JPH0635213Y2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an optical scanning device of an fθ lens double pass that causes a light beam, such as a laser beam, to be incident on a rotating polygon mirror in the front direction for deflection and scanning.

[Conventional technology]

As a conventional double-pass optical scanning device, for example, the fourth
There is an example shown in FIG. 5 and FIG. 5, FIG. 4 is a plan view of the double-pass optical scanning device, and FIG. 5 is a side view thereof. In this device, a laser beam 30A modulated according to a recording signal is output from the laser beam generator 1, passes through the front of a window 4 provided on the fθ lens 2 and the motor cover 3, and passes through the rotary polygon mirror 5. The deflected beam that enters the center and is deflected by the rotary polygon mirror 5 passes through the window 4 and the fθ lens again, is reflected by the cylindrical mirror 6 which is the surface tilt correction optical system, and is imaged on the photosensitive drum 7. As the rotary polygon mirror 5 is rotated by the drive motor 8, scanning is performed from the laser beam 30B to the laser beam 30C. Note that FIG. 4 shows a state in which the rotary polygon mirror 5 exposes the center of the area of the photosensitive drum 7 to be scanned.

[Problems to be solved by the invention]

In the above-mentioned conventional optical scanning device, since both the incident light and the reflected light of the rotary polygon mirror 5 pass through the fθ lens 2, the collimator lens can be omitted and the laser beam is directly incident on the rotary polygon mirror 5. There is an advantage that the surface size of the rotary polygon mirror 5 and thus the outer diameter can be reduced to reduce the load on the drive motor 8 of the rotary polygon mirror 5.

However, in the conventional double-pass optical scanning device, as shown in FIG. 5, the laser beams 30B and 30C are fθ.
There is a problem in that the laser beam scanning line on the photosensitive drum 7 is bent because it passes through a portion of the lens 2 away from the optical axis 50.

Further, since the surface reflected light beam 40A of the laser beam 30A in the window 4 is exposed on the photosensitive drum 7,
There is also a problem that print quality is adversely affected.

The present invention solves the above problem, and an object of the present invention is to provide an optical scanning device capable of correcting the deflection of the scanning line of the light beam scanned onto the photosensitive drum.

[Means for solving problems]

In the optical scanning device of the present invention, a light beam is incident on the fθ lens at a predetermined angle with respect to the optical axis, emitted light is deflected by a rotating polygon mirror, and then passed through the fθ lens again to be exposed through a surface tilt correction optical system. In a double-pass optical scanning device that scans and exposes a body surface, a prism having an angle with the sub-scanning direction is provided between the fθ lens and a rotary polygon mirror, and a light beam reflected by the rotary polygon mirror is It is characterized in that it is arranged so as to pass near the optical axis.

[Action]

In the present invention, for example, as shown in FIG. 1, a laser beam 30A modulated according to a recording signal is output from a laser beam generator 1, passes through an fθ lens 2, and then is directed to a prism 9 with respect to an optical axis 50. The laser beam is incident on the center of the rotary polygon mirror 5, and the deflected beam deflected by the rotary polygon mirror 5 is refracted by the prism 9 and passes through the fθ lens. The light is reflected by a cylindrical mirror 6 which is a surface tilt correction optical system to form an image on the photosensitive drum 7, and the rotation of the rotary polygon mirror 5 causes scanning from a laser beam 30B to a laser beam 30C.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side view showing an embodiment of the optical scanning device of the present invention, FIG. 2 is a view for explaining the prism of FIG. 1, and FIG. 3 is a view for explaining the effect of the present invention. is there. In the figure,
Reference numeral 1 is a laser beam generator, 2 is an fθ lens, 3 is a motor cover, 5 is a rotary polygon mirror, 6 is a cylindrical mirror, 7 is a photosensitive drum, 8 is a drive motor, and 9 is a prism.

In FIG. 1, the present invention is different from the above conventional example in that
The point is that a prism 9 is arranged between the fθ lens 2 and the rotary polygon mirror 5. That is, a laser beam 30A modulated according to a recording signal is output from the laser beam generator 1, and after passing through the fθ lens 2, the prism 9 shown in FIG. Then, the laser beam is incident on the center of the rotary polygonal mirror 5, and the deflected beam deflected by the rotary polygonal mirror 5 is refracted by the prism 9 and passes through the fθ lens to the plane tilt correction optical system. An image is formed on the photosensitive drum 7 by being reflected by a certain cylindrical mirror 6, and the rotary polygon mirror 5 is rotated by the drive motor 8 to scan from the laser beam 30B to the laser beam 30C.

As shown in FIG. 2, the prism 9 makes the angle between the optical axis 50 and the laser beam 30A incident on the prism 9 θ (0 ° <θ
.Ltoreq.5.degree.), When the prism 9 has an apex angle .alpha. On the side where the scanning light passes and the rotary polygon mirror side is horizontal to the rotary polygon mirror, when the refractive index is n, .theta. = 2α
The prisms 9 satisfying the relationship (n-1) or a relationship close thereto are arranged. As a result, the beam reflected by the rotating polygon mirror 5 and refracted by the prism 9 is reflected by the optical axis 50 of the fθ lens.
Since the light passes through the vicinity of, the deflection of the laser beam scanning line on the photosensitive drum 7 is corrected.

FIG. 3 shows the measurement result of the deflection amount of the laser beam scanning line on the photosensitive drum 7, and the solid line is the scanning line deflection generated in the conventional double-pass optical scanning device. In the optical scanning device of the present invention, As the prism 9, θ = 2α (n-
It will be understood that when the one satisfying the relation close to 1) is arranged, the deflection of the scanning line is considerably corrected as shown by the dotted line. Further, as shown in FIG. 1, since the reflected light 40B of the laser beam 30A on the prism 9 does not enter the photosensitive drum 7, it does not adversely affect the print quality.

[Effect of device]

As described above, in the present invention, the light beam reflected by the rotary polygon mirror passes through the prism having an angle with respect to the sub-scanning direction between the fθ lens and the rotary polygon mirror near the optical axis of the fθ lens. Since the arrangement is made so that the deflection of the scanning line of the laser beam scanned onto the photosensitive drum can be corrected.

Further, when compared with a conventional double-pass optical scanning device provided with a window, the photosensitive drum 7 is affected by surface reflected light.
The drawback of over-exposure and adversely affecting print quality is eliminated.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of the optical scanning device of the present invention, FIG. 2 is a diagram for explaining the prism of FIG. 1, and FIG. 3 is a diagram for explaining the effect of the present invention. FIG. 4 is a plan view of a conventional double-pass optical scanning device, and FIG. 5 is a side view of FIG. DESCRIPTION OF SYMBOLS 1 ... Light beam generator, 2 ... fθ lens, 5 ... Rotating polygon mirror, 6 ... Cylindrical mirror, 7 ... Photosensitive drum, 9 ...
prism.

Claims (2)

[Scope of utility model registration request] 1. A light beam is incident on an fθ lens at a predetermined angle with respect to the optical axis, and the emitted light is deflected by a rotary polygon mirror, and then the light beam is reflected again by the f.
In a double-pass optical scanning device that passes a θ lens and scans and exposes a surface of a photoconductor through a surface tilt correction optical system, a prism having an angle with respect to a sub scanning direction is provided between the fθ lens and a rotary polygon mirror. The optical scanning device is arranged such that the light beam reflected by the rotary polygon mirror passes near the optical axis of the fθ lens. 2. When the angle between the optical axis and the light beam incident on the prism is θ (0 ° <θ ≦ 5 °), there is an apex angle α on the side of the prism through which the scanning light passes, and a rotating polyhedral surface. A utility model registration request characterized in that a prism that is horizontal with respect to the rotary polygonal mirror is provided with a refractive index n and a relation of θ = 2α (n-1) or a relation close to this. 2. An optical scanning device according to claim 1.