JPH04336518A - Scanning optical device - Google Patents

Abstract

PURPOSE:To prevent the deflection of the optical axis of a lens due to the thermal expansion rate by setting each height of the fixed surface of a toric lens made of synthetic resin and the fixed surface of a glass lens on the basis of the thermal expansion rate of the lens and the thermal expansion rate of an optlcal box and allowing each optical axis to coincide even if temperature variation exists. CONSTITUTION:A toric lens 11 which is made of synthetic resin and long in the main scan direction is adhesion-fixed through an installation arm 11a on an installation surface 12c in the upper part of an installation pillar 12b having a height n+n1 from the installation seat surface of an optical box 12. Further, a glass lens 13 which is long in the main scan direction is adhesion-fixed on the installation seat surface 12a behind the optical box 12. The installation position of either the synthetic resin lens 11 or the glass lens 13 is set through the calculation from the thermal expansion rate between the synthetic resin lens 11 and the installation member 12 of the glass lens 13, so that the deflection in the direction crossing at right angle with the optical axis direction of the synthetic resin lens 11 due to the temperature variation and the deflection of the optical axis of the glass lens 13 become nearly equal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device having an optical system combining a synthetic resin lens and a glass lens.

0002

2. Description of the Related Art A scanning optical system is an optical system used in laser beam printers, etc. FIG. 5 is a perspective view, and FIG.
FIG. Laser light emitted from a laser oscillator 1 reaches a polygon mirror 3 while being converged in the vertical direction by a cylindrical lens 2. The polygon mirror 3 scans the laser beam while rotating, and this scanning light passes through an fθ lens that combines a spherical lens 4 made of glass and a toric lens 5 made of synthetic resin, becomes uniform velocity light, and is emitted from the optical box. The light is emitted to the outside and is imaged on a photoreceptor (not shown). Further, the cylindrical lens 2 and the toric lens 5 are combined to constitute a tilt correction optical system, which corrects variations in the tilt angle of the mirror surface of the polygon mirror 3.

0003

However, in the conventional example described above, two types of lenses, a synthetic resin lens and a glass lens, are used, so the difference in the amount of expansion of the lenses due to the difference in the coefficient of thermal expansion of the materials is There is a problem in that a relative shift of the lens optical axis in the vertical direction occurs. In other words, Figure 7
As shown in the figure, two lenses 4 and 5 are installed on the mounting surface with the same height.
When fixed, the optical axes L of the two lenses 4 and 5 coincide in the initial state, but as the ambient temperature rises, the two lenses 4 and 5 expand and become in the states 4' and 5'. At this time, the optical axes of the two lenses 4 and 5 move to L4 and L5.
Therefore, a difference δ occurs between the optical axes L4 and L5, which deteriorates the optical performance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scanning optical device that can suppress deviation of the optical axis due to temperature changes in the lens group even if the optical system is constructed using synthetic resin lenses and glass lenses. be.

[0005]

[Means for Solving the Problems] A scanning optical device according to the present invention for achieving the above-mentioned object is provided with a scanning optical system configured using a synthetic resin lens and a glass lens, in which the synthetic resin lens changes due to temperature changes. The mounting position of at least one of the synthetic resin lens and the glass lens is adjusted so that the deviation in the direction perpendicular to the optical axis direction and the deviation of the optical axis of the glass lens are approximately equal. It is characterized by being selected by calculating the coefficient of thermal expansion of the lens and the mounting member.

[0006]

[Operation] In the scanning optical device having the above structure, even if the temperature of the optical system rises, the positions of the optical axes of the synthetic resin lens and the glass lens change equally.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail based on the embodiments shown in FIGS. 1 to 4. FIG. 1 is a cross-sectional view of the main part as seen from the side, and FIG. 2 is a front view of the synthetic resin lens. Thin plate-like mounting arms 1 are installed on both sides above the optical axis plane in the main scanning direction by h1.
1a and is long in the main scanning direction, the synthetic resin toric lens 11 is attached to the mounting seat surface 1 on the upper part of the mounting column 12b, which has a height h+h1 higher than the mounting seat surface 12a of the optical box 12.
2c through the attachment arm 11a. A glass lens 13 that is long in the main scanning direction is adhesively fixed to the mounting seat surface 12a at the rear of the optical box 12, and the toric lens 11 made of synthetic resin and the glass lens 13 constitute an fθ lens group. At this time, the vertical heights of the optical axes of the toric lens 11 and the glass lens 13 are exactly the same, and are at a height h from the mounting seat surface 12a.

The thermal expansion coefficients of the optical box 12, glass lens 13, and synthetic resin toric lens 11 are β0 and β, respectively.
1, β2, with the mounting seat surface 12c as a reference,
Mounting seat surface 1 by mounting column 12b when temperature increases by Δt
The upward movement amount Δh of 2a is Δh=β0・(h+h1)・Δt

The amount of upward movement Δh1 of the glass lens 13 is Δh1=β1·h·Δt. Furthermore, since the mounting position of the synthetic resin toric lens 11 is h1 above the optical axis, the optical axis moves downward as the temperature rises, and the amount of movement Δh2 at this time is Δh
2=β2・h1・Δt.

The condition for the relative change in the optical axes of the two lenses 11 and 13 to be zero is Δh−Δh2=Δh1, so h1=h (β0 −β1 )/(β2 −β0 )
get.

If the optical box 12 is made of thermoplastic resin, the synthetic resin toric lens 11 is made of polycarbonate resin, and the glass lens 13 is made of BK7, and the height of the optical axis of the glass lens 13 is h=5 mm, then β0 = 2. Since 4×10-5/℃ β1 = 0.74×10-5/℃ β2 = 9.2×10-5/℃,

[0012] h1=1.2 mm. In other words, if the mounting position of the synthetic resin toric lens 11 is set at a position 1.2 mm higher than the optical axis,
It is possible to suppress relative displacement of the vertical optical axes of the two lenses 11 and 13 due to temperature changes.

FIG. 3 is a sectional view of the second embodiment, and FIG. 4 is a front view of the glass lens. In this embodiment, the synthetic resin toric lens 11 is attached to the mounting seat surface 12d of the optical box 12.
The glass lens 13 is suspended from the top of a gate-shaped lens holder 14, and the lens holder 1
4 is adhesively fixed to the optical box 12. In this embodiment as well, by appropriately selecting the dimensions as in the previous embodiment, it is possible to suppress the relative deviation of the optical axes between the synthetic resin toric lens 11 and the glass lens 13.

In the above embodiment, the two lenses 11 and 13 constituting the fθ lens group have been described, but this also applies if there are multiple lenses made of different materials in other lens groups. , it is possible to suppress relative displacement of the optical axis in the vertical direction by using a similar lens holding means.

Furthermore, if the tolerance range of optical performance is large,
The relative deviation of each optical axis does not have to be zero;
In this case, since high accuracy is not required, the cost is further reduced.

[0016]

[Effects of the Invention] As explained above, although the scanning optical device according to the present invention uses both a synthetic resin lens and a glass lens, the mounting position of the lens can be adjusted in consideration of the coefficient of thermal expansion. By doing so, optical axis misalignment due to thermal expansion caused by temperature changes can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a first embodiment.

FIG. 2 is a front view of a synthetic resin toric lens.

FIG. 3 is a sectional view of a second embodiment.

FIG. 4 is a front view of a glass lens.

FIG. 5 is a perspective view of the scanning optical device.

FIG. 6 is a sectional view taken along line AA in FIG. 5;

FIG. 7 is an explanatory diagram of problems in the conventional example.

[Explanation of symbols]

11 Synthetic resin toric lens 11a Mounting arm 12 Optical box 12a, 12c Mounting seat 12b Mounting pillar 13 Glass lens 14 Lens holder

Claims (1)

[Claims] 1. In a scanning optical system configured using a synthetic resin lens and a glass lens, the deviation in the direction perpendicular to the optical axis direction of the synthetic resin lens due to temperature change and the deviation of the optical axis of the glass lens are approximately equal to each other. Scanning characterized in that the mounting position of at least one of the synthetic resin lens and the glass lens is calculated and selected from the thermal expansion coefficients of the synthetic resin lens, the glass lens, and the mounting member so that they are equal to each other. optical equipment.