JPS61254920A - Optical deflecting element - Google Patents

Abstract

PURPOSE:To provide an ftheta characteristic to the cylindrical optical deflecting element itself and to make possible uniform speed scanning without a costly ftheta lens by the constitution consisting in reflecting the incident light beam on the element in the optical axis direction thereof at the slope thereof and emitting the beam from the non-cylindrical side face. CONSTITUTION:The incident light beam L on the transparent cylindrical optical deflecting element 10 in the optical axis direction from the inside thereof is reflected by the slope 10A and is emitted from the non-cylindrical face 10B. The beam L inclines by an angle theta as well when the element 10 turns by the angle theta from the reference position where the face 10B is symmetrical to the center line with respect to the x-axis. The inclined beam is then further refracted by an angle beta and is thereby deflected at the angle (theta-beta). The value of the angle beta is determined as a function of theta by the distance De between the axis AX of rotation and incident point P and the beam has consequently the ftheta characteristic. The uniform speed scanning of the surface to be scanned is thus made possible without the need for the costly ftheta lens and the reduction of the cost is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (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 an optical deflection element that deflects a light beam by rotation, a rotating polygon mirror and a hologram disk are conventionally known in connection with optical printers and the like.

However, a light beam deflected by a rotating polygon mirror or a hologram disk has a constant angular velocity of deflection. Therefore,
If a scanned surface is to be scanned at a constant speed using such a deflected beam, an expensive fθ lens is required. Furthermore, when using an fθ lens, the positional relationship between the deflection point, the fθ lens position, and the scanned surface is uniquely determined, so if the design conditions change, the fθ lens must be redesigned accordingly. No.

(Objective) The present invention has been made in view of the above-mentioned circumstances, and its object is to provide an optical deflection element which itself has an fθ characteristic.

(composition) One aspect of the present invention will be explained below.

FIG. 1 shows an example of a light deflection element according to the present invention. 1st
Figure (1) is a plan view, and Figure 1 (II) is a side view. The present invention will be described in detail based on this example.

In FIG. 1, reference numeral 10 indicates a light deflection element.

The entire optical deflection element 10 is transparent. As the transparent material constituting the light deflection element, glass, transparent plastic, acrylic, polystyrene, polycarbonate, etc. can be used. When using glass, it can be manufactured by polishing, and when using resin material, it can be manufactured by molding.

The optical deflection element 10 has a slope 10A inclined by α with respect to the rotation axis AX. In this example, α is 45 degrees.

α may be an angle other than 45 degrees.

When a light beam L is incident on this slope 10A from inside the element, the light beam L is reflected by the slope 10A and exits as shown in FIG. 1 (If). In addition.

In order to increase the reflectance of the slope 10A, total reflection may be used or a reflective film may be formed on the slope 10A. Now, the surface 10B from which the reflected light beam exits is formed into a non-cylindrical surface.

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

The light beam L to be deflected enters a point P on the slope 10A from inside the element, as shown in FIG. 1 (II).

In this example, the light beam L is parallel to the rotation axis AX, and the slope 1
Although the light is incident at 0A, the light is not limited to this and may be made incident at an angle with respect to the rotation axis. However, the incident position P of the light beam L on the slope must be at a position other than the intersection of the one-rotation axis AX and the slope 10A.

Note that although the incident position P of the light beam L on the slope 10A was described above, as the element 10 rotates, this incident position P changes relative to the slope 10A. Slope 10
The positional relationship between the light beam L incident on A and the rotation axis AX remains unchanged.

Now, it was mentioned that the non-cylindrical surface 10B has a special surface shape, but when the optical deflection element 1o is rotated at a constant speed, the light beam emitted from the non-cylindrical surface 10B is f
It is determined to have a θ characteristic. The fθ characteristic refers to a characteristic such that when a deflected light beam scans a predetermined plane, the scanning speed component in the main scanning direction is constant.

Therefore, regarding the optical deflection element 10, the direction of the rotation axis AX is set to Z.
As the direction, determine the x and y coordinates as shown in Figure 2.

The xy coordinates are fixed in space, and the position shown in FIG. 2 with respect to the xy coordinates is the reference position of the optical deflection element 10. It is easily understood that when in the reference position, the light beam passes on the X axis and exits from the non-cylindrical surface 10B.As shown in FIG. Let us consider a state where the state is tilted by an angle θ from the reference state.

At point P, the light beam L reflected from the slope 10A is tilted by an angle θ with respect to the X axis inside the element, but when it exits from the non-cylindrical surface 10B, it changes direction by an angle β due to refraction. Turn around. Therefore, when the element 10 is rotated by the angle θ, the light beam emitted from the non-cylindrical surface 10B is rotated by the angle (
deflect by θ−β).

The value of the angle β is uniquely determined by the shape of the non-cylindrical surface 10B, the distance Da between the refractive index rotation axis AX of the optical deflection element and the light beam L incident parallel thereto (see Fig. 2). ,θ
By appropriately selecting these values, it is possible to make the deflected light beam have fθ characteristics.

Specific examples are given below.

α=45°, the refractive index of the element material is 1.5, and the above Da is 2
0111, and the shape of the non-cylindrical surface 10B is in the standard state shown in FIG.
y'') (1) and constant a g b y
When various values of Q p d + et f were selected and fθ characteristics were investigated, a = -2,085X 10-@, b = 1.215
X10-', c = -3,102X10-', d =
2.082X10-”, e=1.307XIO””
, when f=1, good fθ characteristics could be obtained.

The unit of Xe'/ is 1. Since the intersection x0 of the non-cylindrical surface 10B and the X-axis in the reference attitude shown in FIG. 2 is given as y=o in equation (1), x=f, and f=P
From 1 rotation axis AX and X, which distance is 1 Peng ■.

FIG. 4 shows how the light beam L is deflected by the light deflection element 10. As the optical deflection element 10 rotates in the direction of the arrow, the deflected light beam changes as shown in FIG. 4 (■).

(II) and (III). That is, when the rotation angle of the element 10 is θ, the position of the light beam is on the scanned surface P.
It is at point A on L (Fig. 4 (■)), and when θ=O, it is 0.
It is at point B (Fig. 4 (If)), and when the rotation angle is θ', it is at point B. Generally, as shown in FIG. 4(I), the rotation angle θ
If the optical deflection element has a perfect fθ characteristic, where S(θ) is the distance between point 0 and point A on the scanned surface PL, then S(θ)=θ・Lo It is. However, Lo is the distance between the deflection point, that is, point P, and the scanned surface PL.

Therefore, the value of Ω-X100 (%) (2) θ・Lo is called the fθ characteristic value. In the ideal fθ characteristic, f
The θ characteristic value (2) is always O regardless of the value of θ.

The fθ characteristics of the above embodiment are shown in FIG. 5. The vertical axis represents the deflection angle, that is, the difference (θ
-β), and the horizontal axis is the fθ characteristic value shown by the above equation (2). Curve 5-1 is for L 0 = 200+as, and 1 curve 5-2 beams. =300+am. When L O = 200+mm, θ-β = 3
0,074% (0,18w+n) up to 1.4@,
When L, = 300mm, θ-β = 21.4°
Excellent fθ of 0.023% (0,055mm)
The same optical deflection element can be used regardless of the change in the value of Lo.

(Effects) According to the first aspect of the present invention, a novel optical deflection element can be provided. Since this optical deflection element itself has an fθ characteristic, it is possible to scan a surface to be scanned at a constant speed without requiring an expensive fθ lens, and the cost of an optical printer or the like can be reduced. Furthermore, even if the distance between the deflection point and the scanned surface changes, it has excellent fθ characteristics, making it easy to change the design of the optical scanning device.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention, FIGS. 2 to 4 are diagrams for explaining light deflection according to the above embodiment, and FIG. 5 is a diagram showing fθ characteristics of the embodiment. It is. lO...light deflection element, IOA...slope, AX...
Rotation axis, 10B...non-cylindrical surface, L...light beam.

Claims (1)

[Claims] An optical element that deflects a light beam by rotation, and is entirely transparent and rotatable around a predetermined rotation axis.
It has a slope inclined with respect to the rotation axis, and a non-cylindrical surface is formed on the slope from which reflected light is emitted when light is applied from inside the element, and the slope is located at a position other than the intersection of the rotation axis and the slope. While irradiating a light beam in a directional manner from inside the element,
When the element is rotated around the rotation axis at a constant speed, the light beam emitted from the non-cylindrical surface and reflected by the slope is f_
An optical deflection element characterized in that the shape of the non-cylindrical surface is determined so as to have a θ characteristic.