JPH09127956A - Air-cooled fan silencing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a silencing system requiring neither digital signal processing part nor duct. SOLUTION: When a fan 11 starts to operate, a fan noise having an extremely strong correlation with the frequency (characteristic frequency) corresponding to the rotating speed of the fan x the nubmer of blades 17, 17... is generated. A reference signal generating circuit 18 generates a reference signal. RS of the frequency corresponding to the value obtained by multiplying the rotating speed of the fan 11 by the number of the blades 17, 17.... A phase inverting circuit 19 inverses the phase of the inputted reference signal RS and outputs the resulting signal as a control sound signal SP. An amplifier 20 amplifies the control sound signal SP in a preliminarily regulated prescribed amplification degree, and outputs the resulting control sound signal. A silencing speaker 12 emits a control sound of an opposite phase having the same amplitude as the fan noise on the basis of the amplified control sound signal SP. Thus, the fan noise is interfered with the control sound and silenced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-cooling fan silencer system, and more particularly, to an air-cooling fan silencer system for reducing noise generated by an air-cooling fan mounted on an electronic device such as a liquid crystal projector or OA equipment.

[0002]

2. Description of the Related Art Since electronic parts such as amplifiers and attenuators generally change their characteristics depending on temperature, electronic parts having a "heat source" such as a power source, a light source and a memory, such as a liquid crystal display, a printer and a personal computer. The OA equipment is equipped with an air-cooling fan that sends air for cooling the electronic components inside. In particular, the liquid crystal projector has a conversion efficiency from electricity to light of about 2%, and the rest is converted into heat. Therefore, it is necessary to provide a plurality of air cooling fans such as an air supply fan and an exhaust fan. By the way, the installation of the air-cooling fan is effective for preventing overheating of the apparatus, but has a disadvantage of disturbing the indoor sound environment. In order to eliminate this inconvenience, a fan noise can be silenced to some extent by using a sound absorbing material or a sound insulating material for the enclosure structure of the air-cooling fan. Therefore, recently, for example, Japanese Unexamined Patent Publication No. 5-4419 and Japanese Utility Model Publication No.
As described in Japanese Patent No. 64897, active muffling technology has been adopted in which an interference sound having a phase opposite to that of noise is created and the sound is actively silenced by sound interference.

FIG. 9 shows a conventional active silencer applied to a printer. This active silencer is emitted from an air-cooling fan (exhaust fan) 2 provided in the vicinity of an inlet 1a of a duct 1 and is connected to the duct 1. This is a device for canceling fan noise radiated to the outside of the device via the noise suppression speaker 3 provided on the side of the outlet 1b of the duct 1 by causing control noise to interfere with the noise level (primary sound). Sensor microphone 4 that detects and converts to a noise signal (reference signal) SM
An amplifier (AMP) 5 for amplifying the noise signal SM output from the sensor microphone 4, a bandpass filter (BPF) 6 for passing a predetermined frequency band component of the output signal of the amplifier 5, and an input Based on the control sound signal SP that is generated, a muffling speaker 3 that emits a control sound (secondary sound) having the same amplitude as the fan noise but an opposite phase, and the outlet 1b of the duct 1.
An error microphone 8 that detects residual noise in the vicinity and outputs a residual noise signal EM, a noise signal (reference signal) SM supplied via the bandpass filter 6, and a residual noise signal EM supplied from the error microphone 8. Based on the above, the controller 9 that performs the adaptive control to constantly minimize the residual noise and outputs the control sound signal SP, and the control sound signal SP that is input.
And an amplifier 10 which amplifies and supplies the amplified noise to the muffling speaker 3.

[0004]

However, based on the noise signal (reference signal) SM output from the sensor microphone 4, a control sound (secondary sound) having the same amplitude as the fan noise but an opposite phase is created. In the conventional device configuration (FIG. 9), since the closed loop is formed by the electro-acoustic system including the sensor microphone 4 and the muffling speaker 3, the operation of the controller 9 becomes unstable and the muffling performance is deteriorated. Occasionally, it caused howling and, on the contrary, increased noise. In order for the controller 9 to perform such adaptive control for preventing such howling and constantly reducing noise, introduction of digital signal processing is indispensable. However,
Digital signal processing requires analog / digital (A / D) conversion, digital / analog (D / A) conversion, and numerical operation. For example, a dedicated digital signal processor (D
Even if SP) is used, there is a limit in shortening the processing time. Therefore, in order to enhance the muffling effect, it is necessary to lengthen the duct (noise propagation path), which has a drawback that the entire system becomes large.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an air-cooling fan silencer system which is small in size, inexpensive, highly reliable, and capable of quickly following a change in rotation of the air-cooling fan. .

[0006]

In order to solve the above-mentioned problems, an air-cooling fan silencing system according to a first aspect of the present invention synchronizes with the rotation of the air-cooling fan and the rotation speed and the number of blades of the air-cooling fan. Control sound signal generating means for generating a control sound signal having a frequency corresponding to the product of the control sound signal and a muffling speaker for emitting a control sound having a phase opposite to the fan noise based on the control sound signal input. It is characterized by that.

In the air-cooling fan muffler system according to the second aspect of the invention, the reference signal having a frequency corresponding to the product of the number of revolutions of the air-cooling fan and the number of blades is generated in synchronization with the rotation of the air-cooling fan. Reference signal generating means, a phase inverting circuit for inverting the phase of the input reference signal and outputting it as a control sound signal, and a control sound of a phase opposite to the fan noise based on the input control sound signal. It is characterized in that it is provided with a muffling speaker that radiates.

Further, in the air-cooling fan silencing system according to the third aspect of the present invention, the frequency corresponding to the product of the number of revolutions of the air-cooling fan and the number of blades is set as the fundamental frequency in synchronization with the rotation of the air-cooling fan. A control sound signal generating means for generating a control sound signal containing a harmonic component; and a muffling speaker for emitting a control sound having a phase opposite to that of the fan noise based on the input control sound signal. It has a feature.

Further, in the air-cooling fan silencing system according to the fourth aspect of the present invention, the frequency corresponding to the product of the number of revolutions of the air-cooling fan and the number of blades is set as a fundamental frequency in synchronization with the rotation of the air-cooling fan. On the basis of the input control sound signal, reference signal generation means for generating a reference signal containing a harmonic component, a phase inversion circuit for inverting the phase of the input reference signal and outputting it as a control sound signal, , And a muffling speaker that emits a control sound having a phase opposite to that of the fan noise.

[0010] The invention according to claim 5 is based on claim 1,
An air-cooled fan silencer system according to 2, 3, or 4,
An amplifier for amplifying the control sound signal with a predetermined amplification degree is added, and the muffler speaker controls the amplitude of the fan noise to be substantially the same as that of the fan noise based on the control sound signal input from the amplifier. It is characterized by emitting sound.

[0011] The invention according to claim 6 is based on claim 1,
The air-cooling fan silencing system according to 2, 3, 4 or 5 is characterized in that the control sound signal generating means has a timing detecting means for detecting the passage timing of each blade constituting the air-cooling fan. There is.

Further, the invention according to claim 7 is based on claim 1,
The air-cooling fan silencing system according to 2, 3, 4 or 5 is characterized in that the silencing speaker is provided on or near a main shaft of the air-cooling fan.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The description will be specifically made using an embodiment. First Embodiment FIG. 1 is a sectional view showing the structure of an air-cooling fan unit to which the air-cooling fan muffling system according to the first embodiment of the present invention is applied. FIG. 2 shows the electrical structure of the air-cooling fan muffling system. The block diagram shown in FIG. 3 and FIG. 3 are frequency-noise characteristic diagrams for showing the silencing effect of the air-cooling fan silencing system. The air-cooling fan unit of this example is provided in a liquid crystal projector, a printer, or the like, and relates to an air supply unit that sends air inside to cool electronic components. As shown in FIG. 1, an outer rotor type brushless DC motor is used. A fan 11, a muffling speaker 12 for actively muffling fan noise, a housing 13 with a double-sided opening for accommodating these, a filter 14 and a sponge sequentially fitted to the air supply port of the housing 13. It is roughly composed of a louver 15 and a louver 16. The fan 11 is an outer rotor type, and the plurality of blades 17, 17, ... Are themselves extensions of the rotor and rotate. Inside the cylindrical magnet of the rotor, not only a stator iron core (not shown) and windings (not shown) but also a drive circuit are incorporated. Further, the muffler speaker 12 is fixed to the front surface of the stator of the fan 11 so that the sound wave emitting surface faces the air supply port of the housing 13 and has a size that does not cause flow path resistance. Further, the filter 14 and the sponge 15 are
To remove dust from the air W to be taken in,
It also has a function to passively reduce fan noise.

The air-cooling fan silencing system of this example relates to a system for silencing the first characteristic frequency sound (fundamental frequency sound). As shown in FIG. 2, the number of rotations of the fan 11 is synchronized with the rotation of the fan 11. × Reference signal generation circuit 1 for generating reference signals RS having a frequency corresponding to the number of wings 17, 17, ...
8, a phase inversion circuit 19 that inverts the phase of the input reference signal RS and outputs it as a control sound signal SP, and an amplifier 2 that amplifies the control sound signal SP with an adjustable predetermined amplification degree.
0 and a muffling speaker 12 that emits a control sound having the same amplitude as the fan noise but an opposite phase based on the amplified control sound signal SP. The reference signal generation circuit 18 is
It is provided as an internal circuit of the fan 11 and magnetically detects the passage timing of each blade 17 that constitutes the fan 11 to generate a rectangular-wave timing pulse.
A reference signal RS having a frequency corresponding to the number of fan rotations times the number of blades 17, 17, ... Is generated.

In the above structure, when the fan 11 starts to operate, fan noise having a strong correlation with a frequency (characteristic frequency) corresponding to the number of fan revolutions multiplied by the number of blades 17, 17 ,. a)). Reference signal generation circuit 1
Synchronized with the rotation of the fan 11, the reference numeral 8 generates a reference signal RS having a frequency corresponding to a value obtained by multiplying the rotation speed of the fan 11 by the number of blades 17, 17, .... The phase inversion circuit 19 inverts the phase of the input reference signal RS to output the control sound signal S.
Output as P. The amplifier 20 amplifies the control sound signal SP with a predetermined amplification degree adjusted in advance and outputs it. The muffling speaker 12 is based on the amplified control sound signal SP,
It emits a control sound with the same amplitude as the fan noise but in the opposite phase. This causes fan noise to be interfered by the control sound,
The sound is muted (FIG. 3 (b)).

As described above, according to the configuration of the first embodiment, the reference signal RS is directly obtained from the rotational movement of the fan 11, so that the waveform processing time can be remarkably shortened and the expensive digital signal processing unit can be used. Can be omitted. Therefore, a long duct is not required, and the device can be made compact and inexpensive.
As is clear from the sound deadening principle, the rotational change of the fan 11 can be swiftly followed, so that the reliability is also improved.

Second Embodiment FIG. 4 is a block diagram showing the electrical construction of an air-cooling fan silencing system according to the second embodiment of the present invention, and FIG.
It is a frequency-noise characteristic figure for showing the noise reduction effect of the air cooling fan noise reduction system. The air-cooled fan system of this example relates to a system that silences not only characteristic frequency sounds (fundamental frequency sounds) but also harmonic components of fan noise.
As shown in, a reference signal is generated in synchronization with the rotation of the fan 21 to generate an FS reference signal including a harmonic component whose fundamental frequency is a frequency corresponding to the number of fan rotations × the number of blades 17, 17 ,. The signal generation means 22 and a plurality of band pass filters (hereinafter referred to as BPFs) 23 ₁ , 2 as frequency division means for dividing the reference signal FS into a plurality of frequency bands.
3 ₂ , ... 23 _n and these BPFs 23 ₁ , 23 ₂ , ... 23
provided after the _n, the reference signal FS ₁ of each frequency band, FS _2, ..., control sound signal SP ₁ by inverting the phase of the FS _n, SP _2, ..., the phase inverting circuit 24 to output as SP _{n 1,} 24 _2, ..., and 24 _n, the control sound signal SP ₁ to be input to each, SP _2, ..., an amplifier 25 _1, 25 ₂ to a predetermined amplification degree adjustable to SP _n, ... 25 _n When,
A signal synthesis circuit 26 that synthesizes the amplified control sound signals SP ₁ , SP ₂ , ..., SP _n and outputs a synthesized control sound signal TSP.
And a muffling speaker 12 that emits a control sound having the same amplitude as the fan noise but an opposite phase based on the input synthesized control sound signal TSP. Since the overall structure of the air-cooling fan unit of this example is substantially the same as that of FIG. 1 (first embodiment), the same parts as those of FIG. To do.

The reference signal generating means 22 is a fan 21.
, A photo encoder 22a that is a rotating disk having radially the same number of slits as the number of wings 17, 17, and a photo interrupter 22b in which a light emitting element and a light receiving element are arranged to face each other with the photo encoder 22a interposed therebetween. And has a common axis with the fan 21 and is provided in the vicinity of the fan 21 so as to prevent flow path resistance. The photo encoder 22a is configured to rotate in synchronization with the fan 21, and the slits are in one-to-one correspondence with the blades 17 of the fan 21. Therefore, the reference signal generation means 22 uses the slit (that is, the wing 1
7, 17, ...) Optically detecting the passage timing of
FS is generated as a reference signal including a harmonic component whose fundamental frequency is a frequency corresponding to the number of fan rotations × the number of blades 17, 17, ....

In the above configuration, when the fan 21 starts to operate, fan noise is generated which has a very strong correlation with the frequency (characteristic frequency) corresponding to the number of fan revolutions × the number of blades 17, 17 ,. (A)). The reference signal generation means 22 includes a harmonic component whose fundamental frequency is a frequency corresponding to a value obtained by multiplying the number of revolutions of the fan 21 by the number of blades 17, 17, ... In synchronization with the rotation of the fan 21. Generate a signal FS. The BPFs 23 ₁ , 23 ₂ , ... 23 _n are
The reference signal FS is divided into a plurality of frequency bands. The phase inversion circuits 24 ₁ , 24 ₂ , ..., 24 _n invert the phases of the reference signals FS ₁ , FS ₂ , ..., FS _n of the respective frequency bands to control sound signals SP ₁ , SP ₂ ,. Output as _n . The amplifiers 25 ₁ , 25 ₂ , ... 25 _n amplify the control sound signals SP ₁ , SP ₂ , ..., SP _n respectively input thereto by a predetermined amplification degree and output the amplified signals. The signal synthesizer circuit 26 controls the amplified control sound signals SP ₁ , SP ₂ , ..., SP.
_n is synthesized and the synthesized control sound signal TSP is muted speaker 12
To supply. The muffler speaker 12 emits a control sound having the same amplitude as the fan noise but an opposite phase based on the input synthetic control sound signal TSP. As a result, the fan noise is muted by being interfered with by the control sound from the fundamental frequency component to the harmonic component (FIG. 5B).

As described above, also with the configuration of the second embodiment, it is possible to obtain substantially the same effects as those described in the first embodiment. In addition, according to the configuration of the second embodiment, the fan noise is from the fundamental frequency component to the harmonic component,
Since it is silenced by the control sound, the silencing performance is further improved.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and there are design changes and the like that do not depart from the gist of the present invention. Is also included in the present invention. For example, the air cooling fan to which the present invention is applied is not limited to the air supply fan,
Exhaust fan is also included. Further, the present invention can be applied not only to the air cooling fan installed in the liquid crystal projector and the printer but also to the air cooling fan installed in all kinds of devices. Further, in the above-described first embodiment, the muffling speaker 12 is directly attached to the front surface of the stator of the fan 11, but the present invention is not limited to this, and may be provided on the inner wall of the housing 13 as shown in FIG. Alternatively, the air-cooling fan unit and the muffler speaker may be completely separate bodies.

Further, in the above-mentioned second embodiment, the reference signal generating means 22 is constituted by the photo encoder 22a and the photo interrupter 22b (FIG. 4), but instead of this, for example, in FIG. As shown, wings 17, 17,
... itself functions as a photo encoder, and the light-emitting element 28a and the light-receiving element 28b form a blade 1 of the fan 27.
The reference signal generating means 28 may be configured by sandwiching the portion 7 in FIG. Further, the reference signal output from the reference signal generation circuit or the reference signal generation means may already be in the opposite phase to the fan noise. In such a case, since the reference signal itself can function as a control signal,
As a modification of the first embodiment, the phase inversion circuit can be omitted as shown in FIG.

[0023]

As described above, according to the configuration of the present invention, the reference signal (or the control sound signal) is directly obtained from the rotational movement of the air-cooling fan, so that the waveform processing time can be significantly shortened. The expensive digital signal processing unit can be omitted. Therefore, a long duct is not required, and the device can be made compact and inexpensive. As is clear from the sound deadening principle, it is possible to quickly follow changes in the rotation of the air-cooling fan, so reliability and reliability are also improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of an air cooling fan to which an air cooling fan silencing system according to a first embodiment of the present invention is applied.

FIG. 2 is a block diagram showing an electrical configuration of the air-cooling fan silencing system.

FIG. 3 is a frequency-noise characteristic diagram showing the silencing performance of the air-cooling fan silencing system.

FIG. 4 is a block diagram showing an electrical configuration of an air-cooling fan silencing system according to a second embodiment of the present invention.

FIG. 5 is a frequency-noise characteristic diagram showing a silencing effect of the air-cooling fan silencing system.

FIG. 6 is a cross-sectional view showing the structure of an air-cooling fan that is a modification of the first embodiment.

FIG. 7 is a block diagram showing the electrical configuration of an air-cooling fan silencing system that is a modification of the second embodiment.

FIG. 8 is a block diagram showing an electrical configuration of an air-cooling fan silencing system which is another modification of the first embodiment.

FIG. 9 is a block diagram showing a conventional active silencer applied to a printer.

[Explanation of symbols]

11, 21, 27 Fan (air-cooling fan) 12 Silent speaker 17 Blades 18 Reference signal generation circuit (reference signal generation means) 19, 24 ₁ , 24 ₂ , ..., 24 _n Phase inversion circuit 20, 25 ₁ , 25 ₂ , ... 25 _n amplifier 22, 28 reference signal generating means (reference signal generating means) 22 a photo encoder 22 b photo interrupter 28 a light emitting element 28 b light receiving element 23 ₁ , 23 ₂ , ... 23 _n BPF 26 signal combining circuit RS, FS reference signal SP control sound Signal TSP Synthetic control sound signal

Claims (7)

[Claims] 1. A control sound signal generation means for generating a control sound signal having a frequency corresponding to the product of the rotation speed of the air cooling fan and the number of blades in synchronization with the rotation of the air cooling fan, and the control input. An air-cooling fan muffling system, comprising: a muffling speaker that emits a control sound having a phase opposite to that of a fan noise based on a sound signal. 2. A reference signal generating means for generating a reference signal having a frequency corresponding to the product of the number of revolutions of the air cooling fan and the number of blades in synchronization with the rotation of the air cooling fan, and the reference signal input. A phase inversion circuit that inverts the phase and outputs as a control sound signal, and a muffling speaker that emits a control sound having a phase opposite to the fan noise based on the input control sound signal. Air cooling fan silencing system. 3. A control sound for generating a control sound signal including a harmonic component whose fundamental frequency is a frequency corresponding to the product of the rotation speed of the air cooling fan and the number of blades in synchronization with the rotation of the air cooling fan. An air-cooling fan silencing system comprising: a signal generating means and a silencing speaker that emits a control sound having a phase opposite to that of the fan noise based on the input control sound signal. 4. A reference signal generation for generating a reference signal including a harmonic component whose fundamental frequency is a frequency corresponding to the product of the rotation speed of the air cooling fan and the number of blades in synchronization with the rotation of the air cooling fan. Means, a phase inverting circuit that inverts the phase of the input reference signal and outputs it as a control sound signal, and a muffling speaker that emits a control sound having a phase opposite to the fan noise based on the input control sound signal An air-cooled fan silencing system characterized by comprising: 5. An amplifier for amplifying the control sound signal with a predetermined amplification degree is added, and the silence speaker has substantially the same amplitude as fan noise based on the control sound signal input from the amplifier. 5. The air-cooling fan silencing system according to claim 1, 2, 3 or 4, wherein control sound of opposite phase is emitted by. 6. The control sound signal generating means comprises a timing detecting means for detecting a passage timing of each blade constituting the air-cooling fan.
The air-cooled fan silencer system according to 2, 3, 4 or 5. 7. The air-cooling fan muffling system according to claim 1, wherein the muffling speaker is provided on or near a main shaft of the air-cooling fan.