JPS5929220A - Plane scanning mechanism - Google Patents

Abstract

PURPOSE:To decrease the distortion in a scanning beam by such constitution wherein an encoder for outputting the pulses corresponding to the position of the mirror surface of a rotary polyhedral mirror and the inclination of faces and the aberration of a scanning lens are corrected with the output signal thereof. CONSTITUTION:The pulse signal from an encoder installed to the revolving shaft of a rotary polyhedral mirror is inputted to an input terminal 16 and is integrated in an integrator 11 via a waveform shaping circuit 10. The integrated signal thereof is made into the memory address signal for accessing a storage part 12 consisting of a memory stored beforehand with the correction values for correcting the inclination of the various specular surfaces of the rotary polyhedral mirror and the aberration of a scanning lens. The correction value corresponding to the position of the encoder read out from the part 12 is outputted as a correction signal to the output terminal through a DA converter 13 and an LP filter 14. On the other hand, a timing controller 15 controls synchronously an integrator 12 and the converter 13 according to the pulse signal from the encoder. The distortion of the scanning beam is thus decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mechanism for performing plane scanning by main scanning a light beam using a rotating polygon mirror and feeding a photosensitive medium in the sub-scanning direction.

Conventionally, when performing main scanning with a light beam using a rotating polygon mirror, the scanning beam may shift in the sub-scanning direction for each mirror surface of the rotating polygon mirror due to the surface tilt of the rotating polygon mirror or aberrations caused by the scanning lens. , - There was a drawback that the scanning line was curved in the sub-scanning direction.

An object of the present invention is to provide a plane scanning mechanism that eliminates such conventional drawbacks.

That is, according to the present invention, there is provided an optical modulator that modulates a light beam, a rotating polygon mirror that deflects the light beam in the main scanning direction, and a rotary polygon mirror that condenses the deflected light beam and focuses it on the surface of the sensitive medium. In a plane scanning mechanism consisting of a scanning lens having a rotation angle and a feeding mechanism that moves a photosensitive medium in the sub-scanning direction, the surface tilt of the rotating polygon mirror with respect to the rotation axis and the aberration of the scanning beam on the photosensitive medium due to the scanning lens are corrected. In order to do this, an encoder that outputs pulses corresponding to the mirror surface position of the rotating polygon mirror, an integrator that integrates the pulses from the encoder, and an integer of the mirror surface position of the rotating polygon mirror indicated by the integrator,
a storage unit that stores correction values for correcting distortions on the photosensitive medium due to aberrations of the scanning process; a digital/analog cog converter that converts the read digital correction values into analog; - It is characterized by being equipped with an acousto-optic deflector of δ6 for deflecting the light beam using the output of the analog converter.

FIG. 1 is a diagram showing a conventional plane scanning mechanism.

In FIG. 1, a light beam from a light beam 1 is modulated by an optical modulator 2, and then passes through an original beam expanding optical system 3 to expand the light beam into a circular shape. Thereafter, main scanning is performed by the rotating polygon mirror 4, and the resulting light beam is focused onto a scanning mirror by a scanning lens 5 and projected onto a photosensitive medium on a scanning doublet.

FIG. 3 is a diagram showing fluctuations in the main scanning direction X and sub-scanning direction Y of the scanning beam caused by the conventional method.

In the figure, F1, F2...1°゛8 is the mirror surface number 1, which counts the eight-faced bowl portion of the rotating polygon mirror 4. Mirror surface 2.
...Indicates mirror surface number 8.

To facilitate understanding, consider a situation in which the scanning table 6 is not moved in the sub-scanning direction Y.

At this time, in the method shown in FIG. 1, the mirror surface F1 of the rotating polygon mirror 4
...) There is a change in the sub-scanning direction Y due to the fall. Further, a convex curvature in the sub-scanning direction Y due to the scanning lens 5 can be seen. Next, an example of 66 tJ will be explained.

In FIG. 2, a light beam from a light source 1 is modulated by a modulator 2, passes through an acousto-optic deflector 7, and is expanded by a light beam expansion optical system 3.

Thereafter, main scanning is performed using a rotary polygon mirror 4 that can detect the position of the mirror surface by a low-resolution encoder 8, and the light is focused by a scanning lens 5 and projected onto a photosensitive medium 6.

At this time, the pulse signal from the low reencoder 8 causes the acousto-optic deflector 7 to be
Then, a correction signal for correcting the surface tilt of the rotating polygon mirror and the aberration of the scanning lens is output.

FIG. 4 shows a scanning beam corrected by the correction circuit and acousto-optic deflector having the configuration shown in FIG. Next, the correction circuit will be explained in detail.

FIG. 5 is a block diagram of the correction circuit 9 shown in FIG. 2. The pulse signal from the low cryo encoder 8 is input to the input terminal 16 of the correction circuit, passes through the waveform shaping circuit 10, and is integrated by the multiplier 11. This integrated signal becomes a memory address signal for accessing a storage unit 12 which is a memory that stores correction values for correcting the surface tilt of each mirror surface of the rotating polygon mirror 4 and the aberration of the scanning lens. The correction value according to the position of the encoder read from the storage unit 12 is converted into an analog signal by the digital-to-analog converter 13,
Low pass filter 1 to remove high frequency components in the signal
4, the corrected signal is outputted to the output terminal 17.

Timing controller] 5 calculates the product q based on the pulse signal from the encoder 8 in 2G 2 figure.

device 11, storage section 12, digital/analog converter 13
performs synchronous control.

This signal at the output terminal 17 is applied as a correction signal to the acousto-optic deflector 7 shown in FIG. The acousto-optic deflector 7 deflects the light beam that has passed through the optical modulator 2 in FIG. 2 in the sub-scanning direction Y in accordance with the input signal, thereby correcting the surface tilt of the rotating polygon mirror and the aberration of the scanning lens.

As explained above, according to the present invention, it is possible to extremely reduce distortion of the scanning beam due to the surface tilt of the rotating polygon mirror and the aberration of the scanning lens, which was previously impossible.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram showing a conventional plane scanning mechanism, FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 3 is a diagram showing distortion of a scanning beam in the conventional method, and FIG. FIG. 4 is a diagram showing distortion of a scanning beam according to an embodiment of the present invention, and FIG. 5 is a block diagram of a correction circuit according to an embodiment of the present invention. In the figure, 1 is a light source, 2 is an optical modulator, 3 is a light beam expansion optical system, 4 is a rotating polygon mirror, 5 is a scanning lens, 6 is a scanning table, 7 is an acousto-optic deflector, 8 is a rotary encoder, 9 10 is a correction circuit, 10 is a waveform shaping circuit, 11 is an integrator, 12 is a storage section, 13 is a digital/analog converter,
4 is a low-pass filter, 15 is a timing controller, 16 is an input terminal, and 17 is an output terminal. X is the main scanning direction, Y is the sub-scanning direction, Fl...F8 is the mirror surface 1.
...8 is shown.

Claims (1)

[Claims] an optical modulator that modulates a light beam; a rotating polygon mirror that deflects the light beam in a rotational direction (hereinafter referred to as the main scanning direction);
In the plane scanning mechanism, which comprises a scanning lens that focuses a deflected light beam on the surface of a photosensitive medium, and a feeding mechanism that feeds the photosensitive medium in a direction perpendicular to the main scanning direction (hereinafter referred to as the sub-scanning direction), In order to correct the surface tilt of the rotating polygon mirror with respect to the rotation axis and the aberration of the scanning beam on the photosensitive medium caused by the scanning lens, an encoder outputs pulses according to the mirror surface position of the rotating polygon mirror, and the pulses from the encoder are integrated. a storage unit that stores correction values for correcting distortions on the photosensitive medium caused by the tilt of the mirror surface position of the rotating polygon mirror indicated by the multiplier and the aberration of the scanning lens; A digital-to-analog converter converts the corrected digital correction value to analog;
A plane scanning mechanism comprising: an acousto-optic deflector for deflecting a light beam using the output of an analog converter.