JPH10293261A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning device capable of exactly compensating the deviation of an image forming position due to the temp. characteristic of a plastic lens and a plastic mirror. SOLUTION: Relating to an optical scanning device using a plastic lens for an image forming lens B, a light source 1 and a collimator lens 2 are integrated with a lens barrel and this lens barrel is composed of a first lens barrel member and a second lens barrel member. When the temp. of the optical scanning device rises. the refractive index, etc., of the plastic lens B is changed and the image forming position is displaced by Δx from 7 to 7', the collimator lens 2 is moved by ΔL by the expansion of the lens barrel and the image forming position is returned to 7. By composing a lens barrel 10 of plural members having different linear expansion coefficients, careful adjustment and exact temp. compensation are enabled.

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 used for an image forming apparatus such as a laser printer, a laser facsimile or a digital copying machine.

[0002]

2. Description of the Related Art An optical scanning device used in an image forming apparatus such as a laser printer or a laser facsimile has a configuration shown in FIG. That is, a laser beam emitted from a light source 1 such as a semiconductor laser is converted into a parallel light beam by a collimator lens 2, passes through a cylinder lens 3, and forms an image on a rotating polygon mirror 4 as a linear image. Then, the light is reflected by the polygon mirror 4, is deflected and scanned by the rotation thereof, and forms an image as a spot image on a scanning surface 7 formed of the surface of the photosensitive drum via imaging lenses 5 and 6, such as fθ lenses. The spot image formed on the scanning surface 7 is scanned in the y direction (main scanning direction) by the rotation of the polygon mirror 4 to form a linear electrostatic latent image on the scanning surface 7.

In the above arrangement, the light source 1, the collimator lens 2 and the cylinder lens 3 constitute a first optical system A, and the imaging lenses 5 and 6 constitute a second optical system B. When the polygon mirror 4 rotates, a new spot image is formed by the next reflection surface. However, since the photosensitive drum is also rotating, a linear static image parallel to the previous electrostatic latent image is formed on the scanning surface 7. An electrostatic latent image is formed. As the polygon mirror 4 continues to rotate, linear electrostatic latent images are successively formed, and these are connected to form a surface image as a whole. When the semiconductor laser emits a signal corresponding to the image of the document, the image of the document is formed on the photosensitive drum.

In such an optical scanning device, since the cylinder lens 2 and the imaging lenses 5 and 6 are relatively large lenses and are also aspherical, the plastic lens can be manufactured easily and at low cost. Is used.

[0005] However, the refractive index of a plastic lens changes with temperature. For this reason, it is known that the optical performance of the optical scanning device is reduced, the image forming position by the image forming lens is shifted, and the definition of the image is reduced. Further, the image forming apparatus includes heat sources such as various drive motors and a fixing unit, and these greatly change the environmental temperature of the plastic lens.

It is sufficient that the magnitude of the shift due to the temperature change is negligible. However, in recent high-quality image orientations, quite high accuracy is required. The effect is small if the depth of focus of the lens is large, but in the case of a lens with a small depth of focus, this shift must be further reduced.

On the other hand, in Japanese Patent Application Laid-Open No. Hei 8-29716, the amount of displacement of the imaging position due to the temperature characteristics of the lens is determined by combining the focal length of the plastic lens and the material of the lens barrel. Has been proposed which cancels out by the amount of displacement of the lens position due to.

[0008]

However, in the above configuration, the two can only be canceled out, and cannot be accurately canceled. Therefore, when the depth of focus of the lens is small, it becomes insufficient.

When a plastic mirror is used, the light is reflected on the mirror surface, and is not affected by a change in the refractive index. However, the mirror expands, so that the image formation position is shifted.

However, the above configuration relates to a transmission type imaging lens, and cannot be applied when a mirror such as a plastic fθ mirror is used for the imaging lens system. The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an optical scanning device capable of accurately correcting an imaging position shift due to a temperature characteristic of a plastic lens or a plastic mirror.

[0011]

In order to achieve the above object, an optical scanning device according to the present invention comprises a first optical system including a light source and a collimator lens, and a light beam emitted from the first optical system. And a second optical system for scanning the scanning surface with the light beam deflected by the deflection device, wherein the light source and the collimator lens are integrated by a lens barrel. In the scanning device, the second optical system includes at least one plastic lens or a plastic mirror, and the lens barrel is formed by connecting a plurality of members having different linear expansion coefficients in an optical axis direction, and is connected by a temperature change. It is characterized in that a shift in the image position is offset by a change in the position of the collimator lens due to expansion and contraction of the lens barrel.

The focal length of the first optical system is f
1. When the focal length of the second optical system is f2, the dimension at the reference temperature between the light source and the collimator lens is L, and the deviation of the imaging position when the temperature changes by 1K is Δx, Required displacement ΔL between the collimator lens
Is obtained from the following formula: ΔL = (f1 / f2) ² Δx, and the lens barrel has a linear expansion coefficient of α1, α2,.
.. May be constituted by members having different lengths in the optical axis direction L1, L2..., And these lengths satisfy the following equation: L1α1 + L2α2 +.

Further, the connecting portions of the different members of the lens barrel may have a spigot structure, or the connecting portions of the different members of the lens barrel may have a pin and hole fitting structure.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically illustrates the principle of the present invention. Although the overall configuration is almost the same in appearance as that described in the conventional example of FIG. 5, when a plastic lens is used for the second optical system B, the optical structure in the main scanning section (xy plane) is used. Since the characteristics (beam diameter, etc.) fluctuate greatly, a description will be given of this cross section.

The collimator lens 2 shown in FIG.
And is fixed to a lens barrel 10 having a length L in the optical axis direction. When the temperature inside the apparatus rises due to the heat generated by the polygon motor and the fixing unit, the plastic lens constituting the second optical system B expands in shape and decreases in the refractive index. It acts in a direction that reduces the effect. Then, the imaging position is shifted from the surface of the scanning surface 7 to a position 7 'on the opposite side to the imaging lens. Assuming that this amount is Δx, this causes deterioration of the image quality.

In order to correct the deviation Δx, there is a method of changing the light incident on the second optical system from parallel light to focused light.
This can be realized by moving the collimator lens 2 by ΔL when the temperature rises.

At this time, the focal length of the first optical system A is f
1. Assuming that the focal length of the second optical system B is f2, in the main scanning section, the light source and the scanning surface 7 (the surface of the photosensitive drum) have a conjugate relationship of a vertical magnification of (f1 / f2) ^2. And ΔL = (f1 / f2) ² Δx. Here, ΔL and Δx are displacement amounts with respect to a change in temperature 1K.

Although the embodiment represented by specific numerical values is omitted, the second optical system B is formed of one or two sheets of polycarbonate (P
When composed of a plastic lens made of C),
At the time of temperature rise, it is affected by two factors, that is, a decrease in the refractive index and expansion of the shape, and a relatively large value of Δx = 1.17 × 10 ⁻¹ mm / K is obtained. 0.6 × 10 ⁻⁴ mm / K Here, if L = 8 mm, ΔL / L = 45 × 10 ⁻⁶ / K.

FIG. 2 shows a lens barrel 10 having the above-mentioned expansion characteristics.
FIG. 3 is a diagram of an embodiment in which is formed using brass and ABS resin. In FIG. 1, a light source 1 side is a first barrel member 1 made of brass.
1. The collimator lens 2 side is a second lens barrel member 12 made of ABS resin, the length of the first lens barrel member 11 is L1, and the length of the second lens barrel member 12 is L2.

The linear expansion coefficient α1 of brass is α1 = 17.5 ×
The linear expansion coefficient α2 of 10 ⁻⁶ / K ABS resin is α2 = 85 × 10 ⁻⁶ / K
Therefore, (L1 × α1 + L2 × α2) ÷ (L1 + L2) = ΔL /
L1 and L2 may be determined so that L is satisfied. Note that L
Since 1 + L2 = L = 8 mm, the above equation becomes L1 × α1 + L2 × α2 = ΔL. When this is solved, L1 = 4.7 mm L2 = 3.
3 mm.

In FIG. 2, a socket 11a is provided on the second lens barrel member side of the first lens barrel member 11, and has a spigot structure that fits into the hole 12a of the second lens barrel member 12. With such a configuration, even when the temperature changes, a coaxial relationship in which both optical axes coincide with the optical axis of the collimator lens 2 can be maintained.

In the present invention, the focal length of the lens can be determined arbitrarily. Generally, when you change the focal length of a lens,
Since the image formation position changes, the influence on other things, such as changing the mounting position of the lens, is large. However, in the present invention, since the material of the lens barrel is changed, there is almost no spillover to other parts, which is very advantageous.

FIG. 3 is a diagram showing an optical scanning device using a plastic fθ mirror, which is schematically shown in FIG. The laser light emitted from the light source 1 is transmitted to a collimator lens 2
To form a parallel light beam, passes through the cylinder lens 4, is deflected by the polygon mirror 4, reflected by the fθ mirror 8, passes through a plastic toroidal lens 9, and forms an image on the scanning surface 7 on the surface of the photosensitive drum. In this case, the fθ mirror 8 and the toroidal lens 9 constitute a second optical system.

Since the power of the toroidal lens 9 is extremely small in the main scanning section (xy plane), the effect of temperature fluctuation is negligible. On the other hand, if the fθ mirror 8 is formed of plastic, since it is used for surface reflection, it is not affected by refractive index fluctuation due to temperature change, but is affected by shape change due to expansion and contraction. That is, f
The θ-mirror expands when the temperature rises, and is deformed in a direction in which the curvature of the reflection surface becomes gentle (in a direction in which the radius of curvature becomes large). In the direction away from the optical system B.

In order to cancel out Δx, the light emitted from the collimator lens 2 is made into a converging light, thereby canceling the displacement and returning the light to the surface 7 to be scanned. Although the intermediate progress is omitted, assuming that f1 and f2 are the same values as in the embodiment of FIG. 1, the expansion characteristic required for the lens barrel member of the collimator in the embodiment of FIG. 3 is ΔL / L = 26 × 10 ⁻⁶ / K (however, L = 8 mm).

This characteristic is realized by using brass for the first lens barrel member 11 and aluminum for the second lens barrel member 12. The linear expansion coefficient α1 of brass is α1 = 17.5 × 10 ⁻⁶ / K The linear expansion coefficient α2 of aluminum is α2 = 30.2 × 10
⁻⁶ / K. By substituting the above values into the following equations, L1 and L2
Solving (L1 × α1 + L2 × α2) ÷ (L1 + L2) = ΔL /
L L1 = 2.65 mm L2 = 5.35 mm

FIG. 4 shows a state in which a plurality of pins 11 b are implanted in the first lens barrel member 11 and holes 12 formed in the second lens barrel member 12.
4 shows an embodiment in which positioning is performed by fitting to b.
With such a configuration, the central axes of the first lens barrel member and the second common member can always be aligned with the optical axis of the collimator lens 2.

In the present invention, either the first lens barrel member or the second lens barrel member constituting the lens barrel can be integrally formed of the same material as the casing of the apparatus. In this case, either the linear expansion coefficient α1 or α2 is fixed, but the other can be freely designed, so that there is no great restriction.

The material that can be used as the first and second lens barrel members is nickel steel having a small linear expansion coefficient (α ≒ 10 × 10 ⁻⁶ / K) to a large linear expansion coefficient (α = 2).
A wide range of polyethylene and polypropylene (00 × 10 ⁻⁶ / K) can be used, and it can meet various requests. In addition, by combining a plurality of members having different linear expansion coefficients, fine adjustment can be performed and temperature correction can be accurately performed.

In the above embodiment, the first and second lens barrel members are two types. However, it is obvious that three or more types of members may be combined. In that case, the above equation L1 × α1 + L2 × α2 = ΔL is as follows. L1α1 + L2α2 +... = ΔL Further, L1 + L2 +.

[0031]

According to the present invention as described above,
An optical system including at least one plastic lens or a plastic mirror, and a lens barrel in which a light source and a collimator lens are integrated is formed by connecting a plurality of members having different linear expansion coefficients in an optical axis direction, and is formed by a temperature change. The shift in the image position is compensated for by the change in the position of the collimator lens due to the expansion and contraction of the lens barrel. Image shift can be eliminated. Therefore, even if the lens has a small depth of focus or a reflective mirror is used, the correction can be reliably performed. With a configuration in which a plurality of members are joined by a spigot structure or a pin-hole fitting structure, the optical axis can always be positioned even when the temperature changes.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an optical system of an optical scanning device according to the present invention.

FIG. 2 is a sectional view of a lens barrel used in the optical scanning device of the present invention.

FIG. 3 is a diagram corresponding to FIG. 1 of an optical scanning device using a reflection mirror in an optical system.

FIG. 4 is a sectional view showing a lens barrel having a different configuration from the lens barrel shown in FIG. 2;

FIG. 5 is a perspective view showing a configuration of a conventional optical scanning device.

[Explanation of symbols]

 Reference Signs List A First optical system B Second optical system 1 Light source 2 Collimator lens 4 Deflection device 7 Scanning surface 5, 6 Coupling optical system (plastic lens) 8 fθ mirror (plastic mirror) 10 Lens barrel 11 First lens barrel member 12 Second lens barrel member

Claims (4)

[Claims] A first optical system including a light source and a collimator lens; a deflecting device for deflecting a light beam emitted from the first optical system; and a light beam deflected by the deflecting device on a scanning surface. A light source and a collimator lens are integrated by a lens barrel, wherein the second optical system has at least one plastic lens or plastic mirror. The lens barrel is formed by connecting a plurality of members having different linear expansion coefficients in the optical axis direction, and a shift in an imaging position due to a temperature change is caused by a change in a position of a collimator lens due to expansion and contraction of the lens barrel. An optical scanning device characterized by canceling out. 2. The focal length of the first optical system is f1, the focal length of the second optical system is f2, the dimension at the reference temperature between the light source and the collimator lens is L, and the temperature changes by 1K. Where Δx is the displacement of the image forming position, the required displacement amount ΔL between the light source and the collimator lens is obtained from the following equation: ΔL = (f1 / f2) ² Δx, α1, α2, ...
2. The optical scanning device according to claim 1, wherein the lengths in the optical axis direction are made of members having different lengths L1, L2,..., And these lengths satisfy the following formula: L1α1 + L2α2 +. apparatus. 3. The optical scanning device according to claim 1, wherein a connection portion between different members of the lens barrel has a spigot structure. 4. The optical scanning device according to claim 1, wherein a connection portion between different members of the lens barrel has a pin-hole fitting structure.