JP3458973B2 - Optical scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device.

[0002]

2. Description of the Related Art An optical scanning device deflects a light beam by a light deflecting means such as a polygon mirror and converges it as a light spot on a surface to be scanned by an image forming optical system such as an fθ lens.
It is well known that it is known as a device that performs optical scanning and is used in a writing unit of an optical printer or a digital copying machine.

Recently, it has been proposed to use a reflection image-forming element having a concave mirror surface as an image-forming optical system for converging the light beam deflected by the light-deflecting means as a light spot on the surface to be scanned. In addition, there is also proposed a reflective imaging element having a function of making the movement of the light spot uniform (function corresponding to the fθ function in the fθ lens).

Such a reflective imaging element has an advantage that it can be easily and inexpensively manufactured by molding a plastic. However, since it is made of plastic, it is easily affected by temperature, and dimensional changes due to temperature changes affect optical scanning. This effect mainly appears as a magnification error or a change in linearity.

Recently, by adopting an aspherical surface for the mirror surface, the field performance and linearity are corrected to improve the optical performance of the reflective image-forming element, and it can be shared with a toroidal lens or the like to provide accurate light. Although it is intended to perform scanning, there is no known optical scanning device that takes measures against the influence of the temperature.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and in optical scanning using a reflective imaging element made of plastic, the effect of temperature change on the optical scanning characteristics can be effectively reduced. To provide a simple optical scanning device.

[0007]

In the "optical scanning device" of the present invention, the "deflected light beam deflected by the light deflecting means is reflected by a reflective imaging element, and the reflected light beam is scanned through a long lens. It is a device that focuses light as a light spot on the surface and performs optical scanning. " That is, the light beam from the light source side is deflected by the light deflecting means such as a polygon mirror, and is incident on the reflective imaging element and reflected. The reflected light flux is condensed as a light spot on the surface to be scanned through the elongated lens, and optically scans the surface to be scanned.

The optical scanning device of the present invention has the following features in the above configuration. "Reflective imaging element"
Is made of plastic,
With respect to the main scanning corresponding direction, it has a function of "substantially" focusing on the surface to be scanned and a function of making the moving speed of the light spot substantially constant. The "main scanning corresponding direction" means a direction corresponding to the main scanning direction in parallel on a virtual optical path in which the optical path from the light source to the surface to be scanned is linearly developed, and on the virtual optical path. The direction corresponding to the sub-scanning direction in parallel is referred to as "sub-scanning corresponding direction".

The "long lens" is made of plastic and has a function of converging the deflected light beam on the surface to be scanned in the sub-scanning corresponding direction in cooperation with the reflective image forming element.
It has "negative power" in the main scanning direction.

That is, when viewed in the main scanning corresponding direction, the deflected light flux is condensed on the surface to be scanned by "mainly the image forming action of the reflection image forming element", but the long lens also has a main scanning corresponding direction. The negative power of the long lens also participates in the imaging action in the main scanning corresponding direction. However, as described above, the image forming action in the main scanning corresponding direction is mainly the image forming action by the reflection image forming element, and the participation of the long lens is “auxiliary”. Therefore, the reflective imaging element is said to "substantially condense" the deflected light beam on the surface to be scanned in the main scanning corresponding direction.

On the other hand, in the direction corresponding to sub-scanning, the deflected light beam is covered by the image forming action of the reflective image forming element and the image forming action of the elongated lens, that is, by the combined image forming function of these optical elements. Focus on the scan plane.

In the optical scanning device according to claim 1,
The long lens can be a “long toroidal lens”. In this case, the radius of curvature of the long toroidal lens in the direction corresponding to the main scanning is given by the lens surface on the incident side: r
_If the lens surface on the exit side is _{1 m} , and r _2m , then the magnitude relationship of these radii of curvature is “r _1m / r _2m <1”, and the reflecting surface shape of the reflective imaging element is a coaxial aspherical surface. The central curvature and the aspherical surface coefficient of the coaxial aspherical surface can be optimized according to the optical characteristics of the long lens (claim 2).

Alternatively, of a long toroidal lens,
The lens surface on the exit side is a normal toroidal surface having a radius of curvature: r _2m with respect to the main scanning corresponding direction, and the lens surface on the incidence side is “center curvature: r, conical constant: K, and the direction from the center to the main scanning corresponding direction. Distance: y, high-order aspheric coefficient:
Using a, b, c and d, x = y ² / [r + √ {r ² − (1 + K) y ² }] + ay ⁴ +
The curve represented as by ⁶ + cy ⁸ + dy ¹⁰ is defined as an aspherical shape obtained by rotating about a shaft parallel to the main scanning corresponding direction, and the magnitude relation of the above-mentioned respective curvature radii is “r / r _2m <1] and the reflective surface shape of the reflective imaging element is “coaxial aspherical surface”,
The central curvature and the aspherical coefficient can be optimized according to the optical characteristics of the long toroidal lens (claim 3).

Further, in the optical scanning device according to the first to third aspects, when the linear expansion coefficient of the material plastic of the reflective imaging element is α and the linear expansion coefficient of the material plastic of the long lens is β, these It is desirable that the magnitude relationship be "α≤β" (claim 4). When the magnitudes of the linear expansion coefficients: α and β are set to be equal to each other, they are set to “α = β = 7.0 ×
10 to ⁵ (mm / degree c) "(Claim 5), when β is set to be larger than α, these are
α = 5.0 × 10 to ⁵ (mm / degree c), β = 7.0 × 10
It can be set to ~ ⁵ (mm / degree c) (claim 6).

[0015]

When both the reflective imaging element and the elongated lens are made of plastic, both of them have a tendency to expand as the temperature rises. Since the reflective imaging element has a concave reflecting surface shape, it has a property of reflecting the deflected light beam in a direction approaching the optical axis in the main scanning corresponding direction. However, when the reflective imaging element expands as the temperature rises, The curvature of the shape of the reflecting surface changes to a smaller direction, and the function of “reflecting the deflected light flux toward the optical axis” weakens accordingly.

On the other hand, since the long lens has a negative power in the main scanning corresponding direction, the lens action of the long lens in the main scanning corresponding direction causes the outgoing light beam to be "side away from the optical axis of the incident light beam direction. To turn to. " When the long lens expands due to the temperature rise, the radius of curvature in the main scanning corresponding direction increases. Also, the refractive index of plastics generally tends to decrease with increasing temperature. Therefore, the negative power in the direction corresponding to the main scanning tends to become weaker as the temperature rises due to the increase in the radius of curvature and the phenomenon of the refractive index.

Therefore, when the function of "reflecting the deflected light beam in the direction approaching the optical axis" in the reflective image forming element weakens as the temperature rises, the "emitted light beam of the elongated lens is directed to the optical axis rather than the direction of the incident light beam. Since the function of "turning away from" is weakened, the functional changes of both tend to cancel each other out. When the temperature decreases, both the reflective imaging element and the long lens contract, and the above functions are strengthened, but the function changes at that time also tend to cancel each other out.

However, since the function of the reflective imaging element is achieved by reflection and the function of the elongated lens is achieved by refraction, the change in the function due to the temperature change is caused by the change in the reflection angle of the reflective imaging element. It tends to appear strongly on the side.

Considering these points, the linear expansion coefficient of the material plastic of the reflective imaging element: α and the linear expansion coefficient of the material plastic of the long lens: β are expressed as “α ≦”.
By setting β, it becomes possible to more effectively cancel the functional change of the reflective imaging element and the long lens due to the temperature change.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows only an essential part of an optical scanning device in which the present invention can be implemented. The divergent laser light flux emitted from the laser light source 1 is given a converging tendency by the lens 2, and is made a parallel light flux, a converging light flux, or a divergent light flux depending on the degree of the given converging tendency.
The light flux is condensed by the cylinder lens 3 only in the sub-scanning corresponding direction and is formed as a long "line image" in the main scanning corresponding direction.

The tenon mirror 4 which is the "light deflector" is
A deflection reflection surface is provided in the vicinity of the image forming position of the line image, and the light flux is deflected at a constant angular velocity while being reflected. A polygon mirror, a galvanometer mirror, a pyramidal mirror, or the like can be used as the light deflecting means.

The light beam deflected by the hoso-type mirror 4 becomes a "deflected light beam", which is incident on the reflection image-forming element 5 and, when reflected, is passed through the elongated lens 6 to form a "light spot" on the "scanned surface". Collect as. The drum-shaped photoconductor 7 is arranged so that the generatrix is in contact with the surface to be scanned, and the light spot is focused on the peripheral surface of the photoconductor 7 and optically scanned.

The horizontal mirror 4 reflects the deflected light beam obliquely upward with respect to the plane perpendicular to the rotation axis of the deflective reflection surface. The reflective imaging element 5 is arranged so as to be displaced upward in the rotation axis direction, and separates the incident light flux and the reflected light flux in the rotation axis direction. Therefore, the optical path of the incident light beam and the optical path of the reflected light beam to the reflective imaging element 5 are separated from each other in the sub-scanning corresponding direction, and the reflected light beam from the reflective imaging element 5 can return to the deflecting / reflecting surface of the tenon mirror 4. Absent.

The long lens 6 is shifted in the sub-scanning direction, and is further arranged so as to be rotated around an axis parallel to the main scanning corresponding direction, so that the light spot on the surface to be scanned is The curve of the "scan line" that is the locus of is effectively corrected.

The reflecting surface shape of the reflective imaging element 5 is a "coaxial aspherical surface", and the shape is a well-known aspherical expression, that is, "X = Y ² / [R + √ {R ^2- (1 + K) Y ² }] + AY ⁴
+ BY ⁶ + CY ⁸ + DY ¹⁰ where X: coordinates in the optical axis direction with the intersection of the optical axis and the reflecting surface as the origin, Y: distance from the optical axis, R: radius of curvature on the optical axis, K: conical constant , A, B, C, D: higher-order aspherical surface coefficients ”. The conical constant K and the higher-order aspherical surfaces A to D are collectively referred to as an aspherical coefficient.

Concrete Example 1 Concrete example 1 given first is an embodiment of the invention described in claims 1, 2, 4, and 5. That is, in the configuration of FIG. 1, the long lens 6 is a “long toroidal lens”, and the radius of curvature in the direction corresponding to the main scanning is given to the lens surface on the incident side:
r _{1 m,} per lens surface on the exit side: When a r _2m, r _1m
/ R _2m <1, and in the reflecting surface shape of the reflective imaging element, the central curvature: R and the aspherical surface coefficient: K, A, B, C,
D is optimized according to the optical characteristics of the long toroidal lens.

The reflective imaging element and the long toroidal lens are the same plastic material (having a linear expansion coefficient of 7.0 ×).
10 to ⁵ (mm / degree c)).

In each of the following specific examples, the sign of the radius of curvature of the surface, etc., is (+) in FIG. 1 from the horizontal mirror 4 to the reflective imaging element 5. Further, among the aspherical surface coefficients: K and A to D, a higher-order aspherical surface coefficient:
In the notations A to D, E and the number following it represent "power". For example, "E-10" means 1
It means 0 to the -10th power, and this "exponentiation" is multiplied by the numerical value before it.

The above-mentioned R, K, A, B, C, and D for specifying the shape of the reflecting surface of the reflective imaging element have the following values. R = -370.4, K = -1.5767, A = 5.75
7E-10, B = -7.54E-14, C = 1.67E
-18, D = -7.69E-23 distance reaches the reflective image forming element 5 from the deflecting reflective surface of the tenon type mirror 4: D ₀ is image height in 0, D ₀ = 115.3.

In the long toroidal lens, the entrance side lens surface and the exit side lens surface are in the main scanning corresponding direction,
The radii of curvature are r _1m and r _2m , respectively, and the radii of curvature are r _1s and r _2s respectively in the sub-scanning corresponding directions, and these have the following values. r _1m = 700, r _2m = 780, r _1s = 57.3, r _2s =
25.1 Thickness of the long toroidal lens on the optical axis: d
₀ is d ₀ = −3, and refractive index: n is n = 1.572
Is.

The distance from the reflective imaging element to the long toroidal lens: D ₁ is D ₁ = -118.
3. Distance D ₂ from the long toroidal lens to the surface to be scanned
Is D ₂ = −93 at an image height of 0.

The reflective imaging element and the long toroidal lens are designed with the "design value of operating temperature" being 20 degrees C, and the above data are values at the operating temperature in design.

At temperatures of 10 ° C. and 55 ° C., the above data are as follows. 10 degrees C: R = -370.44051, K = -1.5767, A =
5.769E-10, B = -7.57E-14, C =
1.68E-18, D = -7.74E- 23 r 1m = 699.5100, r 2m = 779.4540, r
_{1s = 57.2599, r 2s = 25.0824} , d 0 = -
2.9979, n = 1.573 55 degrees C: R = -371.34809, K = -1.5767, A =
5.727E-10, B = -7.48E-14, C =
1.65E-18, D = -7.57E- 23 r 1m = 701.7150, r 2m = 781.9910, r
_{1s = 57.4404, r 2s = 25.1615} , d 0 = -
3.00735, n = 1.568.

Operating temperature is 20 degrees C (design value) and 10
The magnification error at C and 55 C is shown in FIG. The "magnification error" is an amount defined as follows. In the optical scanning, using an ideal scanning width (corresponding to the width of the original in a digital copying machine): L ₀ and an actual scanning width by the optical scanning device: L, {(L−L ₀ ) / An amount defined by L ₀ } × 100 (%) is called a magnification error, and for example, L ₀ = 10
The magnification error at 0 mm is called "magnification error for 100 mm width". The magnification error is a function of image height: H.

A certain angle of view: "real image height" for θ is H
And At this time, when the optical system is ideally realized, the “ideal angle of view” that gives the image height H is θ ₀ . That is, the ideal image height for the angle of view: θ ₀ is h (θ ₀ )
Then, ideally the optical system is H = h (θ ₀ ), but in reality, the image height: H is given by the angle of view: θ.

[0036] Therefore, the angle of view: in relation to theta, 2 single _{angle: {θ + (θ 0/} 2)}, consider _{{θ- (θ 0/2)} }, the reality for each of the two angle Image height of
_{Each, H (θ + {θ 0} /2}), H (θ- {θ 0 /
2}).

[0037] In this case, [H (θ + {θ 0/2}) - H (θ- {θ 0/2})] /
Depending on h (θ ₀ ), magnification error with respect to angle of view: θ, that is, image height: H
Define the magnification error at the position. Shown in FIG. 2 is the magnification error as a function of image height: H, the magnification error for a maximum scan width of 100 mm.

Comparative Example 1 In order to compare with the above specific example 1, an example in which a long toroidal lens having a positive power is used will be described.

The data of the reflective imaging element and the long toroidal lens will be shown below in accordance with the above-described first specific example.

Reflective imaging element: R = -374.5, K = -1.4737, A = 5.23
3E-10, B = -1.39E-14, C = -1.53
E-18, D = -3.38 E-23 D ₀ = 115.3 Long toroidal lens: r _1m = 783.0, r _2m = 752.9, r _1s = 57.
3, r _2s = 25.1 d ₀ = -3, n = 1.572 D ₁ = -118.3, D ₂ = -97.
.

The reflective imaging element and the long toroidal lens are designed with the "design value of the working temperature" being 20 degrees C, and the above data are values at the designed working temperature.

When the temperature is 10 ° C. and 55 ° C., the above data are as follows. 10 degree C: R = -374.238, K = -1.4737, A =
5.244E-10, B = -1.39E-14, C =-
1.54E-18, D = -3.40E- 23 r 1m = 782.4520, r 2m = 752.3730, r
_1s = 57.2599, r _2s = 25.182336, d ₀ =
-2.9979, n = 1.573 55 degrees C: R = -375.418, K = -1.4737, A =
5.195E-10, B = -1.37E-14, C =-
1.50E-18, D = -3.31E- 23 r 1m = 784.9184, r 2m = 754.7446, r
_{1s = 57.4404, r 2s = 25.2617} , d 0 = -
3.00735, n = 1.568.

The operating temperature is 20 degrees C (design value) and 10
The magnification error for the 100 mm width at C and 55 C is as shown in FIG. From the comparison between FIG. 2 and FIG. 3, it can be seen that the variation of the magnification error due to the temperature is smaller in the specific example 1 which is the embodiment of the invention described in claims 1, 2, 4, and 5 than in the comparative example 1.

SPECIFIC EXAMPLE 2 The following specific example 2 is one embodiment of the invention described in claims 1, 3, 4, and 5. In Concrete Example 2, in the optical scanning device, the long lens 6 is a long toroidal lens in the configuration of FIG. 1, but in this long toroidal lens, the lens surface on the exit side has a radius of curvature in the main scanning corresponding direction. Is a normal toroidal surface having r _2m , and the lens surface on the incident side has “center curvature: r, conic constant: K, distance from the center in the direction corresponding to main scanning: y, high-order aspherical coefficient: a, b, c,
Using d, x = y ² / [r + √ {r ² − (1 + K) y ² }] + ay ⁴ +
By ⁶ + cy a curve represented as ⁸ + dy ^10, the main scanning corresponding direction aspherical shape obtained by rotating around an axis parallel to the ".

The magnitude relationship between the above-mentioned respective radii of curvature is expressed by "r / r _2m <
1 ", the reflecting surface shape of the reflective imaging element is a" coaxial aspherical surface ", and its center curvature and aspherical surface coefficient are optimized according to the optical characteristics of the long toroidal lens.

The data relating to the reflective image forming element will be described below in accordance with Specific Example 1. Reflective imaging element: R = -370.4, K = -1.5767, A = 5.75
7E-10, B = -7.54E-14, C = 1.67
E-18, D = -7.69 E-23 D ₀ = 115.3 The data regarding the long toroidal lens are as follows.

Long toroidal lens: Lens surface on incident side; r _1m = r = 700, k = −1.384, a = −3.62
9E-9, b = 1.679E-13, c = -5.361
E-18, d = 1.919 E-22, r _1s = 57.3 exit side lens surface; r _2m = 780, r _2s = 25.1 d ₀ = -3, n = 1.572, D ₁ =- 118.3, D ₂
= -93.

The reflective imaging element and the long toroidal lens are designed with the "design value of operating temperature" being 20 degrees C, and the above data is the value at the designed operating temperature.

At temperatures of 10 ° C. and 55 ° C., the above data are as follows. 10 degrees C: R = -370.44051, K = -1.5767, A =
5.769E-10, B = -7.57E-14, C =
1.68E-18, D = -7.74E- 23 r 1m = r = 699.51, k = -1.384, a = -
3.64E-9, b = 1.685E-13, c = -5.
39E-18, d = 1.931E-22 r _1s = 57.2599, r _2m = 779.4540, r _{2s
= 25.0824 d 0 = -2.998, n} = 1.573 55 ° C: R = -371.34809, K = -1.5767, A =
5.727E-10, B = -7.48E-14, C =
1.65E-18, D = -7.57E- 23 r 1m = r = 701.72, k = -1.384, a = -
3.60E-9, b = 1.659E-13, c = -5.
27E-18, d = 1.877E-22 r _1s = 57.4404, r _2m = 781.9110, r _{2s
= 25.1615 d 0 = -3.007, n} = 1.568
.

Operating temperature is 20 degrees C (design value) and 10
FIG. 4 shows the magnification error at C and 55 C.

Comparative Example 2 In order to compare with the above-mentioned specific example 2, the case where the lens surface on the incident side is the same aspherical surface as in the specific example 2 and which has a positive power in the main scanning corresponding direction is used. Give an example.

The data of the reflective imaging element and the long toroidal lens are shown below in accordance with Specific Example 1 above.

Reflective imaging element: R = -374.5, K = -1.4737, A = 5.23
3E-10, B = -1.39E-14, C = -1.53
E-18, D = -3.38 E-23 D ₀ = 115.3 This reflective imaging element is the same as the reflective imaging element in Comparative Example 1 above.

The data regarding the long toroidal lens are as follows:
It is as follows.

Long Toroidal Lens: Lens Surface on Incident Side; r _1m = r = 783.0, k = -1.578, a = -2.
28E-10, b = 6.845E-15, c = 2.07
7E-18, d = 6.162E-23 r _1s = 57.3 exit side lens surface; r _2m = 752.9, r _2s = 25.1 d ₀ = −3, n = 1.572, D ₁ = -118.3, D ₂
= -97.

The reflective imaging element and the long toroidal lens are designed with the "design value of operating temperature" being 20 degrees C, and the above data are values at the designed operating temperature.

Working temperature for Comparative Example 2: 20 ° C.,
FIG. 5 shows the magnification error for a width of 100 mm at 10 degrees C and 55 degrees C.

From the comparison between FIG. 4 and FIG.
It can be seen that in Concrete Example 1, which is an embodiment of the invention described in Nos. 4 and 5, the variation in magnification error with temperature is smaller than that in Comparative Example 2, and the variation in magnification error with temperature is reduced.

SPECIFIC EXAMPLE 3 The final specific example 3 is one embodiment of the invention described in claims 1, 3, 4, and 6. That is, in this specific example 3, FIG.
In the configuration of the optical scanning device, the long lens 6 is a long toroidal lens, the reflecting surface shape of the reflective imaging element is a coaxial aspherical surface, and the aspherical coefficient thereof depends on the optical characteristics of the long toroidal lens. Has been optimized.

The reflective imaging element has the same shape as that of the reflective imaging element in the second embodiment, but is made of a plastic material having a linear expansion coefficient: α of 5.0 × 10 to ⁵ (mm / degree C). The long toroidal lens, which is formed, is the same as the specific example 2 described above.
It is the same as the long toroidal lens in.

The reflective imaging element and the long toroidal lens are designed with the "design value of operating temperature" being 20 degrees C, and the data at this time is the operating temperature in the specific example 2:
It is exactly the same as at 20 degrees C.

At temperatures of 10 ° C. and 55 ° C., the respective data relating to the reflective imaging element and the long toroidal lens are as follows. 10 degree C: R = -370.51465, K = -1.5767, A =
5.766E-10, B = -7.56E-14, C =
1.68E-18, D = -7.72E- 23 r 1m = r = 699.51, k = -1.384, a = -
3.64E-9, b = 1.685E-13, c = -5.
39E-18, d = 1.931E-22 r _1s = 57.2599, r _2m = 779.4540, r _{2s
= 25.0824 d 0 = -2.998, n} = 1.573 55 ° C: R = -371.16305, K = -1.5767, A =
5.735E-10, B = -7.50E-14, C =
1.66E-18, D = -7.60E- 23 r 1m = r = 701.72, k = -1.384, a = -
3.60E-9, b = 1.659E-13, c = -5.
27E-18, d = 1.877E-22 r _1s = 57.4404, r _2m = 781.9110, r _{2s
= 25.1615 d 0 = -3.007, n} = 1.568
.

Operating temperature is 20 degrees C (design value) and 10
The magnification error for the 100 mm width at C and 55 C is as shown in FIG.

As is apparent from a comparison of FIG. 6 with FIG. 4, the variation of the magnification error due to the temperature change is further reduced and improved by reducing the linear expansion coefficient of the material of the reflective imaging element. I understand.

Therefore, it is effective to select the material of the reflective imaging element to have a smaller linear expansion coefficient than the material of the long lens in order to reduce the fluctuation of the scanning characteristics due to the temperature change. The material of the long lens is also limited to some extent due to conditions such as the refractive index.However, since the reflective imaging element does not use refraction, the degree of freedom of the material is large, and the linear expansion coefficient of the material of the long lens is larger than that of the material of the long lens. It is easy to select a small material.

Although the influence of the temperature change has been described above by the "magnification error", it is confirmed that the variation of the linearity due to the temperature change is effectively reduced in each of the above specific examples as compared with the comparative example. Was done.

[0067]

As described above, according to the present invention, a novel optical scanning device can be provided. Since the optical scanning device of the present invention is configured as described above, it uses a reflective imaging element and a long lens which can be realized at a low cost by using plastic as a material, and scan characteristics such as linearity and magnification error due to temperature change. It is possible to suppress the fluctuations of 2 to be small and realize good optical scanning.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an optical arrangement of an optical scanning device to which the present invention can be applied.

FIG. 2 is a diagram showing a variation of a magnification error in Specific Example 1 due to a temperature change.

FIG. 3 is a diagram showing a variation of a magnification error in Comparative Example 1 due to a temperature change.

FIG. 4 is a diagram showing a variation of a magnification error in a second specific example due to a temperature change.

FIG. 5 is a diagram showing a variation of a magnification error in Comparative Example 2 due to a temperature change.

FIG. 6 is a diagram showing a variation of a magnification error in Specific Example 3 due to a temperature change.

[Explanation of symbols]

4 Light deflection means 5 Reflective imaging element 6 long lens

Claims (6)

(57) [Claims] 1. An apparatus for performing optical scanning, wherein a deflected light beam deflected by an optical deflecting means is reflected by a reflective imaging element, and the reflected light beam is condensed as a light spot on a surface to be scanned through a long lens. The reflective imaging element is formed of plastic as a material, and has a function of substantially condensing the deflected light flux on the surface to be scanned in the direction corresponding to the main scanning and a movement speed of the light spot to be substantially constant. The long lens is made of plastic and has a function of converging the deflected light beam on the surface to be scanned in the sub-scanning corresponding direction in cooperation with the reflective imaging element. An optical scanning device having a negative power in the corresponding direction. 2. The optical scanning device according to claim 1, wherein the long lens is a long toroidal lens, and a radius of curvature in a direction corresponding to main scanning is given to a lens surface on an incident side:
r _{1 m,} per lens surface on the exit side: When a r _2m, r _1m
/ R _2m <1, the reflecting surface shape of the reflective imaging element is a coaxial aspherical surface, and the central curvature and the aspherical surface coefficient are optimized according to the optical characteristics of the long lens. Characteristic optical scanning device. 3. The optical scanning device according to claim 1, wherein, in the long lens, the lens surface on the exit side is a normal toroidal surface having a radius of curvature: r _2m in the main scanning corresponding direction, and the lens surface on the entrance side is , Central curvature: r, conic constant: k, distance measured from the center in the main scanning corresponding direction: y, high-order aspherical coefficients: a, b, c, d, x = y ² / [r + √ ^{{r 2 - (1 + k} ) y 2}] + ay 4 +
by the ⁶ + cy ⁸ + dy ¹⁰ and curve represented has a main scanning corresponding direction aspherical shape obtained by rotating about an axis parallel to a r / r _2m <1, the reflective image forming element An optical scanning device characterized in that a reflecting surface has a coaxial aspherical surface, and a central curvature and an aspherical surface coefficient are optimized in accordance with optical characteristics of the elongated lens. 4. The optical scanning device according to claim 1, wherein the linear expansion coefficient of the material plastic of the reflective imaging element is α, and the linear expansion coefficient of the material plastic of the long lens is β. An optical scanning device characterized in that α ≦ β. 5. The optical scanning device according to claim 4, wherein α = β = 7.0 × 10 to ⁵ (mm / degree c). 6. The optical scanning device according to claim 4, wherein α = 5.0 × 10 to ⁵ (mm / degree c), β = 7.0 × 10.
An optical scanning device characterized in that the optical scanning device has a thickness of ⁵ (mm / degree c).