JP2001066527A - Multibeam scanning optical system and multibeam scanner using the system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mutlibeam scanning optical system and a multibeam scanner using the system capable of performing scanning at high speed with low power consumption without spoiling the uniformity of light quantity on a surface to be scanned. SOLUTION: This multibeam scanning optical system is provided with plural light sources, an optical device 4 advancing beams respectively emitted from the plural light sources nearly in the same direction, a light deflector 25 deflecting the plural beams passing through the device 4, and an image-formation optical system 20 forming the plural beams deflected by the deflector 25 into an image on the surface to be scanned 30. In the optical system, the plural beams made incident on the deflector 25 from the device 4 are made incident on the deflection surface at a specified angle to the surface normal of the deflection surface of the deflector 25 on a subscanning cross section, and made incident on the deflection surface from the center or almost the center of the deflection angle of the deflector 25 on a main scanning cross section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam scanning optical system and a multi-beam scanning apparatus using the same, and more particularly, to a multi-beam scanning optical system which can operate at high speed and with low power consumption without deteriorating the uniformity of light quantity on a surface to be scanned. The present invention is suitable for a device such as a laser beam printer (LBP) or a digital copier, which can simultaneously scan a scanning surface with a plurality of light beams.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for a high-speed and high-definition printing process in a scanning optical system used in an image forming apparatus such as a laser beam printer or a digital copying machine. Development of a multi-beam scanning optical system that simultaneously scans light beams emitted from the light sources has been advanced.

A multi-beam scanning optical system of this type has been proposed in, for example, Japanese Patent Application Laid-Open No. 9-230260. FIG. 5 is a schematic perspective view of a multi-beam scanning optical system disclosed in the publication. In the figure, the first light source 102
a, the luminous flux emitted from the second light source 102b is shaped by the corresponding shaping lens systems 122a and 122b, respectively. These two light beams are both linearly polarized lights that vibrate in the sub-scan section. Among them, the first light source 10
The luminous flux emitted from 2a is converted into linearly polarized light oscillating in the main scanning section by rotating the oscillating surface by 90 degrees by the 波長 wavelength plate 105. The two light beams are substantially superimposed on the optical path by the polarizing beam splitter 104, and are simultaneously incident on the deflecting surface 124a of the optical deflector (rotating polygon mirror) 124. The two light beams deflected by the optical deflector 124 form an image on the surface to be scanned (photosensitive drum surface) 130 via the scanning lens 125 and the mirror 127, and the two light beams simultaneously travel on the surface to be scanned 130. Scan. In this manner, in the publication, a plurality of light sources are used, so that the
The image is formed at high speed on 0.

[0004]

However, the above-described multi-beam scanning optical system has a problem that the intensity of the light beam in one scanning line on the surface to be scanned becomes non-uniform.
This problem will be described with reference to FIG. FIG. 6 is a graph showing a change in reflectance on the deflection surface (reflection surface) of the optical deflector. In the figure, the horizontal axis is the angle θ between the light beam incident on the optical deflector and the surface normal of the deflection surface of the optical deflector. An angle when the light beam scans one end of the effective scanning area is represented by θa, and an angle when the other end of the effective scanning area is scanned is represented by θb. The vertical axis is the reflectance R on the deflection surface. The reflectance corresponding to the angle θa is Ra, and the angle θb is
Is represented by Rb.

In the multi-beam scanning optical system shown in FIG. 5, | θa | ≠ | θb |. Therefore, as can be understood from FIG. 6, an area in which the amount of change in the reflectance R with respect to the change in the angle θ, that is, a region where | Ra−Rb | is large, is used. Therefore, the amount of light reaching the surface to be scanned is also affected by this, and as a result, the problem that the amount of light reaching the scanning line changes significantly is caused. This is unsuitable for a demand for obtaining a high-speed and high-definition image. The degree of change of the reflectance R with respect to the change of the angle θ also depends on the material of the deflecting surface of the optical deflector, and is particularly remarkable when the deflecting surface is formed of aluminum.

The present invention achieves high speed by simultaneously scanning the surface to be scanned using a plurality of light beams, and also achieves high image quality by reducing non-uniformity of the light amount on the surface to be scanned. It is an object of the present invention to provide a multi-beam scanning optical system that can be achieved and a multi-beam scanning device using the same.

[0007]

According to a first aspect of the present invention, there is provided a multi-beam scanning optical system comprising: a plurality of light sources; an optical element for causing light beams emitted from the plurality of light sources to travel in substantially the same direction; A multi-beam scanning optical system having an optical deflector for deflecting a plurality of light beams passing through the optical element, an imaging optical system for forming an image of the plurality of light beams deflected by the optical deflector on a surface to be scanned, A plurality of light beams incident on the optical deflector from the optical element are incident on the deflection surface at a predetermined angle with respect to the surface normal of the deflection surface of the optical deflector in the sub-scanning cross section; In the main scanning section, the light enters the deflecting surface from the center or substantially the center of the deflection angle of the optical deflector.

According to a second aspect of the present invention, in the first aspect of the present invention, the light beam width of the plurality of light beams incident on the optical deflector from the optical element in the main scanning direction is smaller than the width of the deflecting surface of the light deflector in the main scanning direction. It is characterized by being wider than the width.

According to a third aspect of the present invention, in the first or second aspect, the imaging optical system includes at least one lens,
It has at least one mirror, and a plurality of light beams incident on the optical deflector from the optical element pass through the at least one lens.

A fourth aspect of the present invention is characterized in that, in the first or second aspect of the invention, the material of the deflection surface of the optical deflector is made of aluminum.

According to a fifth aspect of the present invention, there is provided a multi-beam scanning apparatus including the multi-beam scanning optical system according to any one of the first to fourth aspects and a recording medium.

According to a sixth aspect of the present invention, there is provided a multi-beam scanning optical system, comprising: an incident optical system for causing a plurality of light beams emitted from light source means having a plurality of light emitting portions to enter an optical deflector; An imaging optical system for imaging a plurality of light beams on the surface to be scanned, and a multi-beam scanning optical system having
A plurality of light beams incident on the optical deflector from the incident optical system,
In the sub-scanning section, the light deflector enters the deflecting surface at a predetermined angle with respect to the surface normal of the deflecting surface, and in the main scanning section, the center of the deflection angle of the optical deflector, Alternatively, the light enters the deflection surface from substantially the center.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, the light beam width of the plurality of light beams entering the optical deflector from the incident optical system in the main scanning direction is determined by the main scanning of the deflection surface of the light deflector. It is characterized by being wider than the width in the direction.

According to an eighth aspect of the present invention, in the sixth or seventh aspect, the imaging optical system includes at least one lens,
The light deflector has at least one mirror, and a plurality of light beams incident on the light deflector from the light source pass through the at least one lens.

The invention of claim 9 is characterized in that, in the invention of claim 6 or 7, the material of the deflecting surface of the optical deflector is made of aluminum.

According to a tenth aspect of the present invention, there is provided a multi-beam scanning apparatus including the multi-beam scanning optical system according to any one of the sixth to ninth aspects and a recording medium.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a top view of an essential part when a multi-beam scanning optical system according to a first embodiment of the present invention is applied to a multi-beam scanning device such as a laser beam printer. FIG. 2 is a side view of a main part of FIG. 1 and shows a state where each element is projected in a sub-scanning section.

In this specification, the plane formed by the optical axis of the imaging optical system and the light beam deflected by the optical deflector is a main scanning section, and the plane including the optical axis of the imaging optical system is orthogonal to the main scanning section. Is defined as a sub-scan section.

In FIG. 1, reference numerals 1 and 11 denote first and second light sources, respectively, which are, for example, semiconductor lasers. 2,12
Numerals denote first and second collimator lenses, respectively, which convert light beams emitted from the corresponding first and second light sources 1 and 11 into substantially parallel light beams. 3 and 13 are the first and second respectively
Aperture stop, which shapes the beam diameter. 1st, 2nd
Of the aperture stops 3 and 13 correspond to the first and second light sources 1 and 1, respectively, in order to obtain a light spot on the surface to be scanned in a desired spot size and obtain an appropriate light quantity.
1 based on the far field pattern, the maximum rated output value, the focal length of the imaging optical system described later, and the like. 1
Reference numeral 4 denotes a half-wave plate, which rotates the oscillating surface of the incident light beam by 90 degrees to convert it into linearly polarized light that oscillates in the main scanning section. Reference numeral 4 denotes a polarization beam splitter as an optical element, which has a polarization characteristic of transmitting a light beam emitted from the first light source 1 and reflecting a light beam emitted from the second light source 11. Reference numeral 21 denotes a quarter-wave plate, which converts linearly polarized light into circularly polarized light. Reference numeral 22 denotes a negative lens (concave lens) that converts a light beam that has passed through the quarter-wave plate 21 into a weakly divergent light beam. Reference numeral 23 denotes a cylindrical lens having a predetermined refractive power only in the sub-scanning direction.
The light beam passing through the negative lens 22 is formed as a substantially linear image on a deflecting surface (reflection surface) 25a of an optical deflector 25 described later in the main scanning section. Reference numeral 24 denotes a folding mirror that reflects a light beam that has passed through the cylindrical lens 23 toward the optical deflector 25.

The first and second collimator lenses 2,
12, first and second aperture stops 3, 13, 1/2 wavelength plate 1
4, the polarizing beam splitter 4, the quarter-wave plate 21, the negative lens 22, the cylindrical lens 23, the folding mirror 24, and the like constitute one element of the incident optical system.

An optical deflector 25 is composed of, for example, a rotating polygon mirror (polygon mirror), and is rotated at a constant speed in a direction indicated by an arrow A in the figure by a driving means (not shown) such as a motor. The material of the deflection surface 25a of the optical deflector 25 is made of aluminum.

Reference numeral 20 denotes an imaging optical system having a light condensing function and fθ characteristics, and includes first, second, and third lenses 26, 27, and 2.
8 and a mirror 29, and the three lenses 2
At least one of the lenses 6, 27 and 28 is formed of an anamorphic lens. The image forming optical system 20 forms an image of the deflected light beam from the optical deflector 25 on the surface to be scanned 30 and, within the sub-scanning section, the deflection surface 2 of the optical deflector 25.
The inclination of the deflecting surface 25a is corrected by making the scanning surface 5a and the scanning surface 30 have a substantially conjugate relationship. 1st, 2nd
Lenses 26 and 27 also constitute one element of the incident optical system. Note that the configuration of the imaging optical system 20 is not limited to the configuration described above, and may be configured by, for example, one lens and one mirror. Reference numeral 30 denotes a surface (scanned surface) of a photosensitive drum (image carrier) as a recording medium.

In the present embodiment, the light beam emitted from the first light source 1 is converted into a substantially parallel light beam by a first collimator lens 2, the light beam diameter is shaped by a first aperture stop 3, and a polarization beam splitter is formed. 4 and is transmitted by the polarization characteristics of the polarizing beam splitter 4. The light beam emitted from the first light source 1 is linearly polarized light that oscillates in the sub-scan section.

On the other hand, the light beam emitted from the second light source 11 is converted into a substantially parallel light beam by the second collimator lens 12, and the light beam diameter is shaped by the second aperture stop 13.
The light enters the half-wave plate 14. The light beam emitted from the second light source 11 is linearly polarized light that oscillates in the sub-scan section.
The light beam incident on the half-wave plate 14 is
Is converted into linearly polarized light that oscillates in the main scanning section, enters the polarization beam splitter 4, and is reflected by the polarization characteristics of the polarization beam splitter 4.

The light beam emitted from the polarizing beam splitter 4 from the first light source 1 and the light beam emitted from the second light source 11 are substantially overlapped and emitted. In this case, the two light beams are not strictly parallel to each other but at a finite angle at least in the sub-scan section. This is because the two light beams are simultaneously scanned on the surface to be scanned 30 while being separated in the sub-scanning direction.

The two linearly polarized light beams emitted from the polarizing beam splitter 4 are converted into circularly polarized light beams by a quarter-wave plate 21, then converted into a weakly divergent light beam by a negative lens 22, and a cylindrical lens 23. Incident on Of the weakly divergent light beams incident on the cylindrical lens 23, the light beams are converged in the sub-scanning cross section, and the second and first lenses 27 and 26 are turned through the turning mirror 24.
And enters the deflecting surface 25a of the optical deflector 25, and is substantially a line image near the deflecting surface 25a (a line image elongated in the main scanning direction).
As an image. At this time, the deflecting surface 2 of the optical deflector 25
The deflection surface 25 has a predetermined angle with respect to the surface normal of 5a.
a. That is, the two light beams enter the deflecting surface 25a obliquely at a predetermined angle. This is to separate the optical path so that the reflected light beam from the deflection surface 25a reaches the turning mirror 24 and does not return to the first and second light sources 1 and 11.

In the other main scanning section, the light beam is converted into a substantially parallel light beam by passing through the second and first lenses 27 and 26 as it is (a weakly divergent light beam), and the light deflector 25 is turned on. Is incident on the deflecting surface 25a from the center or almost the center of the deflection angle (front incidence). At this time, the light beam width of the substantially parallel light beam is changed by the light deflector 25 in the main scanning direction.
Is set to be sufficiently large with respect to the facet width of the deflection surface 25a (overfield optical system).

The two light beams deflected by the deflecting surface 25a of the light deflector 25 are first, second, and third lenses 26, 2
7, 28, and the photosensitive drum surface 30 via the mirror 29
The light is guided upward, and the light deflector 25 is rotated in the direction of arrow A, thereby simultaneously scanning the photosensitive drum surface 30 in the direction of arrow B (main scanning direction). Thus, an image is recorded on the photosensitive drum surface 30 as a recording medium.

FIG. 3 is a graph showing a change in reflectance on the deflection surface 25a of the optical deflector 25 of the present embodiment.
In the figure, the surface normal of the deflecting surface 25a when both ends of the effective scanning area on the scanned surface 30 are scanned, and both ends of the effective scanning area from the folding mirror 24 toward the deflecting surface 25a are scanned. The angles formed by the light beam are θa and θb, respectively.
And The reflectance of the deflection surface 25a at that time is R1. The surface normal of the deflecting surface 25a when scanning the center of the effective scanning area and the deflecting surface 2
The angle formed by the light beam scanning the center of the effective scanning area toward 5a is substantially 0 degree, and the reflectance of the deflecting surface 25a at that time is R0. Therefore, the reflectance R shows a characteristic characteristic centering on the angle 0 °, and the angle θ becomes θ with the deflection scanning.
The change in reflectivity corresponding to the state of changing from a to 0b through 0 degrees is | R0-R1 |.

In the present embodiment, the difference value of the reflectance represented by | R0-R1 | is | Ra-R described in FIG.
It is smaller than the difference value of the reflectance represented by b |. This means that the change in the amount of light on the surface to be scanned in one scanning line is small. In particular, when the deflection surface is formed by using aluminum as a material, the characteristics are preferable. That is, the time required to form the shape of the rotating polygon mirror can be reduced, and the power consumption required for rotation can be reduced because the material is a lightweight material.

In this embodiment, in order to obtain a more uniform light quantity distribution on the surface to be scanned, the surfaces of the first, second, and third lenses 26, 27, and 28 constituting the imaging optical system 20 are formed. Can be set in consideration of the angle dependence of the characteristic value of the antireflection film applied to the mirror and the reflection film of the mirror 29. That is, when the optical deflector having the reflectance characteristic shown in FIG. 3 is used, the characteristic of the off-axis light beam corresponding to the angle θa or the angle θb is different from the characteristic of the on-axis light beam corresponding to the angle θ0 on the surface to be scanned. It is considered that the efficiency of reaching the light amount to the light source becomes R0 / R1 times. This is because, in the main scanning section shown in FIG.
This is made possible by allowing the light beam traveling toward 5a to enter the deflection surface 25a from the center or substantially the center of the deflection angle of the light deflector 25.

The characteristics of the reflection film on the deflection surface 25a, the antireflection film used in the first, second, and third lenses 26, 27, and 28, and the reflection film of the mirror 29 are generally different between P-polarized light and S-polarized light. different. Therefore, as described above, the 1/4 wavelength plate 2
Converting both light beams emitted from the first light source 1 and the second light source 11 into circularly polarized light using the light source 1 requires that both light beams have substantially equal P-polarized light components and S-polarized light components. It is preferable because it is possible to reduce the non-uniformity of the light amount on the surface to be scanned, which is given by the polarization characteristics of the various films.

FIGS. 4A and 4B respectively show a light beam 31 traveling from the deflecting surface 25a of the optical deflector 25 and the turning mirror 24 to the deflecting surface 25a in the main scanning section shown in FIG.
FIG. 4 is a partial schematic diagram showing a relationship with a light beam width of FIG. FIG. 4 (A)
Is an example in which the width of the light beam 31 is smaller than the width of the deflection surface 25a (underfield scanning optical system). FIG. 4 (B)
Is an example in which the width of the light beam 31 is wider (overfield scanning optical system). This embodiment can deal with any setting.

However, in the setting shown in FIG. 4B, the circumscribed circle diameter of the optical deflector (rotating polygon mirror) 25 can be reduced. When spots of the same size are formed on the surface to be scanned by using the same imaging optical system, the width of the light beam traveling from the optical deflector to the imaging optical system is the same. However, in the reflection and deflection methods shown in FIG. 4A, the width of the light beam going to the optical deflector and the width of the reflected light beam are the same.
In order to keep the width of the reflected light beam constant even if the deflection surface moves in the paper due to the rotation of the optical deflector, a deflection surface with a width wider than the width of the light beam going to the imaging optical system is required. It is.

On the other hand, in the reflection and deflection system shown in FIG. 4B, the width of the light beam going to the image forming optical system is
It is determined by the width of a. Therefore, if the number of deflecting surfaces of the optical deflector is the same, the circumscribed circle diameter of the optical deflector 25 used in the method shown in FIG. Therefore, the power required for the rotation of the optical deflector is small, which is preferable from the viewpoint of energy saving. Alternatively, if the same power consumption is allowed, the reflection and deflection method shown in FIG. 4B can rotate the optical deflector at a higher speed. That is, the configuration is more effective for high-speed scanning.

In this embodiment, the two light sources 1
Although the polarizing beam splitter 4 is used as an optical element for causing the light beams respectively emitted from the light beams 11 to travel in substantially the same direction, the present invention is not limited to this. For example, the beam splitter has a transmittance and a reflectance of 50%. (Half mirror) may be used. In this case, the configuration can be made without using the half-wave plate 14 and further without using the quarter-wave plate 21.

In this embodiment, two light sources 1
11 are provided separately, and the light beams emitted from the two light sources 1 and 11 are made to travel in substantially the same direction by the optical element 4. However, the present invention is not limited to this. Semiconductor array lasers arranged in rows may be used as light source means. In this case, the optical element 4, 1 /
The configuration can be made without using the two-wavelength plate 14, the quarter-wavelength plate 21, and the like. Other configurations and optical functions are substantially the same as those in the first embodiment.

In this embodiment, a multi-beam scanning optical system and a multi-beam scanning device using the same have been described. However, it is needless to say that the present invention can be applied to a single-beam scanning optical system and a scanning device using the same. Needless to say.

[0039]

According to the present invention, as described above, the scanning speed is increased by scanning the surface to be scanned using a plurality of light beams,
Further, it is possible to achieve a multi-beam scanning optical system and a multi-beam scanning apparatus using the same, which can perform scanning at high speed and with low power consumption without deteriorating the uniformity of the light amount on the surface to be scanned. .

[Brief description of the drawings]

FIG. 1 is a top view of a main part according to a first embodiment of the present invention.

FIG. 2 is a side view of a main part of FIG. 1;

FIG. 3 is a graph showing a change in reflectance on a deflection surface of the optical deflector according to the first embodiment of the present invention.

FIG. 4 is an explanatory view showing a form of an optical system according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram of a main part of a conventional multi-beam scanning device.

FIG. 6 is a graph showing a change in reflectance on a deflection surface of a conventional optical deflector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st light source 2 1st collimator lens 3 1st aperture stop 4 optical element 11 2nd light source 12 2nd collimator lens 13 2nd aperture stop 14 1/2 wavelength plate 20 imaging optical system 21 Quarter Wavelength Plate 22 Negative Lens 23 Cylindrical Lens 24 Folding Mirror 25 Optical Deflector 25a Deflection Surface 26 First Lens 27 Second Lens 28 Third Lens 29 Mirror 30 Scanned Surface (Photosensitive Drum Surface)

Claims (10)

[Claims] A plurality of light sources; an optical element that causes light beams emitted from the plurality of light sources to travel in substantially the same direction; an optical deflector that deflects the plurality of light beams that have passed through the optical element; An imaging optical system that forms an image of a plurality of light beams deflected by the light deflector on a surface to be scanned; and a multi-beam scanning optical system having the plurality of light beams incident on the light deflector from the optical element. In the sub-scanning section, the light deflector enters the deflecting surface at a predetermined angle with respect to the surface normal of the deflecting surface, and in the main scanning section, the center of the deflection angle of the optical deflector, Alternatively, a multi-beam scanning optical system characterized by being incident on the deflection surface from substantially the center. 2. A light beam width in a main scanning direction of a plurality of light beams entering the optical deflector from the optical element is wider than a width of a deflection surface of the light deflector in a main scanning direction. Item 2. The multi-beam scanning optical system according to Item 1. 3. The imaging optical system has at least one lens and at least one mirror, and a plurality of light beams entering the optical deflector from the optical element pass through the at least one lens. 3. The multi-beam scanning optical system according to claim 1, wherein: 4. A multi-beam scanning optical system according to claim 1, wherein a material of a deflecting surface of said optical deflector is made of aluminum. 5. A multi-beam scanning apparatus comprising the multi-beam scanning optical system according to claim 1 and a recording medium. 6. An incident optical system for causing a plurality of light beams emitted from light source means having a plurality of light emitting portions to enter an optical deflector, and connecting the plurality of light beams deflected by the optical deflector onto a surface to be scanned. An imaging optical system for imaging, and a multi-beam scanning optical system having a plurality of light beams incident on the optical deflector from the incident optical system;
In the sub-scanning section, the light deflector enters the deflecting surface at a predetermined angle with respect to the surface normal of the deflecting surface, and in the main scanning section, the center of the deflection angle of the optical deflector, Alternatively, a multi-beam scanning optical system characterized by being incident on the deflection surface from substantially the center. 7. The light beam width of a plurality of light beams entering the optical deflector from the incident optical system in the main scanning direction is wider than the width of the deflection surface of the light deflector in the main scanning direction. A multi-beam scanning optical system according to claim 6. 8. The imaging optical system has at least one lens and at least one mirror, and a plurality of light beams incident on the optical deflector from the light source pass through the at least one lens. The multi-beam scanning optical system according to claim 6, wherein: 9. The multi-beam scanning optical system according to claim 6, wherein a material of a deflection surface of said optical deflector is made of aluminum. 10. A multi-beam scanning apparatus comprising the multi-beam scanning optical system according to claim 6 and a recording medium.