JPH0460433A - Measuring method of curve in scanning optical system - Google Patents

Abstract

PURPOSE:To reduce a curve of a linear image due to rotation of a rotary polyhedral mirror to a specific value or below and to improve the quality of a scanning optical system by providing three or more sensors at an imaging position and by setting a unit of the scanning optical system on a rotary pulse stage. CONSTITUTION:Three or more sensors 5 are provided at an imaging position and a unit of a scanning optical system is set on a rotary pulse stage 7, while the rotary pulse stage 7 is constructed so that it can rotate coaxially with the center of rotation of a rotary polyhedral mirror 3. In a state wherein the rotation of the rotary polyhedral mirror 3 is stopped, the stage 7 is moved, an emission beam is sensed by each sensor 5 and the barycenter of the beam is measured by each sensor 5. The stage 7 being fixed with a measured value used as a reference point, subsequently, the rotary polyhedral mirror 3 is rotated, the barycenter of the beam of each sensor 5 on each reflecting surface of the rotary polyhedral mirror 3 is measured, a difference in the barycenter of the beam at the position of each sensor on each reflecting surface of the rotary polyhedral mirror 3 is calculated, and a curve of the scanning beam on each reflecting surface is measured. According to this constitution, the curve of a linear image can be reduced to about 100 to 200 mum or below for 300 mm.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a beam shape measurement method in a scanning optical system of a laser printer, etc. The present invention relates to a measurement method and can be used for lens assembly and inspection adjustment of scanning optical systems.

[Prior Art] 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 known, for example, as described in Japanese Patent Application Laid-Open No. 55-6771
It is described in Publication No. 0.

The present inventor has recently been developing a beam shape measurement method in a scanning optical system, and as one of the methods, although not known before this application, each scan scanned by a rotating polygon mirror and an fθ lens A mirror and a beam splitter are installed at the intersection of the axis and the measurement axis where the light receiver is set, and in order to adjust the optical path length of each scanning beam, the light receiver is moved along the measurement axis and the brightness distribution of the beam is adjusted. There is a way to measure it.

[Problem to be solved by the invention]

In the measurement method described above in which the light receiving section is moved along the measurement axis in order to adjust the optical path length of each scanning beam, the rotating polygon mirror is measured at a scanning speed lower than the scanning speed in actual use, and the light receiving section is Since a reference in the scanning direction is not set, it has a drawback that the position of the absolute brightness coordinate in the sub-scanning direction at the scanning position of the scanning beam, that is, the bending of the beam in the scanning direction cannot be measured.

The present invention eliminates the above-mentioned drawbacks and also eliminates the bending of a straight line image by 30 degrees due to the rotation of a rotating polygon mirror.
01 to approximately 100 to 200 μm or less, and to provide a beam shape measurement method in a scanning optical system that can improve the quality of the scanning optical system for digital images. It is.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a scanning optical system that includes a light source, a cylindrical lens, a rotating polygon mirror, and an fθ lens, at the imaging position of the beam emitted from the fθ lens. In the method of arranging the sensor and measuring the beam shape,
Three or more sensors are installed at the image forming position, a unit of the scanning optical system is placed on a rotating pulse stage, and the rotating pulse stage is configured to be able to rotate coaxially with the center of rotation of the rotating polygon mirror. Then, with the rotation of the rotating polygon mirror stopped, the rotating pulse stage is moved, each sensor receives the emitted beam, the center of gravity of the beam is measured at each sensor, and this measurement value is used as a reference point for the next step. First, fix the rotating pulse stage, rotate the rotating polygon mirror, measure the center of gravity of each sensor beam on each reflecting surface of the rotating polygon mirror, and then measure the center of gravity of each sensor beam on each reflecting surface of the rotating polygon mirror. This method is characterized by calculating the difference in the center of gravity of the beam and measuring the curvature of the scanning beam for each reflecting surface.

[Function] With the configuration of the present invention, it is possible to measure the curvature of the scanning beam for each reflecting surface, and based on the measurement results of the curvature of the scanning beam, modifications such as the installation of the rotating polygon mirror can be made, and the beam brightness distribution can be adjusted. enables accurate measurement of

〔Example〕

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

In FIG. 1, beam B generated by laser light source 1
A scanning optical system consisting of an fθ lens 4 equipped with a cylindrical lens 2 that condenses and scans the beam, and a polygon mirror 3, 41, and 42 that rotate around axis 0 is mounted on a unit frame 8 to measure beam curvature. It is installed in Reference numeral 6 denotes a rotating polygon mirror drive motor that can drive the rotating polygon mirror 3 to rotate.

The unit frame 8 is fixed to the rotating part 71 of the rotating pulse stage 7 and can rotate coaxially with the rotation axis 0 of the rotating polygon mirror 3.

The rotating part 71 of the rotating pulse stage 7 is connected to the controller 1
Microcomputer 10 through 2! The unit frame 8 is driven by a rotary motor 72.

Three line sensors 51 , 52 , 53 are installed behind the fθ lens 4 within the scanning range of the beam, and the line sensors 51 , 52 , 53 are connected to the microcomputer 10 via the A/D converter 9 . connected.

In the embodiment, three line sensors 3 are provided, but the number is not limited to three, and an appropriate number of three or more may be provided.

In the present invention having such a configuration, measurement of the curvature of a beam scanned by a rotating polygon mirror will be explained.

In order to measure the reflective surface 31 of the rotating polygon mirror 3, first, the emitted beam B from the laser light source 1 is scanned by the cylindrical lens 2, the reflective surface 31 of the rotating polygon mirror 3, and the fθ lens 4, and the scanning beam B, and line sensor 51
Upper imaging point P. on the unit frame 8 so that the image is formed on the unit frame 8,
The rotating polygon mirror 3 is set in a fixed state.

Next, the unit frame 8 in which the rotating polygon mirror 3 is fixedly set so that the reflection position on the reflecting surface 31 of the rotating polygon mirror 3 does not change is rotated by the rotating pulse stage 7 operated by the rotating motor 72 and the rotating part 71, so that the emitted beam is B is used as a scanning beam B2 and is rotated so that an image is formed on the line sensor 52. At this rotational position of the unit frame 8, an imaging point P0' is obtained on the line sensor 52.

Similarly, the unit frame 8 is rotated so that the emitted beam B is imaged on the line sensor 53 via the reflective surface 31 of the rotating polygon mirror 3 as a scanning beam B3.

Then, an imaging point P is formed on the line sensor 53. ′ is obtained.

This imaging point P. %POPo" is the center of gravity position of the light amount as a reference.

After this, the unit frame 8 is configured so that the emitted beam B is the scanning beam B.
, and is returned by the rotating pulse stage 7 until it reaches the position where it forms an image at the imaging point Po on the line sensor 51, at which point the unit frame 8 is fixed.

Next, when the rotating polygon mirror 3 is driven by the rotating polygon mirror drive motor 6, the emitted beam B from the laser light source 1 becomes a scanning beam reflected by each reflecting surface 31, 32, 33, . . . of the rotating polygon mirror 3. B2, B, , B, and are imaged on the line sensors 52, 51, and 53.

In this case, each line sensor 5 is scanned by the scanning beams B2, B, B3 scanned by the reflecting surface 31 of the rotating polygon mirror 3.
The image forming points on 2, 51, and 53 are P2, P,, P3
Then, the bending due to scanning of each scanning beam a, ~a3
has a value as shown in the graph of FIG. The image forming points PI, PZ, and P:l are the center of gravity of the amount of light in the rotating state of the rotating polygon mirror.

That is, by setting Po=P, =P, ``-P, =O, and calculating the difference between the image formation points on each line sensor 52, 51, 53, it is possible to measure the bending of the scanning beam. can.

Here, the bend al of the scanning beam B1 is a,=P,−
P, =0 The bend a2 of the scanning beam B2 is az =P, -P The bend a3 of the scanning beam B3 is a:1=P3-P.

becomes.

The results shown in FIG. 2 are displayed on a display 11 connected to the microcomputer 10.

Similarly, it is possible to measure the curvature of the scanning beam on the reflective surface 32 of the rotating polygon mirror 3, and sequentially measure the curvature of the scanning beam on other reflective surfaces.

FIG. 3 shows another embodiment of the present invention, in which a two-dimensional sensor 15 is provided instead of the line sensor in the previous embodiment, and three two-dimensional sensors 15L are provided.
152 and 153 are placed opposite the scanning beams B, , B2, and B3, and measurements similar to those in the previous embodiment can be made.

Effects: With the configuration of the present invention, the bending of the scanning line can be measured from the center of gravity of the light amount as a reference and the center of gravity of the light amount when the rotating polygon mirror is in operation. This has the effect of improving the quality of the scanning optical system for digital images by, for example, correcting the inclination of the rotating polygon mirror.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram showing the configuration for implementing the scanning curvature measurement method of the present invention, and Fig. 2 is an example of displaying the position of the center of gravity of the calculated light amount in the rotating state of the rotating polygon mirror on the display. FIG. 3 is a partially schematic explanatory diagram showing another implementation configuration different from the first one. l...Laser light source, 2...Cylindrical lens,
3... Rotating polygon mirror, 4... fθ lens, 5... Line sensor, 6... Rotating polygon mirror driving motor, 7...
・Rotating pulse stage, 8...Unit frame, 9...
A/Dim device, lO...microcomputer, 1
1...Display, 12...Controller, 15
...Two-dimensional sensor.

Claims (1)

[Claims] In a scanning optical system consisting of a light source, a cylindrical lens, a rotating polygon mirror, and an fθ lens, three or more sensors are placed at the imaging position of the beam emitted from the fθ lens, and three or more sensors are placed at the imaging position. The unit of the scanning optical system is placed on a rotating pulse stage, and the rotating pulse stage is configured to be able to rotate coaxially with the rotation center of the rotating polygon mirror, so that the rotation of the rotating polygon mirror is controlled. In the stopped state, move the rotary pulse stage to receive the emitted beam with each sensor, measure the center of gravity of the beam at each sensor, use this measurement value as a reference point, and then fix the rotary pulse stage. Then, rotate the rotating polygon mirror, measure the center of gravity of each sensor's beam on each reflecting surface of the rotating polygon mirror, and then calculate the difference in the center of gravity of the beam at each sensor position on each reflecting surface of the rotating polygon mirror. ,
A method for measuring curvature in a scanning optical system, the method comprising measuring the curvature of a scanning beam for each reflecting surface.