JPH0668578B2 - Light deflection element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a light deflection element, and more particularly to a light deflection element that deflects a light beam by rotation.

(Prior Art) As a light deflection element that deflects a light beam by rotation, a rotary polygon mirror and a hologram disk have been conventionally known in relation to an optical printer and the like.

However, the light beam deflected by the rotating polygon mirror or the hologram disk has a constant angular velocity of deflection. Therefore,
An expensive fθ lens is required to scan the surface to be scanned at a constant speed using such a deflected beam. Further, when the fθ lens is used, the positional relationship among the deflection point, the fθ lens position, and the surface to be scanned is uniquely determined. Therefore, if the design conditions change, the fθ lens must be redesigned accordingly. .

(Purpose) The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical deflecting element having an fθ characteristic in the element itself.

(Structure) Hereinafter, the present invention will be described.

FIG. 1 shows an example of a light deflection element according to the present invention. First
FIG. 1 (I) is a plan view and FIG. 1 (II) is a side view. The features of the present invention will be described with reference to this example. In FIG. 1, reference numerals
Reference numeral 10 indicates an optical deflecting element.

The light deflection element 10 is entirely transparent. As the transparent material forming the light deflection element, glass, transparent plastic, acrylic, polystyrene, polycarbonate or the like can be used. When glass is used, it can be made by polishing, and when a resin material is used, it can be made by molding.

The light deflection element 10 has a slope 10A inclined by α with respect to the rotation axis AX.
Have. In this example, α is 45 degrees, but α may be an angle other than 45 degrees.

When the light beam L is made incident on the slope 10A from the inside of the device, the light beam L is reflected by the slope 10A and is emitted as shown in FIG. 1 (II). In addition, in order to increase the reflectance of the slope 10A, total reflection may be used, or a reflection film may be formed on the slope 10A. The surface 10B from which the reflected light beam exits is formed as a non-cylindrical surface.

The non-cylindrical surface 10B has no curvature in the direction parallel to the rotation axis AX as shown in the side view FIG. 1 (II), but as shown in the plan view FIG. 1 (I) as the rotation axis AX. The shape in the plane orthogonal to is a special surface shape.

The light beam L to be deflected enters the point P on the slope 10A from the inside of the element as shown in FIG. 1 (II). In this example, the light beam L is incident on the inclined surface 10A in parallel with the rotation axis AX, but the invention is not limited to this, and the light beam L may be incident with an inclination with respect to the rotation axis. However, the incident position P of the light beam L on the slope must be a position other than the intersection of the rotation axis AX and the slope 10A. In the above, the slope 10 of the light beam L is
Although it is the same as the incident position P on A, the incident position P changes relative to the slope 10A due to the rotation of the element 10.
The positional relationship between the light beam L incident on the slope 10A and the rotation axis AX is unchanged.

Now, the non-cylindrical surface 10B is said to have a special surface shape,
The non-cylindrical surface 10B is determined so that the light beam emitted from the non-cylindrical surface 10B has the fθ characteristic when the light deflection element 10 is rotated at a constant speed. The fθ characteristic is a characteristic such that when the deflected light beam scans a predetermined plane, the scanning velocity component in the main scanning direction becomes constant velocity.

Therefore, with respect to the light deflection element 10, the direction of the rotation axis AX is set to the Z direction, and the xy coordinates are determined as shown in FIG. The xy coordinates are fixed in space, and when the xy coordinates are in a position as shown in FIG. It will be readily understood that when in the home position, the light beam passes on the x-axis and exits the non-cylindrical surface 10B. Next, as shown in FIG. 3, consider a state in which the light deflection element 10 is tilted by an angle θ from the reference state with respect to the xy coordinates.

At point P, the light beam L reflected from the slope 10A is
Inside the element, it is inclined by an angle θ with respect to the x-axis, but when emitted from the non-cylindrical surface 10B, it is deflected by an angle β due to refraction. Therefore, when the element 10 is rotated by the angle θ, the light beam emitted from the non-cylindrical surface 10B has an angle (θ−
Bias only.

The value of the angle β is unique depending on the shape of the non-cylindrical surface 10B, the refractive index of the light deflection element, and the distance De (see FIG. 2) between the rotation axis AX and the light beam L incident parallel thereto. In addition, since it is determined as a function of θ, it is possible to appropriately select these so that the deflected light beam has the fθ characteristic.

FIG. 2 shows a standard state of the light deflection element. The x-axis is a coordinate axis in the direction orthogonal to the rotation axis in the symmetry plane including the rotation axis of the light deflection element 10, and the element 10 is plane-symmetric with respect to the plane defined by the x-axis and the rotation axis. The y-axis is the rotation axis and x
It is an axis orthogonal to the axis. At this time, the non-cylindrical surface 10B is
The shapes are the same in the direction orthogonal to the drawing, and can be represented by a functional relationship of x and y coordinates.

The above-mentioned functional relationship representing the shape of the non-cylindrical surface 10B is determined so that the deflected light beam realizes a substantial fθ characteristic, that is, an fθ characteristic that can be practically used for constant velocity optical scanning without any practical problem.

Specific examples will be given below.

alpha = 45 °, 1.5 the refractive index of the element material, the De and 2 mm, the shape of the non-cylindrical surface 10B, in the standard state shown in FIG. 2, | x | = f- (ay 10 + by 8 + cy 6 + dy ⁴ + ey ² ) (1), and select various values of constants a, b, c, d, e, f, and f
When the θ characteristics were examined, it was found that a = −2.085 × 10 ⁻⁶ , b = 1.215 × 10 ⁻⁴ , c = −3.102 × 1
When 0 ⁻⁴ , d = 2.082 × 10 ⁻² , e = 1.307 × 10 ⁻⁶ , and f = 1, good fθ characteristics could be obtained.

The unit of x and y is 1 mm. The intersection x ₀ between the non-cylindrical surface 10B and the x-axis in the reference posture shown in FIG. 2 is given as y = 0 in the equation (1), and therefore x = f, and from f = P, the rotation axis AX The distance between and x ₀ is 1 mm.

FIG. 4 shows how the light beam L is deflected by the light deflector 10. As the light deflection element 10 rotates in the direction of the arrow,
The deflected light beam changes as shown in FIGS. 4 (I), (II), and (III). That is, when the rotation angle of the element 10 is θ, the position of the light beam is at point A on the surface PL to be scanned (FIG. 4 (I)), and when θ = 0, it is at point C (FIG. 4). (I
I)), at the rotation angle θ ′, it is at point B. Generally, the fourth
As shown in FIG. 1I, when the rotation angle is θ, the distance between points C and A on the surface PL to be scanned is S (θ). If the light deflection element has perfect fθ characteristics, S (θ) = θ ·
L ₀ . However, L ₀ is the deflection point, that is, the point P and the surface to be scanned
It is the distance from PL.

Therefore, Is referred to as fθ characteristic value. In the ideal fθ characteristic, f
The θ characteristic value (2) is always 0 regardless of the value of θ.

The fθ characteristic of the above embodiment is shown in FIG. The vertical axis represents the deflection angle, that is, the difference between the rotation angle θ of the light deflection element 10 and the correction angle β (θ−
β) and the horizontal axis are the fθ characteristic values represented by the above equation (2).
Curve 5-1 is for L ₀ = 200 mm and curve 5-
2 is for L ₀ = 300 mm. When L ₀ = 200 mm, θ−β = 31.4 ° up to 0.074% (0.18 mm), and when L ₀ = 300 mm, θ−β = 21.4 ° up to 0.023% (0.055 mm), showing excellent fθ characteristics. The same light deflection element can be used regardless of the change in the value of L ₀ .

(Effect) As described above, according to the present invention, a novel optical deflector can be provided. Since the light deflecting element itself has the fθ characteristic, the surface to be scanned can be scanned at a constant speed without the need for an expensive fθ lens, and the cost of the optical printer or the like can be reduced. Further, even if the distance of the surface to be scanned at the deflection point changes, the excellent fθ characteristic is provided, so that the design change of the optical scanning device becomes easy.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, FIGS. 2 to 4 are diagrams for explaining light deflection according to the above-mentioned embodiment, and FIG. 5 is a diagram showing an fθ characteristic of the embodiment. Is. 10 ... Light deflection element, 10A ... Slope, AX ... Rotation axis, 10B ... Non-cylindrical surface, L ... Light beam.

Claims (1)

[Claims] 1. An optical element that deflects a light beam by rotation, is entirely transparent, is rotatable about a predetermined rotation axis, and has an inclined surface inclined with respect to the rotation axis. The surface from which reflected light is emitted when light is applied from the inside of the element is formed as a non-cylindrical surface, and the x axis is taken in the direction orthogonal to the rotation axis in the symmetry plane including the rotation axis, and The y-axis is taken in the direction orthogonal to the x-axis, and the shape of the non-cylindrical surface whose origin is the position of the rotation axis is calculated using constants: a, b, c, d, e, f, | x | = ^{f- (ay 10 + by 8 +} cy 6 + dy 4 + ey 2) and to represent, to a predetermined position other than the intersection between the rotation axis and the slope, while irradiating the directed manner the light beam from the element inside the element When rotating at a constant speed around the rotation axis, the light beam reflected by the inclined surface, which is emitted from the non-cylindrical surface, is substantially An optical deflecting element, characterized in that the values of the constants: a to f are determined so as to have a typical fθ characteristic.