JP2011018055A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that can reduce changes of beam diameter due to temperature change and pitch deflection of a sub-scanning beam pitch of multiple beams.SOLUTION: The optical scanner includes: a first optical system 21 having a coupling lens 2, that couples a light flux from a light source 1; a second optical system 22, that includes a lens 3 having a positive power in a sub scanning direction and forms the light flux into a line image extending in the main scanning direction on a deflector 4; and a third optical system 23, that condenses the light flux deflected by a deflector 4 as an optical beam spot on a surface to be scanned 9a and includes a first scanning lens 5 having positive power in the main scanning direction and a second scanning lens 6, having positive power in the sub scanning direction. The lateral magnification |βm| in the main scanning direction of the whole optical system is set larger than the lateral magnification |βs| in the sub-scanning direction. Ribs 20A and 20B satisfy the relation "the temperature T1 in the vicinity of the first scanning lens 5> the temperature T2 in the vicinity of the second scanning lens 6".

Description

  The present invention relates to an optical scanning device used in a laser beam printer (LBP), a plain paper facsimile (PPF), a digital copying machine, and the like, and an image forming apparatus including the optical scanning device.

  In recent years, a scanning density in an optical scanning device is required to be as high as 1200 dpi (dots per inch) or 2400 dpi. In order to achieve high density optical scanning, it is necessary to reduce the beam diameter of the light beam condensed on the surface to be scanned. As the density of optical scanning devices is increased in this way, the demand for smaller beam diameters is increasing, while the cost reduction is also required. Resin lenses are often used as scanning lenses to meet this demand for cost reduction, but resin lenses have a large imaging position shift due to temperature fluctuations, making it difficult to reduce the beam diameter. there were.

  As apparatuses that suppress such image position deviation, apparatuses described in Patent Document 1 and Patent Document 2 are known.

  In the above-mentioned Patent Document 1, a collimator unit including a semiconductor laser, a collimator lens, and a holding member for fixing and holding these components, and a light beam deflected by a deflecting unit from the collimator unit is imaged on a photoconductor. A scanning imaging optical system, and by optimizing the linear expansion coefficient, refractive index, etc. of the collimator lens, the scanning imaging optical system and the holding member, the imaging position deviation of the entire optical system is reduced. Is.

  Further, the above-mentioned Patent Document 2 discloses a deflecting device having a first imaging optical system for linearly imaging light from a light source, and a deflection reflection surface at an imaging position of the first imaging optical system. And a second imaging optical system for converging the light beam deflected in step S2 on the surface to be scanned, and using a resin lens (plastic lens) having negative power for the first imaging optical system Thus, the image forming position shift generated in the second image forming optical system is canceled, and the image forming position shift of the entire optical system is reduced.

  By the way, as the optical scanning speed of the optical scanning device increases, it becomes necessary to rotate a deflector such as a polygon scanner at a high speed. For this reason, the temperature in the vicinity of the deflector is caused by heat generated from the deflector rotating at high speed. And the temperature near the position at a distance away from the deflector, the temperature distribution in the optical scanning device, that is, the optical housing becomes non-uniform. For this reason, it is necessary to take measures to suppress the imaging position deviation on the assumption that the temperature distribution in the optical housing is non-uniform.

  However, the above Patent Documents 1 and 2 do not describe that the image position deviation is suppressed on the assumption that the temperature distribution in the optical scanning device (that is, in the optical housing) is non-uniform. There is no suggestion. That is, the optical scanning devices described in Patent Documents 1 and 2 are based on the premise that the temperature distribution in the optical housing is non-uniform due to heat generated from the deflector rotating at high speed. It is not intended to suppress image position deviation. Therefore, in the optical scanning devices described in the above-mentioned Patent Documents 1 and 2, even if the countermeasures described in the respective Patent Documents are taken, the beam diameter of the light beam and the sub-scanning beam pitch of the multi-beam are adjusted. There was a problem of degrading the pitch deviation.

  Further, in the optical scanning device disclosed in Patent Document 2, as described above, a resin lens having negative power is used for the first imaging optical system, and an imaging position shift generated in the second imaging optical system. However, in order to improve the correction effect of the image position deviation, it is necessary to set the negative power of the resin lens to a large value, which makes it difficult to process the resin lens. In addition, there is a problem that the wavefront aberration is deteriorated.

  The present invention has been made in view of the above, and a first object thereof is to provide an optical scanning device capable of reducing beam diameter variation due to temperature variation and pitch deviation of multi-beam sub-scanning beam pitches. That is.

  The second object is to provide an optical scanning device capable of reducing the beam diameter variation due to temperature variation and the pitch deviation of the multi-beam sub-scanning beam pitch, and realizing a small beam diameter by obtaining a good wavefront aberration. Is to provide.

  A third object is to reduce the beam diameter variation due to temperature variation and the pitch deviation of the multi-beam sub-scanning beam pitch, and at the same time, use an optical scanning device capable of realizing the beam diameter reduction, and the granularity, resolution, and gradation. An object of the present invention is to provide an image forming apparatus capable of outputting a stable and high-quality image excellent in tonality.

  In order to solve the above-described problem and achieve the first object, an optical scanning device according to a first aspect of the present invention includes a first optical system having a coupling lens for coupling a light beam from a light source, A second optical system that guides the light beam from the first optical system to a deflector; and a scanning imaging element that condenses the light beam deflected by the deflector as a light spot on the surface to be scanned. A horizontal magnification | βm | in the main scanning direction of the entire optical system formed from the first optical system, the second optical system, and the third optical system. Is larger than | βs |, and the second optical system is formed of a glass lens having a positive power in the sub-scanning direction or a resin lens having a positive power in the sub-scanning direction. The third optical system has power in the main scanning direction. And a second resin optical element having power in the sub-scanning direction, and the temperature in the atmosphere in the vicinity of the first resin optical element is T1, When the temperature in the atmosphere in the vicinity of the second resin optical element is T2, a heat insulating member is further provided so as to satisfy the relationship of T1> T2.

  According to the first aspect of the present invention, it is possible to reduce the beam diameter variation caused by temperature variation and the pitch deviation of the multi-beam sub-scanning beam pitch.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the first resin optical element has a positive power in the main scanning direction, and the second resin optical element. The element has a positive power in the sub-scanning direction.

  According to a third aspect of the present invention, there is provided the optical scanning device according to the first or second aspect, wherein the heat insulating member is provided in the vicinity of the first resin optical element.

  An optical scanning device according to a fourth aspect of the present invention is the optical scanning device according to any one of the first to third aspects, wherein the heat insulating member is a rib.

  An optical scanning device according to a fifth aspect of the present invention is the optical scanning device according to any one of the first to fourth aspects, wherein the rib is on the casing around the deflector, and It is arranged adjacent to the first resin optical element.

  Furthermore, in order to achieve the third object, an image forming apparatus according to a sixth aspect of the present invention includes the optical scanning device according to any one of the first to fifth aspects.

  According to the sixth aspect of the present invention, by using the optical scanning device according to any one of the first to fifth aspects, a stable and high-quality image excellent in granularity, resolution, and gradation. Can be output.

  In order to achieve the second object, an optical scanning device according to another aspect of the invention includes a first optical system having a coupling lens for coupling a light beam from a light source, and the light beam as a main component in a deflector. A second optical system that forms a line image that is long in the scanning direction; and a third optical system that includes a scanning imaging element that focuses the light beam deflected by the deflector as a light spot on the surface to be scanned; The horizontal magnification | βm | in the main scanning direction of the entire optical system formed from the first optical system, the second optical system, and the third optical system is greater than the horizontal magnification | βs | in the sub-scanning direction. The second optical system is formed of a glass lens having a positive power in the sub-scanning direction and a resin lens having a negative power in the sub-scanning direction, and The third optical system provides positive power mainly in the main scanning direction. And a second resin optical element mainly having a positive power in the sub-scanning direction, and further, the temperature in the atmosphere in the vicinity of the first resin optical element is set. When T1 is set and T2 is the temperature in the atmosphere in the vicinity of the second resin optical element, temperature distribution generating means that satisfies the relationship of T1> T2 is further provided.

  According to this invention, the second optical system includes the resin lens having negative power in the sub-scanning direction and the glass lens having positive power in the sub-scanning direction. By reducing the beam diameter variation and the pitch deviation of the multi-beam sub-scanning beam pitch and satisfying the relationship of T1> T2, the negative power in the sub-scanning direction of the resin lens can be reduced.

  In an optical scanning device according to another aspect of the invention, the second optical system includes a resin lens and a plurality of glass lenses, and the resin lens has negative power in both the main scanning direction and the sub-scanning direction. And at least one of the plurality of glass lenses has a positive power in the sub-scanning direction.

  According to this invention, the second optical system includes a resin lens having negative power in both the main scanning direction and the sub-scanning direction, and at least one glass lens having positive power in the sub-scanning direction. Therefore, it is possible to reduce the negative power in the sub-scanning direction of the resin lens by reducing the beam diameter variation due to temperature variation and the pitch deviation of the multi-beam sub-scanning beam pitch and satisfying the relationship of T1> T2. Can be small.

  As described above, according to the present invention, it is possible to reduce the beam diameter variation caused by the temperature variation and the pitch deviation of the sub-scanning beam pitch of the multi-beam, and the multi-beam conversion becomes easy. As a result, the number of rotations of a deflector such as a polygon scanner can be reduced, and thus an optical scanning device that achieves high durability, low noise, and low power consumption can be provided.

  Further, according to the present invention, it is possible to provide an image forming apparatus that outputs a stable and high-quality image having excellent granularity, resolution, and gradation.

  According to another invention, the first optical system having a coupling lens for coupling the light beam from the light source, and the second optical for forming the light beam on the deflector as a long line image in the main scanning direction. And a third optical system having a scanning imaging element for condensing the light beam deflected by the deflector as a light spot on the surface to be scanned, the first optical system and the second optical system. The lateral magnification | βm | in the main scanning direction of all the optical systems formed from the system and the third optical system is set to be larger than the lateral magnification | βs | in the sub-scanning direction, and the second optical system includes The third optical system is formed mainly of a glass lens having a positive power in the sub-scanning direction and a resin lens having a negative power in the sub-scanning direction. The third optical system is mainly positive in the main scanning direction. A first plastic optical element having power, mainly in the sub-scanning direction A second resin optical element having a positive power, and T1 is an atmosphere in the vicinity of the first resin optical element, and an atmosphere in the vicinity of the second resin optical element. Since the temperature distribution generating means that satisfies the relationship of T1> T2 is further provided when the temperature is T2, the beam diameter variation due to the temperature variation and the pitch deviation of the multi-beam sub-scanning beam pitch are reduced, and T1 By satisfying the relationship of> T2, it is possible to reduce the negative power in the sub-scanning direction of the resin lens, and it is possible to reduce the beam diameter by obtaining a favorable wavefront aberration.

  According to another invention, the second optical system includes a resin lens having negative power in both the main scanning direction and the sub scanning direction, and at least one of a plurality of glasses having positive power in the sub scanning direction. Therefore, by reducing the beam diameter variation due to temperature variation and the pitch deviation of the multi-beam sub-scanning beam pitch, and satisfying the relationship of T1> T2, the negative direction of the resin lens in the sub-scanning direction is reduced. The beam diameter can be reduced by obtaining a good wavefront aberration.

FIG. 1 is a configuration diagram illustrating the configuration of the optical scanning device according to the first embodiment. 2 is a cross-sectional view showing a cross section taken along line FF in FIG. FIG. 3 is a diagram for explaining an optical system of the optical scanning device shown in FIG. 4 is a cross-sectional view of a plane perpendicular to the optical axis (a plane perpendicular to the paper surface) in the optical system of FIG. FIG. 5 is a configuration diagram illustrating the configuration of another optical scanning device according to the first embodiment. 6 is a cross-sectional view of a plane perpendicular to the optical axis (a plane perpendicular to the paper surface) in the optical system of FIG. FIG. 7 is an enlarged view enlarging the shape and positional relationship of each lens constituting the second optical system shown in FIG. FIG. 8 is a main part configuration diagram showing the configuration of the image forming apparatus according to the second embodiment.

  Exemplary embodiments of an optical scanning device and an image forming apparatus according to the present invention are explained in detail below with reference to the accompanying drawings.

(Embodiment 1)
1 is a block diagram showing a configuration of an optical scanning apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a cross-sectional view showing a cross section taken along line FF in FIG.

  As shown in FIG. 1, the light beam emitted from the light source 1 is coupled to a desired light beam state by a coupling lens 2. Here, it is coupled to a substantially parallel light beam. As the light source 1, a semiconductor laser, a semiconductor laser array having a plurality of light emitting points, or a multi-beam using a beam combining type light source that combines light beams from the semiconductor laser with a prism or the like can be used. The coupling lens 2 is a single aspherical lens. The wavefront aberration of the coupling lens 2 alone is corrected well. The light beam emitted from the coupling lens 2 is incident on a lens 3 having power in the sub-scanning direction, and is condensed in a substantially linear shape in the vicinity of the deflection reflection surface of the deflector 4 in the main scanning direction.

  The light beam deflected by the deflecting / reflecting surface of the deflector 4 is deflected equiangularly with the constant speed rotation of the deflector 4, and the first scanning lens 5 mainly having power in the main scanning direction and mainly the sub-scanning. The light passes through the second scanning lens 6 having power in the scanning direction. The transmitted light beam is bent through the first scanning lens 5 and the second scanning lens 6 while the optical path such as field curvature and fθ characteristic in the main scanning direction and the sub-scanning direction are corrected, and the optical path is bent by the bending mirror 7. As shown in FIG. 2, an image is formed on the scanned surface 9 a of the image carrier 9 through the window 8.

  The beam is incident on the mirror 10 prior to optical scanning, and is focused on the light receiving element 12 by the lens 11. Based on the output of the light receiving element 12, the write timing of optical scanning is determined. Further, the optical components (optical elements) indicated by reference numerals 1 to 7 described above are accommodated in the housing 13. The housing 13 is covered with a cover 14 and the inside thereof is substantially sealed.

  Reference numerals 20A and 20B in FIG. 1 are ribs for preventing heat generated from the deflector 4 from being transmitted to the second scanning lens 6 side. The ribs 20A and 20B do not completely block heat transfer, but the temperature T1 in the atmosphere near the first scanning lens 5 is higher than the temperature T2 in the atmosphere near the second scanning lens 6. It is formed in a shape. That is, the ribs 20A and 20B generate a temperature distribution so that the relationship of temperature T1> temperature T2 is satisfied. These ribs 20A and 20B correspond to the temperature distribution generating means described in the claims.

  The optical system of the optical scanning device according to the first embodiment will be described with reference to FIG. FIG. 3 is a diagram for explaining an optical system of the optical scanning device shown in FIG. In FIG. 3, the light source 1 to the coupling lens 2 are the first optical system 21, the lens 3 is the second optical system 22, and the optical system composed of the first and second scanning lenses 5 and 6 is used. The third optical system 23 is assumed. The first scanning lens 5 corresponds to the first resin optical element recited in the claims, and the second scanning lens 6 corresponds to the second resin optical element recited in the claims.

  By the way, as is well known, the deflector 4 rotates at a high speed and becomes a heat source. In the first embodiment, the ribs 20A and 20B are first formed as shown in FIG. 1 in order to actively use the heat source. By providing in the vicinity of the scanning lens 5, a temperature distribution is generated so that the relationship of “temperature T <b> 1> temperature T <b> 2” is established in a stable state.

Specifically, the first to third optical systems have the following temperature distribution.
Temperature T01 = 45 ° C. in the first optical system 21
Temperature T02 = 45 ° C. in the second optical system 22
Temperature T1 near the first scanning lens 5 = 45 ° C.
Temperature T2 near the second scanning lens 6 = 35 ° C.

  The expression of the lens surface shape of the scanning imaging element, that is, the lens constituting the scanning optical system is expressed by the following equation.

(Non-arc shape in the main scanning section)
The surface shape of the lens surface in the main scanning section has a non-arc shape, and this non-arc shape has a paraxial radius of curvature in the main scanning section of Rm, a distance in the main scanning direction from the optical axis of Y, and a cone. It is expressed by the following polynomial (1) where K is the constant, and X is the depth in the optical axis direction when the higher-order coefficients are A1, A2, A3, A4, A5, A6,.
X = (Y ² / Rm) / [1 + √ {1− (1 + K) (Y / Rm) ² }
+ A1 ・ Y + A2 ・ Y ² + A3 ・ Y ³ + A4 ・ Y <sup>4
+ A5 · Y 5 + A6 ·</sup> Y 6 ··· ·· (1)

  Here, in Formula (1), when a numerical value other than zero is substituted for odd-order coefficients A1, A3, A5,..., The non-arc shape becomes an asymmetric shape in the main scanning direction. In the first embodiment, since only the even order is used in the equation (1), the non-arc shape is a symmetrical shape in the main scanning direction.

(Curvature radius in the sub-scan section)
The radius of curvature in the sub-scan section of the lens surface is the following polynomial (2) when the radius of curvature changes in the main scan direction (represented by coordinates (coordinate value Y) with the optical axis as the origin) in the sub-scan section. It is represented by
Cs (Y) = 1 / Rs (0) + B1 · Y + B2 · Y ² + B3 · Y ³
+ B4 · Y ⁴ + B5 · Y ⁵ + ... (2)

  Here, Rs (0) represents the radius of curvature on the optical axis (Y = 0) in the sub-scan section, and B1, B2, B3, B4, B5,... Are higher-order coefficients. Further, in equation (2), when a value other than zero is substituted for odd-order coefficients B1, B3, B5,... Of Y, the change in the radius of curvature in the sub-scanning section becomes asymmetric in the main scanning direction. .

(Sub non-arc surface)
The sub non-arc surface is expressed by the following equation (1).

  The expression of the fourth term of Equation 1 is defined as the following Equation 2.

  This number 2 can be decomposed as shown in the following number 3.

Here, in Equations 1 to 3, Y represents the position in the main scanning direction of the sub-scanning section (coordinate with the optical axis position as the origin), Z represents the coordinate in the sub-scanning direction, and Cm or 1 / Rm is The paraxial curvature in the direction corresponding to the main scanning near the optical axis, Cs (0) or 1 / Rs (0) represents the paraxial curvature in the direction corresponding to the sub-scanning near the optical axis, and Cs (Y) corresponds to the main scanning. The paraxial curvature in the sub-scanning corresponding direction in the direction Y, Kz (Y) represents a conic constant representing the quadratic surface in the sub-scanning corresponding direction in the main scanning corresponding direction Y, and f _SAG (Y, Z) is an aspherical surface. Represents a high-order correction amount.

The paraxial curvature Cs in the sub-scanning corresponding direction is expressed by the following polynomial (3), and the conic constant Kz representing the quadric surface in the sub-scanning corresponding direction is expressed by the following polynomial (4).
Cs = 1 / Rs (0) + B1 · Y + B2 · Y ² + B3 · Y ³
+ B4 · Y ⁴ + B5 · Y ⁵ + ... (3)
Kz = C0 + C1 · Y + C2 · Y ² + C3 · Y ³
+ C4 · Y ⁴ + C5 · Y ⁵ + ... (4)

  Here, in Equation (3), when a numerical value other than zero is substituted for the odd-order coefficients B1, B3, B5,..., The change in the radius of curvature in the sub-scanning section is asymmetric in the main scanning direction. Become.

  Similarly, the odd-order coefficients of Y representing non-arc amounts such as C1, C3, C5,..., F1, F3, F5,..., G1, G3, G5,. When the numerical value is substituted, the change in the amount of non-arc in the sub-scanning section becomes asymmetric in the main scanning direction.

Example 1
The size and arrangement relationship of each component of the optical system in the optical scanning apparatus according to the first embodiment will be described with reference to FIGS. FIG. 4 is a cross-sectional view of a plane perpendicular to the optical axis (a plane perpendicular to the paper surface) in the optical system shown in FIG.

The light source 1 oscillates laser light having a wavelength of 780 nm. The coupling lens 2 has a focal length of 27 mm, and has a collimating action as a coupling action. The linear expansion coefficient of the coupling part 2 and the mounting part (base member) (not shown) of the light source 1 is “2.31 × 10 ⁻⁵ ”.

  The deflector 4 is composed of a polygon mirror, the number of deflecting reflection surfaces is 5, the inscribed circle radius is 18 mm, the incident direction of the beam from the light source 1 side and the scanning optical system (first and second scanning lenses 5 and 6). The angle formed by the optical axis is 60 degrees (see FIG. 3).

The lens 3 is formed of a glass lens having a positive power in the sub-scanning direction. The refractive index of the glass lens as the lens 3 is “1.51119” at 25 ° C. and “1.51113” at 45 ° C. The linear expansion coefficient of the glass lens is “7.5 × 10 ^{− 6} ”. Thickness of lens 3 (distance between surfaces 3a and 3b on the optical axis) d5 = 3 mm, distance d6 between surface 3b of lens 3 and the reflecting surface of deflector 4 on the optical axis 8 mm (see FIG. 4). The curvature radius of the surface 3a of the lens 3 is “∞” in the main scanning direction and “23 mm” in the sub-scanning direction, and the curvature radius of the surface 3b is “∞ (plane)”.

A resin scanning lens is used as the first scanning lens 5, and a resin scanning lens is used as the second scanning lens 6. The refractive indexes of the resin scanning lenses as the first and second scanning lenses 5 and 6 are “1.523978” at 25 ° C., “1.523088” at 35 ° C., and “1.523088” at 45 ° C. 1.522197 ". The linear expansion coefficient of the resin scanning lenses as the first and second scanning lenses 5 and 6 is “7 × 10 ⁻⁵ ”.

  The distance d7 = 71.6 mm between the reflecting surface of the deflector 4 on the optical axis and the surface 5a (incident surface) of the first scanning lens 5, the thickness of the first scanning lens 5 (the surface 5a on the optical axis and Distance between the surface 5b) d8 = 30 mm and a distance d9 = 66. Between the surface 5b (exit surface) of the first scanning lens 5 and the surface 6a (incident surface) of the second scanning lens 6 on the optical axis. 3 mm, the thickness of the second scanning lens 6 (distance between the surface 6a and the surface 6b on the optical axis) d10 = 8.5 mm, the surface 6b (exit surface) of the second scanning lens 6 on the optical axis and the surface to be covered The distance d11 to the scanning surface 9a is 159.3 mm, the distance d12 is 0.2 mm, and the distance d13 is 0.2 mm (see FIG. 4). The distances d12 and d13 are shift amounts given by moving the optical axes of the first and second scanning lenses 5 and 6 parallel to the main scanning direction with respect to the optical axis.

Here, the coefficients in the main scanning direction and the sub-scanning direction of the surfaces 5a and 5b of the first scanning lens 5 and the surfaces 6a and 6b of the second scanning lens 6 are listed in Tables 1 to 4, respectively. In Tables 1 to 4, Rm represents a radius of curvature in the main scanning direction, and Rs represents a radius of curvature in the sub-scanning direction. “E + 02” represents 10 ² , and “E−08” represents 10 ⁻⁸ , and these numerical values depend on the immediately preceding numerical values.

  In the first embodiment, the temperature distribution is as follows by the heat source of the deflector 4 that rotates at high speed. T01 = T02 = T1 = 45 ° C. and T2 = 35 ° C. Here, T01 is the temperature in the first optical system 21, T02 is the temperature T02 in the second optical system 22, T1 is the temperature in the atmosphere in the vicinity of the first scanning lens 5, and T2 is in the vicinity of the second scanning lens 6. Each represents the temperature in the atmosphere. The definition contents of T01, T02, T1, and T2 are the same in the second to fourth embodiments described later.

  Table 5 shows an example of the result of the field curvature fluctuations generated in the first to third optical systems 21, 22, and 23 under the temperature distribution as described above.

  In Example 1, the lateral magnification of the entire optical system formed by the first optical system 21, the second optical system 22, and the third optical system 23 is the lateral magnification βm = 8.45 in the main scanning direction. Yes, the horizontal magnification βs in the sub-scanning direction is 1.55. In Table 5, since T01 = T02 = T1 = T2 = 45 ° C. before the countermeasure, no temperature distribution is generated in the optical housing.

  In the first optical system 21, since the base member to which the light source 1 and the coupling lens 2 are attached expands, the curvature of field fluctuates in the negative direction in both the main scanning direction and the sub scanning direction when the temperature rises. Since the lateral magnification of the optical system is set so that the relationship | βm |> | βs | is established, the correction amount of the field curvature by the first optical system 21 is the sub-scanning in the main scanning direction. Greater than direction. Therefore, it is necessary to suppress the sub-scanning direction for the field curvature fluctuation generated in the third optical system 23. Therefore, by setting T1 (45 ° C.)> T2 (35 ° C.) as described above, it is possible to suppress the image curvature variation of the entire optical system.

  As described above, according to the first embodiment, it is possible to reduce the field curvature change caused by the temperature variation of the first to third optical systems 21, 22, and 23, thereby reducing the beam diameter and Stabilization can be realized, and even when a multi-beam is used as the light source 1, the field deviation in the sub-scanning direction is small, so that the pitch deviation of the sub-scanning beam pitch can be reduced.

(Example 2)
In the second embodiment, the optical system in the optical scanning device is linearly expanded in the attachment portion (base member) of the coupling lens 2 and the light source 1 in the configuration of the optical system in the optical scanning device in the first embodiment shown in FIG. The coefficient is changed from “2.31 × 10 ⁻⁵ ” to “3.1 × 10 ⁻⁵ ”, and the glass lens as the lens 3 of the second optical system 22 is changed to a resin lens. Yes.

The curvature radius of the surface 3a (incident surface) of the lens 3 formed of a resin lens is “∞” in the main scanning direction and “23.57 mm” in the sub-scanning direction, and the surface 3b (exit) of the lens 3 The curvature radius of (surface) is “∞ (plane)”. The refractive index of the resin lens is “1.523978” at 25 ° C. and “1.522197” at 45 ° C. Furthermore, the linear expansion coefficient of the resin lens is “7 × 10 ⁻⁵ ”.

  In the second embodiment, similarly to the first embodiment, the temperature distribution is such that T01 = T02 = T1 = 45 ° C. and T2 = 35 ° C. by the heat source of the deflector 4 that rotates at high speed. Table 6 shows an example of the results of the field curvature fluctuations that occur in the first to third optical systems 21, 22, and 23 described above under such a temperature distribution.

  In Example 2, the lateral magnification of the entire optical system formed by the first optical system 21, the second optical system 22, and the third optical system 23 is the lateral magnification βm = 8.45 in the main scanning direction. Yes, the horizontal magnification βs in the sub-scanning direction is 1.55. In Table 6, since T01 = T02 = T1 = T2 = 45 ° C. before the countermeasure, no temperature distribution is generated in the optical housing.

  In the first optical system 21, since the base member to which the light source 1 and the coupling lens 2 are attached expands, the curvature of field fluctuates in the negative direction in both the main scanning direction and the sub scanning direction when the temperature rises. Since the lateral magnification of the optical system is set so as to satisfy the relationship | βm |> | βs |, the correction amount of the curvature of field by the first optical system 21 is sub-scanning in the main scanning direction. The field curvature in the sub-scanning direction moves in the plus direction in the second optical system 22 (the field curvature variation is 0.18 mm). Accordingly, it is necessary to suppress the sub-scanning direction with respect to the field curvature fluctuation generated in the third optical system 23. Therefore, by setting T1 (45 ° C.)> T2 (35 ° C.) as described above, it is possible to suppress image curvature variation of the entire optical system.

  As described above, according to the second embodiment, the same operational effects as in the first embodiment can be obtained.

(Example 3)
The size and arrangement relationship of each component in the optical system of the optical scanning apparatus according to the third embodiment will be described with reference to FIGS. The optical system of the optical scanning device shown in FIG. 5 has a configuration in which lenses 31 and 32 are added to the second optical system 22 in the configuration of the optical system of the first embodiment shown in FIG. In FIG. 5, parts having the same functions as those of the optical system of the optical scanning device shown in FIG. 3 are denoted by the same reference numerals. 6 is a cross-sectional view of a plane perpendicular to the optical axis (a plane perpendicular to the paper surface) in the optical system of FIG. Further, FIG. 7 is an enlarged view in which the shape and arrangement relationship of the lens 3 and the lenses 31 and 32 of the second optical system 22 are enlarged.

  In FIG. 7, the lens 31 is formed of a resin lens having negative power only in the sub-scanning direction. The lens 32 is formed of a glass lens having a negative power in the sub-scanning direction.

  The curvature radius of the surface 31a of the lens 31 is “∞ (plane)”, and the curvature radius of the surface 31b is “∞” in the main scanning direction and “19.82 mm” in the sub-scanning direction. On the other hand, the curvature radius of the surface 32a of the lens 32 is “∞” and the sub-scanning direction is “−18.7 mm”, and the curvature radius of the surface 32b is “1.0E + 8” in the main scanning direction and in the sub-scanning direction. It is “18.03 mm (sub non-arc surface)”. Further, the curvature radius of the surface 3a of the lens 3 is “∞”, the sub-scanning direction is “13.54 mm”, and the curvature radius of the surface 3b is “∞ (plane)”.

The refractive index of the resin lens as the lens 31 is “1.523978” at 25 ° C. and “1.522197” at 45 ° C. The linear expansion coefficient of the resin lens as the lens 31 is “ 7 × 10 ⁻⁵ ”. The refractive index of the glass lens as the lens 32 is “1.51119” at 25 ° C. and “1.51113” at 45 ° C. The linear expansion coefficient of the glass lens as the lens 32 is “ 7.5 × 10 ⁻⁶ ”. Further, the refractive index of the glass lens as the lens 3 is “1.73278” at 25 ° C. and “1.733058” at 45 ° C., and the linear expansion coefficient of the glass lens as the lens 3 is “ 5.4 × 10 ⁻⁶ ”.

  In FIG. 6, the thickness of the lens 31 on the optical axis (distance between the surface 31a and the surface 31b on the optical axis) d1 = 3 mm, the surface 31b (exit surface) of the lens 31 on the optical axis, and the lens 32. Distance d2 from the surface 32a (incident surface) = 9.2 mm, thickness of the lens 32 (distance between 32a and the surface 32b on the optical axis) d3 = 3 mm, surface 32b of the lens 32 on the optical axis The distance d4 between the (exiting surface) and the surface 3a (incident surface) of the lens 3 is 8.15 mm, the thickness of the lens 3 (the distance between the surface 3a and the surface 3b on the optical axis) d5 = 6 mm, The distance d6 = 144 mm between the surface 3b of the lens 3 and the reflecting surface of the deflector 4 on the optical axis. In FIG. 6, the values of d7 to d11 are the same as the values of d7 to d11 in the optical system of Example 1 shown in FIG.

Here, Table 7 lists coefficients in the main scanning direction and the sub-scanning direction of the surface 32a of the lens 32. The surface 32a has power almost only in the sub-scanning direction. In Table 7, Rm represents the radius of curvature in the main scanning direction, and Rs represents the radius of curvature in the sub-scanning direction. Further, “E + 01” represents 10 ¹ , and “E-07” represents 10 ⁻⁷ , and these numerical values depend on the immediately preceding numerical values.

  In the third embodiment, similarly to the first embodiment, the temperature distribution is such that T01 = T02 = T1 = 45 ° C. and T2 = 35 ° C. by the heat source of the deflector 4 that rotates at high speed. Table 8 shows an example of the result of the field curvature fluctuation generated in the first to third optical systems 21, 22, and 23 described above under such a temperature distribution.

  In Example 3, the lateral magnification of the entire optical system formed by the first optical system 21, the second optical system 22, and the third optical system 23 is the lateral magnification βm = 8.45 in the main scanning direction. Yes, the horizontal magnification βs in the sub-scanning direction is 1.55. In Table 7, since T01 = T02 = T1 = T2 = 45 ° C. before countermeasures, no temperature distribution is generated in the optical housing.

  As can be seen from Table 8, in the second optical system, by using a resin lens as the lens 31 having negative power in the sub-scanning direction in the second optical system 21, the field curvature in the sub-scanning direction can be reduced. Although it is corrected, it is inadequately corrected as it is. However, in order to give the resin lens as the lens 31 more correction functions, it is necessary to further increase the negative power of the resin lens, which causes a problem in processing the resin lens. At the same time, the wavefront aberration is deteriorated. Therefore, by setting T1 (45 ° C.)> T2 (35 ° C.) as described above, it is possible to suppress the image curvature variation of the entire optical system.

  Here, an example of the beam spot diameter at each image height in the third embodiment is shown in Table 9.

  As described above, according to the third embodiment, the same operational effects as in the first embodiment can be obtained. Further, in Example 3, since it is not necessary to reduce the curvature radius in the sub-scanning direction of the resin lens as the lens 31 having negative power, the wavefront aberration is not deteriorated, which is good as is clear from Table 9. A beam spot diameter is obtained.

Example 4
The optical system in the optical scanning device of the fourth embodiment adds negative power in the main scanning direction to the resin lens as the lens 31 in the configuration of the optical system in the optical scanning device of the third embodiment shown in FIG. In addition, a positive power is applied to the glass lens as the lens 32 in the main scanning direction.

  That is, the resin lens as the lens 31 has a negative power in the main scanning direction and a positive power in the sub-scanning direction. The glass lens as the lens 32 has positive power in both the main scanning direction and the sub-scanning direction, and the glass lens as the lens 3 has positive power in the sub-scanning direction.

  The curvature radius of the surface 31a of the lens 31 is “∞ (plane)”, and the curvature radius of the surface 31b is “150 mm” in the main scanning direction and “19.82 mm” in the sub-scanning direction. The radius of curvature of the surface 32a of the lens 32 is “151 mm” in the main scanning direction and “150 mm” in the sub-scanning direction. The radius of curvature of the surface 32b of the lens 32 and the radius of curvature of the surfaces 3a and 3b of the lens 3 are the same as in the third embodiment. Further, the refractive indexes and linear expansion coefficients of the lenses 31 and 32 and the lens 3 are the same as those in the third embodiment. Further, in FIG. 6, the values of d1 to d11 are the same as those in the third embodiment.

  In the fourth embodiment, similarly to the first embodiment, the temperature distribution is T01 = T02 = T1 = 45 ° C. and T2 = 35 ° C. by the heat source of the deflector 4 that rotates at high speed. Table 10 shows an example of the result of the field curvature fluctuation generated in the first to third optical systems 21, 22, and 23 described above under such a temperature distribution.

  In Example 4, the lateral magnification of the entire optical system formed by the first optical system 21, the second optical system 22, and the third optical system 23 is a lateral magnification βm = 8.45 in the main scanning direction. Yes, the horizontal magnification βs in the sub-scanning direction is 1.55. In Table 7, since T01 = T02 = T1 = T2 = 45 ° C. before the countermeasure, no temperature distribution is generated in the optical housing.

  As is apparent from Table 10, in the second optical system, by using a resin lens as the lens 31 having a negative power in the sub-scanning direction in the second optical system 21, the field curvature in the sub-scanning direction can be reduced. Although it is corrected, it is inadequately corrected as it is. However, in order to give the resin lens as the lens 31 more correction functions, it is necessary to further increase the negative power of the resin lens, which causes a problem in processing the resin lens. At the same time, the wavefront aberration is deteriorated. Therefore, by setting T1 (45 ° C.)> T2 (35 ° C.) as described above, it is possible to suppress the image curvature variation of the all optical system, and the image plane of the all optical system in the sub-scanning direction. The bending fluctuation can be suppressed.

  In Example 4, the number of the resin lenses as the lens 31 is one, but the number of the resin lenses may be two. In this case, the two resin lenses may be a combination of a lens having only negative power in the sub-scanning direction and a lens having power only in the main-scanning direction, and both lenses are in the main-scanning and sub-scanning directions. It may have negative power.

  As described above, according to the fourth embodiment, the same operational effects as in the first embodiment can be obtained.

(Embodiment 2)
FIG. 8 is a main part configuration diagram showing the configuration of the image forming apparatus according to the second embodiment of the present invention. In the image forming apparatus shown in FIG. 8, around the image carrier 41, a charger 42, an optical scanning device 43, a developing device 44, a transfer charger 45, a fixing device 46, and a cleaning device 47 are arranged. . The optical scanning device 43 is, for example, an optical scanning device according to any one of Examples 1 to 4 of the first embodiment.

  One representative image forming process for forming an image is an electrophotographic process. In this electrophotographic process, a light spot from the optical scanning device 43 is irradiated onto a photoconductor as an image carrier 41 uniformly charged by a charger 42 to form a latent image (exposure) and develop. The toner is attached to the latent image by the device 44 to form a toner image (development), the toner image is transferred (transferred) to the recording paper S by the transfer charger 45, and pressure and heat are applied by the fixing device 46. An image is formed by a series of processes of fusing (fixing) the recording paper S.

  As described above, according to the second embodiment, a high-quality image can be obtained by using the optical scanning device as the exposure unit of the image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Light source 2 Coupling lens 3 Lens 4 Deflector 5 1st scanning lens 6 2nd scanning lens 7 Bending mirror 8 Window 9 Image carrier 20A, 20B Rib 21 1st optical system 22 2nd optical system 23 3rd optical system Optical system 31 Plastic lens 32 Glass lens

Japanese Patent No. 2736984 Japanese Patent No. 2804647

Claims (6)

A first optical system having a coupling lens for coupling a light beam from a light source;
A second optical system for guiding a light beam from the first optical system to a deflector;
A third optical system having a scanning imaging element that focuses the light beam deflected by the deflector as a light spot on the surface to be scanned;
With
The lateral magnification | βm | in the main scanning direction of all the optical systems formed from the first optical system, the second optical system, and the third optical system is set larger than the lateral magnification | βs | in the sub-scanning direction. As well as
The second optical system is formed of a glass lens having a positive power in the sub-scanning direction or a resin lens having a positive power in the sub-scanning direction,
The third optical system includes a first resin optical element having power in the main scanning direction, and a second resin optical element having power in the sub-scanning direction,
Furthermore, when the temperature in the atmosphere in the vicinity of the first resin optical element is T1, and the temperature in the atmosphere in the vicinity of the second resin optical element is T2, the relationship of T1> T2 is satisfied. An optical scanning device further comprising a heat insulating member.   2. The light according to claim 1, wherein the first resin optical element has a positive power in the main scanning direction, and the second resin optical element has a positive power in the sub-scanning direction. Scanning device.   The optical scanning device according to claim 1, wherein the heat insulating member is provided in the vicinity of the first resin optical element.   The optical scanning device according to claim 1, wherein the heat insulating member is a rib.   5. The rib according to claim 1, wherein the rib is disposed on the housing around the deflector and adjacent to the first resin optical element. 6. Optical scanning device. An image forming apparatus comprising the optical scanning device according to claim 1.

Images