JP2010039325A - Optical scanning optical apparatus, image forming apparatus using the same, and method of correcting change in position of focal point in sub-scanning direction due to temperature change - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the price, size and weight of an image forming apparatus including an optical scanning optical apparatus, and to form a high definition image even when ambient temperature changes. <P>SOLUTION: The optical scanning optical apparatus includes: a scanning optical means which scans a face to be scanned in a main scanning direction; a first optical system which converts the light from a light source into a substantially parallel light beam, forms a long linear light beam in a main scanning direction using an aperture and focuses the light beam; and a second optical system which scans the light deflected by the scanning optical means on the face to be scanned at a constant speed and has at least one resin optical element. The first optical system is provided with: a diffraction grating member which is perpendicular to the plane in the main scanning direction of the scanning optical means, has a circular arc grating shape whose center exists in the plane including the optical axis of the first optical system, and is movable in the main scanning direction perpendicular to the optical axis, thus the change in the position of the focal point in the subscanning direction in the optical scanning optical apparatus due to the temperature change is corrected by the change in power at the diffraction part of the diffraction grating member due to the change in the wavelength in the light source. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention corrects a focal position change in a sub-scanning direction accompanying a temperature variation with an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an optical scanning optical device and an electrophotographic system using the optical scanning optical device. In particular, an optical scanning optical device that deflects light from a light source such as a laser diode by a rotating polyhedral mirror (polygon mirror) and performs main scanning on the photosensitive member, and an image forming apparatus using the optical scanning optical device The present invention relates to a method of correcting a focal position change in the sub-scanning direction accompanying a temperature change.

  In image forming apparatuses such as copiers, printers, facsimiles, and composite machines using electrophotography, a photoconductor uniformly charged with light modulated by image data to be formed is exposed, so that high-speed images are obtained. In the forming apparatus, an optical scanning composed of a rotating polyhedral mirror (polygon mirror) for deflecting light from a light source such as a laser diode and an fθ lens so that the deflected light scans the photosensitive member at a constant speed. An optical device is used.

  On the other hand, in these image forming apparatuses, due to the demand for personalization, there is a demand for price reduction, size reduction, weight reduction, and in addition, high definition of images to be formed. For this reason, the optical scanning optical device is also required to be low-priced, miniaturized, light-weighted, and capable of forming a high-definition image even when there are environmental fluctuations such as temperature.

  Among them, for reduction of cost and weight, for example, Patent Document 1 discloses that a lens is aspherical or a single lens. In addition, as shown in Patent Document 2, a plastic lens is generally used.

  Further, in order to reduce the size of the optical scanning optical device, Patent Document 3 discloses that an incident optical unit 11 that causes a light beam emitted from the light source unit 1 to enter the deflecting unit 5 and a light beam reflected and deflected by the deflecting unit are scanned surfaces. In the optical scanning optical apparatus having the scanning optical means 9 that forms an image on the scanning optical means 9, the scanning optical means has a first lens 6 on the deflection means side and a second lens 7 on the scanned surface side, The lens has a positive power in the main scanning direction and a negative power in the sub-scanning direction. The power of the first lens in the main scanning direction is larger than the power of the second lens in the main scanning direction. An optical scanning device having a positive power in the sub-scanning direction, a short length from the deflecting means 5 to the first lens, and a long length from the second lens to the imaging surface, and The image forming apparatus used is shown.

  However, when compared with a glass lens, the plastic lens has a problem that the degree of linear expansion and refractive index change with respect to temperature change is large, and drawing quality is likely to deteriorate due to focus shift. Further, in order to reduce the influence of the surface deflection error of the optical deflector (polygon mirror), the optical scanning optical device generally forms a light beam (light beam) once in the vicinity of the polygon mirror only in the sub-scanning direction. Therefore, the power (refractive power) in the sub-scanning direction is often configured as an anamorphic optical system that is stronger than the power in the main scanning direction. Therefore, focus shift due to temperature change is also a problem mainly in the sub-scanning direction.

  In order to incorporate such a response to environmental temperature fluctuations in the design, the above-mentioned Patent Document 2 forms a first image of a light beam that has been modulated and emitted from the light beam generating means as a long line in the main scanning direction. An optical system having a deflection surface in the vicinity of the imaging position of the first optical system, and deflecting and scanning the incident light beam in the main scanning direction, and the light beam deflected by the optical deflector And a second optical system that forms an image on the surface to be scanned. The first optical system has a cylindrical lens made of a glass material having a positive power in the sub-scanning direction, and a negative power in the sub-scanning direction. A cylindrical lens made of a plastic material, the second optical system has a plurality of lenses, and at least one of the plurality of lenses is made of a plastic material. Negative power of the system And a cylindrical lens made of plastic material, has been shown to cancel the temperature change of the plastic lens in the second optical system plastic lens.

  Similarly, in Patent Document 3, the first lens in the scanning optical means 9 has a positive power in the main scanning direction and a negative power in the sub-scanning direction, and the power of the first lens in the main scanning direction is the first power. The power of the second lens is larger than the power in the main scanning direction, and the second lens has a positive power in the sub scanning direction, thereby reducing the magnification in the sub scanning direction and changing the focal position in the sub scanning direction. It is said that the sensitivity can be lowered.

  As a countermeasure against environmental temperature fluctuations, Patent Document 4 discloses that light from a laser diode is transmitted through a condensing lens having a diffraction effect to form an image on a rotating polyhedral mirror (polygon mirror), and temperature compensation is performed. Patent Document 5 discloses an optical scanning optical device in which a light beam deflected by a deflecting element (polygon mirror) is imaged on a surface to be scanned by a scanning optical element having a refracting section and a diffracting section. 6, the light beam from the light source is imaged on the deflecting element by the anamorphic optical element having the diffractive portion, and the surface to be scanned is scanned by the light beam deflected by the deflecting element via the scanning optical element having the refracting portion. An optical scanning optical device is shown, and an optical scanning optical device in which a focus change in the main scanning direction due to a temperature change is corrected by a power change of a diffraction unit due to a wavelength change of a light source due to the temperature change is shown.

Japanese Patent No. 3567408 (Japanese Patent Laid-Open No. 10-148755) JP 2000-206432 A JP 2002-48993 A Japanese Patent No. 3317355 (Japanese Patent Laid-Open No. 4-328951) Japanese Patent No. 3432085 (Japanese Patent Laid-Open No. 10-68903) JP 2003-337295 A

  However, as described above, the plastic lens has a greater degree of linear expansion and refractive index change with respect to a temperature change than a glass lens, and is liable to cause deterioration in drawing quality due to focus shift. Further, as shown in Patent Document 3, the first lens has a positive power in the main scanning direction, a negative power in the sub scanning direction, and the second lens has a positive power in the sub scanning direction. If the first lens is brought close to the deflecting means and the length from the second lens to the imaging surface is increased, the optical scanning optical device can be made compact, but conversely, due to temperature fluctuations, the optical scanning optical device There is a problem that a slight change in the refractive index of the lens constituting the lens becomes a large focal position change on the surface to be scanned.

  For this reason, in Patent Document 3, the magnification in the sub-scanning direction is reduced by providing negative power in the sub-scanning direction of the first lens and positive power in the sub-scanning direction of the second lens. Although the sensitivity to the change in the focal position in the sub-scanning direction can be reduced, there may be a case where the effect is insufficient in the present situation where high performance is required. Further, in Patent Document 2, a glass lens is used for the optical set, and a concave cylinder lens is added only for reducing the focus variation in the sub-scanning direction, resulting in high cost.

  In Patent Document 4, Patent Document 5, and Patent Document 6, a diffraction grating is introduced as temperature compensation, and the focus change in the main scanning direction is corrected by the power change of the diffraction section due to the wavelength variation of the light source due to the temperature variation. However, no consideration is given to the sub-scanning direction.

  Therefore, in the present invention, the image forming apparatus including the optical scanning optical device is reduced in price, size, and weight, and further, high-definition image formation is possible even when the environmental temperature varies. An optical scanning optical device capable of forming a highly accurate image over a long period of time when used in an image forming apparatus without causing a change in the focal position in the sub-scanning direction due to fluctuations, and an image forming apparatus and temperature using the optical scanning optical device It is an object to provide a method for correcting a change in the focal position in the sub-scanning direction due to fluctuations.

In order to solve the above problems, an optical scanning optical device according to the present invention and an image forming apparatus using the same are provided.
A light source comprising a semiconductor laser; scanning optical means for deflecting light from the light source to scan the surface to be scanned in the main scanning direction; and light from the light source on the reflecting surface of the scanning optical means. A first optical system that is shaped by an aperture and imaged as a long line in the main scanning direction, and a scanning speed of light deflected by the scanning optical means on the surface to be scanned is constant, and at least In the optical scanning optical device comprising the second optical system in which one optical element made of resin is arranged,
The first optical system includes a diffraction grating member having an arcuate grating shape perpendicular to a surface in the main scanning direction of the scanning optical means and having a center on a surface including the optical axis of the first optical system. The diffraction grating member is provided so as to be movable in the main scanning direction perpendicular to the optical axis of the optical system, and the effective diameter of the diffraction grating is formed larger than the aperture diameter,
The focal position change in the sub-scanning direction in the optical scanning optical apparatus due to temperature fluctuation is corrected by power change in the diffraction part of the diffraction grating member due to wavelength fluctuation in the light source.

In addition, a method of correcting a focal position change in the sub-scanning direction accompanying a temperature change performed in the optical scanning optical device and an image forming apparatus using the optical scanning optical device includes:
The light from the light source consisting of a semiconductor laser is made into substantially parallel light and then shaped by an aperture, and is formed into a long line in the main scanning direction and formed on the reflecting surface of the deflecting means. The scanning optical system changes the scanning speed on the surface to be scanned. In a method of correcting a focal position change in the sub-scanning direction due to a temperature change in an optical scanning optical apparatus using an optical scanning method in which the deflection unit scans the main scanning direction on the surface to be scanned at a constant speed.
Diffraction by a diffraction grating member provided with an arc-shaped grating shape perpendicular to the surface in the main scanning direction and centered on the surface including the optical axis of the optical system when the light from the light source is linearly formed in the main scanning direction. And the tilt of the diffraction grating can be corrected by moving the diffraction grating in the main scanning direction orthogonal to the optical axis of the optical system. As the ambient temperature rises, a change in the diffraction index of the diffraction grating is brought about. The relationship between the optical element and the diffraction grating so that the amount of change in the focal point, the amount of change in the focal point caused by the change in refractive index due to the wavelength change of the light source, and the amount of change in the focal point of the optical system cancel each other. And the change of the focal position in the sub-scanning direction of the optical scanning device due to the temperature rise is corrected.

  As described above, the diffraction grating member is formed in a circular arc shape, the effective diameter of the diffraction grating is formed larger than the aperture diameter, and is provided to be movable in the main scanning direction perpendicular to the optical axis of the optical system. Even if the grating member is tilted and attached to the housing of the optical scanning optical device due to manufacturing errors, component variations, assembly errors, etc., the center of the arc in the diffraction grating is perpendicular to the plane in the main scanning direction by moving in the main scanning direction. Since it comes to the plane including the optical axis, the diffraction grating in the diffraction grating member can be corrected in the same manner as when the inclination disappears.

  In addition, when making a lens mold with a diffraction grating parallel to the main scanning direction, it is necessary to reciprocate the tool in parallel, and it is difficult to achieve accuracy, but the grating shape provided on the diffraction grating member is circular. By using the arc shape, the lens mold can be rotated concentrically and cut, the processing becomes very easy, and it can be manufactured at a lower cost. In addition, the focal position change in the sub-scanning direction due to temperature fluctuations is corrected by the power change of the diffraction section caused by wavelength fluctuations in the light source due to temperature fluctuations. An optical scanning optical device that does not cause a change in the focal position in the scanning direction can be provided.

  The second optical system includes a first lens disposed on the scanning optical means side and a second lens disposed on the scanned surface side, and the first lens is aligned in the main scanning direction. The second lens has a negative power in the sub-scanning direction orthogonal to the main scanning direction, and the power in the main scanning direction is larger than the power in the main scanning direction of the second lens. Has a positive power in the sub-scanning direction, and one of the first and second lenses has an aspherical shape, thereby shortening the distance between the scanning optical means and the first lens, Since the distance between the surface to be scanned and the second lens can be increased, and the optical scanning optical device can be configured to be small and light, an image forming apparatus using the optical scanning optical device can also be configured to be small and light. it can.

  The curvature of the arc-shaped diffraction grating shape in the diffraction grating member is a height in the sub-scanning direction of the arcuate portion of the diffraction grating cut by the beam diameter Dm of the light shaped by the aperture in the first optical system. By setting the thickness Rc between 1/400 and 1/1200, and preferably 1/800, the light beam diameter on the surface to be scanned is almost the same as the ideal state, and the ideal beam diameter It can be.

  Moreover, the element which condenses the light from the light source as a long line in the main scanning direction is formed of an olefin resin material, so that the olefin resin material absorbs less moisture even in a place with high humidity. Since no refractive index change occurs, the refractive index variation can be minimized.

  As described above, the optical scanning optical apparatus according to the present invention, the image forming apparatus using the optical scanning optical apparatus, and the method of correcting the focal position change in the sub-scanning direction due to the temperature fluctuation include the manufacturing error, component variation, and assembly of the diffraction grating member. Even if it is attached to the housing of the optical scanning optical device due to an error, the center of the arc in the diffraction grating comes to the plane including the optical axis perpendicular to the plane in the main scanning direction due to the movement in the main scanning direction. The diffraction grating in the grating member can be corrected in the same way as when the tilt is lost, so that it has a very simple configuration and does not change the focal position in the sub-scanning direction due to fluctuations in the environmental temperature. The optical scanning optical apparatus and the image forming apparatus that are small, light, and inexpensive, and a method of correcting the focal position change in the sub-scanning direction due to temperature fluctuation can be provided.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  First, the configuration of the optical scanning optical device according to the present invention will be briefly described. The optical scanning optical device according to the present invention is shaped by a light source composed of a semiconductor laser and an aperture after making the light from the light source substantially parallel light. In the image forming apparatus, the first optical system including a cylindrical lens that is long in the main scanning direction and has a cylindrical lens that forms an image on the reflecting surface of a scanning optical unit such as a polygon mirror is used. Scanning optical means including the polygon mirror for scanning light from a linear light source in the main scanning direction on the surface to be scanned, etc., and scanning speed of the deflected light on the surface to be scanned at a constant speed And a second optical system including an fθ lens.

  The first optical system includes a diffraction grating member having an arcuate grating shape that is orthogonal to a surface in the main scanning direction of the scanning optical means and has a center on a surface including the optical axis of the first optical system. The focal position change in the sub-scanning direction in the optical scanning optical device due to temperature fluctuations can be corrected by the power change in the diffraction part of the diffraction grating member due to wavelength fluctuations in the light source, and the diffraction grating member is optical system light. It is provided so as to be movable in the main scanning direction orthogonal to the axis. In this way, when the diffraction grating member is mounted with an inclination, the diffraction grating is moved in the main scanning direction so that the center of the arc of the diffraction grating includes the optical axis perpendicular to the surface in the main scanning direction. Since it comes to the surface, it can be corrected in the same manner as when the tilt of the diffraction grating in the diffraction grating member disappears.

  Furthermore, in the case of a diffraction grating parallel to the main scanning direction that has been used in the past, it is necessary to reciprocate the tool in parallel when making a lens mold, and it is difficult to achieve accuracy. By making the lattice shape provided in the arc shape, the lens mold can be rotated by concentric rotation to be cut, and the processing becomes very easy and can be manufactured at a lower cost. In addition, the focal position change in the sub-scanning direction due to temperature fluctuations is corrected by the power change of the diffraction section caused by wavelength fluctuations in the light source due to temperature fluctuations. An optical scanning optical device that does not cause a change in the focal position in the scanning direction can be provided.

  The second optical system including the fθ lens is composed of a first lens arranged on the polygon mirror side and a second lens arranged on the scanned surface side, and the first lens is arranged in the main scanning direction. Positive power is given in the sub-scanning direction orthogonal to the main scanning direction, respectively, the power in the main scanning direction is larger than the power in the main scanning direction of the second lens, and the second lens is in the sub-scanning direction. A positive power is provided in the scanning direction, and either one of the first lens and the second lens is provided with an aspherical shape so that the distance between the polygon mirror and the first lens is shortened. The optical scanning optical device is configured to be small and light by increasing the distance between the first lens and the second lens.

  By configuring the optical scanning optical device in this way, the focal position change in the sub-scanning direction accompanying the temperature fluctuation in the second optical system is caused by the wavelength fluctuation of the semiconductor laser as the light source accompanying the temperature fluctuation in the diffraction grating member. It is possible to correct by changing the power of the diffraction section, and even if the diffraction grating member is tilted and attached, it can be easily corrected, and the mold can be manufactured at low cost. It is possible to provide an optical scanning optical device and an image forming apparatus that do not cause a change in the focal position in the sub-scanning direction even if there is a change, and that are small, light, and inexpensive.

  FIG. 1 is a schematic perspective view of an optical scanning optical device according to the present invention applied to a photoconductor exposure device in an image forming apparatus. FIG. 2 is a cross-sectional view of the optical scanning optical device shown in FIG. FIG. In the following description, the same number is attached | subjected to the same component.

  An optical scanning optical device according to the present invention includes, for example, a light source 1 made of a 780 nm band semiconductor laser, a glass aspherical collimating lens 2 as a coupling lens that makes parallel light from the light source 1 made of the semiconductor laser, On the surface in the main scanning direction of an aperture stop (aperture) 3 having an opening 31 having parallel light of a predetermined size and a rotating reflecting mirror (polygon mirror) 5 that scans the surface 9 to be scanned with light from the light source 1. A diffraction grating member 20 having an arc-shaped grating that is orthogonal and has a center on a plane that includes the optical axis of the optical system, and an olefinic system such as ZEONEEXE 48R (registered trademark of Nippon Zeon Co., Ltd.) having a cylindrical surface on one side. A rotating reflecting mirror (polygon mirror) 5 that scans the surface to be scanned 9 by making light from the light source 1 made of resin or the like into parallel light that is long in the main scanning direction 10. It is composed of a linear condensing element such as a cylindrical lens 4 that forms an image on the reflecting surface 5a, and fθ lenses 6 and 7 that make the scanning speed of light deflected by the polygon mirror 5 on the surface to be scanned constant. A second optical system, a reflecting mirror 8 and the like. The reflecting mirror 8 may be provided if necessary, and may not be provided.

  As described above, the diffraction surface of the diffraction grating member 20 is an arc-shaped grating that is orthogonal to the surface in the main scanning direction of the rotary reflecting mirror (polygon mirror) 5 and has a center on the surface including the optical axis of the optical system. Thus, the main scanning direction 10 has no power so that the diffraction effect due to temperature fluctuations does not affect the main scanning direction. The second optical system such as the fθ lenses 6 and 7 is positive in the sub-scanning direction and the first lens 6 having positive power in the main scanning direction and negative power in the sub-scanning direction orthogonal to the main scanning direction. The second lens 7 has the following power, and either lens has an aspherical shape. In the present invention, the change in the focal position in the sub-scanning direction accompanying the temperature fluctuation in the second optical system such as the fθ lenses 6 and 7 is caused by the wavelength fluctuation accompanying the temperature fluctuation in the light source 1 such as a semiconductor laser. 20 is corrected by the power change of the diffraction part.

  By configuring the optical scanning optical device in this way, the focal position change in the sub-scanning direction does not occur even when the environmental temperature varies, and the fθ lenses 6 and 7 are positive in the main scanning direction. By the distribution of the negative power, the distance between the first lens 6 and the polygon mirror 5 can be shortened, and the distance between the photoconductor 9 and the second lens 7 can be lengthened, and the optical scanning optical device can be reduced in size and weight. Therefore, an image forming apparatus using this optical scanning optical device can also be formed in a small, light and high-definition image.

  FIG. 3 is a plan view of the diffraction grating member 20 and an enlarged view of a portion indicated by a dotted circle 22 in the plan view. The diffraction grating member 20 shown in FIG. 3 is provided with an arc-shaped diffraction grating 21 having R in the sub-scanning direction. A range 24 in which the arc-shaped diffraction grating 21 is provided is formed by an opening 31 provided in an aperture indicated by 3, which is emitted from the light source 1 shown in FIG. The range is larger than the diameter of the light beam 23.

  As described above, the arc-shaped diffraction grating 21 is provided as an arc that is orthogonal to the surface in the main scanning direction of the optical scanning optical device and has a center on the surface including the optical axis. By doing in this way, the metal mold | die for manufacturing the diffraction grating 21 can be rotated by concentric shape and can be cut, and processing will become very easy. On the other hand, in the conventional diffraction grating 41 parallel to the main scanning direction, it is necessary to reciprocate the tool in parallel when making the mold, and it is difficult to obtain accuracy.

  If the radius R of the arc-shaped diffraction grating 21 is increased, it becomes close to a straight line and the above-described processability is reduced. If the radius R is too small, the diameter of the light beam 23 emitted from the light source 1 shown in FIG. It will not be able to squeeze enough. Therefore, if the diameter of the aperture 23 in the main scanning direction is Dm, and the arc-shaped diffraction grating 21 is cut by the diameter (Dm) of the aperture 23, the height in the sub-scanning direction of the arcuate portion is Rc. If the aperture 23 is about 1/400 or less of the diameter Dm in the main scanning direction, the optical performance can be designed. This is the lower limit, but 1/800 or less is more preferable. The upper limit is about 1/1200.

  Now, when the diameter Dm of the aperture 23 in the main scanning direction is 3 mm, Rc is 7.5 μm at the lower limit of 1/400, 3.75 μm is preferable at 1/800, and 2.5 μm at the upper limit 1/1200. At 10 μm exceeding the lower limit of 1/400, the beam diameter on the image plane changed from the ideal state by Δ20 μm or more due to aberration deterioration. At 5 μm, no aberration deterioration was observed, and the beam diameter on the image plane was almost the same value as in the ideal state.

  When the radius Dm in the main scanning direction and the height Rc of the arcuate portion in the sub-scanning direction are calculated, the arc radius R is calculated to be 149.99 (mm) at 1/400, and 300.000 at 1/800. 00 (mm) and 1/1200 are 449.99 (mm).

  Next, a description will be given of the response to the focal position change accompanying the temperature fluctuation in the optical scanning optical device. Now, for example, if the cylindrical lens 4 as a linear condensing element is made of an olefin-based resin such as the ZEONEEXE 48R described above, the entire system becomes an optical system having a sensitivity with a temperature variation of 0.2 mm / 1 ° C.

Here, consider a case where the temperature of the optical scanning optical device is increased by, for example, dt. As the temperature rises, the refractive index n of the scanning optical element changes by dn / dt, and the accompanying focal length change dφI can be expressed as a function of the refractive index of the following equation (1).
dφI = L (n) dn / dt (1)

On the other hand, the oscillation wavelength λ of the light source 1 such as a semiconductor laser also changes by dλ / dt due to temperature rise, and the accompanying refraction and diffraction focal length changes dφL and dφD are expressed by the following equations (2) and (3), respectively. Both can be expressed as a function of wavelength. Here, the constants Lw and Dw are constants indicating changes in refractive index due to wavelength fluctuations.
dφL = L _w (λ) dλ / dt (2)
dφD = D _w (λ) dλ / dt (3)

In order to suppress the change in magnification and focus in the main scanning direction caused by the temperature rise, if the diffraction grating 21 in the diffraction grating member 20 is formed so as to satisfy the following expression (4), it is caused by environmental fluctuations (temperature rise). A change in magnification and a change in focus in the sub-scanning direction can be improved by canceling with a change in focal length due to refraction and diffraction of the diffraction grating 21.
dφI + dφL + dφD≈0 (4)

  That is, by forming the diffraction grating 21 of the diffraction grating member so as to have dφL and dφD satisfying the expression (4), it is necessary to correct the wavelength change of the light source 1 such as a semiconductor laser correspondingly. The power distribution of refraction and diffraction of the scanning optical system can be determined.

In addition, although it is possible to improve the focus shift only by the diffraction power, in this case, there is a possibility that the interval of the diffraction grating may become a size that cannot be manufactured (depending on the manufacturer), in order to avoid this. If the power of refraction is also used, the focus shift can be corrected more easily. Further, the refractive index at a certain wavelength can be obtained from a dispersion formula in which the refractive index is expressed as a function of the wavelength, for example, as such a dispersion formula, for example, n is the refractive index, λ is the wavelength, A, B , C,... Are constants, and Cauchy's dispersion formula represented by the following formula (5) is known.
n = A + (B / λ ² ) + (C / λ ⁴ ) + (5)

As described above, when the focal variation amount due to the temperature of the optical scanning optical device is 0.2 mm / 1 ° C., the temperature change with respect to the combined focal length f of the optical system is expressed by the following equation (5) f (T). As a function.
f (T) = f + 0.2T (6)

  Therefore, the focus fluctuation dφI due to refraction accompanying the temperature fluctuation expressed by the above equation (1) is substantially the same as f (T) in the above equation (6), and therefore the focal length variation due to temperature in the diffractive optical element dφL + dφD. Is offset by −1 / f (T).

  By adding a diffraction grating to the cylindrical lens that is a linear condensing element in this way, without losing the characteristics of the optical elements having different powers in the main scanning direction and the sub-scanning direction, which are characteristics of the anamorphic optical system, An optical scanning optical device that does not cause a change in focus due to temperature fluctuation can be obtained.

  As described above with reference to FIG. 3, in the diffraction grating member 20 formed with the diffraction grating 21 having R in the sub-scanning direction, as shown in FIG. Due to component variations, assembly errors, etc., the diffraction grating member 20 may be attached to the housing of the optical scanning optical device at an angle α.

  Originally, when a member having such a diffraction grating is normally mounted without tilting, the light beam from the light source 1 is diffracted symmetrically on both sides of the center of the beam diameter Dm by each diffraction grating, Thus, the beam is narrowed by coping with temperature fluctuations evenly. On the other hand, when the member having the diffraction grating is tilted, the light beam is diffracted in the direction corresponding to the tilt of the diffraction grating, causing the same problem as the tilting around the optical axis. When the diffractive portion is provided, not only the diffracted light but also the light beam imaged on the polygon mirror 5 is linear with an inclination with respect to the main scanning direction.

  In this case, in the diffraction grating member 20 formed with the diffraction grating 21 having R in the sub-scanning direction, this is the same as correcting the inclination of the diffraction grating member 20 by sliding the diffraction grating member 20 in the main scanning direction. An effect is obtained.

  That is, when the diffraction grating member 20 is inclined by α as shown in FIG. 4A, the diffraction grating 21 having R in the sub-scanning direction is also inclined by the angle α in the direction of the arrow 26 as shown in FIG. . However, as shown in FIG. 4C, the diffraction grating member 20 is slid in the main scanning direction as indicated by an arrow 27 so that the center of R in the diffraction grating 21 is perpendicular to the surface in the main scanning direction. The inclination of the diffraction grating member 20 can be corrected by coming to the plane including the axis.

  That is, when the diffraction grating member 20 is inclined by α, the tangent parallel to the diameter (Dm) of the aperture 23 of the light beam 23 in the diffraction grating 21 having R in the sub-scanning direction is the same as that of the diffraction grating 21. Is not on the plane passing through the center of the diffraction grating 21, but by sliding the diffraction grating member 20 in the main scanning direction, the contact point with the diffraction grating 21 comes to the plane passing through the center of the diffraction grating 21. is there.

  Thus, even if the diffraction grating member 20 is attached to the housing of the optical scanning optical device at an angle α due to manufacturing errors, component variations, assembly errors, etc., it can be easily adjusted. Can be corrected, and the tolerance can be increased accordingly, which is advantageous in terms of cost.

  The mechanism for sliding the diffraction grating member 20 in the main scanning direction is provided with, for example, a rail that holds the diffraction grating member 20 from both sides so as to be slidable in the main scanning direction, and is slid with a feed screw or the like to allow slight displacement. Various methods can be used.

  According to the present invention, even if the diffraction grating member is tilted and attached, it can be easily corrected, and even if the environmental temperature fluctuates, the conventional focal position change in the sub-scanning direction does not occur, and the beam diameter always has a normal value. Therefore, if this optical scanning optical device is used in an image forming apparatus, an image forming apparatus capable of forming a high-definition image over a long period of time can be provided.

1 is a perspective view of a schematic configuration in which an optical scanning optical device according to the present invention is applied to a photoconductor exposure apparatus in an image forming apparatus. FIG. 2 is a cross-sectional view in the sub-scanning direction of the optical scanning optical device shown in FIG. 1. FIG. 6 is a plan view of a diffraction grating member 20 provided independently of other optical members, and an enlarged view of a portion indicated by a dotted circle 22 in this plan view. It is a figure for demonstrating the coping method when the diffraction grating member 20 inclines and is attached to the housing of the optical scanning optical apparatus.

Explanation of symbols

1 Light source (semiconductor laser)
2 Collimating lens 3 Aperture (aperture stop)
31 Aperture 4 Cylindrical Lens 41 Fresnel Diffraction Grating 42 Negative Power Cylindrical Surface 5 Polygon Mirror 6, 7 fθ Lens 8 Reflecting Mirror 9 Photosensitive Member (Scanned Surface)
10 Scanning Direction 20 Diffraction Grating Member 21 Arc-shaped Diffraction Grating 22 Enlarged Illustrated Range 23 Light Beam 26 Tilt Direction Arrow 27 Slide Direction

Claims (6)

A light source comprising a semiconductor laser; scanning optical means for deflecting light from the light source to scan the surface to be scanned in the main scanning direction; and light from the light source on the reflecting surface of the scanning optical means. A first optical system that is shaped by an aperture and imaged as a long line in the main scanning direction, and a scanning speed of light deflected by the scanning optical means on the surface to be scanned is constant, and at least In the optical scanning optical device comprising the second optical system in which one optical element made of resin is arranged,
The first optical system includes a diffraction grating member having an arcuate grating shape perpendicular to a surface in the main scanning direction of the scanning optical means and having a center on a surface including the optical axis of the first optical system. The diffraction grating member is provided so as to be movable in the main scanning direction perpendicular to the optical axis of the optical system, and the effective diameter of the diffraction grating is formed larger than the aperture diameter,
An optical scanning optical device, wherein a change in a focal position in the sub-scanning direction in the optical scanning optical device due to a temperature change is corrected by a power change in a diffraction portion of the diffraction grating member due to a wavelength change in the light source.   The second optical system includes a first lens disposed on the scanning optical means side and a second lens disposed on the scanned surface side, and the first lens has a positive power in the main scanning direction. Each having a negative power in the sub-scanning direction orthogonal to the main scanning direction, the power in the main scanning direction being larger than the power in the main scanning direction of the second lens, and the second lens The optical scanning optical apparatus according to claim 1, wherein the optical scanning optical apparatus has a positive power in a scanning direction, and one of the first and second lenses has an aspherical shape.   The curvature of the arc-shaped diffraction grating shape in the diffraction grating member is the height Rc of the arcuate portion in the diffraction grating cut by the beam diameter Dm of the light shaped by the aperture in the first optical system. The optical scanning optical apparatus according to claim 1, wherein the ratio is between 1/400 and 1/1200, preferably 1/800.   4. The optical scanning optical apparatus according to claim 1, wherein the element that condenses the light from the light source as a long line in the main scanning direction is formed of an olefin resin material.   An image forming apparatus comprising the optical scanning optical device according to claim 1. The light from the light source consisting of a semiconductor laser is made into substantially parallel light and then shaped by an aperture, and is formed into a long line in the main scanning direction and formed on the reflecting surface of the deflecting means. The scanning optical system changes the scanning speed on the surface to be scanned. In a method of correcting a focal position change in the sub-scanning direction due to a temperature change in an optical scanning optical apparatus using an optical scanning method in which the deflection unit scans the main scanning direction on the surface to be scanned at a constant speed.
Diffraction by a diffraction grating member provided with an arc-shaped grating shape perpendicular to the surface in the main scanning direction and centered on the surface including the optical axis of the optical system when the light from the light source is linearly formed in the main scanning direction. And the tilt of the diffraction grating can be corrected by moving the diffraction grating in the main scanning direction orthogonal to the optical axis of the optical system. As the ambient temperature rises, a change in the diffraction index of the diffraction grating is brought about. The relationship between the optical element and the diffraction grating so that the amount of change in the focal point, the amount of change in the focal point caused by the change in refractive index due to the wavelength change of the light source, and the amount of change in the focal point of the optical system cancel each other. And correcting the change in the focal position in the sub-scanning direction of the optical scanning device due to the temperature rise in the optical scanning optical device.

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