JP2633560B2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a light scanning a beam on a recording medium using a pyramidal polygon mirror having a trapezoidal cross section including a rotation axis and an imaging lens. It relates to a scanning device.

(Background of the Invention) FIG. 9 is a conceptual diagram of a configuration of a conventionally known optical scanning device. In the figure, reference numeral 1 denotes a laser light source, and 2 denotes a polygon mirror for scanning an incident beam I from the laser light source 1, which is rotated at a constant speed in the direction of an arrow by a motor (not shown). 3
Is an imaging lens (fθ lens), and 4 is a recording medium such as a photosensitive drum or photosensitive paper, on which a reflected beam (scanning beam) R from the polygon mirror 2 is imaged to perform horizontal scanning.

FIG. 10 is a side sectional view of the polygon mirror 2 in FIG. 9. The polygon mirror 2 is a reflecting surface of a light beam.
21 is configured to be parallel to the rotation axis 20, and the incident beam I and the reflected beam R to the polygon mirror 2 are in the same plane perpendicular to the reflecting surface 21 (usually the meridional plane of the imaging lens 3). In). The rotation axis 20 is arranged perpendicular to the meridional plane of the imaging lens 3.

In the conventional apparatus, the polygon mirror 2 is generally made of aluminum as its material, and the reflection surface 21 is formed by cutting. However, polygon mirrors formed by cutting aluminum are expensive.

Therefore, in recent years, attempts have been made to reduce the cost by forming the main body of the polygon mirror by plastic molding and forming the reflection surface by aluminum evaporation. Note that a protective film such as silicon oxide is formed on the reflective surface on which aluminum is deposited.

However, when the polygon mirror body is formed by plastic molding, it is necessary to perform a die cutting operation, so that a so-called draft angle that is slightly inclined with respect to the rotation axis is formed on the reflection surface.

FIG. 11 (a) is a perspective view showing the configuration of a polygon mirror formed by plastic molding, and FIG. 11 (b) is a side sectional view of FIG. 11 (a). As shown in the figure, each reflecting surface 21 is not parallel to the rotation axis 20 and has an inclination angle (taper angle) φ corresponding to the draft angle. In other words, a polygon mirror having a trapezoidal cross section including the rotation axis (this configuration is called a pyramidal polygon mirror).

(Problems to be Solved by the Invention) FIG. 12 is a conceptual diagram of a configuration of an optical scanning device using a pyramidal polygon mirror as shown in FIG. Here, the rotation axis 20 of the pyramidal polygon mirror 2 is perpendicular to the meridional plane, and the incident beam I is incident parallel to the meridional plane. And the reflection surface 21
Is reflected on the recording medium 4 through the imaging lens 3 to form an image. The scanning trajectory of the reflected beam R draws a downwardly convex curve as shown in the figure because the inclination angle φ of the reflecting surface 21 of the pyramidal polygon mirror 2 apparently changes due to rotation. Therefore, the image obtained on the recording medium 4 is distorted.

The present invention has been made in view of such a problem, and an object of the present invention is to use a pyramidal polygon mirror while maintaining the scanning trajectory of the reflected beam formed on the recording medium 4 in a substantially straight line. It is intended to realize an optical scanning device capable of obtaining a faithful image without distortion.

(Means for Solving the Problems) The present invention as means for solving the above-mentioned problems is based on a pyramidal polygon mirror having a trapezoidal cross-section including a rotation axis and an imaging lens, and is formed on a recording medium. An optical scanning device for scanning a beam, wherein the pyramidal polygon
The angle between the projected incident beam obtained by projecting the incident beam to the pyramidal polygon mirror onto the meridional plane and the optical axis of the imaging lens, with the rotation axis of the mirror being perpendicular to the meridional plane of the imaging lens Is selected so that the angle of incidence does not become 0, the beam incident on the pyramidal polygon mirror is inclined with respect to the meridional plane of the imaging lens, and the angle ω formed between the meridional plane and the incident beam. With respect to the angle φ between the rotation axis of the pyramidal polygon mirror and the reflecting surface of the pyramidal polygon mirror, ω ≒ 1.
An optical scanning device, characterized in that the optical scanning device is provided with an inclination correcting means which is selected to have a relationship of 5φ and corrects an inclination of scanning of a light beam passing through the imaging lens toward the recording medium.

(Operation) The incident beam inclined so as to have a predetermined relationship with respect to the meridional plane of the imaging lens is reflected by the pyramidal polygon mirror, and the reflected beam becomes substantially straight. The inclination of the substantially linear reflected beam is corrected by the inclination correcting means, and the recording medium is scanned with the substantially linear beam having no inclination.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a conceptual diagram showing an example of an optical scanning device according to the present invention. In the figure, the same parts as those in FIG. 12 are denoted by the same reference numerals, and description thereof will be omitted.

In the apparatus according to the present invention, the incident beam I is directed to the meridional plane of the imaging lens (fθ lens) 3 (as shown in FIG. 2, the optical axis l _O of the imaging lens 3 and the center line l _{C in} the longitudinal direction of the lens). (A plane including a).
The pyramidal polygon mirror 2 has a main body made of, for example, plastic, and has a rotation axis 20.
Is perpendicular to the meridional plane 30.

Next, as shown in FIG. 3, the angle between the meridional plane, 30, and the incident beam I is ω, and the pyramidal polygon
The angle (inclination angle) between the rotation axis 20 of the mirror 2 and the reflection surface 21 is φ, and the angle of incidence of the incident beam I on the pyramidal polygon mirror 2 is θ as shown in FIG. And
When the angle of incidence φ and the angle ω between the meridional plane 30 and the incident beam I are changed with the inclination angle φ = 1 °, the reflected beam R
5 to 7 are shown in FIG. At this time, the focal length of the imaging lens 3 was set to 150 mm. As can be seen from these figures, when ω ≒ 1.5φ, the scanning trajectory of the reflected beam R is substantially straight.
In addition, although these scanning trajectories have an upward slope, it is preferable to use the plane mirror 5 as an inclination correcting means, as shown in FIG. 8, to correct the inclination. With such a configuration, pyramidal polygons
The reflected beam R that is incident on the reflecting surface 21 of the mirror 2 and reflected there is incident on the imaging lens 3 in a substantially linear state, despite the presence of the draft (inclination angle) φ, The scanning trajectory of the beam formed on the recording medium 4 is substantially straight, and a faithful image without distortion can be obtained.

In the above-described embodiment, the pre-positioning lens in which the imaging lens 3 is disposed between the pyramidal polygon mirror 2 and the recording medium 4 is used.
It is an objective scanning type optical scanning device,
The present invention is also applicable to a post-objective scan type optical scanning device in which the imaging lens 3 is disposed in front of the polygon mirror 2.

In addition to the present invention, it is more effective to combine a conventionally known surface tilt correction optical system of a polygon scanner.

(Effects of the Invention) As described in detail above, according to the present invention, while using an inexpensive pyramidal polygon mirror made of plastic, for example, as a polygon mirror, the beam on the recording medium is The scanning trajectory can be made substantially straight, so that an optical scanning device capable of obtaining a faithful image without distortion can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of an optical scanning device according to the present invention,
FIG. 2 is an explanatory view of a meridional plane of an imaging lens, and FIG.
The figure shows the relationship between the angle φ and the angle ω. FIG. 4 shows the angle of incidence θ of the incident beam. FIGS. 5 to 7 show the angle of incidence ω and the angle ω between the meridional plane and the incident beam I. FIG. 8 is a diagram showing the scanning trajectory of the reflected beam when it is changed, FIG. 8 is a diagram using a plane mirror to correct the scanning trajectory going up to the left, FIG. FIG. 9 is a side sectional view of a polygon mirror in the apparatus shown in FIG. 9, FIG. 11 (a) is a perspective view of a pyramidal polygon mirror formed by plastic molding, and FIG. 11 (b) is FIG. 11 (a). )
FIG. 12 is a conceptual view of the configuration of an optical scanning device using a pyramidal polygon mirror as shown in FIG. DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Polygon mirror 3 ... Imaging lens 4 ... Recording medium 5 ... Plane mirror 20 ... Rotation axis 21 ... Reflection surface

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshihiro Motoi 2970 Ishikawacho, Hachioji City Konishi Roku Photo Industry Co., Ltd. (56) References JP-A-60-80819 (JP, A) JP-A-57- 181521 (JP, A)

Claims (1)

(57) [Claims] 1. An optical scanning apparatus for scanning a beam on a recording medium using a pyramidal polygon mirror having a trapezoidal cross section including a rotation axis and an imaging lens, wherein the rotation axis of the pyramidal polygon mirror is Is perpendicular to the meridional plane of the imaging lens, and the angle formed by the projected incident beam obtained by projecting the beam incident on the pyramidal polygon mirror onto the meridional plane and the optical axis of the imaging lens does not become zero. The incident angle of the incident beam is selected as described above, and the incident beam to the pyramidal polygon mirror is inclined with respect to the meridional plane of the imaging lens. For an angle φ between the rotation axis of the polygon mirror and the reflecting surface of the pyramidal polygon mirror, ω ≒ 1. An optical scanning device, comprising: a tilt correction unit that selects a relationship of 5φ and corrects a tilt of scanning of a light beam passing through the imaging lens toward the recording medium.