JPH0354515A - Noise eliminating device for rotary polygon mirror - Google Patents

Abstract

PURPOSE:To securely eliminate a noise such as a wind noise generated by the rotary polygon mirror by providing a sound collecting means, a sound source in the opposite direction from a converged sound wave, and a sound source control means. CONSTITUTION:When the rotary polygon mirror 1 is placed at the focus position of a parabolic reflecting plate 2, a sound wave generated by the rotary polygon mirror 1 is converged in a constant direction and projected as a nearly plane wave. A directional speaker 3 which generates a plane sound wave in the opposite direction from the traveling direction of the converged sound wave is arranged at the front of the mirror in the traveling direction, and controlled by a control system 14. The control system 4 is constituted of a microphone 5 which is arranged in the traveling path of the converged sound wave, an inverting amplifier 6 which inverts and amplifies its output, a phase shifter 7 which adjusts the phase of the output of the amplifier 6 corresponding to the delay time of the control system 4, and an amplifier 8 which drives the speaker 3 corresponding to the output of the phase shifter 7. In this constitution, the noise generated by the rotary polygon mirror 1 is securely eliminated by the cancellation of the sound wave generated by the directional speaker 3.

Description

[Detailed description of the invention] Technical field The present invention relates to a muffling device for a rotating polygon mirror.

BACKGROUND OF THE INVENTION Rotating polygon mirrors are used, for example, as scanning means in high-speed laser scanning systems such as laser projection displays. An example of the structure of a high-speed laser scanning system using this rotating polygon mirror is shown in FIG.

In FIG. 2, a laser beam whose intensity is modulated according to a video signal enters the mirror surface of a polygon mirror 22 through a first cylindrical lens 21 for correcting pitch unevenness of the scanning line. The polygon mirror 22 is used for horizontal deflection, and is rotated at high speed by a drive motor 23. The laser beam deflected in the horizontal scanning direction by the multifaceted m22 passes through the first relay lens 24, the second cylindrical lens 25 for correcting pitch unevenness of the scanning line, and the second relay lens 26, and then passes through the galvanometer mirror 27 for vertical deflection. incident on . The laser beam deflected in the vertical scanning direction by the galvanometer mirror 27 is projected onto a screen (not shown) via an imaging lens 28.

In such a high-speed laser scanning system, in the case of NTSC horizontal scanning, the horizontal scanning frequency t5,75 [KHz
] for 945.000 [c. p. I1. ], for example, a 25-sided polygon mirror 2.
2, the cost would be 37,800[r. p. m. ] It is necessary to drive the polygon mirror 22 to rotate at an extremely high speed.

As described above, since the rotating polygon mirror rotates at an extremely high speed, there is a problem in that the wind noise generated by the rotation is large. In particular, with air bearing structures that omit thrust bearings by providing a spiral groove on the rotating shaft so that the rotating shaft floats in the air during rotation, it is also impossible to create a vacuum state around the rotating shaft for sound insulation. Therefore, conventional measures for noise reduction have been limited to providing an enclosure around the rotating polygon mirror.

SUMMARY OF THE INVENTION [Object of the Invention] Therefore, an object of the present invention is to provide a noise reduction device that can reliably muffle noise such as wind noise emitted from a rotating polygon mirror.

[Structure of the Invention] The noise reduction device for a rotating polygon mirror according to the present invention focuses sound waves emitted from the rotating polygon mirror in a certain direction using a sound collecting means, and also includes a sound source that emits sound waves in a direction opposite to the traveling direction of the focused sound waves. The sound source is provided and controlled so that the sound source has a phase opposite to that of the focused sound wave.

[Operation of the Invention] With this configuration, sound waves such as wind noise emitted from the rotating polygon mirror are canceled out by sound waves emitted from the sound source.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, a reflecting plate 2 having, for example, a parabolic shape is arranged around a rotating polygon mirror 1 as a sound collecting means so that the rotating polygon mirror 1 is located at its focal position. This reflecting plate 2 functions to reflect sound waves such as wind noise emitted from the rotating polygonal chain 1 and focus them in a certain direction. The sound waves focused by the reflection plate 2 (hereinafter referred to as focused sound waves) are emitted as substantially plane waves.

For example, a directional speaker 3 is disposed in front of the focused sound wave in the traveling direction as a sound source that emits a substantially plane wave sound wave in a direction opposite to the traveling direction. This speaker 3 is controlled by a control system 4 so as to generate a sound wave having a phase opposite to that of the focused sound wave. The control system 4 includes a microphone 5 disposed in the traveling path of the focused sound wave, an inverting amplifier 6 that inverts and amplifies the output of the microphone 5, and a phase of the output of the inverting amplifier 6 according to a delay time in the control system 4. It is comprised of a phase shifter 7 that adjusts accordingly, and a drive amplifier 8 that drives the speaker 3 in accordance with the output of the phase shifter 7.

In this configuration, when noise such as wind noise is emitted from the rotating polygon mirror 1 due to high-speed rotation, the sound waves are focused by the reflection plate 2 and emitted as focused sound waves in a certain direction. At this time, under the control of the control system 4, the directional speaker 3 emits a sound wave having a phase opposite to that of the focused sound wave.

As a result, the sound waves such as wind noise emitted from the rotating polygon mirror 1 are canceled out by the sound waves emitted from the speaker 3, so that noises such as wind noise can be reliably purified.

Effects of the Invention As explained above, in the rotary polygon mirror silencing device according to the present invention, the sound waves emitted from the rotary polygon mirror are focused in a certain direction by the sound collecting means, and the sound waves emitted from the rotary polygon mirror are focused in a certain direction, and the sound waves are focused in a direction opposite to the traveling direction of the focused sound waves. Since a sound source that emits sound waves is provided and the sound source is controlled to generate sound waves having a phase opposite to that of the focused sound waves, the focused sound waves cancel out the sound waves emitted from the sound source.

Therefore, according to the silencer according to the present invention, noise such as wind noise emitted from the rotating polygonal chain can be reliably silenced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of a high-speed laser scanning system using a rotating polygon mirror. Explanation of symbols of main parts 1...Rotating polygon mirror 2...Reflector plate 3...Directional beamer 4...Control system 5...・Microphone 6・・・Inverting amplifier

Claims (2)

[Claims] (1) Sound collecting means for focusing sound waves emitted from a rotating polygon mirror in a certain direction; a sound source for emitting sound waves in a direction opposite to the traveling direction of the focused sound waves by the sound collecting means; and a sound wave having a phase opposite to the focused sound waves. 1. A sound muffling device for a rotating polygon mirror, comprising a control means for controlling the sound source to generate sound. (2) The rotating polygon mirror according to claim 1, wherein the sound collecting means is a reflecting plate having a parabolic shape and arranged so that the rotating polygon mirror is located at the focal point of the reflecting plate. Silencer.