ sandwiching the optical path from the imaging optical element 6 for detection to the detection section 9 ′ may be divided into two equal parts.
Although not shown, the same applies to the case where the light beam is guided to the detection unit at the position 9 "in FIG.

Next, in the optical scanning device of the present invention, for example, in the case of the embodiment shown in FIG.
However, as shown in FIG. 5, (a) the power in the main scanning direction and (b)
If the power in the sub-scanning direction has an anamorphic shape different from that in the sub-scanning direction, the light beam can be focused on the detection surface in both the main scanning direction and the sub-scanning direction. At this time, the deflector 4
Since the deflecting reflection surface and the detection unit 9 have a conjugate relationship with respect to the sub-scanning direction, the deflecting surface has a function of correcting surface tilt, and can guide the light flux to the detection unit 9 even if the deflector 4 slightly tilts. Becomes possible.

Incidentally, the optical element having the anamorphic shape may be restricted in processing. So in this case, the detection imaging optical element 6 is a coaxial spherical mirror, Ru is focused only in the main scanning direction. At this time, the shape of the beam spot on the detection unit 9 is long in the sub-scanning direction as shown in FIG. 6 and has a large width in the sub-scanning direction. Detection is possible. In addition, in the case of this configuration, face tilt is not corrected, but has a large width in the sub-scanning direction, so that even if there is some face tilt, it can be detected.

Next, a description will be given of a configuration example in which a part of the light beam guided to the detection unit 9 by the deflector 4 causes vignetting by the deflector 4. Since the detector 9 detects a light beam at a position where the deflection angle of the deflector 4 exceeds the effective writing range, the light beam incident on the deflector 4 may cause vignetting due to the end of the deflecting reflection surface. In this case, the light beam reflected by the deflector 4 has an asymmetric shape with respect to the principal ray. Therefore, as in the example shown in FIG. 7, a light-shielding plate 13 that blocks a part of the light beam is arranged between the deflector 4 and the detection unit 9, and the principal ray passes through the light-shielding plate 13 in accordance with the center of the opening. Thereby, the light intensity distribution of the light beam after passing through the light shielding plate 13 can be made symmetrical with respect to the principal ray, and the light intensity distribution can be detected via the detection imaging optical element 12 ′ formed of a cylinder lens or a toroidal lens. An image can be formed on the unit 9. At this time, the width W of the light shielding plate 13 in the main scanning direction
Is Δd in the figure (the width of the luminous flux on the vignetting side with respect to the principal ray)
In this case, W <2Δd may be satisfied.

When the light beam incident on the deflector 4 causes vignetting due to the end of the deflecting reflection surface, the light shielding plate 13 is used.
When the light does not pass through, the beam shape (main scanning direction) at the detection unit 9 becomes asymmetrical as shown in FIG. 8 and an error occurs when the position is detected, but as shown in FIG. When the light passes through the light shielding plate 13, the beam shape (main scanning direction) at the detection unit 9 becomes symmetric as shown in FIG.
Position detection can be performed accurately.

The light shielding plate 13 can be applied to the conventional device shown in FIG. 11 in the same manner, and the accuracy of position detection by the detection unit can be improved. Also,
In the example of FIG. 7, a detection imaging optical element 12 ′ including a cylinder lens or a toroidal lens is provided in order to form the light beam reflected by the imaging mirror 5 on the detection unit 9, as shown in FIG. 1. In the case where the reflection type imaging optical element 6 is provided integrally with the imaging mirror 5, only the light shielding plate 13 need be provided, and the detection imaging optical element 12 ′ in FIG. 7 can be omitted. it can.

Next, as in the optical scanning device shown in FIG. 1, in the case where the reflection type imaging optical element 6 for detection is provided integrally with the imaging mirror 5, as shown in FIG. If the effective diameter of the imaging optical element for detection 6 is reduced and the light beam reflected by the imaging optical element for detection 6 is made symmetrical with respect to the principal ray, even if vignetting due to the deflector 4 occurs, the detection unit 9 can be used. Figure 9 in position
It is possible to obtain an almost symmetric beam shape as shown in
Accurate position detection can be performed. The effective diameter R of the imaging optical element 6 for detection may be set to satisfy R <2Δd when Δd (width of the light beam on the vignetting side with respect to the principal ray) in the figure is used. As described above, in the example illustrated in FIG. 10, the effective diameter of the imaging optical element 6 for detection is reduced, and the light intensity distribution of the light beam reflected by the imaging optical element 6 for detection is substantially linear with the principal ray as the center. Since a symmetrical shape is used, a substantially symmetrical beam shape can be obtained at the position of the detection unit 9 without providing a light shielding plate, so that the number of components can be reduced as compared with the configuration of FIG.

By the way, in the optical scanning device according to the first aspect, the image forming optical element for guiding the light beam to the detecting section is integrated with the image forming mirror. 1-4) While the detection imaging optical element 6 and the imaging mirror 5 is characterized in that integrated by integral molding using a plastic material as, the other, the following references
As described in the embodiment, there is a method of connecting a mirror used as a detection imaging optical element to an imaging mirror. However, this
In this case, the imaging mirror and the imaging optics for detection are separate components.
Therefore, the number of parts increases and the cost increases as compared with the integral molding.
As a connection method, an imaging optical element for detection may be bonded to the imaging mirror, or may be fixed using a leaf spring or the like. Further, any shape of mirror may be used for the imaging optical element for detection.

FIG. 12 is a view showing an embodiment in which a mirror used as a detecting image forming optical element is connected to and integrated with an image forming mirror. When the image forming mirror 5 is formed, an image forming mirror is formed. A projection 5a for connecting an imaging optical element for detection is provided in advance at one end of 5, and a coaxial spherical mirror or an anamorphic mirror is bonded to the projection 5a as an imaging optical element 6 for detection. It is an example.

FIG. 13 shows another embodiment in which a flat mirror is bonded as a detection imaging optical element 6 to the projection 5a of the imaging mirror 5 to be integrated. In this case, since a plane mirror is used, it is necessary to provide the imaging lens 14 in the optical path to the detection unit 9 ', but this is an effective method in terms of increasing the degree of freedom in layout. By the way,
The imaging lens 14 only needs to form an image in the main scanning direction on the photodiode of the detection unit 9 ', and any of a cylinder lens (having power only in the main scanning direction), a spherical lens, and an anamorphic lens may be used. .

As another method of connecting a mirror used as a detection imaging optical element to the imaging mirror, a hole or a concave shape is provided in advance at a connection position of the detection mirror on the imaging mirror. It is also possible to adopt a configuration in which the convex portion of the imaging optical element for detection is fitted into that portion. FIG. 14 shows an example of this, in which a hole 5b is provided at one end of the imaging mirror 5 and a projection 6a is provided on the side of the imaging optical element 6 for detection. This is an example in which the convex portion 6a of the imaging optical element 6 for detection is press-fitted, fitted, and integrated. still,
The hole or concave shape provided in the imaging mirror 5 can be provided at the time of molding the imaging mirror, but may be processed after the molding.

[0026]

As described above, according to the first aspect of the present invention, the detection imaging optical element for guiding the light flux to the synchronization detection detection unit and the light scanning imaging mirror are integrally formed of a plastic material. Since the number of parts can be reduced and assembly adjustment can be facilitated by using a member formed and mirror-coated on the surface, an optical scanning device having a low-cost and compact optical system can be provided.

The imaging mirror and the imaging optical element for detection are concave at least in the main scanning direction, and the power of the imaging optical element for detection in the main scanning direction is set to be larger than that of the imaging mirror. This makes it possible to dispose the detection unit at a position shorter than the position where the light beam is formed by the optical scanning optical element, thereby increasing the degree of freedom in layout, and providing a low-cost and compact optical scanning device. Can be provided.

In the case where the detection imaging optical element has an anamorphic shape in which the power in the main scanning direction and the power in the sub-scanning direction are different, a high-precision position capable of coping with the tilting of the deflector. An optical scanning device capable of detection can be provided, and the imaging optical element for detection is a coaxial spherical mirror, and a light beam forms an image only in the main scanning direction near the detection surface of the detection unit. Is capable of high-accuracy position detection that can cope with surface tilt of the deflector.
An optical scanning device that can be easily processed can be provided.

Further, according to the first aspect of the present invention, the effective diameter of the imaging optical element for detection is made smaller than the diameter of the incident light beam, and the light intensity distribution of the light beam after passing through the imaging optical element for detection is mainly determined. By having a substantially line-symmetric shape with the light beam as the center, even if vignetting occurs due to the deflector, the detection unit can obtain a substantially symmetric beam shape, enabling high-accuracy position detection. The number of points can be reduced, and a low-cost and compact optical scanning device can be provided.

According to the second and third aspects of the invention, a part of the light beam guided to the detection unit by the deflector causes vignetting by the deflector, and vignetting occurs between the deflector and the detection unit. By placing a light-shielding plate that blocks a part of the light beam, the light intensity distribution of the light beam after passing through the light-shielding plate can be made almost line-symmetrical about the principal ray. Even if vignetting occurs, a substantially symmetrical beam shape can be obtained in the detection section, and highly accurate position detection can be performed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an optical system of an optical scanning device according to the present invention.

FIG. 2 is an explanatory diagram of an arrangement position of a detection unit in the optical scanning device shown in FIG.

FIG. 3 is an explanatory diagram of a deflector, an optical axis of a detection imaging optical element, and an arrangement position of a detection unit.

FIG. 4 is an explanatory diagram of a deflector, an optical axis of a detection imaging optical element, and an arrangement position of a detection unit.

FIG. 5 is an explanatory diagram of the power in the main scanning direction and the power in the sub-scanning direction of the imaging optical element for detection having an anamorphic shape.

FIG. 6 is an explanatory diagram of a beam spot shape in a detection unit when a detection imaging optical element is a coaxial spherical mirror.

FIG. 7 is a plan view of a main part of an optical system of an optical scanning device showing an example in which a light shielding plate that shields a part of a light beam having vignetting is disposed between a deflector and a detection unit.

FIG. 8 is a diagram illustrating a beam shape (light intensity distribution in a main scanning direction) at a detection unit when vignetting due to a deflector occurs.

9 is a diagram illustrating a beam shape (light intensity distribution in a main scanning direction) at a detection unit when the light passes through a light shielding plate illustrated in FIG. 7;

FIG. 10 is a plan view of a main part of the optical system of the optical scanning device showing an example in which the effective diameter of the imaging optical element for detection is smaller than the diameter of the incident light beam.

FIG. 11 is a perspective view showing an example of an optical system of a conventional optical scanning device.

12 is a fragmentary plan view showing an example of an optical system that is integrated by connecting the mirror used as the detection imaging optical element in the image forming mirror.

FIG. 13 is a main part plan view showing another example of an optical system in which a mirror used as a detection imaging optical element is connected to and integrated with an imaging mirror.

FIG. 14 is a plan view of a principal part showing still another example of an optical system in which a mirror used as a detection imaging optical element is connected to and integrated with an imaging mirror.

[Explanation of symbols]

1: Light source (semiconductor laser, etc.) 2: Coupling lens 3: Cylinder lens 4: Deflector 5: Imaging mirror (coaxial aspherical reflection mirror) 5a: Projection for connecting imaging optical element for detection 5b: Detection Hole (or concave portion) for connecting imaging optical element for use 6: Imaging optical element for detection 6a: Convex portion 7: Optical element for correcting surface tilt (barrel-shaped toroidal lens, etc.) 8: Surface to be scanned (photoconductor, etc.) 9, 9 ', 9 ": detection unit 12': imaging optical element for detection (cylinder lens or toroidal lens) 13: light shielding plate 14: imaging lens

Claims (3)

(57) [Claims] 1. A light source for emitting a laser beam, a deflector for deflecting the light beam from the light source at a uniform angular velocity, and a light beam deflected by the deflector is condensed on a surface to be scanned, and is converged on the surface to be scanned. An image forming mirror having a function of equalizing light scanning, a detecting unit for receiving a light beam deflected by the deflector and detecting a position where the light beam is scanned, and a detecting unit for guiding the light beam to the detecting unit. An optical scanning device having an image optical element, wherein the detection image forming optical element and the image forming mirror are integrally formed of a plastic material, and are formed of a member having a surface coated with a mirror, and the detection image forming optical element. The optical scanning is characterized in that the effective diameter of the element is smaller than the diameter of the incident light beam, and that the light intensity distribution of the light beam after passing through the image-forming optical element for detection has a substantially line-symmetrical shape centered on the principal ray. apparatus. 2. A light source for emitting a laser beam, a deflector for deflecting the light beam from the light source at a constant angular velocity, and a light beam deflected by the deflector is condensed on a surface to be scanned and is converged on the surface to be scanned. An imaging optical element having a function of making light scanning uniform,
In an optical scanning device having a detection unit that receives a light beam deflected and scanned by the deflector and detects a position where the light beam is scanned, a part of the light beam guided to the detection unit by the deflector causes vignetting by the deflector. An optical scanning device, wherein a light-shielding plate is provided between the deflector and the detection unit, the light-shielding plate shielding a part of a light beam having vignetting. 3. An optical scanning device according to claim 2, wherein the light intensity distribution of the light beam after passing through said light shielding plate has a substantially line-symmetrical shape with respect to the principal ray. Optical scanning device.