JPH0933833A - Optical scanning device - Google Patents

Abstract

(57) Abstract: When scanning with a plurality of beams, the angle of the range in which all the beams can be scanned is maximized. Moreover, even if some error occurs, the angle of the scannable range is not made small. SOLUTION: The intersection of a plurality of beams is arranged so as to be a point which is advanced by L1 after being reflected from the surface of the rotary polygon mirror. Further, it was arranged so that L1 would come to the center of a good region where the angle of the range in which all the beams can be scanned was large.

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 in laser beam printers, copying machines and the like.

[0002]

2. Description of the Related Art FIG. 2 is a schematic view of a conventional optical scanning device, and FIG. 3 is a view of the vicinity of a rotary polygon mirror. In this description, an example of two beams is shown to simplify the description. Further, in the case of more beams, if the two light beams at both ends are considered to be two, it can be considered as in the case of two beams.

As shown in FIG. 2, a point light source 1 such as a semiconductor laser having at least two light sources, a collimator lens 2 for condensing the two lights, and a central axis of the two lights are a rotary polygon mirror. Relay lens 3 arranged to intersect on surface 4
And an Fθ lens 5 that forms an image of the two lights on a predetermined image plane, that is, a predetermined position on the photoconductor 6, by a rotary polygon mirror 4 for deflecting and scanning the two lights. As shown in FIG. 3, the center lines A and B of the two beams intersect exactly on the surface of the rotary polygon mirror 4 when the surface of the rotary polygon mirror 4 is at the position where the two beam centers A and B are the scanning centers. It was arranged so that it would reflect afterwards.

On the other hand, in the optical scanning device, when a printing device such as a laser beam printer is used for high speed printing, the rotary polygon mirror needs to be rotated in proportion to the high speed. However,
A rotating polygon mirror having a large radius of an inscribed circle may be damaged by centrifugal force if it rotates quickly. Also, if the amount is too large, the optical system becomes large, which leads to an increase in price. Therefore, it is preferable that the rotating polygon mirror be as small as possible because it can be rotated more quickly and can be made smaller. In addition, even if the number of faces of the rotating polygon mirror is enlarged, it is 1
It is suitable for high-speed printing because it can scan more light by rotation. In addition, high-speed printing can be performed even if the number of beams is plural.

Further, the optical scanning device is required to make a minute light spot and finely scan the photoconductor in order to perform printing with a higher resolution than the current state. If the diameter of the light spot is δ, the focal length of the Fθ lens is F, the wavelength of the light used is λ, the circular constant is π, and the width of the beam incident on the Fθ lens is D, then equation (4) may hold. Are known. D = 4λF / πδ (4) From this equation (4), it is understood that D must be increased in order to reduce δ for high resolution printing.

At present, in a printing device such as a laser beam printer, an optical scanning device having a large printing width, that is, a scanning width is desired in addition to the above-mentioned high-speed printing and high-definition printing. In general,
Equation (5) is established, where W is a predetermined scanning width, F is a focal length of the Fθ lens, and θ is a scanning angle of view. W = Fθ (5) From this equation, it is desirable that the larger the scanning angle of view is, the smaller the focal length of the Fθ lens can be when the predetermined printing width is scanned, and the apparatus becomes compact.

From the above, in order to perform high-speed, high-definition, wide-width printing in a printing apparatus such as a laser beam printer, it is desired to use a rotary polygon mirror having a large number of surfaces and a small inscribed circle radius. For high resolution, the beam width must be increased. It is understood that when both of these are executed, the scannable width becomes smaller than that of the conventional one, and the optical scanning device having the same configuration as the conventional one cannot scan a predetermined area. Therefore, it has become possible to realize a high-speed and high-definition optical scanning device by using a plurality of beams.

[0008]

However, in the configuration of the conventional two-beam system as shown in FIGS. 2 and 3, the scanning area in which both the two beams can be scanned is narrower than the scanning area in which the one beam can scan. However, there is a problem that the area cannot be scanned. Therefore, it has been desired to develop a multi-beam scanning device having an optical system having almost the same size and having a scanning region as wide as possible. An example will be given below for the actual description.
In the case of one beam, the number of faces of the rotating polygon mirror is 10, the width of incident light is 4.4 mm, and the radius of the inscribed circle of the rotating polygon mirror is 38.5.
mm, the distance between the intersection of the perpendicular from the center of one surface of the rotating polygon mirror and the center of the entire multiple beams to be incident and the center of one surface of the rotating polygon mirror is 1.9 mm, and the position of the rotating polygon mirror is When the center of the plurality of beams becomes the center of the scanning region, the angle formed by the normal line of the surface of the rotating polygon mirror and the center line of the entire plurality of incident beams is 30 degrees, and the radius of the circumscribed circle of the rotating polygon mirror is 40 degrees. If it is 0.48 mm, the scannable range is -2.
57.60 from 8.807 degrees to +28.801 degrees
It will be 8 degrees. However, the incident beam direction is +. This becomes two beams, and if the half of the angle at which the two beams intersect is 2 degrees, the range that can be scanned by both beams is -2.
From 8.660 degrees to +28.642 degrees, a total of 57.
It will be 302 degrees. Therefore, 0.30 for 2 beams
It can be seen that the range that can be scanned by 6 degrees becomes narrow.

An object of the present invention is to reduce the reduction of the scannable range of the optical scanning device by forming a plurality of beams as described above. Therefore, after the point where a plurality of beams intersect is reflected by the rotating polygon mirror, it is placed at a predetermined distance.
In addition, by keeping the point where a plurality of beams intersect in a stable area where the scanning is wide, the scanning range can be kept wide and stable even when some error occurs.

[0010]

The above object has a light source such as a plurality of lasers, and a light beam incidence optical system for converging a plurality of beams from the light source by a collimator lens and making the beams enter a rotating polygon mirror. In the optical scanning device, this is achieved by causing the center lines of the respective beams of the plurality of beams to intersect at substantially one point in the vicinity of the reflecting surface of the rotary polygon mirror.

[0011]

According to the present invention, in the multi-beam scanning device, the positions of the intersections of the plural beams are optimized, so that the scanning range can be maximized and the margin for error can be widened. A high-performance optical scanning device can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A schematic view of the whole of the embodiment is shown in FIG. 2, which is generally the same as the conventional example. 1 and 4 show the vicinity of the rotary polygon mirror of the embodiment. Here, two beam center lines whose beam width in the scanning direction is D are shown as A and B. However, even if it is three or more, if the light at both ends is considered to be A and B, it can be considered in the same way as in the case of two beams, so only the case of two beams will be described below.

In FIG. 1, when the reflection position of the rotary polygon mirror is at the center of the scanning area, the lights A and B are reflected from the rotary polygon mirror and are arranged so as to intersect each other at a position advanced by L1. . Further, in FIG. 4, similarly, the lights of A and B are arranged so as to intersect with each other by L2 in front of the rotary polygon mirror. When this L1 is set to an appropriate value, the area where both the A beam and the B beam can scan becomes the maximum. Also, L1 is positive, L
When 2 is a negative amount, there is a widest scanning region when it is between L1 and L2, and when it is smaller than L2, the region that can be rapidly scanned decreases. Therefore, if the intersecting position is set in the middle of L1 and L2, even if the position of the intersecting point changes for some reason, the amount of narrowing the scannable area can be reduced.

From the above, in the optical scanning device using a plurality of light sources, when the scannable area is maximized, the intersection may be set to L1, and even if there is some variation, the scannable area is wide and stable. If you want to keep it, it is sufficient to set the intersection just in the middle of L1 and L2.

The above will be described in more detail below. First, consider the reflection of two beams, the A beam and the B beam. As shown in FIG. 5, the angle formed by the A and B beams is 2α, the angle between the center lines of the A and B beams and the perpendicular from the center of the surface of the rotating polygon mirror is β, and the triangle OPQ is one of the rotating polygon mirrors. The beam width in the scanning direction of the plane A, B is D,
The radius of the circumscribed circle of the rotating polygon mirror is y, the distance between the extension line of the A beam and the center O of the rotating polygon mirror is M, the distance between the extension line of the B beam and the center O of the rotating polygon mirror is m, and the number of faces of the rotating polygon mirror Let N and R be the intersections of beam A, beam B and the surface of the rotating polygon mirror, and S be the intersection of the line perpendicular to the center of the rotating polygon mirror and line O. Further, regarding the lines after the central lines of A and B are reflected, if the beam deflection directions are θ1 and θ2 as shown in FIG. 5, four equations are obtained as follows.

Assuming that the deflection angle of the A beam in the θ1 direction with respect to the scanning center is Aθ1, Aθ1 can be expressed by the equation (6). Aθ1 = 2 [180 / N-arcsin {(D-2M) / 2y}]-2 (β + α) (6) The deflection angle in the θ2 direction with respect to the scanning center of the A beam is Aθ2.
Then, Aθ2 can be expressed as in Expression (7). Aθ2 = 2 [180 / N-arcsin {(D + 2M) / 2y}] + 2 (β + α) (7) The deflection angle in the θ1 direction with respect to the scanning center of the B beam is Bθ1.
Then, Bθ1 can be expressed as in equation (8). Bθ1 = 2 [180 / N-arcsin {(D-2m) / 2y}]-2 (β-α) (8) The deflection angle in the θ2 direction with respect to the scanning center of the B beam is Bθ2.
Then, Bθ2 can be expressed as in Expression (9). Bθ2 = 2 [180 / N-arcsin {(D + 2m) / 2y}] + 2 (β-α) (9) The above equations (6) to (9) are the intersections of two beams and the rotating polygon mirror. This is an expression when the distance L to the surface of is 0.

When L is not 0, the result is as shown in FIG. 6, and the equations (10), (11) and (12) are established. In this figure,
A and B are the center lines of the two beams, O is the center line of the beams of A and B, F is the intersection of the beams A and B, G is the intersection of the perpendicular from the center of the surface of the rotating polygon mirror and beam A, H Is the intersection of the perpendicular from the center of the surface of the rotating polygon and beam B, C is the foot of the perpendicular from the center D of the rotating polygon to beam A, and E is the foot of the perpendicular from the center D of the rotating polygon to beam B ,. | DF | = L ... (10) | DG | = Lsinα / sin (α + β) ... (11) | DH | = Lsinα / sin (β−α) (12) However, | DH | The amount enclosed by || indicates the length of the line segment. Further, FIG. 7 is a diagram showing the surroundings of FIG. 6, and m and M in the figure can be expressed as in equations (13) and (14). m = (R + | DH |) sin ([beta]-[alpha]) (13) M = (R- | DG |) sin ([beta] + [alpha]) (14) where R is the inscribed circle of the rotary polygon mirror. Is the radius. further,
When r is determined as shown in FIG. 8, it is sufficient to replace R in equations (13) and (14) with (R + r). When this and Equations (11) and (12) are summarized, Equations (15) and (1
It becomes like 6). m = (R + r) sin (β−α) + Lsinα (15) M = (R + r) sin (α + β) −Lsinα (16) On the other hand, when L is on the front side, the value of L is changed. If it is negative, the equations (15) and (16) are satisfied. That is, M and m in equations (15) and (16) should be inserted into M and m in equations (6), (7), (8), and (9). Now, let's think about it by actually entering numerical values. Number of rotating polygon mirrors N = 10, beam width in scanning direction D = 4.4 m
m, radius of inscribed circle of the rotating polygon mirror R = 38.5 mm, length r = 1.903 mm shown in FIG. 8, angle β = 30 formed between the center lines of the A and B beams and the perpendicular from the center of the rotating polygon mirror. Every time,
When the circumscribed circle radius of the rotating polygon mirror is y = 40.481 mm, and half the angle formed by the A beam and the B beam is α = 2 degrees, the angle of the A beam in FIG. 1 in the θ1 direction in FIG. 5 is represented by Aθ1 and θ2. Assuming that the angle of the direction is Aθ2, and similarly Bθ1 and Bθ2, equations (6), (7), (8), (9), (15), and (16)
FIG. 9 is a graph summarizing the calculated results.
Here, the sum of the angle of view in the θ1 direction and the angle of view in which the A beam and B beam can be scanned is calculated as shown in FIG. From this figure, the maximum scanning range for both the A beam and the B beam is at Aθ1 in FIG.
= Bθ1 and L = + 1.2545 mm. Therefore, in this example, when the rotary polygon mirror and the beam are arranged so as to intersect each other at 1.2545 mm after the reflection of the rotary polygon mirror, it is understood that the range in which the two beams can be scanned together becomes the maximum.

Further, in FIG. 10, Bθ1 = A
It is at L where θ1 is found, and if this is found, L = −
It is 1.2287 mm. Therefore, if the value of L is set at the center of and in FIG. 10, that is, at L = + 0.0258, even if L is deviated by about ± 1.2 mm for some reason, the scanning area is Therefore, it becomes possible to stably obtain a wide scanning angle of view. This and this are shown by the general formula
These are equation (3) and equation (1), respectively.

[0019]

According to the structure of the present invention, in the multi-beam optical scanning device, since the intersection of the beams is arranged after the reflection of the reflecting surface of the rotary polygon mirror, the scanning range can be increased as compared with the prior art. Can be widened. Further, by using the configuration of the present invention, even in a multi-beam optical scanning device, the intersection of the beams is set at an appropriate position. Therefore, even if the size of L is changed due to some cause, the multi-beam may be changed. The range that can be scanned can be widened.

[Brief description of drawings]

FIG. 1 is a diagram showing the vicinity of a rotary polygon mirror according to an embodiment of the present invention.

FIG. 2 is a schematic view of an entire optical scanning device.

FIG. 3 is a diagram of the vicinity of a rotary polygon mirror of a conventional optical scanning device.

FIG. 4 is another diagram showing the vicinity of the rotary polygon mirror according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of an embodiment of the present invention.

FIG. 6 is an explanatory diagram of an example of the present invention, and is an explanatory diagram when L is not 0.

FIG. 7 is a diagram showing a state around FIG. 6;

FIG. 8 is a diagram for explaining a size r.

FIG. 9 is a graph showing calculation results of Aθ1, Aθ2, Bθ1, and Bθ2.

FIG. 10 is a graph showing a result of calculating a scanning angle of view.

[Explanation of symbols]

Reference numeral 1 is a point light source, 2 is a collimator lens, 3 is a relay lens, 4 is a rotary polygon mirror, 5 is an Fθ lens, and 6 is a photoconductor.

Claims (5)

[Claims] 1. An optical scanning device comprising a light source such as a plurality of lasers and a light beam incidence optical system for condensing a plurality of beams from the light source by a collimator lens and making them incident on a rotating polygon mirror. An optical scanning device characterized in that the center lines of the respective beams are crossed at substantially one point in the vicinity of the reflecting surface of the rotating polygon mirror. 2. The optical scanning device according to claim 1, wherein the plane containing the plurality of beams substantially coincides with the plane of rotation of the rotary polygon mirror. 3. When the centers of the plurality of beams are scanned by a rotating polygon mirror, the intersections of the plurality of beams are after the reflection of the rotating polygon mirror when the centers of the plurality of beams are directed toward the center of the scanning region. It is arranged in
The optical scanning device according to claim 1. 4. If the distance between the intersection of the plurality of beams and the point where the centers of the plurality of beams intersect with the reflecting surface of the rotating polygon mirror is L, then approximately L is arranged so as to satisfy equation (1). The optical scanning device according to claim 3, wherein arcsin [{D + 2 (R + r) sin (α + β) -2Lsinα} / 2y] -arcsin [{D + 2 (R + r) sin (β-α) + 2Lsinα} / 2y] = 2α ... (1) However, D is a rotating polyhedral surface. Width of one of the beams incident on the mirror in the scanning direction, R is the radius of the inscribed circle of the rotating polygon mirror, r is the perpendicular from the center of one surface of the rotating polygon mirror and the center of the entire multiple beams incident The distance between the intersection of the rotating polygonal mirror and the center of one surface of the rotating polygonal mirror, β is the number of incidents with respect to the normal of the surface of the rotating polygonal mirror when the rotating polygonal mirror position becomes the center of the area for scanning the centers of the multiple beams. The angle formed by the center lines of the entire beams, α is half the angle formed by the center lines of the two outermost beams at the centers of the plurality of beams, and y is the radius of the circumscribed circle of the rotating polygon mirror. 5. The optical scanning according to claim 1, wherein when the position of the intersection of the plurality of beams is L from the rotating polygonal mirror surface, L is set within the range of the general formula (2). apparatus. B ≦ L ≦ A (2) However, the value of B is L that satisfies the following expression (3), and the value of A is L that satisfies the expression (1). arcsin [{D-2 (R + r) sin (β-α) + 2Lsinα} / 2y] -arcsin [{D-2 (R + r) sin (α + β) -2Lsinα} / 2y] = 2α (3)