JPS60227220A - Optical scanner - Google Patents

Abstract

PURPOSE:To simplify control of recording data and to enable effective use of the specular faces of a rotary polyhedral mirror by constituting an optical scanner in such a way that the recording time region of one optical scanning system does not overlap on the recording time region of the other optical system. CONSTITUTION:The reflecting points of the specular faces of the rotary polyhedral mirror 10 when the modulated light 15a, 15b from light sources 21a, 21b are reflected by said faces and when said light coincide with the optical axes of ftheta lenses 13a, 13b are designated as A and B and the center of rotation of the rotary polyhedral mirror is designated as O. The optical scanner is so constituted as to safisty the equation (in which thetar is the partial angle of the rotary polyhedral mirror, (n) is an optical integer, thetamax is the max. scanning angle, beta is the angle between the perpendicular from the center O of rotation to the specular face when the center of the modulated light reflected by the specular face coincides with the optical optical axis of the scanning lens system and the line connecting the center O of rotation and the reflecting point of the modulated light) when the above-mentioned reflecting points are made <AOB=<alpha. The scanning without overlapping and interruption is thus made possible by the simple control system using one set of buffer.

Description

DETAILED DESCRIPTION OF THE INVENTION (al) Technical Field of the Invention The present invention relates to a laser scanning optical system, and in particular, the present invention relates to a laser scanning optical system, and in particular, a laser scanning optical system that scans two portions of the total scanning width using a pair (two) of modulated beams for one rotating polygon mirror. The present invention relates to a method of arranging a scanning optical system that simplifies control of recording data for -scanning in an optical scanning device configured to share scanning duties.

(bl) Prior Art and Problems FIG. 1 is an example of an optical scanning device configured so that scanning of two portions of the total scanning width is shared by a pair of modulated lights for one rotating polygon mirror.

As shown in FIG. 1, this optical scanning device includes one rotating polygon mirror 10, two light source sections 12a and 12b, and an imaging optical system 1.
3a, 13b, and reflecting mirrors 14a, 14b.

The light beam from the light source section 12a is reflected by one mirror surface of the rotating polygon mirror 10 and scans the partial scanning area via the imaging optical system 13a6 and the reflecting mirror 14a, and the light beam from the light source section 12b scans the other scanning areas. It is reflected by the mirror surface and scans the partial scanning mirror area 1.2 via the imaging optical system 13b2 and the reflecting mirror 14b.

The following proposals have been made regarding the arrangement of such optical scanning devices.

In other words, in the optical scanning device shown in FIG. 1, even if the exposure of one partial scanning area is completed, if the exposure of the other partial area is not completed, the data is transferred to the data buffer that records the data to be exposed. Writing cannot be performed until the exposure of the other partial area is completed.

A possible solution to this problem would be to divide the data buffer into two corresponding to each partial area and control the timing of data writing for each divided data buffer, but in this case, two sets of optical Data writing is controlled at different cycles for each system, making the control circuit complex.

Therefore, as an arrangement condition for simultaneously writing data to the data buffer in two parts W, the reflection on the mirror surface when the modulated light reflected on the mirror surface of the rotating polygon mirror coincides with the optical axis of the scanning lens system. Let the points be point A and point B, respectively, and let the rotation center of the rotating polygon mirror be point 0, then /A
OB at a dividing angle θ2. Regarding the maximum scanning angle θmax,
(n-1)θ, +θmax<l^OB<(n+1)θ
, -〇may---- However, n is an integer of 2 or more.

A proposal has been made to set it so that it satisfies the following.

However, such conventional arrangement conditions are based on analyzing the incident position of the modulated light onto the rotating polygon mirror as the center point of the mirror surface, which has the drawback of hindering more effective use of the mirror surface.

FIG. 2 is a diagram for explaining the incident position of modulated light on a conventional rotating polygon mirror.

As shown in the figure, conventionally, modulated light 15 is directed to a rotating polygon mirror 10.
Since the incident position of a was set at the center point of the mirror surface 10", the mirror surface 10" was not effectively utilized. This will be explained in detail with reference to FIG.

FIG. 3 is a diagram for explaining the positional relationship between a conventional mirror surface and modulated light, where (a) shows the case where the scanning angle of the modulated light 15a is maximum, and the c-th one shows the case where it is the minimum. .

As shown in figure fa), the modulated light 15a is transmitted to the rotating polygon mirror 10.
When the scanning angle is maximum (0
1111M), the modulated light 15a is so dense that there is no blank space.
1, but as shown in the same figure (bl), when the scanning angle is the minimum (-θ, 8X), the other second ridgeline P
2 and the modulated light 15a, which hinders the effective use of the mirror surface 10''. (This is because the ridge lines PI, Pg
This phenomenon occurs due to differences in the scanning angles at which scanning can be performed without being obstructed by the object. (C1 Object of the Invention The object of the present invention is to transmit data to the recording data buffer of the entire scanning width at the same time even though there are two sets (a pair) of scanning optical systems, and furthermore, it is possible to send data to the recording data buffer of the entire scanning width at the same time. The objective is to provide conditions for arranging an optical system that can be used effectively.

+dl Structure and object of the invention According to the invention, there is provided a rotating polygon mirror and a pair of scanning lens systems that scan modulated light reflected from two different mirror surfaces of the polygon mirror to form an image on the same image plane. , a reflecting mirror, wherein the sum of the scanning widths LIILZI of the pair of scanning lens systems is equal to the scanning width of the entire scanning optical system, and L = LI +12. When the modulated light reflected by the two mirror surfaces is set as the optical axis of the pair of scanning lens systems, the reflection points are A and B, and the rotation center of the rotating polygon mirror is 0, /Ao
B is (n-1)θ, +θ1IaX+2β</AOB<(n+
1) This is achieved by providing an optical scanning device configured to satisfy the following equation: x01-θmix+2β.

(el　Embodiments of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 4 is a diagram for explaining means for improving the incident position of modulated light on a rotating polygon mirror, which is the basis of the present invention. Note that the same reference numerals indicate the same objects throughout the figures.

As shown in the figure, the scanning optical system of the present invention changes the incident position of the modulated light 15a onto the rotating polygon mirror 10 to the conventional position (first
By moving the rotating polygon mirror 10 from the intermediate point between the ridge line P and the second ridge line P2 to the position A near the second ridge line P2, a blank area Δ as shown in FIG. 3 (bl) is generated. The structure is such that it does not.

At this time, the center O of the rotating polygon mirror 10 and the mirror surface 10' -1-
The angle β formed by the line connecting the positions A and A' is the radius r of the rotating polygon mirror 10, the incident angle Φ of the modulated light 15a, the maximum scanning angle θIIIX l of the modulated light 15a, the diameter d This value is determined by the value shown in Figure 3 above (
The blank portion Δ explained in b) is eliminated.

The following FIG. 5 is a diagram for explaining one embodiment of the present invention.

The figure shows a scanning optical system whose incident position of modulated light has been improved by the means explained in FIG. This embodiment has a structure in which a predetermined image is obtained by making the light incident on different mirror surfaces and dividing and scanning the same image plane with the pairs of modulated light beams.

In FIG. 5, 10 is a rotating polygonal mirror, 21a and 21b are semiconductor laser light sources, 22a and 22b are collimating lenses, 13a and 13b are scanning lens systems composed of fθ lenses, 14a and 14b are reflecting mirrors, and . Total scanning area, L
L+Ll respectively indicate partial scanning areas.

Modulated light 15a from the light source 21a is reflected by one mirror surface of the rotating polygon mirror 10, and modulated light 15b from the light source 21b is reflected by another mirror surface of the rotating polygon mirror 10. Now modulated light 15
When light a is reflected by a mirror surface and the light coincides with the optical axis of the fθ lens 13a, let the reflection point of the mirror surface be a point, and similarly, the light source 2
The reflection point of the mirror surface when the light from 1b is reflected by the mirror surface and collides with the optical axis of the fθ lens 13b is point B, the center of rotation of the two-rotation polygon mirror 10 is point O, and the angle α-ZAOB
It is defined as

Here, e−(α−2β)/θ, −n −−−−−−−−■θ
, : Dividing angle β of polygon mirror : / to 〇 in Fig. 4' n knee Q, an integer satisfying 5<e≦0.5.

A time chart of a lucky scan when e, /I<0 is shown in FIG. 6 (fal), and a time chart of a scan when e is 0.5 is shown in FIG. 6 (bl).

In FIG. 6, T3 is the time required for each optical system to perform one scan, and the shaded portion corresponds to the time for actually exposing the area.

Time T, , T, □, To is point Sa in the previous figure 5.
.

Corresponding to Ca and Co, similarly, the times T b l and T
b z + T n 1 corresponds to points Co, Cb, and Sb. When e=Q, that is, in the case of FIG. 6(a), the scanning from point Sa to point Go and the scanning from point Co to point sh start and end at the same time. In other words, the start and end of scanning of partial areas 1, I+l, and 2 are synchronized.

However, when e=0.5, in the 51st case, 411+), the scanning from point E to point sb is delayed by 0.5 Ts with respect to the scanning from point Sa to point Co. In other words, there is a possibility that the exposure time area of the partial scanning area L2 spans two consecutive exposure time areas of the partial scanning area L2.

Therefore, in this case, as described above, partial scanning area 1. .

The data write timing for the data buffer in the partial scanning areas 1 and 2 must be completely different from the data write timing for the data buffer in the partial scanning areas 1 and 2.

Here, we will consider the conditions for preventing the exposure time area of the partial scanning area L2 from spanning two consecutive exposure time areas of the partial scanning area L2.

The length of the exposure area time (the shaded area in Figure 6) is η
It can be expressed as T. However, η−θmax /θ
F −−−−−−−−−−−−−■θmax: Maximum scanning angle θ, polygon mirror division angle η, partial scanning area 1, divided into two consecutive exposure time areas depending on the scanning efficiency The condition for e so that the exposure time regions of the scanning region L2 do not straddle is -(1-η)<e<l-η-1--1---■.

Substituting equations ■ and ■ into 2■, we get (n −1) θ1 +θmnχ +2β〈α＜(n+1
)θ,.

−θmax+2β. .

That is, if α-,<AOB is set to satisfy this equation, the exposure time region of the partial scan area L2 will not span two consecutive exposure time regions of the partial scan area L2.

Therefore, by implementing the present invention configured to satisfy the above conditions, it is no longer necessary to write data to the data buffer at different timings for each N area of partial scanning, and it is possible to write data to all scanning areas at the same time. Since the control becomes possible, the control is significantly simplified.

ff) Effects of the Invention As explained in detail above, although the optical scanning device of the present invention is a scanning method using two (pair of) scanning optical systems, the recording time domain of one scanning optical system is Since the scanning optical system does not extend over the recording time domain of the other scanning optical system, the control of recorded data is simplified, and the mirror surface of the rotating polygon mirror can be used effectively, which is a great effect.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining an example of an optical scanning device using a pair of scanning optical systems, Figure 2 is a diagram for explaining the incident position of modulated light on a conventional rotating polygon mirror, and Figure 3 is a diagram for explaining the conventional FIG. 4 is a diagram for explaining the positional relationship between the mirror surface and modulated light; FIG. 5
The figure is a diagram for explaining an embodiment of the present invention, and FIG. 6 is a diagram for explaining an embodiment of a scanning time chart of the present invention. In the drawing, 1 is an image plane, 10 is a rotating polygon mirror, 10゛ is a mirror surface, 12 is a light source section, 13 is an rθ lens, 14 is a reflecting mirror, 15 is modulated light, 21 is a light source, 22 is a collimating lens, 1. , L, , L2 is the scanning width of the optical system, θ is the scanning angle,
0 is the rotation center of the rotating polygon mirror, 8' is the center point of the mirror surface, PI
, P2 is the ridgeline of the mirror surface, β is the perpendicular line drawn from the rotation center O to the mirror surface when the center of the modulated light reflected by the mirror surface coincides with the optical axis of the scanning lens system, and the rotation center O and the reflection point of the modulated light. The angle formed by the line connecting Sa, Ca, Co, Cb,
Sb indicates the scanning position of the modulated light that falls on the image plane 1-A, respectively. Figure 1 Figure 2 Figure 3 (Q) Figure 4 Figure 6 (CI)

Claims (1)

[Claims] An optical system comprising a rotating polygon mirror, a pair of scanning lens systems that scan modulated light reflected by two different mirror surfaces of the polygon mirror to form an image on the same image plane, and a reflecting mirror. The scanning device is configured such that L = L such that the sum of the individual scanning widths L++Lz+ of the pair of scanning lens systems is equal to the scanning width of the entire scanning optical system.
I +l, and when the modulated light reflected by the two mirror surfaces is set as the optical axis of the pair of scanning lens systems, the reflection points are A and B, and the rotation center of the rotating polygon mirror is O.
Then, ZAOB is (n −1)θ, 10θmax+2β<7AOB<(n+
1) × θP - θmax + 2β [where θ is the division angle of the rotating polygon mirror, n is any positive integer, and β is the center of rotation when the center of the modulated light reflected on the mirror surface coincides with the optical axis of the scanning lens system An angle formed by a perpendicular drawn from O to the mirror surface and a line connecting the rotation center 0 and the reflection point of the modulated light.