JPH0756103A - Optical deflecting device of optical scanning device - Google Patents

Abstract

PURPOSE:To provide a new optical deflecting device which can effectively reduce the wind whistle of a rotary polygon mirror and exerts no substantial adverse influence upon optical characteristics of an image formation optical system. CONSTITUTION:The side wall part of an enclosure which encloses the rotary polygon mirror 2 is formed of a material, whose refractive index is <=1.5, into a transparent hollow cylinder 1, which is arranged having its center axis of curvature aligned with the center axis of rotation of the rotary polygon mirror 2 and meets a condition of 0<d<=0.0004.fMo, where (d) is the thickness and fM is the focal distance of the image formation optical system 5 of the optical scanning device in the direction corresponding to a main scan.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflecting device in an optical scanning device.

[0002]

2. Description of the Related Art An optical scanning device for performing optical scanning by converging a light beam deflected at a constant angular velocity as a light spot on a surface to be scanned by an image forming optical system is related to an optical printer or a digital copying machine. Widely known. The "rotating polygon mirror" is generally used in such an optical scanning device as an optical deflecting device for deflecting a light beam incident from the light source side at a constant angular velocity.

In recent years, with the increase in the speed of optical scanning, the rotation of the rotary polygon mirror tends to increase. However, when the rotary polygon mirror is rotated at a high speed, the harsh "wind noise" generated at the edge portion becomes high. However, there is a problem that a person in the vicinity of the optical scanning device feels uncomfortable.

As a method for reducing the wind noise, it is known to chamfer the edges of the deflecting and reflecting surfaces of the rotary polygon mirror, but it is difficult to sufficiently reduce the wind noise during high-speed rotation. is there.

Sealing the rotary polygon mirror with a sealing means is extremely effective in preventing the wind noise, but it requires a transparent window for taking in light from the light source side and emitting a deflected light beam. It is necessary to design the optical system in consideration of the influence of this window, which makes the device design troublesome.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and can effectively reduce the wind noise of the rotary polygon mirror, and also have a bad effect on the optical characteristics of the imaging optical system. An object of the present invention is to provide a novel optical deflecting device in an optical scanning device which is substantially absent.

[0007]

The optical deflector of the present invention is an optical scanning device which performs optical scanning by converging a light beam deflected at a constant angular velocity as a light spot on a surface to be scanned by an imaging optical system. , A device for deflecting a light beam incident from a fixed direction periodically and at a constant angular velocity, comprising a rotating polygon mirror,
And surrounding means.

As is well known, the "rotary polygon mirror" has a plurality of deflecting / reflecting surfaces for reflecting a light beam and rotates at a constant speed.

The "surrounding means" surrounds the rotary polygon mirror and closes it to the outside, and the side wall portion thereof is formed of a material having a refractive index of 1.5 or less into a transparent hollow cylinder. The "transparent hollow cylinder" is arranged such that its central axis of curvature coincides with the central axis of rotation of the rotary polygonal mirror, and the thickness: d is the focal point in the main scanning corresponding direction of the imaging optical system in the optical scanning device. Distance: For f _M , condition (1) 0 <d ≦ 0.0004 · f _M is satisfied. The transparent hollow cylinder is for accommodating the rotary polygon mirror inside, and since the center axis of curvature thereof is arranged so as to match the center axis of rotation of the rotary polygon mirror, the radius of curvature of the inner cylindrical surface is, of course, It goes without saying that the size must be larger than the radius of the circumscribed circle of the rotating polygon mirror.

The above "main scanning corresponding direction" is a virtual optical path in which the optical path from the light source of the optical scanning device to the surface to be scanned is linearly expanded along the optical axis and is parallel to the main scanning direction. This is the direction that corresponds to each other.

The surrounding means may be fixed in the device space of the optical scanning device and the rotary polygon mirror may be rotated inside the surrounding means (Claim 2), or the surrounding means itself may be the rotary polygon mirror. It may be made to rotate integrally with (Claim 3). In the case of the optical deflector according to the third aspect, the surrounding means is composed of a transparent hollow cylinder and a pair of circular lids that close both ends thereof. When the surrounding means is fixed in the device space of the optical scanning device, the transparent hollow cylinder may be fixed to, for example, a supporting substrate that supports the rotating polygon mirror, and the shape of the lid that closes the upper end is circular. It does not have to be.

[0012]

As described above, in the optical deflector of the present invention, the rotary polygon mirror is closed to the outside by the surrounding means. When the surrounding means is fixed to the optical scanning device, only the rotary polygon mirror rotates inside the surrounding means, but the wind noise is blocked by the surrounding means and does not leak to the outside.

When the surrounding means rotates integrally with the rotary polygonal mirror, the wind noise caused by the rotary polygonal mirror is blocked by the surrounding means and does not leak to the outside, and the surrounding means itself is cylindrical and has no edges. Does not generate wind noise.

However, the transparent hollow cylinder has a "lens action" in the direction corresponding to the main scanning due to its curvature, and when it is formed to have an arbitrary thickness, it forms an image forming optical system (generally, fθ lens) of the optical scanning device. Optical characteristics, that is, field curvature, fθ characteristics, linearity, etc. are affected.

The condition (1) is that when the material of the transparent hollow cylinder has a refractive index of 1.5 or less, the transparent hollow cylinder has a substantial adverse effect on the field curvature, fθ characteristic and linearity of the imaging optical system. Is a condition for not giving.

The smaller the refractive index, the smaller the lens action of the transparent hollow cylinder in the main scanning corresponding direction. By setting the refractive index to 1.5 or less, it becomes possible to form a transparent hollow cylinder with plastic having good workability.

[0017]

EXAMPLES Specific examples will be described below. Figure 1
(A) shows an example of the optical scanning device which implemented the invention of Claims 1 and 3. The light source device shown by reference numeral 6 is, for example, a combination of a semiconductor laser and a collimator lens, and emits a parallel light flux. The parallel light flux from the light source device 6 is directed by the cylinder lens 4 in the sub-scanning corresponding direction (the direction corresponding to the sub-scanning direction on the virtual optical path described above in relation to the main scanning corresponding direction, FIG. 1A). In a direction orthogonal to the drawing) and is incident on the optical deflector.

The optical deflecting device is one in which the rotary polygon mirror 2 is surrounded by a surrounding means. That is, as shown in FIG. 1 (b), the surrounding means is composed of the transparent hollow cylinder 1 which constitutes the “side wall” thereof, the upper lid 8 and the lower lid 9. As shown in (a) of the transparent hollow cylinder 1, the radius of curvature of its inner peripheral surface is formed to be equal to the radius Aout of the circumscribing circle of the rotary polygon mirror 2, and the rotary polygon mirror 2 is fitted in the internal space.

The upper end of the transparent hollow cylinder 1 in which the rotary polygon mirror 2 is fitted in the internal space is closed by a circular upper lid 8 and the lower end is closed by a circular lower lid 9 as shown in FIG. As a whole, it is peeled off and is integrally penetrated and fixed to the shaft 10 of the drive motor. Therefore, the central axis of curvature of the transparent hollow cylinder 1 coincides with the central axis of rotation of the rotary polygon mirror 2.

A light beam from the light source device 1 side passes through the transparent hollow cylinder 1 and, by the action of the cylinder lens 4,
An image is formed as a long line image in the direction corresponding to the main scanning in the vicinity of the deflecting / reflecting surface of the rotary polygon mirror 2, and when reflected by the deflecting / reflecting surface, the transparent hollow cylinder 1 is transmitted outwardly, and an fθ lens as an imaging optical system. By the image forming action of 5, the light is condensed as a light spot on the surface 7 to be scanned.

When the rotary polygonal mirror 2 and the surrounding means are integrally rotated at a constant angular velocity, the light flux reflected by the deflecting / reflecting surface is deflected at a constant angular velocity, and the light spot illuminates the surface 7 to be scanned. To scan.

The fθ lens 5 has a two-lens structure, and its specifications are given as follows. That is, counting from the optical deflector side, the radius of curvature of the i-th lens surface is r _ip in the main scanning corresponding direction and r _is (i = 1 to 1) in the sub scanning corresponding direction.
4), the distance on the optical axis between the i-th lens surface and the (i + 1) th lens surface is d _i (i = 1 to 3), and the refractive index of the j-th lens is n _j (counted from the optical deflector side. j = 1, 2).
In addition, each element regarding the length is the focal length in the main scanning corresponding direction:
It is a value obtained by normalizing f _M to 100.

I r _ip r _is d _i j n _j 1 −107.955 −107.955 5.68 1 1.7121 2 ∞ +59.091 10.98 3 ∞ −59.091 6.82 2 1.6749 4−45.64 −45.64 When the fθ lens 5 is used and the surrounding means is not used, that is, when the light flux from the light source side is deflected only by the rotary polygon mirror 2, the field curvature, fθ characteristic, and linearity. Is shown in FIG. Radius of circumscribed circle of rotating polygon mirror 2: Aout is 0.144
f _M.

In the transparent hollow cylinder 1, the radius of curvature of the inner peripheral surface is 0.144 f _M , and the wall thickness: d is 0.000.
FIG. 3 shows the field curvature, fθ characteristic, and linearity when 1 f _M is set.

Further, in the transparent hollow cylinder 1, the radius of curvature of the inner peripheral surface is 0.163 f _M , and the wall thickness d is 0.
FIG. 4 shows the field curvature, fθ characteristic, and linearity when 0001f _M is set.

Further, the radius of curvature of the inner peripheral surface of the transparent hollow cylinder 1 is 0.163 f _M , and the wall thickness: d is 0.
FIG. 5 shows field curvature, fθ characteristics, and linearity when 0004f _M is set.

In any of the above cases, the transparent hollow cylinder 1 is made of a transparent plastic material having a refractive index of 1.485. Comparing the diagrams of field curvature, fθ characteristic, and linearity when the surrounding means is not used with the cases where the surrounding means is used, the presence of the surrounding means shows that the field curvature, fθ characteristic, and linearity are substantially There is no adverse effect.
Even if the rotary polygon mirror is rotated at a high speed, the "wind noise" that is unpleasant to the ear hardly exists outside.

[0028]

As described above, according to the present invention, it is possible to provide a novel optical deflecting device in an optical scanning device.
Since the present invention has the above-mentioned configuration, it is possible to effectively prevent the wind noise caused by the high speed rotation of the rotary polygon mirror from leaking to the outside of the optical scanning device. There is no substantial adverse effect on the optical properties.

According to the second aspect of the invention, the surrounding means does not rotate, but only the rotary polygon mirror rotates. Therefore, the energy required for the light deflection can be reduced as compared with the case of the third aspect of the invention.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram showing the field curvature, fθ characteristic, and linearity of the imaging optical system when the surrounding means is not used in the above embodiment.

FIG. 3 is a diagram showing the field curvature, fθ characteristic, and linearity of the imaging optical system in one example when the surrounding means is used in the above embodiment.

FIG. 4 is a diagram showing the field curvature, fθ characteristic, and linearity of the imaging optical system in another example in which the surrounding means is used in the above embodiment.

FIG. 5 is a diagram showing the field curvature, fθ characteristic, and linearity of the imaging optical system in another example using the surrounding means in the above-described embodiment.

[Explanation of symbols]

 1 Transparent hollow cylinder 2 Rotating polygon mirror 8 Upper lid 9 Lower lid

Claims (3)

[Claims] 1. In an optical scanning device for performing optical scanning by converging a light beam deflected at a constant angular velocity as a light spot on a surface to be scanned by an imaging optical system, a light beam incident from a fixed direction is periodically and equalized. A device for deflecting at an angular velocity, comprising a rotating polygon mirror that rotates at a constant speed, and surrounding means that surrounds the rotating polygon mirror and closes it to the outside, and the side wall portion of the surrounding means has a refractive index. : The transparent hollow cylinder is made of a material of 1.5 or less, and the transparent hollow cylinder is arranged so that its central axis of curvature coincides with the central axis of rotation of the rotary polygon mirror. Focal length in the main scanning corresponding direction of the imaging optical system at f: f
_{For M} , the condition (1) 0 <d ≦ 0.0004 · f _M is satisfied. 2. The optical deflector according to claim 1, wherein the surrounding means is fixed in the device space of the optical scanning device. 3. The optical deflector according to claim 1, wherein the surrounding means comprises a transparent hollow cylinder and a pair of circular lids closing both ends thereof, and is rotated integrally with the rotary polygon mirror. An optical deflector characterized by.