JPH0436629A - Beam shape measuring instrument of scanning optical system - Google Patents

Abstract

PURPOSE:To accurately measure the shape of a beam at a high speed by providing a mirror and a beam splitter between an ftheta lens and an inspection part. CONSTITUTION:A rotary polygon mirror 2 rotates clockwise as shown by an arrow A and the beam B emitted by a laser light source 1 for measurement is reflected by the rotary polygon mirror 2 and passes through the ftheta lens 3; and beams a1 - a3 are reflected by mirrors 4 - 7 and passed through BFs 8 and 9 to form an image at a point P on a two-dimensional sensor 11 through an objective 10 at the inspection part 15 fixed and arrayed. An A/D converting device 12 and a microcomputer 13 are connected to the two-dimensional sensor 11 and a display 14 is connected to the computer 13. Therefore, the brightness distribution shape of the light image formed at the point P on the two-dimensional sensor 11 is digitized by the A/D converter 12 and computer 13 and displayed 14. Consequently, the beam shape is accurately measured at the high speed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a beam shape measuring device for a scanning optical system such as a laser printer, and is applicable to lens assembly and inspection adjustment of a scanning optical system such as a laser printer. be.

[Conventional technology]

In such a scanning optical system, measuring the beam shape by aligning the rotating light beam on the light emitting side with the optical axis of the light receiving side lens barrel equipped with a photometric element is described in, for example, Japanese Patent Laid-Open No. 55-6771.
It is described in Publication No. 0.

Further, the present inventor has been conducting various developments regarding beam shape measuring devices in scanning optical systems.

[Problem to be solved by the invention]

In order to measure the brightness at each scanning position of a rotating polygon mirror, the present invention provides a scanning optical system that can perform measurements without moving an inspection unit consisting of an objective lens and a two-dimensional sensor placed behind an fθ lens. The purpose of the present invention is to provide a beam shape measuring device in There is no need to consider misalignment, inclination due to movement, etc., and the measurement time required to move the inspection section can be shortened, making it possible to perform measurements at various rotational speeds of the rotating polygon mirror. The purpose of this invention is to provide a means that can eliminate the accompanying measurement errors and perform measurements with higher accuracy.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a rotating polygon mirror, f
In a beam shape measuring device of a scanning optical system comprising a θ lens, an objective lens for measuring the beam brightness emitted from the fθ lens, and an inspection section consisting of a two-dimensional sensor, the f
A mirror and a beam splitter are installed between the θ lens and the inspection section so that the optical path length measured on the optical path of each beam emitted from the fθ lens is equalized, and the optical image of each beam is moved. This is characterized in that the image is formed on a two-dimensional sensor of the inspection section, which is composed of an objective lens and a two-dimensional sensor, and the brightness at each scanning position is calculated by a microcomputer.

[For production]

With the configuration of the present invention, the brightness for each scanning position of the scanning optical system consisting of a rotating polygon mirror and an fθ lens is determined by the objective lens,
Measurements can be made with high accuracy in a short time without moving the inspection section consisting of a two-dimensional sensor.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

In FIG. 1, a beam B generated by a measurement laser light source 1 is transmitted to a polygon mirror 2.0 which rotates around an axis 2a. After passing through the fθ lens 3, the beam alya! It is scanned like a3.

In the present invention, an inspection section 15 consisting of an objective lens 10 and a two-dimensional sensor 11 fixedly arranged with an fθ lens 3
The beam a, which has passed through the fθ lens 3, is reflected by the first mirror 5, and is connected to the first beam splitter 8. The beams are reflected by the second beam splitter 9 and focused on a point P on the two-dimensional sensor 11 by the objective lens 10 of the inspection section 15 . Also, the beam a passing through the fθ lens 3
2 is reflected by the second mirror 4, passes through the second beam splitter 9, and is similarly focused on a point P on the two-dimensional sensor 11 by the objective lens 10 of the inspection section 15, and further, The beam a that has passed through the fθ lens 3 is reflected by the third mirror 6 and fourth mirror 7, passes through the first beam splitter 8, is reflected by the second beam splitter 9, and is inspected. An image is formed on a point P on the two-dimensional sensor 11 by the objective lens 10 of the section 15 .

Each mirror 4, 5°6.7 so that the optical path lengths of the beams ax and attax passing through the fθ lens 3 are equal.
And each beam splitter 8, 9 is installed between the fθ lens 3 and the inspection section 15, both of which are fixedly located.

Further, by setting the ratio of transmittance to reflectance to be 1:1 in the beam splitter 8 and 1:3 in the beam splitter 9, the beams al, az, a,.

The amount of light can be made equal.

Then, the rotating polygon mirror 2 rotates in the clockwise direction A from the position shown in FIG. The beams ava2 and a2 are transmitted to a point on the two-dimensional sensor 11 by the objective lens lO in the fixedly arranged inspection section 15 by the installed mirrors 4°5.6, 7 and the beam splitters 8, 9, respectively. The image is formed on P.

An A/D converter 12 and a microcomputer 13 are connected to the two-dimensional sensor 11.
3 is connected to a display 14.

Therefore, the brightness distribution shape of the optical image formed on the point P on the two-dimensional sensor 11 is digitized by the A/D converter 12 and the microcomputer 13 and displayed on the display 14.

Figure 2 shows the brightness distribution curve of the light amount, and the beam diameter d1 and e -2% (approximately 13.5%) when the brightness is 50%.
By measuring the beam diameter d2, the shape of the beam is calculated and displayed.

In this way, it is possible to accurately measure the brightness distribution at the scanning position of each beam, corresponding to the scanning position of each beam scanned by the reflection of the rotating polygon mirror.

FIGS. 2(a) and 2(b) are luminance distributions shown by beam diameter dimensions in the main scanning direction (X direction) and the sub-scanning direction (X direction) displayed on the display.

■...Laser light source, 2...Rotating polygon mirror, 3...r
θ lens, 4 to 9...mirror and beam splitter,
10... Objective lens, 11... Two-dimensional sensor, 15
···Inspection unit.

〔effect〕

According to the configuration of the present invention, there is an inspection section consisting of an objective lens and a two-dimensional sensor that does not move the beam at a plurality of scanning positions, and a mirror and a beam that keep the optical path length constant between the fθ lens and the inspection section. The splitter has the advantage of being able to measure the beam shape at high speed and with high precision.

Claims (1)

[Claims] In a beam shape measuring device having a scanning optical system, which includes a rotating polygon mirror, an fθ lens, an objective lens for measuring the beam brightness emitted from the fθ lens, and an inspection section consisting of a two-dimensional sensor, the fθ lens and the inspection section Between fθ
A mirror and a beam splitter are installed on the optical path of each beam emitted from the lens so as to equalize the measured optical path length, and an objective lens that does not require movement of the optical image of each beam,
A beam shape measuring device in a scanning optical system, characterized in that an image is formed on a two-dimensional sensor of an inspection section consisting of a two-dimensional sensor, and the brightness at each scanning position is calculated by a microcomputer.