JP2005202038A - Optical scanner and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a low-cost optical scanner reducing a beam spot diameter by considering even temperature variation and also securing beam spot positional accuracy with high precision. <P>SOLUTION: The optical scanner is equipped with: a light source 11; a deflector 14 for deflecting light beams 21 from the light source; a coupling lens 12 for coupling the light beams from the light source; a first optical system for guiding the light beams from the coupling lens to the deflector 14; a scanning optical system 15 for guiding the light beams deflected by the deflector on a surface 16 to be scanned; and liquid crystal elements 43 which are arranged in the optical path from the light source to the surface to be scanned and which is phase modulated and driven by an electric signal. The first optical system is characterized in that it is composed of lenses 13, 22 having at least [1] a positive power face in the sub scanning direction and [2] a positive power face in the main scanning direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device and a multi-beam optical scanning device used in a laser writing optical system, etc., and a laser printer, a digital copying machine, a laser facsimile, a laser plotter, etc. using the optical scanning device and the multi-beam optical scanning device. The present invention relates to an image forming apparatus.

In recent years, image forming apparatuses such as laser printers and digital copying machines have been improved in image quality, speed, and color, and the quality required by users has increased.
To meet the demand for higher speed, it is effective to use a multi-beam optical scanning device. In this case, however, pitch adjustment between a plurality of beams is necessary. As a method of adjusting the pitch between a plurality of beams, there are a method of rotating a multi-beam light source unit around an optical axis and a method of using an optical element for pitch adjustment (see, for example, Patent Document 1).
On the other hand, in response to the demand for higher image quality, it is necessary to reduce the beam spot diameter. ). However, when reducing the beam spot diameter, in particular, the image forming apparatus and the optical scanning apparatus are equipped with many heat sources such as a fixing unit and a polygon scanner, and the temperature fluctuation is considered in view of the temperature fluctuation of the use environment. It is necessary to reduce the beam spot diameter in consideration of the above.

JP-A-9-131920 Japanese Patent Laid-Open No. 3-116112 Japanese Patent Laid-Open No. 5-19190 JP 2001-166237 A

In the conventional example in which the light source unit is rotated around the optical axis, the reliability of the electrical components becomes a problem because the light source unit itself is moved. Further, in the conventional example using the optical element for pitch adjustment, a high-precision optical element made of glass is required, leading to an increase in cost.
On the other hand, even if the beam spot diameter is initially adjusted with high accuracy, the beam spot position shifts with time changes including temperature fluctuations.
Therefore, a “liquid crystal element” driven by an electric signal has been proposed as a pitch adjusting means. This liquid crystal element is a beam pitch adjusting means having features such as low voltage driving, no heat generation, no noise, no vibration, small size and light weight.

  The liquid crystal element has a cell structure in which a liquid crystal layer of about several [μm] to several tens [μm] is sealed with two glass substrates. Therefore, when the ambient temperature changes, the liquid crystal layer having a relatively high expansion coefficient thermally expands as the ambient temperature changes, and the central portion of the liquid crystal element swells, and as a result, a lens effect (positive power) may occur. there were. As a result, the beam waist position is changed, and the beam spot diameter may be deteriorated (increased).

The present invention has been made in order to solve the above-described problems of the prior art, and it is possible to reduce the beam spot diameter in consideration of temperature fluctuations, and to achieve high-precision beam spot position accuracy. It is an object (problem) to provide a low-cost optical scanning device and a multi-beam optical scanning device that can be secured.
It is another object of the present invention to provide an image forming apparatus capable of outputting a high-quality image using the optical scanning device or the multi-beam optical scanning device.

As means for solving the above problems, the present invention has the following features.
(1): a light source, a deflector that deflects the light beam from the light source, a coupling lens that couples the light beam from the light source, and a light guide that guides the light beam from the coupling lens to the deflector. One optical system, a scanning optical system that guides the light beam deflected by the deflector to the surface to be scanned, and a phase modulation that is arranged in the optical path from the light source to the surface to be scanned and driven by an electric signal In the optical scanning device having a liquid crystal element, the first optical system includes at least
[1] Positive power surface in the sub-scanning direction,
[2] Positive power surface in the main scanning direction,
It is comprised from the optical element which has these.

(2): In the optical scanning device according to (1), the first optical system includes at least two optical elements.
(3): In the optical scanning device according to (1), at least one of the optical elements constituting the first optical system can be moved and adjusted in the optical axis direction.
(4): In the optical scanning device described in (1), at least one of the optical elements constituting the first optical system is made of resin.
(5): In the optical scanning device according to (1), at least one surface of one of the optical elements constituting the first optical system is coaxial (rotationally symmetric).
(6): In the optical scanning device according to (5), the coaxial (rotationally symmetric) surface has an aspherical shape.
(7): In the optical scanning device described in (1), the optical path of the light beam incident on the liquid crystal element is deflected by phase modulation by the liquid crystal element.

(8): a plurality of light sources, a deflector for deflecting the light beam from the light source, a coupling lens for coupling the light beam from the light source, and the light beam from the coupling lens to the deflector A first optical system for guiding, a scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned, and a phase disposed in the optical path from the light source to the surface to be scanned and driven by an electrical signal In the multi-beam optical scanning device, wherein the first optical system has at least a positive power surface in the sub-scanning direction and a positive power surface in the main scanning direction. The liquid crystal element is disposed in at least one of the optical paths of a plurality of light beams emitted from the light source, and at least two light beams are guided to a common surface to be scanned.

(9): a plurality of light sources, a deflector for deflecting the light beam from the light source, a coupling lens for coupling the light beam from the light source, and the light beam from the coupling lens to the deflector A first optical system for guiding, a scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned, and a phase disposed in the optical path from the light source to the surface to be scanned and driven by an electrical signal In the multi-beam optical scanning device, wherein the first optical system has at least a positive power surface in the sub-scanning direction and a positive power surface in the main scanning direction. The liquid crystal element is disposed in at least one of optical paths of a plurality of light beams emitted from the at least one light beam, and at least one of the plurality of light beams is guided to a surface to be scanned different from other light beams. .

(10): an image carrier, an exposure unit that exposes the image carrier to a light beam to form a latent image, and a developing unit that develops and visualizes the latent image formed on the image carrier. In the image forming apparatus including a transfer unit that transfers an image visualized on the image carrier to a recording medium and a fixing unit that fixes the image transferred to the recording medium, the exposure unit includes (1 ) To (7), or the multi-beam optical scanning device according to (8) or (9) is used to form a latent image on the image carrier. And

In the configuration of the solution (1), the light source, the deflector for deflecting the light beam from the light source, the coupling lens for coupling the light beam from the light source, and the light beam from the coupling lens. A first optical system for guiding the light beam to the deflector, a scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned, and an optical signal from the light source to the surface to be scanned. In the optical scanning device having the phase-modulable liquid crystal element driven in the above-described manner, the first optical system includes at least
[1] Positive power surface in the sub-scanning direction,
[2] Positive power surface in the main scanning direction,
The beam waist position can be adjusted when the optical scanning device is assembled, and the beam spot position on the surface to be scanned can be varied, thereby reducing the beam spot diameter. In addition, it is possible to realize a low-cost optical scanning device that can ensure high-precision beam spot position accuracy.

In the configuration of (2), in addition to the configuration and effect of the above (1), the first optical system includes at least two optical elements. Therefore, the function of adjusting the beam waist position during assembly of the optical scanning device The function of correcting the beam waist position accompanying the temperature change inside the optical scanning device can be separated.
In the configuration of (3), in addition to the configuration and effect of the above (1), at least one of the optical elements constituting the first optical system can be moved and adjusted in the optical axis direction. Sometimes the beam waist position can be adjusted.
In the configuration of (4), in addition to the configuration and effect of (1) above, at least one of the optical elements constituting the first optical system is made of resin, so that the beam waist accompanying the temperature change inside the optical scanning device. Position fluctuation can be reduced.
In the configuration of (5), in addition to the configuration and effect of the above (1), at least one surface of one of the optical elements constituting the first optical system is coaxial (rotationally symmetric), so that the surface shape is increased. It can be processed with high accuracy.
In the configuration of (6), in addition to the configuration and effect of (5) above, the coaxial (rotationally symmetric) surface has an aspherical shape, so that the generated aberration can be reduced.
In the configuration of (7), in addition to the configuration and effect of the above (1), the optical path of the light beam incident on the liquid crystal element is deflected by phase modulation by the liquid crystal element. Can be variable.

  In the configuration of the solution (8), a plurality of light sources, a deflector that deflects the light beam from the light source, a coupling lens that couples the light beam from the light source, and the coupling lens A first optical system for guiding the light beam to the deflector; a scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned; and an optical path from the light source to the surface to be scanned. A phase-modulated liquid crystal element driven by a signal, wherein the first optical system has at least a positive power surface in the sub-scanning direction and a positive beam surface in the main scanning direction. In the optical scanning device, the liquid crystal element is disposed in at least one of the optical paths of the plurality of light beams emitted from the light source, and at least two light beams are guided to a common scanned surface. Scan up A multi-beam optical scanning device capable of correcting the interval (scanning line interval) between a plurality of beam spots can be realized, and this can be used as an exposure unit of an image forming apparatus, thereby enabling high-speed and high-density print output images. Can be earned.

  In the configuration of (9) of the above solution, a plurality of light sources, a deflector that deflects the light beam from the light source, a coupling lens that couples the light beam from the light source, and the coupling lens A first optical system for guiding the light beam to the deflector; a scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned; and an optical path from the light source to the surface to be scanned. A phase-modulated liquid crystal element driven by a signal, wherein the first optical system has at least a positive power surface in the sub-scanning direction and a positive beam surface in the main scanning direction. In the optical scanning device, the liquid crystal element is disposed in at least one of optical paths of a plurality of light beams emitted from the light source, and at least one of the plurality of light beams is on a surface to be scanned different from the other light beams. As led, A multi-beam scanning device that can correct the relative positions between a plurality of beam spots that scan a number of surfaces to be scanned can be realized and used as an exposure unit of a tandem color image forming apparatus. As a result, it is possible to acquire a print output image with little color misregistration between the image carriers (scanned surfaces).

  In the configuration of the solution means (10), the image carrier, exposure means for exposing the image carrier with a light beam to form a latent image, and developing the latent image formed on the image carrier. In an image forming apparatus comprising: a developing unit that visualizes; a transfer unit that transfers an image visualized on the image carrier to a recording medium; and a fixing unit that fixes the image transferred to the recording medium. As the exposure means, the optical scanning device according to any one of (1) to (7) or the multi-beam optical scanning device according to (8) or (9) is used, and the latent image is placed on the image carrier. Since the image is formed, the beam spot can be scanned at a desired position on the surface to be scanned (image carrier), and a high-speed, high-density, and high-quality print output image can be obtained.

  Hereinafter, the configuration and operation of the present invention will be described in detail based on the embodiments shown in the drawings.

[Example 1]
First, an optical scanning device capable of adjusting the sub-scanning beam spot position using a liquid crystal element will be described.
FIG. 1 is a diagram illustrating an example of an “optical scanning device” used for an exposure unit of an image forming apparatus. In FIG. 1, reference numeral 11 is a light source, 12 is a coupling lens, 13 is a cylindrical lens, 14 is a polygon mirror as an example of a deflector, and 15 includes a first scanning lens 15-1 and a second scanning lens 15-2. A scanning optical system, 16 is a surface to be scanned (for example, a photosensitive drum), 22 is a correction lens, and 43 is a liquid crystal element.

This optical scanning device is an optical scanning device that scans a surface to be scanned with a single laser beam emitted from a single light source (for example, a semiconductor laser) 11, and is emitted from a plurality of light sources (for example, a semiconductor laser array). It is also possible to apply to a “multi-beam optical scanning device” that simultaneously scans a plurality of laser beams.
The laser beam 21 emitted from the semiconductor laser 11 and emitted from the coupling lens 12 is imaged on the deflection reflection surface of the polygon mirror 14 which is a deflector by the action of the cylindrical lens 13 (imaged in the sub-scanning direction and in the main scanning direction). The image is formed as a long line image, and is scanned as a beam spot on the surface to be scanned (photosensitive drum) 16 by the scanning optical system (first and second scanning lenses) 15.
Such a device that scans the light beam emitted from the light source unit as a beam spot on the scanned surface 16 is referred to as an “optical scanning device” 20.

  Normally, the “main scanning direction” and the “sub-scanning direction” mean the direction in which the beam spot is scanned on the surface to be scanned and the direction orthogonal thereto. The directions corresponding to the main scanning direction and the sub-scanning direction (in a broad sense) are called “main scanning direction” and “sub-scanning direction”, respectively.

An optical scanning device, particularly a multi-beam scanning device, is often provided with “light beam position correcting means” for initial adjustment of a beam spot position on a surface to be scanned and correction of environmental / time-dependent fluctuations.
As a basic configuration of the light beam position adjusting means,
・ Rotate the folding mirror,
・ Shift / rotate the cylindrical lens,
・ Shift / rotate the prism,
・ Use electro-optic element, AOM,
-Rotate a parallel plate arranged between the semiconductor laser and the coupling lens,
For example, a configuration of an “optical path deflecting unit” that deflects an optical path (deflects a laser beam by a minute angle) has been proposed. However, the conventional method has problems such as an increase in the size of the apparatus and large power consumption / heat generation / noise.

Therefore, in the present invention, as shown in FIG. 1, a “liquid crystal element” 43 having features such as miniaturization / weight reduction / capable of energy saving, noiseless / no heat generation, etc. is employed as the optical path deflecting means.
The phase of the laser beam incident on the liquid crystal element can be changed by the function of “modulating the phase” of the liquid crystal element 43. Further, it is possible to configure a liquid crystal element that forms a gradient in the sub-scanning direction in the liquid crystal layer by an external electric signal. Such a liquid crystal element can be used as an optical path deflecting means for deflecting a laser beam by a minute angle, that is, a “deflecting element” (configuration (7) of the solving means). By using the liquid crystal element 43 shown in FIG. 1 as a deflecting element, the beam spot position on the scanned surface (photosensitive drum surface) 16 can be moved in the sub-scanning direction.

Next, correction of the beam waist position by the correction lens 22 (during assembly; initial adjustment) will be described.
The laser light emitted from the semiconductor laser 11 is coupled into a parallel light beam, a weak divergent light beam, or a weak convergent light beam by the coupling lens 12 in accordance with the characteristics of the optical system thereafter. Even when the alignment between the semiconductor laser 11 and the coupling lens 12 is performed with high accuracy and the “parallelism” of the laser beam emitted from the coupling lens 12 is optimally adjusted (as designed), the optical system to be combined The beam waist position in the vicinity of the surface to be scanned often shifts due to the effects of component variations and assembly variations. Further, when the liquid crystal element 43 having the cell structure is added as in the first embodiment, pressure variation when the liquid crystal layer is sealed between the two glass substrates, or the liquid crystal layer has a constant thickness. Due to the influence of the dimensional variation of the spacer member for maintaining the thickness, the vicinity of the central portion of the liquid crystal element has a convex shape or a concave shape, which may cause a lens effect. The following correcting lens 22 can be added as means for correcting such a beam waist position shift.

  In the optical scanning device 20 shown in FIG. 1, the correction lens 22 having the following characteristics is disposed between the liquid crystal element 43 and the cylindrical lens 13. The correction lens 22 and the cylindrical lens 13 constitute a first optical system (configuration (2) of the solving means). Further, as in the configuration (1) of the above solution, the first optical system includes at least [1] an optical element (such as a lens) having a positive power surface in the sub-scanning direction, and [2] main An optical element (such as a lens) having a positive power surface in the scanning direction.

In the first embodiment, the “[1] optical element having a positive power surface in the sub-scanning direction” is the cylindrical lens 13 (and the correction lens 22), in the vicinity of the deflection reflection surface of the polygon mirror 14, A line image that is long in the main scanning direction (imaged in the sub-scanning direction) is formed.
On the other hand, “[2] optical element having a positive power surface in the main scanning direction” is the correction lens 22. In the case of an optical scanning device for an image forming apparatus, a laser beam (beam spot) moves in the main scanning direction to expose the surface to be scanned (photosensitive member surface), so the exposure beam in the main scanning direction is the main scanning at rest. It becomes thicker than the beam spot diameter. Therefore, the beam spot diameter at rest needs to be set smaller in the main scanning direction than in the sub-scanning direction. Therefore, it is desirable to preferentially correct the beam waist position in the main scanning direction by “a lens having a positive power surface in the main scanning direction”. Specifically, if at least one of the optical elements constituting the first optical system (for example, the correction lens 22) is provided so as to be movable and adjustable in the direction of the optical axis, the beam waist can be used during assembly of the optical scanning device. The position can be adjusted (configuration (3) of the solving means).

  In the correction lens 22 described in Example 1, the first surface is a coaxial surface (rotationally symmetric surface). By using such a coaxial surface, it is possible to facilitate surface processing. In addition, it is possible to reduce the mounting tolerance (in the direction of the rotation axis) during assembly to the optical scanning device (configuration (5) of the solving means). As described above, as the function of the correction lens, it is sufficient that at least the beam waist position in the main scanning direction can be corrected. Therefore, the correction lens 22 may have at least a positive power surface in the main scanning direction.

By adding the correction lens 22, the following effects can be obtained.
[1] By moving the correction lens in the optical axis direction, the beam waist position can be adjusted in the entire system of the optical scanning device, and the component tolerance / mounting tolerance of other optical elements can be relaxed.
[2] A stable small-diameter beam spot can be obtained.
[3] Beam shaping is possible.
From the above, by adding the liquid crystal element (deflection element) 43 and the correction lens 22, it is possible to achieve high precision of the scanning line interval on the scanned surface 16 and a small-diameter beam spot.

Next, beam waist position correction when the temperature changes will be described.
The behavior of the beam waist position when the temperature in the vicinity of the liquid crystal element changes will be examined with reference to FIGS. 5 and 6 showing the optical path diagram of the optical system in front of the polygon mirror of the optical scanning device. 5 and 6, the X direction is the direction along the optical path (optical axis), the Y direction is the main scanning (corresponding) direction, and the Z direction is the sub scanning (corresponding) direction. Further, (main) shows a cross section in the main scanning direction of the optical system before the polygon mirror (main scanning cross section), and (sub) shows a cross section in the sub scanning direction of the optical system in front of the polygon mirror (sub scanning section).

<< Conventional example >> For an optical system without a correction lens:
FIG. 5 shows an example in which the correction lens 22 is not added as a conventional example.
5B, the laser beam (light beam) converted into a parallel light beam by the coupling lens 12 passes through the liquid crystal element 43 and enters the cylindrical lens 13 in the state of the parallel light beam. Accordingly, the laser beam (light beam) incident on the polygon mirror 14 is a parallel light beam in the main scanning direction, and forms a line image (long in the main scanning direction) by the action of the cylindrical lens 13 in the sub scanning direction.

However, as described in the above-mentioned “Problems to be Solved by the Invention”, the liquid crystal element 43 has a cell structure in which a liquid crystal layer of about several [μm] to several tens [μm] is sealed with two glass substrates. It has become. Therefore, when the temperature in the vicinity of the liquid crystal element 43 in the optical scanning device rises (FIG. 5A), the central portion of the liquid crystal element 43 may swell, and as a result, a lens effect (positive power) may occur. Accordingly, the laser beam (light beam) incident on the polygon mirror 14 in the main scanning direction becomes a convergent light beam, and a line image is formed on the cylindrical lens 13 side from the polygon mirror 14 in the sub-scanning direction. As a result, the beam waist position in the vicinity of the scanned surface 16 is shifted toward the polygon mirror 14 in both the main scanning direction and the sub-scanning direction.
When the vicinity of the liquid crystal element 43 becomes low temperature (FIG. 5 (c)), the liquid crystal element 43 exhibits a negative power lens effect. Therefore, contrary to the case of FIG. The beam waist position is shifted away from the polygon mirror 14.

<< Embodiment of the Invention >> In the case of an optical system to which a correction lens (made of resin) 22 is added:
Next, a case where a correction lens 22 made of a resin having a high coefficient of thermal expansion and having positive power is added will be described with reference to FIG.
In the case of room temperature shown in FIG. 6B, the laser beam (light beam) coupled by the coupling lens 12 is coupled to a weak divergent light beam. This laser beam is converted into a parallel light beam in both the main scanning direction and the sub-scanning direction by the action of the correction lens 22 having positive power, and then enters the cylindrical lens 13. Accordingly, the laser beam (light beam) incident on the polygon mirror 14 is a parallel light beam in the main scanning direction, and forms a line image (long in the main scanning direction) by the action of the cylindrical lens 13 in the sub scanning direction.

When the vicinity of the liquid crystal element 43 and the correction lens 22 becomes high temperature (FIG. 6A), the liquid crystal element 43 generates positive power, and the laser beam (light flux) emitted from the liquid crystal element 43 is “ The “divergence degree” becomes weak (close to parallel light flux). However, since the radius of curvature of the incident surface of the correction lens 22 (having positive power on the incident surface) increases as the temperature rises, the positive power of the correction lens 22 becomes weaker, and the laser emitted from the correction lens 22 The beam can be converted into a parallel light beam in the same manner as at room temperature. Accordingly, the characteristics of the laser beam incident on the polygon mirror 14 (the degree of parallelism of the light beam) can be set to the same state as that at room temperature, so that the occurrence of beam waist position deviation in the vicinity of the scanned surface 16 can be suppressed. . That is, when the temperature rises, the effects of “the positive power is generated in the liquid crystal element 43” and “the positive power of the correction lens 22 is weakened” are offset, and the beam waist position deviation in the vicinity of the scanned surface 16 is reduced. Generation | occurrence | production can be suppressed and the stable small diameter beam spot can be acquired (structure of (4) of a solution means).
Further, when the vicinity of the liquid crystal element 43 and the correction lens 22 becomes a low temperature (FIG. 6C), the liquid crystal element 43 exhibits a negative power lens effect, but the correction lens 22 has a strong positive power. Become. For this reason, the effects of both are canceled out, and the occurrence of a beam waist position shift near the scanned surface 16 can be suppressed.

  Another advantage of using the correction lens 22 made of resin is that mass production is possible at low cost using a molding die. When using a molding die, it is easy to create an aspherical shape. On the other hand, when the material is glass, it is necessary to grind and polish the correction lenses one by one by machining, which is not suitable for mass production.

[Numeric example]
In the optical scanning device according to the first embodiment, correction of the beam waist position (when assembling; initial adjustment) by the correction lens 22 will be described with reference to FIG.
Here, the oscillation wavelength of the semiconductor laser 11 is 655 nm, and the focal length fCOL of the coupling lens 12 is 15 mm. However, the first surface and the second surface of the coupling lens 12 are coaxial aspheric surfaces, and numerical values are not shown, but the wavefront aberration due to the coupling lens 12 is well corrected. The light beam emitted from the coupling lens 12 is a divergent light beam and is naturally condensed at a position 189.8 mm away from the second surface of the coupling lens 12 on the light emitting point side (the opposite side to the scanned surface).

  The laser beam emitted from the coupling lens 12 is shaped by an aperture (opening) (not shown), passes through the liquid crystal element 43, and then enters the correction lens 22. The distance from the second surface of the coupling lens 12 to the aperture was 10.9 mm, the distance from the aperture to the liquid crystal element 43 was 1.0 mm, and the distance from the liquid crystal element 43 to the first surface of the correction lens 22 was 24 mm. . The aperture (opening) has a rectangular shape of main scanning × sub scanning: 3.54 mm × 1.44 mm.

  Next, Table 1 shows optical system data from the correction lens 22 to the scanned surface 16. In Table 1, the radius of curvature in the main scanning direction is Rm, the radius of curvature in the sub-scanning direction is Rs, and the refractive index at the used wavelength is N. Here, the incident side and the exit side of the correction lens 22 are designated as surface number 1 and surface number 2, the incident side and the exit side of the cylindrical lens 13 are designated as surface number 3 and surface number 4, and the deflecting / reflecting surface of the polygon mirror 14 is defined. The surface number is 5, the incident side and the emission side of the first scanning lens 15-1 are surface number 6 and surface number 7, and the incident side and the emission side of the second scanning lens 15-2 are surface number 8 and surface number 9. The surface 16 to be scanned is designated as surface number 10. The angle formed by the incident angle and the reflection angle of the laser beam reaching the image height H = 0 with respect to the polygon mirror 14 is 60 °. In Table 1, a surface marked with “*” indicates an aspherical shape.

  When the correction lens 22 is moved in the optical axis direction, the main scanning beam waist position in the vicinity of the scanning surface 16 moves substantially linearly with respect to the movement amount of the correction lens 22 as shown in Table 2 below. . Accordingly, it is possible to adjust the main scanning beam waist position with high accuracy, and to secure a small diameter and a stable beam spot diameter. Here, the correction lens 22 is moved in a direction to approach the polygon mirror. The minus sign of the main scanning waist position change amount indicates that the beam waist position moves to the polygon mirror side. Further, the beam waist position in the sub-scanning direction also changes as the correction lens 22 moves. When it is necessary to correct this, if the cylindrical lens 13 is configured to be movable in the optical axis direction, the sub-scanning beam waist position can be corrected independently.

  Although the first surface (surface number 1) of the correction lens 22 has a spherical shape as shown in Table 1, there is a possibility that the wavefront aberration is deteriorated. In order to avoid this, an aspherical component may be added (configuration (6) of the solving means). In this case, mass production is possible at low cost even if it is an aspherical shape by molding using a molding die.

Next, beam waist position correction when the temperature changes will be described.
The temperature in the optical scanning device often changes due to the influence of a heat source (such as a polygon motor that rotates the polygon mirror 14) inside the optical scanning device or an external heat source (such as a fixing device described later). The beam waist position change when the temperature in the optical scanning device is changed from 25 ° C. to 45 ° C. is shown below. In this examination, it is assumed that only the vicinity of the liquid crystal element 43 and the correction lens 22 in the optical scanning device has changed in temperature.

  The liquid crystal element 43 has a cell structure in which a liquid crystal layer is sealed with two glass substrates, and a center portion is swollen with a rise in temperature, thereby producing a positive power lens effect. For example, experimentally, a liquid crystal in which a liquid crystal layer having a layer thickness of several tens [μm] is sealed with two glass substrates of length × width: 16 × 16 [mm] (thickness: 0.3 [mm]). In the case of the element, a transmission wavefront aberration corresponding to λ / 0.4 (λ = 655 nm) occurred at a temperature increase of 20 ° C. (25 ° C. → 45 ° C.). Due to this influence, when the correction lens 22 is not added, the beam waist position in the main scanning direction moves to the polygon mirror side. When the correction lens 22 is not added, the laser beam 21 emitted from the coupling lens 12 is coupled to a substantially parallel light beam, and the aperture (opening) is in the main scanning direction × sub-scanning direction: 4. A rectangular shape of 0.0 [nm] × 1.64 [nm].

Table 3 below shows the amount of change in the beam waist position at 45 ° C. with reference to the beam waist position at a temperature of 25 ° C. in the vicinity of the central image height as compared with the case where the following correction lens 22 is added. It is a thing.
Consider beam waist position correction when the correction lens 22 is added. The linear expansion coefficient of the correction lens 22 (made of resin) is 7.0E-05 [1 / ° C.] (E-05 is × 10 ⁻⁵ ), and the curvature radius R of the first surface (coaxial surface) is R = 120 [mm], so as the temperature rises (temperature difference 20 ° C.), the curvature radius R of the first surface is
R = 120 × (1 + 7.0E−05 × 20) = 120.168 [mm]
To change. As a result, the positive power of the correction lens 22 is reduced. That is, the main scanning beam waist position moves away from the polygon mirror 14 due to the effect of the correction lens 22.
That is, even if the liquid crystal element 43 exhibits a lens effect as the temperature rises, the power changes of the liquid crystal element 43 and the correction lens 22 are offset, and the occurrence of changes in the main scanning beam waist position can be reduced.

[Example 2]
Next, an example of a multi-beam optical scanning device will be described.
As a first embodiment (first embodiment) for explaining the configuration and operation of the present invention, a “single beam optical scanning device” that scans one laser beam has been described with reference to FIG. The demand for higher printing speed and higher printing density in copiers has increased, and “multi-beam optical scanning devices” that simultaneously scan multiple laser beams have become the mainstream as optical scanning devices that achieve them. .

  FIG. 2 is a diagram illustrating a multi-beam scanning device that simultaneously scans two laser beams as a specific example. In FIG. 1, reference numerals 11a and 11b are light sources, 12a and 12b are coupling lenses, 13 is a cylindrical lens, 14 is a polygon mirror as an example of a deflector, 15 is a first scanning lens 15-1 and a second scanning lens 15. -2 is a scanning optical system, 16 is a surface to be scanned (for example, a photosensitive drum), 22a and 22b are correction lenses, and 43a and 43b are liquid crystal elements.

  The two laser beams 21a and 21b emitted from the two semiconductor lasers 11a and 11b, which are multi-beam light sources, and emitted from the coupling lenses 12a and 12b, respectively, are converted into a polygon mirror 14 which is a deflector by the action of the common cylindrical lens 13. Is formed as a line image (imaged in the sub-scanning direction and long in the main scanning direction), and is scanned by the scanning optical system (first and second scanning lenses) 15 (photosensitive drum). ) 16 is scanned as a beam spot. In the multi-beam optical scanning device 20-1, the two laser beams 21a and 21b are guided to a common scanned surface (photosensitive drum) 16 (configuration (8) of the solving means).

In such a “multi-beam optical scanning device” that scans a common surface to be scanned with a plurality of laser beams, liquid crystal elements 43a and 43b having a deflection function disposed in at least one optical path of the laser beam are provided. By driving / controlling, it is possible to correct an interval (scan line interval) between a plurality of beams on the surface to be scanned to a predetermined value. Accordingly, it is possible to provide a “multi-beam optical scanning device” capable of scanning a plurality of beams while maintaining a scanning line interval with high accuracy.
Further, when used as an exposure unit of an image forming apparatus, it is possible to cope with scanning density switching (switching between high speed and high density) according to the request of an operator (user).
Further, unlike the configuration of the embodiment of FIG. 2 in which all the liquid crystal elements 43a and 43b are arranged in the optical paths of the (two) laser beams 21a and 21b, the number of liquid crystal elements used can be reduced as necessary. I do not care.

  In FIG. 2, the two laser beams 21a and 21b are configured to intersect each other in the vicinity of the deflection reflection surface of the polygon mirror 14 in the main scanning section. By adopting such a configuration, it is possible to suppress the occurrence of optical characteristic deviations (imaging position, magnification, etc.) between the two laser beams due to the difference in reflection point at the polygon mirror 14. Become.

[Example 3]
Next, another example of the multi-beam optical scanning device will be described.
Unlike the case of the “multi-beam optical scanning device” of the second embodiment described above, it is possible to adopt a configuration in which a plurality of laser beams emitted from a plurality of light sources are guided to different scanning surfaces (the solution means ( 9)).
Hereinafter, the multi-beam optical scanning apparatus according to the third embodiment will be described with reference to FIG. FIG. 3 is a diagram showing an optical layout (sub-scanning cross section) from the polygon mirror 14 of the “multi-beam optical scanning device” to the scanned surfaces (for example, photosensitive drums) 16Y and 16M. In this figure, two laser beams emitted from two light sources (not shown) are deflected and reflected by a common polygon mirror 14, and then pass through a common first scanning lens 15-1. The light passes through the two scanning lenses 15-2Y and 15-2M, and irradiates the different scanned surfaces (photosensitive drums) 16Y and 16M.

  Although not shown, in the optical path from the light source to the polygon mirror 14, a coupling lens that couples the light beam from the light source and the first optical that guides the light beam from the coupling lens to the polygon mirror 14. The first optical system has at least a positive power surface in the sub-scanning direction and a positive power surface in the main scanning direction. A liquid crystal element (not shown) having a phase modulation function is disposed on at least one of the optical paths of the two laser beams emitted from the light source. The photoconductors 16Y and 16M to be scanned surfaces rotate in the direction of the arrow in the figure (corresponding to the sub-scanning direction), but the two photoconductors are deflected by using the liquid crystal element to deflect the optical path of the laser beam. It is possible to correct the “relative” positional relationship between the scanning lines (positions in the sub-scanning direction of the laser beam irradiation position) on the drums 16Y and 16M.

  In FIG. 3, only the optical system arranged on the right side of the polygon mirror 14 is shown. However, a similar optical system is arranged symmetrically on the left side of the polygon mirror, and four light beams are scanned by one polygon mirror. Then, if the yellow (Y), magenta (M), cyan (C), and black (Bk) latent images are formed on the four photosensitive drums, the exposure means of the tandem color image forming apparatus And a print output image with little color misregistration between the photosensitive drums (scanned surfaces) can be obtained.

[Example 4]
Next, an embodiment of the image forming apparatus according to the present invention will be described.
FIG. 4 is a schematic sectional view showing an embodiment of the image forming apparatus according to the present invention. The image forming apparatus includes an optical scanning device 20, a charger 61, a developing device 62, a transfer device 63, a fixing device 64, an image carrier (for example, a photosensitive drum) 16, and a cleaning unit 65, and an exposure unit. Optical writing is performed from the optical scanning device 20 to the photosensitive drum 16, and an electrostatic latent image is formed on the photosensitive member 16 by electrophotography.

  More specifically, the principle of image formation by this image forming apparatus is well known, and the photosensitive drum 16 is uniformly charged by the charger 61 and has a potential according to the exposure distribution formed by the optical scanning device 20. Decreases, and an electrostatic latent image is formed on the photosensitive drum 16. The electrostatic latent image formed on the photosensitive drum is developed by the developing device 62, and toner is attached to the latent image to be visualized. After the toner image formed on the photosensitive drum 16 is transferred to a recording medium (for example, recording paper) by the transfer device 63, the toner image on the recording paper is fused and fixed to the recording paper by the fixing device 64. The cleaning unit 65 removes toner remaining on the photoconductor 16 after transfer.

  In FIG. 4, the toner image formed on the photosensitive drum 16 is directly transferred onto the recording sheet. However, the toner image formed on the photosensitive drum 16 is temporarily transferred to an intermediate transfer member (intermediate transfer belt or the like). After transferring to an intermediate transfer drum or the like, the intermediate transfer member may be transferred to a recording sheet. When an intermediate transfer member is used, if a plurality of color developing devices (for example, yellow, magenta, cyan, and black developing devices) are provided for one photosensitive drum 16, so-called one drum-intermediate. A transfer type color image forming apparatus can be constructed. Furthermore, if four image forming units having the configuration shown in FIG. 4 are arranged in parallel in the conveying direction of the recording medium (or intermediate transfer member) to form yellow, magenta, cyan, and black image forming units, tandem color An image forming apparatus can be configured.

  Here, as the optical scanning apparatus 20 of the image forming apparatus (or color image forming apparatus) as described above, the optical scanning apparatus (first embodiment) or multi-beam optical scanning apparatus (second embodiment) according to the present invention described so far is described. ) Is applied to reduce the beam spot diameter as described above, and it is possible to adjust the beam spot position and beam pitch with high accuracy, or to correct the beam spot diameter by initial adjustment. In addition, since it is possible to reduce the change in the beam spot diameter due to temperature fluctuation, a high-quality output image can be obtained.

If the optical scanning device and the image forming apparatus according to the present invention are used, as described above, one component has many functions, that is, temperature compensation, beam spot stabilization by initial adjustment, and beam by coaxialization. In addition to stabilizing the spot diameter, adjusting the beam spot position, adjusting the scanning line pitch, preventing ghosting, and reducing the incident angle to the polygon mirror when using multiple beams,
[1] Lower costs by reducing the number of parts,
[2] Since unnecessary parts do not increase, optical characteristics are prevented from deteriorating due to part errors.
Can be obtained, and overall optical characteristics can be improved.

  As described above, the optical scanning device and the multi-beam optical scanning device according to the present invention are laser writing optics of an image forming apparatus (or color image forming apparatus) such as a laser printer, a digital copying machine, a laser facsimile, and a laser plotter. An image forming apparatus (or color image forming apparatus) that can be suitably used for a system (exposure means) and can obtain a high-quality output image can be realized. The optical scanning device and multi-beam optical scanning device according to the present invention can be used for a laser scanning image display device, a laser scanning measurement device, and the like.

It is a schematic block diagram of the optical scanning device which shows one Example of this invention. It is a schematic block diagram of the multi-beam optical scanning apparatus which shows another Example of this invention. It is a figure which shows another Example of this invention, Comprising: It is a figure which shows the optical layout (subscanning cross section) from the polygon mirror of a multi-beam optical scanning apparatus to a to-be-scanned surface. It is a schematic block diagram of the image forming apparatus which shows another Example of this invention. It is explanatory drawing of the optical path in case a correction lens is not added to the polygon mirror front optical system of an optical scanning device. It is explanatory drawing of the optical path at the time of adding the correction lens to the polygon mirror front optical system of the optical scanning device.

Explanation of symbols

11, 11a, 11b: Semiconductor laser 12, 12a, 12b: Coupling lens 13: Cylindrical lens 14: Polygon mirror (deflector)
15: Scanning optical system 15-1: First running lens 15-2, 15-2M, 15-2Y: Second scanning lens 16, 16M, 16Y: Photosensitive drum (scanned surface)
20: Optical scanning device (exposure means)
20-1: Multi-beam optical scanning device (exposure means)
21, 21a, 21b: Laser beam (light beam)
22, 22a, 22b: correction lenses 43, 43a, 43b: liquid crystal element 61: charger 62: developing device (developing means)
63: Transfer device (transfer means)
64: Fixing device (fixing means)
65: Cleaning section

Claims (10)

A light source;
A deflector for deflecting the light beam from the light source;
A coupling lens for coupling a light beam from the light source;
A first optical system for guiding a light beam from the coupling lens to the deflector;
A scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned;
A phase-modulable liquid crystal element disposed in an optical path from the light source to the surface to be scanned and driven by an electrical signal;
In an optical scanning device having
The first optical system includes at least
[1] Positive power surface in the sub-scanning direction,
[2] Positive power surface in the main scanning direction,
An optical scanning device comprising an optical element having The optical scanning device according to claim 1,
The first optical system is composed of at least two optical elements. The optical scanning device according to claim 1,
An optical scanning device characterized in that at least one of the optical elements constituting the first optical system is movable and adjustable in the optical axis direction. The optical scanning device according to claim 1,
An optical scanning device characterized in that at least one of the optical elements constituting the first optical system is made of resin. The optical scanning device according to claim 1,
An optical scanning device, wherein at least one surface of one of the optical elements constituting the first optical system is coaxial (rotationally symmetric). The optical scanning device according to claim 5.
2. The optical scanning device according to claim 1, wherein the surface that is coaxial (rotationally symmetric) has an aspherical shape. The optical scanning device according to claim 1,
An optical scanning device characterized by deflecting an optical path of a light beam incident on the liquid crystal element by phase modulation by the liquid crystal element. Multiple light sources;
A deflector for deflecting the light beam from the light source;
A coupling lens for coupling a light beam from the light source;
A first optical system for guiding a light beam from the coupling lens to the deflector;
A scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned;
A phase-modulable liquid crystal element disposed in an optical path from the light source to the surface to be scanned and driven by an electrical signal;
The first optical system has at least a positive power surface in the sub-scanning direction and a positive power surface in the main scanning direction.
A multi-beam optical scanning device, wherein the liquid crystal element is disposed in at least one of optical paths of a plurality of light beams emitted from the light source, and at least two light beams are guided to a common scanned surface. Multiple light sources;
A deflector for deflecting the light beam from the light source;
A coupling lens for coupling a light beam from the light source;
A first optical system for guiding a light beam from the coupling lens to the deflector;
A scanning optical system for guiding the light beam deflected by the deflector to the surface to be scanned;
A phase-modulable liquid crystal element disposed in an optical path from the light source to the surface to be scanned and driven by an electrical signal;
The first optical system has at least a positive power surface in the sub-scanning direction and a positive power surface in the main scanning direction.
The liquid crystal element is disposed in at least one of optical paths of a plurality of light beams emitted from the light source, and at least one of the plurality of light beams is guided to a surface to be scanned different from other light beams. Multi-beam optical scanning device. An image carrier, an exposure unit that exposes the image carrier with a light beam to form a latent image, a developing unit that develops and visualizes the latent image formed on the image carrier, and the image carrier. In an image forming apparatus comprising a transfer unit that transfers an image visualized on a body to a recording medium, and a fixing unit that fixes the image transferred to the recording medium.
A latent image is formed on the image carrier using the optical scanning device according to any one of claims 1 to 7 or the multi-beam optical scanning device according to claim 8 or 9 as the exposure means. An image forming apparatus.

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