JPH09127445A - Optical scanning device - Google Patents

Abstract

Provided is an optical scanning device capable of realizing the dimensions of a cylinder lens, a rotary polygon mirror, and an Fθ lens when scanning a plurality of beams with substantially the same size as when scanning with a single beam. To do. A first lens (3) and a second lens (4) are provided between a collimator lens (2) and a rotary polygon mirror (6), and a focal length of the first lens is B and a second lens is a second lens. , C is the focal length of the lens, D is the beam diameter of the collimator lens, E is the beam diameter of the second lens, G is the distance from the position where the plurality of beams intersect near the collimator lens to G, when the distance between the second lens and the rotary polygon mirror and a J, J = C + (C 2 / B) - (C 2 G / B 2) constituting the optical scanning device so as to satisfy the condition of C = bE / D did.

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 a laser beam printer or the like.

[0002]

2. Description of the Related Art In an optical scanning device such as a laser printer, a multi-beam optical scanning device has been required as the printing speed increases and the printing dot density increases. Multi-beam optical scanning is scanning with a plurality of light beams at the same time. By doing so, it is possible to scan a plurality of beams in one scan, and high speed printing and high dot density printing can be performed without increasing the rotation speed of the rotary polygon mirror. Further, in multi-beam scanning using a plurality of light sources, it is advantageous that the beam scanning start signal is independent for each beam in order to obtain high print quality.
For this reason, the respective light beams are arranged at positions shifted in the scanning plane. This optical system will be described below.

A conventional multi-beam optical scanning device will be described with reference to FIGS. The number of light sources in this case is two for simplicity, but basically the same description can be applied to any number of light sources. FIG. 3 is a view of a cross section orthogonal to the scanning plane of the optical system. In the light source 1, the two light sources are substantially overlapped with each other in this figure. In the figure, light rays 9 and 10 are separately displayed. The light beam emitted from the light source 1 is converted by the collimator lens 2 into parallel light beams, which are arranged so as to be focused on the surface of the rotary polygon mirror 6 by the cylinder lens 5. The cylinder lens 5 is provided for the purpose of correcting the surface tilt of the rotary polygon mirror 6. After that, the light reflected by the rotary polygon mirror 6 is F
An image is formed at a point on the photoconductor 8 by the θ lens 7.

On the other hand, FIG. 4 is a view in the scanning plane. In the case of this figure, since it becomes complicated, only the respective chief rays are shown as the rays 9 and 10. The light sources are arranged at different positions as shown in FIG. The chief rays indicating the centers of the beams from the respective light sources travel parallel to the collimator lens 2 and, after the collimator lens 2, travel by the focal length B of this lens.
0 crosses. After that, the respective light rays go straight while increasing the distance between them, pass through the cylinder lens 5, the rotary polygon mirror 6, and the Fθ lens 7, and are imaged on the photoconductor 8 at positions where the distance between them is enlarged.

[0005]

From the above, the size corresponding to the spread of the beam interval is larger than when scanning the cylinder lens 5, the rotary polygon mirror 6, the Fθ lens 7 and the like with one beam. It is necessary to design the optical system whose size is increased correspondingly to the divergence of the two beams in FIG. In this case, if the size of each surface of the rotary polygon mirror becomes large, the windage loss becomes large, making it difficult to rotate at high speed, and there is also a problem that it may be damaged by deformation due to centrifugal force. Others, cylinder lens, F
Another problem is that the θ lens must be designed with a large size. In addition to the above, the conventional configuration has a problem that the beam diameter cannot be changed to an appropriate value.

An object of the present invention is to provide an optical scanning device capable of realizing the dimensions of a cylinder lens, a rotary polygon mirror, and an Fθ lens when scanning a plurality of beams with almost the same size as when scanning with a single beam. To do.

[0007]

SUMMARY OF THE INVENTION The above-mentioned object is to provide an optical scanning device having a light beam incidence optical system which collects a plurality of beams emitted from a light source by a collimator lens and makes the beams incident on a rotating polygon mirror. A first lens and a second lens are provided between the lens and the rotary polygon mirror, the focal length of the first lens is B, the focal length of the second lens is C, the beam diameter in the collimator lens is D, and When the beam diameter of the second lens is E, the distance from the position where the plurality of beams intersect near the collimator lens to the first lens is G, and the distance between the second lens and the rotary polygon mirror is J, J ^{= C + (C 2 / B} ) - (C 2 G / B 2) is achieved by C = meets the bE / D.

[0008]

According to the present invention, since the two lenses are added, the beam diameter can be enlarged or reduced. Also, since multiple beams can be crossed on the rotating polygon mirror at the same time,
Cylinder lens, rotating polygon mirror, Fθ lens size 1
This can be realized with substantially the same size as an optical scanning device that scans with this beam.

[0009]

FIG. 1 is a diagram showing an embodiment of a multi-beam scanning device according to the present invention. FIG. 1 is a view of the light scanning surface. In FIG. 1, the case where the number of multi-beams is 2 is shown, and the light beams 9 and 10 are displayed. The light emitted from the multi-beam light source 1 is collimated by the collimator lens 2 to be parallel light. After that, it is made into convergent light by the first lens 3. After that, it passes through the cylinder lens 5 that is put in to correct the tilt of the rotating polygon mirror,
Only the sub-scanning direction is focused on the rotary polygon mirror 6. After that, the polygonal mirror 6 is deflected and scanned, and the Fθ lens 7 narrows down the image onto the photoconductor 8. FIG. 2 shows the same embodiment of the present invention as in FIG. 1 and displays the center light of each of the two light rays. In FIG. 2, the central rays 11 of the two multi-beams,
Reference numeral 12 advances in parallel to the collimator lens 2, exits from the collimator lens 2, crosses once, and enters the first lens 3. After that, the light enters the fourth lens and is arranged so as to intersect with the reflecting surface of the rotary polygon mirror 6 approximately.

The above embodiment will be described in detail below. The distance between the collimator lens and the light source is A, the focal length of the collimator lens is A, the focal length of the first lens is B, the focal length of the second lens is C, the distance between the first lens and the second lens is ( B + C), the beam diameter at the collimator lens is D, the beam diameter at the second lens is E, the distance from the position where a plurality of beams intersect near the collimator lens to the first lens is G, the collimator lens And the first
(A + G), and the distance between the second lens and the rotary polygon mirror is J. These are shown in FIGS. 5 and 6, both of which are views in the scanning plane.
FIG. 5 is a diagram showing the spread of one light beam among a plurality of light sources, and FIG. 6 shows the optical paths of only the central rays of each of the plurality of beams. First, the case of G = B will be described first. In order for the light of the width D to become the light of the width E, the formula (3) may be established. Equation (2) is obtained from this equation (3). D: B = E: C (3) C = BE / D (2) Since B = G, the central rays of each of the plurality of beams between the first lens 3 and the second lens 4 Becomes parallel light. Therefore, in order for this central light to intersect on the reflecting surface of the rotary polygon mirror, it is sufficient if J = C.
Actually enter the numerical value and examine. A = 15 mm, B = 10
When 0 mm, B = G, D = 6 mm, and E = 8 mm, C = 100 × 8/6 = 133.33 mm is obtained from the equation (2). Also, because J = C, J = 133.33m
It should be m. These are shown in FIGS. 7 and 8. Both are views in the scanning plane, FIG. 7 shows the spread of one light of the two beams, and FIG. 8 is a view showing the optical paths of the central lights of the two beams. This is the first
Example of

Second, the case of G> B will be described.
Since G> B, the center light of each beam emitted from the first lens 3 enters the second lens 4 while converging. The distance between this convergence point and the first lens 3 is H. This is shown in FIG. FIG. 9 is a diagram showing the optical paths of the central lights of the two beams. Other parameters are shown in FIGS. 5 and 6 which are explanatory views of the first embodiment.
Set in the same way as.

Here, for the first lens 3, the formula (4) is established from the lens formula. If this is put together, it will become like Formula (5). (G−B) × (H−B) = B ² (4) H = GB / (G−B) (5) Next, from the lens formula for the second lens 3, the formula (6) is It holds. If this is put together, it will become like Formula (7). 1 / C = (1 / J ) -1 / (H-B-C) ... (6) H = (JB-CB-C 2) / (J-C) ... (7) Equation (5) and ( From (7), formula (8) is established, and when this is arranged, it becomes like formula (1). ^{(JB-CB-C 2)} / (J-C) = GB / (GB) ... (8) J = C + (C 2 / B) - (C 2 G / B 2) ... (1) Width D Since the light of (1) becomes the light of the width E, the formula (2) is established as in the case of the first embodiment. Let's examine by actually entering the numerical value. A = 15 mm, B = 100 mm, G = 110
When mm, D = 6 mm, E = 8 mm, C from the formula (2)
= 133.33 mm. Also, to equation (1),
When the above numerical values are entered, the equation (9) is obtained, and J = 1
It is required to be 15.55 mm. J = 133.33 + 177.77-195.55 = 115.55 (9) When this is shown in the figure, it becomes like FIG. Both are views in the scanning plane, FIG. 10 shows the spread of one light of the two beams, and FIG. 11 is a view showing the optical paths of the central lights of the two beams. This is the second embodiment.

Third, the case of G <B will be described.
Since G <B, the central light beams of the plurality of beams emitted from the first lens 3 diverge and enter the second lens 4.
The distance between the base point of divergence and the second lens 4 is M. FIG. 12 shows this state. FIG. 12 is a diagram showing the optical paths of the central lights of the two beams. Also in this case, other parameters are set in the same manner as in FIGS. 5 and 6 which are explanatory views of the first embodiment. First, regarding the first lens, the formula (10) is established from the lens formula, and the formula (10) is summarized. (1 / G) -1 / (M-B-C) = 1 / B (10) M = (B ² + CB-CG) / (B-G) (11) Next, regarding the second lens 4. , The formula from the lens formula (1
2) is established, and it can be summarized as shown in Expression (13). (M−C) × (J−C) = C ² (12) M = JC / (J−C) (13) Formula (14) is established from Formula (11) and Formula (13). In summary, it becomes like the formula (1). JC / (JC) = (B 2 + CB-CG) / (B-G) ... (14) J = C + (C 2 / B) - (C 2 G / B 2) ... (1) The width Since the light of D becomes the light of width E, the equation (2) holds as before.

A numerical value will be actually entered for consideration. A = 15m
m, B = 100 mm, G = 90 mm, D = 6 mm, E =
When it is 8 mm, C = 133.33 mm is obtained from the equation (2). Further, from Expression (1), Expression (15) is obtained, and J = 151.11 mm is obtained. J = 133.33 + 177.77-160 = 151.11 (15) When this is shown in the figure, it becomes like FIG. 13 and FIG. Both are views in the scanning plane, FIG. 13 shows the spread of one light of the two beams, and FIG. 13 is a view showing the optical path of the central light of each of the two beams. This is the third embodiment.

From the above, it can be seen that the equations (1) and (2) hold even when G = B, G> B, and G <B. Therefore, if the formulas (1) and (2) are satisfied, it is possible to change the plurality of beams into free sizes and to intersect the beams near the rotary polygon mirror reflecting surface. In the above description, the case of two beams has been described, but it is clear that the same applies to the case of three or more beams.

Further, the scanning optical system including the cylinder lens and the Fθ lens has been described, but the same effect can be obtained also in the optical scanning optical system which does not include these lenses.

[0017]

According to the present invention, a multi-beam laser scanning device is realized by using a cylinder lens, a rotary polygon mirror, and an Fθ lens, which have substantially the same size as those of a laser scanning device which scans with one beam. In addition, the beam diameter can be set to an arbitrary size.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

2 is a view showing the same embodiment of the present invention as in FIG. 1 in another way. FIG.

FIG. 3 is a diagram showing an example of a conventional optical system.

FIG. 4 is a diagram showing an example of the same conventional optical system as in FIG. 3 from another angle.

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

FIG. 6 is a diagram showing the explanatory view of the first embodiment of FIG. 5 by another method.

FIG. 7 is a diagram showing a first embodiment.

FIG. 8 is a view showing the first embodiment of FIG. 7 by another method.

FIG. 9 is an explanatory diagram of a second embodiment of the present invention.

FIG. 10 is a diagram showing a second embodiment.

FIG. 11 is a view showing the second embodiment of FIG. 10 by another method.

FIG. 12 is an explanatory diagram of the third embodiment of the present invention.

FIG. 13 is a diagram showing a third embodiment.

FIG. 14 is a view showing the third embodiment of FIG. 13 by another method.

[Explanation of symbols]

1 is a multi-beam light source, 2 is a collimator lens, 3 is a first lens, 4 is a second lens, 5 is a cylinder lens,
6 is a rotating polygon mirror, 7 is an Fθ lens, 8 is a photoconductor, 9 and 1
0 is a multi-beam ray.

Claims (1)

[Claims] 1. An optical scanning device having a light beam incidence optical system for condensing a plurality of beams emitted from a light source by a collimator lens and making the beams incident on a rotating polygonal mirror, between the collimator lens and the rotating polygonal mirror. A first lens and a second lens are provided in the first lens, the focal length of the first lens is B, the focal length of the second lens is C, the beam diameter of the collimator lens is D, and the beam diameter of the second lens is E. , G is the distance from the position where a plurality of beams intersect near the collimator lens to the first lens, and J is the distance between the second lens and the rotating polygon mirror, J = C + (C ² / B) -(C ² G / B ² ) An optical scanning device characterized by satisfying the condition of C = BE / D.