JPH04268529A - scanning optical device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device used in laser printers and the like which has an image forming function by scanning a light beam.

0002

2. Description of the Related Art In recent years, semiconductor lasers as light beam generating elements have been improved in performance and miniaturized, and electrophotographic copying machines and laser beam printers using them have been put into practical use and are becoming widespread. Various developments are also underway regarding scanning optical devices that scan light beams generated by semiconductor lasers.

A conventional scanning optical device will be explained below. FIG. 3 is a perspective view showing the basic configuration of a conventional scanning optical device. As shown in FIG. 3, as components, 1 is a semiconductor laser, 2 is a collimator lens, and 3 is a cylindrical lens. The collimator lens 2 and the cylindrical lens 3 are a first imaging optical system that shapes the oscillated light beam. It is. 4 is a polygon mirror that deflects and scans the light beam formed by the first imaging optical system; 5 and 6 are polygon mirrors that converge the deflected and scanned light beams onto the imaging plane 7 and perform uniform linear scanning. The first and second fθ lenses form a second imaging optical system. 12 is a horizontal synchronization mirror, and 9 is a photodetector for detecting the timing at the start of scanning. 10 is a housing of the scanning optical device.

Regarding the conventional scanning optical device constructed as described above, the related operations of its constituent elements will be explained below.

Laser light generated by a semiconductor laser 1 is converted into parallel light by a collimator lens 2 and condensed by a cylindrical lens 3. This light is deflected by a polygon mirror 4 and then focused on an imaging plane by a second imaging optical system. 7. The scanning start timing is detected by forcibly turning on the semiconductor laser 1 outside the effective scanning area, and detecting a portion of the light beam with the photodetector 9 near the position of the imaging plane 7.

[0006]

However, in the conventional configuration described above, as shown in FIG.
The light beam that hits the edge surface of the fθ lens 6 and is reflected by this surface forms a ghost image on the imaging surface 7. Therefore, if the forced lighting time of the semiconductor laser 1 is shortened, the photodetector 9 will not be able to detect it, and if the first f-theta lens 5 and the second f-theta lens 6 are made larger so as not to cover the edge surface, the size will increase, so the blackness of the lens edge surface will become larger. Painting or multi-coating was required.

The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a scanning optical device that can detect the deflection start timing of a laser beam without interfering with the scanning screen and can be constructed in a small size.

[0008]

[Means for Solving the Problems] In order to achieve the above object of the present invention, a first imaging optical system that shapes a light beam;
In a scanning optical device that includes a polygon mirror that deflects this light and a second imaging optical system that focuses and images this deflected light beam, the second imaging optical system uses the deflected light beam. It has detection means for detecting a light beam that does not pass through and obtaining a scanning start signal.

[0009]

[Operation] With the above configuration, the detection means detects the scan timing using the scan start signal by forcibly turning on the semiconductor laser outside the effective scanning area to obtain the light beam for detection. It does not pass through the second imaging optical system. Therefore, ghost images due to reflection on the lens edge surface are not generated, and there is no need to paint the lens edge surface black or use multi-coating. Further, since the photodetector does not necessarily need to be positioned near the imaging plane, it is possible to reduce the size.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view showing the basic configuration of a scanning optical device according to an embodiment of the present invention. Its components include a semiconductor laser 1, a collimator lens 2, a cylindrical lens 3, and 5 and 6. 1st and 2nd fθ lenses, 7
10 is an image forming surface, and 10 is a housing. Since these are the same as those in the conventional example, they are given the same numbers and their explanation will be omitted. 8 is a cylindrical lens, and 9 is a photodetector as a detection means for detecting a scanning start signal of a light beam. In this embodiment, a light beam emitted from a semiconductor laser 1 is deflected by a polygon mirror 4 and then arranged. . 8 is a cylindrical lens, which may be the same as the cylindrical lens 3. The cylindrical lens 8 functions to convert the light beam focused in the vertical direction by the cylindrical lens 3.

Here, the number of surfaces of the polygon mirror 4 must be wider than the lens width of the second imaging optical system, so it is better to reduce the number of surfaces of the polygon mirror 4 to increase the scanning angle. . Although the scanning angle of the polygon mirror 4 is larger on 5 surfaces than on 6 surfaces, and on 4 surfaces than on 5 surfaces, any number of surfaces may be used as long as the light beam can be deflected to the installed photodetector 9. In this embodiment, there are four surfaces in order to make the deflection angle larger than in the conventional case.

Regarding the scanning optical device of this embodiment constructed as described above, the related operations of its constituent elements will be explained below.

FIG. 2 is a top view of the basic configuration of the same embodiment, showing the optical path of the light beam. Since the light beam oscillated from the semiconductor laser 1 is diffused light, it is converted into parallel light by the collimator lens 2. The light beam converted into parallel light is focused in a vertical direction by a cylindrical lens 3 between a polygon mirror 4 and a collimator lens 2. The reason why the light beam is focused is because there is a machining error on each side of the polygon mirror 4 that deflects the light beam.
The light beam deflected in the axial direction of the polygon mirror 4 is shifted. In order to prevent this, the beam is narrowed down by the cylindrical lens 3, and the second fθ lens 6 is provided with a toric function to perform optical correction. This takes advantage of the property that when light oscillates from a point and passes through a lens, it always passes through the same point.

The focused light beam is deflected at a constant angular velocity by a polygon mirror 4, converted into uniform linear scanning by first and second fθ lenses 5 and 6, and forms an image on an imaging plane 7.

The scan start timing is determined by forcibly turning on the semiconductor laser 1 outside the effective scan area, passing the light beam reflected by the polygon mirror 4 through the cylindrical lens 8, and detecting the scan start signal by the photodetector 9. Let's do it. Therefore, it is not necessary to arrange the photodetector 9 at a position where the image forming plane 7 is located, that is, at the distance where the image is formed, as in the conventional case, and it is possible to arrange the photodetector 9 near the polygon mirror 4 in combination with the cylindrical lens 8. can.

In this way, the first imaging optical system, which is the second imaging optical system,
, the scan start signal is obtained without passing through the second fθ lenses 5 and 6, that is, outside the effective scan area, so the scan start timing can be adjusted with a compact configuration without interfering with the imaging action of the second imaging optical system. can be taken.

[0017]

As is clear from the above description, in the scanning optical device of the present invention, the photodetector is positioned so that the scan start timing is detected with a light beam that does not pass through the second imaging optical system. This detection means eliminates the generation of ghost images due to reflection on the lens edge surface in conventional forced lighting, eliminates the need to paint the lens edge surface black, and reduces cost.
Since the position of the photodetector does not necessarily have to be on the scanning image, a compact and excellent laser scanning device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the basic configuration of a scanning optical device according to an embodiment of the present invention.

[Fig. 2] A top view showing the basic configuration of the scanning optical device of the same embodiment.

[Fig. 3] A perspective view showing the basic configuration of a conventional scanning optical device.

[
Figure 4: Top view showing the basic configuration of the conventional scanning optical device

[Explanation of symbols]

1 Semiconductor laser 2 Collimator lens 3 Cylindrical lens 4 Polygon mirror 5 First fθ lens 6 Second fθ lens 7 Imaging plane 8 Cylindrical lens 9 Photodetector

Claims (2)

[Claims] 1. A semiconductor laser that emits a light beam; a first imaging optical system that shapes the light beam; and a polygon mirror that deflects and scans the light beam that is shaped by the first imaging optical system. a second imaging optical system that focuses and images the light beam deflected by the polygon mirror on an image plane;
detection means for detecting a light beam that is outside the effective scanning area of the deflected light beam and does not pass through the second imaging optical system, and the deflected light beam is detected by the output of the detection means. A scanning optical device that obtains a scanning start signal. 2. The scanning optical device according to claim 1, wherein the detection means comprises a cylindrical lens and a photodetector.