JP2571589B2 - Optical scanning device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical scanning device.

(Prior Art) An optical scanning device that deflects a light beam and forms an image of the deflected light beam into a spot on a scanning surface by an imaging lens to perform optical scanning is related to a laser printer or a document reading device. Known, but the most commonly known is
This is an apparatus using a rotary polygon mirror as shown in FIG. 4 as a deflector. In the figure, the light beam from the LD unit 1 containing a semiconductor laser, a collimating lens and a slit is a parallel light beam, but is reflected by a cylinder lens 2 in the direction corresponding to the main scanning direction near the reflecting surface of the rotating polygon mirror 3. And is reflected by the reflecting surface of the rotary polygon mirror 3 and is incident on the scanning surface 6, specifically, the surface of the photosensitive drum or the like via the fθ lens 4 and the cylinder lens 5,
By the action of the fθ lens 4 and the cylinder lens 5, an image is formed on the scanning surface 6 in the form of a spot.

When the rotating polygon mirror 3 is rotated at a constant speed by a motor (not shown) in the direction of the arrow, the reflected light beam is deflected at a constant angular velocity, but the scanning surface 6 is moved at a constant speed by the spot-shaped imaging point by the action of the fθ lens 4. Is scanned.

The deflected light beam enters the mirror 7 on the way to the scanning area, and enters the synchronous detector 8 when reflected.

The synchronization detector 8 generates a detection signal when receiving the light beam, and the start of scanning of the scanning area is synchronized based on the detection signal.

Now, the rotating polygon mirror has a plurality of reflecting surfaces, and the reflecting surfaces are switched by rotation. However, an error cannot be avoided in the division angle of each reflecting surface. For this reason, assuming that after the light beam shown by the solid line in FIG. 4 scans and this reflecting surface looks like a broken line due to an error in the division angle of the adjacent succeeding reflecting surface, the anti-slope surface The state of the light beam deflected by the above becomes like a broken light beam. The light beam of the solid line and the light beam of the broken line almost coincide with each other on the scanning surface 6 as shown in the figure, but the optical path between the starting point of deflection by the rotary polygon mirror 3 and the scanning surface 6 deviates considerably from each other. For this reason, the synchronization detector 8 cannot perform accurate synchronization detection unless it is arranged on the image forming plane by the fθ lens 4, that is, on the scanning plane. However, since it is not possible to actually provide a synchronization detector on the scanning surface due to the presence of the photosensitive drum or the like, the light beam is turned back by the mirror 7 and the synchronization detector 8 is placed at a position equivalent to the scanning surface. Deployed and performed synchronization detection. For this reason, there is a problem that a space for synchronization detection becomes unnecessarily large, which hinders downsizing of the optical scanning device.

(Purpose) The present invention has been made in view of the above-mentioned circumstances, and a purpose thereof is to provide a novel space-saving synchronous detection space and a small optical scanning device. An optical scanning device is provided.

(Configuration) Hereinafter, the present invention will be described.

An optical scanning device according to the present invention is an optical scanning device that deflects a light beam, forms an image of the deflected light beam in a spot shape on a scanning surface by an imaging lens, and performs optical scanning, and has the following features. Having.

That is, first, the deflector that deflects the light beam is a single-surface deflector. The single-surface deflector has a single reflecting surface for reflecting and deflecting a light beam, that is, a deflector using a so-called pyramidal mirror or galvano mirror.

Second, a synchronization detector that detects a light beam deflected toward the scanning area and synchronizes the optical scanning is provided at a position between the imaging lens and its image plane, which is close to the imaging lens. I do.

Thus, in the present invention, a single-sided deflector is used as a deflector, but the single-sided deflector is different from a rotating polygon mirror,
There is no room for the division angle error of the reflection surface, and the deflection state of the light beam deflected toward the scanning surface is always the same. Therefore, even if the synchronous detector is provided immediately after the imaging lens, no detection error occurs.

(Example) Hereinafter, a description will be given according to a specific example.

FIG. 1 is a simplified view of a main part of an embodiment of the present invention. FIG. 1 (I) is a plan view, and FIG.
(III) shows the state from the deflector to the scanning plane as viewed from the left side of (I).

An LD unit 11 containing a semiconductor laser and a collimating lens emits a parallel light beam. This light beam enters the deflector 30 via the mirror 12.

The deflector 30 is a single-sided deflector, and in this embodiment, a pyramidal mirror is used. That is, the deflector 30 is composed of the motor 15 and the pyramidal mirror 14 integrated with its axis.
And a slit member 13.

The pyramidal mirror 14 is positioned at 45 degrees with respect to the rotation axis of the motor 15.
It has a single reflecting surface inclined at an angle and is rotated by the motor 15.

The slit member 13 is mounted coaxially with the motor 15. After being reflected by the mirror 12, the light beam is incident on the reflection surface of the pyramidal mirror 14 along the rotation axis of the motor 15. In order to make this incidence possible, the slit member 13 is provided with an entrance hole 13a. The light beam incident from the entrance hole 13a is reflected by the pyramidal mirror 14,
Injection slit perforated on the peripheral surface of the slit member 13
Inject from 13b.

The slit member 13 is provided to prevent the elliptical cross section of the light beam of the emission deflection light beam from rotating due to the rotation of the pyramidal mirror 13.
Has an elliptical shape whose diameter in the direction corresponding to the main scanning and in the direction corresponding to the sub-scanning direction is determined according to the spot shape on the scanning surface. When the pyramidal mirror 14 is rotated by the motor 15, the reflected light beam is deflected. The deflected light beam forms an image in the form of a spot on the surface of the photosensitive drum 18 as a scanning surface by the imaging lens 16. Toroidal lens 17 placed close to the scanning plane
Is for correcting the field curvature.

The synchronization detector 19 is provided at a position close to the imaging lens between the imaging lens 16 and its image plane, that is, immediately after the imaging lens when viewed from the starting point of deflection, and performs synchronization detection.

The synchronization detector 19 is a photosensor in this example, but as another example, for example, a light incident end of an optical fiber is placed at the position of the synchronization detector in FIG. 1, and the synchronization light is transmitted to another position by this optical fiber. It may be guided to a photo sensor placed.

As shown in FIG. 2, a cylinder lens 20 may be combined with the synchronization detector 19. In this manner, even if the direction of the light beam deflected due to the reflection surface angle error of the pyramidal mirror 14 is displaced as indicated by a broken line, or is deviated in parallel as indicated by a dashed line, the detection can be reliably performed. When a cylinder lens and a synchronization detector are combined, it is preferable that the light receiving section of the synchronization detector be located at the focal position of the cylinder lens. Fig. 3 shows the light receiving part of the synchronous detector
In the case of 24 light incident ends, a cylinder lens
23 is coupled and integrated with the end of the optical fiber 24 by a coupler 25 such that the focal position coincides with the light incident end.

(Effects) As described above, according to the present invention, a novel optical scanning device can be provided. Since the optical scanning device of the present invention uses a single-sided deflector, a synchronous detector can be provided immediately after the imaging lens,
Therefore, the space for disposing the synchronization detector is small. In addition, a single-sided deflector is smaller than a rotating polygon mirror.
Therefore, it is possible to make the optical scanning device compact. In the case of the conventional apparatus shown in FIG. 4, if there is an error of θ in the mounting angle of the mirror 7, the synchronous light detection position is shifted by 2θ · L, resulting in a synchronous error. Is detected directly at the position immediately after the imaging lens, such a synchronization error does not occur.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing only a characteristic portion of another embodiment, FIG. 3 is a diagram showing only a characteristic portion of another embodiment, and FIG. 4 is a diagram for explaining a conventional technique and its problems. 11 LD unit, 30 Single plane deflector, 13 Slit member, 14 Pyramidal mirror, 15 Motor, 16
…… image forming lens, 18… photosensitive drum (the surface of which is the scanning surface), 19… sync detector

Claims (1)

(57) [Claims] An optical scanning device for deflecting a light beam and performing optical scanning by forming an image of the deflected light beam into a spot on a scanning surface by an imaging lens, comprising: a deflector for deflecting the light beam. Is a single-sided deflector, and a synchronous detector that detects the light beam deflected toward the scanning area and synchronizes the optical scanning is located close to the imaging lens between the imaging lens and its image plane. An optical scanning device, wherein the optical scanning device is disposed at a predetermined position.